1.         K. Ajito

            "Direct structural observation of liquid molecules in single picoliter microdroplets using near-infrared Raman microprobe spectroscopy combined with laser trapping and chemical-tomographic imaging techniques"

            Thin Solid Films 331 (1-2), 181-188 (1998).

 

            ABSTRACT: Two near-infrared (NIR) Raman microprobe spectroscopic techniques were developed for the direct structural observation of liquid molecules in single picoliter microdroplets. The use of NIR laser light as the excitation light source instead of visible laser light provides Raman spectra with lower fluorescence interference, which makes it easier to determine the structure of liquid molecules. Combining an NIR Raman microprobe with a laser trapping technique makes it possible to classify molecular species in a single picoliter microdroplet during laser trapping in solution. An NIR Raman microprobe chemical-tomographic (RMCT) imaging technique provides the three-dimensional distribution of molecular species in a picoliter microdroplet with a spatial resolution of several femtoliters in volume. Both techniques show sufficient sensitivity to obtain Raman spectra of liquid molecules in single picoliter microdroplets. (C) 1998 Elsevier Science S.A. All rights reserved.

 

2.         K. Ajito

            "Combined near-infrared Raman microprobe and laser trapping system: Application to the analysis of a single organic microdroplet in water"

            Appl. Spectrosc. 52 (3), 339-342 (1998).

 

            ABSTRACT: A combined Raman microprobe and laser trapping system using near-infrared (NIR) laser light was developed for the investigation of single organic microdroplets. The NIR laser light is noninvasive and reduces fluorescence interference in the Raman spectrum for organic molecules. The focused laser beam used for the laser trapping of a microdroplet serves simultaneously as the laser microprobe for Raman measurement. With this system, the focused laser spot is about 1 mu m in diameter, which is small enough for the laser trapping of a single toluene microdroplet in water. The system also makes it possible to visualize a focused laser spot together with a laser-trapped microdroplet by using holographic notch filters. The Raman spectrum for a single laser-trapped toluene microdroplet can be obtained from below 100 cm(-1) to above 3000 cm(-1) with a charge-coupled device (CCD) detector. Fluorescence interference in the Raman spectrum is completely removed by using NIR laser light. The signal-to-noise ratio (SNR), defined as the ratio of the peak height to the standard deviation of the baseline noise in the spectrum, exceeded 250 for the 1003 cm(-1) band of a toluene microdroplet at 1 s, which is sufficient to allow identification of the molecular species of a microdroplet.

 

3.         T. Akasaka, Y. Kobayashi, S. Ando, N. Kobayashi, and M. Kumagai

            "Selective MOVPE of GaN and AlxGa1-xN with smooth vertical facets"

            J. Cryst. Growth 190, 72-77 (1998).

 

            ABSTRACT: Selective metalorganic vapor-phase epitaxy (MOVPE) of GaN and AlxGa1-xN was investigated as a function of growth conditions such as substrate temperature and partial pressure of NH3. GaN hexagonal microprisms (HMPs) with Vertical {1 (1) over bar 0 0} facets were grown when the surface coverage of atomic nitrogen was rather low, while GaN hexagonal micro-pyramids with {1 (1) over bar 0 1} facets were grown when the surface coverage was higher. This is because the growth rate of a GaN {1 (1) over bar 0 0} surface is more sensitive to the nitrogen surface coverage than a {1 (1) over bar 0 1} surface. The GaN HMPs have atomically smooth top surfaces because the growth mode is a balance between adsorption and desorption of film forming precursors and also because of the finite-area effect. HMPs and stripes of Al0.05Ga0.95N with smooth vertical facets were also fabricated. Stimulated emission was observed at room temperature from photopumped GaN HMPs 50 mu m in diameter. The longitudinal modes having a 0.33 nm separation indicate an inscribed hexagonal optical path in the GaN HMP. (C) 1998 Elsevier Science B.V. All rights reserved.

 

4.         T. Akasaka, T. Nishida, S. Ando, and N. Kobayashi

            "Surface flattening of GaN by selective area metalorganic vapor phase epitaxy"

            Jpn. J. Appl. Phys. Part 2 - Lett. 37 (7B), L842-L844 (1998).

 

            ABSTRACT: The surface flattening of GaN films by selective area metalorganic vapor phase epitaxy is demonstrated. Selectively grown GaN films 30-50 mu m in diameter have smooth surfaces with neither bunched steps nor ridge growth. These surfaces consist of bilayer height spiral steps that originate from screw dislocations. The surface flattening is probably due to the disappearance of steps at the edges of the selectively grown GaN. Desorption of the film forming precursors from the growing surface is increased on the smooth GaN surface during growth at substrate temperatures of 1000 degrees C ol higher in H-2 carrier gas. A low dislocation density is essential for a smooth GaN surface, because the spirals determine the step structure.

 

5.         T. Akazaki, H. Takayanagi, J. Nitta, and T. Enoki

            "InAs-inserted-channel InAlAs/InGaAs inverted HEMTs with direct ohmic contacts"

            Physica E 2 (1-4), 458-462 (1998).

 

            ABSTRACT: We have investigated the device characteristics of InAs-inserted-channel In0.52Al0.48As/In0.53Ga0.47As inverted high electron mobility transistors (HEMTs) with a novel ohmic structure. The ohmic contact between the ohmic electrodes and the two-dimensional electron gas (2DEG) formed in the InAs layer is obtained by direct contact with the ohmic electrodes-InAs, instead of an alloyed normal-metal and semiconductor as in a conventional inverted HEMT, The contact resistance of 0.11 Omega mm between the ohmic electrodes and the channel is smaller by a factor of 4, than that obtained using a conventional AuGeNi alloyed ohmic contact. For a 0.5 mu m-gate device, a maximum extrinsic transconductance of 1.2 S/mm was obtained at 4.2 K, even at a very low drain voltage of 0.2 V. These results show that this ohmic contact formation allows us to obtain the improved HEMT characteristics. (C) 1998 Elsevier Science B.V. All rights reserved.

 

6.         L. Alff, A. Beck, R. Gross, A. Marx, S. Kleefisch, T. Bauch, H. Sato, M. Naito, and G. Koren

            "Observation of bound surface states in grain-boundary junctions of high-temperature superconductors"

            Phys. Rev. B 58 (17), 11197-11200 (1998).

 

            ABSTRACT: We have performed a detailed study of the tunneling spectra of bicrystal grain-boundary junctions (GBJ's) fabricated from the high-temperature superconductors (HTS) YBa2Cu3O7-delta (YBCO), Bi2Sr2CaCu2O8+delta (BSCCO), La1.85Sr0.15CuO4 (LSCO), and Nd1.85Ce0.15CuO4-y,(NCCO). In ail experiments the tunneling direction was along the CuO2 planes. With the exception of NCCO, for all materials a pronounced zero bias conductance peak (ZBCP) was observed that decreases with increasing temperature and disappears at the critical temperature. These results can be explained by the presence of a dominating d-wave symmetry of the order parameter resulting in the formation of zero-energy Andreev bound states at surfaces and interfaces of HTS. The absence of a ZBCP for NCCO is consistent with a dominating s-wave symmetry of the pair potential in this material. The observed nonlinear shift of spectral weight to finite energies by applying a magnetic field is in qualitative agreement with recent theoretical predictions. [S0163-1829(98)08441-0].

 

7.         H. Ando, T. Sogawa, and H. Gotoh

            "Photon-spin controlled lasing oscillation in surface-emitting lasers"

            Appl. Phys. Lett. 73 (5), 566-568 (1998).

 

            ABSTRACT: We report on photon-spin controlled lasing oscillation in GaAs surface-emitting lasers at room temperature. We demonstrate experimentally that the partial electron-spin alignment, created by optically pumping the GaAs laser active media with circularly polarized pulses, drastically changes the polarization state of the lasing output, causing circularly polarized lasing emission. We discuss the laser polarization characteristics in relation to the measured electron-spin relaxation time. (C) 1998 American Institute of Physics.

 

8.         S. Ando, N. Kobayashi, and H. Ando

            "Short-cavity Fabry-Perot lasers using crystal facets"

            Jpn. J. Appl. Phys. Part 2 - Lett. 37 (2A), L105-L107 (1998).

 

            ABSTRACT: GaAs/AlGaAs short-cavity Fabry-Perot (F-P) lasers using vertical crystal facets as reflectors are fabricated by using selective area metalorganic vapor phase epitaxy (MOVPE). The laser structures consist of a (111)B growth plane and (110) sidewall facets vertical to the substrate surface. The sidewall facets are also crystallographically parallel to each other. These features are suitable for mu m-size short-cavity F-P lasers. In addition, by using the lateral growth on the (110) facets in the selective area epitaxy, the edge of a GaAs active layer is covered with an AlGaAs layer to reduce the carrier loss caused by surface recombination. As a result, we successfully obtained a room-temperature lasing with a cavity length as short as 5 mu m. This is the shortest cavity length in lateral F-P lasers that has so far been reported.

 

9.         H. Arimoto, T. Saku, Y. Hirayama, and N. Miura

            "Angular dependent cyclotron resonance of two-dimensional electron gas in GaAs/AlGaAs quantum wells in high magnetic fields up to 150 T"

            Physica B 258, 343-346 (1998).

 

            ABSTRACT: We have observed angular dependent cyclotron resonance (CR) of two-dimensional electrons confined in GaAs/AlGaAs multi quantum wells in ultra high magnetic fields up to 150 T generated by the single-turn coil technique. We changed the tilt angle between the magnetic fields and the direction normal to the two-dimensional plane. Three samples with different well widths and aluminum concentrations of barrier layers were measured. We found four different types of angular dependence of CR and interpreted these comprehensively on the basis of the relations among barrier height energy V-b, subband spacing energy E-10 and cyclotron energy (h) over bar omega(c). (C) 1998 Elsevier Science B.V. All rights reserved.

 

10.       K. Arimura and N. Hagita

            "Feature space design for statistical image recognition with image screening"

            IEICE Trans. Inf. Syst. E81D (1), 88-93 (1998).

 

            ABSTRACT: This paper proposes a design method of feature spaces in a two-stage image recognition method that improves the recognition accuracy and efficiency in statistical image recognition. The two stages are (1) image screening and (2) image recognition. Statistical image recognition methods require a lot of calculations for spatially matching between subimages and reference patterns of the specified objects to be detected in input images. Our image screening method is effective in lowering the calculation load and improving recognition accuracy. This method selects a candidate set of subimages similar to those in the object class by using a lower dimensional feature vector, while rejecting the rest. Since a set of selected subimages is recognized by using a higher dimensional feature vector, overall recognition efficiency is improved. The classifier for recognition is designed from the selected subimages and also improves recognition accuracy, since the selected subimages are less contaminated than the originals. Even when conventional recognition methods based on linear transformation algorithms, i.e. principal component analysis (PCA) and projection pursuit (PP), are applied to the recognition stage in our method, recognition accuracy and efficiency may be improved. A new criterion, called a screening criterion, for measuring overall efficiency and accuracy of image recognition is introduced to efficiently design the feature spaces of image screening and recognition. The feature space for image screening are empirically designed subject to taking the lower number of dimensions for the feature space referred to as L-S and the larger value of the screening criterion. Then, the recognition feature space which number of dimensions is referred to as L-R is designed under the condition L-S less than or equal to L-R. The two detection tasks were conducted in order to examine the performance of image screening. One task is to detect the eye-and-mouth-areas in a face image and the other is to detect the text-area in a document image. The experimental results demonstrate that image screening for these two tasks improves both recognition accuracy and throughput when compared to the conventional one-stage recognition method.

 

11.       D. G. Austing, T. Honda, K. Muraki, Y. Tokura, and S. Tarucha

            "Quantum dot molecules"

            Physica B 251, 206-209 (1998).

 

            ABSTRACT: Vertically coupled dots can be employed to study the filling of electrons in quantum dot molecules. When the dots are quantum mechanically strongly coupled, the electronic states in the system are not localized, and the Coulomb diamonds and addition energy spectra of the molecule resemble those of a single artificial atom. When the dots are quantum mechanically weakly coupled, the electronic states in the system are usually localized, although the dots can be electrostatically coupled, and this leads to a pairing of conductance peaks. (C) 1998 Elsevier Science B.V. All rights reserved.

 

12.       D. G. Austing, T. Honda, and S. Tarucha

            "Manipulation of the lateral potential geometry of a quantum dot located in a multiple gated vertical single electron transistor"

            Physica E 2 (1-4), 583-587 (1998).

 

            ABSTRACT: We exploit a new technology for fabricating a vertical quantum dot with more than one gate to demonstrate that the area and geometry of such a dot can be systematically and independently manipulated. By 'mapping' the conductance oscillations we can investigate the effect of distorting geometrically the lateral confining potential on the atomic-like properties of artificial atoms. We find that pairing of conductance peaks due to spin-degeneracy is insensitive to geometric distortion, whereas the single-particle states and underlying 'shell' structure are altered as the dot is deformed. (C) 1998 Elsevier Science B.V. All rights reserved.

 

13.       S. Baker, K. Nayar, and H. Murase

            "Parametric feature detection"

            Int. J. Comput. Vis. 27 (1), 27-50 (1998).

 

            ABSTRACT: Most visual features are parametric in nature, including, edges, lines, corners, and junctions. We propose an algorithm to automatically construct detectors for arbitrary parametric features. To maximize robustness we use realistic multi-parameter feature models and incorporate optical and sensing effects. Each feature is represented as a densely sampled parametric manifold in a low dimensional subspace of a Hilbert space. During detection, the vector of intensity values in a window about each pixel in the image is projected into the subspace. If the projection lies sufficiently close to the feature manifold, the feature is detected and the location of the closest manifold point yields the feature parameters. The concepts of parameter reduction by normalization, dimension reduction, pattern rejection, and heuristic search are all employed to achieve the required efficiency. Detectors have been constructed for five features, namely, step edge (five parameters), roof edge (five parameters), line (six parameters), corner (five parameters), and circular disc (six parameters). The results of detailed experiments are presented which demonstrate the robustness of feature detection and the accuracy of parameter estimation.

 

14.       S. M. Barnett, N. Imoto, and B. Huttner

            "Photonic de Broglie wave interferometers"

            J. Mod. Opt. 45 (11), 2217-2232 (1998).

 

            ABSTRACT: In the recently proposed photonic de Broglie wave interferometer, sophisticated beam splitters are used to split the de Broglie wave of a set of photons. The photonic de Broglie or collective phase shift can, however, be found in conventional interferometry if the full photon statistics are recorded. We propose a variation of the original photonic de Broglie wave interferometer. We show that the collective phase shift can and has been found in interferometry using photon pairs and propose two new photonic de Broglie wave interferometers in which normal beam splitters are used. Both of these rely on conditioning to select the cases for which all the photons behave as a single object.

 

15.       S. M. Barnett and R. Loudon

            "Sum rule for environmentally modified spontaneous emission rates"

            Quantum Semiclass. Opt. 10 (4), 591-599 (1998).

 

            ABSTRACT: We present a detailed derivation of our recent sum rule for spontaneous emission rates that are modified from their free-space values by the immersion of an excited atom in an arbitrary environment. The rule is applied to the problems of emission by an atom in a homogeneous and isotropic dielectric and by an atom in free space adjacent to a perfectly reflecting surface.

 

16.       S. M. Barnett, L. S. Phillips, and D. T. Pegg

            "Imperfect photodetection as projection onto mixed states"

            Opt. Commun. 158 (1-6), 45-49 (1998).

 

            ABSTRACT: We provide an expression for the state of a single field mode, conditioned only on the outcome of an imperfect photon-counting measurement. This suggests that we can view such a measurement as projection onto one of a non-orthogonal set of mixed states. We briefly discuss some of the implications of this result for state preparation. (C) 1998 Elsevier Science B.V. All rights reserved.

 

17.       F. Bugge, U. Zeimer, M. Sato, M. Weyers, and G. Trankle

            "MOVPE growth of highly strained InGaAs/GaAs quantum wells"

            J. Cryst. Growth 183 (4), 511-518 (1998).

 

            ABSTRACT: The indium incorporation into strained InGaAs quantum wells grown on GaAs substrate by metalorganic vapour-phase epitaxy is found to be reduced in comparison to relaxed layers. Additionally, the indium uptake into strained QWs is limited to approximately 30% InAs at 650 degrees C. Excessive trimethyl indium supply in the vapour phase leads to a drop of the In-content of the QW and to a reduced total In-content in the whole structure. Only a small amount of the excess indium is incorporated into InAs-rich clusters observed as dark-spot defects and into a graded interfacial layer. A model for this behaviour based on the enhanced In-reevaporation from In-rich areas is presented. (C) 1998 Elsevier Science B.V. All rights reserved.

 

18.       A. Chavez-Pirson, J. Temmyo, H. Kamada, H. Gotoh, and H. Ando

            "Near-field optical spectroscopy and imaging of single InGaAs/AlGaAs quantum dots"

            Appl. Phys. Lett. 72 (26), 3494-3496 (1998).

 

            ABSTRACT: We use near-field optical probing at low temperatures (T=5 K) to image and examine the linear and nonlinear luminescence properties of single InGaAs/AlGaAs quantum dots grown on (311)B oriented GaAs substrates. The high spatial resolution of near-field "nanoprobing," which is typically 200 nm or less, makes the observation of single dots at different locations on the sample possible, even though the spatial density of quantum dots is on the order of 100/mu m(2). We observe narrow excitonic emission lines at low excitation powers and, with increasing excitation; we observe biexcitonic emission strongly shifted (3 meV) to the low-energy side of the exciton emission. (C) 1998 American Institute of Physics.

 

19.       J. Chen, S. Machida, and Y. Yamamoto

            "Simultaneous measurement of amplitude and phase in surface second-harmonic generation"

            Opt. Lett. 23 (9), 676-678 (1998).

 

            ABSTRACT: The intensity and the phase in surface second-harmonic generation were simultaneously measured by use of an ac optical balanced homodyne detection system. in this system the surface second-harmonic wave was superimposed upon a local oscillator wave generated by a barium berate nonlinear optical crystal and then detected as an interference signal. Extremely high sensitivity of 3 aW (6 photons/s) and high precision were achieved by use of a lock-in amplifier, in which an interference signal of fundamental waves was used as a reference signal. Simultaneous measurement of the intensity and the phase in surface second-harmonic waves generated From native-oxidized Si(111) surfaces is demonstrated. (C) 1998 Optical Society of America.

 

20.       A. Dana, F. Ho, and Y. Yamamoto

            "Mechanical parametric amplification in piezoresistive gallium arsenide microcantilevers"

            Appl. Phys. Lett. 72 (10), 1152-1154 (1998).

 

            ABSTRACT: Preamplification of mechanical signals in external force detection systems can improve overall sensitivity in a case where sensitivity is limited by secondary detection noise. We report experimental data on degenerate and nondegenerate mechanical parametric amplification in GaAs piezoresistive atomic force microscopy cantilevers due to an inherent mechanical nonlinearity. The mechanical nonlinearity is estimated to be a result of curvature at the cantilever base. Characteristics of parametric amplification such as phase sensitive gain, small signal gain, gain saturation, and self-oscillation have been studied. A small signal phase sensitive gain of 19.5 dB was observed for the degenerate parametric amplifier. (C) 1998 American Institute of Physics. [S0003-6951(98)00610-X].

 

21.       K. Ebata, K. Furukawa, and N. Matsumoto

            "Synthesis and characterization of end-grafted polysilane on a substrate surface"

            J. Am. Chem. Soc. 120 (29), 7367-7368 (1998).

 

            ABSTRACT:

22.       J. L. Edwards and H. Murase

            "Coarse-to-fine adaptive masks for appearance matching of occluded scenes"

            Mach. Vis. Appl. 10 (5-6), 232-242 (1998).

 

            ABSTRACT: In this paper, we discuss an appearance-matching approach to the difficult problem of interpreting color scenes containing occluded objects. We have explored the use of an iterative, coarse-to-fine sum-squared-error method that uses information from hypothesized occlusion events to perform run-time modification of scene-to-template similarity measures. These adjustments are performed by using a binary mask to adaptively exclude regions of the template image from the squared-error computation. At each iteration higher resolution scene data as well as information derived from the occluding interactions between multiple object hypotheses are used to adjust these masks. We present results which demonstrate that such a technique is reasonably robust over a large database of color test scenes containing objects at a variety of scales, and tolerates minor 3D object rotations and global illumination variations.

 

23.       M. Edwards, D. R. Badcock, and A. T. Smith

            "Independent speed-tuned global-motion systems"

            Vision Res. 38 (11), 1573-1580 (1998).

 

            ABSTRACT: Several experiments were conducted to investigate the role of speed in global-motion processing; the extraction of the direction of motion of a small subset of coherently-moving (signal) dots in a stimulus in which the other (noise) dots move in random directions. The specific aim of the experiments was to determine whether multiple speed-tuned global-motion systems exist. The results of these experiments are: (1) when the signal dots were chosen from a group of dots moving at 1.2 degrees s(-1), the speed of additional-noise dots had to be below 4.8 degrees s(-1) for them to affect global-motion extraction; (2) the addition of static dots did not impair the extraction of a global-motion signal carried by dots moving at 1.2 degrees s(-1) (3) noise dots moving at 1.2 degrees s(-1) impaired the extraction of a global-motion signal from dots moving at 10.8 degrees s(-1), though not to the same extent as dots moving at a higher speed; and (4) these results were dependent upon speed, not spatial-step size or luminance contrast. These results are interpreted as indicating that global-motion extraction occurs within at least two independent speed tuned systems. One of these systems is sensitive to high speeds and the other to low speeds. (C) 1998 Elsevier Science Ltd. All rights reserved.

 

24.       H. Ezaki, M. Koashi, N. Imoto, and E. Hanamura

            "Photon number squeezing enhanced by multi-photon absorption in microcavity"

            J. Phys. Soc. Jpn. 67 (8), 2721-2728 (1998).

 

            ABSTRACT: We demonstrate that m-photon resonant absorption (m = 2, 3.) in a microcavity produce strong photon number squeezing. The dependence of the Fano factor and the mean photon number on the pumping rate, linear damping rate and m-photon decay rate is investigated analytically and numerically. We show the existence of a lower limit equaling 50% of the Fano factor for the radiation field within the cavity in both transient and steady-state cases. This photon-number squeezing is robust against pumping and one-photon dissipation processes.

 

25.       X. D. Fan, T. Takagahara, J. E. Cunningham, and H. L. Wang

            "Pure dephasing induced by exciton-phonon interactions in narrow GaAs quantum wells"

            Solid State Commun. 108 (11), 857-861 (1998).

 

            ABSTRACT: We investigate both dephasing and population relaxation of excitons localized in quantum dot like islands in narrow GaAs quantum wells by using stimulated photon echoes. A direct comparison of these two closely related decay processes reveals a pure dephasing contribution that dominates excitonic dephasing at elevated temperatures but does not involve exciton population relaxation. The pure dephasing contribution arises from coupling of excitonic states with a continuum of acoustic phonons and is enhanced by 3D quantum confinement. Both the magnitude and the temperature dependence of the pure dephasing rate can be described by a theoretical model that generalizes the Huang-Rhys theory of F-centers. (C) 1998 Elsevier Science Ltd. All rights reserved.

 

26.       P. Finnie and Y. Homma

            "Atomic step networks as selective epitaxial templates"

            Appl. Phys. Lett. 72 (7), 827-829 (1998).

 

            ABSTRACT: A technique to control epitaxial growth laterally across a wafer is presented, which does not use a mask A vicinal Si(111) substrate was patterned by optical lithography and heated to fabricate a regular pattern of bunches of atomic steps. Under appropriate growth conditions, it is seen that epitaxial material, here GaAs, sticks only to the step bunches, not to the terraces. It is possible to fabricate large-scale complex networks of GaAs with micron scale and submicron scale features. The conditions required to obtain selective growth are presented. It is shown that there are two regimes of selective growth-high temperature (> 550 degrees C), or low temperature (< 400 degrees C). Selectivity is obtained via two distinct mechanisms: desorption and diffusion, respectively. (C) 1998 American Institute of Physics.

 

27.       S. R. Friberg and S. Machida

            "Ultrafast optical pulse noise suppression using a nonlinear spectral filter: 23 dB reduction of fiber laser 1/f noise"

            Appl. Phys. Lett. 73 (14), 1934-1936 (1998).

 

            ABSTRACT: Nonlinear spectral filtering provides a simple method for reducing noise in optical pulses to below the shot noise level. We show its effectiveness for excess noise reduction in an ultrafast optical pulse train by demonstrating 23 dB reduction of low frequency 1/f noise in pulses from a passively mode-locked erbium-doped fiber laser. The noise reduction is achieved by spectrally filtering pulses propagated as solitons through a 1.5 km length of optical fiber. (C) 1998 American Institute of Physics. [S0003-6951(98)01540-X].

 

28.       M. Fujiki, S. Toyoda, C. H. Yuan, and H. Takigawa

            "Near-UV, circular dichroism, and fluorescence spectra of a rigid rodlike helical polysilane bearing trietheral moiety in ethanol/water"

            Chirality 10 (7), 667-675 (1998).

 

            ABSTRACT: An optically active, rigid rodlike helical polysilane with 6,9,12-trioxatetradecyl and (S)-2-methylbutyl substituents (1) was newly obtained as a very high molecular weight polymer of several million. Due to the presence of trietheral substituent, 1 was readily soluble in a polar solvent such as ethanol and a mixture of ethanol and water, but was insoluble in pure water. Polysilane 1 in pure ethanol at room temperature exhibited an intense and narrow ultraviolet (UV) and circular dichroism (CD) absorptions at 323 nm, associated with an almost mirror imaged fluorescence (FL) at 328 nm, that are characteristic of rigid rodlike, single-screw-sense helical polysilanes reported previously. When solution temperature was changed from 60 degrees C to -104 degrees C, a global shape of 1 expanded associated with an increase of segment length, whereas a screw pitch tended to be wound tightly. On the other hand, as a solvent polarity became poor, a global shape of 1 shrunk associated with an decrease of segment length and formed a chiral motif with an M-helicity between two helical segments with a kink. At a ratio of 50% of ethanol/water of 50:50 (v/v), 1 became insoluble and formed aggregates. (C) 1998 Wiley-Liss, Inc.

 

29.       T. Fujisawa, T. H. Oosterkamp, W. G. van der Wiel, B. W. Broer, R. Aguado, S. Tarucha, and L. P. Kouwenhoven

            "Spontaneous emission spectrum in double quantum dot devices"

            Science 282 (5390), 932-935 (1998).

 

            ABSTRACT: A double quantum dot device is a tunable two-level system for electronic energy states. A de electron current was used to directly measure the rates for elastic and inelastic transitions between the two levels. For inelastic transitions, energy is exchanged with bosonic degrees of freedom in the environment. The inelastic transition rates are well described by the Einstein coefficients, relating absorption with stimulated and spontaneous emission. The most effectively coupled bosons in the specific environment of the semiconductor device used here were acoustic phonons. The experiments demonstrate the importance of vacuum fluctuations in the environment for quantum dot devices and potential design constraints for their use for preparing long-lived quantum states.

 

30.       A. Fujiwara, Y. Takahashi, H. Namatsu, K. Kurihara, and K. Murase

            "Suppression of effects of parasitic metal-oxide-semiconductor field-effect transistors on Si single-electron transistors"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 37 (6A), 3257-3263 (1998).

 

            ABSTRACT: Si single-electron transistors (SETs), which are fabricated in ultrathin Si of a silicon-on-insulator substrate by pattern-dependent oxidation, are accompanied by parasitic metal-oxide-semiconductor field-effect transistors (MOSFETs) on both sides of the SET. While the Si island of a SET is formed by design in a one-dimensional Si wire, the parasitic MOSFETs are inevitably formed in two-dimensional Si pad layers, between which the Si wire runs, because the poly-Si gate covers the Si pad layers as well as the Si island. Electrical characteristics of the device are strongly affected by these parasitic MOSFETs because of their relatively high resistance or the Coulomb blockade effect due to multiple islands unintentionally formed in the pad Si layers. We found that backgate voltage is useful for reducing or analyzing such parasitic effects. We propose a new fabrication technique; the use of a SiN mask for oxidation avoids unnecessary thinning of pad Si layers and parasitic effects can be suppressed.

 

31.       A. Fujiwara, Y. Takahashi, K. Yamazaki, and K. Murase

            "Si single-electron devices with integrated Si islands - Towards ultralow-power electronics"

            Ntt Rev. 10 (6), 114-118 (1998).

 

            ABSTRACT: Si single-electron devices with multiple Si islands integrated by design have been fabricated. Current switching was performed using the principle of the Coulomb blockade at two closely packed Si islands which were as small as several tens of nanometers. Capacitive coupling between the two islands was also demonstrated, which opens up the possibility of ultralow-power integrated circuits that manipulate electrons individually.

 

32.       K. Fukasaku, K. Takeda, and K. Shiraishi

            "First-principles study on electronic structures of protein nanotubes"

            J. Phys. Soc. Jpn. 67 (11), 3751-3760 (1998).

 

            ABSTRACT: The electronic structures of protein nanotubes (PNTB), which are formed by the periodical stacking of cycle-peptide-ring (CPR) rings, are theoretically investigated in terms of the ab initio calculations. The inter-ring H bonds among the CPRs cause the electronic interaction when CPRs are periodically stacked. This interaction has a potential to delocalize electrons and holes along the tube axis as if the band conduction occurs through the bridging H bonds. The protonation of this system is also investigated. The migrated proton (charged H* species) is expected to create the impurity (acceptor) level in the hand gap of the PNTB.

 

33.       T. Fukuda

            "Oxygen-induced missing dimer row formation on the Ge(100) surface"

            Surf. Sci. 417 (2-3), L1149-L1153 (1998).

 

            ABSTRACT: The initial stage of O-2 etching of the Ge(100) surface was studied by scanning tunneling microscopy. The etched surface showed two types of missing dimer rows with widths of half a dimer (S) and one dimer (2S). Two different internal structures were identified for the 2S missing dimer rows. The migration of adsorbed oxygen plays a major role in the formation of the 2S missing dimer row, whereas the S missing dimer row is formed by a 2S missing dimer row splitting under the anisotropic stress on the surface dimers. (C) 1998 Elsevier Science B.V. All rights reserved.

 

34.       T. Fukuda, K. Furukawa, M. Fujino, T. Ogino, and N. Matsumoto

            "STM study of the initial adsorption stage of octa-tert-butyloctasilacubane on Si(100) 2x1 surface"

            Surf. Sci. 397 (1-3), 58-62 (1998).

 

            ABSTRACT: The initial adsorption stage of octa-tert-butyloctasilacubane (TBOSC) on a clean Si(100) 2 x 1 surface was investigated with a scanning tunneling microscope in an ultra-high vacuum. Most TBOSC molecules were observed as isolated irregular protrusions on the surface. Some of them, however, had hexagonal shapes. The topographic heights of these molecules were suppressed around the sample bias of -1.6 V in filled-state images. Small clusters decomposed from TBOSC were also identified. Some of them had a three-fold symmetry, indicating that a tert-butyl group was decomposed from TBOSC and adsorbed on the surface. Small atomic-size bright and dark sites were also formed by reaction with the surface. (C) 1998 Elsevier Science B.V.

 

35.       T. Fukuda and T. Ogino

            "STM study of the initial oxidation stage of Ge(100)2x1"

            Appl. Phys. A-Mater. Sci. Process. 66, S969-S972 (1998).

 

            ABSTRACT: The initial stage of oxygen chemisorption on the Ge(100) surface was studied by scanning tunneling microscopy. By using a defect-free surface and in situ oxidation, oxygen-induced products could be unambiguously determined. Two types of bright products and two types of dark products were identified. One of the bright products is a major product and it protrudes at the center of the dimer. Since this product was observed even after annealing at 300 degrees C, it is a stable product. The other bright product is a bright spot at one of the dimer atoms, and dimer buckling is stabilized near this product. The two dark products are similar to the missing dimer defects in filled-state images, but they appeared as bright spots in empty-state images. After annealing of the oxygen-chemisorbed surfaces, the dark product aligned in the dimer row with a 2x periodic structure inside.

 

36.       T. Fukuda and T. Ogino

            "Initial oxidation stage of the Ge(100)2x1 surface studied by scanning tunneling microscopy and ultra-violet photoelectron spectroscopy"

            Appl. Surf. Sci. 132, 165-169 (1998).

 

            ABSTRACT: The initial stage of oxygen chemisorption on the Ge(100) surface and its annealing behavior were studied by scanning tunneling microscopy (STM) and ultra-violet photoelectron spectroscopy (UPS). Atomically resolved dark and bright sites were identified by the interaction at room-temperature exposure to molecular oxygen. These surfaces showed a prominent peak at 4.6 eV in the UPS spectra. After annealing at 300 degrees C, the oxygen-induced products clustered along the dimer rows and formed an aligned dark structure. Isolated bright products still remained, and some of them were the same as those on the room-temperature exposure. UPS spectra showed a shift on the peak energy to 5.5 eV, indicating that a stable Ge-O-Ge complex has been formed by the annealing. (C) 1998 Elsevier Science B.V. All rights reserved.

 

37.       F. Gollnik and M. Naito

            "Doping dependence of normal- and superconducting-state transport properties of Nd2-xCexCuO4 +/- y thin films"

            Phys. Rev. B 58 (17), 11734-11752 (1998).

 

            ABSTRACT: The electric and thermomagnetic transport properties of an underdoped, an optimally doped, and an overdoped c-axis oriented, epitaxial Nd2-xCexCuO4+/-y thin film have been investigated in the temperature range from 4.2 K to 300 K and in magnetic fields up to 11 T oriented perpendicular to the CuO2 planes. In the normal state, the resistivity rho, Hall coefficient R-H, and magnetoresistivity Delta rho/rho(B) can be described quantitatively within a simple two-carrier model if the existence of an electronlike and a holelike band is assumed, where each of the two groups of charge carriers is characterized by a temperature-independent Hall coefficient. A corresponding analysis of the thermoelectric effects appears to be more difficult since they depend on more subtle details of the band structure and the scattering mechanisms. In the superconducting regime, the critical field B-rho*(T) determined from the shift of the resistive transition in an external magnetic field exhibits a positive curvature. In contrast, an analysis of the fluctuation conductivity and the transport entropy of magnetic flux line S-phi consistently gives higher values for the upper critical field B,(T). The fluctuation conductivity clearly exhibits two-dimensional scaling behavior, indicating that the quast-two-dimensional nature of the single-layer compound Nd2-xCexCuO4+/-y might be responsible for the difference between B-rho*(T) and B-c2(T). The order of magnitude of S-phi is consistent with the predictions of the Ginzburg-Landau theory. We derived material parameters as B-c2(0), the in-plane coherence length xi(ab)(0), the Ginzburg-Landau parameter kappa, and the London penetration depth lambda(0). We also present experimental data on the Hall effect in the mixed state. [S0163-1829(98)00341-5].

 

38.       H. Gomi and R. Osu

            "Task-dependent viscoelasticity of human multijoint arm and its spatial characteristics for interaction with environments"

            J. Neurosci. 18 (21), 8965-8978 (1998).

 

            ABSTRACT: Human arm viscoelasticity is important in stabilizing posture, movement, and in interacting with objects. Viscoelastic spatial characteristics are usually indexed by the size, shape, and orientation of a hand stiffness ellipse. It is well known that arm posture is a dominant factor in determining the properties of the stiffness ellipse. However, it is still unclear how much joint stiffness can change under different conditions, and the effects of that change on the spatial characteristics of hand stiffness are poorly examined. To investigate the dexterous control mechanisms of the human arm, we studied the controllability and spatial characteristics of viscoelastic properties of human multijoint arm during different cocontractions and force interactions in various directions and amplitudes in a horizontal plane. We found that different cocontraction ratios between shoulder and elbow joints can produce changes in the shape and orientation of the stiffness ellipse, especially at proximal hand positions. During force regulation tasks we found that shoulder and elbow single-joint stiffness was each roughly proportional to the torque of its own joint, and cross-joint stiffness was correlated with elbow torque. Similar tendencies were also found in the viscosity-torque relationships. As a result of the joint stiffness changes, the orientation and shape of the stiffness ellipses varied during force regulation tasks as well. Based on these observations, we consider why we can change the ellipse characteristics especially in the proximal posture. The present results suggest that humans control directional characteristics of hand stiffness by changing joint stiffness to achieve various interactions with objects.

 

39.       H. Gomi, M. Shidara, A. Takemura, Y. Inoue, K. Kawano, and M. Kawato

            "Temporal firing patterns of Purkinje cells in the cerebellar ventral paraflocculus during ocular following responses in monkeys I. Simple spikes"

            J. Neurophysiol. 80 (2), 818-831 (1998).

 

            ABSTRACT: Thp simple-spike firing frequency of 30 Purkinje cells (P cells) in the ventral paraflocculus (VPFL) of alert monkeys was studied in relation to vertical slow eye movements, termed ocular following response (OFR). induced by large field visual motions of different velocities and durations. To quantitatively analyze the relationship between eye movement and firing frequency, an inverse dynamics representation of the eye movement was used for reconstructing the temporal waveform of firing. Coefficients of eye-acceleration, velocity, and position, bias, and time lag between firing and eye movement were estimated by least-square error method. In the regression analyses for each stimulus condition, 86% (146/170) of the well-modulated temporal firing patterns taken from those 30 P cells were reconstructed successfully from eye movement. The model with acceleration, velocity, and position terms, which we used, was shown as the best among several potential models by Cp statistics, consistent with t-test of significance of each term. Reliable coefficients were obtained from 75% (109/146) of the well-reconstructed firing patterns of 28 cells among 30. The estimated coefficients were larger(statistically significant) for slow stimuli than for fast stimuli, suggesting changes in sensitivities under different conditions. However, firing patterns of each cell under several different conditions were frequently well reconstructed by an inverse dynamics representation with a single set of coefficients (13 cells among 21). This indicates that the relationships between P cell firing and OFR are roughly linear in those stimulus ranges. The estimated coefficients for acceleration and velocity suggested that the VPFL P cells properly encode the dynamic components of the motor command during vertical OFR. As for the positional component, however, these P cells are correlated with eye movement in the opposite direction. In the regression analysis without positional component, remarkable differences between observed and reconstructed firing patterns were noted especially in the initial phase of the movements, indicating that the negative positional component was not negligible during OFR Thus we conclude that during OFR, the VPFL P cells cannot provide the necessary final motor command, and other brain regions, downstream neural structures, or other types of P cells must provide lacking position-dependent motor commands. This finding about the negative correlation with the position is in the opposite sign with previous studies obtained from the fixation and the smooth pursuit movement. From these comparisons, how the VPFL contributes to a parr of the final motor command or how other brain regions complement the VPFL is suggested to be different for early and late phases of the movements.

 

40.       H. Gotoh, H. Ando, H. Kamada, A. Chavez-Pirson, and J. Temmyo

            "Spin relaxation of excitons in zero-dimensional InGaAs quantum disks"

            Appl. Phys. Lett. 72 (11), 1341-1343 (1998).

 

            ABSTRACT: We report the observation of spin relaxation of excitons in zero-dimensional semiconductor nanostructures. The spin relaxation is measured in InGaAs quantum disks by using a polarization dependent time-resolved photoluminescence method. The spin relaxation time in a zero-dimensional quantum disk is as long as 0.9 ns at 4 K, which is almost twice as long as the radiative recombination lifetime and is considerably longer than that in quantum wells. The temperature dependence of the spin relaxation time suggests the importance of exciton-acoustic phonon interaction. (C) 1998 American Institute of Physics.

 

41.       K. Hamada, K. Tamaki, T. Sasado, Y. Watai, S. Kani, Y. Wakamatsu, K. Ozato, M. Kinoshita, R. Kohno, S. Takagi, and M. Kimura

            "Usefulness of the medaka beta-actin promoter investigated using a mutant GFP reporter gene in transgenic medaka (Oryzias latipes)"

            Mol. Mar. Biol. Biotechnol. 7 (3), 173-180 (1998).

 

            ABSTRACT: The activity of the medaka beta-actin promoter as a ubiquitous expression Vector in transgenic medaka was examined using complementary DNA of the green fluorescent protein (GFP). Plasmid pOBA-GFP contained both the medaka beta-actin promoter and cDNA of the wild-type GFP, while pOBA-hGFP contained the medaka beta-actin promoter and cDNA of the mutant GFP in which serine was substituted for threonine at position 65 and codon usage was humanized to promote translation in vertebrate cells. The ApaI-SmaI fragment of both plasmids was microinjected into the nuclei of oocytes or the cytoplasm of embryos at the one-cell stage. The gene expression was detected, using a fluorescent stereomicroscope, from early stages of development to 1 week after hatching. The expression of the wild-type GFP was detected in early embryos, in the yolk sac and in small portions of the muscle and epidermis. This expression pattern was similar to that of the Escherichia coli beta-galactosidase reporter gene (lacZ), driven by the medaka beta-actin promoter, which was examined in our previous studies. The mutant GFP was expressed in early embryos and in many tissues such as the epidermis, blood vessels, muscle, notochord, fin ray, gut, eyes, and yolk sac, and the fluorescence was much stranger than that of the wild-type GFP. Thus, the usefulness of the medaka beta-actin promoter as a ubiquitous expression vector was confirmed using the mutant GFP as a reporter gene.

 

42.       A. Hamoudi, M. Ogura, X. L. Wang, T. Okada, and H. Matsuhata

            "High quality GaAs quantum wires grown by flow rate modulation epitaxy"

            Appl. Phys. A-Mater. Sci. Process. 66 (2), 137-141 (1998).

 

            ABSTRACT: Transmission electron microscopy, photoluminescence and photoluminescence excitation studies pointed out the significant impact of the flow rate modulation epitaxy technique in the growth of nanoscale quantum wires. Our results confirmed experimentally its ability to grow GaAs quantum wire layers of high crystalline and optical quality.

 

43.       A. Hamoudi, T. Sogawa, T. Saitoh, and J. Yumoto

            "Reflection high-energy electron diffraction real-time monitoring of an etch process implemented in molecular beam epitaxy technology: hydrogen chloride versus GaAs(001) epilayers"

            Appl. Phys. A-Mater. Sci. Process. 67 (3), 357-359 (1998).

 

            ABSTRACT: The effective implementation of an etch process in molecular beam epitaxy (MBE) technology is confirmed by reflection high-energy electron diffraction (RHEED). Preliminary experimental results obtained on hydrogen chloride (HCl)-etched GaAs(001) epilayers pointed out the remarkable ability to reproducibly fine-tune the etch process down to a single monolayer (ML) scale under the usual (2 x 4) arsenic-stabilized surface.

 

44.       I. Hashimoto, T. Mashiko, T. Kimura, and T. Imada

            "Human somatosensory evoked magnetic fields to vibratory stimulation of the index finger: is there frequency organization in SI?"

            Electromyogr. Mot. Control-Electroencephalogr. Clin. Neurophysiol. 109 (5), 454-461 (1998).

 

            ABSTRACT: Objective: Frequency organization in the human somatosensory cortex was studied, Design and methods: Somatosensory evoked magnetic fields (SEFs) from 12 subjects were measured following vibratory stimulation of the index finger by using a 122 channel whole head SQUID system. Sensory stimuli comprising a 40 ms vibration at frequencies of 50, 100, 200 and 400 Hz were delivered to the volar surface of the tip of the right index finger. Using a singled/pole model, the sources of the magnetic fields were estimated and mapped onto magnetic resonance images of each subject. The analysis of variance test(ANOVA) was used for statistics. Results: Source localization was determined on the main two peaks (M60 and M110) of the SEFs. All of the sources were located in the area 3b of somatosensory cortex (ST). There were no statistically significant differences between the locations of the dipoles evoked by different frequency stimulations. Conclusions: These results demonstrate the absence of systematic frequency organization at the hand representation area of the SI cortex. We speculate that high frequency vibration above 100 Hz are coded by the fast-spiking interneurons which synapse with Pacinian pyramidal neurons in SI. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved

 

45.       N. Hatakenaka

            "Josephson pi states"

            J. Phys. Soc. Jpn. 67 (11), 3672-3674 (1998).

 

            ABSTRACT: The Josephson effect under particle-number restriction is investigated based on the Feynman two-state model. The existence of a new dynamical mode of the Josephson phase, at the metastable state inherent in such a restricted situation; is shown. The new mode describes a number of features recently observed in a superfluid He-3 weak-link system.

 

46.       N. Hatakenaka

            "Andreev-reflected quasiparticle interference revisited"

            J. Phys. Soc. Jpn. 67 (10), 3360-3363 (1998).

 

            ABSTRACT: We reconsider the processes of the interference of Andreev-reflected quasiparticles with phases at each side of a Josephson junction. We show that a quasiparticle interference in a normal-metal region strongly depends on whether the Cooper pair tunneling across the junction is coherent or incoherent, which is affected hy the charge on the junction as well as dissipation. We also discuss the connection between the interference and duality of the phase and number in the mesoscopic Josephson junction and find that the Andreev-reflected quasiparticle interference is closely related to the applicability of quantum mechanics on a macroscopic scale.

 

47.       N. Hatakenaka

            "Quantum decay from Josephson pi states"

            Phys. Rev. Lett. 81 (17), 3753-3756 (1998).

 

            ABSTRACT: Quantum decay from Josephson pi states, which is inherent in the Josephson system with fixed particle numbers, is investigated. Since the pi states have two different decay paths, they can interfere during the decay processes by quantum tunneling due to a topological phase originating from total particle-number restriction and result in parity effect for tunneling. [S0031-9007(98)07457-2].

 

48.       N. Hatakenaka and H. Ezaki

            "Squeezing of Josephson phases in d.c. superconducting quantum interference devices"

            J. Phys. Chem. Solids 59 (10-12), 2062-2064 (1998).

 

            ABSTRACT: We theoretically study the two-mode squeezing of Josephson phases in d.c, superconducting interference devices. The non-linearity of phase interactions required for the squeezing is mediated by the external electromagnetic fields. Since the squeezing is one quantum aspect based on the Heisenberg uncertainty relation, the Josephson phase squeezing provides another scheme for investigating the quantum nature of macroscopic objects. The squeezing of the Josephson phases can be observed by detecting the quantum fluctuation of the supercurrent through the Josephson current-phase relation. (C) 1998 Elsevier Science Ltd. All rights reserved.

 

49.       N. Hatakenaka, M. Shiobara, K. Matsuda, and S. Tanda

            "Dimensional crossover of quantum nucleation processes in charge-density-wave phase slips"

            Phys. Rev. B 57 (4), R2003-R2005 (1998).

 

            ABSTRACT: A phenomenological model for quantum phase slips of charge-density waves that takes into account the system-size effect is presented. The process of quantum nucleation leading to the phase slip changes from vortex-pair to vortex-ring creations as the external electric field increases, which is analogous to the evolution of a ripple in a rectangular water tank. The crossover field is determined by the system size. The present model describes a number of features observed in the nonohmic conductivity in TaS3 at low temperature.

 

50.       J. Herfort, D. G. Austing, and Y. Hirayama

            "Electron transport in MIS-like GaAs/AlxGa1-xAs heterostructures with nanostructured gates"

            Solid-State Electron. 42 (7-8), 1135-1139 (1998).

 

            ABSTRACT: A novel approach to realize quasi-one-dimensional electron gases with high electron densities using an undoped GaAs/AlxGa1-xAs heterostructure is studied. The quasi-one-dimensional electron gas is field effect induced via a narrow top gate and the electrons are extracted from ion-implanted ohmic regions. The wires are characterized by low temperature magnetotransport experiments. The quasi-one-dimensional nature of the transport manifests itself in the observed depopulation of the one-dimensional subbands in a magnetic field perpendicular to the heterointerface and a model is presented to obtain a realistic estimation of the density distribution underneath the narrow gate and to determine the effective wire width. The effective width is found to be comparable to the gate width. Finally, the applicability of this approach to design electron-electron coupling structures is demonstrated by studying samples containing a narrow split across the gate. (C) 1998 Elsevier Science Ltd. All rights reserved.

 

51.       H. Hibino, Y. Homma, and T. Ogino

            "Triangular-tiled arrangement of 7x7 and '1x1' domains on Si(111)"

            Phys. Rev. B 58 (12), R7500-R7503 (1998).

 

            ABSTRACT: Ultrahigh-vacuum scanning electron microscopy reveals the presence of an ordered domain pattern with threefold symmetry on Si(111). During the transition between 7 x 7 and '1 x 1' phases on a Si(111) surface misoriented to [11 (2) over bar], triangular 7 x 7 domains nucleate at the upper edge of the step, and grow into the terrace. When the apex of the domain reaches the lower edge, the 7 x 7 and '1 x 1' domains form a triangular-tiled arrangement. This triangular-tiled arrangement is explained in terms of elastic-stress relaxation effects. [S0163-1829(98)50236-6].

 

52.       H. Hibino and T. Ogino

            "Formation of twinned two-bilayer-high islands during initial stages of Si growth on Si(111)root 3x root 3-B"

            Surf. Sci. 413, 132-140 (1998).

 

            ABSTRACT: We investigated the initial stages of Si molecular-beam epitaxial growth on a Si(111)root 3 x root 3-B surface using scanning tunneling microscopy. Ln the initial stapes, Si islands one or two bilayers (BL) high are formed. The number of Si atoms contained in these islands depends on the surface B concentration. The larger the surface B concentration, the more Si atoms there are in the 2BL-high islands. Furthermore, comparison between the positions of adatoms in the root 3 x root 3 reconstruction On the Si islands and the substrate shows that the 2BL-high islands are twinned with the substrate, but that the BL-high islands are not twinned. (C) 1998 Elsevier Science B.V. All rights reserved.

 

53.       H. Hibino, K. Sumitomo, T. Fukuda, Y. Homma, and T. Ogino

            "Disordering of Si(111) at high temperatures"

            Phys. Rev. B 58 (19), 12587-12589 (1998).

 

            ABSTRACT: Reflection high-energy electron diffraction (RHEED) and medium-energy ion scattering (MEIS) were used to investigate the disordering of a Si(lll) surface at high temperatures. RHEED intensities exhibit a steplike decrease around 1470 K during heating. There is a steplike increase in the surface-peak area measured using MEIS around this temperature. These results are consistent with the formation of a thin layer of positionally disordered atoms at the transition. [S0163-1829(98)05544-1].

 

54.       H. Hibino, K. Sumitomo, and T. Ogino

            "Growth process of twinned epitaxial layers on Si(111)root 3x root 3-B and their thermal stability"

            Appl. Surf. Sci. 132, 41-46 (1998).

 

            ABSTRACT: We investigated the growth of twinned epitaxial Si layers on a Si(111)root 3 X root 3 -B surface. In the initial growth stages, untwinned bilayer-high (BL-high) and twinned 2-BL-high islands are nucleated, and the ratio of the number of Si atoms included in the twinned 2-BL-high islands to the number of the total deposited Si atoms increases as the surface B concentration increases. Preferred nucleation of Si islands occurs at domain boundaries of the root 3 X root 3 reconstruction. Moreover, BL-high islands rather than 2-BL-high islands nucleate there. Coalescence of 2-BL-high islands causes the domain boundary density on the first two bilayers to be much larger than that on the substrate. Therefore, after completion of the first twinned two bilayers, BL-high islands are formed predominantly. BL-high islands follow the stacking sequences of the twinned two bilayers. Thus, grown layers are totally twinned. We also investigated the thermal stability of twinned epitaxial layers. The temperature at which twinned epitaxial layers are transformed into untwinned layers strongly depends on the thickness. (C) 1998 Elsevier Science B.V. All rights reserved.

 

55.       H. Hibino, K. Sumitomo, and T. Ogino

            "Twinned epitaxial layers formed on Si(111)root 3x root 3-B"

            J. Vac. Sci. Technol. A-Vac. Surf. Films 16 (3), 1934-1937 (1998).

 

            ABSTRACT: We investigate the growth process of twinned epitaxial Si layers on Si(111)root 3X root 3-B and their thermal stability. In the initial growth stages, twinned two-bilayer-high (2-BL-high) and untwinned BL-high islands are formed, and at higher surface B concentration, there are more twinned 2BL islands than untwinned BL islands. Domain boundaries of the root 3X root 3 reconstruction act as preferential island nucleation sites, especially for untwinned BL islands. Therefore, to grow epitaxial layers twinned with the already-grown twinned layers, post-growth anneal is essential to increase the surface B concentration and to reduce the domain boundary density. On the other hand, the temperature at which twinned layers are transformed into untwinned layers strongly depends on the thickness. We demonstrate the possibility of growing superlattices of layers that have twinned and untwinned orientations with the substrate (polytypes) by precisely controlling the growth and post-growth anneal parameters. (C) 1998 American Vacuum Society.

 

56.       A. Hirata, K. Machida, S. Maeyama, Y. Watanabe, and H. Kyuragi

            "Diffusion barrier mechanism of extremely thin tungsten silicon nitride film formed by ECR plasma nitridation"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 37 (3B), 1251-1255 (1998).

 

            ABSTRACT: The diffusion barrier mechanism of tungsten silicon nitride (WSIN) film formed by ECR plasma nitridation is investigated. For this purpose, we examined film thickness, nitrogen content, surface composition, and local atomic ordering of this WSiN and correlated these characteristics with its barrier capability. It is revealed that WSIN shows good barrier capability when RF bias is applied to the substrate during nitridation even though it is less than 6-nm thick. Applying RF bias increases the nitrogen content in WSiN. Moreover, Si atoms are preferentially sputtered and the local atomic ordering in WSiN is lowered because the effect of ion bombardment is remarkably pronounced. It is supposed that these film characteristics contribute to the suppression of phosphorus diffusion through interstitial sites. As a result, WSiN functions as an excellent barrier layer even though it is extremely thin.

 

57.       Y. Hirayama, K. Muraki, and T. Saku

            "Two-dimensional electron gas formed in a back-gated undoped heterostructure"

            Appl. Phys. Lett. 72 (14), 1745-1747 (1998).

 

            ABSTRACT: By using a back-gate operation, a high-quality two-dimensional electron gas (2DEG) is formed in an undoped GaAs/AlGaAs inverted heterostructure. A high mobility of around 3 x 10(6) cm(2)/V s at 1.6 K is obtained for the structure without any compensating surface doping. The electron density is controllable down to 7 x 10(9) cm(-2). The relation between electron density and mobility is studied for samples both with and without a surface gate. The obtained results indicate that background impurities and an inhomogeneity of the electric field coming from the surface govern the mobility in a low-electron-density region and that the interface inhomogeneity becomes important at a high electron density. (C) 1998 American Institute of Physics. [S0003-6951(98)02214-1].

 

58.       Y. Hirayama and T. Saku

            "AlGaAs/GaAs heterostructures grown on a focused-Be-ion-beam written backgate"

            J. Vac. Sci. Technol. B 16 (4), 2543-2546 (1998).

 

            ABSTRACT: Novel structures, in which an A1GaAs/GaAs modulation doped structure is overgrown on an underlying Be-implanted p-type region, are successfully fabricated using a system in which focused-ion-beam (FLB) implantation and molecular-beam epitaxy chambers are connected through a high vacuum tunnel. The two-dimensional electron; gas (2DEG) at the heterointerface is well controlled by a voltage applied to the Be-FIB written backgate. Though Be out diffusion into the overgrown layer is observed, the sharp front of the out diffusion enables us to fabricate devices with a small separation between the 2DEG and p-type backgate. The three-dimensional hole gas (3DHG) formed by the Be-FIB implantation is used not only as a backgate but also for measuring the interaction between 2DEG and 3DHG. (C) 1998 American Vacuum Society.

 

59.       Y. Homma

            "Secondary electron imaging of nucleation and growth of semiconductors for nanostructure fabrication"

            Thin Solid Films 332 (1-2), 262-266 (1998).

 

            ABSTRACT: In situ scanning electron microscopy (SEM) images of growing surfaces provide valuable insights into the control of growing structures. Surface morphology evolution due to 2D island nucleation and coalescence is clearly imaged in GaAs molecular beam epitaxy, and compared between (001) and (111)A surfaces. Nucleation sites of 3D islands are identified in solid phase epitaxy of Ge on Si(111). Nucleation sites can be controlled using atomic step networks, as demonstrated by the selective growth of GaAs wires and Au dots on Si(111). (C) 1998 Elsevier Science S.A. All rights reserved.

 

60.       Y. Homma

            "Sublimation and phase transitions on Si(111) surface observed by ultrahigh vacuum scanning electron microscopy"

            Surf. Rev. Lett. 5 (3-4), 685-691 (1998).

 

            ABSTRACT: We studied the atomic step behavior on Si(lll) during sublimation using ultrahigh vacuum scanning electron microscopy. A (111) plane with step spacings as large as several tens of micrometers could be obtained at the bottom of a crater by heating a vicinal Si(lll) substrate with craters at around 1200 degrees C in an ultrahigh vacuum. The step spacing on the plane was determined by nucleation of macrovacancies at the center of the plane while steps moved in a step flow manner, and was related to the adatom diffusion length. Above 1200 degrees C, we found a transition-like increase in the step spacing. The electric current direction that induced step bunching changed at around the transition temperature. We attributed these phenomena to incomplete surface melting on the Si(lll) surface. We also investigated the influence of heating current on the 7 x 7 phase transition using the wide Si(lll) plane and found that the size of the 7 x 7 phase just below the transition temperature depended on the current direction.

 

61.       Y. Homma, H. Hibino, T. Ogino, and N. Aizawa

            "Sublimation of a heavily boron-doped Si(111) surface"

            Phys. Rev. B 58 (19), 13146-13150 (1998).

 

            ABSTRACT: We investigated sublimation of a heavily boron-doped Si(lll) surface in comparison with that of a normal Si(lll) surface in ultrahigh vacuum. Step spacing during step-flow sublimation is analyzed as a measure of the adatom diffusion length using >50-mu m-wide (111) planes created at the bottom of craters. On the heavily doped 1x1 surface, the step spacing is smaller and the step-spacing transition (or "incomplete surface melting'' transition) temperature is 60 degrees higher than those on the normal 1x1 surface. These results are interpreted in terms of the effect of boron at S-5 substitutional sites. Below 1100 degrees C, the sublimation of heavily doped surface on the wide terrace turns into a two-dimensional vacancy-island nucleation mode from step-flow sublimation observed above 1100 degrees C. [S0163-1829(98)05243-6].

 

62.       Y. Homma, F. Tohjou, A. Masamoto, M. Shibata, H. Shichi, Y. Yoshioka, T. Adachi, T. Akai, Y. Gao, M. Hirano, T. Hirano, A. Ihara, T. Kamejima, H. Koyama, M. Maier, S. Matsumoto, H. Matsunaga, T. Nakamura, T. Obata, K. Okuno, S. Sadayama, K. Sasa, K. Sasakawa, Y. Shimanuki, S. Suzuki, D. E. Sykes, I. Tachikawa, H. Takase, T. Tanigaki, M. Tomita, H. Tosho, and S. Kurosawa

            "Secondary ion mass spectrometry round-robin study of relative sensitivity factors in gallium arsenide"

            Surf. Interface Anal. 26 (2), 144-154 (1998).

 

            ABSTRACT: Round-robin studies on relative sensitivity factors (RSFs) in secondary ion mass spectrometry (SIMS) were conducted using bulk GaAs samples uniformly doped with various impurity elements. A total of 31 laboratories participated in two round-robins, More than 30 sets of relative ion intensities were obtained for a Si, Cr, Mn, Pe, Cu, Zn, In and Te in GaAs. The RSFs for both positive and negative ions were derived for several types of SIMS instruments. The effect of primary ion incident angle was examined using quadrupole-based instruments and feued to be the determining factor of the instrumental dependence of RSF. (C) 1998 John Whey dr Sons, Ltd.

 

63.       T. Honda, S. Tarucha, and D. G. Austing

            "Gate performance in resonant tunneling single electron transistor"

            IEICE Trans. Electron. E81C (1), 2-7 (1998).

 

            ABSTRACT: Gate performance for observing Coulomb oscillations and Coulomb diamonds are compared for two types of gated sub-mu m double-barrier heterostructures, Thr first type of device contains modulation-doped barriers. whereas the second type of device contains a narrower band gap material for the well and no barriers with doped impurities. Both the Coulomb oscillations and Coulomb diamonds are modified irregularly as a function of ate voltage in the first type of device, while in the second type of device they are only systematically modified, reflecting atom-like properties of a quantum dot. This difference is explained in terms of the existence of Impurities in the first type of device, which inhomogeneously deform the rotational symmetry of the lateral confining potential as the gate voltage is varied. The absence of impurities is the reason why we observe the atom-like properties only in th second type of device.

 

64.       S. Horiguchi

            "Conditions for a direct band gap in Si quantum wires"

            Superlattices Microstruct. 23 (2), 355-364 (1998).

 

            ABSTRACT: The condition for a direct band gap in Si quantum wires is investigated within the effective mass theory for wires coherent in every direction perpendicular to the wire direction. The condition is calculated using the equivalent condition that the minimum energy of the one-dimensional sub-bands of electrons is at the Gamma-point, because holes always have a minimum energy at this point. It is shown that only Si quantum wires on the {100} plane can have a direct band gap. In particular, [100]-oriented Si quantum wires have a direct band gap regardless of their cross-sectional shape. For wires other than (100)-oriented ones, the condition of a direct band gap for rectangular, elliptic, triangular and trapezoidal cross-sectional shapes is investigated, assuming that the confinement potential is infinitely high in order to have the condition determined only by their cross-sectional shape and direction independently of their cross-sectional size. In all cases, wires have a direct band gap when the ratio of wire height (size perpendicular to the {100} plane) to width (size parallel to the {100} plane) decreases, and [110]-oriented wires have the largest ratio of height to width for a direct band gap. (C) 1998 Academic Press Limited.

 

65.       T. Horiuchi, O. Niwa, and N. Hatakenaka

            "Evidence for laser action driven by electrochemiluminscence"

            Nature 394 (6694), 659-661 (1998).

 

            ABSTRACT: Emission of light from excited-state dye molecules can be driven by the electron transfer between electrochemically generated anion and cation radicals-a process known as electrochemiluminescence(1-5) (ECL). ECL has been investigated for both display(6) and laser applications(7-9). The latter is of particular interest as, in contrast to conventional dye lasers, a laser operating by this principle would not require an additional laser source optically to pump the dye into the required excited state, and may offer additional advantages in terms of power, tunability and range of available wavelengths. But the pumping rate hitherto achieved by ECL is two orders of magnitude lower than the optical pumping threshold(9). Here we describe a device structure designed to enhance the efficiency of the ECL process, and present evidence that laser action has been realized in such a structure: the ECL spectrum is strongly modulated by the device structure, the output intensity shows a clear threshold as the drive current increases, and spectral narrowing is observed as the intensity increases.

 

66.       N. Ishikawa, Y. Chimi, A. Iwase, H. Maeta, K. Tsuru, O. Michikami, T. Kambara, T. Mitamura, Y. Awaya, and M. Terasawa

            "Electronic excitation effects in ion-irradiated high-T-c superconductors"

            Nucl. Instrum. Methods Phys. Res. Sect. B-Beam Interact. Mater. Atoms 135 (1-4), 184-189 (1998).

 

            ABSTRACT: We have measured the fluence dependence of the c-axis lattice parameter in EuBa2Cu3Oy (EBCO) irradiated with various ions from He to Au over the wide energy range from 0.85 MeV to 3.80 GeV. We have observed a linear increase of the c-axis lattice parameter with increasing fluence for all irradiations. The slope of c-axis lattice parameter against fluence, which corresponds to the defect production rate, is separated into two contributions; the effect via elastic displacement and the effect via electronic excitation. The former contribution exhibits a linear increase against the nuclear stopping power, S-n. The latter contribution is scaled by the primary ionization rate, dJ/dx, rather than by the electronic stopping power, S-e, and is nearly proportional to (dJ/dx)(4). (C) 1998 Elsevier Science B.V.

 

67.       T. Ishiyama, E. Katayama, K. Murakami, K. Takahei, and A. Taguchi

            "Electron spin resonance of Er-oxygen complexes in GaAs grown by metal organic chemical vapor deposition"

            J. Appl. Phys. 84 (12), 6782-6787 (1998).

 

            ABSTRACT: We have performed electron spin resonance (ESR) measurements on Er-doped GaAs grown with oxygen codoping by metal organic chemical vapor deposition. An isotropic line (an effective g value, g = 5.95) which had been already reported was observed in samples without oxygen codoping. On the other hand, for samples with oxygen codoping other strong anisotropic ESR lines originated from four kinds of Er3+ (4f(11)) centers (A, B, C, and D) were newly observed in addition to the weaker isotropic line. The anisotropic g tensors obtained by analyzing the angular dependence of the ESR lines indicate that B and C centers are of orthorhombic C-2 upsilon symmetry, A center has lower symmetry than orthorhombic symmetry, and D center is of trigonal C-3i symmetry. The ESR intensities of A, B, and C centers were approximately two orders of magnitude higher than that of the isotropic line with g = 5.95. The ESR intensity of D center was one order of magnitude lower than those of A, B, and C. The Er concentration dependence of the relative ESR intensities of these centers was investigated, which indicates (i) the ESR intensities of A and D increase with increasing Er concentration, and (ii) those of B and C are saturated above the Er concentration [Er] greater than or equal to 10(18) cm(-3). The ESR measurement under light illumination, as well as the Er concentration dependence, suggests that the B center with C-2 upsilon symmetry corresponds to the dominant Er luminescent center under host photoexcitation. (C) 1998 American Institute of Physics. [S0021-8979(98)03724-4].

 

68.       T. Ito and K. Shiraishi

            "Theoretical investigations of adsorption behavior on GaAs(001) surfaces"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 37 (8), 4234-4243 (1998).

 

            ABSTRACT: Adsorption behavior an GaAs(001)-(2 x 4)beta 2 and -c(4 x 4) surfaces is systematically investigated by the calculation of migration potentials for Ga adatoms and Monte Carlo simulation. In the calculation procedure, we use an energy formalism based on the empirical interatomic potentials and the electron counting model in order to incorporate the strain and electronic energy contributions. The calculated migration potentials for Ga adatoms imply that Ga adatoms preferentially reside in missing dimer sites on both (2 x 4)beta 2 and c(4 x 1) surfaces. On the (2 x 4)beta 2 surface, lattice sites in the missing dimer row near As-dimer kinks and B-type step edges are stable for Ga adatoms, whereas no preferential adsorption site is found near A-type step edges. Opposite qualitative trends are found in the migration potentials near step edges on the c(4 x 4) surface. The calculated results are consistent with experimental results and are discussed in terms of atomic configurations and the number of electrons remaining in Ga dangling bonds. Based on the energy formalism, an electron counting Monte Carlo (ECMC) simulation was performed to investigate the adsorption or desorption sequences on GaAs(001)-(2 x 4)beta 2 and -c(4 x 4) surfaces in MBE growth. The results imply that Ga adatoms impinging on the GaAs(001) surfaces play an important role in the incorporation or desorption of As to restore the electron counting model.

 

69.       T. Ito and K. Shiraishi

            "Electron counting Monte Carlo simulation of the structural change of the GaAs(001)-c(4x4) surface during Ga predeposition"

            Jpn. J. Appl. Phys. Part 2 - Lett. 37 (3A), L262-L264 (1998).

 

            ABSTRACT: An electron counting Monte Carlo (ECMC) simulation is performed to investigate the structural change of As-rich GaAs(001)-c(4 x 4) surfaces during Ca predeposition, incorporating the As desorption process as a function of Ga adatom coverage based on ab initio calculations. The ECMC simulation results indicate that predepositing 0.5 monolayers of Ga on the GaAs(001)-c(4 x 4) surface induces As desorption and reduces effective As coverage theta(As) to 1.25, where four Ga dimers and two As dimers co-exist in the (4 x 4) surface unit cell used in this simulation. Subsequent equilibration of this surface changes its structure to (2 x 4)-like surface with theta(As) = 0.75 and one As-dimer row and three missing As-dimer rows. These simulated results successfully give one possible interpretation to some puzzling questions in experimental results.

 

70.       T. Ito, K. Shiraishi, H. Kageshima, and Y. Y. Suzuki

            "A theoretical investigation of the potential for inter-surface migration of Ga adatoms between GaAs(001) and (111)B surfaces"

            Jpn. J. Appl. Phys. Part 2 - Lett. 37 (5A), L488-L491 (1998).

 

            ABSTRACT: The potential for inter-surface migration of Ga adatoms between GaAs(001)-(2x4) and GaAs(111)B-(root 19 x root 19) or -(2 x 2) is theoretically investigated. We used empirical interatomic potential and an energy term as a function of the number of electrons remaining in the Ga dangling bonds. The calculated results indicate that the lattice sites on the (001)-(2 x 4)beta 2 surface are more favorable for Ga adatoms than those on the (111)B-(root 19 x root 19) and -(2x2) surfaces. This is because the formation of Ga-Ga dimers in the missing dimer rows on the (001)-(2x4)beta 2 surface suppresses the number of electrons remaining in the Ga dangling bonds. These results suggest that Ga atoms favorably adsorb on the (001) top surface and that Ga atoms impinging on the (111)B side surface basically diffuse to the (001) top surface so long as both top and side surfaces are single-domain structures. This conclusion is consistent with some aspects of other experimental studies.

 

71.       M. Itoh, Y. Hirayama, and S. Tarucha

            "Low-energy focused-ion-beam shape observation and its noise reduction for nanofabrication"

            Microelectron. Eng. 40 (1), 21-34 (1998).

 

            ABSTRACT: Two types of noise from the variable landing-energy focused-ion-beam (FIB) system appeared when FIB was line-scanned on an n-GaAs wafer and implantation-induced damage was estimated by using selective etching and secondary electron microscope (SEM) observation. The first had a rough surface with small craters away from implanted lines and the second had clearly observable scratchiness along implanted lines. Cathode luminescence measurement and auger analysis were performed to estimate beam-tail spreading. Both the long-beam-tail and the scratchy noise probably originated from unintentionally scattered beams in the ion-beam lens column and/or neutral particles emitted from the liquid metal ion source. As a result, these noises could be greatly reduced by locating a new aperture at an appropriate position. Using this refined FIB system, low landing-energy-ion-beams should be able to be applied to fabricate high-quality mesoscopic devices.

 

72.       Y. Iwasaki, T. Horiuchi, M. Morita, and O. Niwa

            "Analysis of electrochemical processes using surface plasmon resonance"

            Sens. Actuator B-Chem. 50 (2), 145-148 (1998).

 

            ABSTRACT: We simultaneously employed voltammetry and surface plasmon resonance (SPR) measurements and monitored electrochemical processes on gold electrode. SPR is sensitive not only to the adsorbed layer on the gold electrode, but also to the dielectric properties of the solution phase. Therefore, an electrochemically modulated diffusion layer can be detected by SPR. We tested the relationship between the time differential SPR data and the electrode current for two electrochemical processes and confirmed the possibility of using electrochemical SPR measurement. (C) 1998 Elsevier Science S.A. All rights reserved.

 

73.       S. Jiang, S. Machida, Y. Takiguchi, H. Cao, and Y. Yamamoto

            "Wide band AC balanced homodyne detection of weak coherent pulses"

            Opt. Commun. 145 (1-6), 91-94 (1998).

 

            ABSTRACT: A wide band AC balanced homodyne detection technique was applied to measure the amplitude of coherent pulses. The ultimate sensitivity given by a peak signal to noise ratio (S/N) = 1 of our system is estimated to be about 0.25 fW (3.3 X 10(-24) J/pulse or a photon number 1.25 X 10(-5) photons/pulse). As a demonstration for probing very weak ultrafast coherent optical processes, an exciton-polariton oscillation in a GaAs single quantum well microcavity was observed up to nine oscillation periods. (C) 1998 Elsevier Science B.V.

 

74.       S. D. Jiang, S. Machida, Y. Takiguchi, Y. Yamamoto, and H. Cao

            "Direct time-domain observation of transition from strong to weak coupling in a semiconductor microcavity"

            Appl. Phys. Lett. 73 (21), 3031-3033 (1998).

 

            ABSTRACT: We measured temporal evolution of the coherent emission from a semiconductor microcavity by a very sensitive ac balanced homodyne detection system. The experimental results can be well explained by the coupled exciton-photon model with varying exciton linewidth. (C) 1998 American Institute of Physics. [S0003-6951(98)00347-7].

 

75.       Y. Jimbo, A. Kawana, P. Parodi, and V. Torre

            "The dynamics of a neuronal culture from dissociated cortical neurons of neonatal rats"

            Eur. J. Neurosci. 10, 403-403 (1998).

 

            ABSTRACT:

76.       Y. Jimbo, H. P. C. Robinson, and A. Kawana

            "Strengthening of synchronized activity by tetanic stimulation in cortical cultures: Application of planar electrode arrays"

            IEEE Trans. Biomed. Eng. 45 (11), 1297-1304 (1998).

 

            ABSTRACT: Rat cortical neurons were cultured on planar electrode arrays with 64 embedded electrodes, Whole-cell recording from single neurons and multisite extracellular recording were carried out simultaneously in the cultured cortical networks, and the effects of focal tetanic stimulation of the culture were studied. Both the number of action potentials and the propagation velocity of stimulated bursts were increased after tetanic stimulation. These changes were associated with a marked increase in the number of late components in the synaptic current, but with little or no increase in the early peak synaptic current. The effects of tetanic stimulation were consistent with a widespread increase in the reliability of monosynaptic transmission.

 

77.       Y. Jimbo, T. Tateno, and H. P. C. Robinson

            "Simultaneous induction of potentiation and depression in cortical network activity"

            Eur. J. Neurosci. 10, 222-222 (1998).

 

            ABSTRACT:

78.       M. R. Junnarkar and N. Uesugi

            "Computer simulation of ultra-short optical pulse propagation in solid and hollow wave-guides"

            IEICE Trans. Electron. E81C (2), 240-245 (1998).

 

            ABSTRACT: We examine effects of higher order dispersion and optical non-linearity, including linear attenuation on intense short pulses propagating along solid and Noble-gas-filled waveguides. In order to simulate realistic pulse and spectral shapes. we have taken into account quadratic and cubic dispersion as well as Raman (solid wave-guide) and 'shock' nonlinear terms in the generalized Schrodinger equation of propagation. The phonon oscillation corresponding to 13.3 THz in SiO2 gets superimposed on to the exit pulse in the normal dispersion regime of solid fiber for lengths exceeding root 6L(D)L(NL). The super continuum spectrum from hollow Noble-gas-filled fibers shows remarkably deep modulations.

 

79.       H. Kageshima and K. Shiraishi

            "First-principles study of oxide growth on Si(100) surfaces and at SiO2/Si(100) interfaces"

            Phys. Rev. Lett. 81 (26), 5936-5939 (1998).

 

            ABSTRACT: The energetics of the atomic process of Si-oxide growth on Si(100) surfaces and at SiO2/Si(100) interfaces are theoretically studied by first-principles calculation. It is found that the stress induced during the growth plays a crucial role in the growth procedure itself. The preferential growth direction of the oxide nucleus on the surfaces is vertical to the substrate, whereas that at the interfaces is lateral. Moreover, Si atoms are inevitably emitted from the interface to release the stress induced during Si oxide growth.

 

80.       H. Kageshima and K. Shiraishi

            "Theoretical study of the band offset at silicon-oxide/silicon interfaces with interfacial defects"

            Surf. Sci. 407 (1-3), 133-139 (1998).

 

            ABSTRACT: The role of interfacial defects in determining the band offset at silicon-oxide/silicon interfaces is studied using the first-principles band-offset evaluation method. The calculations are based on the cristobalite/Si(100) interface model. The results show that interfacial Si-OH bonds greatly enhance the valence band offset while interfacial Si-H bonds slightly enhance the offset. The changes in the band offsets can be explained by measuring the changes in the interfacial dipoles. These results indicate that interfacial Si-OH bonds can cause gate oxide deterioration in a metal-oxide-semiconductor device. It was also found that the experimentally reported hydrogen annealing effects on the barrier height cannot be explained only by termination of interfacial Si dangling bonds by H atoms or only by the creation of interfacial OH defects. (C) 1998 Elsevier Science B.V. All rights reserved.

 

81.       H. Kageshima and K. Shiraishi

            "Silicon-kicking-out mechanism in initial oxide formation on hydrogen-terminated silicon (100) surfaces"

            Appl. Surf. Sci. 132, 176-181 (1998).

 

            ABSTRACT: The initial oxide formation process on hydrogen-terminated Si(100) surfaces and the creation of interstitial Si atoms during oxidation are studied by using a first-principles method. The results suggest that oxide regions tend to form islands. It is also found that Si atoms are preferably kicked out of the surface during the oxidation to release stress induced by the oxidation. An atomic model for the Si-kicking-out process is proposed and its microscopic origin is discussed. (C) 1998 Elsevier Science B.V. All rights reserved.

 

82.       H. Kamada, H. Ando, J. Temmyo, and T. Tamamura

            "Excited-state optical transitions of excitons and biexcitons in a single InxGa1-xAs quantum disk"

            Phys. Rev. B 58 (24), 16243-16251 (1998).

 

            ABSTRACT: The photoluminescence of In(x)Gal(1-x)As/A1(x)Ga(1-x)As quantum disks is investigated by microscope photoluminescence (PL) and PL excitation spectroscopies. The excited-state transitions of excitons and biexcitons are studied in terms of their dependence on excitation photon polarization. Their origins are analyzed on the basis of symmetry properties expected of excitons and biexcitons. Dominant excited-state resonances are ascribed to successive two-step absorptions of two photons of opposite optical orientation, one into an exciton excited state followed by another into a densely distributed biexciton excited state. Filling of the exciton state is found to lead to absorption from the exciton ground state to the biexciton excited state. Remaining excitation resonances with large oscillator strength are identified as two-photon absorption processes that directly create weakly correlated exciton pair states. [S0163-1829(98)05147-9].

 

83.       M. Kasu, N. Kobayashi, H. Tanaka, and O. Mikami

            "Nitrogen radical adsorption on InAs (001) surface studied by scanning tunneling microscopy and x-ray photoelectronic spectroscopy"

            Appl. Phys. Lett. 73 (25), 3754-3756 (1998).

 

            ABSTRACT: The adsorption of nitrogen (N) radicals (nitridation) on InAs (001) surfaces has been studied by ultrahigh-vacuum scanning tunneling microscopy and x-ray photoelectronic spectroscopy. The nitridation proceeds as Langmuir adsorption. The N adsorption at 350 degrees C is faster than that at 100 degrees C, but N adsorption rates at 100 degrees C on InAs and GaAs are almost the same. These results are explained as follows: at 350 degrees C, N radicals bond mainly with the topmost In atoms on an In-stabilized surface, and at 100 degrees C, N radicals replace As atoms in the topmost layer on an As-stabilized surface, and subsequently bond with In atoms in the second layer. The amorphous 100 degrees C nitrided surface layer is found to have an insulating characteristic without surface states. (C) 1998 American Institute of Physics. [S0003-6951(98)03551-7].

 

84.       M. Kasu, T. Makimoto, and N. Kobayashi

            "Selectivity mechanism of all ultra high vacuum scanning tunneling microscopy based selective area growth"

            Appl. Surf. Sci. 132, 452-456 (1998).

 

            ABSTRACT: We describe a selective area growth based on ultra-high-vacuum (UHV)-scanning-tunneling-microscopy (STM) lithography. After nitridation of GaAs surfaces and selective depassivation by UHV-STM, an array of uniform 6.4 +/- 0.8-nm high GaAs dots was successfully grown on the depassivated areas (50 nm x 50 nm) using trimethylgallium (TMG) and tertiarybutylarsine. On the side walls of dots, (114) or (117) facets appeared. It was found that unintentional growth on the nitrided mask surface is due to TMG decomposition on the nitrided surface. The unintentional growth can be suppressed by using an amorphous-like nitrided surface and by increasing the thickness of the nitrided surface layer, and consequently the selectivity is improved. (C) 1998 Elsevier Science B.V. All rights reserved.

 

85.       A. Kawaharazuka, K. Shiraishi, and Y. Horikoshi

            "Electric field induced recombination centers in GaAs"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 37 (3B), 1622-1625 (1998).

 

            ABSTRACT: We investigated the lateral electric field effect in a GaAs/AlGaAs single quantum well and in AlGaAs and GaAs single layers. We observed the quenching of photoluminescence spectra at low temperatures even when the electric field was much lower than that required for the dissociation of the excitons. To explain this phenomenon we propose a model of new recombination center formation by considering the displacement of charged atoms. We also performed theoretical calculations. By ab initio calculations, we found that a meta-stable state exists when negatively charged Ga atoms are displaced to the interstitial sites. The calculated potential barrier height from the stable state to the meta-stable state was as high as 0.5 eV. However, the meta-stable to stable transition barrier height was only 0.05 eV. These results are consistent with the experimental results.

 

86.       T. Kawamura, J. J. Delaunay, H. Takenaka, T. Hayashi, and Y. Watanabe

            "High-performance EUV/soft X-ray ellipsometry system using multilayer mirrors"

            J. Synchrot. Radiat. 5, 735-737 (1998).

 

            ABSTRACT: A high-performance EUV/soft X-ray ellipsometry system using multilayer mirrors has been developed. A couple of multilayer mirrors were used for the polarizer, and two multilayer mirrors were used for the rotating analyser. The multilayer mirrors were optimized to obtain a medium extinction of about 2000. An extinction ratio of the polarizer up to 10(4) can be achieved by using two multilayer mirrors, and the calculated reflectivity was more than 35%. The calculated error of the optical elements reveals that the error of the polarizer and misalignment optical parts is mainly of the first order, and that of the analyser is of the second order.

 

87.       D. R. T. Keeble and R. F. Hess

            "Orientation masks 3-Gabor alignment performance"

            Vision Res. 38 (6), 827-840 (1998).

 

            ABSTRACT: Several workers have concluded that Gabor alignment tasks are performed by using central tendencies of the micropatterns as a cue, One reason for this conclusion was that the 3-Gabor alignment task is performed equally well whether the orientations of the patches are collinear or orthogonal to the group orientation, We wished to find out if the orientation of the micropatterns has any effect on performance, We tested subjects in 3-micropattern alignment tasks using a variety of orientational conditions, If three vertically-aligned Gabor patches were vertical, horizontal or both, or if bullseye or Gaussian blobs were used, no difference in performance was found, If, however, the orientation of the patches was randomized, performance became much worse, Similarly, if the three patches were at 45 deg, thresholds were raised, The effect of orientation was maintained across different spatial frequencies, Control conditions involving randomization of the phase of the sinusoidal carrier, or jitter on the size of Gaussian blobs, confirmed that a central tendency of the micropatterns was indeed being used by subjects, indicating that the role of orientation in this task is that of a mask, rather than of a cue. (C) 1998 Elsevier Science Ltd. All rights reserved.

 

88.       T. Kiyokura, F. Maeda, and Y. Watanabe

            "Optical design for a bending-magnet beamline based on a varied-line-spacing plane grating"

            J. Synchrot. Radiat. 5, 572-574 (1998).

 

            ABSTRACT: A vacuum ultraviolet beamline with a grazing-incidence constant-deviation-angle monochromator, equipped with varied-line-spacing plane grating, has been designed for a bending-magnet light source. This type of monochromator has become very popular because of its high resolution, high throughput, simple scanning mechanism and fixed exit slit. To improve the energy resolution for a wide spectral range, Yan & Yagishita [(1995), KEK Report 95-9. KEK, Tsukuba, Ibaraki 305, Japan] proposed eliminating the defocus aberration at two specific energies in the spectral range, and their monochromator successfully achieved higher energy resolution by using an undulator light source. The possibility of applying this method to a bending-magnet beamline was examined and it was found that high performance can be achieved even using a bending-magnet light source with wide emittance. Performance evaluation relating to energy resolution, photon flux and spot size are reported.

 

89.       T. Kiyokura, F. Maeda, Y. Watanabe, Y. Kadota, Y. Iketaki, Y. Horikawa, M. Oshima, E. Shigemasa, and A. Yagishita

            "Photoelectron microspectroscopy observations of a cleaved surface of semiconductor double heterostructure"

            J. Vac. Sci. Technol. A-Vac. Surf. Films 16 (3), 1086-1090 (1998).

 

            ABSTRACT: We have developed a submicron-area high energy resolution photoelectron spectroscopy system equipped with a multilayer-coated Schwarzschild objective for forming a soft x-ray microbeam. We show the photoelectron microspectroscopy results of the cross section of a semiconductor double heterostructure sample, namely an epitaxial film [InP (50 nm thick)/In0.53Ga0.47As (2.3 mu m thick)/InP (100) substrate] grown by metalorganic chemical vapor deposition. The core-level photoelectron spectra were obtained from the cross section of the cleaved sample. The As 3d, Ga 3d, and In 4d peaks were observed in the In0.53Ga0.47As region. In the InP region, the As 3d and Ga 3d peaks were not observed, and only the In 4d peak was. This result corresponds to the structure observed by cross-sectional scanning electron microscopy. Moreover, we observed an irradiation effect that was caused by the microbeam. These results suggest that this photoelectron microspectroscopy system is a powerful tool for studying chemical and electronic states of submicron-area surfaces. (C) 1998 American Vacuum Society.

 

90.       T. Kiyokura, F. Maeda, Y. Watanabe, E. Shigemasa, A. Yagishita, M. Oshima, Y. Iketaki, and Y. Horikawa

            "Submicrometre-area high-energy-resolution photoelectron spectroscopy system"

            J. Synchrot. Radiat. 5, 1111-1113 (1998).

 

            ABSTRACT: A submicrometre-area photoelectron spectroscopy system that uses a multi-layer-coated Schwarzschild objective as the soft X-ray microbeam optics has been developed. The system is located at an undulator beamline (BL-16U) at the Photon Factory in the High Energy Accelerator Research Organization. By knife-edge measurement, the microbeam size was estimated to be 160 nm at the sample position using a 25-75% criterion. Photoelectron spectral measurements revealed that the Fermi edge width was 0.12 eV, which means that the instrumental resolution was 0.05 eV, after removing the natural broadening of the Fermi edge at room temperature. This system offers both high energy resolution and high spatial resolution.

 

91.       S. Kleefisch, L. Alff, U. Schoop, A. Marx, R. Gross, M. Naito, and H. Sato

            "Superconducting Nd1.85Ce0.15CuO4-y bicrystal grain boundary Josephson junctions"

            Appl. Phys. Lett. 72 (22), 2888-2890 (1998).

 

            ABSTRACT: We have studied the electric transport properties of symmetrical [001] tilt Nd1.85Ce0.15CuO4-y (NCCO) bicrystal grain boundary Josephson junctions (GBJs) fabricated on SrTiO3 bicrystal substrates with misorientation angles of 24 degrees and 36.8 degrees. The superconducting properties of the NCCO GBJs are similar to those of GBJs fabricated from the hole doped high temperature superconductors (HTS). The critical current density J(c), decreases strongly with increasing misorientation angle. The products of the critical current I-c and the normal resistance R-n (similar to 100 mu V at 4.2 K) an small compared to the gap voltage and ht weIl to the universal scaling Iaw IcRn infinity root J(c) found for GBJs Fabricated from the hole doped HTS. This suggests that the symmetry of the order parameter, which most likely is different for the electron and the hole doped HTS, has little influence on the characteristic properties of symmetrical [001] tilt GBJs. (C) 1998 American Institute of Physics.

 

92.       M. Koashi and N. Imoto

            "Maximum amount of information obtainable from a single quantum query of a database"

            Phys. Rev. Lett. 81 (23), 5233-5236 (1998).

 

            ABSTRACT: The maximum amount of information obtainable from a single query of a database through an n-bit bus register is n bits in a classical algorithm. A quantum algorithm can exceed this bound by a factor of 2, and this limit can be reached by encoding the excess n bits of information on the quantum phases of the register. We further show that the information in amounts close to this limit can also be extracted even if the database does not utilize quantum phases directly.

 

93.       M. Koashi and N. Imoto

            "No-cloning theorem of entangled states"

            Phys. Rev. Lett. 81 (19), 4264-4267 (1998).

 

            ABSTRACT: We derive a necessary and sufficient condition for two pure states, each entangled in two remote systems, to be clonable by the sequential access to the two systems. The result shows to what extent the correlation to other systems can be read out from a subsystem without altering its marginal density operators. This extends the standard no-cloning theorem to the case of a subsystem correlated to others.

 

94.       M. Koashi and M. Ueda

            "Matter-field theory of the Casimir force"

            Phys. Rev. A 58 (4), 2699-2707 (1998).

 

            ABSTRACT: A matter-field theory of the Casimir force is formulated in which the electromagnetic field and collective modes of dielectric media are treated on an equal footing. In our theory, the Casimir force is attributed to zero-point energies of the combined matter-field modes. We analyze why some of the existing theories favor the interpretation of the Casimir force as originating from zero-point energies of the electromagnetic field and others from those of the matter. [S1050-2947(98)02810-8].

 

95.       N. Kobayashi

            "Surface photoabsorption monitoring of III-V and GaN MOVPE surfaces"

            J. Cryst. Growth 195 (1-4), 228-233 (1998).

 

            ABSTRACT: Surface photoabsorption method is based on the measurement of the reflectance of p-polarized light at near Brewster angle. When the surface changes due to the adsorption and the desorption of constituent atoms and/or the surface is modified chemically, the reflectance can respond sensitively to both changes in anisotropic and isotropic dielectric constants of the surface. For the two-fold symmetric surfaces such as (0 0 1) oriented III-V surfaces, the anisotropic part can be extracted by taking a difference between the reflectances measured in the two orthogonal directions of [1 1 0] and [(1) over bar 1 0] and the spectrum thus obtained corresponds to the optical transition of anisotropic bond on the surface, i.e., the electronic transitions in the visible region and the vibrational transitions in the infrared region. The vibrational transition of the anisotropic GaN bonding can be observed by the nitridation of GaAs(0 0 1) surface. For the surfaces with symmetries other than two-fold, the anisotropic and the isotropic parts are indivisible but the reflectivity changes sensitively with the surface stoichiometry. Three surface phases of As-rich (2 x 2), root 19 x root 19 and Ga-rich (1 x 1) can be distinguished for the three-fold GaAs(1 1 1)B surface. For the three-fold wurtzite GaN(0 0 0 1) surface, Ga-rich and N-rich stoichiometry can be monitored in MOVPE. (C) 1998 Elsevier Science B.V. All rights reserved.

 

96.       Y. Kobayashi, T. Akasaka, and N. Kobayashi

            "In-situ monitoring of GaN MOVPE by shallow-angle reflectance using ultraviolet light"

            J. Cryst. Growth 195 (1-4), 187-191 (1998).

 

            ABSTRACT: The surface flatness of GaN grown by metalorganic vapor phase epitaxy (MOVPE) on c-plane sapphire substrates was monitored in situ by shallow-angle reflectance using p-polarized ultra-violet light (325 nm). During low-temperature GaN (LT-GaN) buffer growth at 600 degrees C, an oscillation due to an optical interference was observed, indicating the thickness can be controlled in situ to a few nm accuracy. During GaN growth at 1050 degrees C on LT-GaN, clear oscillations and no decrease of reflectivity indicate that the growth proceeds smoothly within a roughness of 10 nm. When both the surface roughness and hexagon density on the surface increased, the oscillation was quickly damped and the reflectivity decreased monotonously. The decrease in reflectivity is proportional to the product of the surface roughness and hexagon density. These results indicate that this method is a powerful tool for monitoring in situ the surface flatness and also for optimizing growth parameters, which are interrelated in GaN MOVPE. (C) 1998 Elsevier Science B.V. All rights reserved.

 

97.       Y. Kobayashi, T. Akasaka, and N. Kobayashi

            "Thermal stability of low-temperature GaN and AlN buffer layers during metalorganic vapor phase epitaxy monitored by in situ shallow angle reflectance using ultraviolet light"

            Jpn. J. Appl. Phys. Part 2 - Lett. 37 (10B), L1208-L1210 (1998).

 

            ABSTRACT: The thermal stability of low-temperature (LT) GaN and AlN buffer layers during the annealing process in metalorganic vapor phase epitaxy (MOVPE) was monitored in situ by shallow-angle reflectance using p-polarized ultra-violet light (325 nm). A LT-GaN or LT-AlN buffer layer was grown on c-plane sapphire substrates at 600 and 700 degrees C, respectively, by low pressure (76 Torr) MOVPE. These LT-buffer layers were annealed in H-2 or N-2 carrier gases and their thermal stability was examined. During annealing at 1020 degrees C under NH3 supply with H-2 carrier gas, the reflectivity dipped, indicating the desorption of the LT-GaN. In contrast, the reflectivity remained constant during annealing in N-2 carrier gas, indicating the LT-GaN layer was stable in N-2. The LT-AlN buffer layer was stable even in H-2 carrier gas. These results indicate that N2 carrier gas stabilizes the LT-GaN buffer layer during annealing over 1000 degrees C.

 

98.       Y. Kobayashi, H. Isaka, and T. Ogino

            "Composition of dimers on Ge/Si(001)2x1 surfaces analyzed by infrared (IR) reflection spectroscopy of surface hydrogen vibration"

            Appl. Surf. Sci. 132, 314-320 (1998).

 

            ABSTRACT: The composition of dimer structures formed on a Ge/Si(001)2 x 1 surface was investigated under various conditions of Ge coverage and annealing temperature using surface infrared (IR) spectroscopy on Si substrates with a buried metal layer (BML). Dimer structures were modified by atomic hydrogen to visualize the surface species in the IR spectra, where the signals from the mixed Ge-Si and pure Si-Si/Ge-Ge dimers as well as the non-dimer structures have different frequencies and thus are distinguishable from each other. These surface modes can be assigned to specific dimer structures on the basis of the surface selection rule on the BML substrate. Ge grows as mixed Ge-Si dimers for 0.2 monolayer (ML) of initial Ge coverage, as a mixture of the mixed and pure dimers for 0.6 ML, and as the pure Ge-Ge dimers for 1.2 ML. On annealing, Ge in the Ge-Ge and Ge-Si dimers diffuses into the second or deeper layers of Si and the dimers converted into pure Si-Si dimers at 810 degrees C, through the formation of the mixed dimer from the pure Ge-Ge dimer at medium annealing temperature. These results show the potential of IR spectroscopy as a sensitive probe for evaluating the composition of semiconductor surfaces. (C) 1998 Elsevier Science B.V. All rights reserved.

 

99.       Y. Kobayashi, K. Kawano, A. Takemura, Y. Inoue, T. Kitama, H. Gomi, and M. Kawato

            "Temporal firing patterns of Purkinje cells in the cerebellar ventral paraflocculus during ocular following responses in monkeys II. Complex spikes"

            J. Neurophysiol. 80 (2), 832-848 (1998).

 

            ABSTRACT: Many theories of cerebellar motor learning propose that complex spikes (CS) provide essential error signals for learning and modulate parallel fiber inputs that generate simple spikes (SS). These theories, however, do not satisfactorily specify what modality is represented by CS or how information is conveyed by the ultra-low CS firing rate (1 Hz). To further examine the function of CS and the relationship between CS and SS in the cerebellum, CS and SS were recorded in the ventral paraflocculus (VPFL) of awake monkeys during ocular following responses (OFR). In addition, a new statistical method using a generalized linear model of Bring probability based on a binomial distribution of the spike count was developed for analysis of the ultra-low CS firing rate. The results of the present study showed that the spatial coordinates of CS were aligned with those of SS and the speed-tuning properties of CS and SS were more linear for eye movement than retinal slip velocity, indicating that CS Contain a motor component in addition to the sensory component identified in previous studies. The generalized linear model to reproduce Bring probability confirmed these results, demonstrating that CS conveyed high-frequency information with its ultra-low Bring frequency and conveyed both sensory and motor information. Although the temporal patterns of the CS were similar to those of the SS when the sign was reversed and magnitude was amplified similar to 50 times, the velocity/acceleration coefficient ratio of the eye movement model, an aspect of the CS temporal firing profile, was less than that of the SS, suggesting that CS were more sensory in nature than SS. A cross-correlation analysis of SS that are triggered by CS revealed that short-term modulation, that is, the brief pause in SS caused by CS, does not account for the reciprocal modulation of SS and CS. The results also showed that three major aspects of the CS and SS individual cell firing characteristics were negatively correlated on a cell-to-cell basis: the preferred direction of stimulus motion, the mean percent change in firing rate induced by upward stimulus motion, and patterns of temporal firing probability. These results suggest that CS may contribute to long-term interactions between parallel and climbing fiber inputs, such as long-term depression and/or potentiation.

 

100.    Y. Kobayashi and N. Kobayashi

            "Influence of N-2 carrier gas on surface stoichiometry in GaN MOVPE studied by surface photoabsorption"

            J. Cryst. Growth 190, 301-304 (1998).

 

            ABSTRACT: The surface stoichiometry of GaN grown by metal-organic vapor-phase epitaxy (MOVPE) on (0 0 0 1) sapphire substrate at temperatures up to about 1000 degrees C in N-2 and H-2 carrier gases was monitored in situ by surface photoabsorption (SPA). In the N-2 carrier gas with NH3 supply, a stable N-rich surface was formed at temperatures up to 1030 degrees C. In contrast, the surface in H-2 carrier gas was N-rich at temperatures below 850-900 degrees C. Above these temperatures the surface became Ga-rich. These results indicate that GaN MOVPE growth at temperatures around 1000 degrees C proceeds under N-rich and Ga-rich surface stoichiometry in N-2 and H-2, respectively, The N desorption rate in N-2 was lower than the rate in H-2, indicating that the N-2 carrier gas suppresses the N desorption from the GaN MOVPE surface compared with H-2. (C) 1998 Elsevier Science B.V. All rights reserved.

 

101.    L. P. Kouwenhoven, T. H. Oosterkamp, S. Tarucha, D. G. Austing, and T. Honda

            "Coulomb oscillations in few-electron quantum dot"

            Physica B 251, 191-196 (1998).

 

           ABSTRACT: We study atomic-like properties of artificial atoms by measuring Coulomb oscillations in vertical quantum dots containing a tunable number of electrons starting from zero. At zero magnetic field the energy needed to add electrons to a dot reveals a shell structure for a two-dimensional harmonic potential. As a function of magnetic field the current peaks shift in pairs, due to the filling of electrons into spin-degenerate single-particle states. When the magnetic field is sufficiently small, however, the pairing is modified, as predicted by Hund's rule, to favour the filling of parallel spins. (C) 1998 Elsevier Science B.V. All rights reserved.

 

102.    M. Kumagai, S. L. Chuang, and H. Ando

            "Analytical solutions of the block-diagonalized Hamiltonian for strained wurtzite semiconductors"

            Phys. Rev. B 57 (24), 15303-15314 (1998).

 

            ABSTRACT: Analytical solutions using a recently derived block-diagonalized Hamiltonian for strained wurtzite crystals are shown. The theoretical results are used to extract the deformation potentials from the experimental results of the A-, B-, and C-line exciton transition energies as a function of the c-axis strain using a set of recently reported elastic stiffness constants. The obtained parameters are then applied to calculate the wave functions, valence band energies, effective masses, optical-momentum matrix elements, exciton Bohr radius, and binding energy as a function of strain. These analytical and numerical results are useful for understanding the optical and electronic properties near the band edges of strained wurtzite crystals.

 

103.    E. Kuramochi, J. Temmyo, H. Kamada, and T. Tamamura

            "Perfect spatial ordering of self-organized InGaAs/AlGaAs quantum disks on GaAs (311)B substrate with silicon-nitride dot array"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 37 (3B), 1559-1564 (1998).

 

            ABSTRACT: To control the position of self-organized InGaAs/AlGaAs quantum disks on a GaAs (311)B substrate, the use of fine silicon nitride dot array was examined. The pentagonally shaped hollow arrays were formed on the metal-organic vapor phase epitaxy grown AlGaAs layer by buried SiN dots due to the competition between the facet and the lateral growth. The following InGaAs layer grew preferentially in these hollows and self-organized quantum disks were formed during growth interruption. Successive growth of AlGaAs/InGaAs epi-layers induced the stacking of quantum disks right on top of the bottom disks. The upper quantum disks were perfectly spatially ordered when the pitch of the array was matched with the self-organized growth mode, with a simultaneous achievement of lateral positioning.

 

104.    R. C. Liu, B. Odom, Y. Yamamoto, and S. Tarucha

            "Quantum interference in electron collision"

            Nature 391 (6664), 263-265 (1998).

 

            ABSTRACT: The indistinguishability of identical quantum particles can lead to quantum interferences that profoundly affect their scattering(1,2). If two particles collide and scatter, the process that results in the detection of the first particle in one direction and the second particle in another direction interferes quantum mechanically with the physically indistinguishable process where the roles of the particles are reversed. For bosons such as photons, a constructive interference between probability amplitudes can enhance the probability, relative to classical expectations, that both are detected in the same direction-this is known as 'bunching'. But for fermions such as electrons, a destructive interference should suppress this probability ('anti-bunching'); this interference is the origin of the Pauli exclusion principle, which states that two electrons can never occupy the same state. Although two-particle interferences have been shown for colliding photons(3,4), no similar demonstration for electrons exists(2,5,6). Here we report the realization of this destructive quantum interference in the collision of electrons at a beam splitter. In our experiments, the quantum interference responsible for the Pauli exclusion principle is manifest as the suppression in electron current noise after collision.

 

105.    R. C. Liu, Y. Yamamoto, and S. Tarucha

            "Signs of quantum statistical effects in electron collision"

            Physica B 251, 152-156 (1998).

 

            ABSTRACT: A suppression of the output current noise relative to classical partition noise is observed in a ballistic electron beam splitter when the electron streams from two inputs are collided. This noise suppression reflects the quantum statistical interference between colliding identical quantum particles which underlies the Pauli exclusion principle. (C) 1998 Elsevier Science B.V. All rights reserved.

 

106.    P. X. Lu, E. Fill, Y. L. Li, J. Maruhn, and G. Pretzler

            "Spatial coherence of prepulse-induced neonlike x-ray lasers"

            Phys. Rev. A 58 (1), 628-635 (1998).

 

            ABSTRACT: We report a series of Young's double-slit experiments to measure the transverse spatial coherence of prepulse-induced low-Z neonlike x-ray lasers for two prepulse levels. The experiments were performed using the Asterix IV iodine laser with a prepulse 5 ns before the main pulse. The main pulse energy was 400 J, with a pulse duration of 450 ps. Two slit separations of 80 and 110 mu m were used to measure coherence in the vertical direction. We also present data for the horizontal transverse coherence, obtained with only a single-slit separation of 110 mu m. The equivalent incoherent source sizes of the x-ray lasers along the vertical direction, as derived by the Van Cittert-Zernike theorem, were found to be 100-120 mu m for the 1.5% prepulse, and 110-170 mu m for the 15% prepulse level, respectively. Compared to the near-field patterns, the equivalent source sizes obtained with the lower prepulse level (1.5%) are found to be significantly smaller, indicative of an enhancement of the spatial coherence by the gain medium. The observation of a higher degree of coherence for the 1.5% prepulse is corroborated by simulations using a two-dimensional hydrocode and a ray-tracing postprocessor.

 

107.    E. Maeda, Y. Kuroda, H. P. C. Robinson, and A. Kawana

            "Modification of parallel activity elicited by propagating bursts in developing networks of rat cortical neurones"

            Eur. J. Neurosci. 10 (2), 488-496 (1998).

 

            ABSTRACT: Networks of cultured cortical neurones exhibit regular, synchronized, propagating bursts which are synaptically mediated, and which are hypothesized to play a part in activity-dependent formation of connections during development in vivo. The relationship between the strength of synaptic connections and the characteristics of synchronized propagating bursting, however, is unclear. Modification of synchronized activity in cortical cultures in response to electrical stimulation was examined using multisite electrode array recording. By measuring the response of the network to weak, localized, test stimulation (TS), we observed a potentiation of activity following a relatively stronger inducing stimulation (IS). This potentiation was evident as an increased probability of eliciting bursts by TS, an increased frequency of spontaneous bursts and number of spikes per burst, and increased speed of burst propagation, and it lasted for at least 20 min. Changing the parameters of IS revealed that high frequency tetanic stimulation is not necessary to induce potentiation, while it is essential for IS to produce a regeneratively propagating burst. The results provide a direct demonstration of modification of both the spatial and temporal characteristics of synchronized network activity, and suggest an important physiological role for propagating synchronized bursting, as a mechanism for inducing plastic modifications in the developing cortex.

 

108.    F. Maeda and Y. Watanabe

            "Time-resolved core-level photoelectron spectroscopy on Sb-terminated GaAs(001) under Sb supply control at growth temperature"

            J. Electron Spectrosc. Relat. Phenom. 88, 779-785 (1998).

 

            ABSTRACT: The Sb desorption process from Sb-terminated GaAs(001) substrates has been analysed by time-resolved core-level photoelectron spectroscopy to investigate the influence of the substrate on the desorption. From the time dependence of the Ga 3d intensity, and the spectrum changes of Ga 3d and Sb 4d under Sb Bur and during Sb desorption, three series of time constants for Sb desorption were found and activation energies of 2.5 eV and 1.1 eV were obtained for two of the desorption series. Spectrum analysis clarified that Sb double layers lie on the surface under Sb flux exposure and that Sb atoms corresponding to activation energies of 2.5 and 1.1 eV desorb from the topmost site of the Sb double layers. This is the same in the case of GaSb (001) substrate without the activation energy and shows that the bonding strength between the Sb atoms of the topmost layer site and the second layer site depends on the substrate materials. (C) 1998 Elsevier Science B.V.

 

109.    F. Maeda, Y. Watanabe, M. Oshima, M. Taguchi, and R. Oiwa

            "Real-time analysis for MBE by time-resolved core-level photoelectron spectroscopy"

            J. Synchrot. Radiat. 5, 1026-1028 (1998).

 

            ABSTRACT: A system has been developed for the real-time analysis of surface reactions during molecular beam epitaxial growth which uses photoelectron spectroscopy with VUV light taken from synchrotron radiation. This system consists of a synchrotron radiation beamline and growth/analysis apparatus in which photoelectron spectroscopy is performed with sub-second time resolution. In this system, photoelectron spectra are measured in sequence by a 'non-scanning' measurement method that enables the acquisition of snapshot photoelectron spectra using a multi-channel detector. This non-scanning measurement method was enabled by equipping an electric field correction grid. This system was used to monitor the photoelectron spectra of a GaSb(001) surface.

 

110.    N. Maeda, T. Nishida, N. Kobayashi, and M. Tomizawa

            "Two-dimensional electron-gas density in AlxGa1-xN/GaN heterostructure field-effect transistors"

            Appl. Phys. Lett. 73 (13), 1856-1858 (1998).

 

            ABSTRACT: We have calculated maximum two-dimensional electron-gas densities in AlXGa1-XN/GaN heterostructure field-effect transistors with wurtzite crystal structures in (0001) orientation, by self-consistently solving Schrodinger's and Poisson's equations, taking the piezoelectric effect into account. In order to obtain a guideline for increasing electron densities in the devices, we have examined dependences of the maximum electron densities on both Al compositions of AlXGa1-XN layers and lattice relaxations at the heterointerfaces. The maximum electron density was found to depend more strongly on the lattice relaxation than on the Al composition, which determines the conduction-band discontinuity. Controlling the lattice relaxation is shown to be crucial for obtaining high electron densities in the devices. (C) 1998 American Institute of Physics. [S0003-6951(98)02339-0].

 

111.    N. Maeda, K. Nozawa, Y. Hirayama, and N. Kobayashi

            "Effect of thermal annealing on electrical properties in MBE-grown n-type GaN films"

            J. Cryst. Growth 190, 359-363 (1998).

 

            ABSTRACT: We have examined the effects of thermal annealing on electrical properties in molecular beam epitaxy (MBE) grown n-type GaN films by using variable temperature Hal; effect measurement. We have investigated both undoped and Si-doped samples, and have found that the electron mobility increases by thermal annealing along with an increase or decrease in the carrier concentration, which eventually leads to the decrease in resistivity. The observed changes in the mobility and the carrier concentration can be explained by the model whereby shallow donors and deep accepters both are diminished by thermal annealing. Changes in donor and acceptor concentrations have been estimated based on Hall effect measurement data at low temperatures. (C) 1998 Elsevier Science B.V. All rights reserved.

 

112.    S. Maeyama and M. Sugiyama

            "Recent performance of the Photon Factory grating/crystal monochromator station BL-1A in the soft X-ray region"

            J. Synchrot. Radiat. 5, 786-787 (1998).

 

            ABSTRACT: This paper describes the recent performance of the Photon Factory beamline 1A with InSb(111) crystals used as the diffracting elements of the grating/crystal monochromator for monochromatizing soft X-rays. Pt-coated collimating and focusing mirrors located upstream and downstream of the monochromator have recently been replaced with Ni-coated mirrors in order to remove absorption structures at the Pt M-edges from output spectra in the soft X-ray region. Output spectra without the absorption structures and with higher intensity in the range 2000-3400 eV were obtained by using the Ni-coated collimating and focusing mirrors.

 

113.    Y. Manabe and S. Aoyagi

            "A feasibility decision algorithm for rate monotonic and deadline monotonic scheduling"

            Real-Time Syst. 14 (2), 171-181 (1998).

 

            ABSTRACT: Rate monotonic and deadline monotonic scheduling are commonly used for periodic real-time task systems. This paper discusses a feasibility decision for a given real-time task system when the system is scheduled by rate monotonic and deadline monotonic scheduling. The time:complexity of existing feasibility decision algorithms depends on both the number of tasks and maximum periods or deadlines when the periods and deadlines are integers. This paper presents a new necessary and sufficient condition for a given task system to be feasible and proposes a new feasibility decision algorithm based on that condition. The time complexity of this algorithm depends solely on the number of tasks. This condition can also be applied as a sufficient condition for a task system using priority inheritance protocols to be feasible with rate monotonic and deadline monotonic scheduling.

 

114.    Y. Manabe, R. Baldoni, M. Raynal, and S. Aoyagi

            "k-Arbiter: A safe and general scheme for h out of k mutual exclusion"

            Theor. Comput. Sci. 193 (1-2), 97-112 (1998).

 

            ABSTRACT: Mutual exclusion is a well-known problem that arises when multiple processes compete, in an uncoordinated way, for the acquisition of shared resources over a distributed system. In particular, k-mutual exclusion allows at most k processes to get one unit of the same resource simultaneously. These paradigms do not cover all the cases in which resource accesses must be serialized over a distributed system. There exist cases (e.g. the bandwidth of communication lines) where the amount of shared resource might differ from request to request (for example, audio and video communications). In this paper, we formalize this problem as the h-out of-k mutual exclusion problem, in which each request concerns some number h (1 less than or equal to h less than or equal to k) of units of shared resource and no unit is allocated to multiple processes at the same time. Former simple and k-mutual algorithms cannot be used to solve this problem. We present a general scheme for a quorum-based h-out of-k mutual exclusion algorithm that relies on a collection of quorums called k-arbiter. Several examples of k-arbiters are discussed, two particular classes of k-arbiters are investigated and a metric to evaluate the resiliency with respect to failures of k-arbiters is also given.

 

115.    N. Matsumoto

            "Overview of silicon-based materials"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 37 (10), 5425-5436 (1998).

 

            ABSTRACT: A comprehensive review, including some recent results, of the structures, properties and fabrication methods of inorganic and organic silicon-based materials with backbone dimensions from 0 to 3 is presented. Quantum effects in low-dimensional silicon structures are discussed using organosilicon materials, such as polyhedral compounds and oligosilanes (quantum dots), polysilanes (quantum wires), heterocopolymers (one-dimensional superlattices), and polysilynes (quantum planes). The luminous properties of silicon-based materials are also summarized.

 

116.    T. Matsuo, A. Sekiguchi, M. Ichinohe, K. Ebata, and H. Sakurai

            "Synthesis and reduction of octasilyl[4]radialene. Structure and dynamic study of [4]radialene dianion with eight-center ten-electron pi-system"

            Bull. Chem. Soc. Jpn. 71 (7), 1705-1711 (1998).

 

            ABSTRACT: The intramolecular reaction of 3,3,5,5,8,8,10,10,13,13,15,15,18,18,20,20-hexadecamethyl-3,5,8,10,13,15, 18,20-octasilacycloicosa-1,6,11,16-tetrayne (1) with three molar amounts of [Mn(CO)(3)(Me-Cp)] in THF under photochemical and refluxing conditions produced octasilyl[4]radialene derivative (2). The reaction of 2 with alkali metals (Li, Na, and K) in THF gave dialkali metal salts of the corresponding dianion (4) with an eight-center ten-electron pi-system. The molecular structure of dilithium salt of octasilyl[4]radialene dianion (4a) has been established by X-ray crystallography. The two lithium atoms are located above and below and are bonded to the atoms of the radialene framework to give a bis-CIP structure. The structural parameters of 4a are discussed in comparison to those of 2. The structure of 4a in solution has also been discussed on the basis of NMR spectroscopic data. The two Li+ ions of 4a are not fixed to the pi-skeleton in toluene-d(8), but are fluxional, giving a symmetric structure (bis-CIP) on the NMR time scale. In a solvating medium such as THF-d(8), one of the Li+ ions dissociates to yield an ion pair (CIP and SSIP). Some evidence for the Li+ ion walk on the pi-skeleton is demonstrated.

 

117.    T. Matsuo, A. Sekiguchi, M. Ichinohe, K. Ebata, and H. Sakurai

            "The first isolation and full characterization of fulvene dianion. Synthesis and x-ray structure of dilithium hexasilylfulvene dianion"

            Organometallics 17 (15), 3143-3145 (1998).

 

            ABSTRACT: Treatment of hexasilylfulvene (4) with lithium metal in, tetrahydrofuran yields yellow crystals of the dilithium hexasilylfulvene dianion (5). The dilithium hexasilylfulvene dianion (5) has a monomeric structure and forms a contact ion pair (bis-CIP) in the crystals. One of the lithium atoms is located above the center of the five-membered ring, whereas the other one is bonded to the exocyclic carbon atom. The bis-CIP structure determined by X-ray crystallography is maintained in solution.

 

118.    T. Matsuoka

            "Unstable mixing region in wurtzite In1-X-YGaXAlYN"

            J. Cryst. Growth 190, 19-23 (1998).

 

            ABSTRACT: In In1-xGaxN epitaxially grown by MOVPE, phase separation is experimentally found to occur at an indium composition of more than 20% from X-ray diffraction and microscopic examination using an analytical electron transmission microscope. Fitting the spinodal isotherms calculated from the free energy of mixing based on a strictly regular solution approximation using delta-lattice-parameter method to the experimental data, the constant of proportionality K between a lattice constant and the pseudobinary interaction parameter is determined. Using this K value, the pseudobinary interaction parameter is calculated using the delta-lattice-parameter method, and the unstable mixing region in a wurtzite structure In1-X-YGaXAlYN quaternary system is predicted. (C) 1998 Elsevier Science B.V. All rights reserved.

 

119.    M. Mitsunaga, M. Yamashita, M. Koashi, and N. Imoto

            "Temperature diagnostics for cold sodium atoms by transient four-wave mixing"

            Opt. Lett. 23 (11), 840-842 (1998).

 

            ABSTRACT: Transient four-wave mixing signals were observed in cold sodium atoms. This phenomenon-is interpreted as Bragg diffraction of a probe pulse by a population grating of the ground-state hyperfine level induced by pump pulses. The decay time of this grating is directly related to the temperature of the cold atoms and can serve as a novel technique for temperature diagnostics. (C) 1998 Optical Society of America.

 

120.    K. Muraki and Y. Hirayama

            "Re-entrant behavior of the v=4/3 fractional quantum Hall effect in a front-and-back-gated 2D hole gas"

            Physica B 258, 86-89 (1998).

 

            ABSTRACT: The fractional quantum Wall (FQH) effect of a two-dimensional hole gas has been studied in a modulation-doped quantum well (QW) with front and back gates. We found that the v=4/3 state shows intriguing re-entrant behavior; as the hole density was varied with the front gale, the v=4/3 state was observed to weaken in two regions of magnetic field. Temperature-dependent measurements reveal that the energy gap Delta(4/3) exhibits two minima as a function of magnetic field. This double re-entrant behavior contrasts markedly with the spin transition of electron systems which occurs around only one critical magnetic field. Results for different back-gate biases, i.e., For different Landau-level (LL) structures for the same density, are presented to discuss the effect of the valence-band LL structure. (C) 1998 Elsevier Science B.V. All rights reserved.

 

121.    K. Muraki and Y. Hirayama

            "Effect of valence band structure on the fractional quantum Hall effect of two-dimensional hole systems"

            Physica B 251, 65-69 (1998).

 

            ABSTRACT: We have studied the effect of the valence band structure on the fractional quantum Hall effect (FQHE) of two-dimensional hole systems (2D HS) in a symmetrically modulation-doped quantum well (QW). While keeping the hole density constant, we used front and back gates to vary the valence band structure in situ by changing the QW potential symmetry. The remarkable transitions we observed in the FQHE at v = 4/3 and 7/5 had a striking resemblance to the spin transitions reported for tilted-field experiments. We show that the effective g-factor determining the spin configuration of 2D HS in the FQHE is not a material-specific value, but reflects the valence band structure determined by the confinement potential of the 2D HS. (C) 1998 Elsevier Science B.V. All rights reserved.

 

122.    M. Murayama, K. Shiraishi, and T. Nakayama

            "Reflectance difference spectra calculations of GaAs(001) As- and Ga-rich reconstruction surface structures"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 37 (7), 4109-4114 (1998).

 

            ABSTRACT: The reflectance difference (RD) spectra of nine GaAs(001) surface reconstructions. (2 x 4)beta 2, (2 x 4)alpha, (2 x 4)gamma 2, (2 x 4)beta 1, (2 x 4)gamma 1 and c(4 x 4) reconstructions on As-rich surface and (4 x 2)beta 2, (4 x 2)alpha and (4 x 2)beta 1 reconstructions on Ga-rich surface, were studied by using the nearest-neighbor sp(3)s* tight-binding method. The surface atomic positions and the tight-binding interaction parameters were obtained by the ab inito pseudopotential calculations. We found that the RD spectra have considerably different features between As- and Ga-rich surface reconstructions. The RD spectra of As-rich surfaces are mainly understood by transitions between top As-dimer states, while the RD spectra of Ga-rich surfaces are explained by the surface electronic states resulting from the sinkage of surface Ga atoms Into bulk layers. These calculations are compared with the results of recent experiments.

 

123.    T. Nagaoka, Y. Matsuda, H. Obara, A. Sawa, T. Terashima, I. Chong, M. Takano, and M. Suzuki

            "Hall anomaly in the superconducting state of high-T-c cuprates: Universality in doping dependence"

            Phys. Rev. Lett. 80 (16), 3594-3597 (1998).

 

            ABSTRACT: We have measured the flux flow Hall effect in the superconducting state of various high-T-c superconductors (HTSC) from the underdoped to the overdoped regime. We show that the Hall sign is universal and is determined by the doping level; the sign is electronlike in the underdoped regime and holelike in the overdoped regime. This tendency contradicts the prediction or the time dependent Ginzburg-Landau equation based on the s-wave weak coupling theory, suggesting that such a theory fails to evaluate the Hall force acting on the vortices in HTSC. This discrepancy may be attributed to the novel electronic structure of the vortex in HTSC.

 

124.    M. Nagase, A. Fujiwara, K. Yamazaki, Y. Takahashi, K. Murase, and K. Kurihara

            "Si nanostructures formed by pattern-dependent oxidation"

            Microelectron. Eng. 42, 527-530 (1998).

 

            ABSTRACT: A quantitative evaluation of the local Si thickness of oxidized Si nanostructures was performed by scanning probe microscopy. Suppression of oxidation by mechanical stress is a dominant factor in determining the shape of Si structures of widths <100 nm. Oxidation from below caused by oxygen diffusion in the buried oxide layer extends to a few hundred nanometers from the pattern edge. The vertical position of the Si structure can be changed within a few tens of nanometers by oxidation from be:ow. As a result of co-occurence of these two phenomena, the local thickness of the patterned Si layer can be controlled within a range of 0-300% of the unpatterned area thickness.

 

125.    M. Naito, H. Yamamoto, and H. Sato

            "Reflection high-energy electron diffraction and atomic force microscopy studies on homoepitaxial growth of SrTiO3(001)"

            Physica C 305 (3-4), 233-250 (1998).

 

            ABSTRACT: This paper reports a systematic study on the homoepitaxial growth of SrTiO3(001) conducted using reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM) in order to improve our understanding of the basic processes in the epitaxial growth of perovskite thin films. Under certain growth conditions, the homoepitaxial growth of SrTiO3 essentially proceeds in the layer-by-layer (2D nucleation) growth mode with the basic unit of a molecular layer. This cyclic process due to unit-cell-by-unit-cell (uc-by-uc) growth is confirmed by undamped RHEED oscillations and the corresponding temporal evolution of AFM images of the growth front. Furthermore, the surface mobility is controlled by growth temperature and oxidation condition. By changing growth temperature or oxidation condition, crossovers from layer-by-layer growth to step-flow like growth and from layer-by-layer growth to 3D island growth through Stranski-Krastanov growth are observed. On the basis of these results, a universal phase diagram is proposed or the growth mode of the epitaxial film growth of complex oxides. (C) 1998 Elsevier Science B.V. All rights reserved.

 

126.    Y. Nakajima, S. Horiguchi, M. Shoji, and Y. Omura

            "Physical origin and characteristics of gate capacitance in silicon metal-oxide-semiconductor field-effect transistors"

            J. Appl. Phys. 83 (9), 4788-4796 (1998).

 

            ABSTRACT: The physical origin of gate capacitance in both bulk and silicon-on-insulator (SOI) metal-oxide-semiconductor field-effect transistors (MOSFETs) is studied. The gate capacitance is theoretically derived as the series capacitance comprising the oxide capacitance, number capacitance (C-N), level capacitance (C-level), and held capacitance (C-field). C-N is in proportion to the thermodynamic density of states under the hypothetical condition that the subband energy levels remain constant when the total electron density is differentiated by the Fermi level. C-level is inversely proportional to the result of differentiating the subband energy level by the total electron density. In the case of bulk MOSFETs or SOI MOSFETs with thick buried oxide, C-field, which originates from the electric field at the edge of the depletion layer, is negligible. In addition to the fact that our new theoretical model corresponds to the intuitive conventional model expressed in terms of the effective thickness of the inversion layer in bulk MOSFETs, it is demonstrated that the conventional capacitance model is also applicable to SOI MOSFETs at 300 K. We have calculated self-consistently the capacitance of a bulk MOSFET and of SOI MOSFETs with various top-silicon layer thicknesses at 300 K. At the fixed total electron density near 10(12) cm(-2), the gate capacitance becomes large with decreasing top-silicon layer thickness. This difference in the gate capacitance mainly comes from C-level, which means that in the case of SOI MOSFETs with a thin top-silicon layer, a small increase in the subband energy level with increasing electron density results in large gate capacitance and high performance of the SOI MOSFETs at 300 K. (C) 1998 American Institute of Physics.

 

127.    M. Nakamura, M. Shuzo, K. Ono, H. Fujioka, M. Tanaka, T. Nishinaga, Y. Watanabe, and M. Oshima

            "The evidence for a preferential growth of a MnAs thin film on an as-preadsorbed Si(001) surface"

            Appl. Surf. Sci. 132, 128-132 (1998).

 

            ABSTRACT: We have investigated the initial stage of the MnAs film growth using photoelectron spectroscopy. Two types of p-type Si(001) substrates, with a Mn first layer and an As first layer were used. It is found that, a manganese silicide (MnSi) and silicon oxide are formed around the interface when 1 ML of Mn is deposited first on Si. On the other hand, there is no silicon oxide formed at the interface when As is deposited first. Because of this As-passivation, the sample on which As is deposited first, has the sharper interface and the better film quality than the Mn-first sample. The interfacial alloys were analyzed by cross-sectional transmission electron microscope (TEM) observation in the MnAs/Si system. To prevent the formation of interfacial alloys, we have tried to insert GaAs between MnAs and Si, resulting in the growth of MnAs film with improved film quality. (C) 1998 Elsevier Science B.V. All rights reserved.

 

128.    T. Nakanishi, N. Mori, C. Murayama, H. Takahashi, T. Nagata, M. Uehara, J. Akimitsu, K. Kinoshita, N. Motoyama, H. Eisaki, and S. Uchida

            "High-pressure transport properties of the superconducting spin-ladder system Sr14-xCaxCu24O41+delta"

            J. Phys. Soc. Jpn. 67 (7), 2408-2414 (1998).

 

            ABSTRACT: We report the electrical resistivity, the Hall coefficient, Rw, and the magnetoresistance, MR, at pressures up to 2.0 GPa, of the spin-ladder compound Sr14-xCaxCu24O41+delta, on both a polycrystal (x = 13.6) and single crystals (x = 11 and 12), in which superconductivity has been observed only in a range of both Ca content (similar to 11 < x < 14) and pressure (similar to 1.5 < P < similar to 8 GPa). The pressure dependence of the R-H, with positive sign, indicates that carrier density increases with increasing pressure and localization of hole carriers at low temperature is substantially suppressed by applying pressure. We have also found that a positive MR, which violates Kohler's rule, seems to appear below the temperature at which a spin gap begins to open and strongly depends on the temperature as well as both on Ca content and applied pressure, suggesting that this MR is closely related to the mobile holes in the spin singlet state.

 

129.    H. Nakano, T. Nishikawa, and N. Uesugi

            "Strongly enhanced soft x-ray emission at 8 nm from plasma on a neodymium-doped glass surface heated by femtosecond laser pulses"

            Appl. Phys. Lett. 72 (18), 2208-2210 (1998).

 

            ABSTRACT: We have demonstrated efficient soft x-ray generation from femtosecond laser plasma created on a neodymium-doped glass target. Nd ions doped in glass target enhanced soft x-ray emission near 8 nm without broadening the soft x-ray pulse duration when there is no prepulse. A weak prepulse caused strong enhancement in soft x-ray intensity at 8 nm. By introducing a prepulse at 50 ns before the main pulse, 1% energy conversion efficiency from laser pulse into soft x-ray at 8 +/- 0.5 nm was achieved by using a neodymium-doped glass target. This value is 1.2 times as high as that for Nd metal target case. (C) 1998 American Institute of Physics.

 

130.    H. Namatsu, M. Nagase, T. Yamaguchi, K. Yamazaki, and K. Kurihara

            "Influence of edge roughness in resist patterns on etched patterns"

            J. Vac. Sci. Technol. B 16 (6), 3315-3321 (1998).

 

            ABSTRACT: We report on the linewidth fluctuations in resist patterns and their influence on etched patterns. The linewidth fluctuations observed as line edge roughness are mainly caused by polymer aggregates in the resist materials. Polymer aggregates more than 30 nm in diameter are observed in both the positive and negative resist films. Because the polymer aggregates are not dissolved but extracted during development, they; remain stuck on the pattern sidewall and cause Linewidth fluctuations. When substrates, such as Si, are etched using resist patterns as a mask, the linewidth fluctuations of the resist patterns are faithfully transferred to the substrate. This means that the linewidth fluctuations in device patterns are originally due to the polymer aggregates in the resist films. The linewidth fluctuation is also found to decrease through substrate etching, depending on resist thickness loss. This possibly results from degradation of the resist patterns in lateral directions through etching. However, it does not provide a sufficient decrease in linewidth fluctuations because the large thickness loss of the resist during etching results in critical dimension loss. Therefore, the reduction of the effect of the aggregate size, for example, by using the resist with small aggregates, such as hydrogen silsesquioxane, is necessary. (C) 1998 American Vacuum Society. [S0734-211X(98)12306-5].

 

131.    H. Namatsu, Y. Takahashi, K. Yamazaki, T. Yamaguchi, M. Nagase, and K. Kurihara

            "Three-dimensional siloxane resist for the formation of nanopatterns with minimum linewidth fluctuations"

            J. Vac. Sci. Technol. B 16 (1), 69-76 (1998).

 

            ABSTRACT: Linewidth fluctuation of resist patterns is a serious problem in fabricating nanodevices when lithographic resolution is improved to the nanometer scale. As a resist material for reducing linewidth fluctuations, we evaluate hydrogen silsesquioxane (HSQ) with a three-dimensional framework from the standpoints of resist patterning and its ability to reduce linewidth fluctuation. Infrared analyses indicate that SiH bonds in HSQ are broken by electron-beam irradiation, and consequently, the crosslinking required for negative tone patterning is generated. By applying a TMAH developer suitable for the dissolution of the siloxane bonds in HSQ, we improve contrast and reduce the thickness loss of the lightly exposed resist area. In addition, the HSQ resist has relatively high sensitivity for resist materials without any reactive groups. The etching durability sacrificed for the attainment of high sensitivity is improved by oxygen plasma treatment. No damage, such as pattern-shape deformation after the oxygen plasma treatment, is observed. Linewidth fluctuation due to edge roughness of resist patterns results from aggregates in the resist polymer. Aggregates in HSQ are small owing to its three-dimensional framework. In addition, the excellent development properly of HSQ avoids any influence from polymer aggregates on development. Consequently, linewidth fluctuation can be reduced to less than 2 nm. This leads to a decrease in the variation of gate capacitance in single-electron transistors. (C) 1998 American Vacuum Society.

 

132.    H. Namatsu, T. Yamaguchi, M. Nagase, K. Yamazaki, and K. Kurihara

            "Nano-patterning of a hydrogen silsesquioxane resist with reduced linewidth fluctuations"

            Microelectron. Eng. 42, 331-334 (1998).

 

            ABSTRACT: A new resist system providing small linewidth fluctuation has been developed for nanolithography. Hydrogen silsesquioxane (HSQ) resist used here has a small polymer size because of its three-dimensional framework. This framework reduces the size of aggregates in the resist film which strongly influence linewidth fluctuation of resist patterns. The scission of SiH bonds in HSQ by e-beam leads to the crosslinking required for the nega-patterning. In addition, the application of a TMAH developer realizes higher contrast an less thickness loss. Consequently, 20-nm-wide nega-patterns with a rectangular cross-sectional shape are successfully formed with linewidth fluctuation less than 2 nm.

 

133.    F. Neumann, H. Teramae, J. W. Downing, and J. Michl

            "Gauche, ortho, and anti conformations of saturated A(4)X(10) chains: When will all six conformers exist?"

            J. Am. Chem. Soc. 120 (3), 573-582 (1998).

 

           ABSTRACT: Geometries of A(4)X(10) molecules (A = C, Si; X = H, F, Cl, Br, CH3, SiH3) have been optimized at the HF/6-31G* level as a function of the AAAA dihedral angle omega. In addition to the generally known gauche and trans conformational minima, some have an additional ("ortho") minimum near omega = 90 degrees. This appears only within a certain critical range of sizes of substituents X. It is attributed to a splitting of the ordinary gauche minimum by 1,4 interactions between substituents, similarly as the twisting of the anti minimum from 180 degrees is attributable to 1,3 interactions. A universal model is proposed to rationalize the appearance and subsequent disappearance of the ortho minimum as X increases in size. It contains intrinsic barriers described according to Weinhold, van der Waals interactions described by a Lennard-Jones 6-12 potential, and Coulomb charge-charge interactions.

 

134.    S. Nishida and M. Shinya

            "Use of image-based information in judgments of surface-reflectance properties"

            J. Opt. Soc. Am. A-Opt. Image Sci. Vis. 15 (12), 2951-2965 (1998).

 

            ABSTRACT: We examined how well we can recover surface-reflectance properties from shading patterns under changes in surface shape. The stimulus we used was a square surface modulated in depth by a low-pass-filtered random field and rendered by the Phong illumination model [Commun. ACM 18, 311 (1975)]. Two different surface images (target and match) were presented side by side, with either the viewing direction or the surface-normal direction rotating around the horizontal axis. The target shape was manipulated by changing the spatial spectrum, and the target reflectance was manipulated by changing the diffuse-reflection coefficient and the specular-reflection exponent (shininess) of the Phong model. The shape parameters of the match stimulus were fixed, but its reflectance parameters were under the control of subjects, who had to make the apparent reflectance of the two surfaces as similar as possible. The results showed that the constant error (difference between simulated and matched values) was large except when the two surfaces had the same shape parameters or when they differed only in scale. The pattern of the constant errors and response variabilities suggests that the judgments of the subjects were based on the similarity of the luminance histogram of the surface image. Our results demonstrate a limitation of surface-reflectance constancy for changes in shape and the importance of image-based information in reflectance judgments. The results are discussed in relation to previous studies that showed effects of spatial layout on surface-reflectance perception. (C) 1998 Optical Society of America [S0740-3232(98)00512-2].

 

135.    T. Nishida, T. Akasaka, and N. Kobayashi

            "Step-flow metalorganic vapor phase epitaxy of GaN on SiC substrates"

            Jpn. J. Appl. Phys. Part 2 - Lett. 37 (4B), L459-L461 (1998).

 

            ABSTRACT: Metalorganic Vapor Phase Epitaxy (MOVPE) growth of GaN on SiC substrates is dominated by the step-flow growth mode within a 10 mu m(2) area. Compared to the growth on sapphire substrates, there is no spiral growth originating from screw dislocations and two dimensional islands within the 10 mu m(2) area, showing that the step-flow growth mode is dominant. The surface mostly consists of 140-nm-wide atomic terraces and doubly stacked monolayers (DSM) corresponding to a unit cell height. This coupling of DSM dissolves into a pair of monolayer steps at the adjacent DSM steps forming a twilled step (TWS) structure, due to the asymmetry between these two layers in a GaN unit cell.

 

136.    T. Nishida, T. Akasaka, Y. Yamauchi, and N. Kobayashi

            "Step-free surface and interface by finite area metalorganic vapor phase epitaxy"

            J. Cryst. Growth 195 (1-4), 459-465 (1998).

 

            ABSTRACT: By using finite area metalorganic vapor phase epitaxy (FAE), atomically step-free surfaces and interfaces are obtained. Their flatness is confirmed by ex situ atomic force microscopy (AFM) and low-temperature spatially resolved photoluminescence (SR-PL) measurement. We suggest a step elimination principle by FAE, where two-dimensional (2D) nucleation is suppressed on a facet due to surface migration or desorption. We conclude that, by utilizing desorption, a step-free surface of any size can be formed as long as the size is finite. To demonstrate this; we formed an extraordinarily wide step-free GaAs(1 1 1)B surface 100 mu m in diameter. Surface stoichiometry control based on in situ monitoring of surface photo-absorption (SPA) is indispensable for flatness control. We investigate the feasibility of FAE with respect to growth methods, materials, and thickness by forming GaAs/Al0.3Ga0.7As quantum well on patterned GaAs(1 1 1)B substrate. We also show the potential of FAE of InP and GaN. (C) 1998 Elsevier Science B.V. All rights reserved.

 

137.    T. Nishida and N. Kobayashi

            "Interface flattening and optical characteristics of GaAs/Al0.3Ga0.7As quantum wells grown on finite patterns on a GaAs(111)B substrate"

            Appl. Phys. Lett. 72 (22), 2847-2849 (1998).

 

            ABSTRACT: The formation of an atomically flat quantum well is studied by using metalorganic vapor phase epitaxy on a GaAs(111)B substrate. The surface of a 1-nm-thick GaAs layer on Al0.3Ga0.7As, corresponding to the upper interface of a quantum well, becomes stepfree on a 3.5-mu m-wide mesa, and the surface of an Al0.3Ga0.7As barrier becomes stepfree on a 2.5-mu m-wide mesa. On 15-mu m-wide mesas, the stepfree area becomes 4-6 mu m for the GaAs surface and 3-4.5 mu m for Al0.3Ga0.7As, which are a few times wider than those obtained on planar substrates. The photoluminescence from different thick:ness quantum wells are spatially separated. (C) 1998 American Institute of Physics.

 

138.    T. Nishida and N. Kobayashi

            "Formation of a 100-mu m-wide stepfree GaAs (111)B surface obtained by finite area metalorganic vapor phase epitaxy"

            Jpn. J. Appl. Phys. Part 2 - Lett. 37 (1AB), L13-L14 (1998).

 

            ABSTRACT: To perfectly flatten crystal facets, we propose a procedure that utilizes the balance between growth-material supply and desorption. By the suppression of two dimensional nucleation due to this desorption balance, stepfree facets can be obtained however large their area becomes, as long as their size is finite. We also confirm the validity of this assumption by obtaining a 100-mu m-wide atomically stepfree surface on a GaAs (111)B substrate by using metalorganic vapor phase epitaxy.

 

139.    T. Nishida, N. Maeda, T. Akasaka, and N. Kobayashi

            "Step-flow MOVPE of GaN on SiC substrates"

            J. Cryst. Growth 195 (1-4), 41-47 (1998).

 

            ABSTRACT: Step-flow MOVPE of GaN on SIC substrates is confirmed by AFM observation. Compared to the growth on sapphire substrates, there are no step terminations and no 2D nuclei within a 10 micron square area, showing step-flow mode is dominant. The surface mostly consists of 190-nm-wide atomic terraces and 0.6-nm-high doubly stacked monolayers (DSM) along [11 (2) over bar 0]. This DSM dissolves into a pair of monolayers at the adjacent DSM steps, due to the asymmetry between these two monolayers which have different bond configurations at the step edge. By the homogeneity of step-flow growth, FWHMs of about 100 arcsec in X-ray locking curve and sharp photoluminescence (FWHM: 20 meV) from 1.1-nm-thick GaN/AL(0.15)Ga(0.85)N quantum well are obtained. We also found, in finite area selective epitaxy (FAE), steps originate from a single 2D nucleus,which shows heterointerface flatness will be significantly improved by using the combination of SiC substrates and FAE. (C) 1998 Elsevier Science B.V. All rights reserved.

 

140.    T. Nishikawa, H. Nakano, N. Uesugi, and T. Serikawa

            "Porous layer effects on soft x-ray radiation emitted from a plasma generated by 130-fs laser pulses irradiating a porous silicon target"

            Appl. Phys. B-Lasers Opt. 66 (5), 567-570 (1998).

 

            ABSTRACT: Differences in the X-ray emission by double-pulse excitation with a porous Si target and a solid Si target are investigated. The optimum delay time between the prepulse and the main pulse for obtaining the highest soft X-ray emission on porous Si is longer than that for solid Si. The soft X-ray pulse duration on the porous Si is shorter than that for the solid Si and is independent of the prepulse intensity. These differences can be explained by the ablation of Si clusters with solid density from the porous Si target by the prepulse. A plasma with low average density but high local density is thereby excited by the main pulse.

 

141.    J. Nitta, T. Akazaki, H. Takayanagi, and T. Enoki

            "Gate control of spin-orbit interaction in an InAs-inserted In0.53Ga0.47As/In0.52Al0.48As heterostructure"

            Physica E 2 (1-4), 527-531 (1998).

 

            ABSTRACT: We have confirmed by analyzing beating patterns of Shubnikov-de Haas oscillations that a spin-orbit interaction of the conduction band in an InAs-inserted In0.53Ga0.47As/In0.52Al0.48As heterostructure can be controlled by applying the gate voltage. The change in the spin-orbit interaction can be attributed to the Rashba term. Comparison with an In0.53Ga0.47As/In0.52Al0.48As heterostructure reveals that the spin-orbit interaction in the InAs-inserted system is more sensitive to the carrier concentration. (C) 1998 Elsevier Science B.V. All rights reserved.

 

142.    T. Nittono, Y. K. Fukai, F. Hyuga, and N. Maeda

            "Electrical characterization of InGaP/GaAs heterointerfaccs grown by metalorganic chemical vapor deposition"

            Jpn. J. Appl. Phys. Part 2 - Lett. 37 (11A), L1288-L1289 (1998).

 

            ABSTRACT: The electrical properties of InGaP/GaAs heterointerfaces grown by metalorganic chemical vapor deposition have been studied using capacitance-voltage and Hall-effect measurements. It is found that n-type carriers at concentrations near 1 x 10(12) cm(-2) accumulate unintentionally at the heterointerface. it is also found that the accumulated-carrier concentration does not vary in the temperature range of 4 to 296 K. These results indicate that a donor-type defect exists in the InGaP side of die heterointerface and that its energy level is higher than that of the lowest conduction band of GaAs.

 

143.    O. Niwa, T. Horiuchi, R. Kurita, H. Tabei, and K. Torimitsu

            "Microfabricated on-line sensor for continuous monitoring of L-glutamate"

            Anal. Sci. 14 (5), 947-953 (1998).

 

            ABSTRACT: An on-line sensor was developed by using a micro-machining technique for the continuous measurement of extracellular glutamate. The sensor was made by bonding two glass plates together. One of the plates has a rectangular flow channel which is connected to both a sampling and an outlet capillary. The other has a carbon film-based electrochemical cell, which consists of an enzyme-modified electrode surrounded by polymer film to form a thin-layer-channel flow cell. The sensor has a high analyte conversion efficiency due to the cell structure. As a result, we obtained a low detection limit of 44 nM (S/N=3). The cathodic current started to increase about 10 s after sample introduction at a flow rate of 2 mu l/min due to its small inner volume. Using the sensor, we can monitor the extracellular L-glutamate increase caused by stimulating it with KCl and gamma-aminobutyric acid (GABA) by locating the sampling capillary very close to the cell.

 

144.    O. Niwa, T. Horiuchi, R. Kurita, and K. Torimitsu

            "On-line electrochemical sensor for selective continuous measurement of acetylcholine in cultured brain tissue"

            Anal. Chem. 70 (6), 1126-1132 (1998).

 

            ABSTRACT: An on-line acetylcholine (ACh) sensor was developed in order to determine extracellular ACh concentrations without interference from choline (Ch). The sensor is composed of a small-volume enzymatic prereactor (22-mu L inner volume) in which choline oxidase and catalase are immobilized in series. Carbon electrodes were modified with an acetylcholine esterase (AChE), choline oxidase (ChOx), and osmium poly(vinylpyridine)-based redox polymer containing horseradish peroxidase (Os-gel-HRP). The sensor sensitivity was 43.7 nA/mu M (+/-0.15, n = 3) for ACh under optimized conditions. Almost no response was seen when 100 mu M Ch was continuously injected. The detection limit for ACh with the sensor was comparable to that obtained using liquid chromatography with electrochemical detection combined with an enzymatic reactor. The electrical stimulation of cultured rat hippocampal tissue resulted in an extracellular ACh increase of 20 nM (+/-11 nM, n = 3). This increase was observed continuously with our online sensor combined with a microcapillary sampling probe located very close to the tissue. The continuous measurement of ACh and Ch using a split disk carbon film dual electrode in which one electrode surface was modified with ChOx/Os-gel-HRP and the other with AChE-ChOx/Os-gel-HRP bilayer film was also demonstrated to improve the response time by eliminating the prereactor.

 

145.    O. Niwa, R. Kurita, T. Horiuchi, and K. Torimitsu

            "Small-volume on-line sensor for continuous measurement of gamma-aminobutyric acid"

            Anal. Chem. 70 (1), 89-93 (1998).

 

            ABSTRACT: We report the first on-line electrochemical sensor for the continuous measurement of gamma-aminobutyric acid (GABA), which is a well-known inhibitory neurotransmitter in the nervous system. The sensor is composed of a glutamate oxidase (GluOx) and catalase immobilized small-volume enzymatic reactor and a glassy carbon (GC) electrode modified with a top layer film consisting of gabase and GluOx coimmobilized bovine serum albumin and an Os-poly(vinylpyrridine) bottom layer film containing horseradish peroxidase. The response of the sensor depends on the a-ketoglutarate concentration and is almost saturated when its concentration is 100 times higher than GABA, The sensor exhibits a sensitivity of 1.56 nA/mu M for GABA under optimized conditions and shows almost no response when 10 mu M glutamate is continuously injected. A detection limit of 0.1 mu M is obtained with a linear range of 0.1-10 mu M. GABA can be measured in the absence of alpha-ketoglutarate when there is L-glutamate in the sample solution, which is a typical condition for the extracellular measurement of cultured nerve cells.

 

146.    S. Nojima

            "Polarization anisotropy of optical gain in two-dimensional photonic crystals with active lattice points"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 37 (12A), 6418-6424 (1998).

 

            ABSTRACT: Polarization anisotropic properties of optical gain are theoretically investigated for the first time for photonic crystals with active lattice points, in which all lattice points are made of the same gain material embedded in other dissipative medium. The study of light scattering by an isolated gain cylinder rod indicates that the reaction producing optical gain fur the light whose electric field is parallel to the rod axis always occurs more strongly than that for the one perpendicular to it. This anisotropy stems from the geometrical asymmetry of the rod. This polarization anisotropy is taken over by the above photonic crystal, i.e., the periodic array of gain rods. In photonic crystals, however, the anisotropy becomes more sensitive to the variation of the rod radius than in an isolated rod. Morever, the polarization anisotropy is found to be more pronounced for smaller I od radii or longer periods, indicating that it is approximately determined soley by the filling rate of the rod. These results can be: regarded as a consequence of periodic arraying of multiple gain rods.

 

147.    S. Nojima

            "Enhancement of optical gain in two-dimensional photonic crystals with active lattice points"

            Jpn. J. Appl. Phys. Part 2 - Lett. 37 (5B), L565-L567 (1998).

 

            ABSTRACT: Photonic crystals with active lattice points (two-dimensional gain photonic crystals) are proposed, in which all lattice points are made of the same gain material embedded in other dissipative medium. The optical gain spectrum is found to exhibit a pronounced gain enhancement in the vicinity of the band edge of the photonic band. This gain value also shows a spatial anisotropy reflecting the symmetry of the photonic band. These gain values have a strong correlation with the variation of the group velocity of light, indicating that;he marked reduction in the group velocity near the photonic band edge causes the optical gain enhancement.

 

148.    S. Nojima

            "Excitonic polaritons in one-dimensional photonic crystals"

            Phys. Rev. B 57 (4), R2057-R2060 (1998).

 

            ABSTRACT: Nonlocal investigations are presented for the exciton-photon coupling in one-dimensional periodic alternating layered structures consisting of two kinds of slabs (photonic crystals), in which excitons are present only in one of the two slabs. The lower branch of the excitonic polariton for this system is found to split into many small bands separated by small band gaps. This phenomenon is explained as the band splitting caused by the coherent interference of polaritonic waves in the periodic systems. The present nonlocal study also demonstrates a double exciton-photon coupling, in which the upper branch of the polariton couples again with the size-quantized exciton states.

 

149.    K. Nozawa, N. Maeda, Y. Hirayama, and N. Kobapashi

            "Growth of AlxGa1-xN (0 <= x <= 0.2) and fabrication of AlGaN/GaN superlattice by RF-source MBE"

            J. Cryst. Growth 190, 114-118 (1998).

 

            ABSTRACT: Based on the two-step growth, GaN and AlGaN on sapphire (0 0 0 1) were grown by MBE using an RF-source. We have attained a very flat growing surface by optimizing growth conditions both for the buffer layer and the main growth. We also grew AlGaN/GaN superlattices to demonstrate the flatness achieved on the growth surface. From X-ray diffraction and transmission electron microscopy observations, the abruptness of the interfaces and excellent controllability of the thickness were confirmed. (C) 1998 Published by Elsevier Science B.V. All rights reserved.

 

150.    T. Ohno, A. Ohki, and T. Matsuoka

            "Surface cleaning with hydrogen plasma for low-defect-density ZnSe homoepitaxial growth"

            J. Vac. Sci. Technol. A-Vac. Surf. Films 16 (4), 2539-2545 (1998).

 

            ABSTRACT: This article investigates in depth the conditions for cleaning of the (100) ZnSe substrate surface for ZnSe homoepitaxial growth. Wet etching with a K2Cr2O7-based etchant as a pre-growth treatment is found to result in a Se-rich ZnSe surface that retains its original flatness. Reflection high energy electron diffraction patterns show that plasma irradiation during thermal cleaning is indispensable for removing the oxide layer on ZnSe substrate and keeping the flatness. In hydrogen plasma cleaning, the etch pit density (EPD) of the homoepitaxial film increases at rf power higher than 265 W, indicating the optimum cleaning temperature is between 260 and 280 degrees C. As for the dependence of the EPD on the cleaning time, a minimum EPD of 2.7 x 10(4)/cm(2) can be obtained for a plasma cleaning time of 20 min. A correlation between the interfacial residual oxygen concentration and the defect density in an epitaxially grown ZnSe film is also found. (C) 1998 American Vacuum Society. [S0734-2101(98)00904-X].

 

151.    T. Ohno, A. Ohki, and T. Matsuoka

            "Room-temperature CW operation of II-VI lasers grown on ZnSe substrates cleaned with hydrogen plasma"

            J. Cryst. Growth 185, 550-553 (1998).

 

            ABSTRACT: Hydrogen plasma cleaning was applied for ZnSe homoepitaxial growth along with a novel wet etching technique for ZnSe substrates. The dependencies of etch-pit density (EPD) on RF power and cleaning temperature were investigated; for RF power below 250 W, the EPD is suppressed to about 1 x 10(5)/cm(2), and the optimum temperature range is between 260 and 280 degrees C. The EPD of ZnSe film grown on ZnSe substrate cleaned at 260 degrees C and 220 W for 20 min is 2.7 x 10(4)/cm(2). SCH II-VI laser diodes (LDs) containing ZnMgSSe cladding layers were fabricated on semi-insulating ZnSe substrates cleaned under the optimum conditions. LDs with HR coating on both facets demonstrate CW oscillation at room temperature. Typical threshold current and wavelength are 84 mA and 517 nm, respectively. (C) 1998 Elsevier Science B.V. All rights reserved.

 

152.    H. G. Okuno, S. Minato, and H. Isozaki

            "On the properties of combination set operations"

            Inf. Process. Lett. 66 (4), 195-199 (1998).

 

            ABSTRACT: The problem of constructing a combination set to represent a collection of all solutions by solving constraint satisfaction problems is considered. Two kinds of combination set operations, restriction and exclusion, are invented. Simplification theorems on these two operations plays an important role to avoid combinatorial explosions. In addition, a zero-suppressed BDD, a variation of ordered binary decision diagrams, is adopted to represent a combination set and efficient implementations of the two operations are presented. (C) 1998 Elsevier Science B.V. All rights reserved.

 

153.    H. Omi and T. Ogino

            "Self-organization of nanoscale Ge islands in Si/Ge/Si(113) multilayers"

            Appl. Surf. Sci. 132, 781-785 (1998).

 

            ABSTRACT: Multilayers of coherent Ge islands and Si spacer layers were grown on Si(113) substrate at 400 and 450 degrees C by molecular-beam epitaxy. The islands grown on the substrates have a wire-like shape with (159) facets. The islands become more uniform as layer number increases when the growth temperature is 400 degrees C. When the temperature is 450 degrees C, the island shape changes from wire-like in the 1st Ge layer to dash-like in 6th Ge layer. The self-organized Ge islands are vertically aligned at both temperatures. The temperature-dependent self-organization can be explained by considering that the filtering effect acts one-dimensionally at 400 degrees C and two-dimensionally at 450 degrees C as predicted theoretically. (C) 1998 Elsevier Science B.V. All rights reserved.

 

154.    T. H. Oosterkamp, T. Fujisawa, W. G. van der Wiel, K. Ishibashi, R. V. Hijman, S. Tarucha, and L. P. Kouwenhoven

            "Microwave spectroscopy of a quantum-dot molecule"

            Nature 395 (6705), 873-876 (1998).

 

            ABSTRACT: Quantum dots are small conductive regions in a semiconductor, containing a variable number of electrons (from one to a thousand) that occupy well-defined, discrete quantum states-for which reason they are often referred to as artificial atoms(1). Connecting them to current and voltage contacts allows the discrete energy spectra to be probed by charge-transport measurements. Two quantum dots can be connected to form an 'artificial molecule'. Depending on the strength of the inter-dot coupling (which supports quantum-mechanical tunnelling of electrons between the dots), the two dots can form 'ionic' (refs 2-6) or 'covalent' bonds. In the former case, the electrons are localized on individual dots, while in the latter, the electrons are delocalized over both dots. The covalent binding leads to bonding and antibonding states, whose energy difference is proportional to the degree of tunnelling. Here we report a transition from ionic bonding to covalent bonding in a quantum-dot 'artificial molecule' that is probed by microwave excitations(5-8). Our results demonstrate controllable quantum coherence in single-electron devices, an essential requirement for practical applications of quantum-dot circuitry.

 

155.    P. G. Osborne, O. Niwa, and K. Yamamoto

            "Plastic film carbon electrodes: Enzymatic modification for on line, continuous, and simultaneous measurement of lactate and glucose using microdialysis sampling"

            Anal. Chem. 70 (9), 1701-1706 (1998).

 

            ABSTRACT: Ring and split-disk plastic film carbon electrodes (PFCEs) were fabricated for use in thin-layer radial now cells which were coupled to a microdialysis sampling system. PFCEs, were initially coated with osmium poly(vinylpyridine) redox polymer horseradish peroxidase (Os-gel-HRP), Then a second coat of oxidase enzyme was applied to produce enzyme bilayer (oxidase/Os-gel-HRP) PFCEs which were subsquently over-coated with cellulose acetate for use in the determination of glucose or lactate at 0 mV (vs Ag/AgCl). Split-disk electrode geometry enabled different oxidase enzymes to be immobilized on each half of a split-disk, Os-gel-HRP-coated, PFCE to facilitate the electrochemically independent yet continuous on-line determination of these two analytes from a single dialysate. In continuous-flow experiments, cellulose acetate overcoated oxidase/Os-gel-HRP cast-coated PFCEs were quick to stabilize background current and displayed linear and sensitive responses to substrates. The effect of ascorbic acid was minimal and cross talk between partner split-disk electrodes was demonstrated to be acceptable for in vivo applications. The utility of this analytical system is demonstrated by the quantitative on-line continuous assay of changes in dialysate striatal extracellular glucose and lactate from a conscious rat during (a) local stimulation of neurons by perfusion with the depolarizing agent, Veratridine, and (b) physical restraint.

 

156.    T. Ouisse, D. K. Maude, S. Horiguchi, Y. Ono, Y. Takahashi, K. Murase, and S. Cristoloveanu

            "Subband structure and anomalous valley splitting in ultra-thin silicon-on-insulator MOSFET's"

            Physica B 251, 731-734 (1998).

 

            ABSTRACT: Shubnikov-de Haas oscillations have been investigated in Silicon-on-insulator MOSFET's with silicon film thicknesses down to 3 nm, The lifting of the valley degeneracy may reach 20 meV. This anomalous valley splitting is tentatively attributed to a combination of a higher quantum confinement and a rough back interface. (C) 1998 Elsevier Science B.V. All rights reserved.

 

157.    P. Parodi, Y. Jimbo, A. Kawana, D. Macri, and V. Torre

            "Segmentation of the response of a neuronal network into clusters with similar activity"

            Biosystems 48 (1-3), 171-178 (1998).

 

            ABSTRACT: An important question in the analysis of the electrical activity of a large population of neurons is the detection of families of neurons having a similar pattern of electrical activity, so that the original neuronal network can be decomposed into distinct clusters. This paper describes how it is possible to segment the activity of a neuronal network into clusters of sites with similar patterns of activity. Such a segmentation gives insight on how the network is organized, on how it functions and on its behavior as a dynamical system. Simulation and experiments on real data suggest that the correct approach to solve these problems must use multiresolution analysis. The method has been applied to both synthetic data and real data coming from a network of dissociated cortical neurons from neonatal rat brain. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.

 

158.    D. T. Pegg, L. S. Phillips, and S. M. Barnett

            "Optical state truncation by projection synthesis"

            Phys. Rev. Lett. 81 (8), 1604-1606 (1998).

 

            ABSTRACT: We show how the number-state expansion of an optical state can be truncated so as to leave only its vacuum and one photon components. This can be achieved using a "quantum scissors" device, the operation of which relies on a nonlocal quantum effect.

 

159.    L. S. Phillips, S. M. Barnett, and D. T. Pegg

            "Optical measurements as projection synthesis"

            Phys. Rev. A 58 (4), 3259-3267 (1998).

 

            ABSTRACT: We present an extension of the projection synthesis technique which allows us, at least in principle, to determine the probability distribution for any physical observable associated with a quantized optical field mode. This probability can be inferred from the photodetection statistics obtained by causing the field mode to be measured to interfere with a second mode prepared in a suitable reference state. We give an explicit expression for the required reference state. Weak-field homodyne detection using photon counting is, perhaps, the simplest system to which projection synthesis can be applied. We find the complete set of synthesized projectors for this system and show that they form a probability operator:measure. We apply this set of projectors to study the discrimination between coherent states and to measure a quasiprobability distribution. [S1050-2947(98)01110-X].

 

160.    K. Prabhakaran, Y. Kobayashi, and T. Ogino

            "Improved thermal stability of ultrathin silicon oxynitride layer due to nitrogen incorporation at the interface"

            Appl. Surf. Sci. 132, 182-186 (1998).

 

            ABSTRACT: This paper describes the effect of annealing on ultrathin oxynitride films on Si(100) surface prepared by the dissociative interaction of nitric oxide (NO) at room temperature. Ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS) and Auger electron spectroscopy (AES) have been employed to understand the clustering phenomenon of approximately monolayer thick oxynitride layer. On annealing the oxynitride at similar to 500 degrees C, nitrogen atoms move preferentially towards the interface. In the UPS, absence of the reappearance of surface states even after annealing the oxynitride to similar to 720 degrees C suggests a resistance to clustering of the oxynitride layer. This is in contrast to the annealing behavior of pure SiO2 film where clustering begins at temperatures as low as 190 degrees C. On further annealing of the oxynitride film at 830 degrees C, the SiN species remain on the surface due to the selective desorption of SiO species. Upon exposing oxygen to this surface, selective adsorption takes place on the bare Si areas exposed by the desorption of SiO. We believe that the enhanced thermal stability of ultrathin silicon oxynitride is due to the stabilization of the interface by the nitrogen atoms incorporated preferentially at the Si/SiO2 interface. (C) 1998 Elsevier Science B.V. All rights reserved.

 

161.    K. Prabhakaran, T. Matsumoto, T. Ogino, and Y. Masumoto

            "Fabrication of multiperiod Sr/SiO2/Ge layered structure through chemical bond manipulation"

            Appl. Phys. Lett. 72 (24), 3169-3171 (1998).

 

            ABSTRACT: In this letter, we report a method called chemical bond manipulation for fabrication of multiperiod nanometer sized Si/SiO2/Ge layered structure. Chemical bond manipulation is a self-organization process which involves selective breaking and making of surface chemical bonds and thereby enable formation of the desired species on a full wafer scale. We show that oxygen of germanium oxide layer formed on Si(111) are picked up by the Si atoms arriving at the surface during subsequent growth. This phenomenon involves breaking of Ge-O bonds and making of Si-O bonds and leads to the formation of ultrathin Si and Ge layers sandwiched between ultrathin silicon oxide layers, preserving the original wafer morphology. This material exhibits blue-green light emission at room temperature when excited by ultraviolet laser. (C) 1998 American Institute of Physics.

 

162.    H. Saito, T. Makimoto, and N. Kobayashi

            "MOVPE growth of strained InGaAsN/GaAs quantum wells"

            J. Cryst. Growth 195 (1-4), 416-420 (1998).

 

            ABSTRACT: The strained In0.3Ga0.7As1-xNx (x = 0.001)/GaAs quantum wells (QWs) with 10 nm well thicknesses were grown by MOVPE at 500 degrees C using dimethylhydrazine (DMHy) as the nitrogen source. The nitrogen was nonlinearly incorporated into the solid by increasing the partial pressure of DMHy in the vapor phase. The peak energy of photoluminescence (PL) was red-shifted by increasing the composition of nitrogen up to x = 0.002 and showed a large band-gap bowing of - 82 eV. The as-grown In0.3Ga0.7As0.99N0.01 QW had a weak PL intensity of more than two orders of magnitude lower than that of In0.3Ga0.7As QW, but by annealing in a N-2 atmosphere at 650 degrees C, the PL intensity recovered and peaked at 1.26 mu m at 10 K. The PL recovery seems to have been related to the depassivation of hydrogen. From a SIMS analysis, the as-grown In0.3Ga0.7As0.99N0.01 QW showed a hydrogen concentration as high as 6 x 10(19) cm(-3), but decreased to 2.5 x 10(19) cm(-3) after annealing in N-2 for 1 h. (C) 1998 Elsevier Science B.V. All rights reserved.

 

163.    A. Sakamoto, H. Kudo, T. Ishihara, S. Seki, and K. Sumitomo

            "Ion-induced electron emission from crystal targets with noncrystalline overlayers"

            Nucl. Instrum. Methods Phys. Res. Sect. B-Beam Interact. Mater. Atoms 140 (1-2), 47-54 (1998).

 

            ABSTRACT: We have measured keV secondary electrons induced by 56 MeV O8+ under channeling and nonchanneling incidence conditions for Si and Ge crystals covered with noncrystalline Al, Si, Ag, and Au layers less than 350 Angstrom thick. The analysis indicates that the enhanced electron yield due to the thin overlayer in the channeling case results dominantly from the effective increase in the number of high-energy recoiled electrons that are incident on the underlying crystal region. In the nonchanneling case, backscattering of the recoiled electrons from the overlaid atoms is of essential importance to account for the observed yield. (C) 1998 Elsevier Science B.V.

 

164.    T. Saku, K. Muraki, and Y. Hirayama

            "High-mobility two-dimensional electron gas in an undoped heterostructure: Mobility enhancement after illumination"

            Jpn. J. Appl. Phys. Part 2 - Lett. 37 (7A), L765-L767 (1998).

 

            ABSTRACT: High-mobility two-dimensional electron gas (2DEG) is formed at an undoped GaAs/AlGaAs inverted heterointerface through the field-effect using a back-gate. Despite the structure being undoped, mobility enhancement is observed at 1.6 K after illumination. This suggests effective reduction of background impurity scattering by illumination. The maximum mobility reached after illumination, 5 x 10(6)cm(2)/V.s, is the highest value ever reported for gated undoped heterostructures: including both normal- and inverted-type structures. This mobility is also the highest ever reported for inverted GaAs/AlGaAs heterostructures.

 

165.    S. Sasaki, D. G. Austing, and S. Tarucha

            "Spin states in circular and elliptical quantum dots"

            Physica B 258, 157-160 (1998).

 

            ABSTRACT: The effects of asymmetry on the spin states are studied in elliptical quantum dots. Circular dots possess rotational symmetry. They clearly show atom-like electronic properties such as a shell structure, and Hund's rule which favors parallel spins. Hund's rule is easily broken in elliptical dots because the asymmetric lateral confining potential lifts the degeneracy of the single particle states. The resultant change of the spin states in the elliptical dots is directly confirmed by Zeeman effect measurements. (C) 1998 Elsevier Science B.V. All rights reserved.

 

166.    S. Sasaki, A. Matsuda, and C. W. Chu

            "K-39-NMR observation of temperature-dependent spin susceptibility in K3C60"

            Physica C 302 (4), 319-324 (1998).

 

            ABSTRACT: K-39-NMR spectra of superconducting fulleride K3C60 are obtained in the normal state. The K-39-NMR shifts of two symmetrical lines observed with no quadrupolar-split satellites, that are assigned to the potassium tetrahedral- and octahedral-sites, are found to show the same temperature (T) dependence as the C-13-NMR shifts. From roughly estimated spin-lattice relaxation time, it is found that the conduction-electron density at the potassium site is nearly the same as that at the carbon site. These confirm that the uniform Pauli spin susceptibility, whose T dependence is considered to come from the predicted band effect, causes the reductions of both the C-13- and K-39-NMR shifts with decreasing T. Two experimental facts are pointed out for the T' site observed. (C) 1998 Elsevier Science B.V. All rights reserved.

 

167.    S. Sasaki, K. Tsubaki, S. Tarucha, A. Fujiwara, and Y. Takahashi

            "Observation of shot noise suppression at the peaks of Coulomb oscillations"

            Solid-State Electron. 42 (7-8), 1429-1431 (1998).

 

            ABSTRACT: Shot noise in Si-based single electron transistors has been measured for the first time in 2-12 MHz at 1.5 K with a lock-in technique. The magnitude of the shot noise normalized by the full shot noise, 2eI, clearly shows oscillatory structures as a function of the gate voltage, having a minima at the Coulomb oscillation peaks and a maxima in the Coulomb blockade region. The value of the maxima is approximately unity, reflecting a tunneling event with no correlation. On the other hand, the value of the minima is significantly smaller than half the full shot noise, which is smaller than in the previous theoretical and experimental reports and suggests that some current regulation mechanism is present. (C) 1998 Elsevier Science Ltd. All rights reserved.

 

168.    M. Sawaki and N. Hagita

            "Text-line extraction and character recognition of document headlines with graphical designs using complementary similarity measure"

            IEEE Trans. Pattern Anal. Mach. Intell. 20 (10), 1103-1109 (1998).

 

            ABSTRACT: A method for recognizing characters on graphical designs is proposed. A new projection feature that separates text-line regions from backgrounds, and adaptive thresholding in displacement matching are introduced. Experimental results for newspaper headlines with graphical designs show a recognition rate of 97.7 percent.

 

169.    H. Shibata and T. Yamada

            "Double Josephson plasma resonance in T* phase SmLa1-xSrxCuO4-delta"

            Phys. Rev. Lett. 81 (16), 3519-3522 (1998).

 

            ABSTRACT: Far-infrared sphere resonance in T*-phase SmLa0.8Sr0.2CuO4-delta powder samples is measured down to 7 cm(-1). Below T-c, two peaks are observed at 11 and 30 cm(-1) for delta = 0.05. Based on a comparison with the.S/I/S/I'/S/I/S/I'/S. (superconductor/insulator1/superconductor/insulator2/superconductor.)-type Josephson junction array model discussed by van der Marel and Tsvetkov [(Czech. J. Phys. 46, 3165 (1996)], these peaks are attributed to the Josephson plasma resonances of the intrinsic Josephson junctions at the fluorite-type Sm2O2 block layer and the rocksalt-type (La,Sr)(2)O2-delta block layer, respectively. The relation between the multiple Josephson plasma and the crystal structure of high-T-c cuprates is also discussed.

 

170.    K. Shiraishi and T. Ito

            "Theoretical investigation of the adsorption behavior of Si adatoms on GaAs(001)-(2x4) surfaces"

            Jpn. J. Appl. Phys. Part 2 - Lett. 37 (10B), L1211-L1213 (1998).

 

            ABSTRACT: We theoretically investigate the adsorption behavior of Si adatoms on GaAs(001)-(2 x 4) surfaces by ab initio calculations. The calculated results show that Si adatoms tend to be incorporated in the missing dimer trench when the Si coverage is small. Whereas favorable Si adsorption sites change from the missing dimer trench to the upper As dimers as Si coverage increases. This coverage dependence of Si adsorption sites is qualitatively consistent with recent experiments. Moreover, we comment on the mechanism that governs the adsorption behavior of Si adatoms on GaAs surfaces.

 

171.    K. Shiraishi and T. Ito

            "Ga-adatom-induced As rearrangement during GaAs epitaxial growth: Self-surfactant effect"

            Phys. Rev. B 57 (11), 6301-6304 (1998).

 

            ABSTRACT: GaAs(001) surfaces, on which epitaxial growth is widely performed, generally contain either missing dimer rows or excess As ad-dimers and As coverage is not equal to 1.00. We investigated theoretically how layer-by-layer growth is maintained on GaAs(001) surfaces by controlling the excess and deficiency of surface As atoms. Our calculations indicate that preadsorbed Ga atoms act as "self-surfactant atoms" and induce the As rearrangement on the surface during GaAs epitaxial growth. We show that this effect originates from the band-energy stabilization of the surfaces.

 

172.    K. Shiraishi, Y. Y. Suzuki, H. Kageshima, and T. Ito

            "Theoretical investigation of inter-surface diffusion on non-planar GaAs surfaces"

            Appl. Surf. Sci. 132, 431-435 (1998).

 

            ABSTRACT: We investigate the Ga adatom inter-surface diffusion between GaAs(001)-(2 x 4) top and GaAs(111)B-(2 x 2) side surfaces theoretically, based on microscopic calculations and a statistical mechanical discussion. The calculated migration potential based on the microscopic calculations imply that Ga adatoms are predominantly adsorbed on (001) surfaces. The results indicate that Ga adatoms basically diffuse from the (111)B side surface to the (001) top surface, so long as both top and side surfaces are single-domain structures. However, around the critical As pressure of surface transition, where (2 x 2) and (root 19 x root 19) structures coexist on the (111)B side surface, boundaries exist that are covered with neither (2 x 2) nor (root 19 x root 19) units. Since these non-covered boundaries can contain very reactive Ga adsorption sites, Ga adatoms tend to diffuse from the (001) top to the (111)B side surface, so long as non-covered boundaries appear on the (111)B side surfaces. Our theoretical investigation implies that the direction of the inter-surface diffusion between the GaAs(001) top and the (111)B side surfaces is reversed twice with increasing As pressure, which is in good agreement with the recent experimental reports. (C) 1998 Elsevier Science B.V. All rights reserved.

 

173.    T. Sogawa, H. Ando, S. Ando, and H. Kanbe

            "Spin-polarization spectroscopy in rectangular GaAs quantum wires"

            Phys. Rev. B 58 (23), 15652-15659 (1998).

 

            ABSTRACT: We measured spin-polarized photoluminescence excitation spectra and spin-relaxation times in rectangular GaAs/AlAs quantum wires (QWRs) with small (<20 nm) lateral sizes. We found that the degree of spin polarization had its maximum value near the transition edge, and varied greatly with the excitation photon energy. The results agreed qualitatively with theoretically analyzed spin-polarization spectra, where the heavy-hole-light-hole mixing states in the one-dimensional (1D) valence subbands were taken into account. To clarify the effects of 1D confinement on the spin-relaxation process, we also investigated the temperature dependence of the spin-relaxation time in the QWRs. A comparison of the QWR and quantum-well spin-relaxation times revealed that the spin-relaxation rate is reduced in 1D structures in the low-temperature region of 15-80 K. [S0163-1829(98)01148-5].

 

174.    O. M. Stoll, S. Kaiser, R. P. Huebener, and M. Naito

            "Intrinsic flux-flow resistance steps in the cuprate superconductor Nd2-xCexCuOy"

            Phys. Rev. Lett. 81 (14), 2994-2997 (1998).

 

            ABSTRACT: We have observed a novel intrinsic step structure in the flux-flow resistance of epitaxial c-axis-oriented films of Nd2-xCexCuOy as a function of current at intermediate magnetic fields B-c1 much less than B < B-c2. The effect is observed only if the sample is cooled with superfluid helium. For explaining the underlying instability, we propose a model based on the strongly energy-dependent density of states available near the Fermi energy for quasiparticle scattering in the superconducting mixed state for the clean limit.

 

175.    M. Sugiyama and S. Maeyama

            "An ultrahigh-vacuum goniometer for in situ soft X-ray standing-wave analysis of semiconductor surfaces"

            J. Synchrot. Radiat. 5, 1029-1031 (1998).

 

            ABSTRACT: An ultrahigh-vacuum goniometer was developed for in situ X-ray standing-wave (XSW) analysis of semiconductor surfaces prepared by molecular-beam epitaxy (MBE). Although two ultrahigh-vacuum motors for chi and phi rotating axes are inside the analysis chamber, low-energy photoelectrons can still be collected as the magnetic field is sufficiently suppressed by using metal shields. Furthermore, the sample can be annealed at temperatures higher than 870 K on the goniometer in the analysis chamber. This goniometer is used at beamline 1A (BL-1A) at the Photon Factory, where both monochromated soft X-rays and UV radiation are available. This analysis system was shown to be suitable not only for in situ soft-XSW and X-ray absorption near-edge structure (XANES) studies but also for synchrotron radiation photoelectron spectroscopy (SRPES) studies. The annealing effects on an S-adsorbed GaAs(001) surface could be studied by SRPES, XANES and XSW using this new goniometer.

 

176.    M. Sugiyama and S. Maeyama

            "Chemical-state-resolved x-ray standing-wave analysis of Te-adsorbed GaAs(001)-(2x1) surface"

            Phys. Rev. B 57 (12), 7079-7084 (1998).

 

            ABSTRACT: A Te-adsorbed GaAs(001)-(2x1) surface is studied by back-reflection x-ray standing-wave analysis, and average position of adsorbed Te atoms on GaAs(001) is found to be close to the As atomic site and bond with Ga atoms. Chemical-state-resolved x-ray standing-wave analysis using chemical shift in Te 3d(5/2) core-level photoelectron spectra suggest that Te atoms in two different chemical states correspond to two different distributions. Te atoms in a lower binding-energy chemical state are found to be in higher atomic positions and to be less ordered, whereas those in a higher binding-energy chemical state are found to be in lower atomic position and are highly ordered.

 

177.    M. Sugiyama, S. Maeyama, Y. Watanabe, S. Tsukamoto, and N. Koguchi

            "Ga-S-Ga bridge-bond formation on in-situ S-treated GaAs(001) surface observed by synchrotron radiation photoemission spectroscopy, X-ray absorption near edge structure, and X-ray standing waves"

            Appl. Surf. Sci. 132, 436-440 (1998).

 

            ABSTRACT: The chemical and structural changes of an in-situ S-treated GaAs(001)surface induced by thermal treatments were studied by synchrotron radiation photoemission spectroscopy (SRPES), X-ray absorption near edge structure (XANES), and X-ray standing waves (XSW). SRPES results revealed that As-S chemical states in the As 3d core level disappear from the surface with annealing at 400 degrees C. S K-edge XANES spectra showed that most of the S atoms are in a S-Ga chemical state after annealing at about 350-400 degrees C. XSW results suggested that the exchange reaction between the S and As atoms begins to occur at an annealing temperature lower than 300 degrees C, and that the Ga-S-Ga bridge-bond formation is almost completed with annealing at about 350-400 degrees C. (C) 1998 Elsevier Science B.V. All rights reserved.

 

178.    K. Sumitomo, T. Nishioka, and T. Ogino

            "Dimer structures of Ge/Si(001) and Sb/Si(001) studied by medium-energy ion scattering"

            Appl. Surf. Sci. 132, 133-138 (1998).

 

            ABSTRACT: We have determined the structure and positions of Ge and Sb dimer atoms on a Si(001)-2 X 1 surface using medium-energy ion scattering (MEIS), and demonstrated that the surface structure can be determined with a much higher accuracy by modifying the layer structure of the substrate. When a heavy atom layer (in this case Ge layer) is embedded with atomic scale layer precision, the blocking processes of scattered ions from the embedded layer are restricted and dips in the blocking profiles can be uniquely assigned to the scattering-blocking pairs. In addition, the effect of thermal vibration becomes small because a suitable distance between scattering and blocking atoms can be selected. Therefore, we can observe sharp blocking dips in the profile of embedded Ge signals, and they can be assigned to the dimer structures on the reconstructed surface. Based on the proposed method, the bond length and the tilt angle of asymmetric Ge-Ge dimers are determined to be 2.4 +/- 0.1 Angstrom and 13.5 +/- 2.0 degrees. The bond length of symmetric Sb-Sb dimers is determined to be 2.84 +/- 0.1 Angstrom. (C) 1998 Elsevier Science B.V. All rights reserved.

 

179.    D. Suzuki, H. Yamaguchi, and Y. Horikoshi

            "Scanning tunneling microscopy study of GaAs (001) surfaces grown by migration-enhanced epitaxy at low temperatures"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 37 (3A), 758-761 (1998).

 

            ABSTRACT: Using a molecular beam epitaxy/scanning tunneling microscopy (MBE/STM) system, we have compared the surface morphology of GaAs grown by MBE and migration-enhanced epitaxy (MEE) at a substrate temperature of 300 degrees C, which is much lower than normal MBE growth temperature. In terms of surface flatness, the difference between MBE and MEE was clearly visible. The surface roughness of MEE-grown GaAs was at most 2-monolayer and the surface was covered with large terraces with small islands on them. On the other hand, in spite of the clear reflection high energy electron diffraction (RHEED) intensity oscillation during the growth, the low-temperature MBE-grown surface was very rough and large terraces could not be seen on the surface. We concluded that these results are due to the differences in the growth mechanisms of MBE and MEE.

 

180.    H. Suzuki, S. Hoshino, C. H. Yuan, M. Fujiki, S. Toyoda, and N. Matsumoto

            "Near-ultraviolet electroluminescence from polysilanes"

            Thin Solid Films 331 (1-2), 64-70 (1998).

 

            ABSTRACT: We report the electroluminescent (EL) characteristics of a new class of polymeric material, polysilanes, which were employed in Light-emitting diodes (LEDs) as an emissive material. In contrast to the LEDs utilizing pi-conjugated polymers and small molecules that have been reported to date, LEDs made from polysilanes exhibit EL in the near-ultraviolet (NUV) or ultraviolet (NUV) region due to their sigma-conjugation. Three types of polysilanes, dialkyl, monoalkyl-aryl and diaryl polysilanes, have been used as the emissive material, together with an indiumtin-oxide (ITO) and metal electrode for the injection of holes and electrons, respectively. The LED characteristics were observed to depend strongly on the chemical, optical and electronic properties of the emissive polysilanes. The development of emissive polysilanes has led to the successful fabrication of single-layer LEDs which emit NUV light at 107 nm (3.05 eV) with a quantum efficiency of 0.1% photons/electron at room temperature. (C) 1998 Elsevier Science S,A. An rights; reserved.

 

181.    H. Suzuki, S. Hoshino, C. H. Yuan, M. Fujiki, S. Toyoda, and N. Matsumoto

            "Near-ultraviolet light-emitting diodes based on sigma-conjugated linear silicon-backbone polymers"

            IEEE J. Sel. Top. Quantum Electron. 4 (1), 129-136 (1998).

 

            ABSTRACT: We report the basic device characteristics of light-emitting diodes (LED's) based on linear silicon-backbone polymers, polysilanes, with a view to the possibility of employing them as an emissive material in a solid-state light source in the near-ultraviolet (NUV) or ultraviolet (UV) region. The LED's we fabricated have a single-layer structure consisting of a thin film of polysilane polymer, together with an indium-tin-oxide (ITO) and metal electrode for the injection of holes and electrons, respectively. The device characteristics of these LED's depend strongly on the nature of the polysilane, reflecting its chemical, optical and electronic properties. Efforts to optimize the emissive polysilane have led to the successful fabrication of single-layer LED's that emit NUV light of 407 nm (3.05 eV) with a quantum efficiency of 0.1% photons/electron and a spectral bandwidth of less than 15 nm (0.11 eV) at room temperature (RT), Future improvement in the device characteristics of NUV-LED's or UV-LED's based on polysilanes are discussed in terms of the fundamental properties of polysilanes and the device structure.

 

182.    H. Suzuki, S. Hoshino, C. H. Yuan, K. Furukawa, and N. Matsumoto

            "High-efficiency near-ultraviolet electroluminescence from a new class of emissive polymers: A one-dimensional poly[bis(p-butylphenyl)silane]"

            Abstr. Pap. Am. Chem. Soc. 216, U88-U88 (1998).

 

            ABSTRACT:

183.    K. Suzuki, K. Saito, K. Muraki, and Y. Hirayama

            "Photoluminescence from a modulation-doped Al0.33Ga0.67As/GaAs heterointerface under cyclotron resonance"

            Phys. Rev. B 58 (23), 15385-15388 (1998).

 

            ABSTRACT: Magnetophotoluminescence and change in photoluminescence (PL) intensities, due to far-infrared irradiation at the cyclotron resonance (CR) magnetic fields, in modulation-doped Al0.33Ga0.67As/GaAs single heterostructures are measured. The changes in PL intensities due to CR absorption strongly depend on the Landau-level filling factor (nu) and CR energy; i.e., the Landau-level separation. When nu<2 and CR energy is more than intersubband energy separation, luminescence from the ground subband is almost quenched and that from the second subband is greatly enhanced by CR absorption. [S0163-1829(98)04148-4].

 

184.    M. Suzuki and S. Karimoto

            "Properties of intrinsic Josephson junctions in Bi2Sr2CaCu2O8+delta single crystals"

            IEICE Trans. Electron. E81C (10), 1518-1525 (1998).

 

            ABSTRACT: We describe several properties of very thin stacks of 10 to 20 intrinsic Josephson junctions fabricated on the surface of Bi2Sr2CaCu2O8+delta single crystals. We show that the Joule heating is significantly reduced in these stacks and that the gap structure is clearly observable in the quasiparticle current-voltage (I - V) characteristics. The I - V curves are characterized by a large subgap conductance and a significant gap suppression due to the injection of quasiparticle current. It is found that the IcRn product of these intrinsic Josephson junction stacks is significantly small compared with that expected from the BCS theory. It is also found that there is a tendency that IcRn decreases with increasing c-axis resistivity. Both I9c and the gap voltage exhibit unsaturated temperature dependence at low temperatures. The behavior presents a sharp contrast to that of Josephson junctions made of conventional superconductors. The characteristics are discussed in relation to the d-wave symmetry of the order parameter.

 

185.    M. Suzuki, S. Karimoto, and K. Namekawa

            "Interlayer tunneling spectroscopy and evidence for the evolution of a pseudogap in Bi2Sr2CaCu2O8"

            J. Phys. Soc. Jpn. 67 (3), 732-735 (1998).

 

            ABSTRACT: We report on interlayer tunneling spectroscopy using very thin stacks of intrinsic Josephson junctions fabricated on the surface of a Bi2Sr2CaCu2O8 Single crystal. It is found that a pseudogap evolves below 180 K and continues to exist below T-c. It is also found that the superconducting gap evolves below T-c within the pseudogap. As a consequence of this finding, it is shown that the semiconductive c-axis resistivity can be interpreted in a straightforward manner in terms of the pseudogap and that the tunneling resistance is temperature independent.

 

186.    M. Suzuki, K. Mogi, and Y. Homma

            "Two-dimensional imaging of surface morphology by energy-analyzed secondary electrons and Auger electron spectroscopy for stepped Si(111) surfaces"

            Journal Of Vacuum Science & Technology A 16 (3), 1122-1126 (1998).

 

            ABSTRACT: We have experimentally investigated two-dimensional imaging of stepped Si surfaces by energy-analyzed electrons and Auger electron spectra from atomically flat surfaces. A stepped Si(111) surface was prepared by direct-current heating to around 1250 degrees C in ultrahigh vacuum. The stepped surface consisted of atomically flat terraces and step bands where atomic steps bunched in the height of about 5 nm. We found that the stepped structure could be imaged by using only the energy-analyzed secondary electrons (SEs) when the intensity was defined as the difference between the peak height and the background intensity. The image from the energy-analyzed SEs was in good agreement with the conventional SEM image obtained with non-energy-analyzed SEs. The electron-emission spectrum obtained in the direct mode included only characteristic Auger peaks of silicon SE peak. It is found that the electron-emission spectrum obtained from the atomically flat Si(111) terrace has relatively higher background than that from a sputter-cleaned Si surface. Also, it is revealed that the fine structure exists at 2.2 eV in the SE peak. (C) 1998 American Vacuum Society.

 

187.    M. Suzuki, T. Watanabe, and A. Matsuda

            "Josephson current and dissipation of the c-axis transport in magnetic fields in Bi2Sr2CaCu2O8+delta"

            Phys. Rev. Lett. 81 (19), 4248-4251 (1998).

 

            ABSTRACT: We have measured the c-axis resistivity, magnetoresistance, current-voltage characteristics, and the maximum Josephson current I-c in magnetic fields H parallel to the c axis for a very thin mesa of a Bi2Sr2CaCu2O8+delta crystal, which is equivalent to 20 tunnel Josephson junctions in series. It is found that I-c decreases proportionally to H-1, which agrees with a recent theory and Josephson plasma resonance experiments. This provides a basis for the straightforward application of the Ambegaokar-Halperin theory to the dissipation mechanism of the c-axis transport.

 

188.    S. Suzuki

            "Constructive function-approximation by three-layer artificial neural networks"

            Neural Netw. 11 (6), 1049-1058 (1998).

 

            ABSTRACT: Constructive theorems of three-layer artificial neural networks with (1) trigonometric, (2) piecewise linear, and (3) sigmoidal hidden-layer units are proved in this paper. These networks approximate 2 pi-periodic pth-order Lebesgue-integrable functions (L-2 pi(p)) on R-m to R-n for p greater than or equal to 1 with L-2 pi(p) - norm. (In the case of (1), the networks also approximate 2 pi-periodic continuous functions (C-2 pi) with C-2 pi-norm.) These theorems provide explicit equational representations of these approximating networks, specifications for their numbers of hidden-layer units, and explicit formulations of their approximation-error estimations. The function-approximating networks and the estimations of their approximation errors can practically and easily be calculated from the results. The theorems can easily be applied to the approximation of a nonperiodic function defined in a bounded set on R-m to R-n. (C) 1998 Elsevier Science Ltd. All rights reserved.

 

189.    Y. Y. Suzuki, S. Saito, and S. Kurihara

            "Quantum phase transition in the infinite dimensional Hubbard model"

            J. Low Temp. Phys. 113 (5-6), 897-902 (1998).

 

            ABSTRACT: We investigated the ground state of the infinite dimensional Hubbard model for both attractive and repulsive interactions by applying Gutzwiller type variational wave functions. Our variational wave functions have bower energies than the simple BCS weave function for the attractive case, and lover energies than the Brinkman-Rice state for the repulsive case. We found that the system has several phases depending on the density of electrons and the interaction strength. Investigated phases include antiferromagnetic, Fermi liquid, superconducting, charge density wave, and supersolid phases. The East one is a coexistence phase of superconducting and charge density wave states.

 

190.    A. Taguchi and H. Kageshima

            "First-principles investigation of the oxygen negative-U center in GaAs"

            Phys. Rev. B 57 (12), R6779-R6782 (1998).

 

            ABSTRACT: We investigated the atomic configuration of the oxygen negative-U center in GaAs, which has a Ga-O-Ga structure, based an first-principles calculations. We calculated the stable atomic configurations and formation energies for two Ga-O-Ga structures. One is Ga-{O-V-As}-Ga, which has been proposed as the atomic structure of the negative-U center. The other is Ga-O-i-Ga, which we propose in this paper. Five charge states from +1 to -3 were considered. For both Ga-{O-V-As}-Ga and Ga-O-i-Ga, the stable atomic configurations depend on the charge states. For Ga-{O-V-As}-Ga, the calculated atomic configurations cannot explain the experimentally obtained tendency in the local-vibrational-mode absorption frequencies for different charge states. The calculated formation energy as a function of the Fermi level indicates that the Ga-{O-V-As}-Ga structure does not have a negative-U nature. In contrast, the calculated results of the Ga-O-i-Ga structure well explain the experimental results such as the local-vibrational-mode absorption frequencies for different charge states and the negative-U nature. Thus, it is concluded that the atomic configuration of the negative-U center in GaAs is Ga-O-i-Ga, not Ga-{O-V-As}-Ga.

 

191.    A. Taguchi and K. Takahei

            "Erbium in Si: Estimation of energy transfer rate and trap depth from temperature dependence of intra-4f-shell luminescence"

            J. Appl. Phys. 83 (5), 2800-2805 (1998).

 

            ABSTRACT: We investigated the temperature dependence of erbium (Er) 4f-shell luminescence decay time and intensity in silicon based on a multiphonon-assisted energy transfer model, which has been verified for the Yb-doped InP system and has already been successfully applied to various ran-earth doped III-V semiconductors. The temperature dependence of the decay time of-Er 4f-shell luminescence was calculated using two fitting parameters: the depth of a trap level related to the 4f-shell luminescence and the energy transfer probability between the Er 4f shell and the electronic state of the silicon host. For Si:Er codoped with oxygen and Si:Er codoped with nitrogen, the calculated temperature dependence was compared with the experimentally observed temperature dependence. A reasonably good fit was obtained between the calculated results and the experimental results, suggesting that the Er 4f-shell luminescence is caused by the multiphonon-assisted energy transfer. The estimated energy transfer probability for Si:Er,N is larger than that for Si:Er,O, suggesting a stronger interaction between the Er 4f-shell and the Si host in Si:Er,N than in Si:Er,O. (C) 1998 American Institute of Physics.

 

192.    A. Taguchi, K. Takahei, M. Matsuoka, and S. Tohno

            "Evaluation of the energy-transfer rate between an Er 4f shell and a Si host in Er-doped Si"

            J. Appl. Phys. 84 (8), 4471-4478 (1998).

 

            ABSTRACT: We estimated the energy-transfer rate between an erbium (Er) 4f shell and a Si host by using two independent measurements. The first method involved measuring the temperature dependence of the decay time of Er 4f-shell luminescence and obtaining the energy-transfer rate by assuming that the energy transfer is assisted by nonradiative multiphonon processes and that thermal quenching is due to an energy back-transfer mechanism. The estimated value was 2 x 10(8) s(-1). The second method involved measuring the time response for luminescence intensity after pulsed host photoexcitation. Although some tens of mu s luminescence delay after host excitation has been reported, we found that the slow response time of the detection system may cause spurious delay. We measured the luminescence decay curve using a system with a fast response time and analyzed the data, taking into account the system response time. The energy transfer rate was estimated to be at least 10(7) s(-1). This estimation is consistent with the result obtained by the first method, mentioned above, confirming a rather large energy-transfer rate between the Er 4f shell and Si host. (C) 1998 American Institute of Physics. [S0021-8979(98)04120-6].

 

193.    Y. Takagaki

            "Transport properties of semiconductor-superconductor junctions in quantizing magnetic fields"

            Phys. Rev. B 57 (7), 4009-4016 (1998).

 

            ABSTRACT: We present the results of a numerical calculation on the quantum transport properties in junctions of a two-dimensional electron gas and a superconductor in the presence of a perpendicular magnetic field. The low-field conductance drops in a steplike manner, whenever the Landau levels are depopulated, provided that quasiparticle excitations are almost perfectly Andreev reflected from the interface. If the normal reflection is enhanced, the conductance exhibits a sinusoidal oscillation. In contrast to the behavior in conventional conductors, the maxima of the oscillation take place at the depopulation thresholds. In high magnetic fields, a periodic transmission resonance with a complete disappearance of the conductance is found, irrespective of the Andreev-reflection probability. The current distribution indicates that this high-field oscillation is ascribed to the skipping orbit along the interface. We show that the plateau value in the Hall resistance remains unchanged when one of the leads is replaced by the superconductor. Using the selective edge-state detection technique, the distribution of Andreev-reflected quasiparticles among the edge states can be evaluated. [S0163-1829(98)00107-6].

 

194.    Y. Takagaki, K. J. Friedland, D. K. Maude, R. Hey, S. Tarucha, K. H. Ploog, and J. C. Portal

            "Negative bend resistance in narrow cross junctions near v=1"

            Solid State Commun. 106 (9), 627-630 (1998).

 

            ABSTRACT: We report on the bend resistance in junctions of crossed wires in the quantum Hall regime. The vanished resistance associated with the nu = 1 quantum Hall state becomes negative for the filling factor nu just below unity when the channel width is reduced. The negative resistance dip is independent of temperature in the measured range of 0.08-0.9 K. Although these features indicate the interboundary scattering between the nu = 1 edge states to be the origin, simple single-particle models fail to reproduce the negative resistance because of the cancellation of the change in the transmission probabilities caused by the scattering. (C) 1998 Elsevier Science Ltd. All rights reserved.

 

195.    Y. Takagaki, K. J. Friedland, K. H. Ploog, and K. Muraki

            "Metastability of the quantum Hall states in asymmetric two-layer systems"

            J. Phys.-Condes. Matter 10 (37), 8305-8311 (1998).

 

            ABSTRACT: A GaAs-AlxGa1-xAs asymmetric double-quantum-well structure exhibits a meta-stability in the quantum Hall regime when the system is illuminated, under a high magnetic field sufficient to depopulate the excited-state subband. The photo-generated electrons are transferred to the excited-state subband when its bottom Landau level falls below the Fermi level at lower magnetic fields. The metastability is attributed to the potential renormalization associated with the charge transfer. The amount of the transferred charge can be controlled by varying the minimum magnetic field and remains unchanged as long as the magnetic field stays above the previous minimum value.

 

196.    Y. Takagaki, K. Muraki, and S. Tarucha

            "Quantum Hall effect in asymmetric double quantum well systems"

            Semicond. Sci. Technol. 13 (3), 296-301 (1998).

 

            ABSTRACT: We have experimentally determined the phase diagram of the quantum Hall effect in asymmetric double quantum well heterostructures. The charge redistribution induced by a crossing of the Landau levels of the two-dimensional electron gases is strongly regulated by the electrons in the excited subband. The self-consistency of the potential imposes a reduction in the charge transfer when the layer separation is large, For a range of electron densities beyond the population threshold of the excited subband, subpeaks are generated from the resistance peaks due to the ground subband. The split-off peaks grow larger in amplitude to become comparable with the contribution from the ground subband when the electron density in the excited subband increases. The relocation of the electrons between the subbands leads to a hybridization of the behaviour in each layer. The Hartree potential is found to yield a metastability of the electron state with the assistance of the discrete nature of the density of states in high magnetic fields.

 

197.    Y. Takahashi, A. Fujiwara, and S. Murase

            "Quantized conductance in a small one-dimensional Si wire on a thin silicon-on-insulator substrate fabricated using SiN-film-masked oxidation"

            Semicond. Sci. Technol. 13 (9), 1047-1051 (1998).

 

            ABSTRACT: A new fabrication technique for a one-dimensional (1D) Si wire on a separation-by-implanted-oxygen (SIMOX) substrate, which is effective in reducing the parasitic resistance caused by the thin lead Si regions, is proposed. Thermal oxidation of the Si layer on which a stacked structure of SiO2 and SIN films is formed does not reduce the thickness of the wide two-dimensional (2D) Si layer, though the 1D wire becomes thinner by the oxidation. A MOS-type 1D Si wire fabricated using this technique shows a clear step-like conductance as a function of gate voltage. Though the measured conductance step is slightly lower than the theoretically predicted value, it is much larger than previously reported values. The inherent conductance of the 1D wire can be extracted from the measured overall conductance owing to low parasitic resistance. The first conductance step thus obtained agrees well with the theoretical value of 4e(2)/h.

 

198.    Y. Takahashi, A. Fujiwara, K. Yamazaki, H. Namatsu, K. Kurihara, and K. Murase

            "Si memory device operated with a small number of electrons by using a single-electron-transistor detector"

            Electron. Lett. 34 (1), 45-46 (1998).

 

            ABSTRACT: A novel Si memory device is proposed, and its fundamental characteristics are demonstrated. The device uses a MOSFET as a gateway for electrons transported to and from the memory island. The stored electrons are detected by a highly sensitive single-electron transistor. The device features ultra-low-power and highspeed operation.

 

199.    H. Takayanagi and T. Akazaki

            "Semiconductor-coupled superconducting junctions using NbN electrodes with high H-c2 and T-c"

            Physica B 251, 462-466 (1998).

 

            ABSTRACT: We investigated normal transport in a superconductor (S)-two-dimensional electron gas (2DEG)-superconductor(S) junction in the quantum Hall regime. Andreev reflection takes place between the two S-2DEG interfaces through the edge states. The differential resistance-bias voltage characteristics of the junction are strongly dependent on the Hall conductance regimes, that is, the plateau or the threshold regimes. (C) 1998 Elsevier Science B.V. All rights reserved.

 

200.    K. Takeda and K. Shiraishi

            "Theoretical studies of the molecular and electronic structures of polyarsine"

            Phys. Rev. B 57 (12), 6989-6997 (1998).

 

            ABSTRACT: The electronic and polymeric structures of the ladder polyarsine (PAs) have been theoretically investigated based on first-principles electronic structure calculations. The isolated PAs ladder chain prefers to be planar. The laddering causes the band overlap among the valence band and conduction band, and produces a metallic electronic structure by the help of the excess electrons of As atoms.

 

201.    H. Takenaka, H. Ito, T. Haga, and T. Kawamura

            "Design and fabrication of highly heat-resistant Mo/Si multilayer soft X-ray mirrors with interleaved barrier layers"

            J. Synchrot. Radiat. 5, 708-710 (1998).

 

            ABSTRACT: Introducing interleaved carbon barrier layers improves the heat-resistance of Mo/Si multilayers. The soft X-ray reflectivities of the multilayers were calculated, and the effects of heating on both the reflectivities and layer structures of Mo/Si multilayers with and without barrier layers were investigated using X-ray diffraction and transmission electron microscopy. The results show that, for applications using intense soft X-ray beams, Mo/Si multilayers with interleaved carbon barrier layers are better mirrors than Mo/Si multilayers because they have much better heat resistance and almost the same soft X-ray reflectivity as the Mo/Si multilayers.

 

202.    H. Takesue, F. Yamamoto, K. Shimizu, and T. Horiguchi

            "1THz lightwave synthesised frequency sweeper with synchronously tuned bandpass filter"

            Electron. Lett. 34 (15), 1507-1508 (1998).

 

            ABSTRACT: A broadband lightwave synthesised frequency sweeper has been realised. An acousto-optic frequency shifter with a large frequency shift (1 GHz) and a synchronously tuned bandpass filter in an amplified fibre optic ring were employed, and a frequency sweep span of 1.1 THz was achieved.

 

203.    T. Takeuchi

            "Effect of contrast on the perception of moving multiple Gabor patterns"

            Vision Res. 38 (20), 3069-3082 (1998).

 

            ABSTRACT: The present study examined the way in which the perception of motion coherency depends on luminance contrast. Pseudo-plaid patterns were presented to subjects who judged whether coherent motion or component motion of the Gabor patterns was perceived. Michelson contrast, eccentricity, spatial separation: and angular separation between two groups of Gabor patches were varied systematically. When the contrast was high, coherent motion perception was dominant in peripheral viewing but not in foveal viewing. When the contrast was low, coherent motion was perceived at all eccentricities. Under low-contrast conditions and with peripheral viewing? coherent motion was perceived over broader spatial areas and at wider angular separations. The contrast dependency of motion coherency can be qualitatively explained in terms of the relative activity of hypothetical local-motion units in area V1 and global-motion units in area MT of the visual cortex. (C) 1998 Elsevier Science Ltd. All rights reserved.

 

204.    H. Tamura

            "Numerical study of spin effects in single and double quantum dots"

            Physica B 251, 210-213 (1998).

 

            ABSTRACT: Spin effects in single and vertically coupled double quantum dots are studied using an unrestricted self-consistent Hartree-Fock approximation. In a single dot, spin-parallel electrons occupy the two uppermost levels in magnetic fields, which leads to a cusp structure recently observed in the experiment in the magnetic-field dependence of addition spectra. In vertically coupled double dots, it is suggested that the absence of Hund's states observed in the experiment in the strongly coupled region is caused by the effect of dot thickness. In the intermediate region, we find high-spin states appear in the mixed shell of bonding and anti-bonding states. In the weakly coupled region, the pairing of addition spectra has been obtained. (C) 1998 Elsevier Science B.V. All rights reserved.

 

205.    S. Tanda, K. Kagawa, T. Maeno, T. Nakayama, K. Yamaya, A. Ohi, and N. Hatakenaka

            "Possibility of macroscopic resonant tunneling near the superconductor-insulator transition in YBa2Cu3O7-gamma thin films"

            Europhys. Lett. 41 (4), 425-429 (1998).

 

            ABSTRACT: Experimental results of the I-V characteristics near the superconductor-insulator transition observed for disorder-tuned YBa2Cu3O7-delta thin films are presented. The I-V characteristics exhibit new quasiperiodic structures as a function of the current. The current interval, the number of the dI/dV peaks, and the magnetic-field dependence of the peaks are consistent with the theoretical predictions of the resonant tunneling of a phase particle in a tilted-cosine potential for a single Josephson junction with small capacitance.

 

206.    S. Tarucha

            "Transport in quantum dots: Observation of atomlike properties"

            MRS Bull. 23 (2), 49-53 (1998).

 

            ABSTRACT:

207.    S. Tarucha, T. Honda, D. G. Austing, Y. Tokura, K. Muraki, T. H. Oosterkamp, J. W. Janssen, and L. P. Kouwenhoven

            "Electronic states in quantum dot atoms and molecules"

            Physica E 3 (1-3), 112-120 (1998).

 

            ABSTRACT: We study electronic states in disk-shaped semiconductor artificial atoms and molecules containing just a few electrons. The few-electron ground states in the artificial atom show atomic-like properties such as a shell structure and obey Hund's rule. A magnetic field induces transitions in the ground states, which are identified as crossings between single particle states, singlet-triplet transitions and spin polarization. These properties are discussed in conjunction with exact calculation in which the effect of finite thickness of the disk is taken into account. An artificial molecule is made from vertically coupling two disk-shaped dots. When the two dots are quantum mechanically strongly coupled, the few-electron ground states are de-localized throughout the system and the electronic properties resemble those of a single artificial atom. (C) 1998 Elsevier Science B.V. All rights reserved.

 

208.    T. Tateno

            "Characterization of stochastic bifurcations in a simple biological oscillator"

            J. Stat. Phys. 92 (3-4), 675-705 (1998).

 

            ABSTRACT: This study of the effect of noise on bifurcations in a simple biological oscillator with a periodically modulated threshold uses the first-passage-time problem of the Ornstein-Uhlenbeck process with a periodic boundary to define the operator governing the transition of a threshold phase: density. Stochastic phase locking is analyzed numerically by evaluating the evolution of the probability density function of the threshold phase. A firing phase map in a noisy environment is extended to a stochastic kernel ss that stochastic bifurcations can be investigated by spectral analysis of the kernel.

 

209.    J. Temmyo, E. Kuramochi, H. Kamada, and T. Tamamura

            "Resonant self-organization in semiconductor growth"

            J. Cryst. Growth 195 (1-4), 516-523 (1998).

 

            ABSTRACT: We describe, for the first time, resonant self-organization using a novel technique that combines selective epitaxy with the Turing-type self-organization phenomenon in the InGaAs/AlGaAs system on GaAs (3 1 1)B surface during metalorganic vapor-phase epitaxy. The resonant self-organization indicates a direct experimental evidence of nonlinear cooperative phenomenon in semiconductor growth. (C) 1998 Elsevier Science B.V. All rights reserved.

 

210.    Y. Tokura

            "Quantum Hall ferromagnet in a parabolic quantum wire"

            Phys. Rev. B 58 (19), 12597-12600 (1998).

 

            ABSTRACT: The spin phase diagram of interacting electrons in a quantum wire under a high magnetic field is investigated by finite-system exact,diagonalization. Various phases emerge as a function of interaction strength and aspect ratio. Stable spin-polarized states correspond to two-dimensional fractional quantum Hall states of filling fractions 1/q, with q odd. Spin-singlet ground states for six electrons with filling fractions around 2/5-1/2 are inspected in detail, and a real-space singlet pairing state peculiar to wire systems is found for a larger aspect ratio. [S0163-1829(98)06640-5].

 

211.    Y. Tokura

            "Two-dimensional electron transport with anisotropic scattering potentials"

            Phys. Rev. B 58 (11), 7151-7161 (1998).

 

            ABSTRACT: Anisotropic scattering potential has been found at the heterointerface of a two-dimensional electron gas in low-temperature transport experiments. This scattering potential has various symmetries depending on the crystalline direction of the interface. The conductivity tensor of a two-dimensional electron gas is theoretically investigated with a Boltzmann equation. Several models of anisotropic elastic scattering potentials are examined. Explicit formulas of the conductivity tensor are given to the lowest order of the potential anisotropy. If isotropic scatterings and anisotropic scatterings coexist, Matthiessen's rule gives larger mobility than the exact value. The conductivity is isotropic if the number of the symmetry axes of the scattering probability is more than 2.

 

212.    Y. Tokura, L. P. Kouwenhoven, D. G. Austing, and S. Tarucha

            "Many-body effect in an artificial atom"

            Physica B 246, 83-87 (1998).

 

            ABSTRACT: Atomic-like properties of vertical quantum dots are studied by measuring Coulomb oscillations. The Coulomb oscillations in the linear transport regime become irregular in period, reflecting a shell structure and the obedience to Hund's rule, as the number of electrons in the dot approaches zero. Under a high magnetic field, many-body effects become important, and we observe kink structures in the few-electron regime in the Coulomb oscillation peak positions versus the magnetic field. The kink structures are well assigned to transition in spin and angular momentum states, which we predict by the exact diagonalization approach. (C) 1998 Elsevier Science B.V. All rights reserved.

 

213.    K. Torimitsu and O. Niwa

            "Direct detection of uncaged glutamate and the laser photostimulation of cultured rat cortex"

            Neuroreport 9 (4), 599-603 (1998).

 

            ABSTRACT: THE photostimulation of nerve cells using a caged compound is very useful because it is non-invasive and non-destructive compared with standard electrophysiological techniques. There are no methods, however, for continuously measuring the photo-uncaged 'free' compound concentration at high temporal and spatial resolutions which can detect how much uncaged compound has been applied to cells. Here, we used an electrochemical detection method for the real-time measurement of photo-uncaged glutamate. In this way, we were able to determine the amount of uncaged glutamate and investigate neural activities by tracing [Ca](i) while simultaneously employing photostimulation and on-line glutamate measurement. The combination of an on-line sensor and laser-photostimulation with [Ca](i) measurement could be a powerful tool with which to investigate synaptic connections and activities.

 

214.    E. Toyoda and H. Takayanagi

            "Magnetoresistance oscillations of quasi-ballistic two-dimensional electron gas coupled with a superconducting ring"

            Physica B 251, 472-475 (1998).

 

            ABSTRACT: We have investigated normal transport in a quasi-ballistic two-dimensional electron gas (2DEG) coupled with a superconducting Nb loop. The oscillations in the resistance are observed as a function of the applied magnetic field which tunes the macroscopic phase difference of the loop. Around zero bias voltage, the resistance maxima occur at even multiples of pi. For energies higher than 0.17 meV the sign of the oscillations becomes opposite, and for the middle energies both types of oscillations are observed. We interpret this crossover to be a manifestation of the two types of contributions from Andreev interfered quasi-particles. The temperature dependence of the oscillation amplitude exhibits reentrant behavior which is similar to that shown in phase-dependent conductance of a diffusive S/N system. (C) 1998 Elsevier Science B.V. All rights reserved.

 

215.    S. Toyoda and M. Fujiki

            "Photoluminescence and absorption spectra of poly(pentylphenylsilylene). Absence of broad photoluminescence of poly(alkylarylsilylene) around 2.7 eV"

            Chem. Phys. Lett. 293 (1-2), 38-42 (1998).

 

            ABSTRACT: Absorption, photoluminescence (PL) and PL excitation (PLE) spectra of a solution and a thin film of poly(pentylphenylsilylene) (1) are measured and compared to those of poly(methylphenylsiIylene) (2). The sharper and stronger 3.6 eV absorption and the mirror image of the absorption and PL spectra of 1 suggest that 1 is spatially homogeneous. The broad PL which appears in 2 is scarcely observable in the 1 film around 2.7 eV, in the range from room temperature to 20 K. A comparison of the PLE spectra shows that the origins of the broad PL of 1 and 2 are different, To obtain poly(alkylarylsilylene) derivatives with high molecular weights which show no visible FL, the all;yl pendants should be pentyl or longer. (C) 1998 Elsevier Science B.V, All rights reserved.

 

216.    K. Tsubaki

            "Longitudinal magnetoresistance in magnetic barrier systems"

            Physica B 258, 392-396 (1998).

 

            ABSTRACT: In contrast with reflection by an electric-potential barrier, the reflection probability by a magnetic barrier depends not only on the electrons' momentum perpendicular to the barrier but also on the electrons' momentum parallel to the barrier. A magnetic barrier system allows new aspects of electron transport to be studied. In this paper, the fabrication of a magnetic barrier in a 2-dimensional electron gas with two current contacts and four potential probes, and the observation of quantized magnetoresistance due to the magnetic barrier are described. A resistance plateau of h/6e(2) is observed near a magnetic field of 4.7 T and the gate voltage of 0.0 V. Anther resistance plateau of h/12e(2) is observed near a magnetic field of 4 T and the gate voltage of 0.2 V. Such quantized resistances are explained by the Landauer-Buttiker formula. (C) 1998 Elsevier Science B.V. All rights reserved.

 

217.    M. Uematsu

            "Simulation of clustering and transient enhanced diffusion of boron in silicon"

            J. Appl. Phys. 84 (9), 4781-4787 (1998).

 

            ABSTRACT: We have simulated the postimplantation clustering and transient enhanced diffusion (TED) in boron profiles with peak concentrations below the boron (B) solubility limit. First, we derive an analytical formula for B clustering in terms of the reaction between B atoms and supersaturated self-interstitials. Then, using this formula and taking into account the dissolution of B clusters to emit self-interstitials, a unified simulation is done with just three essential parameters for the B clusters and based on the self-interstitial cluster model and the B diffusion model. We have satisfactorily fitted B TED profiles not only for implanted B layers but also for initially active B layers. Moreover, a comparison with TED induced by P implantation is made in terms of the trapping and diffusivities of self-interstitials. (C) 1998 American Institute of Physics. [S0021-8979(98)09720-5].

 

218.    M. Uematsu

            "Transient enhanced diffusion of boron in the presence of dislocations produced by amorphizing implantation in silicon"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 37 (11), 5866-5869 (1998).

 

            ABSTRACT: We have simulated transient enhanced diffusion (TED) of boron in the presence of dislocations produced by amorphizing implantation. A unified simulation was done, taking into account that end-of-range (EOR) dislocations act as both a sink fbr and source of self-interstitials, depending on temperature and annealing time. We have simulated B TED profiles bath in regrown regions and beneath EOR dislocations produced by Si implantation at room temperature. Simulation results indicate that EOR dislocations do not act as a perfect barrier to self-interstitial diffusion. In addition, the simulation well reproduces the experimental profiles by taking into account another type of defect that maintain self-interstitial concentration at thermal equilibrium values in the regrown region.

 

219.    Y. Utsumi and J. Takahashi

            "Synthesis of amino acids from N-2, H2O vapor and CO2 gas mixture by synchrotron radiation induced photochemical reactions at atmospheric pressure"

            Jpn. J. Appl. Phys. Part 2 - Lett. 37 (10B), L1268-L1270 (1998).

 

            ABSTRACT: Amino acid precursors are synthesized from an N-2, CO2 and H2O vapor mixture by synchrotron radiation induced photochemical reactions at atmospheric pressure and at room temperature. It was found that the alanine and aspartic acid in the precursors are enriched in the L-isomer by about 15% over the antipodal D-isomer.

 

220.    K. Uwai, Y. Watanabe, and N. Kobayashi

            "Dielectric changes of GaAs surfaces determined using the Kramers-Kronig analysis of surface photoabsorption spectra"

            Thin Solid Films 313, 583-586 (1998).

 

            ABSTRACT: Dielectric response spectra of GaAs surfaces are determined using Kramers-Kronig transformation of the surface photoabsorption (SPA) spectra for the surface conversion caused by Ga-deposition and H adsorption on the As-stabilized (001)-(2 x 4) surface. A method to determine the change in the phase shift associated with the reflectance change is developed to obtain dielectric changes of the surface. The surface dielectric changes show peaks that coincide with the critical points of the bulk GaAs dielectric function as well as features that can be assigned to surface localized states. (C) 1998 Elsevier Science S.A.

 

221.    W. G. van der Wiel, T. H. Oosterkamp, J. W. Janssen, L. P. Kouwenhoven, D. G. Austing, T. Honda, and S. Tarucha

            "Singlet-triplet transitions in a few-electron quantum dot"

            Physica B 258, 173-177 (1998).

 

            ABSTRACT: We have measured spin-singlet-spin-triplet (ST) transitions in a vertical quantum dot containing up to four electrons. Current through the dot is measured as a function of gate voltage and magnetic field (0-9 T) at both small and large source drain voltages. The ST transitions cannot be explained within the framework of single-particle states in combination with a constant Coulomb interaction. Taking into account exchange interaction and a magnetic field dependent direct Coulomb interaction is essential for describing the observed ST transitions. (C) 1998 Elsevier Science B.V. All rights reserved.

 

222.    V. V. Vinod and H. Murase

            "Image retrieval using efficient local-area matching"

            Mach. Vis. Appl. 11 (1), 7-15 (1998).

 

            ABSTRACT: We present an efficient and accurate method for retrieving images based on color similarity with a given query image or histogram. The method matches the query against parts of the image using histogram intersection. Efficient searching for the best matching subimage is done by pruning the set of subimages using upper bound estimates. The method is fast, has high precision and recall and also allows queries based on the positions of one or more objects in the database image. Experimental results showing the efficiency of the proposed search method, and high precision and recall of retrieval are presented.

 

223.    J. Wang, D. B. Luo, and T. Horiuchi

            "Anodic stripping with collection at interdigitated carbon film microelectrode arrays"

            Electroanalysis 10 (2), 107-110 (1998).

 

            ABSTRACT: Interdigitated arrays of microband electrodes are used for highly sensitive anodic stripping with collection experiments, Compared to analogous experiments at rotating ring-disk electrodes, the interdigitated microelectrode array offers high collection efficiencies and the use of quiescent solutions. New lithographically fabricated carbon band microelectrodes, made by pyrolysis of 3,4,9,10-peryleneterracarboxylic dianhydride, are employed for supporting the mercury film. Metal cations stripped from one microband electrode diffuse across the narrow gap and are redeposited (collected) at the second electrode, kept at a suitable negative potential. The elimination of the charging current (accrued from the fixed collection potential) results in well-defined peaks, superimposed on a constant background, and hence in a greatly improved detectability. Experimental variables affecting the collection efficiency and the response, including the gap and scan rate, are examined.

 

224.    Y. Watanabe

            "Effects of annealing on oxygen depth profiles and chemical etching rates of thermally grown silicon oxides"

            J. Electrochem. Soc. 145 (4), 1306-1309 (1998).

 

            ABSTRACT: Effects of annealing on oxygen depth profiles and chemical etching rates of thermally grown silicon oxides are investigated in order to characterize the intermediate layer, adjacent to the oxide/silicon interface. We found that the oxygen Auger signal intensity for the samples grown at 800 and 900 degrees C with a thickness of 11 nm, increases in the region that is several nanometers thick, adjacent to the oxide/silicon interface. Furthermore, the chemical etching rates of the samples grown at 800 and 900 degrees C decrease in just about the same region, adjacent to the interface. However, we found no intermediate layer in the samples grown at 1000 degrees C, or annealed at 1000 degrees C. These experimental results indicate the existence of an intermediate layer that has a higher oxygen content, and dissolves slower in an etching solution, than the bulk oxide. The intermediate layer is believed to contain highly dense quasi-stable silica that is compacted by the compression stress. Annealing at 1000 degrees C must result in a transformation of the intermediate layer to a more stable structure with a lower density.

 

225.    M. J. Werner

            "Quantum soliton generation using an interferometer"

            Phys. Rev. Lett. 81 (19), 4132-4135 (1998).

 

            ABSTRACT: For the first time a method for realizing macroscopic quantum optical solitons is presented. Simultaneous photon-number and momentum squeezing is predicted using soliton propagation in an interferometer. Extraction of soliton pulses closer to true quantum solitons than their coherent counterparts from mode-locked lasers is possible. Moreover, it is a general method of reducing photon-number fluctuations below the shot-noise level for nonsoliton pulses as well. It is anticipated that similar reductions in particle fluctuations could occur for other forms of interfering bosonic fields whenever self-interaction nonlinearities exist, for example, interacting ultracold atoms. [S0031-9007(98)07605-4].

 

226.    E. Yamaguchi and M. R. Junnarkar

            "Effects of nitrogen vacancy on optical properties of nitride semiconductors"

            J. Cryst. Growth 190, 570-574 (1998).

 

            ABSTRACT: Band structures and deep levels are calculated for both the cubic and hexagonal nitride semiconductors, using the sp(3)s* tight-binding formulation and the Green's function technique. An anti-bonding s-like state produced by nitrogen vacancy is predicted to appear at 0.3 eV below the conduction-band (CB) edge for GaN, which gets shallower and then resonant with the CB for InxGa1-xN with In content (x), The theoretical results can provide a new and consistent model for explaining anomalous optical properties in nitride semiconductors. (C) 1998 Elsevier Science B.V. All rights reserved.

 

227.    F. Yamaguchi, D. H. Huang, and Y. Yamamoto

            "Coulomb blockade oscillation in a single atomic junction"

            Semicond. Sci. Technol. 13 (8A), A124-A126 (1998).

 

           ABSTRACT: The first observation of the Coulomb blockade effect in the smallest possible system with a single atom as the central island of a double-barrier tunnel junction is reported. Our system consists of a single tungsten atom as the central island and a tungsten STM tip and a silicon (100)2 x 1 reconstructed surface as the two electrodes. The use of a single atom as the central island makes the change in the electrostatic potential due to a variation of number of electrons in the island of the order of 1 eV and thus the Coulomb blockade effect is made more controllable and stable even at room temperature. A specific shape of the tip apex forms a tunnel junction between an apex atom and the rest of the tip with the energy-level broadening of the apex atom smaller than the change in the charging energy due to the change in the number of electrons in the single tungsten atom. This theoretical prediction was confirmed by the experimental results of I-V measurements with an SIM tip made from a W(111) single-crystal wire where the change in the charging energy is 1.1 eV.

 

228.    H. Yamaguchi and Y. Hirayama

            "Imaging of local charge density in an InAs/GaAs two-dimensional heterostructure by scanning tunneling microscopy"

            Jpn. J. Appl. Phys. Part 2 - Lett. 37 (8A), L899-L901 (1998).

 

            ABSTRACT: We have studied the bias-voltage dependence of constant-current images obtained by scanning tunneling microscopy (STM) at 4.8 K on an InAs thin film grown on GaAs (111)A substrates. In-plane surface-height variation as large as 0.1-0.2 nm was detected on the step-free region, only with the negative sample voltages higher than similar to 0.6 V. Because the bias condition corresponds to the tunneling of electrons accumulated in the InAs film to the STM tip, we believe that the image reflects the local electron density in InAs/GaAs two-dimensional heterostructures.

 

229.    H. Yamaguchi and Y. Hirayama

            "Improvement in the electrical properties of GaAs/InAs/GaAs structures through the use of (111)A substrates"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 37 (3B), 1599-1602 (1998).

 

            ABSTRACT: We compare the electrical properties of InAs thin films embedded in GaAs layers grown by solid source molecular beam epitaxy on (111)A and (001) substrates. A major improvement in Hall mobility through the use of (111)A substrates is confirmed. The carrier concentration is found to saturate at a value of 3 x 10(12) cm(-2) after 50 nm as a function of the InAs thickness. Self-consistent calculation assuming interface Fermi level pinning produces results which are in good agreement with the experimental results, and the pinning position is estimated to be about 0.15 eV above the bottom of the conduction band. The origin of Fermi level pinning seems to be the misfit dislocations confined at the InAs/GaAs interfaces based on structural characterization by transmission electron microscopy.

 

230.    H. Yamaguchi and Y. Homma

            "Imaging of layer by layer growth processes during molecular beam epitaxy of GaAs on (111)A substrates by scanning electron microscopy"

            Appl. Phys. Lett. 73 (21), 3079-3081 (1998).

 

            ABSTRACT: When we use a scanning electron microscope-molecular beam epitaxy system with a GaAs (111)A substrate that dramatically improves the flatness of the growing surface, it makes possible detailed observations of the near-equilibrium growth processes of island nucleation, coalescence, and step motion. These observations allow the quantitative analysis of the growth processes based on the standard model of crystal growth. As an example, the Ga adatom surface diffusion length is directly determined from the dependence of measured step velocity on the Ga arrival rate. (C) 1998 American Institute of Physics. [S0003-6951(98)04547-1].

 

231.    H. Yamaguchi, J. L. Sudijono, B. A. Joyce, T. S. Jones, C. Gatzke, and R. A. Stradling

            "Thickness-dependent electron accumulation in InAs thin films on GaAs(111)A: A scanning-tunneling-spectroscopy study"

            Phys. Rev. B 58 (8), R4219-R4222 (1998).

 

            ABSTRACT: Scanning tunneling spectroscopy has been used to study quantum size effects on the electronic structure of thin InAs films grown on GaAs(111)A substrates, an example of a heterostructure with a relatively large lattice mismatch. The band gap of the InAs films, as measured from current-voltage curves, decreases gradually with film thickness, and electron accumulation occurs in layers that are thicker than 6 nm. Self-consistent calculations suggest the thickness-dependent accumulation is due to quantum size effects and Fermi-level pinning caused by the dislocation network at the InAs/GaAs interface.

 

232.    M. Yamaguchi, K. Koyama, T. Suemoto, and M. Mitsunaga

            "Mapping of site distribution in Eu3+: YAlO3 on RF-optical frequency axes by using double-resonance spectroscopy"

            J. Lumines. 76-7, 681-684 (1998).

 

            ABSTRACT: We measured the high-resolution excitation spectrum and optical-RF (radio frequency) double-resonance spectra of Eu3+:YAlO3 in F-7(0)-->D-5(0) region at about 2K. Optical excitation spectrum showed more than 40 weak satellite lines spreading over some 400 GHz. These lines are ascribed to the sites differently perturbed by defects or other Eu3+ ions. Using optical-RF double-resonance measurement in the main and some satellite lines, we have obtained RF double-resonance frequencies of hyperfine transition in ground states at various optical frequencies. From these results we can identify the sites which cannot be distinguished by a simple optical measurement. (C) 1998 Elsevier Science B.V. All rights reserved.

 

233.    Y. Yamamoto

            "Generation of squeezed light from semiconductor lasers and its application to precision measurements"

            Phys. Scr. T76, 103-109 (1998).

 

            ABSTRACT: The generation and application of nonclassical light (number-phase squeezed states and single-photon states) from semiconductor lasers and mesoscopic LEDs are discussed. The shot noise suppression in the three-partition processes such as the electron transport in a highly dissipative conductor, the electron injection and tunneling in a pn junction, and the radiative recombination of an electron-hole pair inside a cavity is the basic principle for this generation scheme.

 

234.    K. Yamazaki

            "Semiconductor fabrication process evaluation by scanning tunneling microscopy atomic force microscopy and related techniques: Mainly impurity concentration observation"

            in Defect Recognition And Image Processing In Semiconductors 1997, Institute Of Physics Conference Series Vol. 160 (Iop Publishing Ltd, Bristol, 1998), pp. 437-448.

 

            ABSTRACT: Scanning tunneling microscopy (STM)/atomic force microscopy (AFM) and related techniques are widely used to evaluate semiconductor fabrication processes. AFM is now an invaluable method far evaluating thin-film surface microroughness at various stages of these processes because of its resolution and convenience. On the other hand, methods of electronic measurement related to STM/AFM have been developed for the electronic evaluation of semiconductor processes and devices, like impurity concentration observation.

 

235.    K. Yamazaki, A. Fujiwara, Y. Takahashi, H. Namatsu, and K. Kurihara

            "Sub-10-nm overlay accuracy in electron beam lithography for nanometer-scale device fabrication"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 37 (12B), 6788-6791 (1998).

 

            ABSTRACT: A high-performance electron beam nanolithography system with an overlay accuracy of better than 10 nm has born developed and applied to nanodevice fabrication. Owing to the suppression of charge-up and precise beam position control by taking into account stage position error as well as improvements in other factors, we have obtained a stable beam (< 2 nm/5 min.), the exposure position reproducibility with stage movement (< 3 nm/500 times), and high mark-locating accuracy (3 nm). The resulting overlay accuracy is 6-9 nm in [mean] + 2 sigma. Using this system, we have made multi-island single-electron devices with line gates overlaid on the Si islands within a 10-nm error. The high overlay accuracy in electron beam nanolithography will allow the study of highly functional single-electron devices.

 

236.    P. D. Ye, D. Weiss, R. R. Gerhardts, K. von Klitzing, and S. Tarucha

            "Huge magnetoresistance oscillations in periodic magnetic fields"

            Physica B 251, 330-333 (1998).

 

            ABSTRACT: By depositing ferromagnetic gratings on top of two-dimensional electron gases (2DEG), it is possible to generate periodic magnetic fields on a submicron scale in the plane of the electrons. Here, we show that the amplitude of the periodic magnetic field can be notably enhanced if the externally applied magnetic field B-0 is tilted towards the plane of the 2DEG while kept normal to the gratings. (C) 1998 Elsevier Science B.V. All rights reserved.

 

237.    U. Zeimer, F. Bugge, S. Gramlich, M. Nasarek, M. Sato, and M. Weyers

            "Relaxation behaviour of highly strained GaAs/InxGa1-xAs/GaAs quantum wells depending on MOVPE growth conditions"

            in Defect Recognition And Image Processing In Semiconductors 1997, Institute Of Physics Conference Series Vol. 160 (Iop Publishing Ltd, Bristol, 1998), pp. 393-396.

 

            ABSTRACT: For highly strained GaAs/InxGa1-xAs/GaAs-quantum wells (QWs) with x greater than or equal to 0.25, grown by metalorganic vapour deposition (MOVPE), the relaxation with increasing layer thickness does not take place in the classical way via elongated misfit dislocation formation. Already below the critical layer thickness a transition of the growth mode from step flow mode to the Stranski-Krastanov growth mechanism is observed resulting in formation of clusters with a higher In concentration than the surrounding material.

 

238.    H. L. Zhou, A. V. Nurmikko, C. C. Chu, J. Han, R. L. Gunshor, and T. Takagahara

            "Observation of antibound states for exciton pairs by four-wave-mixing experiments in a single ZnSe quantum well"

            Phys. Rev. B 58 (16), R10131-R10134 (1998).

 

            ABSTRACT: We have employed spectrally resolved, subpicosecond transient four-wave-mixing techniques to identify and to study the four-particle "antibound states" associated with excitonic molecules in a binary ZnSe single quantum well. Previously, the existence of robust bound biexcitons have been observed in this wide band-gap semiconductor heterostructure, including a density regime where optical gain is dominated by the molecular states. We employ selective circular polarization excitation to suppress the bound (ground state) exciton-pair state contribution and find a spectrally distinct and isolated feature emerging approximately 3.5 meV higher in photon energy than the n=1 heavy-hole exciton transition. The new resonance is distinct only in the negative time delay regime, and is interpreted as a manifestation of coherent four-particle correlated states within the biexciton continuum. [S0163-1829(98)51736-5].