1.         K. Ajito and M. Morita

            "Imaging and spectroscopic analysis of single microdroplets containing p-cresol using the near-infrared laser tweezers Raman microprobe system"

            Surf. Sci. 428, 141-146 (1999).

 

            ABSTRACT: The near-infrared (NIR) laser tweezers/Raman microprobe system features two charge-coupled device (CCD) cameras with holographic notch filters (HNFs for the imaging and spectroscopic analysis of molecules in a single microdroplet (MD), One CCD camera and a HNF are used to record an image of the laser microprobe in a trapped MD. The other CCD camera and two HNFs are used with a polychromator to obtain a Raman spectrum of molecules in the MD. A dielectric multilayer coated beam splitter divides the scattered NIR light into two optical paths for the cameras. The system provides sufficient sensitivity to obtain a Raman spectrum of p-cresol contained in a single picoliter toluene MD and sufficient spatial resolution to record an image of the laser microprobe in a trapped MD simultaneously. Furthermore, a difference in the solubility for the p-cresol in bulk solvent and in the MD solvent was clearly observed using this system. (C) 1999 Elsevier Science B.V. All rights reserved.

 

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

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

            IEEE Trans. Appl. Supercond. 9 (2), 4253-4256 (1999).

 

            ABSTRACT: We report on the fabrication of InAs-inserted-channel InAlAs/InGaAs inverted HEMTs with NbN electrodes made by using a DC magnetron sputtering deposition and we describe the device characteristics we obtained. Excellent pinch-off characteristics were obtained even at similar to 10 K when NbN electrodes retain their superconductivity. For a 3-mu m-gate device, the maximum extrinsic transconductance at 10 K was 300 mS/mm, even at the very low drain voltage of 0.2 V. We found that the HEMTs with NbN electrodes, not only have superior characteristics at similar to 10 K that exceed the critical temperature of Nb, but are also able to combine with NbN Josephson junctions.

 

3.         T. Akazaki, H. Yamaguchi, J. Nitta, and H. Takayanagi

            "Superconductor-semiconductor-superconductor junctions using NbN"

            Supercond. Sci. Technol. 12 (11), 901-903 (1999).

 

            ABSTRACT: We report on the fabrication of the superconductor-semiconductor-superconductor (S-Sm-S) junction formed by two superconducting NbN electrodes and a two-dimensional electron gas (2DEG) in an Al0.7Ga0.3Sb/InAs heterostructure and we describe the superconducting characteristics we obtained. A critical current I-C of similar to 0.9 mu A at similar to 70 mK was obtained for the first time in the S-Sm-S junction using NbN. Although T-C of NbN was about 12 K, I-C decreased with increasing temperature and then disappeared at similar to 1.7 K. This phenomenon can be qualitatively explained by considering that the 2DEG underneath the NbN changed places with the pseudo-superconductor because of proximity-induced superconductivity.

 

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

            "Anomalous low temperature behavior of superconducting Nd1.85Ce0.15CuO4-y"

            Phys. Rev. Lett. 83 (13), 2644-2647 (1999).

 

            ABSTRACT: We have measured the temperature dependence of the in-plane London penetration depth lambda(ab)(T) and the maximum Josephson current I-c(T) using bicrystal grain boundary Josephson junctions of the electron-doped cuprate superconductor Nd1.85Ce0.15CuO4-y. In contrast to the usual monotonous decrease (increase) of lambda(ab)(T) [I-c(T)] with decreasing temperature, lambda(ab)(T) and I-c(T) are found to increase and decrease, respectively, with decreasing temperature below 4 K. We attribute this anomalous behavior to the presence of the Nd3+ paramagnetic moments. Correcting the measured lambda(ab)(T) dependence for the temperature dependent susceptibility due to the Nd moments, an exponential dependence is obtained indicating isotropic s-wave pairing.

 

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

            "Photon-spin controlled lasing oscillation in GaAs vertical cavity surface emitting lasers"

            in Compound Semiconductors 1998, Institute Of Physics Conference Series Vol. 162 (Iop Publishing Ltd, Bristol, 1999), pp. 61-66.

 

            ABSTRACT: We investigate spin-optical effects in GaAs vertical cavity surface emitting lasers at room temperature. We show experimentally that optical excitation of the GaAs laser gain medium with circularly polarized pump pulses results in lasing emission of circularly polarized light. We demonstrate that the polarization of the lasing output can be controlled by tuning the polarization states of the pump pulses. We discuss the laser polarization characteristics of the surface emitting lasers in terms of the electron-spin alignment created by optical excitation with circularly polarized pump in GaAs gain medium.

 

6.         D. G. Austing, S. Sasaki, S. Tarucha, S. M. Reimann, M. Koskinen, and M. Manninen

            "Vertical quantum dots with elliptically deformed cross sections"

            Physica B 272 (1-4), 68-71 (1999).

 

            ABSTRACT: Few-electron vertical quantum dot artificial atoms with circular and elliptically deformed cross sections are investigated. Because of the high symmetry of the lateral confining potential, circular dots show a pronounced shell structure. With the lifting of level degeneracies, even a small deformation in shape is found to radically alter the shell structure leading to significant modifications of the addition energy spectra, and to induce change in the total spin. (C) 1999 Elsevier Science B.V. All rights reserved.

 

7.         D. G. Austing, S. Sasaki, S. Tarucha, S. M. Reimann, M. Koskinen, and M. Manninen

            "Ellipsoidal deformation of vertical quantum dots"

            Phys. Rev. B 60 (16), 11514-11523 (1999).

 

            ABSTRACT: Addition energy spectra at 0 T of circular and ellipsoidally deformed few-electron vertical quantum dots ore measured and compared to results of model calculations within spin-density-functional theory. Because of the rotational symmetry of the lateral harmonic confining potential, circular dots show a pronounced shell structure. With the lifting of the single-particle level degeneracies, even a small deformation is found to radically alter the shell structure leading to significant modifications in the addition energy spectra. Breaking the circular symmetry with deformation also induces changes in the total spin. This "piezomagnetic" behavior of quantum dots is discussed, and the addition energies for a set of realistic deformation parameters an provided. Far the case of the four-electron ground state at 0 T, a spin-triplet to spin-singlet transition is predicted, i.e., Hund's first rule no longer applies. Application of a magnetic field parallel to the current confirms that this is the case, and also suggests that the anisotropy of an elliptical dot, in practice, may be higher than that suggested by the geometry of the device mesa in which the dot is located. [S0163-1829(99)05839-7].

 

8.         D. G. Austing, S. Tarucha, P. C. Main, M. Henini, S. T. Stoddart, and L. Eaves

            "Multiple gated InAs dot ensembles"

            Appl. Phys. Lett. 75 (5), 671-673 (1999).

 

            ABSTRACT: We adapt a multiple gating technology to characterize electrically an ensemble of "self-assembled" InAs dots embedded in a plane within an Al0.20Ga0.80As tunneling barrier. Although the mu m-sized mesa incorporates several hundred dots, we find that only a few of them contribute to the current close to threshold. Gating allows us to probe the origin of the sharp current peaks, and we can classify these peaks into families in a simple way according to their gate voltage dependence. (C) 1999 American Institute of Physics. [S0003-6951(99)01431-X].

 

9.         G. Austing, Y. Tokura, T. Honda, S. Tarucha, M. Danoesastro, J. Janssen, T. Oosterkamp, and L. Kouwenhoven

            "Several- and many-electron artificial-atoms at filling factors between 2 and 1"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 38 (1B), 372-375 (1999).

 

            ABSTRACT: We introduce new phenomena that can be studied in an artificial-atom vertical single electron transistor. As we move from the few-electron regime to the several-electron regime, and then the many-electron regime, features in the conductance peaks related to magnetic field induced spin polarization evolve. This allows us to probe the spin-flip region bounded by the lest single-particle crossing at low field, and the eventual formation of a maximum density droplet at high field.

 

10.       Y. Avishai, Y. Band, and D. Brown

            "Conductance distribution between Hall plateaus"

            Phys. Rev. B 60 (12), 8992-8998 (1999).

 

            ABSTRACT: Mesoscopic fluctuations of two-port conductance and four-port resistance between Hall plateaus an studied within a realistic model for a two-dimensional electron gas in a perpendicular magnetic field and a smooth disordered potential. The two-port conductance distribution P(g) is concave between g=0 and g=1 and is nearly flat between g=0.2 and g=0.8. These characteristics are consistent with recent observations. The distribution is found to be sharply peaked near the end points g=0 and g=1. The distribution functions for the three independent resistances in a four-port Hall bar geometry are, on the ether hand, characterized by a central peak and a relatively large width.

 

11.       O. Benson and Y. Yamamoto

            "Master-equation model of a single-quantum-dot microsphere laser"

            Phys. Rev. A 59 (6), 4756-4763 (1999).

 

            ABSTRACT: We present a theoretical model for the electrically pumped single-quantum-dot microsphere laser. We solve the master equation of the system and analyze the steady state and dynamical properties of the optical field, such as output power, photon number fluctuation, and linewidth, for realistic experimental parameters. The laser threshold power is several orders of magnitude lower than is currently possible with semiconductor microlasers. A semiclassical approximation for the output power and laser linewidth is derived and compared to the exact solution. Electrical pumping together with Coulomb blockade effect allows for the realisation of regular pumping in the system. We discuss the possibility for the generation of heralded single photons and of sub-Poissonian laser light.

 

12.       I. Bleyl, K. Ebata, S. Hoshino, K. Furukawa, and H. Suzuki

            "Conformational phase transition in a high-efficiency near-ultraviolet electroluminescent diarylpolysilane"

            Synth. Met. 105 (1), 17-22 (1999).

 

            ABSTRACT: We report on the observation of a structural phase transition in a diarylpolysilane, poly[bis(p-n-butylphenyl)silane] (PBPS), which was recently shown to emit high-efficiency room-temperature electroluminescence (EL) in the near-ultraviolet region. Spectroscopic and calorimetric experiments have revealed that this structural phase transition accompanies a conformational change in the Si-backbones of PBPS from the disorder form (lower temperature form) to the trans-planar form (higher temperature form). The spectroscopic changes induced by this structural phase transition are discussed in relation to the EL characteristics of PBPS, and found to have positive effects on them. (C) 1999 Elsevier Science S.A. All rights reserved.

 

13.       A. Chavez-Pirson and S. T. Chu

            "Polarization effects in near-field excitation - collection probe optical microscopy of a single quantum dot"

            J. Microsc.-Oxf. 194, 421-425 (1999).

 

            ABSTRACT: We solve numerically the three-dimensional Vector form of Maxwell's equation for the situation of near-field excitation and collection of luminescence from a single quantum dot, using a scanning near-field optical fibre probe with subwavelength resolution. We highlight the importance of polarization-dependent effects in both the near-field excitation and collection processes. Applying a finite-difference time domain method, we calculate the complete vector fields emerging from a realistic probe structure which is in close proximity to a semiconductor surface, We model the photoluminescence from the quantum dot in terms of electric dipoles of different polarization directions, and determine the near-field luminescence images of the dot captured by the same probe. We show that a collimating effect in the high index semiconductor significantly im proves the spatial resolution in the excitation-collection mode. We find that the spatial resolution, image shape and collection efficiency of near-field luminescence imaging strongly depend on the polarization direction as represented by the orientation of the radiating electric dipoles inside the quantum dot.

 

14.       A. Chavez-Pirson and S. T. Chu

            "A full vector analysis of near-field luminescence probing of a single quantum dot"

            Appl. Phys. Lett. 74 (11), 1507-1509 (1999).

 

            ABSTRACT: We solve numerically the three-dimensional vector form of Maxwell's equation for the situation of near-field excitation and collection of luminescence from a single quantum dot using a scanning near-field optical fiber probe with sub-wavelength resolution. Applying a finite-difference time-domain method, we calculate the complete vector fields emerging from a realistic probe structure, as well as the near-field luminescence image of the dot captured by the same probe. We show that a collimating effect in the high index semiconductor significantly improves the spatial resolution in excitation/collection mode. We find that the spatial resolution, image shape, and collection efficiency of near-field luminescence strongly depend on the orientation of the radiating dipole in the dot. (C) 1999 American Institute of Physics. [S0003-6951(99)01111-0].

 

15.       R. Crespo, H. Teramae, D. Antic, and J. Michl

            "Calculation of the conformational dependence of valence and Rydberg states in n-tetrasilane"

            Chem. Phys. 244 (2-3), 203-214 (1999).

 

            ABSTRACT: Previous CIS/6-31G** and CASSCF/6-31G* calculations of valence excited states of n-tetrasilane accounted qualitatively for the observed conformational dependence of condensed-phase UV absorption spectra. In an attempt to understand this result, we have performed CIS calculations with a larger basis set (MC-311G(2d) on Si, 6-311G on H, and 2s, 2p, and 2d diffuse orbitals at molecular center of mass). The first two excited states are of valence character at all dihedral angles if the molecule is isolated. When it is embedded in a rare gas cluster, the lowest four states are of valence character, and the results are nearly identical with those obtained without diffuse orbitals in the basis set, since all Rydberg states are shifted to higher energies relative to valence states. Similar behavior was observed for ethylene and disilene, and basis sets without diffuse functions seem appropriate for the computation of low-energy parts of condensed-phase spectra. Valence vs. Rydberg character was judged from the total [R-2] values, the Mulliken population of molecule-centered diffuse functions, and the [r(2)](1/2) values of the two 'singly occupied' natural orbitals). (C) 1999 Elsevier Science B.V. All rights reserved.

 

16.       K. Ebata, K. Furukawa, N. Matsumoto, and M. Fujiki

            "End-grafted polysilanes on substrate surfaces: Surface-tethered sigma-conjugated polymer chains"

            Abstr. Pap. Am. Chem. Soc. 218, U523-U524 (1999).

 

            ABSTRACT:

17.       M. Edwards and S. Nishida

            "Global-motion detection with transparent-motion signals"

            Vision Res. 39 (13), 2239-2249 (1999).

 

            ABSTRACT: A number of experiments were conducted to compare the ability of observers to extract unidirectional and bidirectional (transparent) global-motion signals. In the unidirectional condition, the noise signal consisted of purely randomly-moving dots while in the bidirectional condition, a number of the randomly moving dots were replaced by the same number of dots moving in a specific (secondary-signal) direction. The threshold measure was the minimum number of signal dots required to determine the global-motion direction. For the bidirectional condition, parameters varied were the angular separation between the global-motion and secondary-signal directions and the strength of the secondary signal. Thresholds for unidirectional and bidirectional conditions were the same when the angular difference between global-motion and secondary-signal directions were 90 degrees or greater, i.e. the ability of observers to extract a transparent signal was the same as their ability to extract a unidirectional one. Similarly, with motion-in-depth signals, thresholds for extracting a centripetal signal were not elevated by replacing a number of the randomly-moving noise dots with the same number centrifugally-moving dots. The results are interpreted as indicating that motion signals moving between 90 and 180 degrees to the global-motion direction provide uniform masking of the global-motion signal. For angular separations less than 90 degrees, a suprathreshold secondary signal resulted in threshold elevation. This result could be due, to stronger inhibition from motion units tuned to similar (< 90 degrees) directions, broad directional-tuning of the underlying motion units (changing the task from signal detection to a signal discrimination) or a combination of the two. (C) 1999 Elsevier Science Ltd. All rights reserved.

 

18.       T. Endo, Y. Sugimoto, K. Takeda, and K. Shiraishi

            "Electronic structures of polysilanes having pyrrole and thiophene groups"

            Synth. Met. 98 (3), 161-172 (1999).

 

            ABSTRACT: The electronic structures of polysilanes (PSi) having Pyrrole (Pyr) side-chains and Thiophene (Thi) side-chains have been theoretically investigated. Two kinds of the characteristic sigma-pi mixing occur between Si's delocalized sigma electrons and Pyr (Thi) localized pi electrons. In the valence band states, N's (S's) non-bonding (n) pi electrons localizing at Pyr and Thi groups splits the PSi's p sigma band (sigma-n mixing). In the band gap, two pi states localized at Pyr (Thi) groups are produced (sigma-pi mixing). The rotation of Pyr and Thi groups varies the degree of the sigma-pi mixing and cause the energy dispersion toward the Si skeleton axis. This energy dispersion has a potential to change the PSi system, being a semimetallic electronic structure from a semiconducting one in the limited form. (C) 1999 Elsevier Science S.A. All rights reserved.

 

19.       H. Enomoto, M. S. Miyauchi, and K. Ota

            "Lower bounds for the number of edge-crossings over the spine in a topological book embedding of a graph"

            Discret Appl. Math. 92 (2-3), 149-155 (1999).

 

            ABSTRACT: In a topological book embedding of a graph, the graph is drawn in a topological book by placing the vertices along the spine of the book and drawing the edges in the pages; edges are allowed to cross the spine. Earlier results show that every graph having n vertices and m edges can be embedded into a 3-page book with at most O(m log n) edge-crossings over the spine. This paper presents lower bounds on the number of edge-crossings over the spine for a variety of graphs. These bounds show that the upper bound O(m log n) is essentially best possible. O 1999 Elsevier Science B.V. All rights reserved.

 

20.       T. Ernst, D. Munteanu, S. Cristoloveanu, T. Ouisse, S. Horiguchi, Y. Ono, Y. Takahashi, and K. Murase

            "Investigation of SOI MOSFETs with ultimate thickness"

            Microelectron. Eng. 48 (1-4), 339-342 (1999).

 

            ABSTRACT: Ultra-thin SOI MOSFETs with 1-5nm thick SOI film, are experimentally and theoretically investigated. Single- and double-gate configurations are compared; the double-gate MOSFET exhibits a substantial increase in transconductance, presumably resulting from volume inversion. Most of the experimental data can be explained by combining classical models with self-consistent quantum calculations. The characteristics are well-behaved and reveal unique "ultra-thin" film properties: enhanced interface coupling and body-substrate coupling, degraded mobility, increased threshold voltage.

 

21.       P. Finnie and Y. Homma

            "Island growth and surface roughness scaling of epitaxial GaAs on Si observed by in situ scanning electron microscopy"

            Phys. Rev. B 59 (23), 15240-15245 (1999).

 

            ABSTRACT: The growth by molecular beam epitaxy of GaAs on Si(100) has been studied by in situ scanning electron microscopy. The island growth process and subsequent surface roughness evolution was observed for substrate temperatures ranging from 375 degrees C to 500 degrees C. Two types of islands are formed: those that cease to grow beyond about 20 nm in size, and those that continue to grow, eventually forming a continuous layer. The large islands show preferred facets and grow slowly unless they merge with neighboring islands. After merging, they grow quickly until they complete the preferred facet again. Continuous layers are formed with small-scale roughness originating from the outline of the large islands. This evolution is quantified by calculating autocorrelation lengths. This characteristic length scale of the roughness grows with time, showing little variation with substrate temperature at early times. The in-plane roughness is seen to scale as a power law in time with exponent 1/z = 0.29 +/- 0.01. Like the original islands, the roughness scale grows by the successive merger of facetted structures with neighbors. The roughness evolution is compared qualitatively and quantitatively to self-affine models and mound coarsening models. [S0163-1829(99)04523-3].

 

22.       P. Finnie and Y. Homma

            "Maskless selective area molecular beam epitaxy of semiconductors and metals using atomic step networks on silicon"

            J. Cryst. Growth 202, 604-609 (1999).

 

            ABSTRACT: Step-patterned substrates of vicinal Si(111) were used for the selective growth of a variety of materials, both semiconductor (GaAs and Ge) and metal (Au and Ag) Step patterning was performed by etching substrates photolithographically, and annealing them. Subsequent growth by molecular beam epitaxy was observed by in situ ultra-high vacuum scanning: electron microscopy. Materials grew preferentially on the prepared step bands either by a desorption mechanism or by a diffusion mechanism, depending on the temperature. The growth of silver was different, although the initial monolayer was also selective. This growth technique can be applied to a small region or an entire wafer. Growth areas fan be several microns wide, or, in principle, can be of nanometer scale (C) 1999 Elsevier Science B.V. All rights reserved.

 

23.       P. Finnie and Y. Homma

            "Dynamics, interactions, and collisions of atomic steps on Si(111) in sublimation"

            Phys. Rev. Lett. 82 (13), 2737-2740 (1999).

 

            ABSTRACT: The dynamics of atomic steps and the interactions between them were observed by in situ scanning electron microscopy for the sublimation of a Si(111) surface which was atomically flat on a large (similar to 100 mu m X 50 mu m) scale. Newly nucleated widely spaced steps moved at a constant velocity. For more narrowly spaced steps, diffusion mediated step-step interactions reduced the step velocity. To further probe these interactions, steps were made to collide. In destructive collisions, steps decelerated and flattened. In constructive collisions double atomic steps were produced. [S0031-9007(99)08702-5].

 

24.       T. Fujisawa, T. H. Oosterkamp, W. G. van der Wiel, S. Tarucha, and L. P. Kouwenhoven

            "Photon assisted tunneling spectroscopy on a double quantum dot"

            in Compound Semiconductors 1998, Institute Of Physics Conference Series Vol. 162 (Iop Publishing Ltd, Bristol, 1999), pp. 493-498.

 

            ABSTRACT: Semiconductor quantum dots are often referred to as artificial atoms since they contain well-defined discrete levels. When two of these quantum dots axe coupled, bonding and anti-bonding states are formed, analogous to covalent diatomic molecules. We use microwaves to excite an electron from the bonding to the anti-bonding state and measure a photon-assisted-tunneling current through the quantum dot molecule. We can in-situ change the tunnel coupling and find a clear transition from electrostatic (ionic) to covalent coupling in a double-quantum-dot system.

 

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

            "Asymmetric tunnel barrier in a Si single-electron transistor"

            Microelectron. Eng. 47 (1-4), 197-199 (1999).

 

            ABSTRACT: Strong asymmetry was found in conductance versus source-drain voltage in Si single-electron transistors. This suggests that the potential profile of the tunnel barrier is asymmetric along the direction of current flow.

 

26.       A. Fujiwara, Y. Takahashi, K. Yamazaki, H. Namatsu, M. Nagase, K. Kurihara, and K. Murase

            "Double-island single-electron devices - A useful unit device for single-electron logic LSI's"

            IEEE Trans. Electron Devices 46 (5), 954-959 (1999).

 

            ABSTRACT: We fabricated a single-electron device that is useful as a unit device for single-electron logic circuits. The device is a three-current-terminal device fabricated on a silicon-on-insulator (SOI) wafer, which includes two Si islands whose electric potential can be controlled by gates, Sub-50-nm Si islands were integrated in an area smaller than 0.02 mu m(2) through self-aligned formation of the islands by pattern-dependent oxidation (PADOX) of a T-shaped mire. By PADOX, each island was embedded in one branch of the T-shaped wire, We show two electrical characteristics which demonstrate the usefulness of this device as a circuit element. First, current switching between two branches was performed at 30 K by using gate voltage to control the Coulomb blockade in each island. Second, a correlation between the two currents was observed because the two islands were integrated close to each other, The latter indicates a capacitive coupling between the islands, which opens up the possibility of one-by-one transfer of electrons in this device. These findings show that the proposed island-integration technique is applicable to making ultra-low-power and highly integrated single-electron circuits.

 

27.       T. Fukuda

            "Initial oxygen interaction between Ge(100) and Ge/Si(100) surfaces compared by scanning tunneling microscopy"

            Jpn. J. Appl. Phys. Part 2 - Lett. 38 (12A), L1450-L1452 (1999).

 

            ABSTRACT: The initial stage of oxygen interaction on epitaxially grown cc overlayers formed on Si(100) (Ge/Si(100)) surfaces and on the Cie(100) surface was compared by scanning tunneling microscopy in an ultrahigh vacuum. Although both surfaces were terminated with Ge dimers, suppression of the reaction by molecular oxygen on the Ge/Si(100) surface was demonstrated at an atomic resolution. In addition, two new types of oxygen-induced reaction products were identified on the Ge/Si(100) surface.

 

28.       T. Fukuda

            "Initial surface reconstructions on solid-phase homoepitaxially grown amorphous silicon overlayers on Si(111)-7 x 7 surface"

            Surf. Sci. 442 (1), 107-114 (1999).

 

            ABSTRACT: The initial nucleation stage of surface reconstructions which appear during the crystallization of vacuum-deposited amorphous silicon (a-Si) overlayers on clean Si(111)-7 x 7 surfaces was investigated by scanning tunneling microscopy. When the initial a-Si coverage of less than similar to 4 ML (monolayers) was annealed at 300 degrees C, the surface exhibited reordered adatoms. The adatom trimers were confined in half-units of the substrate 7 x 7 dimer-adatom-stacking fault reconstruction and T-4-adatom domains with 2 x 2 or c(2 x 4) configuration were stabilized. When more than similar to 4 ML thick a-Si overlayers were annealed, however, the surface exhibited reconstructed islands at the initial nucleation stage of the surface reconstruction. For both cases, a corner hole structure consisting of a six-adatom ring was noticed at the same time as the 2 x 2 and c(2 x 4) formation. The nucleation of these surface reconstructions is discussed in terms of the buried substrate dimer-stacking fault structure. (C) 1999 Elsevier Science B.V. All rights reserved.

 

29.       T. Fukuda

            "Nickel-induced effect on the surface morphology of rapid-quenched Si(111)"

            J. Vac. Sci. Technol. A-Vac. Surf. Films 17 (5), 2800-2804 (1999).

 

            ABSTRACT: The morphology and atomic structures of Ni-stabilized ''1 X 1'' domains formed on rapid-quenched Si(lll) surfaces were studied using atomic force microscopy (AFM) in air and scanning tunneling microscopy (STM) in a vacuum. Quantitative analysis of the surface morphologies by ex situ AFM showed that the widths for inhibiting the 1 X 1 stabilization near monoatomic steps depended on Ni deposition of between 1.8 X 10(-2) and 9 x 10(-4) monolayers (ML). For Ni depositions of less than 9 X 10(-4) ML, the protrusion of the 1 X 1 domain decreased. In situ STM study revealed that the 7 X 7 reconstruction had nucleated in the 1 X 1 domains. (C) 1999 American Vacuum Society. [S0734-2101(99)06205-3].

 

30.       T. Fukuda

            "Formation of pi-bond chains on solid-phase homoepitaxially grown Si(111) surfaces"

            Phys. Rev. B 59 (15), 9752-9755 (1999).

 

            ABSTRACT: The stabilization of the rr-bonded 2x1 reconstruction and adatomlike structure that appeared during the crystallization of vacuum-deposited amorphous Si (a-Si) overlayers on a clean Si(lll) 7x7 surface was investigated by scanning tunneling microscopy. The structure was only seen on the surface for initial a-Si thicknesses of 2-4 ML and annealing at 350-500 degrees C. Based on high-resolution dual-bias scanning tunneling microscopy images, an atomic model of the structure is proposed. Because the adatomlike structure was formed on the dimer row of the substrate 7x7 reconstruction, the buried dimer-stacking fault, network and high surface atom density play essential roles in the stabilization of the structure. [S0163-1829(99)06515-7].

 

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

            "An isolated silicon single chain end-grafted onto a substrate surface"

            Appl. Phys. Lett. 75 (6), 781-783 (1999).

 

            ABSTRACT: We report atomic force microscopy images of one-dimensional silicon chains (polysilanes) individually bonded to a substrate surface [quartz glass (SiO2), sapphire (Al2O3), and Si(111)]. The sample was prepared by a one-to-one chemical reaction between a reactive anchor of alkylbromide on the surface and a polysilanyl lithium. We observed dot images with variable densities which depended on the reactive anchor density. Each dot, with a diameter of about 20 nm and a height of about 5 nm, corresponded to an isolated single polysilane molecule with a collapsed structure typical of usual end-grafted polymers under poor solvent conditions. (C) 1999 American Institute of Physics. [S0003-6951(99)00232-6].

 

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

            "Bipolar carrier behavior in a near ultraviolet electroluminescent silicon polymer: Poly[bis(p-n-butylphenyl)silane]"

            Mol. Cryst. Liquid Cryst. 327, 181-184 (1999).

 

            ABSTRACT: Bipolar carrier behavior in a near ultraviolet electroluminescent polymer, poly [bis(p-n-butylphenyl)silane], was investigated by means of time-of-flight measurements. We observed a hole drift mobility of about 10(-4) cm(2)V(-1)sec(-1) at room temperature and a clear trace of electron migration. This unique electron behavior is an essential factor as regards observing efficient electroluminescence from the polymer.

 

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

            "Bipolar carrier behavior in a near ultraviolet electroluminescent silicon polymer: Poly[bis(p-n-butylphenyl)silane]"

            Mol. Cryst. Liq. Cryst. Sci. Technol. Sect. A-Mol. Cryst. Liq. Cryst. 327, 181-184 (1999).

 

            ABSTRACT: Bipolar carrier behavior in a near ultraviolet electroluminescent polymer, poly[bis(p-n-butylphenyl)silane], was investigated by means of time-of-flight measurements. We observed a hole drift mobility of about 10(-4) cm(2)V(-1)sec(-1) at room temperature and a clear trace of electron migration. This unique electron behavior is an essential factor as regards observing efficient electroluminescence from the polymer.

 

34.       L. F. Giles and Y. Kunii

            "Crystallographic defects in thermally oxidized wafer bonded silicon on insulator (SOI) substrates"

            J. Electron. Mater. 28 (4), 372-376 (1999).

 

            ABSTRACT: The crystalline duality of wafer bonded (WB)silicon on insulator (SOI) structures thermal treated in dry oxygen ambients has been investigated by means of transmission electron microscopy and defect etching. The main crystallographic defects present in the SOI layers are dislocations, amorphous precipitates, and oxidation induced stacking faults (OISF), The evolution of the OISFs with time and temperature has also been investigated. The main feature observed is that the OISF in WE SOI structures undergo a retrogrowth process at temperatures around T = 1195 degrees C for times of t = 2 h. This result is very similar to that recently reported for oxygen implanted SOI (SIMOX) but considerably different from that observed in bulk silicon. The experimetal data fits nicely a model recently proposed for the retrogrowth of OISF in thin SOI layers. This model considers that the self-interstitial supersaturation is considerably reduced compared to bulk silicon due to the relative fast point defect recombination inside the top silicon layer.

 

35.       L. F. Giles, Y. Kunii, and K. Izumi

            "Nucleation, growth and retrogrowth of oxidation induced stacking faults in thin silicon-on-insulator"

            J. Electron. Mater. 28 (1), 13-18 (1999).

 

            ABSTRACT: The nucleation, growth, and retrogrowth of stacking faults were investigated for thermally oxidized silicon-on-insulator substrates formed by the separation by implanted oxygen (SIMOX) method. It has been observed that for high oxidation temperatures (T >1150 degrees C) oxidation induced stacking faults (OISFs) undergo a retrogrowth (shrinkage) process at noticeably lower temperatures than in bulk silicon. The retrogrowth process in thin film SIMOX substrates starts at approximately 1190 degrees C for the 2 h thermal oxidations. In this paper, a model for the retrogrowth process is proposed based on the assumption that at high oxidation temperatures vacancies may be injected from the thermal oxide/top silicon interface. We suggest that the vacancy injection reduces the self-interstitial supersaturation and as a direct consequence, attenuates the OISF growth. We also propose that the self-interstitial supersaturation is reduced through point defect recombination inside the silicon overlayer and at the top-silicon/buried-oxide interface where a high density of steps and kink sites are found.

 

36.       T. Hanaguri, M. Naito, and K. Kitazawa

            "Superconducting phenomenology of cuprates: effect of pseudo-gap and other anomalies"

            Physica C 318, 345-352 (1999).

 

            ABSTRACT: This paper discusses new aspects of the superconducting phenomenology of the cuprate high-T-c superconductors in terms of the change in superconducting condensation energy and the electronic states in the vortex core due to the extreme phenomenological parameters, the d-wave superconducting gap and the presence of the 'pseudo-gap' in the normal state. It is shown that the extreme phenomenological parameters and the d-wave superconducting gap make the vortex state of high-T-c superconductors quite different from that of conventional superconductors in many aspects both thermodynamically and dynamically. Further, we show that the presence of the 'pseudo-gap' should reduce the condensation energy and increase the penetration depth. The effect of the 'pseudo-gap' on the vortex pinning is discussed in relation to the empirical scaling laws observed in the phase diagram in the mixed state. (C) 1999 Elsevier Science B.V. All rights reserved.

 

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

            "The effect of surface roughness on infrared external reflection spectroscopy"

            Vib. Spectrosc. 19 (2), 199-203 (1999).

 

            ABSTRACT: The effect of surface roughness of the back-side of a film-supporting material on Fourier transform infrared (FTIR) external reflection (ER) spectra was studied by using 9-monolayer cadmium stearate Langmuir-Blodgett (LB) films. The LB films are prepared on two infrared-transparent ZnSe substrates whose top surfaces are optically polished and bottom surfaces have controlled surface roughness with 1.2 and 0.1 mu m of protrusions, Although the roughness of 0.1 mu m is smaller than the wave-length of the infrared ray, both LB films show typical ER spectra qualitatively. On closer inspection, however, the LB film on the substrate with 0.1 mu m protrusions is irregular and the LB film on 1.2 mu m protrusions is better. These results indicate that the surface roughness of the backside of substrate is necessary for ER analyses. (C) 1999 Elsevier Science B.V. All rights reserved.

 

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

            "Are there discrete distal-proximal representations of the index finger and palm in the human somatosensory cortex? A neuromagnetic study"

            Clin. Neurophysiol. 110 (3), 430-437 (1999).

 

            ABSTRACT: Objective: The distal-proximal representations of the finger and palm in the first somatosensory cortex (SI) were studied in humans. Methods: Somatosensory evoked magnetic fields (SEFs) from 11 subjects were measured, following mechanical stimulation of the skin by using a 122 channel whole head SQUID system. Sensory stimulus comprising of a 10 ms vibration at the frequency of 200 Hz was delivered to 6 successive sites in 3 cm increments, along the distal-proximal direction over the volar surface of the right index finger and palm. Using a single dipole model, the sources of the magnetic fields were estimated and mapped onto magnetic resonance images of each subject. ANOVA was used for statistics. Results: Source localization was determined on the main peak (M50) of the SEFs. All of the sources were located in the area 3b of SI. Contrary to the well-defined distal-proximal representations in the hand area of simian:SI cortex, there was no statistically significant differences between the locations of the dipoles in human SI cortex evoked by stimulation of different sites; Conclusion: The result, however, should be interpreted with caution, because it cannot be denied that the spatial separation of sources in the distal-proximal somatotopy is beyond the resolving capacity of magnetoencephalography (MEG). In addition, at variance with the discrete distal-proximal gradient in the mechanoreceptor density, there was no statistically significant differences between the signal strengths of the dipoles for stimulation of the different locations. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.

 

39.       N. Hatakenaka and H. Takayanagi

            "Theoretical studies on Josephson pi states"

            Superlattices Microstruct. 25 (5-6), 1075-1082 (1999).

 

            ABSTRACT: The Josephson effect under particle-number restriction is investigated based on the Feynman two-state model. The existence of new dynamical states of the Josephson phase inherent in such a restricted situation is shown. The new state describes a number of features recently observed in a superfluid He-3 weak-link system. Quantum decay from Josephson pi states is also investigated. Since the pi state has two different decay paths, they can interfere during the decay processes by quantum tunneling due to a topological phase originating from total particle-number restriction, and result in a parity effect for tunneling. (C) 1999 Academic Press.

 

40.       N. Hatakenaka and H. Takayanagi

            "Macroscopic quantum tunneling in particle-number conserved Josephson systems"

            Microelectron. Eng. 47 (1-4), 381-383 (1999).

 

            ABSTRACT: The Josephson effect is one manifestation of the quantum aspect of macroscopic objects. It has been tested in various macroscopic systems to confirm their quantum-mechanical nature. In some of the systems, the total number of particles in the system is fixed. In such a case, the dynamics of the system is restricted and hence a new dynamical state might be expected to appear. In this paper, we discuss the Josephson effect under a particle-number restriction, and explore the new dynamical state that emerges from the restriction. We also discuss macroscopic quantum tunneling from the state.

 

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

            "High-quality two-dimensional electron gas at an inverted undoped heterointerface"

            Superlattices Microstruct. 25 (1-2), 295-300 (1999).

 

            ABSTRACT: A back-gated undoped heterostructure, in which a two-dimensional electron gas (2DEG) is formed at the inverted undoped heterointerface through the back-side field effect, offers the possibility of high mobility and the feasibility of fabricating several kinds of back-gated structures. We used such a DEG system to fabricate a Corbino-disk structure. The results for the back-gated Corbino-disk structure show that the density of the 2DEG is well controlled by the back-gate bias and the fine structures corresponding to the integer and fractional quantized Hall effects are clearly observed, reflecting the high quality of the 2DEG formed in the undoped heterostructure. The characteristics in a low magnetic field region confirm the homogeneous back-gate control of the 2DEG down to a density of less than 10(10) cm(-2). (C) 1999 Academic Press.

 

42.       Y. Homma and P. Finnie

            "Steps on subliming Si(111) surfaces"

            J. Phys.-Condes. Matter 11 (49), 9879-9888 (1999).

 

            ABSTRACT: We investigated sublimation-related phenomena and dynamics of atomic steps on Si(lll) surfaces that were atomically flat on a large scale (similar to 100 x 50 mu m) by ultrahigh-vacuum scanning electron microscopy. Step spacing during step-flow sublimation was analysed as a measure of the adatom diffusion length, and compared between a normal Si(111) and a heavily boron-doped Si(lll). The spacing showed a transition-like increase, which is related to incomplete surface melting. The step-flow velocity was obtained for the ultralarge terraces. The step-step interactions were directly examined by making two steps collide.

 

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

            "Aligned island formation using an array of step bands and holes on Si(111)"

            Appl. Phys. Lett. 74 (6), 815-817 (1999).

 

            ABSTRACT: We investigated the control of island formation using a patterned Si(111) surface with a periodic array of holes. During annealing, Au and Ga form islands at fixed locations on the array of step bands surrounding the holes. These materials or their silicides are in liquid phase at elevated temperatures. They diffuse along the step bands and accumulate at particular points on the periodic step bands. The size of the islands can be precisely designed by controlling the size of the pattern. (C) 1999 American Institute of Physics. [S0003-6951(99)02706-0].

 

44.       Y. Homma, P. Finnie, T. Ogino, H. Noda, and T. Urisu

            "Aligned island formation using step-band networks on Si(111)"

            J. Appl. Phys. 86 (6), 3083-3088 (1999).

 

            ABSTRACT: We have achieved control of island formation using a patterned Si(111) surface with a periodic array of atomic-step bands and holes. Liquid metals, Au-Si or Ga, migrate on the patterned surface by annealing and form an island at a particular position in each pattern unit. The islands show highly uniform positions and narrow size distributions. To obtain such good uniformity, the diffusion length of surface atoms should be comparable with the pattern period. High mobility on step bands is also a necessary factor. Periodic arrays of Au islands are used as seeds for selective growth using a vapor-liquid-solid reaction. (C) 1999 American Institute of Physics. [S0021-8979(99)04218-8].

 

45.       Y. Homma, H. Yamaguchi, and P. Finnie

            "In situ scanning electron microscopy of epitaxial processes"

            in Microscopy Of Semiconducting Materials 1999, Proceedings, Institute Of Physics Conference Series Vol. 164 (Iop Publishing Ltd, Bristol, 1999), pp. 161-166.

 

            ABSTRACT: Using scanning electron microscopy we have observed the nucleation and growth of 2-D islands in the initial stages of GaAs growth by molecular beam epitaxy and migration enhanced epitaxy. We have made in situ observations of site selective growth on an atomic-step-controlled Si substrate, and demonstrate the formation of a regular network pattern of GaAs and a regular array of Au dots on the Si substrate.

 

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

            "Zero-field spin splitting in an inverted In0.53Ga0.47As/In0.52Al0.48As heterostructure: Band nonparabolicity influence and the subband dependence"

            Phys. Rev. B 60 (11), 7736-7739 (1999).

 

            ABSTRACT: A gated inverted In0.52Al0.48As/In0.53Ga0.47As/Ln(0.52)Al(0.48)As quantum well is studied via magnetotransport. By analyzing the gate-voltage-dependent beating pattern observed in the Shubnikov-de Haas oscillation, we determine the gate voltage (or electron concentration) dependence of the spin-orbit coupling parameter alpha. Our experimental data and its analysis show that the band nonparabolicity effect cannot be neglected. For electron concentrations above 2 x 10(12) cm(-2), it causes a reduction of alpha up to 25%. We report the alpha value for the second subband. [S0163-1829(99)09335-2].

 

47.       R. Huang, F. Tassone, and Y. Yamamoto

            "Stimulated scattering of excitons into microcavity polaritons"

            Microelectron. Eng. 47 (1-4), 325-327 (1999).

 

            ABSTRACT: We have observed the bosonic enhancement of the elastic exciton-exciton scattering rate in a semiconductor microcavity. The bosonic signature is in the enhancement of the scattering rate that is proportional to the final state occupation number. This gain process for exciton-polaritons is distinctly different from that in a conventional photon laser, because of the fermionic nature of the exciton's constituents, the electron and hole. This distinction becomes prominent at large final state occupation numbers, where we observe a saturation and reduction in the gain. We discuss the origins of this saturation behavior.

 

48.       T. Ichikawa, Y. Yamada, J. Kumagai, and M. Fujiki

            "Suppression of the Anderson localization of charge carriers on polysilane quantum wire"

            Chem. Phys. Lett. 306 (5-6), 275-279 (1999).

 

            ABSTRACT: Comparison of the ESR and electronic absorption spectra of the radical ions of poly(cyclohexylmethylsilane) and poly(n-decyl-(s)-2-methylbutylsilane) has shown that the Anderson localization of charge carriers on part of the Si-Si polymer skeleton can be suppressed by replacing the pendant groups with bulky ones. Replacement reduces the flexibility of the polymer skeleton and therefore the dispersion of the resonance energies of the charge carriers between adjacent Si atoms, which suppresses the localization of the charge carriers arising from irregularity of the periodic potential field on the skeleton. (C) 1999 Elsevier Science B.V. All rights reserved.

 

49.       Y. Ishida, K. Naganuma, and H. Kamada

            "Multi-sideband generation in a femtosecond Cr4+: YAG laser"

            Opt. Rev. 6 (1), 37-41 (1999).

 

            ABSTRACT: We describe the behavior of multi-sidebands in a self-mode-locked femtosecond Cr4+:YAG laser operating near 1.54 mu m. Stokes and anti-Stokes sideband components are extended over 20 THz around the center frequency. An interesting feature here is that when the spectral width of the mode-locked pulse is increased, the specific Stokes sideband near 1.65 mu m (a shift of 13.5 THz) is strongly enhanced due to an induced-Raman process in the laser rod. The measured frequency shifts for all sidebands are well explained by four-wave-mixing processes in the laser rod, accompanied by the resonance effect of the soliton and dispersive wave, both of which are affected mainly by cavity dispersions.

 

50.       H. Ishikane, A. Kawana, and M. Tachibana

            "Short- and long-range synchronous activities in dimming detectors of the frog retina"

            Visual Neurosci. 16 (6), 1001-1014 (1999).

 

            ABSTRACT: In the visual system, nearby neurons of similar functional type have a tendency to fire synchronously. Cross-correlation analysis of spike discharges recorded from pairs of neurons has revealed that the synchronized activity is frequently associated with oscillatory firing patterns. However, the underlying neural mechanisms and functions of synchronization and oscillations are not well understood. In the present study, we simultaneously recorded spike discharges from multiple OFF-sustained type ganglion cells with no antagonistic surround (the dimming detectors) of the frog retina using a planar multi-electrode array and analyzed the temporal properties of light-evoked spike discharges. With full-field, temporally modulated diffuse illumination, cross-correlation analysis revealed the presence of the synchronous oscillatory pattern. The strength of the synchronized activity decreased slightly with increased intercellular distance. Synchronized spike discharges were detected even in cell pairs more than 2 mm apart. The frequency of oscillations peaked at approximately 30 Hz. The shuffled cross-correlogram was nearly flat, indicating that the synchronous oscillatory activities are most probably of neural origin. When GABAA antagonists were applied to the retina, oscillations were suppressed almost completely and the strength of the synchronized activity decreased with increased intercellular distance more sharply than control. When small spot illumination was applied to the overlapping receptive fields of an adjacent cell pair, a weak synchronized activity was evoked without accompanying oscillations. The same cell pair generated a strong synchronized activity accompanied with oscillations with full-field illumination. Our results suggest that local synchronous activities are generated via short-range neural interactions, and that the oscillatory activities are induced by long-range neural interactions and may contribute to the establishment of synchrony between widely separated neuronal populations.

 

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

            "Electrochemical reaction of Fe (CN)(6)(3-)/(4-) on gold electrodes analyzed by surface plasmon resonance"

            Surf. Sci. 428, 195-198 (1999).

 

            ABSTRACT: Surface plasmon resonance (SPR) measurements were combined with cyclic voltammetry (CV) to analyze the electrochemical reactions of Fe(CN)(6)(3-/4-) on gold electrodes in the phosphate electrolyte. The time differential of the SPR signal was correlated with the current. When a low concentration of Fe(CN)(6)(3-/4-) was introduced, the replacement of adsorbed phosphate ions with Fe(CN)(6)(3-/4-) was observed in SPR. At higher concentrations, the SPR signal reflected the refractive index difference of the redox state of Fe(CN)(6)(3-/4-). After continuous potential scanning, the potential dependence of the SPR signal changed completely. However, the cyclic voltammogram was almost identical to that for the first cycle. The change in the SPR signal reflected the formation of a surface film, but electrochemical data showed that this film did not affect the electron transfer reaction in the experimental time window. (C) 1999 Elsevier Science B.V. All rights reserved.

 

52.       Y. Iwasaki, O. Niwa, and M. Morita

            "Electrochemical reaction of cytochrome c on polyaspartic acid modified gold electrodes"

            Sens. Mater. 11 (1), 51-56 (1999).

 

            ABSTRACT: Gold electrodes were modified with a polyaspartic acid thin film as a macromolecular recognition element for electrochemical reactions. The effect of electrode modification on the direct electron transfer reaction of cytochrome c was examined. Cytochrome c exhibited quasi-reversible redox reaction on the polyaspartic acid modified gold electrode. The ionic strength dependence and reactivity of the charged redox species suggested that the polyaspartic acid layer provided a matrix structure of charge groups which formed an attractive environment for the electron transfer reaction of cytochrome c.

 

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

            "Simultaneous induction of pathway-specific potentiation and depression in networks of cortical neurons"

            Biophys. J. 76 (2), 670-678 (1999).

 

            ABSTRACT: Activity-dependent modification of synaptic efficacy is widely recognized as a cellular basis of learning, memory, and developmental plasticity. Little is known, however, of the consequences of such modification on network activity. Using electrode arrays, we examined how a single, localized tetanic stimulus affects the firing of up to 72 neurons recorded simultaneously in cultured networks of cortical neurons, in response to activation through 64 different test stimulus pathways. The same tetanus produced potentiated transmission in some stimulus pathways and depressed transmission in others. Unexpectedly, responses were homogeneous: for any one stimulus pathway, neuronal responses were either all enhanced or all depressed. Cross-correlation of responses with the responses elicited through the tetanized site revealed that both enhanced and depressed responses followed a common principle: activity that was closely correlated before tetanus with spikes elicited through the tetanized pathway was enhanced, whereas activity outside a 40-ms time window of correlation to tetanic pathway spikes was depressed. Response homogeneity could result from pathway-specific recurrently excitatory circuits, whose gain is increased or decreased by the tetanus, according to its cross-correlation with the tetanized pathway response. The results show how spatial responses following localized tetanic stimuli, although complex, can be accounted for by a simple rule for activity-dependent modification.

 

54.       H. Kageshima and K. Shiraishi

            "Relation between oxide growth direction and stress on silicon surfaces and at silicon-oxide/silicon interfaces"

            Surf. Sci. 438 (1-3), 102-106 (1999).

 

            ABSTRACT: The effects of stress on oxide growth direction are found to be important on Si(100) surfaces and at SiO2/Si(100) interfaces from the energetics of the oxide growth. The results of first-principles calculations show that the oxide nuclei on the clean Si(100) surfaces preferentially grow vertically into the substrate. The growth direction is the same even for dihydride Si(100) surfaces. In contrast, the initial oxide nuclei at SiO2/Si(100) interfaces preferentially grow laterally, parallel to the interface. These results can be explained by the difference in the distribution of the induced stress. The results also show that the oxide growth direction is governed by the stress remaining in the oxidized region. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

 

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

            "Universal theory of Si oxidation rate and importance of interfacial Si emission"

            Jpn. J. Appl. Phys. Part 2 - Lett. 38 (9AB), L971-L974 (1999).

 

            ABSTRACT: The essential role that Si atoms emitted from the interface play in determining the silicon-oxidation rate is theoretically pointed out, and a universal theory for the oxide growth rate taking account of the interfacial Si-atom emission is developed. Our theory can explain the oxide growth rate for the whole range of the oxide thickness without any empirical modifications, while the rate for an oxide thickness of less than 10 nm in dry oxidation cannot be explained with the Deal-Grove theory.

 

56.       H. Kamada, H. Gotoh, H. Ando, J. Temmyo, and T. Tamamura

            "Spin-selective excitation spectroscopy of excitons and biexcitons in InxGa1-xAs quantum disks: Suppression of the spin-flip process in semiconductor zero-dimensional systems"

            Phys. Rev. B 60 (8), 5791-5796 (1999).

 

            ABSTRACT: The spin relaxation of photocreated excitons in InxGa1-xAs/Al(y)Ga(1-y)AS quantum disks is investigated by microscope photoluminescence experiments under spin-selective optical excitation. Complete quantization of the two-dimensional energy structure of the quantum well into comb-shaped density of states results in inhibition of the elastic spin-flip processes, allowing only a simultaneous exchange of energy and momentum for spin relaxation. This slows down the spin flip in both the thermalization and recombination of exciton and substantially increases the spin-relaxation time. For some exciton excited states, the spin-flip relaxation into another spin state is efficient, thereby allowing the second photon absorption into a biexciton state even under the selective-spin excitation. [S0163-1829(99)00732-8].

 

57.       H. Kamada, J. Temmyo, E. Kuramochi, H. Ando, and T. Tamamura

            "InGaAs quantum disk: Fabrication via self-organization and spectroscopies"

            Bull. Mat. Sci. 22 (3), 543-552 (1999).

 

            ABSTRACT: We have examined the spontaneous rearrangement of a strained InGaAs/AlGaAs heterostructure, on a (311)B, substrate into naturally ordered array of InGaAs disks automatically buried in Al-rich alloy. Unlike nano-islands formed via Stranski-Krastanov mechanism, it serves as a strong tendency to align themselves, We have stressed important interplay of islanding of the material with lattice mismatch, atomic diffusion across the interface between unstrained and strained materials, lateral mass transport, and development of the surface into low index surfaces with low surface energies: all these seek to lower the total energy. Because of the damageless fabrication, these quantum disks showed excellent optical properties, which facilitated single-dot spectroscopy, Such spectroscopy revealed that lateral together with vertical confinement of exciton motion discretizes the exciton density-of-states resulting in sharp and distinct photo emission/absorption spectra despite their mesoscopic confinement. These characterize optical properties which are specific only to zero-dimensional system, thereby proving quantum dot characteristic. As for future device application, we undertook an attempt to artificially position the self-organized structure more accurately by periodic seeding an the virgin (311)B substrate. The results show that it is feasible to further improve the ordering of the array of quantum disks.

 

58.       S. Karimoto and M. Naito

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

            Jpn. J. Appl. Phys. Part 2 - Lett. 38 (3B), L283-L285 (1999).

 

            ABSTRACT: We report the synthesis of a new superconducting cuprate PbSr2CuO5+delta (T-c similar to 40 K) by a novel low-temperature synthetic route using molecular beam epitaxy. The new superconductor is the first member of the (Pb-12(n-1)n) homologous series, which contains a single PbO layer as the charge reservoir block. Low temperature synthesis by molecular beam epitaxy (MBE) and an appropriate choice of lattice-matched substrates are essential to our discovery of PbSr2CuO5+delta superconductor. This work demonstrates that MBE opens up a novel synthetic route for new cuprates.

 

59.       A. Karlsson, M. Koashi, and N. Imoto

            "Quantum entanglement for secret sharing and secret splitting"

            Phys. Rev. A 59 (1), 162-168 (1999).

 

            ABSTRACT: We show how a quantum secret sharing protocol, similar to that of Hillery, Buzek, and Berthiaume (Los Alamos e-print archive quant-ph/9806063), can be implemented using two-particle quantum entanglement, as available experimentally today. We also discuss in some detail how both two- and three-particle protocols must be carefully designed in order to detect eavesdropping or a dishonest participant. We also discuss the extension of a multiparticle entanglement secret sharing and splitting scheme toward a protocol so that m of n persons with m less than or equal to n can retrieve the secret. [S1050-2947(99)09301-4].

 

60.       N. Kasai, I. Sugimoto, M. Nakamura, and T. Katoh

            "Odorant detection capability of QCR sensors coated with plasma deposited organic films"

            Biosens. Bioelectron. 14 (6), 533-539 (1999).

 

            ABSTRACT: Odorant-detection experiments were conducted on major single-odor substances in various types of botanical species. The sensing devices we used were quartz-crystal resonators (QCRs), radio-frequency (RF) sputtered with amino acids or polymers. The odorants were generated at very low concentrations (ppb level) by using the diffusion-tube method. The tested odorants were detected at concentrations between 0.3 and 940 ppb. These deposited films had high partition coefficients for the odorants, confirming their high sensitivity to organic vapors, especially to terpenoids. This indicates that the odorant solvation is due to odorant-film interaction related to Gibbs free energy. (C) 1999 Elsevier Science S.A. All rights reserved.

 

61.       K. Kashino and H. Murase

            "A sound source identification system for ensemble music based on template adaptation and music stream extraction"

            Speech Commun. 27 (3-4), 337-349 (1999).

 

            ABSTRACT: Sound source identification is an important problem in auditory scene analysis when multiple sound objects are simultaneously present in the scene. This paper proposes an adaptive method for sound source identification that is applicable to real performances of ensemble music. For musical sound source identification, the feature-based methods and template-matching-based methods were already proposed. However, it is difficult to extract features of a single note from a sound mixture. In addition, sound variability has been a problem when dealing with real music performances. Thus this paper proposes an adaptive method for template matching that can cope with variability in musical sounds. The method is based on the matched filtering and does not require a feature extraction process. Moreover, this paper discusses musical context integration based on the Bayesian probabilistic networks. Evaluations using recordings of real ensemble performances have revealed that the proposed method improve the source identification accuracy from 60.8% to 88.5% on average. (C) 1999 Elsevier Science B.V. All rights reserved.

 

62.       T. Kawamura, J. J. Delaunay, H. Takenaka, and Y. Watanabe

            "Design of a VUV/soft x-ray ellipsometry system that uses laser produced plasma x-rays"

            in X-Ray Lasers 1998, Institute Of Physics Conference Series Vol. 159 (Iop Publishing Ltd, Bristol, 1999), pp. 609-612.

 

            ABSTRACT: We proposed a new VUV/soft x-ray ellipsometry system dedicated for laser produced x-ray plasmas. It consists of two parts: one is a high throughput monochromator, and the other is a high performance polarimeter which uses multilayer mirrors. The monochromator is designed as an incident slitless type with two cylindrical mirrors and one concave grating for obtaining as many photons as possible from a plasma source. The calculated acceptance is around 2x10(-3)sr, and the available wavelength range is 7 nm to 30 nm, considering the reflectivity of optical elements. The polarimeter uses a set of multilayer mirrors as a polarizer to obtain a high extinction ratio more than 1000. The optimized multilayer mirrors are used to prevent the large angle and wavelength selectivity. Simulation results show that the required divergence to obtain an extinction ratio higher than 1000 is 15 for the wavelength (lambda/Delta lambda at 14 nm) and 2 mrad for the angle.

 

63.       T. Kawamura, H. O. Hibino, and T. Ogino

            "Origin of reducing domain boundaries of Si(111)-7x7 during homoepitaxial growth"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 38 (3A), 1530-1533 (1999).

 

            ABSTRACT: The origin of reducing out-of-phase boundaries (OPBs) of 7 x 7 reconstructed domains on Si(111) surfaces during homoepitaxial growth is analyzed. Two conditions are necessary. One is that along a step, two or more starting points of OPBs should exist on the upper terrace in a region bounded by two adjacent terminating points of OPBs in the lower terrace. The other is that the step advancement in the region must be different from site to site so that the OPBs in the upper terrace bend to coalesce with each other. We first simulate the creation process of OPBs and then their reducing process using the above two conditions. The reduction process is closely related to the initial nucleation sites of 7 x 7 reconstruction along a step edge and to the propagation velocity of the 7 x 7 reconstructed region. The reported layer coverage dependence on the reduction of the average distance between the OPBs is reproduced by the simulation.

 

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

            "A single-photon turnstile device"

            Nature 397 (6719), 500-503 (1999).

 

            ABSTRACT: Quantum-mechanical interference between indistinguishable quantum particles profoundly affects their arrival time and counting statistics. Photons from a thermal source tend to arrive together (bunching) and their counting distribution is broader than the classical Poisson limit(1). Electrons from a thermal source, on the other hand, tend to arrive separately (anti-bunching) and their counting distribution is narrower than the classical Poisson limit(2-4). Manipulation of quantum-statistical properties of photons with various non-classical sources is at the heart of quantum optics: features normally characteristic of fermions-such as anti-bunching, sub-poissonian and squeezing (sub-shot-noise) behaviours-have now been demonstrates. A single-photon turnstile device was proposed(6-8) to realize an effect similar to conductance quantization. Only one electron can occupy a single state owing to the Pauli exclusion principle and, for an electron waveguide that supports only one propagating transverse mode, this leads to the quantization of electrical conductance: the conductance of each propagating mode is then given by G(Q) = e(2)/h (where e is the charge of the electron and h is Planck's constant; ref. 9), Here we report experimental progress towards generation of a similar now of single photons with a well regulated time interval.

 

65.       J. S. Kim, S. Takeuchi, Y. Yamamoto, and H. H. Hogue

            "Multiphoton detection using visible light photon counter"

            Appl. Phys. Lett. 74 (7), 902-904 (1999).

 

            ABSTRACT: Visible light photon counters feature noise-free avalanche multiplication and narrow pulse height distribution for single photon detection events. Such a well-defined pulse height distribution for a single photon detection event, combined with the fact that the avalanche multiplication is confined to a small area of the whole detector, opens up the possibility for the simultaneous detection of two photons. In this letter, we investigated this capability using twin photons generated by parametric down conversion, and present a high quantum efficiency (similar to 47%) detection of two photons with good time resolution (similar to 2 ns), which can be distinguished from a single-photon incidence with a small bit-error rate (similar to 0.63%). (C) 1999 American Institute of Physics. [S0003-6951(99)00307-1].

 

66.       M. Koashi and M. Ueda

            "Reversing measurement and probabilistic quantum error correction"

            Phys. Rev. Lett. 82 (12), 2598-2601 (1999).

 

            ABSTRACT: We consider a probabilistic reversing operation that returns the measured system to its original state by means of a physical process, and derive a trade-off oration between the unsharpness of the measurement and the best efficiency of the reversing operation. Such a reversing operation is shown to serve as a probabilistic quantum error correction, which will be useful when the numbers of qubits and gate operations are limited. [S0031-9007(99)08786-4].

 

67.       Y. Kobayashi, K. Sumitomo, and T. Ogino

            "Observation of Ge surface segregation during Si-MBE on Ge/Si(001) probed by Si-H/Ge-H surface vibrations"

            Surf. Sci. 428, 229-234 (1999).

 

            ABSTRACT: The dimer composition on the Ge-segregated surface of a MBE-grown Si-layer/Ge/Si(001) structure was investigated using surface infrared (IR) spectroscopy on Si substrates with a buried metal layer (BML). The Ge-segregated surface was modified by atomic hydrogen in order to visualize dimer composition by IR spectroscopy. When the Si growth-layer is relatively thin (similar to 10 ML), almost all Ge atoms are segregated at the surface and form Ge-Ge pure dimers and a small amount of Ge-Si mixed dimers. As the growth-layer thickness increases, the portion of pure Ge-Ge dimers decreases, and finally, the surface is covered with mixed Ge-Si and pure Si-Si dimers at the thickness of 64 hit. This result indicates that mixed dimer formation should be considered as an important factor in the Ce segregation mechanism and Ge incorporation profiles. (C) 1999 Elsevier Science B.V. All rights reserved.

 

68.       Y. Kobayashi, K. Sumitomo, K. Shiraishi, T. Urisu, and T. Ogino

            "Control of surface composition on Ge/Si(001) by atomic hydrogen irradiation"

            Surf. Sci. 436 (1-3), 9-14 (1999).

 

            ABSTRACT: The surface composition of Ge/Si(001)2 x 1 surfaces after atomic hydrogen (H) irradiation was investigated using IR reflection spectroscopy in UHV. It was confirmed that an extremely high dose of H at room temperature causes an etching reaction of the surface Ge layer. However, when H is irradiated at a temperature higher than 150 degrees C, the etching reaction does not occur; instead, Ge segregated at the surface is observed to move into a subsurface and Si tends to exist on the topmost surface as a hydride in mixed Ge-Si and pure Si-Si dimers. This is in remarkable contrast to the Ge/Si(001) surface in the absence of hydrogen, where Ge is segregated at the surface and forms Ge-Ge pure dimers. The phenomenon of 'reverse segregation' by H irradiation may be understood by the thermochemical consideration that Si-H bonds are much more stable than Ge-H bonds. The result of the first-principles total energy calculations in which the presence of hydrogen changes the stable composition at the surface from Ge to Si is also consistent with the phenomenon. (C) 1999 Elsevier Science B.V. All rights reserved.

 

69.       J. R. Koe, M. Fujiki, and H. Nakashima

            "First optically active diarylpolysilanes: Facile helical screw sense control with only (S)-enantiopure side chains"

            J. Am. Chem. Soc. 121 (41), 9734-9735 (1999).

 

            ABSTRACT:

70.       T. Kojima and A. Yoshikawa

            "A two-step model of pattern acquisition: Application to Tsume-Go"

            in Computers And Games, Lecture Notes In Computer Science Vol. 1558 (Springer-Verlag Berlin, Berlin, 1999), pp. 146-166.

 

            ABSTRACT: It has been said to be very useful for Go playing systems to have knowledge. We focus on pattern level knowledge and propose a new model of pattern acquisition based on our cognitive experiments. The model consists of two steps: pattern acquisition step, using only positive examples, and pattern refinement step, using both positive and negative examples. The latter step acquires precise conditions to apply and/or the way of conflict resolution. This model has advantages in computational time and precise control for conflict resolution. One algorithm is given for each step, and each algorithm can change independently, it is possible to compare algorithms with this model. Three algorithms are introduced for the first step and two for the second step. Patterns acquired by this model are applied to Tsume-Go problems (life and death problems) and the performance between six conditions are compared. In the best condition, the percentage of correct answers is about 31%. This result equals the achievement of one dan human players. It is also shown that the patterns enhance search techniques when the search space is very large.

 

71.       K. Kumakura and N. Kobayashi

            "Increased electrical activity of Mg-acceptors in AlxGa1-xN/GaN superlattices"

            Jpn. J. Appl. Phys. Part 2 - Lett. 38 (9AB), L1012-L1014 (1999).

 

            ABSTRACT: We grew uniformly Mg-doped AlxGa1-xN/GaN superlattices (SLs) by low-pressure metalorganic vapor phase epitaxy and investigated the electrical properties of these SLs parallel to the SL plane. Sheer hole concentration depends strongly on the SL period thickness and Al male fraction, and the maximum sheet concentration is 8 x 10(12) cm(-2) for AlxGa1-xN/GaN (240 Angstrom/120 Angstrom) SLs in the Al mole fraction range between 0.15 and 0.3, which corresponds to the hole concentration of 3 x 10(18) cm(-3). One possible explanation for this high sheet hole concentration is that the strain-induced piezoelectric field greatly increases the electrical activity of the relatively deep Mg-acceptors in the SLs.

 

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

            "Spatial ordering of self-organized InGaAs AIGaAs quantum disks on GaAs (311)B substrates"

            J. Electron. Mater. 28 (5), 445-451 (1999).

 

            ABSTRACT: We report the control of self-organization of InxGa1-xAs/AlGaAs quantum disks on GaAs (311)B surfaces using a novel technique based upon lithography-defined SiN dot arrays. A strained InGaAs island array selectively grown using the SiN dots provides periodic strain field. When the pitch of lateral ordering corresponds with the period of the strain field, self-organized quantum disks stacked on the InGaAs islands are precisely arranged just as the buried SiN dot array. The spacing of the array element is 250-300 nm (x = 0.3) and around 150 nm (x = 0.4). Vertical alignment by strain is achieved at a very thick (95 nm) separating layer. Characterization using atomic force microscopy reveals the size-fluctuation of disk is dramatically improved with spatial ordering.

 

73.       K. Kurihara, Y. Watanabe, and M. Nagase

            "Si nanostructures fabricated by nanoscale local oxidation using an ECR plasma nitride nanomask"

            Microelectron. Eng. 46 (1-4), 117-120 (1999).

 

            ABSTRACT: A new method for Si nanofabrication was developed by exploiting nanoscale local oxidation using an ultrathin ECR plasma oxynitride nanomask (NANOLOX). ECR nitrogen plasma exposure with resist mask patterns directly forms a nanomask on Si surface. This oxynitride is 2-3-nm thick and acts as an excellent oxidation mask. Using this method, 10-nm-scale Si nanostructures, such as wires, dots, and single electron device structures, can be fabricated. This the first report of lithographically controlled Si nanostructures fabricated using nanoscale local oxidation.

 

74.       S. Lathi, K. Tanaka, T. Morita, S. Inoue, H. Kan, and Y. Yamamoto

            "Transverse-junction-stripe GaAs-AlGaAs lasers for squeezed light generation"

            IEEE J. Quantum Electron. 35 (3), 387-394 (1999).

 

           ABSTRACT: We fabricated 850-nm GaAs transverse-junction-stripe (TJS) lasers by an improved metal-organic chemical vapor deposition (MOCVD) and double Zn diffusion process. The high V/III ratio used during the MOCVD growth significantly reduced the intermixing of GaAs active layer and AlGaAs cladding layers. The modified process realized good confinement for both carriers and photons and smaller saturable loss. We measured squeezing of -2.8 dB (-4.5 dB after correction for detection efficiency) at a pumping rate of I/I-th approximate to 20 from these lasers, which is in close agreement with the theoretical limit. This squeezing remained unchanged under injection locking, indicating almost perfect conservation of the intensity noise correlation among the longitudinal modes. These TJS lasers had very small low-frequency 1/f noise.

 

75.       S. Lathi and Y. Yamamoto

            "Influence of nonlinear gain and loss on the intensity noise of a multimode semiconductor laser"

            Phys. Rev. A 59 (1), 819-825 (1999).

 

            ABSTRACT: We developed a model for the intensity noise of a multimode semiconductor laser which includes both the nonlinear gain and the nonlinear loss. The nonlinear gain stems from spectral hole burning and population pulsation. Saturable absorption by deep trap levels results in the nonlinear lass. We find that the nonlinear gain alone does not enhance the total intensity noise above the quantum efficiency limit. The nonlinear loss, however, does increase the intensity noise when longitudinal side modes have considerable intensities, and thus explains the observed excess intensity noise. In this case the perfect anticorrelation among the longitudinal modes is degraded, which in turn converts the mode-partition noise to the total intensity noise. We remark that larger (smaller) saturable absorption in the quantum-well (transverse-junction-stripe) lasers could explain the larger (smaller) excess noise behavior observed in these lasers. [S1050-2947(99)06201-0].

 

76.       Z. M. Liu, O. Niwa, T. Horiuchi, R. Kurita, and K. Torimitsu

            "NADH and glutamate on-line sensors using Os-gel-HRP/GC electrodes modified with NADH oxidase and glutamate dehydrogenase"

            Biosens. Bioelectron. 14 (7), 631-638 (1999).

 

            ABSTRACT: We have developed a highly sensitive and selective on-line biosensor for detecting the reduced form of nicotinamide adenine dinucleotide (NADH) produced by the enzymatic reactions of dehydrogenases with Various substrates such as glutamate. The sensor consists of a glassy carbon electrode modified with an osmium-polyvinylpyridine-based bottom layer containing horseradish peroxidase, and a bovine serum albumin (BSA)-gluteraldehyde (Glut) top layer containing NADH oxidase (NOX) or glutamate dehydrogenase (GluDH) and NOX. We assembled the modified electrode in a thin-layer radial flow cell and sample solution was continuously introduced into the cell with a syringe pump. We optimized the sensitivity of the NADH sensor by adjusting the glutaraldehyde amount in the immobilized layer, the applied potential and the pH of buffer solution. We examined the flow-rate effect on the current response and the conversion efficiency of NADH at the modified electrode. As a result, we achieved a sensitivity of 48.8 nA cm(-2) mu M-1, a detectable concentration range of 25 nM similar to 10 mu M and a detection limit of 20 nM (S/N = 3) for the NADH sensor. The interference from ascorbic acid and other electroactive interferents can be greatly reduced since the sensor can be operated below 0 mV versus Ag/AgCl. The NADH sensor is relatively stable since it retains 70% of its original response after I month if stored at 2-8 degrees C in a dry state after use. Furthermore, we fabricated a glutamate sensor by coimmobilizing GluDH and NOX in the BSA-Glut top layer. The detectable glutamate concentration range is from 0.1 to 10 mu M and the detection limit is 0.1 mu M (S/N = 3). Our glutamate dehydrogenase-based sensor offers good selectivity as regards other amino acids. (C) 1999 Elsevier Science S.A. All rights reserved.

 

77.       P. Lu and E. E. Fill

            "Reduced absorption of neon-like bromine X-ray laser radiation in helium"

            Appl. Phys. B-Lasers Opt. 69 (4), 333-336 (1999).

 

            ABSTRACT: We have measured the absorption of the 19.47-nm neon like bromine (J = 2-1) X-ray laser line in low-pressure helium. The experiment was motivated by the coincidence of this line with the low-absorption wing of an autoionizing transition in helium. We observe that, with 1 mbar of helium, the continuum background and another bromine X-ray laser line at 19.82 nm are strongly reduced, enhancing the relative strength of the 19.47-nm laser line. Increasing the helium pressure to 1.5 mbar makes the continuum virtually disappear, resulting in an almost monochromatic emission of the X-ray laser line. An estimate of the absorption cross section for the 19.47-nm line is given as approximate to 3.9 x 10(-19) cm(2) and for the nearby continuum as 0.9-1.3 x 10(-18) cm(2).

 

78.       P. X. Lu, H. Nakano, T. Nishikawa, and N. Uesugi

            "Demonstration of XUV amplification to the ground state in low-charged nitrogen ions"

            Opt. Commun. 170 (1-3), 71-78 (1999).

 

            ABSTRACT: We report the first demonstration of the gain to the ground state in low-charged nitrogen ions by optical-field ionization. A small signal gain coefficient of 9.6 cm(-1) and a gain-length product that it is in the range 3.8-3.9 for the NIII 3s(S-2) - 2p(P-2) transition XUV laser at a wavelength of 45.2 nm were obtained by an only 25-mJ Linearly-polarized 100-fs laser pulse. (C) 1999 Elsevier Science B.V. All rights reserved.

 

79.       P. X. Lu, H. Nakano, T. Nishikawa, and N. Uesugi

            "Design of a 1TW/100fs-laser-driven Ne-like S x-ray laser at 60.8nm"

            in X-Ray Lasers 1998, Institute Of Physics Conference Series Vol. 159 (Iop Publishing Ltd, Bristol, 1999), pp. 159-162.

 

            ABSTRACT: A table-top Ne-like S x-ray laser scheme is proposed and designed based on our 10 Hz, 100 fs, 1 TW Ti:sapphire laser facility. The tunneling ionization process in S under different circularly polarized laser intensities is investigated, and a four-level model is built to calculate gains for Ne-like S 3p-3s transition at 60.8nm both in H2S and SF, gases under a peak intensity of 2X10(16)W/cm(2).

 

80.       F. Maeda and Y. Watanabe

            "Sb-induced reconstruction on Sb-terminated GaAs(001)"

            Phys. Rev. B 60 (15), 10652-10655 (1999).

 

            ABSTRACT: The surface structural changes occurring on Sb-rich Sb-terminated GaAs(001) was investigated by using reflection high-energy electron diffraction and tore-lever photoelectron spectroscopy. Another surface reconstruction of 2 x 8 superstructure was found, and the analysis of the core-level photoelectron spectra revealed that more of the Sb atoms on this surface are bonded to Sb atoms than to Ga atoms. This indicates the presence of a local structure of stacking double (or triple) Sb layers in which the Sb atoms in the lowest-layer bond with the underlying Ga atoms and in which the number of Sb atoms in the lowest layer is smaller than the number in the other layer(s). [S0163-1829(99)12635-3].

 

81.       F. Maeda and Y. Watanabe

            "Sb desorption from Sb/GaAs(001) and GaSb(001) analyzed by core-level photoelectron spectroscopy"

            J. Electron Spectrosc. Relat. Phenom. 103, 293-298 (1999).

 

            ABSTRACT: The process of Sb desorption from GaSb(001) and Sb-terminated GaAs(001) was investigated by using a real-time analysis system that uses time-resolved core-level photoelectron spectroscopy. From the photoelectron intensity analysis, two competing processes with fast and slow time constants were found on the Sb desorption from both substrates and the activation energies were determined to be 0.71 eV and 0.90 eV for GaSb(001) and 1.1 eV and 2.5 eV for Sb-terminated GaAs(001). We investigated the relationship between the activation energies and surface bonding structure using spectrum differences based on the assignment of conventional core-level photoelectron spectroscopy of the surfaces whose Sb coverage is well controlled. This indicated that the activation energy of the desorption related to the transition from 2X8 to 2X4 of an Sb-terminated GaAs(001) is larger than the other desorption processes and it can be explained that the large potential barrier for bonding structure rearrangement between 2X8 superstructure and 2X4 superstructure exist in addition to Sb atoms desorption. (C) 1999 Elsevier Science B.V. All rights reserved.

 

82.       H. Maeda, K. Ikeda, K. Hashimoto, K. Ajito, M. Morita, and A. Fujishima

            "Microscopic observation of TiO2 photocatalysis using scanning electrochemical microscopy"

            J. Phys. Chem. B 103 (16), 3213-3217 (1999).

 

            ABSTRACT: Photocatalytic reactions were monitored on a macroscopic model system, containing millimeter scale regions for oxidation and reduction, for a microscopic photocatalytic particle containing both oxidizing and reducing sites, with the use of the scanning electrochemical microscopy (SECM) technique. We employed a TiO2-ITO (indium-tin oxide) composite film: half of a macroscopic ITO glass substrate was coated with a TiO2 film, leaving the ITO exposed on the other half of the sample, in an aqueous solution containing 5 mM K4Fe(CN)(6) and 0.1 M K2SO4. When the microelectrode was placed at a relatively large distance above the TiO2 portion of the illuminated surface, there was a small effect: ferrocyanide was photooxidized, thereby decreasing the amount that could be oxidized at the microelectrode. In contrast, when the microelectrode was placed very close to the TiO2 portion of the surface, the oxidation current at the microelectrode increased significantly after turning on the UV light, and the oxidation current increase observed after turning on the UV light became even larger when the exposed ITO portion was covered by epoxy resin. This current increase is due to positive feedback; i.e., ferricyanide produced electrochemically at the microelectrode is rereduced at the illuminated TiO2 surface by photogenerated electrons. We propose that both oxidation and reduction reactions can occur simultaneously on the illuminated unbiased TiO2 photocatalyst film. These results indicate the utility of the SECM method for clarifying the mechanisms of photocatalytic reactions on TiO2 surfaces.

 

83.       N. Maeda, T. Nishida, T. Saitoh, and N. Kobayashi

            "I-V characteristics and two-dimensional electron gas transport properties above room temperature in gate-controlled Al0.15Ga0.85N/GaN heterostructure"

            in Compound Semiconductors 1998, Institute Of Physics Conference Series Vol. 162 (Iop Publishing Ltd, Bristol, 1999), pp. 861-864.

 

            ABSTRACT: We have measured both the I-V characteristics and the Hall effect in the Al0.15Ga0.85N/GaN heterostructutre under the gate-voltage application from 30 to 400 K. Specific features characteristic of this material system have been observed, i.e., (i) improved pinch-off characteristics at high temperatures, (ii) very small degradation characteristics in the mobility (mu) at high electron densities (N-s) at high temperatures, and (iii) very large N(s)mu products (> 10(16) (Vs)(-1)) at 300 K. These are the features favorable for high-power and high-temperature device operations in the devices of this material system.

 

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

            "Enhanced two-dimensional electron gas confinement effect on transport properties in AlGaN/InGaN/AlGaN double-heterostructures"

            Phys. Status Solidi B-Basic Res. 216 (1), 727-731 (1999).

 

            ABSTRACT: A striking effect of polarization-induced electron confinement on transport properties has been observed in nitride double-heterostructures. The two-dimensional electron gas mobility has shown to be drastically enhanced in the AlGaN/GaN/AlGaN double-heterostructure, compared with that in the conventional AlGaN/GaN single-heterostructure. The observed mobility enhancement results from the strong polarization-induced electron confinement in the double-heterostructure. Device operation of an AlGaN/GaN/AlGaN double-heterostructure field effect transistor has been demonstrated: a maximum transconductance of 180 mS/mm has been obtained for a 0.4 mu m gate length device. In the AlGaN/InGaN/AlGaN double-heterostructure, the increased capacity for the two-dimensional electron gas has been observed in addition to the enhanced electron mobility. The AlGaN/(In)GaN/AlGaN double-heterostructures are promising for field effect transistor applications because of their superior electron transport properties.

 

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

            "Enhanced electron mobility in AlGaN/InGaN/AlGaN double-heterostructures by piezoelectric effect"

            Jpn. J. Appl. Phys. Part 2 - Lett. 38 (7B), L799-L801 (1999).

 

            ABSTRACT: A striking effect of piezoelectric electron confinement on transport properties has been observed for the first time in nitride double-heterostructures. The two-dimensional electron gas mobility has shown to be drastically enhanced in the AlGaN/GaN/AlGaN double-heterostructure, compared with that in the conventional AlGaN/GaN single-heterostructure. The observed mobility enhancement results from the piezoelectrically enhanced electron confinement in the double-heterostructure. The electron transport properties in the AlGaN/InGaN/AlGaN double-heterostructure have also been examined for the first time. The increased capacity for the two-dimensional electron gas density has been observed in addition to the enhanced electron mobility. The AlGaN/(In)GaN/AlGaN double-heterostructures are promising for field effect transistor applications because of their superior electron transport properties.

 

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

            "Superior pinch-off characteristics at 400 degrees C in AlGaN/GaN heterostructure field effect transistors"

            Jpn. J. Appl. Phys. Part 2 - Lett. 38 (9AB), L987-L989 (1999).

 

            ABSTRACT: AlGaN/GaN field effect transistors have been fabricated on SiC(0001) substrates, and the I-V characteristics in the devices have been examined from room temperature to 400 degrees C. In addition to excellent current saturation characteristics, sufficient pinch-off characteristics have been obtained up to a temperature of 400 degrees C for the first time, as the result of reduced crystal defects and reduced etching damage in the devices. The temperature dependence of the transconductance has been also examined. The degradation rate in the transconductance has been proved to be low above 300 degrees C: the transconductance degraded by only 8% for a temperature increase from 350 to 400 degrees C. Sufficient pinch-off characteristics and a relatively low degradation rate in the transconductance ensure the practical use of the devices at high temperatures.

 

87.       H. Masuda, M. Ohya, H. Asoh, M. Nakao, M. Nohtomi, and T. Tamamura

            "Photonic crystal using anodic porous alumina"

            Jpn. J. Appl. Phys. Part 2 - Lett. 38 (12A), L1403-L1405 (1999).

 

            ABSTRACT: Two-dimensional (2D) photonic crystals in the visible wavelength region were fabricated using anodic porous alumina with a highly ordered hole array configuration. The transmission properties of an ordered triangular array of an air cylinders with high aspect ratio in alumina matrix showed a stop band in the spectrum which corresponds to the band gap in the 2D photonic crystals.

 

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

            "Temperature and doping dependence of the Bi2.1Sr1.9CaCu2O8+delta pseudogap and superconducting gap"

            Phys. Rev. B 60 (2), 1377-1381 (1999).

 

            ABSTRACT: The temperature and doping dependence of Bi2.1Sr1.9CaCu2O8+delta vacuum tunneling spectra was measured. The tunneling spectra show a clear gaplike feature for almost all the measured temperatures (10-300 K) and doping levels [overdoped (T(c)similar to 80 K) to underdoped (T(c)similar to 80 K), via optimum-doped (T(c)similar to 90 K)]. The superconducting gap structure below T-c develops into a pseudogap above T-c. The model analysis based on the BCS-type density of states showed a sudden increase in the gap value and inelastic scattering rate at T-c. [S0163-1829(99)14825-2].

 

89.       S. Matsumoto, T. Maekawa, H. Kato, S. Yoda, and K. Kinoshita

            "Crystal growth of a binary semiconductor of uniform composition"

            in Gravitational Effects In Materials And Fluid Sciences, Advances In Space Research Vol. 24 (Pergamon Press Ltd, Oxford, 1999), pp. 1241-1244.

 

            ABSTRACT: We proposed a new method of growing a binary semiconductor crystal which has a uniform composition and investigated the validity of the method numerically. We developed a calculation method of InAs-GaAs binary crystal growth and checked the effect of the cooling rate and the temperature gradient on the generation of constitutional supercooling and the compositional uniformity of the grown crystal. It has been found that a crystal of a uniform composition can be grown by setting a positive concentration gradient of InAs in the direction of the growing crystal in the solution initially, which we call the "One-directional growth method with a Nonuniform Concentration Gradient in the solution (NCG method)". A map of constitutional supercooling, that is the dependence of the degree of constitutional supercooling on the initial temperature gradient and the cooling rate is produced and the optimal conditions for the production of uniform crystals are discussed. (C) 1999 COSPAR. Published by Elsevier Science Ltd.

 

90.       J. Maxka and H. Teramae

            "Electronic structures of polymers containing carbon multiple bond and disilane units in their backbone"

            Macromolecules 32 (21), 7045-7050 (1999).

 

            ABSTRACT: The electronic structures of poly(ethynylenedisilanylene) FED (Si2H4C2)(x) and both cis- and trans-poly(vinylenedisilanylene) PVD (Si2H4C2H2)(x) are studied by means of the ab initio crystal orbital calculations with 6-31G* and 3-21G basis sets. PED in its antiperiplanar form shows sigma/pi conjugation; however, for PVD, of the three possible conformers studied only shew can be classified as sigma/pi. In fact, the anticonformer of PVD, the one usually found drawn in the literature, displays only sigma conjugation and should be unstable, according to vibrational frequency analysis. Eclipsed and shew structures are minima for PVD; the eclipsed conformer displays pi conjugation, but the skew conformer is true sigma/pi and the global minimum for PVD. cis-Configurational isomers for PVD are higher in energy than the trans-isomers. Analyses of the ionization potential and the effective hole mass suggest that PED is delocalized, but the properties of PVD are highly dependent on conformation: anti PVD and eclipsed PVD are localized, but skew PVD is predicted to have a lower ionization potential than PED. Overall, the electronic delocalization of PVD and PED is inferior to that of either pure polysilane or pure polyacetylene, because the nature of sigma/pi conjugation is not very effective.

 

91.       M. Mitsunaga and N. Imoto

            "Observation of an electromagnetically induced grating in cold sodium atoms"

            Phys. Rev. A 59 (6), 4773-4776 (1999).

 

            ABSTRACT: We have observed diffraction signals by a grating originating from electromagnetically induced transparency (EIT) in a three-level Lambda system of cold sodium atoms. Theoretical and experimental analyses of this phenomenon, called the electromagnetically induced grating (EIG), have revealed that EIG spectra exhibit background-free, Lorentzian signal profiles regardless of the pump frequencies, making a clear contrast to the case of ordinary EIT spectra.

 

92.       M. Morita, O. Niwa, S. Tou, and N. Watanabe

            "Nickel content dependence of electrochemical behavior of carbohydrates on a titanium-nickel alloy electrode and its application to a liquid chromatography detector"

            J. Chromatogr. A 837 (1-2), 17-24 (1999).

 

            ABSTRACT: A highly sensitive amperometric detector for the liquid chromatographic analysis of carbohydrates has been developed based on the optimization of the Ni content in a Ni-Ti alloy electrode. An optimum nickel content of 30 at. % was obtained from a signal-to-noise analysis in a flow injection experiment on glucose in 0.1 M NaOH. An optimum working potential of 0.5 V vs. Ag/AgCl was obtained from a hydrodynamic voltammogram. The glucose detection limit in the flow injection analysis was 11 fmol. The electrode was applied to an LC detector with a microbore column and the detection limit was 50 fmol. (C) 1999 Elsevier Science B.V. All rights reserved.

 

93.       K. Muraki and Y. Hirayama

            "Spin transition of a two-dimensional hole system in the fractional quantum Hall effect"

            Phys. Rev. B 59 (4), R2502-R2505 (1999).

 

            ABSTRACT: The effect of the complex valence-band Landau-level (LL) structure on the fractional quantum Hall (FQH) effect of a two-dimensional hole system has been studied in a modulation-doped quantum well (QW) with front and back gates. Owing to the spin-orbit interaction and the band mixing in the valence band, changing the potential asymmetry of the QW with the front and back gates allows us to vary the LL structure for a fixed hole density. We observed a remarkable transition in the nu = 4/3 FQH effect with a striking resemblance to the spin transitions observed for tilted-field experiments. Self-consistent effective-mass calculations were carried out to confirm that the transition is driven by the change in the effective Zeeman energy. [S0163-1829(99)51004-7].

 

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

            "Interlayer charge transfer in bilayer quantum Hall states at various filling factors"

            Solid State Commun. 112 (11), 625-629 (1999).

 

            ABSTRACT: We have studied bilayer quantum Hall (QH) effects in double-quantum-well structures at various Landau-level (LL) filling factors nu. The stability of various QH states are examined by varying the density balance between the two layers. We observe a remarkable nu-dependent behavior; the interlayer charge transfer is allowed for particular values of nu, which then repeat in a characteristic sequence with a period of 4. We employ a pseudospin picture, by which the interlayer charge transfer is expressed as a rotation of the total pseudospin. The ability or inability to accommodate the charge transfer represents the degree of pseudospin polarization in the bilayer QH state. (C) 1999 Elsevier Science Ltd. All rights reserved.

 

95.       S. Nakagawa, S. Ueno, and T. Imada

            "Measurements and source estimations of extremely low frequency brain magnetic fields in a short-term memory task by a whole-head neurogradiometer"

            IEEE Trans. Magn. 35 (5), 4130-4132 (1999).

 

            ABSTRACT: To investigate the characteristics of visual short-term memory in humans, brain magnetic fields evoked during a delayed paired comparison task were recorded using a whole-head neuromagnetometer. The visual stimulus consisted of a circle with different colors in each quadrant. In the memory condition, subjects reacted with the index finger, when the first stimulus (Sample) was identical in color configuration to the second stimulus (Test), and with the middle finger when they differed. For the control condition, the Subjects ignored the Sample, and moved the index or middle finger alternately in response to the Test. Extremely low frequency components of brain magnetic fields were observed 500 ms after the Sample onset in the temporal and/or the occipital region in the memory condition, but not in the control condition, Sources for the low frequency components were localized in the inferior part of the occipital lobe, in the vicinity of the supramarginal gyrus and the angular gyrus, and the inferior frontal gyrus, The results suggest that the activities in the inferior part of the occipital lobe controls the storage process of shortterm visual memory.

 

96.       S. Nakagawa, S. Ueno, and T. Imada

            "Changes in parameters of auditory evoked magnetic fields with click train patterns"

            J. Appl. Phys. 85 (8), 5708-5710 (1999).

 

            ABSTRACT: N1m is an auditory evoked brain magnetic field with a magnitude of 100 fT order observed over the auditory cortex, 100 ms after the onset of auditory stimuli. The N1m is often used as a landmark of functional localization in the cortex. However, the mechanism of the N1m has not yet been clarified. The N1m peak amplitude and latency are dependent on the specifics of the stimulus; duration, intensity, and sequence of stimuli. In this study, we examined the dependency of the N1m peak amplitude and latency on the stimulus duration and frequency. Trains of 0.2 ms clicks were used for auditory stimuli by changing the number of clicks and the click interval. Auditory brain magnetic responses evoked by the click trains were recorded from seven human adult subjects by a dc superconducting quantum interference device magnetometer. In the results of this study, the N1m amplitudes significantly increased as the stimulus duration increased and the amplitudes leveled when the stimulus duration reached 32 ms. The amplitudes produced by the trains with the same number of clicks showed greater values for 4-ms-interval trains. The N1m latencies significantly decreased as the stimulus duration increased and leveled at 32 ms. It is concluded that all clicks received within 32 ms were integrated and that this integration mechanism is dependent upon the click interval. Increased synchrony of neuronal cells at the cortical level can explain this integration mechanism. (C) 1999 American Institute of Physics. [S0021-8979(99)42908-1].

 

97.       H. Nakano, Y. Goto, P. Lu, T. Nishikawa, and N. Uesugi

            "Time-resolved soft x-ray absorption spectroscopy of silicon using femtosecond laser plasma x rays"

            Appl. Phys. Lett. 75 (16), 2350-2352 (1999).

 

            ABSTRACT: We measured time-resolved soft x-ray absorption of photoexcited silicon by means of pump-probe spectroscopy, using a picosecond soft x-ray pulse from femtosecond laser-produced plasma as a probe. We observed a 5% increase in the absorption caused by 10(10) W/cm(2) intensity laser pulse irradiation near the L-II,L-III edge at 100 eV. The change was observed only when the laser and the soft x-ray pulses overlapped on the sample both in time and space. (C) 1999 American Institute of Physics. [S0003-6951(99)02742-4].

 

98.       H. Nakano, P. X. Lu, T. Nishikawa, and N. Uesugi

            "Prepulse effects on x-ray emission in keV and sub-keV ranges from Al plasma produced by femtosecond Ti: sapphire laser pulses"

            in X-Ray Lasers 1998, Institute Of Physics Conference Series Vol. 159 (Iop Publishing Ltd, Bristol, 1999), pp. 535-538.

 

            ABSTRACT: We report the influence of an ultrashort prepulse on x-ray emission from Al plasma produced by 100-fs Ti:sapphire laser pulses at an intensity near 10(16) W/cm(2) in the ranges of 0.83-0.77 nm (keV range) and 4-10 nm (sub-keV range). A prepulse (8.4x10(14) W/cm(2)) 2 ns before the main pulse (2.4x10(16) W/cm(2)) enhances x-ray emission from Al9+-Al11+ in the keV range as well as in the sub-keV range. Significant enhancement of x-ray emission was observed at prepulse intensities higher than 10(12) W/cm(2).

 

99.       H. Nakashima, M. Fujiki, and J. R. Koe

            "Helical poly(alkylalkoxyphenylsilane)s bearing enantiopure chiral groups on the phenyl rings"

            Macromolecules 32 (22), 7707-7709 (1999).

 

            ABSTRACT:

100.    J. Nakata

            "Annealing of ion-implanted defects in diamond by mega-electron-volt ion beam irradiation"

            New Diam. Front. Carbon Technol. 9 (2), 141-143 (1999).

 

            ABSTRACT:

101.    J. Nakata

            "Annealing of ion-implanted defects in diamond by MeV ion-beam irradiation"

            Phys. Rev. B 60 (4), 2747-2761 (1999).

 

            ABSTRACT: Defects and amorphous C layers or clusters in a type-Ib diamond formed by C- or P-ion implantation under certain doses are clearly annealed or epitaxially crystallized during thermal annealing at 750 degrees C or during mega-electron-volt (MeV) ion-beam irradiation at 750 degrees C. Implanted P atoms are incorporated into substitutional sites after complete crystallization by using MeV-ion-beam irradiation. This is confirmed by using the Rutherford-backscattering-spectroscopy channeling method. A considerable amount of defects or amorphous clusters are formed by C-ion implantation at a 50-keV energy for a 1x10(15)/cm(2) dose. However, they are crystallized epitaxially to the crystalline diamond by using only thermal annealing at 750 degrees C or by using MeV-ion-beam irradiation at 750 degrees C. Above 2x10(15)/cm(2) C doses, continuous amorphous layers are formed internally in the substrate and epitaxial crystallizations proceed from both the crystalline substrate and the crystalline-surface region. Moreover, the rate of crystallization is higher for annealing with MeV-ion-beam irradiation than for thermal annealing at the same temperature. Epitaxial crystallization of the internal amorphous layer, however, stops in both thermal annealing and MeV-ion-beam irradiation, even if annealing time or irradiation dose increases. This is probably due to amorphous C changing into the graphite layers that occurs during thermal annealing or MeV-ion-beam irradiation. Graphite formation is also observed for the as implanted sample before annealing. Direct evidence of graphite formation is given from the channeling yield difference between samples for a 2x10(15)/cm(2) dose and for a 3x10(15)/cm(2) dose, showing clearly the stopping power difference between sp(2) (graphite) and sp(3) (diamond) bonding. Amorphous layers in diamond can be formed by C-ion implantation at a more than one order of magnitude smaller amount of doses, compared with those needed for the amorphization of the Si substrates. A calculated number of vacancies created per incident C ion in Si is larger than in diamond. Nevertheless, diamond is amorphized faster than Si. A mechanism is proposed for forming the amorphous layer in diamond. This consists of a bond-breaking process due to inelastic electronic scattering and the movement process of C atoms after bond breaking with the assistance of elastic nuclear scattering without recoil, induced by ion implantation. Atomistic models for ion-beam-induced epitaxial crystallization (IBIEC) and for low-temperature crystallization of implantation-amorphized epitaxial Si layer formed by ultrahigh vacuum chemical-vapor deposition are proposed and discussed, putting particular emphasis on the role of both nuclear and electronic scattering of incident MeV-ion beam. A similar atomistic model for the inclusion of implanted P atoms into substitutional sites is also proposed, based on this atomistic IBIEC model. [S0163-1829(99)10227-3].

 

102.    T. Nakatani and H. G. Okuno

            "Harmonic sound stream segregation using localization and its application to speech stream segregation"

            Speech Commun. 27 (3-4), 209-222 (1999).

 

            ABSTRACT: Sound stream segregation is essential to understand auditory events in the real world. In this paper, we present a new method of segregating a series of harmonic sounds. The harmonic structure and sound source direction are used as clues for segregation. The direction information of the sources is used to extract fundamental frequencies of individual harmonic sounds, and harmonic sounds are segregated according to the extracted fundamental frequencies. Sequential grouping of harmonic sounds is achieved by using both sound source directions and fundamental frequencies. An application of the harmonic stream segregation to speech stream segregation is presented. It provides effective speech stream segregation using binaural microphones. Experimental results show that the method reduces the spectrum distortions and the fundamental frequency errors compared to an existing monaural system, and that it can segregate three simultaneous harmonic streams with only two microphones. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

 

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

            "Supercritical drying for nanostructure fabrication without pattern collapse"

            Microelectron. Eng. 46 (1-4), 129-132 (1999).

 

            ABSTRACT: Supercritical drying has been proposed for the fabrication of nanostructures made up of silicon or resist. Pattern collapse, which is a very serious problem in the fabrication of fine patterns, is related to the spacing, the aspect ratio and the surface tension of rinse solution. Among them, surface-tension reduction is the most effective way to reduce pattern collapse, because it is independent of pattern size. Using supercritical carbon dioxide, which is completely free of surface tension, as a final rinse, we have obtained silicon patterns without collapse. For resist, we have found that avoidance of water contamination is the key factor in suppressing pattern deformation in supercritical drying. Consequently, a drying technique which results in resist patterns without pattern collapse and deformation has been proposed.

 

104.    T. Nishida and N. Kobayashi

            "346 nm emission from AlGaN multi-quantum-well light emitting diode"

            Phys. Status Solidi A-Appl. Res. 176 (1), 45-48 (1999).

 

            ABSTRACT: To realize short wavelength light emitting diodes, nitride quantum structures are studied. Control of the piezoelectric field and thickness design of wurtzite nitride quantum wells are important for band edge emission in the short wavelength region. By reducing the: strain between the AlGaN well and the barrier layers of multi-quantum wells, ultraviolet light emitting diodes operating at the wavelength of 346 nm were successfully fabricated.

 

105.    T. Nishida, M. Kumagai, H. Ando, and N. Kobayashi

            "Photoluminescence excitation spectrum study on GaN/Al0.15Ga0.85N MQWs"

            Phys. Status Solidi B-Basic Res. 216 (1), 233-236 (1999).

 

            ABSTRACT: To clarify the subband profile of nitride quantum structures, we performed photoluminescence excitation spectrum measurements of GaN/Al0.15Ga0.85N multiquantum well structures grown by metalorganic Vapor phase epitaxy on an on-axis 6H-SiC(0001)(Si) substrate. Clear absorption due to the ground state is confirmed. Further, two types of absorption related to the excited states of the nitride quantum wells are found.

 

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

            "Enhancement of soft x-ray emission from femtosecond laser-produced plasma with a rectangular groove target"

            in X-Ray Lasers 1998, Institute Of Physics Conference Series Vol. 159 (Iop Publishing Ltd, Bristol, 1999), pp. 539-542.

 

            ABSTRACT: We show that x-ray emission can be enhanced by confining a laser-produced plasma in a rectangular groove. By using the plasma collision process, a time and wavelength (4-10 nm) integrated soft x-ray emission enhancement of 35 times was obtained at a groove width of 20 mu m ana a groove depth of 100 mu m on a grooved Nd-doped glass target. The peak intensity of the x-ray pulse became 2.4 times larger due to the plasma confinement.

 

107.    T. Nishikawa, H. Nakano, N. Uesugi, M. Nakao, and H. Masuda

            "Greatly enhanced soft x-ray generation from femtosecond-laser-produced plasma by using a nanohole-alumina target"

            Appl. Phys. Lett. 75 (26), 4079-4081 (1999).

 

            ABSTRACT: By making an array of nanoholes on an alumina target, x-ray emission from laser-produced plasma can be greatly enhanced even in soft x-ray energy regions (< 0.25 keV). X-ray fluence enhancement around 30 times was achieved in the 5-25 nm wavelength range. The enhancement increases as the ionization level of Al becomes higher and the x-ray wavelength becomes shorter. Over 50-fold enhancement was obtained at a soft x-ray wavelength around 6 nm, which corresponds to the emission from Al-8+,Al-9+ ions. X-ray pulse duration was 17 ps, which is much shorter than that obtained by using the prepulse technique. (C) 1999 American Institute of Physics. [S0003-6951(99)02652-2].

 

108.    J. Nitta, F. E. Meijer, and H. Takayanagi

            "Spin-interference device"

            Appl. Phys. Lett. 75 (5), 695-697 (1999).

 

            ABSTRACT: We propose a spin-interference device which works even without any ferromagnetic electrodes and any external magnetic field. The interference can be expected in the Aharonov-Bohm (AB) ring with a uniform spin-orbit interaction, which causes the phase difference between the spin wave functions traveling in the clockwise and anticlockwise direction. The gate electrode, which covers the whole area of the AB ring, can control the spin-orbit interaction, and therefore, the interference. A large conductance modulation effect can be expected due to the spin interference. (C) 1999 American Institute of Physics. [S0003-6951(99)03031-4].

 

109.    J. Nitta, H. Takayanagi, and S. Calvet

            "Magnetoresistance oscillations in an Aharonov-Bohm ring using two-dimensional electron gas InAs"

            Microelectron. Eng. 47 (1-4), 85-87 (1999).

 

            ABSTRACT: The Fourier spectrum of the magnetoresistance oscillations in an Aharonov-Bohm ring using two-dimensional electron gas (2DEG) InAs has been studied from the view point of Berry's phase. The ensemble averaged spectrum of the AB-oscillations shows a splitting of h/e-peak as well as a splitting of h/2e-peak. Such a splitting in the spectrum is indicative of Berry's phase.

 

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

            "Continuous monitoring of L-glutamate released from cultured rat nerve cells with a microfabricated on-line sensor at a slow flow rate"

            Electroanalysis 11 (5), 356-361 (1999).

 

            ABSTRACT: A microfabricated online L-glutamate sensor was developed to monitor changes in the local concentration of L-glutamate released from cultured nerve cells. The sensor consists of two glass plates and a fused silica sampling capillary. One of the glass plates has rectanglar flow channels cut into it with a dicing saw and the other has three carbon film based electrodes. One of the electrodes was modified with an Os-polyvinylpyrridine-based polymer layer containing horseradish peroxidase. A GluOx enzyme layer was immobilized upstream of the working electrode. A syringe pump in the suction mode was used to sample extracellular fluid continuously via a glass capillary with a pointed end. The sensor sensitivity did not decrease with decreasing flow rate when the Bow rate was reduced to about 200 nL/min. This is because the increase in the conversion efficiency compensated for the decrease in the analyte flow into the sensor. As a result, a low detection limit (6.4 nM) was obtained at a slow flow rate. In an in vitro experiment, the extracellular fluid near a particular nerve cell was sampled through a capillary and continuously introduced into the sensor via the suction provided by a syringe pump. The nerve cells were stimulated by KCl and a transient L-glutamate release with a sharp peak was monitored with a slow Bow rate of 500 nL/min to 2 mu L/min.

 

111.    S. Nojima

            "Semiconductor photonic crystals with active lattice points"

            in Compound Semiconductors 1998, Institute Of Physics Conference Series Vol. 162 (Iop Publishing Ltd, Bristol, 1999), pp. 79-83.

 

            ABSTRACT: Photonic crystals with active lattice points (two-dimensional gain photonic crystals) are proposed and theoretically investigated, in which all lattice points are made of the same semiconductor gain material embedded in other dissipative medium. This class of photonic crystals is found to exhibit the nature for intensifying the optical gain and possessing its polarization mode selectivity.

 

112.    S. Nojima

            "Single-mode laser oscillation in semiconductor gain photonic crystals"

            Jpn. J. Appl. Phys. Part 2 - Lett. 38 (8A), L867-L869 (1999).

 

            ABSTRACT: A theory is presented for calculating the intensity of light emitted from the two-dimensional photonic crystal with cylindrical gain rods at their lattice points. The results obtained theoretically demonstrate for the first time that an oscillation occurs in this kind of photonic crystal laser with no ordinary external cavities, and, moreover, that it occurs in the single mode in a certain frequency range studied. The light is found to have a strong intensity toward the direction of the M-point in the Brillouin zone.

 

113.    S. Nojima

            "Optical response of excitonic polaritons in photonic crystals"

            Phys. Rev. B 59 (8), 5662-5677 (1999).

 

            ABSTRACT: Nonlocal investigations are presented for exciton-photon coupling in photonic crystals consisting of two kinds of alternating slabs (CuCl/NaCl), for which, excitons exist only in one (CuCl) of the two slabs. Studies are carried out for several typical combinations of period and slab thickness. The lower branch of the excitonic polariton for this system is found to split into many small bands separated by small band gaps (polariton gaps). This phenomenon is explained as the band splitting caused by the coherent interference of polaritonic waves in periodic systems. At the same time, the group velocity of light is greatly reduced in the presence of the excitons. The present nonlocal study demonstrates a double exciton-photon coupling, in which the upper branch of the polariton couples again with the size-quantized exciton states. A long-wavelength approximation is also presented along with a discussion of its validity for simplifying the nonlocal theory. The absorbance and reflectance spectra computed using the transfer matrices exactly reproduce the above small bands for the same systems. An examination of the coupling scheme among excitons, photons, and the structural periodicity indicates that the former two couple with each other more strongly than the other combinations of them. The exciton component of polariton, which is localized in each slab in darkness,could be construed as being delocalized with the assistance of the photon. [S0163-1829(99)05208-X].

 

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

            "Kinetics and thermodynamics of surface steps on semiconductors"

            Crit. Rev. Solid State Mat. Sci. 24 (3), 227-263 (1999).

 

            ABSTRACT: Controls of atomic step arrangement on Si(111) surfaces that have been developed in our laboratory are reviewed. The basis of step bunching on vicinal surfaces is first described using the free energies of uniform and hill-and-valley surfaces. Then experimental results of step rearrangement occurring on Si(111) surfaces during the phase transition between '1 x 1' to 7 x 7-reconstruction are be discussed on this basis. The surfaces misoriented toward the [11(2) over bar] direction consist of wide terraces and stepped regions. The stepped regions are transformed to (331) facets when the misorientation angle is large. The surfaces misoriented toward the [<(11)over bar>2] direction are covered with one-layer-high and three-layer-high steps. The misorientation-direction dependence of the step arrangement is interpreted by considering free energies of terrace surfaces and steps and by considering step-step interaction energies. Step motions associated with adatom evaporation at high temperatures can be controlled by using etched patterns and the step arrangement on the patterned surfaces therefore can be artificially positioned. This technique can be used to form ultralarge step-free terraces, which is useful to study step dynamics. Step-flow homoepitaxial growth can also be utilized to control step arrangement. On Si(111) surfaces, out-of-phase boundaries of the 7 x 7 reconstructed domains exist and influence the evolution of step arrangement during growth. In particular cases, ordered networks of step and out-of-phase boundaries patterns are self-organized. These techniques for step arrangement control can be applied to the standard Si processes because similar results are obtained when furnace processing are used. Finally, the impact of the step arrangement controls is discussed. Step observation techniques are summarized in the Appendix.

 

115.    T. Ogino, H. Hibino, Y. Homma, Y. Kobayashi, K. Prabhakaran, K. Sumitomo, and H. Omi

            "Fabrication and integration of nanostructures on Si surfaces"

            Accounts Chem. Res. 32 (5), 447-454 (1999).

 

            ABSTRACT:

116.    Y. Ohtera, T. Sato, T. Kawashima, T. Tamamura, and S. Kawakami

            "Photonic crystal polarisation splitters"

            Electron. Lett. 35 (15), 1271-1272 (1999).

 

            ABSTRACT: The design, fabrication, and measurement of an a-Si/SiO2 photonic crystal polarisation splitter are reported. The device consists of a 10-period corrugated multilayer film and is made by a combination of sputter-deposition and sputter-etching processes. The measured insertion loss and extinction ratio at lambda = 1.55 mu m are 0.4dB and > 40dB, respectively.

 

117.    T. Okadome and M. Honda

            "Kinematic construction of the trajectory of sequential arm movements"

            Biol. Cybern. 80 (3), 157-169 (1999).

 

            ABSTRACT: A kinematic construction rule determining the trajectory of human sequential movements is formulated using minimum-jerk and minimum-angular-jerk trajectories. The kinematic construction rule states that the observed trajectory of sequential movements coincides with a weighted average of the minimum-jerk trajectory and the segmented minimum-angular-jerk trajectory. This rule covers not only point-to-point movements but also simple sequential movements. Five kinds of experiments that measure the trajectories in planar, multijoint sequential arm movements were conducted. The measured trajectories coincide with the predictions made on the basis of the kinematic construction rule presented here. Moreover, predictions of previous models such as the minimum-jerk, the equilibrium-trajectory, and the minimum-torque-change models are shown to be incompatible with our observations of sequential movements.

 

118.    H. G. Okuno, T. Nakatani, and T. Kawabata

            "Listening to two simultaneous speeches"

            Speech Commun. 27 (3-4), 299-310 (1999).

 

            ABSTRACT: Speech stream segregation is presented as a new speech enhancement for automatic speech recognition. Two issues are addressed: speech stream segregation from a mixture of sounds, and interfacing speech stream segregation with automatic speech recognition. Speech stream segregation is modeled as a process of extracting harmonic fragments, grouping these extracted harmonic fragments, and substituting non-harmonic residue for non-harmonic parts of a group. The main problem in interfacing speech stream segregation with hidden Markov model (HMM)-based speech recognition is how to improve the degradation of recognition performance due to spectral distortion of segregated sounds, which is caused mainly by transfer function of a binaural input. Our solution is to re-train the parameters of HMM with training data binauralized for four directions. Experiments with 500 mixtures of two women's utterances of an isolated word showed that the error reduction rate of the 1-best/10-best word recognition of each woman's utterance is, on average, 64% and 75%, respectively. (C) 1999 Elsevier Science B.V. All rights reserved.

 

119.    W. D. Oliver, J. Kim, R. C. Liu, and Y. Yamamoto

            "Hanbury Brown and Twiss-type experiment with electrons"

            Science 284 (5412), 299-301 (1999).

 

            ABSTRACT: Fermion anti-bunching was directly observed by measuring the cross-covariance of the current fluctuations of partitioned electrons. A quantum paint contact was used to inject single-mode electrons into a mesoscopic electron beam splitter device. The beam splitter output currents showed negative cross-covariance, indicating that the electrons arrived individually at the beam splitter and were randomly partitioned into two output channels. As the relative time delay between the outputs was changed, the observed ringing in the cross-covariance was consistent with the bandwidths used to monitor the fluctuations. The result demonstrates a fermion complement to the Hanbury Brown and Twiss experiment for photons.

 

120.    H. Omi and T. Ogino

            "Control of atomic step arrangements on a patterned Si(111) substrate by using molecular beam epitaxy"

            Journal Of Vacuum Science & Technology A 17 (4), 1610-1614 (1999).

 

            ABSTRACT: We present a new approach for designing atomic step arrangements on the Si(111) surface on a wafer scale. Steps on the surfaces patterned with mesas and trenches are rearranged during step-flow growth in molecular beam epitaxy. The step-flow growth produces straight arrays of [(11)over-bar-2]-type steps along the mesa tops. On the bottom of the trenches, however, resulting atomic steps curve toward [(11)over-bar-2] direction, and are randomly distributed. These results show that step-flow growth on Si(111) mesa tops is promising for large-scale control of step arrangement and that the steps can be used as templates for step-initiated nanofabrication.

 

121.    H. Omi and T. Ogino

            "Self-organization of Ge islands on high-index Si substrates"

            Phys. Rev. B 59 (11), 7521-7528 (1999).

 

            ABSTRACT: Films of Ge were grown on Si(113) and Si(331) substrates by molecular-beam epitaxy (MBE). We found mat the Ge films grow in the Stranski-Krastanow (SK) mode on both substrates. The SK islands are bounded by facet planes, and have a wirelike shape on Si(113) and a dotlike shape on Si(331). The resulting island shapes are stable equilibrium ones, and are strongly governed by the mechanism of anisotropic strain relief. Moreover, multilayers of coherent Ge islands were stacked on a Si(113) substrate with spacer layers of Si by MBE. In the multilayers of Ge/Si, the wirelike Ge islands become more uniform as the number of layers is increased at a growth temperature of 400 degrees C. When the temperature is 450 degrees C, the shape of the islands changes from wirelike in the first Ge layer to dashlike in the sixth Ge layer. This temperature-dependent self-organization is caused by inhomogeneous strain distributions induced by the buried Ge islands that are vertically aligned in the Ge/Si multilayers. [S0163-1829(99)09911-7].

 

122.    T. H. Oosterkamp, J. W. Janssen, L. P. Kouwenhoven, D. G. Austing, T. Honda, and S. Tarucha

            "Maximum-density droplet and charge redistributions in quantum dots at high magnetic fields"

            Phys. Rev. Lett. 82 (14), 2931-2934 (1999).

 

            ABSTRACT: We have measured electron transport through a vertical quantum dot containing a tunable number (between 0 and 40) of electrons. Over a region of the magnetic field the electrons are spin polarized and occupy successive angular momentum states. This is the maximum-density-droplet (MDD) state. The stability region where the MDD is the ground state decreases for increasing electron number. The instability of the MDD and other transitions in this high B region are accompanied by a redistribution of charge which abruptly changes the area of the electron droplet. [S0031-9007(99)08873-0].

 

123.    N. Oyama, E. Ohta, K. Takeda, K. Shiraishi, and H. Yamaguchi

            "First-principles calculation for misfit dislocations in InAs/GaAs(110) heteroepitaxy"

            Surf. Sci. 435, 900-903 (1999).

 

            ABSTRACT: The misfit dislocation core structures in InAs/GaAs(110) heterostructures were calculated for InAs thicknesses of 2 and 4 ML using first-principles calculations. Dislocation cores with asymmetric five-fold coordinated In atoms were formed at the InAs/GaAs interface. This core structure is maintained even if the thickness of InAs epilayer increases. We also calculated for the GaAs/InAs(110) heterostructure and the core has a different structure at the very initial stage of heteroepitaxy. (C) 1999 Elsevier Science B.V. All rights reserved.

 

124.    N. Oyama, E. Ohta, K. Takeda, K. Shiraishi, and H. Yamaguchi

            "First-principles calculations on atomic and electronic structures of misfit dislocations in InAs/GaAs(110) and GaAs/InAs(110) heteroepitaxies"

            J. Cryst. Growth 202, 256-259 (1999).

 

            ABSTRACT: We investigated the atomic and electronic structures of the misfit dislocations of InAs/GaAs(1 1 0) and GaAs/InAs(1 1 0) heterointerfaces by first-principles calculations and scanning tunneling microscopy (STM). The calculated results show that the core confined at the InAs/iGaAs(1 1 0) heterointerface has five-fold coordinated In atoms. The surface just above the dislocation line was depressed and the calculated vertical displacement was about 0.52 Angstrom when the InAs epilayer thickness is 4 ML, which is in good agreement with the STM observations. In the GaAs/InAs heteroepitaxy, core structures drastically change with the increase of GaAs epilayer thickness. (C) 1999 Elsevier Science B.V. All rights reserved.

 

125.    M. Pelton and Y. Yamamoto

            "Ultralow threshold laser using a single quantum dot and a microsphere cavity"

            Phys. Rev. A 59 (3), 2418-2421 (1999).

 

            ABSTRACT: We propose a novel semiconductor microlaser, made by capturing the light emitted from a single InAs/GaAs quantum dot in the whispering-gallery mode of a glass microsphere. We demonstrate that such an arrangement allows the laser threshold condition to be satisfied. The corresponding threshold current should be several orders of magnitude lower than is currently possible in semiconductor lasers. [S1050-2947(99)05403-7].

 

126.    K. Prabhakaran and T. Ogino

            "High temperature reaction of nitric oxide with Si surfaces: Formation of Si nanopillars through nitride masking and oxygen etching"

            J. Vac. Sci. Technol. B 17 (4), 1346-1349 (1999).

 

            ABSTRACT: In this article, we report the fabrication of Si nanopillars by surface reaction with nitric oxide (NO) at high temperature. NO was leaked onto clean Si surfaces, at a temperature of similar to 850 degrees C, in ultrahigh vacuum chamber and examined in situ by x-ray and ultraviolet photoelectron spectroscopy, Auger electron spectroscopy, low energy electron diffraction, and ex situ by atomic force microscopy. NO molecules dissociate on the surface and nitrogen atoms thus produced form nitride islands. These islands act as protective masks for the etching of Si by the oxygen atoms, through the desorption of SiO species. Occurrences of these two simultaneous processes results in the formation of nanometer sized Si pillars (typical basewidth 100-150 nm and height 5-15 nm) capped by silicon nitride. These pillar structures are separated by clean Si areas as shown by the clear presence of two domains. We also show that the height of these Si pillars can be increased by ex situ chemical etching. (C) 1999 Americnn Vacuum Society. [S0734-211X(99)00304-2].

 

127.    K. Prabhakaran and T. Ogino

            "Chemical bond manipulation for nanostructure integration on wafer scale"

            Bull. Mat. Sci. 22 (3), 553-562 (1999).

 

            ABSTRACT: In this paper, we have briefly summarized our activity in the area of chemical bond manipulation for the integration of nanostructures on a full wafer scale. Chemical bond manipulation involves a judicious combination of surface phenomena: reactions or diffusion, and growth process such as molecular beam epitaxy (MBE). Here, we present our results on oxidation, metallization and nitridation and their role in the formation of nanostructures. We find that oxygen changes the bonding partner from Ge to Si and this phenomenon can be controlled by controlling the annealing temperature. We have employed this phenomenon for the fabrication of novel, multiperiod Si/SiO2/Ge layered structure which exhibits interesting light emitting properties. Further, by making use of selective diffusion of cobalt atoms through Ge layers it is possible to incorporate metallic features into Ge quantum dots. Moreover, it is possible to fabricate Si nanopillars through high temperature reaction of nitric oxide. NO molecules dissociate on the surface,and nitrogen atoms thus produced form nitride islands. These islands act as protective masks for the etching of Si by the oxygen atoms, through the desorption of SiO species. Occurrence of these two simultaneous processes result in the formation of nanometre-sized Si pillars capped by silicon nitride. All these results emphasize the fact that we can extend information obtained through traditional surface science experiments for the fabrication of novel structures on a full wafer scale.

 

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

            "Oxidation of cobalt pre-reacted SiGe epilayer grown on Si(100)"

            Surf. Sci. 429 (1-3), 274-278 (1999).

 

            ABSTRACT: In this paper, we describe the results of a study of the interaction of oxygen with a SiGe epilayer which is already reacted with cobalt atoms. The epilayer was grown on Si(100) substrate using solid source molecular beam epitaxy. Techniques of ultra-violet and X-ray photoelectron spectroscopy and medium energy ion scattering are employed for the study. In a recent paper, we reported that the reaction of Co with epitaxially grown SiGe alloy leads to the selective formation of CoSi2 on the surface. On exposing such a Co reacted surface to oxygen at 285 degrees C, the surface Co-Si bonds break and Si-O bonds are formed. Further, the cobalt atoms thus released move inward and bond with Si atoms in the subsurface regions. These results indicate that it is possible to incorporate metallic and insulator features into SiGe alloy, which is an important device material, through in situ processes. (C) 1999 Elsevier Science B.V. All rights reserved.

 

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

            "Interaction of Co with SiGe epilayer grown on Si(100)"

            Surf. Sci. 421 (1-2), 100-105 (1999).

 

            ABSTRACT: The interaction of Co with a thin layer of SiGe (similar to 80:20), epitaxially grown on Si(100) surface, is investigated by combined use of ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS) and medium energy ion scattering spectroscopy (MEIS). Deposition of Co onto the alloy surface at room temperature forms a mixture of CoxSiy and CoxGey phases on the surface. Upon annealing at 300 degrees C, Co diffuses inward and Co-Ge bonds are broken. This leads to the formation of CoSi2 layers. MEIS blocking profile data indicate that the cobalt silicide layer formed is strain free, and therefore suggest that CoSi2 can be a potential candidate for achieving metallic interconnections in SiGe based devices. (C) 1999 Elsevier Science B.V. All rights reserved.

 

130.    S. M. Reimann, M. Koskinen, J. Kolehmainen, M. Manninen, D. G. Austing, and S. Tarucha

            "Electronic and magnetic structure of artificial atoms"

            Eur. Phys. J. D 9 (1-4), 105-110 (1999).

 

            ABSTRACT: The concept of shell structure has been found useful in the description of semiconductor quantum dots, which today can be made so small that they contain less than 20 electrons. We review the experimental discovery of magic numbers and spin alignment following Hnd's rules in the addition spectra of vertical quantum dots, and show that these results compare well to model calculations within spin density functional theory. We further discuss the occurrence of spin density waves in quantum dots and quantum wires. For deformable two-dimensional quantum dots (for example, jellium clusters on surfaces), we study the interplay between Hund's rules and Jahn-Teller deformations and investigate the effect of magnetic fields on the ground-state shapes.

 

131.    M. S. M. Saifullah, G. A. Botton, C. B. Boothroyd, and C. J. Humphreys

            "Electron energy loss spectroscopy studies of the amorphous to crystalline transition in FeF3"

            J. Appl. Phys. 86 (5), 2499-2504 (1999).

 

            ABSTRACT: Electron beam-induced crystallization studies in amorphous FeF3 films using electron energy loss spectroscopy (EELS) are discussed in this letter. Time-resolved EELS studies show that the coordination polyhedra in amorphous FeF3 (a-FeF3) are randomly arranged FeF6 octahedra. They arrange themselves to give long range order during crystallization to FeF2 and FeF3 under the electron beam. Changes in the d-band occupancy by one electron as well as the sensitivity of the ratio of the Fe L-3 and L-2 edges to the electronic configuration of the iron ion are clearly seen during the crystallization process. (C) 1999 American Institute of Physics. [S0021-8979(99)03817-7].

 

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

            "Effect of chelating agents on high resolution electron beam nanolithography of spin-coatable Al2O3 gel films"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 38 (12B), 7052-7058 (1999).

 

            ABSTRACT: The effect of chelating agents on the electron beam exposure characteristics as well as environmental stability of the spin-coatable Al2O3 gel films is discussed. It was found that the Al2O3 gel films prepared by reacting aluminium tri-sec-butoxide, Al(OBu5)(3), with acetylacetone (AcAc), AcAc/Al2O3, gave better environmental stability and patterning characteristic than the gel films prepared by reacting the Al(OBu5)(3) with ethylacetoacetate (EAcAc), EAcAc/Al2O3. The latter suffered from a faster moisture attack in the laboratory atmosphere. Both EAcAc/Al2O3 and AcAc/Al2O3 films are similar to 10(6) times more electron beam sensitive than sputtered AlOx films, thus bringing the formers' sensitivity very close to some of the organic electron beam resists. It was seen that the baking temperature up to 70 degreesC has almost no effect on either the sensitivity or the contrast in both the films; but it has a significant effect on the developing characteristics. Electron beam nanolithography gave 20 nm linewidth with a rectangular cross-section in both EAcAc/Al2O3 and AcAc/Al2O3 films. It was observed that the etching characteristics of Al2O3 films in the electron cyclotron resonance (ECR) plasma are dependent upon the final baking temperature of the developed pattern. Preliminary plasma etching studies show that 15 nm lines on polysilicon can be etched.

 

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

            "Quantum transition to supersolid phase"

            J. Supercond. 12 (1), 231-232 (1999).

 

            ABSTRACT: We study a possible coexistence of superconducting state and charge density waves which, in a broad sense, might be called a supersolid phase. We investigate the infinite dimensional (d = infinity) attractive Hubbard model by applying a sublattice dependent Gutzwiller wave function g(A)(DA)g(B)(DB)\BCS] as a variational wave function describing the ground state. One may naively expect that the BCS superconducting state evolves continuously to the Bose-Einstein condensed state of bipolarons as the attractive interaction increases, as far as the system is dilute. However, we show that our variational wave function has lower energy than the simple BCS wave function for all electron densities and the interaction strengths. Our variational parameters increase (g(A,B)-->infinity) as we increase the interaction strength (U-->infinity). The energy gap turns out to be a mixture of s and extended-s waves. In the vicinity of half-filling, we find a quantum transition from a simple superconducting phase to a supersolid phase with increase of the electron density and/or the interaction strength.

 

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

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

            IEEE Trans. Appl. Supercond. 9 (2), 3409-3412 (1999).

 

            ABSTRACT: The study of the detailed influence of the order parameter (OP) symmetry on the properties of high temperature superconducting (HTS) Josephson junctions still is a key issue. Whereas the hole doped HTS such as YBa2Cu3O7-delta (YBCO), Bi2Sr2CaCu2O8+x (BSCCO), or La1.85Sr0.15CuO4-delta (LSCO) are known to have a dominating d-wave component of the OF, there is significant evidence that the electron doped material Nd1.85Ce0.15CUO4-y (NCCO) has a s-wave symmetry of the OF. Therefore, we have studied the electrical transport properties of [001] tilt NCCO bicrystal grain boundary Josephson junctions (GBJs) with misorientation angles between 7 degrees and 36.8 degrees and compared them to those of the hole doped HTS. For the NCCO-GBJs an exponential decay of the critical current density J(c) with increasing misorientation angle as well as a scaling of the characteristic junction voltage V-c proportional to J(C)(P) was found very similar to what is observed for the hole doped HTS. This strongly suggests that the OP symmetry is not the key parameter controlling the characteristic properties of HTS-GBJs. In contrast, they are most likely related to the presence of a disorder induced, insulating grain boundary barrier which is similar for both the d- and s-wave HTS.

 

135.    E. Schroer and M. Uematsu

            "Simulation of clustering and pile-up during post-implantation annealing of phosphorus in silicon"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 38 (1A), 7-11 (1999).

 

            ABSTRACT: We report on the simulation of the annealing behavior of medium dose (10(13)-10(14) cm(-2)) implanted phosphorus in silicon. It is shown that the transient clustering of phosphorus has to be taken into account in order to achieve consistent simulation results. The pile-up of phosphorus at the silicon-silicondioxide interface is considered by including a diffusion-segregation term in the diffusion-reaction equations. We show how the phosphorus clustering impacts the phosphorus amount in the pile-up layer and compare the simulation results with available experimental data.

 

136.    S. Seki, Y. Yoshida, S. Tagawa, K. Asai, K. Ishigure, K. Furukawa, M. Fujiki, and N. Matsumoto

            "Effects of structural defects on hole drift mobility in aryl-substituted polysilanes"

            Philos. Mag. B-Phys. Condens. Matter Stat. Mech. Electron. Opt. Magn. Prop. 79 (10), 1631-1645 (1999).

 

            ABSTRACT: The effects of a silicon-based structural defect on the hole transport properties of poly(methylphenylsilane) were studied by the DC time-of-flight technique. The defect was chemically introduced as silicon branching of the silicon backbone by copolymerizing methylphenyldichlorosilane and p-tolyltrichlorosilane with sodium. A good empirical relation was obtained between the hole drift mobility (mu(E=0)) at a zero electric field limit and the defect density. The value of mu(E=0) decreased exponentially from 4x10(-4) to 5x10(-6) cm(2) V-1 s(-1) with an exponential increase in defect density from 0.0024 to 0.18. On the basis of Bassler's disorder formalism, hole transport in the polymers was quantitatively analysed, revealing the different contributions of diagonal and off-diagonal disorder with the defect density. The degree of fluctuation in the density of state mainly determined the hole drift mobility in specimens with fewer defects, while intersite hopping distance controlled the mobility in the polymers with more defects.

 

137.    H. Shibata

            "Josephson plasma in various high-T-c cuprates"

            J. Low Temp. Phys. 117 (5-6), 1077-1081 (1999).

 

            ABSTRACT: Josephson plasma in various high-T-c cuprates with and without magnetic field is studied by using the sphere resonance method. For Bi2Sr2CaCu2O8+delta, the plasma in a zero magnetic field exists at 5 cm(-1) for a slightly overdoped sample (T-c = 85 K) and shifts to 11 cm(-1) as the doping increases (T-c = 71 K). For SmLa1-xSrxCuO3.95 (T* phase), two peaks appear at 11 and 30 cm(-1) in a zero magnetic field, and both peals shift to lower frequencies as the magnetic field increases. These peaks are identified as the Josephson plasma of the intrinsic Josephson junction at the fluorite-type Sm2O2 block layer and the rock salt-type (La,Sr)(2)O2-delta block layer, respectively. This indicates that the T* phase can be regarded as the.S/I/S/I'/S/I/S/I'/S. (superconductor/insulator1/superconductor/insulator2/superconductor.)-type Josephson junction array.

 

138.    H. Shibata and A. Matsuda

            "Josephson plasma frequencies in overdoped Bi2Sr2CaCu2O8+delta"

            Phys. Rev. B 59 (18), R11672-R11674 (1999).

 

            ABSTRACT: Far-infrared sphere resonance in Bi2Sr2CaCu2O8+delta samples with various:oxygen concentrations is measured down to 5 cm(-1). Although no peaks are observed in this frequency range for the optimumly doped sample, the Josephson plasma peak is observed at 5 cm(-1) for a 1-atm-O-2-annealed sample. The peak shifts to higher frequencies as the doping increases, and is observed at 11 cm(-1) for a 150-atm-O-2-annealed sample. The c-axis penetration depth lambda(c) obtained from the peak frequencies is determined to be 77 to 35 mu m. These large lambda(c) values are larger than the value estimated from the Josephson-coupled layer model,while the doping dependence is qualitatively explained by the model. [S0163-1829(99)50718-2].

 

139.    K. Shimizu

            "Photon emission from metal surfaces induced by electron capture of slow ions at grazing incidence"

            Phys. Rev. B 60 (24), 17091-17101 (1999).

 

            ABSTRACT: This paper is a theoretical report on a resonant photon emission process assisted by surface plasmons in the charge-exchange scattering of ions at a metal surface. Slow protons, for example, moving parallel to the surface induce an image charge. A proton and the image charge form an electric dipole at the boundary. When a proton captures a surface electron, the dipole vanishes rapidly, and this necessarily results in a photon emission in accordance with classical electrodynamics. We calculate the photon emission probability in a semiclassical way on the basis of a boundary value problem for a radiation field converted from a surface plasmon excited by the inelastic tunneling current of an electron. Photons with the same frequency as the surface plasmon are emitted dominantly, provided that the energy conservation law is satisfied. The probability is estimated at approximately 0.001 for one collision, which is similar to 10(4) larger than that of the direct photon emission process caused by the inelastic tunneling current. [S0163-1829(99)04448-3].

 

140.    K. Shimizu and N. Imoto

            "Communication channels secured from eavesdropping via transmission of photonic Bell states"

            Phys. Rev. A 60 (1), 157-166 (1999).

 

            ABSTRACT: This paper proposes a quantum communication scheme for sending a definite binary sequence while confirming the security of the transmission. The scheme is very suitable for sending a ciphertext in a secret-key cryptosystem so that we can detect any eavesdropper who attempts to decipher the key. Thus we can continue to use a secret key unless we detect eavesdropping and the security of a key that is used repeatedly can be enhanced to the level of one-time-pad cryptography. In our scheme, a pair of entangled photon twins is employed as a bit carrier which is encoded in a two-term superposition of four Bell states. Different bases are employed for encoding the binary sequence of a ciphertext and a random test bit. The photon twins are measured with a Bell state analyzer and any bit can be decoded from the resultant Bell state when the receiver is later notified of the coding basis through a classical channel. By opening the positions and the values of test bits, ciphertext can be read and eavesdropping is simultaneously detected.

 

141.    K. Shimizu, N. Imoto, and T. Mukai

            "Dense coding in photonic quantum communication with enhanced information capacity"

            Phys. Rev. A 59 (2), 1092-1097 (1999).

 

            ABSTRACT: We propose a scheme for enhancing the information capacity to more than 2 bits in dense coding quantum communication that involves transmitting a polarization entangled twin photon and a subsequent joint measurement with a Bell-state analyzer. Although direct modulation of the timing position and optical frequency of the photon play no role in dense coding quantum communication, we show that the frequency-dependent phase correlation of polarization entangled twin photons can be used for this enhancement if photon twins are generated through optical parametric down-conversion. With our proposed Bell-state analyzer containing a nonlinear optical gate, the capacity can be enhanced from the reported 2 bits to 3 bits by the local operation of a frequency-dependent phase shift on the transmitted photon. [S1050-2947(99)04802-7].

 

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

            "Diffraction of circularly polarized light from near-field optical probes"

            J. Microsc.-Oxf. 194, 353-359 (1999).

 

            ABSTRACT: Diffracted fields from 100-mm aperture near-field scanning optical microscopy (NSOM) probes and uncoated tapered fibres are measured and analysed. Using a solid angle scanner, the two-dimensional intensity distribution and polarization state of the diffracted light are resolved experimentally. Polarization analyses show that circularly polarized input light does not maintain its polarization state for all diffraction angles, and is completely filtered into linearly polarized light at large polar diffraction angles. This drastic decomposition originates from the vector nature of light diffracted by the sub-wavelength aperture. There is a fundamental difficulty in generating circularly polarized light near the aperture of NSOM probes owing to polarization-dependent diffraction in the near-field regime. This is illustrated by the Bethe-Bouwkamp model using circularly polarized input light.

 

143.    K. Shiraishi, T. Ito, Y. Y. Suzuki, H. Kageshima, K. Kanisawa, and H. Yamaguchi

            "Microscopic investigation of the surface phase transition on GaAs(001) surfaces"

            Surf. Sci. 435, 382-386 (1999).

 

            ABSTRACT: We investigated the microscopic mechanism of the surface phase transition from c(4 x 3) to (2 x 4)beta 2 structures on GaAs(001) surfaces using scanning tunneling microscopy (STM) and first-principles calculations. According to the STM image, the structure where (2 x 4)beta 2 units are located higher than c(4 x 4) units (A structure) appears during the surface phase transition, but the structure where (2 x 4)beta 2 units are located deeper than c(4 x 4) units (B structure) never appears. First-principles calculations show that the A structure is more stable than the B structure. This is in fairly good agreement with the STM experiments. It was also found that the microscopic details of the stable A structure induce very complicated processes during the surface phase transition on GaAs(001) surfaces, such as incorporation and emission of gallium atoms. The stability of the A structure originates from the characteristics of the (2 x 4)beta 2 atomic structures, which contain missing dimer trenches with a height of two atomic layers. Moreover, we also point out the possibility of the existence of an intermediate mixed 'phase' between c(4 x 4) and (2 x 4)beta 2 phases. (C) 1999 Elsevier Science B.V. All rights reserved.

 

144.    T. Shodai, Y. Sakurai, and T. Suzuki

            "Reaction mechanisms of Li2.6Co0.4N anode material"

            Solid State Ion. 122 (1-4), 85-93 (1999).

 

            ABSTRACT: We report the reaction mechanisms of Li2.6Co0.4N anode material which we studied using chemical composition analysis, X-ray diffraction data for lithium extracted samples and core level electron energy loss spectroscopy. The only mobile ions in the Li2.6Co0.4N were lithium ions. The capacity depended on the amount of amorphous phase formed during the first lithium extraction. We found that the amorphous phase can accommodate a large quantity of lithium ions. By contrast, the nitrogen-K spectrum of electrochemically obtained Li1.0Co0.4N showed that there were a large number of holes in the nitrogen 2p orbital. It became clear that both cobalt and nitrogen play an important role in maintaining the charge balance. Based on these results, we propose a model of the reaction mechanism and electronic structure. (C) 1999 Elsevier Science B.V. All rights reserved.

 

145.    M. Shoji and S. Horiguchi

            "Electronic structures and phonon-limited electron mobility of double-gate silicon-on-insulator Si inversion layers"

            J. Appl. Phys. 85 (5), 2722-2731 (1999).

 

            ABSTRACT: Electronic structures and the phonon-limited electron mobility of inversion layers have been studied at 300 K for the thin Si (100) layer of double-gate (DG) silicon- on- insulator (SOI) structures by using a one-dimensional self-consistent calculation and a relaxation time approximation. Both symmetric and asymmetric DG SOI systems have been investigated. The self-consistent calculation presents the electronic structures specific to DG SOI Si inversion layers and the range of the specific electronic structures as functions of Si layer thickness t(Si) and the vertical effective electric field E-eff. Outside this range, the mobility behavior as a function of E-eff is almost identical to that of bulk Si inversion layers. In this range, however, as t(Si) decreases, the phonon-limited electron mobility mph increases gradually to a maximum around t(Si) = 10 nm, decreases for t(Si) = 10-5 nm, rises rapidly to another maximum in the vicinity of t(Si) = 3 nm and finally falls. The former gradual increase in the mobility mph results from a reduction of phonon scattering caused by the interaction of upper and lower inversion layers. For t(Si) of less than approximately 10 nm, the mobility of each subband is reduced by an enhancement of scattering rates due to a confinement effect in general. However, the rapid increase of the fraction of electrons in the lowest energy subband that has a higher mobility than other subbands brings about the latter mobility increase in the vicinity of t(Si) = 3 nm. (C) 1999 American Institute of Physics. [S0021-8979(99)00305-9].

 

146.    T. Sogawa, H. Ando, S. Ando, and K. Kanbe

            "Spin relaxation of one-dimensional excitons in GaAs rectangular quantum wires"

            in Compound Semiconductors 1998, Institute Of Physics Conference Series Vol. 162 (Iop Publishing Ltd, Bristol, 1999), pp. 397-402.

 

            ABSTRACT: We investigated exciton-spin relaxation in GaAs rectangular quantum wires (QWRs) with 12 nm x 12 nm and 19 nm x 13 nm cross-sections by time-resolved photoluminescence spectroscopy. In order to clarify effects of one-dimensional (1-D) confinement on the spin relaxation process, we compared spin-relaxation times of these QWRs with those of GaAs quantum wells (QWs) of various thicknesses. We found that QWRs exhibited longer spin-relaxation times than QWs in the low temperature region from 15 to 80 K presumably due to enhanced exciton-exciton collision in the narrow 1-D confinement structures.

 

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

            "Magnetic field and temperature dependence of the intrinsic resistance steps in the mixed state of the cuprate superconductor Nd2-xCexCuOy"

            Phys. Rev. B 60 (17), 12424-12428 (1999).

 

            ABSTRACT: In epitaxial c-axis oriented films of the cuprate superconductor Nd2-xCexCuOy we have studied the magnetic field and temperature dependence of the two intrinsic steps of the flux flow resistance appearing under current bias. The two steps are explained in terms of the field induced energy shift of the normal excitations in the superconducting mixed state. Because of the strong interaction between vortices in the magnetic fields used in our experiments, we propose that narrow subbands develop between the Fermi energy and the energy gap, and that the quasiparticles undergo Bloch oscillations in the subbands, thereby leading to the first resistance step. The second step, appearing at electric fields about a thousand times higher than the fields of the first step, may be explained in terms of a second subband at higher energy or, alternatively, by a sharp upturn of the density of states near the gap energy and of the corresponding phase space available for quasiparticle scattering. [S0163-1829(99)02341-3].

 

148.    K. Sumitomo, Y. Kobayashi, T. Ito, and T. Ogino

            "Ge segregation mechanism during Si/Ge multilayer growth"

            Thin Solid Films 357 (1), 76-80 (1999).

 

            ABSTRACT: The Ge segregation mechanism during Si/Ge multilayer growth has been investigated using medium-energy ion scattering (MEIS) and computer simulation with the stochastic Monte Carlo technique. We found that Ge atoms segregated not only in the topmost layer but also in the second and third layers. The segregation probability is found to be quadratic in the Ge concentration at the surface. The exchange between the second and the third layer also occurs readily during growth, even although these layers are buried and therefore are not expected to reduce the surface free energy. We found that the activation energy for the site exchange process at the subsurface is lower than the previously believed value, and flip-flop exchange at the subsurface plays a more important role in the Ge segregation process. (C) 1999 Elsevier Science S.A. All rights reserved.

 

149.    S. C. Sung and Y. Manabe

            "Coterie for generalized mutual exclusion problem"

            IEICE Trans. Inf. Syst. E82D (5), 968-972 (1999).

 

            ABSTRACT: This paper discusses the generalized mutual exclusion problem defined by H. Kakugawa and M. Yamashita. A set of processes shares a set of resources of an identical type. Each resource must be accessed by at most one process at any time. Each process may have different accessible resources. If two processes have no common accessible resource, it is reasonable to ensure a condition in resource allocation, which is called allocation independence in this paper, i.e., resource allocation to those processes must be performed without any interference. In this paper, we define a new structure, sharing structure coterie. By using a sharing structure coterie, the resource allocation algorithm proposed by H. Kakugawa and M. Yamashita ensures the above condition. We show a necessary and sufficient condition of the existence of a sharing structure coterie. The decision of the existence of a sharing structure coterie for an arbitrary distributed system is NP-complete. Furthermore, we show a resource allocation algorithm which guarantees the above requirement for distributed systems whose sharing structure coteries do not exist or are difficult to obtain.

 

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

            "Magnetophotoluminescence in n- and p-type Si-modulation-doped AlGaAs/GaAs single-heterostructures"

            in Compound Semiconductors 1998, Institute Of Physics Conference Series Vol. 162 (Iop Publishing Ltd, Bristol, 1999), pp. 155-160.

 

            ABSTRACT: Si-modulation-doped AlGaAs/GaAs heterostructures, which are grown on (100) and (311)A GaAs substrates, behave n- and p-type modulation-doped structures, respectively. We measure magnetophotoluminescence (MPL) spectra and discuss the difference of the carrier recombinations in these structures. Both n- and p-type structures show the MPL spectra reflecting the Landau level quantization. Though interband transitions coming from the ground subband are suppressed for v >2 in the n-type, this rule is broken in the p-type.

 

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

            "Short pulse tunneling measurements of the intrinsic Josephson junctions in Bi-Sr-Ca-Cu-O"

            IEEE Trans. Appl. Supercond. 9 (2), 4507-4510 (1999).

 

            ABSTRACT: We have measured the I-V characteristics of intrinsic Josephson junction stacks fabricated on the surface of a Bi2Sr2CaCu2O8+delta crystal. In order to reduce the Joule heating, which necessarily occurs associated with these measurements, we have reduced the number of junctions in the stack to approximately 10, and then adopted the short pulse measurement method. With these measures, it becomes possible to observe I-V characteristics which have a clear gap structure with slight gap suppression due to current injection. The voltage response analysis indicates that the magnitude of the gap suppression is no greater than 3% at the maximum. The estimated gap parameter is 50 mV for a single junction.

 

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

            "Characteristic temperature dependence of the maximum Josephson current in Bi-Sr-Ca-Cu-O intrinsic junctions"

            IEEE Trans. Appl. Supercond. 9 (2), 4511-4514 (1999).

 

            ABSTRACT: We have measured the temperature dependence of the maximum Josephson current I-c for 15 - 30 nm thick stacks comprised of 10 to 20 Bi2Sr2CaCu2O8+delta intrinsic junctions. It is found that I-c typically shows little saturation at low temperatures but continues to increase noticeably as temperature decreases towards T = 0. This behavior becomes significant as the normal tunneling resistance increases with decreasing oxygen content.

 

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

            "Interlayer tunneling spectroscopy for slightly overdoped Bi2Sr2CaCu2O8+delta"

            Phys. Rev. Lett. 82 (26), 5361-5364 (1999).

 

            ABSTRACT: We have measured the interlayer tunneling characteristics of slightly overdoped Bi2Si2CaCu2O8+delta in the c-axis direction from 10 to 220 K by using very thin mesas containing approximately ten CuO2 double layers, The superconducting gap 2 Delta is 50 meV at 10 K and shows a temperature (T) dependence similar to that of the BCS theory. A pseudogap evolves below 150 K, where the c-axis resistivity rho(c) is semiconducting. The normal-state tunneling resistance R-N shows a linear T dependence down to T-c exhibits an abrupt decrease at T-c, and saturates at low T. This reflects scattering arising from an electronic interaction that is relevant to the high-T-c superconductivity.

 

154.    S. Suzuki, F. Maeda, Y. Watanabe, and T. Ohno

            "Work function changes of GaAs surfaces induced by Se treatment"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 38 (10), 5847-5850 (1999).

 

            ABSTRACT: Effects of a Se treatment on the work function of epitaxially grown GaAs surfaces were measured by photoemission spectroscopy. Although the Se treatments reduced the band bending of n-type GaAs, the work function increased. This result indicates that the surface component of the work function increased and that the surface dipole moment, whose direction was from the surface to the bulk (outer layer: -, inner layer: +), was formed at the Se-treated GaAs surface. On the other hand, qualitative analysis based on the electron counting model revealed that the direction of the surface dipole in the previously proposed structural model of Se/GaAs(001) was completely opposite to that obtained in our experimental results. It is suggested that this discrepancy is due to the vacancies in the internal Ga layer in the structural model.

 

155.    S. Suzuki and T. Shodai

            "Electronic structure and electrochemical properties of electrode material Li7-xMnN4"

            Solid State Ion. 116 (1-2), 1-9 (1999).

 

            ABSTRACT: The electronic structure and the charge balance mechanism of the Li7-xMnN4 system were investigated by core-level electron energy loss spectroscopy. The spectra are strongly affected by configuration interactions and reveal the existence of a considerable amount of nitrogen 2p holes in the ground state. Based on the results, we conclude that the Li7MnN4 system can be classified into the charge transfer-type compounds. The systematic variation of the operating voltages versus Li/Li+ of the Li7MnN4 system and the other transition metal nitrides and oxides can be qualitatively explained by classification into the Mott-Hubbard and the charge transfer regimes. (C) 1999 Elsevier Science B.V. All rights reserved.

 

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

            "Gutzwiller-type projected BCS ground states for attractive Hubbard model in infinite dimensions"

            Prog. Theor. Phys. 102 (5), 953-963 (1999).

 

            ABSTRACT: In order to develop our theoretical understanding of the superconducting state of strongly correlated electron systems, we investigate the many-body ground state of the attractive Hubbard model in infinite dimensions using the Gutzwiller-type projected BCS variational (GBCS) wave function. We first calculate various physical quantities by numerically evaluating analytical equations for systems in the thermodynamic limit. We then show that the GBCS wave function has the lowest energy when the gap parameter has a mixture of s wave and extended s wave pairing symmetry and that the ground state energy of the GBCS is lower than that of either the BCS or Fermi liquid at any electron density and any strength of the attractive interactions in our model. We also show that with infinite strength interactions, each pair of electrons with opposite spins forms a tightly bound pair on a lattice site (BEC-like state). We find a smooth crossover from a BCS-like state with large, overlapping Cooper pairs (for weakly attractive interactions) to a BEG-like state of composite bosons formed out of the tightly bound pairs of fermions (for strongly attractive interactions).

 

157.    A. Taguchi and H. Kageshima

            "Diffusion and stability of oxygen in GaAs and AlAs"

            Phys. Rev. B 60 (8), 5383-5391 (1999).

 

            ABSTRACT: We investigated various basic properties of oxygen in GaAs and AlAs by using first-principles calculations and considering the charge states and Fermi-level effect. For GaAs, the obtained stable atomic configurations and their stability showed good agreement with experimentally obtained results. We found that many features, such as a stable site, a negative-U nature, a charge-state-dependent diffusion path, and a rather high diffusion barrier height in the negatively charge state, are similar between GaAs and AlAs. Some features, however, were dependent on the host. We found that an asymmetry effect during the diffusion is pronounced in p-type host in both GaAs and AlAs, but the effect shows different characters depending on the host. O is more stable in AlAs than in GaAs. All of the obtained basic properties can be explained by three characteristics: the large electron negativity of oxygen, the strong O-Al bond, and the large polarization of AlAs hosts. From our theoretical study, the experimentally observed higher O concentration for AlAs layers in GaAs/AlAs systems can be clearly explained. [S0163-1829(99)06531-5].

 

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

            "Stable adsorption sites and potential-energy surface of a Ga adatom on a GaAs(111)A surface"

            Phys. Rev. B 60 (16), 11509-11513 (1999).

 

            ABSTRACT: We theoretically investigated the stable adsorption sites and potential-energy surface of Ga adatoms on a GaAs(111)A surface. Although Ga-vacancy sites on the surface were expected to be the most stable for Ga adatoms, the first-principles calculation results contradict this. Comparing the results with those obtained by the empirical interatomic potential calculations, we found that electronic contributions, such as valence electron redistribution, are crucial for stabilizing Ga adatoms on a GaAs(111)A surface. Based on the energies at several sites, a potential-energy surface was also obtained and the diffusion barrier height of a Ga adatom was estimated. The estimated height was 0.4 eV, which is much lower than that calculated for a GaAs(001) surface. This is consistent with the experimentally observed results. The present calculation results further suggest that mechanisms of Ga-vacancy-site stabilization, such as the self-surfactant effect, play an important role in epitaxial growth processes. [S0163-1829(99)07939-4].

 

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

            "First-principles investigation of Ga adatom migration on a GaAs(111)A surface"

            J. Cryst. Growth 202, 73-76 (1999).

 

            ABSTRACT: The migration of Ga adatoms on a (1 1 1)A GaAs surface was investigated by calculating the total energy at various absorption sites by using the first-principles pseudopotential method. The Ga-vacancy structure, which has been experimentally observed, was assumed as the reconstructed surface structure. Although it was expected that the Ga-vacancy sites on the surface would be the most stable for Ga adatoms, the calculations showed that it is not. Some mechanisms stabilizing the Ga-vacancy sites may play an important role in epitaxial growth processes. Based on the obtained energy potential surface, the migration barrier height was estimated to be about 0.4 eV. This height is much lower than that for GaAs(0 0 1) surfaces, consistent with the observation of a rather long diffusion length for Ga adatoms on (1 1 1)A surfaces. (C) 1999 Elsevier Science B.V. All rights reserved.

 

160.    T. Takagahara

            "Theory of exciton dephasing in semiconductor quantum dots"

            Phys. Rev. B 60 (4), 2638-2652 (1999).

 

            ABSTRACT: We formulate a theory of exciton dephasing in semiconductor quantum dots extending the Huang-Rhys theory of F centers to include the mixing among the exciton state manifold through the exciton-acoustic-phonon interaction and we identify the mechanisms of pure dephasing. We can reproduce quantitatively the magnitude as well as the temperature dependence of the exciton dephasing rate observed in GaAs quantum dotlike islands. In this system it turns out that both the diagonal and off-diagonal exciton-phonon interactions are contributing to the exciton pure dephasing on the same order of magnitude. Examining the previous data of the exciton dephasing rate in GaAs islands, CuCl and CdSe nanocrystals, we point out the correlation between the temperature dependence of the dephasing rate and the strength of the quantum confinement and we explain the gross features of the temperature dependence in various materials quantum dots. Furthermore, we discuss likely mechanisms of the exciton population decay. [S0163-1829(99)02728-9].

 

161.    T. Takagahara

            "Theory of multi-exciton states in semiconductor nanocrystals"

            Phase Transit. 68 (1), 281-363 (1999).

 

            ABSTRACT: In this article, the fundamental physics of multi-exciton states in semiconductor nanocrystals is reviewed focusing on the mesoscopic enhancement of the excitonic radiative decay rate and the excitonic optical nonlinearity and the mechanism of their saturation with increase of the nanocrystal size. In the case of the radiative decay rate the thermal excitation of excited exciton slates having small oscillator strength within the homogeneous linewidth of the exciton ground state is essential in determining the saturation behavior. 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 the first consistent understanding of the experimentally observed saturation of the mesoscopic enhancement of the excitonic optical nonlinearity. The presence of the weakly correlated exciton pair states is confirmed convincingly from the good correspondence between theory and experiments on the induced absorption spectra from the exciton state in CuCl nanocrystals. Furthermore, ultrafast relaxation processes of biexcitons are discussed in conjunction with the observed very fast rise of the biexciton gain in nanocrystals. In prospect of future progress in research, the theoretical formulation to calculate the triexciton states as one of the multi-exciton states beyond the biexciton is presented for the first time including the electron-hole exchange interaction.

 

162.    J. Takahashi, T. Hosokawa, H. Masuda, T. Kaneko, K. Kobayashi, S. Saito, and Y. Utsumi

            "Abiotic synthesis of amino acids by x-ray irradiation of simple inorganic gases"

            Appl. Phys. Lett. 74 (6), 877-879 (1999).

 

            ABSTRACT: 1-2 keV x-ray irradiation was carried out using a synchrotron radiation source on simulated primitive earth environment: a gas mixture of carbon monoxide, nitrogen, and water at atmospheric pressure. High-speed liquid chromatography of the hydrolyzed product solution detected amino acids. The amount of amino acids increased with the total energy absorbed by the gas molecules, and the antipodal optical isomers were generated in almost equal quantities. These imply that the precursors for amino acids were produced through x-ray-induced photolysis of inorganic molecules followed by recombination and polymerization into bio-organic compounds. These results suggest that prebiotic formation of amino acids is possible in primitive earth atmosphere by x ray as well as cosmic ray. (C) 1999 American Institute of Physics. [S0003-6951(99)00906-7].

 

163.    Y. Takahashi, A. Fujiwara, M. Nagase, H. Namatsu, K. Kurihara, K. Iwadate, and K. Murase

            "Silicon single-electron devices"

            Int. J. Electron. 86 (5), 605-639 (1999).

 

            ABSTRACT: Silicon single-electron transistors (SETs) were fabricated by using very flat silicon-on-insulator (SOI) substrates, high resolution electron beam (EB) lithography and etching techniques. In addition, we developed a special fabrication method called pattern-dependent oxidation with which a one-dimensional Si wire can be converted into a small Si island with a tunnelling barrier at each end. Since the Si island is around 10 nm, we could observe the conductance oscillation in the SET even at room temperature. The controllability and reproducibility of this method were confirmed through analysing the effects of size on electrical characteristics. We were also able to observe single-electron memory effects by using these novel techniques.

 

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

            "A Si memory device composed of a one-dimensional metal-oxide-semiconductor field-effect-transistor switch and a single-electron-transistor detector"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 38 (4B), 2457-2461 (1999).

 

            ABSTRACT: A novel Si memory device composed of a small one-dimensional (1D) Si-wire metal-oxide-semiconductor (MOS) field-effect transistor (FET) and a single-electron transistor (SET) is proposed, and its fundamental characteristics at 40 K are demonstrated. The small Si SET is fabricated by means of pattern-dependent oxidation (PADOX), which is almost completely compatible with Si MOSLSI processes. The 1D MOSFET provides a very steep subthreshold slope that is very close to the physical limit at room temperature in spite of the very short channel. This guarantees low voltage operation as well as small size. The memory device uses a 1D MOSFET as a switch for electrons transported to and from the memory node. The very small number of stored electrons is detected by a highly sensitive SET electrometer. The device can operate with an extremely small number of electrons, which assures ultralow-power and high-speed operation.

 

165.    H. Takayanagi, V. N. Antonov, and E. Toyoda

            "Superconducting proximity effect in mesoscopic superconductor/normal-metal junctions"

            J. Korean Phys. Soc. 34, S148-S154 (1999).

 

            ABSTRACT: The superconducting proximity effect is discussed in mesoscopic superconductor/normaI-metal junctions. The newly-developed theory shows long-range phase-coherent effect which explaines early experimental results of giant magnetoresistance oscillations in an Andreev interferometer. The theory also shows that the proximity correction to the conductance (PCC) has a reentrant behavior as a function of energy. The reentrant behavior is systematically studied in a gated superconductor-semiconductor junction. A negative PCC is observed in the case of a weak coupling between the normal metal and the external reservoir. Phase coherent ac effect is also observed when rf is irradiated to the junction.

 

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

            "A superconductor/semiconductor/superconductor junction with a long-split gate"

            Superlattices Microstruct. 25 (5-6), 993-1004 (1999).

 

            ABSTRACT: Measurements of superconducting and normal transport in a superconductor/semiconductor/superconductor junction with a long-split gate show that when the two-dimensional electron gas in the semiconductor is put into the pinched-off state by applying a gate voltage, the two superconducting electrodes couple through a long and narrow channel with a small number of modes. Multiple Andreev reflections the focusing of Andreev-reflected holes are observed in this situation, but the supercurrent decreases quickly as gate voltage is increased and it disappears when the channel is long and narrow. A sharp conductance peak due to the coherent motion of the electrons and holes in the narrow channel is also observed. (C) 1999 Academic Press.

 

167.    H. Takenaka, H. Ito, and T. Kawamura

            "Characteristics and thermal behaviour of Mo/Si multilayer soft x-ray mirrors with interleaved barrier-layers"

            in X-Ray Lasers 1998, Institute Of Physics Conference Series Vol. 159 (Iop Publishing Ltd, Bristol, 1999), pp. 605-608.

 

            ABSTRACT: Introducing interleaved Low-Z material (C, SiC, SiN) barrier-layers with high-melting point improves the heat resistance of Mo/Si multilayers. The soft x-ray reflectivities of the multilayers were calculated, and the effects of heating on both the reflectivities and layer structures of Mo/Si multilayers with and without barrier-layers were investigated using x-ray diffraction. The results show that, for applications using intense soft x-ray beams, Mo/Si multilayers with interleaved those barrier-layers are better mirrors than Mo/Si multilayers because they have much better heat resistance and almost the same soft x-ray reflectivity of the Mo/Si multilayers.

 

168.    H. Tamura, Y. Takahashi, and K. Murase

            "Theory of activated conduction in a Si single-electron transistor"

            Microelectron. Eng. 47 (1-4), 205-207 (1999).

 

            ABSTRACT: Transport in a silicon single-electron transistor is theoretically studied. By solving a master equation, assuming that the potential barrier has a parabolic potential, we show that the linear conductance has an activated behavior at high temperatures. This result is in quantitative agreement with a recent experimental observation.

 

169.    K. Tanahashi, K. Kawamura, N. Inoue, and Y. Homma

            "Asymmetric behavior of monolayer holes after growth in GaAs molecular beam epitaxy revealed by in situ scanning electron microscopy"

            J. Cryst. Growth 202, 141-145 (1999).

 

            ABSTRACT: The behavior of monolayer holes on the GaAs (0 0 1) surface during post-growth annealing in molecular beam epitaxy (MBE) is examined in detail by in situ scanning electron microscopy (SEM). Submicron scale monolayer-deep holes are formed after small islands and holes are eliminated. Their growth and shrinkage are found to proceed asymmetrically: for example, they grow only into the right-hand side, and shrink only from the top. The mechanism is discussed in terms of environmental step structure. Ga adatoms migrate tenths of micron in several minutes. It was found that in the regrowth after annealing, three-dimensional islands are formed preferentially on the step edges. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

 

170.    S. Tarucha, T. Fujisawa, K. Ono, D. G. Austing, T. H. Oosterkamp, W. G. van der Wief, and L. P. Kouwenhoven

            "Elastic and inelastic single electron tunneling in coupled two dot system"

            Microelectron. Eng. 47 (1-4), 101-105 (1999).

 

            ABSTRACT: Elastic and inelastic tunneling between zero-dimensional states are studied for a laterally coupled two dot device and for a vertically coupled two dot device. The resonance current observed in both devices consists of a symmetric peak of elastic tunneling and an asymmetric broad peak of inelastic tunneling The elastic peak width compares to the energy of tunnel coupling. The inelastic current is related to acoustic phon on emission from detailed study on the temperature dependence.

 

171.    T. Tateno and Y. Jimbo

            "Activity-dependent enhancement in the reliability of correlated spike timings in cultured cortical neurons"

            Biol. Cybern. 80 (1), 45-55 (1999).

 

            ABSTRACT: To study the use-dependent modification of activity in neural networks, we investigated the spike timing by simultaneously recording activity at multiple sites in a network of cultured cortical neurons. We used dynamical analysis to study the temporal structure of spike trains and the activity-dependent changes in the reliability and reproducibility of spike patterns evoked by a stimulus. We also used cross-correlation analysis to evaluate the interactions of neuron pairs. Our main conclusions are that even when no obvious change in spike numbers can be seen, use-dependent modification occurs, either enhancing or reducing in the reliability and reproducibility of spike trains evoked by a stimulus, and the fine temporal structure of stimulus-evoked spike trains and interactions between neurons are also modified by tetanic stimulation.

 

172.    Y. Tokura, D. G. Austing, and S. Tarucha

            "Single-electron tunnelling in two vertically coupled quantum dots"

            J. Phys.-Condes. Matter 11 (31), 6023-6034 (1999).

 

            ABSTRACT: Electron states in two vertically coupled quantum dots are analysed using an exact-diagonalization method. In the two-electron system, the ground state at zero field is a spin-singlet stare, and this stare is eventually replaced by spin-tripler states by applying a vertical magnetic field. One of the triplet states is stable under the conditions of very weak Coupling and larger asymmetry between the two dots. In the transition from the three- to the four-electron state, we find a parameter region where the tunnelling current is strongly suppressed because of the orthogonality of the quantum states. An isospin selection rule is effective under strong-coupling conditions.

 

173.    K. Torimitsu, Y. Furukawa, N. Kasai, Y. Jimbo, and T. Tsumoto

            "Effect of neurotrophins on intracellular ca concentration and electrical activity in cultured rat cortex"

            Mol. Biol. Cell 10, 229A-229A (1999).

 

            ABSTRACT:

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

            "Transient response of synaptic glutamate release and intracelluar Ca concentration induced by neurotrophins in cultured rat cortex"

            J. Neurochem. 73, S93-S93 (1999).

 

            ABSTRACT:

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

            "Systematic gate-controlled reentrant conductance of a superconductor-semiconductor two-dimensional electron gas junction"

            Phys. Rev. B 59 (18), R11653-R11656 (1999).

 

            ABSTRACT: We have investigated the temperature and voltage dependencies of the conductance in a superconductor-semiconductor two-dimensional electron gas (2DEG) junction with a gate. We observed the systematically controlled reentrant behavior of the conductance by using the gate to change diffusion constant of the 2DEG. We confirmed that the correlation energy of the proximity correction to the conductance is proportional to the diffusion constant of the normal part. We also examined the effect of the magnetic field on the reentrance and found that even a small magnetic field changed it drastically. [S0163-1829(99)50918-1].

 

176.    S. Toyoda and M. Fujiki

            "Experimental evidence for helical conformation of poly(methylphenylsilylene) in solution"

            Chem. Lett. (7), 699-700 (1999).

 

            ABSTRACT: This paper describes a simple methodology designed to prove that poly(methylphenylsilylene) (1) in solution has a helical conformation by a comparing the optical properties of optically inactive 1 with those of its optically active copolymer derivative. This approach can clarify the main-chain conformation from spectroscopic evidence.

 

177.    K. Tsubaki

            "Quantized magnetotransport through magnetic barriers"

            in Compound Semiconductors 1998, Institute Of Physics Conference Series Vol. 162 (Iop Publishing Ltd, Bristol, 1999), pp. 373-378.

 

            ABSTRACT: A magnetic barrier system allows new aspects of electron transport. In this paper, the fabrication of a magnetic barrier in a 2-dimensional electron gas with two current contacts and four potential probes, and the observation of quantized magnetoresistance due to the magnetic barrier are described. A resistance plateau of h/6e(2) is observed near a magnetic field of 4.7 T and the gate voltage of 0.0 V. A quantized resistance is explained by the Landauer-Buttiker formula.

 

178.    M. Uematsu

            "Simulation of high-concentration phosphorus diffusion in silicon taking into account phosphorus clustering and pile-up"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 38 (11), 6188-6192 (1999).

 

            ABSTRACT: We have simulated the transient enhanced diffusion (TED) of high-concentration phosphorus (P) in silicon during postimplantation annealing. Based on the models for P diffusion, for TED by self-interstitial clusters, and for end-of-range (EOR) dislocations as both a sink for and source of self-interstitials, a unified simulation is done: taking into account P clustering and P pile-up. P clustering is taken into account only beneath EOR dislocations, and P pile-up is estimated by a diffusion-segregation term in the diffusion equations. We have satisfactorily fitted P depth profiles at high doses (similar to 10(15) cm(-2)) in a wide range of annealing conditions (700-1000 degrees C).

 

179.    M. Uematsu

            "Influence of Ostwald ripening of end-of-range defects on transient enhanced diffusion in silicon"

            Jpn. J. Appl. Phys. Part 2 - Lett. 38 (11A), L1213-L1215 (1999).

 

            ABSTRACT: We have simulated transient enhanced diffusion (TED) in the presence of end-of-range (EOR) defects produced by amorphizing implantation. We have taken; into account Ostwald ripening of EOR defects, which reduces the efficiency of the dCfects as a source of self-interstitials. We derived a formula to describe this reduction of efficiency with time and used this formula for the simulation. The simulation satisfactorily predicts the TED at annealing conditions, where the influence of Ostwald ripening is significant.

 

180.    M. Uematsu

            "Clustering and transient enhanced diffusion of B doping superlattices in silicon"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 38 (8), 4718-4719 (1999).

 

            ABSTRACT: We have simulated the clustering and transient enhanced diffusion (TED) of boron profiles with superlattice structures. Using an analytical formula for B clustering in terms of the reaction between B atoms and supersaturated self-interstitials, we have satisfactorily fitted B TED profiles not only in the implant;implantation-damaged regions but also deep in the bulk. In the simulation, we: have also assumed TED reduction by C diffusion and self-interstitial trapping.

 

181.    M. Uematsu

            "Simulation of high-concentration boron diffusion in silicon during post-implantation annealing"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 38 (6A), 3433-3439 (1999).

 

            ABSTRACT: We have simulated the transient enhanced diffusion (TED) and electrical activation of high-concentration boron (B) in silicon during post-implantation annealing. Based on the models for B diffusion, for TED by self-interstitial clusters, and for B clustering, a unified simulation is done, taking into account implantation-induced dislocations as a sink for self-interstitials and the solid solubility limit of B. To establish the initial profiles for higher doses, we used the maximum area density of self-interstitials and B concentration effective for the TED and B clustering. We have satisfactorily fitted B depth profiles at different doses (5 x 10(14)-5 x 10(15) cm(-2)) in a wide range of experimental conditions (800-1000 degrees C and 10 s-8 h).

 

182.    W. G. van der Wiel, T. Fujisawa, T. H. Oosterkamp, and L. P. Kouwenhoven

            "Microwave spectroscopy of a double quantum dot in the low- and high-power regime"

            Physica B 272 (1-4), 31-35 (1999).

 

            ABSTRACT: Microwave experiments on an artificial two-level system formed by a double quantum dot, are discussed for different coupling and microwave power regimes. When the inter-dot coupling, T, is weak, an ionic-like bonding is observed. The current through the double dot is power dependent. In the strong coupling regime, a covalent-like bonding is formed and the energy separation between the symmetric and anti-symmetric eigenstates, Delta E*, becomes power dependent as well. It is given by Delta E* = root{Delta E}(2) + {2J(0) (eV(AC)/hf)T}(2), where Delta E is the uncoupled energy splitting, J(0) the zeroth-order Bessel function of the first kind, V-AC the microwave amplitude, and f the frequency. We show that in the case of strong coupling and low microwave power (eV(AC) much less than hf, J(0) approximate to 1), the observed energy separation is well described by Delta E* = J{Delta E}(2) + {2T}(2). For larger microwave powers (eV(AC) greater than or similar to hf) it is shown that the energy separation is modified according to the Bessel function term. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

 

183.    Y. Watanabe

            "Detection of a transition layer near the external surface of thermally-grown silicon oxides"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 38 (1A), 31-35 (1999).

 

            ABSTRACT: This study was undertaken to detect the oxide transition,layer near the external surface of a silicon oxide layer thermally grown at 800-1000 degrees C in dry O-2. A difference between the O content of the oxide near the external surface and of the bulk oxide is found using an improved depth profiling method, namely, Auger electron spectroscopy in conjunction with ion sputtering. We also found a difference in chemical etching rate between the oxide near the surface and that of the bulk oxide. From our result, we confirm that a 1-2-nm-thick transition layer that is high in O content and has a high chemical etching rate, exists at the surface of the oxide layer. The surface transition layer is inferred to be composed of an incomplete SiO2 network containing an appreciable number of end groups or peroxides.

 

184.    Y. Watanabe, S. Heun, T. Schmidt, and K. C. Prince

            "Preliminary spectromicroscopic measurements of self-organized InAs nanocrystals by SPELEEM"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 38, 556-559 (1999).

 

            ABSTRACT: Preliminary spectromicroscopic measurements of self-organized InAs nanocrystals by soft x-ray photoemission electron microscopy (XPEEM) are presented. The InAs nanocrystals were fabricated on Se-terminated GaAs(100) surfaces by molecular beam epitaxy (MBE) in a dedicated chamber in Tsukuba, Japan. The measurements were performed with the Spectroscopic Photo Emission and Low Energy Electron Microscope (SPELEEM) of the Technical University of Clausthal at beamline 6.2LL at the synchrotron radiation light source ELETTRA in Trieste, Italy. The samples were protected during transfer in air to ELETTRA by an As capping layer deposited in-situ in the MBE chamber. The capping layer was desorbed in the SPELEEM sample preparation chamber. We performed tests on As-capping and decapping of InAs nanocrystals by synchrotron radiation photoelectron spectroscopy at the Photon Factory, Tsukuba, Japan. We found that the electronic properties of the sample were not changed by capping and decapping. Low energy electron microscopy and XPEEM measurements proved the feasibility of spectromicroscopic experiments on InAs nanocrystals.

 

185.    G. Wendin, V. S. Shumeiko, P. Samuelsson, and H. Takayanagi

            "Model study of ballistic S-2DEG-S Josephson field effect transistors"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 38 (1B), 354-356 (1999).

 

            ABSTRACT: We analyze the variation of the critical Josephson current with gate voltage in a ballistic SNS heterostructure. With increasing gate voltage the number of bound Andrev levels increases, the junction becomes effectively long, and the critical current is suppressed.

 

186.    E. Yamaguchi, K. Shiraishi, and H. Kageshima

            "Level-resonance transition of deep states produced by nitrogen vacancies in nitride semiconductors"

            Phys. Status Solidi B-Basic Res. 211 (1), 157-161 (1999).

 

            ABSTRACT: The electronic structure, total energy and atomic geometry of N vacancies in GaN are calculated using the first-principles ultra-soft pseudopotential method, in order to confirm the recently proposed model that N vacancies may give rise to anomalous optical properties in InxGa1-xN. Our calculations reveal that localized p-like resonances are formed at 0.26 eV above the conduction-band edge due to N vacancies in GaN. Therefore, N vacancies are again proposed as a promising candidate for the strong localization of excitons in InxGa1-xN.

 

187.    F. Yamaguchi and Y. Yamamoto

            "Crystal lattice quantum computer"

            Microelectron. Eng. 47 (1-4), 273-275 (1999).

 

            ABSTRACT: A quantum computer can be constructed from nuclear spins in a crystal lattice of a rare-earth monophosphide such as cerium-monophosphide (CeP). The 1/2 spin of a P-31 nucleus can be used to represent a quantum bit ('qubit') with a relatively long relaxation time. In a CeP crystal lattice, P-31 nuclei are periodically situated in three dimensions at distances of about 12 Angstrom. The application of a static magnetic field gradient in one direction causes differences in the Zeeman frequencies of separate nuclei. This allows thousands of distinct qubits to be individually addressed. Initializations of the qubits can be done efficiently by the Pound-Overhauser double resonance effect on the nuclear spins and the antiferromagnetically ordered 4f electron spins of cerium ions. Logic operations can be performed by simple pulse sequences, and computational results after logic operations can be measured by the nuclear magnetic resonance of neighboring nuclei, or the electron resonance of neighboring 4f electrons of cerium ions.

 

188.    F. Yamaguchi and Y. Yamamoto

            "Crystal lattice quantum computer"

            Appl. Phys. A-Mater. Sci. Process. 68 (1), 1-8 (1999).

 

            ABSTRACT: A quantum computer can be constructed from nuclear spins in a crystal lattice of a rare-earth monophosphide such as cerium-monophosphide (CeP), The 1/2 spin of a P-31 nucleus can be used to represent a quantum bit ('qubit') with a relatively long relaxation time. In a CeP crystal lattice, P-31 nuclei are periodically situated in three dimensions at distances of about 6 Angstrom. The application of a static magnetic field gradient in one direction causes differences in the Zeeman frequencies of separate nuclei. This allows thousands of distinct qubits to be individually addressed. Initializations of the qubits can be done efficiently by the Pound-Overhauser double resonance effect on the nuclear spins and the antiferromagnetically ordered 4f electron spins of cerium ions. Logic operations can be performed by simple pulse sequences, and computational results after logic operations can be measured by the nuclear magnetic resonance of neighboring nuclei, or the electron resonance of neighboring 4f electrons of cerium ions.

 

189.    H. Yamaguchi and Y. Hirayama

            "Vertical transport properties through pseudo-metallic InAs thin films grown on GaAs (111)A substrates"

            J. Cryst. Growth 202, 778-781 (1999).

 

            ABSTRACT: The electron transport properties in the growth direction of novel (Al)GaAs/InAs/GaAs structures are examined. Both the InAs/n-GaAs and n-GaAs/InAs heterojunctions formed on (1 1 1)A surfaces showed rectifying characteristics as similar to those of Schottky junctions, demonstrating the possibility of using heterojunctions as a substitution for conventional metal-semiconductor junctions. We have fabricated pseudo-metallic InAs-base transistors in which InAs film is used instead of the metal layer that is used in metal-base transistors. The operation of thermionic-injection hot-electron transistors at room temperature is confirmed. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

 

190.    H. Yamaguchi and Y. Homma

            "SEM imaging of fundamental growth processes during MBE of GaAs on (111)A substrates"

            J. Cryst. Growth 202, 124-127 (1999).

 

            ABSTRACT: Microscopic growth processes are quantitatively analyzed based on in situ scanning electron microscopy observations made during molecular beam epitaxy of Cads on (1 1 1)A substrates. The time development of monomolecular-high steps is clearly visible, and the step velocity as well as the nucleation density of 2D islands is measured directly from the images obtained under various growth conditions. Analysis using the classical BCF theory was made to investigate the growth processes in detail. (C) 1999 Elsevier Science B.V. All rights reserved.

 

191.    H. Yamaguchi, Y. Homma, K. Kanisawa, and Y. Hirayama

            "Drastic improvement in surface flatness properties by using GaAs (111)A substrates in molecular beam epitaxy"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 38 (2A), 635-644 (1999).

 

            ABSTRACT: We have studied the surface flatness properties of (111)A planes in both homoepitaxial growth of GaAs on GaAs and highly-mismatched heteroepitaxial growth of InAs and InSb on GaAs by molecular beam epitaxy. The homo-epitaxially grown GaAs (111)A surface has atomically Bat terraces as wide as about 1 mu m, which make it possible to clearly image the layer-by-layer growth processes of GaAs by in-situ scanning electron microscopy, in contrast with conventionally used (001) surfaces where the high density of steps prevents clear imaging. The surface flatness improvement using (111)A substrates is much more drastic in highly-mismatched heteroepitaxy. The three-dimensional islanding governed by the Stranski-Krastanov mechanism is strongly suppressed for the growth of both InAs and InSb on GaAs substrates. The lateral and vertical electron transport properties of Ga(AI)As/lnAs/GaAs heterostructures are studied, verifying the improved electric properties by using the (111)A substrates. The application for novel hot-electron transistors is clearly demonstrated.

 

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

            "Perturbed ion sites in Eu3+: YAlO3 studied by optical-rf double-resonance spectroscopy"

            Phys. Rev. B 59 (14), 9126-9131 (1999).

 

            ABSTRACT:

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

            "A new approach to reducing line-edge roughness by using a cross-linked positive-tone resist"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 38 (12B), 7114-7118 (1999).

 

            ABSTRACT: We propose a cross-linking technique as a new approach to reducing the line-edge roughness (LER) of resist patterns. In addition, we also develop a cross-linked positive-tone resist called the suppressed aggregate extraction development (SAGEX) resist, based on this technique. Our key approach to reducing the LER is the suppression of the aggregate extraction development, which causes LER We demonstrate successful suppression of the aggregate extraction development by cross-linking polymers in the surrounding regions and by reducing the difference between dissolution rates inside and outside the aggregates, and clarify that the LER of the resist patterns in the SAGEX resist is reduced.

 

194.    M. Yamashita, M. Koashi, and N. Imoto

            "Quantum kinetic theory for evaporative cooling of trapped atoms: Growth of Bose-Einstein condensate"

            Phys. Rev. A 59 (3), 2243-2249 (1999).

 

            ABSTRACT: Evaporative cooling of trapped atoms is studied based on the quantum kinetic theory. We extend the classical analysis of Luiten ct al. [Phys. Rev. A 53, 381 (1996)] to treat Bose statistics of alkali-metal atoms. Dynamics in evaporative cooling process is described by a kinetic equation for the truncated Bose-Einstein distribution function under the assumption that the system is close to the thermal equilibrium. This approach is applicable to the "slow" evaporative cooling normally adopted in most experiments for the efficient production of Bose-Einstein condensates. Time-evolution calculations explain the current experiment well with sodium atoms using a slow evaporative cooling and demonstrate a rapid growth of condensate in the cooling process. [S1050-2947(99)06003-5].

 

195.    R. Yano and N. Uesugi

            "Demonstration of partial erasing of picosecond temporal optical data by use of accumulated photon echoes"

            Opt. Lett. 24 (23), 1753-1755 (1999).

 

            ABSTRACT: We demonstrated partial erasing of temporal optical data on a picosecond time scale by use of accumulated photon echoes. In a photon-echo memory the temporal data at time tau are stored as a frequency grating of period 1/tau in the absorption spectrum of a material. Partial erasing of the temporal data is achieved by irradiation of the material with a pulse pair at time separation tau, but the phase of one of the pulses is shifted 180 degrees. This process does not produce a frequency grating, and no echo is emitted. The experiment was performed with a dye-doped polymer film. The 180 degrees phase shift was obtained by use of a half-wave plate. (C) 1999 Optical Society of America.

 

196.    R. Yano, N. Uesugi, T. Fukuda, and Y. Takahashi

            "Observation of persistent multiple-holes for F-4(3/2)(1)-I-4(9/2) transition of Nd3+ ion doped silicate glass fiber using diode laser"

            Phys. Lett. A 262 (4-5), 376-382 (1999).

 

            ABSTRACT: A multiple-hole structure with a center hole of more than 20% depth was observed in the persistent hale-burning spectroscopy for the F-4(3/2)(1)-I-4(9/2) transition of the Nd3+ doped silicate glass fiber at 1.5 K using a diode laser. The multiple-hole structure was attributed to the hyperfine interaction between the effective electron spin and the nuclear spin of the Nd3+ ion. The hole grow and decay processes were observed to be logarithmic time-dependent. Finally the demonstration of optical memory was presented. (C) 1999 Elsevier Science B.V. All rights reserved.

 

197.    P. D. Ye and S. Tarucha

            "Internal magnetic focusing in an array of ballistic cavities"

            Phys. Rev. B 59 (15), 9794-9797 (1999).

 

            ABSTRACT: We study the ballistic motion of electrons in an array of submicron circular cavities, fabricated by electron beam lithography and dry etching techniques. Pronounced magnetoresistance oscillations are observed that can be understood in terms of internal magnetic focusing or commensurability between the electron trajectories and the geometry of the cavities. The depletion distance in the two-dimensional electron gas caused by the dry etching process can be deduced by analysis of the resonance peak positions within a simple magnetic focusing picture. [S0163-1829(99)01216-3].

 

198.    P. D. Ye and S. Tarucha

            "Internal magnetic focusing in an array of open quantum dots"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 38 (1B), 319-321 (1999).

 

            ABSTRACT: The ballistic motion of electrons is studied in an array of open quantum dots. The submicron dots are fabricated by electron beam lithography and dry etching techniques. Pronounced oscillations are observed in the magnetoresistance which can be understood in terms of the commensurability effect between the ballistic trajectories and the geometry of the circular cavity or the internal magnetic focusing. By breaking the symmetry of the entrance/exit openings, or by inducing a large antidot at the center of the cavity, the commensurability effect disappears.

 

199.    A. Yokoo, M. Nakao, H. Yoshikawa, H. Masuda, and T. Tamamura

            "63-nm-pitch pit pattern fabricated on polycarbonate surface by direct nanoprinting"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 38 (12B), 7268-7271 (1999).

 

            ABSTRACT: Nanoscale pit patterns were fond on a polycarbonate substrate surface, which is commonly used for compact disks, by direct nanoprinting. Pit patterns with 100, 70, and 63nm pitches were imprinted on the disk surface using a SiC mold with a nanostructure projection pattern. These pitches correspond to the the storage densities of 75, 150, and 185 Gbit/in(2). We evaluated the mold-holding temperature and press-pressure dependence of the pit depth. We also evaluated the press-time dependence. With a relatively low press-pressure of 1.3 kg/mm(2) at room temperature, a 100-nm-Ditch pit pattern with a pit depth of over 40 nm was fabricated using a mold with a projection height of 60 nm.

 

200.    H. Yokoyama, N. Kasai, T. Matsue, I. Uchida, H. Ohya-Nishiguchi, and H. Kamada

            "In vivo simultaneous monitoring by Pt-disk microelectrodes of intracerebral hydrogen peroxide and dopamine in rats"

            Chem. Lett. (6), 497-498 (1999).

 

            ABSTRACT: A technique was developed for simultaneous monitoring of temporal changes in hydrogen peroxide (H2O2) and dopamine (DA) levels by using Pt-disk microelectrodes (phi 30 mu m). H2O2 and DA were determined by differential double-pulse amperometry (for H2O2; 1st step, 750 mV, 1000 ms; 2nd step, 1100 mV, 1000 ms: far DA; 1st step, 150 mV, 600 ms; 2nd step, 250 mV, 50 ms). The electrode for H2O2 or DA is capable of determining each target substance and these substances do not interfere with each other. For an in vivo application, the electrodes were implanted into the striatum of rats and used successfully to monitor intrastriatal changes in H2O2 and DA simultaneously after intraperitoneal injection of methamphetamine while the animals were moving freely.

 

201.    A. Yoshikawa, T. Kojima, and Y. Saito

            "Relations between skill and the use of terms - An analysis of protocols of the game of Go"

            in Computers And Games, Lecture Notes In Computer Science Vol. 1558 (Springer-Verlag Berlin, Berlin, 1999), pp. 282-299.

 

            ABSTRACT: The use of Go terms while playing Go differs according to the player's skill. We conduct three experiments to examine this in detail. In the first experiment, players' spontaneous utterances (called protocols) were collected. We analyze these protocols in two ways. One is the number of Go terms used, and the other is the contents of the terms, such as strategic or tactical. The second experiment examines how well the players knew the configurations of the stones. From the two experiments, we find that even if the subjects know of many Go terms, their use depends on the subject's skill. The third experiment considers "Soudan-Go," where two players form a team. They are in the same room and can freely talk to each other; their spontaneous utterances (protocols) were collected. We also analyze reports of "Houchi Soudan-Go," which is a Soudan-Go match between professional players. We find that expert players often use Go terms and they understood their partner's intentions without needing a full explanation. Intermediate level players often talked over their plan and their opponent's plan using many Go terms. From our analyses we developed a hypothesis which we call the iceberg model. The purpose of the model is to explain the structure of a term in the human brain from the viewpoint of the role of the term. Although this is still a hypothesis, it will become an important guide when carrying out protocol analyses and modeling the thought processes of Go players.

 

202.    J. S. Zhou, J. B. Goodenough, H. Sato, and M. Naito

            "Optimal superconductivity in La2-xSrxCuO4"

            Phys. Rev. B 59 (5), 3827-3830 (1999).

 

            ABSTRACT: The temperature dependence of the resistivity rho(T) and the thermoelectric power alpha(T) have been measured under hydrostatic pressure on a single-crystal film of La1.85Sr0.15CoO4 deposited on a LaSrAlO4 substrate. The compressive biaxial stress built into the film raises T-c at ambient pressure. T-c increased with pressure P <3.3 kbar, but saturated at a pressure-independent T-c=43.7 at pressures P>3.3 kbar. A low-temperature enhancement of alpha(T) having a T(max)approximate to 140 K increased with T-c. The data are discussed within the framework of a vibronic model of the superconductive phase. [S0163-1829(99)07005-8].