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

            "Improving The Mobility Of An In0.52al0.48as/In0.53ga0.47as Inverted Modulation-Doped Structure By Inserting A Strained Inas Quantum-Well"

            Appl. Phys. Lett. 65 (10), 1263-1265 (1994).

 

            ABSTRACT: The mobility of two-dimensional electrons in an In0.52Al0.48As/In0.53Ga0.47As inverted modulation-doped structure improved by inserting an InAs quantum well into the InGaAs channel. This letter addresses the main cause of this mobility improvement. By optimizing the thickness of the InAs quantum well, its distance from the underlying InAlAs spacer layer, and the InAlAs spacer-layer thickness, maximum mobilities of 16 500 cm2/V s at 300 K and 155 000 cm2/V s at 10 K are attained. The improvement in mobility is attributed to a decrease in scattering caused by ionized impurities, interface-roughness, and trap impurities. This decrease is a result of the superior confinement of two-dimensional electron gas in the InAs quantum well.

 

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

            "Selective-Area Metalorganic Chemical-Vapor-Deposition Growth For Hexagonal-Facet Lasers"

            J. Cryst. Growth 145 (1-4), 302-307 (1994).

 

            ABSTRACT: In order to obtain low threshold hexagonal-facet (HF) lasers by reducing their size! it is necessary to know the selective growth conditions of a hexagonal prism on a smaller area. We describe the metalorganic chemical vapor deposition (MOCVD) growth conditions for GaAs and AlGaAs hexagonal prisms on a SiO2 masked (111)B substrate. The crystal shape and the facet strongly depend on the size of the mask windows, on the working pressure during growth, and on the growth parameters of the substrate temperature and the partial pressure of arsine. Furthermore, we explain the mechanism of the hexagonal prism growth by using the change of growth rate between low-index facet planes. By using optimized growth conditions, a 2 mu m sized I-IF laser structure with flat GaAs/AlGaAs heterointerface can be grown.

 

3.         H. M. Appelboom, H. Sato, and M. Naito

            "Lanthanum And Calcium-Doped Yba2cu3oy Films Grown At Low-Temperature And Pressure"

            Physica C 221 (1-2), 125-135 (1994).

 

            ABSTRACT: We have fabricated lanthanum and calcium doped YBa2Cu3Oy films with co-evaporation at low oxygen/ozone pressures according to the stoichiometric formulae YLaxBa2-xCu3Oy and Y1-xCaxBa2Cu3Oy. The lanthanum doped films show a strong reduction or absence of solid solubility of lanthanum on the barium site compared to bulk material made at atmospheric oxygen pressure, analogous to what has been reported previously for Sm1+xBa2-xCu3Oy films [Physica C 214 (1993) 323]. In the calcium doped films we find a solid solubility limit which is apparently similar to that reported for bulk material synthesized at atmospheric oxygen pressure. The reduction of solid solubility in the YLaxBa2-xCu3Oy system is explained by a shift of the low oxygen pressure decomposition line to higher pressure with lanthanum doping. We also report here on the successful synthesis of oxygen-deficient superconducting Y1-xCaxBa2Cu3O6 films.

 

4.         E. Atsumi, M. Takagi, and K. Yokosawa

            "Local Motion Detection By Hierarchical Neural-Network"

            Syst. Comput. Jpn. 25 (11), 24-35 (1994).

 

            ABSTRACT: Perception of visual motion is thought to consist of two stages: generation of candidates and their interaction to determine true motion. In this paper, a three-layered neural network is applied to detect local visual motion. The network, after learning, could categorize nine types of motion and obtained a motion detection algorithm that included the two states of perception. The internal representations for the first stage agree with the functions of on-center and off-center cells, and those for the second stage agree with the functions of lateral inhibition. We also tried to detect arbitrary motions by combining multi-resolution representation of images with the neural network.

 

5.         T. Bever, Y. Hirayama, and S. Tarucha

            "Quantized Conductance In Ingaas Point Contacts At High-Temperatures"

            Jpn. J. Appl. Phys. Part 2 - Lett. 33 (6A), L800-L803 (1994).

 

            ABSTRACT: We used focused ion beam insulation writing to fabricate quantum point contacts in the two-dimensional electron gas of an InGaAs/InAlAs heterostructure. The conductance as a function of voltage on an adjacent in-plane gate exhibited steps for temperatures up to 60 K. From the temperature and source-drain voltage and magnetic field dependence of the conductance steps, we estimated the one-dimensional subband spacing to be 15 meV.

 

6.         T. Bever, Y. Hirayama, and S. Tarucha

            "Strong Negative Transconductance In In-Plane-Gate Transistors Written By Focused-Ion-Beam Implantation"

            J. Appl. Phys. 75 (11), 7573-7575 (1994).

 

            ABSTRACT: A strong negative transconductance is investigated in in-plane-gate transistors written by focused-ion-beam implantation in the two-dimensional electron gas in modulation-doped AlGaAs/GaAs heterostructures. This occurs in a configuration where two in-plane gates G1 and G2 used to control the current through a channel lying between them are biased with different voltages V(g1), and V(g2). When the voltage V(g2)<0 is held constant, the current through the channel can be reduced to zero by increasing V(g1) beyond a critical value. In an earlier study this effect was attributed to velocity modulation. It is found, however, that in this regime V(g1) causes a very small current I(g2) to flow across gate G2. It is observed that changes in I(d) are correlated to changes in I(g2) and thus conclude that I(g2) is responsible for the strong negative transconductance.

 

7.         T. Bever, Y. Hirayama, and S. Tarucha

            "Enhanced Collimation In Narrow Channels Fabricated By Focused-Ion-Beam Implantation"

            J. Appl. Phys. 75 (5), 2477-2480 (1994).

 

            ABSTRACT: We investigate the collimation factor of narrow channels defined by focused-ion-beam insulation writing in the highly mobile two-dimensional electron gas of an AlGaAs/GaAs heterostructure. We show that the degree of collimation can be enhanced by appropriate channel design. Additional boundary roughness caused by selective implantation of ions along the channel boundary considerably increases the collimation.

 

8.         G. Bjork, A. Karlsson, and Y. Yamamoto

            "Definition Of A Laser Threshold"

            Phys. Rev. A 50 (2), 1675-1680 (1994).

 

            ABSTRACT: We propose that the threshold of a laser is more appropriately described by the pump power (or current) needed to bring the mean cavity photon number to unity, rather than the conventional ''definition'' that it is the pump power at which the optical gain equals the cavity loss. In general the two definitions agree to within a factor of 2, but in a class of microcavity lasers with high spontaneous emission coupling efficiency and high absorption loss, the definitions may differ by several orders of magnitude. We show that in this regime the laser undergoes a transition from a linear (amplifier) behavior to a nonlinear (oscillatory) behavior at our proposed threshold pump rate. The photon recycling resulting from the high spontaneous emission coupling efficiency and high absorption may in this case result in lasing without population inversion, and coherent light is generated via ''loss saturation'' instead of gain saturation. This mechanism for lasing without inversion is very different from lasing without inversion using a radiation trapped state.

 

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

            "Wannier Exciton Superradiance In A Quantum-Well Microcavity"

            Phys. Rev. B 50 (23), 17336-17348 (1994).

 

            ABSTRACT:

10.       S. J. Chang and K. Takahei

            "Studies Of Gaaser Impact Excited Electroluminescence Devices"

            Appl. Phys. Lett. 65 (4), 433-435 (1994).

 

            ABSTRACT: We report on the study of impact excitation of Er ions in GaAs. The metalorganic chemical vapor deposition grown, p+-n structured electroluminescence (EL) devices were fabricated by growing, at different temperatures, GaAs:Er layers on top of the n+ GaAs substrates. P+ layers of GaAs were made by Zn diffusion from the top surfaces. When we forward biased these diodes, the EL spectra were similar to the respective photoluminescence (PL) spectra of each sample. The spectra of the samples differed for the various growth temperatures. However, when we reverse biased these diodes, the EL spectra are the same for all samples but different from the PL spectra. These results indicate that the Er center(s) excited by direct impact is different from the Er center(s) excited through electron-hold recombination and the subsequent energy transfer.

 

11.       A. Chavezpirson, H. Ando, H. Saito, and H. Kanbe

            "Quantum-Wire Microcavity Laser Made From Gaas Fractional Layer Superlattices"

            Appl. Phys. Lett. 64 (14), 1759-1761 (1994).

 

            ABSTRACT: We report the first demonstration of lasing action in a quantum wire microcavity semiconductor laser made from an array of (AlAs)1/4(GaAs)3/4 fractional-layer superlattice (FLS) quantum wires. The FLS growth method produces uniform, densely packed, damage-free arrays of nanometer-size quantum wires which are integrated into an optical microcavity that is the size of the wavelength of the light. We obtain room temperature optically pumped lasing for wavelengths from 670 to 690 nm. The lasing output is linearly polarized parallel to the quantum wires, reflecting the higher optical gain for polarization direction parallel to the wires. The combination of a semiconductor quantum wire active material with an optical microcavity offers the possibility of ultimately compact, highly efficient laser sources.

 

12.       S. Friberg

            "Quantum-Wire Microcavity Laser Exhibits Unique Modulation Properties"

            Laser Focus World 30 (9), 80-80 (1994).

 

            ABSTRACT:

13.       S. Friberg

            "Noninvasive Readout Technique Preserves Soliton Signal"

            Laser Focus World 30 (1), 15-16 (1994).

 

            ABSTRACT:

14.       M. Fujiki

            "Optically-Active Polysilane Homopolymer - Spectroscopic Evidence Of Double-Screw-Sense Helical Segmentation And Reconstruction Of A Single-Screw-Sense Helix By The Cut-And-Paste Technique"

            J. Am. Chem. Soc. 116 (26), 11976-11981 (1994).

 

            ABSTRACT: We have studied the skeleton conformation of optically active polysilane homopolymer, poly(methyl((S)-2-methylbutyl)silane) (1), as a model of flexible chainlike polymers in solution, by means of various optical spectra (UV absorption, circular dichroism, fluorescence, fluorescence excitation, and fluorescence anisotropy), NMR spectra (C-13 and Si-29), intrinsic viscosity as a function of molecular weight of polymer, screw-sense-selective photolysis, and GPC analysis equipped with a photodiode array UV detector. From a comparison among its circular dichroism, UV absorption, fluorescence, and fluorescence excitation spectra, we concluded that both P-screw-sense, tight helical and M-screw-sense, loose helical segments coexist in the same chain of 1-diastereomeric helical segment-like block structure. The screw-sense-selective photolysis suggests that segments responsible for P- and M-screw-senses consist of nine silicon atoms. On the basis of this conformational model, modified 1* with almost a single P-screw-sense was reconstructed by the screw-sense-selective ''cut-and-paste'' procedure used for original 1.

 

15.       M. Fujiki

            "Effect Of Main-Chain Length In The Exciton Spectra Of Helical-Rod Polysilanes As A Model Of A 5-Angstrom Wide Quantum-Wire"

            Appl. Phys. Lett. 65 (25), 3251-3253 (1994).

 

            ABSTRACT:

16.       M. Fujiki

            "Ideal Exciton Spectra In Single-Screw And Double-Screw Sense Helical Polysilanes"

            J. Am. Chem. Soc. 116 (13), 6017-6018 (1994).

 

            ABSTRACT:

17.       T. Fujisawa, T. Bever, Y. Hirayama, and S. Tarucha

            "Nanostructure Fabrication And The Science Using Focused Ion-Beams"

            J. Vac. Sci. Technol. B 12 (6), 3755-3759 (1994).

 

            ABSTRACT:

18.       T. Fujisawa, Y. Hirayama, and S. Tarucha

            "Algaas/Ingaas/Gaas Single-Electron Transistors Fabricated By Ga Focused Ion-Beam Implantation"

            Appl. Phys. Lett. 64 (17), 2250-2252 (1994).

 

            ABSTRACT: Single electron transistors are formed in an AlGaAs/InGaAs/GaAs modulation-doped heterostructure by Ga focused ion beam implantation. The AlGaAs/InGaAs/GaAs system has a high two-dimensional electron gas density and facilitates a lateral constriction whose depletion length is much smaller than that in a conventional AlGaAs/GaAs system. A dot structure confined by a small depletion spreading of less than 0.15 mum is formed by the ion implantation. This ion implantation is also employed to form in-plane gates for controlling the tunneling junctions between the dot and reservoirs, and the number of electrons in the dot. Coulomb oscillations and a Coulomb staircase have been clearly observed by controlling three in-plane gates.

 

19.       T. Fukuda

            "Determination Of Silver Coverage On Si(111) 3x1 (6x1)-Ag Surfaces"

            Phys. Rev. B 50 (3), 1969-1972 (1994).

 

            ABSTRACT: The number of silver atoms incorporated into a Si(111)3 X 1(6 X 1)-Ag structure is determined by scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES). Silver MNN Auger intensities from surfaces with two different compositions were compared between clean 7 X 7, (square-root 3 X square-root 3)R 30-degrees-Ag, and 3 X 1(6 X 1)-Ag structures, which were determined from scanning tunneling microscopy images. From the AES intensity ratio and known occupancies of each reconstruction, the number of Ag atoms incorporated into the 3 X 1(6 X 1)-Ag structure was determined to be 0. 36+/-0.16 ML. This value is close to 1/3 ML, suggesting that one of the two rows observed by STM does not consist of Ag atoms.

 

20.       T. Fukuda

            "Preservation Of The Phase-Boundary Of Si(111) 7x7 Structure In Air Studied By Force Microscopy"

            Jpn. J. Appl. Phys. Part 2 - Lett. 33 (6A), L797-L799 (1994).

 

            ABSTRACT: Si(111) surfaces cleaned under ultrahigh vacuum were studied by force microscopy in air. 7 x 7 domain boundaries associated with the phase transition from 1 x 1 to 7 x 7 during cooling were imaged as 1.0 approximately 1.5 angstrom high protrusions. The morphology was quite consistent with results from in situ techniques. For rapidly quenched surfaces, disordered 1 x 1 triangles were also seen in the middle of terraces. These structures may be related to the difference in surface atom densities and the difference in reaction to oxygen.

 

21.       U. Geigenmuller and M. Ueda

            "Nonadiabatic Analysis Of The Josephson Critical-Current Influenced By Quantum Phase Fluctuations"

            Phys. Rev. B 50 (13), 9369-9375 (1994).

 

            ABSTRACT: The influence of the electromagnetic environment on the dc Josephson current is studied allowing for nonadiabatic motion of the phase difference across a junction. The critical current is evaluated nonperturbatively within mean-field theory, fully taking into account the nonlocal kernels in the Ambegaokar-Eckern-Schon effective action. It turns out that the adiabatic approximation, which can be justified when the superconducting energy gap exceeds the charging energy, yields qualitatively correct results even for the opposite case, although quantitative deviations from the adiabatic approximation are found to be substantial in some experimentally accessible regions.

 

22.       U. Geigenmuller and M. Ueda

            "Suppression Of The Josephson Current By Quantum Phase Fluctuations - Beyond The Adiabatic Approximation"

            Physica B 194, 1005-1006 (1994).

 

            ABSTRACT: We study how the Josephson current in a shunted junction is suppressed when the energy gap DELTA is not large compared to the charging energy E(C). Then the time dependence of the nonlocal kernels in the effective action describing the junction becomes important. For low ratios of the Josephson energy to E(C), the Josephson current deviates by tens of percent from what one obtains in the adiabatic limit (i.e. DELTA >> E(C)).

 

23.       M. Georgiou, P. Mandel, and K. Otsuka

            "Modulation Of A 2-Model Laser"

            IEEE J. Quantum Electron. 30 (3), 854-859 (1994).

 

            ABSTRACT: We analyze a two-mode laser; described by rate equations, whose gain is periodically modulated. The nature of the response varies significantly with the modulation amplitude. We study both the small modulation in which the pump parameter remains always above the lasing threshold for the second mode, and the deep modulation in which the pump parameter is located during part of the,cycle between the single-mode and the two-mode thresholds. Apart from the strong McCumber nonlinear resonance at the relaxation oscillation frequency, we describe a rich variety of nonlinear properties such as multistability among periodic and quasi-periodic solutions, and small resonances in the vicinity of the second (and lower) internal frequency. We also identify domains that suggest the occurrence of the traditional routes to chaos.

 

24.       O. Hasegawa, M. Ishizuka, and K. Yokosawa

            "Realtime Parallel And Cooperative Recognition Of Human Face For A Naturalistic Visual Human Interface"

            Syst. Comput. Jpn. 25 (11), 11-23 (1994).

 

            ABSTRACT: The concept of a Visual Software Agent (VSA), i.e., an anthropomorphic agent possessing a realistic human form and communication functions that create an interface with the user, is proposed. Research is proceeding on its implementation on a parallel computer. In this paper, we describe a method that is effective as the visual input function of the anthropomorphic agent. This method recognizes and extracts only one person (user) directly facing the camera in a moving image in which several people occasionally enter and leave. The recognition method can be executed in real time in a typical indoor environment. The background and the lighting do not have to be restricted and recognition can be achieved in real time by a parallel computer. In addition, this technique simulates the initial stage of human visual functions and is based on the parallel extraction and integration of multiple image features. The movements of visual attention of cognitive psychology can also be simulated. An anthropomorphic agent derived from this approach successively looks at multiple human faces, fixes its gaze only on a specific person, and synthesizes agent behavior that approximate that of humans. These moving image recognition and synthesis processes were implemented on a newly designed parallel computer.

 

25.       I. Hashimoto, T. Mashiko, T. Mizuta, T. Imada, K. Iwase, and H. Okazaki

            "Visualization Of A Moving Quadrupole With Magnetic Measurements Of Peripheral-Nerve Action Fields"

            Electroencephalogr. Clin. Neurophysiol. 93 (6), 459-467 (1994).

 

            ABSTRACT: Magnetic compound action fields (CAFs) over the right arm were measured from 63 sensor positions with two 7-channel SQUID gradiometer systems following electrical stimulation of the median nerve at the wrist. The field mapping of the CAFs revealed a propagating quadrupolar pattern with the leading depolarization and trailing repolarization fronts. The average distribution of the CAFs in the longitudinal direction was 9.0 cm in length for the depolarization field and 7.3 cm for the repolarization field in good agreement with a theoretical prediction based on the duration (3 msec) of the CAFs and the conduction velocity of the nerve (50 m/sec); The distance between the maxima of the depolarization front and the minima of the repolarization front was 6.3 cm. This spatial separation of the learning and trailing dipole locations suggests in part mutual cancellation of the fields with opposite polarity at or near the depolarized segment of nerve fibers.

 

26.       N. Hatakenaka, S. Kurihara, and T. Ogawa

            "Andreev-Reflected Photons"

            Physica B 194, 1699-1700 (1994).

 

            ABSTRACT: We investigate theoretically the Andreev-reflected photons in a system with two vacuum-semiconductor and semiconductor-superconductor interfaces, taking into account the multiple reflections of a polariton at two interfaces. With the use of the Andreev reflection of an electron-hole pair in this geometry, we propose a novel generation scheme of a phase-conjugated photon with respect to the incident one. This mechanism is quite different from conventional methods using optical nonlinearities. The additional-boundary-condition problems axe also reexamined from a viewpoint of an electron-hole picture.

 

27.       N. Hatakenaka, T. Ogawa, and S. Kurihara

            "Squeezing Of Photons Through Josephson Tunnel-Junctions"

            Physica B 194, 1701-1702 (1994).

 

            ABSTRACT: We propose a novel scheme for generating squeezed states of photon, which scheme is based on a nonadiabatic effect of photons on a two-state system. This is realized in a Josephson tunnel junction weakly coupled with photon fields in an optical cavity. The supercurrent fluctuation is also shown to be affected by its surrounding electromagnetic field as well as by the electronic system.

 

28.       H. Hayakawa, S. Nishida, Y. Wada, and M. Kawato

            "A Computational Model For Shape Estimation By Integration Of Shading And Edge Information"

            Neural Netw. 7 (8), 1193-1209 (1994).

 

            ABSTRACT: In constructing a computational model for human perception of shape-from-shading, we must solve two major problems: (1) How do we estimate the shape within a small number of iterations? and (2) How do we integrate the shading and edge information for shape estimation? To solve the first problem, we propose a solution for the shape-from-shading problem by using forward and approximated inverse optics. Because the surface normal modification required due to the brightness error is separated from that required due to the smoothness constraint, we can use a simple and fast algorithm for each modification. To solve the second problem, we propose a computational model for shape estimation by integration of shading and edge information. The model is comprised of three modules for the surface normal, discontinuity, and light direction estimation. A rather weak interaction among the three modules can undo the shape-from-shading problem that resembles the chicken-and-egg problem.

 

29.       O. Hellman

            "Impurity-Mediated One-Dimensional Crystallization Of Thin Amorphous-Ge Films On Si(111)"

            J. Appl. Phys. 76 (6), 3818-3822 (1994).

 

            ABSTRACT: We have observed peculiar low temperature crystallization dynamics of thin amorphous Ge films deposited on Si (111):7X7 substrates. The one-dimensional geometry and low temperature kinetics of this crystallization indicate an impurity mediated mechanism similar to that suggested by Nygren, McCallum, Thornton, Williams, and Olson [Mater. Res. Soc. Symp. Proc. 100, 403 (1988)]. Interaction is observed between the buried surface structure and the crystallizing Ge film, in some cases resulting in Ge which grows epitaxially not on the bulk Si, but on the 7X7 reconstruction, effectively a two-dimensional substrate.

 

30.       O. Hellman

            "Buried Reconstruction Inhibition Of Solid-Phase Epitaxy Of Ge On Si(111)"

            J. Vac. Sci. Technol. A-Vac. Surf. Films 12 (5), 2825-2829 (1994).

 

            ABSTRACT: We study the epitaxial crystallization of a thin film of amorphous Ge deposited at room temperature on Si (111). Silicon surface features which are buried beneath the Ge film are seen to affect the rate of crystallization. In particular, solid phase growth is observed to be enhanced at surface steps and defects in the surface reconstruction. We demonstrate that control of Ge crystallization morphology is possible through manipulation of Si surface structure.

 

31.       H. Hibino and T. Ogino

            "Scanning-Tunneling-Microscopy Observations Of Ge Solid-Phase Epitaxy On Si(111)"

            Appl. Surf. Sci. 82-3, 374-379 (1994).

 

            ABSTRACT: Solid-phase epitaxy (SPE) of Ge on a clean, 7 x 7-reconstructed Si(111) surface is investigated by scanning tunneling microscopy. Although Ge layers of four monolayers (ML) thick crystallize in the registry of the 7 x 7 reconstruction preserved at the amorphous Ge/Si interface, the 7 x 7 reconstruction hardly influences the SPE of 2 ML thick Ge layers. This difference is due to the reduced movement of atoms at the interface with thicker overlayers.

 

32.       H. Hibino and T. Ogino

            "Trace Of Interface Reconstruction In Ge Solid-Phase Epitaxy On Si(111)"

            Phys. Rev. B 49 (8), 5765-5768 (1994).

 

            ABSTRACT: We describe the mechanism of solid-phase epitaxy (SPE) of Ge on a Si(111)-7 X 7 surface using reflection high-energy electron diffraction and scanning tunneling microscopy. Amorphouslike Ge layers crystallize in the registry of the 7 X 7 reconstruction preserved at the Ge/Si interface. The preferred basic unit of epitaxy is a triangular domain corresponding to four half-units of the 7 X 7 reconstruction. Faultedly stacked (twinned) domains cover almost half of the surface at the initial stage of SPE because Ge grows epitaxially on both the unfaulted and faulted halves of the 7 X 7 reconstruction. These twinned Ge layers are transformed into normally stacked Ge layers above 400-degrees-C.

 

33.       H. Hibino and T. Ogino

            "Transient Step Bunching On A Vicinal Si(111) Surface"

            Phys. Rev. Lett. 72 (5), 657-660 (1994).

 

            ABSTRACT: We used high-temperature scanning tunneling microscopy to observe, in real time, the step rearrangement induced by a (7 x 7) reconstructive phase transition on a vicinal Si(111) surface misoriented toward [112BAR]. A new transient step bunching is found between a high-temperature phase consisting of single-layer steps with nonreconstructed terraces and a low-temperature phase of a mixture of single-and triple-layer steps with (7 x 7) reconstructed terraces. The transient step bunching indicates that the free energy of the (7 x 7) reconstructed step edge is larger than that of the nonreconstructed step edge just below the phase transition temperature.

 

34.       H. Hibino, N. Shimizu, K. Sumitomo, Y. Shinoda, T. Nishioka, and T. Ogino

            "Pb Preadsorption Facilitates Island Formation During Ga Growth On Si(111)"

            J. Vac. Sci. Technol. A-Vac. Surf. Films 12 (1), 23-28 (1994).

 

            ABSTRACT: On a clean Si(111)-7X7 surface, Ge grows in the Stranski-Krastanov mode. At 300-450 degrees C, relaxed islands begin to form when. the Ge growth is 6 monolayers (ML) thick. When Ge is grown on a Pb/Si(111)-root 3X root 3 surface, Pb segregates on the surface and agglomerates into two-dimensional islands. And the critical thickness for the formation of relaxed island becomes 4 ML. This change in critical thickness is explained by Pb reducing the surface energy or by an improved crystallinity of Ge layers (due to a simplified substrate surface reconstruction), or by both.

 

35.       Y. Hirota

            "Effects Of Dissolved-Oxygen In A Deionized Water-Treatment On Gaas Surface"

            J. Appl. Phys. 75 (3), 1798-1803 (1994).

 

            ABSTRACT: This article presents a new passivation method with an As and/or hydrogenated As layer on a GaAs surface. X-ray photoelectron spectroscopy was employed to investigate the influences of dissolved oxygen on a GaAs surface during the de-ionized water treatment. It is shown that reduction of dissolved oxygen in de-ionized water accelerates the removal of Ga and As oxides from the surface, and that the de-ionized water treatment in an extremely low concentration of dissolved oxygen produces arsenic and/or hydrogenated arsenic layer due to the liberation of Ga atoms near the surface. These phenomena are discussed based on the chemical reaction between the GaAs surface and dissolved oxygen in de-ionized water. The arsenic and hydrogenated arsenic layer is available for preserving the oxide-free and damage-free GaAs surface.

 

36.       Y. Hirota, T. Ogino, Y. Watanabe, and M. Oshima

            "Synchrotron-Radiation Photoelectron-Spectroscopy Study For Gaas (001) Surface Prepared By Deoxygenated And Deionized Water-Treatment"

            Appl. Phys. Lett. 65 (16), 2036-2038 (1994).

 

            ABSTRACT: The thermal effects on an n-type GaAs (001) surface prepared by deoxygenated and de-ionized water (DODIW) treatment are investigated by synchrotron-radiation photoelectron spectroscopy (SRPES) in the temperature range from room temperature (RT) to 500-degrees-C. SRPES confirms there are no oxides. There is, however, excess elemental arsenic and/or hydrogenated arsenic on the surface before heating, which evaporates when heated in a high vacuum. SRPES also shows that the surface Fermi level lies almost 0.9 eV above the maximum of valence band before heating, and moves toward the midgap during heating. After cooling to RT, it returns to the near-flat band position (1.0 eV). These experimental results suggest that DODIW-treated GaAs (001) surface can attain a low-density surface state. (C) 1994 American Institute of Physics.

 

37.       Y. Horikoshi, M. R. Fahy, M. Kawashima, K. Furukawa, M. Fujino, and N. Matsumoto

            "A New Si Doping Source For Gaas Growth By Molecular-Beam Epitaxy"

            Jpn. J. Appl. Phys. Part 2 - Lett. 33 (3B), L413-L416 (1994).

 

            ABSTRACT: A new Si cluster material, tertiary-butyloctasilacubane (tBuSi)8, is used as an efficient Si doping source for molecular beam epitaxy of GaAs. The vapor pressure of this material varies according to an activation energy of 1.51 eV. A Si concentration of 2 x 10(20) /cm3 is obtained at a Si cluster cell temperature of 210-degrees-C and a GaAs growth rate of 1 mum/h. Although the grown layers suffer from heavy carbon contamination from the Si cluster, this problem can be alleviated by increasing the substrate temperature.

 

38.       Y. Horikoshi and S. Minagawa

            "Metalorganic Vapor-Phase Epitaxy 1994 - Proceedings Of The 7th International-Conference On Metalorganic Vapor-Phase Epitaxy - Yokohama, Japan, 31-May-1994 3-June-1994 - Preface"

            J. Cryst. Growth 145 (1-4), R9-R10 (1994).

 

            ABSTRACT:

39.       T. Horiuchi, O. Niwa, and H. Tabei

            "Detection Of Reversible Redox Species By Substitutional Stripping Voltammetry"

            Anal. Chem. 66 (8), 1224-1230 (1994).

 

            ABSTRACT: We have achieved the highly sensitive electrochemical detection of reversible redox species by a new type of stripping analysis named substitutional stripping voltammetry (SSV). This analysis requires an interdigitated array (IDA) microelectrode in a sample solution Combined with a macroelectrode in a second cell. The second cell contains an electroactive species which deposits reversibly on the electrode: The charge generated by the redox cycling reaction of the sample at the IDA is transmitted to the macroelectrode and accumulated by the deposition of metal ion species on the macroelectrode. A large signal can be obtained immediately by stripping the deposited species. A linear relationship was achieved between the concentration and the stripping peak current when ruthenium hexaammine was used as the sample and silver ions were used as the reversibly deposited species. A very low detection limit of 10 pmol/dm(3) was also obtained because the underpotential deposition of silver ions accompanies the ruthenium hexaammine redox cycling. This is because the stripping peak potential is different from that of ordinary deposition which occurs in the initial stage of the potential scan of the macroelectrode. The charge accumulation by SSV is superior to the electrical integration of the redox current of ruthenium hexaammine at the IDA.

 

40.       R. Hull, J. C. Bean, L. J. Peticolas, B. E. Weir, K. Prabhakaran, and T. Ogino

            "Misfit Dislocation Propagation Kinetics In Ge(X)Si(1-X) Ge(100) Heterostructures"

            Appl. Phys. Lett. 65 (3), 327-329 (1994).

 

            ABSTRACT: We report measurements of misfit dislocation propagation velocities in GexSi1-x epilayers grown upon Ge(100) substrates, as opposed to the more usual Si(100) substrates. This geometry allows us to study structures with high Ge concentration (x greater-than-or-equal-to 0.8) and to compare with previous extensive measurements for lower Ge concentration layers (x less-than-or-equal-to 0.35) grown upon Si(100). It is found that all data are well described by a misfit dislocation velocity which is linear with excess stress, and which incorporates a compositionally dependent activation energy with linear interpolation between bulk values for Si and Ge. The combined data sets from structures grown on Si(100) and Ge(100) substrates is analyzed in the framework of the diffusive double kink model for dislocation motion.

 

41.       B. Huttner and A. K. Ekert

            "Information Gain In Quantum Eavesdropping"

           J. Mod. Opt. 41 (12), 2455-2466 (1994).

 

            ABSTRACT: We analyse the information obtained by an eavesdropper during the various stages of a quantum cryptographic protocol associated with key distribution. We provide both an upper and a lower limit on the amount of information that may have leaked to the eavesdropper at the end of the key distribution procedure. These limits are restricted to intercept/resend eaves-dropping strategies. The upper one is higher than has been estimated so far, and should be taken into account in order to guarantee the secrecy of the final key, which is subsequently obtained via the so-called privacy amplification.

 

42.       A. Imamoglu and Y. Yamamoto

            "Quantum Monte-Carlo Wave-Function Approach To Dissipative Processes In Mesoscopic Semiconductors"

            Phys. Lett. A 191 (5-6), 425-430 (1994).

 

            ABSTRACT: We extend the quantum Monte Carlo wave-function approach of quantum optics to analyze the dissipative electron-phonon interaction in semiconductors. The non-unitary time-evolution of a stochastic wave-function by an effective Hamiltonian is combined with continuous ''gedanken measurements'' of phonon emission events, to simulate the electron dynamics.

 

43.       A. Imamoglu and Y. Yamamoto

            "Turnstile Device For Heralded Single Photons - Coulomb-Blockade Of Electron And Hole Tunneling In Quantum-Confined P-I-N Heterojunctions"

            Phys. Rev. Lett. 72 (2), 210-213 (1994).

 

            ABSTRACT: We show that if a double-barrier mesoscopic p-i-n heterojunction is driven by an alternating voltage source, then Coulomb blockade and quantum confinement effects together can suppress the quantum fluctuations usually associated with electron and hole injection processes in semiconductors. It is therefore possible to generate heralded single-photon states without the need for a high-impedance current source. Since the frequency of the alternating voltage source determines the repetition rate of the single-photon states and the magnitude of the junction current, the present scheme promises high precision photon-flux and current standards.

 

44.       F. Ishiyama and K. Otsuka

            "Intensity Probability-Distribution Of Spiking-Mode Oscillations In Lasers - Power-Law Universality"

            Int. J. Bifurcation Chaos 4 (1), 225-230 (1994).

 

            ABSTRACT: We theoretically investigated the probability distributions of the output intensity of lasers with external perturbations. These perturbations were loss modulation and incoherent delayed feedback. We found that the intensity probability distributions usually obey a distinct power-law in spiking-mode oscillations both in periodic and chaotic regimes.

 

45.       T. Ito, K. Shiraishi, and T. Ohno

            "A Monte-Carlo Simulation Study For Adatom Migration And Resultant Atomic Arrangement In Alxga(1-X)As On A Gaas(001) Surface"

            Appl. Surf. Sci. 82-3, 208-213 (1994).

 

            ABSTRACT: The Monte Carlo method is applied to investigate adatom migration of cations in Al(x)Ga1-xAs (x = 0, 0.5 and 1.0) and the resultant atomic arrangements on a reconstructed As-stabilized GaAs(001) surface in the adatom coverage range of theta less-than-or-equal-to 0.5. Cation adatom migration strongly depends on the adatom coverage on the surface. Randomly impinging cations occupy lattice sites on the As dimers at the low coverage of theta less-than-or-equal-to 0.1. As the coverage increases in the range of 0.1 < theta less-than-or-equal-to 0.3, impinging cations predominantly migrate along the missing dimer rows. At a higher coverage of theta > 0.3, adatoms tend to favor the lattice sites on the As dimers including those with non-tetrahedral coordination. In Al0.5Ga0.5As, lattice sites along the missing dimer are mainly occupied by Al adatoms, while those on As dimers are favored by Ga adatoms. This is because Al adatom migration proceeds several times more slowly than Ga adatom migration. These resultant atomic arrangements are discussed in terms of the coverage dependence of the migration potential.

 

46.       M. Itoh, T. Saku, T. Fujisawa, Y. Hirayama, and S. Tarucha

            "Transport-Properties Of Modulation-Doped Structures Grown By Molecular-Beam Epitaxy After Focused Ion-Beam Implantation"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 33 (1B), 771-774 (1994).

 

            ABSTRACT: Modulation-doped structures are grown by molecular beam epitaxy after focused ion beam writing. The growth and implantation chambers are connected in a high vacuum to minimize the effect of growth interruption. The electron channel is drastically depleted by the buried Be+ implanted region, but only slightly depleted by the buried Au+ and AU(2+) implanted regions. This is because Be+ implantation forms a p-type material, while Au+ or Au2+ implaniation leaves damage only in the n-type material. Be+ implantation is therefore used to fabricate 0.1 mu m-wide wires with electron mobility of 2.1x10(5) cm(2)/Vs.

 

47.       J. M. Jacobson, Y. Yamamoto, and A. I. Glu

            "A Quantized-Current Standard Based On Coherent Pi-Pulse Excitation Of A Quantum-Dot"

            Europhys. Lett. 26 (2), 129-133 (1994).

 

            ABSTRACT: A quantized-current standard tied to the frequency standard (I = ef) is proposed based on coherent optical pi-pulse excitation of a quantum dot. Fluctuations in the current are calculated by averaging the quantum dot density matrix over the basis states of an incident coherent-state pi-pulse. The effects of a finite population lifetime (T1) and dipole lifetime (T2) via an appropriate Markoff approximation are included. We show that a quantized-photocurrent accuracy, (ef - [I])/ef, of 1 part in 10(4) at a current of I = 1.6 pA (f = 10 MHz) is possible in a semiconductor quantum dot system operating at 2 K. Such a device may be useful for the generation of photon number states in quantum optics, i.e. the realization of a photon current standard.

 

48.       W. Jhe, M. Ohtsu, H. Hori, and S. R. Friberg

            "Atomic Wave-Guide Using Evanescent Waves Near Optical Fibers"

            Jpn. J. Appl. Phys. Part 2 - Lett. 33 (12A), L1680-L1682 (1994).

 

            ABSTRACT: We discuss an atomic waveguide that guides atoms in a similar way a quadrupole mass spectrometer guides charged particles. A two dimensional guiding potential barrier is produced by repulsive optical dipole forces caused by evanescent waves from optical fibers. A realization of this new atom optical element is proposed.

 

49.       T. Kaburagi and M. Honda

            "Determination Of Sagittal Tongue Shape From The Positions Of Points On The Tongue Surface"

            J. Acoust. Soc. Am. 96 (3), 1356-1366 (1994).

 

            ABSTRACT: This paper describes a method for determining the shape of the midsagittal tongue contour from the positions of points on the tongue surface. The positions of the points and the tongue shape were measured simultaneously by using an alternating magnetic field device and an ultrasonic B-mode scanner for continuous speech utterances. A comparison between the magnetic and the ultrasonic data revealed that the average measurement difference between the two types of data was 1.16 mm. The shape of the tongue contour was then represented by multivariable linear regression of the magnetically determined positions. The results of the regression analysis showed that the tongue contour was estimated, from four positions on the tongue, with an average estimation error of 1.24 mm. This estimation error could be reduced to 0.84 mm when there was no measurement error between the magnetic and the ultrasonic data, and it was further reduced to 0.43 mm when the receiver coils of the magnetic device were positioned optimally on the tongue. It was also shown that the number of data frames for calculating the regression coefficients could be reduced, while maintaining the estimation accuracy, by appropriately selecting data frames. Finally, the tongue shape was estimated successfully for several phonemes from the magnetically determined positions, thus demonstrating the usefulness of this method for observing the articulatory configuration of the tongue.

 

50.       T. Kaburagi and M. Honda

            "An Ultrasonic Method For Monitoring Tongue Shape And The Position Of A Fixed-Point On The Tongue Surface"

            J. Acoust. Soc. Am. 95 (4), 2268-2270 (1994).

 

            ABSTRACT: An ultrasonic method is presented that combines B-mode ultrasonic imaging with pulsed-transmission ultrasound to image the lateral contour of the tongue and to detect the position of an ultrasonic sensor placed on the tongue surface in the same plane. Measurement accuracy was investigated with respect to the distance between the ultrasonic transducer and the sensor, and with respect to the tilt and lateral displacement of the sensor. An experiment measured movements of the tongue during continuous speech.

 

51.       Y. Kanemitsu, T. Ogawa, K. Shiraishi, and K. Takeda

            "Exciton Confinement On A Spherical-Shell - Visible Photoluminescence From Oxidized Si And Ge Nanoballs"

            J. Lumines. 60-1, 337-339 (1994).

 

            ABSTRACT: We report strong visible photoluminescence (PL) at room temperature from oxidized Si and Ge nanoballs, which are composed of a spherical crystalline core and a surface oxide layer. To explain the experimental results, a model is proposed in which excitons are confined to a spherical shell, an interfacial layer between the crystalline core and the surface oxide layer, and in which the exciton confinement enhances the PL intensity.

 

52.       M. Kasu and N. Kobayashi

            "Scanning-Tunneling-Microscopy Study Of 2-Dimensional Nuclei On Gaas Grown By Metalorganic Chemical-Vapor-Deposition"

            J. Cryst. Growth 145 (1-4), 120-125 (1994).

 

            ABSTRACT: Two-dimensional (2D) nuclei of GaAs grown on a singular (001) surface by metalorganic chemical vapor deposition have been observed by using high-vacuum scanning tunneling microscopy (STM). The 2D nuclei extend in the [110] direction, which is opposite to that of molecular beam epitaxy growth. The 2D nucleus-number density is measured from the STM images, and the relation between the density and the surface diffusion coefficient of Ga species is obtained from simulation of growth at the surface. The surface diffusion coefficient is estimated to be 10(-7.0+/-0.9) cm(2)/s at 530 degrees C.

 

53.       M. Kasu and N. Kobayashi

            "Scanning-Tunneling-Microscopy Study Of Gaas Step Structures On Vicinal Substrate Grown By Metalorganic Chemical-Vapor-Deposition"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 33 (1B), 712-715 (1994).

 

            ABSTRACT: Scanning tunneling microscopy (STM) is used to study the step structure of metalorganic chemical vapor deposition (MOCVD)-grown GaAs on a vicinal substrate. We passivated the as-grown surfaces with As in a vacuum chamber connected to the MOCVD system in order to protect it from oxidation during its transfer to the STM system. The undulation amplitude of the monolayer steps grown on a surface misoriented in the [110] direction is about twice that of these grown on a surface misoriented in the [($) over bar 110] direction. On a substrate at misorientation angles equal to or less than 7.0 degrees, surfaces show a monolayer step staircase when the growth temperature (T-g) >650 degrees C; step bunching occurs and the vicinal surface decomposed into (001) terraces and facets on which steps bunch when 575 degrees C less than or equal to T-g less than or equal to 650 degrees C; and elliptical two-dimensional islands form between the monolayer steps because of a decrease of Ga diffusion coefficient when T-g<575 degrees C.

 

54.       T. Kawabata

            "Predictor Codebook For Speaker-Independent Speech Recognition"

            Syst. Comput. Jpn. 25 (1), 37-46 (1994).

 

            ABSTRACT: This paper discusses a method to handle the diversified dynamic features of speech by representing the dynamic features of speech by spectrum predictors and constructing the codebook containing predictors as the elements. The effectiveness of the method for speaker-independent speech recognition is examined. Three kinds of predictor structures, i.e., the forward predictor, the backward predictor and the interpolator, are examined. The predictor codebook is constructed by the predictor quantization procedure, which is a small modification of the LBG algorithm. For the evaluation of the phoneme recognition level, two kinds statistical evaluation quantities and the phoneme recognition rate have been considered. It is seen as a result that the predictor codebook can realize a high phoneme separation capability and the robustness against the speaker variation. By combining the process actually into the phrase recognition system, the performance at the continuous speech recognition level is evaluated. In either case, the codebook with the backward predictor as the elements exhibited the highest performance.

 

55.       A. Kawana and H. P. C. Robinson

            "A Programmable Relay Matrix For Parallel Stimulation Of Cultured Neurons On Planar Electrode Arrays"

            J. Physiol.-London 480P, P2-P2 (1994).

 

            ABSTRACT:

56.       Y. Kido, A. Ikeda, Y. Yamamoto, J. Nakata, H. Yamaguchi, and K. Takahei

            "Impact-Parameter Dependent Stopping Powers For Axially Channeled And Semichanneled Mev He Ions In Gaas-Er"

            Phys. Rev. B 49 (20), 14387-14396 (1994).

 

            ABSTRACT: We have investigated the impact-parameter dependence of stopping powers for axially channeled and semichanneled MeV He ions in Er-sheet-doped GaAs epitaxial layers grown by molecular-beam epitaxy. Ion channeling analysis using 2.0 MeV He+ coupled with the observation by transmission-electron microscope has revealed the formation of fine ErAs clusters, whose lattice constant shrinks and coincides exactly with that of the GaAs host. Thus the Er atoms take the position corresponding to the tetrahedral interstitial site of the GaAs lattice. The Er peak energies in the backscattering spectra strongly depend on the impact-parameter dependent stopping powers, in particular for the incidence along [110] and the directions slightly tilted from [110] and [100]. We divide the stopping power into two parts-contributions from outer electrons and from inner electrons of GaAs. The former is calculated from the dielectric response theory. For the latter, we consider four types of stopping powers dependent upon impact parameter; (1) Dettmann-Robinson theory, (2) the binary-encounter model, (3) the binary encounter combined with the local-density approximation, and (4) the extended-local-electron-density model. The Er peak energies observed are well reproduced employing model (3).

 

57.       N. Kobayashi

            "In-Situ Monitoring And Control Of Surface Processes In Metalorganic Vapor-Phase Epitaxy By Surface Photoabsorption"

            J. Cryst. Growth 145 (1-4), 1-11 (1994).

 

            ABSTRACT: In-situ surface photo-absorption (SPA) was applied to study the dynamic surface processes and the static surface structures during metalorganic vapor phase epitaxy (MOVPE). The static surface structure in MOVPE can be analyzed by the spectrum in near-ultra-violet and visible regions, which comprises an anisotropic dielectric response due to the surface dimer bond as well as an isotropic response probably due to the surface back-bond. Time-resolved spectra showing dynamic changes of the surface can be measured by the use of optical multichannel analyzer. The rate of surface decomposition of source molecule and the rate of desorption of surface species were measured as the change of reflectivity at a fixed wavelength. The decomposition of source molecules was characterized quantitatively, and a correlation between the rate of desorption of group V atoms and the bond strength of a surface back-bond was found. During heteroepitaxy, the surface exchange of group V atom was monitored in situ, and the growth was accordingly controlled to suppress this exchange reaction and obtain a compositionally abrupt interface.

 

58.       N. Kobayashi and T. Makimoto

            "Carbon Incorporation Mechanism In Atomic Layer Epitaxy Of Gaas And Algaas"

            Appl. Surf. Sci. 82-3, 284-289 (1994).

 

            ABSTRACT: By an in-situ surface photo-absorption study of the ALE process and carbon atomic layer doping, an other than the so far proposed carbon incorporation mechanism via formation of a CH2 bridge bond has been found, i.e. carbon incorporation via an exchange reaction between dissociated CH3 radicals from TMG and As atoms of the surface onto which TMG is deposited. We also propose a method for reducing the carbon incorporation by thermal desorption of the CH3 groups.

 

59.       Y. Kobayashi and N. Kobayashi

            "Effect Of Strain On Source Gas Decomposition And Group-V Desorption In Metalorganic Vapor-Phase Epitaxy Studied By Surface Photoabsorption"

            J. Cryst. Growth 145 (1-4), 17-21 (1994).

 

            ABSTRACT: The decomposition rate of source gas and the desorption rate of group V atom were measured by surface photo-absorption during metalorganic vapor phase epitaxy (MOVPE). We found that the decomposition of PH3 on GaAs and InAs surfaces, which produces a large tensile strain, is slower than that on GaP and InP surfaces. We also found that P desorption from P-stabilized GaAs and InAs surfaces, which relieves a large tensile strain, is faster than P desorption from GaP and InP surfaces, respectively. Strain-enhanced desorption was also observed for the As-stabilized InP surface. The difficulty of forming the strained surface bond evidently decreases the rate of decomposition and the ease of breaking the strained surface bond evidently increases the rate of desorption.

 

60.       Y. Kobayashi and N. Kobayashi

            "In-Situ Control Of Strained Heterostructure Growth"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 33 (5A), 2463-2467 (1994).

 

            ABSTRACT: This paper reports the metalorganic vapor phase epitaxial growth of pseudomorphic InAs/InP single quantum wells (SQWs) on (001) InP substrates using in-situ surface photo-absorption (SPA) monitoring, and reports on the optical characterization of them. By adjusting the arsine flow rate, arsine exposure time and substrate temperature on the basis of in-situ SPA monitoring, we are able to grow pseudomorphic InAs/InP SQWs comprising up to 10-monolayer InAs wells having metallurgically abrupt and atomically flat strained heterointerfaces. Photoluminescence excitation measurement for an 8-monolayer InAs well shows energy splitting as large as 0.4 eV between heavy and light holes subbands, indicating the InAs well layer is coherently strained to a maximum extent within the critical layer thickness.

 

61.       R. C. Liu and Y. Yamamoto

            "Nyquist Noise In The Transition From Mesoscopic To Macroscopic Transport"

            Phys. Rev. B 50 (23), 17411-17414 (1994).

 

            ABSTRACT:

62.       R. C. Liu and Y. Yamamoto

            "Suppression Of Quantum Partition Noise In Mesoscopic Electron Branching Circuits"

            Phys. Rev. B 49 (15), 10520-10532 (1994).

 

            ABSTRACT: A partitioned system of fermions is mathematically equivalent to an assembly of two-level atoms described by spin operators. A number-phase uncertainty relation can therefore be derived to describe the noise properties of divided electrons. We examine both the number (or electron flux) and phase (or electron wave phase) decorrelation introduced by electron branching in mesoscopic circuits. Initially Poissonian, this electron number partition noise is increasingly suppressed by inelastic scattering in the transition from ballistic to dissipative electron division. Graphical results from our model show a trend from a coherent spin state in the ballistic regime toward a number-squeezed spin state in the dissipative regime, even when detrimental elastic scattering is present.

 

63.       Y. Maeda, K. Takei, and D. J. Rogers

            "Compositional Microstructures In Co-Cr Films For Magnetic Recording (Vol 134, Pg 315, 1994)"

            J. Magn. Magn. Mater. 137 (1-2), 233-233 (1994).

 

            ABSTRACT:

64.       Y. Maeda, K. Takei, and D. J. Rogers

            "Compositional Microstructures In Co-Cr Films For Magnetic Recording"

            J. Magn. Magn. Mater. 134 (2-3), 315-322 (1994).

 

            ABSTRACT: Using spin echo Co-59 nuclear magnetic resonance and preferential chemical etching, we have examined compositional inhomogeneities in Co-Cr based alloy thin film media for magnetic recording. We found that drastic compositional separation (CS), which produces highly Co-enriched regions within grains, occurs in both perpendicular and longitudinal recording media. CS is expected to promote the change from a continuous to a particulate-type magnetic microstructure suitable for high density magnetic recording.

 

65.       A. Matsuda, K. Semba, and T. Watanabe

            "Anisotropy And Impurity Effect In High T-C Superconductors"

            Physica C 235, 1395-1396 (1994).

 

            ABSTRACT: The impurity effect on both superconducting and normal state properties has been investigated to clarify the dimensionality of the one-electron state. Our previous study showed that fully oxidized Ba2Y(Cu1-xZnx)(3) O-7-delta (BYCZO) shows essentially three-dimensional (3D) behavior. This study extends the work toward more two-dimensional materials, namely oxygen-deficient BYCZO and Bi2Sr2Ca(Cu1-xCox)(2)O-8. The electronic system of the former stays in 3D, while that of the latter behaves essentially in a 2D manner, suggesting that two-dimensionality is irrelevant to high Tc superconductivity.

 

66.       N. Mitani and S. Kurihara

            "Spin Gap And High-Temperature Superconductivity"

            Phys. Lett. A 184 (4-5), 374-379 (1994).

 

            ABSTRACT: The relationship between the spin excitation spectrum and the symmetry of Cooper pairs in cuprous oxide superconductors is studied. It is found that d-wave superconductivity in the hole system induces an Ising-type anisotropy in the effective coupling between Cu spins. The resulting spin gap structure at zero temperature agrees fairly well with recent neutron experiMentS.

 

67.       M. Mitsunaga, N. Uesugi, H. Sasaki, and K. Karaki

            "Holographic Motion-Picture By Eu3+-Y2sio5"

            Opt. Lett. 19 (10), 752-754 (1994).

 

            ABSTRACT: Real-time recording of a moving object was made with persistent spectral hole burning of a cryogenic Eu3+:Y2SiO5 crystal. In a basic holographic configuration the ultrastable laser frequency was continuously scanned within the F-7(0)-5D0 absorption line (typically 200 MHz in 20 s) while the object was in motion, thus permitting the storage and reconstruction of the moving image. The success of this motion picture is attributable to (1) the kilohertz-wide hole width, (2) the quasi-persistent hole lifetime, and (3) the high hole-burning quantum efficiency of this material.

 

68.       M. S. Miyauchi

            "An O(Mn) Algorithm For Embedding Graphs Into A 3-Page Book"

            IEICE Trans. Fundam. Electron. Commun. Comput. Sci. E77A (3), 521-526 (1994).

 

            ABSTRACT: This paper studies the problem of embedding a graph into a book with nodes on a line along the spine of the book and edges on the pages in such a way that no edge crosses another. Atneosen as well as Bernhart and Kainen has shown that every graph can be embedded into a 3-page book when each edge can be embedded in more than one page. The time complexity of Bernhart and Kainen's method is OMEGA(nu(G)), where nu(G) is the crossing number of a graph G. A new O(mn) algorithm is derived in this paper for embedding a graph G = (V,E), where m = Absolute value of E and n = Absolute value of V. The number of points at which edges cross over the spine in embedding a complete graph into a 3-page book is also investigated.

 

69.       M. S. Miyauchi

            "Topological Ramsey Theorem For Complete Bipartite Graphs"

            J. Comb. Theory Ser. B 62 (1), 164-179 (1994).

 

            ABSTRACT: An embedding of a graph into a space is linear if each edge is a straight line segment. In 1991, Negami showed that for any given knot, link, or spatial graph there is a sufficiently large complete graph K-n such that every linear embedding of K-n into a space always contains that knot, link, or spatial graph. This paper generalizes this result to cover complete bipartite graphs. The results for complete multipartite graphs and for complete graphs are obtained as corollaries. (C) 1994 Academic Press, Inc.

 

70.       H. Murase and S. K. Nayar

            "Illumination Planning For Object Recognition Using Parametric Eigenspaces"

            IEEE Trans. Pattern Anal. Mach. Intell. 16 (12), 1219-1227 (1994).

 

            ABSTRACT: This correspondence presents a novel approach to the problem of illumination planning for robust object recognition in structured environments. Given a set of objects, the goal is to determine the illumination For which the objects are most distinguishable in appearance from each other. Correlation is used as a measure of similarity between objects. For each object, a large number of images is automatically obtained by varying pose and illumination direction. Images of all objects, together, constitute the planning image set. The planning set is compressed using the Karhunen-Loeve transform to obtain a row-dimensional subspace, called the eigenspace. For each illumination direction, objects are represented as parametrized manifolds in eigenspace. The minimum distance between the manifolds of two objects represents similarity between tbe objects in the correlation sense. The optimal source direction is therefore one that maximizes the shortest distance between object manifolds. Several experiments have been conducted using real objects. Results produced by the illumination planner have been used to enhance the performance of an object recognition system.

 

71.       M. Naito and H. Sato

            "Reflection High-Energy Electron-Diffraction Study On The Srtio3 Surface-Structure"

            Physica C 229 (1-2), 1-11 (1994).

 

            ABSTRACT: This paper reports a reflection high-energy electron diffraction investigation of the surface structures of the (001) and (110) crystal faces of SrTiO3 given various surface treatments. The as-polished surface has a (1 X 1) unreconstructed structure on both the (001) and (110) crystal faces. The vacuum annealed surface has a two-domain (2 X 1) superstructure on the (001) face and a (4 X 4) structure on the (110) face. The oxygen annealed surface has two superstructures on the (001) face: a two-domain (square-root 13 X square-root 13-R33.7-degrees) structure and a c(6 X 2) structure, and a (4 X 2) or a (4 X 4) structure on the (110) face. Of these surfaces, the oxygen annealed surface has the highest quality.

 

72.       K. Nakada, K. Takeda, and H. Hosoya

            "Electronic Band Structures Of Penta-Heptagonal Carbon Networks"

            Theochem-J. Mol. Struct. 117, 79-86 (1994).

 

            ABSTRACT: The electronic band structures of planar carbon networks consisting solely of pentagons and heptagons were calculated. Two delocalized structures analogous to graphite were proposed as the candidates of the most possible penta-heptagonal network. The electronic structures of these networks were found to show rather metallic properties marking quite a contrast to graphite.

 

73.       H. Nakano and H. Takayanagi

            "2nd Quantization Description Of Andreev Reflection"

            Physica B 194, 1759-1760 (1994).

 

            ABSTRACT: A second quantization description is given for Andreev reflection. The Andreev reflection is obtained as an elementary excitation for superconductor-normal-metal coupled systems. This gives us a powerful tool for investigating the macroscopic quantum mechanical aspects of Andreev reflection.

 

74.       H. Nakano and H. Takayanagi

            "2nd-Quantization Description Of Andreev Reflection And The Relation To Quasi-Particle Wave Approaches"

            Phys. Rev. B 50 (5), 3139-3148 (1994).

 

            ABSTRACT: A second-quantization description is given for Andreev reflection. We introduce an effective interaction Hamiltonian for the interface between the superconductor and the normal metal, which enables us to treat transmission and reflection consistently. The interaction Hamiltonian couples quasiparticles in the normal region (N) and Bogoliubov quasiparticles in the superconducting region (S). It facilitates the description of the elementary excitations of the SN-coupled system, that are generated by Andreev reflections. Moreover, it naturally brings us to the description where the effect of macroscopic quantum fluctuations of the superconducting state on Andreev reflections is considered. This provides a powerful tool for investigating of the mesoscopic aspects of Andreev reflection.

 

75.       S. Nishida, H. Ashida, and T. Sato

            "Complete Interocular Transfer Of Motion Aftereffect With Flickering Test"

            Vision Res. 34 (20), 2707-2716 (1994).

 

            ABSTRACT: It has been suggested that motion aftereffect with static test patterns (static MAE) reflects activities at a lower level system that dominantly processes first-order motion, while MAE with a directionally ambiguous test (flicker MAE) reveals a higher level system where second-order motion signals as well as first-order signals are available. To test this hypothesis, we examined interocular transfer of static and flicker MAE. Flicker MAE should transfer more efficiently than static MAE if it occurs at a higher level system. In the first experiment, the adaptation stimulus was a drifting luminance grating (first-order motion), or a drifting grating defined by flicker or texture difference (second-order motion). The test stimulus was a luminance grating, either static or counterphasing. The results indicated that static MAE, which was induced only by first-order motion, transferred partially, as has been reported in previous studies, but: the transfer of flicker MAE was nearly perfect with either first- or second-order adaptation stimuli. The second experiment with varied adaptation contrast indicated that this complete transfer was not due to a ceiling effect. These results supported the hypothesis that the underlying mechanism for flicker MAE is located at a level higher than the mechanism for static MAE.

 

76.       S. Nishida, H. Ashida, and T. Sato

            "Perfect Interocular Transfer Of Flicker Motion After-Effect"

            Invest. Ophthalmol. Vis. Sci. 35 (4), 2157-2157 (1994).

 

            ABSTRACT:

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

            "Anomalous Magnetic-Field Dependence Of Differential Resistance In A Superconducting Nb-Inas-Nb Junction"

            Physica B 194, 1757-1758 (1994).

 

            ABSTRACT: The differential resistance in an InAs-inserted-channel InAlAs/InGaAs heterostructure coupled superconducting junction is enhanced within the Nb superconducting gap energy by applying a magnetic field. The enhancement saturates under a magnetic field of several mT. This behavior suggests that the pair-potential in the InAs-channel is induced by the superconducting proximity effect. The magnetic field reduces the penetration of the pair-potential and the Andreev reflection probability, which causes the enhancement of the differential resistance.

 

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

            "Magnetic-Field Dependence Of Andreev Reflection In A Clean Nb-Inas-Nb Junction"

            Phys. Rev. B 49 (5), 3659-3662 (1994).

 

            ABSTRACT: The differential resistance in an InAs-inserted-channel In0.52Al0.48As/In0.53Ga0.47As heterostructure-coupled superconducting junction is enhanced within the Nb superconducting gap energy by applying a magnetic field. However, the enhancement saturates under a magnetic field of several mT. This behavior suggests the reduction of Andreev-reflection (AR) probabilities by the magnetic field. The AR probabilities are calculated as a function of the pair-potential penetration length into the InAs channel. The enhanced AR probabilities decrease with decreasing pair-potential penetration length. The magnetic field reduces the penetration of the pair potential in the channel and therefore reduces the AR probability. This reduction of AR probability causes an enhancement of dV/dI.

 

79.       O. Niwa, T. Horiuchi, and H. Tabei

            "Electrochemical Properties Of Carbon-Based Interdigitated Microarray Electrodes Fabricated By The Pyrolysis Of Electrochemically Prepared Conducting Films"

            J. Electroanal. Chem. 367 (1-2), 265-269 (1994).

 

            ABSTRACT:

80.       O. Niwa, M. Morita, and H. Tabei

            "Highly Selective Electrochemical Detection Of Dopamine Using Interdigitated Array Electrodes Modified With Nafion Polyester Ionomer Layered Film"

            Electroanalysis 6 (3), 237-243 (1994).

 

            ABSTRACT: The highly selective electrochemical detection of dopamine has been developed using an interdigitated microarray (IDA) electrode coated with Nafion and polyester ionomer (Kodak AQ29D) layered films. Because high redox cycling of dopamine can be maintained in the AQ29D bottom layer, a low detection limit of 50 nmol/dm3 is obtained. Since the upper Nafion layer prevents L-ascorbic acid from diffusing into the AQ29D layer, the acid concentration in this layer rapidly decreases when potentiostating one IDA electrode (anode) above and the other (cathode) below the redox potential of dopamine. This is because L-ascorbic acid molecules in the AQ29D layer are removed quickly by the electrochemical or electrocatalytic oxidation at the anode. On the other hand, almost all of the oxidized dopamine molecules are reduced at the cathode, which maintains a constant dopamine concentration in the film during measurement. After the potential step, the influence Of L-ascorbic acid is almost completely eliminated within a few seconds due to the reduction in acid concentration in the modified layer. As a result, dopamine can be detected quantitatively at the cathode in the presence of 100-fold excess Of L-ascorbic acid.

 

81.       O. Niwa and H. Tabei

            "Voltammetric Measurements Of Reversible And Quasi-Reversible Redox Species Using Carbon-Film Based Interdigitated Array Microelectrodes"

            Anal. Chem. 66 (2), 285-289 (1994).

 

            ABSTRACT: A carbon-based interdigitated array (IDA) microelectrode was applied to the highly sensitive voltammetric detection of reversible and quasi-reversible redox species in both the anodic and cathodic potential regions. Carbon film was prepared on a surface-oxidized Si wafer by the pyrolysis of 3,4,9,10-perylenetetracarboxylic dianhydride and was designated as amorphous by X-ray diffraction and Raman spectroscopy. The Carbon IDA microelectrode was fabricated by photolithography and dry etching. The IDA electrode had 50 microband pairs. The bandwidth of the IDAs was 3 mu m, and the gap between two microbands was 2 lambda m. In the measurement of ferrocene derivatives, the iR drop was negligible when the ferrocene concentration was less than 0.1 mM at a moderate scan rate due to the low resistivity of carbon film. The cathodic potential window without redox species extended further in the negative direction than that of platinum and gold IDAs. The collector current of ruthenium hexaammine in a generation collection measurement using an IDA agreed well with the theoretical value even if the sample concentration was in the tens of nanomoles per liter range due to the flat baseline current at the collector in the cathodic region and high collection efficiency. The generation-collection voltammogram of dopamine was greatly improved after pretreating only the generator electrode. A low detection limit of 10 nM and a wide linear range from 10 nM to 1 mM were obtained at the collector electrode because the collector response of dopamine was improved by the generator pretreatment without increasing the background current at the collector electrode.

 

82.       T. Ohno and K. Shiraishi

            "Novel Core Effects In Cs/Gaas(110) Overlayers - Adsorption-Induced Buckling Enhancement"

            Solid State Commun. 92 (5), 397-400 (1994).

 

            ABSTRACT: The structural and electronic properties of Cs/GaAs(110) overlayers are investigated using an ab initio pseudopotential method, in which we include a ''double valence pseudopotential'' (DVPP) to treat Cs 5p core electrons explicitly. The Cs adsorption enhances the buckling of GaAs(110) surface due to the Cs 5p, core repulsion, contrary to usual expectations. The buckling enhancement has a significant effect on the formation of Cs overlayer structures. The origin of the semiconductor-to-metal transition is also discussed.

 

83.       M. Okuya, T. Kimura, R. Kobayashi, J. Shimoyama, K. Kitazawa, K. Yamafuji, K. Kishio, K. Kinoshita, and T. Yamada

            "Single-Crystal Growth And Anisotropic Electrical-Properties Of (La1-Xcax)2cacu2o6"

            J. Supercond. 7 (2), 313-318 (1994).

 

            ABSTRACT: Large single crystals of (La1-xCax)2CaCu2O6 were synthesized by the travelling solvent floating zone (TSFZ) technique. The dimension of the grown boules was typically 4 mm phi x 30 mm long with the c-axis perpendicular to the growth direction. After oxygen loading at 1080-degrees-C in 400 atm Of O2, they became superconductive with a sharp transition at around 50 K. The resistivity was metallic both along the c-axis and within the ab-plane, with an anisotropy ratio of gamma2 = (rho(c)/rho(ab)) approximately 50 which is almost independent of temperature. Details of the crystal growth, heat treatment procedures, and the results of electrical and magnetic property measurements are presented.

 

84.       K. Otsuka

            "Gain Circulation And Transverse Effects In Antiphase Laser Dynamics"

            Chaos Solitons Fractals 4 (8-9), 1547-1558 (1994).

 

            ABSTRACT: The underlying physical processes inherent in self-organized antiphase dynamics in multi-longitudinal-mode lasers are explored in terms of gain circulation, a new physical quantity. Transverse effects on antiphase dynamics in multi-longitudinal-mode lasers are investigated, and three-dimensional self-organization is shown to result from the cross-saturation dynamics in the longitudinal and transverse directions.

 

85.       K. Otsuka

            "Ultrahigh Sensitivity Laser-Doppler Velocimetry With A Microchip Solid-State Laser"

            Appl. Optics 33 (6), 1111-1114 (1994).

 

            ABSTRACT: Highly sensitive laser Doppler velocimetry featuring the simultaneous measurement of light-scattering objects moving at different velocities and vibration sensing based on Doppler-shifted light-injection-induced intensity modulation in an externally pumped microchip solid-state laser is demonstrated.

 

86.       K. Otsuka and Y. Aizawa

            "Gain Circulation In Multimode Lasers"

            Phys. Rev. Lett. 72 (17), 2701-2704 (1994).

 

            ABSTRACT: Self-organized collective behavior in globally coupled multimode lasers is investigated by introducing a new physical quantity, gain circulation, that characterizes the gain transfer among lasing modes. Numerical simulations indicate that the self-organization is established such that the gain circulations in all the closed interaction paths involving arbitrary multiple lasing modes become negligibly small as compared with direct mode-to-mode gain circulations. This implies that the nonreciprocal local (i.e., mode-to-mode) gain transfers are self-organized so as to ensure reciprocal average gain flow among modes approximately and that temporal evolutions of individual mode intensities are determined accordingly.

 

87.       K. Otsuka and J. L. Chern

            "Variation Of Lyapunov Exponents On A Strange Attractor For Spiking Laser Oscillation"

            Int. J. Bifurcation Chaos 4 (4), 1053-1060 (1994).

 

            ABSTRACT: We analyze temporal variations in local Lyapunov exponents for chaotic spiking lasers in terms of standard deviation and Allan variance as a function of integral time tau. We show that standard deviations for local Lyapunov exponents become saturated in short tau regimes. The calculated Allan variance and power spectrum analysis suggest that the transition between stationary and nonstationary chaos takes place around the relaxation oscillation period of lasers, and that local Lyapunov exponents become nonstationary in time in the short tau regime.

 

88.       K. Otsuka, D. Pieroux, and P. Mandel

            "Modulation Dynamics And Spatiotemporal Pattern Generation In A Microchip Multimode Laser"

            Opt. Commun. 108 (4-6), 265-272 (1994).

 

            ABSTRACT: 2N-1 different periodic oscillations are obtained experimentally in a microchip N-mode laser by different combinations of modulations at multiple relaxation oscillation frequencies that appear on the basis of antiphase dynamics among lasing modes. Application of mode-dependent periodic oscillations to generation of dynamic spatial patterns is demonstrated using a shear plate interferometer.

 

89.       D. Pieroux, T. Erneux, and K. Otsuka

            "Minimal Model Of A Class-B Laser With Delayed Feedback - Cascading Branching Of Periodic-Solutions And Period-Doubling Bifurcation"

            Phys. Rev. A 50 (2), 1822-1829 (1994).

 

            ABSTRACT: A minimal model for a laser with delayed feedback is analyzed. The model is motivated by two independent studies of a laser controlled by a fully optical feedback [Otsuka and Chem, Opt. Lett. 16, 1759 (1991)] and a laser with an optoelectronic feedback [Loiko and Samson, Opt. Commun. 93, 66 (1992)]. By reformulating the original laser equations in terms of dimensionless quantities, we obtain a simpler problem which is valid for both lasers. We then investigate the limit of small-amplitude feedback and small damping and determine a bifurcation equation for all periodic solutions. We analyze this condition in terms of increasing values of the delay time and show that each branch of solutions emerges from the basic state and becomes isolated as the delay time is progressively increased. The overlap of bifurcating and isolated branches of solutions explains the coexistence of nearly harmonic and pulsating solutions. Pulsating solutions may change stability through period-doubling bifurcation. We determine a simple approximation for this bifurcation point and study its validity numerically.

 

90.       D. Pieroux, P. Mandel, and K. Otsuka

            "Modulation Dynamics In A Multimode Laser With Feedback"

            Opt. Commun. 108 (4-6), 273-277 (1994).

 

            ABSTRACT: The response of an N-mode solid-state laser when the output field is reinjected in the cavity after N frequency shifts is analyzed. The results obtained with up to four modes are described and it is tried to infer general rules. The emphasis is on comparing the dynamics of the partial and the total mode intensities.

 

91.       F. E. Pollick, S. Nishida, Y. Koike, and M. Kawato

            "Perceived Motion In Structure-From-Motion - Pointing Responses To The Axis Of Rotation"

            Percept. Psychophys. 56 (1), 91-109 (1994).

 

            ABSTRACT: We investigated the ability to match finger orientation to the direction of the axis of rotation in structure-from-motion displays. Preliminary experiments verified that subjects could accurately use the index finger to report direction. The remainder of the experiments studied the perception Of the axis of rotation from full rotations of a group of discrete points, the profiles of a rotating ellipsoid, and two views of a group of discrete points. Subjects' responses were analyzed by decomposing the pointing responses into their slant and tilt components. Overall, the results indicated that subjects were sensitive to both slant and tilt. However, when the axis of rotation was near the viewing direction, subjects had difficulty reporting tilt with profiles and two views and showed a large bias in their slant judgments with two views and full rotations. These results are not entirely consistent with theoretical predictions. The results, particularly for two views, suggest that additional constraints are used by humans in the recovery of structure from motion.

 

92.       K. Prabhakaran, T. Nishioka, Y. Kobayashi, and T. Ogino

            "In-Situ Oxidation Of Ultrathin Layers Of Ge On Si(001) - Evidence For Bonding Partner Exchange"

            Appl. Surf. Sci. 75, 341-347 (1994).

 

            ABSTRACT: Ultra-thin layers of Ge grown on Si(001) surface are oxidized in situ and investigated using XPS, AES, MEIS, AFM and TEM. The samples used are Ge layer formed by deposition at room temperature (RT) and SiGe mixed layer formed by deposition at 550 degrees C. Oxidation of the RT-grown layer forms GeO on the surface and on annealing the surface to 360 degrees C, oxygen changes the bonding partner and forms SiO2, thereby reducing GeO to elemental Ge. In the SiGe mixed layer, after oxidation, SiO2 and a small amount of GeO are formed. On annealing, a similar reaction takes place on this surface also, forming SiO2 as the final product on the surface. Air oxidation of the RT-deposited sample forms Ge suboxides and GeO2 on the surface. GeO is reduced selectively by annealing at 360 degrees C in vacuum. On the other hand, by rinsing the sample in warm water, GeO2 is removed selectively.

 

93.       K. Prabhakaran, T. Nishioka, K. Sumitomo, Y. Kobayashi, and T. Ogino

            "Oxidation Of Ultrathin Sige Layer On Si(001) - Evidence For Inward Movement Of Ge"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 33 (4A), 1837-1838 (1994).

 

            ABSTRACT: An ultrathin SiGe layer prepared by growing Ge epitaxially on Si(001) was oxidized and investigated using X-ray photoelectron spectroscopy (XPS) and medium energy ion scattering (MEIS). Growth at a substrate temperature 550-degrees-C leads to the formation of a mixed SiCe layer on Si(001). Oxidation of this sample at 250-degrees-C forms predominantly SiO2 and a small amount of GeO. MEIS shows evidence for the diffusion of Ge inwards by 2-3 angstrom and of Si towards the surface resulting in the pile up of Ge at the SiO2/SiGe interface. On annealing the oxidized surface at 360-degrees-C, oxygen leaves the Ge sites and form SiO2 thereby reducing GeO to elemental Ge. The concentration of oxygen remains the same through out this reaction.

 

94.       K. Prabhakaran, T. Ogino, T. Scimeca, and M. Oshima

            "Interaction Of Al With Oxidized Ge/Si(001) - A Synchrotron-Radiation Photoelectron-Spectroscopy Study"

            J. Vac. Sci. Technol. A-Vac. Surf. Films 12 (2), 509-572 (1994).

 

            ABSTRACT: Interaction of aluminum with an oxidized sample of ultrathin layer Ge (7 angstrom) deposited on Si(001) at room temperature [Ge (7 angstrom)/Si(001) RT] is studied employing synchrotron radiation photoelectron spectroscopy. Ge (7 angstrom)/Si(001) RT, on exposure to air, forms Ge suboxides, GeO2 and Si suboxides on the surface. GeO2 is selectively removed completely by rinsing the sample in warm water, and during this process a small amount of Si oxides is also formed. Upon depositing Al on this surface, it reacts with oxides of Si and Ge and forms an overlayer of Al2O3 on the surface, thereby reducing the oxides to elemental Si and Ge. Further, the reaction is activated by an increase in surface temperature. In the early stages of the reaction, reduction of suboxides take place in preference to Si02.

 

95.       K. Prabhakaran, T. Ogino, T. Scimeca, Y. Watanabe, and M. Oshima

            "Bonding Partner Change Reaction In Oxidation Of Ge On Si(001) - Observation Of 2-Step Formation Of Sio2"

            Appl. Phys. Lett. 64 (14), 1839-1841 (1994).

 

            ABSTRACT: Oxidation of 5 angstrom Ge deposited at room temperature on Si(001) and the dependence of temperature on the oxidation behavior are investigated by employing synchrotron radiation photoelectron spectroscopy. The sample on exposure to air forms a mixture of Ge oxides and a small amount of Si oxides. Upon annealing, oxygen changes its bonding partner from Ge to Si forming SiO2 as the predominant final product. Two distinct steps have been observed in such a reaction. First step is the cleavage of all the Ge-O bonds and formation of Si-O bonds to form mainly Si suboxide. The second step is the rearrangement of Si-O bonds to form SiO2. The former one takes place in the temperature range 200-300-degrees-C whereas the latter one in the range 300-600-degrees-C.

 

96.       K. Prabhakarana, T. Ogino, R. Hull, J. C. Bean, and L. J. Peticolas

            "An Efficient Method For Cleaning Ge(100) Surface"

            Surf. Sci. 316 (1-2), L1031-L1033 (1994).

 

            ABSTRACT: We report an efficient method for cleaning Ge substrates similar to the Ishizaka and Shiraki method for cleaning of Si. The Ge wafers are cleaned in running deionized water and etched with HF. A thin oxide layer was prepared by dipping in a mixture of H2O2 and H2O for a few seconds and the oxide layer was removed by dipping in HF. This procedure was repeated several times to ensure the removal of several atomic layers of Ge. Finally the thin oxide layer prepared as described above was thermally decomposed in ultrahigh vacuum by annealing in the temperature range 300-500-degrees-C. The resulting surface gave rise to sharp emission peaks due to surface states in UPS illustrating a clean surface. Impurities such as carbon and oxygen were below detection level in XPS and AES. Cross sectional TEM studies showed no defects associated with the cleaning procedure. Ge buffer layer growth and subsequent SiGe growth showed good morphology and no substrate/buffer defects.

 

97.       H. P. C. Robinson and A. Kawana

            "A Static Induction Transistor Camera For Fast Fluorescence Imaging"

            J. Physiol.-London 480P, P3-P3 (1994).

 

            ABSTRACT:

98.       D. J. Rogers, Y. Maeda, and K. Takei

            "The Dependence Of Compositional Separation An Film Thickness For Co-Cr And Co-Cr-Ta Magnetic Recording Media"

            IEEE Trans. Magn. 30 (6), 3972-3974 (1994).

 

            ABSTRACT: The dependence of the compositional distribution on film thickness was investigated for Co78Cr22 and Co86Cr12Ta2 films. Spin-echo NMR and preferential chemical etching revealed that the extent of compositional separation was greatest in thinner films and decreased during film growth for both Co Cr and Co-Cr-Ta. Thinner films exhibited enhanced Ms and a higher density of smaller Co-enriched regions. Ta addition was observed to change the compositional distribution, promoting a finer pattern of Co enriched regions.

 

99.       D. J. Rogers, Y. Maeda, K. Takei, J. N. Chapman, J. P. C. Bernards, and C. P. G. Schrauwen

            "Investigations Of Compositional Separation In Co-Cr Thin-Film Recording Media"

            J. Magn. Magn. Mater. 130 (1-3), 433-441 (1994).

 

            ABSTRACT: We investigated the effect of a Ge underlayer and substrate temperature during film deposition (T(s)) on the compositional distribution in Co79Cr21 films using spin echo nuclear magnetic resonance and preferential chemical etching. For films deposited at elevated T(s) we observed drastic compositional separation (CS) leading to a Co enriched phase with approximately 5 at% Cr on both Ge and polyester. Chemical etching revealed chrysanthemum pattern (CP) type microstructures. For lower T(s) films we observed less marked CS with a distinct etched microstructure in the film deposited on Ge and no clear etched microstructure in the film deposited on polyester. Results from NMR and chemical etching studies agreed very well with those from X-ray microanalysis.

 

100.    D. J. Rogers, Y. Maeda, K. Takei, Y. Shen, and D. E. Laughlin

            "Investigtions Of Compositional Separation Of Co-Cr-Ta Cr Thin-Film Recording Media"

            J. Magn. Magn. Mater. 135 (1), 82-88 (1994).

 

            ABSTRACT: The compositional distribution in Co-Cr-Ta thin films is investigated as a function of Cr underlayer texture and substrate temperature (T(s)) using spin-echo nuclear magnetic resonance and preferential chemical etching. Both the extent and pattern of compositional separation (CS) show no variation with Cr underlayer texture. Elevated T(s) is observed to promote both CS and grain boundary Cr enrichment. The magnetic anisotropy fields of Co-enriched components in the films are observed to increase with T(s), explaining the T(s), dependence of H(c). Ta addition is observed to control the distribution of Co and Cr, leading to a unique compositional microstructure which may enhance the magnetic and recording properties.

 

101.    T. Saku, Y. Horikoshi, and S. Tarucha

            "High-Mobility Inverted Modulation-Doped Gaas/Algaas Heterostructures"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 33 (9A), 4837-4842 (1994).

 

            ABSTRACT: High-quality inverted GaAs/AlGaAs modulation-doped heterostructures have been grown by MBE. An AlAs/GaAs superlattice buffer layer is grown below the AlGaAs spacer layer to improve the morphology at the inverted heterointerface. An atomic layer doping and a thick spacer layer are adopted to alleviate the scattering by ionized donors. The observed electron mobility at 1.5 K is 4.3 x 10(6) cm(2)/Vs at a 2D electron density of 2.8x10(11)/cm(2). Two 2D electron channels; one formed at the inverted interface and the other at the normal interface are found to be operative in the observed characteristic. The electron mobility in the inverted channel is estimated to be as high as 4.9 x 10(6) cm(2)/Vs at an electron density of 2.2 x 10(11)/cm(2), while, in the normal channel, it is 2.1 x 10(6) cm(2)/Vs at a density of 6 x 10(10)/cm(2).

 

102.    E. T. Sano and Y. Horikoshi

            "Selenium Doping In Gaas Grown By Molecular-Beam Epitaxy"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 33 (10), 5636-5639 (1994).

 

            ABSTRACT: Using elementary Se as n-type dopant, Se-doped GaAs films were grown by molecular beam epitaxy. Characteristics of the films can be classified according to the amount of Se doped into areas where carrier concentration increases linearly [area I] (Se concentration less than or equal to 4 x 10(18) cm(-3)), saturates [area II] (4 x 10(18)-1 x 10(20) cm(-3)) and decreases [area III] (greater than or equal to 1 x 10(20) cm(-3)). In each area, we found a close correlation between electrical activity and photoluminescence spectra. The activation ratio of Se donors was found to be high in the samples classified in area I. These samples showed an efficient photoluminescence, although the observed spectra included deep level emissions at 890 nm and 1050 nm in addition to the band-edge excitonic emission. For the samples in areas II and III, however, photoluminescence efficiency dropped considerably and only a broad band emission (1300-1500 nm) appeared. This broad band emission is probably caused by complexes that include Ga vacancies and Se atoms because distinct electron concentration saturation takes place in this region.

 

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

            "Fermi-Liquid Behavior And Bcs S-Wave Pairing Of K3c60 Observed By C-13-Nmr"

            J. Phys. Soc. Jpn. 63 (5), 1670-1673 (1994).

 

            ABSTRACT: This Letter reports on NMR studies of C-13 in K3 C60 above and below T(c) with an applied field of 2.93 T. It is found that non-single-exponential recovery data can be fitted by two components and normalized to an identical shape. With T1 defined in this way, Fermi-liquid behavior is identified above T(c), and a broadened Hebel-Slichter peak observed below T(c) is well explained by the Eliashberg theory with 2DELTA(0)/k(B)T(c)=4.31. The possibility of strong electron correlation and the origin of the multi-exponential recovery are discussed.

 

104.    M. Sato

            "Growth Of Gaasn By Low-Pressure Metalorganic Chemical-Vapor-Deposition Using Plasma-Cracked N-2"

            J. Cryst. Growth 145 (1-4), 99-103 (1994).

 

            ABSTRACT: GaAsN epitaxial layers were grown on GaAs substrates by plasma-assisted low-pressure metalorganic chemical vapor deposition (MOCVD). Pure N-2 gas, which is neither corrosive nor toxic, was chosen as the safest nitrogen precursor. More nitrogen atoms were incorporated from plasma-cracked N-2 than from plasma-cracked NH3 indicating that N-2 is better precursor for GaAsN growth. Photoluminescence from GaAsN was red-shifted with increasing nitrogen concentration. No significant difference was observed in the photoluminescence results between GaAsN layers grown using the two precursors.

 

105.    T. Sato and S. Nishida

            "Does An Envelope-Detecting Mechanism Mediate Stereopsis For Band-Limited Stimuli"

            Invest. Ophthalmol. Vis. Sci. 35 (4), 1916-1916 (1994).

 

            ABSTRACT:

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

            "Uv Photoelectron-Spectroscopy Of Polysilanes And Polygermanes"

            in Polymeric Materials For Microelectronic Applications, Acs Symposium Series Vol. 579 (Amer Chemical Soc, Washington, 1994), pp. 398-407.

 

            ABSTRACT: UV photoelectron spectra were measured for ten polymers with main chains composed of Si and Ge atoms. The spectra of poly(dialkylsilane)s were described well as the overlap of the spectra of constituent parts, while polysilanes with aryl side groups showed the effect of sigma-pi mixing. The spectra of polygermanes and Si-Ge block copolymers are fairly similar to those of corresponding polysilanes, while Si-Ge random copolymers show indications of the effect of the presence of many Si-Ge bonds.

 

107.    K. Semba and A. Matsuda

            "Effect Of Impurity On Anisotropy Of High-Tc Superconductivity In Yba2(Cu1-Xznx)3o7-Delta Single-Crystals"

            Physica B 194, 1955-1956 (1994).

 

            ABSTRACT: The effect of Zn doping on anisotropy of high-T(C) superconductivity is studied in single-crystal YBa2(Cu1-xZnx)3O7-delta (YBCZO) within the range 0<x<0.03. The resistive transition curves under a magnetic field for these impurity-containing systems axe successfully described for the first time by the renormalized fluctuation theory including psi4 term. The derived coherence length ratio xi(ab)/xi(c), which indicates anisotropy in superconductivity, decreases as the impurity concentration increases. However, both rho(c) and the normal state anisotropy rho(c)/rho(ab) increase. This situation is not consistent with the Lawrence-Doniach (LD) model. The anisotropic 3-D metal model seems to be appropriate for the YBCZO system. This result excludes certain types of high-T(c) theories which assume strict two dimensionality of the electronic system.

 

108.    K. Semba, A. Matsuda, and T. Ishii

            "Normal And Superconductive Properties Of Zn-Substituted Single-Crystal Yba2(Cu1-Xznx)3o7-Delta"

            Phys. Rev. B 49 (14), 10043-10046 (1994).

 

            ABSTRACT: Zn-impurity-induced anisotropy reduction of superconductivity is obtained from a resistive transition analysis of single-crystal YBa2(Cu1-xZnx)3O7-delta. The out-of-plane resistivity (rho(c)) increases with Zn doping, while the carrier concentration remains almost unchanged. The results are not consistent with the simple Lawrence-Doniach model. Instead, an anisotropic three-dimensional metal model seems to be promising. A Zeeman-contribution-subtracted magnetoresistance analysis indicates that a Zn impurity does not cause any magnetic pair breaking.

 

109.    H. Shibata, K. Kinoshita, and T. Yamada

            "Crystal-Structure And Growth Of (Ba1-Xsrx)(2)Cu1.1o2.2+Delta(Co3)(0.9) Single-Crystals"

            Physica C 235, 519-520 (1994).

 

            ABSTRACT: Single crystals of copper-oxycarbonate (Ba1-xSrx)(2)Cu1.1O2.2+delta(CO3)(0.9) are obtained by solid state recrystallization and their structures are analyzed by single crystal X-ray diffraction. The size of the crystals are up to 2x2x2 mm(3), and become superconducting at 32K(onset) and 26K(endpoint). Single crystal X-ray diffraction shows that the crystals have a tetragonal unit cell with lattice parameters a = 5.570(2)Angstrom and c = 7.868(2)Angstrom, which are almost equal to those of ceramic samples.

 

110.    H. Shibata, K. Kinoshita, and T. Yamada

            "Single-Crystal Growth Of (Ba1-Xsrx)2cu1.1o2.2+Delta(Co3)0.9 By Solid-State Recrystallization"

            Physica C 232 (1-2), 181-183 (1994).

 

            ABSTRACT: Single crystals of copper-oxycarbonate (Ba1-xSrx)2Cu1.1O2.2+delta(CO3)0.9 are obtained using abnormal grain growth. Although there are some voids in the crystals, cubic crystals up to 2x2x2 mm3 are obtained. Electrical resistivity measurements show that the transition temperature is between 32 K(onset) and 26 K (endpoint), and magnetic susceptibility measurements show about a 25% shielding volume fraction, which is comparable to the ceramic samples.

 

111.    H. Shibata, A. Matsuda, K. Kinoshita, T. Watanabe, and T. Yamada

            "Origin Of The Semiconducting-To-Superconducting Transition Of La2-Xca1+Xcu2o6+/-Delta Under High-Oxygen-Pressure Annealing"

            Phys. Rev. B 49 (17), 12315-12317 (1994).

 

            ABSTRACT: The Madelung energy of La2-xCa1+xCu2O6+/-delta system, whose properties change from semiconductor to superconductor under high-oxygen-pressure annealing, is calculated. We find the, increase in DELTAV(A), the difference in Madelung site potential between the apex and the CuO2 planes' oxygen, promotes the superconducting transition in this system. Slight intercalation of oxygen between two CuO2 planes is found to be of primary importance in determining DELTAV(A).

 

112.    K. Shiraishi, T. Ito, and T. Ohno

            "Coverage Dependence Of Migration Potential Of Cation Adatoms On Gaas(001)-(2x4) Surface"

            Solid-State Electron. 37 (4-6), 601-604 (1994).

 

            ABSTRACT: We theoretically investigate the migration potential of cation adatoms on the reconstructed As-rich GaAs (001)-(2 x 4) surface by ab initio calculation. By increasing the number of cation adatoms, we also study how migration potential depends on coverage. The calculated results for Ga adatoms suggest that the long-bridge sites are energetically the most favorable at the iniital stage of crystal growth. However, as the Ga coverage increases, the missing dimer row sites become the most favorable. Migration potentials strongly depend on the adatom coverage. Similar results were obtained for Al adatom migration. Furthermore, based on these migration potentials, we demonstrate the dynamical behavior of cation adatoms on GaAs(001) surface by performing Monte-Carlo simulations at finite temperatures.

 

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

            "Growth Of Gaas/Alas Trench-Buried Multiple-Quantum Wires By Metalorganic Chemical-Vapor-Deposition On V-Grooved Substrates"

            Appl. Phys. Lett. 64 (24), 3299-3301 (1994).

 

            ABSTRACT: We report the fabrication of GaAs/AlAs multiple trench-buried quantum wires (TBWs) by metalorganic chemical vapor deposition on V-grooved substrates. The shape of AlAs layers grown on the V-grooves can be changed significantly from a V-shape to U-shape by varying growth temperatures and group-V/III ratios. 30-nm-wide and 100-nm-deep AlAs trenches with nearly vertical sidewalls are formed at the growth temperature of 650-degrees-C with the group-V/III ratio of 165, while V-shaped AlAs grooves are formed at 700-degrees-C with the V/III ratio of 110. Vertically stacked double TBWs are formed using the 30-nm-wide trenches. The low-temperature (15 K) photoluminescence spectrum for the double TBWs shows two distinct emission peaks corresponding to the 6.5- and 8.0-nm-thick wires.

 

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

            "Gaas/Alas Trench-Buried Quantum Wires With Nearly Rectangular Cross-Sections Grown By Metalorganic Chemical-Vapor-Deposition On V-Grooved Substrates"

            Appl. Phys. Lett. 64 (4), 472-474 (1994).

 

            ABSTRACT: GaAs trench-buried quantum wires were fabricated by using V-grooved AlAs trenches grown on V-grooved (001) substrates. These trench structures with vertical (110) sidewalls were formed by the faceting of (110) planes, and lateral growth of these planes reduced the trench width to less than 20 nm. A cross-sectional scanning electron microscope image of these trench-buried structures showed GaAs wires about 20 nm wide and 20 nm thick. The growth of these wires is enhanced by the capture of Ga species into the trenches. Blueshifts and strong anisotropy of photoluminescence confirm two-dimensional quantum confinement.

 

115.    L. C. Su, I. H. Ho, N. Kobayashi, and G. B. Stringfellow

            "Order-Disorder Heterostructure In Ga0.5in0.5p With Delta-E(G)=160 Mev"

            J. Cryst. Growth 145 (1-4), 140-146 (1994).

 

            ABSTRACT: Ordering in Ga0.5In0.5P can be controlled by variations in the substrate temperature during organometallic vapor phase epitaxial (OMVPE) growth. Growth at 720 degrees C at a rate of 0.5 mu m/h is shown to produce completely disordered material, as evidenced by the transmission electron diffraction (TED) and the photoluminescene (PL) results. The ordering produced at a growth temperature of 620 degrees C is found to depend strongly on the substrate misorientation, Transmission electron micrographs and TED patterns for misorientations of 0 degrees, 3 degrees, 6 degrees, and 9 degrees from (001) toward the [110] direction in the lattice show that increasing the misorientation from 0 degrees to 3 degrees leads to the elimination of one variant, the elimination of twin boundaries, and an overall increase in the degree of order. Further increases in the misorientation angle to 6 degrees and 9 degrees at this growth temperature lead to increasing disorder, although only one variant is formed and the distance between antiphase boundaries (APBs) increases monotonically with increasing theta(m). This wide variation in ordering behavior has allowed the growth of an order/disorder heterostructure for a substrate misorientation of 3 degrees. The heterostructure consists of a Ga0.52In0.48P layer 0.5 mu m thick grown at 740 degrees C followed by an ordered layer 0.4 mu m thick grown at 620 degrees C. The X-ray diffraction results show that both layers are precisely lattice-matched to the GaAs substrate. TED patterns show that the first layer is completely disordered and the top layer is highly ordered, with only a single variant. High resolution images indicate that the interface is abrupt, with no dislocations or other defects. 10 K PL shows two sharp and distinct peaks at 1.995 and 1.830 eV for high excitation intensities. The peak separation is even larger at lower excitation intensities. The two peaks come from the disordered and ordered material, respectively. The peak separation represents the largest energy difference between ordered and disordered material reported to date. This large energy difference, 6.6kT at room temperature, may make such heterostructures useful for photonic devices such as light emitting diodes, lasers, and solar cells.

 

116.    H. Tabei, M. Takahashi, S. Hoshino, O. Niwa, and T. Horiuchi

            "Subfemtomole Detection Of Catecholamine With Interdigitated Array Carbon Microelectrodes In Hplc"

            Anal. Chem. 66 (20), 3500-3502 (1994).

 

            ABSTRACT: An IDA carbon microelectrode for HPLC was fabricated by photolithographic techniques from the carbon film of pyrolyzed 3,4,9,10-perylenetetracarboxylic dianhydride on thermally oxidized silicon wafers. The IDA electrode consisted of 300 pairs, the finger widths and gaps were 5 mu m, and each finger was 2 mm long. The electrode in a small-volume thin-layer cell incorporated in a microbore HPLC system achieved a low detection limit for dopamine due to current enhancement by redox cycling and low background noise at the carbon IDA microelectrode. The detection Limit of 0.5 fmol of dopamine can be realized because of the low noise level and high current density.

 

117.    A. Taguchi, K. Takahei, and Y. Horikoshi

            "Multiphonon-Assisted Energy-Transfer Between Yb 4f Shell And Inp Host"

            J. Appl. Phys. 76 (11), 7288-7295 (1994).

 

            ABSTRACT:

118.    K. Takahei and A. Taguchi

            "Efficient Er Luminescence-Centers Formed In Gaas By Metalorganic Chemical-Vapor-Deposition With Oxygen Codoping"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 33 (1B), 709-711 (1994).

 

            ABSTRACT: Er-doped GaAs is grown by low-pressure metalorganic chemical vapor deposition with and without oxygen codoping. Optically efficient Er-oxygen complex centers are formed when a small amount of oxygen is present in the growth atmosphere. In situ monitoring of the surface morphology by light scattering from the growing surface with and without oxygen codoping suggests that migration of Er atoms on the surface is pinned by the formation of an Er-oxygen complex. We speculate that this effect suppresses the formation of Er-rich clusters and allows the formation of a high concentration of uniformly dispersed Er-oxygen complex centers that have a high luminescence efficiency.

 

119.    K. Takahei, A. Taguchi, Y. Horikoshi, and J. Nakata

            "Atomic Configuration Of The Er-O Luminescence Center In Er-Doped Gaas With Oxygen Codoping"

            J. Appl. Phys. 76 (7), 4332-4339 (1994).

 

            ABSTRACT: This article investigates the structure of an Er luminescence center in GaAs by using its intra-4f-shell luminescence spectrum as an atomic probe to identify the atomic configuration. This Er center is formed in GaAs by metalorganic chemical vapor deposition with O codoping and the center shows a high efficiency and a sharp luminescence spectrum under above-band-gap photoexcitation. A single luminescence line in the spectrum of a GaAs:Er,O splits into more than eight lines in the spectrum of Al0.01Ga0.99As:Er,O. This drastic change due to the addition of 1% Al can be explained by assuming that, because of the high tendency of Al atoms to react with O atoms, the Al atoms preferentially occupy the nearest-neighbor Ga sites of two O atoms, both of which are coupled with the Er atom. Based on the luminescence spectra and additional experiments of Rutherford backscattering and secondary ion mass spectroscopy, we propose that the structure of the Er luminescence center under study is Er occupying the Ga sublattice with two O atoms most likely located at the nearest-neighbor As sites. An Er-related spectrum of GaAs0.97P0.03:Er,O can also be understood based on this model if the chemical difference of Al and P is taken into account.

 

120.    H. Takayanagi, J. B. Hansen, and J. Nitta

            "Mesoscopic Fluctuations In The Critical-Current In Inas-Coupled Josephson-Junctions"

            Physica B 203 (3-4), 291-297 (1994).

 

            ABSTRACT: Mesoscopic fluctuations were confirmed for the critical current in a p-type InAs-coupIed Josephson junction. The critical current was measured as a function of the gate voltage corresponding to the change in the Fermi energy. The critical current showed a mesoscopic fluctuation and its behavior was the same as that of the conductance measured at the same time in both the weak and strong localization regimes. The magnitude and the typical period of the fluctuation are discussed and compared to theoretical predictions.

 

121.    K. Takeda

            "Electronic-Structure Of Random Copolymers"

            J. Math. Chem. 15 (3-4), 323-337 (1994).

 

            ABSTRACT: The electronic structure of random copolymers (RCP) is theoretically investigated by the single-site coherent potential approximation. The results are also compared with those by the band calculation for the corresponding ordered system. In the A1-xBx binary RCP, a strong reduction in the system band gap (E(g)(A1-xBx)) is found in the dilute B region when the system has the relation of E(g)(A) > E(g)(B). This dependence is caused by the asymmetric quenching in the density-of-states (DOS) singularity at the band-edge states. The gap-opening mechanism and the asymmetric quenching are discussed by focusing on the role of the spatial dimension on the electronic structure of the random system, and the theoretical treatment is finally applied to the calculation of the joint DOS for the Si-Ge RCP system.

 

122.    K. Takeda and K. Shiraishi

            "Theoretical Possibility Of Stage Corrugation In Si And Ge Analogs Of Graphite"

            Phys. Rev. B 50 (20), 14916-14922 (1994).

 

            ABSTRACT:

123.    K. Takeda, K. Shiraishi, M. Fujiki, M. Kondo, and K. Morigaki

            "Photocreated Metastable States In Polysilanes"

            Phys. Rev. B 50 (8), 5171-5179 (1994).

 

            ABSTRACT: Photocreated metastable states in organopolysilane (PSi) solids are observed using the electron-spin-resonance (ESR) technique. Two types of light-induced ESR (LESR) spectra are found depending on the excitation photon energy. These two types of LESR centers are annihilated by thermal annealing. Based on a first-principle electronic calculation, the origins of these LESR centers have been discussed. The lowest photoexcitation (approximately 3.5 eV) in PSi induces the Si skeleton stretching forces, which creates a weak bond (WB) in several places of the Si skeleton. Electronically, this WB acts as a self-trapping center for the photoexcited sigma electron. The other higher photoexcitation (over 4.8 eV) causes side-pendant dissociation, which creates a dangling bond (DB) and causes the localized midgap state. The four lines found in the higher-energy excitation are considered to arise from hyperfine interaction between this DB electron and a sodium impurity nucleus.

 

124.    K. Takei, D. J. Rogers, and Y. Maeda

            "Bias Effect On Compositional Separation In Sputtered Co-Cr Films"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 33 (10), 5739-5742 (1994).

 

            ABSTRACT: The effect of de substrate bias on compositional separation (CS) in sputtered Co-Cr films is examined using spin-echo Co-59 NMR and transmission electron microscopy. It is observed that the degree of CS decreases monotonically with increasing negative bias voltage. Slight positive bias voltage, however, is found to enhance CS, resulting in increased saturation magnetization and a higher anisotropy field. The elimination of Ar ion bombardment at the film surface during deposition is thought to be effective in enhancing CS.

 

125.    K. Takei, D. J. Rogers, and Y. Maeda

            "Nmr-Study Of Magnetic And Compositional Inhomogeneities In Co-Cr Thin-Films"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 33 (2), 1027-1028 (1994).

 

            ABSTRACT: Spin-echo Co-59 NMR is employed to detect magnetically distinct components in a Co-Cr thin film. Magnetic components with different values of the anisotropy field can be detected by measuring spin-echo intensity as a function of rf pulse field applied to the sample. For a film deposited at 400-degrees-C, two magnetic components are observed. The chemical composition is estimated for each component from the NMR frequency spectra.

 

126.    K. Takei, J. Suzuki, Y. Maeda, and Y. Morii

            "Micromagnetic Domain Observations Of Co-Cr Films By Neutron-Scattering"

            IEEE Trans. Magn. 30 (6), 4029-4031 (1994).

 

            ABSTRACT: Magnetic microstructures revealed by neutron small angle scattering are correlated with the compositional separation (CS) in sputtered Co-22at%Cr thin films for. high density magnetic recording. The CS is confirmed to be strongest for deposition temperatures from 150 degrees C to 400 degrees C, using nuclear magnetic resonance. The finest magnetic particles, less than 10 mm in diameter, are detected in a film deposited at 200 degrees C, in good agreement with the smallest features observed in the etched microstructure by transmission electron microscopy. This indicates that CS produces magnetic grains much smaller than the crystal grains which can, therefore, de applied to synthesize Co-Cr thin film media for ultra high density magnetic recording.

 

127.    Y. Tanaka, A. Hasegawa, and H. Takayanagi

            "Tunneling Conductance Of A Quantum-Dot Formed By A Super-Conducting Pari Potential"

            Physica B 194, 1761-1762 (1994).

 

            ABSTRACT: The tunneling conductance of the quasiparticle of a quantum dot structure, which is a normal region surrounded by a superconducting pair potential, is obtained under a magnetic field weaker than the lower critical field of the superconductor. It strongly depends on the number of the magentic flux quanta that penetrates the normal dot region.

 

128.    S. Tarucha, T. Honda, T. Saku, and Y. Tokura

            "Charging Effects In Small-Area Modulation-Doped Double-Barrier Heterostructures"

            Surf. Sci. 305 (1-3), 547-552 (1994).

 

            ABSTRACT: Charging effects on resonant tunneling are studied in modulation-doped double-barrier heterostructures. We observe a blockade of the tunneling current around zero-bias in small-area devices, while in large-area devices we observe a tunneling current with a zero-threshold bias due to the modulation doping. The blockade voltage width varies in proportion to the inverse square of the conducting diameter, and agrees well with the calculated charging energy for a single electron. At the high voltage end of this blockade region we observe step-like current-voltage features and fine structure in the form of small peaks and shoulders. This fine structure is related to the interplay between charging and size quantization effects.

 

129.    H. Teramae and J. Michl

            "Electronic States Of Linear Tetrasilane And Polysilanes"

            Mol. Cryst. Liq. Cryst. Sci. Technol. Sect. A-Mol. Cryst. Liq. Cryst. 256, 149-159 (1994).

 

            ABSTRACT: The standard Sandorfy C model of electronic structure of polysilanes is inherently incapable of providing a physical interpretation of the observed conformational effects on UV spectra. We describe a more complicated ladder C model, which still considers only the two backbone hybrid orbitals on each silicon atom, but includes the transfer integrals between all pairs of orbitals on a pair of neighboring silicons. Already at the Huckel level, this model accounts for the general features of the observed spectra both as a function of chain length and of conformation. Results of our ab initio calculations suggest, however, that for general non-planar conformations the backbone orbitals should not be treated separately from those that carry the substituents, at least not in relatively short chains. The simplest level at which the conformational effects on the spectra of oligosilanes of all lengths can be accounted for simultaneously will probably be the even more complicated ladder H model, in which all four valence orbitals of each silicon and one orbital of each substituent are considered explicitly.

 

130.    Y. Tokura and S. Tarucha

            "Exchange Interaction In Quantum-Wire Subbands"

            Phys. Rev. B 50 (15), 10981-10989 (1994).

 

            ABSTRACT: The many-electron ground state is studied in a quantum wire with several populated spin and orbital subbands. The many-body effect is treated in the lowest order. The phase diagram of the subband population is obtained as a function of magnetic field and the strength of the confining potential. If the magnetic field is small, there is a phase boundary between spin-polarized states and partially spin-polarized states. Using these results, transport characteristics are calculated using Landauer's formula and a dip is predicted in the conductance plateau of 2e(2)/h.

 

131.    Y. Tomioka, M. Naito, K. Kishio, and K. Kitazawa

            "The Meissner And Shielding Effects Of High-Temperature Oxide Superconductors"

            Physica C 223 (3-4), 347-360 (1994).

 

            ABSTRACT: The Meissner and shielding effects were investigated systematically on single crystals of (La1-xSrx)2CuO4, YBa2Cu3O7 and Bi2Sr1.8CaCu2O8. Significant differences in the low-temperature Meissner fraction (f(M)) in the same materials observed under various fields and sample sizes, were explained consistently and quantitatively, based on the vortex-pinning model. Extending the model employed, the pinning critical current could be estimated as a function of T from the set of the shielding and Meissner curves. The Meissner and shielding effects in the polycrystalline samples were also measured in a similarly systematic manner and could be interpreted by considering the effective sample size of the polycrystals, showing a cross-over of this quantity from the grain size at high fields to macroscopic sample size at low fields.

 

132.    M. Tsukada, A. Misawa, J. Nishikido, Y. Shimazu, and H. Nakano

            "Experiments On Photonic Cell Switching With An Optical Input Buffer"

            Electron. Lett. 30 (13), 1081-1082 (1994).

 

            ABSTRACT: The authors describe photonic cell switching experiments using an optical input buffer. The buffer controls cell throughput to a switch module according to back-pressure signals from a switch controller. The buffer has a size of three cells consisting of two kinds of fibre delay line. The optical cells are switched to dual ports through the optical buffer. Buffering and switching experiments are performed for 2.5Gbit/s 64bit optical cells, and the bit error rate is measured.

 

133.    M. Ueda and T. Ando

            "Effects Of Barrier Traversal Time On Escape Rate Through A Small-Capacitance Tunnel Junction"

            Superlattices Microstruct. 16 (3), 279-281 (1994).

 

            ABSTRACT: This paper describes self-consistent determination of the transfer-energy-dependent escape rate and barrier traversal time of electrons under the influence of the electromagnetic environment. This rate lets us examine dissipative and nondissipative tunneling rate separately and its integral over the transfer energy gives the total escape rate that is obtained by the instanton technique. It is found that the escape rate is exponentially enhanced as the capacitance of the junction is reduced.

 

134.    M. Ueda and T. Ando

            "Potential Renormalization In Mesoscopic Tunneling - Reply"

            Phys. Rev. Lett. 73 (20), 2785-2785 (1994).

 

            ABSTRACT:

135.    M. Ueda and T. Ando

            "Transfer-Energy-Dependent Escape Rate Of Electrons Through A Small-Capacitance Tunnel Junction"

            Phys. Rev. B 50 (11), 7820-7832 (1994).

 

            ABSTRACT: The dynamics of a tunneling electron through a small-capacitance tunnel junction are studied by developing a method for self-consistently determining escape rate and barrier traversal time for those electrons that transfer a given energy to the electromagnetic environment. The transfer-energy-dependent escape rate lets us examine dissipative and nondissipative tunneling rates separately and its integral over the transfer energy gives the total escape rate that is obtained by the instanton technique. It is found that the escape rate increases exponentially with increasing the ratio of the elementary charging energy to the quantized energy of the environment, but that the traversal time peaks at one particular ratio. As the frequency of the electromagnetic mode increases, an effective potential is shown to change from linear (dominated by the zero-point fluctuations of charge on the junction) to parabolic (dominated by the static polarization of the charge). Possible experimental situations for observing the predicted effects are discussed.

 

136.    M. Ueda and T. Ando

            "Electron-Escape Rate And Barrier Traversal Time Influenced By The Electromagnetic Environment"

            Phys. Rev. Lett. 72 (11), 1726-1729 (1994).

 

            ABSTRACT: Self-consistent determination of electron escape rate and barrier traversal time under the influence of the electromagnetic environment reveals that the escape rate increases monotonically with increasing ratio of the elementary charging energy to the barrier height but that the traversal time peaks at one certain ratio. As the frequency of the electromagnetic mode increases, an effective potential for a tunneling electron changes from linear to parabolic, dominated, respectively, by the zero-point fluctuations of the charge on the junction and its static polarization. Possible experimental situations for observing these predictions are discussed.

 

137.    M. Ueda and N. Imoto

            "Anomalous Commutation Relation And Modified Spontaneous Emission Inside A Microcavity"

            Phys. Rev. A 50 (1), 89-92 (1994).

 

            ABSTRACT: Usual quantum-optical operator relations for a beam splitter are shown to lead to an anomalous commutation relation inside a microcavity. The physical origin of this anomaly is identified as self-interference of the mode whose coherence length is longer than the round-trip length of the cavity. Altered spontaneous emission of an excited atom is found to be a direct manifestation of this anomalous commutation relation. The anomalous Heisenberg uncertainty relations, which are derived from the commutation relation according to the Schwartz inequality, cannot be detected by probing the internal field with a beam splitter. The anomalous commutation relation, however, can be related to the change in the effective reflectivity of the beam splitter. The similarity and difference between an excited atom and a probe beam splitter are discussed.

 

138.    K. Y. Uomori and S. Y. Nishida

            "The Dynamics Of The Visual-System In Combining Conflicted Kde And Binocular Stereopsis Cues"

            Percept. Psychophys. 55 (5), 526-536 (1994).

 

            ABSTRACT: The dynamics of the visual system in combining multiple depth cues were investigated by measuring the temporal change in the perceived 3-D shape of a random-dot stimulus with conflicting kinetic depth effect (KDE) and binocular stereopsis cues. The KDE shape perception dominated for the first few seconds, and then was gradually supplanted by the stereo shape perception. The effects of various pre-adaptation stimuli suggested that the temporal change in the perceived shape resulted from a self-adaptation of the KDE mechanism that occurs mainly at the levels of motion and relative motion detection.

 

139.    K. Uwai and N. Kobayashi

            "Real-Time Observation Of Surface Dielectric Responses Of Gaas(001) Using Surface Photoabsorption"

            Appl. Surf. Sci. 82-3, 290-297 (1994).

 

            ABSTRACT: Surface photo-absorption is used to observe the changes in isotropic and anisotropic surface dielectric responses caused by As desorption during surface conversion from c(4 x 4) to (2 x 4) gamma of As-stabilized GaAs(001) surfaces. The anisotropic part agrees with the change in the surface dielectric anisotropy spectrum observed in reflectance-difference measurements during this surface conversion. The spectral evolutions of surface dielectric response are observed in real time with a time resolution of 0.1 s during surface conversion.

 

140.    K. Uwai and N. Kobayashi

            "Dielectric Response Of As-Stabilized Gaas-Surfaces Observed By Surface Photoabsorption"

            Appl. Phys. Lett. 65 (2), 150-152 (1994).

 

            ABSTRACT: This letter discusses changes in the isotropic and anisotropic surface dielectric response caused by surface conversion from c(4x4) to (2X4) of a GaAs(001) As-stabilized surface, observed using surface photo-absorption. The anisotropic part quantitatively reproduces the change in the surface dielectric anisotropy spectra observed in reflectance difference measurements during this surface conversion. The isotropic part can be measured only by surface photo-absorption and comparison is made with a calculation using a three-phase model consisting of vacuum/As/GaAs.

 

141.    L. M. Weegels, T. Saitoh, and H. Kanbe

            "Real-Time Investigations Of Gaas Surface Cleaning With A Hydrogen Electron-Cyclotron-Resonance Plasma By Optical Reflection Spectroscopy"

            Appl. Phys. Lett. 65 (24), 3117-3119 (1994).

 

            ABSTRACT:

142.    L. M. Weegels, T. Saitoh, H. Oohashi, and H. Kanbe

            "In-Situ Monitoring Of Electron-Cyclotron-Resonance Plasma Processing Of Gaas-Surfaces By Optical Reflection Spectroscopy"

            Appl. Phys. Lett. 64 (20), 2661-2663 (1994).

 

            ABSTRACT: In situ reflection spectroscopy is demonstrated to be a useful technique for monitoring the damage to the surface of GaAs substrates induced by ions from an electron cyclotron plasma. Distinct differences in the reflectance spectra of GaAs substrates are observed between etching by argon ions and chemical cleaning by hydrogen ions. For argon it is found that the damage layer thickness increases linearly with the argon ion energy. Hydrogen ions induce a damage layer of 3.1 nm and arsenic atoms are preferentially removed from the surface as the ion energy increased.

 

143.    S. Yamada, K. Maezawa, W. T. Yuen, and R. A. Stradling

            "X-Conduction 2-Dimensional Subband Structure And Order In Algaas/Alas Quantum-Wells"

            Physica B 201, 295-300 (1994).

 

            ABSTRACT: The subband structure of two-dimensional X-band electrons in modulation-doped very thin (25-75 angstrom) AlAs quantum wells was studied in magnetotransport experiments and analyzed in self-consistent calculations. Effective mass estimation based on temperature dependent magnetoresistances clearly showed X(z) - X(xy) crossover at an AlAs thickness of about 45 angstrom, which is much less than the crossover thickness in AlAs/GaAs type II superlattices (60 angstrom). Considering the results of self-consistent calculations together with some observed anomalies in X(xy) electron magnetoresistances, we can conclude that this difference is due to the effect of doping and to the degeneracy change in k-space occurring at the crossover thickness of AlAs.

 

144.    S. Yamada, K. Maezawa, W. T. Yuen, and R. A. Stradling

            "X-Conduction-Electron Transport In Very Thin Alas Quantum-Wells"

            Phys. Rev. B 49 (3), 2189-2192 (1994).

 

            ABSTRACT: Magnetotransport behavior of two-dimensional X-band electrons created in modulation-doped very thin (25-75 Angstrom) AlAs quantum wells was studied. Effective-mass analysis based on temperature-dependent magnetoresistances clearly showed X(z)-X(xy) crossover at an AlAs thickness of about 45 Angstrom. This value is much smaller than that in an AlAs/GaAs type-II superlattice (60 Angstrom). Origins of this difference were discussed in terms of the effect of doping and degeneracy change and of the change of strain due to the structure difference.

 

145.    T. Yamada and Y. Horikoshi

            "Comparison Of Gaas Facet Formation On Patterned Substrate During Molecular-Beam Epitaxy And Migration-Enhanced Epitaxy"

            Jpn. J. Appl. Phys. Part 2 - Lett. 33 (7B), L1027-L1030 (1994).

 

            ABSTRACT: We compare the film thickness profile and facet formation of GaAs films grown on a patterned substrate by migration-enhanced epitaxy (MEE) and by molecular beam epitaxy (MBE). The film thickness profile indicates that the Ga diffusion length during MBE growth decreases as the As pressure increases. In contrast, the diffusion length during MEE growth is independent of the As pressure. The facets resulting from MBE and MEE diff er greatly. The dominant facet produced by MBE is in the (111)B plane, whereas (110), (113)B and (221)B are the most observable facet planes resulting from MEE. From these results, it is found that Ga atoms migrate to occupy every available site on each plane, with excess atoms moving to other index planes in MEE growth.

 

146.    T. Yamada, K. Kinoshita, and H. Shibata

            "Synthesis Of Superconducting T'-(La1-Xcex)(2)Cuo4"

            Jpn. J. Appl. Phys. Part 2 - Lett. 33 (2A), L168-L169 (1994).

 

            ABSTRACT: A new preparation method far obtaining superconducting T'-(La1-xCex)(2)CuO4 is presented. The method consists of three processes: precursor material synthesis, oxidation and T'-phase formation. The single phase has been obtained for 0.065 less than or equal to x less than or equal to 0.08. The maximum superconducting onset (T-c(onset)) and zero-resistance (T-c (zero)) temperatures are 30 K and 17 K, respectively, which are obtained when x=0.065. The T-c(onset) obtained here is higher than those of other T'-type cuprates.

 

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

            "In-Situ Monitoring Of 1st-Order Phase-Transition On Inas(001) Surfaces By Scanning Electron Surface Microscopy"

            Appl. Surf. Sci. 82-3, 223-227 (1994).

 

            ABSTRACT: Domain formation during the phase transition on an InAs(001) surface under As pressure was observed directly for the first time by using scanning electron surface microscopy, which is a surface-sensitive scanning electron microscopy technique. Detailed analysis also verified that the role of step edges during transition differs between As-atom desorption and adsorption.

 

148.    H. Yamaguchi and Y. Horikoshi

            "Unified Model For Structure Transition And Electrical-Properties Of Inas (001) Surfaces Studied By Scanning-Tunneling-Microscopy"

            Jpn. J. Appl. Phys. Part 2 - Lett. 33 (10A), L1423-L1426 (1994).

 

            ABSTRACT: Thermal stability of the (2x4) structures on InAs and GaAs (001) surfaces is studied by using scanning tunneling microscopy with atomic resolution. Even just before the transition to a (4x2) structure, the annealed InAs surface has much lower density of kinks in the dimer vacancy rows than the annealed GaAs. This difference leads to a unified model that can explain both the 1st order phase transition and the peculiar electric properties of an InAs (001) surface.

 

149.    H. Yamaguchi and Y. Horikoshi

            "Arsenic Pressure-Dependence Of 1st-Order Phase-Transition On Inas (001) Surface"

            Appl. Phys. Lett. 64 (19), 2572-2574 (1994).

 

            ABSTRACT: The role of As pressure in the first-order phase transition between As-covered (2X4) and In-covered (4X2) structures on InAs (001) surfaces is investigated using reflection high-energy electron diffraction. The dependence of transition temperatures on As pressure is well explained by Monte Carlo simulation with a two-dimensional lattice gas model, and the interaction energy is quantitatively obtained. The influence of metastability on As desorption is also clarified by comparing the experiments and simulations.

 

150.    H. Yamaguchi and Y. Horikoshi

            "Step Motion And Structure Transition On Inas And Gaas (001) Surfaces Observed By Scanning-Tunneling-Microscopy"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 33 (1B), 716-720 (1994).

 

            ABSTRACT: The step motion and structure transition on InAs and GaAs (001) surfaces are directly observed by scanning tunneling microscopy at high temperatures. A stable (2x4) structure is observed for the InAs surface even at temperatures high enough to cause the motion of monomolecular steps and kinks. At higher temperatures, domains with an In stable (4x2) Structure (As desorbed region) are clearly observed surrounded by As stable (2x4) structures. These results differ from those for GaAs surfaces and indicate strong lateral interaction in (2x4) structures on InAs.

 

151.    R. Yano, M. Mitsunaga, N. Uesugi, and M. Shimizu

            "Temperature-Dependence Of The Homogeneous Width Of Eu(3+) Spectral-Lines In Silicate Glass Measured By Accumulated Photon-Echoes"

            Phys. Rev. B 50 (13), 9031-9034 (1994).

 

            ABSTRACT: The temperature-dependent homogeneous width of the 5D(0)-7F(0) transition of Eu3+ in a pure silicate glass fiber has been measured by accumulated photon echoes between 1.6 and 44 K. The temperature dependence of the homogeneous width shows a crossover from T-linear (T < 7 K) to T2 (T > 7 K). The whole temperature dependence of the homogeneous width between 1.6 and 44 K can be explained by the configurational changes of the glass which is modeled by two-level systems (TLS's) and a Raman process involving low-frequency vibrational modes of the silicate glass (the rotations of SiO4 tetrahedra). The T-linear temperature dependence is attributed to the TLS process. The anomalous T2 dependence down to 10 K cannot be explained by only one process, but can be explained by the contributions of both the TLS process and the Raman process. Above 40 K, the Raman process becomes the dominant dephasing mechanism.

 

152.    J. Yumoto, K. W. Delong, and N. Uesugi

            "Coherent Transients In Cdsse Microcrystallites Doped In Glasses"

            Phys. Rev. B 49 (16), 11322-11326 (1994).

 

            ABSTRACT: Coherent transient effects, in CdSSe microcrystallites are observed by a pump-probe measurement. The probe transmission shows oscillatory structures in the temporal and spectral domains when the probe reaches the sample before the pump. This oscillation is attributed to the photon echo propagating in the direction of the probe. The A-B splitting of the valence sublevel in CdSSe microcrystallites hidden in the wide inhomogeneous broadening can be resolved using the polarization dependence of the transitions from A and B valence sublevels to the conduction sublevel.