1.         H. Ahn, H. Nakano, T. Nishikawa, and N. Uesugi

            "Simultaneous measurement of absorption and X-ray emission from preformed plasma generated by ultrashort prepulse"

            Japanese Journal Of Applied Physics Part 2-Letters 35 (2A), L154-L157 (1996).

 

            ABSTRACT: The first simultaneous measurement of the reflectivity and the X-ray yield from the preformed plasma was performed with a fine temporal resolution between the prepulse and the main ionization pulse. Enhancement of the X-ray emission at the long temporal separation is due to the increase of the absorption of an intense ultrashort laser pulse in a preformed plasma with a scale length longer than laser wavelength. The maximum response of X-ray emission at 22.5 degrees and the weak dependence on the polarization of input laser light infer that collisional absorption with additional resonance absorption in a nonuniform critical density profile is the main absorption process in the preformed plasma.

 

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

            "Superconducting transistors using InAs-inserted-channel InAlAs/InGaAs inverted HEMTs"

            Supercond. Sci. Technol. 9 (4A), A83-A86 (1996).

 

            ABSTRACT: A newly fabricated Josephson field effect transistor (JOFET) is coupled with a two-dimensional electron gas (2DEG) in a strained InAs quantum well inserted into an In0.52Al0.48As/In(0.53)Ga(0.47)AS inverted modulation-doped structure with an HEMT-type gate. We indicate the improved characteristics of the JOFET with the HEMT-type gate, instead of the MIS-type gate. The superconducting critical current l(c) as well as the junction's normal resistance R(N) can be completely controlled via a gate voltage of about -1 V; this provides voltage gain over unity, the first time for a JOFET.

 

3.         T. Akazaki, J. Nitta, H. Takayanagi, T. Enoki, and K. Arai

            "Highly confined two-dimensional electron gas in an In0.52Al0.48As/In0.53Ga0.47As modulation-doped structure with a strained InAs quantum well"

            J. Electron. Mater. 25 (4), 745-748 (1996).

 

            ABSTRACT: This paper examines a detailed analysis by Shubnikov-de Haas measurements of the effective mass of two-dimensinal electron gas (2DEG) in an In0.52Al0.48As/In0.53Ga0.47As modulation-doped (MD) structure with an InAs quantum well inserted into the InGaAs channel (InAs-inserted channel). The measured effective mass of 2DEG in the InAs-inserted-channel MD structure is in good agreement with the calculated one of the strained InAs layer on In0.53Ga0.47As. This indicates that almost all of the 2DEG forms in the strained InAs quantum well. These results show that the InAs-inserted-channel MD structure improves the electron confinement, since the BDEG is confined in the InAs quantum well with the thickness of 4 nm.

 

4.         T. Akazaki, H. Takayanagi, and T. Enoki

            "Kink effect in an InAs-inserted-channel InAlAs/InGaAs inverted HEMT at low temperature"

            IEEE Electron Device Lett. 17 (7), 378-380 (1996).

 

            ABSTRACT: The authors have investigated the kink effect in an InAs-inserted-channe1 InAlAs/InGaAs inverted HEMT at low temperature. The kink effect was not observed at both 77 and 300 K, but it appeared at 3.2 K. It is shown that the kink effect is caused at low drain voltages by the suppression of the drain current due to an increase in the source access resistance and at higher drain voltages by the increase in the drain current due to holes generated by impact ionization.

 

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

            "A Josephson field effect transistor using an InAs-inserted-channel In0.52Al0.48As/In0.53Ga0.47As inverted modulation-doped structure"

            Appl. Phys. Lett. 68 (3), 418-420 (1996).

 

            ABSTRACT: A Josephson field effect transistor (JOFET) was coupled with a two-dimensional electron gas in a strained InAs quantum well inserted into an In0.52Al0.48As/In0.53Ga0.47As inverted modulation-doped structure. The characteristics df this JOFET are much improved over previous devices by using a high electron mobility transistor (HEMT)-type gate instead of the usual metal-insulator-semiconductor (MIS)-type gate. The superconducting critical current as well as the junction normal resistance are completely controlled via a gate voltage of about -1 V; this provides voltage gain over 1 for a JOFET. (C) 1996 American Institute of Physics.

 

6.         B. Albinsson, H. Teramae, J. W. Downing, and J. Michl

            "Conformers of saturated chains: Matrix isolation, structure, IR and UV spectra of n-Si(4)Me(10)"

            Chem.-Eur. J. 2 (5), 529-538 (1996).

 

            ABSTRACT: Infrared and ultraviolet spectra of the gauche and anti conformers of matrix-isolated permethyl-n-tetrasilane have been obtained separately by taking advantage of thermally induced gauche-to-anti conversion and of wavelength-selective photochemical destruction of either conformer. The resolved UV spectrum of the gauche conformer provides the first piece of experimental evidence in favor of the recently proposed reinterpretation of conformational effects on tetrasilane electronic states. According to this, it is not the energy but the intensity of the lowest singlet excitation that changes dramatically as the SiSiSiSi dihedral angle is varied, as a result of an avoided crossing between sigma sigma* and sigma pi* states. Implications for the general understanding of sigma conjugation in simple terms are discussed. Unconstrained MP2/6-31G* optimization predicts the existence of a third backbone conformer (ortho), with a dihedral angle of about 90 degrees. Its predicted (HF/3-21G*) mid-IR spectrum is indistinguishable from that of the gauche conformer, and the matrix-isolation spectra thus provide no evidence for or against its presence.

 

7.         B. Albinsson, H. Teramae, H. S. Plitt, L. M. Goss, H. Schmidbaur, and J. Michl

            "Matrix-isolation IR and UV spectra of Si3H8 and Si4H10: Isomers and conformers of oligosilanes"

            J. Phys. Chem. 100 (21), 8681-8691 (1996).

 

            ABSTRACT: Matrix-isolation IR and UV spectra of Si3H8, i-Si4H10, and the two conformers of n-Si4H10 have been recorded. A quantitative separation of the IR spectrum of n-Si4H10 into contributions from the anti and gauche forms was accomplished by a combination of matrix annealing and selective monochromatic photodestruction experiments. A qualitative separation of their UV spectra was achieved as well. The IR spectra of Si3H8, i-Si4H10, and the two conformers of n-Si4H10 have been assigned by comparison with results of ab initio calculations, which reproduce the frequencies and even the relative intensities quite well. The calculations predict dihedral angles omega of 180 degrees and 57 degrees for the anti and the gauche conformer of n-Si4H10, respectively, and confirm earlier predictions of nearly equal stability for an isolated molecule. In the matrix, the anti conformer is more stable, The conformational effects on the UV spectrum of n-Si4H10 are not those anticipated from simple models of the Sandorfy or ladder C type, in that it is primarily not the energy but the intensity of the low-energy excited singlet states that depends strongly on the SiSiSiSi dihedral angle omega. This result is interpreted in terms of data from 6-in-8 CASSCF 6-31G* calculations, which predict an avoided crossing between a strongly allowed sigma sigma* B state and a very weakly allowed sigma pi* B state as omega changes, with the former lower in energy at 180 degrees and the latter lower at 0 degrees. Consequences for attempts to understand the effects of conformation on optical spectra of polysilanes are noted.

 

8.         S. B. Altner and M. Mitsunaga

            "Dephasing-rephasing balancing in photon echoes by excitation induced frequency shifts"

            Phys. Rev. Lett. 76 (10), 1747-1750 (1996).

 

            ABSTRACT: The excitation dephasing in solids resulting from the interaction with neighboring species' excitations is investigated. The frequency shifts due to these interactions are identified by the observation of partial dephasing-rephasing balancing in bichromatic photon-echo experiments applied to rare-earth ion doped crystals. The experimental observations are in good agreement with the predictions obtained from a model which accounts for the disorder in the crystal and for the stochastic nature of the excitations.

 

9.         S. B. Altner, G. Zumofen, U. P. Wild, and M. Mitsunaga

            "Photon-echo attenuation in rare-earth-ion-doped crystals"

            Phys. Rev. B 54 (24), 17493-17507 (1996).

 

            ABSTRACT: We study the optical properties of rare-earth-ion-doped inorganic crystals with an emphasis on the dependence of two-pulse photon echoes on the excitation density in the system. The experimental investigations concentrate on Pr3+: Nd3+: Eu3+ codoped Y2SiO5 and YAlO3 crystals at low temperatures. With two pulses of one laser the echo is induced in one ion species and with a third, ''scrambler'' pulse of a second laser another species is excited. These scrambler excitations lead to a dephasing and thus to an echo attenuation which depends on the strength, frequency, and time of the scrambler pulse. The spectral sensitivity of the echo attenuation is used for a spectroscopic technique: ''photon-echo attenuation spectroscopy.'' As a function of the delay time t(s) between the scrambler pulse and the onset of the two-pulse echo sequence the attenuation shows a very specific behavior dictated by the excitation-induced frequency shifts (EFS's). For t(s) between the two echo-inducing pulses the echo intensity is partially regained by the ''dephasing-rephasing balancing'' of the reversible EFS's. For the theoretical description a stochastic model is introduced and the dephasing by excitation-induced lattice vibrations and by EFS's are analyzed in detail. The present results are discussed in the light of previous experimental and theoretical investigations.

 

10.       H. Ando, H. Saito, A. ChavezPirson, H. Gotoh, and N. Kobayashi

            "Excitonic optical properties in fractional-layer-superlattice wire structures"

            Appl. Phys. Lett. 69 (11), 1512-1514 (1996).

 

            ABSTRACT: We report on the evolution of the excitonic optical features from two dimensions (2D) to one dimension (1D) in GaAs/AlAs fractional-layer-superlattice (FLS) wire structures. We demonstrate for the first time how the excitonic optical properties continuously evolve from 2D to 1D by introducing the FLS lateral compositional modulation in an AlGaAs quantum well. We also present a theory numerically analyzing the optical absorption properties in the FLS wires. Present theory accurately reproduces the experimental results using the AlAs/GaAs FLS wires and clarifies the main optical features associated with excitons in the intermediate quantum-confinement regime between 1D and 2D. (C) 1996 American Institute of Physics.

 

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

            "Triangular-facet laser with optical waveguides grown by selective area metalorganic chemical vapor deposition"

            Japanese Journal Of Applied Physics Part 2-Letters 35 (4A), L411-L413 (1996).

 

            ABSTRACT: A triangular prism-shaped GaAs/AlGaAs laser with rectangular optical waveguides at three corners is proposed and its preliminary lasing characteristics and waveguiding of lasing light are presented. This structure is grown by selective area metalorganic chemical vapor deposition (MOCVD) and consists of a (111)B growth plane and (110) sidewall facets. The advantage of the triangular facet is that the prism growth proceeds while maintaining the equilateral triangle shape even if there is a little fluctuation in the size or shape of the mask and if the layer thickness is increased up to about 1.5 mu m. Lasing at room temperature is observed by optical pumping of low energy (E(th) < 10 pJ). The lasing light can be successfully extracted from the point of the rectangular waveguides. The lasing mode is found to be a ring cavity made of an inscribed equilateral triangle by the longitudinal mode spacing.

 

12.       V. N. Antonov and H. Takayanagi

            "Essence of ''proximity'' model for interference phenomena in mesoscopic normal metal-superconducting structures"

            Czech. J. Phys. 46, 2313-2314 (1996).

 

            ABSTRACT: In this work we studied the transport properties of mesoscopic silver wires with three types of superconducting loops at the stubs. The geometry of the structures was chosen to verify the models proposed to explain interference phenomena in such systems. In two types of structures we observed magnetoresistance oscillations of the silver wire, which are consistent with the predictions of quasi-classical ''proximity'' theory. The oscillations resulted from the periodic suppression of the induced condensate by the Meissner current.

 

13.       K. Arimura and N. Hagita

            "Image screening based on projection pursuit for statistical image recognition"

            Syst. Comput. Jpn. 27 (3), 60-70 (1996).

 

            ABSTRACT: A preprocessing method, called image screening, is presented to improve the recognition rate and efficiency in statistical image recognition. The problem of detecting a specified object in input images is treated as a two-class classification problem in which the image falls into both a set of subimages in the target object (figure) class and the other set of subimages in the ground class. An image screening algorithm based on projection pursuit selects a candidate set of subimages that is similar to the object class, it rejects the remaining set using screening filters whose design is based on projection pursuit. The feature space for recognition is obtained from the selected subimages, Two binds of measures to evaluate the performance of image screening are defined. The error rate in image screening is related to the total recognition rate of the system and the rejection rate of the noise image is related to the recognition efficiency. Two kinds of experiments were conducted, one to detect the eye and mouth areas in a face image and the other to detect the text area in a document image. Experimental results for these two tasks demonstrate that our method improves the recognition accuracy and efficiency.

 

14.       M. Asahi, K. Takei, and Y. Maeda

            "Selective dry etching to reveal compositional inhomogeneity in Co-Cr magnetic films"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 35 (4A), 2149-2150 (1996).

 

            ABSTRACT: We studied a selective dry-etching method designed to reveal compositional inhomogeneity in Co-Cr alloy magnetic films. The dry etching was carried out using reactive sputtering with CO2 as the working gas. Preferential etching of Co was confirmed by depth profiling using Auger electron spectroscopy. The compositional microstructure revealed by the dry etching was observed using scanning electron microscopy.

 

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

            "Single electron charging and single electron tunneling in sub-micron AlGaAs/GaAs double barrier transistor structures"

            Solid-State Electron. 40 (1-8), 237-240 (1996).

 

            ABSTRACT: Transport phenomena in a specially optimized vertical asymmetric sub-micron Al0.28Ga0.72As/GaAs double barrier structure with modulation-doped barriers is investigated by applying a bias to a special Schottky side gate, which allows the effective area of the conducting channel to be finely ''tuned''. For a sufficiently small device, the electrical properties of the controllable quantum dot bounded by well defined heterostructure barriers and an adjustable side wall potential are expected to be governed by single electron charging, and single electron resonant tunneling. Single electron transistor (SET) operation is possible because the number of electrons in the dot, n, can be varied one-by-one with the side gate. The drain current flowing through the conducting channel in response to a small drain voltage is strongly modulated by the gate voltage close to ''pinch-off'' as n approaches zero, and oscillations in the drain current persist up to about 25 K. A gate modulated zero current region of Coulomb blockade, step-like features, and resonances exhibiting negative differential resistance are clearly observed at low bias. Although this technology is very promising for the realization of SET operation at temperatures well above 4.2 K, the temperature dependence of the Coulomb blockade is an important limitation. We describe the evolution of the conductance oscillations and the degradation of Coulomb blockade with temperature from 0.3 K up to 25 K, and propose that co-tunneling in a small system containing just a ''few'' electrons in which the zero-dimensional energy level spacing is significant and comparable to the Coulomb charging energy is important, and is likely to be more complex than that documented for large planar dot structures containing ''many'' electrons.

 

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

            "A new design for submicron double-barrier resonant tunneling transistors"

            Semicond. Sci. Technol. 11 (3), 388-391 (1996).

 

            ABSTRACT: A new fabrication technique is described for a submicron vertical AlGaAs/GaAs double-barrier resonant tunnelling transistor which is ideal for investigating single electron charging of, and single electron tunnelling through, a quantum dot containing just a 'few' electrons. The electrical characteristics and figures of merit are presented to demonstrate the improved 'squeezing' capability of the Schottky gate which is located around, and partially on, the etched side wall of the device mesa after a combined dry and wet etch to a point below the two barriers, and contrasted with those of an earlier design where etching is stopped above the two barriers.

 

17.       S. M. Barnett, C. R. Gilson, B. Huttner, and N. Imoto

            "Field commutation relations in optical cavities"

            Phys. Rev. Lett. 77 (9), 1739-1742 (1996).

 

            ABSTRACT: We introduce a simple quantum theory of the lossy beam splitter. When applied to describe a Fabry-Perot cavity this leads to apparently anomalous commutation relations for the intracavity operators. We show that these unfamiliar properties are nevertheless consistent with the fundamental canonical commutator for the vector potential and electric field operators. This result is derived as a consequence of causality as applied to the properties of mirror reflection coefficients.

 

18.       S. M. Barnett, B. Huttner, R. Loudon, and R. Matloob

            "Decay of excited atoms in absorbing dielectrics"

            J. Phys. B-At. Mol. Opt. Phys. 29 (16), 3763-3781 (1996).

 

            ABSTRACT: We present calculations of the rates of decay of an excited atom embedded in an absorbing dielectric. Decay can occur by spontaneous emission into transverse radiative modes of the electromagnetic field and by Joule heating via longitudinal coupling of the atom to the dielectric. The spontaneous emission (transverse) decay rate is modified in a dielectric, being the free-space rate multiplied by the real part of the refractive index at the transition frequency of the atom. There is a further modification due to the difference between the macroscopic dielectric field and the local field at the position of the atom. In addition there is a longitudinal decay rate which is proportional to the imaginary part of the dielectric constant and therefore vanishes in non-absorbing media. We derive expressions for each of these rates of decay and discuss the physical mechanisms leading to them.

 

19.       A. ChavezPirson, H. Ando, H. Saito, N. Kobayashi, and H. Kanbe

            "Rapid relaxation of hot carriers in GaAs fractional-layer superlattice quantum wires"

            Appl. Phys. Lett. 69 (2), 218-220 (1996).

 

            ABSTRACT: We measure the hot carrier relaxation in two GaAs quantum wire arrays made from fractional-layer superlattices (FLS). Using femtosecond optical pump-probe spectroscopy, we measure the differential transmission spectra for various pump-probe time delays from which we determine the carrier thermalization times. Although the two FLS structures have different degrees of one-dimensional confinement at the band edge, we observe rapid (<2 ps) and efficient carrier relaxation in both cases with no sign of the inhibited relaxation predicted for ideal one-dimensional structures. We believe that FLS quantum wife structures avoid relaxation bottlenecks because the shape of the FLS confinement potential produces high energy states which are two dimensional in character and which facilitate rapid energy relaxation. (C) 1996 American Institute of Physics.

 

20.       K. Ebata, T. Matsuo, T. Inoue, Y. Otsuka, C. Kabuto, A. Sekiguchi, and H. Sakurai

            "Intramolecular oligomerization of disilalkylene {-Me(2)Si(CH2)(n)SiMe(2)-} bridged cyclic triacetylenes"

            Chem. Lett. (12), 1053-1054 (1996).

 

            ABSTRACT: Disilalkylene bridged cyclic triacetylenes are prepared and subjected to the transition metal complex mediated reactions. In particular, the reaction with (methylcyclopentadienyl)tricarbonyl-manganese gave a variety of pi-electron systems such as fulvene, dimethylenecyclobutene, and biallene. Structures and reactions of these pi-electron systems are described.

 

21.       M. Edwards and D. R. Badcock

            "Global-motion perception: Interaction of chromatic and luminance signals"

            Vision Res. 36 (16), 2423-2431 (1996).

 

            ABSTRACT: A global dot-motion stimulus was employed in order to investigate the interaction between luminance and chromatic signals in motion processing. Thresholds are determined by measuring the minimum number of dots which need to move in a coherent fashion in a field of randomly moving dots in order for the observers to be able to determine the direction of coherent motion. We found that: (1) observers could not track an achromatic signal-dot which changes its luminance polarity between frame transitions. The addition of a consistent chromatic signal allowed observers to track such a dot when the dot contained low- (8%) luminance contrast but this ability was impaired as the luminance contrast was increased; (2) the addition of chromatic contrast to a dot which contained consistent low-luminance contrast could result in threshold elevation. For fixed contrast chromatic and luminance signals, the presence and degree of threshold elevation depended upon the spatiotemporal properties of the dot motion; (3) the ability of observers to extract a global-motion signal carried by a group of dots of one colour was impaired by the addition of a number of additional-noise dots of a different colour. These results are interpreted as indicating that: (1) the motion-selective cells that are sensitive to chromatic signals are also sensitive to luminance signals; (2) the combined chromatic and luminance and purely luminance motion cells are pooled to form a single pathway prior to global-motion extraction; and (3) the negative interaction observed between the chromatic and luminance signals is likely to be due to the differences in the processing speeds of the combined luminance and chromatic and the purely luminance sensitive motion cells. Copyright (C) 1996 Elsevier Science Ltd.

 

22.       M. Edwards, D. R. Badcock, and S. Nishida

            "Contrast sensitivity of the motion system"

            Vision Res. 36 (16), 2411-2421 (1996).

 

            ABSTRACT: A number of experiments were conducted to investigate how global-motion performance varies with luminance contrast. When all the dots in the stimulus were the same contrast, performance improved with increasing contrast up to about the 15% level (Experiment 1). Increasing the contrast beyond this level had no additional effect on performance. When the contrast of a subgroup of the dots was varied, differential effects on performance could be obtained for contrasts up to the 80% level (Experiment 2). These results are interpreted as indicating that the performance saturation observed in Experiment 1 was due to the attainment of a performance ceiling at the global-motion level, and not due to contrast-response saturation of the underlying local-motion detectors. The results of earlier studies that have apparently found conflicting results (saturation vs no saturation) are discussed in light of the present results. Copyright (C) 1996 Elsevier Science Ltd.

 

23.       M. Edwards and S. Nishida

            "Extraction of motion transparency: No direction specific masking"

            Invest. Ophthalmol. Vis. Sci. 37 (3), 3382-3382 (1996).

 

            ABSTRACT:

24.       S. R. Friberg, S. Machida, M. J. Werner, A. Levanon, and T. Mukai

            "Observation of optical soliton photon-number squeezing"

            Phys. Rev. Lett. 77 (18), 3775-3778 (1996).

 

            ABSTRACT: We report the photon-number squeezing of optical solitons. 2.7 ps pulses were launched as solitons down a 1.5 km optical fiber. For energies slightly above that of fundamental solitons, they broadened spectrally due to self-phase modulation caused by chi((3)) nonlinearities. Filtering away outlying components of the broadened spectra squeezed the soliton's photon-number fluctuations to 2.3 dB (41%) below the shot-noise limit. Accounting for losses, this corresponds to 3.7 dB (57%) photon-number squeezing. A quantum field-theoretic model shows that the outlying spectral components have large energy fluctuations, so that their removal causes squeezing.

 

25.       K. J. Friedland, Y. Hirayama, T. Fujisawa, T. Saku, and S. Tarucha

            "Tunnelling and transfer between 1D and 2D electrons in adjusted quantum wells with thin barrier"

            Physica B 227 (1-4), 31-33 (1996).

 

            ABSTRACT: By the technique of in situ focused ion-beam implantation in an underlying doping layer followed by molecular beam epitaxy overgrowth of a double quantum-well we have fabricated adjusted one-dimensional and two-dimensional electrons with very thin barrier between them. Each of the electron systems could be contacted separately. The tunnelling resistance between electron layers increases at high in-plane magnetic fields. With magnetic fields perpendicular to the wire we can investigate the coupling of lower one-dimensional subband while in the parallel direction higher subband states hybridise. In the first case, we observed clear resonance in the tunnelling and electron transfer.

 

26.       O. M. Froehlich, A. Beck, R. Gross, H. Sato, and M. Naito

            "In-plane penetration depth of high-temperature superconductors with single and double CuO layers"

            Europhys. Lett. 36 (6), 467-472 (1996).

 

            ABSTRACT: A dc technique based on the measurement of the magnetic-field dependence of the critical current of bicrystal grain boundary Josephson junctions (GBJs) is used to precisely determine the temperature change Delta lambda(ab)(T) = lambda(ab)(T) = lambda(ab)(0) of the in-plane London penetration depth of YBa2Cu3O7-delta (YBCO) and La1.85Sr0.15CuO4-delta (LSCO) thin films. The resolution of the applied measuring technique is better than 0.2 Angstrom and the measured dependences are not sensitive to extrinsic influences. Over a wide temperature range the data obtained for different high-temperature superconductors confirm with high accuracy the theoretical prediction for a d(x)2(-y)2-symmetry of the superconducting order parameter. The same temperature dependence is measured for materials with single and double CuO layers.

 

27.       M. Fujiki

            "Polysilane helix. Cooperative single-screw-sense helix takeover effects"

            Abstr. Pap. Am. Chem. Soc. 212, 203-POLY (1996).

 

            ABSTRACT:

28.       M. Fujiki

            "A correlation between global conformation of polysilane and UV absorption characteristics"

            J. Am. Chem. Soc. 118 (31), 7424-7425 (1996).

 

            ABSTRACT:

29.       T. Fujisawa and S. Tarucha

            "Resonant tunneling properties of single electron transistors with a novel double-gate geometry"

            Appl. Phys. Lett. 68 (4), 526-528 (1996).

 

            ABSTRACT: We describe the operation of single electron transistors with a double-gate geometry defined by Ga focused ion beam implanted in-plane gates and line Schottky gates. The in-plane gates are used to squeeze the channel and to increase the charging energy. The Schottky gates are placed on the channel to form the tunnel junctions. lndependent control of these gates is useful to define the geometry of single electron transistors. We found strong resonances exhibiting negative differential resistance in the small devices, which is attributed to tunneling through zero-dimensional states when the barrier has a parabolic-shaped potential. (C) 1996 American Institute of Physics.

 

30.       T. Fukuda

            "Random adatom heights in Ge/Si(111)-5x5 surfaces"

            Surf. Sci. 351 (1-3), 103-110 (1996).

 

            ABSTRACT: Germanium-induced 5 x 5 reconstruction on Si(111) surfaces was investigated by scanning tunneling microscopy and spectroscopy. Although all adatoms in the Ge/Si(111)-5 x 5 structure were crystallographically equivalent, their topographic heights were not the same in the filled-state image. Height differences up to similar to 0.8 Angstrom between neighboring adatoms in the same unit were recognized. Site specific tunneling spectroscopy showed that according to the height depression the adatom dangling bond states shifted towards the empty-state across the surface Fermi level. The adatom undulation may originate from mixing of the substrate silicon atoms into the Ge/Si(111)-5 x 5 structure. Preferential sites for Ge/Si replacement are discussed in terms of the strain energy due to the mixing. The distributions of the height differences did not change for Ge thicknesses from 2-6 ML, indicating that 5 x 5 reconstruction may contain substrate Si atoms even for a 6 ML thick Ge layer.

 

31.       T. Fukuda and T. Ogino

            "Oxygen adsorption on Ge-covered Si(100) surfaces"

            Surf. Sci. 358 (1-3), 748-752 (1996).

 

            ABSTRACT: We studied oxygen chemisorption on GB-covered Si(100) surfaces by AES, XPS and STM. Epitaxial Ge overlayers, 1 and 2 ML, on Si(100) sur-faces were oxidized in situ at room temperature. Initial uptake of oxygen adsorption on the surface terminated by a monolayer Ge was reduced by similar to 1/5 compared with that on a Si(100) surface measured in O-KLL AES intensities. The oxygen interaction for the surface covered by 2 ML Ge was in the same range as that of a Ge(100) surface, indicating that the top two layers, surface dimers and the underneath layer, play critical roles in oxygen interaction. The STM study for the surface partly covered by Ge showed that oxygen reacted with the Si substrate in preference to the Ge islands.

 

32.       K. Furukawa, M. Fujino, and N. Matsumoto

            "Superlattice structure of octa-tert-butylpentacyclo[4.2.0.0(2,5).0(3,8).0(4,7)]octasilane found by reinvestigation of X-ray structure analysis"

            J. Organomet. Chem. 515 (1-2), 37-41 (1996).

 

            ABSTRACT: X-ray structure analysis is reinvestigated for octa-tert-butylpentacyclo[4.2.0.0(2,5).0(3,8).0(4,7)]octasilane ((t)BuSi)(8) (trigonal, R32, a = b = 12.232(3)Angstrom, c = 125.186(4)Angstrom gamma = 120 degrees, V = 16221(2)Angstrom(3), Z = 15, R = 0.049, R(w) = 0.052). The crystal symmetry and the molecular structure are the same as those in our previous report. It is, however, found that the molecule forms a superlattice structure, in which the c axis of the unit cell is five times as long as that given in the previous report.

 

33.       H. Gomi

            "Is stiffness a byproduct or a target?"

            Behav. Brain Sci. 19 (3), 450-& (1996).

 

            ABSTRACT: To examine the model of the biological motor control proposed by A. Smith, this commentary briefly introduces some result of stiffness measurements during multi-joint arm movements, and, in the light of these results, discusses how likely it is that stiffness is a control parameter and that the cerebellum solely codes the stiffness.

 

34.       H. Gomi and M. Kawato

            "Equilibrium-point control hypothesis examined by measured arm stiffness during multijoint movement"

            Science 272 (5258), 117-120 (1996).

 

            ABSTRACT: For the last 20 years, it has been hypothesized that well-coordinated, multijoint movements are executed without complex computation by the brain, with the use of springlike muscle properties and peripheral neural feedback loops. However, it has been technically and conceptually difficult to examine this ''equilibrium-point control'' hypothesis directly in physiological or behavioral experiments. A high-performance manipulandum was developed and used here to measure human arm stiffness, the magnitude of which during multijoint movement is important for this hypothesis. Here, the equilibrium-point trajectory was estimated from the measured stiffness, the actual trajectory, and the generated torque. Its velocity profile differed from that of the actual trajectory. These results argue against the hypothesis that the brain sends as a motor command only an equilibrium-point trajectory similar to the actual trajectory.

 

35.       T. Goto, T. Watanabe, K. Kiinoshita, A. Matsuda, M. Sera, and T. Fukase

            "Cu-NMR study on high-T-c cuprate La1.89Ca1.11Cu2O6+delta (La2126)"

            Czech. J. Phys. 46, 2175-2176 (1996).

 

            ABSTRACT: The temperature dependence of Cu-NMR relaxation rate T-1(-1) and spectra have been measured for La-based high-T-c, cuprate La1.89Ca1.11Cu2O6+delta with the bilayer type of CuO planes. The shift showed a monotonic decrease with lowering temperature in the normal state, showing that this compounds belongs to the lightly doped region. The Curie Weiss temperature dependence of (T1T)(-1) down to T-c shows that the pseudo spin-gap does nor always exist in the bilayer systems.

 

36.       T. Goto, T. Watanabe, K. Kinoshita, A. Matsuda, M. Sera, and T. Fukase

            "Cu-NMR study on high-T-c cuprate La(1.89)Ca(1.11)Cu(2)O6+delta (La2126)"

            J. Low Temp. Phys. 105 (3-4), 401-406 (1996).

 

            ABSTRACT: Cu-NMR spectra and the nuclear spin-lattice relaxation rate T-1(-1) have been studied intensively on the bilayer type high-T-C cuprate La1.89Ca1.11Cu2O6+delta (La2126). The resonance line shift showed a monotonic decrease with lowering temperature in the normal state, indicating that this compound belongs to the lightly-doped region. The Curie-Weiss temperature dependence of (T1T)(-1) in the normal state shows that the pseudo spin-gap does nor always exist in the light-doped bilayer systems.

 

37.       T. Goto, T. Watanabe, K. Kinoshita, A. Matsuda, M. Sera, S. Sakatsume, and T. Fukase

            "Cu-NMR study on bilayer high-T-c cuprate La1.89Ca1.11Cu2O6+delta (La2126)"

            J. Phys. Soc. Jpn. 65 (9), 2768-2771 (1996).

 

            ABSTRACT: The temperature dependence of the Cu-63/65-NMR relaxation rate T-1(-1) and the spectrum of the lightly doped high-T-c cuprate La1.89Ca1.11Cu2O6+delta (La2126) with bilayer CuO planes have been studied. The field-swept spectrum tvas explained by assuming that there are two Cu sites with quadrupole frequencies of (63)nu(Q) = 25.6 and 32 MHz. The Knight shift decreased monotonically with decreasing temperature in the normal state, which is consistent with the reported result that the system belongs to the Lightly doped region where the hole content is less than the optimum value. The Curie-Weiss temperature dependence of (T1T)(-1) = 2600/(T + 110) (K. s)(-1) in the normal state down to T-c indicates that the pseudo-spin gap does not always exist in lightly doped bilayer systems.

 

38.       Y. Goto, T. Kaneko, and N. Uesugi

            "Elimination of spherical aberration in grazing-incidence optics with cylindrical mirrors"

            Japanese Journal Of Applied Physics Part 2-Letters 35 (10B), L1378-L1380 (1996).

 

            ABSTRACT: The design of an optics system consisting of four cylindrical mirrors is described. Two symmetrically installed cylindrical mirrors reduce spherical aberration. This set of cylindrical mirrors can focus vertically or horizontally. Astigmatism is also eliminated by using a second set of mirrors. The spot size of this optics system is estimated to be about 2 mu m.

 

39.       H. Gotoh, H. Ando, and H. Kanbe

            "Excitonic optical properties in semiconductor thin quantum boxes of intermediate regime between zero and two dimensions"

            Appl. Phys. Lett. 68 (15), 2132-2134 (1996).

 

            ABSTRACT: We discuss the optical properties in thin quantum boxes based on a theoretical analysis that rigorously treats excitonic confinement effects in the intermediate regime between zero and two dimensions. Our theory can exactly analyze not only the excitonic ground state but also higher energy states, and thus can simulate whole absorption spectra near the band edge region. We also report novel exciton electro-absorption effects found in the intermediate confinement regime. (C) 1996 American Institute of Physics.

 

40.       Y. Harada, H. Takayanagi, and A. A. Odintsov

            "Cooper-pair tunneling in small junctions with tunable Josephson coupling"

            Phys. Rev. B 54 (9), 6608-6613 (1996).

 

            ABSTRACT: We investigate Cooper-pair tunneling in a circuit consisting of two dc-superconducting quantum interference devices in series, with a gate capacitively coupled to the central island. Measurements cover a wide range of values of the ratio between Josephson coupling energy E(J) and charging energy E(C). The E(J)/E(C) ratio dependence of the supercurrent is well described by the orthodox theory provided that strong fluctuations of the Josephson phase due to the electromagnetic environment are taken into account. Our data can be interpreted in terms of squeezing of the charge fluctuations with decreasing E(J)/E(C) ratio.

 

41.       I. Hashimoto, T. Mashiko, and T. Imada

            "Somatic evoked high-frequency magnetic oscillations reflect activity of inhibitory interneurons in the human somatosensory cortex"

            Evoked Potential.-Electroencephalogr. Clin. Neurophysiol. 100 (3), 189-203 (1996).

 

            ABSTRACT: High-frequency potential oscillations in the range of 300-900 Hz have recently been shown to concur with the primary response (N20) of the somatosensory cortex in awake humans. However, the physiological mechanisms of the high-frequency oscillations remained undetermined. We addressed the issue by analyzing magnetic fields during wakefulness and sleep over the left hemisphere to right median nerve stimulation with a wide bandpass (0.1-2000 Hz) recording with subsequent high-pass (> 300 Hz) and low-pass (< 300 Hz) filtering. With wide bandpass recordings, high-frequency magnetic oscillations with the main signal energy at 580-780 Hz were superimposed on the N20m during wakefulness. Isofield mapping at each peak of the high-pass filtered and isolated high-frequency oscillations showed a dipolar pattern and the estimated source for these peaks was the primary somatosensory cortex (area 3b) very close to that for the N20m peak. During sleep, the high-frequency oscillations showed dramatic diminution in amplitude while the N20m amplitude exhibited a moderate increment, This reciprocal relation between the high-frequency oscillations and the N20m during a wake-sleep cycle suggests that they represent different generator substrates. We speculate that the high-frequency oscillations represent a localized activity of the GABAergic inhibitory interneurons of layer 4, which have been shown in animal experiments to respond monosynaptically to thalamo-cortical input with a high-frequency (600-900 Hz) burst of short duration spikes. On the other hand, the underlying N20m represents activity of pyramidal neurons which receive monosynaptic excitatory input from the thalamus as well as a feed-forward inhibition from the interneurons.

 

42.       N. Hatakenaka and S. Kurihara

            "Josephson micromaser"

            Czech. J. Phys. 46, 2311-2312 (1996).

 

            ABSTRACT: A maser action using a current-biased mesoscopic Josephson junction within a high-Q micro-cavity is discussed. A Josephson junction behaves like an artificial atom as far as the interaction with the photon field is concerned. Under a certain bias current, the Josephson atom is excited or pumped;by macroscopic resonant tunneling. When the pumping overcomes the loss of photons from the cavity, the maser action is possible. Quantum statistical properties of photons are also investigated numerically, based on a Jayns-Cummings model with pumping and cavity damping. We found that a mesoscopic Josephson junction placed in the high-Q microcavity acts as a thresholdless maser with sub-Poissonian photon statistics.

 

43.       N. Hatakenaka and S. Kurihara

            "Josephson cascade micromaser"

            Phys. Rev. A 54 (2), 1729-1732 (1996).

 

            ABSTRACT: The possibility of maser action using a current-biased mesoscopic Josephson junction in a high-Q microcavity is discussed. A mesoscopic Josephson junction behaves like an artificial atom as far as the interaction with the photon field is concerned. Under a certain bias current, the Josephson ''atom'' is resonantly excited or pumped by quantum-mechanical fluctuations of the Josephson phase, i.e., macroscopic resonant tunneling. When the pumping overcomes the loss of photons from the cavity, maser action is possible. Quantum statistical properties of photons are also investigated numerically, taking into acount the microcavity effect on the basis of a Jaynes-Cummings model with pumping and cavity damping. We found that a mesoscopic Josephson junction within the high-Q microcavity acts as a thresholdless maser with sub-Poissonian photon statstics.

 

44.       N. Hatakenaka and S. Kurihara

            "Supercurrent-controlled multiple-beam interference of Andreev-reflected quasiparticle waves"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 35 (5A), 2638-2641 (1996).

 

            ABSTRACT: Multiple-beam interference of Andreev-reflected quasiparticle waves is studied. Unlike the two-beam interferometer, the multiple-beam interferometer produces sharp and large interference fringes. The interference can be controlled by the supercurrent flowing through one-dimensional superconductors.

 

45.       N. Hatakenaka and S. Kurihara

            "Effect of surface acoustic waves on single electron tunneling in scanning tunneling microscopes"

            Physica B 220, 723-726 (1996).

 

            ABSTRACT: We study the effect of surface acoustic waves (SAWs) on single electron tunneling (SET) in scanning tunneling microscopes (STMs). SAWs periodically change the distance between STM tips and substrates. Since tunneling rates have an exponential dependence on the tunneling distance, SAWs strongly affect tunneling phenomena, especially SET oscillations. We numerically study the regularity of the SET oscillations through distributions of tunneling events under both current and voltage biases. It is found that the degree of the regularity is associated with the localization of the phase difference between SAW and SET at tunneling.

 

46.       N. Hatakenaka and S. Kurihara

            "Locking of the tunneling distance in STM-type junctions: The influence of surface acoustic waves"

            Phys. Rev. B 53 (15), 10402-10405 (1996).

 

            ABSTRACT: We numerically investigate the influence of surface acoustic waves on single-electron tunneling in STM-type tunnel junctions. Surface acoustic waves (SAW's) propagate dong a solid surface and periodically change the distance between STM tips and substrates. Since tunneling rates have an exponential dependence on tunneling distance, SAW strongly affects tunneling phenomena. It is found that the regularity of the SET oscillations is associated with a locking phenomenon of the tunneling distance, where the tunneling distance behaves like the Brownian motion of a particle in the tilted-washboard potential.

 

47.       J. Herfort and Y. Hirayama

            "Transport in gated undoped GaAs/AlxGa1-xAs heterostructures in the high density and high mobility range"

            Appl. Phys. Lett. 69 (22), 3360-3362 (1996).

 

            ABSTRACT: The two-dimensional electron gas with electron densities higher than 10(16) m(-2) which is formed at the interface in undoped GaAs/AlxGal-xAs heterostructure by the electric field generated by a top gate is studied. Despite the high electron density in the sample, rather high mobilities of about 100 m(2)/Vs can be achieved with sufficient small gate leakage currents. The population of the second subband is studied from Shubnikov-de Haas measurements in these devices. (C) 1996 American Institute of Physics.

 

48.       J. Herfort, Y. Takagaki, K. J. Friedland, R. Hey, K. Ploog, J. Takahara, and K. Gamo

            "Temperature dependence of the bend resistance of composite fermions in narrow cross junctions"

            Physica B 227 (1-4), 170-172 (1996).

 

            ABSTRACT: The bend resistance in narrow cross junctions exhibits dips near filling factors v = 1/2p. We show that the temperature dependence of the dip near v = 1/2 is consistent with the interpretation that the dips arise due to the ballistic transmission of composite fermions. At temperatures higher than 0.3 K the temperature dependence is strong reflecting small Fermi energy of the composite fermions. The bend resistance saturates at lower temperatures as expected for the ballistic transmission of fermionic particles.

 

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

            "'1x1' to (7x7) phase transition on Si(111) under heating current"

            Surf. Sci. 364 (2), L587-L590 (1996).

 

            ABSTRACT: We investigated the influence of heating current on the phase transition of the (7 x 7) reconstruction on a Si(lll) surface using ultra-high vacuum scanning electron microscopy. Just below the phase transition temperature, the (7 x 7) reconstruction nucleates at the upper edges of the steps, and the (7 x 7) phase coexists with the '1 x 1' phase on the terrace. In this situation, the size of the (7 x 7) phase depends on the direction of the heating current, and the (7 x 7) phase is larger under the step-up current than under the step-down current. This dependence can be explained assuming that adatoms in the '1 x 1' phase are forced to move in the same direction as the current.

 

50.       H. Hibino and T. Ogino

            "Exchanges between group-III (B, Al, Ga, In) and Si atoms on Si(111)-root 3x root 3 surfaces"

            Phys. Rev. B 54 (8), 5763-5768 (1996).

 

            ABSTRACT: High-temperature scanning tunneling microscopy (HT-STM) observation of exchanges between group-III and Si atoms on Si(111)-root 3X root 3 surfaces is reported. The exchange rates are obtained from the HT-STM images as a function of the temperature. The activation energies of the exchange are 1.4, 1.7, and 1.4 eV for Al, Ga, and In adatoms, respectively. The prefactors are within the range 10(10)-10(13) s(-1). These prefactors are close to that for the exchange between Pb and Si adatoms on a Si(111)-root 3X root 3 surface and much larger than that for the exchange between Pb and Ge adatoms on a Ge(111)-c(2X8) surface. The adatom exchange mechanisms on Si(111)-root 3X root 3 and Ge(111)-c(2 X 8) are different. We also investigated exchanges between B and Si atoms in the second layer of the Si(111)-root 3X root 3 surface. The obtained activation energy and prefactor are 3.5 eV and 1X10(18) s(-1) and the activation energy is close to that of B diffusion in bulk Si.

 

51.       H. Hibino and T. Ogino

            "Exchanges between Si and Pb adatoms on Si(111) (vol 328, pg L547, 1995)"

            Surf. Sci. 364 (1), L547-L547 (1996).

 

            ABSTRACT:

52.       H. Hibino and T. Ogino

            "Phase transition of 12x1 reconstruction on Si(331)"

            Surf. Sci. 358 (1-3), 102-106 (1996).

 

            ABSTRACT: Reconstructive phase transition on Si(331) has been investigated using scanning tunneling microscopy (STM) and reflection high-energy electron diffraction (RHEED). The (12 x 1)-to-(1 x 1) phase transition proceeds in two stages. In the first stage, more and more domain boundaries of the reconstruction appear in STM image as the temperature increases. During this stage, the RHEED spot intensities show changes characteristic to the domain boundary proliferation In the second stage, all the RHEED spots related to the reconstruction disappear, and the RHEED pattern changes into 1 x 1.

 

53.       H. Hibino and T. Ogino

            "Two-stage phase transition of 12x1 reconstruction on Si(331)"

            Phys. Rev. B 53 (23), 15682-15687 (1996).

 

            ABSTRACT: Reconstructive phase transition on Si(331) has been investigated using scanning tunneling microscopy and reflection high-energy electron diffraction. The (12x1)-to-(1x1) phase transition consists of two stages. In the lower-temperature stage, the domain size of the reconstruction decreases as the temperature increases. This stage is the process of domain boundary proliferation and is a continuous phase transition. In the higher-temperature stage, the reconstructed (331) facets disappear, and this stage is a first-order phase transition.

 

54.       T. Hirahara

            "Auditory modeling in Japan"

            Acustica 82, S88-S88 (1996).

 

            ABSTRACT:

55.       Y. Hirayama

            "Gate-controlled lateral diodes formed in undoped heterostructure"

            Japanese Journal Of Applied Physics Part 2-Letters 35 (10A), L1245-L1248 (1996).

 

            ABSTRACT: We developed a gate-controlled diode that has a Schottky gate on an undoped heterostructure with n- and p-type ohmic regions at opposite ends of the gate. Either two-dimensional electron or hole gas (2DEG or 2DHG) can be formed at the same heterointerface by an electric field from the surface gate. When this diode is biased in the forward direction, current flow is observed in the two gate voltage ranges corresponding to the formation of 2DEG and 2DHG in the undoped heterostructure. When the drain voltage between the p- and n-type contacts exceeds a certain value, a double injection forms a novel current channel that differs from the conventional 2DEG or 2DHG.

 

56.       Y. Hirayama

            "Formation of two-dimensional electron and hole gases in undoped AlxGa1-xAs/GaAs heterostructures"

            J. Appl. Phys. 80 (1), 588-590 (1996).

 

            ABSTRACT: Two-dimensional electron or hole gases (2DEG or 2DHG) are confined at the same interface in an undoped heterostructure by an electric field generated by a top gate. The combination of ion-implanted ohmic regions, an undoped heterostructure with superlattice barriers, and a metal gate is used to fabricate structures by a conventional process without self-alignment. High-quality 2DEG and 2DHG with a carrier density up to 8X10(11) cm(-2) are formed with a small gate leakage current. Switching between 2DEG and 2DHG at the same heterointerface is achieved by changing the sign of the gate voltage. (C) 1996 American Institute of Physics.

 

57.       S. Hirono, Y. Koshimoto, S. Umemura, M. Igarashi, and Y. Maeda

            "Control of the compositionally separated microstructure of Co-Cr films prepared by electron cyclotron resonance plasma sputtering"

            IEEE Trans. Magn. 32 (5), 4013-4015 (1996).

 

            ABSTRACT: Compositional separation (CS) has been observed to occur in Co-Cr based alloy thin films. This CS produces fine Co-enriched regions within grains, which are expected to give a magnetic microstructure suitable for high density recording. We studied the compositional microstructure in Co-Cr films grown by electron cyclotron resonance plasma (ECR) sputtering to reduce media noise. ECR sputtering produced fine grains which caused particularly small and closely packed magnetic microstructure. The media noise measurement suggested that the grain growth which caused degrading of magnetic isolation should be suppressed to reduce media noise.

 

58.       Y. Hirota and T. Fukuda

            "STM and tunneling current studies of a GaAs(001) surface prepared by deoxygenated and deionized water treatment"

            Surf. Sci. 358 (1-3), 504-508 (1996).

 

            ABSTRACT: The thermal effects on an n-type highly Si-doped GaAs(001) surface prepared by deoxygenated and deionized water (DODIW) treatment are investigated by scanning tunneling microscopy (STM) and photoluminescence (PL) measurements. STM reveals that the tunneling current and the area of high tunneling current for positive sample voltage decrease as the temperature is increased above 500 degrees C, even though the surface keeps the 2 x 4 structure. PL measurements suggest that the decrease in tunneling current is related to accepters formed near the surface by a thermal process.

 

59.       Y. Hirota and K. Sumitomo

            "Thermal effects on surface Fermi level for GaAs(001)"

            J. Appl. Phys. 79 (10), 7785-7789 (1996).

 

            ABSTRACT: Thermal effects in a high vacuum on horizontal Bridgman grown GaAs(001) surface prepared by deoxygenated and de-ionized water treatment were investigated by x-ray photoelectron spectroscopy, low-energy electron diffraction, ultraviolet photoelectron spectroscopy, and photoluminescence (PL) measurement. The ultraviolet photoelectron spectra show that, below 450 degrees C, the surface Fermi level lies at almost 0.85-1.0 and 0.68-0.8 eV above the valence-band maximum, respectively, for lightly and highly Si-doped GaAs surfaces. Above 480 degrees C, the surface Fermi levels of both the surfaces gradually come close to 0.45-0.54 eV above the valence-band maximum even though the surface keeps the 2X4 structure. PL measurements suggest that the surface Fermi level position is strongly affected by arsenic and gallium vacancies created near the surface during thermal processing. (C) 1996 American Institute of Physics.

 

60.       R. A. Hogg, K. Takahei, and A. Taguchi

            "Photoluminescence excitation spectroscopy of GaAs:Er,O in the near-band-edge region"

            J. Appl. Phys. 79 (11), 8682-8687 (1996).

 

            ABSTRACT: We report a spectroscopic study of GaAs:Er,O samples grown by metalorganic chemical vapor deposition, with excitation in the near-band-edge region, 1.22-1.62 eV. Photoluminescence under host-excitation is dominated by luminescence due to the Er-2O center (an erbium atom at a gallium site coupled with two adjacent oxygen atoms) in these samples. The characterization of different Er centers is demonstrated by the observation of I-4(15/3)-->I-4(11/2) intra-4f-shell transitions by photoluminescence excitation (PLE) spectroscopy. The transitions between these crystal-field-split 4f-shell levels are observed at similar to 1.26 eV (similar to 980 nm) which is at an energy attainable by PLE spectroscopy with a Ti:Sapphire laser. Two lines are assigned to the Er-2O center. This allows a semi-quantitative measurement of the relative concentrations of different centers to be made. PLE spectroscopy was also employed to study the trap levels related to the Er-2O center. However, we find no evidence for such a trap level in this energy range. The expected position of this trap is discussed in the light of these results and recent calculations. (C) 1996 American Institute of Physics.

 

61.       R. A. Hogg, K. Takahei, A. Taguchi, and Y. Horikoshi

            "Preferential alignment of Er-2O centers in GaAs:Er,O revealed by anisotropic host-excited photoluminescence"

            Appl. Phys. Lett. 68 (23), 3317-3319 (1996).

 

            ABSTRACT: When GaAs is co-doped with Er and O by metalorganic chemical vapor deposition, the host-excited photoluminescence (PL) is dominated by I-4(13/2)-->I-4(15/2) intra-4f-shell luminescence (1.54 mu m) from a center identified as an Er atom substituting for Ga, coupled with two O atoms (Er-2O). The preferential alignment of the Er-2O center is revealed by the optical anisotropy exhibited by such samples when detecting host-excited PL polarized parallel to the [110] crystallographic directions. The preferential alignment of a specific symmetry axis of the Er-2O center is determined to be along the growth direction, [001]. This observation contrasts previous work on rare-earth (RE) doped materials where the RE luminescence center itself exhibits anisotropic luminescent properties, but a random distribution of differently oriented centers results in isotropic host excited PL. (C) 1996 American Institute of Physics.

 

62.       Y. Homma, N. Aizawa, and T. Ogino

            "Ultra-large-scale step-free terraces formed at the bottom of craters on vicinal Si(III) surfaces"

            Japanese Journal Of Applied Physics Part 2-Letters 35 (2B), L241-L243 (1996).

 

            ABSTRACT: We report the self-controlled planarization of Si(111) surfaces at the bottom of craters. A (111) plane with a step spacing as large as 10 micrometers can be obtained at the bottom of a crater by heating a misoriented Si(111) substrate with craters at around 1200 degrees C in ultrahigh vacuum. The (111) plane grows preferentially by filling adatoms in the crater until the plane surface reaches one of the top edges of the crater. The resulting surface has an extremely small miscut angle (<0.002 degrees), making it useful for fundamental research into crystal growth as well as for device fabrication.

 

63.       Y. Homma, H. Yamaguchi, and Y. Horikoshi

            "Direct comparison of GaAs surface morphology between migration enhanced epitaxy and molecular beam epitaxy using in situ scanning electron microscopy"

            Appl. Phys. Lett. 68 (1), 63-65 (1996).

 

            ABSTRACT: We have used scanning electron microscopy (SEM) for real-time-observation to compare the surface evolution during the early stage growth of GaAs with molecular beam epitaxy (MBE) and migration enhanced epitaxy (MEE), at the substrate temperature of 500 degrees C. Surface roughness during MEE growth is about 1 ML and much smaller than during MBE growth. Immediately after growth termination, monolayer steps can be seen and the surface recovers to initial smoothness in MEE, while islands do not disappear without higher temperature annealing in MBE. Present results confirm high surface atom mobility in MEE growth. (C) 1996 American Institute of Physics.

 

64.       S. Hoshino, O. Niwa, H. Tabei, M. Takahashi, and M. Morita

            "Hydrodynamic properties of the electrochemical behavior using interdigitated array microelectrodes"

            Denki Kagaku 64 (3), 195-201 (1996).

 

            ABSTRACT: The electrochemical behavior of an interdigitated array (IDA) microelectrode in now systems was investigated. The current densities at the IDA electrodes are much higher than those of a conventional disk electrode, resulting in a higher signal-to-noise ratio. The amperometric, quasi-amperometric and coulometric responses at an IDA electrode in flow system were compared with theoretical predictions. The flow rate dependence of redox cycling in the dual mode is constant in the amperometric region and depends only on the IDA dimensions. In the quasi-amperometric region, the flow rate dependence of redox cycling varies with coulometric yield. Recox cycling is inversely proportional to the 2/3 power of the volume flow rate in the coulometric region. The now rate dependence of the amperometric detector response in LC was also examined.

 

65.       S. Hoshino and H. Suzuki

            "Electroluminescence from triplet excited states of benzophenone"

            Appl. Phys. Lett. 69 (2), 224-226 (1996).

 

            ABSTRACT: We report the electroluminescent characteristics of organic multilayer light-emitting diodes (LEDs) with a benzophenone (BP) dispersed poly(methylmethacrylate) (PMMA) film as an emitting layer. The electroluminescence (EL) intensity of these LEDs increases with decreasing temperature from 273 to 100 K when they are operated at the same voltages or the same current densities. The EL spectrum of the LEDs, which peaks at around 450 nm, is identical to the phosphorescence spectrum of BP in PMMA. In addition, the EL decay time was determined as 46.8 mu s at 100 K by applying a rectangular voltage pulse. These results indicate that the EL of the LEE originates from the triplet excited states of BP. (C) 1996 American Institute of Physics.

 

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

            "Short distance applications of quantum cryptography"

            J. Nonlinear Opt. Phys. Mater. 5 (4), 823-832 (1996).

 

           ABSTRACT: We present an identification protocol based on quantum mechanics. The first user, Alice, needs to identify herself in front of a second user, Bob, by means of a password, known only to both. The safety requirement for Alice is that somebody impersonating Bob, who only pretended to know Alice's password, shall not be able to obtain information on the password from the exchange. This is an example of a potentially practical new application of quantum mechanics to cryptography.

 

67.       M. Ichikawa, H. Ono, S. Nishida, and T. Sato

            "Depth perception from second order motion yoked to head movement"

            Invest. Ophthalmol. Vis. Sci. 37 (3), 3416-3416 (1996).

 

            ABSTRACT:

68.       A. Ikeda, K. Sumitomo, T. Nishioka, and Y. Kido

            "Stopping powers and energy straggling for 50-300 keV H+ in amorphous Si and Ge films"

            Nucl. Instrum. Methods Phys. Res. Sect. B-Beam Interact. Mater. Atoms 115 (1-4), 34-38 (1996).

 

            ABSTRACT: Stopping powers and energy straggling for 50-300 keV H+ beams in amorphous Si and Ge films were measured with a toroidal electrostatic analyzer. The samples prepared are Sb(1ML)/Si(001) and amorphous Si(a-Si)/Sb(1ML)/Si(001) and a-Ge/Si(111) formed by molecular beam epitaxy and with an electron beam evaporator, Atomic force and cross sectional transmission electron microscopes revealed the formation of uniform. and amorphous thin films with sharp interfaces. Ion scattering measurements were performed in situ first for Sb(1ML)/Si(001) and subsequently for a-Si films deposited on Sb(1ML)/Si(001) under an ultrahigh vacuum condition. The Sb peak shift and the broadening of the Sb energy spectrum give the stopping power and energy straggling, respectively. For a-Ge films, we extracted the stopping power and straggling values from the energy width and the slopes at the front and rear edges of the Ge spectrum, respectively. The present results are compared with the theoretical predictions and other experimental data.

 

69.       N. Imoto

            "Controlling two-level atoms with a quantized pi or pi/2 pulse"

            Prog. Cryst. Growth Charact. Mater. 33 (1-3), 295-301 (1996).

 

            ABSTRACT: We discuss the quantum effect of the optical control field such as a pi pulse and a pi/2 pulse on the decoherence of a two-level system to be controlled in the experiments such as atom interference and quantum computation. A general solution for the Jaynes-Cummings model is obtained for this purpose, and the reduced density operator of the controlled two-level atom after the interaction is calculated. Examining typical initial quantum states for the control field such as number state, large-amplitude coherent state and small-amplitude coherent state, we can compare these states in the scope of atomic coherence controllability. It became clear that a number state field mostly destroys the purity of the two-level atom, and that a large-amplitude coherent state is ideal (except that large energy is required to control the atomic state). Use of a coherent state with considerably small photon number will cause decoherence, but not too much.

 

70.       T. Irino and R. D. Patterson

            "Temporal asymmetry in the auditory system"

            J. Acoust. Soc. Am. 99 (4), 2316-2331 (1996).

 

            ABSTRACT: When a damped exponential with a half-life of 4-8 ms is repeated every 25-50 ms and used to modulate a sinusoid or a wideband noise, it suppresses the sound quality typically associated with the carrier. When the envelopes of these ''damped'' sounds are reversed in time, producing ''ramped'' sounds, a continuous component with the sound quality of the carrier is restored to the perception. This paper presents an experiment that measures the temporal asymmetry revealed by this perceptual contrast. A ramped sinusoid or noise with a given half-life was presented with a damped sinusoid or noise having the same or greater half-life, to determine the damped half-life required to produce a continuous component with the equivalent relative strength in the two sounds. The results with sinusoidal carriers show that the half-life of the damped sound has to be, on average, about five times the half-life of the ramped sound if the tonal component of the two perceptions is to have the same relative strength. The asymmetry for the noise carrier is about half that of the sinusoidal carrier and, again, the damped sound has the greater matching half-life. Several multichannel auditory models based on a gammatone filterbank are used to try to explain the data in terms of traditional leaky integration, but they produce neither sufficient asymmetry nor the correct pattern of asymmetry. A ''delta-gamma'' theory is then developed to provide a framework for understanding temporal asymmetry in the auditory system. The theory is used to compare the temporal asymmetry produced by several auditory models and to explain when and how they can accommodate the perceptual asymmetry observed in the experiments. (C) 1996 Acoustical Society of America.

 

71.       H. Ishii, A. Yuyama, S. Narioka, S. Hasegawa, M. Fujino, H. Isaka, M. Fujiki, K. Furukawa, N. Matsumoto, and K. Seki

            "Electronic structures of silicon-based organic compounds studied by UV photoemission"

            Mol. Cryst. Liq. Cryst. Sci. Technol. Sect. A-Mol. Cryst. Liq. Cryst. 285, 205-210 (1996).

 

            ABSTRACT: The electronic structures of five polysilanes and octa(t-butyl)octasilacubane were investigated by ultraviolet photoemission spectroscopy (UPS). The spectral features were assigned by comparison with spectra of the constituents parts. The UPS spectra of the polyalkylsilanes indicate that the valence electronic structure can be regarded as an overlap of those of the Si-backbone and substituents. In the case of polyarylsilanes, all the spectral features except those in the uppermost energy region correspond one by one to each band in the spectra of the substituents as in the case of polalkylsilanes. The deviation of the spectral features in the uppermost energy region from those of the constituents suggests sigma-pi interaction between the pi HOMO states of benzene and the Si sigma HOVB states of the Si backbone. The results of octa(t-butyl) octasilacubane are also discussed.

 

72.       T. Ito and K. Shiraishi

            "A theoretical investigation of migration potentials of ga adatoms near kink and step edges on GaAs(001)-(2x4) surface"

            Japanese Journal Of Applied Physics Part 2-Letters 35 (8A), L949-L952 (1996).

 

            ABSTRACT: Migration potentials of Ga adatoms near kink and step edges are qualitatively investigated using empirical interatomic potential and an energy term. The energy term, as a function of the number of electrons remaining in the Ga dangling bond, is extracted from ab initio pseudopotential calculations. The calculated results imply that the lattice sites in the missing dimer row are favorable for Ga adatoms on the GaAs(001)-(2 x 4)beta 2 surface, since the formation of Ga dimers reduces the number of electrons remaining in Ga dangling bonds. Lattice sites in the missing dimer row near a kink and B-type step edge are stable for a Ga adatom, whereas no preferential adsorption site is found near an A-type step edge. This is simply because a Ga adatom in the missing dimer row near a kink and B-type step edge is weakly stretched by an As atom and As-dimer on the plane one layer below as opposed to being strongly stretched by two As-dimers near an A-type step edge.

 

73.       T. Ito and K. Shiraishi

            "A theoretical investigation of migration potentials of Ga adatoms near step edges on GaAs(001)-c(4x4) surface"

            Japanese Journal Of Applied Physics Part 2-Letters 35 (8B), L1016-L1018 (1996).

 

            ABSTRACT: Migration potentials of Ga adatoms near step edges on c(4 x 4) surface are investigated using the empirical interatomic potential and an energy term due to the charge redistribution on the surface. The energy term; as a function of the number of electrons remaining in the Ga dangling bonds, is extracted from ab initio calculations. The calculated results imply that the lattice sites along A-type step edges are stable for Ga adatoms, whereas no preferential adsorption site is found near B-type step edges. This is simply because the number of electrons remaining in the Ga dangling bond is suppressed by Ga adatoms occupying lattice sites along A-type step edges as opposed to being unchanged by those occupying lattice sites near B-type step edges.

 

74.       T. Ito and K. Shiraishi

            "A Monte Carlo simulation study on the structural change of the GaAs(001) surface during MBE growth"

            Surf. Sci. 358 (1-3), 486-489 (1996).

 

            ABSTRACT: A newly developed Monte Carlo (MC) simulation based on the electron counting model called electron counting Monte Carlo (ECMC) simulation, is used to investigate the structural change of the As-stabilized GaAs(001) surface during MBE growth. The calculated results imply that the GaAs(001) surface changes its structure from initial(2 x 4)beta 2 to (2 x 4)alpha with an increase in Ga adatoms and show that subsequent As adsorption produces the (2 x 4)beta 1 structure. Ga adatoms on the GaAs(001)-(2 x 4)beta 1 structure occupy?he lattice sites on the As-dimers at the low Ga adatom coverage of theta(Ga) less than or equal to 2/16. As the coverage increases in the range of theta(GA) greater than or equal to 3/16, Ga adatoms tend to reside in the lattice sites in the missing dimer region. These results are qualitatively consistent with those obtained by ab initio calculations. Further As incorporation onto the missing dimer row is also simulated by considering the dependence of As adsorption energy on Ga adatom coverage.

 

75.       Y. Iwasaki, O. Niwa, M. Morita, H. Tabei, and P. T. Kissinger

            "Selective electrochemical detection using a split disk array electrode in a thin-layer radial flow system"

            Anal. Chem. 68 (21), 3797-3800 (1996).

 

            ABSTRACT: An eight-sector array (split disk) electrode was designed for a low now rate (< 100 mu L/min) amperometric detector, This electrode was fabricated photolithographically for dimensional accuracy and reproducibility. This array of a pie-shaped electrode was combined with a thin-layer radial now cell, and a conversion efficiency of 94% was achieved at the lowest now rate tested (0.01 mL/min). Each electrode worked free from the effects of electrochemical reactions of the other electrodes. A coulometric hydrodynamic voltammogram of reversible redox species obtained using this system exhibited a Nernstian curve, These properties enabled this electrochemical detector to be used for determining the ratio of two redox species (redox potential difference approximate to 100 mV) with small injection volume (5 mu L).

 

76.       M. R. Junnarkar and E. Yamaguchi

            "Anti-stokes photoluminescence from Si modulation doped AlyGa1-yAs/AlxGa1-xAs QW and Si double delta doped AlxGa1-xAs"

            Solid-State Electron. 40 (1-8), 665-671 (1996).

 

            ABSTRACT: We have observed for the first time band-edge photoluminescence (PL) corresponding to the quantum well (QW) first subbands transition (similar to 1.93 eV) for below-gaps (QWs and barriers) photo-excitation (1.8-1.92 eV) in Si: modulation doped multiple QWs (MDMQW) in which barriers are intentionally doped. In order to unambiguously identify this PL to be anti-Stokes PL (ASPL), the MDMQW structure was selected to be in the form of 21 Angstrom Al0.2Ga0.8As quantum wells and Si doped Al0.4Ga0.6As barriers. ASPL observed from MDMQW (1.35 x 10(16) cm(-3) in Al0.4Ga0.6 As barriers) is stronger than bulk Si doped (1.35 x 10(16) cm(-3)) Al(0.4)G(0.6)As taking into account the total number of Si atoms. A similar band-edge photoluminescence (PL) for below-gap photo-excitation in Si double delta-doped (DDD) (60 Angstrom separation) AlxGa1-xAs(x = 0.35) has been observed. Observation of ASPL at low photon fluence of 20 W cm(-2) with linear intensity dependence is a clear indication of hole generation via below gap one photon excitation. Relatively strong ASPL is due to the strong hole confinement and combined influence of spatial and thermal barriers on electronic occupancy of Si-deep centers in the barrier. We will describe temperature dependence, doping concentration dependence and excitation spectrum of this luminescence and correlate its origin to the deep centers within the frame work of small lattice relaxation (SLR) and large lattice relaxation (LLR) models.

 

77.       T. Kaburagi and M. Honda

            "A model of articulator trajectory formation based on the motor tasks of vocal-tract shapes"

            J. Acoust. Soc. Am. 99 (5), 3154-3170 (1996).

 

            ABSTRACT: This paper presents a modeling study of articulator movements for continuous speech utterances. The model determines the trajectories of the articulator movements that form the vocal tract into phoneme-specific shapes. Vowels, for example, are generated based on the specifications of the tract shape (motor tasks) related to the shape of the tongue and lips. Consonants, such as /p/ and /k/, on the other hand, can be generated by specifying a closure in the tract between the lips, or between the tongue and the palate. In the model, state variables represent the active movements of each articulatory organ as the displacement relative to the neutral position. In addition, tract variables are defined to specify the motor tasks of the lips and tongue as functions of the state variables of the jaw, lips, and tongue: The definition of the tract variables incorporates the representation of the coordinative structure of the articulatory system between the jaw and the lower lip and between the jaw and the tongue. This coordinative structure allows for an infinite number of trajectories that satisfy all of the given motor tasks. This redundancy is overcome by minimizing the cost function so that the movements of each articulatory organ are uniquely determined. Articulator movements were simulated for several utterances, and the simulated movements of the jaw, lips, and tongue agree well with measured data. The results show that it is valid to use the features of vocal-tract shapes to represent motor tasks when modeling articulator movements acid that the model accurately represents the coordinated movements of the articulatory organs. (C) 1995 Acoustical Society of America.

 

78.       J. Kaczanowski, Y. Yamamoto, Y. Kido, J. Nakata, and K. Takahei

            "Monte Carlo simulation of channeling spectra for compound crystals with point defects and crystalline precipitates"

            Nucl. Instrum. Methods Phys. Res. Sect. B-Beam Interact. Mater. Atoms 117 (3), 275-282 (1996).

 

            ABSTRACT: The Monte Carlo program was developed for calculation of ion trajectories and channeling spectrum synthesis. The program was adapted for the analysis of channeling spectra of compound crystals containing point defects and crystalline precipitates. The method of the ion trajectory simulation and spectrum synthesis under the above condition is discussed in detail. The program was applied to the structure analysis of GaAs crystals doped with Er and codoped with C and O. The present analysis has determined the lattice location of Er in GaAs:Er-C and GaAs:Er-O. The simulations also revealed the formation of ErAs crystalline precipitates in Er heavily doped GaAs crystal which is consistent with TEM observation.

 

79.       H. Kageshima and K. Shiraishi

            "A method for calculating momentum matrix elements with pseudopotentials"

            Japanese Journal Of Applied Physics Part 2-Letters 35 (12A), L1605-L1607 (1996).

 

            ABSTRACT: A convenient method for calculating momentum matrix elements with pseudopotentials is proposed. To eliminate errors due to poor representation by the pseudopotentials of the atomic core region, a core-repair term is introduced. This approach is very efficient, especially for the separable-type pseudopotentials, to reduce computational time. It is also applicable to non-norm-conserving ultrasoft pseudopotentials as well as general norm-conserving pseudopotentials. Therefore, various optical properties can be calculated easily with this approach.

 

80.       H. Kamioka, E. Maeda, Y. Jimbo, H. P. C. Robinson, and A. Kawana

            "Spontaneous periodic synchronized bursting during formation of mature patterns of connections in cortical cultures"

            Neurosci. Lett. 206 (2-3), 109-112 (1996).

 

            ABSTRACT: Long-term recording of spontaneous activity in cultured cortical neuronal networks was carried out using substrates containing multi-electrode arrays. Spontaneous uncorrelated firing appeared within the first 3 days and transformed progressively into synchronized bursting within a week. By 30 days from the establishment of the culture, the network exhibited a complicated non-periodic, synchronized activity pattern which showed no changes for more than 2 months and thus represented the mature state of the network. Pharmacological inhibition of activity only during the period when regular synchronized bursting was observed was capable of producing a different mature activity pattern from the control. These results suggest that periodic synchronized bursting plays a critical role in the development of synaptic connections.

 

81.       K. Kanisawa, H. Yamaguchi, and Y. Horikoshi

            "Electronic properties of monolayer steps on (2x4)/c(2x8) reconstructed GaAs(001) surfaces"

            Phys. Rev. B 54 (7), 4428-4431 (1996).

 

            ABSTRACT: The electronic properties of monolayer steps on (2x4)/c(2x8) reconstructed GaAs(001) surfaces are measured using ultrahigh vacuum scanning tunneling microscopy. We propose unit structures for steps and demonstrate that steps play the role of acceptor arrays. An electron-counting consideration on the steps explains the densities of kinks in the As dimer rows on vicinal surfaces. We found that the acceptors at the steps are identical to those at the kinks. We confirmed that the surface states related to surface Fermi-level pinning are located at breaking points of a coherent arrangement of semiconducting (2x4) unit cells.

 

82.       N. Kasai, T. Matsue, I. Uchida, T. Horiuchi, M. Morita, and O. Niwa

            "Femto-mole acetylcholine detection with microdisk array electrodes"

            Denki Kagaku 64 (12), 1269-1271 (1996).

 

            ABSTRACT:

83.       M. Kasu and N. Kobayashi

            "Surface-diffusion and step-bunching mechanisms of metalorganic vapor-phase epitaxy studied by high-vacuum scanning tunneling microscopy (vol 78, pg 3026, 1995)"

            J. Appl. Phys. 79 (3), 1822-1823 (1996).

 

            ABSTRACT:

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

            "Scanning-tunneling-microscopy modification of nitrogen-passivated GaAs(001) surfaces on a nanometer scale"

            Appl. Phys. Lett. 68 (13), 1811-1813 (1996).

 

            ABSTRACT: Using scanning tunneling microscopy (STM), we perform nanometer-scale modifications on nitrogen (N)-passivated GaAs (001) surfaces. After the surface is passivated with nitrogen gas through a heated tungsten filament in an ultrahigh-vacuum chamber, STM modification is performed by increasing the tunnel current. A 200X200 nm(2) square groove was successfully fabricated. The smallest grooves are 0.5 nm deep and 5 nm wide when sample bias is -3 V and tunnel current is 5 nA. The threshold current for modification is 5 nA for surfaces with N passivation, but more than 50 nA for surfaces without N passivation. (C) 1996 American Institute of Physics.

 

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

            "Anisotropic surface morphology of GaAs (001) surfaces passivated with nitrogen radicals"

            Appl. Phys. Lett. 68 (7), 955-957 (1996).

 

            ABSTRACT: We have studied GaAs (001) surfaces passivated with nitrogen (N) radicals at submonolayer N coverage mainly using scanning tunneling microscopy and transmission electron microscopy. We determined that GaN-rich regions are elongated in the [<(1)over bar 10>] direction, suggesting that N passivation proceeds in the [<(1)over bar 10>] direction. This can be explained in terms of minimization of the tensile strains in the [<(1)over bar 10>] direction induced when the supplied N atoms replace first-layer As atoms on the (2x4)surface. (C) 1996 American Institute of Physics.

 

86.       T. Kato, J. K. Liu, K. Yamamoto, P. G. Osborne, and O. Niwa

            "Detection of basal acetylcholine release in the microdialysis of rat frontal cortex by high-performance liquid chromatography using a horseradish peroxidase-osmium redox polymer electrode with pre-enzyme reactor"

            J. Chromatogr. B-Biomed. Appl. 682 (1), 162-166 (1996).

 

            ABSTRACT: To determine the basal acetylcholine level in the dialysate of rat frontal cortex, a horseradish peroxidase-osmium redox polymer-modified glassy carbon electrode (HRP-GCE) was employed instead of the conventional platinum electrode used in high-performance liquid chromatography-electrochemical detection (HPLC-ED), In initial experiments, an oxidizable unknown compound interfered with the detection of basal acetylcholine release on HPLC-HRP-GCE. An immobilized peroxidase-choline oxidase precolumn (pre-reactor) was included in the HPLC system, to eliminate the interference from the unknown compound. This combination could detect less than 10 fmol of standard acetylcholine and basal acetylcholine levels in the dialysate from a conventional concentric design microdialysis probe, without the use of cholinesterase inhibitor, and may facilitate physiological investigation of cholinergic neuronal activity in the central nervous system.

 

87.       J. Kawahara, K. Yokosawa, S. Nishida, and T. Sato

            "Illusory line motion in visual search: Attentional facilitation or apparent motion?"

            Perception 25 (8), 901-920 (1996).

 

            ABSTRACT: A line, presented instantaneously, is perceived to be drawn from one end when a dot is flashed at that end prior to the presentation of the line. Although this phenomenon, called illusory line motion, has been attributed to accelerated processing at the locus of attention, preattentive (stimulus-driven) motion mechanisms might also contribute to the line-motion sensation. We tested this possibility in an odd-target-search task. The stimulus display consisted of two, four, or eight pairs of dots and lines. All lines were presented on the same side of the dots (eg right), except for the target line, which was presented on the opposite side (left). Subjects were asked to report the presence or absence of the target, which was presented in half of the trials. Low error rates for target detection (about 10%) even when the display consisted of eight dot-line pairs (ie display size was eight) indicated that illusory line motion could be perceived simultaneously at many locations. The interstimulus interval (ISI) between the dots and lines (0-2176 ms) and the contrast polarity (both dots and lines were brighter than the background, or dots were darker and lines were brighter) were also manipulated. When an ISI of a few hundred milliseconds was inserted, target detection was nearly impossible with larger display sizes. When the contrast polarity was changed, the target-detection performance was impaired significantly, even with no ISI. Moreover, it was found that the effects of display size, ISI, and contrast polarity were comparable in searches for a two-dot apparent-motion target. These results support the idea that preattentive, apparent-motion mechanisms, as well as attentional mechanisms, contribute to illusory line motion.

 

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

            "Inverse-dynamics representation of eye movements by cerebellar Purkinje cell activity during short-latency ocular-following responses"

            in New Directions In Vestibular Research, Annals Of The New York Academy Of Sciences Vol. 781 (New York Acad Sciences, New York, 1996), pp. 314-321.

 

            ABSTRACT:

89.       M. G. Kim, N. Imoto, K. Cho, and M. S. Kim

            "Quantum noise in optical beam propagation in distributed amplifiers"

            Opt. Commun. 130 (4-6), 377-384 (1996).

 

            ABSTRACT: Quantum effects on optical beam propagation in a gain medium having distributed loss are analyzed using an amplifier-attenuator array model. For the amplifier-attenuator set, the Wigner function of the output field is related to that of the input field by a convolution law. Using this, we derive the Fokker-Planck equation for the beam propagation in the distributed amplifier with loss, and the added quantum noise is analyzed by solving this equation. When the amplification just compensates the attenuation, the mean amplitude of the signal does not change but the mean energy increases due to the added noise. Even in this case, the photon number variance can be reduced when a proper phase-sensitive reservoir is incorporated.

 

90.       K. Kinoshita and T. Yamada

            "Spherical crystals of Pb1-xSnxTe grown in microgravity"

            J. Cryst. Growth 165 (1-2), 75-80 (1996).

 

            ABSTRACT: Pb1-xSnxTe spherical crystals were unintentionally obtained along with a cylindrical Pb1-xSnxTe crystal grown during the SL-J/FMPT mission on board the space shuttle ''Endeavor''. About 25 spherical crystals ranged from 0.5 to 11 mm in diameter. Melt leaked from the melt reservoir into the spring that plays the role of pushing the melt toward a seed crystal and eliminating free surface areas of the melt. Because of the surface tension of the melt, spherical melt drops formed in the hollow of the spring, then solidified into spherical crystals during the cooling process. Some of the crystals had lower dislocation densities, in the order of 10(4) cm(-2), two orders smaller than those of terrestrially grown crystals from a melt. The experiment showed a way of stably positioning a large volume of liquid in microgravity without touching the crucible wall and a way of reducing crystalline defects by such growth.

 

91.       K. Kinoshita, S. Yoda, T. Nakamura, H. Sameshima, H. Ando, S. Anzawa, and Y. Arai

            "Video imaging of the melting and solidification processes of the PbBr2-PbCl2 system under microgravity"

            J. Cryst. Growth 166 (1-4), 266-270 (1996).

 

            ABSTRACT: Using a sounding rocket, real-time observation of the melting and solidification of the PbBr2-PbCl2 system sealed in a quartz ampoule was successfully performed under microgravity. The interface shape is convex toward the melt during melting and becomes almost flat on solidification, which agrees well with the results of a computational thermal analysis. The liquid flow observed during melting had a velocity between 0.2 and 1.5 mm/s. This is much higher than expected and is most likely due to Marangoni convection. Although the PbBr2 melt wets the quartz ampoule, traces of microscopic free-surface areas during solidification are observed on the crystal surface. The microscopic free surface is the origin of Marangoni convection. Results from this ''first-time'' observation of the Marangoni flow in a liquid sealed in an ampoule, and capable of wetting the ampoule wall, will be useful in future microgravity experiments and will lead to a better understanding of crystal growth from a melt.

 

92.       M. Koashi and N. Imoto

            "Quantum cryptography based on two mixed states"

            Phys. Rev. Lett. 77 (10), 2137-2140 (1996).

 

            ABSTRACT: Although it is known that any two nonorthogonal pure states can constitute a secure quantum cryptosystem, the generalization of this scheme to the use of two mixed states is not trivial. It is shown here that even if a condition corresponding to the nonorthogonality in the pure-state case is satisfied, the mixed-state cryptosystem is still vulnerable to attack by an eavesdropper. A necessary and sufficient condition for the secure communication is derived. It states that the two mixed states must be connected by a rotation operator with a nonorthogonal angle.

 

93.       Y. Kobayashi and T. Ogino

            "Angle-variable infrared external reflection spectroscopy in UHV and its application to the observation of Si-H vibrations on Si(001) substrates with a buried metal layer"

            Surf. Sci. 368, 102-107 (1996).

 

            ABSTRACT: We have constructed a system with a variable-angle mechanism for infrared (IR) reflection spectroscopy in UHV. Hydrogen-adsorbed Si(001) substrates with a buried metal layer (BML) are examined in vacuo to demonstrate the utility of this system for surface IR spectroscopy on semiconductors. The available range of the angle is between 60 and 85 degrees, and the noise level of the 100% line after averaging 1000 scans on an Si BML substrate is <1 x 10(-4) at 2000 cm(-1) and <5 x 10(-4) at 650 cm(-1), which is sufficiently low to observe vibrations from surface species at submonolayer coverage. The results show that analysis of the spectral dependence on polarization, angle of incidence and Si overlayer thickness is very useful in examining the origin of the signals from surface species and their surface structures, including the orientation.

 

94.       Y. Kobayashi and T. Ogino

            "Infrared external reflection spectroscopy of self-assembled monolayer films on Si substrate with a buried metal layer (BML) structure"

            Appl. Surf. Sci. 101, 407-411 (1996).

 

            ABSTRACT: This paper reports a study of the signal behavior of IR reflection spectra on the flat Si substrate with a buried metal layer (BML) and MBE-grown Si overlayer. A self-assembled monolayer of octadecyltrichlorosilane on the surface was used as a typical sample of a well-oriented layer. The signal intensities strongly depend on the orientation of surface vibration, the polarization of IR radiation and the angle of incidence. The dependence is quite different from that seen on metal and normal (without BML) semiconductor surfaces and can be explained by local electric field intensity based on classical electromagnetic treatment. On a relatively thin Si overlayer (typically 700-1200 Angstrom), vibration modes only with the transition moment in the vertical direction were observed for p-polarization and modes only in the lateral direction were observed for s-polarization. On a relatively thick Si overlayer (typically 2000 Angstrom), modes with lateral as well as vertical components show significant signals for p-polarization, and only lateral modes could be detected at significant intensity for s-polarization. These results show that the orientation of surface species can be determined by analyzing the spectral dependence on polarization, angle of incidence and the thickness of the Si overlayer.

 

95.       Y. Kobayashi, K. Sumitomo, K. Prabhakaran, and T. Ogino

            "Preparation and characterization of a well-ordered surface on a Si(001) substrate with a buried metal layer for application of infrared reflection spectroscopy"

            J. Vac. Sci. Technol. A-Vac. Surf. Films 14 (4), 2263-2268 (1996).

 

            ABSTRACT: The preparation and characterization of an atomically flat and well-ordered surface on the Si(001) substrate with a buried metal layer (BML) are reported. The BML substrate was formed by implantation of Co+ ion and subsequent annealing. After molecular beam epitaxy growth of the Si overlayer on the cleaned BML sample in ultrahigh vacuum, clear 2x1 patterned and ordered steps with regular terrace width were observed by reflection high energy electron diffraction and atomic force microscopy. No contamination, including Co, was observed in the spectra of Auger electron spectroscopy and x-ray photoelectron spectroscopy. Ultraviolet photoelectron spectra showed a distinct surface peak that originated from surface dangling bonds and is characteristic of a clean and ordered surface. The surface atomic structure, including stress and damage caused by ion implantation, was characterized by medium energy ion scattering (MEIS). Very low chi(min) (1.7% with 300 keV H+) and a dip pattern in blocking profile in the MEIS spectra indicate that surface crystal quality is comparable to that of a homoepitaxially grown Si layer on normal Si substrate without BML. These results show that the BML substrate obtained by the procedure is quite useful for the structural investigation of surface species on Si by infrared (IR) reflection spectroscopy. Typical examples of IR spectra qualifying the BML substrate for surface studies are also presented. (C) 1996 American Vacuum Society.

 

96.       K. Kurihara, H. Namatsu, M. Nagase, and T. Makino

            "Sub-10-nm Si lines fabricated using shifted mask patterns controlled with electron beam lithography and KOH anisotropic etching"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 35 (12B), 6668-6672 (1996).

 

            ABSTRACT: We developed a new method for Si nanofabrication that provides sub-10-nm resolution using electron beam lithography combined with KOH anisotropic etching of a Si(1(1) over bar0$) substrate. The method, called shifted mask pattern method, uses two shifted mask patterns to reduce the Si linewidth. The two shifted mask patterns delineated in the [11(2) over bar] direction are used as a KOH etching mask where the masks are shifted vertically to each other in the [11(2) over bar] direction. During KOH anisotropic etching, Si linewidth under the shifted part of the masks is reduced due to the etching's smoothing resulting from the low etching rate of the Si(111) plane. The linewidth can be controlled by changing the mask shift. An image reversal process using electron cyclotron resonance (ECR) plasma oxidation mas used to form a plasma oxide mask for KOH etching. This mask was obtained by ECR oxygen plasma irradiation using a ZEP520 resist mask pattern. Highly accurate position and linewidth control was achieved with a 70-kV electron beam nanolithography system that has a minimum deflection step of 3 nm. The variation of pattern position and linewidth was about 1 nm. Using this method, we have been able to fabricate lines as narrow as 2 nm.

 

97.       P. Kurz and T. Mukai

            "Frequency stabilization of a semiconductor laser by external phase-conjugate feedback"

            Opt. Lett. 21 (17), 1369-1371 (1996).

 

            ABSTRACT: We report the stabilization of a laser diode by external phase-conjugate feedback from a broad-area laser diode. The linewidth of the stabilized laser diode was reduced from 5 MHz to 25 kHz, approaching the limit set by the fluctuations of the pump beam for the phase conjugator. Clear evidence of phase conjugation was the observation of paired half-axial side modes spaced at frequencies of c/4L with respect to the main mode. (C) 1996 Optical Society of America

 

98.       P. Kurz, R. Nagar, and T. Mukai

            "Highly efficient phase conjugation using spatially nondegenerate four-wave mixing in a broad-area laser diode"

            Appl. Phys. Lett. 68 (9), 1180-1182 (1996).

 

            ABSTRACT: We report spatially nondegenerate few-wave mixing in a broad-area laser diode that acts as a fast phase conjugate mirror with nanosecond response times and high efficiencies. Phase conjugate reflectivities were found to depend strongly on the bias current of the broad-area laser diode. Operating the laser diode in an injection-locked regime above the lasing threshold gave phase conjugate reflectivities as high as 165%. (C) 1996 American Institute of Physics.

 

99.       A. Levanon, S. R. Friberg, and Y. Fujii

            "Solitons for optical time-domain reflectometry"

            J. Opt. Soc. Am. B-Opt. Phys. 13 (6), 1179-1187 (1996).

 

            ABSTRACT: We describe the propagation of solitons in an optical time-domain reflectometry geometry. Intense nonsolitons usually broaden nonlinearly as they propagate out to a scatterer and broaden linearly as they return to their origin. In contrast, solitons propagate with a fixed pulse width or narrow on their way out to the scatterer. Returning, they broaden or narrow depending on their chirp at the scattering point. For a fixed return-pulse timing resolution we find 2.6 times or more energy can be launched when solitons are used than for normal dispersion pulses. (C) 1996 Optical Society of America

 

100.    A. Levanon, S. R. Friberg, T. Mukai, and Y. Fujii

            "Direct observation of soliton and normal pulse propagation by spectral domain reflectometry"

            Opt. Lett. 21 (14), 1023-1025 (1996).

 

            ABSTRACT: We report what are to our knowledge the first continuous observations of optical fiber solitons and nonsoliton pulses in the spectral domain. Using a novel optical time-resolved spectral reflectometer that measures the backscattered Light spectrum, we directly observed (with 200-m spatial resolution) the propagation of similar to 8.5-ps solitons and nonsolitons traveling down 5-km fibers. Spectral breathing and the recovery of the original spectral widths are clearly seen for higher-order solitons. Possible applications include in situ measurements of soliton parameters, fiber dispersions, and nonlinearities, experimental verifications of pulse propagation theories, and optical sensing. (C) 1996 Optical Society of America

 

101.    Y. Maeda, D. J. Rogers, O. Song, J. I. Suzuki, Y. Morii, and K. Takei

            "Magnetic microstructure observations of Co-Cr-Ta films using neutron scattering"

            J. Appl. Phys. 79 (3), 1819-1821 (1996).

 

            ABSTRACT: Using small-angle neutron scattering (SANS), we examined the magnetic microstructure of Co-12 at. % Cr-2 at. % Ta films sputter-deposited at 200 degrees C. Nuclear magnetic resonance confirmed the presence of highly Co-enriched regions produced by compositional separation. The SANS spectrum exhibited a main magnetic scattering peak corresponding to a size of several nm in the magnetic microstructure. This is indicative of a fine and uniform distribution of Co-enriched regions suitable for high-density magnetic recording. (C) 1996 American Institute of Physics.

 

102.    T. Makimoto and N. Kobayashi

            "Extremely strong and sharp photoluminescence lines from nitrogen atomic-layer-doped GaAs, AlGaAs and AlGaAS/GaAs single quantum wells"

            J. Electron. Mater. 25 (9), 1527-1530 (1996).

 

            ABSTRACT: We have performed nitrogen atomic-layer doping into GaAs, AlGaAs, and AlGaAs/GaAs single quantum wells using atomic nitrogen cracked by a hot tungsten filament. While the atomic-layer-doped GaAs layers show a series of sharp and strong photoluminescence lines relating to excitons bound to nitrogen atoms at 8K, atomic-layer-doped AlGaAs layers show several broad nitrogen-related lines. For the atomic-layer-doped single quantum well at the center of the GaAs layer, the quantum well luminescence itself disappears and a dominant and sharp luminescence is observed at a longer wavelength. It is found that the As pressure during the atomic-layer doping greatly affects the luminescence characteristics.

 

103.    T. Makimoto and N. Kobayashi

            "Nitridation of GaAs surfaces using nitrogen molecules cracked by a hot tungsten filament"

            Appl. Surf. Sci. 101, 403-406 (1996).

 

            ABSTRACT: We performed the nitridation of (001) GaAs surfaces using nitrogen molecules (N-2) cracked by a hot tungsten filament, After nitridation of a GaAs surface at 620 degrees C for 90 min, the [110] RHEED pattern shows the mixed spotty pattern of GaAs and GaN, while the <[(1)over bar 10]> RHEED pattern shows a streak pattern with the spacing of a GaAs lattice. The nitridation rate is independent of the substrate temperature below 530 degrees C. Above 590 degrees C, N-2 desorbs from the surface during nitridation. This desorption rate of N-2 from the nitrided GaAs surface is the smallest among those of column V molecules in InAs, InP, GaAs and GaP, due to the large standard heat of formation for GaN.

 

104.    T. Makimoto and N. Kobayashi

            "Extremely sharp photoluminescence lines from nitrogen atomic-layer-doped AlGaAs/GaAs single quantum wells"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 35 (2B), 1299-1301 (1996).

 

            ABSTRACT: We have applied nitrogen atomic-layer-doping to AlGaAs/GaAs single quantum wells. The atomic-layer-doping was performed at the center of the GaAs quantum well. The resulting structures show sharp photoluminescence lines with a full width at half maximum of 0.3 meV at 8 K. These lines are observed at longer wavelength than those obtained for undoped single quantum wells, indicating that they correspond to the excitons bound to nitrogen atoms in the quantum wells. The full width at half maximum of these nitrogen-related lines depends on the quantum well width. The lines remain sharp above a well width of 10 nm, while they become broad at 5 nm. This suggests that the diameter of the exciton bound to N atoms is about 10 nm. Furthermore, the binding energy of the excitons increases with increasing substrate temperature during the atomic-layer-doping.

 

105.    H. Matsubara, Y. Saito, and H. Iida

            "Proceedings of the game programming workshop in Japan '96"

            Icca J. 19 (4), 242-246 (1996).

 

            ABSTRACT:

106.    N. Matsumoto

            "Neurotransmitters and multimedia"

            Ntt Rev. 8 (2), 78-78 (1996).

 

            ABSTRACT:

107.    M. Mitsunaga, T. Mukai, K. Watanabe, and T. Mukai

            "Dressed-atom spectroscopy of cold Cs atoms"

            J. Opt. Soc. Am. B-Opt. Phys. 13 (12), 2696-2700 (1996).

 

            ABSTRACT: Absorption spectra of cold Cs atoms in a magneto-optical trap under the influence of a strong external pump laser field with arbitrary detuning and intensity have been systematically investigated. The spectra featured the Rabi sidebands of each transition, and their behavior was nicely fitted by the dressed-atom theory. A pronounced dispersion-type profile with sub-natural linewidth at the pump frequency may be attributable to the stimulated Raman process by sublevels that are lightshifted and optically pumped by the pump laser. (C) 1996 Optical Society of America.

 

108.    H. Miyamoto, S. Schaal, F. Gandolfo, H. Gomi, Y. Koike, R. Osu, E. Nakano, Y. Wada, and M. Kawato

            "A Kendama learning robot based on bi-directional theory"

            Neural Netw. 9 (8), 1281-1302 (1996).

 

            ABSTRACT: A general theory of movement-pattern perception based on bi-directional theory for sensory-motor integration can be used for motion capture and learning by watching in robotics. We demonstrate our methods using the game of Kendama, executed by the SARCOS Dextrous Slave Arm, which has a very similar kinematic structure to the human arm. Three ingredients have to be integrated for the successful execution of this task. The ingredients are (1) to extract via-points from a human movement trajectory using a forward-inverse relaxation model, (2) to treat via-points as a control variable while reconstructing the desired trajectory from all the via-points, and (3) to modify the via-points for successful execution. In order to test the validity of the via-point representation, we utilized a numerical model of the SARCOS arm, and examined the behavior of the system under several conditions. Copyright (C) 1996 Elsevier Science Ltd.

 

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

            "Selective electrochemical detection of catechol and catecholamines on modified electrodes with molecular template"

            Denki Kagaku 64 (12), 1239-1243 (1996).

 

            ABSTRACT: A new separation approach is demonstrated which combines electrochemical detection and molecular imprinting technique. The electrode was first partly covered with template molecules and next modified by silane coupling reagent, The template molecules were then extracted to form recognition cavities. Template of catechol and catecholamines can be prepared on a gold electrode by using 3-aminopropyltriethoxysilane as a insulation layer. The catechol-template electrode showed the usual diffusion-limited cyclic voltammogram of catechol and diminished response against all catecholamines. The selectivity between catechol and epinephrine was about 10. The epinephrine-template electrode exhibited the usual diffusion limit response against catechol and catecholamines. This means the selection took place mainly on the basis of the size of the template cavities. An electrode with a low template density showed a steady state dopamine response and the active density of template cavities was calculated as 3.26 fmol/cm(2) from the limiting current and that is 1/100 the density with an ideal situation.

 

110.    M. Morita and O. Niwa

            "Electrochemical detection using interdigitated array carbon microelectrodes - Detection limit of 5/1,000 trillionths grams achieved"

            Ntt Rev. 8 (2), 77-80 (1996).

 

            ABSTRACT: The detection limit of neurotransmitters can be lowered by using a carbon-based inter digitated array (IDA) microelectrode. The repeated redox reaction between band electrodes in the IDA amplifies the signal current, and the low background noise level of the carbon film allows for an increased signal-to-noise ratio. A low detection limit of 5 femtograms was obtained for dopamine, a neurotransmitter, by combining a micro-column LC and the carbon IDA electrode.

 

111.    K. Muraki and Y. Horikoshi

            "Fermi-level effect on Ga self-diffusion studied using (GaAs)-Ga-69/(GaGaAs)-Ga-69-Ga-71 isotope superlattice"

            in Compound Semiconductors 1995, Institute Of Physics Conference Series Vol. 145 (Iop Publishing Ltd, Bristol, 1996), pp. 547-552.

 

            ABSTRACT: We have studied the Ga self-diffusion in GaAs and its dependence on Si doping using (GaAs)-Ga-69/(GaGaAs)-Ga-69-Ga-71 isotope superlattices with [Si] = 1 x 10(17) -8 x 10(18) cm(-3) grown by molecular-beam epitaxy. The depth profiles of Ga-71 atoms before and after thermal anneals at 900 degrees C have been investigated via secondary-ion mass spectrometry (SLMS) to obtain the Ga self-diffusion coefficient as a function of the Si concentration. We find that the Fermi-level effect becomes dominant only in the high-doped regime. i.e., [Si] greater than or equal to 1 x 10(18) cm(-3), where the Ga self-diffusion coefficient increased in proportion to the third power of the electron concentration. On the other hand, no change in the diffusion coefficient was observed in the low-doped regime. Our results show that the Ga self-diffusion is driven by the Fermi-level effect and mediated by triply charged Ga vacancies in the high-doped regime, while it is suggested that some other Fermi-level independent mechanisms are operating in the intrinsic and low-doped regime.

 

112.    H. Murase and R. Sakai

            "Moving object recognition in eigenspace representation: Gait analysis and lip reading"

            Pattern Recognit. Lett. 17 (2), 155-162 (1996).

 

            ABSTRACT: This paper describes a new method to calculate the spatio-temporal correlation efficiently in a parametric eigenspace representation for moving object recognition. A parametric eigenspace compactly represents the temporal change of an image sequence by a trajectory in the eigenspace. This representation reduces the computational cost of correlation-based comparison between image sequences. Experiments for human gait analysis and lip reading show this method is computationally useful for motion analysis and recognition.

 

113.    S. V. Nair and T. Takagahara

            "Weakly correlated exciton pair states in large quantum dots"

            Phys. Rev. B 53 (16), 10516-10519 (1996).

 

            ABSTRACT: We present a calculation of the two-exciton states in semiconductor quantum dots much larger in size than the exciton Bohr radius, and identify a weakly correlated exciton pair state that has a large oscillator strength, increasing proportionately to the volume of the quantum dot. This state is shown to be responsible for the saturation of the size dependence of the resonant excitonic optical nonlinearity. It also provides a satisfactory understanding of the blueshift of the excited-state absorption in quantum dots. These results and the biexciton binding energy and oscillator strength are in good agreement with reported experimental results on CuCl.

 

114.    S. Naito

            "Gravity lens illusion: Magnitude prediction by gauge theory including size constancy"

            Invest. Ophthalmol. Vis. Sci. 37 (3), 4367-4367 (1996).

 

            ABSTRACT:

115.    H. Nakano, T. Nishikawa, H. Ahn, and N. Uesugi

            "Temporal evolution of soft X-ray pulse emitted from aluminum plasma produced by a pair of Ti:sapphire laser pulses"

            Appl. Phys. Lett. 69 (20), 2992-2994 (1996).

 

            ABSTRACT: The temporal and spectral evolution of soft x-ray pulses (40-100 Angstrom) emitted from Al plasma produced by a pair of femtosecond Ti:sapphire laser pulses at normal incidence was studied. Both the soft x-ray emission and the pulse duration increased with increase in the scale length of the preformed plasma. Prepulse enhanced soft x-ray emission about 100 times with a pulse duration of 100-130 ps. A spectrally resolved time history revealed that the emission at shorter wavelengths started and decayed relatively more quickly, and emissions at longer wavelengths built up and decayed more slowly. (C) 1996 American Institute of Physics.

 

116.    H. Nakano, T. Nishikawa, H. Ahn, and N. Uesugi

            "Effects of an ultrashort prepulse on soft X-ray generation from an aluminium plasma produced by femtosecond Ti:sapphire laser pulses"

            Appl. Phys. B-Lasers Opt. 63 (2), 107-111 (1996).

 

            ABSTRACT: The influence of a prepulse on soft X-ray emission in the range of 50-200 Angstrom from an aluminium plasma produced by 130 fs Ti:Sapphire laser pulses with an intensity of 10(14) W/cm(2) at normal incidence is studied. An ultrashort prepulse with an intensity of 10(13) W/cm(2) significantly enhances soft X-ray emission when there is a long time separation (> 100 ps) between the prepulse and an intense main pulse. It is also observed for the first time that a prepulse with a short pulse time separation can slightly reduce soft X-ray emission, contrary to the previous work done using 248 nm laser pulses. This can be explained qualitatively in terms of the dependence of absorption on the length scale.

 

117.    H. Namatsu, M. Nagase, K. Kurihara, S. Horiguchi, and T. Makino

            "Fabrication of one-dimensional silicon nanowire structures with a self-aligned point contact"

            Japanese Journal Of Applied Physics Part 2-Letters 35 (9B), L1148-L1150 (1996).

 

            ABSTRACT: The propose a novel one-dimensional Si nanowire structure with a point contact. Wire structures are fabricated in a {110} Si layer by using KOH solution. Both the {111} planes projecting obliquely along the wire and the vertical {111} sidewalls of the wire are spontaneously exposed. By oxidation of this {111} plane structure, the wire structure is converted into the one-dimensional nanowire structure. In addition, since the nanowire structure is based on a form of the {111} plane structure, the planes projecting obliquely produces a point-contact structure which gradually increases in diameter toward the source and drain regions. The Si nanowires fabricated by this technique shows clear quantized conductance with little fluctuation on the plateaus.

 

118.    S. K. Nayar, S. A. Nene, and H. Murase

            "Subspace methods for robot vision"

            IEEE Trans. Robot. Autom. 12 (5), 750-758 (1996).

 

            ABSTRACT: In contrast to the traditional approach, visual recognition is formulated as one of matching appearance rather than shape. For any given robot vision task, all possible appearance variations define its visual workspace. A set of images is obtained by coarsely sampling the workspace. The image set is compressed to obtain a low-dimensional subspace, called the eigenspace, in which the visual workspace is represented as a continuous appearance manifold. Given an unknown input image, the recognition system first projects the image to eigenspace. The parameters of the vision task are recognized based on the exact location of the projection on the appearance manifold. An efficient algorithm for finding the closest manifold point is described, The proposed appearance representation has several applications in robot vision. As examples, a precise visual positioning system, a real-time visual tracking system, and a real-time temporal inspection system are described.

 

119.    S. Nishida, M. Edwards, and T. Sato

            "Can second-order stimuli generate simultaneous motion contrast?"

            Invest. Ophthalmol. Vis. Sci. 37 (3), 4165-4165 (1996).

 

            ABSTRACT:

120.    T. Nishida and N. Kobayashi

            "Step-free surface grown on GaAs (111)B substrate by selective area metalorganic vapor phase epitaxy"

            Appl. Phys. Lett. 69 (17), 2549-2550 (1996).

 

            ABSTRACT: Selective metalorganic vapor phase epitaxy of GaAs within a finite area was investigated on (111)B substrate, The surface stoichiometry is determined based on surface photo-absorption measurement, High-temperature growth at 800 degrees C on stable GaAs (111)B and a cooling procedure with the (2x2)-like surface to improve flatness result in an intentionally step-free surface with device dimensions as wide as 8 mu m on a selectively grown GaAs mesa. (C) 1996 American Institute of Physics.

 

121.    T. Nishida and N. Kobayashi

            "Low temperature growth of GaAs and InAs/GaAs quantum well on (111)B substrate by metalorganic vapor phase epitaxy"

            Japanese Journal Of Applied Physics Part 2-Letters 35 (7B), L930-L932 (1996).

 

            ABSTRACT: Metalorganic vapor phase epitaxy of InAs quantum wells on GaAs (111)B substrate is investigated by simultaneous monitoring of surface photo-absorption. To lower the growth temperature of the GaAs barrier, we adopted the flow-rate-modulation method and obtained specular morphology of GaAs at 600 degrees C. Indium segregation is confirmed by surface photo-absorption and suppressed by introducing a capping layer grown under an arsenic rich condition. We obtained a one-monolayer InAs/GaAs quantum well; and confirmed its abrupt interfaces by TEM and a photoluminescence narrower than 6 meV.

 

122.    T. Nishikawa and N. Uesugi

            "Pulse narrowing characteristics in traveling-wave optical parametric generation in KTiOPO4 crystals"

            J. Appl. Phys. 80 (5), 2589-2594 (1996).

 

            ABSTRACT: Pulse narrowing characteristics in traveling-wave optical parametric generation in KTiOPO4 crystals are investigated. By utilizing the pulse narrowing effect, output pulses with pulse duration of 250 fs can be obtained from 550 fs pump pulses in the experiment. It is also demonstrated that when the conversion efficiency becomes large by increasing the pump intensity or by changing the phase-matching angle, the pulse narrowing effect becomes small. These tendencies are confirmed by numerical calculations of the parametric propagation process, which include the effects of temporal pulse shape, group-velocity difference, transverse beam profile, walk-off, two-photon absorption, and depletion. The theoretical results indicate that when the conversion efficiency becomes greater than 1%, the back-conversion process becomes large at the high-intensity part of the signal and idler pulses. This causes the pulse width to increase and reduces the pulse narrowing effect. (C) 1996 American Institute of Physics.

 

123.    T. Nishikawa and N. Uesugi

            "Transverse beam profile characteristics of traveling-wave parametric generation in KTiOPO4 crystals"

            Opt. Commun. 124 (5-6), 512-518 (1996).

 

            ABSTRACT: Transverse beam profile characteristics of traveling-wave parametric generation in KTiOPO4 crystals are investigated. Transverse beam profile depression and splitting due to the back-conversion in the parametric propagation process were observed even when the conversion efficiency was less than 10%. We measured the walk-off angle dependence and pump energy dependence of the transverse beam profiles. The transverse beam profile is ring shaped when there is no walk-off and deforms by expanding to the walk-off direction when walk-off exists. By decreasing the pump intensity, the deformation of the profile can be reduced due to the subsequent reduction in back-conversion. Walk-off compensation with two crystals placed next to each other with one in the opposite direction is also useful for getting a better transverse beam profile.

 

124.    J. Nitta, B. J. vanWees, J. P. Heida, T. M. Klapwijk, A. Dimoulas, W. vandeGraaf, and G. Borghs

            "Transport through a 2DEG channel with superconducting boundaries"

            Surf. Sci. 362 (1-3), 320-323 (1996).

 

            ABSTRACT: We have investigated transport through a channel with superconducting boundaries where-electrons are confined by Andreev reflection. Superconducting phase-sensitive transport is discussed using qualitative arguments. The transfer resistance R(t) through the channel as well as the resistance R(i) between the injector and the channel have been measured as a function of the phase difference phi Between the superconducting boundaries. It is not yet clear that the observed oscillation in resistance can be attributed to quasi-particle phase-sensitive transport. The oscillation amplitude in R(t) due to the transmitted current modulation is less than 0.1% in this experiment.

 

125.    O. Niwa, T. Horiuchi, M. Morita, T. H. Huang, and P. T. Kissinger

            "Determination of acetylcholine and choline with platinum-black ultramicroarray electrodes using liquid chromatography with a post-column enzyme reactor"

            Anal. Chim. Acta 318 (2), 167-173 (1996).

 

            ABSTRACT: A method for the highly sensitive determination of acetylcholine (ACh) and choline (Ch) was developed using platinum (Pt) black microarray electrodes as detectors in a microbore liquid chromatography (LC) with a post column enzyme reactor. The electrodes were prepared by plating a gold (Au) film electrode with sub-mu m Pt-black particles. Since hydrogen peroxide generated by the enzymatic reaction of ACh and Ch was oxidized only at the Pt-black microarray electrode, each Pt-black particle (typically 0.1-0.2 mu m in size) operated as an ultramicroelectrode. A high signal-to-noise ratio was achieved because of the high current density at the Pt-black microarray electrodes and because the Au film has a much lower baseline noise than the Pt. Detection limits of 5.7 (ACh) and 6.0 (Ch) fmol were obtained, with a wide linear range. The ACh and Ch signals with an Au film electrode modified with Pt-black particles retained more than 70% of their initial value after 5 days with continuous potential application. This is better stability than for a bare platinum electrode which retained only 40% of its initial response under comparable conditions.

 

126.    O. Niwa and M. Morita

            "Carbon film-based interdigitated ring array electrodes as detectors in radial flow cells"

            Anal. Chem. 68 (2), 355-359 (1996).

 

            ABSTRACT: We have fabricated the first carbon film-based interdigitated ring array (IDRA) electrodes for application as detectors in thin-layer radial now cells. The limiting current of dopamine (DA) at the electrode is proportional to the one-third power of the volume now rate (upsilon(1/3)) when two electrodes in the IDRA are held at 750 and 50 mV, respectively. In contrast, it is not proportional to upsilon(1/3) when only one electrode is held at 750 mV with the other electrode disconnected, due to the high conversion of DA in the now cell at a low now rate, The collection efficiency (CE) and redox cycles (Rc) increase with decreasing now rate, since the redox cycling of the IDRA suffers less influence from the now. The IDRA electrode was used in combination with microbore liquid chromatography (LC) for catecholamine detection. The CE and Re are particularly high in the usual now rate range for microbore LC, which is from 0.02 to 0.1 mL/min. Re values of 4.3 and 3.2 were achieved for DA and epinephrine, respectively, at a now rate of 0.02 mL/min, and the noise level of the electrode is low. This indicates that the IDRA electrode is very useful as a highly sensitive electrochemical detector in a radial now cell.

 

127.    O. Niwa, M. Morita, B. P. Solomon, and P. T. Kissinger

            "Carbon film based ring-disk and split-disk dual electrodes as detectors for microbore liquid chromatography"

            Electroanalysis 8 (5), 427-433 (1996).

 

            ABSTRACT: The electrochemical properties of carbon film based ring-disk and split-disk electrodes in small active volume (0.24-2 mu L) radial flow cells were studied in order to employ them in conjunction with microbore liquid chromatography (LC) for determining catecholamines. The high conversion of dopamine (DA) at the disk of a ring-disk electrode makes the DA limiting current lower than the theoretical value at a low flow rate. The collection efficiency (CE) increases with decreasing how rate and cell thickness, which is different from previously reported results. A high CE of 0.96 was achieved because of the narrow gap of 5 mu m. On the other hand, a higher limiting current was observed with the split-disk than with a commercially available dual-disk electrode because of its efficient geometry for analyte collection. The cross talk of the DA after reacting at one of the electrode is only 2%. The ring-disk and split-disk electrodes were suitable as series and parallel electrochemical detectors for small bore LC. A detection limit of 103 fg was obtained for DA at the disk of the ring-disk because of the high signal in the thin-layer radial flow cell and the low noise level of the carbon film. In contrast, very slight interference was observed from neighboring electrodes when determining catecholamines at the split-disk.

 

128.    O. Niwa, K. Torimitsu, M. Morita, P. Osborne, and K. Yamamoto

            "Concentration of extracellular L-glutamate released from cultured nerve cells measured with a small volume online sensor"

            Anal. Chem. 68 (11), 1865-1870 (1996).

 

            ABSTRACT: An online sensor with a low detection limit for L-glutamate was developed in order to monitor the change in the extracellular L-glutamate concentration as a result of stimulated release from cultured nerve cells, The sensor consisted of a microdialysis (MD) probe fixed at the manipulator, a small-volume L-glutamate oxidase enzymatic reactor (0.75 mm i.d, and 2.5 cm long), and an electrochemical detector in a thin-layer radial now cell with an active volume of 70-340 nL, Glassy carbon bulk or carbon film ring-disk electrodes were used as detectors by modifying them with Os poly(vinylpyridine) mediator containing horseradish peroxidase, The overall efficiency of L-glutamate detection with the sensor is 94% under optimum conditions, due to an efficient enzymatic reaction in the reactor and a high conversion efficiency in the radial now cell. As a result, we achieved a sensitivity of 24.3 nA/mu M and a detection limit of 7.2 nM (S/N = 3). The effect of interferents such as L-ascorbic acid can be minimized effectively by applying a low potential to the electrode for hydrogen peroxide detection (O mV) and via the ring-disk electrode geometry by using the disk for preoxidation, In the in vitro experiment, an MD probe for sampling was connected to a manipulator that controls distance between the probe and the stimulated cells. The cells were stimulated by KCI in a glass capillary or electrically with microarray film electrodes fabricated on a substrate, By using the sensor, we can monitor L-glutamate concentration changes at the submicromolar level caused by KCI stimulation of a single nerve cell and micromolar L-glutamate concentration increases caused by electrical stimulation of a brain slice, An increase in L-glutamate concentration can also be measured by positioning the probe near the cell that is connected synaptically to the stimulated cell.

 

129.    K. Odaka, T. Imada, T. Mashiko, and M. Hayashi

            "Discrepancy between brain magnetic fields elicited by pattern and luminance stimulations in the fovea: Adequate stimulus positions and a measure of discrepancy"

            Brain Topogr. 8 (3), 309-316 (1996).

 

            ABSTRACT: A conventional equivalent current dipole estimation provides one of the quantitative measures to evaluate the discrepancy between two single-dipole-like magnetic field patterns, though there is one problem; all stimulus positions in the visual field do not necessarily contribute to the generation of a single-dipole-like magnetic field. Another important problem occurs when the field pattern is complex and cannot be approximated by a dipole. This makes it difficult to evaluate the discrepancy between two magnetic field patterns by the dipole parameters. In this paper, we determined the stimulus positions adequate for generating single-dipole-like magnetic field patterns by evaluating the magnetic field's goodness-of-fit to the field generated by a single dipole. We propose to use a similarity (SIM) as a quantitative measure of the discrepancy between two complex magnetic field patterns. The SIM is defined as an angle between two magnetic field vectors. We evaluated the discrepancy between the 100 ms post-stimulus responses to pattern-reversal (Rv) stimulus, pattern-onset (Pat) stimulus, and luminance-onset (Lumi) stimulus. The following results were obtained: (1) Stimulation of some of the octants in the fovea, far from the vertical meridian, elicited a single-dipole-like magnetic field pattern at a latency of 100 ms, though stimulation of the central part of the fovea, and stimulation of the octants along the vertical meridian, did not elicit a single-dipole-like magnetic field pattern; (2) The discrepancy between responses was quantitatively evaluated by the SIM even if the field patterns were complex; (3) The SIM analysis showed that the discrepancy between the responses to the Rv and the Lumi stimuli, as well as that between the responses to the Pat and the Lumi stimuli, were greater than that between the responses to the Rv and the Pat stimuli.

 

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

            "Step arrangement design and nanostructure self-organization on Si(111) surfaces by patterning-assisted control"

            Appl. Surf. Sci. 107, 1-5 (1996).

 

            ABSTRACT: We propose a new approach to self-organize atomic step arrangement on Si(111) surfaces on a wafer scale. Steps originating in substrate misorientation are rearranged on surfaces patterned with small hole arrays during high temperature annealing in an ultra high vacuum. After further annealing, the holes are completely filled, and only ordered step bands are left on the surface. Inside the unfilled holes appear trimmed nanostructures, reflecting the dependence of step behaviors on the misorientation direction. The present technique is promising for large scale control of step-initiated nanofabrication as well as for improving the conventional Si process in which an atomically flat surface is increasingly required.

 

131.    T. Ogino, H. Hibino, and K. Prabhakaran

            "Fabrication of nanostructures on silicon surfaces on wafer scale by controlling self-organization processes"

            J. Vac. Sci. Technol. B 14 (6), 4134-4139 (1996).

 

            ABSTRACT: We describe a novel route for future Si integration technology in which atomically controlled nanostructures are designed to the level of full wafers based on self-organization processes. As an example of the scenario, we present a Ge quantum dot network where individual dots interact with the neighboring dots through tunneling barriers, Schottky junctions, and so on. Ge dots are patterned on Si(lll) surfaces by preferential nucleation of Ge islands at atomic steps and boundaries between reconstructed domains. It is then demonstrated that atomic step arrangement can be designed by patterning assisted control; this means that Ge quantum dot network can also be designed. Selective oxidation and silicidation in the Si/Ge systems are effectively utilized to form semiconductor/insulator/metal nanostructures from well-ordered semiconductor structures. Based on the above processes, we propose a new approach to design nanostructure integration organized on wafer scale. (C) 1996 American Vacuum Society.

 

132.    H. Oohashi, H. Ando, and H. Kanbe

            "Homogeneous linewidth of bound excitons in high-purity GaAs measured by spectral hole burning"

            Phys. Rev. B 54 (7), 4702-4706 (1996).

 

            ABSTRACT: We measured spectral hole burning in an optical-absorption spectrum of a bound exciton (D-0,X) in high-purity GaAs at 1.8 K. Precise temperature-controlled semiconductor lasers with a lasing wavelength accuracy of less than 0.001 nm are used as wavelength-tunable pump-and-probe light sources in the hole-burning experiments. The homogeneous linewidth of the bound exciton is determined from the burned hole spectral width. The dipole dephasing time T-2 estimated from the measured half width of the burned hole is 300 ps, which is more than an order of magnitude longer than the T-2 value reported for two-dimensional excitons in a GaAs quantum well. Such a long value of T-2 for bound excitons is due to exciton localization or, more specifically, the reduction in the optical-dipole scattering rate is due to zero-dimensional exciton confinement.

 

133.    S. Pau, G. Bjork, J. Jacobson, and Y. Yamamoto

            "Fundamental thermodynamic limit of laser efficiency"

            IEEE J. Quantum Electron. 32 (3), 567-573 (1996).

 

            ABSTRACT: The thermodynamic limits on the efficiency of different types of lasers are calculated both classically and quantum mechanically. In the classical case, the limit is derived from the inequality provided by the population inversion, In the quantum mechanical case, the limit is derived from the inequality of the change of entropy. The Shannon and von Neuman entropies of different light states are worked out.

 

134.    Z. L. Peng and Y. Horikoshi

            "Carrier concentration saturation of double Si doping layers in GaAs"

            Japanese Journal Of Applied Physics Part 2-Letters 35 (9B), L1151-L1154 (1996).

 

            ABSTRACT: Doubly Si delta-doped GaAs samples with different spacer thickness are grown by molecular beam epitaxy. By adopting a growth temperature as low as 400 degrees C, a ''true'' delta-doping profile is realized and confirmed by Shubnikovde Haas measurement. A depopulation of sheet carrier concentration is observed as the two layers approach each other. The carrier concentration saturates in such a way that the depth of the self-consistently calculated Hartree potential is kept constant at around 235 meV. Since carrier concentration saturation due to structural reasons remains unchanged in these structures, the pinning of Fermi level suggests a dominant electronic saturation mechanism most likely through the population of DX center states.

 

135.    Z. L. Peng, T. Saku, and Y. Horikoshi

            "Negative photoconductivity of AlxGa1-xAs:Sn/GaAs modulation-doped heterostructures"

            in Compound Semiconductors 1995, Institute Of Physics Conference Series Vol. 145 (Iop Publishing Ltd, Bristol, 1996), pp. 517-522.

 

            ABSTRACT: Temperature-dependent Hall-effect measurements under different illumination conditions are performed for AlxGa1-xAs:Sn/GaAs modulation doped heterostructures. Two distinct DX center levels are deduced. The two-dimensional electron gas concentration measured under illumination decreases from the value due to persistent photoconductivity to a value less than that measured in the dark when the excitation photon energy is larger than the band gap of the AlGaAs barrier. This decrease occurs only at temperatures below about 90 K. This negative photoconductivity is explained by taking into account the partial freeze-out of electrons into the shallow DX centers and the transfer of holes photo-generated in the barrier into the channel region.

 

136.    Z. L. Peng, T. Saku, and Y. Horikoshi

            "Study of photoconductivity in AlxGa1-xAs/GaAs modulation-doped heterostructures"

            J. Appl. Phys. 79 (7), 3592-3596 (1996).

 

            ABSTRACT: Temperature-dependent Hall effect measurements under different illumination conditions are performed on AlxGa1-xAs/GaAs heterostructures doped with both Si and Sn. For a Sn-doped AlxGa1-xAs/GaAs heterostructure with x=0.35, two distinct DX center levels are observed directly without exposure to light. The two-dimensional electron gas concentration measured under illumination decreases from the value due to persistent photoconductivity to a value less than that measured in the dark when the excitation photon energy is larger than the band gap of the AlGaAs barrier. This decrease occurs only at temperatures below 90 K. This negative photoconductivity is explained by taking into account the partial freeze-out of electrons into the shallow DX centers and the transfer of holes photogenerated in the barrier into the channel region. No such phenomena are observed in Sn-doped heterostructures with x<0.35 or in the Si-doped heterostructures. The reasons for this are also investigated. (C) 1996 American Institute of Physics.

 

137.    K. Prabhakaran, T. G. Andersson, and K. Nozawa

            "Nature of native oxide on GaN surface and its reaction with Al"

            Appl. Phys. Lett. 69 (21), 3212-3214 (1996).

 

            ABSTRACT: In this letter, we describe the surface properties of GaN thin films grown on sapphire substrate by molecular beam epitaxy, as revealed by ultraviolet and x-ray photoelectron spectroscopic and Auger electron spectroscopic studies. The samples are seen to contain overlayer of native oxides, which are predominantly in the Ga2O3 form. Ammonia is shown to be a good etchant for these native oxides. Furthermore, we investigated the early stages of the reaction of monolayer Al with a GaN surface covered with native oxide, Aluminum reacts preferentially with the surface oxygen and leads to the formation of a mixture of oxides at the interface. (C) 1996 American institute of Physics.

 

138.    K. Prabhakaran and T. Ogino

            "Behavior of ultrathin layers of Co on Si and Ge systems"

            Appl. Surf. Sci. 101, 518-521 (1996).

 

            ABSTRACT: Photoelectron spectroscopic study of the interaction of Co with Ge surface is reported for the first time. The behavior of ultrathin layers of Co on Ge(100) has been compared with that on Si(100) surfaces based on ultraviolet and X-ray photoelectron spectroscopic studies (UPS and XPS). Formation of silicides and germanides take place upon depositing Co on clean Si(100) and Ge(100) surfaces, respectively. at room temperature. The Co 2p transition is observed at a slightly higher binding energy in the case of silicide (778.7 +/- 0.2 eV) compared to that of the germanide (778.1 +/- 0.2 eV). Upon annealing the Co covered surfaces, the Co atoms diffuse into the bulk and the onset temperature of inward diffusion is low in Ge (similar to 150 degrees C) compared to that in Si (similar to 350 degrees C). Go-deposition of Co and Ge on clean Ge(100) surface at room temperature leads to the formation of a mixture of different germanide phases.

 

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

            "Diffusion mediated chemical reaction in Co/Ge/Si(100) forming Ge/CoSi2/Si(100)"

            Appl. Phys. Lett. 68 (9), 1241-1243 (1996).

 

            ABSTRACT: We report the occurrence of a diffusion mediated chemical reaction in the layered structure Co/Ge/Si(100) to form Ge/CoSi2/Si(100). This is possible due to the lower onset temperature of inward diffusion of Co in Ge(100) (similar to 150 degrees C) compared to that in Si(100) (similar to 300 degrees C). Deposition of similar to 2 monolayer (ML) of Co at room temperature, onto a Ge covered (similar to 3 ML) Si(100) surface, mainly forms CoxGey species on the surface. However, annealing the sample at 400 degrees C, Co diffuses through the Ge layer and reacts with Si and forms buried cobalt silicide of the structure Ge/CoSi2/Si(100). X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS), medium energy ion scattering (MEIS) are employed for the study. The results open up a possibility to fabricate metal/semiconductor heterostructures in a novel way. (C) 1996 American Institute of Physics.

 

140.    J. J. Rajan and A. Kawana

            "Bayesian model order selection using the Gibbs sampler"

            Electron. Lett. 32 (13), 1156-1157 (1996).

 

            ABSTRACT: A method is described for applying the Gibbs sampler to the problem of evaluating the evidence, or a posteriori probability, of candidate models in a Bayesian model order selection formulation for generalised linear models. The specific example of the discrete Karhunen-Loeve transform is considered.

 

141.    D. J. Rogers, Y. Maeda, and K. M. Krishnan

            "Investigations of the compositional distribution in epitaxially grown Co-Cr thin films with enhanced saturation magnetisation"

            J. Magn. Magn. Mater. 163 (3), 393-396 (1996).

 

            ABSTRACT: The compositional distribution in a Co78Cr22 film grown epitaxially on Ru/mica by electron beam evaporation was investigated using spin-echo Co-59 nuclear magnetic resonance (NMR) and preferential chemical etching of Co. NMR revealed evidence for the occurrence of drastic compositional separation producing a Go-enriched component containing almost pure Co. Chemical etching revealed a particularly fine distribution of Go-enriched regions. These results are consistent with the proposition that the enhanced saturation magnetisation (M(s)) observed in these films is attributable to enhanced compositional inhomogeneities.

 

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

            "Nitrogen atomic-layer-doping on Ga-terminated and misoriented GaAs surfaces by metalorganic vapor phase epitaxy using dimethylhydrazine"

            Jpn. J. Appl. Phys. Part 2 - Lett. 35 (12B), L1644-L1647 (1996).

 

            ABSTRACT: Nitrogen atomic-layer-doping on Ga-terminated and misoriented GaAs surfaces was performed by metalorganic Vapor Phase Epitaxy (MOVPE) using dimethylhydrazine to investigate the role of the surface for nitrogen atom incorporation. Compared with the As-terminated surface, dimethylhydrazine molecules are preferentially decomposed on the Ga-terminated surface due to the catalytic effect, resulting in a higher doping efficiency. We also investigated the crystal orientation dependence of the nitrogen doping concentration. Nitrogen atoms are preferentially incorporated on the (n11)A surfaces (n greater than or equal to 3) than the (100) surface. For the (n11)A surface, the nitrogen doping efficiency increases with decreasing n value. This indicated the doping efficiency increases with the step density. In contrast, nitrogen atoms are incorporated less on the (n11)B surfaces (n greater than or equal to 3) than the (100) surface and their doping efficiency decreases with increasing step density. These results are ascribed to the difference of atomic bonding geometries for adsorption sites between (n11)A and (n11)B surfaces. The doping efficiency for A-type steps is twice as high as that for the (100) terraces while that for B-type steps is negligibly small.

 

143.    T. Saitoh and H. Kanbe

            "Fabrication of a nanometer-scale GaAs ridge structure with a 92-MHz anode-coupled reactive ion etcher using Cl-2/N-2 mixed plasmas"

            Japanese Journal Of Applied Physics Part 2-Letters 35 (1A), L60-L62 (1996).

 

            ABSTRACT: A vertical etch profile of GaAs is achieved at a low bias voltage with a 92-MHx anode-coupled reactive ion etcher using chlorine-nitrogen plasmas. The added nitrogen gas not only dilutes the concentration of reactive chlorine radicals in the plasma also plays an important role in the vertical etching of GaAs. XPS analysis reveals no sidewall passivation by nitrogen. Reactive ion etching: with a Cl-2/N-2 mixed plasma was used to fabricate ultra-fine GaAs patterns with a nanometer-scale ridge structure having a cross-section 15-nm wide by 150-nm high.

 

144.    T. Saku, Y. Horikoshi, and Y. Tokura

            "Limit of electron mobility in AlGaAs/GaAs modulation-doped heterostructures"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 35 (1A), 34-38 (1996).

 

            ABSTRACT: We have achieved electron mobilities as high as 1.05 x 10(7) cm(2)/Vs at 1.5 K with all electron density of approximately 3 x 10(11)/cm(2) for modulation-doped AlGaAs/GaAs by using high purity layers with a residual acceptor concentration of 1 x 10(13)/cm(3), and relatively thick spacer layers similar to(75 nm). We found the electron scattering process caused by spatially separated ionized donors to be most important in limiting the observed low-temperature electron mobility, even in these thick-spacer-layer samples. Theoretical calculation predicts that the mobility caused by this scattering mechanism is approximately 1.6 x 10(7) cm(2)/Vs. The observed electron mobility exhibits an anisotropy with respect to the principal axes ([110] and [<(1)over bar 10>] directions) on the (001) surface. The anisotropy is such that the mobility in the [<(1)over bar 10>] direction is always higher than that in the [110] direction. Theoretical calculations reasonably explained this anisotropy by assuming the existence of islands at the interface which are longer in the [<(1)over bar 10>] direction than in the [110] direction, and revealed that the scattering caused by interface roughness was as important as that caused by ionized donors. Thus, these two major components mainly determine the observed low-temperature electron mobility. We also discuss the mobility expected for residual impurity free limit.

 

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

            "Antiferromagnetically enhanced C-13 spin-lattice relaxation in K3C60-NO evidence of electronic multi-sites"

            J. Phys. Soc. Jpn. 65 (12), 3696-3699 (1996).

 

            ABSTRACT: We report a study of C-13 NMR spin-lattice relaxation in the superconducting fulleride K3C60 at low temperatures (T). The experimentally obtained relaxation data, which are scaled to a T-independent relaxation shape, are found to be well reproduced by the anisotropy parameter alpha(spin) = A(iso)(spin)/A(ax)(spin), where A(iso)(spin) and A(ax)(spin) are the isotropic and anisotropic part of the C-13 hyperfine coupling of conduction electrons, respectively. Simulation for a powder sample with various alpha(spin) values indicates that the deviation from a single-exponential relaxation is largest when the hyperfine coupling is isotropic to some extent (i.e., alpha(spin) approximate to 0.5) instead of purely anisotropic (i.e., alpha(spin) = 0). These results justify a model based on the electronic single site. Moreover, from the validity of the extended Korringa relation with K(alpha) = 5.7, it is found that the electronic state is a Fermi liquid in which the relaxation rate is enhanced substantially by the antiferromagnetic electron interaction.

 

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

            "Isotropy in C-13 hyperfine coupling in K3C60"

            J. Phys. Soc. Jpn. 65 (8), 2389-2392 (1996).

 

            ABSTRACT: We report on a study of carbon thirteen (C-13) NMR spectra in a superconducting fulleride K3C60. It is found that the spectra are reproduced as powder patterns of anisotropic NMR shifts. By analyzing the NMR shifts, the ratio of isotropic hyperfine coupling (A(iso)(spin)) of conduction spin electrons to anisotropic one (A(ax)(spin)) is obtained experimentally for the first time (A(iso)(spin)/A(ax)(spin) = 0.78). The substantial isotropy is consistent with the crystal structure of the C-60 molecule. The contribution of carbon p pi-orbitals to A(ax)(spin) found to be dominant.

 

147.    M. Sato

            "Crystal orientation of GaN films grown on (001)GaAs substrates by plasma-assisted metalorganic chemical vapor deposition"

            in Silicon Carbide And Related Materials 1995, Institute Of Physics Conference Series Vol. 142 (Iop Publishing Ltd, Bristol, 1996), pp. 875-878.

 

            ABSTRACT: Cubic and hexagonal GaN films were grown on (001) GaAs substrates by plasma-assisted low-pressure metalorganic chemical vapor deposition using triethylgallium and N-radicals. Cubic GaN films were epitaxially grown on (001) GaAs substrates under Ga-rich growth conditions. On the other hand, c-axis-oriented hexagonal GaN films, whose domains were arranged as [0 (1) over bar 10] of GaN was parallel to [(1) over bar 10] of GaAs, were grown under N-rich conditions.

 

148.    M. Sato

            "Highly resistive CH-doped GaN grown by plasma-assisted metalorganic chemical vapor deposition"

            Appl. Phys. Lett. 68 (7), 935-937 (1996).

 

            ABSTRACT: Highly resistive (>10(6) Omega cm) GaN thin films were grown on (0001) sapphire substrates by plasma-assisted metalorganic chemical vapor deposition using triethylgallium and N radicals. Considerable amounts of C and H were incorporated in the GaN films and the incorporated C was electrically inactive after annealing in N-2 up to 900 degrees C, suggesting that thermally stable CH complex made the GaN films highly resistive. The C concentrations were reduced when the Ga and N sources were alternately supplied. (C) 1996 American Institute of Physics.

 

149.    M. Sawaki and N. Hagita

            "Recognition of degraded machine-printed characters using a complementary similarity measure and error-correction learning"

            IEICE Trans. Inf. Syst. E79D (5), 491-497 (1996).

 

            ABSTRACT: Most conventional methods used in character recognition extract geometrical features, such as stroke direction and connectivity, and compare them with reference patterns in a stored dictionary. Unfortunately, geometrical features are easily degraded by blurs and stains, and by the graphical designs such as used in Japanese newspaper headlines. This noise must be removed before recognition commences, but no preprocessing method is perfectly accurate. This paper proposes a method for recognizing degraded characters as well as characters printed on graphical designs. This method extracts features from binary images, and a new similarity measure, the complementary similarity measure, is used as a discriminant function; it compares the similarity and dissimilarity of binary patterns with reference dictionary patterns. Experiments are conducted using the standard character database ETL-2, which consists of machine-printed Kanji, Hiragana, Katakana, alphanumeric, and special characters. The results show that our method is much more robust against noise than the conventional geometrical-feature method. It also achieves high recognition rates of over 97% for characters with textured foregrounds, over 99% for characters with textured backgrounds, over 98% for outline fonts and over 99% for reverse contrast characters. The experiments for recognizing both the fontstyles and character category show that it also achieves high recognition rates against noise.

 

150.    K. Seki, H. Ishii, A. Yuyama, M. Watanabe, K. Fukui, E. Ishiguro, J. Yamazaki, S. Hasegawa, K. Horiuchi, T. Ohta, H. Isaka, M. Fujino, M. Fujiki, K. Furukawa, and N. Matsumoto

            "Electronic structures of polysilanes and related compounds"

            J. Electron Spectrosc. Relat. Phenom. 78, 403-406 (1996).

 

            ABSTRACT: UPS and Si K- and L(II,III)-edge NEXAPS spectra of various polysilanes, poly(dimethylsiloxane), and octakis(t-butyl)octa-silacubane (OTBOSC) were measured for elucidating their occupied and vacant electronic structures, in comparison with the results for polysilazane. The results revealed that the electronic structures are sensitive for the main chain structure, pendant, and the dimensionality of the Si-containing backbone.

 

151.    A. Sekiguchi, T. Matsuo, K. Ebata, and H. Sakurai

            "Persilylated dimethylenecyclobutene dianion dilithium as the first 6C-8 pi allyl anion system"

            Chem. Lett. (12), 1133-1134 (1996).

 

            ABSTRACT: Reduction of persilylated dimethylenecyclobutene with lithium metal in 1,2-dimethoxyethane yields green crystals of persilylated dimethylenecyclobutene dianion dilithium as the first 6C-8 pi allyl anion system. The molecular structure, determined by X-ray crystallography, is discussed in comparison to that of the neutral starting molecule.

 

152.    H. Shibata and T. Yamada

            "Superconducting-plasma resonance along the c axis in various copper oxide superconductors"

            Phys. Rev. B 54 (10), 7500-7504 (1996).

 

            ABSTRACT: Superconducting plasma along the c axis in the far-infrared region are observed in various high-ir, cuprates including electron-doped and Bi cuprates. It is shown that the sphere resonance of the powder samples occurs near the frequency where the plasma along the c axis exists, since it is only sensitive to the c-axis dielectric constant in the far-infrared region due to the metal-like property in the ab plane. This method provides an alternative to the reflectivity measurement of single crystals for investigating the plasma along the c axis. By measuring down to 7.5 cm(-1), the resonance is observed in Bi(1.85)Pb(0.35)Sr(2)Ca(2)Cu(3.1)Oy, La1.82Ca1.18Cu2O6+delta, (Nd0.66Sr0.205Ce0.135)(2)CuO4 (T* phase), (Ba0.56Sr0.44)(2)Cu1.1O2.2+delta(CO3)(0.9), Pr1.85Ce1.15CuO4, and Nd2CuO4-xFx. Among the Bi cuprates, however, no resonance is observed in Bi2Sr2CaCu2Oy and Bi2Sr1.6La0.4CuOy in this frequency region, which suggests that the resonance exists below 7.5 cm(-1). The resonance frequencies are discussed based on the Josephson-coupled layer model, and the c-axis penetration depth lambda(c) are estimated from the resonance frequencies. It appears that lambda(c) depends on the insulating nature of the barrier layer between CuO2 planes. Substitution effects on the resonance are also investigated in La2-xSrx(Cu1-zZnz)O-4, Nd1.85Ce0.15(Cu1-zZnz)O-4, and YBa2(Cu1-zCoz)(3)O-6+delta and compared to the results of YBa2(Cu1-zZnz)(3)O-6+delta Through the substitution, the resonance frequencies strongly decrease for all samples, indicating the strong increase of lambda(c). The frequency decrease in YBa2(Cu1-zCo2)(3)O-6+delta suggests that the resonance frequency is determined by the barrier at the (BaO)[Cu(1)O delta](BaO) chain layer, not at the Y layer.

 

153.    K. Shiraishi

            "First-principles calculations of surface adsorption and migration on GaAs surfaces"

            Thin Solid Films 272 (2), 345-363 (1996).

 

            ABSTRACT: This paper investigates surface adsorption and migration on GaAs surfaces theoretically based on the ab initio calculations. First, we calculate the Ga migration potential on GaAs(001)-(2 x 3) surfaces by the ab initio calculations. The calculated migration potential sensitively depends on the Ga coverage. At lower Ga coverages, the most favorable sites are located in the As-dimer region. Whereas, as the Ga coverage increases, favorable lattice sites move from the As-dimer region to the missing-dimer region. Next, we clarify the mechanism of the coverage dependence of migration potential by considering the surface atomic structure and the energy band structure at each Ga coverage. The calculated results show that surface distortion mainly determines the most favorable site at lower Ga coverages. However, after the surface distortions are relaxed at higher Ga coverages, favorable sites are determined by the electron counting model. In addition, to investigate the dynamical behavior of cation adatoms at finite temperatures, we perform Monte Carlo simulations based on the ab initio results. The simulations show that the dynamical behavior of cation adatoms also strongly depends on the Ga coverage. At the initial stage of growth, randomly impinged cation adatoms predominantly occupy the lattice sites in the As-dimer region. While, as the Ga coverage increases, favorable lattice sites change from the lattice sites in the As-dimer region to those in the missing-dimer region, reflecting the coverage dependence of migration potential obtained by the ab initio calculations.

 

154.    K. Shiraishi and T. Ito

            "First principles study of arsenic incorporation on a GaAs (001) surface during MBE growth"

            Surf. Sci. 358 (1-3), 451-454 (1996).

 

            ABSTRACT: Arsenic atom incorporation is a crucial process in epitaxial growth processes. The problem of how surface missing dimer rows on GaAs(001) surfaces are occupied by As atoms, is one of the most fundamental problems in GaAs MBE processes. This paper theoretically investigates As incorporation into the missing dimer row on a reconstructed GaAs(001)-(2 x 4) surface. To examine the coverage dependence of As incorporation, we estimated the As, adsorption energy at several Ga coverages by the ab initio calculation. The calculated results show that As adsorption energy drastically increases as the Ga coverage increases. We conclude from these results that missing dimer rows are occupied by As atoms after Ga atoms have been adsorbed on the surface. We also studied the structural change from a (2 x 4)beta 2 structure with two As dimers and found that a (2 x 4)beta 2 structure changed to a (2 x 4)beta 1 structure via a (2 x 4)alpha structure.

 

155.    T. Sogawa, S. Ando, H. Ando, and H. Kanabe

            "Photoluminescence excitation spectra in GaAs/AlAs trench-buried quantum wires with 20 nm wide rectangular cross-sectional shapes"

            Appl. Phys. Lett. 68 (3), 364-366 (1996).

 

            ABSTRACT: Polarization-dependent photoluminescence excitation spectra (PLE) are measured in GaAs/AlAs rectangular trench-buried quantum wires (QWRs) with 20 nm width and various thicknesses. Experiments demonstrate that the polarization properties of the PLE spectra, which have several clear peaks corresponding to the optical transitions between quantized conduction and valence subbands, significantly depend on the cross-sectional ratios of the rectangular wires. Quantum indices of these transition levels are assigned by comparing the experiments with theory. The distinctive optical features of the QWRs with the rectangular cross sections are discussed in relation to the characteristics of one-dimensional valence subbands. (C) 1996 American Institute of Physics.

 

156.    T. Suhara, M. Fujimura, K. Kintaka, H. Nishihara, P. Kurz, and T. Mukai

            "Theoretical analysis of squeezed-light generation by second-harmonic generation"

            IEEE J. Quantum Electron. 32 (4), 690-700 (1996).

 

            ABSTRACT: Theoretical analysis of squeezed light generation by phasematched SHG, applicable generally to various SHG configurations and appropriate for mutual comparison, is presented, The analysis is based on analytical solutions of the linearized differential equations in space coordinate and the input-output equations for the amplitude fluctuations, and calculations of squeezing spectra using the covariance matrixes, Formulations describing the squeezing characteristics in terms of the device parameters are derived, Typical numerical results are also given to illustrate the features of traveling-wave SHG, singly-resonant SHG, and doubly-resonant SHG configurations including cases where propagation losses are involved, The results, which are consistent with those in previous work, provide many insights for design and application of SHG devices for squeezed-light generation.

 

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

            "Atomic structure analysis of the interfaces in Si/Ge superlattices"

            Appl. Surf. Sci. 101, 503-507 (1996).

 

            ABSTRACT: Using medium-energy ion scattering, we have studied interface structures between Si and Ge thin layers in GenSim strained-layer superlattices (SLSs) grown by molecular beam epitaxy. In this systems, the horizontal strain caused by lattice mismatch, further causes vertical atomic displacement. The embedded Ge layers are compressed horizontally and expanded vertically compared with the ideal cubic crystal. Since the interfaces of Si layers grown onto Ge layers in SLS are not so abrupt at the atomic scale because of the Ge segregation effect, Ge atoms at the interfaces are displaced not only vertically but also laterally. We observed a peculiar blocking dip, which is explained by an interfacial structure characterized as alternate Si and Ge arrangement forming a 2 x n periodicity.

 

158.    K. Sumitomo, H. Yamaguchi, Y. Hirota, T. Nishioka, and T. Ogino

            "Structure analysis of the GaAs(001)-2x4 surface using medium energy ion scattering"

            Surf. Sci. 355 (1-3), L361-L365 (1996).

 

            ABSTRACT: The structure of the GaAs(001)-2 x 4 reconstructed surface is studied using medium-energy ion scattering (MEIS). The MEIS profiles clearly show splitting blocking dips, which originate in the surface reconstruction. We have quantitatively determined the atomic displacement from these blocking dips. The topmost As atoms forming the symmetric dimers are displaced laterally 0.55 +/- 0.05 Angstrom, and the bond length of the As dimer is 2.89 +/- 0.1 Angstrom. The Ga atoms of the second atomic layer, which bond with the As dimer atoms, are also displaced laterally and the displacement is 0.44 +/- 0.05 K. These surface atoms also move vertically and the surface layers shrink.

 

159.    H. Suzuki

            "Fabrication of electron injecting Mg:Ag alloy electrodes for organic light-emitting diodes with radio frequency magnetron sputter deposition"

            Appl. Phys. Lett. 69 (11), 1611-1613 (1996).

 

            ABSTRACT: Electron injecting electrodes made of magnesium and silver alloys (Mg:Ag) with a wide range of Ag concentration from 0 to 26.6 at.% were successfully fabricated for organic light-emitting diodes (LEDs) by using the radio frequency sputter deposition technique. The LED characteristics such as intensity, turn-on voltage, and durability of electroluminescence were strongly dependent on the Mg:Ag composition. Both the work function and the structural order of these Mg:Ag electrodes played a crucial role in determining the LED characteristics. (C) 1996 American Institute of Physics.

 

160.    H. Suzuki

            "Temperature dependence of the electroluminescent characteristics of light-emitting diodes made from poly(methylphenylsilane)"

            Adv. Mater. 8 (8), 657-& (1996).

 

            ABSTRACT: Polysilanes-Si-based sigma-conjugated polymers-have electronic structures markedly different from those of pi-conjugated polymers. The temperature dependence of the electroluminescent properties of single-layer LEDs made from poly(methylphenylsilane) is reported and it is demonstrated that these LEDs can be used as light sources in the near UV region. Observation of electroluminescence from one of the most typical polysilanes is encouraging as it indicates that there is potential for further improvements.

 

161.    H. Suzuki and M. Hikita

            "Organic light-emitting diodes with radio frequency sputter-deposited electron injecting electrodes"

            Appl. Phys. Lett. 68 (16), 2276-2278 (1996).

 

            ABSTRACT: We report a successful fabrication of organic light-emitting diodes (LEDs) with electron injecting electrodes prepared by the radio frequency (rf) magnetron sputtering technique. These LEDs consist of a poly(methylphenylsilane) and a tris-(8-hydroxyquinoline) aluminum (Alq(3)) layer successively formed on an indium-tin-oxide coated glass, and either an aluminum or magnesium electron injecting electrode. Substantial improvements were observed in such device characteristics as intensity and durability of electroluminescence for LEDs with an rf-sputter-deposited electrode as compared to those with a vacuum-heat-deposited electrode. (C) 1996 American Institute of Physics.

 

162.    H. Suzuki and S. Hoshino

            "Effects of doping dyes on the electroluminescent characteristics of multilayer organic light-emitting diodes"

            J. Appl. Phys. 79 (11), 8816-8822 (1996).

 

            ABSTRACT: We report the effects of dyes doped in the emitting layer on the electroluminescent characteristics of multilayer organic light-emitting diodes (LEDs) using a polysilane polymer, poly(methylphenylsilane) (PMPS), as the hole transporting material. We formed the emitting layer by dispersing in poly(styrene) (PS), one of four dyes whose fluorescence ranged from blue to orange. Two- or three-layer LEDs were prepared by combining PMPS and dye doped PS layers with the indium tin oxide and aluminum used for the hole and electron injecting electrodes, respectively. The three-layer LEDs had an additional vacuum-deposited tris-(8-hydroxyquinoline) aluminum layer. The electroluminescent (EL) characteristics of these multilayer organic LEDs, such as the current-voltage-EL intensity curve, the relative EL efficiency, and the EL emitting species, exhibit a marked dependence on the emitting dye. The observed dependence can be described consistently in terms of the dependence of the charge carrier trapping efficiency on the emitting dyes. (C) 1996 American Institute of Physics.

 

163.    H. Suzuki and S. Hoshino

            "Behavior of charge carriers and excitons in multilayer organic light-emitting diodes made from a polysilane polymer as monitored with electroluminescence"

            J. Appl. Phys. 79 (2), 858-865 (1996).

 

            ABSTRACT: Using electroluminescence (EL) as a monitor, we have investigated the behavior of charge carriers injected from electrodes and excitons generated by the recombination of charge carriers in multilayer organic light-emitting diodes (LEDs) using poly(methylphenylsilane) (PMPS) as a hole transporting material. Our multilayer LEDs have two or three functional organic layers including Coumarin 6 [3-(2'-benzothiazolyl)-7-diethylaminocoumarin, abbreviated as C6] and/or tris-(8-hydroxyquinoline) aluminum layers as well as a PMPS layer. When the LEDs were fabricated, two parameters of the C6 layer were changed, the layer thickness (30-120 nm) and the dye concentration (1-100 wt %). We employed a combined analysis of the dependence of the EL spectra on the thickness and dye concentration of the C6 layer, the dye-selective fluorescence spectra and the current-voltage-EL characteristics, to reveal the thickness of the electron-hole capture zone and the behavior of charge carriers and excitons during operation in these LEDs. (C) 1996 American Institute of Physics.

 

164.    M. Suzuki, S. Hayashi, and Y. Murata

            "Trends in information security technology - Cryptography in the limelight"

            Ntt Rev. 8 (1), 24-31 (1996).

 

            ABSTRACT: Advances in information processing technology and networking are creating new types of network services. Security technology for protecting individual privacy and assuring the security of information is taking on added importance because it is indispensable to the provision of these new services. This article surveys recent trends in security technology, especially cryptography, and describes the status of NTT's R&D work on information security techniques.

 

165.    Y. Y. Suzuki, D. Beljonne, and J. L. Bredas

            "Two-band tight-binding model for push-pull polyenes"

            J. Chem. Phys. 104 (18), 7270-7283 (1996).

 

            ABSTRACT: We propose a two-band model for the description of the electronic structure of push-pull polyenes in order to analyze in simple ways their potentially useful electronic and optical features. The polyene part is described by two (valence and conduction) bands, which are coupled with two tight-binding frontier orbitals representing the donor and acceptor end groups. In this model, the ground state consists of the one-electron states of the (pi) valence band hybridized with the donor orbitals, while the charge-transfer excited state is described as an excitation from the highest occupied molecular orbital to the lowest unoccupied molecular orbital, the latter being a hybridized one-electron state between the (pi*) conduction band and the acceptor orbital. It is shown, by the Green's function method, that the electron localizations (the partial density of states) at the end, groups are determined by three factors; (1) the unperturbed energy levels of the frontier orbitals, (2) the density of states of the unperturbed polyene bands, and (3) the coupling constants between the pi (pi*) band and the donor (acceptor) orbital. Based on the results, a simple description is provided for the characteristic nonlinear optical responses and the intramolecular adiabatic charge-transfer mechanism of push-pull polyenes, In order to estimate the magnitude of the coupling constants, we compare the analytical results from the model with numerical calculations based on an established semiempirical method. This kind of modeling provides guidance for the design of functional push-pull polyenes. (C) 1996 American Institute of Physics.

 

166.    A. Taguchi and K. Takahei

            "Trap level characteristics of rare-earth luminescence centers in III-V semiconductors"

            J. Appl. Phys. 79 (8), 4330-4334 (1996).

 

            ABSTRACT: We have applied a multiphonon-assisted energy transfer model, which has been verified for the Yb-doped InP system, to Er-doped GaAs, Nd-doped GaP, and Nd-doped GaAs. By applying this model, the temperature dependence of the decay time of the 4f-shell luminescence can be calculated using two parameters. One parameter is the energy transfer probability between the rare-earth 4f shell and the semiconductor host, and the other is the energy which has to be compensated for in the energy transfer processes. The values of these two parameters were determined by fitting the calculated temperature dependence to the experimentally obtained results. The calculated temperature dependences fit with the experimental results well, showing that the energy transfer mechanism in these materials is similar to that in InP:Yb. The estimated values of energy which have to be compensated for enable us to estimate the energy level positions responsible for the rare-earth intra-4f-shell luminescence. The values of the transition matrix elements obtained by the fitting were rather large, suggesting that the energy transfer between the rare-earth 4f shell and the semiconductor host is efficient in spite of the fact that it is a phonon-assisted process. (C) 1996 American Institute of Physics.

 

167.    A. Taguchi and K. Takahei

            "Band-edge-related luminescence due to the energy backtransfer in Yb-doped InP"

            J. Appl. Phys. 79 (6), 3261-3266 (1996).

 

            ABSTRACT: Band-edge-related photoluminescence in Yb-doped InP was investigated by solving rate equations. For InP:Yb, two characteristic properties have been observed in the band-edge-related luminescence. One is that the decay curve of the band-edge-related luminescence has a slowly decaying component above about 100 K, which has not been observed in undoped InP. The other is that the luminesce intensity shows an increase at around 120 K, although that for undoped InP monotonically decreases as temperature increases. These two properties were investigated based on a proposed model of energy transfer between the Yb 4f shell and the InP-host electrical state. In the model, it is assumed that a nonradiative multiphonon transition process assists the energy transfer. We have shown, in a previous article, that the temperature dependence of the decay time and of the intensity of the Yb 4f shell luminescence can be explained by using this assumption. In this article, we calculated the band-edge-related luminescence properties under the same assumption. Good agreement was obtained between the calculated and experimental results. Thus, the experimentally observed characteristic properties in the band-edge-related luminescence are explained by the energy backtransfer from the excited Yb 4f shell to the host electronic state. (C) 1996 American Institute of Physics.

 

168.    T. Takagahara

            "Electron-phonon interactions in semiconductor nanocrystals"

            J. Lumines. 70, 129-143 (1996).

 

            ABSTRACT: The electron-phonon interactions in semiconductor nanocrystals, especially concerning the acoustic phonon modes are derived and the size dependence of the coupling strength is clarified for typical coupling mechanisms. On the basis of these results, the commonly observed linearly temperature-dependent term of the excitonic dephasing rate and the proportionality of its magnitude to the inverse square of the nanocrystal size are attributed to the pure dephasing due to the deformation-potential coupling. The luminescence Stokes shift and the Huang-Rhys factor due to acoustic phonon modes in Si nanocrystals are discussed in conjunction with the origin of the recently observed luminescence onset energy.

 

169.    T. Takagahara and K. Takeda

            "Excitonic exchange splitting and Stokes shift in Si nanocrystals and Si clusters"

            Phys. Rev. B 53 (8), R4205-R4208 (1996).

 

            ABSTRACT: The size dependence of the electron-hole exchange interaction in Si nanocrystals is investigated and the excitonic exchange splitting is predicted to be as large as 300 meV in extremely small Si clusters. The exciton-phonon interaction in Si nanocrystals for acoustic phonon modes is formulated to calculate the Stokes shift and the Huang-Rhys factor. It is found that the observed onset energy of photoluminescence can be interpreted mainly in terms of the excitonic exchange splitting, although the contribution from the Stokes shift is not negligible. The importance of the self-consistent determination of the effective dielectric constant of Si clusters including the excitonic effect is demonstrated in view of the possibility of resolving the large discrepancy between theories and experiments concerning the size dependence of the exciton energy.

 

170.    Y. Takagaki, Y. Hirayama, T. Saku, and S. Tarucha

            "Ballistic transmission of composite fermions in a side-gated crossed-wire junction"

            Phys. Rev. B 53 (15), 10060-10064 (1996).

 

            ABSTRACT: We have studied the negative bend resistance phenomena in a side-gated crossed-wire junction in the fractional quantum Hall regime. The dip near zero magnetic field due to electrons and that near the filling factor 1/2 due to composite fermions are both enhanced as the channel is squeezed. The width of the dips in the magnetic field exhibits opposite behavior as a function of gate voltage, implying that the effective potential that the composite fermions experience is different from that of the electrons. The gradual variation of the electron density due to the lateral potential depletion is anticipated to result in a deviation of the effective magnetic field in the vicinity of the channel boundary. We numerically examine the effects of a nonuniform magnetic field on the transmission properties.

 

171.    Y. Takagaki and H. Takayanagi

            "Quantized conductance in semiconductor-superconductor-junction quantum point contacts"

            Phys. Rev. B 53 (21), 14530-14533 (1996).

 

            ABSTRACT: We present a numerical calculation of the quantized point contact conductance in a normal-metal-superconductor (NS) junction in the presence of disorder. It is shown that the flared geometry of the constriction improves the quantization. Random potential or interface roughness is found to destroy the quantization. The disorder induced suppression of the conductance is less significant when the constriction narrows due to retroreflection at the NS interface. The conductance approaches the value of normal point contacts when a magnetic field is applied. A good agreement of the magnetic-field dependence with an experiment is obtained.

 

172.    Y. Takagaki and Y. Tokura

            "Transmission resonances in a semiconductor-superconductor junction quantum interference structure"

            Phys. Rev. B 54 (9), 6587-6599 (1996).

 

            ABSTRACT: Transport properties in a quantum resonator structure of a normal-conductor-superconductor (NS) junction are calculated. Quasiparticles in a cavity region undergo multiple reflections due to an abrupt change in the width of the wire and the NS interface. Quantum interference of the reflections modulates the nominal normal reflection probability at the NS boundary. We show that various NS structures can be regarded as the quantum resonator because of the absence of propagation along the NS interface. When the incident energy coincides with the quasibound state energy levels, the zero-voltage conductance exhibits peaks for small voltages applied to the NS junction. The transmission peaks change to dips of nearly perfect reflection when the applied voltage exceeds a critical value. Two branches of the resonance, which are roughly characterized by electron and hole wavelengths, emerge from the individual dip, and the energy difference between them increases with increasing voltage. The electronlike and holelike resonance dips originating from different quasibound states at zero-voltage cross one after another when the voltage approaches the superconducting gap. We find that both crossing and anticrossing can be produced. It is shown that the individual resonance state in the NS system is associated with two zeros and two poles in the complex energy plane. The behavior of the resonance is explained in terms of splitting and merging of the zero-pole pairs. We examine the Green's function of a one-dimensional NS system in order to find out how the transmission properties are influenced by the scattering from the NS interface.

 

173.    Y. Takagaki, Y. Tokura, and S. Tarucha

            "Transmission of interacting electrons through a one-dimensional periodic potential"

            Phys. Rev. B 53 (23), 15462-15465 (1996).

 

            ABSTRACT: Electron transport through a periodic potential in the presence of a short-range repulsive interaction is investigated in the mean-field approximation. The Coulomb repulsion lifts the spin degeneracy at low energies. The peaks in the transmission due to multiple reflections in the periodic potential split into two branches and their amplitude is suppressed by half. For moderate energies and interaction strengths, the quantum dots are filled with spin-up and spin-down states alternately. The nonuniform spin density distribution is found to quench the overall transmission.

 

174.    M. Takahashi, Y. Sakakibara, and J. Nakata

            "Source/drain ion implantation into ultra-thin-single-crystalline-silicon-layer of separation by IMplanted OXygen (SIMOX) wafers"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 35 (10), 5237-5241 (1996).

 

            ABSTRACT: Problems associated with ion implantation into ultra-thin-film SIMOX (Separation by IMplanted OXygen) of SOI (silicon on insulator) structures are discussed. We realized n-type source/drain region with lower resistance by P+ ion implantation. To decrease the resistance of the implanted layer, the amorphized high-dose layer must be recrystallized by annealing. We show that the possibility of recrystallization can be predicted by TRIM simulation. Moreover, it was found that excess phosphorus above the solid solubility segregates in the Si/SiO2 interface.

 

175.    H. Takayanagi

            "Andreev reflection and quantum transport in an S-N-S junction"

            Physica B 227 (1-4), 224-228 (1996).

 

            ABSTRACT: The superconducting and normal transport in a semiconductor-coupled Josephson junction with a submicron split gate electrode has been studied. The maximum supercurrent I-c and the conductance show step-wise changes as a function of gate voltage V-g. This is evidence that I-c is quantized in the superconducting quantum point contact. The current-voltage characteristics also change from current-deficit to excess-current as the absolute value of V-g increases. This change is explained by Andreev reflection, which leads to the reflected holes being focused on the quantum point contact. To study the change, the dependence of the gate voltage and the magnetic field of the differential resistance-voltage characteristics are measured and discussed.

 

176.    H. Takayanagi, T. Akazaki, and J. Nitta

            "Observation of the quantized critical current in a superconducting quantum point contact"

            Surf. Sci. 362 (1-3), 298-301 (1996).

 

            ABSTRACT: Quantization of the critical current has been confirmed in a superconducting quantum point contact consisting of a split-gated superconductor-(two-dimensional electron gas)-superconductor junction. Both the critical current and the conductance show a step-wise change as function of the gate voltage.

 

177.    H. Takayanagi, E. Toyoda, and T. Akazaki

            "Observation of the resistance minimum in a gated superconductor-semiconductor junction with variable transparency"

            Czech. J. Phys. 46, 2507-2508 (1996).

 

            ABSTRACT: We have studied the differential resistance in a gated superconductor-normal-metal junction The zero-bias resistance shows a minimum as a function of the gate voltage, while the junction normal resistance measured at a high bias voltage shows a monotonic increase. The results show good agreement with the reflectionless tunneling theory in the ballistic motion regime.

 

178.    K. Takeda and K. Shiraishi

            "Theoretical studies on electronic structures of polypeptide chains"

            J. Phys. Soc. Jpn. 65 (2), 421-438 (1996).

 

            ABSTRACT: Electronic structures of polypeptide chains are theoretically studied. To extract the electronic tendency and/or electronic functions of individual amino acids, twelve kinds of homopolypeptide chains, which are formed by a single kind of amino acids, are considered, and their electronic structures are investigated by the first-principle band calculation. Polypeptide chains have the potential to be a semiconductor having a wide band gap of 3 similar to 5 eV. Their band-edge states are basically the ir electronic states and can delocalize along the peptide backbone. The degree of the delocalization depends on the kind of constituent amino acids and also the orientation of the amino acid side chains against the peptide backbone. We also investigate how the random alignment of amino acids affects the band-edge electronic structures by using the coherent potential approximation approach. In accordance with the kind of aligned amino acids, the aperiodicity in the alignment produces amalgamated electronic states so as to annihilate the individual amino acid's electronic identity, or produces persistent states in order to maintain their electronic characteristics.

 

179.    T. Takeuchi

            "Effect of contrast on the spatial integration process for moving Gabor patterns"

            Invest. Ophthalmol. Vis. Sci. 37 (3), 3378-3378 (1996).

 

            ABSTRACT:

180.    K. Tanaka, Y. Arikawa, M. Sekine, M. Ohtsu, Y. Harada, and M. Danerud

            "Highly sensitive and wideband optical detection in patterned YBa2Cu3O7-delta thin films"

            Appl. Phys. Lett. 68 (22), 3174-3176 (1996).

 

            ABSTRACT: We have measured the optical responses up to 18 GHz in patterned YBa2Cu3O7-delta thin films at various wavelengths by optical heterodyne mixing. The responsivity of the detectors is higher than 50 V/W below I Hz at various wavelengths and the responsivity is 20 mV/W at 780 nm and 150 mV/W at 1.55 mu m wavelengths in the regime of the modulation frequency from 3 GHz to 18 GHz. (C) 1996 American Institute of Physics.

 

181.    M. Tanimoto, K. Kanisawa, and M. Shinohara

            "Nanometer-scale current-voltage spectra measurement of resonant tunneling diodes using scanning force microscopy"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 35 (2B), 1154-1158 (1996).

 

            ABSTRACT: We demonstrate that a novel method of current-voltage (I-V) spectra measurement by scanning force microscopy (SFM) reveals local electrical characteristics of resonant tunneling diodes (RTDs) on a nanometer scale. Measured SFM I-V spectra of RTDs show negative differential resistance features, and the spatial resolution of this method was found to be 20 nm. Experimental evidence for the quantized nature of an SFM pointcontact was observed for the Brst time. High spatial resolution of this method was confirmed by a simple calculation for the area of current flow through RTD. Fine structure in the SFM I-V spectra was also observed.

 

182.    S. Tarucha, D. G. Austing, T. Honda, R. J. vanderHage, and L. P. Kouwenhoven

            "Shell filling and spin effects in a few electron quantum dot"

            Phys. Rev. Lett. 77 (17), 3613-3616 (1996).

 

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

 

183.    H. Teramae

            "Study on the behavior of energy convergence in ab initio crystal orbital calculations"

            Theor. Chim. Acta 94 (6), 311-331 (1996).

 

            ABSTRACT: This article studies the dependence on the cutoff scheme of ab initio crystal orbital calculations with no long-range correction. We have thoroughly studied the Namur cutoff and cell-wise cutoff schemes through calculations of polyethylene and LiH chains. The Namur cutoff gives the fastest energy convergence with respect to the number of neighbors (N-0). The energy convergence behavior with respect to N-0 depends on the basis set. The Namur cutoff shows the fastest convergence with the STO-3G basis set, intermediate convergence with the MINI basis set, and the slowest convergence with the (7s4p/3s) basis set. The cell-wise cutoff shows exactly the reverse order of the Namur cutoff. The Namur cutoff destroys the translational symmetry. Both the Namur cutoff and cell-wise cutoff schemes introduce slight asymmetry on the two equivalent C-C bonds of polyethylene when calculating with a C2H4 unit cell. The asymmetry with the Namur cutoff can be made to disappear by increasing N-0 a little. The calculations on two different unit-cell structures of trans-polyacetylene show the effect of the cutoff scheme on the total energy. Only the symmetric cutoff energies are the same. Disagreement related to the Namur cutoff disappears at N-0 = 20, however, that related to the cell-wise and modified symmetric cutoff schemes remains at N-0 less than or equal to 20, The optimized geometry and vibrational frequency are not as sensitive to the cutoff method except with the symmetric cutoff. A compilation of all results shows that the Namur cutoff is the superior cutoff scheme when calculating the insulator using the minimal basis set, especially the STO-3G basis set.

 

184.    Y. Tokura, T. Honda, K. Tsubaki, and S. Tarucha

            "Noninvasive determination of the ballistic-electron current distribution"

            Phys. Rev. B 54 (3), 1947-1952 (1996).

 

            ABSTRACT: Direct observation of the lateral current of ballistic electrons by probing with a small superconducting quantum interference device is reported. The current distribution near the end of a quantum wire shows collimation although over 30 subbands are occupied in the wire. Spreading of the collimated distribution corresponding to the transition from a ballistic to a diffusive regime is observed and is compared with simulations.

 

185.    Y. Tokura, T. Saku, and Y. Horikoshi

            "Electron scattering by steps in a vicinal heterointerface"

            Phys. Rev. B 53 (16), 10528-10531 (1996).

 

            ABSTRACT: Anisotropic Hall mobilities of a two-dimensional electron gas are observed in modulation-doped AlxGa1-xAs/GaAs heterostructures grown on a (001) GaAs vicinal substrate cut 2 degrees toward the (111)A direction. The mobility is larger in the [<(1)over bar 10>] direction. There is no anisotropy in mobilities for a sample grown on a 2 degrees vicinal substrate toward the (111)B direction. Electron scattering by an array of steps is proposed to account for the observed anisotropic Hall mobilities. The electron concentration dependence of mobility anisotropy implies that the origin of step potential is not interface roughness but localized dipole.

 

186.    Y. Tokura and S. Tarucha

            "Quasi-one-dimensional transport near the ballistic limit"

            Phys. Rev. B 53 (24), 16403-16407 (1996).

 

            ABSTRACT: Electron conductance of a two-dimensional wire at low temperature is studied in a semiclassical approximation taking into account the angular dependences of the scattering potential. The length dependence of the conductance is found to be nonuniversal, especially in the ballistic transport regime. The angular distribution of the emitting electrons at the end of the wire shows dynamical narrowing by the scattering process in the wire.

 

187.    K. Tsuru, S. Karimoto, S. Kubo, and M. Suzuki

            "Improved morphology and surface resistance of EuBa2Cu3O7-delta thin films on MgO substrates obtained by intermittent magnetron sputter deposition"

            Japanese Journal Of Applied Physics Part 2-Letters 35 (12B), L1666-L1668 (1996).

 

            ABSTRACT: We demonstrate that the surface morphology of off-center magnetron sputtered EUBa(2)Cu(3)O(7-delta) (EBCO) thin films on MgO (100) substrates is improved significantly by using the intermittent deposition method. This method comprises three steps. First, an initial EBCO layer, 2 to 10 unit cell layers thick, is grown at 630-660 degrees C under a low oxygen partial pressure of 0.1 Pa. Then the initial layer is in. situ. annealed for 30 min under the same conditions used for the deposition. Finally, another EBCO layer is grown on top of the first layer. An EBCO thin film grown in this way has an extremely smooth surface and the surface resistance at 50 GHz is 3 m Ohm or less at 77 K; which compares with the best value ever reported.

 

188.    M. Ueda, N. Imoto, and H. Nagaoka

            "Logical reversibility in quantum measurement: General theory and specific examples"

            Phys. Rev. A 53 (6), 3808-3817 (1996).

 

            ABSTRACT: A measurement process is logically reversible if the premeasurement density operator of the measured system is uniquely determined from the postmeasurement density operator and the outcome of the measurement. This paper analyzes the necessary and sufficient condition for a measurement process to be logically reversible and discusses specific examples on quantum-nondemolition measurements. quantum counting, and measurement of spin systems. It is shown that for any sharp measurement we can construct a logically reversible measurement that continuously approaches the sharp measurement with a decrease in the measurement error. A general condition for a measurement process to be reversed by another with a nonzero probability of success is given, and the implications of such physical reversibility are discussed.

 

189.    M. Uehara, T. Nagata, J. Akimitsu, H. Takahashi, N. Mori, and K. Kinoshita

            "Superconductivity in the ladder material Sr0.4Ca13.6Cu24O41.84"

            J. Phys. Soc. Jpn. 65 (9), 2764-2767 (1996).

 

            ABSTRACT: We have observed superconductivity in the ladder material Sr0.4Ca13.6Cu24O41.84 under pressures of 3 GPa and 4.5 GPa by means of electrical measurements. The superconducting transition temperatures T-c (onset) are 12 K and 9 K at 3 and 4.5 GPa, respectively. The superconducting volume fraction was obtained to be about 5% from magnetization measurement under 3.5 GPa at 4.2 K, indicating the bulk nature of the superconductivity in this system.

 

190.    K. Uwai and N. Kobayashi

            "Surface dielectric change of GaAs determined from surface photo-absorption spectra"

            Appl. Surf. Sci. 107, 42-47 (1996).

 

            ABSTRACT: We compare surface photo-absorption spectra observed for various surface structural transformations on GaAs (001) and (111)B surfaces. Surface conversions investigated here are ii) from (2 x 4) to (3 x 1) caused by Ga deposition, (ii) from (2 x 4) to (1 x 1) caused by H-adsorption on GaAs (001) surface, and (iii) from (2 x 2) to (root 19 x root 19) caused by As desorption on (111)B surface. The change in surface dielectric function is determined for each of the surface conversions using curve fitting based on the harmonic oscillator model of the dielectric function, Common peaks that coincide with the critical points of the dielectric function of GaAs are found in the spectra of the surface dielectric change thus determined. This indicates that the effect of bulk electronic states modified by the surface is significant in the surface photo-absorption spectra.

 

191.    K. Uwai and N. Kobayashi

            "Hydrogen adsorption on GaAs(001) surfaces observed by surface photoabsorption and reflectance difference spectroscopy"

            J. Vac. Sci. Technol. A-Vac. Surf. Films 14 (3), 879-884 (1996).

 

            ABSTRACT: Surface reflectance spectra are observed for H-adsorbed GaAs (001) surfaces. Atomic hydrogen produced with a hot tungsten filament is adsorbed on the (2x4) surface, converting it to (1x1). Reflectance difference (anisotropy) spectra show an enhanced peak at 2.8 eV upon H adsorption at room temperature, which is not consistent with the notion that this peak originates from As dimers. Analysis of surface photoabsorption spectra show that surface dielectric changes along [(1) over bar 10] for H adsorption and for Ga deposition can be represented by a superposition of a change at the bulk critical points E(1),E(2),E(0)' of GaAs and a broad feature centering at 2.5-2.7 eV. (C) 1996 American Vacuum Society.

 

192.    K. Uwai, Y. Yamauchi, and N. Kobayashi

            "In situ observation of nitridation of GaAs(001) surfaces by infrared reflectance spectroscopy"

            Appl. Surf. Sci. 101, 412-416 (1996).

 

            ABSTRACT: Nitridation of GaAs (001) surfaces grown by molecular beam epitaxy is observed by detecting the surface reflectance change caused by the formation of Ga-N and As-N bonds. Nitridation is performed by exposing (4 x 2) or (2 x 4) surfaces to atomic nitrogen generated with a heated tungsten filament in an As-free environment. Nitridation of the Ga-rich (4 x 2) surface results in a single reflectance peak at 1200 cm(-1) attributed to the formation of Ga-N bonds, while nitridation of the As-rich (2 x 4) surface results in another peak at 1000 cm(-1) attributed to As-N bonds in addition to the Ga-N peak.

 

193.    V. V. Vinod, S. Ghose, and P. P. Chakrabarti

            "Resultant projection neural networks for optimization under inequality constraints"

            IEEE Trans. Syst. Man Cybern. Part B-Cybern. 26 (4), 509-521 (1996).

 

            ABSTRACT: In this paper we propose Resultant Projection Neural Networks, based on the idea of orthogonal projections onto convex sets for solving optimization problems under inequality constraints, The proposed network is capable of solving optimization problems with inequality constraints which cannot be solved directly using a Hopfield network, The effect of various network parameters on the optimization process are theoretically analyzed, A probabilistic analysis of the expected performance of the network has been carried out for the 0-1 knapsack problem, Simulation results for the 0-1 knapsack, multidimensional 0-1 knapsack and job processing with deadlines are also shown, The average performance (mean and median) of the network compare quite well with optimal and suboptimal solutions obtained using standard techniques in conventional computers, However, there are some instances which do produce bad solutions.

 

194.    A. F. Volkov and H. Takayanagi

            "Effect of gate voltage on critical current in controllable supeconductor-normal-metal-superconductor Josephson junctions"

            Phys. Rev. B 53 (22), 15162-15167 (1996).

 

            ABSTRACT: The effect of gate voltage on critical current I-c ina superconductor-normal-metal-superconductor (S-N-S) Josephson junction of a field-effect transistor was studied theoretically in the dirty limit. The analysis in the case of arbitrary gate width 2L(1) compared to the spacing between the superconducting source and drain showed that two mechanisms are responsible for I-c decreasing with gate voltage. One is related to the decrease in coherence length L(T1) in the region underneath the gate electrode; it dominates when L(1) > L(T1). The second mechanism is related to the additional scattering of carriers at a nonuniform potential arising due to a difference between the carrier density underneath the gate and that outside this region. This mechanism dominates when L(1) much less than L(T1). The calculated carrier density dependence of I-c was in good agreement with the experimental results.

 

195.    A. F. Volkov and H. Takayanagi

            "ac Long-range phase-coherent effects in mesoscopic superconductor normal metal structures"

            Phys. Rev. Lett. 76 (21), 4026-4029 (1996).

 

            ABSTRACT: We calculate the conductance of a normal metal film (N) in contact with two superconductors (S) in the presence of a constant ((V) over bar S) and oscillating (V-omega cos omega t) bias voltage between N and S. It is shown that the conductance as a function of (V) over bar(S) has a Shapiro-like step at (V) over bar(S) = HBAR omega/2e. This exists even in the case when the spacing between two superconductors largely exceeds the coherence length in the normal metal, and the critical Josephson current is exponentially small. The amplitude of the Shapiro step decreases slowly with increasing temperature T in the form of T-1.

 

196.    T. H. Wang and S. Tarucha

            "Effects of finite drain voltage and finite temperature on coherent resonant transport in single electron tunneling regime"

            Appl. Phys. Lett. 69 (3), 406-408 (1996).

 

            ABSTRACT: Effects of a finite drain voltage and a finite temperature on coherent transport in the single electron tunneling regime are investigated for a novel quantum dot structure defined by two shallow etched trenches and two line Schottky gates. A regular amplitude modulation of Coulomb blockade oscillations is observed and attributed to coherent resonant transport. Increasing drain voltage disturbs the amplitude modulation more significantly than raising the temperature. This is explained in terms of the effects of nonmonochromatic electrons on the interference condition. (C) 1996 American Institute of Physics.

 

197.    S. Watanabe, Y. Jimbo, H. Kamioka, Y. Kirino, and A. Kawana

            "Development of low magnesium-induced spontaneous synchronized bursting and GABAergic modulation in cultured rat neocortical neurons"

            Neurosci. Lett. 210 (1), 41-44 (1996).

 

            ABSTRACT: Development of spontaneous synchronized bursting in the early stages of rat neocortical neuronal cultures was studied by whole-cell and extracellular recordings. Neocortical neurons from rat embryos were cultured on planar electrode arrays, and low Mg2+-induced spontaneous activity was recorded from 5 to 16 days in vitro (DIV). At 5-6 DIV the current synchronized to the bursting had only a slow component lasting 3-5 s, whereas in older cultures a fast transient component was dominant. A gamma-aminobutyric acid (GABA)(A) receptor antagonist, bicuculline methiodide, had little effect on the spontaneous activity at 5-6 DIV, whereas in older cultures it had a marked effect on the slow current component. These results suggest a role of GABAergic transmission in the development of synchronized activities.

 

198.    T. Watanabe and A. Matsuda

            "Evidence of the temperature-dependent interlayer coupling from the anisotropic transport properties in co-substituted single-crystal Bi2Sr2Ca(Cu1-xCox)(2)O-8+delta"

            Phys. Rev. B 54 (10), R6881-R6884 (1996).

 

            ABSTRACT: We report on the effect of Co impurity substitution on the anisotropic transport properties of Bi2Sr2Ca(Cu1-xCox)(2)O-8+delta single crystals. With Co doping, there is an increase in anisotropy gamma estimated from the scaling of the angular dependence of the in-plane resistivity with reduced field as well as in the out-of-plane resistivity. These results can be quantitatively explained by the two-dimensional Lawrence-Doniach model, if we assume that the anisotropy in the superconducting state is determined by the interlayer coupling just above T-c. The analysis highlights the specific feature in high-T-c cuprates that the effective interlayer coupling depends on temperature.

 

199.    T. Watanabe and A. Matsuda

            "Magnetoresistance and high-temperature resistivity of Bi2.1Sr1.9Ca1.0Cu2O8+delta single crystals"

            Physica C 263 (1-4), 313-316 (1996).

 

            ABSTRACT: We have measured the normal state magnetoresistance (-Delta sigma(perpendicular to); B perpendicular to I perpendicular to c, -Delta sigma(parallel to); B parallel to I perpendicular to c) of a Bi2.1Sr1.9Ca1.0Cu2O8+delta single crystal. At low temperatures (epsilon=(T-T-c)/T-c less than or equal to 0.1), the orbital magnetoresistance (-Delta sigma(perpendicular to) +Delta sigma(parallel to)) can be well fitted by the 2D limit of the Aslamazov-Larkin (AL) fluctuation (-Delta(ALO) alpha epsilon(-3)). At high temperatures (epsilon > 0.1), it can be fitted either by the contribution of the Maki-Thompson (MT) fluctuation or by the anomalous normal state magnetoresistance. We have also measured the resistivities of these crystals up to 870 K and found that in this slightly overdoped region the scattering rate can be expressed as a sum of the typical T-linear and the T-2 components. The T-2 component can be assigned to electron-electron scattering originating from the Fermi liquid.

 

200.    Y. Watanabe, S. Maeyama, F. Maeda, and M. Sugiyama

            "Application of synchrotron radiation to surface and interface characterization"

            Ntt Rev. 8 (5), 60-69 (1996).

 

            ABSTRACT: Fabrication technology at the nanometer scale to develop advanced devices and low-dimensional structures requires atomic-scale control of thin-film growth, selective-area growth, and ultra-fine photolithography. To develop such atomic-scale control techniques, advanced characterization at the atomic-scale is needed. We are now investigating surface and interface structures and ways to control growth modes by surface modification, and also trying to develop methods that allow realtime observation of thin-film crystal growth by using various methods of advanced materials analysis that use synchrotron radiation. This report presents recent results obtained by these techniques for S/GaAs and SrF2/S/GaAs, Sb/GaAs, and inAs/Se/GaAs, and also describes preliminary results from realtime crystal growth observation.

 

201.    M. J. Werner

            "Quantum statistics of fundamental and higher-order coherent quantum solitons in Raman-active waveguides"

            Phys. Rev. A 54 (4), R2567-R2570 (1996).

 

            ABSTRACT: The quantum dynamics of coherent optical pulses are studied using a nondiagonal coherent-state generalized P representation including photon-phonon interactions. Photon-number squeezing of coherent quantum solitons using spectral filtering is theoretically predicted. It is shown that Raman noise does not significantly reduce photon-number squeezing produced by spectral filtering of 1-ps fundamental coherent quantum solitons in optical fibers. Coherent Nsech pulses with N>1 can show a larger reduction in photon-number fluctuations even at room temperature. The reduction in quantum noise for N>1 is not restricted to photon number and an improvement of more than 3 dB is also found for the quadrature-phase squeezed soliton experiments using a fiber Sagnac interferometer at 77 K.

 

202.    T. Yamada, H. Yamaguchi, and Y. Horikoshi

            "Effect of growth interruption during GaAs/AlGaAs molecular beam epitaxy on (411)A substrates"

            Japanese Journal Of Applied Physics Part 2-Letters 35 (7A), L822-L824 (1996).

 

            ABSTRACT: We have studied the photoluminescent properties of AlGaAs/GaAs quantum wells grown by molecular beam epitaxy on (411)A GaAs substrates. We found that growth interruption with As supply degrades, whereas that under As-free or low-pressure As conditions improves the flatness of the heterointerface. These characteristics are very different from those for (100) GaAs substrates. The flattening transition under As-free conditions appeared to be related to Ga desorption during the growth interruption. We believe that Ga desorption plays an important role in maintaining flat (411)A surfaces.

 

203.    F. Yamaguchi and Y. Yamamoto

            "Current through a single atom"

            Electron. Lett. 32 (24), 2219-2221 (1996).

 

            ABSTRACT: Simple analytical formulas are presented for the current flowing through a single atom located between a pair of metallic electrodes and the number of electrons bound in the atom. the work function of the electrodes W, the highest occupied energy level of the atom -E(0), and the electrostatic charging energy U, determine how the atom becomes charged and how the current features nonlinearity via the Coulomb blockade and the Pauli exclusion principle.

 

204.    H. Yamaguchi, M. R. Fahy, and B. A. Joyce

            "Inhibitions of three dimensional island formation in InAs films grown on GaAs(111)A surface by molecular beam epitaxy"

            Appl. Phys. Lett. 69 (6), 776-778 (1996).

 

            ABSTRACT: A comparison has been made of the surface morphology of thin InAs films grown on GaAs (001) and (111)A substrates by molecular beam epitaxy using in situ reflection high energy electron diffraction and ex situ atomic force microscopy, InAs growth on (001) surface proceeds via the Stranski-Krastanov mechanism, with three-dimensional island formation beginning between one and two monolayers, but on the (111)A surface there is a two-dimensional made, independent of detailed growth conditions. This advantage accruing from the use of a novel index substrate provides the opportunity of fabricating a wide range of high quality heterostructures. (C) 1996 American Institute of Physics.

 

205.    H. Yamaguchi and Y. Horikoshi

            "Surface-defect formation on heavily doped InAs and GaAs layers studied by scanning tunneling microscopy"

            Phys. Rev. B 53 (8), 4565-4569 (1996).

 

            ABSTRACT: The surface atomic structure of GaAs and InAs layers heavily doped with Si is studied by using scanning tunneling microscopy. For GaAs, the straightness of dimer-vacancy rows is degraded by doping. The density df kinks in the rows coincides with the surface state density needed to move the surface Fermi level to the midgap. On the other hand, with InAs, the kink density is much lower than the surface-state density needed to move the level to the midgap. Self-consistent calculations of charge distribution in the neighborhood of the surface suggest that kink formation is governed by the competition between two processes: energy loss by new kink formation and energy gain by the electron trap from the conduction band to the surface state formed by the newly created kink Using this model, the low kink density observed for the InAs surface can be explained in terms of its small band gap of 0.36 eV.

 

206.    H. Yamaguchi, K. Kanisawa, and Y. Horikoshi

            "Reconstruction-dependent electron-hole recombination on GaAs(001) surfaces studied by using near-surface quantum wells"

            Phys. Rev. B 53 (12), 7880-7883 (1996).

 

            ABSTRACT: Using an ultrahigh-vacuum photoluminescence system, electron-hole recombination on clean reconstructed GaAs(001) surfaces is characterized by measuring photoluminescence spectra of near-surface quantum wells. The luminescence from the quantum well with an As-rich (2 x 4) surface is stronger than that with a Ga-rich (4 x 6) surface, showing that the surface recombination is faster with (4 x 6) than with (2 x 4).

 

207.    S. Yamamoto, K. Sato, H. Kurisu, M. Matsuura, S. Hirono, and Y. Maeda

            "Perpendicular Co-Cr magnetic recording media prepared by sputtering using ECR microwave plasma"

            IEEE Trans. Magn. 32 (5), 3825-3827 (1996).

 

            ABSTRACT: Perpendicular Co-Cr media were deposited on polyimide substrates by sputtering using an electron-cyclotron-resonance microwave plasma in an Ar sputtering gas pressure ranging from 3x10(-2) to 8x10(-2) Pa at a target to substrate distance from 170 to 230 mm. The accelerating voltage of the ions which bombard the media surface during deposition drastically affects the crystallographic and magnetic properties of Co-Cr films. Co-Cr media (50 nm in thickness) with good preferred crystal orientation (Delta theta(50) less than 5 degrees), high perpendicular magnetic anisotropy (H-k higher than 4 kOe), high perpendicular coercivity (H-c perpendicular to over 1400 Oe) and no initial layer were successfully deposited when the ion accelerating voltage was reduced less than about 20 V.

 

208.    Y. Yamamoto, J. Kaczanowski, Y. Kido, J. Nakata, H. Yamaguchi, and K. Takahei

            "Direct determination of impact-parameter-dependent stopping powers for million-electron-volt He ions penetrating Er-doped GaAs"

            Phys. Rev. A 53 (3), 1644-1652 (1996).

 

            ABSTRACT: We have directly determined the impact-parameter-dependent stopping powers for 2.0- and 2.5-MeV He ions passing through GaAs single crystals. The points reside in the preparation of the single-crystal sample with a dopant of a heavy element located in some definite interstitial site at definite depth and in synthesis of a Monte Carlo program to simulate accurately the ion trajectories. Er-doped homoepitaxial GaAs layers grown by molecular-beam epitaxy and by metal-organic chemical-vapor deposition were used for this purpose, As previously reported, fine single-crystal clusters of ErAs are formed in the GaAs host and Er takes the position exactly equivalent to the tetrahedral interstitial site. The present Monte Carlo simulation has revealed the fact that some definite impact-parameter region dominates the backscattering Er peak position and this region shifts continuously by tilting the incident beam axis slightly from a major crystal axis. The results obtained are compared with the Oen-Robinson [Nucl. Instrum. Methods 132, 647 (1976)] model and other theoretical predictions and dearly show that inner-shell excitations and ionizations contribute significantly to the stopping power even for large impact parameters.

 

209.    A. Yamashita

            "Capacitance-voltage hysteresis of an electrolyte-GaAs Schottky contact associated with field-enhanced trapping of hot electrons"

            Solid-State Electron. 39 (9), 1269-1275 (1996).

 

            ABSTRACT: Electro-optical properties of n-GaAs crystal were studied by using a transparent, electrolyte Schottky contact and the following results were obtained: highly sensitive detection of some critical-point energies in the band structure of GaAs and the Franz-Keldysh shift of the fundamental absorption edge at high electric fields; the observation of a new capacitance-voltage hysteresis effect of the electrolyte-GaAs contact, with a characteristic threshold-field. Details of this hysteresis are presented with related photocapacitance spectra of the contact. In addition, its mechanism is explained by assuming field-enhanced trapping of hot electrons at complex deep-levels and their succeeding charge-state controlled structural transformation. Copyright (C) 1996 Elsevier Science Ltd

 

210.    Y. Yamauchi, K. Uwai, and N. Kobayashi

            "In situ monitoring of adsorption and desorption of atomic nitrogen on GaAs (001) and (111)A surfaces"

            Japanese Journal Of Applied Physics Part 2-Letters 35 (1B), L80-L83 (1996).

 

            ABSTRACT: Nitridation of GaAs (001) and (111)A surfaces grown by molecular beam epitaxy (MBE) is investigated by in situ Fourier transform infrared spectroscopy. Nitridation is carried out by exposing the GaAs surface to atomic nitrogen in the same MBE chamber used for growth using a tungsten filament resistively heated to 2100 degrees C. After nitridation for 90 minutes, the infrared reflectance spectra indicate that nitridation of the As-rich (2 x 4) surface at 450 degrees C results in two IR reflectance peaks at 1200 and 1000 cm(-1). On the other hand, nitridation of the Ga-rich (4 x 2) surface at 530 degrees C and the (111)A surface at 490 degrees C results in a single peak at 1200 cm(-1). These results indicate that the peak at 1200 cm(-1) is attributed to the Ga-N bond, and that at 1000 cm(-1) to the As-N bonds. Nitrogen desorption from the nitrided surface is found to occur at 450 degrees C and is induced by atomic hydrogen.