1.         T. Akasaka, Y. Kobayashi, S. Ando, and N. Kobayashi

            "GaN hexagonal microprisms with smooth vertical facets fabricated by selective metalorganic vapor phase epitaxy"

            Appl. Phys. Lett. 71 (15), 2196-2198 (1997).

 

            ABSTRACT: Selective growth of GaN was performed by low-pressure metalorganic vapor phase epitaxy using a mask-patterned GaN epitaxial layer on a (0001) sapphire substrate. GaN hexagonal microprisms of 5-16 mu m in diameter, with smooth vertical facets and no ridge growth, were fabricated on a (0001) sapphire substrate. This vertical {<1(1)over bar 00>} of GaN was parallel to a {<11(2)over bar 0>} fact of the sapphire substrate. Both the use of an epitaxial GaN layer on the sapphire substrate and low working pressure contributed to obtaining smooth top and vertical facet surfaces. Also. the stripe structures of GaN were obtained that had a rectangular cross section. Moreover, the selection of rbe mask-patterning direction was found to be important because of the 30 degrees rotation of the crystallographic orientation between the GaN layer and the sapphire substrate. (C) 1997 American Institute of Physics.

 

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

            "InAs-inserted-channel InAlAs/InGaAs inverted HEMTs with superconducting electrodes"

            IEEE Trans. Appl. Supercond. 7 (2), 2921-2924 (1997).

 

            ABSTRACT: We investigate the device characteristics of InAs-inserted-channel In0.52Al0.48As/In0.53Ga0.47As inverted high electron mobility transistors (HEMTs) with superconducting Nb electrodes, In these transistors, the ohmic contact between Nb and the two dimensional electron gas formed in the InAs layer is obtained by contact with the Nb-InAs direct, instead of with an alloyed normal metal and semiconductor as in a conventional HEMT, The contact resistance of 0.15 Omega mm between the Nb ohmic electrodes and the channel decreased by a factor of 3 compared with that when a conventional AuGe/Ni alloyed ohmic contact is used. For a 0.5-mu m-gate device, the maximum extrinsic transconductance at 4.2 K was 1 S/mm, even at a very low drain voltage of 0.2 V. These results indicate that this ohmic contact formation will allow us to utilize in this device both the improved HEMT characteristics and the superior performance of superconducting electrodes.

 

3.         J. Akimitsu, H. Okajima, A. Yamashita, K. Ishii, T. Yokoo, T. Nagata, M. Uehara, R. Kadono, K. Nagamine, N. Kobayashi, Z. Hiroi, M. Takano, H. Takahashi, N. Mori, and K. Kinoshita

            "Appearance of magnetic long range order in the spin ladder compound LaCuO2.5"

            Hyperfine Interact. 104 (1-4), 43-48 (1997).

 

            ABSTRACT: We report here the two current topics in the ladder compounds. 1. The new ladder compound LaCuO2.5 recently discovered by Hiroi and Takano shows a clear sign of magnetic long range order at around 125 K observed by mu(+)SR technique. This result demonstrates that the ground state of LaCuO2.5 is not a spin liquid state, but a magnetically ordered state. 2. Superconductivity has been found in the ladder material (Sr,Ca)(14)Cu24O41 under high pressure between 3 GPa and 4.5 GPa. The superconducting transition temperatures T-c (onset) are 12 K and 9 K at 3 GPa and 4.5 GPa, respectively.

 

4.         T. G. Andersson, K. Nozawa, and Y. Horikoshi

            "Studies of GaN layers grown on sapphire using an RF-source"

            J. Cryst. Growth 175, 117-121 (1997).

 

            ABSTRACT: We have studied the relation between MBE growth parameters and him quality after growth of GaN on the c-plane of sapphire using a conventional Ga-source and an RF-source for the excitation of N-2. The growth rate was varied using Ga-flux, determined by RHEED oscillations on GaAs, r(GaAs) = 0.1-0.8 mu m/h. The N-2-flux was 0.5-1.5 sccm. Most layers of GaN were grown at 760 degrees C as measured by a pyrometer, while higher temperatures were utilised to determine the dismissal of growth. The RF-power and AlN buffer layer parameters were kept constant. The GaN-thicknesses were 0.2-1 mu m/h. For low growth rates of similar to 50 nm/h, there was a preferential growth of microcrystals in the growth direction which therefore overemphasised the measured film thickness. No film could be grown above 800 degrees C as the desorption rate was too high. For a GaN growth rate of 300 nm/h the sticking coefficient was similar to 85%. By varying the Ga- and N-2-fluxes it was evident that the film quality, as provided by the photoluminescence spectra, strongly depended on the growth parameters. Photoluminescence peak intensities generally improved with film thickness below 1 mu m. In 1 mu m thick films, we observed excitonic related peaks close to the band gap as well as peaks 50-60 meV below due to the presence of defects or impurities. We found a strong correlation between growth parameters and optimum growth and therefore the highest layer quality could be obtained only when all parameters were carefully optimised.

 

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

            "Excitonic optical properties in fractional-layer-superlattice wire structures in the intermediate confinement regime between two dimensions and one dimension"

            Phys. Rev. B 55 (4), 2429-2435 (1997).

 

            ABSTRACT: We report on the evolution of the excitonic optical features from two dimensions (2D) to one dimension (1D) in GaAs/AlAs fractional-layer-superlattice (FLS) wire structures. We present a theory numerically analyzing the excitonic optical-absorption properties in the FLS wires. With our calculation method we can treat any FLS wire shape with arbitrary dimension from 2D to 1D and can analyze in detail The excitonic optical properties in the intermediate quantum-confinement regime between 1D and 2D. We also experimentally demonstrate how the excitonic optical properties continuously evolve from 2D to 1D by introducing the FLS lateral compositional modulation in an AlxGa1-xAs quantum well. Present theory accurately reproduces the experimental results using the GaAs/AlAs FLS wires and clarifies the main optical features associated with excitons in the intermediate regime.

 

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

            "Triangular-facet lasers coupled by a rectangular optical waveguide"

            Jpn. J. Appl. Phys. Part 2 - Lett. 36 (2A), L76-L78 (1997).

 

            ABSTRACT: The coupled structure of two triangular prism-shaped micro-ring cavity lasers with a rectangular optical waveguide is achieved by selective area metalorganic vapor phase epitaxy (MOVPE), and its preliminary lasing characteristics are measured by optical pumping. This coupled laser structure consists of a (111)B growth plane and perpendicular (110) sidewall facets on a (111)B GaAs substrate. By using these coupled lasers as an oscillator and a modulator, the lasing light from the oscillator can be modulated at the modulator by changing the optical pumping power of the modulator. The carrier Lifetime in the active layer of the triangular laser can also be estimated with this laser configuration. The sidewall of the triangular laser covered with an. AlGaAs layer exhibits a longer carrier lifetime (similar to 560 ps) and lower threshold (E(th)=8 pJ) because of the reduced surface recombination at the edge of the GaAs active layer.

 

7.         S. Ando, N. Kobayashi, H. Ando, and Y. Horikoshi

            "Hexagonal facet laser with optical waveguides grown by flow-rate modulation epitaxy"

            J. Cryst. Growth 170 (1-4), 719-724 (1997).

 

            ABSTRACT: In selective MOVPE growth on a (111)B plane, the use of the flow-rate modulation epitaxy (FME) method reduces the growth temperature by more than 100 degrees C and drastically improves not only the selectivity but also the shape controllability compared to the conventional simultaneous-flow method. Especially, no polycrystalline deposition occurs on the SiO2 masked area even in the AlAs growth. In addition, intricate structures consisting of concave and convex sidewall facets can be grown in the shapes just like mask patterns. These superior characteristics of FME are used to grow various hexagonal prism-shaped GaAs/AlGaAs lasers with rectangular optical waveguides and, as a result, the grown structures consist of sharp facets having the same shape as the mask pattern. The thresholds of these lasers are extremely low compared with those grown by conventional MOVPE, because of the precise control of the facet shape. It is also found that the lasing light output can be efficiently extracted from the points of waveguides in all laser structures.

 

8.         V. N. Antonov and H. Takayanagi

            "ac effect in the conductance of mesoscopic normal-metal-superconductor structures"

            Phys. Rev. B 56 (14), R8515-R8517 (1997).

 

            ABSTRACT: Resonant peaks in the resistance of a mesoscopic normal-metal wire in contact with two superconductors under rf irradiation are detected. The peaks occur when a potential difference V-S=(h) over bar omega/2e is applied between the superconductors. The peaks can be interpreted as an ac phase-coherent phenomenon in the conductance of mesoscopic normal-metal-superconductor structures. This effect is observed although the critical Josephson current is negligibly small and the Shapiro steps are absent.

 

9.         V. N. Antonov, A. F. Volkov, and H. Takayanagi

            "''Proximity'' effect in the conductance of mesoscopic normal metal-superconductor structures"

            Europhys. Lett. 38 (6), 453-458 (1997).

 

            ABSTRACT: To clarify the nature of the interference effects observed in mesoscopic normal metal-superconductor structures the properties of silver wires with three types of superconducting loops at the stubs were experimentally studied. The geometry of the structures was chosen to enhance the main features of the transport in such systems and verify the models proposed for the interference phenomena. We observed behavior consistent with the proximity model. The role of the condensate, induced in the normal part by the superconductor, is discussed in the framework of this model.

 

10.       V. N. Antonov, A. F. Volkov, and H. Takayanagi

            "Anomalous proximity effect in mesoscopic normal-metal-superconductor structures"

            Phys. Rev. B 55 (6), 3836-3840 (1997).

 

            ABSTRACT: Anomalous corrections to the resistance have been found in mesoscopic normal-metal-superconductor (NS) structures below T-C. They differ from those described by the classical ''proximity'' theory in sensitivity to magnetic field, temperature, and rf irradiation. Contrary to the case of the classical proximity effect the anomalous corrections can be both positive and negative. A possible model which describes the anomalous corrections reported here is discussed.

 

11.       M. J. Ashwin, R. C. Newman, and K. Muraki

            "The infrared vibrational absorption spectrum of the Si-X defect present in heavily Si doped GaAs"

            J. Appl. Phys. 82 (1), 137-141 (1997).

 

            ABSTRACT: Heavily silicon doped GaAs grown by molecular beam epitaxy using a single gallium isotope source (Ga-69) has been studied by infrared absorption to reveal localized vibrational modes (LVMs) of Si complexes. The structure observed close to 367 cm(-1) is the same as that present in normal GaAs:Si spectra and does not result from mixed Ga isotopes. The electron trap Si-X gives three LVMs at 368.4, 370.0, and 399.6 cm(-1), typical of second neighbor donor-acceptor pairs, but inconsistent with a previous proposal that its structure is the planar defect V-Ga-Si-As-As-Ga. It is now suggested that the defect is a perturbed Si-Ga-V-Ga center, involving a second Si atom or a second vacancy. (C) 1997 American Institute of Physics.

 

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

            "Vertical single electron transistors with separate gates"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 36 (6B), 4151-4155 (1997).

 

            ABSTRACT: We demonstrate independent gate action in a vertical sub-micron single electron transistor with four separate gates fabricated by a new technology from a double barrier structure starting material. When the gate voltage is swept over a given range, the number of conductance oscillations increases systematically as the number of gates "squeezing" the quantum dot is varied from one to four. Alternatively, the average period of the conductance oscillations is essentially independent of the number of "squeezing" gates if the gate voltage is appropriately scaled to an "effective gate voltage". We show that subtle changes occur in the appearance of the conductance oscillations when the lateral geometry of the quantum dot is controllably deformed.

 

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

            "Multiple-gated submicron vertical tunnelling structures"

            Semicond. Sci. Technol. 12 (5), 631-636 (1997).

 

            ABSTRACT: We propose and demonstrate a new hybrid technology for fabricating submicron vertical resonant tunnelling structures with separate gates which has the potential to allow single-electron charging of, and single-electron tunnelling through, quantum dot structures containing just a 'few' electrons to be investigated in new ways.

 

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

            "GaAs/AlGaAs/InGaAs vertical triple barrier single electron transistors"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 36 (3B), 1667-1671 (1997).

 

            ABSTRACT: A gated vertical sub-micron triple barrier structure with undoped Al0.22Ga0.78As barriers and In0.05Ga0.95As wells is used to study the properties of two weakly coupled quantum dots containing just a few electrons. We find that the conductance peaks become sparse as the ac excitation voltage is decreased when there is considerable mismatch between the ladders of energy levels in the two dot. Concurrently, the diamond shaped regions of Coulomb blockade are strongly disrupted. On the other hand, when the mismatch between energy levels is ''small''-comparable to or less than the level width-the evolution of conductance peaks in pairs in the presence of a magnetic field applied parallel tb the tunneling current is clearly seen and this can be related to spin-degeneracy.

 

15.       M. Canepari, M. Bove, E. Maeda, M. Cappello, and A. Kawana

            "Experimental analysis of neuronal dynamics in cultured cortical networks and transitions between different patterns of activity"

            Biol. Cybern. 77 (2), 153-162 (1997).

 

            ABSTRACT: Experimental investigation of the dynamics of biological networks is a fundamental step towards understanding how the nervous system works. Spontaneous activity in cultured networks of cortical neurons has been investigated by using a multisite recording technique with planar electrode arrays. In these networks, the spatiotemporal firing patterns were studied in the presence of different extracellular solutions. Transitions from asynchronous firing dynamics to synchronous firing dynamics were observed when the extracellular Ca2+ concentration was increased from 0.1 mM to 1 mM. Addition of extracellular Mg2+ reduced the spontaneous activity at any Ca2+ concentration, and an increase in the extracellular K+ concentration enhanced the frequency of periodical synchronous bursts. N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptor antagonists inhibited synchronous activity, A spatiotemporal analysis of the data has been performed, and the properties of the network such as the synchronization and the periodicity have been quantified in order to clarify how variations of intrinsic parameters of the network can induce structural transitions in the neural dynamics. This experimental study is a possible approach to investigate the computational properties of a neuronal network.

 

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

            "Collapse and revival of exciton-polariton oscillation in a semiconductor microcavity"

            Appl. Phys. Lett. 71 (11), 1461-1463 (1997).

 

            ABSTRACT: We measured temporal evolution of the coherent emission from a semiconductor microcavity by a very sensitive ac balanced homodyne detection system. We observed collapse and revival of the exciton-polariton oscillation due to a three-mode beating. (C) 1997 American Institute of Physics.

 

17.       H. Cao, G. Klimovitch, G. Bjork, S. Pau, and Y. Yamamoto

            "Tunneling spectroscopy for quantum well excitons"

            Appl. Phys. Lett. 70 (15), 1986-1988 (1997).

 

            ABSTRACT: We have demonstrated a technique of directly measuring the exciton binding energy and the valence band split in the quantum well through a tunneling process. We have also measured the emission efficiency of quantum well heavy-hole excitons and light-hole excitons into the normal direction. (C) 1997 American Institute of Physics.

 

18.       H. Cao, S. Pau, J. M. Jacobson, G. Bjork, Y. Yamamoto, and A. Imamoglu

            "Transition from a microcavity exciton polariton to a photon laser"

            Phys. Rev. A 55 (6), 4632-4635 (1997).

 

            ABSTRACT: In a previous paper [Phys. Rev. A 54, R1789 (1996)], we reported the observation of a laserlike transition in a single GaAs quantum well microcavity and gave the interpretation as spontaneous buildup of coherent exciton-polariton population via stimulated polariton-phonon emission. In this Brief Report, we present new experimental data and correct our previous interpretation for the microcavity polariton system at high density. We observe a continuous transition from a microcavity polariton emission to a bare photon laser. This conclusion is based on the measurements of the angular resolved photoluminescence, linewidth, and intensity of the lasing line as well as the reflection spectrum under cw pumping.

 

19.       E. Ebihara, S. Koshihara, M. Yoshimoto, T. Maeda, T. Ohnishi, H. Koinuma, and M. Fujiki

            "Direct observation of helical polysilane nanostructures by atomic force microscopy"

            Jpn. J. Appl. Phys. Part 2 - Lett. 36 (9AB), L1211-L1213 (1997).

 

            ABSTRACT: The nanostructure of a single quantum wire of the silicon: poly[n-decyl-(S)-2-methylbutylsilane] molecule on a hydrophobic ultrasmooth sapphire plate has been observed by atomic force microscopy (AFM). The backbone structure of this molecule is considered to be a rigid rodlike helix and to be fixed securely into a preferential single-screw-sense. The obtained result of the AFM shows that the polysilane molecule, with a length of about 2 mu m, consists of very long rod-like segments linked by kinks as expected for this backbone structure. Networklike aggregated nanostructures of these molecules were also observed for the sample prepared from concentrated solvents.

 

20.       D. Fotland and A. Yoshikawa

            "The 3rd Fost-Cup World-Open Computer-Go Championship"

            Icca J. 20 (4), 276-278 (1997).

 

            ABSTRACT:

21.       S. R. Friberg

            "Physics - Quantum nondemolition: Probing the mystery of quantum mechanics"

            Science 278 (5340), 1088-1089 (1997).

 

            ABSTRACT:

22.       T. Fujisawa and S. Tarucha

            "Multiple photon assisted tunneling between two coupled quantum dots"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 36 (6B), 4000-4003 (1997).

 

            ABSTRACT: We describe photon-assisted tunneling (PAT) between discrete zero-dimensional (OD) levels in two weakly coupled quantum dots. Resonant tunneling current with multiple (up to three) photon absorption is observed when the two OD levels are separated by a multiple of the microwave photon energy. The PAT current shows a Bessel function dependence on the microwave power, which is in agreement with time-dependent tunneling theory The sharp PAT peaks can be well resolved even when the high microwave power increases electron temperature in the reservoirs.

 

23.       T. Fujisawa and S. Tarucha

            "Photon assisted tunnelling in single and coupled quantum dot systems"

            Superlattices Microstruct. 21 (2), 247-254 (1997).

 

            ABSTRACT: We describe photon assisted tunneling (PAT) in single and coupled quantum dot systems which have a relatively large zero-dimensional (OD) level separation. A microwave electric field applied across the tunneling barrier leads to the formation of a sideband structure. For a single quantum dot system, a PAT current peak is clearly observed in addition to the Coulomb oscillation peak. For a weakly-coupled double-dot system, we observe resonant OD-OD PAT. The resonant PAT current appears only when two discrete quantum levels in the neighboring dots are exactly separated by the microwave photon energy. The PAT current shows a narrower peak than the main resonant tunneling current in accordance with time-dependent tunneling theory. The photon stimulated emission associated with PAT from a higher-lying occupied level to a lower-lying empty level is obtained at a drain voltage sufficient that population inversion takes place. (C) 1997 Academic Press Limited

 

24.       A. Fujiwara, Y. Takahashi, and K. Murase

            "Observation of single electron-hole recombination and photon-pumped current in an asymmetric Si single-electron transistor"

            Phys. Rev. Lett. 78 (8), 1532-1535 (1997).

 

            ABSTRACT: We observed a novel type of photocurrent by investigating Coulomb blockade oscillations around the few-electron regime in an asymmetric Si single-electron transistor. Photoexcitation generates new current peaks below the threshold voltage only for one polarity of source-drain voltage. Under low excitation, such photocurrent exhibits intermittent behavior with sudden drops and rises. The phenomena can be ascribed to the interplay of photogenerated holes and single-electron tunneling via the island. The sudden drop is a manifestation of single-electron recombination with a hole in the island.

 

25.       K. Fukasaku, K. Takeda, and K. Shiraishi

            "Electronic structures of protein nanotubes"

            J. Phys. Soc. Jpn. 66 (11), 3387-3390 (1997).

 

            ABSTRACT: The electronic structures of protein nanotubes, which are formed by the periodical stacking of cycle-peptide-rings (CPRs), are theoretically investigated in terms of ab initio calculations. The interring interaction is caused through the interring H bonds, when CPRs are periodically stacked. This interaction has a potential to delocalize electrons and holes toward the tube axis, so that the band conduction occurs throughout the interring H bonds.

 

26.       T. Fukuda and T. Ogino

            "Initial oxygen reaction on Ge(100) 2x1 surfaces"

            Phys. Rev. B 56 (20), 13190-13193 (1997).

 

            ABSTRACT: The initial stage of the interaction of the Ge(100) surface with molecular oxygen was studied by scanning tunneling microscopy. Using defect-free surface and in situ oxidation, oxygen-induced products could be unambiguously determined with atomic resolution. Two types of bright products and two types of dark products were identified. One of the bright products is a major product and it has a protrusion on top of the dimer. Since this product was observed even after annealing at 300 degrees C, it is one of the stable products. The other bright product is a bright spot at a buckled dimer and the buckling is stabilized near the product. The two dark products are similar to the missing dimer defects in filled-state images, but they appeared as bright spots in empty-slate images. These topographic images were compared with theoretical chemisorption geometries for Si(100)-O and Ge(100)-O systems.

 

27.       T. Fukuda and T. Ogino

            "Oxidation kinetics of epitaxial Ge-covered Si(100) surfaces"

            Surf. Sci. 380 (1), L469-L473 (1997).

 

            ABSTRACT: We compared oxidation kinetics on Ge-covered Si(100) surfaces grown at 350 and 600 degrees C for 0.9 and 2.0 ML Ge overlayer thicknesses. The O-KLL intensities showed clear oxidation enhancement on the surfaces grown at 600 degrees C. The oxygen interaction for the surface covered with 2 ML Ge formed at 350 degrees C was weaker than for the Ge(100) surface, indicating that the compressive strain due to the lattice mismatch may suppress the oxygen interaction with surface Ge dimers.

 

28.       H. Gomi and M. Kawato

            "Human arm stiffness and equilibrium-point trajectory during multi-joint movement"

            Biol. Cybern. 76 (3), 163-171 (1997).

 

            ABSTRACT: By using a newly designed high-performance manipulandum and a new estimation algorithm, we measured human multi-joint arm stiffness parameters during multi-joint point-to-point movements on a horizontal plane. This manipulandum allows us to apply a sufficient perturbation to subject's arm within a brief period during movement. Arm stiffness parameters were reliably estimated using a new algorithm, in which all unknown structural parameters could be estimated independent of arm posture (i.e., constant values under any arm posture). Arm stiffness during transverse movement was considerably greater than that during corresponding posture, but not during a longitudinal movement. Although the ratios of elbow, shoulder, and double-joint stiffness were varied in time, the orientation of stiffness ellipses during the movement did not change much. Equilibrium-point trajectories that were predicted from measured stiffness parameters and actual trajectories were slightly sinusoidally curved in Cartesian space and their velocity profiles were quite different from the velocity profiles of actual hand trajectories. This result contradicts the hypothesis that the brain does not take the dynamics into account in movement control depending on the neuromuscular servo mechanism; rather, it implies that the brain needs to acquire some internal models of controlled objects.

 

29.       H. Gotoh and H. Ando

            "Excitonic quantum confinement effects and exciton electroabsorption in semiconductor thin quantum boxes"

            J. Appl. Phys. 82 (4), 1667-1677 (1997).

 

            ABSTRACT: We investigate the excitonic optical properties in thin quantum boxes in the intermediate regime between the two-dimensional (2D) and zero-dimensional (OD) with a theoretical analysis that rigorously treats excitonic confinement effects. It is found that the exciton binding energy is substantially enhanced and that the oscillator strength concentrates to the lowest excitonic transition, even in a thin box whose lateral width is considerably (about five times) larger than the Bohr radius. Novel optical properties experimentally observed in semiconductor quantum disks, which are the intense photoluminescence spectrum and ultranarrow photoluminescence excitation spectrum, are explained well by the theoretical results. We also calculate exciton absorption in a thin box in which an electric field is applied in the lateral direction. The present theory can simulate how the electroabsorption evolves from the quantum confined Stark effect in the OD to the quantum confined Franz-Keldysh effect in the 2D with an increase in the lateral size of the box. In the intermediate regime between 2D and OD, a strong excitonic electric-field effect, distinct from the well-known electroabsorption effects at OD and 2D, is found. These theoretical results demonstrate that even though the lateral confinement is weak, it considerably enhances the electron-hole Coulomb interaction and alters excitonic optical features markedly in the thin quantum box. (C) 1997 American Institute of Physics.

 

30.       H. Gotoh, H. Ando, and T. Takagahara

            "Radiative recombination lifetime of excitons in thin quantum boxes"

            J. Appl. Phys. 81 (4), 1785-1789 (1997).

 

            ABSTRACT: Exciton radiative recombination lifetime in a thin quantum box in the intermediate spatial dimension between the two-dimension and the zero-dimension is investigated by a theoretical analysis which rigorously treats the electron-hole Coulomb interaction. The higher exciton states as well as the ground exciton state are explicitly taken into account to estimate the temperature dependence of exciton recombination lifetime. We clarify how the temperature dependence of the recombination lifetime varies with a change in the quantum confinement dimension which can be controlled by the lateral width of a thin quantum box. We also discuss the effect of the exciton localization due to structural imperfection on the radiative recombination lifetime. (C) 1997 American Institute of Physics.

 

31.       H. Gotoh, H. Ando, T. Takagahara, H. Kamada, A. Chavez-Pirson, and J. Temmyo

            "Effects of dimensionality on radiative recombination lifetime of excitons in thin quantum boxes of intermediate regime between zero and two dimensions"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 36 (6B), 4204-4208 (1997).

 

            ABSTRACT: We report on effects of dimensionality on radiative recombination lifetime in thin quantum boxes of intermediate regime between OD and 2D. The temperature dependence of the recombination lifetime is calculated using a theoretical analysis that rigorously treats the electron-hole Coulomb interaction. We show how the dependence evolves from 2D to OD with a decrease in the lateral width of the box. We also examine the effects of exciton localization, which arises from structural defects in the boxes, on the radiative recombination lifetime. These theoretical results are compared with experimental data obtained from InGaAs quantum disks on a (311)B GaAs substrate. Good agreement between theoretical results and the experimental data is obtained.

 

32.       F. R. Graf, B. H. Plagemann, A. Renn, U. P. Wild, and M. Mitsunaga

            "Total dephasing-rephasing balancing in Stark-pulse-modulated photon echoes"

            Opt. Lett. 22 (3), 181-183 (1997).

 

            ABSTRACT: Using Stark-pulse-modulated photon echoes, we observe a novel type of rephasing phenomenon in a Eu3+- and Pr3+-codoped Y2SiO5 crystal. By adjusting the Stark pulse during the rephasing and dephasing periods one can observe a full recovery of the photon echo, corresponding to perfect dephasing-rephasing balancing of the perturbations. We propose to use this effect as a spectroscopic technique to distinguish between reversible and irreversible Stark interactions. (C) 1997 Optical Society of America

 

33.       F. R. Graf, A. Renn, U. P. Wild, and M. Mitsunaga

            "Site interference in Stark-modulated photon echoes"

            Phys. Rev. B 55 (17), 11225-11229 (1997).

 

            ABSTRACT: We show that Stark-pulse-modulated photon echoes in an impurity-ion-doped crystal are generally characterized by a complex oscillatory behavior with two or more frequency components which results from the interference of the static dipole moment differences of ions located at inequivalent sites. We analyze this phenomenon using group theory and present experimental evidence for a Pr3+ and Eu3+-codoped YAlO3 and a Pr3+-doped Y2SiO5 crystal. It is demonstrated that the orientations of the dipole moments and of the crystal axes can be determined with subdegree accuracy.

 

34.       A. Hamoudi, M. Ogura, X. L. Wang, and T. Okada

            "Optical properties of a lateral array of GaAs quantum wires grown by flow rate modulation epitaxy"

            Superlattices Microstruct. 22 (3), 353-358 (1997).

 

            ABSTRACT: We report on a photoluminescence excitation study of a lateral array of GaAs quantum wires grown by flow rate modulation epitaxy on 4 mu m pitch V-grooves. Several excitonic transitions exhibiting a strong polarization anisotropy and involving the ground and excited quantum wire subbands are clearly observed. (C) 1997 Academic Press Limited.

 

35.       T. Hasegawa, J. Nishijo, Y. Kobayashi, and J. Umemura

            "Effect of substrates on the infrared external reflection spectra of Langmuir-Blodgett films"

            Bull. Chem. Soc. Jpn. 70 (3), 525-533 (1997).

 

            ABSTRACT: The Fourier transform infrared (FTIR) polarized external reflection (ER) spectra of 9-monolayer cadmium stearate Langmuir-Blodgett (LB) films were measured on various kinds of materials (Ge, ZnSe, and GaAs) in order to investigate whether their spectra could be used for a quantitative analysis of the molecular orientation. The FTIR ER spectra on double-side-polished substrates with LB films on both sides would not fit in, even qualitatively, with the 5-layer system (IR//air/LB/substrate/LB/air) theoretical prediction. On the other hand, the ER spectra of a single-side-deposited LB film (IR//air/substrate/LB/air) were qualitatively explained by a simple 3-layer system (IR//substrate/LB/air) in which the reflection in the substrate was treated as a single reflection. This indicated that the output rays from the substrate in the conventional 5-layer system did not interfere sufficiently with each other. A 5-layer system calculation without any interference effect qualitatively explained the ER spectra of LB films on a double-side-polished substrate. It was eventually concluded that double-side-polished materials are not suitable for a precise analysis of ER spectra, since it is almost impossible to estimate the area ratio of interferential and non-interferential rays.

 

36.       N. Hatakenaka and T. Ogawa

            "Quantum nondemolition measurement of the photon number in a Josephson-junction cavity"

            J. Low Temp. Phys. 106 (3-4), 515-520 (1997).

 

            ABSTRACT: This paper proposes a quantum nondemolition measurement of the photon number in a Josephson-junction cavity. Under a current-biased Josephson junction with small capacitance, the Josephson phase fluctuates quantum-mechanically around its classical value due to the charging effect, and it couples to the photons in the junction cavity nonlinearly, which is necessary for the quantum nondemolition measurement. We show that the photon number in the junction cavity can be nondestructively measured by detecting the fluctuation of Josephson supercurrent through the junction.

 

37.       M. Hayashi

            "Analysis of auditory magnetic fields evoked by speech sounds"

            Biomed. Res. 18, 91-100 (1997).

 

            ABSTRACT: Experiments using superconducting quantum interference device magnetometers to measure auditory magnetic fields evoked by speech sounds showed that neuromagnetic fields appear after the onset of the stimulus and after subsequent consonant/vowel transitions, i.e. neuromagnetic fields were more prominent after the onset of vowels. The spatiotemporal characteristics of the equivalent current dipole of the neuromagnetic field evoked by vowels were localized in the superior temporal plane. These current dipoles move in the anterior and inferior directions along the floor of the Sylvian fissure, indicating tonotopic organization: the higher the frequency the deeper the dipole. The dipoles evoked by vowels are located more superficially than those of high-frequency pure tones.

 

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

            "Quasi-one-dimensional electron gases in a gated undoped GaAs/AlxGa1-xAs heterostructure"

            Phys. Low-Dimens. Struct. 12, 69-74 (1997).

 

            ABSTRACT: We describe a novel approach to realize quasi-one-dimensional electron gases with high electron densities using an undoped GaAs/AlxGa1-xAs heterostructure. The quasi-one-dimensional electron gas is field effect induced via a narrow top gate and the electrons are extracted from ion-implanted ohmic regions. The wires are characterized by low temperature magnetotransport experiments. The quasi-one-dimensional nature of the transport manifests itself in the observed depopulation of the one-dimensional subbands in a magnetic field perpendicular to the heterointerface. The effective wire width is found to be comparable to the gate width.

 

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

            "Field effect-induced quasi-one-dimensional electron transport in GaAs/AlxGa1-xAs heterostructures"

            J. Appl. Phys. 82 (9), 4384-4387 (1997).

 

            ABSTRACT: We describe an approach to realize quasi-one-dimensional electron gases using an undoped GaAs/AlxGa1-xAs heterostructure. It is demonstrated that with a combination of ion implanted ohmic regions and a narrow top gate, a quasi-one-dimensional electron gas with a very high electron density can be formed. The width of the narrow top gate is varied between 0.4 and 1.0 mu m. The wires are characterized by low temperature magnetotransport experiments. The effective wire width is found to be comparable to the gate width. The high mobility of about 95 m(2)/V s is only 5%-10% less than that obtained in a two-dimensional electron gas of the same material and is maintained at low temperatures. (C) 1997 American Institute of Physics. [S0021-8979(97)02721-7].

 

40.       J. Herfort and Y. Hirayama

            "High density and high mobility transport characteristics in gated undoped GaAs/AlxGa1-xAs heterostructures"

            Solid-State Electron. 41 (10), 1535-1540 (1997).

 

            ABSTRACT: The two-dimensional electron gas which is formed at the interface in undoped GaAs/AlxGa1-xAs heterostructures by the electric field generated by a top gate is studied. The barrier region consists of an Al0.3Ga0.7As/Al0.5Ga0.5As superlattice to prevent undesirable tunneling through the barrier. Therefore, we are able to achieve high electron densities exceeding 10(16) m(-2) with sufficient small gate leakage currents in a MISFET like device for the first time. Despite the high electron density in the sample rather high mobilities of about 100 m(2) V s(-1) can be maintained at low temperatures. The population of the second subband is studied from Shubnikov-de Haas measurements in these devices. The role of intersubband scattering is important for understanding the magneto-transport experiments. (C) 1997 Elsevier Science Ltd.

 

41.       H. Hibino and T. Ogino

            "Phase transitions on Si(113): A high-temperature scanning-tunneling-microscopy study"

            Phys. Rev. B 56 (7), 4092-4097 (1997).

 

            ABSTRACT: Reconstructive phase transitions on Si(113) have been investigated near the critical temperatures using high-temperature scanning tunneling microscopy. During the phase transition between (3x1) and (3x2) reconstructions. (3x2) domains nucleate and fluctuate within the (3x1) domain, and their size increases as the temperature decreases. During the disordering of the (3x1) reconstruction, highly mobile domain walls are observed, which increase in density as the transition is approached from below. The structure and evolution of the domain walls is consistent with disordering of the (3x1) reconstruction via incorporation of [-] (heavy) domain walls.

 

42.       H. Hibino and T. Ogino

            "Substitution of In for Si adatoms and exchanges between in and Si adatoms on a Si(111)-7x7 surface"

            Phys. Rev. B 55 (11), 7018-7022 (1997).

 

            ABSTRACT: Substitution of In for Si adatoms and exchanges between In and Si adatoms on a Si(111)-7 x 7 surface have been investigated using high-temperature (HT) scanning tunneling microscopy (STM). Indium substitution probability depends on the four different types of adatoms in the 7 x 7 reconstruction. Differences in the In substitution energy between different types of adatoms are estimated from the substitution probability. Adatom exchange rates obtained from sequential HT-STM images are also dependent on the combination of In and Si adatoms. Measured activation energies and prefactors for exchanges on Si(111)-7 x 7 are comparable to those on Si(lll)-root 3x root 3. The adatom exchange is not sensitive to the adatom symmetry. HT-STM results on the adatom exchanges on Si(lll) suggest that the motion of the metal adatoms is a rate-limiting step in this process.

 

43.       Y. Hirayama and T. Saku

            "AlGaAs/GaAs modulation-doped structures grown on a Be-ion-implanted GaAs back gate"

            Semicond. Sci. Technol. 12 (11), 1465-1471 (1997).

 

            ABSTRACT: Novel back-gate devices, in which the two-dimensional electron gas (2DEG) at the heterointerface is controlled by a voltage applied to the underlying Be-implanted p-type region, are successfully fabricated by using focused Be-ion-beam scanning and MBE overgrowth of an AlGaAs/GaAs modulation-doped structure. For the on-junction-type back-gate structure, the control of the 2DEG is realized without inserting an AlGaAs barrier layer between the 2DEG and the back gate. The Be out-diffusion into the overgrown layer increases with increasing Be ion dose. However, the sharp front of the Be out-diffusion enables us to fabricate the devices with a small separation between the 2DEG and the p-type back gate. Even for a separation less than 150 nm, the damage due to Be out-diffusion is negligibly small. The gate leakage current is small when the back-gate voltage is less than 1.5 V where a forward current starts to flow through the pn junction. Within this voltage limit, the carrier density of the 2DEG was well modified in the range of (1-6) x 10(11) cm(-2). Trap-filling effects due to a large forward current through the pn-junction-type gates are also discussed.

 

44.       Y. Hirota, F. Maeda, Y. Watanabe, and T. Ogino

            "Shift of surface Fermi level position toward the conduction band minimum by crystal defects near GaAs(001) surface"

            J. Appl. Phys. 82 (4), 1661-1666 (1997).

 

            ABSTRACT: The effects of crystal defects near the surface on the position of surface Fermi level (E-FS) are investigated using photoluminescence (PL) measurements and synchrotron radiation photoelectron spectroscopy (SRPES). For the lightly Si-doped GaAs(001) surface, PL measurements reveal that after heating to 500 degrees C a layer with lower PL peak intensities related to gallium vacancies than those of the bulk exists just under the thermal degraded layer. SRPES shows that E-FS moves upward to 1.1-1.17 eV above the valence band maximum when this thermal degraded layer is removed by chemical etching and the excess arsenic on the surface, which is formed by rinsing the etched surface with deoxygenated and deionized water, is evaporated by heating in ultrahigh vacuum (UHV). After evaporation of excess arsenic on the surface by heating, the etching-depth dependence of E-FS for a Sample preheated in UHV correlated with the existence of this defect concentration layer. These results suggest that the position of E-FS for the GaAs(001) surface is strongly influenced by crystal defects near the surface. (C) 1997 American Institute of Physics.

 

45.       Y. Hirota, Y. Watanabe, F. Maeda, and T. Ogino

            "Relaxation of band bending on GaAs(001) surface by controlling the crystal defects near the surface"

            Appl. Surf. Sci. 117, 619-623 (1997).

 

            ABSTRACT: The influence of crystal defects near the surface on horizontal Bridgman-grown GaAs(001) surface is investigated by photoluminescence (PL) and synchrotron radiation photoelectron spectroscopy (SRPES). PL measurements reveal that after heating to 500 degrees C a layer with lower defect concentration exists just under the thermal degraded one. SRPES shows that the surface Fermi level (E-FS) moves to the conduction band minimum when this thermally degraded layer is removed by chemically etching and the etched surface is heated in ultra-high vacuum after rinsing with the deoxygenated and deionized water. These results suggest that the position of E-FS for GaAs(001) surface is strongly affected by crystal defects near the surface.

 

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

            "Er-related trap levels in GaAs:Er,O studied by optical spectroscopy under hydrostatic pressure"

            Phys. Rev. B 56 (16), 10255-10263 (1997).

 

            ABSTRACT: An optical spectroscopic study of Er-related luminescence in GaAs:Er,O as a function of temperature and applied hydrostatic pressure is reported. We observed the appearance of different Er-related luminescence under the application of hydrostatic pressure. The temperature dependence of the luminescence intensities for three kinds of Er centers as a function of pressure is measured and discussed in terms of the trap levels formed by the Er centers. It is shown that the energy-transfer process between photoexcited carriers in the host and the 4f shell of the Er3+ ion may occur when trap levels associated with an Er center enter the band gap under the application of hydrostatic pressure. [S0163-1829(97)06840-9].

 

47.       R. A. Hogg, K. Takahei, A. Taguchi, K. Takarabe, T. Mizushima, and S. Minomura

            "Configurational transformation of an Er center in GaAs:Er,O under hydrostatic pressure"

            J. Appl. Phys. 82 (2), 813-816 (1997).

 

            ABSTRACT: An optical spectroscopic study of Er-related luminescence in GaAs:Er,O under hydrostatic pressure is reported. The application of pressure results in new Er-related centers becoming optically active under host photoexcitation. Two new sets of I-4(13/2)-->I-4(15/2) transitions are observed to appear in different pressure ranges. It is concluded that these two sets of crystal-field-split transitions are due to the same Er center, and that this Er center undergoes an abrupt change in local configuration ata specific pressure. (C) 1997 American Institute of Physics.

 

48.       T. Homma, Y. Sezai, T. Osaka, Y. Maeda, and D. M. Donnett

            "Compositional inhomogeneity in electroless-deposited CoNiP films studied by spin-echo Co-59 nuclear magnetic resonance"

            J. Magn. Magn. Mater. 173 (3), 314-320 (1997).

 

            ABSTRACT: A compositionally inhomogeneous state in electroless-deposited CoNiP films with perpendicular magnetic anisotropy is investigated using spin-echo Co-59 nuclear magnetic resonance (NMR), focusing on its correlation with magnetic properties. Bf adjusting pH of the electroless-deposition bath-films were prepared which possess almost the same average composition (Co42Ni50P8) and crystal orientation, but the differing values of coercivity (H-c). By analyzing the shift in peak resonance frequency of NMR spectra of the CoNiP films with respect to that of bulk CoNi alloys, we observed the formation of a compositionally inhomogeneous slate in the film which possesses high H-c of 2600 Oe, whereas formation of inhomogeneities was not observed for the low-H-c films. By assuming that a Go-enriched ferromagnetic component detected by NMR was separated from a non-magnetic amorphous NI-P component, we found that the high-H-c film consists of Co42Ni26 and Ni24P8. Moreover, the results of high spatial resolution X-ray microanalysis on the high-H-c film showed a tendency that the Go-enriched ferromagnetic component segregates to the center of grains and the Ni-P non-magnetic component segregates to grain boundaries. Such evidence indicates that compositional inhomogeneities could be one of the origins of high-H-c in CoNiP films.

 

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

            "Sublimation of the Si(111) surface in ultrahigh vacuum"

            Phys. Rev. B 55 (16), 10237-10240 (1997).

 

            ABSTRACT: We investigated sublimation of a Si(111) surface using a 70-mu m-wide (111) plane created at the bottom of a crater during ultrahigh-vacuum heating. Step spacing on the plane is determined by nucleation of macrovacancies in the center of the plane while steps move in a step-flow manner. The step spacing is related to the adatom diffusion length and decreases with increasing temperature of up to 1190 degrees C. Around 1200 degrees C, the spacing shows a transitionlike behavior and increases to 2.5 times the value at 1190 degrees C. Step flow is maintained above the step-spacing transition.

 

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

            "In situ observation of MEE GaAs growth using scanning electron microscopy"

            J. Cryst. Growth 175, 292-297 (1997).

 

            ABSTRACT: We have used in situ scanning electron microscopy (SEM) for real-time observation of migration enhanced epitaxy (MEE) processes. The surface morphology developed during MEE growth is either monolayer islands or monolayer holes depending on the amount of Ga supply per growth cycle. When island coverage is low, the islands disappear immediately after growth terminates, while the holes remain longer. Resulting surface roughness is much smaller than in molecular beam epitaxy even at a low substrate temperature. The present observations directly confirm enhancement of surface atom migration in MEE.

 

51.       Y. Horikoshi, S. Ando, H. Ando, and N. Kobayashi

            "Surface atomic processes during flow-rate modulation epitaxy"

            Appl. Surf. Sci. 112, 48-54 (1997).

 

            ABSTRACT: Flow-rate modulation epitaxy is the MOCVD-based version of migration-enhanced epitaxy which has been developed to grow atomically flat surfaces and interfaces of III-V compound semiconductors. This method has additional advantages relating to the controllability of the growth process. During flow-rate modulation epitaxy, undesirable gaseous reactions are avoided between group III and group V source gases, and the initial surface condition for every layer growth is precisely controlled. This method has also proved useful for the selective epitaxy of AlGaAs and for the fabrication of low-dimensional structures surrounded by sharp crystal facets. By utilizing these advantages, hexagonal prism-shaped AlGaAs/GaAs dots were successfully grown on patterned (111)B substrates. Each dot lased at an extremely low threshold indicating the desirable effect of flow-rate modulation epitaxy.

 

52.       T. Horiuchi, K. Torimitsu, K. Yamamoto, and O. Niwa

            "On-line flow sensor for measuring acetylcholine combined with microdialysis sampling probe"

            Electroanalysis 9 (12), 912-916 (1997).

 

            ABSTRACT: We have developed an on-line electrochemical sensor for the continuous measurement of acetylcholine (ACh). The sensor comprises a small volume prereactor containing immobilized choline oxidase (ChOx) and catalase (or horseradish peroxidase, HRP), a small volume enzymatic reactor containing immobilized acetylcholine esterase (AChE) and ChOx and a glassy carbon electrode modified with Os-polyvinylpyrridine-HRP. The sensor can measure ACh selectively even when the choline (Ch) concentration is more than 1000 times that of ACh, when the ChOx and catalase are immobilized in the prereactor. The sensor shows a wide linear relationship from 5 nM to 1 mu M and a detection limit of 5 nM (S/N = 2), which is comparable to the ACh detection limit achieved by liquid chromatography/electrochemistry. It also shows high selectivity against other neurotransmitters and interferents. The properties of the sensor combined with a microdialysis (MD) probe were also studied by measuring a solution containing a much higher concentration of Ch than ACh.

 

53.       S. Hoshino and H. Suzuki

            "Electroluminescence from triplet excited states of benzophenone derivatives"

            Mol. Cryst. Liq. Cryst. Sci. Technol. Sect. A-Mol. Cryst. Liq. Cryst. 294, 313-316 (1997).

 

            ABSTRACT: This paper investigated electroluminescent (EL) characteristics of multilayer organic light emitting diodes (LEDs) utilizing poly(methylmethacrylate) films containing typical phosphorescent benzophenone (BP) derivatives such as BP or 4,4'-dichlorobenzophenone as an emitting layer. The EL spectra exhibit agree well with the phosphorescence spectra of emitting materials at a low temperature. Combined analysis of temperature dependence of EL intensity, EL spectra, and EL decay time indicate that the EL of these LEDs originates from the triplet excited states of the BP derivatives.

 

54.       S. Hoshino, H. Suzuki, M. Fujiki, M. Morita, and N. Matsumoto

            "Electroluminescent characteristics of one-dimensional silicon chains in dialkyl polysilanes"

            Synth. Met. 89 (3), 221-225 (1997).

 

            ABSTRACT: We investigate the electroluminescent characteristics of polysilane-based single-layer light-emitting diodes (LEDs) which employ poly(di-n-hexylsilane) (PDHS) or poly(di-n-butylsilane) (PDBS) (PDHS-LED and PDBS-LED, respectively). The PDHS-LED exhibits an electroluminescence (EL) identical to its photoluminescence (PL), which is composed of an emission only in the near-ultraviolet (NUV) region. By contrast, the PDBS-LED exhibits EL in both the visible and NW regions. Although these two polysilanes differ only in terms of their substituent groups, their device characteristics vary considerably: the PDBS-LED exhibits a larger device current, inferior rectifying behavior, and a lower turn-on voltage than the PDHS-LED. This observation is inconsistent with predictions based on the hypothetical band diagrams of these two LEDs. We have demonstrated the fundamental EL characteristics of sigma-conjugated one-dimensional Si chains by using PDHS, which has a highly ordered backbone conformation and negligible structural defects. (C) 1997 Elsevier Science S.A.

 

55.       A. Ikeda, K. Sumitomo, T. Nishioka, T. Yasue, T. Koshikawa, and Y. Kido

            "Intermixing at Ge/Si(001) interfaces studied by surface energy loss of medium energy ion scattering"

            Surf. Sci. 385 (1), 200-206 (1997).

 

            ABSTRACT: Intermixing of Ge(0.15 ML, 1 ML)/Si(001) grown at 400 degrees C was studied by a new method of surface energy loss spectroscopy of medium energy ion scattering. We measured the inelastic energy losses of scattered ions from Ge for 100.0 keV H+ incidence as a function of exit angle. In the previous work for 50 and 100 keV H+ backscattered from the Si(001) 2 x 1-Sb surface [Phys. Rev. B in press], we showed that the surface stopping cross-section was expressed by extending the bulk stopping region from the top atomic plane toward the vacuum side by d, which was given by 2d rho=sigma (sigma is the areal density of top surface and rho is the bulk atomic density) as the first approximation. The above approximation uas applied to analysis of the Ge:/Si(001) interface. The present analysis revealed that the deposited Ge atoms were distributed over the first to third atom layers with a ratio of 4:3:1 or 4:2:2 for both 0.15 ML and 1 ML coverage. This result is consistent with that reported by Sasaki et al. [Appl. Surf. Sci. 82-83 (1994) 387] using Auger electron and X-ray photoelectron diffraction. (C) 1997 Elsevier Science B.V.

 

56.       M. Ikezawa, Y. Masumoto, T. Takagahara, and S. V. Nair

            "Biexciton and triexciton states in quantum dots in the weak confinement regime"

            Phys. Rev. Lett. 79 (18), 3522-3525 (1997).

 

            ABSTRACT: Biexciton and triexciton states in CuCl quantum dots were studied by means of time-resolved size-selective pump-and-probe technique. A clear induced absorption band is observed on the high-energy side of the excitation photon energy. The new induced absorption is assigned to the transition from the exciton ground state to one of the weakly correlated exciton pair states which were theoretically predicted to exist and to play an important role in nonlinear optical processes. Its pump energy dependence and temporal evolution strongly support this assignment. Under high-density or two-color excitation condition, a triexciton state in quantum dots is observed for the first time.

 

57.       T. Imada, M. Watanabe, T. Mashiko, M. Kawakatsu, and M. Kotani

            "The silent period between sounds has a stronger effect than the interstimulus interval on auditory evoked magnetic fields"

            Electroencephalogr. Clin. Neurophysiol. 102 (1), 37-45 (1997).

 

            ABSTRACT: Auditory evoked cortical responses, electric N1 and magnetic N1m, increase when the interstimulus interval (ISI) increases. We assumed that the response to a tone is mainly affected by the immediately preceding ISI, by the immediately preceding pause between stimuli (PBS) and by the previous stimulus duration (PSD). These 3 values are connected by the following expression: ISI = PBS + PSD. We examined the dependence of the auditory evoked brain magnetic responses on the ISI with the constant PSD (conventional paradigm), on the PBS with the constant ISI, and on the ISI with the constant PBS. Peak latencies and peak amplitudes of the 3 components, P1m, N1m and P2m, are recorded in one block using all possible combinations of 5 PSDs (0.05, 0.5, 1.0, 1.5 and 2.0 s) and 5 ISIs (0.5, 1.0, 1.5, 2.0 and 2.5 s). Peak latencies of these 3 components do not show any significant dependence either on the PBS or on the ISI. Neither the PBS nor the ISI brings a statistically significant effect on the P1m peak amplitude. On the other hand, the N1m peak amplitude increases as either the PBS (constant ISI) or the ISI (constant PSD) increases. The regression coefficient to the PBS is more than a double of that to the ISI. Moreover, the ISI does not show any significant effect on the N1m peak amplitude when the PBS is constant. This stronger PBS effect means that the N1m peak amplitude dependence on the ISI, which has been reported in several papers using the constant PSDs, includes more dependence on the PBS. The P2m peak amplitude shows the same tendency as the N1m because of the strong correlation in peak amplitude between them. (C) 1997 Elsevier Science Ireland Ltd.

 

58.       R. Imhof, H. Teramae, and J. Michl

            "Conformational effects in UV absorption spectra of tetrasilanes"

            Chem. Phys. Lett. 270 (5-6), 500-505 (1997).

 

            ABSTRACT: UV absorption of cyclic carbosilanes (SiMe2)(4)(CH2)(n), n=1-4 (1-4), and Si4Me10 (5) provides an experimental counterpart to the singlet transition energy and intensity correlation diagrams for the syn-anti conformational transformation in tetrasilane. A new third transition is found between the two previously known singlet transitions. Transition energies are nearly independent of the dihedral angle, while intensities vary widely. All trends agree with CIS/3-21G*//HF/3-21G* calculations. The Sandorfy C and ladder C models of sigma conjugation fail to describe electronically excited states of tetrasilane, since they do not consider the lateral bonds to substituents.

 

59.       N. Imoto

            "Quantum effects of spatial/temporal modulation of the optical field"

            Mater. Sci. Eng. B-Solid State Mater. Adv. Technol. 48 (1-2), 34-38 (1997).

 

            ABSTRACT: The quantum effects of temporal modulation and spatial confinement of optical field are theoretically analyzed using the continuous mode formalism. The effect of modulation is different from static attenuation regardless of whether the modulation bandwidth is broader or narrower than the photon bandwidth. This effect appears not only in single-photon interferometry but also in multi-photon interferometry, and shows the fundamental difference between deep modulation and static attenuation of the wave function. The effect of spatial confinement of photons in a cavity appears as an anomalous mode commutator inside the cavity, which is related to the spontaneous emission modulation, The canonical field commutator is guaranteed only when the Kramers-Kronig relations for the optical elements are properly incorporated. (C) 1997 Elsevier Science S.A.

 

60.       S. Inoue, S. Lathi, and Y. Yamamoto

            "Longitudinal-mode-partition noise and amplitude squeezing in semiconductor lasers"

            J. Opt. Soc. Am. B-Opt. Phys. 14 (11), 2761-2766 (1997).

 

            ABSTRACT: We have measured the longitudinal-mode-partition noise of free-running, grating-feedback external-cavity and injection-locked semiconductor lasers, using a nonsymmetric Mach-Zehnder interferometer. For an external-cavity laser operated at a high pumping level, the contribution of the longitudinal-mode-partition noise to the total intensity noise was negligible, and 0.9 dB of amplitude squeezing was observed. On the other hand, injection locking suppressed the longitudinal-mode-partition noise by 34 dB, and 1.9 dB of amplitude squeezing was observed when the locking bandwidth was 5 GHz. A further increase in the locking bandwidth reduced the suppression of the longitudinal-mode-partition noise and degraded the amplitude squeezing. (C) 1997 Optical Society of America.

 

61.       S. Inoue and Y. Yamamoto

            "Gravitational wave detection using dual input Michelson interferometer"

            Phys. Lett. A 236 (3), 183-187 (1997).

 

            ABSTRACT: We propose a new scheme for interferometric gravitational wave detection using a dual input Michelson interferometer. The scheme allows us to put a phase modulator outside the interferometer without requiring arm-length unbalance. Moreover, the scheme can realize sub-shot-noise sensitivity using an amplitude squeezed state of light as one of the dual inputs. (C) 1997 Elsevier Science B.V.

 

62.       S. Inoue and Y. Yamamoto

            "Longitudinal-mode-partition noise in a semiconductor-laser-based interferometer"

            Opt. Lett. 22 (5), 328-330 (1997).

 

            ABSTRACT: We observed a periodic intensity-noise variation in the output of a Mach-Zehnder interferometer as we changed the arm-length difference in the range of several millimeters. We found that the period of the variation coincided with that expected for the longitudinal-mode separation of the semiconductor laser. The origin of the huge excess noise of a bright fringe (approximately 30 dB above the shot-noise level) was the longitudinal-mode-partition noise that was due to the selective destructive interference of side modes. (C) 1997 Optical Society of America.

 

63.       T. Irino and R. D. Patterson

            "A time-domain, level-dependent auditory filter: The gammachirp"

            J. Acoust. Soc. Am. 101 (1), 412-419 (1997).

 

            ABSTRACT: A frequency-modulation term has been added to the gammatone auditory filter to produce a filter with an asymmetric amplitude spectrum. When the degree of asymmetry in this ''gammachirp'' auditory filler is associated with stimulus level, the gammachirp is found to provide an excellent fit to 12 sets of notched-noise masking data from three different studies. The gammachirp has a well-defined impulse response, unlike the conventional roex auditory filter, and so it is an excellent candidate for an asymmetric, level-dependent auditory filterbank in time-domain models of auditory processing. (C) 1997 Acoustical Society of America.

 

64.       H. Isaka

            "Synthesis and optical properties of the Si4C-type periodic polycarbosilane poly[(octamethyltetrasilylene)methylene]"

            Macromolecules 30 (3), 344-347 (1997).

 

            ABSTRACT: Poly[(octamethyltetrasilylene)methylene] was prepared by the Wurtz reaction of bis(chlorotetramethyldisilanyl)methane. The periodic structure with Si4C-type sequences was characterized by H-1-, C-13-, and Si-29-NNIR. An investigation of the UV absorption and photoluminescence properties of this polymer in solid-state film revealed the unique character of Si4C-type periodic polycarbosilane. The sigma-sigma* transition energy varied from 5.2 to 4.5 eV due to conformation. The strong Stokes shift (1.2 eV) indicated that the emission is due to a ''self-trapped'' exciton state, in which excitation is weakly delocalized in a skeleton with a nonvertical geometry.

 

65.       H. Ishii and Y. Takahashi

            "Surface reactions of Ge chemical vapor deposition using diethylgermane"

            J. Vac. Sci. Technol. A-Vac. Surf. Films 15 (2), 439-442 (1997).

 

            ABSTRACT:

66.       T. Ishiyama, K. Murakami, K. Takahei, and A. Taguchi

            "4f-shell configuration of Yb in InP studied by electron spin resonance"

            J. Appl. Phys. 82 (9), 4457-4460 (1997).

 

            ABSTRACT: We have performed electron spin resonance (ESR) measurements on Yb-doped n-type and p-type InP layers epitaxially grown by metalorganic chemical vapor deposition. ESR spectra of Yb3+(4f(13)) were observed in both n-type and p-type samples. However, the ESR intensity of Yb3+(4f(13)) for n-type samples was found to be much lower than that for p-type samples. This suggests that most Yb ions in Yb-doped n-type InP are in the Yb2+(4f(14)) State rather than in the Yb3+(4f(13)) state. Thus an electron captured by the trap level formed by Yb in the band gap of InP is not located outside the Yb 4f shell as reported previously, but accommodated in the Yb4f shell. (C) 1997 American institute of Physics. [S0021-8979(97)01821-5].

 

67.       T. Ishiyama and Y. Omura

            "Influences of superficial si layer thickness on band-to-band tunneling current characteristics in ultra-thin n-channel metal-oxide-semiconductor field-effect-transistor by separation by IMplanted OXygen (nMOSFET/SIMOX)"

            Jpn. J. Appl. Phys. Part 2 - Lett. 36 (3A), L264-L267 (1997).

 

            ABSTRACT: The band-to-band tunneling current characteristics of buried-channel nMOSFETs/SIMOX are investigated. It is shown that the drain current due to band-to-band tunneling current increases with decreasing superficial Si layer thickness. Two-dimensional device simulation results indicate that the decrease in superficial Si layer thickness leads to an increase in surface electric field in the gate-overlapped drain region. The device simulation results also suggest that the doping profile in the diffusion region affects the surface electric field moderately. The expression of surface electric field is improved to include the terms that depend on Si layer thickness and diffusion profile. This improved expression results in a quantitative coincidence between calculation and experimental results.

 

68.       T. Ito and K. Shiraishi

            "A theoretical investigation of stable lattice sites for In adatoms on GaAs(001)-(2x4) surface"

            Jpn. J. Appl. Phys. Part 2 - Lett. 36 (11B), L1525-L1527 (1997).

 

            ABSTRACT: Stable lattice sites of In adatoms on the GaAs(001)-(2 x 4)beta 2 surface are qualitatively investigated using empirical interatomic potential and an energy term as a function of the number of electrons remaining in the cation dangling bonds. The calculated results imply that the lattice sites in the missing dimer row are favorable for In adatoms on the GaAs(001)-(2 x 4)beta 2 surface, since the formation of Ga-In dimers suppresses the number of electrons remaining in the cation dangling bonds. Lattice sites in the missing dimer row near the B-type step edge are stable for an In adatom. This creates Schwoebel barriers at the B-type step edge. However, no preferential adsorption sites are found near A-type step edges. These results are comparable with the results on Ga adatoms we obtained in our previous study.

 

69.       T. Ito and K. Shiraishi

            "Theoretical investigations of stable growth sites on GaAs(001) surfaces"

            Appl. Surf. Sci. 121, 171-174 (1997).

 

            ABSTRACT: The stable growth sites on GaAs(001) surfaces are discussed through calculation of migration potentials near steps and kinks using an energy formalism which incorporates the strain and electronic energy contributions based on the empirical interatomic potentials and the electron counting model. On the (2 x 4)beta 2 surface, lattice sites near a B-type step edge are stable for a Ga adatom, whereas no preferential adsorption site is found near an A-type step edge. Opposite qualitative trends were found in the calculations on the c(4 x 4) surface. Moreover, according to the energy formalism, an electron counting Monte Carlo (ECMC) simulation was applied to investigate the role of As-dimer kink sites in thin-film growth. Adatoms impinging on the (2 x 4)beta 2 surface predominantly occupy the kink sites in the missing dimer region. These calculated results are discussed in terms of strain energy and the electron counting model. (C) 1997 Elsevier Science B.V.

 

70.       T. Ito and K. Shiraishi

            "Theoretical investigations of initial growth process on GaAs(001) surfaces"

            Surf. Sci. 386 (1-3), 241-244 (1997).

 

            ABSTRACT: This paper briefly reviews our latest achievements in theoretically approaching the initial growth process including adatom migration and changes in the atomistic structure on the GaAs(001)-(2 x 4) surface. The calculations are performed using the ab initio pseudopotential method, empirical interatomic potential and Monte Carlo (MC) simulation. On the (2 x 4)beta 1 surface, we found that Ga adatom migration strongly depends on the Ga adatom coverage during molecular-beam-epitaxy growth. This can be interpreted by the electron counting model. Based on these findings, migration potentials near the steps on the (2 x 4)beta(2) surface can be successfully calculated using a simple energy formula. Using this energy formula, the newly developed electron-counting MC simulation results imply that the GaAs(001) surface changes its atomic arrangement from an initial (2 x 4)beta(2) to (2 x 4)beta 1 via (2 x 4)alpha. Further Ga and As adsorptions fill up the lattice sites in the missing dimer region continuing layer-by-layer growth. (C) 1997 Elsevier Science B.V.

 

71.       M. Itoh, S. Karimoto, K. Namekawa, and M. Suzuki

            "Current-voltage characteristics of intrinsic Bi2Sr2CaCU2O8 Josephson-junction stacks and an unconventional temperature dependence of the magnitude of the order parameter"

            Phys. Rev. B 55 (18), 12001-12004 (1997).

 

            ABSTRACT: Very thin stacks of five intrinsic Josephson junctions have been fabricated on the surface of Bi2Sr2CaCu2O8 Single crystals. The current-voltage characteristics of these stacks are in good agreement with those of a superconductor-insulator-superconductor tunnel junction made of a two-dimensional d-wave superconductor. This strongly suggests that there is no gap suppression caused by the nonequilibrium heating effect, which is usually significant in stacked junctions of this kind. From these results, we obtain a gap value of 57 meV at 4.2 K for the Bi2Sr2CaCu2O8 system. Furthermore, it is definitely found that the gap magnitude exhibits significant temperature dependence even at low temperatures, which is unlike the BCS behavior.

 

72.       M. Itoh, T. Saku, Y. Hirayama, and S. Tarucha

            "Ga focused-ion-beam shallow-implanted quantum wires"

            J. Vac. Sci. Technol. B 15 (5), 1657-1660 (1997).

 

            ABSTRACT: Quantum wires were fabricated by shallow implantation of Ga ions from a focused-ion-beam source into a modulation-doped AlxGa1-xAs/GaAs heterostructure. This type of implantation reduces crystal damage and keeps the implanted ions away from the two-dimensional electron gas. An electron mobility as high as 5.04 X 10(5) cm(2)/V s was obtained for 10-mu m-long wires with an effective width of 0.152 mu m, which is much higher than any previously reported values. The electron ballistic lengths in the wires were determined from measurements of the bend and transfer resistance and agreed well with the calculated elastic mean free paths. The transfer resistance versus magnetic field profiles exhibited electron focusing peaks associated with good specularity at the boundary. (C) 1997 American Vacuum Society. [S0734-211X(97)00305-3].

 

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

            "Time differential surface plasmon resonance measurements applied for electrochemical analysis"

            Electroanalysis 9 (16), 1239-1241 (1997).

 

            ABSTRACT: The processes of oxide film formation and ion adsorption on gold electrodes were monitored by the simultaneous measurement of electrochemical potential scanning voltammetry and surface plasmon resonance (SPR) condition. The time differential of the SPR incident angle was used for the analysis of the surface reactions of the gold electrode. Each stage of oxide film formation on the sputtered gold electrodes and anion adsorption/desorption was clearly detected by this method and directly correlated to the current. SPR is sensitive to the surface adsorbate while the electrode current reflects the overall electrochemical process. This difference was used to separate adsorption from the diffusion process under different hydrodynamic conditions.

 

74.       T. Kaburagi and M. Honda

            "Calibration methods of voltage-to-distance function for an electromagnetic articulometer (EMA) system"

            J. Acoust. Soc. Am. 101 (4), 2391-2394 (1997).

 

            ABSTRACT: In electromagnetic articulometer (EMA) systems, the relationship between the voltage of the received signal and the distance between the transmitter and receiver coils is represented by a voltage-to-distance (VD) function. This paper describes an adaptive calibration method for determining unknown parameters in the VD function in which the parameters are determined using automatically selected local calibration data. This method is compared with the conventional fixed method in which the parameters are computed from calibration data covering the entire measurement area. Experimental results show that the measurement error of the adaptive method is 0.106 mm for a 14x14-cm measurement area and is less than half of that in the fixed method. In addition, this error is the same as that when the region of the receiver position is restricted to a 4x4-cm local area in the fixed method. (C) 1997 Acoustical Society of America.

 

75.       H. Kageshima and K. Shiraishi

            "Momentum-matrix-element calculation using pseudopotentials"

            Phys. Rev. B 56 (23), 14985-14992 (1997).

 

            ABSTRACT: A method of calculating momentum matrix elements using pseudopotentials is proposed. A core-repair term is introduced in the method to eliminate errors created by the poor representation of the atomic core region by the pseudopotentials. Calculating the core-repair term requires fewer computational resources especially for separable form pseudopotentials. This approach is suitable for non-norm-conserving pseudopotentials as well as general norm-conserving pseudopotentials. The effectiveness of the method is verified for various isolated atoms. The method is also applied to calculate momentum matrix elements for planar polysilane, planar siloxene, gallium arsenide, and gallium nitride.

 

76.       H. Kageshima and K. Shiraishi

            "Microscopic mechanism for SiO2/Si interface passivation: Si=O double bond formation"

            Surf. Sci. 380 (1), 61-65 (1997).

 

            ABSTRACT: The reason why few interface states are observed for interfaces between silicon and thermal silicon dioxide is investigated from first principles using the beta-cristobalite/Si(100) interface model. Based on the calculation, double bond formation between the interface silicon and oxygen atoms is proposed as a promising candidate for the mechanism of passivating the interface states.

 

77.       H. Kamada, J. Temmyo, M. Notomi, T. Furuta, and T. Tamamura

            "Dephasing processes in self-organized strained InGaAs single-dots on (311)B-GaAs substrate"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 36 (6B), 4194-4198 (1997).

 

            ABSTRACT: Single-dot photoluminescence measurements are undertaken on a number of individual InGaAs disks spontaneously formed on the GaAs-(311)B face. Well-isolated distinctive narrow single-dot luminescence lines. the narrowest of which is 34 mu eV in FWHM, is measured using a microscope and their evolution with excitation density is examined. Under very low excitation, individual dot luminescence is well approximated by the Lorentzian lineshape. Excitation via the barrier continuum results in very low luminescence saturation density and simultaneous broadening into a non-lorentzian Lineshape. In contrast, excitation resonant with excited states, causes no such broadening, but saturation power is about three orders of magnitude larger than under barrier excitation. Such phenomena are explained by different carrier flows into the dot states. Carrier-carrier scattering is discussed as a primary dephasing process that causes line broadening.

 

78.       K. Kanisawa and H. Yamaguchi

            "Extremely long surface diffusion of Ga and critical nucleation on As-rich GaAs(001) surfaces caused by phase transitions"

            Phys. Rev. B 56 (19), 12080-12083 (1997).

 

            ABSTRACT: The phase transitions between (2x4)/c(2x8) and c(4x4) on GaAs(001) surfaces are studied by ultrahigh-vacuum scanning tunneling microscopy. It is evident that the Ga diffusion is remarkable for length up to the micrometer range at the beginning of the transition, but the diffusion is prevented by nucleation at the final stage of the transition. We found that the size of the minimum nucleus depends on reconstruction. The structural stability is discussed, taking the surface electronic properties into account.

 

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

            "Electronic properties of monolayer steps on GaAs (001) surfaces studied by scanning tunneling microscopy"

            J. Cryst. Growth 175, 304-309 (1997).

 

            ABSTRACT: The electronic properties of monolayer steps on (2 x 4)/c(2 x 8) reconstructed GaAs (0 0 1) surfaces are studied by ultrahigh-vacuum scanning tunneling microscopy (UHV-STM). We quantitatively demonstrate that steps play the role of acceptor arrays by applying electron counting consideration to proposed structure models for monolayer steps. This suggestion is consistent with experimental results on vicinal GaAs (0 0 1) surfaces measured by STM. Energetical stability of the proposed monolayer step structures is theoretically explained. We found that the accepters at the steps are equivalent to those at the kinks. We confirmed that the surface states responsible for surface Fermi level pinning are located at breaking points of coherent arrangement of semiconducting (2 x 4) unit cells on GaAs (0 0 1) surfaces.

 

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

            "Effects of substrate materials on properties of superconducting Bi2Sr2CaCU2O8 epitaxial thin films"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 36 (1A), 84-89 (1997).

 

            ABSTRACT: We have studied the effects of substrate materials on the surface morphology, crystal quality and electrical properties of Bi2Sr2CaCu2O8 superconducting epitaxial thin films grown on MgO (100), SrTiO3 (100), NdGaO3 (001), LaSrGaO4 (001), LaAlO3 (001) and YAlO3 (001). Films grown on substrates with a large lattice mismatch have a lower T-c and include a number of outgrowth grains. By contrast, films grown on substrates with a small lattice mismatch have a very smooth surface with almost no outgrowth grains or precipitates and have a higher T-c. These results are interpreted in terms of the internal stress caused by the lattice mismatch between the film and substrate.

 

81.       M. Kasu and N. Kobayashi

            "Surface kinetics of metalorganic vapor-phase epitaxy: Surface diffusion, nucleus formation, sticking at steps"

            J. Cryst. Growth 174 (1-4), 513-521 (1997).

 

            ABSTRACT: The surface kinetics of GaAs (001) surfaces during metalorganic vapor-phase epitaxy (MOVPE) has been investigated quantitatively from high-vacuum scanning tunneling microscopy (STM) images of two-dimensional (2D) nuclei and denuded zones. STM observation was achieved by As passivation of grown-sample surfaces in a vacuum chamber directly connected to an MOVPE system. From 2D-nucleus densities of GaAs and AlAs, the surface diffusion coefficients of Ga and Al species on a GaAs (001) surface were estimated to be 2 x 10(-6) and 1.5 x 10(-7) cm(2)/s at 530 degrees C, and the energy barriers for migration were estimated to be 0.62 and 0.8 eV, respectively. The 2D-nucleus size was 1.5-2 times larger in the [110] direction than in the [<(1)over bar 10>] direction. The 2D nucleus size anisotropy is primarily due to a ratio in the lateral sticking probability between steps along the [<(1)over bar 10>] direction (A steps) and steps along the [110] direction (B steps) (more than 2.5 +/- 0.5: 1). Denuded zones on upper terraces were 2 +/- 0.5 times wider than those on lower terraces. This showed that the lateral sticking probability at the descending steps was 10-3 x 10(2) times larger than that at the ascending steps.

 

82.       M. Kasu and N. Kobayashi

            "Surface diffusion kinetics of GaAs and AlAs metalorganic vapor-phase epitaxy"

            J. Cryst. Growth 170 (1-4), 246-250 (1997).

 

            ABSTRACT: We have investigated the surface kinetics during metalorganic vapor-phase epitaxy (MOVPE), using high-vacuum scanning tunneling microscopy (STM) observation of two-dimensional (2D) nuclei and denuded zones. Using Monte Carlo simulations based on the solid-on-solid model, from 2D nucleus densities we estimated the surface diffusion coefficients of GaAs and AIAs to be 2 x 10(-6) and 1.5 x 10(-7) cm(2)/s at 530 degrees C, and the energy barriers for migration to be 0.62 and 0.8 eV, respectively. The 2D nucleus size in the [110] direction was about two times larger than that in the [<(1)over bar 10>] direction. The size anisotropy is caused primarily by a difference in the lateral sticking probability (P-s) between steps along the [<(1)over bar 10>] direction (A steps) and steps along the [110] direction (B steps). The P-s ratio was estimated to be more than 3:1. Denuded zone widths on upper terraces were 2 +/- 0.5 times wider than those on lower terraces. This showed that P-s at descending steps was 10 to 3 x 10(2) times larger than P-s at ascending steps.

 

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

            "Nanoscale patterning and selective growth of GaAs surfaces by ultra-high vacuum scanning tunneling microscopy"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 36 (6B), 3821-3826 (1997).

 

            ABSTRACT: After amorphous-like N-passivated GaAs surfaces with a low defect density are obtained as a mask layer for selective growth, nanometer scale patterning of the surfaces is achieved using ultra-high vacuum scanning tunneling microscopy to selectively depassivate surface N atoms. After patterning, GaAs dots with well-controlled size (typically 6 nm high and 50 x 50 nm(2)) can be successfully grown using trimethylgallium and tertiarybutylarsine in the specific area where the underlying GaAs layer appeared.

 

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

            "Nanometer-scale selective-area GaAs growth on nitrogen-passivated surfaces using STM and MOMBE"

            J. Cryst. Growth 173 (3-4), 589-591 (1997).

 

            ABSTRACT: A selective-area GaAs growth technique in a nanometer scale has been demonstrated by a combination of nitrogen (N)-passivation mask formation, ultra-high-vacuum scanning-tunneling-microscopy (STM) pattern modification, and metalorganic molecular beam epitaxy (MOMBE). GaAs(0 0 I) surfaces were passivated with N radicals dissociated from Na molecules, and were modified by STM in a nanometer scale, and on the surface GaAs nanostructures were grown using trimethylgallium and tertiarybutylarsine. Uniform 6 nm-high, 50 x 50 nm(2) dots were formed on the STM-modified areas, where the underlying GaAs layer appeared.

 

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

            "Selective-area GaAs growth using nitrogen passivation and scanning-tunneling-microscopy modification on a nanometer scale"

            Appl. Phys. Lett. 70 (9), 1161-1163 (1997).

 

            ABSTRACT: A technique for the selective-area growth of GaAs on a nanometer scale is described. The technique comprises nitrogen (N)-passivation mask formation, scanning-tunneling-microscopy (STM) pattern modification, and metalorganic molecular-beam epitaxy. GaAs (001) surfaces are passivated with N radicals dissociated from N-2 molecules and are modified by STM on a nanometer scale. GaAs nanostructures are then grown on the modified areas using trimethylgallium and tertiarybutylarsine. Uniform 6-nm-high and 50 x 50-nm(2) dots were formed on 50 x 50-nm(2) STM-modified areas. The advantage of the technique is that size-controlled nanostructures can be fabricated in specific positions and these nanostructures are free from contamination because all processes are performed in a vacuum. (C) 1997 American Institute of Physics.

 

86.       T. Kasuya and S. Itabashi

            "Charge dipolar orderings and magnetoelastics in rare earth hexaborides"

            J. Phys. Soc. Jpn. 66 (12), 3864-3875 (1997).

 

            ABSTRACT: Magnetoelastic effects measured previously on CexLa1-xB6 were reanalyzed based on the dynamical Jahn-Teller effect as a single site effect and the paired distortion as an interaction effect developed in recent papers for RB6 in general. In the dilute systems, we observe an anomalous Curie-Weiss term caused from competition between the single site effect and the pair effect, while in the dense systems anomalies due to pair formation are observed even in the paramagnetic region. Strong frustration inherent to the pair ordering plays an important role. Anomalous properties in PrB6 and NdB6 were also interpreted based on the above common model in good agreement with the experimental results, in particular with anomalous neutron scattering measurement. Magnetoelastic effects were measured also on PrB6 and NdB6. In PrB6 the effect is 100 time stronger than that in CeB6 due to induced mixing through distortions between the nearly degenerated ground levels, Gamma(1) and Gamma(5). The charge dipolar ordering was also observed clearly at the lower ordering temperature T-2, forcing an incommensurate magnetic ordering to commensurate.

 

87.       J. Kawahara and K. Yokosawa

            "Role of attention in illusory line motion search"

            Invest. Ophthalmol. Vis. Sci. 38 (4), 1734-1734 (1997).

 

            ABSTRACT:

88.       T. Kawamura, H. Takenaka, T. Hayashi, M. Tachikawa, and H. Mori

            "Initial domain structure of GaAs thin films grown on Si(001) substrates"

            Appl. Surf. Sci. 117, 765-770 (1997).

 

            ABSTRACT: The initial domain structure of GaAs films grown on several Si(001) surfaces is investigated using X-ray standing waves. GaAs/Si(001) samples, 4 ML thick, grown on three different Si substrates were used: an epitaxial Si surface (ESS), a mechanochemically polished surface (MCP), and a mechanochemically polished surface with plasma cleaning (plasma MCP). The domain ratio ambiguousness due to the film thickness is avoided by observing independent Bragg reflections of Si substrates. The results of X-ray standing wave measurement reveal that all GaAs films have double domain structures at the initial stage, even though final domain structures are single. The ratio of the two domains was almost 1:1 on the MCP surface, 6:4 on the ESS surface, and 4.5:5.5 on the plasma MCP surface. The dominant GaAs domains on the ESS and plasma MCP surfaces were the same as those obtained on thicker GaAs films. This suggests there is a rapid decrease in the GaAs domain during the early stages of growth on an ESS and plasma MCP surfaces.

 

89.       Z. Khasidashvili and J. Glauert

            "The geometry of orthogonal reduction spaces"

            in Automata, Languages And Programming, Lecture Notes In Computer Science Vol. 1256 (Springer-Verlag Berlin, Berlin 33, 1997), pp. 649-659.

 

            ABSTRACT: We investigate mutual dependencies of subexpressions of a computable expression, in orthogonal rewrite systems, and identify conditions for their concurrent independent computation. To this end, we introduce concepts familiar from ordinary Euclidean Geometry (such as basis, projection, distance, etc.) for reduction spaces. We show how a basis for an expression can be constructed so that any reduction starting from that expression can be decomposed as the sum of its projections on the axes of the basis. To make the concepts more relevant computationally, we relativize them w.r.t. stable sets of results, and show that an optimal concurrent computation of an expression w.r.t. S consists of optimal computations of its S-independent subexpressions. All these results are obtained for Stable Deterministic Residual Structures, Abstract Reduction Systems with an axiomatized residual relation, which model all orthogonal rewrite systems.

 

90.       J. Kim, Y. Yamamoto, and H. H. Hogue

            "Noise-free avalanche multiplication in Si solid state photomultipliers"

            Appl. Phys. Lett. 70 (21), 2852-2854 (1997).

 

            ABSTRACT: Si solid state photomultipliers utilize impact ionization of shallow impurity donor levels to create an avalanche multiplication when triggered by a photoexcited hole. The distribution of pulse height from a single photon detection event shows narrow dispersion, which implies that the avalanche multiplication process in these devices is inherently noise-free. We have measured the excess noise factor using two different techniques, digital pulse height analysis and analog noise power measurement. The results demonstrate nearly noise-free avalanche multiplication accomplished in these devices. (C) 1997 American Institute of Physics.

 

91.       J. S. Kim and Y. Yamamoto

            "Theory of noise in p-n junction light emitters"

            Phys. Rev. B 55 (15), 9949-9959 (1997).

 

            ABSTRACT: The intensity noise of light generated by semiconductor lasers and light-emitting diodes is treated by semiclassical Langevin equations. An independent equation for the junction voltage dynamics is considered, and the non-Markoffian nature of the pump current is decomposed into Markoffian carrier injection and a regulation mechanism due to charging effect at the junction. The intensity noise power spectrum and squeezing bandwidth predicted by these equations agree well with recent experimental results. External current noise generated as a result of the internal noise process and subsequent relaxation process is calculated. Also, correlations between the carrier-number fluctuation and the junction-voltage fluctuation, and between the emitted photon flux fluctuation and the junction-voltage fluctuation are studied in detail.

 

92.       K. Kinoshita

            "A tribute to prof. Dr. Jinzo Kobayashi reminiscences of 27 years with him"

            Ferroelectrics 203 (1-4), XI-XI (1997).

 

            ABSTRACT:

93.       G. Klimovitch, G. Bjork, H. Cao, and Y. Yamamoto

            "Selective resonant tunneling into microcavity exciton-polariton state"

            Phys. Rev. B 55 (11), 7078-7083 (1997).

 

            ABSTRACT: Electron resonant tunneling into the exciton state in a semiconductor quantum well may be turned into the tunneling to hybrid exciton-photon modes (exciton polaritons). The latter process can be used to make electrically pumped light-emitting devices with high (similar to 50%) quantum efficiency and fast (similar to ps) radiative decay time.

 

94.       M. Koashi and N. Imoto

            "Quantum cryptography based on split transmission of one-bit information in two steps"

            Phys. Rev. Lett. 79 (12), 2383-2386 (1997).

 

            ABSTRACT: We propose a simple quantum cryptographic scheme involving truly two orthogonal states. The security of the protocol is based on splitting the transfer of one-bit information into two steps, ensuring that only a fraction of the bit information is transmitted at a time. A particular implementation with an asymmetric interferometer is presented, which does not require the random timing of the packet sending as was used by Goldenberg and Vaidman [Phys. Rev. Lett. 75, 1239 (1995)].

 

95.       N. Kobayashi, Y. Kobayashi, and K. Uwai

            "Origin of surface reflectance spectrum during epitaxy"

            J. Cryst. Growth 174 (1-4), 544-549 (1997).

 

            ABSTRACT: During metalorganic vapor phase epitaxy, the anisotropic surface reflectance spectra are measured for (0 0 1) oriented bulk surfaces and hetero-epitaxial surfaces for III-V materials by taking the difference between the surface photoabsorption (SPA) spectra observed along the [1 1 0] azimuth and that observed along the [<(1)over bar 1 0>] azimuth. Concerning the peak whose intensity depends very much on the coverage of group V atom, the peak in the phosphide compounds is located al a higher energy than in the arsenide compounds. Besides, the peak in each compound shows a red-shift as the lattice constant increases. Good agreement between the energies of anisotropic peaks and the covalent energies of dimer bonds calculated using the Harrison model is obtained. For InAs-on-GaAs hetero-epitaxy, one monolayer of InAs growth results in a drastic change from the spectrum of GaAs surface to the InAs-like surface: the peak sign is reversed and the peak energy is red-shifted. These results support the conclusion that the anisotropic peak originates from an optical transition of the group V dimers. For GaAs surfaces grown by molecular beam epitaxy, independent of incidence azimuth, surface orientation and of various surface modifications, the original SPA spectra before subtraction exhibit a similar peak near the critical point related to bulk electronic states, indicating the possibility of the bulk contribution to the surface reflectance spectrum.

 

96.       N. Kobayashi, Y. Kobayashi, and K. Uwai

            "Chemical trend observed in anisotropic surface reflectance spectra of MOVPE by surface photoabsorption"

            J. Cryst. Growth 170 (1-4), 225-229 (1997).

 

            ABSTRACT: This paper investigates the origin of the surface reflectance spectrum for the group-V-stabilized III-V surface during MOVPE by using surface photoabsorption. A chemical shift is observed for the stoichiometry sensitive peak in the anisotropic spectra of arsenides and phosphides. The peaks observed in the phosphides are located at higher energies than the arsenides, besides the peak in each compound shows a red-shift as the lattice constant increases. To investigate the possibility of the critical point of the bulk energy state appearing in the reflectance spectrum induced by surface modification, the anisotropic spectrum during InAs-on-GaAs heteroepitaxy are measured. One monolayer InAs growth on GaAs results in a drastic change that a peak sign is reversed, accompanied by a red-shift. This can be interpreted by the optical transition change corresponding to the surface conversion from a two-As-layer c(4 x 4)-like surface in GaAs to a one-As-dimer layer having a bond axis perpendicular to the c(4 x 4) As dimer. The contribution of the GaAs bulk electronic state in the reflectance spectrum is not observed. These results support the model that the anisotropic peak originates from an optical transition of the group-V dimer. The anisotropic spectrum measurement also makes it possible to monitor the P/As surface exchange and the As-atom segregation during the InP-on-InAs heteroepitaxy.

 

97.       Y. Kobayashi, F. Scholz, and N. Kobayashi

            "Surface morphology and carbon incorporation for hexagonal GaN/(111)B GaAs metalorganic vapor phase epitaxy using dimethylhydrazine and trimethylgallium"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 36 (5A), 2592-2595 (1997).

 

            ABSTRACT: Using dimethylhydrazine (DMHy) as a group V source, we grew hexagonal GaN layers on (111)B GaAs substrates by low-pressure metalorganic vapor phase epitaxy. The surface morphology of the hexagonal GaN layers and the carbon incorporation in them strongly depend on the V/III ratio and the reactor pressure, A flat GaN surface can be obtained at the V/III ratio of 60 and the substrate temperature of 850 degrees C. The carbon concentration decreases with increasing reactor pressure and the minimum concentration is 2 x 10(19) cm(-3) for hexagonal GaN grown at 300 Torr. Low-temperature photoluminescence measurements reveal that the band edge emission for the GaN grown at 300 Torr is dominant compared with that of a deep level.

 

98.       K. Komoku, K. Shiraishi, T. Ito, and I. Teramoto

            "The stability of a GaAs(001)-(2x4) surface with Si adatoms"

            Appl. Surf. Sci. 121, 175-178 (1997).

 

            ABSTRACT: The stability of GaAs(001)-(2x4)beta 2 surface with Si adatoms is theoretically investigated using the ab initio pseudopotential method. The calculated results imply that stable lattice sites for Si adatoms strongly depend on the adatom coverage. At lower coverage theta=0.125, Si adatoms stably reside in the empty Ga sites in the missing dimer trenches. This is consistent with recent STM observations at low coverages. On the other hand, the surface with Si dimers on the upper As dimers are the most stable at higher coverage theta=0.25. The coverage dependence of adsorption site preferences is qualitatively discussed in terms of energy band structure and excess energy of hetero interatomic bonds such as As-As, Si-As and Ga-Si. (C) 1997 Elsevier Science B.V.

 

99.       L. P. Kouwenhoven, T. H. Oosterkamp, M. W. S. Danoesastro, M. Eto, D. G. Austing, T. Honda, and S. Tarucha

            "Excitation spectra of circular, few-electron quantum dots"

            Science 278 (5344), 1788-1792 (1997).

 

            ABSTRACT: Studies of the ground and excited states in semiconductor quantum dots containing 1 to 12 electrons showed that the quantum numbers of the states in the excitation spectra can be identified and compared with exact calculations. A magnetic field induces transitions between the ground and excited states. These transitions were analyzed in terms of crossings between single-particle states, singlet-triplet transitions, spin polarization, and Hund's rule. These impurity-free quantum dots allow ''atomic physics'' experiments to be performed in magnetic field regimes not accessible for atoms.

 

100.    E. Kuramochi, J. Temmyo, and T. Tamamura

            "Perfect spatial ordering of self-organized InGaAs/AlGaAs box-like structure array on GaAs (311)B substrate with silicon nitride dot array (vol 71, pg 1655, 1997)"

            Appl. Phys. Lett. 71 (23), 3448-3448 (1997).

 

            ABSTRACT:

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

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

            Appl. Phys. Lett. 71 (12), 1655-1657 (1997).

 

            ABSTRACT: The metalorganic vapor phase epitaxial growth of strained InGaAs/AlGaAs box-like structure self-organized on GaAs (311)B substrate was investigated using fine silicon nitride (SIN) dot arrays for improving the controllability of self-organization phenomena. AlGaAs barrier layer grown at 750 similar to C buries SiN dots, forming novel pentagonally shaped hollows on (311)B substrate due to the (-100) facet growth and lateral growth. The In0.3Ga0.7As layer is preferentially grown in these hollows, then box-like structure is formed in these hollows during the growth interruption. Successive growth of AlGaAs/In0.3Ga0.7As epilayers induces the stacking of box-like structures just on top of the bottom boxes. The pairing probability of bottom and upper boxes is strongly dependent on the SiN dot array pitch, and the perfect spatial ordering of upper box arrays is achieved when the SiN dot pitch is in a range of 250-300 nm. This approach allows the exact positioning of self-formed box structure. (C) 1997 American Institute of Physics.

 

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

            "Room temperature operated single electron transistor fabricated by electron beam nanolithography"

            Microelectron. Eng. 35 (1-4), 261-264 (1997).

 

            ABSTRACT: We have fabricated a Si-based single electron transistor (SET) with precisely controlled structure using a newly developed electron beam nanolithography system and a Si nanofabrication process. A Si island and tunnel barriers are fabricated by trench etching with reactive ion etching on a superficial Si layer of SIMOX substrate, combined with an image reversal technique using ECR plasma oxidation. The SET fabricated with this method accommodates a 10-nm Si island and achieved room temperature operation.

 

103.    S. Kurihara, S. Aoyagi, and R. Onai

            "Adaptive selection of reactive/deliberate planning for the dynamic environment - A proposal and evaluation of MRR-planning"

            in Multi-Agent Rationality, Lecture Notes In Artificial Intelligence Vol. 1237 (Springer-Verlag Berlin, Berlin 33, 1997), pp. 112-127.

 

            ABSTRACT: This paper proposes and evaluates a methodology for multi-agent realtime reactive planning. In addition to the feature of conventional real-time reactive planning, which can react in a dynamic environment, our planning can perform deliberate planning when, for example, the robot has enough time to plan its next action. The proposed planning features three kinds of agents: a behavior agent that controls simple behavior, a planning agent that makes plans to achieve its goals, and a behavior selection agent that intermediates between behavior agents and planning agents. They coordinate a plan in an emergent way for the planning system as a whole. We confirmed the effectiveness of our planning by means bf a simulation. Furthermore, we implemented an active vision system, which is the first stage of building the real-world agent, and used it to verify the real-world effectiveness of our planning.

 

104.    P. Kurpas, E. Richter, M. Sato, F. Brunner, D. Gutsche, and M. Weyers

            "MOVPE growth of GaInP/GaAs hetero-bipolar-transistors using CBr4 as carbon dopant source"

            J. Cryst. Growth 170 (1-4), 442-446 (1997).

 

            ABSTRACT: Carbon doping of GaAs with carbon tetrabromide (CBr4) in low pressure MOVPE has been investigated and applied to the fabrication of GaInP/GaAs HBTs. Especially the hydrogen incorporation and the associated acceptor passivation has been studied. The hydrogen found in single GaAs:C layers is predominantly incorporated during cooling the sample under AsH3 after growth. n-Type capping layers can block this H indiffusion and GaAs:C base layers in HBTs show much lower H concentrations than GaAs:C single layers without a cap. A further reduction of acceptor passivation is possible by optimization of the growth procedure. First HBTs processed from layers with a base that was doped using CBr, show promising DC and HF performance (beta = 45, f(T) = 26 GHz for 2 x 20 mu m(2) devices).

 

105.    P. Kurpas, M. Sato, A. Knauer, and M. Weyers

            "On-line growth monitoring of InP-based device structures by reflectance anisotropy spectroscopy"

            J. Electron. Mater. 26 (10), 1154-1158 (1997).

 

            ABSTRACT: Reflectance anisotropy spectroscopy (RAS) has been used to study the metalorganic vapor phase epitaxy growth process for GaxIn1-xAsyP1-y/InP light emitting diodes. The sensitivity of RAS to morphology changes is demonstrated by InP growth on different InP:Fe substrates. RAS reveals not only development of dull surfaces but also detects initial temporary roughness of mirror-like layers. Based on the RAS results the substrate preparation was optimized, RAS spectra measured on n- and p-type InP and p-type GaInAsP during light emitting diodes production are suitable for finger-printing of the growth process. Spectra from InP:Si and InP:Zn layers show characteristic features near 4.3 eV which allow for assessment of doping level at growth temperature (640 degrees C). Correlation of RAS spectra and transients during growth with the? quaternary composition was achieved. A change in composition of only Delta x = 0.01, Delta y = 0.03 corresponding to a shift of photoluminescence-peak position by 16 nm was detectable in RAS spectra. The results demonstrate the high sensitivity and thus the suitability of RAS for online control during growth of device structures.

 

106.    R. C. Liu, P. Eastman, and Y. Yamamoto

            "Inhibition of elastic and inelastic scattering by the Pauli exclusion principle: Suppression mechanism for mesoscopic partition noise"

            Solid State Commun. 102 (11), 785-789 (1997).

 

            ABSTRACT: A semiclassical Monte Carlo simulation which implements a dynamic feedback process based on the Pauli exclusion principle is used to study the suppression of partition noise in a one dimensional mesoscopic conductor. The purely distributed elastic scattering case exhibits a one-third suppression relative to full shot noise. Increasing inelastic scattering can initially increase the noise, but eventually suppresses it. The key mechanism is the redistribution of electrons by random scattering subject to a ''Pauli exclusion principle.'' (C) 1997 Published by Elsevier Science Ltd.

 

107.    F. Maeda, Y. Watanabe, and M. Oshima

            "Real-time observation of alternating growth on GaSb(001) using core-level photoelectron spectroscopy"

            Appl. Surf. Sci. 112, 69-74 (1997).

 

            ABSTRACT: The alternating growth process of GaSb on a (001) surface was analyzed by real-time core-level photoelectron spectroscopy. Using intensity analysis at the Ga supply stage, Ga growth mode was found to change from 2D growth to 3D growth at substrate temperatures between 495 and 520 degrees C. Using intensity analysis at the Sb desorption stage, we found that the behavior of Sb atoms also changed at this temperature. These results show that a substrate temperature of about 500 degrees C is critical for the alternating growth of GaSb(001).

 

108.    Y. Maeda, D. J. Rogers, O. Song, K. Takei, T. Ohkubo, S. Hirono, J. Suzuki, and Y. Morii

            "Magnetic microstructures produced by compositional separations in Co-Cr based alloy thin films"

            IEEE Trans. Magn. 33 (1), 879-884 (1997).

 

            ABSTRACT: Compositional separation (CS) has been observed to occur in Co-Gr based alloy thin films producing fine, Co enriched, strongly ferromagnetic regions within the crystal grains. This CS exhibits a strong correlation with film magnetic properties and may hold the potential for engineering a ''particulate type'' magnetic microstructure suitable for high density magnetic recording. In this study, we first investigated the effect on CS of varying several growth parameters, with the aim of better understanding how to control the compositional and magnetic microstructures, In particular, reduction in film thickness was found to be very effective for enhancing GS and producing finer in-grain ferromagnetic regions with less coalescence. We therefore proceeded to perform point magnetic recording in Co-Cr films of various thicknesses and found that, although thinner films do support smaller bits, further studies on control of CS and promotion of magnetic isolation of Co-enriched, ferromagnetic regions will be necessary in order to utilize the full potential of CS.

 

109.    T. Makimoto, M. Kasu, J. L. Benchimol, and N. Kobayashi

            "In-situ STM observation of GaAs surfaces after nitridation"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 36 (3B), 1733-1735 (1997).

 

            ABSTRACT: Scanning tunneling microscopy was used to study surface morphologies for various GaAs surfaces after nitridation using atomic nitrogen. For the (100) surface, 3-nm-wide stripes were observed along the [011] azimuth. Smooth surfaces densely covered with small GaN grains were observed for the (311)A and (111)A surfaces, while large GaN grains with some voids were observed for the (111)B surface. These results suggest that the (n11)A surfaces are promising for the growth of GaN on GaAs. Among the (100), (111)B, and (111)A GaAs surfaces, the (111)A surface after nitridation showed the largest selectivity of GaAs growth in metalorganic molecular beam epitaxy using trimethylgallium and tertiarybutylarsine. The surface roughness of GaAs after nitridation was also found to have a major effect on the selectivity of GaAs growth.

 

110.    T. Makimoto and N. Kobayashi

            "Formation and etching of thin nitride layers on GaAs using atomic nitrogen and hydrogen"

            Solid-State Electron. 41 (2), 345-347 (1997).

 

            ABSTRACT: This paper reports on the nitridation of (001) GaAs using atomic nitrogen and the etching characteristics of the nitride layers formed using atomic hydrogen. Nitrogen and hydrogen molecules were cracked by a hot W filament to produce atomic nitrogen and hydrogen. After nitridation and etching, GaAs cap layers were grown by molecular beam epitaxy to form GaAs/GaN/GaAs structures. We determine the sheet nitrogen atom concentration for these structures by secondary ion mass spectrometry analysis. As the nitridation temperature decreases, the etched nitrogen atom concentration increases. The N-As bonds might be responsible for this increased concentration. The etching rate also depends on the substrate temperature. (C) 1997 Elsevier Science Ltd.

 

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

            "Origin of nitrogen-pair luminescence in GaAs studied by nitrogen atomic-layer-doping in MOVPE"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 36 (3B), 1694-1697 (1997).

 

            ABSTRACT: Nitrogen atomic-layer-doping and nitrogen uniform doping were performed on (001) GaAs by metalorganic vapor phase epitaxy using dimethylhydrazine as a nitrogen doping source. Nitrogen doped GaAs layers showed several sharp photoluminescence lines relating to excitons bound to nitrogen pairs at 8 K. We investigated the origins of these sharp photoluminescence lines, that is, the distance between the nitrogen atoms of a pair and their pairing direction. The photoluminescence spectra for nitrogen atomic-layer-doped GaAs are different from those for uniformly nitrogen-doped GaAs, as expected from the different dimensions of the nitrogen atom distribution. To estimate the distance between the nitrogen atoms of a pair and their pairing direction, we performed double atomic-layer doping and varied the distance between the two atomic-layer-doped planes. When the two planes are brought to 1 nm of each other, lines observed only in uniformly doped GaAs appear. From this result, it was determined that the pairing directions corresponding to these lines are not included in the (001) plane and the corresponding distance between the nitrogen atoms of a pair is around 1 nm.

 

112.    T. Makimoto, H. Saito, T. Nishida, and N. Kobayashi

            "Excitonic luminescence and absorption in dilute GaAs1-xNx alloy (x<0.3%)"

            Appl. Phys. Lett. 70 (22), 2984-2986 (1997).

 

            ABSTRACT: Dilute GaAs1-xNx, alloys (x<0.3%) were grown by metalorganic vapor phase epitaxy to investigate their photoluminescence and photoluminescence excitation characteristics. Photoluminescence excitation spectra show clear excitonic absorption peaks at low temperatures and their peak energy drastically decreases with increasing nitrogen concentration due to the band-gap bowing in the GaAsN system. This result indicates that the band-gap bowing starts at a nitrogen concentration as low as 10(18) cm(-3), and its bowing parameter is -22 eV. According to this band-gap bowing, the GaAsN alloys show two photoluminescence lines whose peak energy decreases with increasing nitrogen concentration. Their dependence on the nitrogen concentration suggests that these lines correspond to excitonic and carbon-related transitions in the GaAsN alloy. (C) 1997 American Institute of Physics.

 

113.    I. Mareschal, H. Ashida, P. J. Bex, S. Nishida, and F. A. J. Verstraten

            "Linking lower and higher stages of motion processing?"

            Vision Res. 37 (13), 1755-1759 (1997).

 

            ABSTRACT: The spatial frequency selectivity of motion detection mechanisms can be measured by comparing the magnitude of motion aftereffects (MAEs) as a function of the spatial frequency of the adapting and test gratings. For static test gratings, narrow spatial frequency tuning has been reported in a number of studies, However, for dynamic test patterns, reports have been conflicting, Ashida & Osaka [(1994), Perception, 23, 1313-1320] found no tuning whereas Bex et al. [(1996) Vision Research, 36, 2721-2727] reported a narrow tuning. The main difference between the two studies was the temporal frequency of the test pattern, In this study we measured the spatial frequency tuning of the MAE using test patterns for a range of temporal frequencies. The results confirmed that there was narrow spatial frequency tuning when the test pattern was counterphasing at a low temporal frequency. However, the spatial frequency selectivity broadened as the temporal frequency of the test pattern was increased. (C) 1997 Elsevier Science Ltd.

 

114.    T. Matsuoka

            "Calculation of unstable mixing region in wurtzite In1-x-yGaxAlyN"

            Appl. Phys. Lett. 71 (1), 105-106 (1997).

 

            ABSTRACT: The wurtzite structure In1-x-yGaxAlyN quaternary system with a wide band gap, which is useful for light emitters in the wavelength region shorter than green, is studied with respect to the unstable region in mixing. This unstable region in mixing is calculated from the free energy of mixing using the strictly regular solution model. The interaction parameter used in this calculation is obtained using the delta-lattice-parameter method. From this calculation, the ternary alloys of InAlN, InGaN, and GaAlN are, respectively, predicted to always, sometimes, and hardly ever have a unstable mixing region at the temperature lower than 3000 degrees C. (C) 1997 American Institute of Physics.

 

115.    M. Morita, O. Niwa, and T. Horiuchi

            "Interdigitated array microelectrodes as electrochemical sensors"

            Electrochim. Acta 42 (20-22), 3177-3183 (1997).

 

            ABSTRACT: We investigated electrochemical measurements with interdigitated array (IDA) electrodes in both stationary solutions and flow systems. In a stationary solution, we achieved a very low detection limit of 10 pM of reversible redox species by using substitutional stripping voltammetry, which is a new type of stripping voltammetry using an IDA microelectrode. In flow systems, current enhancement by redox cycling is less effective than that in a stationary solution. The flow rate dependence of redox cycling is constant in the amperometric region, varies with coulometric yield in the quasi-amperometric region, and is inversely proportional to the 2/3 power of the volume flow rate in the coulometric region. A low detection limit of 5 fg (32 amol) is obtained for dopamine due to the high current density and low background noise level (0.1pA) at the carbon-based IDA microelectrode used as a detector for liquid chromatography. A new separation approach is demonstrated which combines electrochemical detection and a molecular template. The electrode is first partly covered with print molecules and then modified with silane coupling reagent. The catechol-imprinted electrode shows the usual diffusion-limited cyclic voltammogram of catechol and has a diminished response against all catecholamines. The selectivity between catechol and epinephrine is about 100 when the electrode is used as an electrochemical detector in liquid chromatography. (C) 1997 Published by Elsevier Science Ltd.

 

116.    K. Muraki and Y. Horikoshi

            "Suppression of AlGaAs/GaAs superlattice intermixing by p-type doping"

            J. Cryst. Growth 175, 162-167 (1997).

 

            ABSTRACT: We report a systematic investigation of the effect of n- and p-type doping on the AlGaAs/GaAs superlattice (SL) intermixing using photoluminescence. We find that the SL intermixing is not only enhanced by Si doping but also suppressed by Be doping. Although previous models have suggested the contribution of triply negatively charged Ga vacancies, V-Ga(3-), in n-type and intrinsic materials and of doubly positively charged Ga interstitials, I-Ga(2+), in p-type materials, we find that at 900 degrees C the Al-Ga interdiffusion is mediated by singly negatively charged Ga vacancies, V-Ga(-), in both p- and n-type materials for n < 1 x 10(18) cm(-3). These results are shown to be explained consistently in terms of the Fermi-level effect. Our results demonstrate that the thermal stability of AlGaAs/GaAs heterostructures can be controlled, i.e., weakened or strengthened, by appropriate tuning of the Fermi level.

 

117.    Y. Muramatsu, M. Sugiyama, S. Maeyama, K. Furukawa, K. Ebata, M. Fujino, N. Matsumoto, S. Kawai, and M. Motoyama

            "Soft X-ray emission and absorption spectroscopy for electronic structure analysis of cubic silicon clusters in Si K-shell threshold"

            J. Electron Spectrosc. Relat. Phenom. 85 (1-2), 159-165 (1997).

 

            ABSTRACT: Soft X-ray emission and absorption (SXEA) spectroscopy is presented as a possible method for electronic structure analysis, To demonstrate its feasibility, the electronic structure of silicon backbones in a cubic silicon cluster (octasilacubane) and its related clusters was analyzed by measuring the SXEA spectra in the Si K-shell threshold, Three discrete levels are observed in both Si3p occupied and unoccupied orbitals of octasilacubane, which may be caused by the large degree of degeneracy of the orbitals due to the high symmetry of the cubic silicon backbone structure, The measured narrow energy gap of 2.3 eV between the highest occupied and the lowest unoccupied orbitals of octasilacubane shows that Si3p sigma-electrons in octasilacubane are more widely conjugated than those in the related clusters. (C) 1997 Elsevier Science B.V.

 

118.    H. Murase and S. K. Nayar

            "Detection of 3D objects in cluttered scenes using hierarchical eigenspace"

            Pattern Recognit. Lett. 18 (4), 375-384 (1997).

 

            ABSTRACT: This paper proposes a novel method to detect three-dimensional objects in arbitrary poses and sizes from a complex image and to simultaneously measure their poses and sizes using appearance matching. In the learning stage, for a sample object to be learned, a set of images is obtained by varying pose and size. This large image set is compactly represented by a manifold in compressed subspace spanned by eigenvectors of the image set. This representation is called the parametric eigenspace representation. In the object detection stage, a partial region in an input image is projected to the eigenspace, and the location of the projection relative to the manifold determines whether this region belongs to the object, and what its pose is in the scene. This process is sequentially applied to the entire image at different resolutions. Experimental results show that this method accurately detects the target objects. (C) 1997 Elsevier Science B.V.

 

119.    H. Myoren, R. Bergs, T. Tachiki, J. Chen, K. Nakajima, M. Suzuki, T. Yamashita, H. Sato, and M. Naito

            "Anisotropic resistivity of In-plane-aligned La2-xSrxCuO4(100) films on LaSrGaO4(100) substrates"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 36 (5A), 2642-2645 (1997).

 

            ABSTRACT: We prepared in-plane aligned La2-xSrxCuO4(100) films using LaSrGaO4(100) substrates by KrF laser ablation. The phi scan of X-ray diffraction and the large anistropy of resistivity indicate a high degree of in-plane epitaxy. The T-c of the in-plane-aligned La2-xSrxCuO4 (x = 0.15) was 21.6 K. The critical temperatures measured along the c-axis were usually higher than those measured along the a-axis. We also observed voltage peaks at just above T-c, corresponding to the abrupt decrease of the anistropy of resistivity at T-c.

 

120.    S. V. Nair and T. Takagahara

            "Theory of exciton pair states and their nonlinear optical properties in semiconductor quantum dots"

            Phys. Rev. B 55 (8), 5153-5170 (1997).

 

            ABSTRACT: The exciton and two-exciton states in semiconductor quantum dots much larger in size than the exciton Bohr radius are investigated, and the energies and oscillator strengths of several exciton and biexciton states are calculated. The presence of weakly correlated exciton-pair states are identified and these have a large oscillator strength increasing proportional to the volume of the quantum dot. These states are shown to play a crucial role in determining the nonlinear optical response of large quantum dots. The weakly correlated exciton-pair states are found to cause a cancellation effect in the third-order nonlinear optical susceptibility at the exciton resonance, providing a consistent understanding of the experimentally observed saturation of the mesoscopic enhancement of the excitonic optical nonlinearity. The excited-state absorption in quantum dots is also studied and the excitation of the weakly correlated exciton-pair states is found to dominate the spectrum. The spectral features in the pump-probe spectroscopy are predicted in detail. The biexciton binding energy and oscillator strength are obtained in good agreement with experimental results on CuCl quantum dots. Also: the good correspondence of the excited-state absorption spectra between the theory and experiments provides convincing evidence for the presence of the weakly correlated exciton-pair states.

 

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

            "MBE growth of (La,Sr)(2)CuO4 and (Nd,Ce)(2)CuO4 thin films"

            Physica C 293 (1-4), 36-43 (1997).

 

            ABSTRACT: The growth of (La,Sr)(2)CuO4 and (Nd,Ce)(2)CuO4 thin films by reactive coevaporation is reviewed. By (1) careful adjustment of the cation stoichiometry, (2) optimum oxidation, and (3) appropriate choice of substrates, we have successfully grown c-axis and non-c-axis oriented high-quality thin films of (La,Sr)(2)CuO4 and (Nd,Ce)(2)CuO4. The key points for thin film growth and the characterization of grown films are discussed. (C) 1997 Elsevier Science B.V.

 

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

            "Surface and interface study on MBE-grown Nd1.85Ce0.15CuO4 thin films by photoemission spectroscopy and tunneling spectroscopy"

            Physica C 282, 965-966 (1997).

 

            ABSTRACT: Nd1.85Ce0.15CuO4 (NCCO) surfaces and Pb/NCCO interfaces have been extensively investigated by X-ray/ultraviolet spectroscopies and tunnel spectroscopy using films grown by MBE. The photoelectron spectra obtained in-situ on the surfaces of MBE-grown NCCO films are free from any dirt peak, and make feasible the first systematic investigation of the surface and interface of cuprates. The results indicate that the surface and interface electronic structures of NCCO are strongly influenced by oxygen non-stoichiometry, and that the precise control of oxygen content at the surface (interface) is essential to obtain the bulk-representative surface (interface).

 

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

            "Soft x-ray pulse generation from femtosecond laser-produced plasma with reduced debris using a metal-doped glass target"

            Appl. Phys. Lett. 70 (1), 16-18 (1997).

 

            ABSTRACT: We have demonstrated soft x-ray short pulse generation from femtosecond laser-produced plasma with much lower debris using metal-doped glass as a target. Soft x-ray emission (50-200 Angstrom) from a gold-doped glass target was about 40% of that from a solid gold target while the density of gold in the doped-glass was less than 0.001 vol % and the target was transparent at the wavelength of the laser light. Due to the low metal density, the particulate deposition, which is one of the serious obstacles to putting laser-produced plasma x-ray into practical use, was greatly reduced by the use of metal-doped glass as a target. (C) 1997 American Institute of Physics.

 

124.    J. Nakata

            "Enhanced crystallization of amorphous Si containing hydrogen without oxygen during ion-beam irradiation at 310 degrees C and during furnace annealing below 450 degrees C"

            J. Appl. Phys. 82 (11), 5433-5445 (1997).

 

            ABSTRACT: The epitaxial crystallization rates of amorphous Si layers on crystalline Si substrates containing a considerable number of hydrogen atoms are markedly increased in the absence of oxygen atoms. This enhanced crystallization occurs both during 1-MeV Xe-ion-beam irradiation at 310 degrees C and during furnace annealing in vacuum at temperatures below 450 degrees C. Implantation-amorphized crystal Si layers epitaxially grown on the (100)-crystalline Si substrates by ultrahigh vacuum chemical vapor deposition (UHV-CVD) are epitaxially crystallized by furnace annealing in vacuum at temperatures below 450 degrees C. Implantation-amorphized bulk-crystal Si substrates, however, are not entirely crystallized by the same low-temperature annealing. Nanometer-scale microcrystallites, remaining at the near-surface region in the amorphous Si layer after 80-keV phosphorus implantation into the UHV-CVD epitaxial Si layer, grow three-dimensional during 1-MeV Xe-ion-beam irradiation at 310 degrees C, but not during furnace annealing at 600 degrees C in dry Ar ambient. This three-dimensional crystal growth does not occur in implantation-amorphized bulk-crystal Si substrates, even during 1-MeV Xe-ion-beam irradiation. Amorphous Si layers directly deposited by low-pressure CVD (LP-CVD) are crystallized epitaxially by 1-MeV Xe-ion-beam irradiation at 310 degrees C. The crystallization rate of the LP-CVD sample heated in the deposition furnace after evacuation is twice as high as that of the sample heated before evacuation. All these results are explained consistently by the presence of a considerable amount of hydrogen in polyhydride states in the amorphous Si layers in the absence of oxygen. It is suggested that the mechanism of low-temperature crystalline of amorphous Si containing hydrogen in polyhydride states closely related, in terms of vacant spaces and dangling-bonds, to the mechanism of ion-beam-induced epitaxial crystallization. (C) 1997 American Institute of Physics.

 

125.    J. Nakata

            "Epitaxial crystallization during 600 degrees C furnace annealing of amorphous Si layer deposited by low-pressure chemical-vapor-deposition and irradiated with 1-MeV Xe ions"

            J. Appl. Phys. 82 (11), 5446-5459 (1997).

 

            ABSTRACT: The amorphous Si layers deposited by low-pressure chemical vapor deposition on (100)-crystal-Si substrates and subjected to Xe-ion-beam irradiation are crystallized epitaxially in a layer-by-layer fashion to the surface during 600 degrees C furnace annealing. Layer-by-layer crystallization can be accomplished by irradiating the layers with a 1-MeV Xe-ion-beam for a 2 x 10(15)/cm(2) dose at 310 degrees C prior to furnace annealing. In all cases during furnace annealing that amorphous Si layers are polycrystallized or are grown vertically in isolated epitaxial-columnar-structures and then grown laterally into the amorphous region surrounding each column, the ion-beam-induced epitaxial crystallization (IBIEC) method epitaxially crystallizes them in a layer-by-layer fashion. This is because O atoms that were at the initial interface and that prevented layer-by-layer crystallization or columnar-epitaxial-growth diffuse remarkably because of irradiation. This diffusion decreases the peak concentration and facilitates layer-by-layer crystallization. O atoms at the interface are also diffused by irradiation with XO-keV P, 100-keV As, and 150-keV As ions. This diffusion results in the columnar growth during 600-800 degrees C furnace annealing. Whether layer-by-layer growth or columnar growth occurs during the furnace annealing depends on the peak concentration of oxygen at the interface. Direct evidence is shown that O diffusion is enhanced by the amount of inelastic electronic scattering of incident ion beam under the same elastic nuclear scattering conditions. The rates of IBIEC and of epitaxial crystallization during furnace annealing after 1-MeV Xe-ion-beam irradiation for a 2 x 10(15)/cm(2) dose are affected by the amount of oxygen in the amorphous layer. The rate of layer-by-layer IBIEC using a 1-MeV Xe-ion-beam is nearly twice as high for a sample heated in the deposition furnace after evacuation as it is for a sample heated before evacuation. This difference is due to the smaller amount of oxygen in the amorphous Si layer of the former sample. (C) 1997 American Institute of Physics.

 

126.    J. Nakata, H. Yamazaki, Y. Yamamoto, and Y. Kido

            "In-situ ion-beam annealing of damage in GaAs during O implantation and O-site determination by O-18(p,alpha)N-15 nuclear reaction"

            Nucl. Instrum. Methods Phys. Res. Sect. B-Beam Interact. Mater. Atoms 121 (1-4), 306-310 (1997).

 

            ABSTRACT: Damage introduced by 40 keV O-16,O-18 implantation in the crystalline GaAs substrate is investigated by the Rutherford backscattering spectroscopy (RES) channeling method and cross-sectional transmission electron microscopy (X-TEM). Anomalously little damage was formed at room temperature (< 43 degrees C), in spite of the large energy density being deposited in the nuclear scattering process. In-situ ion-beam annealing during irradiation effectively occurred below 43 degrees C, For the 5 x 10(15)/cm(2) dose sample, the RES channeling yield increases with the annealing temperature, due to the formation of stacking faults, confirmed by X-TEM observation. Yield increase with the temperature was not observed for lower 1 x 10(15)/cm(2) and higher 1 x 10(16)/cm(2) doses. A possible site occupied by (18) 18 O atoms after annealing is determined by O-18(p,alpha)N-15 nuclear reaction. The ratios of channeling-yields to the corresponding random-yields for alpha-particles emitted from O-18 atoms were compared with simulated results.

 

127.    H. Namatsu, S. Horiguchi, M. Nagase, and K. Kurihara

            "Fabrication of one-dimensional nanowire structures utilizing crystallographic orientation in silicon and their conductance characteristics"

            J. Vac. Sci. Technol. B 15 (5), 1688-1696 (1997).

 

            ABSTRACT: We propose a process for fabricating one-dimensional Si nanowires with a point contact. The nanowire structure can be easily obtained through two steps: KOH etching of a {110} Si layer of a silicon on insulator substrate and sufficient oxidation of the Si patterns formed by etching. In the etching process, vertical sidewalls comprised of {111} planes are formed into a wire. In addition, other {111} planes, projecting obliquely along the vertical sidewalls, spontaneously appear in the etched substrate. This is due to the fact that the etching proceeds as {111} planes appear because the etch rate of the {111} plane is the lowest of all planes. The bottom-corner region of two inclined {111} planes becomes a point-contact structure by making the distance between two inclined planes appropriate. The oxidation process converts the two-dimensional wire into one-dimensional nanowire by the stress-dependent oxidation phenomena of the Si wire. Consequently, a Si nanowire with a point contact can be formed in the bottom region. The Si nanowires fabricated through this process show clear conductance steps with little fluctuation on plateaus at 45 K. In addition, we discuss the conductance step characteristics in connection with a calculated energy level for a nanowire in {110} Si. (C) 1997 American Vacuum Society. [S0734-211X(97)03105-3].

 

128.    H. Namatsu, S. Horiguchi, Y. Takahashi, M. Nagase, and K. Kurihara

            "Fabrication of SiO2/Si/SiO2 double barrier diodes using two-dimensional Si structures"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 36 (6A), 3669-3674 (1997).

 

            ABSTRACT: In this article, we demonstrate a technique for fabricating SiO2/two-dimensional (2D)-Si/SiO2 double barrier diodes and discuss their characteristics. Vertical 2D-Si with {111} side planes is formed by orientation-dependent etching of {110} Si using aqueous alkaline solution. The linewidth of the 2D-Si is reduced to nanometer order with NH4F/H2O2 solution. This solution also removes the residue generated on Si planes etched by aqueous alkaline solution. Using a skillful arrangement of dummy patterns and an etchback technique, poly-Si electrodes are successfully formed without any lithographic alignments. A SiO2/2D-Si/SiO2 diode fabricated by this process shows resonant characteristics that are in agreement with the calculated values.

 

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

            "Fabrication of 2-nm-wide silicon quantum wires through a combination of a partially-shifted resist pattern and orientation-dependent etching"

            Appl. Phys. Lett. 70 (5), 619-621 (1997).

 

            ABSTRACT: This article proposes a nanofabrication technique for fabricating quantum wires with dimensions in the sub-10 nm regime. This technique consists of partially shifted resist-pattern formation and orientation-dependent Si etching that takes advantage of the difference in the crystallographic properties of the {111} planes and the other planes. When {110} Si substrates are etched using a partially shifted pattern as a mask, the etching generates a smooth {111} side plane and eventually forms a straight Si line pattern whose width is equal to the difference between the size of the shift and the originally exposed linewidth. Therefore, line patterns smaller than the beam diameter of lithographic tools can be formed. We show the effectiveness of this technique by fabricating a 2-nm-wide Si line. The electrical conductance characteristics of the Si nanoline formed by this technique are also shown. (C) 1997 American Institute of Physics.

 

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

            "Contrast dependencies of two types of motion aftereffect"

            Vision Res. 37 (5), 553-563 (1997).

 

            ABSTRACT: We examined the effects of adaptation and test contrasts on the duration of two types of motion aftereffect (MAE) that presumably reveal different levels of motion processing: MAE with a static test stimulus (static MAE), and that with a counterphasing test stimulus (flicker MAE). MAE duration increased with increasing adaptation contrast. When the test contrast was low, it increased rapidly, and saturated at a low adaptation contrast. When the test contrast was high, however, it gradually increased over a wide range of adaptation contrasts. These complex effects of stimulus contrasts could be well described by a dependency on adaptation contrast normalized by test contrast on a logarithmic axis. Little difference was found between the results for two types of MAE. The interaction between adaptation and test contrasts leads us to reject the idea that the shape of adaptation contrast dependency of MAE duration reflects that of the sensitivity function of motion detecting mechanisms. The results also suggest a functional similarity between the processes underlying static and flicker MAEs with regard to their responses to contrasts. (C) 1997 Elsevier Science Ltd.

 

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

            "Simultaneous motion contrast across space: Involvement of second-order motion?"

            Vision Res. 37 (2), 199-214 (1997).

 

            ABSTRACT: A static or counterphase (target) grating surrounded by drifting (inducer) gratings is perceived to move in the direction opposite that of the inducers. We compared the relative magnitudes of these simultaneous motion contrasts generated by both first-order and second-order stimuli. The first-order stimuli were sinusoidal luminance-modulations of a uniform field, and the second-order stimuli were sinusoidal contrast-modulations of a random-dot field. When the target was a static grating, the second-order stimuli induced little motion contrast, while the first-order stimuli of the same effective contrast produced clear motion contrast. When the target was a counterphase grating, both first- and second-order stimuli produced clear motion contrast. These results are discussed in relation to the involvement of second-order motion pathways in the relative-motion processing, and the two types of motion after effects obtained with static and dynamic test stimuli. Copyright (C) 1996 Elsevier Science Ltd.

 

132.    S. Nishida, T. Ledgeway, and M. Edwards

            "Dual multiple-scale processing for motion in the human visual system"

            Vision Res. 37 (19), 2685-2698 (1997).

 

            ABSTRACT: A number of psychophysical and physiological studies have suggested that first-and second-order motion signals are processed, at least initially, by independent pathways, and that the two pathways both consist of multiple motion-detecting channels that are each narrowly tuned to a different spatial scale (spatial frequency), However, the precise number and nature of the mechanisms that subserve first-and second-order motion perception in human vision remain both controversial and speculative. We sought to clarify this issue by conducting selective adaptation experiments, in which modulation-depth thresholds for identifying the direction of stimulus motion of first-order (luminance-defined) and second-order (contrast-defined) drifting gratings were measured both prior to and following adaptation to motion, The drift direction, spatial frequency and stimulus type (either first-or second-order) of the adaptation and test stimuli were systematically manipulated, When the adaptation and test stimuli were either both first-order gratings or both second-order gratings, robust elevations of direction-identification thresholds were found and, importantly, these aftereffects exhibited both direction-selectivity and spatial-frequency selectivity, Cross-over-adaptation effects between first-and second-order gratings were also sometimes observed, but were very weak and not spatial-frequency selective, These findings give direct support for the existence of multiple-scale processing for first-and second-order motion in the human visual system and provide additional evidence that the two varieties of motion are initially processed by independent pathways, (C) 1997 Elsevier Science Ltd.

 

133.    S. Nishida and M. Shinya

            "Apparent surface reflectance depends on shape"

            Invest. Ophthalmol. Vis. Sci. 38 (4), 4192-4192 (1997).

 

            ABSTRACT:

134.    T. Nishida and N. Kobayashi

            "Formation of a step-free InAs quantum well selectively grown on a GaAs (111)B substrate"

            J. Electron. Mater. 26 (10), 1214-1220 (1997).

 

            ABSTRACT: We investigated the possibility of forming a step-free quantum well structure. A step-free InAs monolayer was grown on a selectively grown mesa by controlling surface phases with in-situ monitoring of surface photo-absorption. We selectively grew a GaAs buffer at 800 degrees C and cooled the sample keeping the (2 x 2)-like As stabilized surface. Atomic force microscopy (AFM) observation demonstrated that fully step-free surfaces were formed on the 8 mu m wide mesa, Then, a monolayer-thick InAs was formed on this step-free surface and this InAs layer was capped by GaAs under the (2 x 2)-like condition. The quantum Level of the step-free InAs layer was evaluated by spatially resolved photoluminescence (mu PL) measurement. Uniform PL intensity and the lack of a double layer peak indicated the formation of a step-free InAs quantum well, which was in good agreement with AFM observation.

 

135.    T. Nishida and N. Kobayashi

            "A step-free InAs quantum well selectively grown on a GaAs (111)B substrate"

            Appl. Phys. Lett. 70 (20), 2726-2728 (1997).

 

            ABSTRACT: By combining finite-area selective growth and surface stoichiometry control, a step-free InAs quantum well was successfully obtained. An InAs/GaAs quantum-well structure was selectively grown by metalorganic vapor phase epitaxy on a GaAs (111)B substrate masked by a SiO2 pattern. A 100 nm thick and 8 mu m diameter step-free GaAs buffer layer was grown at 800 degrees C and a step-free monolayer of InAs was grown on this surface at 650 degrees C. To eliminate indium segregation during the capping procedure, the InAs layer was buried by GaAs under a stable As-rich condition. The formation of a step-free InAs monolayer quantum well was confirmed by es situ atomic farce microscopy, and this observation was also supported by spatially resolved photoluminescence measurement. (C) 1997 American Institute of Physics.

 

136.    T. Nishida and N. Kobayashi

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

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 36 (3B), 1690-1693 (1997).

 

            ABSTRACT: In this paper we describe the realization of a step-free surface by local metalorganic vapor phase epitaxy (MOVPE) on (111)B GaAs surface. Surface stoichiometry is controlled by employing the surface photo-absorption method (SPA). High-temperature growth at 800 degrees C on stable GaAs (111)B and a cooling procedure under the (2 x 2)-like surface conditions result in a step-free surface exceeding 10 mu m in diameter on the selectively grown GaAs mesa. Low two-dimensional nucleus density on the (111)B surface is demonstrated to illustrate the mechanism by which a wide step-free area is obtained, and step generation due to surface phase transition is also discussed.

 

137.    T. Nishikawa, H. Nakano, H. Ahn, N. Uesugi, and T. Serikawa

            "X-ray generation enhancement from a laser-produced plasma with a porous silicon target"

            Appl. Phys. Lett. 70 (13), 1653-1655 (1997).

 

            ABSTRACT: X-ray generation enhancement from a laser-produced plasma with a porous Si target is reported. For a porous surface formed on a Si wafer, the self-reflectivity of a femtosecond pulse becomes considerably small. The observed energy penetration depth is 25-30 mu m, which is much larger than the skin depth of solid density matter. Using a porous Si target, the threshold of the pre-pulse intensity required for soft x-ray emission enhancement can be reduced. It also contributes to enhance the pre-pulse effect, and soft x-ray generation enhancement ranging from 1.6 to 6.5 times is observed depending on the pre-pulse intensity. (C) 1997 American Institute of Physics.

 

138.    T. Nishikawa and N. Uesugi

            "Walk-off and pump energy dependence of transverse beam profiles on traveling-wave parametric generation"

            Opt. Commun. 140 (4-6), 277-280 (1997).

 

            ABSTRACT: The phase-matching angle and pump energy dependence of transverse beam profiles on traveling-wave parametric generation in KTiOPO4 crystals are numerically calculated and compared with the previously measured results. It is found that the idler beam profile stretches in its walk-off direction and the signal beam profile stretches in the opposite direction as the idler walk-off angle becomes large due to the walk-off and back-conversion effects in the propagation process. It is also found that, even if walk-off does not exist, the transverse beam profile has a manifold ring shape as the pump energy is increased due to repeated conversion and back-conversion. (C) 1997 Elsevier Science B.V.

 

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

            "Gate control of spin-orbit interaction in an inverted In(0.53)Ga(0.47)AS/In(0.52)Al(0.48)AS heterostructure"

            Phys. Rev. Lett. 78 (7), 1335-1338 (1997).

 

            ABSTRACT: We have confirmed that a spin-orbit interaction in an inverted In0.53Ga0.47As/In0.52Al0.48As quantum well can be controlled by applying a gate voltage. This result shows that the spin-orbit interaction of a two-dimensional electron gas depends on the surface electric field. The dominant mechanism for the change in the spin-orbit interaction parameter can be attributed to the Rashba term. This inverted In0.53Ga0.47As/In0.52Al0.48As heterostructure is one of the promising materials for the spin-polarized field effect transistor which is proposed by Datta and Das [Appl. Phys, Lett. 56, 665 (1990)].

 

140.    O. Niwa, T. Horiuchi, and K. Torimitsu

            "Continuous monitoring of L-glutamate released from cultured nerve cells by an online sensor coupled with micro-capillary sampling"

            Biosens. Bioelectron. 12 (4), 311-319 (1997).

 

            ABSTRACT: A small volume L-glutamate online sensor was developed in order to monitor changes in the local concentration of L-glutamate released from cultured nerve cells. Syringe pump in the suction mode is used to sample extracellular fluid continuously from a glass micro-capillary and the concentration of L-glutamate can be determined by using a glassy carbon (GC) electrode modified with an Os-polyvinylpyridine mediator bottom film containing horseradish peroxidase and a bovine serum albumin top layer containing L-glutamate oxidase. The overall efficiency of L-glutamate detection with a sensor is 71% under optimum conditions due to an efficient enzymatic reaction at the modified electrode in the thin layer radial flow cell. As a result, we achieved a detection limit of 7-15 nM and a linear range of 50 nM to 10 mu M. In an in vitro experiment, the extracellular fluid near a particular nerve cell can be sampled with this micro-piper and continuously introduced into the modified GC electrode in the radial flow cell via suction provided by a syringe pump. The nerve cells are stimulated by KCl in a glass capillary and the L-glutamate concentration change can be monitored by changing the distance between the sampling pipet and the nerve cells. (C) 1997 Elsevier Science Limited.

 

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

            "The online sensors for real-time measurement of various neurotransmitters in cultured brain tissue"

            Abstr. Pap. Am. Chem. Soc. 213, 116-ANYL (1997).

 

            ABSTRACT:

142.    A. A. Odintsov, Y. Tokura, and S. Tarucha

            "Precursors of a Mott insulator in modulated quantum wires"

            Phys. Rev. B 56 (20), 12729-12732 (1997).

 

            ABSTRACT: We investigate the transport of interacting electrons through single-mode quantum wires whose parameters are periodically modulated on the scale of the electronic Fermi wavelength. The Umklapp scattering and backscattering of electrons can be described in terms of nonuniform quantum sine-Gordon-like models that also incorporate the effects of electronic reservoirs (electrodes) adiabatically coupled to the wire. We concentrate on weak Umklapp scattering and analyze the precursors of the Mott transition. At half-filling the temperature dependence of the extra resistance Delta R=R-pi (h) over bar/e(2) of a modulated quantum wire of length L changes from the interaction-dependent ''bulk'' power-law Delta R proportional to(4K rho-3) high temperatures (T much greater than v(rho)/L) to the universal versal Delta R proportional to T-2 behavior at low temperatures (T much less than v(rho)/L). Away from half-filling the ''bulk'' results are qualitatively incorrect even at high temperatures v(rho)/L much less than T much less than T* despite the fact that the electron coherence in the wire is absent in this regime.

 

143.    T. Ogino

            "Self-organization of nanostructures on Si wafers using surface structure control"

            Surf. Sci. 386 (1-3), 137-148 (1997).

 

            ABSTRACT: The final goal of nanofabrication on Si wafers is the high-density integration of atomically controlled structures on the wafer scale. This paper describes a scenario for nanointegration through the control of the self-organization processes on the Si surfaces. It is demonstrated here that atomic steps on Si(111) surfaces can be regularly rearranged by using a patterning-assisted control and that Ge quantum-dot networks can be self-ordered by controlling the surface structures. Interface reaction controls to equip Si/Ge nanostructures with buried oxide and silicide layers required for device applications are presented. These techniques form the basis of a new approach for nanostructure integration on the wafer scale. (C) 1997 Elsevier Science B.V.

 

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

            "Step arrangement design and nanostructure self-organization on Si surfaces"

            Appl. Surf. Sci. 117, 642-651 (1997).

 

            ABSTRACT: A novel technique for wafer-scale rt arrangement of atomic steps due to misorientation on the Si(111) surfaces is proposed. The process controls step motion at high temperatures by using patterns formed on the surfaces in advance. With high-temperature annealing, steps originally randomly distributed on the surface are rearranged along the pattern and remain ordered on the surface after the initial pattern has disappeared. During this process, a nanostructure consisting of step-bunched and debunched areas is self-organized and forms a micro-step-network. Another application of this process is the formation of ultralarge-scale step-free surfaces. By controlling step behavior on patterned surfaces, a step spacing as large as 10 mu m can be obtained. This paper also compares heating in an ultrahigh vacuum with furnace annealing in hydrogen atmosphere and shows that both techniques can be used for designing step arrangements.

 

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

            "Ab-initio investigations on diffusion of halogen atoms in GaAs"

            in Defects In Semiconductors - Icds-19, Pts 1-3, Materials Science Forum Vol. 258-2 (Transtec Publications Ltd, Zurich-Uetikon, 1997), pp. 1821-1826.

 

            ABSTRACT: The properties of chlorine and fluorine atoms in GaAs, such as stable configurations, migration paths, charge-state effects, and interaction with dopant atoms are investigated using first-principles total-energy calculations. The stable charge state of an isolated halogen atom is determined as a function of the Fermi energy. We have found that the Cl and F atoms exhibit quite different behaviors. The Cl atom occupies preferentially the bond-center site of a Ga-As bond in the positive charge state, whereas the F atom tends to occupy the tetrahedral interstitial site in the negative charge state. In the Si-doped GaAs, the F atom passivates Si donors more effectively than the Cl atoms.

 

146.    H. Omi and T. Ogino

            "Self-assembled Ge nanowires grown on Si(113)"

            Appl. Phys. Lett. 71 (15), 2163-2165 (1997).

 

            ABSTRACT: We grew coherent Ge islands on Si(113) substrates by molecular beam epitaxy. Atomic force microscopy and reflection high energy electron diffraction were used to examine surface morphology as a function of Ge coverage and growth temperature. The as-grown coherent islands were shaped like wires and formed dense arrays over the entire surface. The islands bounded by {519} facets were elongated in the [33(2) over bar] direction and were linearly ordered across steps. The wire-shaped islands formed when Ge coverage was 5-8 monolayers and the growth temperature was 400-500 degrees C. Cross-sectional transmission electron microscope images confirm that the Ge islands are coherently grown on the Si substrates. The anisotropic shape of the Ge islands was due to an anisotropic strain relief mechanism on Si(113), which had been theoretically predicted. Our findings suggest that the coherent island formation of Ge on Si(113) may be a possible method to fabricate self-assembled Ge nanowires. (C) 1997 American Institute of Physics.

 

147.    Y. Omura, K. Kurihara, Y. Takahashi, T. Ishiyama, Y. Nakajima, and K. Izumi

            "50-nm channel nMOSFET/SIMOX with an ultrathin 2- or 6-nm thick silicon layer and their significant features of operations"

            IEEE Electron Device Lett. 18 (5), 190-193 (1997).

 

            ABSTRACT: This paper demonstrates mesoscopic scale nMOSFET's fabricated by Separation by IMplanted OXygen (SIMOX) technology on a trial basis and describes their explicit quantum-mechanical transport phenomena: enhanced threshold voltage in an extremely thin silicon-on-insulator (SOI) structure and enhanced short-channel effect at room temperature as well as a weak interference (WI) effect at relatively high temperatures (similar to 40 K), which are characterized specifically in extremely thin SOI short-channel devices.

 

148.    P. G. Osborne, O. Niwa, T. Kato, and K. Yamamoto

            "On-line, continuous measurement of extracellular striatal glucose using microdialysis sampling and electrochemical detection"

            J. Neurosci. Methods 77 (2), 143-150 (1997).

 

            ABSTRACT: A sensitive, enzymatic glucose electrode was coupled with the microdialysis sampling technique to enable the continuous, on-line measurement of dialysate glucose. The glucose sensitive electrode was fabricated by immobilizing glucose oxidase onto the surface of an osmium-polyvinylpyrridine horse radish peroxidase gel (Os-gel-HRP) which had been cast coated onto a glassy carbon electrode. This 'bilayer' electrode generated a reductive current to glucose at a potential of 0 mV thereby minimizing faradic oxidative interferences. The system utilized the continuous mixing of two fluids immediately prior to the 'bilayer' electrode. One fluid was the dialysate. The other was an oxygenated, low pH phosphate buffer which minimized oxidative interference, buffered the electrode from variations of pH and maximized enzyme efficiency. In practical terms, the 'bilayer' electrode was simple to manufacture, quick to reach stable basal currents (less than 60 min), sensitive (2.5 mu M glucose could he detected in the dialysate) and durable (usable for up to 3 days). In vivo experiments, used the smallest commercially available microdialysis probes to demonstrate that on-line, continuous measurements of EC striatal glucose in the dialysate were receptive to pharmacological (local perfusion with veratridine (50 mu M), systemic hyperglycemia (1.5 ml of 0.55 M glucose intraperitoneal (IP)) and anesthesia (Nembutal 40 mg/kg IF)) and behavioral (restraint) manipulations. This technique allows for greater temporal resolution than conventional HPLC procedures whilst requiring significantly less technical outlay or analytical expertise. The high sensitivity of the analytical technique could facilitate the study of EC glucose levels in very localized regions of the brain if coupled to microdialysis probes of small dimensions. (C) 1997 Elsevier Science B.V.

 

149.    Z. L. Peng and Y. Horikoshi

            "Surfactant effect of atomic H on Si incorporation in GaAs"

            Appl. Phys. Lett. 70 (5), 604-606 (1997).

 

            ABSTRACT: The effect of atomic H on Si incorporation in GaAs was studied with different substrate orientations in molecular beam epitaxy process. It is found that with the irradiation of atomic H, the changeover As-4/Ga flux ratios for the p- to n-type transition in (111)A and (311)A GaAs are shifted to higher values as if the effective surface As pressure is reduced. The Si-doped (100) GaAs grown at the same time shows n-type conductivity with the electrical activation of almost 100%. Photoluminescence measurements for (311)A samples show great influence by atomic H in the self-compensation region. The irradiation of atomic H helps to lessen the degree of self-compensation in the p-type side but seems to aggravate it in the n-type side of the self-compensation region. (C) 1997 American Institute of Physics.

 

150.    K. Prabhakaran and T. Ogino

            "Oxidation behavior of cobalt silicide and cobalt germanide thin films"

            Appl. Surf. Sci. 121, 213-217 (1997).

 

            ABSTRACT: We report the results of ultraviolet and X-ray photoelectron spectroscopic (UPS and XPS) investigation of the in situ oxidation of thin cobalt silicide and cobalt germanide layers. This sort of study is the first study in the case of cobalt germanide. Oxidation leads to the formation of overlayers of SiO2 and GeO on cobalt silicide and cobalt germanide respectively. Spectral changes indicate that oxygen approach to the silicide and germanide surfaces induces breakage of the Co-Si and Co-Ge bonds. The metal atoms generated through the dissociation process further bond with Si or Ge atoms underneath. This process explains the retention of silicide and germanide layers even after the formation of over layers of the respective oxides. The oxidation process enables in situ fabrication of insulator/metal/semiconductor structures. (C) 1997 Elsevier Science B.V.

 

151.    K. Prabhakaran and T. Ogino

            "Selective bond-breaking and bond-making in oxynitride of Si and Ge: a case of chemical bond manipulation"

            Surf. Sci. 387 (1-3), L1068-L1072 (1997).

 

            ABSTRACT: In this letter, we show that manipulation of the surface chemical bonds is possible by making use of the distinctly different thermodynamic pathways of the various surface species. The dissociation temperatures of Ge-O, Ge-N, Si-O and Si-N bonds are found to be respectively about 360 degrees C, 490 degrees C, 740 degrees C and > 1000 degrees C. These vastly different dissociation temperatures enable one to manipulate the surface chemical bonds. We demonstrate this idea by examining the reaction of Si with a Ge oxynitride film. Deposition of Si on to a thin Ge oxynitride film followed by annealing results in stepwise breaking of Ge-O and Ge-N bonds and formation of Si-O and Si-N bonds. This way, one can achieve formation of the desired species on a full-wafer-scale. Surface spectroscopic techniques such as UPS, XPS and AES are employed for the study. (C) 1997 Elsevier Science B.V.

 

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

            "Formation of buried epitaxial CoSi2 layer through diffusion mediated reaction"

            Appl. Surf. Sci. 117, 280-284 (1997).

 

            ABSTRACT: Interaction of Co with a Ge covered Si(111) surface is studied employing ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS), medium energy ion scattering spectroscopy (MEIS), cross sectional transmission electron microscopy (XTEM), low energy electron diffraction (LEED), reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM). 2 ML of Co is deposited on a Si(111) surface, which is covered with similar to 3 ML of Ge, both at room temperature. On annealing the sample at 460 degrees C, Co diffuses through the Ge layer and reacts with the Si atoms underneath. This results in the formation of a buried CoSi2 layer. XTEM pictures as well as the blocking dip pattern in MEIS suggest that the CoSi2 formed at the interface between Si and Ge, is a B-type epitaxial. The Co layer undergoes agglomeration and forms Ge/CoSi2/Si dot structures and Ge/Si terraces. A mixture of 1 x 1 and 5 x 5 patterns originating, respectively, from Ge/CoSi2/Si and Ge/Si regions are observed in RHEED and LEED. The results open up a novel way of fabrication of buried epitaxial metallic layers and semiconductor/metal nanostructures.

 

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

            "Fabrication of buried epitaxial CoSi2 layer through selective diffusion"

            Appl. Phys. Lett. 70 (5), 607-609 (1997).

 

            ABSTRACT: The incorporation of metallic layers into the bulk of semiconductors is gaining tremendous attention for device applications. This is mainly achieved by ion beam synthesis. In the ultrathin film regime, however, this technique is not practical due to the damage incurred. Here we report a technique by which fabrication of buried epitaxial CoSi2 is achieved by making use of the selective diffusion behavior of Co. Co atoms diffuse through a Ge overlayer on a Si(lll) substrate and are terminated by reaction with the Si atoms underneath. Ion scattering as well as high resolution microscopy results confirm that the CoSi2 layer thus formed is in epitaxial form. This method would help in providing functionality to nanostructure based devices. (C) 1997 American Institute of Physics.

 

154.    M. P. Risse, M. G. Aikele, S. G. Doettinger, R. P. Huebener, C. C. Tsuei, and M. Naito

            "Dissipation in the superconducting mixed state in the presence of a small oscillatory magnetic-field component"

            Phys. Rev. B 55 (22), 15191-15196 (1997).

 

            ABSTRACT: We have studied the electric resistivity in superconducting amorphous Mo3Si films in a perpendicular magnetic field B-0 + B-1 sin omega t with B-1 much less than B-0. For B-1 = 0 a resistive voltage only appeared due to flux creep above the critical current I-c. For B-1 > 0 we observed perfectly Ohmic behavior at currents I much less than I-c (B-1 = 0), with the resistivity increasing proportional to omega and B-1. We present a simplified model discussion explaining our results in terms of the magnetic flux transferred across the sample during each cycle of the oscillatory magnetic field because of the electric transport current.

 

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

            "Photoluminescence characteristics of nitrogen atomic-layer-doped GaAs grown by MOVPE"

            J. Cryst. Growth 170 (1-4), 372-376 (1997).

 

            ABSTRACT: Nitrogen atomic-layer-doped and uniformly doped GaAs were grown by MOVPE using dimethylhydrazine on a (001) plane. They showed several sharp photoluminescence lines with a full width at half maximum less than 1 meV at 8 K. Compared with uniformly doped GaAs, the photoluminescence intensity of the nitrogen-related line at the longest wavelength is enhanced in nitrogen atomic-layer-doped GaAs, suggesting that it is easier to form nitrogen pairs during atomic layer doping. To investigate the sharp nitrogen-related lines, we also grew GaAs with double atomic-layer-doped planes and varied the distance between the two planes. When the two planes are brought close to 1 nm, two new lines, NNC, and NND, appear between the two nitrogen-related lines, NNA and NNB, observed in a single nitrogen atomic-layer-doped GaAs. The NNC and NND lines are also observed in uniformly doped GaAs. Therefore, NNA and NNB originate from excitons bound to pairs of nitrogen atoms, both of which are in the (001) plane, while NNC and NND originate from those bound to pairs of nitrogen atoms, of which pairing directions are not included in the (001) plane. From the photoluminescence characteristics, distances between nitrogen atoms of a pair are estimated for each line.

 

156.    T. Saitoh, T. Sogawa, and H. Kanbe

            "Low-temperature dry etching of GaAs and AlGaAs using 92-MHz anode-coupled chlorine reactive ion etching"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 36 (12B), 7650-7654 (1997).

 

            ABSTRACT: The etching characteristics and the damage induced by low-temperature etching have been studied using 92-MHz anode-coupled reactive ion etching. Due to the suppression of sidewall etching, vertical profiles of GaAs and AlGaAs have been obtained by lowering the substrate temperature during etching. The etching rates of GaAs and AlGaAs become identical at low temperatures. The exciton peak intensity in the photoluminescence spectrum decreased with a decrease in etching temperature, suggesting a slight increase in damage in low-temperature etching. It is also found that pronounced stoichiometry change in the subsurface region takes place in low-temperature etching.

 

157.    E. Sano, Y. Hirayama, and Y. Horikoshi

            "Selenium doped high-index GaAs epilayers grown by molecular beam epitaxy"

            Microelectron. J. 28 (8-10), 743-747 (1997).

 

            ABSTRACT: Using elementary Se we grew Se-doped GaAs films on GaAs (111), (411), (711) and (100) substrates by molecular beam epitaxy. The films grown on all the high-index substrates showed n-type conduction and the maximum carrier concentration reached 2.1x10(19) cm(-3) for the film grown on the (411)B substrate. The carrier concentration began to saturate at a Se concentration near 10(19) cm(-3) but continued to increase up to a Se concentration of 2x10(20) cm(-3). Above 2x10(20) cm(-3) Se concentration, slow reduction of the carrier concentration was observed. We obtained excellent surface morphology when n-type GaAs films were grown on (411)A and (711)B substrates even at a Se concentration of 7x10(20) cm(-3). (C) 1997 Elsevier Science Ltd.

 

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

            "Electronic properties of K3C60 studied by C-13 nuclear-magnetic-resonance spectra"

            Physica C 278 (3-4), 223-237 (1997).

 

            ABSTRACT: C-13 nuclear-magnetic-resonance (NMR) spectra are obtained to investigate the electronic properties of a superconducting fulleride K3C60. Asymmetric line shapes below 235 K are reproduced by the powder patterns of anisotropic NMR frequency shifts (K-i) of electronic single-site. The temperature (T) dependence of K-i indicates that the C-13 hyperfine coupling (A(spin)) has both an isotropic part (A(iso)(spin)) and an anisotropic part (A(ax)(spin)) with A(iso)(spin)/A(ax)(spin) = 0.78. Substantial decrease in the spin susceptibility (i.e. chi(spin)(T-c)/chi(spin)(300 K) = 0.55) is not explained by the lattice contraction alone. The Knight shift values can be deduced experimentally without assuming the chemical shift values, since our analysis shows that the line shapes below T-c are affected negligibly by the magnetic-field distribution, which is consistent with the large penetration depth. We also showed the validity and consistency of our analysis. (C) 1997 Elsevier Science B.V.

 

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

            "C-13 spin-lattice relaxation study on the electronic properties of K3C60"

            Physica C 278 (3-4), 238-257 (1997).

 

            ABSTRACT: C-13 spin-lattice relaxation was measured for a superconducting fulleride K3C60. It is found that non-single exponential relaxation (NSER) data at low temperatures (T < 55 K), which have a T-independent shape above and below T-c, are well reproduced by only the anisotropy parameter (alpha(spin)) for the hyperfine coupling that was derived from a line-shape analysis. From the simulation for various values of alpha(spin), the shape of the NSER, as well as the asymmetric line shapes, is found to be caused by the anisotropy of an electronic single-site rather than electronic multi-sites. By extracting the isotropic part of relaxation time, (T-1)(iso), from the NSER, it is found that an extended Korringa relation holds up to 300 K with K(alpha) = 7.4, and that the T dependence of [(T-1)(iso)T](-1) results from a decrease in the density of states. Below T-c, a broadened Hebel-Slichter coherence peak is observed, which means s-wave Cooper pairing. The T dependence of [(T-1)(iso)T](-1) below T-c is well reproduced by a theoretical prediction with the superconducting gap 2 Delta(0)/k(B)T(c) = 4.3. The origin of the isotropic hyperfine coupling is also discussed. (C) 1997 Elsevier Science B.V.

 

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

            "Superconducting thin films of La2CuO4+delta by oxygen doping using ozone"

            Physica C 280 (3), 178-186 (1997).

 

            ABSTRACT: Superconducting (001) thin films of La2CuO4+delta were synthesized by cooling in ozone gas, demonstrating that this simple process produces a strong oxidizing environment. The films cooled in ozone gas until 150 degrees C exhibit the superconducting onset temperature of 52 K and the zero-resistance temperature of 48 K on LaSrAlO4 substrates. The room-temperature resistivity is as low as 500 mu Ohm cm for these films, indicating that they were homogeneously oxidized. The superconducting transition temperatures for the films on LaSrAlO4 substrates are higher than those for the films on SrTiO3 substrates, suggesting a strain effect caused by lattice mismatch with the substrates, which was investigated by X-ray diffraction. Surface analysis by reflection high energy electron diffraction and photo-emission spectroscopy indicate that degraded layers were formed on the surfaces of the films during the oxidation process. The thickness of these degraded layers seems to be much less than 50 Angstrom because they do not seriously affect the resistivity of the films with thickness of 50 Angstrom. (C) 1997 Elsevier Science B.V.

 

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

            "Growth of (001)La1.85Sr0.15CuO4 ultrathin films without buffer or cap layers"

            Physica C 274 (3-4), 227-231 (1997).

 

            ABSTRACT: We report the growth of (001) La1.85Sr0.15CuO4 films with thicknesses less than 5 unit cells on LaSrAlO4 substrates without any buffer or cap layers. Results of surface analyses indicate that all samples with 0.5-unit-cells-thick films are well crystallized and have a finite density of states at the Fermi level. Films 4 unit cells thick show bulk-like transport properties and T-c(R = 0). T-c disappears in films with thicknesses less than 2 unit cells, suggesting that the minimum number of CuO2 planes necessary for superconductivity in LSCO is less than or equal to four, (C) 1996 Elsevier Science B.V.

 

162.    M. Sato

            "Carrier density of epitaxial InN grown by plasma-assisted metalorganic chemical vapor deposition"

            Jpn. J. Appl. Phys. Part 2 - Lett. 36 (6A), L658-L660 (1997).

 

            ABSTRACT: InN epitaxial layers were grown an (0001) sapphire substrates bg plasma-assisted metalorganic chemical vapor deposition, by which large amounts of radicals can be supplied to a surface with little ion damage, using triethylindium and nitrogen radicals as the precursors, Low carrier densities were achieved at a growth temperature of 600 degrees C, which was the highest temperature to grow InN without forming In droplets. Probably because of the slow reaction rate of In-N bond formation; lowering the growth rate was more important than increasing the nitrogen-radical flux. A carrier density of only 4 x 10(19) cm(-3) R as achieved.

 

163.    M. Sato

            "Epitaxial growth of InN by plasma-assisted metalorganic chemical vapor deposition"

            Jpn. J. Appl. Phys. Part 2 - Lett. 36 (5B), L595-L597 (1997).

 

            ABSTRACT: InN epitaxial films were grown on (0001) sapphire substrates by plasma-assisted metalorganic chemical vapor deposition, by which large amounts of radicals can be supplied to a surface with less ion damages; using triethylindium and nitrogen radicals as the precursors. When argon was used as a carrier gas, InN having a rough surface with a lot of indium droplets was grown. When hydrogen was used, the InN surface was specular and few droplets were found. InN was grown in hydrogen at a low temperature of 400 degrees C where no growth occurred in argon. These results suggest that the carrier gas influences the InN growth and that hydrogen enhances both the decomposition of organometallics and the removal of excess metal atoms at the growing surface.

 

164.    M. Sato

            "Nitrogen radical densities during GaN growth by molecular beam epitaxy, plasma-assisted metalorganic chemical vapor deposition, and conventional metalorganic chemical vapor deposition"

            Solid-State Electron. 41 (2), 223-226 (1997).

 

            ABSTRACT: N-radical densities during GaN growth were numerically estimated from the recombination rates of the radicals. In MBE, the lifetime of radicals is so long that almost all radicals effused from a radical source are supplied to a surface. At pressures of 10-100 Pa where plasma-assisted MOCVD is performed, the lifetime of the radicals is of the same order as the flight time of the radicals from the cell to a substrate. Because a larger N-2 flow rate is possible, higher radical flux can be achieved more easily than by MBE. In conventional MOCVD, the radicals formed in the vapor phase cannot be the dominant N-source of the GaN growth. Heterogeneous decomposition of NH3, which is preferentially adsorbed by an electron acceptor (Ga atom), is the dominant reaction path to create N atoms for GaN growth. (C) 1996 Elsevier Science Ltd.

 

165.    M. Sato

            "Critical layer thickness of GaN thin layers embedded in GaAs"

            Solid-State Electron. 41 (2), 323-326 (1997).

 

            ABSTRACT: GaAs/GaN/GaAs thin-layer structures were grown by plasma-assisted low-pressure metalorganic chemical vapor deposition. GaN layers were formed by exposing the surfaces of GaAs epitaxial layers to nitrogen-radical fluxes. When the nitrogen amount exceeded that in one-monolayer-thick GaN, drastic deterioration of the GaN/GaAs interfaces and the GaAs cap layers were observed by X-ray diffraction, etch-pit-density measurement and transmission electron microscopy. This suggests that the critical layer thickness of GaN embedded in GaAs is one monolayer thick. (C) 1997 Elsevier Science Ltd.

 

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

            "Evaluation of strained InGaAs/GaAs quantum wells by atomic force microscopy"

            Appl. Phys. Lett. 70 (9), 1134-1136 (1997).

 

            ABSTRACT: Atomic force microscopy (AFM) is adopted for evaluation of strained InGaAs/GaAs quantum well structures grown by metalorganic vapor phase epitaxy. InAs-rich clusters are formed at the upper interface when the structure is grown with excessive supply of the In precursor. The defects arising from the clusters are clearly observed as convex domains from the irregularity of monolayer steps. The density of the convex domains coincides with the dark spot density measured by cathodoluminescence. Photoluminescence intensity is drastically reduced at high density of this type of defects. Thus, AFM measurements are able not only to give information on the structural quality but also to provide an estimation of the optical quality of such InGaAs/GaAs structures. (C) 1997 American Institute of Physics.

 

167.    K. Semba and A. Matsuda

            "Vanishingly small Maki-Thompson superconducting fluctuation in the magnetoresistance of high-T-c superconductors"

            Phys. Rev. B 55 (17), 11103-11106 (1997).

 

            ABSTRACT: The magnetoresistance (MR) of high-T-c cuprate superconductors (HTSC's) is Studied. We have shown that the Zeeman term of the Maki-Thompson (MT) process could not be detected in the longitudinal MR of 90 K YBCO crystals. We show here that the MT process is thought to be also negligible in the transverse MR of 90 K and Zn-doped YBCO crystals. The MR, which has been assigned previously to a MT-orbital process, is more naturally understood as normal-state orbital MR that is proportional to the square of the Hall angle. We conclude that the MT-fluctuation is vanishingly small, at least above T-c, in these HTSC's. In addition to the Hall measurements, MR measurements also support the hypothesis of two distinct relaxation times in HTSC's.

 

168.    H. Shibata and T. Yamada

            "Far-infrared transmission spectra in high-T-c superconductors"

            Physica C-Superconductivity And Its Applications 293 (1-4), 191-195 (1997).

 

            ABSTRACT: Far-infrared transmission spectra of various high-T-c superconductors are measured down to 7.5 cm(-1). The superconducting plasma resonance along the c-axis is found in Bi1.85Pb0.35Sr2Ca2Cu3.1Oy, La1.82Ca1.18Cu2O6+delta, (Nd0.66Sr0.205Ce0.135)(2)CUO4 (T-* phase), (Ba0.56Sr0.44)(2)CU1.1O2.2+delta(CO3)(0.9), Pr1.85Ce0.15CUO4 Nd1.85Ce0.15CuO4, as well as in La2-xSrxCuO4, YBa2Cu3O6+x (T-c approximate to 60 K) and YBa2Cu4O8, which reveals that the plasma exists in most high-T-c, superconductors. The existence of the sum rule of absorption between the normal state and superconducting state is shown. Substitution effects on the resonance are also investigated in YBa2(Cu1-zMz)(3)O-6.66 (M = Zn, Co, Ni). Through Zn substitution, the resonance frequency and its oscillator strength strongly decrease and the peak becomes broad, indicating both an increase in junction resistivity and a pair breaking effect. However, no pair breaking effect is observed in the case of Co substitution. (C) 1997 Elsevier Science B.V.

 

169.    H. Shibata and T. Yamada

            "Far-infrared spectra along the c axis in high-T-c superconductors"

            Ferroelectrics 203 (1-4), 179-185 (1997).

 

            ABSTRACT: Recent studies of infrared spectra along the c axis in high temperature cuprate superconductors are reviewed. The most prominent features are the existence of the plasma resonance in the superconducting state and its absence in the normal state, which are common in most of high-T-c superconductors. The various methods for observing the plasma and the features of these methods are briefly reviewed. The resonance are discussed based on the Josephson-coupled layer model, and the resonance frequencies and the c-axis penetration depth lambda(c) for the various high-T-c superconductors are summarized.

 

170.    H. Shibata and T. Yamada

            "Far-infrared reflectivity along the c axis in La2CuO4+delta, La1.89Ca1.11Cu2O6+delta, and Nd2CuO4-xF4 single crystals"

            Phys. Rev. B 56 (22), 14275-14278 (1997).

 

            ABSTRACT: The far-infrared reflectivity along the c axis in La2CuO4+delta, La1.89Ca1.11Cu2O6+delta (double pyramidal planes), and Nd2CuO4-xFx (T' phase) single crystals is measured down to 9 cm(-1). All the insulating spectra in the normal states change to show a sharp plasma edge in the superconducting state, which confirms our earlier report of sphere resonance of powder samples [Shibata and Yamada, Phys. Rev. B 54, 7500 (1996)]. The edge of La1.89Ca1.11Cu2O6+delta is broader than that of La2CuO4+delta and Nd2CuO4-xFx, indicating the existence of a large number of unpaired carriers in the superconducting state. The obtained c-axis penetration depth lambda(c) is discussed based on the Josephson-coupled layer model.

 

171.    K. Shiraishi and T. Ito

            "Atomic and electronic structures of surface kinks on GaAs(001) surfaces"

            Appl. Surf. Sci. 121, 98-101 (1997).

 

            ABSTRACT: We investigate the atomic and electronic structures of surface dimer kinks using the ab initio calculations. We investigated the (2 x 4) and the c(2 x 8) dimer kink models. The calculated results show that weak As dimers are formed at (2 x 4) dimer kinks by the de-stabilization of occupied As dangling bond states and that (2 x 4) dimer kinks become favorite Ga adsorption sites during epitaxial growth. On the other hand, no weak As dimers are formed at c(2 x 8) dimer kinks. However, Ga adsorption at the c(2 x 8) dimer kinks induces the weak As dimer formation. Consequently, c(2 x 8) dimer kinks also act as reactive Ga adsorption sites during epitaxial growth as well as the (2 x 4) dimer kinks. (C) 1997 Elsevier Science B.V.

 

172.    M. Shoji and S. Horiguchi

            "Phonon-limited inversion layer electron mobility in extremely thin Si layer of silicon-on-insulator metal-oxide-semiconductor field-effect transistor"

            J. Appl. Phys. 82 (12), 6096-6101 (1997).

 

            ABSTRACT: Phonon-limited inversion layer electron mobility in extremely thin (100) Si layers of silicon-on-insulator field-effect transistors has been studied at 300 K using a relaxation time approximation and a one-dimensional self-consistent calculation. For the Si layer thickness t(Si) of more than approximately 5 nm, the mobility behavior as a function of an effective vertical electric field is found to be almost identical with that of bulk Si inversion layers. For a thickness of less than that, however, the mobility behavior is considerably affected by the change in the electronic structures due to a confinement effect. As the Si layer thickness decreases, the phonon-limited electron mobility mu(ph) increases to a maximum at t(Si) of similar to 3 nm and decreases monotonically. The increase in mobility results from the increase of the fraction of electrons in the lowest energy subband that has a higher mobility than other subbands. The mobility decrease in the extremely thin t(Si) region is attributed to the enhancement of phonon scattering rates caused by a reduction of the spatial widths of the subbands. (C) 1997 American institute of Physics.

 

173.    M. Shoji, Y. Omura, and M. Tomizawa

            "Physical basis and limitation of universal mobility behavior in fully depleted silicon-on-insulator Si inversion layers"

            J. Appl. Phys. 81 (2), 786-794 (1997).

 

            ABSTRACT: The physical basis and the limitation for the universal mobility behavior of fully depleted silicon-on-insulator (SOI) metal-oxide-semiconductor Si inversion layers are shown by means of an analysis of the electronic states (potential profile, subband structure, and electron density distribution). As long as the top Si layer thickness is larger than the inversion layer thickness and the electron density is much higher than the impurity concentration in the inversion region, it is proved that the electronic states of an SOI Si inversion region are equivalent to those of a certain bulk Si inversion region. In this context, the definition of the effective vertical electric field E(eff), for SOI inversion layers is derived and it ensures the identical mobility dependence on E(eff) for SOI and bulk Si inversion layers. The effective carrier mobility mu(eff) behavior in SOI Si inversion layers is universal, irrespective of structural parameters or back gate voltages, over the E(eff) range where the mobility is essentially limited by phonon scattering and/or surface roughness scattering at the upper interface. On the other hand, when the electron density distribution of the inversion region reaches the lower surface of the top Si layer sufficiently, it is predicted that the universal mobility behavior is not maintained, but there exists another kind of mobility behavior which is dependent on the top Si layer thickness. Moreover, self-consistent calculations for the electronic states clarify the range where the equivalence of the electronic states for SOI and bulk Si inversion regions holds as function of the effective field E(eff), the top Si layer thickness, and the top Si layer impurity concentration. The phonon-limited mobility is also evaluated to confirm the equality of the mobility for SOI and bulk Si inversion regions. (C) 1997 American Institute of Physics.

 

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

            "Interband optical transition spectra in GaAs quantum wires with rectangular cross sections"

            Phys. Rev. B 56 (4), 1958-1966 (1997).

 

            ABSTRACT: Interband optical transition spectra of rectangular GaAs quantum wires (QWR's) of various cross-sectional sizes are experimentally and theoretically studied. High-quality GaAs QWR's with lateral sizes below 20 nm are formed in AlAs trench structures with (110) vertical sidewalls by using metal-organic chemical vapor deposition. Polarization-dependent photoluminescence excitation (PLE) spectra in the QWR's clearly exhibit absorption peaks corresponding to optical transitions between quantized one-dimensional conduction and valence subbands. It is found that transition strengths and polarization anisotropies in the lowest- and higher-energy PLE peaks significantly vary, depending on the cross-sectional shape of the rectangular wires. The polarization-dependent interband transition matric; elements and the detailed absorption spectra are calculated by a multiband effective-mass theory considering heavy-hole and light-hole subband mixing. The theoretical results clarify the physical origin of observed PLE peak and explain the strong dependence of interband transition properties on the cross-sectional ratio of QWR's.

 

175.    M. Sugiyama and S. Maeyama

            "Sulfur-adsorbed GaAs(001) surface studied by X-ray absorption near edge structure, X-ray standing waves and X-ray diffraction"

            Surf. Sci. 385 (1), L911-L916 (1997).

 

            ABSTRACT: Sulfur-adsorbed GaAs(001)-(2 x 6) surface was studied by X-ray absorption near edge structure (XANES), X-ray standing waves (XSW) and X-ray diffraction. Strong polarization dependence in S K-edge XANES spectra revealed that most of the sulfur atoms are located in the top layer and form Ga-S-Ga bridge bonds. The XSW results showed the three-dimensional adsorption site of the sulfur atoms to be a bridge site. The sulfur atomic layer was determined to be ca 1.1 Angstrom above the ideal second Ga layer. The crystal truncation rod (CTR) scattering profile near the (002) reflection of the GaAs substrate could not be explained by the unrelaxed Ga layer model. We propose that lattice distortion of the subsurface region is induced by sulfur adsorption. (C) 1997 Elsevier Science B.V.

 

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

            "Energy loss and straggling for 50- and 100-keV H+ ions passing through the Si(001)2x1-Sb surface"

            Phys. Rev. B 56 (11), 7011-7017 (1997).

 

            ABSTRACT: Surface stopping powers were measured for 50- and 100-keV H+ ions passing through the Si(001)2 X 1-Sb surface. The energy losses as a function of the exit angle are fit successfully by a simple relationship involving the time spent near the surface. The fitting parameter is in agreement with the value expected from the bulk Sb stopping cross section and the areal Sb density. This result suggests continuity of the stopping power from the bulk to the surface. It provides a useful method for determining the distance between the plane of deposited atoms and of a substrate surface and for measuring the composition of the topmost atomic layer. The estimated energy loss by surface-plasmon excitation is negligibly small in the present system. The energy straggling as a function of exit angle was also measured for 50- and 100-keV Ht incidence and the results are compared here with the bulk straggling values.

 

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

            "Structure analysis of Ge dimer on Si(001) by medium-energy ion scattering blocking profiles from embedded Ge layers"

            J. Vac. Sci. Technol. A-Vac. Surf. Films 15 (3), 1537-1541 (1997).

 

            ABSTRACT: We propose a novel technique for determining the surface structure quantitatively and accurately by modifying the substrate, and apply it to the structure analysis of Ge dimers on the Si (001) surface. One or two atomic layers of Ge were embedded below 4-12 ML of Si overlayer by molecular-beam epitaxy and with atomic scale layer precision. The ions scattered from embedded Ge layers are blocked by the reconstructed surface atoms. Since the origin of the signals are restricted, the scattering-blocking pairs are uniquely assigned. In addition, the effect of thermal vibration can be minimized by choosing a distance between scattering and blocking atoms that is suitable for analysis. Therefore, we can observe the sharp and simple blocking profile of embedded Ge signals, and can determine the atomic displacements of reconstructed surfaces. The bond length of the Ge-Ge dimer on Si (001) surface was determined by this method to be 2.4 Angstrom. (C) 1997 American Vacuum Society.

 

178.    H. Suzuki

            "Behavior of charge carriers and excitons in poly(methylphenylsilane) as investigated by electroluminescence from single-layer-light-emitting diodes"

            J. Lumines. 72-4, 1005-1006 (1997).

 

            ABSTRACT: The electroluminescent (EL) process of light-emitting diodes (LEDs) made from poly(methylphenylsilane) (PMPS) was studied. The current-voltage-El intensity (I-V-EL) curves and the effects of defect concentrations at the interface between PMPS and electron-injecting electrodes (EIEs) on the EL characteristics were analyzed at temperatures between 28 and 294 K.

 

179.    H. Suzuki

            "Light-emitting diodes based on silicon-backbone polymers"

            Mol. Cryst. Liq. Cryst. Sci. Technol. Sect. A-Mol. Cryst. Liq. Cryst. 294, 127-132 (1997).

 

            ABSTRACT: Recently near-ultraviolet electroluminescence (EL) was observed from a typical Si-backbone polymer, poly(methylphenylsilane) (PMPS). This study investigates the dependence of the EL characteristics on temperature, the electron injecting electrodes and the ''defect'' concentration at the interface between PMPS and electron injecting electrodes, in order to clarify the EL process in PMPS-LEDs.

 

180.    K. Suzuki, K. Saito, T. Saku, and Y. Hirayama

            "Optically detected cyclotron resonance by multichannel spectroscopy"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 36 (2), 926-929 (1997).

 

            ABSTRACT: We developed a novel setup which includes a multichannel detector for optically detected cyclotron resonance. It can be used to record all photoluminescence (PL) spectra under far-infrared radiation at various magnetic fields. Using this setup, intensity changes can be monitored as a function of the magnetic field simultaneously for all recombination peaks. This system is useful not only for high-sensitivity and high-resolution measurement of cyclotron resonance, but also for studying recombination processes.

 

181.    M. Suzuki, K. Tanabe, M. Itoh, S. Karimoto, K. Tsuru, and K. Namekawa

            "Tunneling characteristics for thin stacks of Bi2Sr2CaCu2O8 intrinsic Josephson junctions above and below T-c"

            Physica C-Superconductivity And Its Applications 293 (1-4), 124-129 (1997).

 

            ABSTRACT: We report tunneling characteristics of two very thin stacks, each about 23 and 27 nm thick, of intrinsic Josephson junctions fabricated on the surface of Bi2Sr2CaCu2O8 single crystals at various temperatures above and below T-c. The current-voltage (I-V) characteristics are represented by a set of 15-18 resistive branches, the number of which corresponds to the stack thickness divided by the CuO2 bilayer separation of 1.5 nm. In the quasiparticle I-V curve, a clear gap structure with an almost linear portion above the gap is seen at 18 and 28 meV per single junction for respective stacks. Above T-c, the I-V curve still exhibits nonlinearity up to about 180 K. This nonlinearity is interpreted in terms of a pseudogap which evolves below a certain temperature in this system. (C) 1997 Elsevier Science B.V.

 

182.    M. Suzuki, K. Tanabe, S. Karimoto, and Y. Hidaka

            "Tunneling characteristics of Bi-Sr-Ca-Cu-O intrinsic Josephson junctions"

            IEEE Trans. Appl. Supercond. 7 (2), 2956-2959 (1997).

 

            ABSTRACT: Tunneling-type current-voltage (I - V) characteristics with a clear energy gap structure have been observed for very thin intrinsic Josephson junction stacks fabricated on the surface of underdoped Bi2Sr2CaCu2O8 single crystals with the CuO2 bilayer numbers of 27, 18, and 9, It is found that the nonequilibrium heating effect is significant in this layered material, and that an increase in the number of CuO2 bilayers or a decrease in the c-axis resistivity leads to significant gap suppression and negative resistance. The tunneling properties are characterized by the three points: (I) the energy gap suppression by the nonequilibrium superconductivity effect, (2) a large subgap conductance, and (3) an extraordinarily small maximum Josephson current compared with the BCS value. Numerical calculation shows that the observed I - V curves are consistent with the two-dimensional d-wave order parameter with the gap suppression due to the nonequilibrium effect.

 

183.    Y. Y. Suzuki

            "Small bipolaron conductivity in the Holstein-Hubbard model"

            J. Phys. Soc. Jpn. 66 (2), 306-309 (1997).

 

            ABSTRACT: We examine a narrow-band Holstein-Hubbard model where electrons are coupled to a local lattice distortion and form small polarons. When the on-site Coulomb interactions are overscreened by strong electron-phonon coupling, the polarons attract each other through the effective potential, bind into pairs, and form small bipalarons. The optical conductivity of small bipolaron is calculated as a function of frequency, electron density, and temperature, within a limited temperature and parameter range.

 

184.    A. Taguchi and H. Kageshima

            "Atomic configuration of oxygen negative-U center in GaAs"

            in Defects In Semiconductors - Icds-19, Pts 1-3, Materials Science Forum Vol. 258-2 (Transtec Publications Ltd, Zurich-Uetikon, 1997), pp. 873-878.

 

            ABSTRACT: We investigated the atomic configuration of an oxygen negative-ii center in GaAs, which has a Ga-O-Ga structure, by using an ab-initio pseudopotential method. We calculated stable atomic configurations and formation energies for two possible Ga-O-Ga structures: Ga{O-V-AS}-Ga and Ga-O-i-Ga. The three charge states 0, 1-, and 2- were considered. For both O-V-Ga and Ga-O-i-Ga structures, the stable atomic configuration depends on the charge state. For the Ga-O-i-Ga structure, the configuration change due to the change in the charge state shows the same tendency as that observed in infrared local-vibrational-mode absorption measurements. On the other hand, the configuration change in the O-V-As structure does not show the same tendency. The calculated formation energy shows that the O-V-As structure does not have the negative-U nature, but the Ga-O-i-Ga structure does. These results show that the Ga-O-i-Ga structure is that of the oxygen negative-U center in GaAs, although the O-V-As structure has been thought to be the structure.

 

185.    A. Taguchi and T. Ohno

            "Erbium in GaAs: Coupling with native defects"

            Phys. Rev. B 56 (15), 9477-9487 (1997).

 

            ABSTRACT: We calculated the total energy of Er point defects in GaAs and of Er defects coupled with native defects in GaAs by the ab initio pseudopotential method. The total-energy calculation indicates that various coupled defects comprising an Er atom and native defects will be formed depending on the growth conditions and the Fermi-level position. By investigating the valence charge distribution, it was found that an Er atom forms a strong bond with an As atom. This chemical feature and the lattice relaxation around the coupled defect are the main factors that stabilize the coupled states. The intra-4f-shell luminescence spectrum of Er in GaAs is generally complicated and strongly depends on sample preparation methods and growth conditions. We propose that this tendency is due to the sample-dependent concentration of various defects that form complexes with Er.

 

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

            "Energy transfer rate between erbium 4f shell and Si host"

            in Defects In Semiconductors - Icds-19, Pts 1-3, Materials Science Forum Vol. 258-2 (Transtec Publications Ltd, Zurich-Uetikon, 1997), pp. 1491-1496.

 

            ABSTRACT: We estimated the energy transfer rate between an erbium (Er) 4f shell and a Si host by analyzing the temperature dependence of the decay time of the Er 4f-shell luminescence and its time response at low temperature. We assumed that thermal quenching of the Er luminescence is due to an energy back-transfer mechanism and that the energy transfer is assisted by a non-radiative multiphonon process. Based on these assumptions, the energy transfer rate was estimated to be 2x10(8) s(-1) from the temperature dependence of the decay time. We also measured the time response of the luminescence after the pulsed host excitation and the energy transfer rate was estimated to be larger than 1x10(7) s(-1). These results shows that the energy transfer rate for Si:Er is not so small as 10(4) similar to 10(6) s(-1) as had been suggested by several previous studies.

 

187.    Y. Takagaki

            "Selective suppression of transmission resonance in a double-antidot system"

            Phys. Rev. B 55 (24), 16021-16024 (1997).

 

            ABSTRACT: The results of a numerical calculation on the magnetoresonant transmission mediated by two antidots in a quantum wire are presented. When the antidots and the wire boundary are separated such that atomiclike and molecularlike closed orbits coexist around the antidots, the transmission resonance exhibits two magnetic-field periods corresponding to the two kinds of orbits. The resonance originating from the molecularlike orbit is found to vanish rapidly when a potential disorder is introduced. The atomiclike orbit thus dominates the transmission characteristics, in agreement with a recent experiment by Gould et al. [Phys. Rev. Lett. 77, 5272 (1996)]. Strong disorder-induced cancellation of the resonant transmission and reflection for the molecularlike orbit is responsible for the selective suppression.

 

188.    Y. Takagaki, R. Hey, L. Daweritz, K. Ploog, and S. Tarucha

            "Weak antilocalization in Si delta-doped InxGa1-xAs systems"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 36 (4A), 2212-2213 (1997).

 

            ABSTRACT: We have investigated the transport properties of a quasi-two-dimensional electron gas in Si delta-doped InxGa1-xAs/GaAs (001) systems with x = 0.2 and 0.3 at T = 0.3-3 K. A large electron density of 8.4 X 10(16) m(-2) is obtained for the doping density 10(17) m(-2). We have evluated the phase breaking time and the spin-orbit scattering time by means of the weak antilocalization effect. The two-dimensional electron-electron interaction in disordered systems is found to be responsible for the dephasing.

 

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

            "Splitting of resistance peaks and anomalous Hall plateaus in asymmetric double-quantum-well structures"

            Phys. Rev. B 56 (3), 1057-1060 (1997).

 

            ABSTRACT: The integer quantum Hall effect in asymmetric double-quantum-well structures is investigated. The resistance peaks associated with the Landau levels of the ground subband generate subpeaks when the excited subband is filled with electrons. The split-off peaks shift to higher magnetic fields with increasing electron density. For magnetic fields between the parent and split-off peaks, the Hall resistance shows plateaulike structures. Some of the features can be explained in terms of the crossing of Landau levels originating from the ground and excited subbands at the Fermi energy, although there remain several discrepancies. A self-consistent potential calculation indicates that a fluctuation of the total electron density gives rise to the phenomena.

 

190.    Y. Takagaki and S. Tarucha

            "Collapse of quantized Hall plateaus in asymmetric double-quantum-well systems"

            Semicond. Sci. Technol. 12 (6), 715-721 (1997).

 

            ABSTRACT: The integer quantum Hall effect in asymmetric double-quantum-well structures is investigated for electron concentrations which are varied up to around the population threshold of the excited subband. The scattering time of electrons in the system is shown to be governed by the interface roughness. The ratio between the transport and single-particle scattering times is used to evaluate the fluctuations in the interface. We map out a phase diagram of spin-polarized and spin-unpolarized states. When the Fermi energy is raised to the bottom of the second subband, the resistance peak for the Landau level filling factor nu between 2 and 3 broadens and the nu = 3 Hall plateau collapses. The coupling of the Landau levels in the two quantum wells leads to an enhancement of the dissipative conductivity. The anomalous peak is found to exhibit nonlinear current-voltage characteristics.

 

191.    Y. Takagaki, S. Tarucha, J. Herfort, and K. Ploog

            "Ballistic transport of electrons and composite fermions in narrow cross junctions"

            Chaos Solitons Fractals 8 (7-8), 1359-1379 (1997).

 

            ABSTRACT: We describe the magnetotransport properties in cross junctions of narrow wires in the ballistic regime. The resistance is determined solely by the scattering from the geometry. It is unconventionally nonlocal and can be negative. These properties arise from the four-terminal nature of the resistance measurements. We consider the ballistic transmission under two circumstances: around zero magnetic field and in the vicinity of the half-filling of the lowest Landau level, where an electron and a composite fermion are the relevant particles, respectively. The electron trajectories are made random and chaotic by smooth corners in cross junctions. The magnetic field dependence of the negative bend resistance reflects the nature of the trajectories in the rounded junctions. For the composite fermion, nonuniform effective magnetic fields additionally modify the ballistic trajectories. We also investigate quantum ballistic transmission of quasiparticle excitations in the normal-conductor-superconductor (NS) junctions. In hybrid NS systems, an electron (a hole) is reflected as a hole (an electron) from the NS interface. This Andreev reflection leads to a rich variety of behaviors in the composite structures. (C) 1997 Elsevier Science Ltd.

 

192.    S. Takagi and M. Kimura

            "Low-voltage electric-discharge biolistic device"

            Biotechniques 23 (4), 650-652 (1997).

 

            ABSTRACT:

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

            "Superconductivity in quantum spin-ladder compound Ca13.6Sr0.4Cu24O41+delta at high pressure"

            Physica B 237, 112-114 (1997).

 

            ABSTRACT: Superconductivity has been observed in a spin-ladder compound Ca13.6Sr0.4Cu24O41+delta having Cu2O3 ladder layer. Electrical resistivity measurements show that T-C appears at 7 K at 1.5 GPa and disappears above 6 GPa after having the maximum T-C of 12 K at 3 GPa. The bulk superconductivity was suggested in this system from AC susceptibility measurements, the volume fraction of which was estimated to be about 5% at 4.2 K at 3.5 GPa. In contrast with the oxide superconductor having CuO2-layer, this system shows superconductivity in the very narrow pressure range.

 

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

            "Atomic configurations of Er centers in GaAs:Er,O and AlGaAs:Er,O studied by site-selective luminescence spectroscopy"

            J. Appl. Phys. 82 (8), 3997-4005 (1997).

 

            ABSTRACT: Er-doped GaAs codoped with oxygen was studied by site-selective measurements of photoluminescence spectra and photoluminescence-excitation spectra directly exciting the 4f-shell electrons of one kind of Er center at a time. Within one sample, more than 10 kinds of distinctly different Er centers, showing different Er-related spectra, were observed, although its host-excited photoluminescence spectrum is dominated by the luminescence from one kind of Er center. The atomic configuration of that center has been identified as an Er atom located at the Ga sublattice with two adjacent oxygen atoms (Er-2O center). Seven kinds of Er centers in GaAs:Er, O and two kinds of Er centers in AlGaAs:Er, O were studied in detail. The numbers of lines and the magnitudes of energy separations among the lines in each spectrum indicate that the Er atoms of all nine kinds of centers are coupled with oxygen atoms and have noncubic symmetry. The nine Er centers were grouped into several classes according to similarities in their spectra which should reflect symmetries of the Er centers. The atomic configurations of two classes of Er centers are discussed in detail. The Er centers of both classes have a nearest-neighbor site atomic configuration similar to that of the Er-2O center with a symmetry close to rhombic C-2 upsilon, but Er centers in the two classes have different types of deviation from C-2 upsilon due to the difference in the second-nearest-neighbor atomic configurations of the Er Atoms. We also discuss a large difference in the efficiency of the Er-related luminescence under host photoexcitation caused by the difference in the second-nearest-neighbor atomic configurations. (C) 1997 American Institute of Physics.

 

195.    K. Takarabe, T. Mizushima, S. Minomura, R. A. Hogg, A. Taguchi, and K. Takahei

            "Pressure-induced intra-4f luminescence in GaAs:Er,O"

            Appl. Phys. Lett. 71 (1), 93-95 (1997).

 

            ABSTRACT: In metalorganic chemical vapor deposition grown GaAs:Er,O samples, at ambient pressure, only the Er-Ca-20 center is excited by above band gap host photoexcitation (host excitation) and shows a sharp infrared luminescence spectra due to intra-4f transitions in the Er3+ ion. It is found, at high pressure, that at least two other Er centers become optically active by host excitation. One of these pressure-induced centers is assigned to a specific Er center having slightly different atomic configuration than the Er-Ca-20 center by comparing the pressure-induced photoluminescence (PL) spectra with the site-selective PL spectra. (C) 1997 American Institute of Physics.

 

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

            "Critical current-gate voltage characteristics in short- and long-gated Josephson junctions"

            Appl. Supercond. 5 (7-12), 357-364 (1997).

 

            ABSTRACT: We studied the gate controllability of the critical current and the normal resistance in superconductor-semiconductor-superconductor junctions. The junctions used a two-dimensional electron gas (2DEG) in the InAs-inserted InAlAs/InGaAs heterostructure. It is shown that the interface barrier between the superconductor and the 2DEG affects the controllability in a short-gated junction. In a split-gated junction, the critical current-normal resistance product is almost constant against gate voltage. This is due to quantization of both the critical current and the conductance in a narrow and short semiconductor channel. The long-gated junction in the quasi-ballistic transport regime shows rapid suppression of the critical current by gate voltage. (C) 1998 Elsevier Science Ltd. All rights reserved.

 

197.    H. Takayanagi and A. F. Volkov

            "AC long-range phase-coherent effects of S-N-S junctions in the dirty limit"

            J. Low Temp. Phys. 106 (3-4), 285-290 (1997).

 

            ABSTRACT: The conductance of a normal metal film (N) in contact with two superconductors (S) is calculated in the presence of a constant (V) over bar(s) and oscillating V-omega cos omega t bias voltage between N and S. It is shown that the conductance as a function of (V) over bar(s) has a Shapiro-like step at (V) over bar(s) = HBAR omega/2e. This exists in the case when the spacing between two superconductors largely exceeds the coherence length. It is also shown that the Shapiro step height decreases rapidly when the junction size exceeds the phase breaking length.

 

198.    T. Takeuchi

            "The motion analogue of the Cafe Wall illusion"

            Perception 26 (5), 569-584 (1997).

 

            ABSTRACT: Detecting visual motion is computationally equivalent to detecting spatiotemporally oriented contours. The question addressed in this study is whether the illusory oriented contour in the space-space domain induces corresponding illusory motion perception. Two experiments were conducted. In experiment 1, the Cafe Wall pattern, which elicits a strong illusion of orientation (Cafe Wall illusion), was found to induce an illusion of motion when this pattern was converted to the space-time domain. The strength of the motion illusion depends on the mortar luminance and width, as for the Cafe Wall illusion. In experiment 2, the adaptation to this illusion of motion was found to induce a motion aftereffect in a static test, which indicates that a first-order-motion system contributes to the induction of the motion illusion. In fact, the motion-energy model was able to predict the strength of this motion aftereffect.

 

199.    T. Takeuchi

            "Visual search of expansion and contraction"

            Vision Res. 37 (15), 2083-2090 (1997).

 

            ABSTRACT: The perception of expansion/contraction in human subjects was examined with a visual search paradigm. When searching for a target defined by two-dimensional expansion among distracters defined by two-dimensional contraction, the time needed to find the target did not vary as the number of distracters was increased. However, for a target defined by two-dimensional contraction among distracters defined by two-dimensional expansion, the search time increased as a function of the number of distracters in the display. A similar search asymmetry remained between one-dimensional expansion and one-dimensional contraction, even though one-dimensional expansion was searched in a serial manner. This asymmetry between expansion and contraction reflects a basic characteristic of higher-order motion information processing. (C) 1997 Elsevier Science Ltd.

 

200.    H. Tamura and M. Ueda

            "Energy-level statistics and orbital magnetism of interacting electrons in disordered quantum dots"

            Phys. Rev. Lett. 79 (7), 1345-1348 (1997).

 

            ABSTRACT: The effects of the Coulomb interaction on energy-level statistics and orbital magnetism in disordered two-dimensional quantum dots are studied within a serf-consistent finite-temperature Hartree-Fock (HF) approximation, The nearest-neighbor level-spacing distribution of the HF energy at the Fermi level is shown to depend only weakly on magnetic fields. Fluctuations in the number of electrons, suppressed by a Coulomb gap produced at the Fermi energy, are also insensitive to magnetic fields. This insensitivity leads to the nonexistence of a large paramagnetism predicted for isolated mesoscopic systems of noninteracting diffusive electrons.

 

201.    S. Tarucha, D. G. Austing, T. Honda, R. van der Hage, and L. P. Kouwenhoven

            "Atomic-like properties of semiconductor quantum dots"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 36 (6B), 3917-3923 (1997).

 

            ABSTRACT: We use a gated submicron double-barrier resonant tunneling structure to study transport properties of a semiconductor quantum dot containing a tunable number of electrons starting from zero. At zero magnetic field the addition energy has large maxima for special numbers of electrons in the dot, reflecting a shell structure of electronic states in a circular dot with a harmonic lateral potential. As a function of magnetic field, current peaks evolve in pairs. This arises from the antiparallel filling of spin-degenerate states. Close to zero magnetic field, however, this pairing is rearranged to favour the filling of states with parallel spins in line with Hund's rule. These observations demonstrate that the electronic spectrum for our quantum dots is analogous to that of real atoms. When the dot has asymmetry in the lateral shape, the addition energy spectrum is readily modified reflecting the disruption of the shell structure.

 

202.    H. Teramae and J. Michl

            "Geometry of the localized sigma sigma* excited of n-tetrasilane"

            Chem. Phys. Lett. 276 (1-2), 127-132 (1997).

 

            ABSTRACT: Full optimization of the geometry of the lowest excited singlet of n-tetrasilane, Si4H10, at several levels of CASSCF theory yielded a floppy C-2 structure with an SiSiSiSi dihedral angle of 105 degrees that can be increased to 180 degrees at the cost of only 4 kcal/mol, SiSiSi valence angles of 90 degrees, central SiSi bond stretched to 2.55 Angstrom and terminal ones to 2.42 Angstrom. The sigma sigma* excitation is localized in the central bond. (C) 1997 Published by Elsevier Science B.V.

 

203.    Y. Tokura and S. Tarucha

            "Roughness scattering in a finite-length wire"

            Phys. Rev. B 55 (23), 15740-15747 (1997).

 

            ABSTRACT: Semiclassical conductance of a finite two-dimensional wire is theoretically evaluated. The bulk scattering is neglected. Rigorous formulas for situations with completely diffuse and partially diffuse straight boundaries are given. For the short limit of wire length the conductance decreases according to 1/(1 + ca), where a is an aspect ratio parameter (length divided by wire width), and c is a prefactor depending on the specularity parameter of the boundary. Lf the wire is long enough, conductance decreases with c'lna/a using another constant c', which is consistent with the classical analysis of resistivity by boundary roughness scattering of an infinite wire.

 

204.    K. Torimitsu

            "Substrates for growth cone guidance in brain: Guidance cues for neural connections"

            in Porous Materials For Tissue Engineering, Materials Science Forum Vol. 250 (Transtec Publications Ltd, Zurich-Uetikon, 1997), pp. 69-88.

 

            ABSTRACT: Neurons extend their neurites to a target during neural development in the brain. During this process, guiding substrates play an important role in guiding the growth cones, the tip of the axons/neurites, precisely to their specific targets. This guidance result in the establishment of a neural circuit in the brain. In this review, I will describe the substrates which may guide the growth cone of the axons/neurites to their targets thus forming synaptic neural connections, and also discuss the mechanisms of this neuronal guidance.

 

205.    K. Torimitsu, R. Kurita, and O. Niwa

            "Real-time detection of synaptic glutamate release induced by GABA and neurotrophins in cultured rat cortex"

            J. Neurochem. 69, S64-S64 (1997).

 

            ABSTRACT:

206.    K. Torimitsu and O. Niwa

            "Real-time detection of GABA-induced synaptic glutamate release in cultured rat cortex"

            Neuroreport 8 (6), 1353-1358 (1997).

 

            ABSTRACT: Glutamate is an important neurotransmitter in synaptic transmission. There are no methods, however, for continuous measurement of glutamate concentration at high temporal and spatial resolutions. We have developed a novel electrochemical detection method for the on-line measurement of glutamate release with nanomolar resolution in real time. Using this method, GABA was found to have a modulatory action on the synaptic glutamate release in cultured rat cortical cells. This synaptic modulation largely depends on the GABA(A) receptor and could be a key not only in neural development, but also in signal transduction in the brain. Our detection method is ideal for investigating such synaptic glutamate responses because of its higher sensitivity and real-time measurement capability.

 

207.    S. Toyoda, M. Fujiki, H. Suzuki, and N. Matsumoto

            "Estimation of polysilane band gaps by fractional dimensional theory"

            Solid State Commun. 103 (2), 87-89 (1997).

 

            ABSTRACT: The exciton energy levels of five kinds of polysilane with different substituents were measured by UV absorption, two-photon absorption and electroabsorption spectroscopy. Their band gaps were estimated using the obtained data without any fitting parameters by employing the fractional dimensional theory. (C) 1997 Elsevier Science Ltd.

 

208.    K. Tsuji, K. Shimizu, T. Horiguchi, and Y. Koyamada

            "Coherent optical frequency domain reflectometry using phase-decorrelated reflected and reference lightwaves"

            J. Lightwave Technol. 15 (7), 1102-1109 (1997).

 

            ABSTRACT: We report a new scheme for coherent optical frequency domain reflectometry (C-OFDR) where the coherence length of the lightwaves does not Limit the measurable fiber length, In this scheme, we use the beat spectrum which results when we mix reflected and reference lightwaves whose phases are not correlated, We demonstrated this scheme using a narrow-linewidth-lightwave source and an external electro-optical phase modulator, We measured Rayleigh backscattering and Fresnel reflections from a 30-km optical fiber, and achieved a spatial resolution of 5 m for two neighboring Fresnel reflectors located at the far end of the fiber, We estimated the expected spatial resolution and single-way dynamic range for our new scheme and show that it is capable of measuring long optical fibers with high-spatial resolution.

 

209.    K. Tsuji, K. Shimizu, T. Horiguchi, and Y. Koyamada

            "Spatial-resolution improvement in long-range coherent optical frequency domain reflectometry by frequency-sweep linearisation"

            Electron. Lett. 33 (5), 408-410 (1997).

 

            ABSTRACT: The authors demonstrate long-range coherent optical frequency domain reflectometry (C-OFDR) with an auxiliary feedback-control circuit to linearise frequency sweep. They successfully suppress the sweep nonlinearity, and achieve spatial resolutions of 14 cm and 50 cm, respectively, at the far ends of 1 and 30 km optical fibres.

 

210.    D. M. Turner, K. K. DeValois, and T. Takeuchi

            "Speed perception under scotopic conditions"

            Invest. Ophthalmol. Vis. Sci. 38 (4), 1779-1779 (1997).

 

            ABSTRACT:

211.    R. D. Twesten, J. M. Gibson, and O. C. Hellman

            "Direct measurements of surface stress using transmission electron microscopy"

            Surf. Rev. Lett. 4 (2), 245-269 (1997).

 

            ABSTRACT: Surface stress and energy are concepts which are often misunderstood. In this work, we will clarify the difference between the two. We describe the use of transmission electron microscopy to measure surface stress by quantitative analysis of strain contrast images. We find that images of surface-stress-induced strain fields can be used to measure quantitative differences in surface stress provided the imaging parameters are accurately determined. We have applied this method to measure the stress difference between the 7 x 7 and high temperature ''1 x 1'' phases of the Si(111) surface at the phase coexistence temperature and between metastable phase boundaries on the Si(111) and amorphous-Ge interface. We discuss the significance of these measurements and pitfalls to be avoided in image simulations.

 

212.    K. Uwai and N. Kobayashi

            "Surface termination effect on reflectance spectra of GaAs"

            Phys. Rev. Lett. 78 (5), 959-962 (1997).

 

            ABSTRACT: Dielectric response spectra of GaAs surfaces are determined using surface photoabsorption for surface conversion caused by Ga deposition and H adsorption on As-stabilized (001)-(2 x 4) surfaces and As desorption from As-rich (111)B-(2 x 2) surfaces. All of these spectra show common peaks at 2.6-3.0 and 4.5-4.7 eV, which coincide with critical points of bulk GaAs dielectric function. Model calculations show that the appearance of these critical points in the surface dielectric response can be explained by assuming that light absorption is quenched in the surface layer because of the terminated electronic wave functions at the surface.

 

213.    V. V. Vinod and H. Murase

            "Focused color intersection with efficient searching for object extraction"

            Pattern Recognit. 30 (10), 1787-1797 (1997).

 

            ABSTRACT: We propose focused color intersection with efficient searching for identifying and extracting the objects in a complex scene based on color similarity. The method matches the models against different parts of a scene, called focus regions, using normalized color histogram intersection. The best matching focus region is determined by an efficient search strategy employing upper bound pruning. This search strategy, called active search, concentrates its effort on parts of the scene having high similarity with the object. Consequently, it achieves a large reduction in computational effort without sacrificing accuracy. An efficient algorithm for evaluating the color histogram intersection between a model and a focus region is also given. Experiments conducted demonstrate that multiple known objects in complex scenes can be extracted by this process. The method is stable against scale changes, two-dimensional rotation, moderate changes in shape and partial occlusion. (C) 1997 Pattern Recognition Society. Published by Elsevier Science Ltd.

 

214.    A. F. Volkov and H. Takayanagi

            "Long-range phase-coherent effects in the transport properties of mesoscopic superconductor-normal-metal structures"

            Phys. Rev. B 56 (17), 11184-11194 (1997).

 

            ABSTRACT: We present a theory of long-range phase-coherent effects in the transport properties of st normal-metal film contacting two superconductors. It is shown that the phase-coherent correction to the conductance exists even though the spacing between the two superconductors largely exceeds the coherence length and the critical Josephson current is exponentially small. This effect can appear as a Shapiro step or large conductance oscillation caused by the magnetic field. Moreover, it is shown that in the case of negligible Josephson coupling between superconductors, the Josephson effect can arise in the system if an additional current flows through the normal conductor and a dissipation takes place (dissipative Josephson effect), The amplitude of the phase-coherent correction part of the conductance is discussed from the viewpoint of temperature, bias voltage, magnetic field, and phase-breaking length dependence.

 

215.    A. F. Volkov and H. Takayanagi

            "Absence of Shapiro-like steps in certain mesoscopic S-N-S junctions - Reply"

            Phys. Rev. Lett. 78 (13), 2679-2679 (1997).

 

            ABSTRACT:

216.    T. H. Wang and S. Tarucha

            "Effects of coupling and nonresonant tunneling on Coulomb blockade oscillations in an asymmetric double dot structure"

            Appl. Phys. Lett. 71 (17), 2499-2501 (1997).

 

            ABSTRACT: We report on single electron transport through an asymmetric double dot structure with well-defined dot potential profiles. As the two dots are coupled, the conductance exhibits two pronounced types of Coulomb blockade oscillations. An analysis of the small short-period oscillations indicates the presence of interdot interaction. When the coupling strength is reduced, the oscillations become few irregular peaks but they develop into periodic oscillations again as the drain voltage is increased to 0.6 mV. This appearance with increasing drain voltage is well explained by our model which is based on the stochastic Coulomb blockade model and nonresonant tunneling. (C) 1997 American Institute of Physics. [S0003-6951(97)03043-X].

 

217.    K. Watanabe, T. Mukai, and T. Mukai

            "Stability of solutions of the nonlinear Schrodinger equation for trapped Bose-condensed atoms with negative scattering lengths"

            Phys. Rev. A 55 (5), 3639-3644 (1997).

 

            ABSTRACT: We analyze the time evolution of solutions of nonlinear Schrodinger equations that describe a condensate composed of atoms with negative scattering lengths in a harmonic potential trap. It is theoretically demonstrated that if an initial condensate has negative energies due to negative scattering lengths, then the solutions diverge in a finite time that is determined by the condensate's energy, its initial phase, and the trap parameter.

 

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

            "Anisotropic transport properties of impurity (Co) doped and oxygen controlled single-crystal Bi2Sr2CaCu2O8+delta: Evidence of temperature-dependent interlayer coupling and a pseudogap"

            Physica C 282, 1169-1170 (1997).

 

            ABSTRACT: We investigate the effects of impurity (Co) substitution and carrier doping on the anisotropic transport properties of Bi2Sr2CaCu2O8+delta single crystals, focusing on the interlayer charge dynamics. Our analysis shows that the out-of-plane transport in the Bi2Sr2CaCu2O8+delta system is well described by the tunneling (Lawrence-Doniach) model. By carefully reducing the oxygen content, deviation from T-linear in-plane resistivity, which is similar the behavior in Ba2YCu3O7-delta, can be observed. On the other hand, the out-of-plane resistivity monotonically increases with decreasing temperature, showing no correlation with the anomalous in-plane behavior.

 

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

            "Anisotropic resistivities of precisely oxygen controlled single-crystal Bi2Sr2CaCu2O8+delta: Systematic study on ''spin gap'' effect"

            Phys. Rev. Lett. 79 (11), 2113-2116 (1997).

 

            ABSTRACT: The in-plane resistivity rho(a)(T) and the out-of-plane resistivity rho(c)(T) have been systematically measured for Bi2Sr2CaCu2O8+delta Single crystals with their oxygen contents precisely controlled. In the underdoped region, deviation from T-linear in-plane resistivity, which evidences the opening of the ''spin gap,'' is clearly observed, while the out-of-plane resistivity is well reproduced by the activation-type phenomenological formula rho(c)(T)=(a/T)exp(Delta/T) + c. In contrast to the YBa2Cu3O7-delta system, we find that the onset of the semiconducting rho(c)(T) does not coincide with the opening of the spin gap seen in the rho(c)(T) in this Bi2Sr2CaCu2O8+delta system.

 

220.    Y. Watanabe and F. Maeda

            "Anomalous downward band bending induced by selenium passivation of MBE-grown InAs(001) surfaces"

            Appl. Surf. Sci. 117, 735-738 (1997).

 

            ABSTRACT: In-situ synchrotron radiation photoelectron spectroscopy is used to study the surface chemical bonding structures on InAs(001) with and without Se passivation and to determine changes in the surface Fermi level (E-F) position as a result of Se treatment. Analysis of the As 3d and In 4d core-levels for the epitaxially grown InAs and reflection high-energy electron diffraction pattern observations are found to be almost the same as those for GaAs(001)-(2 X 4), showing that a well-ordered InAs(001)-(2 X 4) surface is achieved. The results of As 3d and In 4d spectra for the Se-passivated InAs show that a Se-terminated surface is formed where the topmost Se atoms bond to In. Anomalous downward band bending, where the E-F position is located at about 0.5 eV above the conduction band minimum, is observed for the first rime at the Se-passivated InAs(001)-(2 X 1), in contrast to the well-known results for Se-passivated GaAs.

 

221.    M. J. Werner and P. D. Drummond

            "Pulsed quadrature-phase squeezing of solitary waves in chi((2)) parametric waveguides"

            Phys. Rev. A 56 (2), 1508-1518 (1997).

 

            ABSTRACT: It is shown that coherent quantum simultons (simultaneous solitary waves at two different frequencies) can undergo quadrature-phase squeezing as they propagate through a dispersive chi((2)) waveguide. This requires a treatment of the coupled quantized fields including a quantized depleted pump field. A technique involving nonlinear stochastic parabolic partial differential equations using a nondiagonal coherent state representation in combination with an exact Wigner representation on a reduced phase space is outlined. We explicitly demonstrate that group-velocity matched chi((2)) waveguides which exhibit collinear propagation can produce quadrature-phase squeezed simultons. Quasi-phase-matched KTP waveguides, even with their large group-velocity mismatch between fundamental and second harmonic at 425 nm, can produce 3 dB squeezed bright pulses at 850 nm in the large phase-mismatch regime. This can be improved to more than 6 dB by using group-velocity matched waveguides.

 

222.    M. J. Werner and P. D. Drummond

            "Robust algorithms for solving stochastic partial differential equations"

            J. Comput. Phys. 132 (2), 312-326 (1997).

 

            ABSTRACT: A robust semi-implicit central partial difference algorithm for the numerical solution of coupled stochastic parabolic partial differential equations (PDEs) is described. This can be used for calculating correlation functions of systems of interacting stochastic fields. Such field equations can arise in the description of Hamiltonian and open systems in the physics of nonlinear processes, and may include multiplicative noise sources. The algorithm can be used for studying the properties of nonlinear quantum or classical field theories. The general approach is outlined and applied to a specific example, namely the quantum statistical fluctuations of ultra-short optical pulses in chi((2)) parametric waveguides. This example uses a non-diagonal coherent state representation, and correctly predicts the sub-shot noise level spectral fluctuations observed in homodyne detection measurements. It is expected that the methods used wilt be applicable for higher-order correlation functions and other physical problems as well. A stochastic differencing technique for reducing sampling errors is also introduced. This involves solving nonlinear stochastic parabolic PDEs in combination with a reference process, which uses the Wigner representation in the example presented here. A computer implementation on MIMD parallel architectures is discussed. (C) 1997 Academic Press.

 

223.    M. J. Werner and S. R. Friberg

            "Phase transitions and the internal noise structure of nonlinear Schrodinger equation solitons"

            Phys. Rev. Lett. 79 (21), 4143-4146 (1997).

 

            ABSTRACT: We predict phase transitions in the quantum noise characteristics of systems described by the quantum nonlinear Schrodinger equation, showing them to be related to the solitonic field transition at half the fundamental soliton amplitude. These phase transitions are robust with respect to Raman noise and scattering losses. We also describe the rich internal quantum noise structure of the solitonic fields in the vicinity of the phase transition. For optical coherent quantum solitons, this leads to the prediction that eliminating the peak sideband noise due to the electronic nonlinearity of silica fiber by spectral filtering leads to the optimal photon-number noise reduction of a fundamental soliton.

 

224.    F. M. Xie, P. T. Kissinger, and O. Niwa

            "Determination of tetrahydrobiopterin and its analogues in biological samples by microbore liquid chromatography"

            J. Liq. Chromatogr. Relat. Technol. 20 (6), 825-837 (1997).

 

            ABSTRACT: Tetrahydrobiopterin and seven of its analogues (neopterin, xanthopterin, biopterin, pterin, tetrahydropterin, 6-methyltetrahydropterin, and 6-methylpterin) were separated on a 1 x 150 mn C-18 microbore column. These analytes were detected by dual-electrode amperometry and UV absorption. Both a conventional glassy carbon electrode and an interdigitated array microelectrode were used. Low fmol amounts of xanthopterin, tetrahydropterin, tetrahydrobiopterin and 6-methyltetrahydropterin could be determined by electrochemical detection in the oxidative mode, but pmol amounts of the other analogues were determined by electrochemical detection in the reductive mode and with UV detection. Catecholamines and their metabolites do not interfere with the determination of tetrahydrobiopterin and its analogues in biological samples. The developed method was explored for the determination of tetrahydrobiopterin in samples of human urine and rat tissue (brain, liver, and kidney).

 

225.    F. Yamaguchi, D. Huang, and Y. Yamamoto

            "Theory of transport through a single atomic junction"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 36 (6B), 3799-3803 (1997).

 

            ABSTRACT: A theory of transport properties through a single atomic junction consisting of a single atom and two electrodes is presented. Such an atomic junction is realized with a system of a scanning tunneling microscope (STM) tip, a single atom located at the tip apex and a sample surface. Electron tunneling between an atom and an electrode through a vacuum potential barrier is governed simultaneously by the Coulomb potential (Coulomb blockade effect) and Pauli exclusion principle due to an atomic discrete energy spectrum. Measurement of conductance oscillation due to the Coulomb blockade effect and Pauli principle in such a system allows one to determine the highest occupied energy level and its degeneracy of the atom as well as the local work function of the tip apex and the band gap of the sample surface.

 

226.    F. Yamaguchi, T. Yamada, and Y. Yamamoto

            "Even-odd conductance oscillation in atomic wires"

            Solid State Commun. 102 (11), 779-783 (1997).

 

            ABSTRACT: The linear response conductance is computed in a one-dimensional atomic wire between two adiabatically expanding metal electrodes. We show that the conductance behavior is significantly different from that of a mesoscopic narrow channel. Specifically, we find that the conductance of such an atomic wire oscillates periodically between quantum unit of conductance Go for odd number of atoms in the wire and rG(Q)(r < 1) for even number of atoms. This even-odd oscillation is very robust and should be observable at room temperature. (C) 1997 Published by Elsevier Science Ltd.

 

227.    H. Yamaguchi, J. G. Belk, X. M. Zhang, J. L. Sudijono, M. R. Fahy, T. S. Jones, and B. A. Joyce

            "RHEED and STM study of the two-dimensional growth of InAs on GaAs (111)A"

            Microelectron. J. 28 (8-10), 825-831 (1997).

 

            ABSTRACT: Reflection high-energy electron diffraction and scanning tunneling microscopy have been used to study the growth of InAs on GaAs (111)A by molecular beam epitaxy. In contrast: to the 3-D growth mode observed for InAs on GaAs (001), there is no evidence for 3-D island formation on the (111)A surface. The precise control of the 2-D growth of InAs layers makes it possible to probe the early stages of strain relaxation by imaging misfit dislocations by STM. The band gap and position of the surface Fermi level of ultra-thin InAs films on GaAs (111)A have also been obtained by scanning tunneling spectroscopy as a function of InAs thickness. The band gap of InAs is established after about 10 MLs of InAs and an accumulation layer is formed at the surface after the growth of 20 MLs of InAs. (C) 1997 Elsevier Science Ltd.

 

228.    T. Yamaguchi and J. Nakata

            "Tetragonal WSi2 formation by 0.5-5 MeV Xe-ion-beam irradiation at 250 degrees C and 450 degrees C"

            J. Appl. Phys. 81 (5), 2219-2228 (1997).

 

            ABSTRACT: We studied two-step tungsten-silicidation processes, which consist of low-energy W implantation followed by high-energy Xe irradiation. The formation of silicides was studied by Rutherford backscattering spectroscopy, x-ray diffraction and transmission electron microscopy. The formed silicide layer is richer in Si than that formed by thermal annealing. The transformation from the hexagonal to tetragonal (usually formed by thermal annealing above 600 degrees C) WSi2 phase occurred and a tetragonal WSi2 layer was successfully formed by 1-MeV Xe+ and 5-MeV Xe++ ion irradiation at under irradiation temperatures of 410 and 450 degrees C. The transformation did not occur by 0.5-MeV Xe+ ions at the same substrate temperature. The tetragonal phase was also observed after irradiation by 1-MeV Xe+ at 250 degrees C. The phase transformation rate normalized to the nuclear energy deposition density E(n) increases with the electronic energy deposition density E(e). This fact indicates that the phase transformation is enhanced by the inelastic electronic scattering of high-energy ion irradiation. The irradiation temperature dependence of the phase transformation was also studied. The mechanism of the silicidation by elastic nuclear scattering and that of the phase transformation by inelastic electronic scattering of high-energy heavy-ion-beam irradiation are qualitatively discussed. (C) 1997 American Institute of Physics.

 

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

            "Nanometer-scale linewidth fluctuations caused by polymer aggregates in resist films"

            Appl. Phys. Lett. 71 (16), 2388-2390 (1997).

 

            ABSTRACT: Linewidth fluctuation in resist patterns is a serious problem in electron beam nanolithography. We have observed granular structures with a diameter of 20-30 nm in resist films, and have determined that these structures cause the linewidth fluctuations. The granules are made up of polymer aggregates, We discuss the origin of the aggregates from the result that their size depends on the polymer molecular weight. We also show that the linewidth fluctuation is reduced, though the developing rate Is slow. when the pattern size is less than the aggregate size, The linewidth dependence of the fluctuation and of the developing rate can be explained by the influence of the resist polymer aggregate on the development behavior. (C) 1997 American Institute of Physics.

 

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

            "Surface stability of MBE-grown Nd1.85Ce0.15CuO4 thin films in air investigated by RHEED, XPS, and UPS"

            Physica C 291 (1-2), 67-72 (1997).

 

            ABSTRACT: This paper reports on the stability of a Nd1.85Ce0.15CuO4 (NCCO) surface investigated by reflection high-energy electron diffraction (RHEED) and photoemission spectroscopy. Experiments were performed on an "intrinsic" surface prepared by molecular beam epitaxy (MBE). Ex situ observation of the time evolution of the MBE-grown NCCO surface showed that it is substantially more stable than previously reported, in that the sharp streaky RHEED patterns an maintained and the above 531 eV component in the O 1s X-ray photoelectron spectra develops only slightly even after exposure to air for two weeks. (C) 1997 Elsevier Science B.V.

 

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

            "Surface and interface study on MBE-grown Nd1.85Ce0.15CuO4 thin films by photoemission spectroscopy and tunnel spectroscopy"

            Phys. Rev. B 56 (5), 2852-2859 (1997).

 

            ABSTRACT: Nd1.85Ce0.15CuO4 (NCCO) surfaces and metal (Au, Ag, and Pb)NCCO interfaces have been extensively investigated by x-ray and ultraviolet photoelectron spectroscopies using films grown by molecular beam epitaxy (MBE). The photoelectron spectra obtained in situ on the surfaces of MBE-grown NCCO films are free from any dirt peak and show a fine structure with a Fermi edge in the valence region. Experiments were performed on the prepared clean surfaces. focusing on the evolution of the surface or interface electronic structure with oxygen nonstoichiometry at the surface or interface regions. The results show (1) a systematic spectral change due to the oxygen content at the surface, and (2) a redox phenomena at the metal/NCCO interface. In oxygenated surfaces or insufficiently reduced surfaces, excess oxygens seem to occupy the interstitial (apical) oxygen sites, which compensates Ce doping, eventually lending to a nonmetallic surface. In excessively reduced surfaces, oxygen deficiencies seem to occur at regular oxygen sites, leading to a metallic but not a superconducting surface. The photoelectron spectroscopy data are discussed in comparison with complementary tunnel spectroscopy data. Both sets of data indicate that precise control of oxygen stoichiometry at NCCO surface is essential to obtain an intrinsic (i.e., superconducting) NCCO surface, which is indispensable in obtaining reliable data using surface sensitive experiments and in fabricating tunnel junctions and superlattices with desirable characteristics.

 

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

            "A new superconducting cuprate prepared by low-temperature thin-film synthesis in a Ba-Cu-O system"

            Jpn. J. Appl. Phys. Part 2 - Lett. 36 (3B), L341-L344 (1997).

 

            ABSTRACT: A new high-T-c superconducting cuprate composed of Ba, Cu and O was prepared on SrTiO3(001) substrate by reactive coevaporation. The superconducting phase is formed only in the limited temperature range between 575 and 625 degrees C and in a narrow compositional range. Observations of the X-ray diffraction and transmission electron microscopy suggests that the superconducting phase is the 214-based structure. Superconductivity is obtained only after strong oxidation after film growth. The resistivity measurement shows T-c(onset) approximate to 60 to 70 K and T-c(end) less than or equal to 38 K and the magnetic measurement shows T-c(onset) approximate to 85 to 90 K.

 

233.    Y. Yamamoto

            "Photonics - A photon in solitary confinement"

            Nature 390 (6655), 17-18 (1997).

 

            ABSTRACT:

234.    Y. Yamamoto, R. Liu, J. Kim, and A. Imamoglu

            "Electron and photon noise suppression in mesoscopic systems - how to teach noisy photons to follow quiet electrons"

            Mater. Sci. Eng. B-Solid State Mater. Adv. Technol. 48 (1-2), 19-25 (1997).

 

            ABSTRACT: Principles of squeezed state generation in semiconductor lasers and light emitting diodes (LEDs) are discussed. Shot noise suppression in electron transport in macroscopic conductors is ultimately due to Pauli exclusion principle for fermion particles, electrons. Shot noise suppression in electron injection in macroscopic pn junctions originates from collective Coulomb blockade effect for changed particles, electrons, Regulated single photon generation in mesoscopic pn junctions is also discussed. (C) 1997 Elsevier Science S.A.

 

235.    M. Yamashita, S. Machida, and T. Mukai

            "Strongly anticorrelated twin beams from symmetric low-Q cavity semiconductor lasers under constant-current operation"

            Phys. Rev. A 55 (6), 4552-4555 (1997).

 

            ABSTRACT: We have observed a strong anticorrelation between the photocurrent fluctuations of two laser outputs from symmetric low-Q cavity laser diodes (LDs) driven far above the threshold in a constant-current mode. The degree of correlation is highly dependent on the mirror reflectivities of the cavity: -66% for the conventional LD with cleaved facets, and -90% for the antireflection-coated LD with residual mirror reflectivities of 5%. In the case of a cleaved LD, the sum of the photocurrent fluctuations of both laser outputs exhibits 2.8 dB noise reduction below the shot-noise level. This is the first observation of subshot-noise photocurrent fluctuations symmetric cavity LDs.

 

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

            "Novel proximity effect including pattern-dependent resist development in electron beam nanolithography"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 36 (12B), 7552-7556 (1997).

 

           ABSTRACT: A novel proximity effect, which includes the effect due to secondary electron scattering to a range of less than a micron and the pattern dependence of resist development, has been found and investigated to develop a precise dose control method in electron beam nanolithography. Experiments and simulations including secondary electron scattering were performed for precise evaluation of the proximity effect. This result revealed that the proximity effect caused by secondary electron scattering to the range between 30nm and a micron is not negligible for nano-patterns. In addition, from experimental estimation of the rate of development of patterns of various sizes, a significant decrease of the rate was found for patterns less than 30-nm wide. The difference of the rate is also modified by the background deposited energy due to surrounding patterns. Therefore, we have to be very careful about how we determine the proper dose for a given nano-pattern.

 

237.    R. Z. Yang and N. Uesugi

            "Femtosecond free induction decay beats in Nd3+:YAG crystal"

            Jpn. J. Appl. Phys. Part 2 - Lett. 36 (12A), L1594-L1597 (1997).

 

            ABSTRACT: Femtosecond free induction decay (FID) beats were observed for the F-4(3/2) - I-4(9/2) transition of Nd3+ ions doped in Y3Al5O12 (YAG) crystal at room temperature using a mode-locked Ti3+:Al2O3 laser. This is the first observation of room-temperature dephasing processes in the time domain for rare-earth ion doped materials. The FID beat signal shows a dip structure produced by the interference between the pump pulse and the FID signal, and a quantum beat. The FID signal became large and comparable to the pump pulse as the crystal length was increased. The FID intensity evolution due to the pulse propagation is explained well by phenomenological equations.

 

238.    R. Yano and N. Uesugi

            "Pulse propagation of accumulated photon echoes in Nd3+ ion-doped silicate glass fiber"

            Appl. Phys. Lett. 71 (12), 1613-1615 (1997).

 

            ABSTRACT: Pulse-propagation phenomena of accumulated photon echo signals was investigated for the F-4(3/2)(1)-I-4(9/2) transition of the Nd3+ ion doped with 20 ppm concentration in silicate glass fiber (core diameter of 6 mu m) at 4.2 K using an 82 MHz mode-locked dye laser. The intensity of the transmitted probe pulses from the Nd3+ fiber was measured as a function of the Nd3+ fiber length. The fiber length for the maximum probe-pulse intensity induced by the pump pulses was determined to be 4 m when the pump pulses of 0.50 mW average power and the probe pulses of 0.25 mW average power were used. We derived the pulse area equations which take into account the coherent interaction between the pulses and the Nd3+ fiber. The fiber-length dependence of the signal intensity was explained well by the pulse area equations. (C) 1997 American Institute of Physics.

 

239.    R. Yano and N. Uesugi

            "Stark-level one-phonon dephasing process of Nd3+-doped silicate glass fiber studied with accumulated photon echoes"

            Phys. Rev. B 55 (9), 5712-5716 (1997).

 

            ABSTRACT: Measurements of the homogeneous width of the (4)G(5/2), (2)G(7/2)-I-4(9/2) transition of Nd3+ in a silicate glass fiber at low temperatures by the technique of accumulated photon echoes show that the dephasing processes are one-phonon processes between the Stark levels of Nd3+. These dephasing processes differ from the commonly observed processes of rare-earth ion-doped glasses: the local-configurational-change-induced dephasing process and the Raman process with low-frequency modes. The densely distributed Stark levels of the (4)G(5/2) and (2)G(7/2) states are responsible for one-phonon processes. The transition-wavelength dependences of the homogeneous widths Gamma(h)(4.2 K) and Gamma(h)(T --> 0) ale explained by using the one-phonon process model.

 

240.    C. H. Yuan, M. Fujino, K. Ebata, and K. Furukawa

            "Novel pyrolytic conversion of poly[(diisobutylsilylene)methylene] to stoichiometric silicon carbide"

            Macromolecules 30 (24), 7618-7620 (1997).

 

            ABSTRACT:

241.    C. H. Yuan, M. Fujino, K. Ebata, K. Furukawa, and N. Matsumoto

            "Stoichiometric silicon carbide semiconductor prepared from a preceramic polycarbosilane"

            Abstr. Pap. Am. Chem. Soc. 214, 114-POLY (1997).

 

            ABSTRACT:

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

            "Room-temperature near-ultraviolet electroluminescence from a linear silicon chain"

            Appl. Phys. Lett. 71 (23), 3326-3328 (1997).

 

            ABSTRACT: Single-layer light emitting diodes (LEDs) were fabricated using poly[bis(p-butylphenyl)silane] as the emissive laver. An efficient and stable electroluminescence with a maximum at 407 nm was observed at room temperature under a forward electric field greater than 6x10(5) V/cm. The coincidence of electroluminescence with photoluminescence suggests the origin of the electroluminescence in an excited silicon chain segment. The high external quantum efficiency (0.1% photons/electron), narrow emission (full width at half maximum=15nm), improved operating stability, and good solubility in organic solvents provide the possibility of using polysilanes for ultraviolet LEDs. (C) 1997 American Institute of Physics.

 

243.    J. M. Zhang, M. Cardona, Z. L. Peng, and Y. Horikoshi

            "Raman scattering studies on Si-doped GaAs grown by hydrogen-assisted molecular beam epitaxy"

            Appl. Phys. Lett. 71 (13), 1813-1815 (1997).

 

            ABSTRACT: The surfactant effect of atomic hydrogen on the incorporation of silicon into (100)-, (111)A-, and (311)A-oriented GaAs grown by hydrogen-assisted molecular beam epitaxy has been studied with Raman spectroscopy. Local vibrational modes (LVMs) of Si-Ga and Si-As impurities are observed for excitation nearly resonant with the E-1 energy gap. Site switch of the doping Si atoms from Ga to As lattice sites due to the surfactant effect of H during growth of the high-index doped layers was directly monitored by changes of the normalized intensity of the LVMs. An increase of the free carrier concentration in p-type samples and a decrease in n-type samples resulting from this site switch were also observed in the plasmon-phonon coupled modes as observed in Raman scattering. Similar changes in carrier concentrations were observed by means of electrical transport measurements. (C) 1997 American Institute of Physics.