1.    K. Ajito, C. X. Han, and K. Torimitsu

            "Detection of glutamate in optically trapped single nerve terminals by Raman spectroscopy"

            Analytical Chemistry 76 (9)2506-2510 (2004).

 

            ABSTRACT: Glutamate is the major excitatory neurotransmitter and is of particular interest in light of current models of memory and learning. The paper describes the first in situ detection of glutamate in single nerve terminals (synaptosomes), which is achieved by using laser trapping Raman spectroscopy. The near-infrared laser light captures a single synaptosome obtained from a Wister rat brain. The release of glutamate in a single laser-trapped synaptosome was detected by subtracting the Raman spectrum before depolarization from that after depolarization with the addition of the K+-channel blocker, 4-aminopyridine. The result indicated that the single synaptosome released similar to3 amol of glutamate and that the release rate depended on the 4-aminopyridine concentration.

 

2.    T. Akasaka, H. Gotoh, T. Saito, and T. Makimoto

            "High luminescent efficiency of InGaN multiple quantum wells grown on InGaN underlying layers"

            Applied Physics Letters 85 (15)3089-3091 (2004).

 

            ABSTRACT: InGaN multiple quantum wells were grown on InGaN underlying layers 50 nm thick by metalorganic vapor phase epitaxy. Photoluminescence (PL) measurements were performed by selective excitation of the quantum wells under a weak excitation condition. The PL intensity was almost constant at temperatures ranging from 17 to 150 K. Assuming that the internal quantum efficiency (eta(int)) equals unity at 17 K, we obtained eta(int) as high as 0.71 even at room temperature. The reason for the high eta(int) is the reduction of nonradiative recombination centers by the incorporation of indium atoms into the underlying layer. (C) 2004 American Institute of Physics.

 

3.    T. Akasaka, T. Nishida, T. Makimoto, and N. Kobayashi

            "An InGaN-based horizontal-cavity surface-emitting laser diode"

            Applied Physics Letters 84 (20)4104-4106 (2004).

 

            ABSTRACT: An InGaN-based horizontal-cavity surface-emitting laser diode (HCSELD) was fabricated by dry-etching of an InGaN-based multilayer on a SiC substrate and selective-area regrowth of a Mg-doped GaN layer. The InGaN-based HCSELD is a Fabry-Perot laser diode equipped with outer micromirrors that reflect the laser beams upward. The cavity mirrors and outer micromirrors are vertical {11 (2) over bar0} and inclined {11 (2) over bar2} facets of the regrown Mg-doped GaN layers, respectively. These grown facets are very smooth and had little angle misalignment. The InGaN-based HCSELD lased by current injection at room temperature. Current-injection lasing for group-III-nitride-based surface-emitting lasers is reported. (C) 2004 American Institute of Physics.

 

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

            "Nonequilibrium transport of InAs/GaAs(111)A heterostructures coupled with superconducting Nb electrodes"

            Semiconductor Science And Technology 19 (4)S182-S184 (2004).

 

            ABSTRACT: We have investigated the nonequilibrium transport of a two-dimensional electron gas (2DEG) in an InAs/GaAs(111)A heterostructure coupled with superconducting Nb electrodes. In the superconductor (S)/normal conductor (N) hybrid system, the transport properties of the N are affected by the superconducting proximity effect. According to the updated theory, this proximity correction to the conductance (PCC) shows the reentrant behaviour to be a function of energy. We observed reentrant behaviour in the voltage and temperature dependences of the conductance of the 2DEG. The conductance peak is observed at T-cmax similar to 6 K and the PCC reaches similar to20% of the normal-state conductance and almost disappears at low energies. These values are one order of magnitude higher than those obtained in the previous works. These results are most likely achieved by diminishing the length of the N channel L because the PCC as well as the correlation energy (Thouless energy) is proportional to 1/L-2. The measured conductance showed a very good agreement with that of the theory.

 

5.    K. Akiba, N. Yamamoto, V. Grillo, A. Genseki, and Y. Watanabe

            "Anomalous temperature and excitation power dependence of cathodoluminescence from InAs quantum dots"

            Physical Review B 70 (16), 165322 (2004).

 

            ABSTRACT: Self-assembled InAs quantum dots (QDs) in GaAs layers were studied with a cathodoluminescense (CL) detection system combined with a transmission electron microscope. Three distinct peaks were observed to appear in the CL spectrum collected from a 1mum(2) region. The excitation power dependence of the CL spectra and monochromatic CL image observations identified those peaks that are the emissions associated with the ground state and excited state of the QDs in different size groups. Anomalous temperature dependence of those QD emission peaks was observed in the temperature range from 20 to around 100 K, where the emission intensities increase with temperature. Steady-state rate equations for the recombination processes of holes and excitons are proposed with introduction of a potential barrier at the interface between the GaAs layer and the wetting layer (WL). This model can explain the temperature dependence of the emission intensities from the QDs and WL in a wide temperature range.

 

6.    T. Akiyama, H. Kageshima, and T. Ito

            "First-principles analyses of O-2 molecules around ultrathin SiO2/Si(100) interface"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 43 (11B)7903-7908 (2004).

 

            ABSTRACT: The microscopic structures and reaction mechanisms of O-2 molecules at ultrathin SiO2/Si(100) interface are investigated based on first-principles total-energy calculations. It is found that the molecular-type oxygen is stable in the SiO2 region of the interface, while the O-2 in the Si substrate dissociates and two Si-O-Si bonds are formed. It is also found that the O-2 in the SiO2 region can directly react with the Si substrate. The energy barrier for its reaction (0.2 eV) does not correspond to (previously consented) severing process of interfacial Si-Si bonds, but to the formation of weak Si-O bonds between the 0 atoms of oxidant and the interfacial Si atoms: The hybridization of the oxygen-2p orbitals of the oxidant and the valence band states of the Si substrate is the principal factor of the reaction. The calculated results imply that other microscopic mechanisms such as accumulation of interfacial strain or its release mechanisms are involved in the interfacial reaction during Si oxidation.

 

7.    A. Aleksov, M. Kubovic, M. Kasu, P. Schmid, D. Grobe, S. Ertl, M. Schreck, B. Stritzker, and E. Kohn

            "Diamond-based electronics for RF applications"

            Diamond And Related Materials 13 (2)233-240 (2004).

 

            ABSTRACT: Advanced RF electronic systems contain active elements as well as passive components like wave guides, filters and switches, most of them realized in MEMS technologies. In this contribution the status of active devices on single crystal diamond, namely p-channel FETs is reviewed, also in comparison to other wide bandgap semiconductors. Next, the status in RF MEMS is discussed. Passive RF circuits on diamond need large surface areas and therefore they are only possible on large area substrates with polycrystalline diamond films. Basic elements have been already demonstrated. To develop integrated RF electronics, a common large single crystal substrate is needed. The status of the development of such substrates is described and finally an integration example is discussed. (C) 2003 Elsevier B.V. All rights reserved.

 

8.    Y. Asari, K. Takeda, and H. Tamura

            "Hund's first and second rules in spherical quantum dots (I) in the zero-magnetic field"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 43 (7A)4424-4433 (2004).

 

            ABSTRACT: We theoretically studied the validity of Hund's first and second rules in the three-dimensionally spherically parabolic quantum dot (3D-SPQD). We extended the unrestricted Hartree-Fock (exUHF) approach in order to determine the ground state while conserving the expectation values of the total orbital angular momentum (L-2) and its z component (L-z) uring the scf procedure. We applied this exUHF method to a GaAs 3D-SPQD and obtained the ground-state energy spectra. Our calculation reveals that, among those states having the largest spin multiplicities, the state giving the largest value of (L-2) is energetically more stable than the others having a smaller value of (L-2); that is the spin filling in the 3D-SPQD obeys Hund's first and second rules.

 

9.    D. G. Austing, S. Tarucha, H. Tamura, K. Muraki, F. Ancilotto, M. Barranco, A. Emperador, R. Mayol, and M. Pi

            "Integer filling factor phases and isospin in vertical diatomic artificial molecules"

            Physical Review B 70 (4), 045324 (2004).

 

            ABSTRACT: Integer filling factor phases of many-electron vertically coupled diatomic artificial quantum dot molecules are investigated for different values of the interdot coupling. The experimental results are analyzed within local-spin density functional theory for which we have determined a simple lateral confining potential law that can be scaled for the different coupling regimes, and Hartree-Fock theory. Maximum density droplets composed of electrons in both bonding and antibonding or just bonding states are revealed, and interesting isospin-flip physics appears for weak interdot coupling when the systematic depopulation of antibonding states leads to changes in isospin.

 

10.    D. G. Austing, S. Tarucha, K. Muraki, F. Ancilotto, M. Barranco, A. Emperador, R. Mayol, and M. Pi

            "Integer filling factor phases in vertical diatomic artificial molecules"

            Physica E-low-dimensional Systems & Nanostructures 22 (1-3)502-505 (2004).

 

            ABSTRACT: We investigate integer filling factor phases of many-N-electron vertically coupled semiconductor quantum dot artificial molecules when the inter-dot coupling is strong and weak. The experimental results are analyzed within local-spin density-functional theory. Maximum density droplets composed of electrons in both bonding and anti-bonding, or just bonding states are revealed. Interesting isospin physics (i.e., isospin transitions) can occur particularly when the inter-dot coupling is reduced. (C) 2003 Elsevier B.V. All rights reserved.

 

11.    P. Bertet, I. Chiorescu, K. Semba, C. J. Harmans, and J. E. Mooij

            "Detection of a persistent-current qubit by resonant activation"

            Physical Review B 70 (10), 100501 (2004).

 

            ABSTRACT: We present the implementation of a scheme to detect the quantum state of a persistent-current qubit. It relies on the dependency of the measuring superconducting quantum interference device plasma frequency on the qubit state, which we detect by resonant activation. With a measurement pulse of only 5 ns, we observed Rabi oscillations with high visibility (65%).

 

12.    S. Bhunia, T. Kawamura, S. Fujikawa, H. Nakashima, K. Furukawa, K. Torimitsu, and Y. Watanabe

            "Vapor-liquid-solid growth of vertically aligned InP nanowires by metalorganic vapor phase epitaxy"

            Thin Solid Films 464-65244-247 (2004).

 

            ABSTRACT: In this study, a detailed investigation of the growth of vertically oriented and surface mounted InP nanowires has been carried out. They were grown by metal organic vapor phase epitaxy on semi-insulating <111> B-oriented InP wafers using An nanoparticle-assisted vapor-liquid-solid growth technique. The proper conditions for the stable nanowire growth were obtained by systematic variation of the pre-growth annealing and the growth temperatures and were found to be 540 and 440 degreesC, respectively. The variation in the length of the nanowires was also studied as a function of time. Transmission electron diffraction studies carried out on the single nanowires revealed the <111> growth direction with the presence of rotational twin structures, the axis of rotation being the growth direction. Analysis of the high-resolution transmission electron microscopic images shows that the orientation and kinks on the nanowires were controlled by the distribution of these twin structures. (C) 2004 Elsevier B.V. All rights reserved.

 

13.    S. Bhunia, T. Kawamura, S. Fujikawa, and Y. Watanabe

            "Systematic investigation of growth of InP nanowires by metalorganic vapor-phase epitaxy"

            Physica E-low-dimensional Systems & Nanostructures 24 (1-2)138-142 (2004).

 

            ABSTRACT: The behavior of the vapor-liquid-solid growth of InP nanowires on (111)B oriented InP substrates by metalorganic vapor-phase epitaxial technique has been reported in details. The nanowires were grown using the colloidal An nanoparticles as the seed to control their diameter in the nanometer scale. The grown nanowires were found to be very uniform in cross section along their longitudinal axis, closely spaced and aligned vertically on the substrate surface. The growth behavior of the nanowires and the sensitive growth and anneal temperature dependence on the stability of the nanowires have been discussed in details. (C) 2004 Elsevier B.V. All rights reserved.

 

14.    S. Bhunia, T. Kawamura, S. Fujikawa, K. Tokushima, and Y. Watanabe

            "Free-standing and vertically aligned InP nanowires grown by metalorganic vapor phase epitaxy"

            Physica E-low-dimensional Systems & Nanostructures 21 (2-4)583-587 (2004).

 

            ABSTRACT: Metalorganic vapor phase epitaxial technique has been used to grow surface mounted vertical and uniform cross-sectional InP nanowires on a wafer scale basis. The growth was carried out under the vapor-liquid-solid mechanism using Au colloidal nanoparticles of nominal diameters of 10 and 20 nm, and their properties were compared. The effect of the pre-growth anneals and growth temperatures on the stability of the nanowires were studied in detail. Scanning electron microscopy and transmission electron microscopic studies showed average diameter of the nanowires in the range of 20-35 nm, and of length 700 nm with growth direction of <111>. Room temperature photoluminescence measurements of the nanowires grown on 10 and 20 mn Au particles showed strong peaks, which were blue shifted by 25 and 32 meV, respectively, compared to bulk InP. (C) 2003 Elsevier B.V. All rights reserved.

 

15.    N. I. Cade, R. Roshan, M. Hauert, A. C. Maciel, J. F. Ryan, A. Schwarz, T. Schapers, and H. Luth

            "Carrier relaxation in GaAs v-groove quantum wires and the effects of localization"

            Physical Review B 70 (19), 195308 (2004).

 

            ABSTRACT: Carrier relaxation processes have been investigated in GaAs/AlxGa1-xAs v-groove quantum wires (QWRs) with a large subband separation (DeltaEsimilar or equal to46 meV). Signatures of inhibited carrier relaxation mechanisms are seen in temperature-dependent photoluminescence (PL) and photoluminescence-excitation measurements; we observe strong emission from the first excited state of the QWR below similar to50 K. This is attributed to reduced intersubband relaxation via phonon scattering between localized states. Theoretical calculations and experimental results indicate that the pinch-off regions, which provide additional two-dimensional confinement for the QWR structure, have a blocking effect on relaxation mechanisms for certain structures within the v groove. Time-resolved PL measurements show that efficient carrier relaxation from excited QWR states into the ground state occurs only at temperatures greater than or similar to30 K. Values for the low-temperature radiative lifetimes of the ground- and first excited-state excitons have been obtained (340 ps and 160 ps, respectively), and their corresponding localization lengths along the wire estimated.

 

16.    B. Chesca, K. Ehrhardt, M. Mossle, R. Straub, D. Koelle, R. Kleiner, and A. Tsukada

            "Phase-sensitive evidence for a predominant d-wave pairing symmetry in the electron doped superconductor La2-xCexCuO4-y"

            Physica C-superconductivity And Its Applications 408-10321-323 (2004).

 

            ABSTRACT: We have performed a phase-sensitive test of the symmetry of the superconducting order parameter of the electron doped cuprate La2-xCexCuO4-y using a superconducting quantum interferometer with spatially distributed Josephson junctions. The magnetic field dependence of the critical current gives strong evidence for a predominant d(x2-y2) (d-wave) symmetry of the superconducting order parameter of the particular sample measured. It also gives upper limits for the s wave component in a mixed order parameter of the type s + id. (C) 2004 Elsevier B.V. All rights reserved.

 

17.    I. Chiorescu, P. Bertet, K. Semba, Y. Nakamura, C. J. Harmans, and J. E. Mooij

            "Coherent dynamics of a flux qubit coupled to a harmonic oscillator"

            Nature 431 (7005)159-162 (2004).

 

            ABSTRACT: In the emerging field of quantum computation(1) and quantum information, superconducting devices are promising candidates for the implementation of solid-state quantum bits (qubits). Single-qubit operations(2-6), direct coupling between two qubits(7-10) and the realization of a quantum gate(11) have been reported. However, complex manipulation of entangled states-such as the coupling of a two-level system to a quantum harmonic oscillator, as demonstrated in ion/atom-trap experiments(12,13) and cavity quantum electrodynamics(14)-has yet to be achieved for superconducting devices. Here we demonstrate entanglement between a superconducting flux qubit (a two-level system) and a superconducting quantum interference device (SQUID). The latter provides the measurement system for detecting the quantum states; it is also an effective inductance that, in parallel with an external shunt capacitance, acts as a harmonic oscillator. We achieve generation and control of the entangled state by performing microwave spectroscopy and detecting the resultant Rabi oscillations of the coupled system.

 

18.    K. Degawa, T. Aoki, T. Higuchi, H. Inokawa, and Y. Takahashi

            "A single-electron-transistor logic gate family for binary, multiple-valued and mixed-mode logic"

            Ieice Transactions On Electronics E87C (11)1827-1836 (2004).

 

            ABSTRACT: This paper presents a model-based study of SET (SingleElectron-Transistor) logic gate family for synthesizing binary, MV (Multiple-Nlalued) and mixed-mode logic circuits. The use of SETS combined with MOS transistors allows compact realization of basic logic functions that exhibit periodic transfer characteristics. The operation of basic SET logic gates is successfully confirmed through SPICE circuit simulation based on the physical device model of SETS. The proposed SET logic gates are useful for implementing binary logic circuits, MV logic circuits and binary-NIV mixed-mode logic circuits in a highly flexible manner. As an example, this paper describes design of various parallel counters for carry-propagation-free arithmetic, where MV signals are effectively used to achieve higher functionality with lower hardware complexity.

 

19.    F. Deppe, S. Saito, H. Tanaka, and H. Takayanagi

            "Determination of the capacitance of nm scale Josephson junctions"

            Journal Of Applied Physics 95 (5)2607-2613 (2004).

 

            ABSTRACT: Superconducting three-Josephson-junction flux qubits (3JFQB) are possible candidates for the basic elements of a (future) scalable quantum computer. An important design parameter is the capacitance of their Josephson junctions. We estimate the capacitance per junction area (specific capacitance) of junctions typically used in 3JFQBs, i.e., of Al/AlOx/Al junctions with 5-10 Angstrom thick oxide layers. The capacitance is obtained by analyzing resonant voltage steps in the current-voltage characteristics of specifically designed dc superconducting quantum interference devices (SQUIDs). The junction area is deduced from scanning electron microscope images. We find that the specific capacitance of our junctions is C-s=100+/-25 fF/mum(2). Finally we compare this result to capacitance estimates obtained with 3JFQB microwave spectroscopy and find that the SQUID resonance method provides a much higher accuracy. (C) 2004 American Institute of Physics.

 

20.    J. M. Elzerman, R. Hanson, J. S. Greidanus, L. H. van Beveren, S. De Franceschi, L. M. Vandersypen, E. Tarucha, and L. P. Kouwenhoven

            "Tunable few-electron double quantum dots with integrated charge read-out"

            Physica E-low-dimensional Systems & Nanostructures 25 (2-3)135-141 (2004).

 

            ABSTRACT: We report on the realization of few-electron double quantum dots defined in a two-dimensional electron gas by means of surface gates on top of a GaAs/AlGaAs heterostructure. Two quantum point contacts (QPCs) are placed in the vicinity of the double quantum dot and serve as charge detectors. These enable determination of the number of conduction electrons on each dot. This number can be reduced to zero, while still allowing transport measurements through the double dot. The coupling between the two dots can be controlled even in the few-electron regime. Microwave radiation is used to pump an electron from one dot to the other by absorption of a single photon. The experiments demonstrate that this quantum dot circuit can serve as a good starting point for a scalable spin-qubit system. (C) 2004 Elsevier B.V. All rights reserved.

 

21.    D. Fattal, K. Inoue, J. Vuckovic, C. Santori, G. S. Solomon, and Y. Yamamoto

            "Entanglement formation and violation of Bell's inequality with a semiconductor single photon source"

            Physical Review Letters 92 (3), 037903 (2004).

 

            ABSTRACT: We report the generation of polarization-entangled photons, using a quantum dot single photon source, linear optics, and photodetectors. Two photons created independently are observed to violate Bell's inequality. The density matrix describing the polarization state of the postselected photon pairs is reconstructed and agrees well with a simple model predicting the quality of entanglement from the known parameters of the single photon source. Our scheme provides a method to create no more than one entangled photon pair per cycle after postselection, a feature useful to enhance quantum cryptography protocols based on shared entanglement.

 

22.    D. Fattal, E. Diamanti, K. Inoue, and Y. Yamamoto

            "Quantum teleportation with a quantum dot single photon source"

            Physical Review Letters 92 (3), 037904 (2004).

 

            ABSTRACT: We report the experimental demonstration of a quantum teleportation protocol with a semiconductor single photon source. Two qubits, a target and an ancilla, each defined by a single photon occupying two optical modes (dual-rail qubit), were generated independently by the single photon source. Upon measurement of two modes from different qubits and postselection, the state of the two remaining modes was found to reproduce the state of the target qubit. In particular, the coherence between the target qubit modes was transferred to the output modes to a large extent. The observed fidelity is 80%, in agreement with the residual distinguishability between consecutive photons from the source. An improved version of this teleportation scheme using more ancillas is the building block of the recent Knill, Laflamme, and Milburn proposal for efficient linear optics quantum computation.

 

23.    K. M. Fu, T. D. Ladd, C. Santori, and Y. Yamamoto

            "Optical detection of the spin state of a single nucleus in silicon"

            Physical Review B 69 (12), 125306 (2004).

 

            ABSTRACT: We propose a method to optically detect the spin state of a P-31 nucleus embedded in a Si-28 matrix. The nuclear-electron hyperfine splitting of the P-31 neutral-donor ground state can be resolved via a direct frequency discrimination measurement of the P-31-bound exciton photoluminescence using single-photon detectors. The measurement time is expected to be shorter than the optically modified lifetime of the nuclear spin at 4 K and 10 T.

 

24.    T. Fujii, I. Terasaki, and A. Matsuda

            "Thermopower anisotropy of lightly-doped and optimally-doped Bi2Sr2-xLaxCaCu2O8+delta single crystals"

            Physica C-superconductivity And Its Applications 408-10674-676 (2004).

 

            ABSTRACT: In-plane and out-of-plane thermopowers have been measured for lightly-doped (insulating) and optimally-doped (superconducting) Bi2Sr2-xLaxCaCu2O8+delta single crystals. The anisotropy of the thermopower S-c/S-ah is very large in the superconducting samples, while it is close to unity in the insulating ones. The thermopower of the insulating samples increases in proportion to rootT, suggesting that the localized carriers around at (pi/2, pi/2) cause the variable range hopping transport. (C) 2004 Elsevier B.V. All rights reserved.

 

25.    T. Fujisawa, T. Hayashi, and Y. Hirayama

            "Controlled decoherence of a charge qubit in a double quantum dot"

            Journal Of Vacuum Science & Technology B 22 (4)2035-2038 (2004).

 

            ABSTRACT: We investigate coherent time evolution of a charge qubit in a semiconductor double quantum dot. A high-speed voltage pulse controls the energy bias and strength of the decoherence of the system. The qubit is effectively isolated from the electrodes in the Coulomb blockade regime, while it is affected by dissipative tunneling processes in the single-electron tunneling regime. We discuss the importance of the controlled decoherence by means of density matrix simulations. (C) 2004 American Vacuum Society.

 

26.    T. Fujisawa, T. Hayashi, H. D. Cheong, Y. H. Jeong, and Y. Hirayama

            "Rotation and phase-shift operations for a charge qubit in a double quantum dot"

            Physica E-low-dimensional Systems & Nanostructures 21 (2-4)1046-1052 (2004).

 

            ABSTRACT: Coherent time evolution of a charge qubit in a semiconductor double quantum dot is demonstrated by means of electrical pulse experiments. The qubit state is manipulated with a rectangular or tailored voltage waveform that controls the energy of the system. The initialization, rotation gate, phase-shift gate, and measurement process are sequencially performed just by changing the voltage in a short time. (C) 2003 Elsevier B.V. All rights reserved.

 

27.    T. Fujisawa, T. Hayashi, Y. Hirayama, H. D. Cheong, and Y. H. Jeong

            "Electron counting of single-electron tunneling current"

            Applied Physics Letters 84 (13)2343-2345 (2004).

 

            ABSTRACT: Single-electron tunneling through a quantum dot is detected by means of a radio-frequency single-electron transistor.. Poisson statistics of single-electron-tunneling events are observed from frequency domain measurements, and individual tunneling events are detected in the time-domain measurements. Counting tunneling events gives an accurate current measurement in the saturated current regime, where electrons tunnel into the dot only from one electrode and tunnel out of the dot only to the other electrode. (C) 2004 American Institute of Physics.

 

28.    A. Fujiwara, N. M. Zimmerman, Y. Ono, and Y. Takahashi

            "Current quantization due to single-electron transfer in Si-wire charge-coupled devices"

            Applied Physics Letters 84 (8)1323-1325 (2004).

 

            ABSTRACT: We observe a quantized current due to single-electron transfer in a small charge-coupled device, which consists of a narrow Si-wire channel with fine gates; the gate is used to form a tunable barrier potential. By modulating two barrier potentials under the fine gates with phase-shifted pulse voltages, quantized numbers of electrons are injected into and extracted from the charge island sandwiched by the two barriers. Current plateaus due to single-electron transfer are clearly observed at 20 K with frequencies up to 100 MHz and a current level of 16 pA. (C) 2004 American Institute of Physics.

 

29.    S. Fukatsu, K. M. Itoh, M. Uematsu, H. Kageshima, Y. Takahashi, and K. Shiraish

            "Effect of Si/SiO2 interface on silicon and boron diffusion in thermally grown SiO2"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 43 (11B)7837-7842 (2004).

 

            ABSTRACT: Silicon self-diffusion and boron diffusion in SiO2 were investigated as functions of the distance of diffusing silicon from the Si/SiO2 interface at various temperatures in the range of 1150-1250degreesC using (SiO2)-Si-nat/(SiO2)-Si-28 isotope heterostructures and Si-30- and B-implanted (SiO2)-Si-28 without and with a 30-nm-thick silicon nitride layer on the surface of each sample. The self-diffusivity of Si in SiO2 did not depend on the oxygen concentration in the annealing ambient without the silicon nitride layer. The diffusion profiles of Si and B in the sample capped with the silicon nitride layer became broader as the distance from the Si/SiO2 interface decreased. This dependence on the distance from the interface was caused by SiO molecules, which are generated at the interface and diffuse into SiO2. The simulated results, taking into account the role of SiO molecules, showed good agreement with each experimental profile of Si-30 and B.

 

30.    K. Furukawa, H. Nakashima, K. Ajito, Y. Kashimura, W. Hu, and K. Torimitsu

            "Observation and manipulation of nanestructures formed by rigid rodlike polymers"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 43 (7B)4521-4524 (2004).

 

            ABSTRACT: We report on the formation of nanostructures based, on rigid rodlike polymers with sigma-conjugated (polysilane) and pi-conjugated (poly (p-phenyleneethynylene)) electronic structured. Different types of nanostructures are formed depending on the sample preparation technique, and they are clearly visualized, by atomic force microscopy (AFM). The nanostructures comprise stretched single molecular structures, nanobundle network's, and needles, all of which are induced by the intrinsic rigid nature of the polymers. We also show Our attempts,to manipulate these nanostructures using an AFM cantilever tip.

 

31.    R. A. Ganeev, T. Kanai, A. Ishizawa, T. Ozaki, and H. Kuroda

            "Development and applications of a compact hybrid tabletop terawatt chirped-pulse amplification Ti : sapphire-Nd : glass laser for x-ray lasing and harmonic generation"

            Applied Optics 43 (6)1396-1403 (2004).

 

            ABSTRACT: A hybrid tabletop (2 m x 3 m) terawatt chirped-pulse amplification Ti:sapphire-Nd:glass laser (1054 nm, 475 fs, 500 mJ, 9 x 10(17) W cm(-2)) has been developed for laser-matter experiments. An overall gain factor of 10(10) was achieved for the laser. The results of laser applications in the studies of soft-x-ray Ni-like Mo 18.9-nm lasing and of harmonic generation from solid surfaces are presented. (C) 2004 Optical Society of America.

 

32.    N. Goel, S. J. Chung, M. B. Santos, K. Suzuki, S. Miyashita, and Y. Hirayama

            "Effect of temperature on ballistic transport in InSb quantum wells"

            Physica E-low-dimensional Systems & Nanostructures 21 (2-4)761-764 (2004).

 

            ABSTRACT: Ballistic transport is observed in 0.5 mum long four-terminal square structures fabricated from InSb quantum wells with AlxIn1-xSb barriers. Negative bend resistance is observed at temperatures between similar to1.5 and similar to200 K. The disappearance of negative bend resistance at higher temperatures is accompanied by evidence of parallel conducting paths. (C) 2003 Elsevier B.V. All rights reserved.

 

33.    N. Goel, S. J. Chung, M. B. Santos, K. Suzuki, S. Miyashita, and Y. Hirayama

            "Ballistic transport in InSb quantum wells at high temperature"

            Physica E-low-dimensional Systems & Nanostructures 20 (3-4)251-254 (2004).

 

            ABSTRACT: Measurements were made on a 0.2 mum four-terminal device, fabricated from an InSb/Al0.15In0.85Sb quantum well structure, at temperatures from 1.5 to 300 K. Negative bend resistance, a signature of ballistic transport, was observed at temperatures up to 205 K. The disappearance of the negative bend resistance at higher temperatures was accompanied by a non-linear dependence of the Hall voltage on magnetic field. The non-linearity indicates multiple-carrier conduction, which we characterize using quantitative mobility spectrum analysis. (C) 2003 Elsevier B.V. All rights reserved.

 

34.    T. Goto, Y. Katagiri, H. Fukuda, H. Shinojima, Y. Nakano, I. Kobayashi, and Y. Mitsuoka

            "Propagation loss measurement for surface plasmon-polariton modes at metal waveguides on semiconductor substrates"

            Applied Physics Letters 84 (6)852-854 (2004).

 

            ABSTRACT: Propagation losses were measured for surface plasmon-polariton (SPP) modes at metal waveguides on semiconductor substrates. The waveguides are simple strips of Au or Al deposited on InP substrates or 300-nm-thick SiO2 film covering the InP substrates. We used a direct method that can clearly discriminate SPP modes in vidicon-camera images, thereby allowing quantitative measurements. The loss coefficients measured at a wavelength of 1.55 mum were, as predicted by theory, in the range of 8.5-17 dB/mm, which shows the waveguides are feasible for practical applications. (C) 2004 American Institute of Physics.

 

35.    H. Gotoh, S. Shigemori, H. Kamada, T. Saitoh, and J. Temmyo

            "Spatially ordered self-assembled quantum dots with uniform shapes fabricated by patterning nanoscale SiN islands"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 43 (10)6894-6899 (2004).

 

            ABSTRACT: We report a method of obtaining position-controlled quantum dots with the uniform spatial shapes. The self-assembled InGaAs quantum dots are grown on a GaAs (311) B substrate with patterned SiN islands. The SiN patterns determine the position of the quantum dots as well as their optical properties. The uniformity of the positions and photoluminescence properties strongly depend on the pitch of the hexagonally patterned SiN islands. With an optimum pattern, the quantum dots have a uniform spatial arrangement. These uniform quantum dots exhibit strong photoluminescence spectra with sharp peaks and spatially isotopic polarization resolved photoluminescence signals. These results show that quantum dots have efficient photoemission processes and that their shapes have the same spatial symmetry.

 

36.    H. Gotoh, H. Kamada, T. Saitoh, S. Shigemori, and J. Temmyo

            "Positional control of self-assembled quantum dots by patterning nanoscale SiN islands"

            Applied Physics Letters 85 (14)2836-2838 (2004).

 

            ABSTRACT: We propose a method for obtaining position-controlled self-assembled quantum dots. The self-assembled InGaAs quantum dots are grown on a GaAs (311) B substrate on which SiN islands have been patterned using a nanolithographic technique. The SiN pattern determines the position of the quantum dots as well as their optical properties. The positional uniformity and photoluminescence spectrum strongly depend on the pitch of the SiN pattern. At an optimum pitch, uniformly arranged quantum dots and intense photoluminescence spectra with sharp peaks are obtained. (C) 2004 American Institute of Physics.

 

37.    H. Gotoh, H. Kamada, T. Saitoh, H. Ando, and J. Temmyo

            "Effects of exciton-biexciton coherent coupling on exciton absorption in quantum dots"

            Applied Physics Letters 85 (16)3480-3482 (2004).

 

            ABSTRACT: We report unusual excitonic absorption spectra with dip-shaped structures caused by exciton-biexciton coherent interactions in quantum dots. The exciton absorption spectrum is measured with the micro-photoluminescence excitation technique in a single InGaAs quantum dot. The spectrum changes from Lorenztian-shaped to dip-shaped with increasing excitation intensity. A theoretical analysis with the density matrix method reveals that exciton-biexciton coherent interactions create dressed states in the exciton-biexciton system and lead to the unusual absorption spectra. (C) 2004 American Institute of Physics.

 

38.    H. Gotoh, H. Kamada, T. Saitoh, H. Ando, and J. Temmyo

            "Effects of biexcitons on exciton decoherence processes in InxGa1-xAs quantum dots"

            Physical Review B 69 (15), 155328 (2004).

 

            ABSTRACT: Exciton decoherence (dephasing) properties are examined for the effects of biexcitons in InxGa1-xAs quantum dots. The dephasing time of higher exciton states is measured from the linewidths of discrete exciton absorption lines by employing a high-energy-resolution microphotoluminescence excitation method in single isolated quantum dots. The excitation intensity dependence and temperature dependence of the exciton linewidth are used to consider the effects of exciton-biexciton and exciton-phonon interactions. The excitation intensity dependence reveals that the exciton-biexciton interaction contributes crucially to the exciton dephasing processes. A numerical calculation undertaken with a density-matrix method interprets this result as an enhancement of the power broadening effect due to coherent coupling between excitons and biexcitons. The temperature dependence indicates that the exciton-biexciton interaction dominates the exciton-phonon interaction below 40 K. These results provide a guideline for achieving a long-lived coherence in quantum dots, which is a key to the implementation of quantum information processing.

 

39.    J. Haruyama, K. Takazawa, S. Miyadai, A. Takeda, N. Hori, I. Takesue, Y. Kanda, T. Akazaki, and H. Takayanagi

            "Supercurrent in diffusive multi-walled carbon nanotubes"

            Physica C-superconductivity And Its Applications 408-1085-87 (2004).

 

            ABSTRACT: We report proximity-induced conductance increase in niobium (Nb)/diffusive multi-walled carbon nanotube (MWNTs)/aluminum (Al) junctions preserving phase of electron waves. We also reveal re-entrant effect in highly transparent MWNT/Al interface sample at low temperatures, whereas we successfully found a proximity-induced superconductivity and supercurrent, implying anomalously enhanced critical magnetic field and Suppression of the critical current by weak localization, in low-transparency samples. (C) 2004 Elsevier B.V. All rights reserved.

 

40.    K. Hashimoto, T. Saku, and Y. Hirayama

            "Nuclear-spin-related resistance enhancements observed over a wide range of magnetic fields"

            Physical Review B 69 (15), 153306 (2004).

 

            ABSTRACT: Slow enhancements in the longitudinal resistance (R-xx) due to nuclear spin polarization are studied around Landau-level filling factors of nu=2/3 and 3/5 as functions of both the filling factor and magnetic field. The R-xx enhancement appears not only at the nu=2/3 and 3/5 spin transitions observed around magnetic fields of B=6.9 and 8.6 T respectively, but also over extended regions at higher and lower magnetic fields along the "flanks" of the nu=2/3 and 3/5 quantum Hall states. Analyses based on the coincidence of spin-split Landau levels for composite fermions provide reasonable account of the R-xx enhancements observed in a wide range of magnetic field.

 

41.    T. Hashizume, S. Anantathanasarn, N. Negoro, E. Sano, H. Hasegawa, K. Kumakura, and T. Makimoto

            "Al2O3 insulated-gate structure for AlGaN/GaN heterostructure field effect transistors having thin AlGaN barrier layers"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 43 (6B)L777-L779 (2004).

 

            ABSTRACT: An Al2O3 insulated-gate (IG) structure was utilized for controlling the surface potential and suppressing the gate leakage in Al0.2Ga0.8N/GaN heterostructure field effect transistors (HFETs) having thin AlGaN barrier layers (less than 10 nm). In comparison with the Schottky-gate devices, the Al2O3 IG device showed successful gate control of drain current up to V-GS = +4V without leakage problems. The threshold voltage in the Al2O3 IG HFET was about -0.3V, resulting in the quasi-normally-off mode operation.

 

42.    R. Hatakeyama, G. H. Jeong, T. Kato, and T. Hirata

            "Effects of micro- and macro-plasma-sheath electric fields on carbon nanotube growth in a cross-field radio-frequency discharge"

            Journal Of Applied Physics 96 (11)6053-6060 (2004).

 

            ABSTRACT: Effects of magnetic-field introduction and micro/macroelectric fields in a plasma sheath on the carbon nanotube growth are investigated by employing a cylindrical magnetron-type radio-frequency (rf) plasma-enhanced chemical-vapor deposition method. The cross-field magnetic-field application is accompanied by the high-density plasma generation and the reduction of direct impinge of high-energy ions to a rf electrode substrate, achieving the carbon nanotube formation without harmful sputtering phenomenon. It is found that microelectric fields in the plasma sheath are useful in the sense of substrate pretreatment and macroelectric fields have to be optimized in order to obtain well-aligned and refined nanotube structures in a large area. These experimental results lead to putting into practice of quite simple methods for the site-selected carbon nanotube growth in a relatively large area, so-called substrate-scratching method and mesh-masking method. (C) 2004 American Institute of Physics.

 

43.    T. Hatano, M. Stopa, W. Izumida, T. Yamaguchi, T. Ota, and S. Tarucha

            "Gate-voltage dependence of inter dot coupling and Aharanov-Bohm oscillation in laterally coupled vertical double dot"

            Physica E-low-dimensional Systems & Nanostructures 22 (1-3)534-537 (2004).

 

            ABSTRACT: We fabricated laterally coupled vertical double-dot devices and measured their electrical transport properties. In these devices, two dots are laterally coupled in parallel and connected to a common source, and drain contacts placed above, and below the two dots. The number of electrons in each dot and the inter-dot tunnel coupling are all tunable. The inter-dot tunnel coupling was changed between the weak and strong coupling regimes, as a function of gate voltage placed between two dots. When a magnetic field was applied parallel to the plane of the two dots and source/drain contacts, we observed oscillations of the current (Aharanov-Bohm oscillation) in the weak coupling regime (for a different device). (C) 2003 Elsevier B.V. All rights reserved.

 

44.    T. Hayashi, T. Fujisawa, H. D. Cheong, Y. H. Jeong, and Y. Hirayama

            "Coherent charge oscillation in a semiconductor double quantum dot"

            Ieee Transactions On Nanotechnology 3 (2)300-303 (2004).

 

            ABSTRACT: The time evolution of a pulse-excited charge qubit in a semiconductor double quantum dot is investigated. All-electrical initialization and coherent gate control of the system are achieved, and coherent charge oscillation is observed through the transport measurements. The oscillation frequency and decoherence time T-2 are estimated by fitting the transport data with a simple model. Possible decoherence mechanisms in a charge qubit system are pointed out and discussed in detail.

 

45.    H. Hibino, Y. Homma, C. W. Hu, M. Uwaha, T. Ogino, and I. S. Tsong

            "Structural and morphological changes on surfaces with multiple phases studied by low-energy electron microscopy"

            Applied Surface Science 237 (1-4)51-57 (2004).

 

            ABSTRACT: We used low-energy electron microscopy to study structural and morphological changes of Si(1 1 1) on which "1 x 1" and 7 x 7 coexist. Because "1 x 1" and 7 x 7 have different thermodynamic and kinetic properties, various interesting phenomena unique to the two-phase surface take place. The difference in the surface mass diffusion constant, coupled with the preferential nucleation of 7 x 7 at the upper step edges, effectively causes a diffusion barrier at the upper side of the step, resulting in the selective slowing down of vacancy island decay and step wandering during homoepitaxial growth. The difference in the surface mass diffusion constant also influences the step motion caused by the difference in the atom density. The 7 x 7 domains coarsen to reduce the energetic cost of the boundaries consisting of narrow "1 x 1" regions. We demonstrate that von Neumann's law governs the coarsening. (C) 2004 Elsevier B.V. All rights reserved.

 

46.    M. Hiroki, K. Kumakura, T. Makimoto, N. Kobayashi, and T. Kobayashi

            "Fabrication of GaN/Alumina/GaN structure to reduce dislocations in GaN"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 43 (4B)1930-1933 (2004).

 

            ABSTRACT: GaN/Alumina/GaN structures were fabricated to reduce dislocation density in GaN. Alumina films were deposited on GaN templates by electron cyclotron resonance plasma Sputtering. GaN was regrown on the alumina films by metalorganic vapor phase epitaxy. It was found that GaN on alumina selectively regrown from pinholes in alumina by annealing prior to GaN regrowth. Hardly any of the dislocations in the GaN template propagated through the interlayer. Most of dislocations were terminated or bent at the interface between the alumina and regrown GaN. On the other hand, new vertical dark lines and horizontal dislocations were generated in regrown layer. The vertical lines were found to correspond to an inversion domain from convergent beam electron diffraction analysis.

 

47.    Y. Homma, S. Suzuki, Y. Kobayashi, M. Nagase, and D. Takagi

            "Mechanism of bright selective imaging of single-walled carbon nanotubes on insulators by scanning electron microscopy"

            Applied Physics Letters 84 (10)1750-1752 (2004).

 

            ABSTRACT: Individual single-walled carbon nanotubes (SWNTs) produce highly bright images of the insulator surface around them when observed by scanning electron microscopy at low primary-electron voltage. We found that the insulator surface near SWNTs emits more secondary electrons due to electrons supplied through SWNTs connecting to the outside area of the primary-electron beam scanning. SWNTs are thus highlighted as bright lines corresponding to the electron-beam-induced current range around them. This technique provides a useful and effective way to investigate lateral growth morphology of SWNTs on the substrate. (C) 2004 American Institute of Physics.

 

48.    T. Hong, M. W. Jack, and M. Yamashita

            "On-demand single-photon state generation via nonlinear absorption"

            Physical Review A 70 (1), 013814 (2004).

 

            ABSTRACT: We propose a method for producing on-demand single-photon states based on collision-induced exchanges of photons and unbalanced linear absorption between two single-mode light fields. These two effects result in an effective nonlinear absorption of photons in one of the modes, which can lead to single-photon states. A quantum nonlinear attenuator based on such a mechanism can absorb photons in a normal input light pulse and terminate the absorption at a single-photon state. Because the output light pulses containing single photons preserve the properties of the input pulses, we expect this method to be a means for building a highly controllable single-photon source.

 

49.    T. Honjo, K. Inoue, and H. Takahashi

            "Differential-phase-shift quantum key distribution experiment with a planar light-wave circuit Mach-Zehnder interferometer"

            Optics Letters 29 (23)2797-2799 (2004).

 

            ABSTRACT: A differential-phase-shift quantum key distribution experiment was carried out with a planar light-wave circuit (PLC) Mach-Zehnder interferometer. This scheme has two advantages: it requires no polarization control and has a high repetition frequency, provided that a stable interferometer is available. Stable polarization-insensitive operation was achieved with an interferometer fabricated by PLC technology. Raw key creation at a rate of 3076 bits/s with a 5.0% quantum bit-error rate was achieved over 20 km of fiber. The stability of the PLC interferometer was examined. (C) 2004 Optical Society of America.

 

50.    S. Horiguchi, A. Fujiwara, H. Inokawa, and Y. Takahashi

            "Analysis of back-gate voltage dependence of threshold voltage of thin silicon-on-insulator metal-oxide-semiconductor field-effect transistor and its application to Si single-electron transistor"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 43 (4B)2036-2040 (2004).

 

            ABSTRACT: The back-gate voltage (V-BG) dependence of threshold voltage (V-th) is analyzed for n- and p-channel thin silicon-on-insulator (SOI) metal -oxide-semiconductor field-effect transistors (MOSFETs) using a self-consistent solution of the coupled Poisson and Schrodinger equations with a variational method. It is found that the slope (dV(th)/dV(BG)) is modulated not only by the gate-oxide and buried-oxide thickness but also by the distribution of the wave functions of carriers in the SOI layer and that the slope can be well described by an approximate equation derived assuming that a delta-function-like charge sheet exists at the average position of carriers in the SOI layer. From these findings, SOI-layer thickness and gate-oxide thickness or average position of carriers are shown to be determined precisely. Moreover, from the back-gate voltage dependence of peak voltage (defined as the gate voltage giving a drain current peak) of a single-electron transistor (SET), the average position of electrons in a Si island is shown to change, particularly in the few-electron regime, probably due to electron-electron interaction.

 

51.    L. F. Houlet, H. Yamaguchi, S. Miyashita, and Y. Hirayama

            "InAs/AlGaSb piezoresistive cantilever for sub-angstrom scale displacement detection"

            Japanese Journal Of Applied Physics Part 2-letters 43 (3B)L424-L426 (2004).

 

            ABSTRACT: We report on the fabrication and characterization of 0.3-mum-thick piezoresistive cantilevers based on the InAs/AlGaSb heterostructure. The dependence of the displacement resolution on the cantilever size, which ranges from 20 x 10 to 2 x 1mum(2), has been studied by a novel characterization method using an atomic force microscope. The results show that downscaling the cantilevers improves their performances, and an optimum resolution of 0.26Angstrom/Hz(0.5) was obtained with a 3 x 1.5 mum(2) cantilever at a modulation frequency of 714 Hz. A finite-element simulator allowed the calculation of the resonance frequencies and a maximum value of 20.5 MHz was obtained for the 3 x 1.5 mum(2) cantilever.

 

52.    W. P. Hu, M. Matsumura, K. Furukawa, and K. Torimitsu

            "Oxygen plasma generated copper/copper oxides nanoparticles"

            Journal Of Physical Chemistry B 108 (35)13116-13118 (2004).

 

            ABSTRACT: Oxygen-plasma-generated CuOx nanoparticles enhanced the carriers injection from indium-tin oxide (ITO) anode into organic materials. Atomic force microscopy images revealed that the CuOx nanoparticles appeared as high-ordered nanotip arrays on substrates. Those nanoparticles induced strong field-emission current. The analysis by X-ray diffraction pattern and Fourier transform infrared spectrum demonstrated that CuOx was actually of a mixture of copper and copper oxides (CuO, CuO2, CuO3, and CuO4).

 

53.    W. P. Hu, H. Nakashima, K. Furukawa, Y. Kashimura, K. Ajito, and K. Torimitsu

            "Self-assembled rigid conjugated polymer nanojunction and its nonlinear current-voltage characteristics at room temperature"

            Applied Physics Letters 85 (1)115-117 (2004).

 

            ABSTRACT: A gold/polymer/gold nanojunction was fabricated by the self-assembly of a rigid polymer, namely poly(p-phenyleneethynylene)s with thioacetyl groups, between gold nanogap electrodes. The self-assembly depends on: (i) the ideal rigidity of the polymer molecules and (ii) the strong affinity of the thioacetyl/thiol end groups of the polymer for the Au surface. The current-voltage (I-V) characteristics of the conjugated polymer nanojunction exhibited stepwise features (some steps appeared as peaks) at room temperature. The I-V can be explained as electron tunneling through the nanojunction. (C) 2004 American Institute of Physics.

 

54.    W. P. Hu, H. Nakashima, K. Furukawa, Y. Kashimura, K. Ajito, C. Han, and K. Torimitsu

            "Carrier injection from gold electrodes into thioacetyl-end-functionalized poly(para-phenyleneethynylene)s"

            Physical Review B 69 (16), 165207 (2004).

 

            ABSTRACT: Carrier injection from a gold electrode into a thioacetyl-end-functionalized polymer, poly(para-phenyleneethynylene)s (TA-PPE), has been investigated by using sandwich and nanogap electrode devices. The results suggest that carrier injection depends on the organized status of the Au/TA-PPE interface. For sandwich devices with spin-coated TA-PPE films, carrier injection is dominated by a thermal emission mechanism with a barrier height of around 1.16 eV. However, as regards devices with nanogap electrodes, when the Au/TA-PPE interface is poorly organized, the carrier injection is dominated by a mixed mechanism consisting of thermal emission and tunneling. When the Au/TA-PPE interface is well organized, i.e., most of the molecules are connected to the Au electrode by Au-S bonds, and the carrier injection is dominated by tunneling, the tunneling barrier height Phi(B) is estimated to be around 1.33-1.43 eV.

 

55.    S. Hughes, and H. Kamada

            "Single-quantum-dot strong coupling in a semiconductor photonic crystal nanocavity side coupled to a waveguide"

            Physical Review B 70 (19), 195313 (2004).

 

            ABSTRACT: We present an intuitive photon Green function formalism to study strong coupling via reflection or transmission of light in a planar-photonic-crystal waveguide that is side coupled to a nanocavity containing only one quantum dot. Analytical results allow physical insight and useful formulas to optimally design such integrated systems in a realistic way and we subsequently demonstrate that strong coupling should be achievable using present day photonic crystals and quantum dots, yielding single-exciton vacuum Rabi splittings of around 0.1-1 meV.

 

56.    S. Hughes

            "Enhanced single-photon emission from quantum dots in photonic crystal waveguides and nanocavities"

            Optics Letters 29 (22)2659-2661 (2004).

 

            ABSTRACT: A theoretical formalism is presented to investigate enhanced radiative decay of excited dipoles in photonic crystal waveguides and nanocavities with a view to achieving efficient single-photon emission from embedded quantum dots. Surprisingly, large enhancement effects are achievable in both waveguides and nanocavities, and enhanced emission in the waveguide is shown to scale proportionally (inversely) with the photon group index (velocity). Further, a way to include radiative coupling of the quantum dot is shown, and the importance of its inclusion is subsequently demonstrated. (C) 2004 Optical Society of America.

 

57.    S. Hughes

            "High-field wave packets in semiconductor quantum wells: A real-space finite-difference time-domain formalism"

            Physical Review B 69 (20), 205308 (2004).

 

            ABSTRACT: An untraditional space-time method for describing the dynamics of high-field electron-hole wave packets in semiconductor quantum wells is presented. A finite-difference time-domain technique is found to be computationally efficient and can incorporate Coulomb, static, terahertz, and magnetic fields to all orders, and thus can be applied to study many areas of high-field semiconductor physics. Several electro-optical and electro-magneto-optical excitation schemes are studied, some well known and some new, and predicted observables are shown to be in qualitative agreement with experiment, where known.

 

58.    H. Inokawa, Y. Takahashi, K. Degawa, T. Aoki, and T. Higuchi

            "A simulation methodology for single-electron multiple-valued logics and its application to a latched parallel counter"

            Ieice Transactions On Electronics E87C (11)1818-1826 (2004).

 

            ABSTRACT: This paper introduces a methodology for simulating single-electron-transistor (SET)-based multiple-valued logics (MVLs). First, a physics-based analytical model for SET is described, and then a procedure for extracting parameters from measured characteristics is explained. After that, simulated and experimental results for basic MVL circuits are compared. As an advanced example of SET-based logics, a latched parallel counter, which is one of the most important components in arithmetic circuits, is newly designed and analyzed by a simulation. It is found that a SET-based 7-3 counter can be constructed with less than 1/10 the number of devices needed for a conventional circuit and can operate at a moderate speed with 1/100 the conventional power consumption.

 

59.    H. Inokawa, and Y. Takahashi

            "Simultaneous-sweep method for evaluation of single-electron transistors with barriers induced by gate electric field"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 43 (8B)L1048-L1050 (2004).

 

            ABSTRACT: In single-electron devices (SEDs) with gate-induced barriers, the barrier height may often be affected by the separate input gate used for controlling the potential of the Coulomb island. To compensate for this adverse effect, we introduce a simultaneous-sweep method, in which the gate voltage for the barrier is changed in inverse relation to the input gate voltage. By using this method, a two-gate narrow-channel metal-oxide-semiconductor (MOS) field-effect transistor was successfully operated as a single-electron transistor (SET). This is the first clear demonstration of a SET with gate-induced barriers in a silicon MOS system, where the presence of a disordered quantum wire or impurity quantum dots is excluded by the independent characterization of the channel using one gate at a time.

 

60.    K. Inoue, and K. Shimizu

            "Generation of quantum-correlated photon pairs in optical fiber: Influence of spontaneous Raman scattering"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 43 (12)8048-8052 (2004).

 

            ABSTRACT: The generation of quantum-correlated photon pairs by spontaneous four-wave mixing (FWM) in an optical fiber is studied. After demonstrating the time correlation between signal and idler photons, the influence of spontaneous Raman scattering on extracting photon pairs is experimentally investigated. It is shown that a short pulse and a narrow filtering bandwidth are preferable for obtaining correlated photon pairs with a better signal-to-noise ratio via FWM in an optical fiber.

 

61.    T. Ishimoto, H. Tokiwa, H. Teramae, and U. Nagashima

            "Development of an ab initio MO-MD program based on fragment MO method - an attempt to analyze the fluctuation of protein"

            Chemical Physics Letters 387 (4-6)460-465 (2004).

 

            ABSTRACT: In order to analyze the fluctuation of proteins, which plays an important role for folding structure and stability, an ab initio MO-MD program (FMO-HA) based on the fragment MO method has been developed and examined its efficiency in comparison with conventional RHF MO-MD. FMO gives the same potential of dissociation energy between fragments as well as RHF. FMO-HA and RHF MO-MD calculations show similar trajectories and geometrical changes. Furthermore. FMO-HA simulation enables us to elucidate the interaction energy between fragments accompanying with the dynamics. FMO-HA method is an efficient tool to determine the driving force of fluctuation of proteins. (C) 2004 Elsevier B.V. All rights reserved.

 

62.    T. Ito, K. Tsutsumida, K. Nakamura, Y. Kangawa, K. Shiraishi, A. Taguchi, and H. Kageshima

            "Systematic theoretical investigations of adsorption behavior on the GaAs(001)-c(4 x 4) surfaces"

            Applied Surface Science 237 (1-4)194-199 (2004).

 

            ABSTRACT: Adsorption behavior on the GaAs(0 0 1)-c(4 x 4) surfaces is systematically investigated by using our ab initio-based approach and the Monte Carlo methods. The change in stable structure of the c(4 x 4) surfaces is clarified by considering adsorption or desorption of surface dimers as functions of temperature and As pressure. The calculated results imply that the c(4 x 4) surface with As dimers is stable at low temperatures less than similar to400 K, whereas the surface with Ga-As dimers is stabilized at high temperatures in the range of similar to400-700 K. The disordered dimer arrangements consisting of Ga and As substituted by each other in the c(4 x 4) unit cell hardly appear even at high temperatures such as similar to800 K. We also investigate the behavior of Ga and As adatoms on these c(4 x 4) surfaces. The calculated results reveal that Ga atoms can adsorb and migrate on the surfaces while desorption of As adatoms proceeds without sufficient migration. Therefore, Ga adatoms play an important role for the epitaxial growth of GaAs on the GaAs(0 0 1)-c(4 x 4) surface. (C) 2004 Elsevier B.V. All rights reserved.

 

63.    S. W. Jung, T. Fujisawa, Y. Hirayama, and Y. H. Jeong

            "Background charge fluctuation in a GaAs quantum dot device"

            Applied Physics Letters 85 (5)768-770 (2004).

 

            ABSTRACT: We investigate background charge fluctuation in a GaAs quantum dot device by measuring 1/f noise in the single-electron tunneling current through the dot. The current noise is understood as fluctuations of the confinement potential and tunneling barriers. The estimated potential fluctuation increases almost linearly with temperature, which is consistent with a simple model of the 1/f noise. We find that the fluctuation increases very slightly when electrons are injected into excited states of the quantum dot. (C) 2004 American Institute of Physics.

 

64.    Y. J. Jung, Y. Homma, R. Vajtai, Y. Kobayashi, T. Ogino, and P. M. Ajayan

            "Straightening suspended single walled carbon nanotubes by ion irradiation"

            Nano Letters 4 (6)1109-1113 (2004).

 

            ABSTRACT: Single walled carbon nanotubes grown suspended between pillars of Si/SiO2 structures are straightened by ion beam scans. In addition, the ion irradiation selectively removes nanotubes lying on the substrate, leaving the suspended nanotubes in place. This strategy provides a facile way to produce large area connected networks of suspended straight nanotubes. Although ion irradiation induces structural modifications to nanotubes and introduces defects into the nanotube lattice, the form and dimensions of the nanotubes remain close to that of original grown structures. Nanotube networks consisting of perfectly straight and suspended structures could serve as a platform for various applications.

 

65.    H. Kageshima, M. Uematsu, K. Akagi, S. Tsuneyuki, T. Akiyama, and K. Shiraishi

            "Theoretical study of excess Si emitted from Si-oxide/Si interfaces"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 43 (12)8223-8226 (2004).

 

            ABSTRACT: The excess Si emitted from the Si-oxide/Si interface is studied using the first-principles calculations. It is shown that the excess Si can have many (meta-) stable positions around the interface. In addition, some positions in the oxide do not have any dangling bonds or floating bonds in contrast to those in the bulk crystalline Si. The results indicate that the emitted Si can be located in the oxide layer but they do not necessarily cause charge traps in the oxide. The emitted Si atoms are thought to just be oxidized and absorbed into the oxide while a portion of them cause the E' centers, the P-b centers or charge traps.

 

66.    H. Kamada, and H. Gotoh

            "Quantum computation with quantum dot excitons"

            Semiconductor Science And Technology 19 (4)S392-S396 (2004).

 

            ABSTRACT: Potential application of elementary excitation in semiconductor quantum dot to quantum computation is discussed. We propose a scalable hardware and all optical implementation of a logic gate that exploits the discrete nature of electron-hole states and their well-concentrated oscillator strength for ultrafast gate operation. A multiple-bit gate function is based on the nearest neighbour dipole-dipole coupling. Rabi population oscillation and long-lived coherence of an excitonic two-level system in an isolated InxGa1-xAs quantum dot guarantees quantum gate functions. Technologies that will realize and facilitate the exciton quantum computing are discussed.

 

67.    S. Karimoto, and M. Naito

            "Electron-doped infinite-layer thin films with T-C(zero)=41 K grown on DyScO3 substrate"

            Physica C-superconductivity And Its Applications 412-141349-1353 (2004).

 

            ABSTRACT: We report high-quality electron-doped infinite-layer (IL) superconducting thin films with a T-C of over 40 K grown on newly introduced DyScO3 substrates by molecular-beam epitaxy (MBE). The optimally-doped film seems to be free from strain, thus leading to a low resistivity of 75 muOmegacm at room temperature, which is the lowest reported value for high-T-C superconductors, and a low residual resistivity of 15 muOmega cm just above T-C. (C) 2004 Elsevier B.V. All rights reserved.

 

68.    S. Karimoto, and M. Naito

            "Electron-doped infinite-layer thin films with T-C over 40 K grown on DyScO3 substrates"

            Applied Physics Letters 84 (12)2136-2138 (2004).

 

            ABSTRACT: We report high-quality electron-doped infinite-layer superconducting thin films with a T-C of over 40 K grown on lattice-matched DyScO3 substrates by molecular-beam epitaxy. The optimally doped film seems to be free from strain, thus leading to a low resistivity of 75 muOmega cm at room temperature and 15 muOmega cm just above T-C. (C) 2004 American Institute of Physics.

 

69.    M. Kasu, M. Kubovic, A. Aleksov, N. Teofilov, R. Sauer, E. Kohn, and T. Makimoto

            "Properties of (111) diamond homoepitaxial layer and its application to field-effect transistor"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 43 (7B)L975-L977 (2004).

 

            ABSTRACT: The (111)-oriented chemical-vapor-deposited diamond homoepitaxial layers with low defect density exhibited well-resolved free-exciton transitions in cathodoluminescence at 13K and a sharp peak at 1332 cm(-1) (linewidth: 1.9 cm(-1)) in Raman scattering. Furthermore, using these (111) layers, we fabricated metal-semi conductor field-effect transistors (FETs). FETs with an 11-mum-long gate exhibited a maximum drain current of 24 mA/mm and maximum transconductance of 14 mS/mm. These values are of the same order as those for the (001) orientation.

 

70.    M. Kasu, M. Kubovic, A. Aleksov, N. Teofilov, Y. Taniyasu, R. Sauer, E. Kohn, T. Makimoto, and N. Kobayashi

            "Influence of epitaxy on the surface conduction of diamond film"

            Diamond And Related Materials 13 (2)226-232 (2004).

 

            ABSTRACT: The influence of the crystalline and surface properties of diamond homoepitaxial layers on device properties in H-terminated surface-channel diamond field effect transistors (FETs) is investigated. Crystalline defects inside the layers result in gate current leakage in FET DC operation. We confirmed incorporation of boron acceptors inside the layers. Their residual acceptors result in buffer leakage in DC operation, but do not affect RF characteristics much. Adsorbates from the environment change the concentration of the surface holes generated by the H-termination. (C) 2003 Elsevier B.V. All rights reserved.

 

71.    G. H. Kim, Y. H. Lee, A. Shinya, and M. Notomi

            "Coupling of small, low-loss hexapole mode with photonic crystal slab waveguide mode"

            Optics Express 12 (26)6624-6631 (2004).

 

            ABSTRACT: Coupling characteristics between the single-cell hexapole mode and the triangular-lattice photonic crystal slab waveguide mode is studied by the finite-difference time-domain method. The single-cell hexapole mode has a high quality factor (Q) of 3.3 x 10(6) and a small modal volume of 1.18(lambda/n)(3). Based on the symmetry, three representative types of coupling geometries (shoulder-couple, butt-couple and side-couple structures) are selected and tested. The coupling efficiency shows strong dependence on the transverse overlap of the cavity mode and the waveguide mode over the region of the waveguide. The shoulder-couple structure shows best coupling characteristics among three tested structures. For example, two shoulder-couple waveguides and a hexapole cavity result in a high performance resonant-tunneling-filter with Q of 9.7 x 10(5) and transmittance of 0.48. In the side-couple structure, the coupling strength is much weaker than that of the shoulder-couple structure because of the poor spatial overlap between the mode profiles. In the direct-couple structure, the energy transfer from the cavity to the waveguide is prohibited because of the symmetry mismatch and no coupling is observed. (C) 2004 Optical Society of America.

 

72.    S. J. Kim, Y. Ono, Y. Takahashi, and J. B. Choi

            "Real-time observation of single-electron movement through silicon single-electron transistor"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 43 (10)6863-6867 (2004).

 

            ABSTRACT: We fabricated, for the first time, a device, which enables us to monitor the transport of individual electrons through a silicon single-electron transistor (SET). The device was fabricated on a silicon-on-insulator substrate. In the device, there is a large extra island in one of the SET leads, which exchanges electrons with the SET. The device also has an electrometer whose current level is sensitive to the potential of the extra island. We observed, at 25 K, that the electrometer current changed in a step like manner as a function of time, which is ascribed to the abrupt change in the extra-island potential due to single-electron movement via the SET. This shows that the present structure makes it possible to investigate tunneling dynamics in a silicon SET and to evaluate transfer accuracy of recently demonstrated silicon-based single-charge-transfer devices.

 

73.    M. Kobayashi, J. Buck, and L. R. Levin

            "Conservation of functional domain structure in bicarbonate-regulated "soluble" adenylyl cyclases in bacteria and eukaryotes"

            Development Genes And Evolution 214 (10)503-509 (2004).

 

            ABSTRACT: Soluble adenylyl cyclase (sAC) is an evolutionarily conserved bicarbonate sensor. In mammals, it is responsible for bicarbonate-induced, cAMP-dependent processes in sperm required for fertilization and postulated to be involved in other bicarbonate- and carbon dioxide-dependent functions throughout the body. Among eukaryotes, sAC-like cyclases have been detected in mammals and in the fungi Dictyostelium; these enzymes display extensive similarity extending through two cyclase catalytic domains and a long carboxy terminal extension. sAC-like cyclases are also found in a number of bacterial phyla (Cyanobacteria, Actinobacteria, and Proteobacteria), but these enzymes generally possess only a single catalytic domain and little, if any, homology with the remainder of the mammalian protein. Database mining through a number of recently sequenced genomes identified sAC orthologues in additional metazoan phyla (Arthropoda and Chordata) and additional bacterial phyla (Chloroflexi). Interestingly, the Chloroflexi sAC-like cyclases, a family of three enzymes from the thermophilic eubacterium, Chloroflexus aurantiacus, are more similar to eukaryotic sAC-like cyclases (i.e., mammalian sAC and Dictyostelium SgcA) than they are to other bacterial adenylyl cyclases (ACs) (i.e., from Cyanobacteria). The Chloroflexus sAC-like cyclases each possess two cyclase catalytic domains and extensive similarity with mammalian enzymes through their carboxy termini. We cloned one of the Chloroflexus sAC-like cyclases and confirmed it to be stimulated by bicarbonate. These data extend the family of organisms possessing bicarbonate-responsive ACs to numerous phyla within the bacterial and eukaryotic kingdoms.

 

74.    Y. Kobayashi, H. Nakashima, D. Takagi, and Y. Homma

            "CVD growth of single-walled carbon nanotubes using size-controlled nanoparticle catalyst"

            Thin Solid Films 464-65286-289 (2004).

 

            ABSTRACT: We investigated single-walled carbon nanotube (SWNT) growth using a novel Fe3O4 nanoparticle catalyst synthesized with a simple organic chemistry process. We characterized the structure of the grown SWNT's through scanning electron microscopy (SEM), atomic force microscopy (AFM) and microscopic Raman spectroscopy. Discrete nanoparticles with a uniform diameter of similar to 4 nm could be deposited on Si substrates with a thermal oxide layer by spin-coating with a nanoparticle solution. Nanoparticles prepared under optimum conditions remained discrete and uniform without aggregation even after chemical vapor deposition (CVD) process and their diameters were reduced to similar to 1.7 nm due to decomposition reactions during CVD. These nanoparticles were found to have remarkable catalytic activity in the CVD growth of the SWNTs. SWNTs with diameters of around 1 nm were produced from the reduced nanoparticle catalyst. The diameters of the grown SWNTs were closely correlated with those of the catalytic nanoparticles and tended to be slightly smaller than the particle size. (C) 2004 Elsevier B.V. All rights reserved.

 

75.    Y. Kobayashi, D. Takagi, Y. Ueno, and Y. Homma

            "Characterization of carbon nanotubes suspended between nanostructures using micro-Raman spectroscopy"

            Physica E-low-dimensional Systems & Nanostructures 24 (1-2)26-31 (2004).

 

            ABSTRACT: We characterized suspended single-wall carbon nanotubes (SWNTs) bridging ultra-fine nano-pillars using microscopic Raman spectroscopy, mainly examining the structural dependence on pillar materials (Si or SiO2) and pillar spacing. The SWNTs were synthesized by thermal CVD, in which CH4 and Fe were the carbon feedstock and catalyst. The frequencies of G bands, D bands and RBM signals show very little dependence on the pillar composition and spacing. The growth yield of the suspended SWNTs evaluated from G band intensity decreases for both Si and SiO2 pillars with increasing pillar spacing, and the rate of the decrease is more rapid for the SiO2 pillar. Defect density evaluated from the intensity ratio of the. D and G bands hardly depends on the pillar spacing but significantly on the pillar materials, indicating that the SWNTs grown on SiO2 Pillars contain fewer defects than on those of Si pillars. The SWNT yield and the defect formation during their bridging growth may be related to the growth mechanism and is consistent with the vibratory growth model. (C) 2004 Elsevier B.V. All rights reserved.

 

76.    Y. Kobayashi, T. Yamashita, Y. Ueno, O. Niwa, Y. Homma, and T. Ogino

            "Extremely intense Raman signals from single-walled carbon nanotubes suspended between Si nanopillars"

            Chemical Physics Letters 386 (1-3)153-157 (2004).

 

            ABSTRACT: Single-wall carbon nanotubes (SWNTs) suspended between ultra-fine Si nanopillars were characterized by microscopic Raman spectroscopy. The Raman signals from the suspended SWNTs are extremely intense, compared with those from the carbon nanotubes that grow on the flat surface of substrates and adhere tightly to the substrate surfaces. This intensity enhancement makes it possible to discriminate the Raman signals of the suspended SWNTs from these of carbon nanotubes on the substrate surface and thereby detect the signals from the suspended SWNTs selectively. Based on this novel phenomenon, the structural features of the suspended SWNTs are analyzed. (C) 2004 Elsevier B.V. All rights reserved.

 

77.    R. Koch, C. Pampuch, H. Yamaguchi, A. K. Das, A. Ney, L. Daweritz, and K. H. Ploog

            "Magnetoelastic coupling of MnAs/GaAs(001) close to the phase transition"

            Physical Review B 70 (9), 092406 (2004).

 

            ABSTRACT: The magnetoelastic coupling of epitaxial MnAs films on GaAs(001) has been investigated with a sensitive cantilever beam magnetometer. We find that even at 10 degreesC, i.e., very close to the combined structural and magnetic phase transition from alpha- to beta-MnAs (10-40 degreesC), the magnetoelastic coupling constants are comparable in magnitude with the small values of the 3d ferromagnets. The coupling is largest within the hexagonal plane of MnAs, described by constant B-1, rather than along the c-axis, where the Mn atoms are nearest neighbors. Our experimental results, therefore, support an indirect exchange mechanism via the Mn-As-Mn bonds in accordance with pair model calculations.

 

78.    R. Koch, A. K. Das, H. Yamaguchi, C. Pampuch, and A. Ney

            "Perpendicular magnetic fields in cantilever beam magnetometry"

            Journal Of Applied Physics 96 (5)2773-2778 (2004).

 

            ABSTRACT: Cantilever beam magnetometry is a common technique to determine the magnetoelastic (ME) coupling constants of thin films by measuring the stress that develops when the film magnetization is changed. In cantilever beam experiments performed so far the film magnetization was mainly rotated within the film plane. Here we discuss the measurement of the ME coupling constants, when the magnetizing field is chosen so that it rotates the film magnetization out of the film plane. A major stress contribution, which arises additionally to the ME stress, originates in the torque that magnetic dipoles experience in a magnetic field. In order to separate torque effects from ME contributions in cantilever beam experiments a general method is proposed. With this method the ME coupling constants can be quantitatively determined and furthermore the film magnetization as well as its perpendicular anisotropy constant are obtained quantitatively. (C) 2004 American Institute of Physics.

 

79.    T. Kodera, W. G. van der Wiel, K. Ona, S. Sasaki, T. Fujisawa, and S. Tarucha

            "High-frequency manipulation of few-electron double quantum dots - toward spin qubits"

            Physica E-low-dimensional Systems & Nanostructures 22 (1-3)518-521 (2004).

 

            ABSTRACT: We use a photon-assisted tunneling (PAT) technique to study the high-frequency response of one- and two-electron states in a semiconductor vertically coupled double-dot system. In particular, PAT associated with two-electron spin states in the spin-blockade regime is observed up to the absorption of 10 photons, indicating the preservation of long relaxation times and hence the robustness of our electron spin device under strong microwave irradiation. An alternative double-dot structure with greater flexibility in tuning the inter-dot coupling is presented and its transport characteristics are discussed. This structure is proposed for high-frequency control of two-electron spin states, as required for quantum computation schemes using electron spins in quantum dots. (C) 2003 Elsevier B.V. All rights reserved.

 

80.    T. Koga, J. Nitta, and M. van Veenhuizen

            "Ballistic spin interferometer using the Rashba effect"

            Physical Review B 70 (16), 161302 (2004).

 

            ABSTRACT: We propose a ballistic spin interferometer using a square loop (SL) geometry, where an incident electron wave packet is split into a pair of partial waves by a "hypothetical" beam splitter. These electron partial waves, then, follow the SL path in the clockwise and counterclockwise directions, respectively, so that they interfere with each other at the incident point, retaining the spin degree of freedom. We find that the backscattering probability of an incident electron can be largely modulated by varying the magnitude of the Rashba spin-orbit coupling constant alpha. We propose to make the proposed spin interferometry experiment using an artificial nanostructure fabricated in, for example, In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As quantum wells.

 

81.    S. M. Koo, A. Fujiwara, J. P. Han, E. M. Vogel, C. A. Richter, and J. E. Bonevich

            "High inversion current in silicon nanowire field effect transistors"

            Nano Letters 4 (11)2197-2201 (2004).

 

            ABSTRACT: Silicon nanowire (SiNW) field effect transistors (FETs) with channel widths down to 20 nm have been fabricated by a conventional "top-down" approach by using electron-beam lithography. The SiNW device shows higher inversion channel current density than the control devices. The extracted electron inversion mobility of the 20 nm width nanowire channel (approximate to1000 cm(2)/Ns) is found to be 2 times higher than that of the reference MOSFET (approximate to480 cm(2)Vs) of large dimension (W greater than or equal to 1 mum). We attribute this mobility increase to strain-induced changes in the band structure of the SiNW after oxidation.

 

82.    A. Kubovic, A. Denisenko, W. Ebert, M. Kasu, I. Kallfass, and E. Kohn

            "Electronic surface barrier characteristics of H-terminated and surface conductive diamond"

            Diamond And Related Materials 13 (4-8)755-760 (2004).

 

            ABSTRACT: Electronic properties of hydrogen terminated diamond have been investigated by comparing the DC and frequency-dependent characteristics of metal-diamond and liquid-diamond interfaces. For this purpose various electronic device structures including Surface Channel FETs and electrodes for investigation in the liquid are fabricated on single crystal diamond substrates with H-induced surface conductive channels. In both experimental configurations (metal and liquid junctions) it has been shown that the p-type H-induced conductive channel is separated from the diamond surface by a thin insulating layer (so-called 'lossy dielectric'). The measurements only allow a description of the surface layer with electrical parameters. An identification of its physical/ chemical nature needs still further analysis. (C) 2003 Elsevier B.V. All rights reserved.

 

83.    M. Kubovic, M. Kasu, I. Kallfass, M. Neuburger, A. Aleksov, G. Koley, M. G. Spencer, and E. Kohn

            "Microwave performance evaluation of diamond surface channel FETs"

            Diamond And Related Materials 13 (4-8)802-807 (2004).

 

            ABSTRACT: Diamond is expected to become an important semiconductor for high power and high frequency applications. Recent progress in fabrication technology has enabled DC, small signal RF, large signal RF and switching experiments on devices with short gatelength leading to the first comprehensive assessment of the performance capability of these devices. Using high-quality diamond buffer layers the highest cut-off frequencies for L-G = 0.2 mum namely f(T) = 24.6 GHz, f(max(MAG)) = 63 GHz and f(max)((U)) = 80 GHz could be extracted from small signal measurements near the pinch-off region. First noise measurements have resulted in a minimum noise figure F-min of approximately 1 dB at 3 GHz. Power measurement at I GHz indicate a saturated output power density of 0.35 W/mm, which is, however, limited by the on-wafer tuning range. (C) 2003 Elsevier B.V. All rights reserved.

 

84.    N. Kumada, D. Terasawa, M. Morino, K. Tagashira, A. Sawada, Z. F. Ezawa, K. Muraki, Y. Hirayama, and T. Saku

            "Phase diagrams of v=2 and v=(2)/(3) quantum Hall states in bilayer systems"

            Physical Review B 69 (15), 155319 (2004).

 

            ABSTRACT: We compare quantum Hall (QH) states at the Landau-level filling factor nu=2 and its composite-fermion (CF) counterpart, nu=2/3, in bilayer systems with various tunneling gaps. By changing the total electron density and the density difference between the two layers, we have made phase diagrams for nu=2 and nu=2/3. A one-particle picture provides a qualitative account of the phase diagrams. By quantitative analyses, we conclude that CF interactions exert strong influences on the fractional QH states as electron interactions do on the integer QH states. In addition, we investigate the temperature dependence of hysteresis observed at nu=2/3 and find that a metastable domain structure only occurs when the magnetic field is swept upward.

 

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

            "Effects of in-plane magnetic fields on spin transitions in bilayer quantum Hall states"

            Physica E-low-dimensional Systems & Nanostructures 22 (1-3)36-39 (2004).

 

            ABSTRACT: In a bilayer system, various phase transitions occur due to the competition among the cyclotron, Zeeman and tunneling energies. We investigate effects of an in-plane magnetic field B-parallel to, which couples subband and Landau levels with the same spin and modulate wave functions extended to both layers, on transitions of quantum Hall states in such a system. As B-parallel to is applied, we observe that crossings between opposite spin levels as well as those between the same spin levels disappear in characteristic sequences. While anticrossings of single-particle levels are sufficient to explain the observed behavior for crossings at nu = 4, the data at nu = 6 are not understood in a single-particle picture, and suggest Coulomb-induced mixing of different spin levels. (C) 2003 Elsevier B.V. All rights reserved.

 

86.    J. Kurian, and M. Naito

            "Low microwave surface resistance in NdBa2Cu3O7-delta films grown by molecular beam epitaxy"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 43 (11B)L1502-L1505 (2004).

 

            ABSTRACT: We report the growth of NdBa2Cu3O7-delta films on (100) MgO substrate by Molecular Beam Epitaxy (MBE). Large area NdBa2Cu3O7-delta films with homogeneous superconducting properties were grown by precise control of stoichiometry and the optimisation of growth parameters. The stoichiometric ratio of Nd:Ba:Cu close to 1:23 yields films with T-c of 94 K and J(c) values above 3.5 MA/cm(2) at 77 K on bare MgO substrate. The NdBa2Cu3O7-delta films grown under optimised conditions had excellent in-plane texture and good metallicity. The most significant characteristic of our MBE grown NdBa2Cu3O7-delta films is the very low microwave surface resistance values at all temperature range compared to its YBa2CU307-5 counterpart with typical value of similar to870 muOmega at 77K & 22GHz. Our results on the MBE grown NdBa2Cu3O7-delta films suggests that NdBa2Cu3O7-delta is a superior choice for the realisation of commercial microwave applications.

 

87.    J. Kurian, M. Naito, H. Sato, and K. Cho

            "Large area RE-123 thin films for microwave applications grown by molecular beam epitaxy"

            Physica C-superconductivity And Its Applications 412-141513-1518 (2004).

 

            ABSTRACT: Many microwave applications of high temperature superconductors require double-sided films on substrates with diameters larger than 2 inches. Although there are different techniques for the growth of fair quality superconductor films, there exists a need for further improvement in quality, uniformity, reproducibility and scalability in order to meet the commercial requirements for RF device applications. We have succeeded in growing high quality RE-123 (RE = Nd Dy, Eu) films by molecular beam epitaxy (MBE). In general, MBE growth of high temperature superconductor films requires strict compositional control and strong, yet controllable, oxidation. By optimizing the growth parameters, we have grown excellent quality RE-123 films on (100) MgO. Nd-123 films grown on MgO under optimized conditions gave a T-C(0) of 94 K with a room temperature resistivity of similar to200 muOmega cm and a J(C) of similar to3.5 MA/cm(2) at 77 K. The films had excellent metallicity and were in-plane aligned. The MBE grown RE-123 films were characterised by low microwave surface resistance values. Best R-S values of Nd-123 films on MgO were 890 muOmega at 77 K and below 100 muOmega at 20 K at 22 GHz. Microstrip bandpass filters fabricated using MBE grown Nd-123 films yielded higher IP3 values than the one made from commercially available Y-123 films indicating the better power handling capability of MBE grown Nd-123 films. (C) 2004 Elsevier B.V. All rights reserved.

 

88.    J. Kurian, and M. Naito

            "Growth of epitaxial CeO2 thin films on r-cut sapphire by molecular beam epitaxy"

            Physica C-superconductivity And Its Applications 402 (1-2)31-37 (2004).

 

            ABSTRACT: Epitaxial (00l) CeO2 films were grown on r-cut sapphire by molecular beam epitaxy. The CeO2 films grown on as supplied r-Al2O3 substrate constituted of (111) oriented CeO2 films. We have found that annealing of r-Al2O3 substrates at 1050 degreesC for 10 h dramatically enhances the epitaxial growth of (00l) oriented CeO2 films on r-Al2O3 substrate. The use of RF activated oxygen source for oxidation during growth further enhances the growth of (001) oriented CeO2 films on r-Al2O3. High quality epitaxial (00l) oriented CeO2 films can be grown on annealed r-Al2O3 substrates by employing lower deposition rate (<1 Angstrom/s) and substrate temperatures above 650 degreesC either from Ce metal or CeO2 ceramic sources. The CeO2 films were characterized by 2theta-theta, omega-scan and phi-scan measurements. The CeO2 films grown on annealed r-Al2O3 substrates showed high crystallinity with rocking curve width of 0.07degrees for (002) reflection of CeO2 and had excellent in-plane epitaxy. These CeO2 films can be used as buffer layers for the growth of high quality high temperature superconductor films on sapphire substrates. (C) 2003 Elsevier B.V. All rights reserved.

 

89.    J. Lagoute, K. Kanisawa, and S. Folsch

            "Manipulation and adsorption-site mapping of single pentacene molecules on Cu(111)"

            Physical Review B 70 (24), 245415 (2004).

 

            ABSTRACT: Low-temperature scanning tunneling microscopy at 7 K is used to study the adsorption and manipulation of single pentacene molecules on Cu(111). Controlled lateral translations of the molecule are performed along different high-symmetry directions of the substrate via attractive tip-molecule interactions. By means of a detailed site-mapping technique combining lateral manipulations of the molecule and of native substrate adatoms we determine the adsorptive configuration of the aromatic molecule. We find a planar adsorption geometry with the long molecular axis aligned with the close-packed Cu atom rows and the benzene units centered over hexagonal close-packed hollow sites of the substrate.

 

90.    J. Lefebvre, P. Finnie, and Y. Homma

            "Temperature-dependent photoluminescence from single-walled carbon nanotubes"

            Physical Review B 70 (4), 045419 (2004).

 

            ABSTRACT: Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy of pillar-suspended single-walled carbon nanotubes has been measured for temperatures between 300 and 5 K. The atmospheric environment strongly affects the low-temperature luminescence. The PL intensity is quenched at temperatures below similar to40 K for nanotubes in high vacuum, while nanotubes in helium ambient remain luminescent. The PL peak emission energy is only very weakly dependent on temperature, with a species-dependent blueshift upon cooling corresponding to a relative shift in bandgap of -3x10(-5) K-1 or less. The integrated peak intensities change by only a factor of 2, with linewidths showing a moderate temperature dependence. In PLE, the second absorption peak energy (E-22) is also only weakly temperature dependent, with no significant shift and a limited reduction in linewidth upon cooling to 20 K. In addition to the previously assigned nanotube PL peaks seen at room temperature, at least two distinct new classes of PL peaks are observed at cryogenic temperatures.

 

91.    J. Lefebvre, J. M. Fraser, Y. Homma, and P. Finnie

            "Photoluminescence from single-walled carbon nanotubes: a comparison between suspended and micelle-encapsulated nanotubes"

            Applied Physics A-materials Science & Processing 78 (8)1107-1110 (2004).

 

            ABSTRACT: Single-walled carbon nanotubes (SWNTs) are luminescent. Up to now, two preparation methods, both of which isolate individual SWNTs, have enabled the detection of nanotube bandgap photoluminescence (PL): encapsulation of individual SWNTs into surfactant micelles and direct growth of individual SWNTs suspended in air between pillars. This paper compares the PL obtained from suspended SWNTs to published PL data obtained from encapsulated SWNTs. We find that emission peaks are blueshifted by 28 meV on average for the suspended nanotubes as compared to the encapsulated nanotubes. Similarly, the resonant absorption peaks at the second set of van Hove singularities are blueshifted on average by 16 meV. Both shifts depend weakly on the particular chirality and diameter of the SWNT.

 

92.    J. Lefebvre, J. M. Fraser, P. Finnie, and Y. Homma

            "Photoluminescence from an individual single-walled carbon nanotube"

            Physical Review B 69 (7), 075403 (2004).

 

            ABSTRACT: Photoluminescence (PL) and photoluminescence excitation (PLE) spectra are obtained from individual single-walled carbon nanotubes (SWNTs). Individual SWNT spectra are compared with spectra from ensembles. The PL spectrum of an individual SWNT in air at room temperature has a single asymmetric peak of width typically 10 to 15 meV, with no detected background. Both absorption and emission are strongly polarized along the tube axis. Photoluminescence excitation spectroscopy on single SWNTs clearly confirms the unique, one-to-one association of optical absorption resonances with individual emission peaks. Resonances in the PLE spectra are typically approximate to30 meV wide, with the PL intensity enhanced tenfold over nonresonant excitation. Whether for emission or absorption, the peak shape and peak width are almost the same for a single nanotube as they are for the corresponding species in a large ensemble. That is, there is no significant inhomogeneous broadening. While ensemble measurements are complicated by the superposition of many PL peaks from many different species, single nanotube spectra clearly isolate a single peak and are thus simpler to interpret.

 

93.    F. Lin, K. Sumitomo, Y. Homma, and T. Ogino

            "STM observations of three-dimensional Ge islands on Si(111) surfaces with different step orientations and step-bunching conditions"

            Surface Science 562 (1-3)15-21 (2004).

 

            ABSTRACT: Ge growth on stepped Si(111) surfaces misoriented toward <(1) over bar(1) over bar2>, <1 (1) over bar0> and <11 (2) over bar > was investigated with a scanning tunneling microscope (STM) on the same Si(111) substrate, where these different steps exist around the sidewall of a hole fabricated photolithographically. After high temperature (1200 degreesC) annealing for several minutes, the steps on the sidewall of a hole exhibit the threefold symmetry, which consists of debunching <(1) over bar(1) over bar2>-type steps and heavy bunching <1 (1) over bar0> and <11 (2) over bar >-type steps. After Ge deposition of up to three bilayers of Ge at 400 degreesC, the distribution of three-dimensional (3D) islands becomes selectable on the three types of stepped surfaces. The step-flow growth in the step band region decreases the critical thickness of the transition from two-dimensional to three-dimensional growth. The surface energy at the step bunch and Ge islands become more important than the strain energy, and selective growth of Ge islands is realized. (C) 2004 Elsevier B.V. All rights reserved.

 

94.    Y. Lin, J. Nitta, T. Koga, and T. Akazaki

            "Electron g factor in a gated InGaAs channel with double InAs-inserted wells"

            Physica E-low-dimensional Systems & Nanostructures 21 (2-4)656-660 (2004).

 

            ABSTRACT: We report the gate-voltage dependence of the electron g factor in InGaAs/InAlAs heterostructures with double InAs-inserted wells. The 9 factor has been determined from a series of Shubnikov-de Haas oscillations at various angles with respect to the layers under different gate voltages. The strain in InAs layers and the penetration of the electron wave function into InGaAs and InAlAs layers are the important factors of the reduction in the \g\ factor. We have also observed the changes of the \g\ factor with respect to the gate voltage, though this dependence is not clear in the simple calculation. (C) 2003 Elsevier B.V. All rights reserved.

 

95.    Y. X. Liu, S. K. Ozdemir, A. Miranowicz, and N. Imoto

            "Kraus representation of a damped harmonic oscillator and its application"

            Physical Review A 70 (4), 042308 (2004).

 

            ABSTRACT: By definition, the Kraus representation of a harmonic oscillator suffering from the environment effect, modeled as the amplitude damping or the phase damping, is directly given by a simple operator algebra solution. As examples and applications, we first give a Kraus representation of a single qubit whose computational basis states are defined as bosonic vacuum and single particle number states. We further discuss the environment effect on qubits whose computational basis states are defined as the bosonic odd and even coherent states. The environment effects on entangled qubits defined by two different kinds of computational basis are compared with the use of fidelity.

 

96.    Y. X. Liu, A. K. Ozdemir, A. Miranowicz, M. Koashi, and N. Imoto

            "Exciton entanglement in two coupled semiconductor microcrystallites"

            Journal Of Physics A-mathematical And General 37 (15)4423-4436 (2004).

 

            ABSTRACT: Entanglement of the excitonic states in the system of two coupled semiconductor microcrystallites, whose sizes are much larger than the Bohr radius of the exciton in the bulk semiconductor but smaller than the relevant optical wavelength, is quantified in terms of the entropy of entanglement. It is observed that the nonlinear interaction between excitons increases the maximum values of the entropy of entanglement more than that of the linear coupling model. Therefore, a system of two coupled microcrystallites can be used as a good source of entanglement with fixed exciton number. The relationship between the entropy of entanglement and the population imbalance of two microcrystallites is numerically shown and the uppermost envelope function for them is estimated by applying the Jaynes principle.

 

97.    F. Maeda, and Y. Watanabe

            "Time-resolved core-level photoelectron spectroscopy and reflection high-energy electron diffraction study of surface phase transition on GaAs(001)"

            Applied Surface Science 237 (1-4)224-229 (2004).

 

            ABSTRACT: The surface phase transition on GaAs(0 0 1) was investigated in real time by core-level photoelectron spectroscopy and reflection high-energy electron diffraction (RHEED). The time dependence of the relative surface band bending was obtained from the deconvolution of core-level photoelectron spectra. We found that band bending on the 4 x 2 surface increases 0.06 eV from that of the 2 x 4 surface and that the time dependence of relative surface band bending is in good agreement with that of core-level photoelectron intensities but not with the RHEED intensities. This indicates that the long-range ordering of surface superstructures and microscopic surface morphology does not influence surface band bending, whereas the termination atoms, As or Ga, does. (C) 2004 Elsevier B.V. All rights reserved.

 

98.    F. Maeda, E. Laffosse, Y. Watanabe, S. Suzuki, Y. Homma, M. Suzuki, T. Kitada, T. Ogiwara, A. Tanaka, M. Kimura, V. A. Mihai, H. Yoshikawa, and S. Fukushima

            "Surface and interface reactions of catalysts for carbon nanotube growth on Si substrates studied by soft X-ray photoelectron spectroscopy"

            Physica E-low-dimensional Systems & Nanostructures 24 (1-2)19-25 (2004).

 

            ABSTRACT: The substrate temperature dependence of the chemical state of Si substrate surface and metal catalysts for the growth of carbon nanotubes (CNTs), Co and Fe, and their morphology were investigated using soft X-ray photoelectron spectroscopy. We found that the temperature at which the chemical states of Co changes depends on the initial thickness of the underlying SiO2 layer. In the case of Fe thin film on a thin SiO2 layer, temperatures of transformation to metal and silicides are higher than those for the Co layer. In addition, Co silicides coexist with the SiO2 layer on the Si substrate at the substrate temperature of 590degreesC, but Fe silicides do not. These results indicate that, in the case of CNT growth by chemical vapor deposition, we have to contrive different ways to control the chemical states of metal catalysts for different substrate surfaces and metal catalysts. (C) 2004 Elsevier B.V. All rights reserved.

 

99.    F. Maeda, and Y. Watanabe

            "Real-time analysis of a surface phase transition of GaAs(001) by core-level photoelectron spectroscopy and photoelectron diffraction"

            Journal Of Electron Spectroscopy And Related Phenomena 137-40107-112 (2004).

 

            ABSTRACT: The surface phase transition of GaAs (0 0 1) from the As-rich 2 x 4 surface to the Ga-rich 4 x 2 surface and the reverse transition were analyzed in real-time using time-resolved core-level photoelectron spectroscopy incorporating the photoelectron diffraction effect. From the analysis of the time dependence of core-level photoelectron intensities and spectra, we found a large anisotropy in the intensities and spectra caused by the photoelectron diffraction effect. This anisotropy in the intermediate state of the transition from the 2 x 4 to the 4 x 2 differs from that of the reverse transition, indicating that the surface phase transition pathways differ. (C) 2004 Elsevier B.V. All rights reserved.

 

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

            "Extrinsic base regrowth of p-InGaN for Npn-type GaN/InGaN heterojunction bipolar transistors"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 43 (4B)1922-1924 (2004).

 

            ABSTRACT: The regrowth of p-InGaN as the extrinsic base layer of Npn-type GaN/InGaN heterojunction bipolar transistors (HBTs) significantly improves the ohmic characteristics of the base layer. The specific contact resistance is 7.8 x 10(-4) Omega(.)cm(2) even after the dry etching. This value for a non-alloyed ohmic contact is much better than that for as-grown p-GaN (1.7 x 10(-3) Omega(.)cm(2)) and decreased turn-on voltage in the emitter-base diodes, which results in high current gains of up to 2000 and reduced offset voltages in the GaN/InGaN HBTs. These results show that the p-InGaN extrinsic base regrowth is an effective way to improve nitride HBT characteristics.

 

101.    T. Makimoto, Y. Yamauchi, and K. Kumakura

            "High-power characteristics of GaN/InGaN double heterojunction bipolar transistors"

            Applied Physics Letters 84 (11)1964-1966 (2004).

 

            ABSTRACT: High-power characteristics have been investigated for GaN/InGaN double heterojunction bipolar transistors (HBTs) on SiC substrates. A base-collector diode showed a high breakdown voltage exceeding 50 V, which is ascribed to a wide band gap of a GaN collector. The maximum collector current is proportional to the emitter size in the emitter-size ranging from 1.5x10(-5) to 1.4x10(-4) cm(2). The corresponding maximum collector current density is as high as 6.7 kA/cm(2), indicating the high current density characteristics of bipolar transistors. A 50 mumx30 mum device operated up to a collector-emitter voltage of 50 V and a collector current of 80 mA in its common-emitter current-voltage characteristics at room temperature. The corresponding power density is as high as 270 kW/cm(2), showing that nitride HBTs are promising for high-power electronic devices in terms of both the material and the device structure. (C) 2004 American Institute of Physics.

 

102.    H. Matsui, T. Sato, T. Takahashi, S. C. Wang, H. B. Yang, H. Ding, T. Fujii, T. Watanabe, and A. Matsuda

            "Spectral evidence for Bogoliubov quasiparticle in triple-layered high-T-c superconductor Bi2Sr2Ca2Cu3O10"

            Physica C-superconductivity And Its Applications 408-10814-815 (2004).

 

            ABSTRACT: The superconducting quasiparticle predicted by BCS theory is investigated in a triple-layered high-T-c cuprate Bi2Sr2Ca2Cu3O10+delta, by angle-resolved photoemission spectroscopy (ARPES). We have succeeded in observing the quasiparticle dispersion below and above the Fermi level, and performed a quantitative analysis based on BCS theory. The excellent agreement in the energy dispersion and the coherence factors between the ARPES experiment and BCS theory indicates the basic validity of BCS formalism in describing the superconducting state of cuprates. (C) 2004 Elsevier B.V. All rights reserved.

 

103.    T. Matsuoka, H. Okamoto, H. Takahata, T. Mitate, S. Mizuno, Y. Uchiyama, and T. Makimoto

            "MOVPE growth and photoluminescence of wurtzite InN"

            Journal Of Crystal Growth 269 (1)139-144 (2004).

 

            ABSTRACT: The crystallographic relationship between InN and its interfaces with GaN and sapphire was investigated using selected area diffraction patterns obtained with a transmission electron microscope, and was confirmed using X-ray diffraction pole figures. The lattice of InN grown on a GaN template corresponded to that of the GaN in the c-plane, while that of InN grown directly on sapphire was rotated with respect to the sapphire by 30degrees. The polarity of InN was investigated using convergent-beam electron diffraction. The InN had the same N-polarity along the growth direction as that reported for Molecular beam epitaxy growth. The growth conditions for high-quality InN with photoluminescence (PL) at room temperature, and no metal indium inclusions are described. The dependence of PL characteristics on the growth conditions was investigated. The PL peak was observed to shift to higher energies as the growth temperature rose. However, it is noteworthy that hardly any PL peak shift was observed with the measurement temperature. From the data reported up to now, uncooled and high-power operation laser diodes for optical communications systems can be expected. (C) 2004 Elsevier B.V. All rights reserved.

 

104.    F. E. Meijer, A. F. Morpurgo, T. M. Klapwijk, T. Koga, and J. Nitta

            "Competition between spin-orbit interaction and Zeeman coupling in Rashba two-dimensional electron gases"

            Physical Review B 70 (20), 210307 (2004).

 

            ABSTRACT: We systematically investigate how the interplay between the Rashba spin-orbit interaction and Zeeman coupling affects the electron transport and the spin dynamics in InGaAs-based 2D electron gases. From the quantitative analysis of the magnetoconductance, measured in the presence of an in-plane magnetic field, we conclude that this interplay results in a spin-induced breaking of time reversal symmetry and in an enhancement of the spin relaxation time. Both effects are due to a partial alignment of the electron spin along the applied magnetic field, and are found to be in excellent agreement with recent theoretical predictions.

 

105.    F. E. Meijer, J. Nitta, T. Koga, A. F. Morpurgo, and T. M. Klapwijk

            "Experiments on Aharonov-Bohm conductance oscillations: a statistical analysis of the averaged Fourier spectrum"

            Physica E-low-dimensional Systems & Nanostructures 22 (1-3)402-405 (2004).

 

            ABSTRACT: We study the shape of the Fourier spectrum of Aharonov-Bohm conductance oscillations measured in a 2D ring in the presence of Rashba spin-orbit interaction. As expected, the shape of the Fourier spectrum of any single measurement is dominated by sample specific effects. This impedes the observation of possible effects due to the electron spin. We show in detail how the analysis of the ensemble averaged Fourier spectrum permits to reduce sample specific features and bow to quantify this reduction in a well-defined statistical way. We find that in the averaged Fourier spectrum a structure appears which is not due to sample specific effects. (C) 2003 Elsevier B.V. All rights reserved.

 

106.    F. E. Meijer, A. F. Morpurgo, T. M. Klapwijk, T. Koga, and J. Nitta

            "Statistical significance of the fine structure in the frequency spectrum of Aharonov-Bohm conductance oscillations"

            Physical Review B 69 (3), 035308 (2004).

 

            ABSTRACT: We discuss a statistical analysis of Aharonov-Bohm conductance oscillations measured in a two-dimensional ring, in the presence of Rashba spin-orbit interaction. Measurements performed at different values of gate voltage are used to calculate the ensemble-averaged modulus of the Fourier spectrum and, at each frequency, the standard deviation associated to the average. This allows us to prove the statistical significance of a splitting that we observe in the h/e peak of the averaged spectrum. Our work illustrates in detail the role of sample specific effects on the frequency spectrum of Aharonov-Bohm conductance oscillations and it demonstrates how fine structures of a different physical origin can be discriminated from sample specific features.

 

107.    F. Morikoshi, M. F. Santos, and V. Vedral

            "Accessibility of physical states and non-uniqueness of entanglement measure"

            Journal Of Physics A-mathematical And General 37 (22)5887-5893 (2004).

 

            ABSTRACT: Ordering physical states is the key to quantifying some physical property of the states uniquely. Bipartite pure entangled states are totally ordered under local operations and classical communication (LOCC) in the asymptotic limit and uniquely quantified by the well-known entropy of entanglement. However, we show that mixed entangled states are partially ordered under LOCC even in the asymptotic limit. Therefore, non-uniqueness of entanglement measure is understood on the basis of an operational notion of asymptotic convertibility.

 

108.    T. Mukai, and M. Yamashita

            "Efficient rapid production of a Bose-Einstein condensate by overcoming serious three-body loss"

            Physical Review A 70 (1), 013615 (2004).

 

            ABSTRACT: We report the efficient production of a large Bose-Einstein condensate in Rb-87 atoms. This is achieved by quickly reducing the radio frequency of the magnetic field at a rate of -96.8 kHz/s during the final stage of evaporative cooling, and we have produced a condensate with (2.2+/-0.1)x10(6) atoms against a serious three-body recombination loss. We observed the dependence of the cooling efficiency on the rate at which the truncated energy changes by measuring the condensate growth for three kinds of radio-frequency sweep. The experimental results quantitatively agree with calculations based on the quantum kinetic theory of a Bose gas.

 

109.    K. Muraki, J. G. Lok, S. Kraus, W. Dietsche, K. von Klitzing, D. Schuh, M. Bichler, and W. Wegscheider

            "Coulomb drag as a probe of the nature of compressible states in a magnetic field"

            Physical Review Letters 92 (24), 246801 (2004).

 

            ABSTRACT: Magnetodrag reveals the nature of compressible states and the underlying interplay of disorder and interactions. At nu=3/2 clear T-4/3 dependence is observed, which signifies the metallic nature of the N=0 Landau level. In contrast, drag in higher Landau levels reveals an additional contribution, which anomalously grows with decreasing T before turning to zero following a thermal activation law. The anomalous drag is discussed in terms of electron-hole asymmetry arising from disorder and localization, and the crossover to normal drag at high fields as due to screening of disorder.

 

110.    M. Nagase, and H. Namatsu

            "A method for assembling nano-electromechanical devices on microcantilevers using focused ion beam technology"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 43 (7B)4624-4628 (2004).

 

            ABSTRACT: We propose a new method for assembling nano-electromechanical devices using focused ion beam (FIB) technology. After milling the area surrounding a device (30 mum x 10 mum), a small chip containing nano-four-point probes with 60-nm-pitch Si electrodes was picked up by a microprobe and transferred to a scanning probe microscopy (SPM) microcantilever with four aluminum electrodes. Interconnections by tungsten (W) lines between the Si electrodes of the nanodevice and the Al electrodes of the cantilever were formed by FIB-induced gas deposition. The connection of FIB-W lines was confirmed by biased scanning electron microscopy (SEM). We successfully demonstrated a nano-four-point probe system on an SPM cantilever.

 

111.    M. Naito, and K. Ueda

            "MgB2 thin films for superconducting electronics"

            Superconductor Science & Technology 17 (7)R1-R18 (2004).

 

            ABSTRACT: This review article describes the developments over the last 30 months in the thin film growth and junction fabrication of superconducting MgB2, including a brief summary of the chemistry and physics of MgB2. The most serious problem is the high Mg vapour pressure required for the phase stability. This problem makes in situ film growth difficult. So, most of the initial efforts were performed by two-step growth, namely ex situ post-annealing. Later, in situ physical vapour deposition and recently in situ chemical vapour deposition were reported. Each growth method is described in detail and compared. The past efforts at fabricating MgB2 junctions are summarized, and the future prospects for MgB2 superconducting electronics are briefly described.

 

112.    K. Nakamatsu, K. Watanabe, K. Tone, T. Katase, W. Hattori, Y. Ochiai, T. Matsuo, M. Sasago, H. Namatsu, M. Komuro, and S. Matsui

            "Bilayer resist method for room-temperature nanoimprint lithography"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 43 (6B)4050-4053 (2004).

 

            ABSTRACT: A compact nanoimprint lithography (NIL) apparatus using the driving power of a servomotor has been newly developed. A bilayer resist method using hydrogen silsequioxane (HSQ) as a top layer and AZ photoresist as a bottom layer has been proposed to achieve high-aspect resist patterns on a nonflat surface for room-temperature nanoimprint lithography (RT-NIL). The etching rate ratio of HSQ to AZ photoresist was higher than 100 for O-2 reactive ion etching (RIE), indicating that the HSQ top layer has sufficient etching tolerance. We have achieved the high-aspect nanostructure patterns of 100-nm-linewidth and 1-mum-height using the NIL apparatus developed here.

 

113.    A. Nakamura, J. Ishihara, S. Shigemori, K. Yamamoto, T. Aoki, H. Gotoh, and J. Temmyo

            "Characterization of wurtzite Zn1-xCdxO films using remote plasma-enhanced metalorganic chemical vapor deposition"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 43 (11A)L1452-L1454 (2004).

 

            ABSTRACT: The optical properties of wurtzite Zn1-xCdxO films were investigated. The films were grown on (1120) a-plane sapphire substrates by remote plasma enhanced metalorganic chemical vapor deposition (RPE-MOCVD) and a characterized by X-ray diffraction, photoluminescence (PL), ultraviolet/visible/near-infrared (UV/VIS/NIR) optical transmission spectroscopy and Hall measurement. The content ratio of the films was controlled by changing the molar ratio of diethyl zinc (DEZn) to dimethyl cadmium (DMCd). The optical band gap of the films at nearly 3.28 eV was shifted by alloying with Cd down to 1.85 eV depending on the alloy composition. The evolution of the PL lineshape was studied as a function of temperature. The activation energy of the films calculated from the variation of the PL peak intensity was as large as the binding energy of ZnO. In addition, the films showed a large Stokes shift at room temperature, which is discussed in terms of the localization of excitons in a ternary alloy.

 

114.    H. Nakano, A. A. Andreev, and J. Limpouch

            "Femtosecond X-ray line emission from multilayer targets irradiated by short laser pulses"

            Applied Physics B-lasers And Optics 79 (4)469-476 (2004).

 

            ABSTRACT: The invention of high-power, ultra-short-pulse lasers has opened the way to investigations aimed at the creation of a new type of bright X-ray source for various uses including material science applications and time-resolved X-ray diffraction for biology. The efficiency with which laser energy incident on a solid target is converted into an X-ray emission depends on many factors, including the temporal profile of the laser pulse. Here we report the results of our theoretical and experimental investigations of the line X-ray emission from layered solid targets irradiated by ultra-short laser pulses. The laser prepulse parameters and target thickness are optimized to convert the maximum laser energy into an emission in the selected X-ray line. Multilayer foils are proposed to increase the energy of the K-alpha-line emission from laser plasma while simultaneously keeping the X-ray pulse duration at a hundred femtoseconds. The emission is studied both experimentally and theoretically by means of an analytical model and numerical simulations.

 

115.    H. Namatsu

            "The impact of supercritical fluoro-compounds on lithography use"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 43 (4A)L456-L459 (2004).

 

            ABSTRACT: This article describes the use of supercritical fluoro-compounds for supercritical resist drying. In contrast to carbon dioxide, fluoro-compounds, which are heavier than water in liquid form, can displace the rinse water on the resist due to the difference in specific gravity. The removal of rinse water from a sample surface by replacing it with a liquid fluoro-compound, followed by the conversion of the compound to the supercritical state, enables patterns to be formed without collapse and without the use of a surfactant. Furthermore, with the, help of helium, which can be released quickly from the chamber, the use of supercritical fluoro-compounds like C2HF5 and SF6 also enable the very fast supercritical resist drying of water-rinsed resists for advanced lithography.

 

116.    Y. Narumi, K. Kindo, M. Hagiwara, H. Nakano, A. Kawaguchi, K. Okunishi, and M. Kohno

            "High-field magnetization of S=1 antiferromagnetic bond-alternating chain compounds"

            Physical Review B 69 (17), 174405 (2004).

 

            ABSTRACT: High-field magnetization and susceptibility measurements have been performed on S=1 antiferromagnetic bond-alternating chain compounds: [Ni-2(dpt)(2)(mu-ox)(mu-N-3)](PF6) [dpt=bis(3-aminopropyl)amine, ox= C2O4] (abbreviated as NDOAP) and [Ni(333-tet)(mu-NO2)]ClO4 [333-tet=N,N-'-bis(3-aminopropyl)-1,3propanediamine] (abbreviated as NTENP). The magnetization of NDOAP shows two steep increases at about 200 and 500 kOe. A magnetization plateau is observed between about 300 and 500 kOe, corresponding to half the value of the saturation moment. Comparison between numerical calculations and the experimental results, including the magnetic susceptibility, shows that NDOAP has a singlet ground state due to dimerization with a bond-alternating ratio alpha=0.1. The half-saturation plateau is also observed around 700 kOe in the magnetization of NTENP. The magnetization process of NTENP is well reproduced by the numerical result calculated for the parameter of alpha=0.45 in the singlet-dimer phase. The alpha dependence of the magnetization processes is discussed.

 

117.    T. Nishida, T. Makimoto, H. Saito, and T. Ban

            "AlGaN-based ultraviolet light-emitting diodes grown on bulk AlN substrates"

            Applied Physics Letters 84 (6)1002-1003 (2004).

 

            ABSTRACT: We have confirmed the potential of a bulk AlN substrate for high current operation of nitride ultraviolet-light-emitting diodes (UV-LEDs). For the high flux UV extraction from nitride UV-LEDs, transparency and high thermal conductivity of the substrates are important issues. The bulk AlN is one of the best candidates, because it satisfies requirements above, and has the same crytallographic symmetry with those of AlGa(In)N families, which is beneficial to the high-quality crystal growth of the nitride device structures. We formed AlGaN-based UV-LEDs on a bulk AlN substrate and compared its performance with that of a reference device grown on an AlN-template grown on a sapphire substrate. The output power linearly increases with a saturation injection current of 300 mA, which is two times higher than that of the reference device. The emission spectrum under high current injection is much more stable than that of conventional substrate. (C) 2004 American Institute of Physics.

 

118.    K. Nishiguchi, H. Inokawa, Y. Ono, A. Fujiwara, and Y. Takahashi

            "Multifunctional Boolean logic using single-electron transistors"

            Ieice Transactions On Electronics E87C (11)1809-1817 (2004).

 

            ABSTRACT: A multifunctional Boolean logic circuit composed of single-electron transistors (SETs) was fabricated and its operation demonstrated. The functions of Boolean logic can be changed by the half-period phase shift of the Coulomb-blockade (CB) oscillation of some SETs in the circuit, and an automatic control based on a feedback process is used to attain an exact shift. The amount of charges in the memory node (MN), which is capacitively coupled to the SET, controls the phase of the CB oscillation, and the output signal of the SET controls the amount of charge in the MN during the feedback process. This feedback process automatically adjusts SET output characteristics in such a way that it is used for the multifunctional Boolean logic. We experimentally demonstrated the automatic phase control and examined the speed of the feedback process by SPICE circuit simulation combined with a compact analytical SET model. The simulation revealed that programming time could be of the order of a few ten nanoseconds, thereby promising high-speed switching of the functions of the multifunctional Boolean logic circuit.

 

119.    K. Nishiguchi, H. Inokawa, Y. Ono, A. Fujiwara, and Y. Takahashi

            "Multilevel memory using an electrically formed single-electron box"

            Applied Physics Letters 85 (7)1277-1279 (2004).

 

            ABSTRACT: A multilevel dynamic random-access memory using a single-electron box (SEB) and single-electron transistor (SET) is fabricated on a silicon-on-insulator substrate. A one-dimensional field-effect transistor (FET), which is connected to the SEB, modulates a barrier potential to precisely control the number of electrons one by one in the SEB by means of the Coulomb-blockade phenomenon. At room temperature and 26 K, we demonstrate a multilevel memory, in which each interval between the levels is given by a single electron, by using the SET electrometer coupled capacitively to the SEB. The control of stored electrons by the FET assures long-retention time and high-speed write/erase operation. (C) 2004 American Institute of Physics.

 

120.    K. Nishiguchi, H. Inokawa, Y. Ono, A. Fujiwara, and Y. Takahashi

            "Multilevel memory using single-electron turnstile"

            Electronics Letters 40 (4)229-230 (2004).

 

            ABSTRACT: A multilevel single-electron memory has been successfully demonstrated. Two fine gates with phase-shifted pulse voltages modulate potential barriers in a one-dimensional Si channel to transfer electrons one by one into a memory node, and the number of electrons in the node is sensed by a single-electron transistor.

 

121.    K. Nishiguchi, H. Inokawa, Y. Ono, A. Fujiwara, and Y. Takahashi

            "Automatic control of oscillation phase of a single-electron transistor"

            Ieee Electron Device Letters 25 (1)31-33 (2004).

 

            ABSTRACT: Automatic phase control of the Coulomb-blockade (CB) oscillation of a single-electron transistor (SET) is proposed and experimentally demonstrated. Charges in the memory node (MN) capacitively coupled to the SET control the phase of the CB oscillation. The output signal of the SET can controls chares in the MN. This feedback mechanism automatically adjusts the amount of charges, so that the output signal is leveled with a requested one for arbitrary input signal of the SET. The electrical phase control realizes the demonstration of a multifunctional Boolean logic.

 

122.    T. Nishikawa, H. Nakano, K. Oguri, N. Uesugi, K. Nishio, and H. Masuda

            "Nanohole-array size dependence of soft x-ray generation enhancement from femtosecond-laser-produced plasma"

            Journal Of Applied Physics 96 (12)7537-7543 (2004).

 

            ABSTRACT: Nanostructured targets are very attractive for enhancing the intensity of x-ray pulses generated from laser-produced-plasma. In order to clarify the enhancement mechanism, the nanohole-array size dependence of the characteristics of soft x-ray pulse generation from femtosecond-laser-produced plasma was investigated in detail. We found that the highest x-ray intensity can be obtained and the x-ray pulse duration kept relatively short with a nanohole-array alumina target with a 500 nm hole interval and a 450 nm hole diameter. A 40-fold soft x-ray fluence enhancement and a nine-fold soft x-ray pulse peak intensity enhancement can be obtained. The relatively short x-ray pulse duration of 19 ps can be maintained because the target structure has high local density and nanometer-sized spaces. Similar enhancement effects can be expected by using a nanostructured target with wall thickness of less than 100 nm, space size of around a few 100 nm, and nanostructure depth larger than 20 mum. (C) 2004 American Institute of Physics.

 

123.    T. Nishikawa, S. Suzuki, Y. Watanabe, O. Zhou, and H. Nakano

            "Efficient water-window X-ray pulse generation from femtosecond-laser-produced plasma by using a carbon nanotube target"

            Applied Physics B-lasers And Optics 78 (7-8)885-890 (2004).

 

            ABSTRACT: We adopt a multiwalled carbon nanotube target to increase the efficiency of water-window and K-alpha X-ray pulse conversion from femtosecond-laser-produced plasma. The diameter of the carbon nanotubes is around 30 nm and the length is about 12-mum. The X-ray fluence enhancement in the water-window region is sevenfold compared with a conventional carbon plate target. Further enhancement can be expected by optimizing the size of the carbon nanotubes. Soft X-ray pulse duration is 26 ps. It is also found that the K-alpha X-ray line emission from the Si substrate of the carbon nanotube target was enhanced. This result indicates that by covering various solid materials with carbon nanotubes, enhanced short K-alpha X-ray pulses with the corresponding wavelength can be obtained. These results show that carbon nanotubes are very attractive as a target for femtosecond laser-produced-plasma X-ray sources in single-shot X-ray microscopy and time-resolved X-ray diffraction.

 

124.    J. Nitta, Y. P. Lin, T. Koga, and T. Akazaki

            "Electron g-factor in a gated InAs-inserted-channel In0.53Ga0.47As/In0.52Al0.48As heterostructure"

            Physica E-low-dimensional Systems & Nanostructures 20 (3-4)429-432 (2004).

 

            ABSTRACT: We report on electron g-factor in an InAs-inserted In0.53Ga0.47As/In0.52Al0.48As heterostructure. The gate voltage dependence of g-factor is obtained from the coincidence method. The obtained g-factor values are surprisingly smaller than the g-factor value of bulk InAs, and it is close to the bare g-factor value of In0.53Ga0.47As. The large change in g-factor is observed by applying the gate voltage. The obtained gate voltage dependence is not simply explained by the energy dependence of g-factor. (C) 2003 Elsevier B.V. All rights reserved.

 

125.    M. Notomi, A. Shinya, S. Mitsugi, E. Kuramochi, and H. Y. Ryu

            "Waveguides, resonators and their coupled elements in photonic crystal slabs"

            Optics Express 12 (8)1551-1561 (2004).

 

            ABSTRACT: The design, fabrication, and measurement of photonic-band-gap (PBG) waveguides, resonators and their coupled elements in two-dimensional photonic crystal (PhC) slabs have been investigated. We have studied various loss mechanisms in PBG waveguides and have achieved a very low propagation loss (similar to1 dB/mm). For these waveguides, we have observed a large group delay (>100 ps) by time-domain measurement. As regards PBG resonators, we realize very high-Q and small volume resonators in PhC slabs by appropriate design. Finally, we demonstrate various forms of coupled elements of waveguides and resonators: 2-port resonant-tunneling transmission devices, 4-port channel-drop devices using the slow light mode, and 3-port channel-drop devices using the resonant-tunneling process. (C) 2004 Optical Society of America.

 

126.    M. Notomi, H. Suzuki, T. Tamamura, and K. Edagawa

            "Lasing action due to the two-dimensional quasiperiodicity of photonic quasicrystals with a Penrose lattice"

            Physical Review Letters 92 (12), 123906 (2004).

 

            ABSTRACT: We have fabricated photonic quasicrystal lasers with a Penrose lattice that does not possess translational symmetry but has long-range order, and observed coherent lasing action due to the optical feedback from quasiperiodicity, exhibiting a variety of 10-fold-symmetric lasing spot patterns. The lattice constant dependence of lasing frequencies and spot patterns show complicated features very different from photonic crystal/random lasers, and we have quantitatively explained them by considering their reciprocal lattice. Unique diversity of their reciprocal lattice opens up new possibilities for the form of lasers.

 

127.    M. Notomi, A. Shinya, E. Kuramochi, S. Mitsugi, H. Y. Ryu, T. Kawabata, T. Tsuchizawa, T. Watanabe, T. Shoji, and K. Yamada

            "Photonic-band-gap waveguides and resonators in SOI photonic crystal slabs"

            Ieice Transactions On Electronics E87C (3)398-408 (2004).

 

            ABSTRACT: The design, fabrication, and measurement of photonic-band-gap (PBG) waveguides and resonators in two-dimensional photonic crystal slabs have been investigated. Although photonic crystal slabs have only partial gaps, efficient waveguides and resonators can be realized by appropriate design. As regards PBG waveguides, we show various designs for efficient single-mode waveguides in PhC slabs with SiO2 cladding, we report group dispersion measurements of PBG waveguides in PhC slabs, and describe the successful fabrication of PBG waveguides with adiabatic connectors that enable us to couple the light from single-mode fibers efficiently to PBG waveguides. As regards PBG resonators, we show how to realize very high-Q and small volume resonators in hexagonal PhC slabs, and report the fabrication of resonant tunneling filters that consist of PBG resonators coupled with PBG waveguides. We also describe the successful fabrication of resonant tunneling mode-gap filters with adiabatic mode connectors.

 

128.    T. Ogino, Y. Homma, K. Ishibashi, and H. Yamaguchi

            "Proceedings of the International symposium on Functional Semiconductors Nanostructures 2003 FSNS2003 - Held in Atsugi, Kanagawa, Japan, 12-14 November 2003 - Preface"

            Physica E-low-dimensional Systems & Nanostructures 24 (1-2)VII-VII (2004).

 

            ABSTRACT:

 

129.    K. Oguri, T. Nishikawa, T. Ozaki, and H. Nakano

            "Sampling measurement of soft-x-ray-pulse shapes by femtosecond sequential ionization of Kr+ in an intense laser field"

            Optics Letters 29 (11)1279-1281 (2004).

 

            ABSTRACT: We propose a sampling technique for measuring the shape of ultrashort soft-x-ray pulses. The technique uses the transient state of Kr+ ions that is produced by the femtosecond sequential evolution of Kr ions during optical-field-induced ionization as an ultrafast x-ray-absorption sampling gate. We demonstrate the technique by measuring the pulse shape of the 51st harmonic (15.6 mn) generated by a 100-fs titanium: sapphire laser pulse. The measured pulse duration is 220 fs. Our experimental result confirms that the sequential evolution of Kr+ ions from neutral Kr to Kr2+ is the dominant contribution to the ionization process from the aspect of time-domain measurement. (C) 2004 Optical Society of America.

 

130.    K. Oguri, T. Ozaki, T. Nishikawa, and H. Nakano

            "Femtosecond-resolution measurement of soft-X-ray pulse duration using ultra-fast population increase of singly charged ions induced by optical-field ionization"

            Applied Physics B-lasers And Optics 78 (2)157-163 (2004).

 

            ABSTRACT: We demonstrate sub-100-fs resolution of a cross-correlation method for measuring the duration of soft-X-ray pulses. The method uses the ultra-fast increase in a singly charged ion population induced by optical-field ionization as a soft-X-ray -absorption switch. We measured the pulse duration of the 51st harmonic of a Ti:sapphire laser pulse using Kr gas as a soft-X-ray absorption medium and found it to be 60 fs assuming that the harmonic envelope is equal to a squared secant hyperbolic. This confirmed that our method achieves a shorter temporal resolution than the 100-fs pulse duration of the ionizing laser pulse. The temporal resolution obtained in this way is expected to be from one-third to one-half the duration of the ionizing laser pulse, according to our calculation of the time-evolving population of the Kr+ ions. The experimental demonstration and calculation show that methods based on optical-field-induced ionization are promising for femtosecond temporal characterization of an ultra-short pulse in the soft-X-ray region.

 

131.    K. Ohtawara, and H. Teramae

            "Study on optimization of molecular structure using Hamiltonian algorithm"

            Chemical Physics Letters 390 (1-3)84-88 (2004).

 

            ABSTRACT: We apply the Hamiltonian algorithm combined with ab initio molecular orbital calculation to the optimization of molecular structure. The 6000 iterative calculations at Hartree-Fock 6-31G** levels shows that the HCN structure can be obtained even starting from the optimized structure of the HNC molecule, which cannot be achieved by conventional optimization methods, such as the Newton-Raphson method. The initial kinetic energies of less than 0.05 hartree and greater than 0.5 hartree fail in the optimization. The incorporation of a mixing term in the momentum space can accelerate the optimization. (C) 2004 Elsevier B.V. All rights reserved.

 

132.    T. Okuda, H. Kiwata, T. Matsushima, T. Wakita, A. Harasawa, K. Ono, T. Kihara, M. Oshima, A. Yokoo, and T. Kinoshita

            "Magnetic domain imaging of Ni micro ring and micro dot array by photoelectron emission microscopy"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 43 (7A)4179-4184 (2004).

 

            ABSTRACT: The magnetic domain structures of Ni micro ring (the inner and outer diameters are changed in a micrometer region) and micro dot array with different shapes and with a small separation between dots were observed by the combined method of photoelectron emission microscopy and X-ray magnetic circular dichroism. For the micro rings with a large inner diameter, a flux-closure (FC) domain structure tends to appear more easily than for those with a small inner diameter. This means that the FC domain structure of the micro rings with a large inner diameter is energetically more stable than those of the micro rings with a small inner diameter and the disks. After applying an external pulsed magnetic field of about 40mT in the in-plane direction, each domain structure switched to an almost perfect single-domain structure. Because of the absence of a central vortex core in the ring as compared with the disks, exchange energy decreases substantially. These phenomena are discussed along with the simulation results. For the micro dot array, the interaction between dots was directly observed. Particularly for the circular disks with a small diameter showing FC domains, no interaction is observed due to the lack of stray fields from each disk. On the other hand, dots with multi domain structures interacted. These types of information may provide us fundamental knowledge for designing high-density magnetic recording media.

 

133.    H. Omi, and Y. Homma

            "Stiffness of step bunches on Si(111)"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 43 (6B)L822-L824 (2004).

 

            ABSTRACT: Configurations of atomic steps on vicinal Si(111) miscut toward the [112] direction after homoepitaxial step-flow growth were studied as a function of growth thickness by ex situ atomic force microsocopy. We found that step bunches coarsen via the zipping-up of single, double, triple, and quadruple bilayer steps during the growth, and that the zipping steps contact neighboring step bunches at characteristic angles depending on their heights. The new finding of the step-height-dependence enabled us to evaluate step bunch stiffness. The step bunches are shown to be significantly stabilized compared with a simple summation of stiffness of individual single bilayer steps.

 

134.    H. Omi, Y. Homma, T. Ogino, S. Stoyanov, and V. Tonchev

            "Design of atomic step networks on Si(111) through strain distribution control"

            Journal Of Applied Physics 95 (1)263-266 (2004).

 

            ABSTRACT: We propose an alternative method to control atomic step networks on silicon for future wafer-scale integration of self-assembling nanostructures. The method is the strain-distribution-control method that we have recently proposed in [H. Omi, D. J. Bottomley, and T. Ogino, Appl. Phys. Lett. 80, 1073 (2002)], which we apply here to design atomic step networks on vicinal Si(111) wafer. Si(111) with its strain patterned by buried silicon oxide inclusions was annealed at 1230 degreesC in ultrahigh vacuum and observed by in situ secondary electron microscopy and ex situ atomic force microscopy. The images show that the method enables us to create the desired arrays of atomic step networks on an arbitrary area of planar silicon wafer. The arrays remain stable during the 1230 degreesC annealing. (C) 2004 American Institute of Physics.

 

135.    K. Ono, and S. Tarucha

            "Nuclear-spin-induced oscillatory current in spin-blockaded quantum dots"

            Physical Review Letters 92 (25), 256803 (2004).

 

            ABSTRACT: We show experimentally that electron transport through GaAs-based double quantum dots can be affected by ambient nuclear spin states in a certain regime where transport is blocked in the absence of electron spin flip. Current through the dots oscillates in time with a period up to 200 s depending on magnetic field. Oscillation is quenched by application of a continuous wave ac magnetic field which can induce nuclear magnetic resonance in Ga-71 or Ga-69. A possible mechanism for dynamically polarizing the nuclear spins is proposed.

 

136.    K. Ono, K. Uchida, N. Miura, Y. Hirayama, K. Ohdaira, and Y. Shiraki

            "Exciton recombination process in GaAs/AlAs type-II heterostructures in pulsed high magnetic fields and a uniaxial pressure"

            Physica E-low-dimensional Systems & Nanostructures 21 (2-4)698-702 (2004).

 

            ABSTRACT: We measured magneto-photoluminescence (PL) spectra in type-II heterostructures of GaAs/AlAs in high magnetic fields up to 40 T under a uniaxial pressure. We observed a remarkable decrease of the integrated magneto-PL intensity with increasing magnetic field at 4.2 K. With increasing temperature or excitation laser power, however, the field-induced decrease of the integrated PL intensity became lesser amount. The experimental observation strongly suggests that electrons and holes are localized in minima of the fluctuating potential due to the interface roughness. We can infer that this is a general feature of the indirect excitons which comprise spatially separated electrons and holes. (C) 2003 Published by Elsevier B.V.

 

137.    K. Onomitsu, H. Fukui, T. Maeda, Y. Hirayama, and Y. Horikoshi

            "Mn and Be codoped GaAs for high hole concentration by low-temperature migration-enhanced epitaxy"

            Journal Of Vacuum Science & Technology B 22 (4)1746-1749 (2004).

 

            ABSTRACT: We report the effect of codoping of Mn-Be and the modified doping on an increment of the total hole concentration. Both the Mn-doped and Be-doped samples exhibit hole concentrations higher than 1 x 10(19) cm(-3) at room temperature. In contrast, the Mn-Be codoped sample shows a remarkable decrease in its hole concentration and mobility. Therefore, the resistivity is increased by more than 10(2) times of the Be-doped sample. This dramatic deterioration is probably caused by the complex defects due to the codoping. We performed the spatially separated doping of Mn and Be in GaAs and found that the hole concentration increases and the mobility shows no decrease for this sample. It is expected that the complex defect concentration is decreased considerably. (C) 2004 American Vacuum Society.

 

138.    K. Onomitsu, T. Okabe, T. Makimoto, H. Saito, M. Ramsteiner, H. J. Zhu, A. Kawaharazuka, K. Ploog, and Y. Horikoshi

            "Magnetic and electric field effects of photoluminescence of excitons bound to nitrogen atom pairs in GaAs"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 43 (6B)L756-L758 (2004).

 

            ABSTRACT: The Magnetic and electric field effects of photoluminescence of excitons bound to nitrogen atom pairs in GaAs have been investigated for nitrogen delta-doped samples grown on (001) GaAs substrates. The excitons bound to nitrogen atom pairs produce a number of photoluminescence lines. However, these lines are much fewer than those observed in uniformly nitrogen-doped samples because of the limited spacing between two-dimensionally distributed nitrogen atoms. Among these lines, those appearing at 1.488, 1.476, and 1.428 eV are the most dominant. In this study, the characteristics of these dominant lines are investigated by an applying external field. The observed phenomena are explained by assuming that there is a continuous flow of excitons from a lower to a higher binding energy state under continuous excitation. Each photoluminescence line is found to split into two or more lines without applying an external field. The lines show a further split under a magnetic field and are finally quenched when the magnetic field is increased. The photoluminescence intensity of each line is modulated by the localization of excitons by a magnetic field and by the delocalization by an electric field.

 

139.    T. Ota, K. Ono, M. Stopa, T. Hatano, S. Tarucha, H. Z. Song, Y. Nakata, T. Miyazawa, T. Ohshima, and N. Yokoyama

            "Single-dot spectroscopy via elastic single-electron tunneling through a pair of coupled quantum dots"

            Physical Review Letters 93 (6), 066801 (2004).

 

            ABSTRACT: We study the electronic structure of a single self-assembled InAs quantum dot by probing elastic single-electron tunneling through a single pair of weakly coupled dots. In the region below pinch-off voltage, the nonlinear threshold voltage behavior provides electronic addition energies exactly as the linear, Coulomb blockade oscillation does. By analyzing it, we identify the s and the p shell addition spectrum for up to six electrons in the single InAs dot, i.e., one of the coupled dots. The evolution of the shell addition spectrum with magnetic field provides Fock-Darwin spectra of the s and p shells.

 

140.    T. Ota, T. Hatano, K. Ono, S. Tarucha, H. Z. Song, Y. Nakata, T. Miyazawa, T. Ohshima, and N. Yokoyama

            "Single electron spectroscopy in a single pair of weakly coupled self-assembled InAs quantum dots"

            Physica E-low-dimensional Systems & Nanostructures 22 (1-3)510-513 (2004).

 

            ABSTRACT: Using a single electron transistor containing a single pair of weakly coupled self-assembled InAs quantum dots, we have studied the transport properties of elastic and inelastic single electron tunneling. We found a series of Coulomb diamonds above pinch off voltage and, below it, characteristic irregular structures in the current vs. source-drain voltage and gate voltage, consisting of "vertical lines" and "kinks". Based on a simple calculation, the vertical lines are assigned to elastic tunneling between aligned states of the two dots. The kinks come from change of electron number in the dots, observed in the inelastic tunneling regime through off-resonant states in the two dots. (C) 2003 Elsevier B.V. All rights reserved.

 

141.    S. K. Ozdemir, J. Shimamura, F. Morikoshi, and N. Imoto

            "Dynamics of a discoordination game with classical and quantum correlations"

            Physics Letters A 333 (3-4)218-231 (2004).

 

            ABSTRACT: Effects of classical/quantum correlations and operations in simultaneous move games are analyzed using a discoordination game, known as Samaritan's dilemma, in which there is no Nash equilibrium (NE) when played with classical pure strategies. We show that although the dilemma can be resolved with quantum operations provided that there is a shared classically correlated state between the players, it is only in the presence of entanglement that the players can receive the highest possible payoff sums. (C) 2004 Elsevier B.V. All rights reserved.

 

142.    S. K. Ozdemir, J. Shimamura, and N. Imoto

            "Quantum advantage does not survive in the presence of a corrupt source: optimal strategies in simultaneous move games"

            Physics Letters A 325 (2)104-111 (2004).

 

            ABSTRACT: Effects of corrupt source on the dynamics of simultaneous move strategic games are analyzed for classical and quantum settings. Corruption rate dependent, changes in payoffs and strategies are observed. It is shown that there is a critical corruption rate at which the players lose their quantum advantage, and that the classical strategies are more robust to the corruption in the source. The characterization of the source corruption rate may help the players choose their optimal strategy. (C) 2004 Elsevier B.V. All rights reserved.

 

143.    K. Prabhakaran, F. Meneau, T. Murashita, G. N. Greaves, G. Sankar, Y. Homma, and T. Gino

            "Reply to "comment on luminescent nanoring structures on silicon""

            Advanced Materials 16 (17)1495-1496 (2004).

 

            ABSTRACT:

 

144.    A. Richter, M. Yamaguchi, T. Akazaki, H. Tamura, and H. Takayanagi

            "Single-electron charging effects in a semiconductor quantum wire with side-coupled quantum dot"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 43 (10)7144-7149 (2004).

 

            ABSTRACT: We report on experimental studies of a quantum wire with side-coupled quantum dot defined by surface gate electrodes patterned on top of a GaAs/AlGaAs heterostructure. The dot is side-coupled to the wire by means of a split-gate electrode allowing for a control of coupling strength. Clear signatures of single-electron charging are observed in the low-temperature wire conductance within a broad range of tunnel couplings and wire widths. The oscillations in wire conductance associated with Coulomb peaks in the dot remain being visible for split-ate conductances exceeding G(0) = 2e(2)/h and for mean wire conductances of up to 2.5G(0). We explain this behavior as consequence of the two-dimensional sample geometry which can lead to asymmetric and effectively reduced coupling between the dot and the conducting modes in the wire and propose a modified sample layout that should be suitable to increase the coupling.

 

145.    M. Rontani, S. Amaha, K. Muraki, F. Manghi, E. Molinari, S. Tarucha, and D. G. Austing

            "Molecular phases in coupled quantum dots"

            Physical Review B 69 (8), 085327 (2004).

 

            ABSTRACT: We present excitation energy spectra of few-electron vertically coupled quantum dots for strong and intermediate interdot coupling. By applying a magnetic field, we induce ground state transitions and identify the corresponding quantum numbers by comparison with few-body calculations. In addition to atomiclike states, we find novel "molecularlike" phases. The isospin index characterizes the nature of the bond of the artificial molecule and this we control. Like spin in a single quantum dot, transitions in isospin leading to full polarization are observed with increasing magnetic field.

 

146.    H. Y. Ryu, M. Notomi, G. H. Kim, and Y. H. Lee

            "High quality-factor whispering-gallery mode in the photonic crystal hexagonal disk cavity"

            Optics Express 12 (8)1708-1719 (2004).

 

            ABSTRACT: We study whispering-gallery-like modes in photonic crystal air-bridge slab micro-cavities having H2 defects using finite-difference time-domain calculations. The defect geometry is optimized to increase the quality factor (Q) of the H2-cavity whispering-gallery mode (WGM). By symmetrically distributing 12 nearest neighbor holes around the defect and controlling size of holes, it is possible to drastically increase the Q of >10(5) while preserving effective mode volume of the order of the cubic wavelength in material. In addition, we investigate the effect of a dielectric circular post located around the center of the H2 cavity. This post can act as current and heat flow paths that promise electrically-pumped thermally-stable lasing operation. It is interesting to observe that the introduction of the post structure increases the Q of the WGM upto 4x10(5) and the high Q >10(5) is still maintained even with large post size. Although diffractive out-coupling through the post is increased, radiated power outside the post is suppressed, which leads to large enhancement of the Q of the H2-cavity WGM. (C) 2004 Optical Society of America.

 

147.    H. Y. Ryu, M. Notomi, E. Kuramoti, and T. Segawa

            "Large spontaneous emission factor (> 0.1) in the photonic crystal monopole-mode laser"

            Applied Physics Letters 84 (7)1067-1069 (2004).

 

            ABSTRACT: 1.55-mum-InGaAsP photonic crystal lasers operating in the monopole mode of a triangular lattice defect cavity are realized by room-temperature optical pumping with a low threshold of <0.5 mW. By analyzing rate equations and the light-light characteristic curve, we evaluate the spontaneous emission factor (beta) of this laser to be larger than 0.1, an extremely high value for photonic crystal lasers. The achievement of this large beta is attributed to the facts that the investigated monopole-mode laser operates at the peak of the spontaneous emission spectrum and it shows a single-mode operation in a wide spectral range. In addition, nonclamping of carrier density near threshold and the beta>0.1 are confirmed by the investigation of carrier-density dependent wavelength blueshift of the lasing mode. (C) 2004 American Institute of Physics.

 

148.    M. S. Saifullah, D. J. Kang, K. R. Subramanian, M. E. Welland, K. Yamazaki, and K. Kurihara

            "Electron beam nanolithography of beta-ketoester modified aluminium tri-sec-butoxide"

            Journal Of Sol-gel Science And Technology 29 (1)5-10 (2004).

 

            ABSTRACT: Electron beam-sensitive spin-coatable Al2O3 resists were prepared by chemically modifying aluminium tri-sec-butoxide with various beta-ketoesters (R-acetoacetates, R = methyl, ethyl, isopropyl, isobutyl, isoamyl, heptyl, benzyl and 2-[methacryloyloxy]ethyl) in isopropyl alcohol. The reaction product was a chelated complex. With increasing molecular weight of R, there was an increase in electron beam sensitivity of spin-coatable Al2O3 resists. This appears to be due to decreased stability of the chelated complex formed by higher molecular weight R-acetoacetates. Fourier transform infrared ( FTIR) spectroscopy studies indicate that exposure to an electron beam results in the breakdown of chelate rings, making the exposed area insoluble during development. Electron beam nanolithography produced 8 nm wide lines. These are the smallest oxide lines written using a sol-gel-based resist.

 

149.    S. Saito, M. Thorwart, H. Tanaka, M. Ueda, H. Nakano, K. Semba, and H. Takayanagi

            "Multiphoton transitions in a macroscopic quantum two-state system"

            Physical Review Letters 93 (3), 037001 (2004).

 

            ABSTRACT: We have observed multiphoton transitions between two macroscopic quantum-mechanical superposition states formed by two opposite circulating currents in a superconducting loop with three Josephson junctions. Resonant peaks and dips of up to three-photon transitions were observed in spectroscopic measurements when the system was irradiated with a strong rf-photon field. The widths of the multiphoton absorption dips are shown to scale with the Bessel functions in agreement with theoretical predictions derived from the Bloch equation or from a spin-boson model.

 

150.    C. Santori, D. Fattal, J. Vuckovic, G. S. Solomon, and Y. Yamamoto

            "Single-photon generation with InAs quantum dots"

            New Journal Of Physics 6, 89 (2004).

 

            ABSTRACT: Single-photon generation using InAs quantum dots in pillar microcavities is described. The effects on performance of the excitation wavelength and polarization, and the collection bandwidth and polarization, are studied in detail. The efficiency and photon state purity of these devices have been measured, and issues affecting these parameters are discussed. Prospects for improved devices are also discussed.

 

151.    C. Santori, D. Fattal, J. Vuckovic, G. S. Solomon, E. Waks, and Y. Yamamoto

            "Submicrosecond correlations in photoluminescence from InAs quantum dots"

            Physical Review B 69 (20), 205324 (2004).

 

            ABSTRACT: Photon correlation measurements reveal memory effects in the optical emission of single InAs quantum dots with time scales from 10 to 800 ns. With above-band optical excitation, a long-time scale negative correlation (antibunching) is observed, while with quasiresonant excitation, a positive correlation (blinking) is observed. A simple model based on long-lived charged states is presented that approximately explains the observed behavior, providing insight into the excitation process. Such memory effects can limit the internal efficiency of light emitters based on single quantum dots, and could also be problematic for proposed quantum-computation schemes.

 

152.    P. V. Santos, J. Nitta, and K. H. Ploog

            "Stern-Gerlach spin filter using surface acoustic waves"

            Solid State Communications 132 (9)631-634 (2004).

 

            ABSTRACT: We propose the ambipolar carrier transport by surface acoustic waves (SAWs) in a semiconductor quantum well (QW) for the realization of the Stern-Gerlach (SG) experiment in the solid phase. The well-defined and very low carrier velocity in the moving SAW field leads to a large deflection angle and thus to efficient spin separation, even for the weak field gradients and short (mum-long) interaction lengths that can be produced by micromagnets. The feasibility of a SG spin filter is discussed for different QW materials. (C) 2004 Elsevier Ltd. All rights reserved.

 

153.    S. Sasaki, S. Amaha, N. Asakawa, M. Eto, and S. Tarucha

            "Enhanced Kondo effect via tuned orbital degeneracy in a spin 1/2 artificial atom"

            Physical Review Letters 93 (1), 017205 (2004).

 

            ABSTRACT: A strong Kondo effect is observed for a vertical quantum dot holding an odd number of electrons and spin 1/2 when an orbital degeneracy is induced by magnetic field. The estimated Kondo temperature for this "doublet-doublet" degeneracy is similar to that for the singlet-triplet degeneracy with an even electron number, indicating that a total of fourfold spin and orbital degeneracy accounts for the enhancement of the Kondo temperature. The experimental observation is qualitatively reproduced by scaling calculations using an SU(4) model at the orbital degeneracy.

 

154.    H. Sato, J. Kurian, and M. Naito

            "Third-order intermodulation measurements of microstrip bandpass filters based on high-temperature superconductors"

            Ieee Transactions On Microwave Theory And Techniques 52 (12)2658-2663 (2004).

 

            ABSTRACT: The insufficient power-handling capability of high-temperature superconducting microwave filters has been a serious barrier to their application. To clarify the key parameters for improving the power-handling capability of RF filters based on high-temperature superconductors (HTSs) with microstrip structures, we synthesized bandpass filters with different layouts using several kinds of HTS thin films and performed third-order intermodulation measurements on them. The experimental results indicate that increasing the film thickness and utilizing molecular-beam-epitaxy-grown films of NdBa2Cu3O7 (NBCO) are effective in obtaining microstrip filters with high power-handling capability. For NBCO filters, we also investigated the effects of oxygen annealing, passband width, and the frequencies of the input signals on the power-handling capability.

 

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

            "La-214 thin films under epitaxial strain"

            Physica C-superconductivity And Its Applications 408-10848-852 (2004).

 

            ABSTRACT: Compressive (or expansive) epitaxial strain was introduced into (0 0 1)-oriented La-214 thin films. For the compressed films of La2-xSrxCuO4 and La2-xBa2CuO4 on LaSrAlO4 substrates, the superconducting transition temperature (T-c) reached 44 and 47 K, respectively. These values are higher than those for bulk samples. The T-c-x phase diagrams for the compressed films did not show a local minimum at around x = 0.125, the so-called "1/8 anomaly". The compressive strain expands the c-axis via the Poisson effect and suppresses formation of the low-temperature tetragonal phase. We speculate that both of the effects lead to an increase in the bond length between Cu and the apical oxygen (O-apex). We also found that the films with higher T-c have lower residual resistivity. These experimental results suggest that antiferromagnetic (AF) spin fluctuation is reduced in the films with higher T-c We propose that the origin of T-c enhancement is the reduced AF spin fluctuation due to the expansion in the Cu-O-apex bond length. This scenario indicates that spin fluctuation may play a negative role in superconductivity in La-214. (C) 2004 Elsevier B.V. All rights reserved.

 

156.    H. Sato, and K. Cho

            "Third-order intermodulation measurements for superconducting bandpass filters"

            Ieice Transactions On Electronics E87C (5)708-713 (2004).

 

            ABSTRACT: An important barrier to the application of high-temperature superconducting microwave filters is their power-handling capability. To clarify the key parameters for improving the power-handling capability of rf filters based on high-temperature superconductors with microstrip structures, we synthesize bandpass filters with different layouts using several kinds of thin film high-temperature superconductors, and subject them to third-order intermodulation measurements. By improving the sensitivity of the measurement set-up through the selective reduction of the fundamental output signals, we succeed in measuring the intermodulation signals of the superconducting filters. The experimental results indicate that increasing the film thickness and utilizing MBE-grown films of NdBa2Cu3O7 films are effective in obtaining high-power handling microstrip filters.

 

157.    T. Sato, H. Matsui, K. Terashima, T. Takahashi, H. Ding, H. B. Yang, S. C. Wang, T. Fujii, T. Watanabe, A. Matsuda, T. Terashima, and K. Kadowaki

            "Magnetic interaction in hole-doped high-T-c superconductors observed by angle-resolved photoemission spectroscopy"

            Physica C-superconductivity And Its Applications 412-1451-58 (2004).

 

            ABSTRACT: We have performed a high-resolution angle-resolved photoemission spectroscopy (ARPES) on high-T-c superconductors (HTSCs) Bi2Sr2Can-1CunO2n+4 (n = 1-3) to study the systematics of the electronic structure and the origin of many-body interactions responsible for superconductivity. We find that a large hole-like Fermi surface and d-wave superconducting gap are generic features of Bi-based HTSCs. For n = 2 and 3, a sudden change in the energy dispersion, so-called "kink", becomes pronounced on approaching (pi, 0) in the superconducting state, while a kink appears only around the nodal direction in the normal state. The kink around (pi, 0) disappears at T-c. For n = 1, the kink shows no significant temperature dependence even across T-c. This could suggest that the coupling of electrons with Q = (pi, pi) magnetic mode is dominant in the superconducting state for multi-layered cuprates, while the interaction at the normal state and that of single-layered cuprates have a different origin. (C) 2004 Elsevier B.V. All rights reserved.

 

158.    T. Sato, H. Matsui, T. Takahashi, H. Ding, H. B. Yang, S. C. Wang, T. Fujii, T. Watanabe, A. Matsuda, T. Terashima, and K. Kadowaki

            "Fermi surface, superconducting gap, and many-body effects in Bi2Sr2Can-1CunO2n+4 (n=1-3)"

            Physica C-superconductivity And Its Applications 408-10812-813 (2004).

 

            ABSTRACT: We have performed a systematic angle-resolved photoemission spectroscopy on the high-T. superconducting family of Bi2Sr2Can-1CunO2n+4 (n = 1-3). We find that large Fermi surface and d-wave superconducting gap are the generic features of Bi-family high-T-c cuprates. Comparison of the nodal dispersion in the superconducting state shows that the kink in energy dispersion becomes more pronounced with increasing layer number n, indicating stronger coupling between electrons and a collective mode. (C) 2004 Elsevier B.V. All rights reserved.

 

159.    Y. Sekine, J. Nitta, T. Koga, A. Oiwa, S. Yanagi, T. Slupinski, and H. Munekata

            "Magnetization reversal process of submicrometer-scale Hall bars of ferromagnetic semiconductor p-In0.97Mn0.03As"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 43 (4B)2097-2100 (2004).

 

            ABSTRACT: The magnetization reversal process of submicrometer-scale Hall bars of the ferromagnetic semiconductor p-In0.97Mn0.03As has been investigated by measuring the Hall resistivity with changing the direction of the applied magnetic field. The angle dependence of the coercive force indicates that the magnetization reversal process is more likely governed by the magnetic domain wall displacement. Furthermore, observation of several Barkhausen jumps on a 0.7-mum-wide Hall bar makes it clear that p-In0.97Mn0.03As has a small-domain-sized multidomain structure near the coercive force. It is also shown that p-In0.97Mn0.03As has an ideal uniaxial magnetic easy axis perpendicular to the plane. The magnetization reversal process of p-In0.97Mn0.03As is distinct from that of a similar ferromagnetic semiconductor p-Ga1-xMnxAs.

 

160.    J. Shimamura, S. K. Ozdemir, F. Morikoshi, and N. Imoto

            "Quantum and classical correlations between players in game theory"

            International Journal Of Quantum Information 2 (1)79-89 (2004).

 

            ABSTRACT: Effects of quantum and classical correlations on game theory are studied to clarify the new aspects brought into game theory by the quantum mechanical toolbox. In this study, we compare quantum correlation represented by a maximally entangled state and classical correlation that is generated through phase damping processes on the maximally entangled state. Thus, this also sheds light on the behavior of games under the influence of noisy sources. It is observed that the quantum correlation can always resolve the dilemmas in non-zero sum games and attain the maximum sum of both players' payoffs, while the classical correlation cannot necessarily resolve the dilemmas.

 

161.    J. Shimamura, S. K. Ozdemir, F. Morikoshi, and N. Imoto

            "Entangled states that cannot reproduce original classical games in their quantum version"

            Physics Letters A 328 (1)20-25 (2004).

 

            ABSTRACT: A model of a quantum version of classical games should reproduce the original classical games in order to be able to make a comparative analysis of quantum and classical effects. We analyze a class of symmetric multipartite entangled states and their effect on the reproducibility of the classical games. We present the necessary and sufficient condition for the reproducibility of the original classical games. Satisfying this condition means that complete orthogonal bases can be constructed from a given multipartite entangled state provided that each party is restricted to two local unitary operators. We prove that most of the states belonging to the class of symmetric states with respect to permutations, including the N-qubit W state, do not satisfy this condition. (C) 2004 Elsevier B.V. All rights reserved.

 

162.    F. Shimizu

            "Scalable quantum computer with optical lattices"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 43 (12)8376-8382 (2004).

 

            ABSTRACT: Quantum computer that is composed of Mott insulator atoms trapped in an optical lattice and a control atom(s) that moves with an independent optical lattice is discussed. A three-dimensional array of Mott insulator atoms functions as memory qubits. The control atom that moves with the second lattice mediates one and two qubit operations among memory qubits with the help of resonant optical beams. Explicit examples of general quantum computational operations are described. In this system all memory qubits are equivalent, and the system is scalable. It is also not necessary to address individual memory qubits by optical means.

 

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

            "Theoretical design of a semiconductor ferromagnet based on quantum dot superlattices"

            Physica E-low-dimensional Systems & Nanostructures 24 (1-2)107-110 (2004).

 

            ABSTRACT: We report on the successful theoretical design of artificial ferromagnetic crystals based on quantum dot superlattices. Our examined quantum dot superlattice has the ferromagnetic ground state when it has a certain number of electrons even though it contains no magnetic elements. In addition, this ferromagnetism can be controlled simply by applying a gate electric field. (C) 2004 Elsevier B.V. All rights reserved.

 

164.    M. Steiner, G. Meier, U. Merkt, and J. Nitta

            "Magnetic transitions of permalloy rings in hybrid devices"

            Physica E-low-dimensional Systems & Nanostructures 24 (1-2)124-128 (2004).

 

            ABSTRACT: Fringe-field-induced local Hall magnetometry is applied to investigate microstructured NiFe rings. The semiconductor-based technique yields a high detection sensitivity of magnetic stray fields. This allows an accurate measurement of different magnetic configurations and their reversible and irreversible transitions. The corresponding spatial magnetic moment distribution is calculated by micromagnetic simulations. Additionally, the stray field of the simulated configurations and the resulting magnetic-force microscopy images are computed. The latter is compared to measurements and thus gives deeper insight into the understanding of magnetic configurations in rings and their modeling. (C) 2004 Elsevier B.V. All rights reserved.

 

165.    M. Steiner, and J. Nitta

            "Control of magnetization states in microstructured permalloy rings"

            Applied Physics Letters 84 (6)939-941 (2004).

 

            ABSTRACT: Magnetization processes of microstructured NiFe rings are studied by the fringe-field-induced local Hall effect and numerical model calculations. The changes in reversible and irreversible magnetization of single rings are detected with very high resolution. We observe that the type of magnetic transition depends on the ratio between the inner and outer ring diameter. For narrow rings, sharp transitions from so-called "onion" to the "vortex" state are observed. In rings with smaller inner diameter, the transitions are more complex. The creation of local vortices and their spatial movement by applying an external magnetic field are detected. (C) 2004 American Institute of Physics.

 

166.    K. Sumitomo, F. Lin, Y. Homma, and T. Ogino

            "Selective formation of Ge nanostructures on Si(111) surface with patterned steps"

            Applied Surface Science 237 (1-4)68-74 (2004).

 

            ABSTRACT: We demonstrate the selective formation of Ge nanostructures on Si(1 1 1) surface with the aid of step-band networks. Step flow growth in the step-band region decreases the critical thickness for transition from 2D to 3D growth. Under the step flow growth, step bunching and faceting are enhanced and the step edge with concentrated strain becomes the nucleation site. The spatial arrangement of Ge islands can be controlled by changing the growth mode locally. (C) 2004 Elsevier B.V. All rights reserved.

 

167.    H. Suzuki, A. Yokoo, and M. Notomi

            "Organic emissive materials and devices for photonic communication"

            Polymers For Advanced Technologies 15 (1-2)75-80 (2004).

 

            ABSTRACT: This article describes our recent progress on the development of organic emissive materials and devices for photonic communication applications. Luminescence properties in the infrared (IR) region were examined for two types of organic emissive material, an organic rare earth complex and an organic ionic dye, and their potential for use as emissive materials in photonic communication applications was discussed. The luminescence mechanism elucidated in this study suggested a guideline for the future development of organic IR emissive materials. Novel organic emissive devices were fabricated by combining organic emissive materials with various types of photonic crystal structure utilizing nanotechnology. These devices utilize the advantages and unique properties of organic materials, and so signal the way towards the breakthroughs needed to realize emissive devices for the photonic communication networks of the future. Copyright (C) 2004 John Wiley Sons, Ltd.

 

168.    K. Suzuki, K. Takashina, S. Miyashita, and Y. Hirayama

            "Landau-level hybridization and the quantum Hall effect in InAs/(AlSb)/GaSb electron-hole systems"

            Physical Review Letters 93 (1), 016803 (2004).

 

            ABSTRACT: The quantum Hall effect in electron-hole hybridized systems is examined using back-gated InAs/(AlSb)/GaSb heterostructures with different electron-hole coupling. When the electrons and holes are strongly coupled, it is found that quantized Hall states appear when the net filling factor [nu(net)=(n-p)h/eB, where n and p are the electron and hole densities, respectively] is an integer, and that it is not a necessary condition for independent electron and hole filling factors (nu(e)=nh/eB and nu(h)=ph/eB) to be integers simultaneously. The observed phenomena can be interpreted in terms of a simple model where the Landau-level fans associated with the electrons and holes hybridize resulting in an effective band gap at nu(net)=0, and the quantized Hall states occur according to the number of hybridized Landau levels occupied above this gap.

 

169.    K. Suzuki, S. Miyashita, K. Takashina, and Y. Hirayama

            "Quantum Hall effect in back-gated InAs/GaSb heterostructures under a tilted magnetic field"

            Physica E-low-dimensional Systems & Nanostructures 20 (3-4)232-235 (2004).

 

            ABSTRACT: We investigate the quantum Hall effect (QHE) in the InAs/GaSb hybridized electron-hole system grown on a conductive InAs substrate which act as a back-gate. In these samples, the electron density is constant and the hole density is controlled by the gate-voltage. Under a magnetic field perpendicular to the sample plane, the QHE appears along integer Landau-level (LL) filling factors of the net-carriers, where the net-carrier density is the difference between the electron and hole densities. In addition, longitudinal resistance maxima corresponding to the crossing of the-extended states of the original electron and hole LLs make the QHE regions along integer-v(net) discontinuous. Under tilted magnetic fields, these R-xx maxima disappear in the high magnetic field region. The results show that the in-plane magnetic field component enhances the electron-hole hybridization and the formation of minigaps at LL crossings. (C) 2003 Elsevier B.V. All rights reserved.

 

170.    S. Suzuki, K. Kanzaki, Y. Homma, and S. Y. Fukuba

            "Low-acceleration-voltage electron irradiation damage in single-walled carbon nanotubes"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 43 (8B)L1118-L1120 (2004).

 

            ABSTRACT: Low-acceleration-voltage electron irradiation effects on single-walled carbon nanotubes were studied by resonant Raman spectroscopy. The irradiation at acceleration voltages of 0.5 to 25 kV was found to extinguish the characteristic optical property of the nanotubes and reduce their tolerance against annealing in air, indicating that the nanotubes are inevitably damaged by ordinary scanning electron microscope observation. The acceleration voltage of around 1 kV caused the most extensive damage. Less defective SWNTs were found to have a higher tolerance against the irradiation damage.

 

171.    S. Suzuki, Y. Watanabe, Y. Homma, S. Fukuba, S. Heun, and A. Locatelli

            "Work functions of individual single-walled carbon nanotubes"

            Applied Physics Letters 85 (1)127-129 (2004).

 

            ABSTRACT: Work functions of individual single-walled carbon nanotubes (SWNTs) were studied by means of photoemission electron microscopy. Work function differences between the nanotubes were clearly observed in secondary electron images. The work functions of 93 SWNTs were found to range within 0.6 eV, but most distributed in a much narrower energy range of 0.2 eV. The work functions of single-walled nanotubes do not seem to have large structural dependence. (C) 2004 American Institute of Physics.

 

172.    S. Suzuki, Y. Watanabe, T. Ogino, Y. Homma, D. Takagi, S. Heun, L. Gregoratti, A. Barinov, and M. Kiskinova

            "Observation of single-walled carbon nanotubes by photoemission microscopy"

            Carbon 42 (3)559-563 (2004).

 

            ABSTRACT: Single-walled carbon nanotube networks grown on SiO2 pillars were studied by means of scanning photoemission microscopy. The individual nanotubes or nanotube bundles growing from the pillar tops were observed in C 1s images. Band bending near catalytic Fe/nanotube contacts in an end-bonded configuration was studied by measuring C 1s spectra along the tube axes. Within our experimental resolution, no band bending was observed. This implies that the depletion width is less than the spatial resolution of the scanning photoemission microscope (90 nm) or that the amount of the band bending is less than 0.1 eV. (C) 2003 Elsevier Ltd. All rights reserved.

 

173.    A. Taguchi, and K. Shiraishi

            "First-principles investigations of GaAs(311)A surface reconstruction - failure of the electron counting model"

            Applied Surface Science 237 (1-4)189-193 (2004).

 

            ABSTRACT: We investigated various surface reconstructions of a GaAs(3 1 1)A surface by using first-principles calculations. The relative stability of the reconstructions was compared by estimating the formation energies taking into account of the chemical potentials of Ga and As. We found that the most stable reconstruction of the (3 1 1)A surface does not satisfy the electron counting model (ECM), although the ECM is a strong guiding principle for determining stable surface reconstructions of Ga-As(1 0 0), (1 1 1)A, and (1 1 0) surfaces. Further investigations indicate that the sp(2)-like-bond formation effectively works at the (3 1 1)A surface. Competition between sp(2)-like-bond formation and As-dimer formation would explain why the ECM is not so effective at this surface. (C) 2004 Elsevier B.V. All rights reserved.

 

174.    A. Taguchi

            "Importance of the sp(2)-like orbital formation for stabilizing surface local structures"

            Physica E-low-dimensional Systems & Nanostructures 24 (1-2)153-156 (2004).

 

            ABSTRACT: Atomic configurations of GaAs (311)A, (111)A, and (110) surfaces were examined by using first-principles calculations to investigate the stabilization mechanism of surface structures. Although the bonds in the bulk state are sp(3) hybridized bonds, it was found that the surface atoms form sp(2) -like bonds. This is because the total energy is not sensitive to the detailed atomic configurations at the surface and the energy level of the sp(2) hybridized orbital is lower than that of the sp(3) orbital. The sp(2) -like bond formation is rather general and important in stabilizing the surface structures. (C) 2004 Elsevier B.V. All rights reserved.

 

175.    D. Takagi, Y. Homma, and Y. Kobayashi

            "Selective growth of individual single-walled carbon nanotubes suspended between pillar structures"

            Physica E-low-dimensional Systems & Nanostructures 24 (1-2)1-5 (2004).

 

            ABSTRACT: Single-walled carbon nanotubes (SWNTs) were grown on pillar-patterned Si and SiO2 substrates to form suspended nanotubes between pillar patterns. The growth was performed by chemical vapor deposition using methane and Fe catalysts. TheSWNT yield was controlled by choosing the catalyst particle size and growth temperature. When the SWNT yield was low, individual SWNTs form between neighboring pillars. At higher yields, bundles of SWNTs formed. The suspended nanotubes were directly characterized by transmission electron microscopy. (C) 2004 Elsevier B.V. All rights reserved.

 

176.    K. Takashina, A. Fujiwara, Y. Takahashi, and Y. Hirayama

            "Resistance spikes induced by gate-controlled valley-splitting in silicon"

            International Journal Of Modern Physics B 18 (27-29)3603-3608 (2004).

 

            ABSTRACT: Landau-level coincidences are examined in a (100) silicon 2DEG by tuning the valley-splitting with front- and back-gates. A coincidence under quantum Hall conditions between levels of opposite spin, opposite valley, but like orbital indices at v = 6 is found to show suppressed resistance, while in marked contrast, coincidences at v = 4i (where i is an integer) between adjacent orbital Landau levels exhibit resistance spikes.

 

177.    K. Takashina, A. Fujiwara, S. Horiguchi, Y. Takahashi, and Y. Hirayama

            "Valley splitting control in SiO2/Si/SiO2 quantum wells in the quantum Hall regime"

            Physical Review B 69 (16), 161304 (2004).

 

            ABSTRACT: SiO2/Si/SiO2 quantum wells fabricated on SIMOX silicon-on-insulator substrates are examined in the quantized Hall regime. An 8 nm quantum well behaves as a single layer of two-dimensional electrons at accessible gate voltages. By using front and back gates, the wave function in the confinement direction can be shifted continuously between two SiO2/Si interfaces formed through different processes. We find that this results in a continuous evolution of the valley splitting which is asymmetric with electrical gate bias. Wider quantum wells show bilayer behavior where the valley splitting is different in each layer, demonstrating that its control shown by the 8 nm well arises due to the different properties of the two interfaces. Estimates of the valley splitting are made through Landau level coincidences and activation energies. The coincidence between Landau levels of opposite spin, opposite valley, and like cyclotron indices at nu=6 shows anticrossing behavior.

 

178.    K. Takashina, Y. Hirayama, A. Fujiwara, S. Horiguchi, and Y. Takahashi

            "A silicon bi-layer system"

            Physica E-low-dimensional Systems & Nanostructures 22 (1-3)72-75 (2004).

 

            ABSTRACT: This report concerns front and back-gated SiO2/Si/SiO2 quantum wells formed by fabricating MOSFET's on (100) SIMOX silicon-on-insulator substrates. By examining the magneto-transport properties of samples with various well-widths, we demonstrate that such structures are suitable for investigating correlation effects under various regimes of behaviour. We find that an 8 nm quantum well behaves as a single layer of two-dimensional electrons at accessible gate voltages. We present convincing evidence that the back-gate provides unique control over the valley splitting unavailable in conventional Si MOSIFET's by shifting the wave function between the two Si/SiO2 interfaces, as first suggested by Ouisse et at, (Physica B 249-251 (1998) 731). A slightly wider 10 nm quantum well behaves as a strongly-coupled bi-layer system, where the valley splitting is different in each layer. A very wide 25 nm-wide quantum well behaves as two totally independent two-dimensional electron layers. (C) 2003 Elsevier B.V. All rights reserved.

 

179.    H. Takesue, and K. Inoue

            "Generation of polarization-entangled photon pairs and violation of Bell's inequality using spontaneous four-wave mixing in a fiber loop"

            Physical Review A 70 (3), 031802 (2004).

 

            ABSTRACT: We report the generation of polarization entangled photon pairs in the 1550-nm wavelength band using spontaneous four-wave mixing in a dispersion-shifted fiber loop. The use of the fiber-loop configuration made it possible to generate polarization entangled states very stably. With accidental coincidences subtracted, we obtained coincidence fringes with >90% visibilities, and observed a violation of Bell's inequality by seven standard deviations. We also confirmed the preservation of the quantum correlation between the photons even after they had been separated by 20 km of optical fiber.

 

180.    H. Takesue, and T. Horiguchi

            "Broad-band lightwave synthesized frequency sweeper using synchronous filtering"

            Journal Of Lightwave Technology 22 (3)755-762 (2004).

 

            ABSTRACT: We describe a broad-band lightwave synthesized frequency sweeper (LSPS) that uses synchronous filtering. We control the center frequency of the bandpass filter (BPF) in the LSFS so that it tracks the frequency of the circulating pulse. In the first half of this paper, We numerically simulate the accumulation of amplified spontaneous emission (ASE) noise in the LSFS and confirm the effectiveness of synchronous filtering in suppressing the noise. We show that the frequency sweep span can be enlarged to cover the erbium-doped fiber amplifier gain bandwidth completely if ideal synchronous filtering is realized. We also describe the way in Which the fluctuation of the BPF center frequency severely limits the number of pulse circulations and we estimate the accuracy required for the BPF center frequency control. In the second half, we report our experimental results. We confirmed the completion of more than, 10 000 pulse, circulations, Which corresponded to a frequency sweep span of > 1.2 THz. We also estimated the accuracy of the BPF center frequency control experimentally. As a result, the relationship between the accuracy and the number of pulse circulations was in good agreement with that obtained in the simulation.

 

181.    I. Takesue, T. Akazaki, S. Miyadai, N. Kobayashi, A. Tokita, M. Nomura, J. Haruyama, and H. Takayanagi

            "Multi-walled carbon nanotubes with NbN superconducting electrodes"

            Physica E-low-dimensional Systems & Nanostructures 24 (1-2)32-36 (2004).

 

            ABSTRACT: We fabricated NbN/multi-walled carbon nanotube (MWNT)/Al junctions using MWNTs standing in nano-porous alumina membranes. We observed a reduction in the resistance within the NbN superconducting energy gap voltage caused by Andreev reflection. Moreover, we found that the conductance scales in the form of power laws with respect to temperature and bias voltage, and the power-law exponent a becomes larger when NbN becomes superconductive. These experimental results can be qualitatively explained by the theory of superconductor-Tomonaga-Luttinger liquid hybrid systems. (C) 2004 Elsevier B.V. All rights reserved.

 

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

            "Tunable exchange interaction in quantum dot devices"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 43 (5B)L691-L693 (2004).

 

            ABSTRACT: We theoretically discuss the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between semiconductor quantum dots (QDs). When each QD having a local spin is coupled to the conduction electrons in semiconductors, an indirect exchange interaction, i.e., the RKKY interaction, is induced between two local spins. The RKKY interaction between QDs, which is mediated by the Fermi sea in semiconductors, is modulated by changing the Fermi energy, and the magnitude or even the sign of the exchange interaction can be tuned, which leads to a tunable magnetic transition in QD devices. We estimate the magnitude of the RKKY interaction in QDs as a function of the electron density and the inter-dot distance.

 

183.    Y. Taniyasu, M. Kasu, and T. Makimoto

            "Electrical conduction properties of n-type Si-doped AlN with high electron mobility (> 100 cm(2) V-1 s(-1))"

            Applied Physics Letters 85 (20)4672-4674 (2004).

 

            ABSTRACT: For n-type Si-doped AlN, we have obtained an electron mobility and concentration of 125 cm(2) V-1 s(-1) and 1.75x10(15) cm(-3) at 300 K, respectively. At 250 K, the mobility reached the maximum of 141 cm(2) V(-1)s(-1). To explain the temperature dependence of the mobility, we calculated mobilities limited by specific scattering mechanisms. We found that the mobility is limited by neutral impurity scattering rather than ionized impurity scattering or lattice scattering because of a large donor ionization energy (similar to250 meV). (C) 2004 American Institute of Physics.

 

184.    Y. Taniyasu, M. Kasu, and T. Makimoto

            "Field emission properties of heavily Si-doped AlN in triode-type display structure"

            Applied Physics Letters 84 (12)2115-2117 (2004).

 

            ABSTRACT: Using heavily Si-doped AlN, a triode-type field emission display is demonstrated. The device consists of the heavily Si-doped AlN field emitter, mesh grid, and phosphor-coated anode screen. The device exhibits a low turn-on electric field of 11 V/mum, and the field emission current exponentially increases as the grid voltage increases. The field emission current reaches 9.5 muA at an electric field strength of 23 V/mum. Luminescence from the phosphor excited by the field-emitted electrons is uniform over the anode screen and is intense enough for the display application. The field emission current is stable over time. (C) 2004 American Institute of Physics.

 

185.    K. Tateno, H. Gotoh, and Y. Watanabe

            "GaAs/AlGaAs nanowires capped with AlGaAs layers on GaAs(311)B substrates"

            Applied Physics Letters 85 (10)1808-1810 (2004).

 

            ABSTRACT: We have investigated GaAs/AlGaAs nanowires capped with AlGaAs layers for optical device applications. GaAs nanowires are not so stable during AlGaAs capping growth at high temperature. However, AlGaAs nanowires retain their shapes, and GaAs nanowires sandwiched between AlGaAs wires were capped at temperatures as high as 700degreesC. The capped structures showed sharp photoluminescence peaks at around 730 nm at 4 K, which originated from excitons in quantum wires. We confirmed that the AlGaAs capping layers were grown smoothly around nanowires so that surface recombination centers in GaAs nanowires were reduced compared with air-exposed GaAs wires. (C) 2004 American Institute of Physics.

 

186.    T. Tawara, H. Gotoh, T. Akasaka, N. Kobayashi, and T. Saitoh

            "Cavity polaritons in InGaN microcavities at room temperature"

            Physical Review Letters 92 (25), 256402 (2004).

 

            ABSTRACT: Cavity polaritons are observed in InGaN quantum well (QW) microcavities at room temperature. High-quality microcavities are fabricated by the wafer-bonding of InGaN QW layers and dielectric distributed Bragg reflectors. The anticrossing behavior of strong exciton-photon coupling is confirmed by vacuum-field Rabi splitting obtained from reflection measurements. This strong coupling is also enhanced by increasing the integrated oscillator strength coupled to the cavity mode. The oscillator strength of InGaN QW excitons is 1 order of magnitude larger than that of GaAs QW excitons.

 

187.    D. Terasawa, K. Nakada, S. Kozumi, Z. F. Ezawa, A. Fukuda, A. Sawada, N. Kumada, K. Muraki, Y. Hirayama, and T. Saku

            "Double magnetoresistance minima induced by the in-plane magnetic field for the v=1 double-layer quantum Hall state"

            International Journal Of Modern Physics B 18 (27-29)3709-3712 (2004).

 

            ABSTRACT: We have investigated v = 1 quantum Hall (QH) state in a double-layer system around the commensurate (C) -incommensurate (IC) transition. Detailed magnetoresistance measurements around the C-IC transition reveal that there axe two minima within the v = 1 QH state. These minima, being induced by the difference of the in-plane magnetic field, correspond to the C and IC phases, respectively. The region between the two minima may be the soliton lattice phase predicted by theoretical analyses.

 

188.    D. Terasawa, M. Morino, K. Nakada, S. Kozumi, A. Sawada, Z. F. Ezawa, N. Kumada, K. Muraki, T. Saku, and Y. Hirayama

            "Simultaneous excitation of spins and pseudospins in the bilayer v=1 quantum Hall state"

            Physica E-low-dimensional Systems & Nanostructures 22 (1-3)52-55 (2004).

 

            ABSTRACT: The tilting angular dependence of the energy gap was measured in the bilayer quantum Hall state at the Landau level filling nu = 1 by changing the density imbalance between the two layers. The observed gap behavior shows a continuous transformation from the bilayer balanced density state to the monolayer state. Even a sample with 33 K tunneling gap shows the same activation energy anomaly reported by Murphy et al. (Phys. Rev. Lett. 72 (1994) 728). We discuss a possible relation between our experimental results and the quantum Hall ferromagnet of spins and pseudospins. (C) 2003 Elsevier B.V. All rights reserved.

 

189.    M. Thorwart, E. Paladino, and M. Grifoni

            "Dynamics of the spin-boson model with a structured environment"

            Chemical Physics 296 (2-3)333-344 (2004).

 

            ABSTRACT: We investigate the dynamics of the spin-boson model when the spectral density of the boson bath shows a resonance at a characteristic frequency Omega but behaves Ohmically at small frequencies. The time evolution of an initial state is determined by making use of the mapping onto a system composed of a quantum mechanical two-state system (TSS) which is coupled to a harmonic oscillator (HO) with frequency Omega. The HO itself is coupled to an Ohmic environment. The dynamics is calculated by employing the numerically exact quasiadiabatic path-integral propagator technique. We find significant new properties compared to the Ohmic spin-boson model. By reducing the TSS-HO system in the dressed states picture to a three-level system for the special case at resonance, we calculate the dephasing rates for the TSS analytically. Finally, we apply our model to experimentally realized superconducting flux qubits coupled to an underdamped dc-SQUID detector. (C) 2003 Elsevier B.V. All rights reserved.

 

190.    Y. Tokura

            "Current noise in a quantum point contact"

            Physica E-low-dimensional Systems & Nanostructures 22 (1-3)284-287 (2004).

 

            ABSTRACT: The current correlation is evaluated for a ballistic quantum point contact interacting with a classical time-dependent field. The formula of low-frequency current noise spectra is obtained and is evaluated analytically for a very short defect and numerically for a smooth potential. in contract to the previous study, there is a parameter region where the current noise with a weak random field is smaller than the Johnson-Nyquist/shot noise expected for a static potential. (C) 2003 Elsevier B.V. All rights reserved.

 

191.    F. Toujou, S. Yoshikawa, Y. Homma, A. Takano, H. Takenaka, M. Tomita, Z. Li, T. Hasegawa, K. Sasakawa, M. Schuhmacher, A. Merkulov, H. K. Kim, D. W. Moon, T. Hong, and J. Y. Won

            "Evaluation of BN-delta-doped multilayer reference materials for shallow depth profiling in SIMS: round-robin test"

            Applied Surface Science 231-2649-652 (2004).

 

            ABSTRACT: SIMS with low energy (down to 250 eV) primary ions has been widely used for ultra-shallow dopant profiling for ULSI device development. In spite of its high performance in depth resolution, there still remain ambiguities to be overcome in SIMS technique for accurate depth and concentration calibrations in the shallow depth regions. In order to get accurate ultra-shallow boron depth profiles, BN-delta-doped multilayer reference materials were developed and evaluated in a round-robin study using low energy SIMS. Those delta-doped layers were used to measure the sputter rate change in the initial stage of oxygen-ion bombardment. (C) 2004 Elsevier B.V. All rights reserved.

 

192.    K. Tsubaki, N. Maeda, T. Saitoh, and N. Kobayashi

            "Hall resistance hysteresis in AlGaN/GaN 2DEG"

            Physica E-low-dimensional Systems & Nanostructures 21 (2-4)676-678 (2004).

 

            ABSTRACT: The Hall resistance of AlGaN/GaN two-dimensional electron gas (2DEG) at low temperatures was measured. The AlGaN/GaN heterostructures were grown by low-pressure metal-organic chemical vapor phase epitaxy on (0001) SiC substrate. The electron mobility and electron concentration at 4.2 K are 9540 cm(2)/V s and 6.6 x 10(12) cm(-2), respectively. When the temperature is lower than 4.5 K the hysteresis of Hall resistance is observed near zero magnetic field. The hysteresis of Hall resistance increases with decreasing temperature. At temperatures higher than 4.5 K, the hysteresis of Hall resistance disappears. From the analysis of the residual Hall resistance dependence on the temperature, the Curie temperature of the Hall resistance hysteresis is calculated to be 4.4 K. In general, the hysteresis implies the possibility of ferromagnetism, but the conformation of the ferromagnetism of AlGaN/GaN heterostructure is still difficult and the detailed physical mechanism is still unclear. (C) 2003 Elsevier B.V. All rights reserved.

 

193.    K. Ueda, and M. Naito

            "Tunnel junctions on as-grown MgB2 films"

            Physica C-superconductivity And Its Applications 408-10134-135 (2004).

 

            ABSTRACT: We prepared MgB2 films by coevaporation of pure Mg and B metals in an ultra high vacuum chamber. These films have c-axis orientation and a slightly depressed T-c (similar to35 K). We fabricated various tunnel junctions (SIN and SIS) using these as-grown MgB2 films. Of these, Au/MgO/MgB2 junctions showed typical SIN characteristics with a clear superconducting gap of Delta similar to 2.5 meV. This gap value may correspond to the smaller gap in the multi-gap scenario. Preliminary MgB2/Al2O3/MgB2 junctions exhibited SIS characteristics, although not ideal, with a similar value of Delta. (C) 2004 Elsevier B.V. All rights reserved.

 

194.    M. Uematsu, H. Kageshima, Y. Takahashi, S. Fukatsu, K. M. Itoh, and K. Shiraishi

            "Simulation of correlated diffusion of Si and B in thermally grown SiO2"

            Journal Of Applied Physics 96 (10)5513-5519 (2004).

 

            ABSTRACT: Simultaneous diffusion of Si and B in thermally grown SiO2 is modeled taking into account the effect of SiO molecules generated at the Si/SiO2 interface and diffusing into SiO2 to enhance both Si and B diffusion. Based on the model, we simulated experimental profiles of coimplanted Si-30 and B in (SiO2)-Si-28, which showed increasing diffusivities with decreasing distance from the interface. The simulation results show that the SiO diffusion is so slow that the SiO concentration at the near-surface region critically depends on the distance from the interface. In addition, the simulation explains that the diffusivities of both Si and B increase with longer annealing times because more SiO molecules arrive from the interface. Furthermore, we examined the effect of high-concentration B on the diffusivities of Si and B in SiO2, both of which increase with higher B concentration. The experimental results were simulated assuming that the diffusivity of SiO, which enhances the diffusivities of Si and B, increases with higher B concentration. The present results indicate that Si and B diffusion in SiO2 are correlated via SiO molecules; namely, the enhancement of SiO diffusion at high B concentrations also causes enhanced diffusion of both Si and B. (C) 2004 American Institute of Physics.

 

195.    M. Uematsu, H. Kageshima, Y. Takahashi, S. Fukatsu, K. M. Itoh, and K. Shiraishi

            "Correlated diffusion of silicon and boron in thermally grown SiO2"

            Applied Physics Letters 85 (2)221-223 (2004).

 

            ABSTRACT: Si self-diffusion and B diffusion in SiO2 were simultaneously investigated in thermally grown (SiO2)-Si-28 co-implanted with Si-30 and B. The B diffusivity increases with decreasing distance between the implanted B and S'/SiO2 interface, in the same way as Si self-diffusivity. This result together with a numerical simulation shows that SiO molecules, which are generated at the Si/SiO2 interface and diffusing into SiO2, enhance not only Si self-diffusion, but also B diffusion. In;. addition, we found that the diffusivities of both Si and B increase with higher B concentration in SiO2. The experimental results can be quantitatively explained by a numerical simulation assuming that the diffusivity of SiO, which enhances the diffusivities of Si and B, increases with higher B concentration. (C) 2004 American Institute of Physics.

 

196.    M. Uematsu, H. Kageshima, Y. Takahashi, S. Fukatsu, K. M. Itoh, K. Shiraishi, and U. Gosele

            "Modeling of Si self-diffusion in SiO2: Effect of the Si/SiO2 interface including time-dependent diffusivity"

            Applied Physics Letters 84 (6)876-878 (2004).

 

            ABSTRACT: Self-diffusion of Si in thermally grown SiO2 is modeled taking into account the effect of SiO molecules generated at the Si/SiO2 interface and diffusing into SiO2 to enhance the self-diffusion. Based on the model, a recent self-diffusion experiment of ion-implanted Si-30 in SiO2, which showed increasing self-diffusivity with decreasing distance between the Si-30 diffusers and Si/SiO2 interface [Fukatsu , Appl. Phys. Lett. 83, 3897 (2003)], was simulated, and the simulated results fit the experimental profiles. Furthermore, the simulation predicts that the self-diffusivity would increase for a longer annealing time because more SiO molecules should be arriving from the interface. Such time-dependent diffusivity was indeed found in our follow-up experiments, and the profiles were also fitted by the simulation using a single set of parameters. (C) 2004 American Institute of Physics.

 

197.    E. Waks, E. Diamanti, B. C. Sanders, S. D. Bartlett, and Y. Yamamoto

            "Direct observation of nonclassical photon statistics in parametric down-conversion"

            Physical Review Letters 92 (11), 113602 (2004).

 

            ABSTRACT: We employ a high quantum efficiency photon number counter to determine the photon number distribution of the output field from a parametric down-converter. The raw photocount data directly demonstrates that the source is nonclassical by 40 standard deviations, and correcting for the quantum efficiency yields a direct observation of oscillations in the photon number distribution.

 

198.    C. X. Wang, N. Maeda, K. Tsubaki, N. Kobayashi, and T. Makimoto

            "Electron transport properties in lightly Si-doped InGaN films grown by metalorganic vapor phase epitaxy"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 43 (6A)3356-3359 (2004).

 

            ABSTRACT: The electronic properties of Si-doped InGaN thin films with different fit compositions were investigated. The samples were grown by metalorganic vapor phase epitaxy (MOVPE), and then evaluated using photoluminescence, X-ray diffraction and variable temperature Hall effect measurements. The Si donor activation energy was found to decrease with the increase in In composition of InGaN as a result of shrinking bandbap energy, and determined to be 17 meV, 10 meV and 6 meV for 4%, 9% and 13% of In compositions through the least square fitting of experimental carrier concentrations versus temperatures. InGaN alloy with 9% of In composition exhibited the best electronic properties with the lowest compensation ratio and the highest mobilities among those three samples over the whole range of measurement temperature. The relatively high mobility of 227 cm(2)/Vs at room temperature was achieved in this sample. Scattering mechanism in InGaN alloy was also studied using a simple model.

 

199.    C. X. Wang, K. Tsubaki, N. Kobayashi, T. Makimoto, and N. Maeda

            "Electron transport properties in AlGaN/InGaN/GaN double heterostructures grown by metalorganic vapor phase epitaxy"

            Applied Physics Letters 84 (13)2313-2315 (2004).

 

            ABSTRACT: Electron transport properties in AlGaN/InGaN/GaN double heterostructures have been investigated. Samples were grown by metalorganic vapor phase epitaxy and evaluated using x-ray diffraction and variable temperature Hall effect measurements. Much higher two-dimensional electron gas density of up to 50% has been obtained in AlGaN/InGaN/GaN structure than in a typical AlGaN/GaN structure due to the larger polarization effect while the mobilities are comparable at room temperature and above in these structures, which demonstrates the suitability of an AlGaN/InGaN/ GaN structure for high-power device applications. Theoretical-simulations were done to investigate the carrier transport mechanism, and they suggest that alloy disorder and interface roughness scattering have a very strong impact on the electron transport properties in AlGaN/InGaN/GaN structures. (C) 2004 American Institute of Physics.

 

200.    Y. Watanabe, S. Bhunia, S. Fujikawa, T. Kawamura, H. Nakashima, K. Furukawa, and K. Torimitsu

            "Heteroepitaxial metalorganic vapor phase epitaxial growth of InP nanowires on GaP(111)B"

            Thin Solid Films 464-65248-250 (2004).

 

            ABSTRACT: Vertically aligned InP nanowires were successfully grown on GaP(111)B substrates by metalorganic vapor phase epitaxy under a Au-catalyzed vapor-liquid-solid growth process. An nanoparticles were used as the seed to control the nanowire diameter in the nanoscale range. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies showed highly dense nanowires with homogeneous diameter along their length axis, and had zinc-blende structure with <111> growth direction. Photoluminescence (PL) measurements showed a significant blueshift in the spectral peak position compared to bulk InP due to the quantum confinement of the carriers in the nanowires. (C) 2004 Elsevier B.V. All rights reserved.

 

201.    Y. Watanabe, N. Yamamoto, S. Bhunia, T. Kawamura, and S. Fujikawa

            "Structural and optical properties of vertically aligned TnP nanowires grown by metal organic vapor phase epitaxy"

            Physica E-low-dimensional Systems & Nanostructures 23 (3-4)305-308 (2004).

 

            ABSTRACT: Vertically aligned InP nanowires were successfully grown by metalorganic vapor phase epitaxy under metal-catalyzed vapor-liquid-solid growth processes. An nanoparticles with a nominal diameter of 20 urn were used as the seed to control the diameter of the nanowires. Scanning and transmission electron microscopic studies showed highly dense nanowires with uniform diameters along the length direction, and the zinc-blende structure of the nanowires with <111> growth direction.. respectively. Cathodeluminescence measurements showed a significant blueshift, in the spectral peak position compared to bulk InP due to the quantum confinement of the carriers in the nanowires. (C) 2004 Elsevier B.V. All rights reserved.

 

202.    Y. Watanabe, H. Hibino, S. Bhunia, K. Tateno, and T. Sekiguchi

            "Site-controlled InP nanowires grown on patterned Si substrates"

            Physica E-low-dimensional Systems & Nanostructures 24 (1-2)133-137 (2004).

 

            ABSTRACT: InP nanowires were successfully grown on Si(100) and patterned Si(100) substrates by metalorganic vapor phase epitaxy under gold-catalyzed vapor-liquid-solid growth processes. Scanning and transmission electron microscopic studies showed InP nanowires grown on both substrates and the zinc-blende structure of the nanowires with <111> growth direction, respectively. Photoluminescence and cathodeluminescence measurements showed a significant blueshift in the spectral peak position compared to bulk InP due to the quantum confinement of the carriers in the nanowires and bright contrast corresponding to the nanowire structures. The site-controlled InP nanowires were grown at the positions where Au nanoparticles have been arranged through liquid An migration and followed Au nanoparticle formation at a particular position on the patterned Si substarte. (C) 2004 Elsevier B.V. All rights reserved.

 

203.    H. Yamaguchi, S. Miyashita, and Y. Hirayama

            "Mechanical and piezoresistive properties of InAs/AlGaSb cantilevers"

            Applied Surface Science 237 (1-4)649-653 (2004).

 

            ABSTRACT: We fabricated piezoresistive micromechanical cantilevers using InAs/AlGaSb heterostructures grown by molecular beam epitaxy on GaAs (1 1 1) A and (0 0 1) substrates. The piezoresistance allows the cantilever displacement and mechanical resonance to be electrically detected. The cantilever fabricated on (0 0 1) substrate showed much smaller quality factors, indicating it has much larger energy dissipation than the one on (1 1 1) A. The measurement of the temperature dependence of the elastic constant suggests increased unharmonic lattice vibration for the (0 0 1) sample. These differences between (1 1 1) A and (0 0 1) samples could be induced by the high density of misfit dislocations formed in the (0 0 1) heterostructures. (C) 2004 Elsevier B.V. All rights reserved.

 

204.    H. Yamaguchi, K. Kanisawa, S. Miyashita, and Y. Hirayama

            "InAs/GaAs (111)A heteroepitaxial systems"

            Physica E-low-dimensional Systems & Nanostructures 23 (3-4)285-292 (2004).

 

            ABSTRACT: We studied the structural, electrical, and mechanical properties of an InAs thin film grown on GaAs (I I I)A substrates by molecular beam epitaxy. In contrast to conventionally used (0 0 1) surfaces, where Stranski-Krastanov growth dominates the highly mismatched heteroepitaxy, layer-by-layer growth of InAs can be established. One of the largest advantages of this unique heteroepitaxial system is that it provides a two-dimensional electron gas system in the near-surface region without the problem of electron depletion. We review the fundamental properties and applications of this unique heteroepitaxial system. (C) 2004 Elsevier B.V. All rights reserved.

 

205.    H. Yamaguchi, S. Miyashita, and Y. Hirayama

            "Piezoresistive cantilevers using InAs-based 2D heterostructures"

            Physica E-low-dimensional Systems & Nanostructures 24 (1-2)70-73 (2004).

 

            ABSTRACT: We measured the magneto-piezoresistance of micromechanical cantilevers fabricated from two-dimensional InAs/AlGaSb heterostructures. The magneto-piezoresistance showed the features of conductance fluctuation and Schbnikov-de Haas oscillation, depending on the sample electron mobility, indicating strong quantum effects on the piezoresistance. A possible mechanism for these quantum effects is discussed based on the comparison between the magneto-piezoresistance and differential magnetoresistance curves. (C) 2004 Elsevier B.V. All rights reserved.

 

206.    H. Yamaguchi, Y. Tokura, S. Miyashia, and Y. Hirayama

            "Quantum interference effects in the magnetopiezoresistance of InAs/AlGaSb quasi-one-dimensional electron systems"

            Physical Review Letters 93 (3), 036603 (2004).

 

            ABSTRACT: We measured the low temperature magnetopiezoresistance of a quasi-one-dimensional electron system by fabricating an InAs/AlGaSb micromechanical cantilever. The magnetopiezoresistance curve showed aperiodic but reproducible oscillation, which was similar to the differential magnetoresistance curve obtained for the same device. A detailed comparison with model calculations strongly suggests that the quantum interference effects that cause the conductance fluctuations in the magnetoresistance are responsible for the peculiar behavior of the magnetopiezoresistance.

 

207.    H. Yamaguchi, S. Miyashita, and Y. Hirayama

            "Quantum-mechanical displacement sensing using InAs/AlGaSb micromechanical cantilevers"

            Physica E-low-dimensional Systems & Nanostructures 21 (2-4)1053-1056 (2004).

 

            ABSTRACT: The piezoresistance of an InAs/AlGaSb heterostructure cantilever was measured as a function of magnetic field at a liquid helium temperature. The piezoresistance showed a similar magnetic-field-dependence to that of universal conductance fluctuation, which was observed in a two-terminal resistance of the same device. This result indicates that the quantum-mechanical interference significantly modulates the piezoresistance and clearly demonstrates the possibility of highly sensitive quantum-mechanical displacement sensing, which is promising for future microelctromechanical/nanoelctromechanical applications. (C) 2003 Elsevier B.V. All rights reserved.

 

208.    T. Yamaguchi, K. Yamazaki, and H. Namatsu

            "Influence of molecular weight of resist polymers on surface roughness and line-edge roughness"

            Journal Of Vacuum Science & Technology B 22 (6)2604-2610 (2004).

 

            ABSTRACT: The effect of molecular weight on the roughness of the dissolution front (surface roughness) and line-edge roughness (LER) was investigated in a chain-scission-type of positive-tone electron-beam resist. Surface roughness and LER were measured by directly observing the surface of flood-exposed resists after development and the sidewall of patterns, respectively, with an atomic force microscope. It was clarified that the molecular weight dependencies of surface roughness and LER are quite different. Surface roughness was found to increase with molecular weight. This is because the size of aggregates protruding from the surface as a result of the development process becomes larger as the molecular weight increases. In contrast, LER was found to be larger in a low-molecular-weight resist than in a high-molecular-weight resist. Moreover, the dependence of LER on the latent-image profile is different for low- and high-molecular-weight resists. For low-molecular-weight resist, LER is independent of the steepness of the latent image; whereas, for high- molecular-weight resist, it increases rapidly as the steepness decreases. These results can be explained by the relationship between the size of aggregates and the width of the transition zone between low- and high-dose regions of the latent-image profile. This strongly suggests that low-molecular-weight resists are not necessarily advantageous in reducing LER. (C) 2004 American Vacuum Society.

 

209.    T. Yamaguchi, and H. Namatsu

            "Effect of developer molecular size on roughness of dissolution front in electron-beam resist"

            Journal Of Vacuum Science & Technology B 22 (3)1037-1043 (2004).

 

            ABSTRACT: This article describes the generation of roughness at the dissolution front of electron-beam positive-tone resist. The effect of a developer solvent molecule on the surface roughness as well as on the dissolution rate is investigated from the viewpoint of the size of a solvent molecule. The relationship between the dissolution rate and solvent molecular size is represented by two straight lines with different slopes in a homologous series of alkyl acetate solvents. A bending point, which corresponds to a critical molecular size, exists between ethyl and propyl acetate. This indicates that the dissolution behavior is largely different between acetates that are larger or smaller than the critical molecular size. The size of a solvent molecule is the dominant factor determining the degree of surface roughness. For a solvent molecule larger than the critical molecular size, the roughness becomes large because polymer aggregates appear on the dissolution front. For a smaller solvent molecule, on the other hand, no aggregates appeared and the dissolution front is flat and smooth. The critical molecular size is about the same as the average size of voids (free volume holes) in resist films. These results indicate that the roughness strongly depends on how a solvent molecule penetrates the resist film through void regions inhomogeneously distributed in the resist polymer matrix due to polymer aggregation. (C) 2004 American Vacuum Society.

 

210.    T. Yamaguchi, and H. Namatsu

            "Impact of developers on roughness of dissolution front in electron-beam resists"

            Journal Of Photopolymer Science And Technology 17 (4)557-565 (2004).

 

            ABSTRACT: We describe the impact of various developers on the roughness of dissolution front of electron-beam positive-tone resist ZEP7000. In this study, two types of developers are investigated: single-solvent developer and binary-solvent developer. Atomic force microscope observations of dissolution fronts reveal that, for a homologous series of n-alkyl acetate as a single-solvent developer, there are three categories of dissolution process: molecular-level dissolution, aggregate extraction development, and their intermediate. Small solvent molecules, such as methyl- and ethyl acetate, are very effective for reducing roughness. For good solvents for ZEP resist as single-solvent developer, molecular-level dissolution also occurs and the dissolution front becomes very flat and smooth. However, these developers, thou-h effective for reducing roughness, lead to lower dissolution contrast. We clarified that binary-solvent developers consisting of these effective developers and n-hexane as a poor solvent, especially 1:1 ethyl acetate/n-hexane developer, provide both low roughness and high dissoluticn contrast.

 

211.    H. Yamamoto, M. Naito, A. Tsukada, and S. Suzuki

            "In situ angle-resolved photoemission study of MBE-grown (La,Ce)(2)CuO4 thin films"

            Physica C-superconductivity And Its Applications 412-14134-138 (2004).

 

            ABSTRACT: We have performed in situ angle-resolved photoemission spectroscopy on the electron doped cuprate superconductor La2-xCexCuO4 (x = 0.1) using high-quality films grown by molecular beam epitaxy. The obtained photoemission spectra were free from "dirt" peaks. In addition, the time evolution of the spectra due to impurity adsorption is rather gradual, and the sample surface is stable even at ambient temperature, which is in contrast with previous reports on bulk Nd2-xCexCuO4 (NCCO) single crystals. The energy distribution curves show clear dispersions near the Fermi energy (E-F) with some E-F crossings. The resultant Fermi surface is hole-like and centered around (pi, pi), which essentially agrees with that predicted for NCCO by band calculations and also with the experimentally determined Fermi surface of optimally doped NCCO (x = 0.15). (C) 2004 Published by Elsevier B.V.

 

212.    H. Yamamoto, K. Aoki, A. Tsukada, and M. Naito

            "Growth of Ba1-xKxBiO3 thin films by molecular beam epitaxy"

            Physica C-superconductivity And Its Applications 412-14192-195 (2004).

 

            ABSTRACT: Single-crystalline Ba1-xKxBiO3 (BKBO) films with x between 0 and 0.54 are prepared on SrTiO3(1 0 0) substrates by molecular beam epitaxy (MBE). The key to the MBE growth of BKBO is the reproducible deposition of K, which is achieved by using an alkaline metal dispenser (K2CrO4 with a reducing agent) to make the K source easy to handle, and also by using atomic absorption spectrometry to provide reliable K flux rate control. The films are superconducting for similar to0.31 less than or equal to x less than or equal to similar to0.54. The best film (x = 0.46) shows T-c(onset) = 24.5 K, T-c(end) = 24 K, rho(300 K) similar to 220 muOmega cm, and rho(30 K) similar to 150 muOmega cm. (C) 2004 Published by Elsevier B.V.

 

213.    M. Yamashita

            "Dynamics of evaporative cooling and growth of a Bose-Einstein condensate"

            Laser Physics 14 (4)597-602 (2004).

 

            ABSTRACT: The dynamics of evaporative cooling of magnetically trapped Rb-87 atoms is studied on the basis of the quantum kinetic theory of a Bose gas. The theoretical optimization of the cooling trajectory clarifies that the acceleration of evaporative cooling around the transition point of Bose-Einstein condensation is very effective against serious three-body recombination loss. The number of condensed atoms is expected to be largely enhanced by the optimization as compared with the typical value produced by the conventional evaporative cooling, where the frequency of the radio-frequency magnetic field is swept exponentially. Next, we precisely examine how the growth of a condensate depends on the experimental parameters of evaporative cooling in this inefficient "exponential-sweep" cooling. We find that, due to large nonlinear three-body loss, the number of condensed atoms finally becomes insensitive to the initial number of trapped atoms, the initial temperature, and the bias field of a magnetic trap. This result opens up the experimental possibility that the final number of condensed atoms can be well stabilized against the shot-to-shot fluctuations of experimental conditions in evaporative cooling.

 

214.    K. Yamazaki, T. Yamaguchi, and H. Namatsu

            "Three-dimensional nanofabrication with 10-nm resolution"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 43 (8B)L1111-L1113 (2004).

 

            ABSTRACT: We have devised three-dimensional (3D) nanofabrication technology using electron-beam (EB) lithography and a sample-rotation drive. Ten-nm resolution of patterning over a 3D sample and 3D fabrication was achieved by precise control of beam focusing for patterns divided based on the depth of focus of the EB. The focus control is carried out using an offline height-measurement system we developed, which provides focusing error of less than 2mum. The depth of focus was accurately derived using the wave optical method. We have demonstrated these techniques and the resulting resolution by making the world's smallest globe, which shows the minimum feature size of 10 nm over the world map.

 

215.    K. Yamazaki, and H. Namatsu

            "5-nm-order electron-beam lithography for nanodevice fabrication"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 43 (6B)3767-3771 (2004).

 

            ABSTRACT: We have developed 5-nm-order electron-beam (EB) lithography with good uniformity within a large main deflection field. The keys are a new electron optics system and a high-resolution resist (hydrogen silsesquioxane). Owing to the high resolution and good uniformity of the EB, the lithography can produce patterns with a minimum linewidth of 5 nm at the center and corners of the 500-mum-square main deflection field. Moreover, we accurately measured the beam diameter using a Si knife edge with Ta visors and thresholds of 50-90%. The measurement results agree well with the lithography results when the effect of secondary electrons is taken into consideration. These results demonstrate that high-precision 5-nm-order lithography has been established.

 

216.    K. Yamazaki, and H. Namatsu

            "Two-axis-of-rotation drive system in electron-beam lithography apparatus for nanotechnology applications"

            Microelectronic Engineering 73-7485-89 (2004).

 

            ABSTRACT: A two-axis-of-rotation drive system has been developed that enables electron-beam lithography (EBL) to be applied to three-dimensional (3D) nanofabrication. It is built on a pallet that can be loaded into the EBL apparatus, and rotates a sample while the e-beam writes on it. It has a positional accuracy of a few milliradians. In addition, a height-measurement system has also been developed. This helps to focus the e-beam on the surface of a rotating or non-planar sample, and enables fine patterns to be formed on such samples. These systems allow samples to be exposed to the e-beam from various directions, resulting in 3D fabrication with a high degree of freedom. A demonstration carried out on a polymethylmethacrylate sphere resulted in the formation of pillars with various shapes and about 100 nm in diameter. (C) 2004 Elsevier B.V. All rights reserved.

 

217.    T. Yamazaki, Y. Murata, K. Komatsu, K. Furukawa, M. Morita, N. Maruyama, T. Yamao, and S. Fujita

            "Synthesis and electrolytic polymerization of the ethylenedioxy-substituted terthiophene-fullerene dyad"

            Organic Letters 6 (26)4865-4868 (2004).

 

            ABSTRACT: [Graphics] Two derivatives of ethylenedioxy-substituted terthiophene-fullerene dyads were newly synthesized as the precursors for polythiophene having fullerene side chains. By electrolytic oxidation of dyad 1, the charm-bracelet type polythiophene, poly-1, was obtained as a purple film, which showed electrochemical activity, electrochromism, and photoelectronic response.

 

218.    R. Yano, H. Gotoh, Y. Hirayama, and S. Miyashita

            "Systematic pump-probe terahertz wave emission spectroscopy of a photoconductive antenna fabricated on low-temperature grown GaAs"

            Journal Of Applied Physics 96 (7)3635-3638 (2004).

 

            ABSTRACT: We performed pump-probe terahertz (THz) wave emission spectroscopy for a photoconductive antenna fabricated on low-temperature grown GaAs. When the pump pulse intensity was increased, the THz wave generated by the probe pulse showed an increase of the spectral amplitude in the low-frequency regime (<0.5 THz) and a decrease of the peak amplitude. The increase of the spectral amplitude and the decrease of the peak amplitude are related to the carrier density generated by the pump pulse, and are explained by the increase of the carrier trap time due to the saturation of the defect levels and by the carrier-carrier scattering process between carriers in the conduction band, respectively. (C) 2004 American Institute of Physics.

 

219.    R. Yano, H. Gotoh, Y. Hirayama, S. Miyashita, Y. Kadoya, K. Kusuda, and M. Yamanishi

            "Low-frequency spectral enhancement of THz electromagnetic waves emitted from InAs surface with increased excitation intensity"

            Journal Of Applied Physics 95 (4)2141-2145 (2004).

 

            ABSTRACT: We studied the excitation intensity dependence of the spectrum of the THz electromagnetic waves emitted from the surface of InAs excited by a femtosecond laser pulse. An enhancement of the spectral amplitude in the low-frequency regime (<0.6 THz) of the THz electromagnetic waves was observed when the excitation intensity was increased. To clarify the mechanism of the above phenomenon, we also performed THz wave emission experiments using a semi-insulating-GaAs sample. Due to the difference of the band-gap energies between InAs and GaAs, carriers excited to the conduction band experience different relaxation processes when they are excited by a laser pulse with a photon energy of 1.5 eV. Comparison of the experimental results for InAs and GaAs showed that the suppression of the intra-band relaxation induces the enhancement of the amplitude of the THz spectrum in the low-frequency regime for InAs. (C) 2004 American Institute of Physics.

 

220.    A. Yokoo, H. Suzuki, and M. Notomi

            "Organic photonic crystal band edge laser fabricated by direct nanoprinting"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 43 (6B)4009-4011 (2004).

 

            ABSTRACT: A direct nanoprinting technique is used to fabricate a pit arrangement on the surface of an organic amorphous emissive layer. A pit arrangement with a closely packed hexagonal pattern with a 400 nm pitch is successfully fabricated within 60 s. Pit depth is more than 70 nm and depends on press pressure. The fabricated structure is considered to be a photonic crystal band edge laser, and laser oscillation is confirmed by optical excitation. It is also confirmed that the oscillation threshold can be controlled simply by changing the press pressure used in the direct nanoprinting procedure. The results show that the use of the direct nanoprinting technique enables the fabrication of organic nanostructure devices such as photonic crystal band edge lasers with an organic emissive material.

 

221.    H. Yokoyama, T. Sato, K. Ono, Y. Hirayama, and S. Tarucha

            "Tunable quantum dot resonator embedded in a quantum wire"

            Physica E-low-dimensional Systems & Nanostructures 21 (2-4)527-531 (2004).

 

            ABSTRACT: Combined quantum wire and quantum dot system is theoretically predicted to show unique conductance properties associated with Coulomb interactions. We use a split gate technique to fabricate a quantum wire containing a quantum dot with two tunable potential barriers in a two-dimensional electron gas. We observe the effects of the quantum dot cavity on the electron transport through the quantum wire, such as Coulomb oscillations near the pinch-off voltage and periodic conductance oscillations on the first conductance plateau. (C) 2003 Elsevier B.V. All rights reserved.

 

222.    G. Yusa, K. Hashimoto, K. Muraki, T. Saku, and Y. Hirayama

            "Self-sustaining resistance oscillations: Electron-nuclear spin coupling in mesoscopic quantum Hall devices"

            Physical Review B 69 (16), 161302 (2004).

 

            ABSTRACT: We study electron-nuclear spin coupled systems implemented in mesoscopic fractional quantum Hall devices. We find that longitudinal resistance in such systems, oscillates with a period of several hundreds of seconds driven by a constant voltage instead of a constant current. The anomalous behavior suggests that an average nuclear spin polarization self-sustainingly oscillates between randomized and polarized states, which reveal the nonlinear nature of the mesoscopic electron-nuclear spin coupled systems.

 

223.    G. Yusa, K. Muraki, T. Saku, and Y. Hirayama

            "Intralayer backscattering in narrow GaAs/AlxGa1-xAs/GaAs bilayer channels"

            Physical Review B 69 (8), 085323 (2004).

 

            ABSTRACT: We study the magnetoresistance R-xx, and the Hall resistance R-xy in GaAs/AlxGa1-xAs/GaAs bilayer systems, in which the electron channel of each layer is latterally confined in a narrow Hall bar of width W=0.3-5mum. We observe that intralayer backscattering destroy some states peculiar to the bilayer system. R-xy plateaus at odd filling factors largely deviate from their integer values in monolayer quantum Hall (QH) states due to backscattering, while the normal R-xy plateau is observed from coupled QH states. Examining the backscattering both in the Hall bars and in their voltage probes, we discuss the suppression of the intralayer backscattering between edge channels strongly modified by the interlayer charge transfer between the front and the back channels.

 

224.    Z. H. Zhang, K. Sumitomo, F. Lin, H. Omi, and T. Ogino

            "Structure transition of Ge/Si(113) surfaces during Ge epitaxial growth"

            Physica E-low-dimensional Systems & Nanostructures 24 (1-2)157-160 (2004).

 

            ABSTRACT: It is observed that a Ge wetting layer on Si(113) changes its surface structure from an initial Si(113)-3 x 2 to Ge/ Si(113)-3 x 2 + 3 x 1, Ge/Si(113)-3 x 2 + 3 x 1 + 2 x 2, and finally Ge/Si(113)-2 x 2 for a few-ML epitaxial growth. It is demonstrated that such transition results from the epitaxial stress evolution. Specifically, the 2 x 2 confines the epilayer along the [33 (2) over bar] direction by tension and releases compression in the perpendicular direction of the [(1) over bar 10], forming trenches. Without reconstruction, the trenches are favorable for adatom nucleation and elongated growth of islands owing to dangling bonds and possible relaxation of the structure along the trenches. (C) 2004 Elsevier B.V. All rights reserved.

 

225.    Z. H. Zhang, K. Sumitomo, H. Omi, T. Ogino, and X. Zhu

            "Ge molecular beam epitaxy on Si(113): surface structures, nanowires and nanodots"

            Surface And Interface Analysis 36 (2)114-118 (2004).

 

            ABSTRACT: By performing epitaxial growth of Ge on Si(113) layer by layer, observed using scanning tunnelling microscopy, we show the Ge/Si(113) surface structure and island shape transition with an increase of Ge coverage and we discuss the transition in terms of epitaxial stress evolution and relaxation of the epitaxial morphologies. Nanofeatures of Ge epitaxial islands, such as nanowires and nanodots, are highlighted. Copyright (C) 2004 John Wiley Sons, Ltd.

 

226.    N. M. Zimmerman, E. Hourdakis, Y. Ono, A. Fujiwara, and Y. Takahashi

            "Error mechanisms and rates in tunable-barrier single-electron turnstiles and charge-coupled devices"

            Journal Of Applied Physics 96 (9)5254-5266 (2004).

 

            ABSTRACT: Si-based single-electron tunneling (SET) devices have of late become an important alternative to the metal-based ones, both for ultralarge scale integration (ULSI) electronics and for electrical metrology. We have very recently been designing, fabricating, and measuring SET turnstiles, pumps, and charge-coupled devices using tunable barriers in silicon. Having shown the potential of these devices, we wish to understand the error mechanisms which may manifest themselves, and to predict the level of these errors, in order to decide how feasible these devices will be. In this paper, we devote a substantial amount of analysis to the consideration of the "dynamical" error mechanism. This particular error considers how electrons split up as the barrier is raised, or alternatively how the Coulomb blockade is formed. We then consider a wide variety of other errors, including thermal, frequency, leakage, and heating errors. We show the dependence of the error rate on each of those mechanisms, and predict maxima or minima for the corresponding parameters. In the conclusion, we discuss the various advantages Si-based turnstiles or pumps would offer with respect to the metal-based ones. (C) 2004 American Institute of Physics.