1.         K. Ajito, M. Morita, and K. Torimitsu

            "Investigation of the molecular extraction process in single subpicoliter droplets using a near-infrared laser Raman trapping system"

            Anal. Chem. 72 (19), 4721-4725 (2000).

 

            ABSTRACT: The near-infrared (NIR) laser Raman trapping system was applied to study liquid-liquid extraction in a single droplet in a subpicoliter range. The system trapped a single subpicoliter toluene droplet in water using the NIR laser beam and provided time-dependent optical images of the droplet during liquid-liquid extraction. The size of the trapped droplet gradually increased after p-nonylphenol solution was added in water. The Raman spectra of the droplet prove that the increase of the droplet size was caused by the absorption of p-nonylphenol from the water. The distribution coefficient of p-nonylphenol in the subpicoliter droplet was much higher than that in bulk solution.

 

2.         K. Ajito and K. Torimitsu

            "Spectroscopy of organic and biological single particles on nanometer and micrometer scales using a near-infrared laser Raman trapping system"

            in Microbeam Analysis 2000, Proceedings, Institute Of Physics Conference Series Vol. 165 (Iop Publishing Ltd, Bristol, 2000), pp. 21-22.

 

            ABSTRACT:

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

            "Determination of the order parameter symmetry in hole and electron doped cuprate superconductors"

            Physica B 284, 591-592 (2000).

 

            ABSTRACT: It is well established that the order parameter symmetry in the hole-doped high-temperature superconductors (HTS) is of d-wave type. For the electron-doped HTS one could expect to find the same order parameter symmetry because both systems have the copper oxygen planes in common. However, our experiments based on bicrystal grain boundary junctions (GBJs) show the absence of zero energy Andreev bound states as well as a s-wave like temperature dependence of the London penetration depth thereby excluding a d-wave symmetry of the order parameter in the electron-doped cuprates. At present, it is not fully established whether the electron-doped HTS have an isotropic or an anisotropic s-wave symmetry of the order parameter. (C) 2000 Elsevier Science B.V. All rights reserved.

 

4.         L. Alff, S. Kleefisch, B. Welter, K. Sengebusch, S. Meyer, U. Schoop, F. Herbstritt, A. Marx, R. Gross, M. Naito, and H. Sato

            "Symmetry of the order parameter in hole and electron doped cuprate superconductors"

            Physica C 341, 1659-1662 (2000).

 

            ABSTRACT: It is well established that the order parameter symmetry in the hole doped high-temperature superconductors (HTS) is of d-wave type. In contrast, there is growing experimental evidence for a s-wave type symmetry in the electron doped cuprate superconductors. We present tunneling spectra and measurements of the London penetration depth, both supporting strongly the s-wave scenario for the electron doped HTS [1]. The absence of Andreev bound states in the tunneling spectra indicates a state without sign change of the pair potential, and the absence of low energy excitations as revealed by the London penetration depth measurements suggests a gapped state. Based on these experiments, for the materials (Nd/Pr)(1.35)Ce0.15CuO4-y an about isotropic s-wave symmetry seems more likely than a strongly anisotropic s-wave symmetry. For the Nd compound we observe anomalous low temperature behavior due to the Nd3+ magnetic moments.

 

5.         L. Alff, S. Meyer, S. Kleefisch, U. Schoop, K. Sengebusch, A. Marx, H. Sato, M. Naito, and R. Gross

            "Low-temperature anomalies of the superconducting properties of Nd1.85Ce0.15CuO4-y"

            Physica B 284, 999-1000 (2000).

 

            ABSTRACT: We have measured the temperature dependence of the change Delta lambda(ab)(T) = lambda(ab)(T) - lambda(ab)(T = 0) of the in-plane London penetration depth lambda(ab) in the electron-doped cuprate superconductor Nd1.85Ce0.15CoO4-y (NCCO). An anomalous temperature dependence below about 4 K is observed. In contrast to the expected monotonous decrease of lambda(ab)(T) With decreasing temperature, lambda(ab)(T) is found to increase with decreasing temperature below 4 K resulting in a non-monotonous overall temperature dependence. This anomalous behavior was found to be absent in analogous measurements performed on Pr1.85Ce0.15CoO4-y (PCCO). From this, we conclude that the anomalous behavior of NCCO is caused by the influence of the Nd3+ magnetic moments. Correcting for the temperature-dependent susceptibility due to the Nd3+ moments, an exponential lambda(ab)(T) dependence is obtained indicating s-wave pairing in the electron-doped superconductors. (C) 2000 Elsevier Science B.V. All rights reserved.

 

6.         V. N. Antonov, H. Takayanagi, F. K. Wilhelm, and A. D. Zaikin

            "pi-shifted magnetoconductance oscillations in mesoscopic superconducting-normal heterostructures"

            Europhys. Lett. 50 (2), 250-256 (2000).

 

            ABSTRACT: Interference of proximity-induced superconducting correlations in mesoscopic metallic rings is sensitive to the magnetic flux Phi inside these rings. This is the reason for magnetoconductance oscillations in such systems. We detected experimentally and explained theoretically a novel effect: the phase of these oscillations can switch between 0 and pi depending on the resistance of intermetallic interfaces and temperature. The effect is due to a nontrivial interplay between the proximity-induced enhancement of the local conductivity and the proximity-induced suppression of the density of states at low energies.

 

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

            "Anomalous hysteretic phenomena in cyclotron resonance spectra of GaAs/AlGaAs quantum well under tilted magnetic fields of short pulse up to 150 T"

            Physica E 6 (1-4), 191-194 (2000).

 

            ABSTRACT: We observed a new type of hysteresis in cyclotron resonance spectra of two-dimensional electron gas confined in GaAs/AlGaAs multi quantum wells when we applied high magnetic fields tilted from the growth direction. Pulsed high magnetic fields up to 150T were generated by the single turn coil technique. We investigated in detail the condition for the occurrence of the hysteresis which is a disagreement between two traces in the up- and down-sweeps of the pulsed magnetic fields. The dependencies of the hysteresis on the wavelength, sweep rate of the fields and temperature has led to the conclusion that the hysteresis is due to inequilibrium states in the up-sweep of tilted magnetic fields. The relaxation time from inequilibrium to equilibrium states was revealed to be of the order of microsecond. (C) 2000 Elsevier Science B.V. All rights reserved.

 

8.         D. G. Austing, Y. Tokura, S. Tarucha, T. H. Oosterkamp, J. W. Janssen, M. W. S. Danoesastro, and L. P. Kouwenhoven

            "Vertical quantum dots at high magnetic fields beyond the few-electron limit"

            Physica E-Low-Dimensional Systems & Nanostructures 6 (1-4), 358-363 (2000).

 

            ABSTRACT: We describe phenomena that can be studied in vertical quantum dot single electron transistors, Moving from the few-electron to the several- and many-electron regimes, features in the conductance peaks initially related to spin polarization evolve with magnetic field. This allows us to first probe the spin-flip region beyond the last single-particle crossing at low field, and then the formation and stability of the spin-polarized maximum density droplet at high field. According to a simple capacitance model, charge redistribution in the dot at higher magnetic fields is accompanied by abrupt changes in the area of the droplet. (C) 2000 Elsevier Science B.V. All rights reserved.

 

9.         G. Bastian

            "Comment on "Critical currents in ballistic two-dimensional InAs-based superconducting weak links""

            Phys. Rev. B 62 (14), 9840-9841 (2000).

 

            ABSTRACT: In ballistic Josephson junctions the experimentally observed IV characteristics deviate from the theoretically predicted behavior. Recently, Heida et al. [Phys. Rev. B 60, 13 135 (1999)] discussed this problem and offered an explanation for the discrepancy. Considering this explanation, several contradictions to the authors' data as wen as to other publications are shown.

 

10.       O. Benson, J. Kim, H. Kan, and Y. Yamamoto

            "Simultaneous Coulomb blockade for electrons and holes in p-n junctions: observation of Coulomb staircase and turnstile operation"

            Physica E 8 (1), 5-12 (2000).

 

            ABSTRACT: The Coulomb blockade effect in a mesoscopic double-barrier p-i-n junction is reported. The electron and hole injection into the central QW of a p - n junction is achieved via resonant tunneling. We present a theoretical model that describes the device operation. When the device is biased with a constant voltage source the model predicts the observation of Coulomb staircase in the current-voltage characteristics. When an additional square wave modulation signal is applied, turnstile operation is achieved. The experimental evidence for Coulomb staircase effect and turnstile operation is presented. (C) 2000 Elsevier Science B,V. All rights reserved.

 

11.       O. Benson, C. Santori, M. Pelton, and Y. Yamamoto

            "Regulated and entangled photons from a single quantum dot"

            Phys. Rev. Lett. 84 (11), 2513-2516 (2000).

 

            ABSTRACT: We propose a new method of generating nonclassical optical field states. The method uses a semiconductor device, which consists of a single quantum dot as active medium embedded in a p-i-n junction and surrounded by a microcavity. Resonant tunneling of electrons and holes into the quantum dot ground states, together with the Pauli exclusion principle, produce regulated single photons or regulated pairs of photons. We propose that this device also has the unique potential to generate pairs of entangled photons at a well-defined repetition rate.

 

12.       E. V. Bezuglyi, E. N. Bratus, V. S. Shumeiko, G. Wendin, and H. Takayanagi

            "Circuit theory of multiple Andreev reflections in diffusive SNS junctions: The incoherent case"

            Phys. Rev. B 62 (21), 14439-14451 (2000).

 

            ABSTRACT: The incoherent regime of multiple Andreev reflections (MAR) is studied in long diffusive SNS junctions at applied voltages larger than the Thouless energy. Incoherent MAR are treated as a transport problem in energy space by means of a circuit theory for an equivalent electrical network. The current through NS interfaces is explained in terms of diffusion flows of electrons and holes through ''tunnel'' and ''Andreev'' resistors. These resistors in diffusive junctions play roles analogous to the normal and Andreev reflection coefficients in Octavio-Tinkham-Blonder-Klapwijk theory for ballistic junctions. The theory is applied to the subharmonic gap structure (SGS); simple analytical results are obtained for the distribution function and current spectral density for the limiting cases of resistive and transparent NS interfaces. In the general case, the exact solution is found in terms of chain fractions, and the current is calculated numerically. SGS shows qualitatively different behavior for even and odd subharmonic numbers n = 2 Delta /eV, and the maximum slopes of the differential resistance correspond to the gap subharmonics, eV = 2 Delta /n. The influence of inelastic scattering on the subgap anomalies of the differential resistance is analyzed.

 

13.       V. V. Borovkov, J. M. Lintuluoto, M. Fujiki, and Y. Inoue

            "Temperature effect on supramolecular chirality induction in bis(zinc porphyrin)"

            J. Am. Chem. Soc. 122 (18), 4403-4407 (2000).

 

            ABSTRACT: The achiral syn folded conformer (face-to-face) of the ethane-bridged bis(Zn porphyrin) gradually transforms into the chiral extended anti form in the presence of enantiopure guest molecules (alcohols or amines) upon lowering the temperature from 293 to 183 K. The mechanism of the supramolecular chirality induction is based upon the formation of right- or left-handed screw diastereomers of the anti form. The split absorption maxima which are caused by the exciton coupling of the corresponding B transitions match the bisigned Cotton effects. The amplitude of the CD bands is found to be dependent on the bulk and ligation strength of the chiral guest, while the sign of the couplets is observed to be determined by the absolute configuration of the external ligand. The formation of the screw structure in the anti conformation is also confirmed by H-1 NMR.

 

14.       D. J. Bottomley

            "Formation and shape of InAs nanoparticles on GaAs surfaces: Fundamental thermodynamics"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 39 (7B), 4604-4608 (2000).

 

            ABSTRACT: Consideration of the heteroepitaxial growth of InAs on GaAs surfaces, and the substrate orientation-dependent growth mode, has led us to examine the thermodynamic aspects of heteroepitaxy in general. We argue that the molar Gibbs free energy G is the appropriate state function for heteroepitaxy, in contrast to Gibbs's approach of using the Helmholtz free energy, since G alone guarrantees mathematical continuity in the theory's predictions in the limit of isotropic stress. An expression for the critical heteroepitaxial strain required to melt a film is given. We comment that evidence of stress-induced surface liquid-like phenomena has been present in experiments for over 30 years, but such liquid phase phenomena had no theoretical basis until the present work. In situ electron microscopy and electron diffraction studies of heteroepitaxial growth are probably the most favourable techniques for investigating the proposed liquid phase.

 

15.       A. Chavez-Pirson, J. Temmyo, and H. Ando

            "Pressure-induced modulation of the confinement in self-organized quantum dots produced and detected by a near-field optical probe"

            Physica E 7 (3-4), 367-372 (2000).

 

            ABSTRACT: Near-field optical probing, or nanoprobing, achieves spatial resolution that surpasses the diffraction limit of light and makes possible the luminescence imaging and spectroscopy of single quantum dots in dense arrays of dots. We use optical nanoprobing to study self-organized InGaAs quantum dots grown on (3 1 1)B oriented GaAs substrates. Here, we emphasize a new feature of nanoprobing: pressure-induced strain modulation near the surface. Operating in near-field optical excitation-collection mode, the probe makes contact with the surface and exerts direct pressure whose main effect is a compressive uniaxial strain under the probe. By adjusting the applied pressure, we modulate the local strain environment in and around a quantum dot, but still preserve the capability to capture its near-field luminescence. Nanoprobe pressure effects modify the confinement potential and radiative emission of single quantum dots, and the coupling strength between dots. This opens new possibilities for the study and control of the optical and electronic properties of single- and coupled-quantum dots. (C) 2000 Elsevier Science B.V. All rights reserved.

 

16.       T. Dotera and Y. Y. Suzuki

            "Polymer confinement in undulated membrane boxes and tubes"

            Phys. Rev. E 62 (4), 5318-5323 (2000).

 

            ABSTRACT: We consider quantum particle or Gaussian polymer confinement between two surfaces and in cylinders with sinusoidal undulations. In terms of the variational method, we show that the quantum-mechanical wave equations have lower ground-state energy in these geometries under long wavelength undulations, where bulges are formed and waves are localized in the bulges. It turns out correspondingly that Gaussian polymer chains in undulated boxes or tubes acquire higher entropy than in exactly flat or straight ones. These phenomena are explained by the uncertainty principle for quantum particles, and by a polymer confinement rule for Gaussian polymers. If membrane boxes or tubes are flexible, polymer-induced undulation instability is suggested. We find that the wavelength of undulations at the threshold of instability for a membrane box is almost twice the distance between two walls of the box. Surprisingly, we find that the instability for tubes begins with a shorter wavelength compared to the "Rayleigh" area-minimizing instability.

 

17.       Z. F. Ezawa, A. Sawada, K. Muraki, and Y. Hirayama

            "Quantum coherence and skyrmion textures in bilayer quantum Hall systems"

            Physica E 6 (1-4), 640-644 (2000).

 

            ABSTRACT: Quantum coherence develops spontaneously in bilayer quantum Hall systems when the Coulomb exchange energy is dominant. We argue that there exists a distinctive transition between the coherent phase and the resonant phase because different types of skyrmions are excited in these two phases. (C) 2000 Elsevier Science B.V. All rights reserved.

 

18.       P. Finnie and Y. Homma

            "Stability-instability transitions in silicon crystal growth"

            Phys. Rev. Lett. 85 (15), 3237-3240 (2000).

 

            ABSTRACT: In order for a crystal to grow, source atoms must be incorporated into the underlying lattice. Typically, this process occurs on the surface in one of two modes: either through island nucleation or through step flow. However, a third, morphologically unstable growth mode has been predicted. Monitoring the surface of ultraflat substrates with an in situ scanning electron microscope, we prove that for the (111) face of silicon there is a transition from stable step flow to morphological instability and then to island nucleation.

 

19.       P. Finnie and Y. Homma

            "Nucleation and step flow on ultraflat silicon"

            Phys. Rev. B 62 (12), 8313-8317 (2000).

 

            ABSTRACT: Step-flow crystal growth is possible on a very large scale on Si(111). The growth mode changes at the (7x7)-("1x1") phase-transition temperature. Nucleation of new Steps can be controlled by intentionally introducing contaminants or particulates. In general, steps bounding small structures move more quickly than those bounding large structures. Step motion appears symmetric under time reversal (erosion versus growth) and is similar under topological inversion (islands versus craters). The observed motion fits well with the simplest reasonable physical theory.

 

20.       P. Finnie and Y. Homma

            "Motion of atomic steps on ultraflat Si(111): Constructive collisions"

            J. Vac. Sci. Technol. A-Vac. Surf. Films 18 (4), 1941-1945 (2000).

 

            ABSTRACT: The motion of atomic steps was studied using ultraflat Si(lll) substrates which have flat terraces of up to 50 mu m in width separated by monoatomic steps. The motion is revealed in time lapse movies made by in situ scanning electron microscopy. When samples are heated to high temperatures (similar to 1000 degrees C) the surface erodes in a step-flow mode: steps retreat in an orderly fashion, one after the other. Here, steps are forced to collide constructively, providing a means to probe step interactions. Diffusion theory is used to explain the collision dynamics, allowing the extraction of physical parameters. After colliding, double steps continue to move at speeds simply related to the precursor steps' velocities. (C) 2000 American Vacuum Society. [S0734-2101(00)03004-9].

 

21.       S. R. Friberg, T. Mukai, and S. Machida

            "Dual quantum nondemolition measurements via successive soliton collisions"

            Phys. Rev. Lett. 84 (1), 59-62 (2000).

 

            ABSTRACT: integral(0)(infinity) dse(-s(m2+2D))[I-0(2s)](D) Quantum mechanics allows quantum nondemolition (QND) variables to be measured without being changed. This requires QND variables to be initially in an eigenstate and measurement backaction noise to be directed into conjugate variables. Experimental demonstrations thus require two measurements: the first to collapse variables toward an eigenstate and the second to show results identical to the first. Here, we report results from two successive soliton-collision QND measurements that optical correlation measurements show to be nearly identical.

 

22.       T. Fujii, T. Watanabe, and A. Matsuda

            "Anisotropy in the superconducting state and c-axis resistivity of precisely oxygen controlled Bi2Sr2CaCu2O8+delta a single crystals"

            Physica C 341, 1873-1874 (2000).

 

            ABSTRACT: We have measured the angle dependence of magneto-resistivity for pure Bi2Sr2CaCu2O8+delta Single crystals with various oxygen contents. Blatter's scaling rule was applied to estimate the anisotropy gamma in the superconducting state. With reducing oxygen content, obtained gamma increases in proportional to the square root of the rho (c) at just above T-c. These results can be quantitatively explained by the Lawrence-Doniach model. However, the obtained gamma has a temperature dependence, which suggests anomalous effect on the interlayer coupling eta near T-c.

 

23.       M. Fujiki

            "Synthesis and structure-property-functionality relationship of optically active polysilanes"

            J. Synth. Org. Chem. Jpn. 58 (12), 1178-1188 (2000).

 

            ABSTRACT: Chainlike polysilanes, which consist of a linear silicon-catenated backbone and organic side chains, exhibit unique optical properties due to the silicon sigma -conjugating electronic structure. Among these polysilanes, it has been established that rodlike polysilanes bearing a special pair of chiral and/or achiral alkyl side chains have unique (chir)optical features due to the highly delocalized silicon sigma electrons associated with very long segment lengths. The author describes several marked cooperative phenomena of optically active rodlike polysilane homopolymers and copolymers bearing (S/R)-2-methylbutyl or (S/R)-3,7-dimethyloctyl chiral side chains by means of UV, circular dichroism (CD), and fluorescence (FL) spectra and molecular mechanics calculation.

 

24.       M. Fujiki

            "Helix magic. Thermo-driven chiroptical switching and screw-sense inversion of flexible rod helical polysilylenes"

            J. Am. Chem. Soc. 122 (14), 3336-3343 (2000).

 

            ABSTRACT: An ideal optically active helical chromophoric polymer comprising a flexible rodlike silicon main chain and enantiopure alkyl side chains, poly{(S)-3,7-dimethyloctyl-3-methylbutylene}, underwent a thermo-driven helix-helix transition at -20 degrees C in isooctane. The transition characteristics. including transition temperature, transition width, the population of right- and left-handed helical motifs, global shape, and screw-pitch, were to be characterized quantitatively by spectroscopically analyzing circular dichroism (CD) and UV absorption characteristics. This is based on the unique property of the rodlike polymer in which the CD band completely matches the corresponding UV band profile at all temperatures. Moreover, fine controlling the contents and chirality of an additional chiral silylene unit incorporated in the copolymers allows free manipulation of the transition temperature in the range from -64 to +79 degrees C. Molecular mechanics calculation showed remarkable differences in the potential energy curve of the main chain torsion angle between flexible and rigid rodlike polysilylenes. These results and knowledge gained should assist in designing and controlling new types of helix-helix transition polymers directed to diverse screw-sense related properties and applications.

 

25.       T. Fujisawa and Y. Hirayama

            "Transmission type RF single electron transistor operation of a semiconductor quantum dot"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 39 (4B), 2338-2340 (2000).

 

            ABSTRACT: A single electron transistor is a highly sensitive electrometer, and can be operated at a high speed using the radio-frequency single electron transistor (RF-SET) technique. In this paper, we propose a modified RF-SET technique, which measures the transmission of the RF signal. It has some advantages, such as simpler circuits and clear frequency resonance as compared with the reflection measurement by RF-SET. We have tested the transmission-type RF-SET operation for a quantum dot in an AlGaAs/GaAs heterostructure.

 

26.       T. Fujisawa and Y. Hirayama

            "Charge noise analysis of an AlGaAs/GaAs quantum dot using transmission-type radio-frequency single-electron transistor technique"

            Appl. Phys. Lett. 77 (4), 543-545 (2000).

 

            ABSTRACT: Radio-frequency (rf)-operated single-electron transistors (SETs) are high-sensitivity, fast-response electrometers, which are valuable for developing new insights into single-charge dynamics. We investigate high-frequency (up to 1 MHz) charge noise in an AlGaAs/GaAs quantum dot using a transmission-type rf SET technique. The electron capture and emission kinetics on a trap in the vicinity of the quantum dot are dominated by a Poisson process. The maximum bandwidth for measuring single trapping events is about 1 MHz, which is the same as that required for observing single-electron tunneling oscillations in a measurable current (similar to 0.1 pA). (C) 2000 American Institute of Physics. [S0003-6951(00)00130-3].

 

27.       T. Fujisawa, W. G. van der Wiel, and L. P. Kouwenhoven

            "Inelastic tunneling in a double quantum dot coupled to a bosonic environment"

            Physica E 7 (3-4), 413-419 (2000).

 

            ABSTRACT: Coupling a quantum system to a bosonic environment always give rise to inelastic processes, which reduce the coherency of the system. We measure energy-dependent rates for inelastic tunneling processes in a fully controllable two-level system of a double quantum dot. The emission and absorption rates are well reproduced by Einstein's coefficients, which relate to the spontaneous emission rate. The inelastic tunneling rate can be comparable to the elastic tunneling rate if the boson occupation number becomes large. In the specific semiconductor double dot, the energy dependence of the inelastic rate suggests that acoustic phonons are coupled to the double dot piezoelectrically. (C) 2000 Elsevier Science B.V. All rights reserved.

 

28.       K. Furukawa and K. Ebata

            "Preparation and single molecule structure of electroactive polysilane end-grafted on a crystalline silicon surface"

            Appl. Phys. Lett. 77 (26), 4289-4291 (2000).

 

            ABSTRACT: Electrically active polysilanes of poly(methylphenylsilane) (PMPS) and poly[bis(p-n-butylphenyl)silane] (PBPS), which are, respectively, known as a good hole transporting material and a near-ultraviolet electroluminescent material, are end-grafted directly on a crystalline silicon surface. The single polysilane molecules are clearly distinguished one from the other on the surface by means of atomic force microscopy observations. End-grafted single molecules of PMPS are observed as dots while end-grafted PBPS appear as worms extending for more than 100 nm on the crystalline silicon surface. (C) 2000 American Institute of Physics. [S0003- 6951(00)03052-7].

 

29.       K. Furukawa, K. Ebata, and M. Fujiki

            "One-dimensional silicon chain architecture: Molecular dot, rope, octopus, and toroid"

            Adv. Mater. 12 (14), 1033-1036 (2000).

 

            ABSTRACT:

30.       J. R. Goldman, T. D. Ladd, F. Yamaguchi, and Y. Yamamoto

            "Magnet designs for a crystal-lattice quantum computer"

            Appl. Phys. A-Mater. Sci. Process. 71 (1), 11-17 (2000).

 

            ABSTRACT: A quantum computer using nuclear spins in a crystal lattice requires a method for addressing individual quantum bits. This identification can be achieved with a spatially varying magnetic field. Spins at different lattice sites can have distinguishable Zeeman frequencies allowing initialization, logic operations, and measurements to be performed through radio frequency (rf) pulse techniques. Here, we present magnet designs that have gradients between 1 and 20 T/mu m, which are necessary to realize quantum computation with particular crystals. PACS: 03.67.Lx; 76.60.Pc; 85.70.w.

 

31.       H. Gotoh, H. Ando, T. Sogawa, H. Kamada, T. Kagawa, and H. Iwamura

            "Effect of electron-hole interaction on electron spin relaxation in GaAs/AlGaAs quantum wells at room temperature"

            J. Appl. Phys. 87 (7), 3394-3398 (2000).

 

            ABSTRACT: We investigated electron spin relaxation with respect to the spatial electron-hole separation in GaAs/AlGaAs quantum wells at room temperature. The polarization dependent time-resolved photoluminescence method was used to measure the electron spin relaxation time by applying an electric field perpendicular to the quantum wells. The spin relaxation time had a strong electric field dependence and largely increased with an increase in the spatial electron-hole separation. These results cannot be explained by only the D'yakonov-Perel process, which has often been considered the cause of spin relaxation. We discuss the possible mechanisms that cause the spin relaxation by taking into account the electron-hole exchange interaction. (C) 2000 American Institute of Physics. [S0021-8979(00)04207-9].

 

32.       H. Gotoh, H. Kamada, H. Ando, and J. Temmyo

            "Lateral electric-field effects on excitonic photoemissions in InGaAs quantum disks"

            Appl. Phys. Lett. 76 (7), 867-869 (2000).

 

            ABSTRACT: Electric-field effects on excitons in zero-dimensional InGaAs quantum disks have been examined at low temperature. Photoluminescence from a single isolated disk was measured under the application of a lateral electric field by using the microphotoluminescence technique. A redshift of sharp excitonic luminescence and a decrease in its intensity under increasing electric field were observed. These were found to distinctively depend on the lateral extent of the disks: these were much more prominent in the larger disk. The exciton luminescence was found to be highly polarized along the direction of the field in the larger disk. (C) 2000 American Institute of Physics. [S0003-6951(00)00207-2].

 

33.       D. M. Halliday

            "Weak, stochastic temporal correlation of large-scale synaptic input is a major determinant of neuronal bandwidth"

            Neural Comput. 12 (3), 693-707 (2000).

 

            ABSTRACT: We determine the bandwidth of a model neurone to large-scale synaptic input by assessing the frequency response between the outputs of a two-cell simulation that share a percentage of the total synaptic input. For temporally uncorrelated inputs, a large percentage of common inputs are required before the output discharges of the two cells exhibit significant correlation. In contrast, a small percentage (5%) of the total synaptic input that involves stochastic spike trains that are weakly correlated over a broad range of frequencies exert a clear influence on the output discharge of both cells over this range of frequencies. Inputs that are weakly correlated at a single frequency induce correlation between the output discharges only at the frequency of correlation. The strength of temporal correlation required is sufficiently weak that analysis of a sample pair of input spike trains could fail to reveal the presence of correlated input. Weak temporal correlation between inputs is therefore a major determinant of the transmission to the output discharge of frequencies present in the spike discharges of presynaptic inputs, and therefore of neural bandwidth.

 

34.       O. Hanaizumi, K. Miura, M. Saito, T. Sato, S. Kawakami, E. Kuramochi, and S. Oku

            "Frontiers related with automatic shaping of photonic crystals"

            IEICE Trans. Electron. E83C (6), 912-919 (2000).

 

            ABSTRACT: Photonic crystals have optical properties characterized by photonic bandgap, large anisotropy and high dispersion, which can be applied to Various optical devices. We have proposed an autocloning method for fabricating 2D or 3D photonic crystals and are developing novel structures and functions in photonic crystals. The autocloning is an easy process based on the combination of sputter deposition and sputter etching and is suitable for industry. We have already demonstrated devices or functions such as polarization splitters and surface-normal waveguides. In this paper, we describe our latest work on photonic crystals utilizing the autocloning technology. Phase plates and polarization selective gratings for optical pick-ups are demonstrated utilizing TiO2/SiO2 photonic crystals. The technology to introduce CdS into 3D photonic crystals is also developed and photoluminescence from the introduced CdS is observed, which is the first step to realize luminescent devices with 3D confinement or high polarization controllability.

 

35.       J. B. Hannon, H. Hibino, N. C. Bartelt, B. S. Swartzentruber, T. Ogino, and G. L. Kellogg

            "Dynamics of the silicon (111) surface phase transition"

            Nature 405 (6786), 552-554 (2000).

 

            ABSTRACT: The manner in which phase transformations occur in solids determines important structural and physical properties of many materials. The main problem in characterizing the kinetic processes that occur during phase transformations is the difficulty of observing directly, in real time, the growth of one phase at the expense of another. Here we use low-energy electron microscopy to study the real-time kinetics of a phase transformation confined to the silicon (111) surface. We show that the transformation is governed by the rate at which material is exchanged between the first layer of the crystal and the surface. In bulk phase transformations. the dynamics are usually governed either by the rate of diffusion of material to the phase boundaries or by the structural rearrangement of atoms at the phase boundary(1). The kinetic process that we have identified here has no bulk analogue and leads to domain dynamics that are qualitatively different from these expected for bulk systems.

 

36.       K. Hashio, M. Tatsumi, H. Kato, and K. Kinoshita

            "Directional solidification of InxGa1-xAs"

            J. Cryst. Growth 210 (4), 471-477 (2000).

 

            ABSTRACT: We have investigated a constitutional supercooling and segregation phenomena in InxGa1-xAs crystals unidirectionally solidified in a Vertical system. The constitutional supercooling generates characteristic fluctuations of composition along the growth direction and this can be explained by a free nucleation ahead from the growth interface. The macroscopic compositional profiles of the grown crystals suggest that a transport of solute is mainly dominated by the diffusion. Such a growth mode is partly attributed to the difference in density between InAs and GaAs, (C) 2000 Elsevier Science B.V. All rights reserved.

 

37.       N. Hatakenaka, H. Takayanagi, Y. Kasai, and S. Tanda

            "Double sine-Gordon fluxons in isolated long Josephson junctions"

            Physica B 284, 563-564 (2000).

 

            ABSTRACT: A quantum flux, a 2 pi fluxon, described by a sine-Gordon equation is an elementary excitation in long Josephson junctions. We investigated the fluxon dynamics in isolated long Josephson junctions. In such isolated systems, the total number of Cooper pairs is conserved, so the fluxon dynamics map change. We found that the fluxons obey a double sine-Gordon (DSG) equation based on this change in the Josephson acceleration relation, i.e., the voltage-phase difference relation. It should be possible to confirm the existence of DSG fluxons by detecting the relative oscillations of two pi fluxons. (C) 2000 Elsevier Science B.V. All rights reserved.

 

38.       K. Hayashi, T. Horiuchi, R. Kurita, K. Torimitsu, and O. Niwa

            "Real-time electrochemical imaging using an individually addressable multi-channel electrode"

            Biosens. Bioelectron. 15 (9-10), 523-529 (2000).

 

            ABSTRACT: We developed a real-time electrochemical imaging method that uses a multiple enzyme-modified microelectrode. The method will enable the investigation of the functions of biological materials and cells. To test its effectiveness, we imaged the two-dimensional concentration distribution for hydrogen peroxide and L-glutamate in a standard solution. The multiple electrode consists of an 8 x 8 array of 30 x 30 mum(2) carbon micro electrode. Each electrode was connected to a 64-channel potentiostat that could apply a potential to all electrodes at the same time. The multiple electrode was coated with an Os-polyvinylpyridine based polymer (Os-gel) containing horse radish peroxidase (HRP) to detect hydrogen peroxide, which is a very common product of oxidase enzyme. When measuring glutamate, which is a well-known neurotransmitter in the mammalian central nerve system, we modified the electrode with a bilayer of Os-gel-HRP and GluOx. The detection limit of our method was 1 muM and images of the glutamate concentration-distribution changes induced by local injection of glutamate through microcapillary were obtained in real time. (C) 2000 Elsevier Science S.A. All rights reserved.

 

39.       H. Hibino, T. Kawamura, and T. Ogino

            "RHEED analysis of twinned homoepitaxial layers grown on Si(111)root 3x root 3-B"

            Thin Solid Films 369 (1-2), 5-9 (2000).

 

            ABSTRACT: Homoepitaxial Si layers grown on Si(111)root 3 X root 3-B have an orientation rotated by 180 degrees with respect to the substrate, i.e. a twinned orientation. The growth of the twinned epitaxial layers is monitored in situ using reflection high-energy electron diffraction (RHEED). RHEED intensities change quite sensitively with respect to the thickness of the twinned layers even at the thickness of two bilayers. After six-bilayer growth, the RHEED pattern is almost the same as the pattern diffracted from the substrate in the incident azimuth rotated by 180 degrees. Calculations of RHEED intensities based on the multiple scattering theory reproduce well the measured intensities. (C) 2000 Published by Elsevier Science S.A. All rights reserved.

 

40.       H. Hibino and T. Ogino

            "Si twinning superlattice: Growth of new single crystal Si"

            Surf. Rev. Lett. 7 (5-6), 631-635 (2000).

 

            ABSTRACT: Si twinning superlattices are grown on Si(111)(root3 x root3)-B by the repeated growth of Si layers with a unit thickness and postgrowth annealing. In order to determine the growth conditions of the Si twinning superlattice, it is essential to measure the crystallographic orientations in the surface regions during growth, Reflection high-energy electron diffraction (RHEED) is very sensitive to the surface orientation. Using the technique to estimate the fraction of the twinned layers in the grown layers by RHEED, we investigate the growth process and thermal stability of the twinned epitaxial layers. The growth of the twinning superlattices is monitored by the oscillation of the twinned layer fraction as a function of the thickness.

 

41.       T. Higashino, J. Osaka, K. Tanahashi, M. Kikuchi, Y. Kawamura, N. Inoue, and Y. Homma

            "The measurement of work function on GaAs (001) surface during MBE growth by scanning electron microscopy"

            J. Cryst. Growth 209 (2-3), 431-434 (2000).

 

            ABSTRACT: Secondary electron (SE) intensity was measured in situ during Ga supply on the molecular beam epitaxy (MBE) grown GaAs (0 0 1) surface using scanning electron microsope-MBE hybrid system. SE intensity changed in the opposite way to the reported work function change and the correspondence was excellent. This is promising for in situ, nondestructive determination of local work function during MBE growth or nanometer device process in vacuum. (C) 2000 Elsevier Science B.V. All rights reserved.

 

42.       Y. Homma and N. Aizawa

            "Electric-current-induced step bunching on Si(111)"

            Phys. Rev. B 62 (12), 8323-8329 (2000).

 

            ABSTRACT: We experimentally investigated step bunching induced by direct current on vicinal Si(111)"1x1" surfaces using scanning electron microscopy and atomic force microscopy. The scaling relation between the average step spacing l(b) and the number of steps N in a bunch, l(b)similar to N-alpha, was determined for four step-bunching temperature regimes above the 7x7-"1x1" transition temperature. The step-bunching rate and scaling exponent differ between neighboring step-bunching regimes. The exponent alpha is 0.7 for the two regimes where the step-down current induces step bunching (860-960 and 1210-1300 degrees C), and 0.6 for the two regimes where the step-up current induces step bunching (1060-1190 and >1320 degrees C). The number of single steps on terraces also differs in each of the four temperature regimes. For temperatures higher than 1280 degrees C, the prefactor of the scaling relation increases, indicating an increase in step-step repulsion. The scaling exponents obtained agree reasonably well with those predicted by theoretical models. However, they give unrealistic values for the effective charges of adatoms for step-up-current-induced step bunching when the ''transparent'' step model is used.

 

43.       Y. Homma, P. Finnie, and T. Ogino

            "Ultrahigh vacuum scanning electron/tunneling combined microscope system"

            in Microbeam Analysis 2000, Proceedings, Institute Of Physics Conference Series Vol. 165 (Iop Publishing Ltd, Bristol, 2000), pp. 375-376.

 

            ABSTRACT:

44.       Y. Homma, P. Finnie, and T. Ogino

            "Control of island formation on silicon surfaces using ultra-high-vacuum scanning electron microscopy"

            J. Electron Microsc. 49 (2), 225-229 (2000).

 

            ABSTRACT: In situ scanning electron microscopy has been used to control Au island formation on a patterned Si(111) surface with a periodic array of atomic-step bunches and holes. Liquid phase Au-Si islands were observed to redistribute on the patterned surface by annealing. The islands accumulate at a particular position of the step bunch in each pattern unit. This phenomenon is interpreted in terms of the energetic stability of a droplet on a patterned surface.

 

45.       Y. Homma, H. Hibino, Y. Kunii, and T. Ogino

            "Transformation of surface structures on vicinal Si(111) during heating"

            Surf. Sci. 445 (2-3), 327-334 (2000).

 

            ABSTRACT: We investigated transformation processes of holes and hillocks on vicinal Si(1 1 1) surfaces during annealing at around 1200 degrees C using ultra-high-vacuum scanning electron microscopy. A hole and a hillock decay symmetrically with one another: their shapes are complementary, and the decay rate is almost the same except during the final stage, where hillocks decay faster than holes. Flat surfaces appear both at the bottom of the hole and at the top of the hillock due to layer-by-layer decay. As a result of transformation, regularly arranged atomic-step bunches are formed in both cases. The electric current used for sample heating greatly affects the final shape of step bunches. The current direction that induces step bunching on a flat surface creates straighter step bunches than the opposite direction. For holes larger than the adatom diffusion length, step-flow sublimation becomes the dominant process instead of layer-by-layer filling-in of the bottom terrace, which is the dominant process for holes smaller than the adatom diffusion length. (C) 2000 Elsevier Science B.V. All rights reserved.

 

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

            "Electrochemiluminescence at a microelectrode in a microscale fluidic system"

            Electroanalysis 12 (9), 672-676 (2000).

 

            ABSTRACT: We describe the real-time visualization of electrochemiluminescence (ECL) in a microscale region using an interdigitated array electrode (IDA) in a thin layer flow cell. We studied the ECL reaction, which is based on the annihilation of cations and anions of 9,10-diphenylanthracene at the IDA, from the spatial and temporal emission patterns in the thin layer. We observed that the ECL emission region moved from the root of the band array to its center and the emission time was limited when the dye solution was static. We found that two kinds of microscale-width solution stream formed spontaneously and were arranged alternately when the solution was under the laminar flow conditions at a specific flow rate. The two streams were composed of different radical components.

 

47.       S. Hoshino, K. Ebata, and K. Furukawa

            "Near-ultraviolet electroluminescent performance of polysilane-based light-emitting diodes with a double-layer structure"

            J. Appl. Phys. 87 (4), 1968-1973 (2000).

 

            ABSTRACT: We fabricated double-layer light-emitting diodes (LEDs) by utilizing poly[bis(p-nbutylphenyl)silane] (PBPS) and oxadiazole derivatives, and investigated their basic LED characteristics. The near-ultraviolet electroluminescence (EL) performance, such as the EL threshold electric field and the current density, depended on the oxadiazole derivatives used as the electron transport materials as well as the components of the EL emission. We observed better EL performance where the EL external quantum efficiency in a double-layer LED with a 2-(4'-tert-butylphenyl)-5-(4'-biphenyl)-1,3,4-oxadiazole based electron transport layer was twice that of a PBPS single-layer LED. By contrast, we observed a worse EL threshold electric field and current density when we used 2,5-bis(1-naphthyl)-1,3,4-oxadiazole as an electron transport material. The reason for the difference in the EL performance was revealed by investigating the charge carrier injection and transport dynamics of the two LEDs. (C) 2000 American Institute of Physics. [S0021-8979(00)01204-4].

 

48.       S. Hoshino, K. Furukawa, K. Ebata, I. Breyl, and H. Suzuki

            "Molecular weight dependence of the conformational phase transition and electroluminescence of diarylpolysilane diodes"

            J. Appl. Phys. 88 (6), 3408-3413 (2000).

 

            ABSTRACT: We investigated the molecular weight dependence of the conformational phase transition behavior of thin films of poly[bis(p-n-butylphenyl)silane] (PBPS), which is a near-ultraviolet (NUV) electroluminescence (EL) material for polysilane-based polymer light-emitting diodes (LEDs). A low molecular weight PBPS with efficient NUV EL exhibited a phase transition from a disordered to an ordered backbone conformation when we increased the temperature. By contrast, the opposite transition behavior was observed for a high molecular weight PBPS. The photoluminescence (PL) quantum yield of the PBPS films changed in association with the thermal phase transition behavior; the PL quantum yield of the low molecular weight PBPS was improved by increasing the temperature, whereas that of the high molecular weight polymer deteriorated. The time dependence of the EL investigation suggests that, although the EL intensity continued to increase for the first few hours, insufficient Joule heat was generated to induce a phase transition in the entire PBPS layer of an LED made of the low molecular weight PBPS during continuous operation. We conclude that the conformational phase transition was not a key factor as regards efficient NUV EL generation, but may have occurred at the molecules in contact with the external electrodes of the LED, and may have been partially responsible for the improvement in the carrier injection efficiency of the external electrodes. (C) 2000 American Institute of Physics. [S0021-8979(00)01019-7].

 

49.       S. Hoshino, K. Furukawa, K. Ebata, C. H. Yuan, and H. Suzuki

            "Molecular weight dependent electroluminescence of silicon polymer near-ultraviolet light-emitting diodes"

            J. Appl. Phys. 88 (5), 2892-2897 (2000).

 

            ABSTRACT: We investigated the electroluminescence (EL) of single-layer near-ultraviolet (NUV) light-emitting diodes (LEDs) made from poly[bis(p-n-butylphenyl)silane] (PBPS) with three different molecular weights (MWs). Although the NUV EL spectra of the three LEDs exhibited no noticeable differences, we observed a marked MW dependence on such aspects of the operating performance as the EL external quantum efficiency, EL threshold current density and electric field, which were improved as the MW of PBPS decreased. The MW dependence of the hole transport behavior suggested that the MW decrease promoted positive space charge formation in the PBPS layer during LED operation. We attributed the origin of the MW dependence of the LED performance to this positive space charge formation, which played an important role in improving the electron-hole supply balance from the external electrodes of the LED. (C) 2000 American Institute of Physics. [S0021- 8979(00)06717-7].

 

50.       C. M. Hu, J. Nitta, T. Akazaki, and H. Takayanagi

            "Evidence of the Coulomb gap observed in an InAs inserted In0.53Ga0.47As/In0.52Al0.48As heterostructure"

            Physica E 7 (3-4), 795-798 (2000).

 

            ABSTRACT: We report studies of the in-plane magneto-transport properties of a 2DEG in an InAs inserted InGaAs/InAlAs heterostructure with a DC bias voltage. Temperature dependent zero-bias reduction of the longitudinal resistance was observed when high magnetic field is applied along the sample growth direction. We interpret the observed resistance reduction as the result of a Coulomb gap existing at the Fermi level of the 2DEG. (C) 2000 Elsevier Science B.V. All rights reserved.

 

51.       C. M. Hu, J. Nitta, T. Akazaki, H. Takayanagi, J. Osaka, P. Pfeffer, and W. Zawadzki

            "Observation of the zero-field spin splitting of the second subband in an inverted In0.53Ga0.47As/In0.52Al0.48As heterostructure"

            Physica E-Low-Dimensional Systems & Nanostructures 6 (1-4), 767-770 (2000).

 

            ABSTRACT: A gated inverted In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As quantum well is studied via magneto transport. By analysing the gate-voltage-dependent beating: pattern observed in the Shubnikov-de Haas oscillation, we determine the gate voltage (or electron concentration) dependence of the spin-orbit coupling parameter alpha, Our experimental data and their analysis show that the band nonparbolicity effect cannot be neglected. For electron concentrations above 2 x 10(12) cm(-2), it causes a reduction of alpha up to 25%. We report for the: first time the alpha value for the second subband. (C) 2000 Elsevier Science B.V. All rights reserved.

 

52.       R. P. Huebener, O. M. Stoll, and M. Naito

            "Vortex core physics in the cuprate superconductor Nd2-xCexCuOy"

            Physica B 280 (1-4), 237-238 (2000).

 

            ABSTRACT: Flux-how voltage steps and negative differential resistivity in the cuprate Nd2-xCexCuOy are explained in terms of subbands between the Fermi energy and the energy gap affecting the quasiparticle dynamics. (C) 2000 Elsevier Science B.V. All rights reserved.

 

53.       R. P. Huebener, O. M. Stoll, A. Wehner, and M. Naito

            "Flux-flow resistance in the cuprate superconductor Nd2-xCexCuOy: subbands, Bloch oscillations, and Zener breakdown"

            Physica C 338 (3), 221-226 (2000).

 

            ABSTRACT: At intermediate magnetic fields B-c1 much less than B < B-c2 and at temperatures T much less than T-c, the flux-flow resistance of the cuprate superconductor Nd2-xCexCuOy (NCCO) displays two intrinsic steps as a function of the electric field. In explaining this strongly nonlinear behavior, we propose a scenario based on two subbands between the Fermi energy and the gap energy, leading to Bloch oscillations and Zener breakdown for the quasiparticle dynamics. The subbands originate from the Andreev bound states in the core of an isolated vortex due to the interaction between the vortices. The proposed scenario appears to explain in particular the observed magnetic field and temperature dependence of the flux-flow resistance steps. (C) 2000 Elsevier Science B.V. All rights reserved.

 

54.       R. P. Huebener, O. M. Stoll, A. Wehner, and M. Naito

            "Nonlinear vortex dynamics in the cuprate superconductor Nd2-xCexCuOy"

            Physica C 332 (1-4), 187-192 (2000).

 

            ABSTRACT: At T much less than T-c, the flux-flow voltage in the cuprate superconductor Nd2-xCexCuOy shows an intrinsic step structure that leads to negative differential resistivity. This is explained in terms of subbands between the Fermi energy and the gap energy affecting the quasiparticle dynamics. In the electric field generated by current-induced vortex motion, the quasiparticle energy can be shifted to the upper band edge, resulting in Bragg reflection and Bloch oscillations. The subbands originate from the Andreev-bound states in the core of an isolated vortex, because of the interaction between vortices. (C) 2000 Elsevier Science B.V. All rights reserved.

 

55.       K. Inoue

            "Penalty-free operation of a DFB-LD in a state of coherence collapse and its application to interferometric noise reduction"

            IEICE Trans. Commun. E83B (12), 2702-2704 (2000).

 

            ABSTRACT: When a single-mode LD is subjected to distant reflection, relative intensity noise and the width of the optical spectrum are drastically increased. This phenomenon is known as 'coherence collapse.' This letter demonstrates that penalty-free operation is possible at 2.5 Gbit/s even when a DFB-LD is in a state of coherence collapse. In addition, an LD in a state of coherence collapse is applied to a situation where signal light suffers from interferometric crosstalk. The results show that the LD reduces the influence of interferometric noise because of its wide spectral width.

 

56.       K. Inoue

            "Optical level equalisation based on gain saturation in fibre optical parametric amplifier"

            Electron. Lett. 36 (12), 1016-1017 (2000).

 

            ABSTRACT: Optical level equalisation operation based on gain saturation in an optical fibre parametric amplifier is reported. The signal output has been measured as a function of the signal input in a fibre parametric amplifier, with the result that the signal gain saturates as the input power increases and the output Fewer reached a maximum value at a particular input level. Utilising this gain saturation property, optical level equalisation has been demonstrated.

 

57.       S. Ishihara

            "Frontiers of semiconductor technologies in the 21st century"

            Ntt Rev. 12 (6), 40-43 (2000).

 

            ABSTRACT: Advances in information technology mean new functionality is required in semiconductor devices. Devices that can work in severe environments, such as high temperatures, are also becoming important as the application fields of semiconductor devices expand. At NTT Basic Research Laboratories, we are investigating a novel device fabrication process based on control of the atomic structures on silicon surfaces and new materials for environmentally-hardened devices.

 

58.       S. Ishihara

            "Quantum physics for future communication technologies - Towards quantum information processing"

            Ntt Rev. 12 (1), 8-11 (2000).

 

            ABSTRACT: NTT Basic Research Laboratories are devoted to discovering new principles and creating new devices that will have major impacts on 21st century communications. As examples of such research, in this special issue, we will introduce a single electron device with ultralow power consumption, a quantum computer that will be able to quickly solve problems that are all but unsolvable by present computers, and quantum cryptography that guarantees tamper-free communications.

 

59.       T. Ishii, T. Tamamura, and K. Shigehara

            "Fullerene-derivative nanocomposite resist for nanometer pattern fabrication"

            Jpn. J. Appl. Phys. Part 2 - Lett. 39 (10B), L1068-L1070 (2000).

 

            ABSTRACT: A nanocomposite resist system that incorporates a fullerene derivative into a conventional positive-type electron-beam resist, ZEP520, is examined. Because of the enhanced solubility of the derivative, the system exhibits a minimal decrease of sensitivity even at an incorporation content of 50 wt% and enables the fabrication of 50 nm patterns with a line dose of 0.39 nC/cm. At higher contents, however, the derivative is not as effective as fullerene C-60 or C-70 in improving dry-etching resistance because of the aggregation of the derivative molecules, which is probably due to the uniqueness of the derivative used and will be avoided by appropriate molecular design.

 

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

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

            Biol. Cybern. 83 (1), 1-20 (2000).

 

            ABSTRACT: Neuronal networks of dissociated cortical neurons from neonatal rats were cultured over a multielectrode dish with 64 active sites, which were used both for recording the electrical activity and for stimulation. After about 4 weeks of culture, a dense network of neurons had developed and their electrical activity was studied. When a brief voltage pulse was applied to one extracellular electrode, a clear electrical response was evoked over almost the entire network. When a strong voltage pulse was used, the response was composed of an early phase, terminating within 25 ms, and a late phase which could last several hundreds of milliseconds. Action potentials evoked during the early phase occurred with a precise timing with a small jitter and the electrical activity initiated by a localized stimulation diffused significantly over the network. In contrast, the late phase was characterized by the occurrence of clusters of electrical activity with significant spatio-temporal fluctuations. The late phase was suppressed by adding small amounts of D(-)-2-amino-5-phosphonovaleric acid to the extracellular medium, or by increasing the amount of extracellular Mg2+. The electrical activity of the network was substantially increased by the addition of bicuculline to the extracellular medium. The results presented here show that the neuronal network may exist in two different dynamical states: one state in which the neuronal network behaves as a non-chaotic deterministic system and another state where the system exhibits large spatio-temporal fluctuations, characteristic of stochastic or chaotic systems.

 

61.       Y. Jimbo and H. P. C. Robinson

            "Propagation of spontaneous synchronized activity in cortical slice cultures recorded by planar electrode arrays"

            Bioelectrochemistry 51 (2), 107-115 (2000).

 

            ABSTRACT: The spatial propagation of synchronized activity in cortical slice cultures was characterized by multi-site extracellular recording. Spontaneous activity was studied in normal culture medium, and in bicuculline- or kainic acid-containing media. A common feature in all these conditions was that activity was generated first in superficial layers (i.e., layer I/II) before spreading over the whole area of the slice. In culture medium or bicuculline-containing medium, the initiation site of the activity was not constant and showed a large variety of patterns of horizontal propagation. Kainic acid induced epileptiform activity, consisting of intense initial bursts followed by repetitive after-discharges. Though the patterns of spatial propagation of the bursts were variable as in the other conditions, the after-discharges followed a constant path. Cross-correlation analysis indicated that the network moved in a graded fashion to a steady state during the sequence of after-discharges. (C) 2000 Elsevier Science S.A. All rights reserved.

 

62.       M. R. Junnarkar and N. Uesugi

            "Near two-photon resonance short pulse compression in atomic noble gases"

            Opt. Commun. 175 (4-6), 447-459 (2000).

 

            ABSTRACT: We simulate a pulse compression mechanism based on a near two-photon resonance (NTPR) transition contribution to the nonlinear refractive index of atomic Noble gas filled hollow waveguides, The negative refractive index contribution in the normal dispersive gas waveguide plays a similar role as in the case of soliton compression with positive Kerr nonlinearity and anomalous dispersion in optical fibers. The sell-pulse compression to similar to 15 fs can be achieved at moderate peak powers (similar to MW) for 100 fs pulses in the spectral range 100-245 nm. We present simulated data concerning pulse and spectral shapes for xenon as a case study. The total throughput of the propagated pulse energy is > 90%, mostly determined by the linear attenuation of the hollow waveguide propagation mode while two-photon absorption and the corresponding enhanced three-photon photo-ionization does not significantly reduce the pulse energy. (C) 2000 Elsevier Science B.V. All rights reserved.

 

63.       H. Kageshima, K. Shiraishi, H. Ikeda, S. Zaima, and Y. Yasuda

            "Selectivity for O-adsorption position on dihydride Si(100) surfaces"

            Appl. Surf. Sci. 159, 14-18 (2000).

 

            ABSTRACT: The physics behind the selectivity for the: O adsorption position on dihydride Si(100) surfaces is studied using HREELS and first-principles calculation. It is known that on dihydride Si(100) surfaces below 300 degrees C the formed Si-O-Si bonds do not jointly own any surface Si atoms when the O coverage is smaller than 80% of the number of outermost surface Si atoms. According to the present study, the selectivity is not governed by the electronic states near the Fermi energy at all. Instead, it is governed only by the energetics, and can be explained in terms of the strain induced by the adsorption itself. (C) 2000 Elsevier Science B.V. All rights reserved.

 

64.       H. Kageshima, A. Taguchi, and K. Wada

            "Theoretical investigation of nitrogen-doping effect on vacancy aggregation processes in Si"

            Appl. Phys. Lett. 76 (25), 3718-3720 (2000).

 

            ABSTRACT: The nitrogen-doping effect on vacancy aggregation in Si is studied by comparing total energies of various complexes of nitrogen atoms and Si vacancies in terms of first-principles calculations. Two nitrogen atoms are found to form a stable complex with two Si vacancies, strongly suggesting that a supersaturation of "isolated" Si vacancies in growth cooling can be suppressed. The delayed void formation observed in N-doped Czochralski Si indeed supports this suggestion. (C) 2000 American Institute of Physics. [S0003-6951(00)03125-9].

 

65.       H. Kamada, H. Ando, T. Takagahara, J. Temmyo, and T. Tamamura

            "Spectroscopies of exciton and biexciton in InGaAs quantum disk"

            J. Lumines. 87-9, 46-50 (2000).

 

            ABSTRACT: Exciton in isolated InxGa1-xAs quantum disk was studied by probing single-dot photoluminescence. Each of the excitonic emission was found to be excited via a number of sharp-excited state resonances, thereby the discrete density of state and long-lived phase coherence of the states were proven. A significant contribution of the biexciton excitation was found to enable two-photon absorption, making optical excitation process complex. It leads to a dynamic quantum mechanical interference in the excitation via exciton/biexciton states. (C) 2000 Elsevier Science B.V. All rights reserved.

 

66.       H. Kamada, T. Takagahara, H. Ando, J. Temmyo, and T. Tamamura

            "Optically self-induced transparency of exciton excitation in a single semiconductor quantum dot"

            Phys. Status Solidi A-Appl. Res. 178 (1), 291-296 (2000).

 

            ABSTRACT: The observation of quantum mechanical interference in the exciton photoluminescence excitation (PLE) process in a semiconductor quantum dot is reported. A simple PLE spectroscopy revealed in a single InGaAs quantum dot a dynamic and continuous evolution of a resonance profile from a peak into a dip and to near transparency caused by an increase of excitation power density of only a few 100 W/cm(2) A one-photon process via exciton states and a two-photon process via biexciton states, both of which return to the radiative exciton stale, interfere quantum mechanically, resulting in a progressive decrease in exciton absorption under increasing excitation.

 

67.       K. Kanisawa, H. Yamaguchi, and Y. Hirayama

            "Two-dimensional growth of InSb thin films on GaAs(111)A substrates"

            Appl. Phys. Lett. 76 (5), 589-591 (2000).

 

            ABSTRACT: Heteroepitaxy of high-quality InSb films was performed directly on GaAs surfaces by using molecular beam epitaxy. Despite the 14.6% lattice mismatch, two-dimensionally grown InSb on GaAs(111)A substrates were obtained from the initial stage, but not on (001) substrates. A conductive layer was formed from the early stage of the growth on the (111)A surface, and the mobilities and carrier concentrations of InSb on (111)A substrates suggested a low defect density due to confinement of the dislocations to the interface. (C) 2000 American Institute of Physics. [S0003-6951(00)03505-1].

 

68.       S. Karimoto and M. Naito

            "New superconducting lead cuprates prepared by molecular beam epitaxy"

            Physica C 338 (1-2), 92-95 (2000).

 

            ABSTRACT: We report the synthesis of a new superconducting cuprate PbSr2CuO5+delta (Pb-1201; T-c similar to 40 K) with a pure PbO charge reservoir layer by a tow-temperature technique using molecular beam epitaxy (MBE). This new superconductor is the first member of the Pb-12(n - 1)n homologous series. Low-temperature synthesis by MBE and an appropriate choice of substrates were essential to our discovery of Pb-1201 superconductor. This work demonstrates that MBE provides a novel synthetic route for new cuprates. (C) 2000 Elsevier Science B.V. All rights reserved.

 

69.       S. Karimoto and M. Naito

            "New superconducting PbSr2CuO5+delta prepared by a novel low-temperature synthetic route using molecular beam epitaxy"

            Physica B 284, 1113-1114 (2000).

 

            ABSTRACT: We report the synthesis of a new superconducting cuprate PbSr2CuO5 + delta (T-c similar to 40 K) by a novel low-temperature synthetic route using molecular beam epitaxy. The new superconductor is the first member of the Pb-12(n - 1)n homologous series. Low-temperature synthesis by MBE and an appropriate choice of lattice-matched substrates are essential to our discovery of PbSr2CuO5 + delta superconductor. This work demonstrates that MBE opens up a novel synthetic route for new cuprates. (C) 2000 Elsevier Science B.V. All rights reserved.

 

70.       M. Kasahara, H. Okamoto, K. Takeda, and K. Shiraishi

            "Theoretical study on the electronic and molecular structures of peptide nanotubes"

            Abstr. Pap. Am. Chem. Soc. 219, U144-U144 (2000).

 

            ABSTRACT:

71.       M. Kasahara, H. Okamoto, K. Takeda, and K. Shiraishi

            "Theoretical study on the electronic and molecular structres of peptide nanotubes"

            Biochemistry 39 (6), 1568-1568 (2000).

 

            ABSTRACT:

72.       N. Kasai, Y. Jimbo, O. Niwa, T. Matsue, and K. Torimitsu

            "Multichannel glutamate monitoring by electrode array electrochemically immobilized with enzymes"

            Electrochemistry 68 (11), 886-889 (2000).

 

            ABSTRACT: We developed a novel method for the fabrication of a multichannel glutamate sensor based on a planar electrode array. By scanning and holding the electrode potential in a solution containing glutamate oxidase and a polymer to which horseradish peroxidase and electron-transfer mediator were bound, we successfully immobilized these enzymes and a mediator on the electrodes of the electrode array through electrochemical deposition of the polymer. We confirmed the resulting sensor possessed high sensitivity and selectivity to glutamate. This multichannel sensor may be useful for the non-invasive, real-time monitoring of the glutamate distribution in biological samples.

 

73.       N. Kasai, I. Sugimoto, and M. Nakamura

            "Discrimination of odorants of definite concentrations by using plasma-organic-film-coated QCR sensors"

            Sens. Actuator B-Chem. 65 (1-3), 114-119 (2000).

 

            ABSTRACT: Odorant-discrimination experiments were conducted for the major single-odor substances in various types of botanical species such as fruits and flowers by using a gas-sensing system consisting of a sensor array of quartz crystal resonators (QCRs) and a pattern-recognition technique. The sensing devices were fabricated by radio-frequency sputtering of biomaterials or polymers on to the QCRs. The 22 tested odorants of definite concentration, 0.1-64 ppm, were well discriminated by principal component analysis, using the sensors steady-state and dynamic properties as parameters. From the 1-nearest-neighbor method, introduced to evaluate the discrimination capability, the best discrimination was obtained, using the frequency changes in QCRs for longer than 10 min and the time constant of adsorption at 5 min as parameters, with the success rate of 83%. This system is thus highly reliable for discriminating trace amounts of odorants. (C) 2000 Elsevier Science B.V. All rights reserved.

 

74.       S. Kasapi, S. Lathi, and Y. Yamamoto

            "Sub-shot-noise frequency-modulation spectroscopy by use of amplitude-squeezed light from semiconductor losers"

            J. Opt. Soc. Am. B-Opt. Phys. 17 (2), 275-279 (2000).

 

            ABSTRACT: We have demonstrated sub-shot-noise FM spectroscopy on thermal cesium atoms, using amplitude-squeezed light from a semiconductor laser. The light source used in our experiment was a custom-made GaAs transverse junction stripe semiconductor laser featuring broadband amplitude squeezing and a large FM bandwidth. We have also developed a new technique by which a semiconductor laser can be frequency modulated with infinitesimally small residual AM and with complete preservation of the squeezed-amplitude fluctuations. (C) 2000 Optical Society of America [S0740-3224(00)00802-X].

 

75.       M. Kasu and N. Kobayashi

            "Large electron field emission from high-quality heavily Si-doped AlN grown by MOVPE"

            J. Cryst. Growth 221, 739-742 (2000).

 

            ABSTRACT: Electron field emission (FE) from high-quality AIN grown by metalorganic vapor-phase epitaxy is studied. The full-widths at half-maximum of the X-ray rocking curve of undoped and heavily Si-doped (Si density: 2.5 x 10(20) cm(-3)) high-quality AIN were as low as 91 and 94 arcsec, respectively. The heavily Si-doped AlN showed a maximum FE current of 347 muA and its density was 11 mA/cm(2) Field emission enhancement as a result of Si doping can be explained by hopping conduction through a Si impurity level. White, red, green, blue light emission (luminance: about 1200 cd/m(2)) from phosphors excited by the field-emitted electrons was observed. (C) 2000 Elsevier Science B.V. All rights reserved.

 

76.       M. Kasu and N. Kobayashi

            "Large and stable field-emission current from heavily Si-doped AlN grown by metalorganic vapor phase epitaxy"

            Appl. Phys. Lett. 76 (20), 2910-2912 (2000).

 

            ABSTRACT: We report on the electron field emission (FE) from heavily Si-doped AlN grown by metalorganic vapor phase epitaxy. We found that, as the Si-dopant density increases, the threshold electric field decreases and, consequently, the FE current from AlN increases drastically. We show that heavily Si-doped (2.5x10(20) cm(-3)) AlN has a threshold electric field of 34 V/mu m, a maximum FE current density of 4.8 mA/cm(2), and stable FE current (fluctuation: 3%). (C) 2000 American Institute of Physics. [S0003-6951(00)03020-5].

 

77.       H. T. Kato, M. Iwai, Y. Muramatsu, K. Kinoshita, and S. Yoda

            "Single crystal growth of compositionally graded InxGa1-xAs"

            Mater. Sci. Eng. B-Solid State Mater. Adv. Technol. 75 (2-3), 143-148 (2000).

 

            ABSTRACT: Directional solidifications were carried out by vertical Bridgman method with GaAs seed and In0.3Ga0.7As feed. Experimental results show that seeding was mon successful in the case of low temperature gradient than a steep one. Lattice mismatch of the seed and the grown crystal is small. Single crystals were reproducibly obtained at low temperature gradient and at small lattice mismatch in these experiments. The grown single crystal is longer than 20 mm with a diameter of 14.5 mm. Indium concentration along the growth axis increased as crystal growth proceeded, which agrees with a compositional profile modeled from the InAs-GaAs pseudo-binary phase diagram. Electron mobility of initial grown crystals obtained at lower temperature gradient is higher than that of crystals grown at higher temperature gradient. (C) 2000 Elsevier Science S.A. All rights reserved.

 

78.       A. Kawaharazuka, T. Saku, Y. Hirayama, and Y. Horikoshi

            "Formation of a two-dimensional electron gas in an inverted undoped heterostructure with a shallow channel depth"

            J. Appl. Phys. 87 (2), 952-954 (2000).

 

            ABSTRACT: We investigated the dependence of transport characteristics of a two-dimensional electron gas (2DEG) on channel depth in an inverted undoped GaAs/AlGaAs heterostructure. We succeeded in forming a high-mobility 2DEG in a sample with 70 nm channel depth. We controlled the carrier density by varying the back-gate bias over a wide range. The highest mobility reached 2.3x10(6) cm(2)/Vs at 3.4x10(11) cm(-2). The relation between mobility and carrier density is determined: the mobility decreases in a low-carrier-density region as the channel depth decreases. This result suggests that the scattering due to the remote surface charges plays a more significant role. (C) 2000 American Institute of Physics. [S0021-8979(00)02002-8].

 

79.       A. Kawaharazuka, T. Saku, Y. Horikoshi, and Y. Hirayama

            "Channel depth dependent transport characteristics of a two-dimensional electron gas in an undoped GaAs/AlGaAs heterostructure"

            in Compound Semiconductors 1999, Institute Of Physics Conference Series Vol. 166 (Iop Publishing Ltd, Bristol, 2000), pp. 151-154.

 

            ABSTRACT: We investigated the channel depth dependence of transport characteristics of a two-dimensional electron gas (2DEG) in an inverted undoped GaAs/AlGaAs heterostructure. We succeeded in forming a 2DEG with high mobility in a sample having a channel depth of 70 nm. The relation between mobility and carrier density is determined: the mobility decreases in a low-carrier-density region as the channel depth decreases. This result suggests that the scattering due to the remote surface charges plays a more significant role.

 

80.       T. Kawamura, Y. Watanabe, Y. Utsumi, K. Uwai, J. Matsui, Y. Kagoshima, Y. Tsusaka, and S. Fujikawa

            "In situ observation of superstructures on InP(001) surface under hydrogen atmospheric environment with using grazing incidence X-ray diffraction"

            J. Cryst. Growth 221, 106-110 (2000).

 

            ABSTRACT: Because of the difficulties of using electron-based techniques in the metalorganic vapor-phase epitaxy (MOVPE) environment, an in situ X-ray diffractometer that combines a goniometer and reactor chamber was developed. Consequent measurements of P-rich InP(001) surface grown by MOVPE show the surface has a (2 x 1) structure. Calculations based on a P-dimer model suggest that this structure is composed of P-dimers whose bonding is parallel to the [(1) over bar 10] direction and indicates indium displacement in the second layer. (C) 2000 Elsevier Science B.V. All rights reserved.

 

81.       T. Kawamura, Y. Watanabe, Y. Utsumi, K. Uwai, J. Matsui, Y. Kagoshima, Y. Tsusaka, and S. Fujikawa

            "Reconstruction of an InP(001) surface grown by metalorganic vapor phase epitaxy in atmospheric hydrogen environment"

            Appl. Phys. Lett. 77 (7), 996-998 (2000).

 

            ABSTRACT: A reconstructed surface of InP (001) substrate, grown by metalorganic vapor phase epitaxy under atmospheric hydrogen environment, is investigated by using grazing incident x-ray diffraction. Fractional-order diffractions of (n/2 m) were observed, showing the existence of a (2 x 1) domain on the surface. Calculations based on the P-dimer model suggest that there are P dimers whose bonding is parallel to the [(1) over bar 10] direction and indium displacement in the second layer. (C) 2000 American Institute of Physics. [S0003-6951(00)02733-9].

 

82.       K. Kinoshita, H. Kato, S. Matsumoto, and S. Yoda

            "Growth of homogeneous In1-xGaxSb crystals by the graded solute concentration method"

            J. Cryst. Growth 216 (1-4), 37-43 (2000).

 

            ABSTRACT: We propose a new crystal growth method named "the graded solute concentration method" for obtaining homogeneous mixed crystals from their melts in the presence of residual acceleration of the order of 10(-3)-10(-4) G in microgravity. In this method, the feed with preinstalled solute concentration profile is used for compensating solute loss at the solid-liquid (S/L) interface due to convection caused by the residual acceleration. By the preliminary ground-based experiments using capillary tubes with a 1.5 mm bore, we obtained homogeneous In0.4Ga0.6Sb and In0.2Ga0.8Sb crystals. These results show the validity of the proposed method. (C) 2000 Elsevier Science B.V. All rights reserved.

 

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

            "Throughput measurement of a multilayer-coated Schwarzschild objective using synchrotron radiation"

            Opt. Rev. 7 (6), 576-578 (2000).

 

            ABSTRACT: The throughput of a Schwarzschild objective using undulator synchrotron radiation was measured. Conventionally, the throughput was estimated from the squared reflectivity of one multilayer mirror and from the obstruction ratio. However, we evaluated the transmission ratio from the input and output photon flux using a precisely calibrated monochromatic beam from an undulator light source. It was found that the objective has a maximum throughput of 8.5% at a wavelength of 13.9 nm.

 

84.       G. Klimovitch, F. Tassone, Y. Yamamoto, and H. Cao

            "Stimulated resonant tunneling into quantum well excitons"

            Phys. Lett. A 267 (4), 281-286 (2000).

 

            ABSTRACT: Stimulated electron resonant tunneling into exciton states is investigated within the pairing approximation and the interacting boson approximation. The tunneling current saturates at large densities due to the fermionic nature of exciton constituents. Conditions under which stimulated tunneling can be observed experimentally are described. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

 

85.       M. Koashi and M. Ueda

            "Exact eigenstates and magnetic response of spin-1 and spin-2 Bose-Einstein condensates"

            Phys. Rev. Lett. 84 (6), 1066-1069 (2000).

 

            ABSTRACT: The exact eigenspectra and eigenstates of spin-1 and spin-2 Bose-Einstein condensates (BECs) are found, and their response to a weak magnetic field is studied and compared with their mean-field counterparts. Whereas mean-field theory predicts the vanishing population of the zero magnetic-quantum-number component of a spin-1 antiferromagnetic BEG, the component is found to become populated as the magnetic field decreases. The spin-2 BEC exhibits an even richer magnetic response due to quantum correlations among three bosons.

 

86.       N. Kobayashi and Y. Kobayashi

            "In-situ optical monitoring of surface morphology and stoichiometry during GaN metal organic vapor phase epitaxy"

            Appl. Surf. Sci. 159, 398-404 (2000).

 

            ABSTRACT: The surfaces during GaN metalorganic vapor phase epitaxy (MOVPE) were in-situ monitored by shallow-angle reflectance using ultraviolet (uv) light and were compared between the growths on sapphire and on 6H-SiC substrates. By this method, stable monitoring is possible without an influence of strong and visible black-body radiation from the substrate heated to high temperatures. The growth-rate was successfully monitored by optical interference, and the morphological change was detected by the reflectivity change due to Rayleigh scattering. The surface of AIN buffer layer deposited on the (0001) sapphire substrate roughens at the thickness thinner than 30 nm, when the temperature is raised to the growth temperature of GaN. From the period of interference oscillation observed, the growth-rate on the (0001) SiC substrate is almost constant but, on the sapphire substrate, the growth-rate is about 14% decelerated in the thickness range approximately from 70 to 140 nm due to the coalescence of islands by lateral growth. Surface photoabsorption (SPA) was applied to monitor the chemical stoichiometry of GaN surface during growth. It is found that the uniform growth dominated by step-now mode is achieved by Ga-rich stoichiometry in H-2 carrier gas. The surface process during uniform growth of GaN is also proposed. (C) 2000 Elsevier Science B.V. All rights reserved. PACS: 81.05.Ea, 81.15.Gh; 82.30.Lp.

 

87.       S. Kodama, Y. Furumura, K. Kinoshita, H. Kato, and S. Yoda

            "Single crystalline bulk growth of In0.3Ga0.7As on GaAs seed using the multi-component zone melting method"

            J. Cryst. Growth 208 (1-4), 165-170 (2000).

 

            ABSTRACT: A 28 mm in length and 15 mm in diameter single-crystalline InxGa1-xAs ternary bulk crystal was grown on GaAs seed crystal using the multi-component zone melting method. The InAs composition of the grown crystal was gradually increased from 0.04 at the initial growth interface to 0.33 by decreasing the growth temperature as in the vertical gradient freeze method during growth of 24 mm length, and then maintained at 0.34 +/- 0.01 for the following growth of 4 mm length by making the sample travel at a rate nearly equal to the growth rate without lowering the furnace temperature. This combination of temperature and sample traveling rate control enabled the growth of homogeneous In0.3Ga0.7As ternary bulk crystal. (C) 2000 Elsevier Science B.V. All rights reserved.

 

88.       J. R. Koe, M. Fujiki, M. Motonaga, and H. Nakashima

            "Temperature-dependent helix-helix transition of an optically active poly(diarylsilylene)"

            Chem. Commun. (5), 389-390 (2000).

 

            ABSTRACT: The poly(diarylsilylene) copolymer mainchain helix in (Ar*Si-2)(x)(Ar2Si)(1-x) [Ar* = 3-(S)-2-methylbutylphenyl, Ar = 4-butylphenyl, x = 0.2] undergoes a thermally driven inversion of helical screw sense with a transition temperature of -10 degrees C.

 

89.       J. R. Koe, M. Fujiki, H. Nakashima, and M. Motonaga

            "Helical diarylpolysilanes: Effects of higher-order structure on optical activity"

            Abstr. Pap. Am. Chem. Soc. 219, U447-U447 (2000).

 

            ABSTRACT:

90.       T. Koga, S. B. Cronin, M. S. Dresselhaus, J. L. Liu, and K. L. Wang

            "Experimental proof-of-principle investigation of enhanced Z(3D)T in (001) oriented Si/Ge superlattices"

            Appl. Phys. Lett. 77 (10), 1490-1492 (2000).

 

            ABSTRACT: An experimental proof-of-principle of an enhanced Z(3D)T (thermoelectric figure of merit) is demonstrated using (001) oriented Si/Ge superlattices. The highest value of the experimental Z(3D)T at 300 K for a (001) oriented Si(20 Angstrom)/Ge(20 Angstrom) superlattice is 0.1 using kappa = 5 Wm(-1) K-1, for the in-plane thermal conductivity, which is a factor of seven enhancement relative to the estimated value of Z(3D)T = 0.014 for bulk Si. The good agreement between experiment and theory validates our modeling approach (denoted as "carrier pocket engineering") to design superlattices with enhanced values of Z(3D)T. Proposals are made to enhance the experimental values of Z(3D)T for Si/Ge superlattices even further. (C) 2000 American Institute of Physics. [S0003-6951(00)05136-6].

 

91.       T. Koga, O. Rabin, and M. S. Dresselhaus

            "Thermoelectric figure of merit of Bi/Pb1-xEuxTe superlattices"

            Phys. Rev. B 62 (24), 16703-16706 (2000).

 

            ABSTRACT: An enhanced thermoelectric figure of merit Z(3D)T is predicted for Bi/(111)Pb1-xEuxTe superlattices. The values of Z(3D)T obtained for x approximate to1 superlattices are 2.31, 1.55, and 1.61 at 300, 150, and 77 K, respectively, showing that they are promising candidates for thermoelectric elements in the temperature range 77-300 K. Even with x as small as 0.1, where the conduction-band offset DeltaE(c) is estimated to be 0.25 eV, the predicted Z(3D)T values are 1.75, 1.16, and 1.18 at 300, 150, and 77 K, respectively. It is proposed that other families of Bi-based superlattices, such as Bi/(111)CdTe superlattices, should also be good candidates for low-temperature thermoelectric elements.

 

92.       H. Kudo, N. Nakamura, K. Shibuya, K. Narumi, S. Yamamoto, H. Naramoto, K. Sumitomo, and S. Seki

            "Ion-induced electron emission from Si crystal targets covered with noncrystalline Si layers"

            Nucl. Instrum. Methods Phys. Res. Sect. B-Beam Interact. Mater. Atoms 168 (2), 181-191 (2000).

 

            ABSTRACT: Ion-induced electron emission has been studied for Si crystal targets bombarded by similar to 100 keV/u H+, He+, and 3.5 MeV/u O8+. Under channeling incidence conditions, we have measured the dependence of the continuum electron yield on the thickness of an overlaid noncrystalline Si layer which increases the number of unshadowed atoms near the crystal surface. The electron yields in the channeling and nonchanneling cases are successfully accounted for using the two parameters determined from the experiments, i.e., the effective target thickness associated with the high-energy shadowing effect mainly on Si L-shells and the effective escape length for the electron yield. (C) 2000 Elsevier Science B.V. All rights reserved.

 

93.       H. Kudo, S. Seki, K. Sumitomo, K. Narumi, S. Yamamoto, and H. Naramoto

            "Ion-induced electron measurements using crystal targets overlaid with noncrystalline layers"

            Nucl. Instrum. Methods Phys. Res. Sect. B-Beam Interact. Mater. Atoms 164, 897-902 (2000).

 

            ABSTRACT: We have measured continuum electron yields from Si crystals covered with noncrystalline Si layers of 150-350 Angstrom thicknesses using 8.0 MeV/u H+ and He2+. These layers provide unshadowed subsurfaces from which target electrons are recoiled under channeling incidence conditions. The production and escape processes of the electrons can be well understood using a few quantities determined from these experiments. The present experimental approach allows general understanding of the continuum electron spectra from solid targets. (C) 2000 Elsevier Science B.V. All fights reserved.

 

94.       N. Kumada, A. Sawada, Z. F. Ezawa, S. Nagahama, H. Azuhata, K. Muraki, T. Saku, and Y. Hirayama

            "Doubly enhanced skyrmions in nu=2 bilayer quantum Hall states"

            J. Phys. Soc. Jpn. 69 (10), 3178-3181 (2000).

 

            ABSTRACT: Skyrmion excitations were measured and compared for the first time in the bilayer quantum Hall (QH) state at the Landau-level filling factor nu = 2 and in the monolayer QH state at nu = 1. The observed number of flipped spins, N-spin, is 14 in the bilayer sample with a large tunnelling gap, and N-spin = 7 in the bilayer sample with a small tunnelling gap, while it is N-spin = 7 in the monolayer sample. The difference is interpreted to be due to the interlayer exchange interaction.

 

95.       K. Kumakura, T. Makimoto, and N. Kobayashi

            "High hole concentrations in Mg-doped InGaN grown by MOVPE"

            J. Cryst. Growth 221, 267-270 (2000).

 

            ABSTRACT: We investigated the electrical properties of Me-doped InxGa1-xN (0 less than or equal to x < 0.75) grown by metalorganic vapor-phase epitaxy with various growth conditions, such as Mg-doping concentration, growth-rate and growth temperature. The hole concentration depends on the growth-rate, the In mole fraction and the crystal quality of the InGaN layers. The hole concentration of Mg-doped InxGa1-xN layers below x = 0.15 increased with the In mole fraction, while those above x = 0.15 decreased. We realized the p-type InGaN with the room-temperature hole concentration above 10(18)cm(-3) and obtained the maximum hole concentration of 7.8 x 10(18) cm (-3) for x = 0.2 by optimizing the growth conditions. (C) 2000 Elsevier Science B.V. All rights reserved.

 

96.       K. Kumakura, T. Makimoto, and N. Kobayashi

            "Activation energy and electrical activity of Mg in Mg-doped InxGa1-xN (x < 0.2)"

            Jpn. J. Appl. Phys. Part 2 - Lett. 39 (4B), L337-L339 (2000).

 

            ABSTRACT: We investigated the electrical properties of Mg-doped InGaN with an In mole fraction of less than 0.2 grown by metaloganic vapor phase epitaxy. We obtained p-type InGaN with a hole concentration above 10(18) cm(-3) at room temperature. The hole concentrations of Mg-doped In0.04Ga0.96N and In0.14Ga0.86N were 1.2 x 10(18) and 6.7 x 10(18) cm-3, respectively, while that of Mg-doped GaN was 3.0 x 10(17) cm(-3) with the same Mg doping concentration. The activation energy of Mg in InGaN, calculated from the temperature dependence of the hole concentration, decreases with the increase in the In mole fraction. Furthermore, the electrical activity of Mg in InGaN increases with the In mole fraction. As a result, higher hole concentrations were obtained at room temperature for Mg-doped InxGa1-xN (x < 0.2) with higher In mole fractions.

 

97.       K. Kumakura, T. Makimoto, and N. Kobayashi

            "Enhanced hole generation in Mg-doped AlGaN/GaN superlattices due to piezoelectric field"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 39 (4B), 2428-2430 (2000).

 

            ABSTRACT: We investigated the electrical properties of uniformly Mg-doped AlGaN/GaN superlattices (SLs) with various Al mole fractions and SL period thicknesses. We found that their sheet hole concentration depended strongly on the Al mole fraction and SL period thickness. We found the maximum spatial averaged hole concentrations for SLs with period thicknesses of 360 Angstrom and 100 Angstrom to be 3 x 10(18) cm(-3) at room temperature. The resistivities of the SLs were less temperature dependent than those of GaN and AlGaN, indicating that the enhanced hole generation in these SLs could be ascribed to the large energy shift of the valence band edge due to the piezoelectric field.

 

98.       K. Kumakura, T. Makimoto, and N. Kobayashi

            "Efficient hole generation above 10(19) cm(-3) in Mg-doped InGaN/GaN superlattices at room temperature"

            Jpn. J. Appl. Phys. Part 2 - Lett. 39 (3AB), L195-L196 (2000).

 

            ABSTRACT: We achieved spatially averaged hole concentrations above 10(19) cm(-3) at room temperature in Mg-doped InxGa1-xN/GaN (4nm/4nm) superlattices grown by metalorganic vapor phase epitaxy. The hole concentrations for the InxGa1-xN /GaN superlattices increased with the In mole fraction, and the maximum hole concentration reached 2.8 x 10(19) cm-3 for the In0.22Ga0.78N/GaN superlattice. The hole concentrations for the superlattices are larger than those for the InGaN bulk layers with the same average In mole fraction. The weak temperature dependence of the resistivities for InGaN/GaN superlattices with higher In mole fractions indicates highly efficient hole generation in the superlattice.

 

99.       E. Kuramochi, M. Notomi, T. Tamamura, T. Kawashima, S. Kawakami, J. Takahashi, and C. Takahashi

            "Drilled alternating-layer structure for three-dimensional photonic crystals with a full band gap"

            J. Vac. Sci. Technol. B 18 (6), 3510-3513 (2000).

 

            ABSTRACT: A new three-dimensional photonic crystal structure is designed to simplify fabrication. A calculation of the band structure predicts that this photonic crystal has a complete photonic band gap in all directions. The entire three-dimensional periodic structure, except for the vertically drilled holes, is formed by automatic shaping during bias sputtering deposition. The fabrication technologies used to construct this photonic crystal are electron beam lithography, bias sputtering, and fluoride aas electron cyclotron resonance etching. Our preliminary fabrication reveals that each technology can be controlled well enough to lead to the creation of a photonic band gap material for an optical communication wavelength. (C) 2000 American Vacuum Society. [S0734-211X(00)07806-9].

 

100.    T. D. Ladd, J. R. Goldman, F. Yamaguchi, and Y. Yamamoto

            "Decoherence in crystal lattice quantum computation"

            Appl. Phys. A-Mater. Sci. Process. 71 (1), 27-36 (2000).

 

            ABSTRACT: Nuclear magnetic resonance (NMR) quantum computation in a crystal lattice holds more promise for scalability than its solution NMR counterpart, but dephasing is a severe concern. Pulse sequence refocusing can help bring the qubit dephasing time closer to the limit of the intrinsic decoherence time, but the intrinsic transverse relaxation time (T-2) and the longitudinal relaxation time (T-1) of the crystal must be sufficiently long for a successful implementation. We discuss these time scales and their relation to parameters relevant to quantum computation for several crystal types, discussing in detail the examples of CaF2, MnF2. and CeP. Included in the calculation of coherence times for CeP is the development of spin-wave spectra in a type-1 antiferromagnetic FCC lattice. PACS: 03.67.Lx; 76.60.Es; 75.30.Ds.

 

101.    D. W. Leung, I. L. Chuang, F. Yamaguchi, and Y. Yamamoto

            "Efficient implementation of coupled logic gates for quantum computation"

            Phys. Rev. A 6104 (4), art. no.-042310 (2000).

 

            ABSTRACT: Most natural Hamiltonians do not couple specific pairs of quantum bits and spurious couplings occur along with the intended one. We present an efficient scheme that couples any designated pair of spins in heteronuclear spin systems. The scheme is based on the existence of Hadamard matrices. For a system of n spins with pairwise coupling, the scheme concatenates cn intervals of system evolution and uses at most cn(2) pulses where c approximate to 1. Our results demonstrate that, in many systems, selective recoupling is possible with linear overhead, contrary to common speculation that exponential effort is always required.

 

102.    T. Machida, S. Ishizuka, K. Muraki, Y. Hirayama, and S. Komiyama

            "Resistance fluctuations in integer quantum-Hall transitions"

            Physica E 6 (1-4), 152-155 (2000).

 

            ABSTRACT: We have studied the resistance fluctuations (RF) in integer quantum-Hall transitions for high-mobility two-dimensional electron gas systems. The role of coherence in RF is examined by investigating the conductance through two scattering regions, that are spatially separated but interfere quantum-mechanically with each other. The phase coherence does not play a substantial role in determining the pattern of RF, whereas it affects the amplitude of RF. (C) 2000 Elsevier Science B.V. All rights reserved.

 

103.    F. Maeda, M. Sugiyama, and Y. Watanabe

            "GaSb(001) 4 x 2-In surface structure studied by core-level photoelectron spectroscopy and X-ray standing-wave analysis"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 39 (7B), 4351-4354 (2000).

 

            ABSTRACT: The surface structure of GaSb(001) 4 x 2-In was investigated by core-level photoelectron spectroscopy (CLPES) using synchrotron radiation and X-ray standing-wave (XSW) analysis. From the CLPES measurement, we found that the 4 x 2 surface was mainly composed of single chemical bondings, which could be assigned to In-Sb bonding. This indicated that an In-Sb molecular layer terminated this 4 x 2 surface. In addition, the In atom position was analyzed by XSW using two different asymmetric (111) and (1-11) reflections. The coherent position values of 0.684 for (111) and 0.015 for (1-11) that were obtained indicated that the In atom position was higher than the top Sb atom position of Sb-double-layer. From these results, we propose a surface local bonding model for GaSb(001) 4 x 2-In, in which the Sb-double layer remains and In atoms terminate the surface.

 

104.    F. Maeda, M. Sugiyama, and Y. Watanabe

            "In-induced surface reconstruction on GaSb(001)"

            Phys. Rev. B 62 (3), 1615-1618 (2000).

 

            ABSTRACT: In-induced surface reconstructions on GaSb(001), prepared by molecular-beam epitaxy, have been investigated in situ by reflection high-energy electron diffraction and core-level photoelectron spectroscopy. Although In grew three dimensionally at room temperature, a 1x3 reconstructed surface appeared at 430 degrees C after the substrates were annealed. After this 1x3 surface was obtained, 4x3 and/or 4x2 reconstructions were observed as the substrate was cooled, which induced an increase in the In coverage in the two-dimensional (2D) layer. On the 4x2 surface, we found the saturation of the Tn coverage in the 2D layer and a single bonding state of In-Sb, while several bonding states were observed on the 1x3 surface. This indicates that a drastic atomic rearrangement results in the termination with an InSb molecular layer at the 1x2 surface.

 

105.    F. Maeda and Y. Watanabe

            "Real-time analysis of alternating growth on GaAs(001) by core-level photoelectron spectroscopy"

            Appl. Surf. Sci. 162, 319-325 (2000).

 

            ABSTRACT: The alternating growth of GaAs on a (001) surface was analyzed by time-resolved core-level photoelectron spectroscopy (CLPES) and measuring reflection high-energy electron diffraction (RHEED) specular beam intensity. When looking at a Ga supply period, a saturation of Ga coverage was found from the time-dependence of Ga CLPES intensity. The RHEED specular beam intensity decreased even after the saturation coverage of Ga. These results indicate that Ga droplets begin to grow after Ga has been grown laterally. The inflection points of photoelectron intensity change were found at about half a monolayer of Ga supply at a substrate temperature of 560 degrees C. The spectrum analysis of the time-resolved CLPES clarifies that the Ga adsorption site changes at about half a monolayer of Ga supply. These results show the potential of using time-resolved CLPES for the real-time analysis of the growth process. (C) 2000 Elsevier Science B.V. All rights reserved.

 

106.    N. Maeda, T. Saitoh, K. Tsubaki, T. Nishida, and N. Kobayashi

            "Two-dimensional electron gas transport properties in AlGaN/(In)GaN/AlGaN double-heterostructure field effect transistors"

            Mrs. Internet J. Nitride Semicond. Res. 5, art. no.-W4.7 (2000).

 

            ABSTRACT: Two-dimensional electron gas transport properties have been investigated in nitride double-heterostructures. A striking effect has been observed that the two-dimensional electron gas mobility has been drastically enhanced in the AlGaN/GaN/AlGaN double-heterostructure, compared with that in the conventional AlGaN/GaN single-heterostructure. The observed mobility enhancement has been shown to be mainly due to the enhanced polarization-induced electron confinement in the double-heterostructure, and additionally due to the improvement of the interface roughness in the structure. Device operation of an AlGaN/GaN/AlGaN double-heterostructure field effect transistor has been demonstrated: a maximum transconductance of 180 mS/mm has been obtained for a 0.4 mum-gate-length device. In the double-heterostructure using InGaN channel, the increased capacity for the two-dimensional electron gas has been observed. The AlGaN/(In)GaN/AlGaN double-heterostructures are effective for improving the electron transport properties.

 

107.    N. Maeda, T. Saitoh, K. Tsubaki, T. Nishida, and N. Kobayashi

            "Enhanced effect of polarization on electron transport properties in AlGaN/GaN double-heterostructure field-effect transistors"

            Appl. Phys. Lett. 76 (21), 3118-3120 (2000).

 

            ABSTRACT: In order to understand the effect of polarization on the electron transport properties in AlGaN/GaN heterostructures, the dependence of the two-dimensional electron gas mobility on the density has been examined both in the GaN single- and 200-Angstrom GaN double- heterostructure field-effect transistors, by means of the Hall effect measurement under the gate-voltage application at 4.2 K. In the single heterostructure, a maximum mobility of 5700 cm(2)/V s has been obtained at 9.0x10(12) cm(-2); whereas in the double heterostructure, a higher maximum mobility of 8100 cm(2)/V s has been obtained at a lower electron density of 6.8x10(12) cm(-2). The results have been analyzed in terms of potential profiles and electron distributions in both structures where both piezoelectric and spontaneous polarization effects are taken into account. The analysis has shown that the observed mobility enhancement is mainly due to the enhanced polarization-induced electron confinement in the double heterostructure and, additionally, to the improvement of the interface roughness in the structure. (C) 2000 American Institute of Physics. [S0003-6951(00)01421-2].

 

108.    T. Makimoto, K. Kumakura, and N. Kobayashi

            "Reduced damage of electron cyclotron resonance etching by In doping into p-GaN"

            J. Cryst. Growth 221, 350-355 (2000).

 

            ABSTRACT: We investigated the effect of In atoms in p-GaN on the damage induced by electron cyclotron resonance etching. After etching the surface of p-GaN without In atoms, the I-V characteristics between two Ni/Au electrodes on the surface showed non-Ohmic behavior. This is ascribed to the damage induced by this etching process, as previously reported. The Ohmic characteristics were much improved for p-GaN doped with In atoms compared with those for p-GaN without In atoms. The Ohmic characteristics were improved as the In mole fraction in the p-(In)GaN was increased. The non-Ohmic behavior arises from the damaged layer between the Ni/Au electrode and the p-(In)GaN layer. This damaged layer is considered to become thinner as the In mole fraction is increased, resulting in improved Ohmic characteristics. (C) 2000 Elsevier Science B.V. All rights reserved.

 

109.    H. Masuda, K. Yasui, T. Yanagishita, M. Nakao, T. Tamamura, and K. Nishio

            "Direct nanomolding of semiconductor single crystals"

            Jpn. J. Appl. Phys. Part 2 - Lett. 39 (3AB), L256-L258 (2000).

 

            ABSTRACT: An ordered array of concaves of nanometer-scale dimensions was fabricated by a direct molding process on an InP single crystal using a SiC master mold. The obtained array of concaves could be applied for the preparation of an ordered textured surface of InP by a post-etching treatment. The treatment in hydrofluoric acid (HF) solution generated a highly ordered and textured surface composed of uniform pyramidal or triangular pits. The mold could be used repeatedly, and this method enables simple maskless patterning of semiconductor single crystals.

 

110.    K. Matsuda, S. Tanda, M. Shiobara, Y. Okajima, K. Yamaya, and N. Hatakenaka

            "Quantum collective dynamics of charge-density waves in quasi-one-dimensional orthorhombic TaS3"

            J. Phys. Soc. Jpn. 69 (4), 1251-1252 (2000).

 

            ABSTRACT:

111.    K. Matsunaga, M. Nishida, D. Matsumoto, S. Kurihara, N. Hatakenaka, and H. Takayanagi

            "Josephson phase dynamics in He-3 weak links"

            Physica B 284, 285-286 (2000).

 

            ABSTRACT: We propose a simple phenomenological model for dissipative dynamics of a superfluid. Qualitative agreement between the results of our numerical calculations and of the experiment on a superfluid helium three weak link system gives strong support for our model. (C) 2000 Elsevier Science B.V. All rights reserved.

 

112.    T. Matsuoka, T. Ito, and T. Kaino

            "First plastic optical fibre transmission experiment using 520nm LEDs with intensity modulation/direct detection"

            Electron. Lett. 36 (22), 1836-1837 (2000).

 

            ABSTRACT: A plastic optical fibre (POF) transmission experiment utilising green LEDs at a wavelength of 520nm is reported. The transmission loss of the 100m POF was 10dB, which is considerably lower than the loss for red (660nm) and blue (470nm) LEDs. The receiver sensitivity at 30Mbit/s was -20.8dB at 10(-9) bit error rate, which suggests the possibility of a longer length signal transmission, 200m or longer.

 

113.    M. Mitsunaga, M. Yamashita, and H. Inoue

            "Absorption imaging of electromagnetically induced transparency in cold sodium atoms"

            Phys. Rev. A 62 (1), art. no.-013817 (2000).

 

            ABSTRACT: Transmissivity of up to 200% has been observed in an absorption imaging study of electromagnetically induced transparency in cold sodium atoms, when a focused coupling beam is applied near the edge of the atom cloud. The signal behavior strongly depends on the frequency difference between the probe beam and the coupling beam. Such high transmissivity can be attributed to the strong focusing effect of the probe beam, when it propagates in a medium with spatially inhomogeneous refractive index induced by the coupling beam. A detailed numerical analysis based upon the Maxwell propagation equations is presented.

 

114.    N. A. Mortensen and G. Bastian

            "Side-gate modulation of critical current in mesoscopic Josephson junction"

            Superlattices Microstruct. 28 (3), 231-237 (2000).

 

            ABSTRACT: We study the normal state conductance and the Josephson current in a superconductor-2DEG-superconductor structure where the size/shape of the 2DEG-region can be modified by an additional side-gate electrode. The considered transport properties follow from the retarded Green function which we compute by employing a tight-binding-like representation of the Hamiltonian in the 2DEG region. Our model studies offer a qualitative demonstration of the recently observed effects caused by side-gate modulation. (C) 2000 Academic Press.

 

115.    K. Muraki, N. Kumada, T. Saku, and Y. Hirayama

            "n(+)-GaAs back-gated double-quantum-well structures with full density control"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 39 (4B), 2444-2447 (2000).

 

            ABSTRACT: We present the fabrication of a novel double-quantum-well (DQW) structure, in which the upper electron layer is supplied via modulation doping while the lower one is fully induced through the field effect from an n(+)-GaAs back Sate. Low-temperature transport measurements demonstrate that two-dimensional electron gases with equally high mobilities are successfully formed in the lower as well as in the upper QWs. By this approach, the electron density in the lower layer can be controlled over a wide range with a small back-gate bias, and hence the electron-density distribution in the DQW can be tuned arbitrarily by using a front gate in conjunction with the back gate.

 

116.    T. Murata, S. Kishimoto, K. Maezawa, T. Mizutani, T. Ishii, and T. Tamamura

            "An electron wave interference transistor with a novel recess-etched grating structure fabricated using electron beam lithography"

            in Compound Semiconductors 1999, Institute Of Physics Conference Series Vol. 166 (Iop Publishing Ltd, Bristol, 2000), pp. 347-350.

 

            ABSTRACT: We have successfully fabricated electron wave interference transistors (EWITs) with a novel recess-etched grating structure. Fine patterns with 60-nm period were fabricated by 100-keV electron beam (EB) lithography with a novel nanocomposite resist. A clear transconductance (g(m)) oscillation was observed in g(m)-V-G characteristics of the EWITs at temperatures up to 50 K. It was confirmed by analyzing the index of g(m) peaks that the observed g(m) oscillation was due to the electron wave interference caused by the periodic potential modulation in the channel produced by the recess-etched grating under the gate. The calculation of the transmission coefficient (TT) of electrons in the channel of the EWIT shows that it is possible to observe clear interference phenomena if the number of the grating is larger than 10.

 

117.    M. Nagase and K. Kurihara

            "Imaging of Si nano-patterns embedded in SiO2 using scanning electron microscopy"

            Microelectron. Eng. 53 (1-4), 257-260 (2000).

 

            ABSTRACT: Detailed shapes of embedded Si nanostructures were clearly observed through a SiO2 layer using scanning electron microscopy (SEM). We Pound a new imaging mechanism by which secondary electron (SE) yield from the oxide surface is greater where an embedded Si structure exists. In the range of acceleration voltages from 5 to 200 kV, we found that 30 kV provides high contrast and high resolution. Controlling the surface contrast by depositing a contaminated film using electron beam irradiation yields a clear, high-resolution SEM image of sub-10-nm Si structures embedded in a 60-nm-thick oxide. The combination of a non-destructive observation method based on SEM with a method based on AFM, which was demonstrated previously, provides detailed information on the three-dimensional shape of embedded Si nanodevices.

 

118.    M. Naito and M. Hepp

            "Superconducting T '-La2-xCexCuO4 films grown by molecular beam epitaxy"

            Jpn. J. Appl. Phys. Part 2 - Lett. 39 (6A), L485-L487 (2000).

 

            ABSTRACT: In this letter we report the synthesis of superconducting T'-La2-xCexCuO4 on SrTiO3(001) by molecular beam epitaxy. Although T'-La2-xCexCuO4 with a very limited range of x can be prepared by bulk synthesis using rather complicated techniques, this compound is very easy to obtain by thin film synthesis. Crucial to our success was the use of SrTiO3 substrates, which seems to stabilize the formation of the T' structure by an epitaxial effect. The best T-c was similar to 30 K by onset and similar to 28 K by zero resistance, which was obtained for x = 0.109. The resistivity showed a metallic temperature dependence, and the film's overall behavior was similar to that for the best (Nd, Ce)(2)CuO4 or (Pr, Ce)(2)CuO4 films. Moreover, the single phase of the T' structure formed for a composition range of 0.09 < x < 0.22, which is much wider than for previously reported bulk synthesis.

 

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

            "Intrinsic problem of cuprate surface and interface: why good tunnel junctions are difficult to fabricate"

            Physica C 335 (1-4), 201-206 (2000).

 

            ABSTRACT: In this article, we point out the key issue to fabricate high-T-c tunnel junctions on the basis of our recent systematic photoemission studies on MBE grown films. As a general feature for cuprates, the Cu-O bond is weak. Therefore, the redox reaction easily occurs at the interface between the cuprate surface and overlayers. This causes significant oxygen deficiencies, leading to serious degradation or complete destruction of superconductivity in the interface region. This is the reason why good tunnel junctions have not been successfully fabricated on high-ir, superconductors. Furthermore, we warn that all surface or interface-sensitive experiments, such as tunneling spectroscopy (including STM), various Josephson-current-based experiments, and even XPS/UPS may suffer from this problem, and hence may not lead to correct conclusions. (C) 2000 Elsevier Science B.V. All rights reserved.

 

120.    H. Nakano and H. Takayanagi

            "Influence of phase quantum fluctuations on superconducting proximity correction in normal-metal wire conductance"

            Phys. Rev. B 61 (22), 15398-15411 (2000).

 

            ABSTRACT: The influence of the charging effect on the proximity correction in the conductance of a mesoscopic superconductor(S)/normal-metal(N) coupled system is theoretically investigated. The most important contribution of the proximity correction in the conductance of a diffusive normal metal comes from the correction in the local conductivity delta sigma(r). The correction in the conductance is given by delta G = (1/L-N(2))integral(vol.)delta sigma(r)dr. Because of the retro property of Andreev reflection and the long rangeness of the Cooperon (particle-particle ladder), Andreev reflection at the SIN interface affects the local conductivity at a point in the normal region far from the interface (within the phase coherence length L-phi) If the SIN interface is very small and has a low transparency, single Andreev reflection is strongly suppressed by the Coulomb blockade at a low temperature (k(B)T<E-C, E-C = e(2)/2C) in an exponential manner exp{-4E(C)/(k(B)T)}, where C is the capacitance of the SIN junction. Nevertheless, the proximity correction in the conductance is only suppressed with power law k(B)T/(4E(C)) because the charged state is an intermediate state in the process of the proximity correction in the conductivity. This is quite different from the charging effect on the proximity correction of the current flowing through the SIN interface, which is strongly suppressed by the charging effect.

 

121.    H. Nakano and H. Takayanagi

            "Superconducting proximity effect and charging effect on the normal transport in normal-metal (semiconductor) wire"

            J. Low Temp. Phys. 118 (5-6), 653-662 (2000).

 

            ABSTRACT: We theoretically investigated superconducting proximity corrections of the conductance of a mesoscopic metal wire in terms of the Kubo-formula. In diagrammatic expression, the electromagnetic response kernel is quite similar to that of reproducible conductance fluctuation However, the proximity correction modifies the average conductance of the wire even though the latter gives a mesoscopic fluctuation. This Kubo-formula expression is applicable to the analysis of charging effects on the proximity correction in a superconductor(S)/Mesoscopic-normal-metal-wire(N) hybrid system with a very small S/N interface. Although the charging effect exponentially suppresses Andreev reflections at the S/N interface, the proximity correction survives. We propose an experiment to confirm this charging effect, where a degenerated semiconductor is used as the normal-metal wire. The proximity correction can be picked from the entire conductance as the magnetoconductance of an interferometer, and the charging effect is depicted by a gate control of the superconducting island. The semiconductor interferometer is more promising than a metallic one because the conductance without the proximity effect is bigger.

 

122.    H. Namatsu

            "Supercritical drying for water-rinsed resist systems"

            J. Vac. Sci. Technol. B 18 (6), 3308-3312 (2000).

 

           ABSTRACT: Two methods of supercritical resist drying (SRD) using CO2 have been developed for water-rinsed resist patterns. The key to their effectiveness is the use of a surfactant. In indirect SRD, a solution of n-hexane, a CO2-philic liquid, and a surfactant, sorbitan fatty acid ether, first replaces the water, and is in turn replaced with liquid CO? before SRD is performed. The addition of a compound with a high hydrophilic-lipophilic balance to the surfactant compensates for the poor miscibility of water in a solution of n-hexane and sorbitan fatty acid ether. In direct SRD, which does not require a CO2-philic liquid, the water is replaced directly with liquid CO2 containing a surfactant, fluoroether carboxylate, which makes water miscible in CO2; and then SRD is performed. The excellent results Obtained by both methods demonstrate that there is no inherent barrier to the use of SRD on water-rinsed resist patterns. (C) 2000 American Vacuum Society. [S0734-211X(00)01406-2].

 

123.    H. Namatsu, K. Yamazaki, and K. Kurihara

            "Supercritical resist dryer"

            J. Vac. Sci. Technol. B 18 (2), 780-784 (2000).

 

            ABSTRACT: We have developed a supercritical resist dryer in which resist patterns are developed and successively dried with a supercritical fluid. The usage of supercritical fluid in pattern drying is most effective for preventing pattern collapse, which is a significant problem in fine patterning of less than 100 nm critical dimensions. The key to performing ideal supercritical resist drying is the prevention of water contamination due to moisture in the dryer chamber. This is because the moisture dissolved in the supercritical fluid causes pattern deformation which results from film swelling. As a technique to prevent water contamination, we have devised pressure-controlled supercritical drying where a supercritical fluid is sent pressurized to a Teflon coated chamber at near the critical point. The supercritical resist dryer made on the basis of this technique is an essential apparatus for next-generation lithography. (C) 2000 American Vacuum Society. [S0734-211X(00)01302-0].

 

124.    K. G. Nath, F. Maeda, S. Suzuki, and Y. Watanabe

            "Epitaxy, modification of electronic structures, overlayer-substrate reaction and segregation in ferromagnetic Co films on Se-treated GaAs(001) surface"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 39 (7B), 4571-4574 (2000).

 

            ABSTRACT: The electronic structure and chemical states of the overlayer and substrate in epitaxially grown Co films on Se-treated GaAs(001) 2 x 1 are investigated by photoemission spectroscopy (PES) using synchrotron radiation. Adatom (Co)-substrate (Ga) intermixing is found at the initial stages of Co deposition. The intermixed layer is then buried and epitaxial growth is achieved following further deposition. During the intermixing, Se is floated over the surface of Co overlayers. A small amount of As-segregation is also observed in the thicker Co films.

 

125.    T. Nishida and N. Kobayashi

            "Nucleation control in MOVPE of group III-nitrides on SiC substrate"

            J. Cryst. Growth 221, 297-300 (2000).

 

            ABSTRACT: We characterized nitride growth on SiC substrates by using surface sensitive in situ monitoring of shallow angle reflectance (SAR). The growth initiation of the AIN wetting layer on SiC substrate, and that of GaN on the AIN wetting layer are studied, flat growth of the AIN wetting layer on SiC substrate is achieved by excess source supply at the start. and the growth evolution of GaN on the AIN wetting layer depends not only on the source flow rate but also on the species of metalorganic source. Flat GaN and AlN wetting layer growth is achieved by intentional nucleation. (C) 2000 Elsevier Science B.V. All rights reserved.

 

126.    J. Nitta, F. Meijer, Y. Narita, and H. Takayanagi

            "Gate voltage-dependent Aharanov-Bohm experiment in the presence of Rashba spin-orbit interaction"

            Physica E 6 (1-4), 318-321 (2000).

 

            ABSTRACT: We measured gate voltage-dependent Aharonov-Bohm oscillations in an InGaAs-based two-dimensional electron gas ring with a gate on top of one of the branches. After ensemble averaging, the h/e oscillation spectrum showed smooth oscillatory behavior as a function of the gate voltage. This could be a manifestation of the spin-orbit interaction induced interference. (C) 2000 Elsevier Science B.V. All rights reserved.

 

127.    O. Niwa, R. Kurita, K. Hayashi, T. Horiuchi, K. Torimitsu, K. Maeyama, and K. Tanizawa

            "Continuous measurement of histamine from rat basophilic leukemia cells (RBL-2H3) with an on-line sensor using histamine oxidase"

            Sens. Actuator B-Chem. 67 (1-2), 43-51 (2000).

 

           ABSTRACT: Histamine release from rat basophilic leukemia (RBL-2H3) cells was continuously measured using a histamine oxidase (HO)-immobilized on-line electrochemical sensor. The sensor has a carbon-based electrode modified with a bilayer of osmium-polyvinylpynidine-based gel containing horseradish peroxidase (HRP) and BSA containing HO. The high specificity of the enzyme made the sensor highly selective with regards to diamines such as putrescine and cadaverine. We obtained a low detection limit of 23 nM owing to the low operation potential of the sensor (below 0 V vs. Ag/AgCl) and the high activity of the enzyme after immobilization. Moreover, the sensor had a high conversion efficiency. The sensor response was unaffected by 400 min of continuous histamine measurement and by more than 2 weeks of storage in a refrigerator. We combined the histamine sensor with a microdialysis (MD) sampling probe and used it to measure the histamine concentration of RBL-2H3 cells stimulated with dinitrophenylated bovine serum albumin (DNP-BSA) after incubation with IgE. We also fabricated a small volume histamine sensor by the microfabrication technique and were able to measure the histamine release from a small mast cell colony in real time with the sensor by drawing the extracellular solution continuously through a sampling capillary located near the cells. (C) 2000 Elsevier Science S.A. All rights reserved.

 

128.    O. Niwa, R. Kurita, Z. M. Liu, T. Horiuchi, and K. Torimitsue

            "Subnanoliter volume wall-jet cells combined with interdigitated microarray electrode and enzyme modified planar microelectrode"

            Anal. Chem. 72 (5), 949-955 (2000).

 

            ABSTRACT: Miniaturized wall-jet type flow cells with an active volume of 0.042 - 15 nL were fabricated for use as highly sensitive electrochemical detectors for capillary electrophoresis/electrochemical detection and small on-line enzyme sensors. The cells consisted of three glass plates and a fused-silica capillary. Two of the plates had microfabricated now channels and guide trenches for the capillary and working, reference, and counter electrodes. The other plate had a film electrode, When an interdigitated microarray electrode (total area, 66 mu m x 64 mu m; bandwidth and gap, 2 mu m) was installed in the now cell, the redox cycling enhanced the current at flow rates of less than 100 nL/min even though there were only eight pairs of microbands. A sharp dopamine peak enhanced by the redox cycling was observed when the cell was used for capillary electrophoresis, A square film electrode modified with glutamate oxidase and Os-poly(vinylpyridine) containing HRP was also installed in the now cell and used to measure neurotransmitter release from cultured nerve cells. When the now rate was relatively high, the response time of the modified electrode was comparable to that of a cylindrical carbon fiber electrode (33 mu m o.d.) modified with the same enzyme and mediator. We observed a transient cathodic current response assigned to the glutamate release with the electrode in the flow cell in a suction mode measurement when we stimulated cultured nerve cells electrically with a dual microelectrode.

 

129.    H. Noda, T. Urisu, Y. Kobayashi, and T. Ogino

            "Initial stage of hydrogen etching of Si surfaces investigated by infrared reflection absorption spectroscopy"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 39 (12B), 6985-6989 (2000).

 

            ABSTRACT: The initial stage of etching reactions (breaking the Si-Si back bonds) of Si(100) and Si(111) surfaces exposed to hydrogen at room temperature was investigated by buried metal layer-infrared reflection absorption spectroscopy. The peaks of SiH2 scissors and SiH3 deformation modes (<1000 cm(-1)) were successfully observed as clear indicators of the initial stage of hydrogen etching reactions. On the Si(100) surface. the hydrogen exposure dependence of these peaks indicated that the etching reaction stal ts in the relatively low-exposure region of <greater than or equal to>300L (1 L = 1 x 10(-6) Torr s). We found that the adjacent dihydride is a precursor to breaking the Si back bonds. On the Si(111) surface, it was found that the adatom's two back bonds are easily broken, and that adatom trihydride is generated at a low H-exposure of 70-500 L. Adding to this dominant reaction, the etching of the rest-atom layer was observed at H-exposures higher than 10000 L.

 

130.    S. Nojima

            "Photonic-crystal laser mediated by polaritons"

            Phys. Rev. B 61 (15), 9940-9943 (2000).

 

            ABSTRACT: A polariton-mediated photonic-crystal laser is proposed, which has a periodic structure containing excitonic and gain materials in its unit cell. This type of structure is shown to significantly intensify optical gain near the polaritonic band edge as a result of using a light, the band of which is split into small polaritonic bands by exciton-photon coupling. Consequently, this laser exhibits much lower threshold gain than those of other lasers studied here and it oscillates in the single mode because of its strong mode selectivity. These advantages stem from the photon field modulated extremely by adding excitons to conventional photonic crystals.

 

131.    M. Notomi

            "Theory of light propagation in strongly modulated photonic crystals: Refractionlike behavior in the vicinity of the photonic band gap"

            Phys. Rev. B 62 (16), 10696-10705 (2000).

 

            ABSTRACT: Although light propagation in weakly modulated photonic crystals is basically similar to propagation in a diffraction grating in which conventional refractive index loses its meaning, we demonstrate that light propagation in strongly modulated two-dimensional (2D)/3D photonic crystals becomes refractionlike in the vicinity of the photonic bandgap. Such a crystal behaves as a material having an effective refractive index controllable by the band structure. This situation is analogous to the effective-mass approximation id electron-band theory. By utilizing this phenomenon, negatively refractive material can be realized, which has interesting optical properties such as mirror-image refraction.

 

132.    M. Notomi, T. Tamamura, T. Kawashima, and S. Kawakami

            "Drilled alternating-layer three-dimensional photonic crystals having a full photonic band gap"

            Appl. Phys. Lett. 77 (26), 4256-4258 (2000).

 

            ABSTRACT: We propose a three-dimensional photonic crystal structure having a wide full photonic band gap in the optical regime, which can be fabricated by an alternating-layer deposition and etching (drilling) process. This fabrication process is much simpler than that previously reported. The combination of current lithographic technology and autocloning bias-sputtering deposition is a promising way of realizing these photonic crystals. (C) 2000 American Institute of Physics. ([)S0003-6951(00)03451-3].

 

133.    M. Notomi, T. Tamamura, Y. Ohtera, O. Hanaizumi, and S. Kawakami

            "Direct visualization of photonic band structure for three-dimensional photonic crystals"

            Phys. Rev. B 61 (11), 7165-7168 (2000).

 

            ABSTRACT: We propose a method to experimentally determine the full photonic band structure of photonic crystals by monitoring the beam propagation, and we demonstrate the experimental results of the band-structure measure ment in the near-infrared regime for Si/SiO2 three-dimensional hexagonal photonic crystals fabricated by autocloning bias-sputtering process.

 

134.    S. Nuttinck, K. Hashimoto, S. Miyashita, T. Saku, Y. Yamamoto, and Y. Hirayama

            "Quantum point contacts in a density-tunable two-dimensional electron gas"

            Jpn. J. Appl. Phys. Part 2 - Lett. 39 (7A), L655-L657 (2000).

 

            ABSTRACT: Quantum point contacts fabricated using a backgated two-dimensional electron-gas system show clear quantized features and a 0.7 anomaly in conductance. Using these density-tunable point contacts, we have studied the behavior of the 0.7 anomaly. The 0.7 step shifts down to around 0.5 as the electron density is decreased under a zero magnetic field. This suggests that electron-electron interactions play an important role in forming the conductance anomalies of quantum point contacts.

 

135.    A. A. Odintsov and Y. Tokura

            "Contact phenomena in carbon nanotubes"

            Physica B 284, 1752-1753 (2000).

 

            ABSTRACT: Poor screening of the long-range Coulomb interaction in one-dimensional carbon nanotubes results in a peculiar picture of contact phenomena. Being brought to a contact with a metal, conducting nanotube accumulates electric charge whose density decays slowly with the distance from the contact. This should be contrasted to a conventional metal-metal contact where the charge density decreases exponentially at atomic distances. Implications for experiments are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.

 

136.    A. A. Odintsov and Y. Tokura

            "Contact phenomena and Mott transition in carbon nanotubes"

            J. Low Temp. Phys. 118 (5-6), 509-518 (2000).

 

            ABSTRACT: We describe the transfer of electric charge in junctions between a metal and carbon nanotube as well as between metallic and semiconducting carbon nanotubes. The long range Coulomb interaction drastically modifies the charge transfer phenomena in one-dimensional nanotube systems compared to conventional semiconductor heterostructures. Being brought into a contact with a metal, conducting nanotube accumulates electric charge whose density decays slowly with the distance from the junction. The length of the Schottky barrier in nanotube heterojunctions varies from the distances of the order of the nanotube radius (nanometers) to the distances of the order of the nanotube length (microns) depending on a doping strength. The Schottky barrier height shows pronounced asymmetry under the forward and reverse bias. This results in rectifying behavior of heterojunctions, in agreement with recent experimental observations by Z. Yao et. al. and P. McEuen et. al. Finally, we discuss observability of recently predicted Mott insulating phase in metallic carbon nanotubes.

 

137.    H. Ofuchi, T. Kubo, M. Tabuchi, K. Takahei, and Y. Takeda

            "Local structures around Er atoms in GaAs: Er,O studied by fluorescence EXAFS and photoluminescence"

            Microelectron. Eng. 51-2, 715-721 (2000).

 

            ABSTRACT: We have investigated Er- and O-doped GaAs samples by fluorescence extended X-ray absorption fine structure (EXAFS) measurements in order to clarify the local structures around the Er atoms. The EXAFS analysis revealed that in the range of Er concentration from 2 X 10(18) cm(-3) to 3 X 10(20) cm(-3) the majority of the Er atoms substituted Ga sublattice with two adjacent oxygen atoms (Er-2O center). On the contrary, in the same range of the Er concentration the PL intensity decreased rapidly with the increase of the Er concentration. The EXAFS analysis also indicated that the averaged arrangements of second or third neighbor atoms are different in each sample. Therefore, the Er-2O centers are considered to be further modified by the local structures of those second and even third nearest neighbors, which in turn change their optical characteristics. (C) 2000 Elsevier Science B.V. All rights reserved.

 

138.    T. Ogino, Y. Homma, H. Hibino, Y. Kobayashi, P. Kuniyil, K. Sumitomo, H. Omi, and P. Finnie

            "Control of Si surfaces for fabrication of integrated functional nanostructures"

            Abstr. Pap. Am. Chem. Soc. 219, U343-U343 (2000).

 

            ABSTRACT:

139.    K. Oguri, N. Funamori, T. Uchida, N. Miyajima, T. Yagi, and K. Fujino

            "Post-garnet transition in a natural pyrope: a multi-anvil study based on in situ X-ray diffraction and transmission electron microscopy"

            Phys. Earth Planet. Inter. 122 (3-4), 175-186 (2000).

 

            ABSTRACT: Post-garnet transition in a natural pyrope under the conditions close to 670 km discontinuity was studied by in situ X-ray diffraction (XRD) using an MA8-type multi-anvil apparatus and analytical transmission electron microscopy (ATEM) on recovered samples. The pyrope with a composition of (Mg0.72Fe0.17Ca0.11)(3)Al2Si3O12 directly breaks down into (Mg, Fe)SiO3-Al2O3 perovskite, CaSiO3 perovskite, stishovite, and the 'NAL' phase with increase in density of about 10%. The presence of the 'NAL' phase that was first discovered in the diamond-anvil cell (DAC) experiments was confirmed by multi-anvil experiments. The transition boundary can be expressed as P (GPa) = 14.4 + 0.0065T (K) between 1200 and 2000 K, suggesting that, below 1400 K, the transition pressure may be lower than 24 GPa, the pressure corresponds to the 670 km discontinuity. These results, together with available information on garnets with various compositions, suggest that chemical compositions of garnets strongly affect both transition conditions and post-garnet high-pressure mineral assemblages. (C) 2000 Elsevier Science B.V. All rights reserved.

 

140.    K. Okajima, K. Takeda, N. Oyama, E. Ohta, K. Shiraishi, and T. Ohno

            "Phenomenological theory of semiconductor epitaxial growth with misfit-dislocations"

            Jpn. J. Appl. Phys. Part 2 - Lett. 39 (9AB), L917-L920 (2000).

 

            ABSTRACT: We have developed a phenomenological theory of growth behavior in semiconductor heteroepitaxy that includes the effects of the formation of Stranski-Krastanov (SK) islands and misfit-dislocations (MDs). Our theory can reproduce the various types of growth behavior observed in hereroepitaxial growth. Moreover, we also formulate a procedure for determining the phenomenological parameters that includes atomistic calculations. The critical thickness of InAs/GaAs(110) obtained by this procedure is in good agreement with the experimentally obtained value.

 

141.    H. Omi and T. Ogino

            "Growth-induced atomic step ordering on patterned and non-patterned Si(111)"

            Thin Solid Films 380 (1-2), 15-19 (2000).

 

            ABSTRACT: Atomic step configurations on the vicinal surfaces of patterned and non-patterned Si(111) during homoepitaxial step-flow growth were studied as a function of film thickness, deposition temperature, deposition rate, and substrate miscut. We found, for the first time, that step-flow growth on the vicinal surfaces of Si(111) miscut toward the [11 (2) over bar] direction results in the formation of collective, in-phase zigzag arrays of [2 (11) over bar]- and [(1) over bar2 (1) over bar]-type steps. We also found that step-flow growth on the lower-level region around the edge of Si(111) mesa ridges significantly improves period uniformity. We explained the shape of atomic steps on the basis of the stability of surface reconstruction on Si(111), and the atomic step ordering on the assumption of the anisotropic barrier for diffusion at the growing steps. (C) 2000 Elsevier Science B.V. All rights reserved.

 

142.    H. Omi and T. Ogino

            "Positioning of self-assembling Ge islands on Si(111) mesas by using atomic steps"

            Thin Solid Films 369 (1-2), 88-91 (2000).

 

            ABSTRACT: Atomic steps were rearranged during step-flow growth of Si epitaxial layers on 0.6- and 1.5-mu m-wide Si(111) mesas oriented in the [11 (2) over bar] direction during molecular beam epitaxy. Ge islands were then grown on the mesa tops to form well-positioned arrays of self-assembling nanodots. On the 0.6-mu m-wide mesas, the Si growth produced arrays of arrowheads composed of [(1) over bar (1) over bar 2]-type bunched steps. Ge islands preferentially grow at the vertices of arrowhead-like steps, aligning along the center of a mesa. On 1.5-mu m-wide mesas, on the other hand, the resulting steps have a zigzag-shaped pattern and Ge islands also preferentially grow at the vertices of zigzag steps. These results demonstrate that by using atomic steps with artificially designed arrangement, it is possible to position and align the Ge islands on Si(111) mesas. (C) 2000 Elsevier Science S.A. All rights reserved.

 

143.    Y. Ono, Y. Takahashi, K. Yamazaki, M. Nagase, H. Namatsu, K. Kurihara, and K. Murase

            "Single-electron transistor and current-switching device fabricated by vertical pattern-dependent oxidation"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 39 (4B), 2325-2328 (2000).

 

            ABSTRACT: Vertical pattern-dependent oxidation, a method of fabricating single-electron transistors, has been advanced so that it can be applied to make various types of single-electron logic circuits. The improved method changes the pattern of Si to be oxidized from the original. Using the improved method, we have demonstrated a single-electron transistor with a new structure and a current-switching device composed of the new single-electron transistors.

 

144.    Y. Ono, Y. Takahashi, K. Yamazaki, M. Nagase, H. Namatsu, K. Kurihara, and K. Murase

            "Si complementary single-electron inverter with voltage gain"

            Appl. Phys. Lett. 76 (21), 3121-3123 (2000).

 

            ABSTRACT: A Si complementary single-electron inverter in which two identical single-electron transistors (SETs) are packed is fabricated on a silicon-on-insulator substrate. For the fabrication, the vertical pattern-dependent oxidation method, which enables the formation of two tiny SETs aligned in parallel, is modified so that the two SETs can be connected in series to realize an inverter configuration. The resultant circuit occupies a very small area: 100x100 nm for each SET. For complementary operation, the electrical characteristics of one of the SETs are shifted using a side gate situated near the SET. Input-output transfer with a voltage gain larger than unity is demonstrated at 27 K. (C) 2000 American Institute of Physics. [S0003-6951(00)04821-X].

 

145.    Y. Ono, Y. Takahashi, K. Yamazaki, M. Nagase, H. Namatsu, K. Kurihara, and K. Murase

            "Fabrication method for IC-oriented Si single-electron transistors"

            IEEE Trans. Electron Devices 47 (1), 147-153 (2000).

 

            ABSTRACT: A new fabrication method for Si single-electron transistors (SET's) is proposed, The method applies thermal oxidation to a Si wire with a fine trench across it on a silicon-on-insulator substrate. During the oxidation, the Si wire with the fine trench is converted, in a self-organized manner, into a twin SET structure with two single-electron islands, one along each edge of the trench, due to position-dependent oxidation-rate modulation caused by stress:accumulation. Test devices demonstrated, at 40K, that the twin SET structure can operate as two individual SET's. Since the present method produces two SET's at the same time in a tiny area, It is suitable for integrating logic circuits based on pass-transistor-type logic and CMOS-type logic, which promises to lead to the fabrication of single-electron logic LSI's.

 

146.    K. Prabhakaran, F. Maeda, Y. Watanabe, and T. Ogino

            "Thermal decomposition pathway of Ge and Si oxides: observation of a distinct difference"

            Thin Solid Films 369 (1-2), 289-292 (2000).

 

            ABSTRACT: In this paper, we report a comparison of the thermal decomposition pathways of ultrathin oxide layers, formed on Ge(100) and Si(100) surfaces, as revealed by photoemission studies, employing synchrotron radiation. The oxide layer, in both the cases, consists of a mixture of, mainly, monoxide and dioxide species. On annealing, both the oxides undergo thermal decomposition and the desorbing species is the corresponding monoxide. However, we find that their decomposition pathways are entirely different. On annealing the Ge oxide layer, the GeO2 species transforms to GeO on the surface and finally desorbs from the surface at similar to 425 degrees C. In contrast, annealing results in the transformation of SiO to SiO2 up to a temperature, lower than the desorption temperature (similar to 760 degrees C). At higher temperatures, SiO2 possibly transforms back to SiO and subsequently desorbs. These phenomena may be related to the interface properties, since the thermodynamic properties of individual oxides predict an opposite trend in their thermal stability. (C) 2000 Elsevier Science S.A. All rights reserved.

 

147.    K. Prabhakaran, F. Maeda, Y. Watanabe, and T. Ogino

            "Distinctly different thermal decomposition pathways of ultrathin oxide layer on Ge and Si surfaces"

            Appl. Phys. Lett. 76 (16), 2244-2246 (2000).

 

            ABSTRACT: The thermal decomposition pathway of an ultrathin oxide layer on Ge(100) and Si(100) surfaces is examined by synchrotron radiation photoelectron spectroscopy and ultraviolet photoelectron spectroscopy with helium I radiation. The as-prepared oxide layer consists of a mixture of oxides, namely, suboxides and dioxides, on both the surfaces. Upon annealing, the oxide layers decompose and desorb as monoxides. However, we find that the decomposition pathways are different from each other. On annealing Ge oxides, GeO2 species transform to GeO and remain on the surface and desorb at > 420 degrees C. In contrast, annealing of Si oxides results in the transformation of SiO to SiO2 up to temperatures (similar to 780 degrees C) close to the desorption. At higher temperatures, SiO2 decomposes and desorbs, implying a reverse transformation to volatile SiO species. (C) 2000 American Institute of Physics. [S0003-6951(00)04816-6].

 

148.    K. Prabhakaran, K. Sumitomo, and T. Ogino

            "Nano-interface engineering of Co/Ge/Si systems: metal incorporation into Ge quantum dots and SiO2/Si structures"

            Appl. Surf. Sci. 159, 492-497 (2000).

 

            ABSTRACT: In this paper, we describe the nano-interface engineering of Co/Ge/Si system, involving interface reactions. Controlled annealing causes the Co atoms to diffuse through an already formed quantum dot network fabricated on a silicon substrate and get incorporated as epitaxial CoSi2. Additionally, we performed in situ examination of the early stages of oxide mediated epitaxial growth of Silicide at the SiO2/Si interface on a Si surface. Cobalt, deposited at room temperature on an SiO2 layer. diffuses through the oxide layer and forms epitaxial CoSi2 at the interface, preserving the original oxide surface morphology. These results suggest the possibility of an alternative and viable method to introduce functionality into nanostructures. (C) 2000 Elsevier Science B.V. All rights reserved.

 

149.    J. H. Roslund, K. Saito, K. Suzuki, H. Yamaguchi, and Y. Hirayama

            "Electron and hole proximity effects in the InAs/AlSb/GaSb system"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 39 (4B), 2448-2451 (2000).

 

            ABSTRACT: We have investigated the properties of InAs/AlSb/GaSb electron-hole proximity systems while focusing on the influence of the AlSb barrier between the two quantum wells. We have seen that for thin AlSb barriers there is a drop in mobility due to scattering of electrons by holes. We have also observed a series of secondary absorption peaks in cyclotron resonance spectra that are caused by interband Landau-level transitions.

 

150.    J. H. Roslund, H. Yamaguchi, and Y. Hirayama

            "Electrical properties of InAs/AlSb/GaSb double quantum well structures"

            in Compound Semiconductors 1999, Institute Of Physics Conference Series Vol. 166 (Iop Publishing Ltd, Bristol, 2000), pp. 127-130.

 

            ABSTRACT: The electrical properties of InAs/AlSb/GaSb double quantum well structures have been investigated and the InAs/AlSb interfaces were seen to be responsible for changing the balance between electrons and holes, creating a surplus of electrons.

 

151.    M. S. M. Saifullah, K. Kurihara, and C. J. Humphreys

            "Comparative study of sputtered and spin-coatable aluminum oxide electron beam resists"

            J. Vac. Sci. Technol. B 18 (6), 2737-2744 (2000).

 

            ABSTRACT: The electron beam exposure characteristics of sputtered AlOx and spin-coatable Al2O3 resists are compared and contrasted. When exposed to an electron beam, sputtered AlOx resists on a silicon substrate undergo an intense mass loss. However, electron energy loss spectroscopy shows that even after a prolonged exposure some aluminum and oxygen remains on the silicon surface. Spin-coatable Al2O3 resist was prepared by reacting aluminum tri-sec-butoxide, Al(OBus)(3), with acetylacetone (AcAc) in isopropyl alcohol. These are negative tone resists and they are > 10(6) times more sensitive to an electron beam than the sputtered AlOx, bringing its sensitivity very close to high resolution organic resists such as calixarene. The exposure properties of spin-coatable and sputtered aluminum oxide resists are discussed together with their sensitivity, damage mechanisms, line edge roughness, and etching characteristics. A brief note on the change of methodology of resist design is added when inorganic resists are to be used in high resolution electron beam nanolithography. (C) 2000 American Vacuum Society. [S0734-211X(00)15706-3].

 

152.    T. Saitoh, T. Sogawa, M. Notomi, T. Tamamura, S. Kodama, T. Furuta, and H. Ando

            "GaAs photonic crystals on SiO2 fabricated by very-high-frequency anode-coupled reactive ion etching and wafer bonding"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 39 (11), 6259-6263 (2000).

 

            ABSTRACT: High-aspect-ratio, two-dimensional (2D) air-column GaAs photonic crystals (PhCs) on SiO2 layers with a lattice constant ranging from 240 nm to 1.0 mum have been fabricated using a novel method combining wafer bonding and low-temperature very-high-frequency (VHF) reactive ion etching (RIE). The obtained PhCs exhibit near-field patterns of sixfold symmetry or fourfold symmetry due to lateral interference, depending on the lattice structure. We have obtained photoluminescence (PL) spectra of PhCs which reveal the low damage feature of the combined process of low-temperature RIE and wafer bonding. Reflectance spectra exhibit fine structures which originate from the resonance coupling of the external light to the zone-folded bands of the photonic structure. This vertical confinement structure, obtained by forming GaAs PhCs on SiO2, is useful for taking advantage of 2D photonic crystals since it prevents photon dissipation from the lattice plane. The fabrication method combining low-temperature RIE with wafer bonding is a promising process for developing 2D photonic crystals on SiO2 layers.

 

153.    S. Sasaki, S. De Franceschi, J. M. Elzerman, W. G. van der Wiel, M. Eto, S. Tarucha, and L. P. Kouwenhoven

            "Kondo effect in an integer-spin quantum dot"

            Nature 405 (6788), 764-767 (2000).

 

            ABSTRACT: The Kondo effect-a many-body phenomenon in condensed-matter physics involving the interaction between a localized spin and free electrons-was discovered in metals containing small amounts of magnetic impurities, although it is now recognized to be of fundamental importance in a wide class of correlated electron systems(1,2). In fabricated structures, the control of single, localized spins is of technological relevance for nanoscale electronics(3,4). Experiments have already demonstrated artificial realizations of isolated magnetic impurities at metallic surfaces(5,6), nanoscale magnets(7), controlled transitions between two-electron singlet and triplet states(8), and a tunable Kondo effect in semiconductor quantum dots(9-12). Here we report an unexpected Kondo effect in a few-electron quantum dot containing singlet and triplet spin states, whose energy difference can be tuned with a magnetic field. We observe the effect for an even number of electrons, when the singlet and triplet states are degenerate. The characteristic energy scale is much larger than in the ordinary spin-1/2 case.

 

154.    H. Sato, A. Tsukada, M. Naito, and A. Matsuda

            "La-214 thin films under epitaxial strain"

            Physica C 341, 1767-1770 (2000).

 

            ABSTRACT: Compressive (or expansive) epitaxial strain was induced in (001)-oriented La-214 thin films. For the compressed films of La2-xSrxCuO4+delta and La2-xBaxCuO4+delta on LaSrAlO4 substrates, the superconducting transition temperature (T-c) reached 44 K and 47 K, respectively, with delta similar to0 When both films had delta > 0, T-c reached 49 K. These values are higher than those for bulk samples. The T-c-x phase diagrams for the films did not show a local minimum at x similar to 0.125, the so-called "1/8 anomaly". The compressive strain expands the c-axis via the Poisson effect and suppresses formation of the low-temperature tetragonal phase. Both effects result in an increase in the bond length between Cu and the apical oxygen (O-apex), which is responsible for the enhancement of T-c Furthermore, based on the experimental fact that the lower residual resistivity gives a higher T-c, we speculate that the T-c enhancement is caused by the reduced antiferromagnetic spin fluctuation in the CuO2 planes due to the change in the Cu-O-apex bond length.

 

155.    H. Sato, A. Tsukada, M. Naito, and A. Matsuda

            "Absence of (1)/(8) anomaly in strained thin films of La2-xBaxCuO4+delta"

            Phys. Rev. B 62 (2), R799-R802 (2000).

 

            ABSTRACT: Compressive and expansive strain was induced into La2-xBaxCuO4+delta thin films with x = 0-0.35 on LaSrAlO4 and SrTiO3 substrates, respectively. For the compressed films, the superconducting transition temperature (T-c) reached 44 K with delta similar to 0 and 49 K with delta>0, and the T-c-x phase diagram did not show a local minimum at x similar to 0.125, the so-called "1/8 anomaly." For the expanded films, we observed strong reduction of T-c. We suggest that the absence of the "1/8 anomaly" in the compressed films is due to the c-axis expansion, as well as the in-plane compression, and suppression of the residual resistivity.

 

156.    H. Sato, A. Tsukada, M. Naito, and A. Matsuda

            "La2-xSrxCuOy epitaxial thin films (x=0 to 2): Structure, strain, and superconductivity"

            Phys. Rev. B 61 (18), 12447-12456 (2000).

 

            ABSTRACT: We have grown (001)-oriented thin films of La2-xSrxCuOy with strontium composition x=0-2 by reactive coevaporation and characterized them by x-ray-diffraction and resistivity measurements. A systematical change in the c-axis length indicates that single-phase films were obtained for the whole compositional range. The films with the oxygen composition gamma similar to 4 showed superconductivity for x between 0.06 and 0.30. For x=0.15, the superconducting transition temperature (T-c) was maximized to 44 K, due to a strain effect caused by the lattice mismatch between films and substrates. Around this composition, it is found that T-c for the films shows a good correlation with the c-axis length. For x=0.30, T-c for the films strongly depends on the residual resistivity [rho(0 K)]: higher T-c for lower rho(0 K). The depression of T-c around x=0.125 is smaller than that for the bulk samples, suggesting that the strain suppresses the "1/8 anomaly." The films with gamma>4 attained by cooling in ozone showed T-c between 40 and 48 K for x<0.15. For x>0.30, the compositional dependence of the resistivity is explained by both oxygen defects and a structural phase transition at x=1.8.

 

157.    C. Sekar, T. Watanabe, and A. Matsuda

            "Crystal growth and characterization of the 4-leg spin ladder compound La2Cu2O5"

            J. Cryst. Growth 212 (1-2), 142-147 (2000).

 

            ABSTRACT: Crystallization of La2Cu2O5, has been investigated in the La2O3-CuO system for various starting compositions both in air and oxygen atmospheres. In air, we find that there exists a new region of crystallization of La8Cu7O19 phase, just above that of La2Cu2O5. However, this region vanishes completely in flowing-oxygen atmosphere. By utilizing this, large single crystals of the 4-leg spin-ladder compound La2Cu2O5 have been successfully grown from CuO flux by the slow cooling method. Room-temperature resistivity parallel to the ladder direction (\b) of the as-grown crystals is estimated to be 1.7 x 10(3) Ohm cm. A significant decrease in the resistivity (798 m Ohm cm at 300 K) is observed upon hole doping by means of high oxygen pressure annealing (approximately 400 atm) using a hot isostatic pressing furnace. However, no transition was observed from the semiconducting behavior. (C) 2000 Elsevier Science B.V. All rights reserved.

 

158.    K. Semba, A. Matsuda, and M. Mukaida

            "Carrier-concentration-driven superconductor-to-insulator transition in YBa2Cu3O6+x"

            Physica B 281, 904-905 (2000).

 

            ABSTRACT: We have succeeded in controlling carrier concentration near the superconductor-to-insulator transition by sample annealing under the equilibrium oxygen pressure of YBa2Cu3O6+x. Near the critical doping, below 60 K, we observed carrier-concentration-driven resistivity scaling of the: pulsed-laser-deposited thin of YBa2Cu3O6+x indicating the large energy scale of the quantum phase fluctuation. This demonstrates that a considerable area in the phase diagram of the pseudo-gapped underdoped YBa2Cu3O6+x is in the critical region of the quantum phase transition. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

 

159.    R. Shaikhaidarov, A. F. Volkov, H. Takayanagi, V. T. Petrashov, and P. Delsing

            "Josephson effects in a superconductor-normal-metal mesoscopic structure with a dangling superconducting arm"

            Phys. Rev. B 62 (22), 14649-14652 (2000).

 

            ABSTRACT: We studied a mesoscopic crosslike normal-metal structure connected to two superconducting (S) and two normal (N) reservoirs. We observed the Josephson effect under unusual conditions when there is no current through one of the two S/N interfaces. The potential difference between the S reservoirs was zero unless the voltage applied between S and N reservoirs exceeded a critical value although the electric potential in the N wire connecting the superconductors varied in a nonmonotonic way. The observed effects are discussed theoretically.

 

160.    K. Shimizu and N. Imoto

            "Single-photon-interference communication equivalent to Bell-state-basis cryptographic quantum communication"

            Phys. Rev. A 62 (5), art. no.-054303 (2000).

 

            ABSTRACT: We propose a single-photon interferometer which provides cryptographic quantum communication equivalent to that obtained using a pair of polarization entangled photon twins as a carrier [Phys. Rev. A 60, 157 (1999)]. Instead of manipulating and measuring the internal states of entangled photon twins, cryptographic quantum communication is possible by manipulating a single photon in an extended interferometer. The use of the single-photon interferometer offers significant experimental advantages compared to our previous approach.

 

161.    K. Shimizu and N. Imoto

            "Quantum information processing - Quantum cryptography toward ultimate security"

            Ntt Rev. 12 (1), 26-31 (2000).

 

            ABSTRACT: Recent progress in digital computer communication networks has increased the awareness of the importance of information security technologies for private communications, message authentication, and data protection. NTT Basic Research Laboratories is pushing towards the realization of quantum cryptography, an innovative new concept of cryptography based on the principles of quantum mechanics. If a quantum cryptographic system can be successfully developed, there will be absolutely no possibility of security violations in private communications.

 

162.    M. Shimoda, S. Tsukamoto, T. Ohno, N. Koguchi, M. Sugiyama, S. Maeyama, and Y. Watanabe

            "Stoichiometry study of S-terminated GaAs(001)-(2 x 6) surface with synchrotron radiation photoelectron spectroscopy"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 39 (7A), 3943-3946 (2000).

 

            ABSTRACT: Synchrotron radiation photoelectron spectroscopy (SRPES) has been performed to investigate the surface stoichiometry of the S-terminated GaAs(001)-(2 x 6), and in particular, to determine the chemical species of the five dimers, which are separated by missing dimers and from the unit structure of the (2 x 6) reconstruction. The S 2p photoemission spectra show a significant decrease in the peak intensity with increasing substrate temperature, whereas no significant changes are observed for the As 3d photoemission spectra The Ga 3d spectra are decomposed into a bulk component and more than one surface component, one of which is attributed to a Ga-S bond and decreases in accordance with the change observed in the S 2p spectra. These results strongly support the model that each pair of the five dimers in the (2 x 6) reconstruction consists of S-S dimers.

 

163.    D. J. Shin, A. Chavez-Pirson, and Y. H. Lee

            "Multipole analysis of the radiation from near-field optical probes"

            Opt. Lett. 25 (3), 171-173 (2000).

 

            ABSTRACT: We experimentally and theoretically analyze the radiation emitted from subwavelength-sized apertures in nearfield optical probes. By decomposing the experimentally obtained radiation patterns into vector spherical waves, we describe the fields in terms of a series of multipole sources. We fit polarization-resolved angular intensity distributions, measured as far as 150 degrees from the normal, with dipole, quadrupole, and octupole radiation. We find that the magnetic and the electric dipole components are dominant but that the interference terms between dipoles and higher-order poles are not negligible. This result can be used as the basis for understanding near-field optical interactions and images. (C) 2000 Optical Society of America. OCIS codes: 260.1960, 180.5810.

 

164.    K. Shiraishi, H. Kageshima, and M. Uematsu

            "Phenomenological theory on Si layer-by-layer oxidation with small interfacial islands"

            Jpn. J. Appl. Phys. Part 2 - Lett. 39 (12B), L1263-L1266 (2000).

 

            ABSTRACT: We theoretically investigate the mechanism of Si layer-by-layer oxidation by taking into account interfacial Si emission. Based on the free energy expression, which includes the oxidation-induced strain within the elastic continuum theory, we simulated the oxidation. Initially, oxidation occurs at the step edge of the interface. However, it stops because of the accumulated strain, and the oxidation at the terrace region begins. As a result, many small islands form at the interface. After their formation, the Si emission occurs to release the interfacial strain. Accordingly, oxidation at the step edges of the small islands becomes possible due to the strain release by Si emission. This process is qualitatively in good agreement with recent observations of Si layer-by-layer oxidation concurrent with the formation of many small oxide islands.

 

165.    K. Shiraishi, M. Nagase, S. Horiguchi, H. Kageshima, M. Uematsu, Y. Takahashi, and K. Murase

            "Designing of silicon effective quantum dots by using the oxidation-induced strain: a theoretical approach"

            Physica E 7 (3-4), 337-341 (2000).

 

            ABSTRACT: We have investigated using partial oxidation of an Si wire for forming quantum dots. Calculated results show oxidation induced strain leads to the formation of effective quantum dots, although actual dot-shaped structures are not formed. By investigating formation conditions, we have found that partial oxidation of an Si wire on a (0 0 1) substrate is very efficient for the formation of oxidation-induced effective quantum dots. Moreover, our calculated results are qualitatively consistent with experimental results obtained with our Si single-electron transistors (Si-SET) fabricated by pattern-dependent oxidation (PADOX). (C) 2000 Elsevier Science B.V. All rights reserved.

 

166.    T. Sogawa, H. Ando, and S. Ando

            "Spin relaxation dynamics of drifting electrons in GaAs narrow (10 nm) quantum wires"

            in Compound Semiconductors 1999, Institute Of Physics Conference Series Vol. 166 (Iop Publishing Ltd, Bristol, 2000), pp. 223-226.

 

            ABSTRACT: We investigated drift and diffusion dynamics of optically spin-polarized electrons in p-type rectangular GaAs/AlAs quantum wires with small (10 nm) lateral sizes by time- and spatially-resolved photoluminescence measurement. It is revealed that the drift process rapidly expands the spin-polarized electrons and that the spin polarization is maintained beyond 10 mum. The spin-reserved transport is probably due to the suppressed scattering between the spin-polarized electrons in a narrow one-dimensional channel.

 

167.    T. Sogawa, H. Ando, and S. Ando

            "Drift and diffusion dynamics of optically spin-polarized electrons in GaAs quantum wires"

            Physica E 7 (3-4), 1020-1024 (2000).

 

            ABSTRACT: We investigated drift and diffusion dynamics of optically spin-polarized electrons in rectangular p-doped GaAs/AlAs quantum wires (QWRs) with small (10 nm) lateral sizes by time resolved and spatially resolved photoluminescence measurement. It is revealed that the drifting electrons tend to maintain the spin polarization beyond 10 mu m, while the diffusion process causes the spatially-uniform spin relaxation with a spin relaxation time of about 300 ps. (C) 2000 Elsevier Science B.V. All rights reserved.

 

168.    T. Sogawa, H. Ando, and S. Ando

            "Spin-transport dynamics of optically spin-polarized electrons in GaAs quantum wires"

            Phys. Rev. B 61 (8), 5535-5539 (2000).

 

            ABSTRACT: We investigate the drift and diffusion dynamics of optically spin-polarized electrons in p-type rectangular GaAs/AlAs quantum wires with small (10 nm) lateral sizes by time- and spatially resolved photoluminescence measurement. The drift process causes a rapid expansion of the spin-polarized electrons, keeping the spin polarization beyond by 10 mu m. We theoretically analyze the transport characteristics of spin-polarized electrons and their spin-relaxation dynamics based on a drift-diffusion model which includes a spin-flip process; Experiment can be consistently explained by considering that the dependence of the diffusivity and mobility on the degree of the spin polarization, demonstrating the possibility of spin-dependent electron-electron scattering that affects the transport properties in one-dimensional structures.

 

169.    G. S. Solomon, M. Pelton, and Y. Yamamoto

            "Spontaneous emission control of single quantum dots"

            in Compound Semiconductors 1999, Institute Of Physics Conference Series Vol. 166 (Iop Publishing Ltd, Bristol, 2000), pp. 269-272.

 

            ABSTRACT: Modification of the spontaneous emission properties of a single InAs quantum dot is demonstrated using a epitaxial distributed-Bragg reflector microcavity that has been processed into posts with diameters ranging in size from 20 mum to 0.5 mum. The micropost structure isolates single quantum dots within the microcavity resonance, and creates a 3-dimensionally (3D) confined optical cavity. The discrete mode structure of the 3D cavity is observed, as well as the coupling of a single quantum dot to one of these modes in the weak coupling cavity QED regime.

 

170.    G. S. Solomon, M. Pelton, and Y. Yamamoto

            "Modification of spontaneous emission of a single quantum dot"

            Phys. Status Solidi A-Appl. Res. 178 (1), 341-344 (2000).

 

            ABSTRACT: Modification of spontaneous emission of a single InAs quantum dot is demonstrated using an epitaxial distributed Bragg reflector microcavity that has been post-growth processed into microposts. The micropost structure isolates single quantum dots within the microcavity resonance, and creates a three-dimensionally (3D) confined photonic cavity. Discrete mode structure from the 3D cavity is observed, as well as the coupling of a single quantum dot to one of these modes in the weak coupling cavity QED regime.

 

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

            "Electric field dependence of the flux-flow resistance and the electronic vortex structure in the cuprate superconductor Nd2-xCexCuOy"

            J. Low Temp. Phys. 118 (1-2), 59-74 (2000).

 

            ABSTRACT: In the temperature limit T much less than T-c c-axis oriented films of the cuprate super-conductor Nd2-xCexCuOy display an intrinsic step structure of the flux-flow resistance. Under current bias hysteretic voltage steps appear, whereas under quasi voltage bias negative differential resistance (NDR) is observed. For explaining these instabilities, we propose an electronic structure in the mixed state, consisting of subbands between the Fermi energy and the superconducting energy gap. The subbands originate from the Andreev bound states in the core of an isolated vortex, because of the interaction between vortices. Bloch oscillations of the quasiparticles in the narrow subbands are proposed as the mechanism generating the NDR.

 

172.    O. M. Stoll, A. Wehner, R. P. Huebener, and M. Naito

            "Negative differential flux-flow resistance and relaxation oscillations in the cuprate superconductor Nd2-xCexCuOy"

            Physica B 284, 827-828 (2000).

 

            ABSTRACT: We report on measurements of the flux-flow resistance in Nd2-xCexCuOy under voltage bias and present a model for the observed relaxation oscillations. (C) 2000 Elsevier Science B.V. All rights reserved.

 

173.    S. Sugita, T. Watanabe, and A. Matsuda

            "Atomic image of a CuO2 plane in the STM image of a Bi2Sr2CaCu2O8+delta cleaved surface"

            Phys. Rev. B 62 (13), 8715-8718 (2000).

 

            ABSTRACT: Clear atomic images of a Bi2Sr2CaCu2O8+delta (BSCCO) cleaved surface were obtained at room temperature by scanning tunneling microscopy (STM). The features of some observed images vary between two extreme cases, that is, the Bi-O plane image and the CuO2 plane image. And we have succeeded in obtaining a clear STM image of a CuO2 plane. From the CuO2 plane image, we found that this plane had two superstructures, one along the a axis and the other along the b axis. The periodicity of the superstructure along the b axis is (4-5)b, the same as that in the Bi-O plane, and the periodicity along the a axis is 2a. To explain these superstructures, we propose a lattice distortion model for the CuO2 plane of BSCCO.

 

174.    K. Sumitomo, H. Hibino, Y. Homma, and T. Ogino

            "Observation of incomplete surface melting of Si using medium-energy ion scattering spectroscopy"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 39 (7B), 4421-4424 (2000).

 

            ABSTRACT: The disordering of Si(lll) and Si(001) surfaces at high temperatures was investigated using medium-energy ion scattering (MEIS). We clearly observed an increase of MEIS scattering yield on channeling geometry at 1470 K for (111) surface and at 1520 K for (001) surface. These results support the formation of a liquid-like layer at the transition. We also found that there is a distinct difference in the mode of disordering on Si(lll) and Si(001) surfaces. The number of disordered atoms increases suddenly at the transition and remains constant above the transition on Si(lll) surface. This picture of the disordering is quite similar to the incomplete surface melting of Ge(lll) surface. On the other hand, the thickness of disordered layer on Si(001) surface continuously increases with temperature.

 

175.    K. Sumitomo, K. Shiraishi, Y. Kobayashi, T. Ito, and T. Ogino

            "Surface segregation and interdiffusion of Ge on Si(001) studied by medium-energy ion scattering"

            Thin Solid Films 369 (1-2), 112-115 (2000).

 

            ABSTRACT: The mechanism of the surface segregation and interdiffusion of Ge on Si(001) during epitaxial growth and annealing was studied using medium-energy ion scattering (MEIS). One monolayer of Ge was grown on Si(001) at 450 degrees C and annealed at 780 degrees C. The Ge was found to redistribute during the very early stages (within 1 min) of the annealing process and remained constant even after annealing at longer periods of time. Therefore, we conclude that the top few layers attain thermal equilibrium in a short period of time, such as less than 1 min. The coverage dependence of Ge distribution in the top few layers was also observed clearly from the surface of Ge deposited on Si(001) at 780 degrees C. This study strongly suggests that the subsurface phenomena should be considered in order to more accurately describe the Si/Ge interface structure. (C) 2000 Elsevier Science S.A. All rights reserved.

 

176.    N. Susa

            "Change in transmittance due to free carriers in two-dimensional photonic crystals"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 39 (11), 6288-6289 (2000).

 

            ABSTRACT: Numerical simulation revealed that photonic crystals consisting of dielectric and air cylinders should have a high contrast at moderate optical power densities (P) (less than 2 kW/cm(2)) when the number of stacked layers (ST, i.e, thickness) is larger than or equal to 32. The peak wavelength shifted by about -32 to -39 nm when P was increased from 0 to 10 kW/cm(2) at ST greater than or equal to 32 The peak wavelength shifted more with P with a Smaller ST because the peak wavelength at P = O became longer for the wavelengths examined.

 

177.    N. Susa

            "Transmittance for a two-dimensional photonic-crystal structure consisting of cylinders and liquid crystal"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 39 (6A), 3466-3467 (2000).

 

            ABSTRACT: The transmittance for a two-dimensional photonic-crystal structure consisting of 8 x 8 cylinders filled with or surrounded by a liquid crystal was numerically calculated using the scattering matrix method. When the refractive index of the liquid crystal was increased from 1.4 to 1.6, the transmittance for the liquid-crystal-filled cylinders increased from 4.5 x 10(-3) to 1 at a wavelength of 825 nm, and that for the cylinders surrounded by the liquid crystal increased from 1.3 x 10(-3) to 1 at 1060 nm (triangular lattice) and from 3.0 x 10(-4) to 1 at 1140 nm (square lattice).

 

178.    H. Suzuki

            "Self-enhancement in the electroluminescence of a near-infrared ionic dye"

            Appl. Phys. Lett. 76 (12), 1543-1545 (2000).

 

            ABSTRACT: This letter reports self-enhancement behavior observed in the near-infrared electroluminescence (EL) of an ionic dye, 2-[6-(4-dimethylaminophenyl)-2,4-neopentylene-1,3,5-hexatrienyl]-3-methy lbenzothiazolium perchlorate doped in poly(N-vinylcarbazole). The EL intensity measured under a constant current, and therefore, the external EL quantum efficiency (phi(ex)), increases with time both when the EL is generated continuously in a constant current mode and kept in a no-bias field, whereas it decreases in a reverse-bias field. With an enhancement factor of about 80 under a constant current of 0.1 mA/cm2, phi(ex) reaches the 1% photons/electron level. I conclude that the behavior originates from the enhanced electron and hole injection caused by the alignment of the doped ionic dye molecules along the bias field. (C) 2000 American Institute of Physics. [S0003-6951(00)01612-0].

 

179.    H. Suzuki, S. Hoshino, K. Furukawa, K. Ebata, C. H. Yuan, and I. Bleyl

            "Polysilane light-emitting diodes"

            Polym. Adv. Technol. 11 (8-12), 460-467 (2000).

 

            ABSTRACT: This paper discusses the material factors which have led to a recent breakthrough in polysilane light-emitting diodes (LEDs) made from a diaryl polysilane, poly[bis(p-n-butylphenyl)silane] (PBPS), by comparing them with LEDs which employ a conventional polysilane, poly(methylphenylsilane). In contrast to LEDs based on conventional polysilanes in which a weak ultraviolet Electroluminescence (EL) plas detected either with a strong broad visible EL or only at low temperatures, room-temperature pure near-ultraviolet EL was observed with a quantum? effciency of 0.1% photons/electron with an electron injecting Al electrode in PBPS-LEDs. We examined the spectroscopic, electronic and structural properties of PBPS, and ascribed to them the improvements observed in the EL characteristics. We also mention the possible future direction of polysilane LED research and other potential optoelectronics applications of polysilanes to the active medium of lasers. Copyright (C) 2000 John Wiley & Sons, Ltd.

 

180.    M. Suzuki and T. Watanabe

            "Discriminating the superconducting gap from the pseudogap in Bi2Sr2CaCu2O8+delta by interlayer tunneling spectroscopy"

            Phys. Rev. Lett. 85 (22), 4787-4790 (2000).

 

            ABSTRACT: Tunneling spectroscopy using a very thin stack of intrinsic Josephson junctions has revealed that the superconducting gap is definitely different from the pseudogap in the Bi2Sr2CaCu2O8+delta system. In the underdoped region, the conductance peak arising from the superconducting gap is independently observed in the dI/dV-V curve and its position is much lower than that of the pseudogap. Near the optimum doping level and in the overdoped region, both peaks are located in close proximity. These findings are in conflict with a previous understanding of the pseudogap.

 

181.    S. Suzuki, C. Bower, Y. Watanabe, and O. Zhou

            "Work functions and valence band states of pristine and Cs-intercalated single-walled carbon nanotube bundles"

            Appl. Phys. Lett. 76 (26), 4007-4009 (2000).

 

            ABSTRACT: The electronic structures and the work functions of pristine and Cs-intercalated single-walled carbon nanotube bundles were investigated using ultraviolet photoemission spectroscopy. The valence bands of the pristine bundles were considerably altered from those of graphite. A spectral shift to the higher binding energy side was observed in the Cs-intercalated sample. The work function of the pristine bundles was found to be 4.8 eV, which is 0.1-0.2 eV larger than that of graphite. A drastic decrease of the work function to about 2.4 eV was observed in the Cs-intercalated sample. (C) 2000 American Institute of Physics. [S0003-6951(00)05326-2].

 

182.    S. Suzuki, T. Kiyokura, F. Maeda, K. G. Nath, Y. Watanabe, T. Saitoh, and A. Kakizaki

            "Resonant photoemission spectroscopy of Ga 3d two-hole states of GaAs"

            J. Phys. Soc. Jpn. 69 (6), 1807-1811 (2000).

 

            ABSTRACT: The Ga 3d two-hole states were observed from GaAs(001)-c(4 x 4), -2 x 4, and (110)-1 x 1 surfaces using resonant photoemission spectroscopy. Multiplet terms (1)G, D-1, and F-3 were clearly distinguished at the photon energy around the 3(p) absorption threshold. The surface components of the two-hole states were observed in the spectra of the (001)-2 x 4 and (110)-1 x 1 surfaces having Ga atoms at the surfaces. The curve-fitting analysis revealed that the intensities of the surface component of the two-hole states were considerably smaller than those of the d(9) states. This is ascribed to the reduced absorption probabilities of the 3p electrons at the surfaces caused by the surface relaxation.

 

183.    A. Taguchi and Y. Hirayama

            "Stable site and stable charge state of a fluorine atom in Si"

            Solid State Commun. 116 (11), 595-597 (2000).

 

            ABSTRACT: We investigated a stable state of a fluorine (F) atom in Si bulk by using first-principles calculations. We considered Various interstitial sites and three charge states from +1 to -1. We found that over a wide range of Fermi levels, the bond center site in the +1 charge state is the most stable for an F atom. The present calculations suggest that the experimentally observed conductivity-dependent etching properties of F for Si are intimately related to the charge-state-dependent stable site of F in the Si bulk. (C) 2000 Elsevier Science Ltd. All rights reserved.

 

184.    A. Taguchi, T. Ohno, and T. Sasaki

            "Fluorine atoms in AlAs, GaAs, and InAs: Stable state, diffusion, and carrier passivation"

            Phys. Rev. B 62 (3), 1821-1827 (2000).

 

            ABSTRACT: We investigated various basic properties of fluorine (F) atoms in AlAs, GaAs, and InAs by using first-principles calculations. In these three semiconductors, we found that the -1 charge state is the most stable in a wide range of Fermi levels and that the F atom prefers sites surrounded by group-III atoms. These characteristics can be understood by considering that F has the largest electronegativity among the elements. We found that the diffusion properties, such as the diffusion path and the diffusion barrier height, are similar in these semiconductors. The estimated barrier heights are also comparable to the experimentally obtained barrier height in Al(0.48)In(0.52)AS, suggesting that the diffusion properties in AlxIn1-xAs are also similar. This implies that the experimentally observed selective F incorporation into AlxIn1-xAs is not due to the diffusion properties. It has been thought that the F atom forms a F-Si defect complex in AlxIn1-xAs, but we found that a F atom in the -1 charge state has stability comparable to that of a F-Si defect complex in binary semiconductors, suggesting that F-Si defect complexes and isolated F atoms in the -1 charge state coexist in AlxIn1-xAs. This coexistence is consistent with the observation of the F-Si defect complex, as well as observed F doping effects such as donor passivation and the decrease in the electron mobility. Based on the present calculations for the binary semiconductors, some characteristic properties of F in AlxIn1-xAs can be understood.

 

185.    A. Taguchi, K. Shiraishi, and T. Ito

            "Stable microstructures on a GaAs(111)A surface: The smallest unit for epitaxial growth"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 39 (7B), 4270-4274 (2000).

 

            ABSTRACT: We investigated the stability of various microstructures constructed by several Ga and As adatoms on a GaAs(111)A surface by using first-principles calculations. We estimated the formation energies of the structures as a function of the chemical potential and found a very stable structure composed of one Ga adatom and three As adatoms. Investigations of the elemental growth process imply that this structure is the smallest unit able to initiate epitaxial growth on the GaAs(111)A surface. Based on the calculation results, we propose a growth mechanism for the (111)A surface, which is characterized by the formation of a stable structure and the subsequent coalescence of the structure. This mechanism qualitatively explains the observed differences in the properties of the growth islands on (111)A and (001) surfaces.

 

186.    A. Taguchi, K. Shiraishi, and T. Ito

            "Self-surfactant effect of As on a GaAs(111)A surface"

            Appl. Surf. Sci. 162, 354-358 (2000).

 

            ABSTRACT: We have theoretically investigated the effects of Ga- and As-adatom adsorption on a GaAs(111)A surface to reveal the epitaxial growth mechanism by using first-principles calculations. We found that the formation of Ga-Ga and Ga-As coupled structures make the Ga-vacancy site stable, while our previous study showed that the site is not the most stable site for one Ga-adatom adsorption. We also found that the Ga-As coupled structure is more stable than the Ga-Ga coupled structure, clearly indicating that As has a stronger stabilization effect on the Ga-vacancy site for a Ga atom. The GaAs lattice is maintained by the As adsorption in a self-organizing manner. Accordingly, As acts as a self-surfactant element. The importance of As suggested by the present calculations is consistent with the experimentally known fact that rather high As pressure is needed for the growth of the GaAs epitaxial layers on a GaAs(111)A surface. (C) 2000 Elsevier Science B.V. All rights reserved.

 

187.    A. Taguchi, K. Shiraishi, and T. Ito

            "First-principles study of the elemental process of epitaxial growth on a GaAs(111)A surface"

            Phys. Rev. B 61 (19), 12670-12673 (2000).

 

            ABSTRACT: We theoretically investigated the elemental process of epitaxial growth on a GaAs(111)A surface by using first-principles calculations. We estimated the formation energies of various microstructures as a function of the chemical potential, and found a very stable microstructure formed by a single Ga and three As adatoms. This structure may be the smallest unit for the epitaxial growth. The formation of such a stable microstructure is crucial for stimulating the growth process. The need for such a stable microstructure characterizes the growth mechanism for a GaAs(111)A surface, and results in the different properties of the growth island between the GaAs(111)A and GaAs(001) surfaces.

 

188.    T. Takagahara

            "Theory of exciton doublet structures and polarization relaxation in single quantum dots"

            Phys. Rev. B 62 (24), 16840-16855 (2000).

 

            ABSTRACT: The mechanism of exciton doublet structures in quantum dots is identified as the long-range part of the electron-hole exchange interaction which is emphasized by the anisotropic shape of quantum dots. The physical origin of the energetic order of the orthogonally polarized exciton states of each doublet is clarified by inspecting the spatial distribution of the exciton polarization. The key concepts to understand the energetic order are the node configuration of the distribution function of exciton polarization and the dipole-dipole interaction energy originating from the long-range electron-hole exchange interaction. The population relaxation and the polarization relaxation of excitons are studied and the extremely slow polarization relaxation within exciton doublet states is predicted. It is also found that the inter-doublet cross-relaxation between orthogonally polarized exciton states occurs as efficiently as the population relaxation.

 

189.    T. Takagahara

            "Theory of exciton fine structures and extremely slow spin relaxation in single quantum dots"

            J. Lumines. 87-9, 308-311 (2000).

 

            ABSTRACT: A comprehensive theory is proposed to describe the polarization-dependent fine splitting of exciton doublet lines and the relation between the polarization direction and the energy level order of doublet states in anisotropic quantum dots. The extremely slow spin relaxation within exciton doublet states is predicted. At the same time, it is found that the cross-relaxation between orthogonally polarized exciton states is significant. (C) 2000 Elsevier Science B.V. All rights reserved.

 

190.    Y. Takahashi

            "Single-electron device - An ultimate device that operates on just a single electron"

            Ntt Rev. 12 (1), 12-16 (2000).

 

            ABSTRACT: As we approach a new age in which the amount of information communication is expected to increase explosively, energy-saving in communication processing has become an urgent issue. The single-electron device is the ultimate low-power-consumption device because, as the name implies, it operates on just a single electron. This article describes the operation mechanism of such devices and new fabrication method for single-electron devices developed by NTT Basic Research Laboratories. It also overviews new promising functions of such devices.

 

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

            "Multigate single-electron transistors and their application to an exclusive-OR gate"

            Appl. Phys. Lett. 76 (5), 637-639 (2000).

 

            ABSTRACT: The two-input exclusive-OR (XOR) function was implemented by a multigate single-electron transistor (SET). Two types of multigate SETs operating at 40 K were fabricated on a top silicon layer of an Si-on-insulator wafer by using a special technique called pattern-dependent oxidation. Two small gate electrodes which act as the input gates were formed over the small SET island. The output current of the devices took a high level when a high voltage was applied to either of the two gates with the other gate grounded, while it took a low level when both gates were grounded or fed with a high voltage. It is striking that such an XOR function can be implemented with just one device. (C) 2000 American Institute of Physics. [S0003-6951(00)02005-2].

 

192.    H. Takayanagi, H. Ando, and T. Fujisawa

            "From quantum effects to quantum circuits - Toward the quantum computer"

            Ntt Rev. 12 (1), 17-25 (2000).

 

            ABSTRACT: The quantum computer is designed to harness the unique uncertainties of quantum mechanics at the micro level to enable ultra-rapid calculations at hitherto unimaginable speeds. In this article, we describe the progress of research from the quantum effect to quantum gate circuits and the quantum computer, citing three research fields at the NTT Basic Research Laboratories - quantum dot molecules, optical quantum dots and superconducting loops.

 

193.    H. Tamura, K. Shiraishi, and H. Takayanagi

            "Ferromagnetism in semiconductor dot array"

            Jpn. J. Appl. Phys. Part 2 - Lett. 39 (3AB), L241-L243 (2000).

 

            ABSTRACT: Ferromagnetism in semiconductor-dot arrays is theoretically predicted. The two types of bipartite semiconductor-dot arrays which we propose exhibit flat band characteristics. According to the Lieb theorem, ferromagnetism is predicted, although our designed dot arrays do not contain any magnetic elements. We also investigate the typical dot-radius and inter-dot distance for the realization of the semiconductor-dot ferromagnetism, and several applications are discussed.

 

194.    S. Tarucha, D. G. Austing, S. Sasaki, Y. Tokura, W. van der Wiel, and L. P. Kouwenhoven

            "Effects of Coulomb interactions on spin states in vertical semiconductor quantum dots"

            Appl. Phys. A-Mater. Sci. Process. 71 (4), 367-378 (2000).

 

            ABSTRACT: The effects of direct Coulomb and exchange interactions on spin states are studied for quantum dots contained in circular and rectangular mesas. For a circular mesa a spin-triplet favored by these interactions is observed at zero and nonzero magnetic fields. We tune and measure the relative strengths of these interactions as a function of the number of confined electrons. We find that electrons tend to have parallel spins when they occupy nearly degenerate single-particle states. We use a magnetic field to adjust the single-particle state degeneracy, and find that the spin-configurations in an arbitrary magnetic field are well explained in terms of two-electron singlet and triplet states. For a rectangular mesa we observe no signatures of the spin-triplet at zero magnetic field. Due to the anisotropy in the lateral confinement single-particle state degeneracy present in the circular mesa is lifted, and Coulomb interactions become weak. We evaluate the degree of the anisotropy by measuring the magnetic field dependence of the energy spectrum for the ground and excited states, and find that at zero magnetic field the spin-singlet is more significantly favored by the lifting of level degeneracy than by the reduction in the Coulomb interaction. We also find that the spin-triplet is recovered by adjusting the level degeneracy with magnetic field.

 

195.    S. Tarucha, D. G. Austing, Y. Tokura, W. G. van der Wiel, and L. P. Kouwenhoven

            "Direct Coulomb and exchange interaction in artificial atoms"

            Phys. Rev. Lett. 84 (11), 2485-2488 (2000).

 

            ABSTRACT: We determine contributions from the direct Coulomb and exchange interactions to the total interaction in artificial semiconductor atoms. We tune the relative strengths of the two interactions and measure them as a function of the number of confined electrons. The electrons tend to have parallel spins when they occupy nearly degenerate single-particle states. We use a magnetic field to adjust the single-particle-state degeneracy, and find that the spin configurations in an arbitrary magnetic field are well explained in terms of two-electron singlet and triplet states.

 

196.    G. Tatara and Y. Tokura

            "Electronic pressure on the ferromagnetic domain wall"

            Solid State Commun. 116 (10), 533-538 (2000).

 

            ABSTRACT: The scattering of electron by a domain wall in a nano-wire is studied perturbatively to the lowest order. The correction to the thermodynamic potential of the electron system due to scattering is calculated from the: phase shift. The wall profile is determined by taking account of this correction, and the result indicates that the wall in a ferromagnet with a small exchange coupling can be squeezed to be very thin to lower the electron energy. (C) 2000 Published by Elsevier Science Ltd.

 

197.    T. Tateno and Y. Jimbo

            "Stochastic mode-locking for a noisy integrate-and-fire oscillator"

            Phys. Lett. A 271 (4), 227-236 (2000).

 

            ABSTRACT: We investigated the ways in which noise influences lower-order mode-locked regions (Arnold tongues) in the parameter space of an integrate-and-fire model with a periodically modulated threshold. To study the stochastic mode-locking in the model, we use the first-passage-time problem of the Ornstein-Uhlenbeck process with a periodic boundary to define the Markov operator governing the transition of a threshold phase density. We present a numerical method for evaluating stochastic bifurcation by spectral analysis of the operator and briefly discuss the implications for biological systems. (C) 2000 Elsevier Science B.V. All rights reserved.

 

198.    Y. Tokura, S. Sasaki, D. G. Austing, and S. Tarucha

            "Single-electron tunneling through two vertically coupled quantum dots"

            Physica E-Low-Dimensional Systems & Nanostructures 6 (1-4), 676-679 (2000).

 

            ABSTRACT: Electron states and tunneling properties of two vertically coupled quantum dots are analyzed. The energy mismatch of the dots affects the phase diagram as a function of the quantum mechanical coupling and magnetic field normal to the plane. A magnetic field parallel to the barrier mixes the single particle states and also induces a singlet-triplet transition. (C) 2000 Elsevier Science B.V. All rights reserved.

 

199.    E. Toyoda, H. Takayanagi, and H. Nakano

            "Gate-modified giant Andreev backscattering in a superconductor-semiconductor junction"

            J. Phys. Soc. Jpn. 69 (6), 1801-1806 (2000).

 

            ABSTRACT: We investigated giant Andreev backscattering (GAB) in a superconductor (S)-semiconductor two-dimensional electron gas (2DEG) junction with a special gate configuration: a split gate which produces a quantum point contact (QPC) and an ordinary wide gate set between S and the QPC, which alters the properties of the diffusive transport in the 2DEG. Different combinations of the two gates voltages offered us a many "samples" for one junction, which enabled us to systematically study GAB. By applying a negative split gate voltage, the number of modes in the QPC was decreased and a crossover from the reentrant conductance of the disordered 2DEG to enhanced (peaked) QPC conductance was observed. The peak width at different degrees of diffusiveness clearly showed that coherent Andreev backscattering is essential for the enhancement. We discuss the influence of the bias voltage and the magnetic field on the enhancement quantitatively.

 

200.    E. Toyoda, H. Takayanagi, and H. Nakano

            "Gate-modified giant Andreev backscattering"

            Physica B 284, 569-570 (2000).

 

            ABSTRACT: We investigated giant Andreev backscattering in a superconductor (S) - two-dimensional electron gas (2DEG) junction with two kinds of gate: a quantum point contact (QPC) and an ordinary wide gate. Though the diffusive 2DEG itself displayed reentrant conductance, by attaching a QPC we observed conductance enhancement (peak) at zero energy. The bias voltage and the magnetic field dependence of the enhancement at different degrees of dirtiness showed that phase conjugation between an electron and a hole is essential for enhancement. (C) 2000 Elsevier Science B.V. All rights reserved.

 

201.    S. Toyoda, M. Fujiki, C. H. Yuan, and R. West

            "Ionochromism and increase in fluorescence quantum yield of an ether-substituted polysilylene upon adding lithium ions in solution"

            Macromolecules 33 (5), 1503-1504 (2000).

 

            ABSTRACT:

202.    M. Uematsu

            "Diffusion simulation of ultra-low-energy implanted boron in silicon"

            Jpn. J. Appl. Phys. Part 2 - Lett. 39 (9AB), L895-L897 (2000).

 

            ABSTRACT: dfWe have simulated the diffusion of boron (B) after ultra-low-energy implantation in silicon during post-implantation annealing, based on our model [M. Uematsu: Jpn. J. Appl. Phys. 38 (1999) 3433]. When the B concentration is not so high (less than or similar to 1 x 10(21) cm(-3)), the experimental B depth profiles are fitted using the model with taking into account B segregation to silicon oxide at the surface. When the B concentration is very high (greater than or similar to 1 x 10(21) cm(-3)), however, the simulation underestimates the diffusion, which is attributable to boron-enhanced diffusion. The self-interstitial emission from a silicon boride layer in the high B concentration region is taken into account, and the simulation well reproduces the experimental profiles.

 

203.    M. Uematsu

            "Simulation of boron diffusion in high-dose BF2 implanted silicon"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 39 (4A), 1608-1611 (2000).

 

            ABSTRACT: We have simulated the transient enhanced diffusion (TED) of boron (B) after amorphizing BF2 ion implantation in silicon. A unified simulation is done based on the models for B diffusion, for TED by self-interstitial clusters, for B clustering and B precipitation, and for end-of-range (EOR) defects. The simulation overestimates the diffusion using the normal values for the efficiency of EOR defects as a source of self-interstitials. The simulation well reproduces the experimental profiles when the efficiency is reduced so that the defects maintain self-interstitial concentration at thermal equilibrium values. This reduction is attributable to the presence of fluorine at EOR defect sites, which may prevent the release of self-interstitials, In addition, the second peak near the amorphous/crystalline (a/c) interface observed in experimental profiles is reproduced, and the peak is attributed to B precipitates.

 

204.    M. Uematsu

            "Transient enhanced diffusion and deactivation of high-dose implanted arsenic in silicon"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 39 (3A), 1006-1012 (2000).

 

            ABSTRACT: We have simulated the transient enhanced diffusion (TED) of high-concentration arsenic (As) in silicon during postimplantation annealing. A unified simulation was done, based on models for As diffusion, for TED by self-interstitial clusters, and for end-of-range (EOR) defects. We have taken into account As complex formation and As precipitation, which cause the As deactivation. We have satisfactorily fitted As depth profiles at high doses (1-5 x 10(15) cm(-2)) in a wide range of annealing conditions (750-1000 degrees C). The As complex formation plays an important role in determining the diffusion profiles through the self-interstitial emission upon the formation at lower temperatures and through As deactivation at higher temperatures. The simulation results suggest that boron (B) segregation toward the As tail regions is associated with self-interstitial distributions determined by EOR defects and As profiles.

 

205.    M. Uematsu, H. Kageshima, and K. Shiraishi

            "Oxidation simulation of (111) and (100) silicon substrates based on the interfacial silicon emission model"

            Jpn. J. Appl. Phys. Part 2 - Lett. 39 (11B), L1135-L1137 (2000).

 

            ABSTRACT: Silicon oxidation of(111) and (100) substrates is simulated based on the interfacial silicon emission model. Large silicon emission from the interface, which governs the oxidation rate at the interface, plays an important role in determining the substrate-orientation dependence. The simulation is done by changing only the rate of Si-atom emission from the interface. the emission rate for (111) is about 0.4 times that for (100). Using a unified set of parameters, the whole range of oxide thickness is fitted in a wide range of oxidation temperatures (800-1200 degreesC) and oxygen pressures (1-20 atm).

 

206.    M. Uematsu, H. Kageshima, and K. Shiraishi

            "Simulation of high-pressure oxidation of silicon based on the interfacial silicon emission model"

            Jpn. J. Appl. Phys. Part 2 - Lett. 39 (10A), L952-L954 (2000).

 

            ABSTRACT: Silicon oxidation using high-pressure oxygen, where the rate shows less-than-linear dependence, is simulated based on the interfacial silicon emission model. The oxidation reaction of the emitted Si atoms in the oxide, which controls the oxidation rare at the interface, plays an important role in determining the oxidation pressure dependence. We introduce reaction terms for the oxidation in the oxide so as to fit the oxide thickness at oxygen pressures of 1-20 arm. The simulation is made using constant parameter values for oxidation reaction by changing only the oxidant solubility in the oxide in proportion to oxygen pressure.

 

207.    M. Uematsu, H. Kageshima, and K. Shiraishi

            "Unified simulation of silicon oxidation based on the interfacial silicon emission model"

            Jpn. J. Appl. Phys. Part 2 - Lett. 39 (7B), L699-L702 (2000).

 

            ABSTRACT: We have simulated silicon oxidation taking into account the emission of a large number of silicon atoms from the interface, which governs the silicon-oxidation rate. The silicon emission model enables the simulation to be done using the oxidant self-diffusivity in the oxide with a single activation energy. The simulation has deduced a silicon emission rate that exhibits a break point in its activation energy at around 1000 degrees C, which is attributed to the viscoelastic properties of the oxide, Using a unified set of parameters, the whole range of oxide thickness is fitted in a wide range of oxidation temperatures (800-1200 degrees C) without any empirical modifications.

 

208.    W. G. van der Wiel, S. De Franceschi, T. Fujisawa, J. M. Elzerman, S. Tarucha, and L. P. Kouwenhoven

            "The Kondo effect in the unitary limit"

            Science 289 (5487), 2105-2108 (2000).

 

            ABSTRACT: We observe a strong Kondo effect in a semiconductor quantum dot when a small magnetic field is applied. The Coulomb blockade for electron tunneling is overcome completely by the Kondo effect, and the conductance reaches the unitary Limit value. We compare the experimental Kondo temperature with the theoretical predictions for the spin-1/2 Anderson impurity model. Excellent agreement is found throughout the Kondo regime. Phase coherence is preserved when a Kondo quantum dot is included in one of the arms of an Aharonov-Bohm ring structure, and the phase behavior differs from previous results on a non-Kondo dot.

 

209.    T. Watanabe, T. Fujii, and A. Matsuda

            "Pseudogap in Bi2Sr2CaCu2O8+delta studied by measuring anisotropic susceptibilities and out-of-plane transport"

            Physica C 341, 931-932 (2000).

 

            ABSTRACT: We find in the Bi2Sr2CaCu2O8+delta system that the characteristic temperatures T-chi* (below which the uniform susceptibilities chi (ab)(T) (H perpendicular to c) and chi (c)(T) (H // c) decrease) and T-rhoc* (below which the out-of-plane resistivity rho (c)(T) shows typical upturn) coincide for all doping levels. We attribute the T dependence of chi 's and rho (c) to the anomalous (pseudogapped) density-of-states (DOS) in high-T-c cuprates. In addition, an analysis of the anisotropy in the T dependence of chi 's shows that the high-temperature component (d chi /dT < 0) is also caused by a DOS effect.

 

210.    T. Watanabe, T. Fujii, and A. Matsuda

            "Pseudogap in Bi2Sr2CaCu2O8+delta studied by measuring anisotropic susceptibilities and out-of-plane transport"

            Phys. Rev. Lett. 84 (25), 5848-5851 (2000).

 

            ABSTRACT: find in the Bi2Sr2CaCu2O8+delta system that the characteristic temperatures T-chi* [below which the uniform susceptibilities chi(ab)(T) (H perpendicular to c) and chi(c)(T) (H parallel to c) decrease] and T-rho c* [below which the out-of-plane resistivity rho(c)(T) shows typical upturn] coincide for all doping levels. We attribute the T dependence of chi's and rho(c), to the anomalous (pseudogapped) density of states (DOS) in high-T-c cuprates, Furthermore, the anisotropy in the T dependence of chi's is universal, i.e., chi, proportional to 1.6 chi(ab), showing that there is only a single T-dependent component in the chi's. This implies that the Curie-like behavior (d chi/dT < 0) observed in overdoped samples is also caused by a DOS effect.

 

211.    Y. Watanabe and F. Maeda

            "Effect of strain on the chemical bonds in InAs nanocrystals self-organized on GaAs and Se-terminated GaAs surfaces"

            Appl. Surf. Sci. 162, 625-629 (2000).

 

            ABSTRACT: We employed surface sensitive photoelectron spectroscopy (PES) using synchrotron radiation to investigate the strain of both deposited InAs and GaAs substrates with and without Se-termination. The two distinct chemical components comprising Ga-As bonding and In-As bonding states in the As 3d spectrum are clearly observed for the first time, which indicates that the strain in both the deposited InAs and GaAs substrates can be separately evaluated using the core-level energy difference between the respective core-level chemical components. This difference between the chemical components of Ga 3d and As 3d levels for both two kinds of samples is found to be independent of InAs deposition time, and to be almost the same as that of a bulk GaAs, implying that no strain is generated in both two type GaAs substrates. On the other hand, in the case of the deposited InAs, this value increases with an increase in the layer thickness of InAs for the InAs/GaAs system and approaches to a bulk InAs value, whereas, there exits only a slight change for the InAs/Se/GaAs system at the very early stages of InAs growth and is almost the same as a bulk InAs value. These results suggest that the driving force for the formation of InAs nanocrystals in the InAs/GaAs system is the elastic strain, whereas, in the InAs/Se/GaAs system, passivation-induced self-organizing mechanism is crucial. (C) 2000 Elsevier Science B.V. All rights reserved.

 

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

            "A new superconducting barium cuprate prepared by molecular beam epitaxy"

            Physica C 338 (1-2), 29-37 (2000).

 

            ABSTRACT: This paper reviews the MBE-synthesis and structural characterization of a new superconducting barium cuprate Ba2CuO4-delta (Te less than or equal to 90 K). The keys to the successful synthesis of this superconductor are (1) the preparation of Ba2CuO3 in a CO2/H2O-free environment and (2) structural transformation from insulating Ba2CuO3 with 1D CuO chains to superconducting Ba2CuO4-delta with 2D CuO2 planes by strong ozone oxidation after growth. The merits of MBE as a potential synthetic route in the search for new cuprate superconductors are also discussed. (C) 2000 Elsevier Science B.V. All rights reserved.

 

213.    Y. Yamamoto

            "Semiconductor physics - Half-matter, half-light amplifier"

            Nature 405 (6787), 629-630 (2000).

 

            ABSTRACT:

214.    M. Yamashita, M. Koashi, T. Mukai, M. Mitsunaga, and N. Imoto

            "Dynamics of evaporative cooling in magnetically trapped atomic hydrogen"

            Phys. Rev. A 62 (3), art. no.-033602 (2000).

 

            ABSTRACT: We study the evaporative cooling of magnetically trapped atomic hydrogen on the basis of the kinetic theory of a Bose gas. The dynamics of trapped atoms is described by the coupled differential equations, considering both the evaporation and dipolar spin relaxation processes. The numerical time-evolution calculations quantitatively agree with the recent experiment of Bose-Einstein condensation with atomic hydrogen. It is demonstrated that the balance between evaporative cooling and heating due to dipolar relaxation limits the number of condensates to 9X10(8) and the corresponding condensate fraction to a small value of 4% as observed experimentally.

 

215.    H. Yoshikawa, Y. Andoh, M. Yamamoto, K. Fukuzawa, T. Tamamura, and T. Ohkubo

            "7.5-MHz data-transfer rate with a planar aperture mounted upon a near-field optical slider"

            Opt. Lett. 25 (1), 67-69 (2000).

 

            ABSTRACT: We fabricated a planar aperture-mounted (PAM) slider by use of a focused ion beam to demonstrate fast data acquisition for near-field optical data storage. The aperture (200 nm X 500 nm) was formed upon the Ti-coated air-bearing surface of the slider and was directly illuminated with a laser (lambda = 532 nm) beam spot by use of an objective lens (N.A., 0.55). The light transmitted through the aperture was modulated by a Ti-coated SiO2 disk with 200- and 400-nm-wide line-and-space (L&S) patterns engraved by electron-beam lithography. The optical throughput of the taperless aperture was greater than 0.02. By use of the PAM slider, 400- and 200-nm L&S signals were detected at linear velocities of 6 and 3 m/s, respectively, corresponding to a data-transfer rate of 7.5 MHz. (C) 2000 Optical Society of America.

 

216.    J. D. Yu, M. Natsuisaka, H. Kato, S. Matsumoto, K. Kinoshita, T. Itami, and S. Yoda

            "Studies on molten glass sealing in diffusion coefficient measurements using shear cell technique"

            Rev. Sci. Instrum. 71 (5), 2111-2116 (2000).

 

            ABSTRACT: To develop a shear cell technique for measuring the diffusion coefficient of molten materials with high vapor pressure, molten silica glass was used to seal the vapor leak from the clearance between the cell and the rotating rod. An apparatus was designed to investigate the sealing ability of several molten silica glasses. Using Corning 0211, 7059, and 7740 silica glasses, Ar could be sealed under 150 kPa in the 1100-1500 K temperature range. The corresponding viscosities of the molten silica glasses in the sealing temperature range were 10(5.3)-10(3.8) Pa s. Based on the results of Ar sealing experiments, the configuration of molten glass sealing was used to seal the As vapor leak in InxGa1-xAs diffusion coefficient measurement experiments. The As vapor leak was successfully sealed and excellent diffusion coefficient measurement data were obtained using the shear cell technique during microgravity experiments carried out on sounding rocket. (C) 2000 American Institute of Physics. [S0034-6748(00)04505-6].