1.    T. Akasaka, and T. Makimoto

            "BGaN micro-islands as novel buffers for GaN hetero-epitaxy"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 44 (50-52)L1506-L1508 (2005).

 

            ABSTRACT: BxGa1-xN (x similar to 0.02) micro-islands provide novel buffers for growing GaN films and AlGaN/GaN heterostructures on sapphire substrates. These films and heterostructures show low threading dislocation density (TDD), low residual carrier concentration, and high two-dimensional electron gas (2DEG) mobility: Non-doped GaN films had the TDD of 2 x 10(8) cm(-2) and the residual electron concentration of 9.4 x 10(9) cm(-3) at 433 K. AlGaN/GaN heterostructures exhibited 2DEG Hall mobility of 1720 and 13100 cm(2) V-1 s(-1) at 300 and 77K, respectively. An almost constant sheet electron density (2.9-4.2 x 10(12) cm(-2)) was obtained in the wide temperature range from 500 to 77 K, indicating the absence of parallel conduction in the GaN buffer layers.

 

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

            "Blue-purplish InGaN quantum wells with shallow depth of exciton localization"

            Applied Physics Letters 86 (19), 191902 (2005).

 

            ABSTRACT: Temperature-dependent time-resolved PL measurements were performed for blue-purplish InGaN multiple quantum wells grown on various kinds of underlying layers (ULs). By using an InGaN UL, excitons recombined radiatively at low temperatures, being confined in the shallow potential minima (7.1 meV), while they radiatively recombined two-dimensionally with high luminescent efficiency at around room temperature, being delocalized thermally from the potential minima. Therefore, the exciton localization is not necessary in order to obtain high luminescent efficiency, but it is important to annihilate the nonradiative recombination centers by incorporation of indium atoms into ULs. (c) 2005 American Institute of Physics.

 

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

            "Observation of enhanced thermal noise due to multiple Andreev reflection in ballistic InGaAs-based superconducting weak links"

            Applied Physics Letters 86 (13), 132505 (2005).

 

            ABSTRACT: We have experimentally obtained clear evidence of enhanced thermal noise in a ballistic superconductor-normal metal-superconductor junction with an InGaAs-based two-dimensional electron gas (2DEG). The thermal noise was estimated from a comparison of measured current-voltage characteristics with those obtained with an extended Ambegaokar and Halperin theory. As a consequence, we have observed enhanced thermal noise that is much larger than that expected with normal reservoirs.. This enhanced thermal noise can be explained by a theory that considers both the ballistic transport of the 2DEG and the thermal fluctuation in the coherent multiple Andreev reflection regime. (C) 2005 American Institute of Physics.

 

4.    T. Akiyama, H. Kageshima, M. Uematsu, and T. Ito

            "Theoretical investigation of oxygen diffusion in compressively strained high-density alpha-quartz"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 44 (10)7427-7429 (2005).

 

            ABSTRACT: The microscopic mechanisms of oxygen diffusion in compressively strained high-density alpha-quartz are investigated on the basis of first-principles total-energy calculations. It is found that both the incorporation energy of. oxygen into SiO2 and the energy barrier for its diffusion are dependent on the density of SiO2. The activation energies show that molecular-type oxygen is the dominant diffusion species over the entire density range. Furthermore, the activation volumes estimated from the results of the present first-principles calculations imply the retardation of oxygen diffusion in the high-density region.

 

5.    T. Akiyama, and H. Kageshima

            "Reaction mechanisms of oxygen at SiO2/Si(100) interface"

            Surface Science 576 (1-3)L65-L70 (2005).

 

            ABSTRACT: First-principles total-energy calculations are performed to clarify the reaction mechanisms of O atoms and O-2 molecules at SiO2/Si(1 0 0) interface. The calculated energies reveal that the incorporation Of O-2 molecules into the substrate dominates the interfacial reaction of the oxidant. The low energy barrier for O-2 incorporation (0.2 eV) corresponds to the hybridization of oxygen-2p orbitals Of O-2 and the valence band states of the Si substrate, while that for O atom incorporation corresponds to the O-O bond dissociation and the formation of Si-O-Si bonds. The cooperative reaction of each O atom in the O-2 molecule with each Si atom at the interface leads to the low energy barrier. (C) 2005 Elsevier B.V. All rights reserved.

 

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

            "New shell structures and their ground electronic states in spherical quantum dots (II) under magnetic field"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 44 (4A)2041-2050 (2005).

 

            ABSTRACT: We theoretically studied the electronic structure of the three-dimensional spherical parabolic quantum dot (3D-SPQD) under a magnetic field. We obtained the quantum dot orbitals (QDOs) and determined the ground state by using the extended UHF approach where the expectation values of the z component of the total orbital angular momentum ((L) over cap (z)) are conserved during the scf-procedure. The single-electron treatment predicts that the applied magnetic field (13) creates k-th new shells at the magnetic field of B-k = k(k + 2)/(k + 1)omega(0) with the shell-energy interval of h omega(0)/(k + 1), where omega(0)(= h/m*l(0)(2)) is the characteristic frequency originating from the spherical parabolic confinement potential. These shells are formed by the level crossing among multiple QDOs. The interelectron interaction breaks the simple level crossing but causes complicated dependences among the total energy, the chemical potential and their differences (magic numbers) with the magnetic field or the number of confinement electrons. The ground state having a higher spin multiplicity is theoretically predicted on the basis of the quasi-degeneracies of the QDOs around these shells.

 

7.    D. G. Austing, R. J. Hill, A. Patane, P. C. Main, M. Henini, L. Eaves, and S. Tarucha

            "Transport properties of gated sub-micron mesas incorporating InAs self-assembled quantum dots that conduct near zero bias"

            Physica E-low-dimensional Systems & Nanostructures 26 (1-4)482-485 (2005).

 

            ABSTRACT: We have fabricated multiple-gate vertical mesa transistors to investigate the Coulomb oscillation and Coulomb diamond-like characteristics of a planar ensemble of self-assembled InAs quantum dots located in the central plane of a single 14 nm Al0.2Ga0.8As tunnel barrier. The current-voltage characteristics are dominated by electron tunneling through the energy levels of just a few (similar to10) dots. Since these dots are located at various distances from the mesa side walls, the dot energy levels up-shift at different rates when the gate-adjustable front of the depletion region spreads towards the center of the mesa. This results in Coulomb-diamond apexes with different gate voltage signatures. (C) 2004 Elsevier B.V. All rights reserved.

 

8.    T. Bauch, E. Hurfeld, V. M. Krasnov, R. Delsing, H. Takayanagi, and T. Akazaki

            "Correlated quantization of supercurrent and conductance in a superconducting quantum point contact"

            Physical Review B 71 (17), 174502 (2005).

 

            ABSTRACT: We have measured the supercurrent and conductance of a superconducting quantum point contact in a superconductor two-dimensional electron gas-superconductor Josephson junction. We observe that the supercurrent and conductance change stepwise in a correlated manner as a function of the gate voltage. This was achieved by simultaneous measurement of the supercurrent and conductance at high bias from the same current voltage characteristic.

 

9.    P. Bertet, I. Chiorescu, G. Burkard, K. Semba, C. J. Harmans, D. P. DiVincenzo, and J. E. Mooij

            "Dephasing of a superconducting qubit induced by photon noise"

            Physical Review Letters 95 (25), 257002 (2005).

 

            ABSTRACT: We have studied the dephasing of a superconducting flux qubit coupled to a dc-SQUID based oscillator. By varying the bias conditions of both circuits we were able to tune their effective coupling strength. This allowed us to measure the effect of such a controllable and well-characterized environment on the qubit coherence. We can quantitatively account for our data with a simple model in which thermal fluctuations of the photon number in the oscillator are the limiting factor. In particular, we observe a strong reduction of the dephasing rate whenever the coupling is tuned to zero. At the optimal point we find a large spin-echo decay time of 4 mu s.

 

10.    I. Bosanac, H. Yamazaki, T. Matsu-ura, T. Michikawa, K. Mikoshiba, and M. Ikura

            "Crystal structure of the ligand binding suppressor domain of type 1 inositol 1,4,5-trisphosphate receptor"

            Molecular Cell 17 (2)193-203 (2005).

 

            ABSTRACT: Binding of inositol 1,4,5-trisphosphate (IP3) to the amino-terminal region Of IP3 receptor promotes Ca2+ release from the endoplasmic reticulum. Within the amino terminus, the first 220 residues directly preceding the IP3 binding core domain play a key role in IP3 binding suppression and regulatory protein interaction. Here we present a crystal structure of the suppressor domain of the mouse type 1 IP3 receptor at 1.8 Angstrom. Displaying a shape akin to a hammer, the suppressor region contains a Head subdomain forming the beta-trefoil fold and an Arm subdomain possessing a helix-turn-helix structure. The conserved region on the Head subdomain appeared to interact with the IP3 binding core domain and is in close proximity to the previously proposed binding sites of Homer, RACK1, calmodulin, and CaBP1. The present study sheds light onto the mechanism underlying the receptor's sensitivity to the ligand and its communication with cellular signaling proteins.

 

11.    Z. A. Burhanudin, R. Nuryadi, Y. Ishikawa, M. Tabe, and Y. Ono

            "Thermally-induced formation of Si wire array on an ultrathin (111) silicon-on-insulator substrate"

            Applied Physics Letters 87 (12), 121905 (2005).

 

            ABSTRACT: We have found that a Si wire array is formed by thermal agglomeration of an ultrathin (111) Si layer in a bonded silicon-on-insulator (SOI) structure, although previous studies for crystalline and amorphous Si layers on SiO2 only showed island formation. As starting material, (111) bonded SOI wafers with the top Si layers thinned to 5-9 nm were used. The samples were then subjected to a thermal treatment at 950 degrees C in an ultrahigh vacuum. Atomic force microscopy revealed that the (111) top Si layer is deformed into three sets of wire arrays in the three equivalent < 112 > directions. It is also shown that the patterning of a Si layer leads to the wire array selectively formed in one of these three directions. (c) 2005 American Institute of Physics.

 

12.    N. I. Cade, H. Gotoh, H. Kamada, T. Tawara, T. Sogawa, H. Nakano, and H. Okamoto

            "Charged exciton emission at 1.3 mu m from single InAs quantum dots grown by metalorganic chemical vapor deposition"

            Applied Physics Letters 87 (17), 172101 (2005).

 

            ABSTRACT: We have studied the emission properties of self-organized InAs quantum dots (QDs) grown in an InGaAs quantum well by metalorganic chemical vapor deposition. Low-temperature photoluminescence spectroscopy shows emission from single QDs around 1300 nm; we clearly observe the formation of neutral and charged exciton and biexciton states, and we obtain a biexciton binding energy of 3.1 meV. The dots exhibit an s-p shell splitting of approximately 100 meV, indicating strong confinement. (C) 2005 American Institute of Physics.

 

13.    B. Chesca, M. Seifried, T. Dahm, N. Schopohl, D. Koelle, R. Kleiner, and A. Tsukada

            "Observation of Andreev bound states in bicrystal grain-boundary Josephson junctions of the electron-doped superconductor La2-xCexCuO4-y"

            Physical Review B 71 (10), 104504 (2005).

 

            ABSTRACT: We observe a zero-bias conductance peak (ZBCP) in the ab-plane quasiparticle tunneling spectra of thin film grain-boundary Josephson junctions made of the electron-doped cuprate superconductor La2-xCexCuO4-y. An applied magnetic field reduces the spectral weight around zero energy and shifts it nonlinearly to higher energies consistent with a Doppler shift of the Andreev bound states (ABS) energy. For all magnetic fields the ZBCP appears simultaneously with the onset of superconductivity. These observations strongly suggest that the ZBCP results from the formation of ABS at the junction interfaces, and, consequently, that there is a sign change in the symmetry of the superconducting order parameter of this compound consistent with a d-wave symmetry.

 

14.    B. R. Choi, A. E. Hansen, T. Kontos, C. Hoffmann, S. Oberholzer, W. Belzig, C. Schonenberger, T. Akazaki, and H. Takayanagi

            "Shot-noise and conductance measurements of transparent superconductor/two-dimensional electron gas junctions"

            Physical Review B 72 (2), 024501 (2005).

 

            ABSTRACT: We have measured the conductance and shot noise of superconductor-normal metal (S-N) junctions between a niobium (Nb) film and a two-dimensional electron gas (2DEG), formed in an InAs-based semiconductor heterostructure. Adjacent to the junction, the 2DEG is shaped into a sub-micrometer beam splitter. The current shot noise measured through one arm of the beam splitter is found to be enhanced due to Andreev reflection. Both noise and conductance measurements indicate that the Nb-2DEG interface is of high quality with a transparency approaching approximate to 60-70 %. The present device can be seen as a quasi-ballistic S-N beam-splitter junction.

 

15.    W. R. Clarke, A. P. Micolich, A. R. Hamilton, M. Y. Simmons, K. Muraki, and Y. Hirayama

            "Fabrication and characterization of a 2D hole system a in novel (311)A GaAsSISFET"

            Microelectronics Journal 36 (3-6)327-330 (2005).

 

            ABSTRACT: We demonstrate a novel heterostructure for inducing 2D hole systems in (311)A GaAs-AlGaAs heterostructures that offers advantages over previous methods including low turn on voltages, easier fabrication and good inter-face roughness. The heterostructure incorporates a metallic p+-GaAs cap layer as an in situ top gate that pins the Fermi energy close to the valence band and can then be used to induce the 2D hole system at the GaAs/AlGaAs interface. (c) 2005 Elsevier Ltd. All rights reserved.

 

16.    N. Clement, and H. Inokawa

            "Foundry metal-oxide-semiconductor field-effect-transistor electrometer for single-electron detection"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 44 (7A)4855-4858 (2005).

 

            ABSTRACT: A conventional metal-oxide-semi conductor field-effect-transistor (MOSFET) fabricated by a foundry complementary metaloxide-semiconductor (CMOS) process has been investigated for use as an electrometer. The estimation of sensitivity in the linear and subthreshold regimes shows that the sensitivity of MOSFETs is comparable to that of single-electron transistors (SETs). In the experiments, charges in an island, which is electrically isolated by two MOSFETs in the "off" state and efficiently coupled to the electrometer via a floating gate, are detected sensitively. The results show clear steps in the drain current corresponding to electrons entering the island one by one, which demonstrates that conventional foundry MOSFETs have the ability to detect single electrons.

 

17.    E. Diamanti, H. Takesue, T. Honjo, K. Inoue, and Y. Yamamoto

            "Performance of various quantum-key-distribution systems using 1.55-mu m up-conversion single-photon detectors"

            Physical Review A 72 (5), 052311 (2005).

 

            ABSTRACT: We compare the performance of various quantum-key-distribution (QKD) systems using a single-photon detector, which combines frequency up-conversion in a periodically poled lithium niobate waveguide and a silicon avalanche photodiode (APD). The comparison is based on the secure communication rate as a function of distance for three QKD protocols: the Bennett-Brassard 1984, the Bennett-Brassard-Mermin 1992, and the coherent differential-phase-shift keying protocols. We show that the up-conversion detector allows for higher communication rates and longer communication distances than the commonly used InGaAs/InP APD for all three QKD protocols.

 

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

            "Band-gap shift transition in the photoluminescence of single-walled carbon nanotubes"

            Physical Review Letters 94 (24), 247401 (2005).

 

            ABSTRACT: Photoluminescence (PL) from single-walled carbon nanotubes suspended in free space is shown to persist to high temperatures, at least to 425 degrees C. A new transition is identified, shifting the optical band gap. This transition is abrupt, is hysteretic, depends simply on the PL emission energy, and is affected by the gas atmosphere. A model is proposed to explain the transition, connecting changes in the PL to the environment.

 

19.    A. Fontes, K. Ajito, A. A. Neves, W. L. Moreira, A. A. de Thomaz, L. C. Barbosa, A. M. de Paula, and C. L. Cesar

            "Raman, hyper-Raman, hyper-Rayleigh, two-photon luminescence and morphology-dependent resonance modes in a single optical tweezers system"

            Physical Review E 72 (1), 012903 (2005).

 

            ABSTRACT: We present a setup of optical tweezers combined with linear and nonlinear microspectroscopies that enhances the capabilities of capture and analysis of both techniques. We can use either a continuous-wave (cw) Ti:sapphire laser for Raman measurements or a pulsed femtosecond Ti:sapphire laser that permitted the observation of nonlinear results such as hyper-Raman, hyper-Rayleigh, and two-photon luminescence. Only the high peak intensity of the femtosecond laser allows the observation of all these nonlinear spectroscopies. The sensitivity of our system also permitted the observation of morphology-dependent resonance (MDR) modes of a single stained trapped microsphere of 6 mu m. The possibility of performing spectroscopy in a living microorganism optically trapped in any desired neighborhood would mean that one can dynamically observe the chemical reactions and/or mechanical properties changing in real time.

 

20.    S. Fujikawa, T. Kawamura, S. Bhunia, Y. Watanabe, K. Tokushima, Y. Tsusaka, Y. Kagoshima, and J. I. Matsui

            "Real-time observation of fractional-order x-ray reflection profiles of InP(001) during step-flow growth"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 44 (1-7)L144-L146 (2005).

 

            ABSTRACT: Fractional -order X-ray reflection profiles of (2 x 1)-InP(001) have been observed for the first time during step-flow growth of metalorganic chemical vapor deposition. Changes of the profiles have revealed that the coverage of (2 x 1) structures during the growth depends on the flow rates of indium and phosphorus sources. After stopping the growth, a slow recovery of peak intensity was observed with a time constant of lager than 1 min which corresponds to the residence time of indium atoms on the surface.

 

21.    Y. Furukawa, K. Hoshina, K. Yamanouchi, and H. Nakano

            "Ejection of triatomic hydrogen molecular ion from methanol in intense laser fields"

            Chemical Physics Letters 414 (1-3)117-121 (2005).

 

            ABSTRACT: The ejection of a triatomic or diatomic hydrogen molecular ion from methanol (CH3OH and CD3OH) in intense laser fields (86 fs, 800 nm, approximate to 10(2)(14 W/cm)) is investigated based on the momentum vector distributions of the fragment ions measured by the mass-resolved momentum imaging technique. From the relative yield of D-3(+), HD2+, D-2(+) and HD+ ejected from CD3OH2+ and the anisotropic distributions of their momentum vectors, the rates of the formation of triatomic (13 and HD+) and diatomic (D-2(+) and HD+) fragment ions, k(t) = 0.15 ps(-1) and k(d) = 0.31 ps(-1), respectively, and the H/D exchange rate, k(ex) = 0. 13 ps(-1), are derived. (c) 2005 Elsevier B.V. All rights reserved.

 

22.    N. Goel, J. Graham, J. C. Keay, K. Suzuki, S. Miyashita, M. B. Santos, and Y. Hirayama

            "Ballistic transport in InSb mesoscopic structures"

            Physica E-low-dimensional Systems & Nanostructures 26 (1-4)455-459 (2005).

 

            ABSTRACT: Two different device geometries are fabricated to investigate ballistic transport of electrons in low-dimensional InSb structures. Negative bend resistance is observed in four-terminal devices of channel widths ranging from 0.2 to 0.65 mum. We also report the observation of conductance quantization in quantum point contacts fabricated using in-plane gates. The one-dimensional subbands depopulate with increasing transverse magnetic field up to 3T. Zeeman splitting is resolved at magnetic fields above similar to0.9T. (C) 2004 Elsevier B.V. All rights reserved.

 

23.    H. Gotoh, T. Akasaka, T. Tawara, Y. Kobayashi, T. Makimoto, and H. Nakano

            "Efficient observation of narrow isolated photoluminescence spectra from spatially localized excitons in InGaN quantum wells"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 44 (42-45)L1381-L1384 (2005).

 

            ABSTRACT: We report discrete photoluminescence (PL) spectra with narrow linewidths from spatially localized excitons obtained in InGaN quantum wells (QWs) that are of a similar structure to those used in conventional optical devices. A micro-PL measurement combined with submicrometer-scale fabrication techniques allows us to create a small number of excitons in a laser spot and to detect the PL from single spatially localized excitons. A sharp PL line (linewidth: 0.34 meV limited by the resolution) is clearly obtained in a 0.2 mu m mesa-shaped QW, which originates from a sin le localized exciton. We show that the technique is a more powerful method of examining excitonic effects-than previously reported methods.

 

24.    H. Gotoh, H. Kamada, H. Nakano, T. Saitoh, H. Ando, and J. Temmyo

            "Optical nonlinearity induced by exciton-biexciton coherent effects in InGaAs quantum dots"

            Applied Physics Letters 87 (10), 102101 (2005).

 

            ABSTRACT: We report on large optical nonlinear effects induced by coherent interactions between excitons and biexcitons in quantum dots. The absorption spectra in an exciton-biexciton system are measured in InGaAs quantum dots by using single dot spectroscopy. The spectra exhibit unusual shapes that have a transparent region under a strong excitation condition. A pump-probe measurement ensures that the exciton state is erased by a quantum interference effect with exciton and biexciton photoabsorption processes. These results suggest that optical functions such as electromagnetically induced transparency are feasible with excitons and biexcitons in quantum dots. (c) 2005 American Institute of Physics.

 

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

            "Exciton absorption properties of coherently coupled exciton-biexciton systems in quantum dots"

            Physical Review B 71 (19), 195334 (2005).

 

            ABSTRACT: Exciton-biexciton coherent coupling effects are examined in semiconductor quantum dots. The exciton absorption spectrum is measured with the microphotoluminescence excitation technique in a single InGaAs quantum dot. The spectrum changes from a Lorenztian-type line shape to an unusual dip-shaped line shape with increasing excitation intensities in a higher exciton state where there is a large oscillator strength between the exciton and biexciton states. The intensity dependence of the dip energy width clearly indicates that coherent Rabi oscillation occurs between the exciton and biexciton states. The absorption properties with excitation light of different polarizations show that the dip-shaped spectra only appear when there is a large biexciton state population with linear polarization. A theoretical analysis undertaken with the density matrix method agrees well with experimental results. This agreement reveals that exciton-biexciton coherent interactions lead to unusual absorption spectra and contribute crucially to the optical properties of quantum dots. The exciton-biexciton coherent effects provide a scheme for controlling four distinguishable states, which can be applied to a demonstration of quantum gate operations.

 

26.    C. X. Han, N. Kasai, and K. Torimitsu

            "CA2: the most vulnerable sector to bicuculline exposure in rat hippocampal slice cultures"

            Neuroreport 16 (4)333-336 (2005).

 

            ABSTRACT: The vulnerability of the CA2 sector to chronic exposure to bicuculline was investigated in rat hippocampal slice cultures. Selective neuronal cell death was observed only in the CA2 sector after exposure to 6 mu M bicuculline for 12h, but the effect of the cell toxicity extended to the CA3 sector after 24 h. The effect was increased by adding 20 mu M roscovitine but was reduced by adding 200 nM omega-agatoxin IVA. Bicuculline also induced a calcium influx into neuronal cells mainly in the CA2 sector. These results suggest that CA2 is the most vulnerable sector to bicuculline exposure in hippocampal slice cultures, and that neuronal cell death in the CA2 sector involves the P/Q-type voltage-dependent calcium channel. NeuroReport 16:333-336 (c) 2005 Lippincott Williams T Wilkins.

 

27.    K. Hashimoto, K. Muraki, N. Kumada, T. Saku, and Y. Hirayama

            "Effects of inversion asymmetry on electron-nuclear spin coupling in semiconductor heterostructures: Possible role of spin-orbit interactions"

            Physical Review Letters 94 (14), 146601 (2005).

 

            ABSTRACT: We show that electron-nuclear spin coupling in semiconductor heterostructures is strongly modified by their potential inversion asymmetry. This is demonstrated in a GaAs quantum well, where we observe that the current-induced nuclear spin polarization at Landau-level filling factor nu=2/3 is completely suppressed when the quantum well is made largely asymmetric with gate voltages. Furthermore, we find that the nuclear spin relaxation rate is also modified by the potential asymmetry. These findings strongly suggest that even a very weak Rashba spin-orbit interaction can play a dominant role in determining the electron-nuclear spin coupling.

 

28.    T. Hattori, T. Yogi, Y. Hama, N. Watanabe, and R. Yano

            "Chirp control of free carrier injection in GaAs using femtosecond optical pulses"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 44 (8)6101-6104 (2005).

 

            ABSTRACT: Control of photoinjection of free carriers in bulk GaAs at room temperature was achieved by changing the chirp of the excitation light pulses having a duration in the 10fs regime. It was observed from pump-probe measurements that the transmittance increases for negatively chirped pump pulses, which is opposite to the trend observed with other materials. The result is explained by a combination of an intrapulse pump-dump process and band-gap renormalization, and shows the possibility of a new way to control the ultrafast dynamics of many-body systems in semiconductors.

 

29.    H. Hibino, Y. Watanabe, C. W. Hu, and I. S. Tsong

            "Thermal decay of superheated 7 x 7 islands and supercooled "1 x 1" vacancy islands on Si(111)"

            Physical Review B 72 (24), 245424 (2005).

 

            ABSTRACT: Low-energy electron microscopy was used to clarify how the thermal decay of two-dimensional (2D) islands and 2D vacancy islands depends on the surface structure. Using the first-order "1x1"-7x7 phase transition on Si(111), we produce 2D islands with superheated 7x7 phases above the critical temperature T-c, and compare their decay kinetics with that of islands with equilibrium surface phases of coexisting "1x1" and 7x7 structures. 2D vacancy islands with supercooled "1x1" phases are also compared with 2D vacancy islands with coexisting "1x1" and 7x7 phases below T-c. The superheated islands decay faster than the coexisting islands, indicating that the equilibrium adatom concentration, c(eq), of the superheated island is higher than that of the coexisting island. The supercooled vacancy islands also decay faster than the coexisting vacancy islands, because the supercooled vacancy islands have lower c(eq) than coexisting vacancy islands. These differences in c(eq) give us an estimate of the energy difference between the "1x1" and 7x7 structures.

 

30.    H. Hibino, and Y. Watanabe

            "Arrangement of Au-Si alloy islands at atomic steps"

            Surface Science 588 (1-3)L233-L238 (2005).

 

            ABSTRACT: We show using low-energy electron microscopy that Au deposition at around 400 degrees C leads to the arrangement of three-dimensional islands at single-layer steps on Si(111). Because the islands nucleate within a narrow coverage window, they have a small size distribution. After the coarsening of the islands during the interruption of the Au deposition, further deposition of Au results in the motion of islands into upper terraces with trenches left behind. This indicates that the islands are Au-Si alloy droplets. Additionally, the islands moved on terraces almost at constant velocities, but when they approach the upper-side steps, they jumped up to the steps. The atomic steps provide stable positions for Au-Si alloy islands, which means that the Au-Si alloy islands are suitable for arrangement using atomic steps. (c) 2005 Elsevier B.V. All rights reserved.

 

31.    H. Hibino, and Y. Watanabe

            "Growth of twinned epitaxial layers on Si(111)root 3x root 3-B studied by low-energy electron microscopy"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 44 (1A)358-364 (2005).

 

            ABSTRACT: Low-energy electron microscopy (LEEM) was used to investigate Si homoepitaxial growth on Si(111)root3 x root3-B. Dark-field LEEM images using the (1,0) spot clearly. indicate that two-dimensional islands twinned with respect to the substrate nucleate in the initial growth stage. Coalescence of the twinned islands forms twinned epitaxial layers at low growth temperatures. At high temperatures, however, twinned islands are transformed into untwinned islands even during growth, which suggests that small islands favor the twinned orientation, but that the energy difference between twinned and untwinned islands is reversed at a certain island size. After twinned epitaxial layer growth, we also observed transformation into untwinned layers by annealing. The transformation proceeds through the motion of the boundary between twinned and untwinned layers along the surface.

 

32.    Y. Homma, D. Takagi, S. Suzuki, K. Kanzaki, and Y. Kobayashi

            "Electron-microscopic imaging of single-walled carbon nanotubes grown on silicon and silicon oxide substrates"

            Journal Of Electron Microscopy 54I3-I7 (2005).

 

            ABSTRACT: Direct imaging of single-walled carbon nanotubes ( SWNTs) suspended on pillar-patterned Si or SiO2 substrates is investigated using transmission electron microscopy ( TEM) and scanning electron microscopy ( SEM). The suspended nanotubes are successfully observed by direct TEM imaging and it is seen that they have either individual or bundles of SWNTs. Low energy ( <= 2 keV) SEM produces high contrast images of suspended SWNTs. On the contrary, when SWNTs contact a SiO2 substrate, they are imaged using electron-beam induced current. The image brightness depends on the length of SWNTs.Direct imaging of single-walled carbon nanotubes (SWNTs) suspended on pillar-patterned Si or SiO2 substrates is investigated using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The suspended nanotubes are successfully observed by direct TEM imaging and it is seen that they have either individual or bundles of SWNTs. Low energy (<= 2 keV) SEM produces high contrast images of suspended SWNTs. On the contrary, when SWNTs contact a SiO2 substrate, they are imaged using electron-beam induced current. The image brightness depends on the length of SWNTs.

 

33.    Y. Homma

            "Summary of ISO/TC 201 standard: X ISO 17560 : 2002 - Surface chemical analysis - Secondary ion mass spectrometry - Method for depth profiling of boron in silicon"

            Surface And Interface Analysis 37 (1)90-91 (2005).

 

            ABSTRACT: This International Standard specifies a secondary ion mass spectrometric method using magnetic-sector or quadrupole mass spectrometers for depth profiling of boron in silicon, and using stylus profilometry or optical interferometry for depth calibration. This method is applicable to single-crystal, polycrystal or amorphous silicon specimens with boron atomic concentrations between 1 x 10(16) and 1 x 10(20) atoms cm(-3), and to the crater depth of 50 nm or deeper. Optical interferometry is generally applicable to crater depths in the range 0.5-5 mum. Copyright (C) 2004 John Wiley Sons, Ltd.

 

34.    T. Honjo, and K. Inoue

            "Plug & play quantum key distribution using modulation sidebands for shifting frequency"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 44 (9A)6550-6552 (2005).

 

            ABSTRACT: A Plug & Play quantum key distribution (QKD) system operating at a high pulse repetition frequency is presented. To avoid Rayleigh backscattering, modulation sidebands are used as frequency-shifted light. As the pulse repetition frequency increases, the quantum bit-error rate (QBER) in our proposed setup remains constant, while it increases in a conventional setup, which indicates that Plug & Play QKD at a high repetition frequency is possible with our scheme.

 

35.    W. P. Hu, H. Nakashima, K. Furukawa, Y. Kashimura, K. Ajito, Y. Q. Liu, D. B. Zhu, and K. Torimitsu

            "A self-assembled nano optical switch and transistor based on a rigid conjugated polymer, thioacetyl-end-functionalized poly(para-phenylene ethynylene)"

            Journal Of The American Chemical Society 127 (9)2804-2805 (2005).

 

            ABSTRACT:

 

36.    S. Hughes

            "Modified spontaneous emission and qubit entanglement from dipole-coupled quantum dots in a photonic crystal nanocavity"

            Physical Review Letters 94 (22), 227402 (2005).

 

            ABSTRACT: The modified spontaneous emission dynamics of two photon-coupled quantum dots in a planar-photonic crystal are theoretically investigated. Based on a photon Green function technique for quantizing the electromagnetic fields in arbitrary surroundings, pronounced vacuum Rabi oscillations and dipole-dipole interactions are self-consistently incorporated and are shown to result in a high degree of quantum-bit entanglement. Quantum dots with different optical dipole moments are also found to yield a very rich display of quantum dynamics and offer several advantages over coupling identical atoms.

 

37.    S. Hughes

            "Quantum emission dynamics from a single quantum dot in a planar photonic crystal nanocavity"

            Optics Letters 30 (11)1393-1395 (2005).

 

            ABSTRACT: A theoretical quantum-optical study of the modified spontaneous emission dynamics from a single quantum dot in a photonic crystal nanocavity is presented. By use of a photon Green function technique, enhanced single-photon emission and pronounced vacuum Rabi flops are demonstrated, in qualitative agreement with recent experiments. (c) 2005 Optical Society of America

 

38.    S. Hughes, L. Ramunno, J. F. Young, and J. E. Sipe

            "Extrinsic optical scattering loss in photonic crystal waveguides: Role of fabrication disorder and photon group velocity"

            Physical Review Letters 94 (3), 033903 (2005).

 

            ABSTRACT: Formulas are presented that provide clear physical insight into the phenomenon of extrinsic optical scattering loss in photonic crystal waveguides due to random fabrication imperfections such as surface roughness and disorder. Using a photon Green-function-tensor formalism, we derive explicit expressions for the backscattered and total transmission losses. Detailed calculations for planar photonic crystals yield extrinsic loss values in overall agreement with experimental measurements, including the full dispersion characteristics. We also report that loss in photonic crystal waveguides scales inversely with group velocity, at least, thereby raising serious questions about future low-loss applications based on operating frequencies that approach the photonic band edge.

 

39.    K. Inoue, and T. Honjo

            "Robustness of differential-phase-shift quantum key distribution against photon-number-splitting attack"

            Physical Review A 71 (4), 042305 (2005).

 

            ABSTRACT: A photon-number-splitting (PNS) attack against differential-phase-shift (DPS) quantum key distribution (QKD) is described. In the conventional 1984 Bennett-Brassard protocol, using weak laser light, the PNS attacks, which involve installing a lossless transmission line and blocking pulses from which extra photons cannot be picked up, impose a limit on the transmission distance. In contrast, use of a coherent pulse train in DPS QKD prevents the PNS attack and removes the distance limitation imposed by it. We carried out a DPS QKD experiment that simulated the situation where some pulses are blocked. The result showed that extra bit errors are induced in an eavesdropped condition, indicating the robustness of DPS QKD against PNS attacks.

 

40.    K. Inoue

            "Quantum key distribution using a series of quantum correlated photon pairs"

            Physical Review A 71 (3), 032301 (2005).

 

            ABSTRACT: The differential-phase-shift quantum key distribution (DPS-QKD) is a recently proposed QKD scheme in which a pulse train is transmitted through a quantum channel. This paper extends the ideal of the DPS-QKD to entanglement-based systems. Two schemes are presented. In one, an entanglement source sends pulse trains of signal and idler to two parties (Alice and Bob), respectively, who phase-modulate the incoming pulses and receive them after one-bit delay interferometers. In the other, two entanglement sources are prepared, one between Alice and a repeating node (Charlie) and one between Charlie and Bob, which send signal and idler pulse trains to Alice and Bob and Charlie, respectively. These schemes offer a longer distance between Alice and Bob than the conventional DPS-QKD.

 

41.    H. Ishizaki, T. Akiyama, K. Nakamura, K. Shiraishi, A. Taguchi, and T. Ito

            "Theoretical investigation of phase transition on GaAs(001)-c(4 x 4) surface"

            Applied Surface Science 244 (1-4)186-189 (2005).

 

            ABSTRACT: The surface phase transition between GaAs(001)-c(4 x 4) and -(2 x 4)beta 2 surfaces is systematically investigated by using our ab initio-based approach. The phase diagram calculations for the c(4 x 4) surfaces as functions of temperature and As pressure reveal that three kinds of c(4 x 4) surfaces consisting of Ga-As dimers and/or Ga-Ga dimers become stable near the phase transition temperature. The electron counting Monte Carlo simulation and ab initio calculations are also performed to investigate the structural change of the c(4 x 4) surface after predepositing a 0.5 monolayer of Ga on the three kinds of c(4 x 4) surfaces. The calculated results suggest that the c(4 x 4) surfaces consisting of three Ga-As dimers or one Ga-Ga dimer and two Ga-As dimers in the (4 x 4) surface unit cell possibly change their structures to (2 x 4)beta 2 structures with Ga-As surface dimers. The conventional (2 x 4)beta 2 surface consisting of As dimers finally appears due to destabilization of Ga-As dimers at high temperature and high pressure. (c) 2004 Elsevier B.V. All rights reserved.

 

42.    A. Ishizawa, and H. Nakano

            "Fluctuation of the carrier-envelope phase of a few-cycle laser pulse from a chirped-pulse amplification system with the gas pressure in a hollow fiber"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 44 (8)6039-6041 (2005).

 

            ABSTRACT: We experimentally confirmed that additional CEP fluctuations induced in a hollow fiber increased with gas pressure. A gas pressure in the hollow fiber of between 2 and 2.5 atm results in both a short-pulse generation and the small CEP fluctuation. We also measured the carrier-envelope phase (CEP) fluctuations of spectrally broadened intense pulses that passed through a hollow fiber. An additional carrier-envelope phase fluctuation of 0.12 rad was induced in white light generated in the hollow fiber under the optimum gas pressure.

 

43.    T. Ito, K. Asano, T. Akiyama, K. Nakamura, K. Shiraishi, and A. Taguchi

            "An ab initio-based approach to Ga adatom migration on GaAs(n 1 1)A-(001) non-planar surfaces"

            Applied Surface Science 244 (1-4)178-181 (2005).

 

            ABSTRACT: The behavior of Ga adatoms on GaAs(n 1 1)A (n = 2, 3, 4), (0 0 1)-(2 x 4)beta 2 and non-planar surfaces consisting of the (2 1 1)A and (0 0 1) are systematically investigated by ab initio-based approach and the Monte Carlo (MC) method. The ab initio total energy calculations clarify strong dependence of Ga adsorption energies on the surface index. Comparing these adsorption energies of Ga with the Ga chemical potentials in the vapor phase, Ga atoms predominantly adsorb on the (2 1 1)A and (3 1 1)A surfaces at high temperatures even beyond similar to 1100 K. On the other hand, Ga atoms tend to desorb from the (4 1 1)A and (0 0 1) surfaces at the high temperatures. Furthermore, the MC simulations reveal that diffusion coefficient of Ga adatoms across the (0 0 1) surface is larger than that on the (2 1 1)A surface. This is because Ga migration potential energies on the (0 0 1) surface are smaller than those on the (2 1 1)A surface. Reflecting these results, Ga adatoms on the (2 1 1)A-(0 0 1) non-planar surface migrate on the (2 1 1)A side surface beyond similar to 1100 K, whereas Ga adatoms mainly diffuse across the (0 0 1) surface below similar to 1100 K. (c) 2004 Elsevier B.V. All rights reserved.

 

44.    M. Iwai, Y. Tateishi, M. Hattori, A. Mizutani, T. Nakamura, A. Futatsugi, T. Inoue, T. Furuichi, T. Michikawa, and K. Mikoshiba

            "Molecular cloning of mouse type 2 and type 3 inositol 1,4,5-trisphosphate receptors and identification of a novel type 2 receptor splice variant"

            Journal Of Biological Chemistry 280 (11)10305-10317 (2005).

 

            ABSTRACT: We isolated cDNAs encoding type 2 and type 3 inositol 1,4,5-trisphosphate (IP3) receptors (IP(3)R2 and IP(3)R3, respectively) from mouse lung and found a novel alternative splicing segment, SIm2, at 176-208 of IP3R2. The long form (IP(3)R2 SIm2+) was dominant, but the short form (IP(3)R2 SIm2-) was detected in all tissues examined. IP(3)R2 SIm2- has neither IP3 binding activity nor Ca2+ releasing activity. In addition to its reticular distribution, IP(3)R2 SIm2+ is present in the form of clusters in the endoplasmic reticulum of resting COS-7 cells, and after ATP or Ca2+ ionophore stimulation, most of the IP(3)R2 SIm2+ is in clusters. IP(3)R3 is localized uniformly on the endoplasmic reticulum of resting cells and forms clusters after ATP or Ca2+ ionophore stimulation. IP(3)R2 SIm2- does not form clusters in either resting or stimulated cells. IP3 binding-deficient site-directed mutants of IP(3)R2 SIm2+ and IP(3)R3 fail to form clusters, indicating that IP3 binding is involved in the cluster formation by these isoforms. Coexpression of IP(3)R2 SIm2+ prevents stimulus-induced IP3R clustering, suggesting that IP(3)R2 SIm2- functions as a negative coordinator of stimulus-induced IP3R clustering. Expression of IP(3)R2 SIm2- in CHO-K1 cells significantly reduced ATP-induced Ca2+ entry, but not Ca2+ release, suggesting that the novel splice variant of IP(3)R2 specifically influences the dynamics of the sustained phase of Ca2+ signals.

 

45.    K. Iwata, M. Morino, M. Suzuki, A. Fukuda, A. Sawada, Z. F. Ezawa, N. Kumada, and Y. Hirayama

            "Anisotropic magnetotransport around the v=1 bilayer quantum Hall state"

            Journal Of Physics And Chemistry Of Solids 66 (8-9)1556-1559 (2005).

 

            ABSTRACT: An anisotropic magnetotransport that depends on a direction of an in-plane magnetic field was investigated in a bilayer quantum Hall system. We have found that the longitudinal resistance around the bilayer v = 1 quantum Hall state strongly varies when we changed the relative angle between the current and the in-plane field. Indeed, the anisotropy becomes remarkable at the phase transition point between the commensurate and incommensurate states. This result suggests that a unidirectional state appears around the transition. (c) 2005 Published by Elsevier Ltd.

 

46.    M. W. Jack, and M. Yamashita

            "Maximal entanglement of two spinor Bose-Einstein condensates"

            Physical Review A 71 (3), 033619 (2005).

 

            ABSTRACT: Starting with two weakly coupled antiferromagnetic spinor condensates, we show that by changing the sign of the coefficient of the spin interaction, U-2, via an optically induced Feshbach resonance, one can create an entangled state consisting of two anticorrelated ferromagnetic condensates. This state is maximally entangled and a generalization of the Bell state from two anticorrelated spin-1/2 particles to two anticorrelated spin-N/2 atomic samples, where N is the total number of atoms.

 

47.    M. W. Jack, and M. Yamashita

            "Bose-Hubbard model with attractive interactions"

            Physical Review A 71 (2), 023610 (2005).

 

            ABSTRACT: We consider the Bose-Hubbard model of atoms in an optical lattice potential when the atom-atom interactions are attractive. If the lowest-energy lattice sites are degenerate (such as in the homogeneous case), then, at a critical value of the interaction strength, a phase-coherent condensate becomes unstable to a quantum superposition such that the number distribution of each of the degenerate sites becomes double peaked. In the limit when the interaction dominates, the superposition becomes macroscopic and has the form \psi>proportional toSigma(j)e(j)(iphi)b(j)(daggerN)\vac>, where N is the total number of atoms and the sum ranges over the energy-degenerate sites.

 

48.    G. H. Jeong, S. Suzuki, Y. Kobayashi, A. Yamazaki, H. Yoshimura, and Y. Homma

            "Effect of nanoparticle density on narrow diameter distribution of carbon nanotubes and particle evolution during chemical vapor deposition growth"

            Journal Of Applied Physics 98 (12), 124311 (2005).

 

            ABSTRACT: Single-walled carbon nanotubes (SWNTs) were synthesized by chemical vapor deposition (CVD) using catalytic nanoparticles both on the substrates and above the substrates in order to investigate the effect of nanoparticle density on diameter-controlled SWNT growth. As the density of the catalytic nanoparticles increased, tube-diameter distribution broadened and the diameter itself also increased. SWNTs observed in this study were grown by the base-growth mechanism and their diameters were much smaller than those of the nanoparticles. Based on elaborate diameter measurements, we reasonably conjecture that the time evolution of catalytic nanoparticles during CVD growth can explain these large size differences. (c) 2005 American Institute of Physics.

 

49.    G. H. Jeong, A. Yamazaki, S. Suzuki, H. Yoshimura, Y. Kobayashi, and Y. Homma

            "Cobalt-filled apoferritin for suspended single-walled carbon nanotube growth with narrow diameter distribution"

            Journal Of The American Chemical Society 127 (23)8238-8239 (2005).

 

            ABSTRACT:

 

50.    A. Kaneko, Y. Homma, H. Hibino, and T. Ogino

            "Ultrahigh vacuum scanning electron microscope system combined with wide-movable scanning tunneling microscope"

            Review Of Scientific Instruments 76 (8), 083709 (2005).

 

            ABSTRACT: A surface analysis system has been newly developed with combination of ultrahigh vacuum scanning electron microscope (SEM) and wide-movable scanning tunneling microscope (STM). The basic performance is experimentally demonstrated. These SEM and STM images are clear enough to obtain details of surface structures. The STM unit moves horizontally over several millimeters by sliding motion of PZT actuators. The motion resolution is proved to be submicrometers. The STM tip mounted on another PZT scanner can be guided to a specific object on the sample surface during SEM observation. In the observation of a Si(111) surface rapidly cooled from high temperature, the STM tip was accurately guided to an isolated atomic step and slightly moved along it during SEM observation. The STM observation shows an asymmetry of the (7x7)-transformed region along the step between the upper and lower terraces. (7x7) bands continuously formed along the edge of terraces, while (7x7) domains distributed on the terraces slightly far from the step. These experiments show the wide-movable STM unit resolves a gap of observation area between SEM and STM and the system enables a specific object found in the SEM image to be observed easily by STM. (c) 2005 American Institute of Physics.

 

51.    N. Kasai, C. X. Han, and K. Torimitsu

            "Hydrogen peroxide distribution and neuronal cell death in a rat hippocampal slice"

            Sensors And Actuators B-chemical 108 (1-2)746-750 (2005).

 

            ABSTRACT: Hydrogen peroxide (H2O2), a by-product of a degenerative reaction of reactive oxygen species in mammalian cells, has been examined in association with the pathology of neurodegenerative disorders. In this study, we monitor the H2O2 release from a rat hippocampal slice culture at multiple positions using our novel electrochemical sensor array. The H2O2 sensor array is fabricated by modifying a 64-channel ITO electrode array with an enzyme, horseradish peroxidase, and an electron transfer mediator. A hippocampal slice is placed on the array and the current at each sensor is monitored using a multipotentiostat. When we introduce kainate (KA) into the solution to stimulate the slice, the H2O2 concentration remained largely unchanged. In contrast, in the presence of 3-amino-1,2,4-triazol (3-AT), a catalase inhibitor, we can observe a distinct increase in the H2O2 concentration as a result of KA stimulation especially in the CA3 region in the hippocampus. KA exposure is also shown to cause neuronal cell death in the CA3 region by Cresyl Violet staining. These results reveal that our H2O2 sensor array can detect H2O2 released from neurons by KA stimulation under catalase inhibition and that this H2O2 is associated with neuronal cell death. (c) 2005 Elsevier B.V. All rights reserved.

 

52.    M. Kasu, K. Ueda, H. Ye, Y. Yamauchi, S. Sasaki, and T. Makitnoto

            "2W/mm output power density at 1 GHz for diamond FETs"

            Electronics Letters 41 (22)1249-1250 (2005).

 

            ABSTRACT: Great improvement in the output power density of diamond FETs on a diamond homoepitaxial layer grown using a high-purity source gas is reported. For a device with a gate length of 0.1 mu m and gate width of 100 pro, at 1 GHz, maximum output power density of 2.1 W/mm, maximum power gain of 10.9 dB, and power added efficiency of 31.8% were obtained.

 

53.    Y. Katagiri, H. Takesue, and E. Hashimoto

            "Wavelength-scanning optical bandpass filters based on optomechatronics for optical-frequency sweepers"

            Ieee Transactions On Industrial Electronics 52 (4)992-1004 (2005).

 

            ABSTRACT: We propose and demonstrate a method for improving optical-frequency sweepers that uses a disk-shaped optical band-pass filter operated under the synchro-scan mode. We optimize the filter layer structure to achieve high linearity in optical-frequency tuning with the rotation angle of the disk, while maintaining a constant band-inhibition performance. We introduce an optical system that narrows the bandwidth by using an optimized beam coupler and improves the filtering performance by using a multiple-path method. The optimized filter enables a stable linear optical-frequency sweep when it is used with a motor stabilized by phase locking. The improved optical frequency sweepers can extend the sweep range to above 2 THz, while suppressing the accumulation of spontaneous emission noise.

 

54.    M. Kawamura, H. Yaguchi, N. Kikugawa, Y. Maeno, and H. Takayanagi

            "Tunneling properties at the interface between superconducting Sr2RuO4 and a Ru microinclusion"

            Journal Of The Physical Society Of Japan 74 (2)531-534 (2005).

 

            ABSTRACT: We have investigated the magnetic field and temperature dependence of the tunneling spectra of the eutectic system Sr2RuO4-Ru. Electric contacts to individual Ru lamellae embedded in Sr2RuO4 enable the tunneling spectra at the interface between ruthenate and a Ru microinclusion to be measured. A zero bias conductance peak (ZBCP) was observed in the bias voltage dependence of the differential conductance, suggesting that Andreev bound states are present at the interface. The ZBCP starts to appear at a temperature well below the superconducting transition temperature. The onset magnetic field of the ZBCP is also considerably smaller than the upper critical field when the magnetic field is parallel to the ab-plane. We propose that the difference between the onset of the ZBCP and the onset of superconductivity can be understood in terms of the existence of the single-component state predicted by Sigrist and Monien.

 

55.    T. Kawamura, S. Bhunia, Y. Watanabe, S. Fujikawa, J. Matsui, Y. Kagoshima, and Y. Tsusaka

            "High-resolution x-ray diffraction analysis of epitaxially grown indium phosphide nanowires"

            Journal Of Applied Physics 97 (8), 084318 (2005).

 

            ABSTRACT: Indium phosphide (InP) nanowires epitaxially grown on InP (111)B were investigated by using grazing incidence x-ray diffraction. A broad scattering at the tail of InP (2 (2) over bar0) diffraction and an additional peak at the low angle side were observed, showing the formation of nanowires and alloys of the gold catalysts and indium. Scattering intensity along the [1 (1) over bar0] direction was compared with calculations based on a cylinder model. The best fit was obtained for a 5.5-nm radius with a 2.5-nm deviation, which was smaller than the values determined from the secondary electron microscopy and photoluminescence spectroscopy measurements. This result is explained by an oxide layer on the nanowire sidewalls and the low quantum efficiency of photoluminescence yields for small nanowires since x-ray diffraction directly detects crystalline structure of nanowires. (C) 2005 American Institute of Physics.

 

56.    V. M. Krasnov, T. Bauch, S. Intiso, E. Hurfeld, T. Akazaki, H. Takayanagi, and P. Delsing

            "Collapse of thermal activation in moderately damped Josephson junctions"

            Physical Review Letters 95 (15), 157002 (2005).

 

            ABSTRACT: We study switching current statistics in moderately damped Nb-InAs-Nb and intrinsic Bi2Sr2CaCu2O8+delta Josephson junctions. A paradoxical collapse of thermal activation with increasing temperature is reported and explained by the interplay of two conflicting consequences of thermal fluctuations, which can both assist in premature escape and help in retrapping back into the stationary state. We analyze the influence of dissipation on the thermal escape by tuning damping with a gate voltage, magnetic field, temperature, and an in situ capacitor.

 

57.    T. Kubo, and Y. Tokura

            "Electron transport in magnetic-field-induced quasi-one-dimensional electron systems in semiconductor nanowhiskers"

            Physica E-low-dimensional Systems & Nanostructures 29 (3-4)525-529 (2005).

 

            ABSTRACT: Many-body effects on tunneling of electrons in semiconductor nanowhiskers are investigated in a magnetic quantum limit. We consider the system with which bulk and edge states coexist. We show that interaction parameters of edge states are much smaller than those of bulk states and the tunneling conductance of edge states hardly depends on temperature and the singular behavior Of tunneling conductance of bulk states can be observed. (c) 2005 Elsevier B.V. All rights reserved.

 

58.    T. Kubo, and Y. Tokura

            "Many-body effects on tunneling of electrons in magnetic-field-induced quasi-one-dimensional electron systems in semiconductor nanowhiskers"

            Journal Of The Physical Society Of Japan 74 (2)519-522 (2005).

 

            ABSTRACT: The effects of electron-electron interaction on tunneling in a semiconductor nanowhisker are studied in a magnetic quantum limit. We consider the system with which bulk and edge states coexist. In bulk states, the temperature dependence of the transmission probability is qualitatively similar to that of a one-dimensional electron system. We investigate the contributions of edge states on transmission probability in bulk states. Those contributions can be neglected within our approximation which takes into account only the most divergent terms at low temperatures.

 

59.    N. Kumada, K. Muraki, K. Hashimoto, and Y. Hirayama

            "Spin degree of freedom in the nu=1 bilayer electron system investigated by nuclear spin relaxation"

            Physical Review Letters 94 (9), 096802 (2005).

 

            ABSTRACT: The nuclear-spin-relaxation rate 1/T-1 has been measured in a bilayer electron system at and around total Landau level filling factor nu=1. The measured 1/T-1, which probes electron spin fluctuations, is found to increase gradually from the quantum Hall (QH) state at low fields through a phase transition to the compressible state at high fields. Furthermore, 1/T-1 in the QH state shows a noticeable increase away from nu=1. These results demonstrate that, as opposed to common assumption, the electron spin degree of freedom is not completely frozen either in the QH or the compressible states.

 

60.    K. Kumakura, T. Makimoto, N. Kobayashi, T. Hashizume, T. Fukui, and H. Hasegawa

            "Minority carrier diffusion length in GaN: Dislocation density and doping concentration dependence"

            Applied Physics Letters 86 (5), 052105 (2005).

 

            ABSTRACT: We investigated the minority carrier diffusion length in p- and n-GaN by performing electron-beam-induced current measurements of GaN p-n junction diodes. Minority electron diffusion length in p-GaN strongly depended on the Mg doping concentration for relatively low dislocation density below 108 cm(-2). It increased from 220 to 950 nm with decreasing Mg doping concentration from 3 X 10(19) to 4 X 10(18) cm(-3). For relatively high dislocation density above 109 cm(-2), it was less than 300 nm and independent of the Mg doping concentration. On the other hand, the minority hole diffusion length in n-GaN was shorter than 250 nm and less affected by the dislocation density and Si doping concentration. We discuss the doping-concentration and dislocation-density dependence of minority carrier diffusion length. (C) 2005 American Institute of Physics.

 

61.    K. Kumakura, and T. Makimoto

            "High-voltage operation with high current gain of pnp AlGaN/GaN heterojunction bipolar transistors with thin n-type GaN base"

            Applied Physics Letters 86 (2), 023506 (2005).

 

            ABSTRACT: A pnp AlGaN/GaN heterojunction bipolar transistor (HBT) with a thin n-GaN base shows high-voltage operation with high current gain in the common-emitter configuration at room temperature. The device structure was grown by metalorganic vapor phase epitaxy on a sapphire substrate. The emitter area is 30 mumx50 mum. The HBT can operate at high voltage of 70 V with the maximum current gain of 40 at the collector current of 10 mA. The maximum output power density is 172 kW/cm(2). Transport characteristics in the HBT were also investigated. At small collector current, the current gain is dominated by the recombination current at the emitter-base heterojunction. At moderate collector current, the calculated minority hole diffusion length well agreed with that determined from electron beam induced current measurements, indicating the current gain is dominated by the minority carrier diffusion. At large collector current, a high injection effect was observed in the current gain characteristics. (C) 2005 American Institute of Physics.

 

62.    E. Kuramochi, M. Notomi, S. Hughes, A. Shinya, T. Watanabe, and L. Ramunno

            "Disorder-induced scattering loss of line-defect waveguides in photonic crystal slabs"

            Physical Review B 72 (16), 161318 (2005).

 

            ABSTRACT: Detailed propagation loss spectrum measurements for line-defect waveguides in silicon photonic crystal slabs are presented, which show record low loss values (5 dB/cm) and complicated frequency dependence. We quantitatively analyze the origin of the loss spectrum shape using a photon Green function theory and obtain a very good agreement, thus providing an explanation of the complex physical mechanisms responsible for the observed propagation loss. In particular, we demonstrate the influence of out-plane, backward, intermode, and in-plane scattering processes on the observed loss spectra, induced by the structural disorder that occurs during fabrication, and highlight the importance of backward and intermode scattering in these waveguides.

 

63.    J. Kurian, H. Sato, T. Makimoto, and M. Naito

            "Silver-assisted growth of NdBa2Cu3O7-delta thin films: An approach for the growth of superior quality ceramic oxide films"

            Applied Physics Letters 87 (2), 022501 (2005).

 

            ABSTRACT: We have grown NdBa2Cu3O7-delta films under silver atomic flux by molecular-beam epitaxy, which show a drastic improvement in microstructure and also crystallinity leading to a 30% enhancement in critical current density. The most remarkable point is that the final film is free from silver. The key to our process in achieving a silver-free film was the use of rf-activated oxygen that oxidizes silver, nonvolatile, to silver oxide, volatile at the deposition temperature. This process enables one to utilize the beneficial effects of silver in the growth of oxide films and at the same time ensures that the final film be free from silver, which is important for high-frequency applications. This method can be used in the growth of thin films of other complex oxide materials. (c) 2005 American Institute of Physics.

 

64.    J. Kurian, and M. Naito

            "MBE growth of large area RE-123 superconductor thin films for microwave applications"

            Ieee Transactions On Applied Superconductivity 15 (2)2966-2969 (2005).

 

            ABSTRACT: Large area high quality epitaxial thin films are required for many commercial microwave applications of high temperature superconductors. Although there exists different techniques for the growth of high temperature superconductor films, molecular beam epitaxy (MBE) growth has the advantage of achieving better homogeneity and scalability. We have succeeded in growing high quality RE-123 (RE = La, Nd, Eu, Gd, Dy) superconductor films by MBE. The growth of high quality films by MBE requires strict compositional control and optimization of growth temperature and oxidation conditions. Strict compositional control is the most vital in achieving best characteristics of the films and we have found that composition close to 123 yields the best results. By optimizing the different growth parameters, we have grown high quality RE-123 films with high T-C(0) & J(C), low resistivity and low microwave surface resistance. Among the different RE-123 films we have investigated so far, Nd-123 superconductor films shows the better characteristics. Nd-123 films grown on (100) MgO under optimized conditions gave a T-C(0) of 94 K with a J(C) above 3.5 MA/cm(2) at 77 K. These Nd-123 films show excellent metallicity (rho(300) kappa/rho 100 kappa similar to 3) with room temperature resistivity of similar to 140 mu Omega.cm. The films had excellent in-plane orientation and high crystallinity. The MBE grown Nd-123 films show low microwave surface resistance (similar to 870 mu Omega at 77 K @ 22 GHz) making them better candidate for microwave applications.

 

65.    T. Kutsuzawa, H. Tanaka, S. Saito, H. Nakano, K. Semba, and H. Takayanagi

            "Coherent control of a flux qubit by phase-shifted resonant microwave pulses"

            Applied Physics Letters 87 (7), 073501 (2005).

 

            ABSTRACT: The quantum state of a flux qubit was successfully pulse controlled by using a resonant microwave. We observed Ramsey fringes by applying a pair of phase-shifted pi/2 microwave pulses without introducing detuning. With this method, the qubit state can be rotated on an arbitrary axis in the x-y plane of the Bloch sphere in a rotating frame. We successfully observed qubit Larmor precession stroboscopically with an angular velocity of 2 pi x11.4G rad/s. In combination with Rabi pulses, this method enables us to achieve full control of single qubit rotation with shorter operation time. (C) 2005 American Institute of Physics.

 

66.    C. Langrock, E. Diamanti, R. V. Roussev, Y. Yamamoto, M. M. Fejer, and H. Takesue

            "Highly efficient single-photon detection at communication wavelengths by use of upconversion in reverse-proton-exchanged periodically poled LiNbO3 waveguides"

            Optics Letters 30 (13)1725-1727 (2005).

 

            ABSTRACT: Conventional single-photon detectors at communication wavelengths suffer from low quantum efficiencies and large dark counts. We present a single-photon detection system, operating at communication wavelengths, based on guided-wave frequency upconversion in a nonlinear crystal with an overall system detection efficiency (upconversion + detection) exceeding 46% at 1.56 mu m. This system consists of a fiber-pigtailed reverse-proton-exchanged periodically poled LiNbO3 waveguide device in conjunction with a silicon-based single-photon counting module. (c) 2005 Optical Society of America.

 

67.    H. S. Lee, H. J. Kim, H. J. Kim, M. H. Jung, Y. Jo, S. I. Lee, A. Tsukada, and M. Naito

            "Three-dimensional superconductivity of the structurally two-dimensional superconductor La1.87Y0.13CuO4: study of an angle-dependent critical current density"

            Superconductor Science & Technology 18 (7)944-947 (2005).

 

            ABSTRACT: The angular dependence of the critical current density (J(c)(theta)) of La1.87Y0.13CuO4 was measured at different fields and temperatures. Jc (theta) showed a strong angular variation, which is typical for uniaxial anisotropic superconductors. Although La1.87Y0.13CuO4 has a quasi-two-dimensional (2D) crystal structure, the angular variation could be consistently described using the usual anisotropic three-dimensional (3D) Ginzburg-Landau theory with a small anisotropy ratio, but not by Tinkham's multi-layer model, which is known to be suitable for describing quasi-2D superconductors. These results indicate that the 2D crystallographic structure plays a minor role in La1.87Y0.13CuO4 because of the elongated c axis coherence length. From our analysis, we were also able to estimate the anisotropy ratio, the ab plane, and the c axis coherence length.

 

68.    Y. P. Lin, T. Koga, and J. Nitta

            "Effect of an InP/In0.53Ga0.47As interface on spin-orbit interaction in In0.52Al0.48As/In0.53Ga0.47As heterostructures"

            Physical Review B 71 (4), 045328 (2005).

 

            ABSTRACT: We report the effect of the insertion of an InP/In0.53Ga47As Interface on the Rashba spin-orbit interaction in In0.52Al0.48As/In0.53Ga0.47As quantum wells. A small spin split-off energy in InP produces a very intriguing band lineup in the valence bands in this system. With or without this InP layer above the In0.53Ga47As well, the overall values of the spin-orbit coupling constant alpha turned out to be enhanced or diminished for samples with the front- or back-doping position, respectively. These experimental results, using weak antilocalization analysis, are compared with the results of the k.p theory. The actual conditions of the interfaces and materials should account for the quantitative difference in magnitude between the measurements and calculations.

 

69.    H. W. Liu, T. Fujisawa, T. Hayashi, and Y. Hirayama

            "Pauli spin blockade in cotunneling transport through a double quantum dot"

            Physical Review B 72 (16), 161305 (2005).

 

            ABSTRACT: We study spin correlation in a double quantum dot containing a few electrons in each dot (around 10). Clear current rectification with negative differential conductance is observed in the cotunneling regime, which is well explained by a Pauli spin blockade. The current feature is discussed in connection with exchange singlet-triplet splitting based on two simple models, one of which takes coherent interdot coupling and the other incoherent interdot coupling into account.

 

70.    N. Maeda, T. Makimura, T. Maruyama, C. X. Wang, M. Hiroki, H. Yokoyama, T. Makimoto, T. Kobayashi, and T. Enoki

            "DC and RF characteristics in Al2O3/Si3N4 insulated-gate AlGaN/GaN heterostructure field-effect transistors"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 44 (20-23)L646-L648 (2005).

 

            ABSTRACT: Al2O3/Si3N4 insulated-gate AlGaN/GaN heterostructure field-effect transistors (HFETs) have been fabricated, where excellent RF characteristics have been obtained in addition to the low gate leakage current as the result of employing the metal-insulator-semiconductor (MIS) structure. In an HFET with a gate length (L-g) of 0.1 mu m, the cutoff frequency (f(T)) and maximum oscillation frequency (f(max)) were estimated to be 70 and 90 GHz, respectively. The drain current density (I-d) and transconductance (g(m)) were 1.30 A/mm and 293 mS/mm, respectively. The gate leakage current (I-g) was as low as 4 x 10(-5) A/mm even at a forward bias voltage of +3 V.

 

71.    N. Maeda, T. Makimura, C. X. Wang, M. Hiroki, T. Makimoto, T. Kobayashi, and T. Enoki

            "Al2O3/Si3N4 insulated gate channel-doped AlGaN/GaN heterostructure field-effect transistors with regrown ohmic structure: Low gate leakage current with high transconductance"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 44 (4B)2747-2750 (2005).

 

            ABSTRACT: An advanced structure of AlGaN/GaN heterostructure field-effect transistors (HFETs) has been proposed and fabricated, which is characterized by the following structural features: (i) a metal-insulator-semiconductor (MIS) structure using an Al2O3/Si3N4 bilayer gate insulator to reduce the gate leakage current, (ii) a thin AlGaN barrier with a doped channel to simultaneously obtain the high transconductance and high drain current, and (iii) a regrown ohmic structure to reduce the contact resistance. The fabricated devices have been proved to exhibit attractive characteristics such as low gate leakage current, low contact resistance, high drain current, and high transconductance. An HFET with a gate length of 0.1 mu m has exhibited a gate leakage Current density of below 10(-4) A/mm even at a gate voltage of +3 V. It has also exhibited a low contact resistance of 0.3 Omega mm, a high maximum drain current density of 1.23 A/mm, and a high transconductance of 280 mS/mm, which is the highest transconductance ever reported in the category of MIS-HFETs. The cutoff frequency and maximum oscillation frequency, measured with the pad capacitances included, were 52 and 75 GHz, respectively. The proposed structure has thus been proved to be effective in further improving the device performance in GaN-based HFETs.

 

72.    T. Makimoto, Y. Yamauchi, T. Kido, K. Kumakura, Y. Taniyasu, M. Kasu, and N. Matsumoto

            "Strained thick p-InGaN layers for GaN/InGaN heterojunction bipolar transistors on sapphire substrates"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 44 (4B)2722-2725 (2005).

 

            ABSTRACT: Thick p-InGaN layers were grown on GaN by metalorganic vapor phase epitaxy to investigate the strain inside p-InGaN using a reciprocal space map of X-ray diffraction intensity. It was found that a large part of p-InGaN grows coherently on the GaN buffer layer, even though it is much thicker than the calculated critical thickness. This result means that few dislocations are generated at the InGaN/GaN interface. Using this strained thick p-InGaN as a base, a GaN/InGaN heterojunction bipolar transistor was fabricated on a sapphire substrate. Its maximum current gain was as high as 1000 and its offset voltage as low as 0.2 V, which matches that calculated from the conduction-band discontinuity between the n-GaN emitter and the p-InGaN base.

 

73.    K. Maruyama, F. Morikoshi, and V. Vedral

            "Thermodynamical detection of entanglement by Maxwell's demons"

            Physical Review A 71 (1), 012108 (2005).

 

            ABSTRACT: Quantum correlation, or entanglement, is now believed to be an indispensable physical resource for certain tasks in quantum information processing, for which classically correlated states cannot be useful. Besides information processing, what kind of physical processes can exploit entanglement? In this paper, we show that there is indeed a more basic relationship between entanglement and its usefulness in thermodynamics. We derive an inequality showing that we can extract more work out of a heat bath via entangled systems than via classically correlated ones. We also analyze the work balance of the process as a heat engine, in connection with the second law of thermodynamics.

 

74.    T. Matsumoto, Y. Homma, and Y. Kobayashi

            "Bridging growth of single-walled carbon nanotubes on nanostructures by low-pressure hot-filament chemical vapor deposition"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 44 (10)7709-7712 (2005).

 

            ABSTRACT: Suspended single-walled carbon nanotubes (SWNTs) bridging between Si- or SiO2 nano-pillars were synthesized at low pressure using hot-filament chemical vapor deposition. The relation between the bridging probability of SWNTs and growth conditions was analyzed statistically. The bridging probability of the SWNTs strongly depends on pillar configuration, including pillar spacing, but is not significantly affected by the pressure, growth method, pillar material, and gas flow. These results indicate that environment in the gas phase has little influence on the suspended growth of SWNTs, and they support our vibratory growth model, in which the. vibration of growing nanotubes plays a crucial role in bridging to an adjacent pillar.

 

75.    T. Matsuoka

            "Progress in nitride semiconductors from GaN to InN - MOVPE growth and characteristics"

            Superlattices And Microstructures 37 (1)19-32 (2005).

 

            ABSTRACT: This paper reviews the field of nitride semiconductors ranging from GaN to InN with respect to metalorganic vapor phase epitaxy growth and characteristics starting from the period of singlecrystalline films. Progress has been made on many fronts. For InGaN, a key material for the emitting layer of blue light-emitting-diodes, using nitrogen as the carrier and bubbling gases for metalorganic sources has been found to enhance indium incorporation, and composition control of InGaN has been achieved. The phase separation of the InGaAIN system has been semiempirically predicted using the strictly regular solution model. Regarding InN, which is a mysterious material, its band-gap energy has been found to be half the reported value. The polarity of the substrate has been found to affect the characteristics of epitaxially grown GaN. Finally, from a future perspective, InGaAIN laser diodes promise a laser diode with uncooled and high power operation, which is strongly required for optical communications systems. (C) 2004 Elsevier Ltd. All rights reserved.

 

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

            "Universal spin-induced time reversal symmetry breaking in two-dimensional electron gases with Rashba spin-orbit interaction"

            Physical Review Letters 94 (18), 186805 (2005).

 

            ABSTRACT: We have experimentally studied the spin-induced time reversal symmetry (TRS) breaking as a function of the relative strength of the Zeeman energy (E-Z) and the Rashba spin-orbit interaction energy (E-SOI), in InGaAs-based 2D electron gases. We find that the TRS breaking, and hence the associated dephasing time τ(φ)(B), saturates when E-Z becomes comparable to E-SOI. Moreover, we show that the spin-induced TRS breaking mechanism is a universal function of the ratio E-Z/E-SOI, within the experimental accuracy.

 

77.    T. Mitate, S. Mizuno, H. Takahata, R. Kakegawa, T. Matsuoka, and N. Kuwano

            "InN polarity determination by convergent-beam electron diffraction"

            Applied Physics Letters 86 (13), 134103 (2005).

 

            ABSTRACT: To establish an accurate determination technique for the polarity of InN by convergent-beam electron diffraction (CBED), we clarified the influence of the electron incidence direction, film thickness, and the temperature factor B on CBED patterns by simulation. The electron incidence direction of [1(1) over bar 00] and a film thinner than 50 nm were found to be preferable for easy and reliable polarity determination. Using an InN film grown on a (000(1) over bar) GaN template on (0001) sapphire by metalorganic vapor-phase epitaxy, observation of the CBED pattern in the thin region of the film was confirmed from the simulation result. This InN film was clearly determined to have N polarity and the value of B was estimated to be less than 2.0 angstrom(2). (C) 2005 American Institute of Physics.

 

78.    M. Nagase, K. Nakamatsu, S. Matsui, and H. Namatsu

            "Carbon multiprobes with nanosprings integrated on Si cantilever using focused-ion-beam technology"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 44 (7B)5409-5412 (2005).

 

            ABSTRACT: A new multiprobe system for scanning probe microscopy for electrical property measurements has been developed. Four carbon probes with nanosprings have been grown using focused-ion-beam chemical vapor deposition (FIB-CVD) on a Si cantilever with A1 electrodes. The diameter of the carbon probe is 110 nm, and the diameter of the nanospring is 380 nm. The total height of the probe with the nanospring is approximately 10 mu m. The stiffness of the probe is sufficiently high for imaging in the contact mode. The nanosprings compensate for the height differences between the four probes. It is confirmed that electrical contacts between a conductive sample and all four probes are established. This is the first report on a FIB-CVD probe with a nanospring actually operating as a nano-electromechanical system.

 

79.    K. Nakamatsu, M. Nagase, J. Y. Igaki, H. Namatsu, and S. Matsui

            "Mechanical characteristics and its annealing effect of diamondlike-carbon nanosprings fabricated by focused-ion-beam chemical vapor deposition"

            Journal Of Vacuum Science & Technology B 23 (6)2801-2805 (2005).

 

            ABSTRACT: Our investigation of diamondlike-carbon (DLC) nanosprings with a 130-nm spring section diameter, which were fabricated by focused-ion-beam chemical vapor deposition (FIB-CVD), showed for the first time that nanosprings can be stretched. We observed large displacements of the FIB-CVD nanosprings in situ optical microscopy; in other words, the nanosprings showed behavior similar to that of macroscale springs. In addition, we investigated the dependence of the spring constant of the DLC nanosprings on the spring diameter. The spring constants, measured using commercially available cantilevers, ranged from 0.47 to 0.07 N/m. The diameter dependence of the measured spring constant could be accurately expressed by the conventional formula for a coil spring. The estimated shear modulus of the DLC nanosprings was about 70 GPa. This value is very close to the value of conventional coil springs made of steel. Furthermore, We measured the stiffness of the annealed nanospring at 1000 degrees C in vacuum. The stiffness was decreased to approximately half compared to the stiffness of the spring without annealing. (c) 2005 American Vacuum Society.

 

80.    K. Nakamatsu, M. Nagase, H. Namatsu, and S. Matsui

            "Mechanical characteristics of diamond-like-carbon nanosprings fabricated by focused-ion-beam chemical vapor deposition"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 44 (37-41)L1228-L1230 (2005).

 

            ABSTRACT: Our investigation of diamond-like-carbon (DLC) nanosprings with a 130-nm spring section diameter, which were fabricated by focused-ion-beam chemical vapor deposition (FIB-CVD), showed for the first time that nanosprings can be stretched. We observed large displacements of the FIB-CVD nanosprings with in-situ optical microscopy; in other words, the nanosprings showed behavior similar to that of macroscale springs. In addition, we investigated the dependence of the spring constant of the DLC nanosprings on the spring diameter. The spring constants, measured using commercially available cantilevers, ranged from 0.47 to 0.07 N/m. The diameter dependence of the measured spring constant was accurately expressed by the conventional formula for a coil spring. The estimated shear modulus of the DLC nano-springs was about 70 GPa. This value is very close to the value of conventional coil springs made of steel.

 

81.    K. Nakamatsu, K. Watanabe, K. Tone, H. Namatsu, and S. Matsui

            "Nanoimprint and nanocontact technologies using hydrogen silsesquioxane"

            Journal Of Vacuum Science & Technology B 23 (2)507-512 (2005).

 

            ABSTRACT: Room-temperature nanoimprint lithography (RT-NIL) and nanocontact printing (RT-NCP) processes using hydrogen silsesquioxane (HSQ) are promising techniques for fabricating various nanostructure devices. We have evaluated the linewidth dependence of the HSQ imprinted depth and the baking-temperature dependence.of HSQ replicated patterns after RT-NIL. We have also demonstrated an advanced bilayer resist process with HSQ as a top layer and AZ photoresist as a bottom layer; this process can be used to fabricate high-aspect resist patterns on a Si substrate for RT-NlL and RT-NCP. The etching-rate ratio of the AZ photoresist to HSQ exceeds 100 for O-2 reactive-ion etching, which means the etching tolerance of the HSQ top layer is sufficient to enable its use as a mask. We have fabricated high-aspect nanostructure patterns with 100 nm linewidth and 1 gm height using RT-NIL and 150 nm linewidth and I pm height by using RT-NCP. Furthermore, we have successfully transferred An electrode patterns from a mold onto HSQ resin by using the adhesion properties of HSQ. (c) 2005 American Vacuum Society.

 

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

            "Zn1-xCdxO/ZnO heterostructures for visible light emitting devices"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 44 (1-7)L4-L6 (2005).

 

            ABSTRACT: Wurtzite Zn1-xCdxO/ZnO heterostructures were successfully grown by remote plasma enhanced metalorganic chemical vapor deposition (RPE-MOCVD) and were investigated by photoluminescence (PL) spectroscopy. The flatness of Zn1-xCdxO films was investigated by an atomic force microscope (AFM), indicating the typical RNIS value of 0.5 nm. The optical properties of the Zn0.96Cd0.04O film were characterized by micro-PL at 4 K, exhibiting micro-structural and positional uniformities in the films. In the double heterostructure consisting of ZnO/Zn0.92Cd0.08O/ZnO, temperature and excitation intensity dependencies of PL spectra were examined. The PL emission is characterized as localized and free exciton emission. A dependence with a slope near unity is obtained from the excitation dependence of the PL intensity. Blue-green emission (2.78 eV) was demonstrated from the double-heterostructure at room temperature.

 

83.    H. Nakashima, K. Furukawa, K. Ajito, Y. Kashimura, and K. Torimitsu

            "Selective chemisorption of end-functionalized conjugated polymer on macro- and nanoscale-surfaces"

            Langmuir 21 (2)511-515 (2005).

 

            ABSTRACT: Linear and conjugated poly(p-phenylene ethynylene)s (PPEs) with three different types of functionalized end groups (thiolacetate, isocyanide, and carboxylic acid groups) were synthesized, and their selective chemisorption behavior on various substrate surfaces were investigated using UV/vis transmission absorption spectroscopy. The UV/vis spectra of the PPEs were clearly dependent on the chemical affinity between the PPE end group and the solid surfaces. Furthermore, regarding the chemisorption of thiolacetate modified polymer on a nanoscopic gold particle surface. we visualized novel polymer-colloid nanoarchitectures such as a barbell-type nanohybrid and interconnected polymer nanowire structures that are successively linked through gold nanoparticles.

 

84.    H. Namatsu, and M. Sato

            "Supercritical improvement of resist patterns by introducing functional molecules"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 44 (1-7)L227-L229 (2005).

 

            ABSTRACT: A new performance enhancement technique for resists has been developed that involves the use of supercritical fluid and functional molecules. Because it is an excellent solvent, the supercritical fluid dissolves the molecules, which provide functions originally lacking in the resist material; and the good diffusivity of supercritical fluid distributes the molecules throughout the resist. Thus, functions can be added to a resist without degrading its sensitivity or development characteristics because the process is performed after exposure and development. Furthermore, since the molecules are dispersed uniformly, there is no change in the line width of resist patterns. This advanced technique for improving resists using supercritical fluid has great potential to change the current concept of resist processes.

 

85.    A. K. Newaz, W. Song, E. E. Mendez, Y. Lin, and J. Nitta

            "Shot-noise characteristics of triple-barrier resonant-tunneling diodes"

            Physical Review B 71 (19), 195303 (2005).

 

            ABSTRACT: We have found experimentally that the shot noise in InAlAs-InGaAs-InAlAs triple-barrier resonant-tunneling diodes (TBRTD) is reduced over the 2eI Poissonian value whenever their differential conductance is positive, and is enhanced over 2eI when the differential conductance is negative. This behavior, although qualitatively similar to that found in double-barrier diodes, differs from it in important details. In TBRTDs the noise reduction is considerably greater than that predicted by a semiclassical model, and the enhancement does not correlate with the strength of the negative differential conductance. These results suggest an incomplete understanding of the noise properties of multiple-barrier heterostructures.

 

86.    K. Nishiguchi, O. Crauste, H. Namatsu, S. Horiguchi, Y. Ono, A. Fujiwara, Y. Takahashi, and H. Inokawa

            "Back-gate effect on Coulomb blockade in silicon-on-insulator trench wires"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 44 (10)7717-7719 (2005).

 

            ABSTRACT: A back-gate (BG) effect on a Coulomb blockade in a double-gate silicon-on-insulator (SOI) nanowire is investigated. The nanowire, which is situated at the bottom of a trench and connected to thicker source/drain regions, has a naturally formed barrier at both ends and works as a single-electron transistor at low temperatures. We found that a negative BG voltage increases the charging energy of the Coulomb-blockade island in the nanowire as well as the tunnel resistance of the barriers. This indicates the possibility that the BG voltage shifts the electron wave functions in the source/drain area away from the Coulomb-blockade island and decreases the capacitance of the small junctions located at both ends of the island.

 

87.    A. Nishikawa, K. Kumakura, T. Akasaka, and T. Makimoto

            "Current-voltage characteristics of p-InGaN/n-GaN vertical conducting diodes on n(+)-SiC substrates"

            Applied Physics Letters 87 (23), 233505 (2005).

 

            ABSTRACT: p-InGaN/n-GaN vertical conducting diodes have been grown on n(+)-SiC substrates by low-pressure metalorganic vapor phase epitaxy and their current-voltage characteristics have been investigated. The typical forward voltage drop was 3.8-4.0 V at a forward current density of 100 A/cm(2) with an on-state resistance of similar to 1.3 m Omega cm(2). The ideality factor of the samples was similar to 2, meaning that the tunneling current through defects is small enough in these devices. The breakdown voltage (V-B) increased with increasing n-GaN layer thickness, while it increased with decreasing carrier concentration of the layer by substituting undoped GaN for n-GaN. When the undoped GaN layer thickness was increased to 1800 nm, the highest breakdown voltage of 305 V was obtained with a low on-state resistance (R-on) of 1.51 m Omega cm(2), leading to the figure-of-merit, (V-B)(2)/R-on, of 62 MW/cm(2). (c) 2005 Americian Institute of Physics.

 

88.    J. Nitta, and M. Steiner

            "Magnetization properties of microstructured NiFe rings investigated using semiconductor/ferromagnet hybrid structures"

            Journal Of Superconductivity 18 (3)331-334 (2005).

 

            ABSTRACT: Magnetization reversal processes in microstructured NiFe rings are studied by fringe-field-induced local Hall magnetometry. This semiconductor-based technique yields a high sensitivity of magnetic stray fields and allows us to detect magnetization hysteresis loops of single NiFe rings. The transition fields can be controlled by the ratio between inner- and outer-ring diameter. Comparison between Hall measurements and numerical simulation suggests that there are four different magnetization states in two integrated rings.

 

89.    J. Nitta, and M. Steiner

            "Semiconductor/ferromagnet hybrid devices to probe magnetisation states in microstructured NiFe rings"

            Iee Proceedings-circuits Devices And Systems 152 (4)297-300 (2005).

 

            ABSTRACT: Magnetisation reversal processes of tiricrostructured NiFe rings are studied by fringing-field-induced local Hall effect (LHE) and numerical model calculations. This semiconductor-based technique yields a high sensitivity of magnetic stray fields and allows the authors to detect magnetisation hysteresis loops of single NiFe rings. For narrow rings, sharp transitions from so called 'onion' to the 'vortex' state are detected. Only onion and global vortex states are possible magnetisation configurations in narrow rings. In rings with smaller inner diameter, the transitions are more complex. The minor loop analysis of rings shows that onion and global vortex states are stable and independent of the magnetic history, but the local vortex state depends on the way the magnetic field has been swept beforehand. The switching fields can be controlled by the inner diameter in good agreement with the computational results.

 

90.    M. Noda, A. Tsukada, H. Yamamoto, and M. Naito

            "Origin of superconducting carriers in "non-doped" T'-(La,RE)(2)CuO4 (RE = Sm, Eu, Gd, Tb, Lu, and Y) prepared by molecular beam epitaxy"

            Physica C-superconductivity And Its Applications 426220-224 (2005).

 

            ABSTRACT: We have performed a systematic investigation of the variations of the lattice constants with substituent rare-earth element concentration x in the nominally undoped superconductors T'-La2-x3+REx3+CuO4 (RE = Sm, Eu, Gd, Tb, Lu, and Y), which we have recently discovered using MBE. The results show both the in-plane and out-of-plane lattice constants (a(0) and c(0) linearly decrease with x, whose extrapolation to x = 2 agrees well with the reported a(0) and c(0) values for each T'-RE2CuO4. This behavior is what one would expect simply from the ionic size difference between La3+ and RE3+. The absence of the Cu-O bond stretching due to electron-doping, which is commonly observed in electron-doped T' and infinite-layer superconductors, implies that electron-doping via oxygen deficiencies is, at least, not a main source of charge carriers. (c) 2005 Published by Elsevier B.V.

 

91.    M. Notomi, A. Shinya, S. Mitsugi, G. Kira, E. Kuramochi, and T. Tanabe

            "Optical bistable switching action of Si high-Q photonic-crystal nanocavities"

            Optics Express 13 (7)2678-2687 (2005).

 

            ABSTRACT: We have demonstrated all-optical bistable switching operation of resonant-tunnelling devices with ultra-small high-Q Si photonic-crystal nanocavities. Due to their high Q/V ratio, the switching energy is extremely small in comparison with that of conventional devices using the same optical nonlinear mechanism. We also show that they exhibit all-optical-transistor action by using two resonant modes. These ultrasmall unique nonlinear bistable devices have potentials to function as various signal processing functions in photonic-crystal-based optical-circuits. (C) 2005 Optical Society of America.

 

92.    H. Oberst, Y. Tashiro, K. Shimizu, and F. Shimizu

            "Quantum reflection of He-* on silicon"

            Physical Review A 71 (5), 052901 (2005).

 

            ABSTRACT: A cold beam of He-* (2 S-3(1)) atoms is used at grazing incidence to study the quantum reflection on a flat polished silicon surface. We measure the reflectivity as a function of the normal incident velocity component between 3 and 30 cm/s. Our result is in reasonable agreement with a calculation of the attractive van der Waals surface potential using the dielectric function of Si and the dipole polarizability of He-*. We discuss the influence of the conductivity and of a thin oxide layer on the potential. By comparing our data to those previously measured with Ne-* atoms, we are also able to confirm the scaling of the reflectivity with atomic mass.

 

93.    H. Oberst, D. Kouznetsov, K. Shimizu, J. Fujita, and F. Shimizu

            "Fresnel diffraction mirror for an atomic wave"

            Physical Review Letters 94 (1), 013203 (2005).

 

            ABSTRACT: We have experimentally demonstrated a material-independent mirror for atomic waves that uses the Fresnel diffraction at an array of parallel ridges. He* (2 S-3(1)) and Ne* (1s(3)) atomic waves were reflected coherently on a silicon plate with a microfabricated grating structure, consisting of narrow wall-like ridges. We measured the reflectivity at grazing incidence as a function of the incident velocity and angle. Our data show that the reflectivity on this type of mirror depends only on the distance between the ridges, the wavelength, and the incident angle, but is insensitive to the material of the grating structure. The reflectivity is observed to increase by 2 orders of magnitude, compared to that of a flat polished silicon surface, where the reflection is caused by the attractive surface potential. For He* atoms, the measured reflectivity exceeds 10% for normal incident velocities below about 25 cm/s.

 

94.    K. Oguri, Y. Okano, T. Nishikawa, and H. Nakano

            "Transient observation of extended x-ray absorption fine structure in laser-melted Si by using femtosecond laser-produced-plasma soft x ray"

            Applied Physics Letters 87 (1), 011503 (2005).

 

            ABSTRACT: We have demonstrated the time-resolved measurement of the extended x-ray absorption fine structure (EXAFS) in laser-melted Si foil by using a pump-probe absorption spectroscopy system that utilizes a femtosecond laser-produced-plasma soft x-ray source. By using 100-fs laser irradiation, we observed the transient change in the Si L-edge EXAFS, that is, a slight shortening of its oscillation period and a decrease in its oscillation amplitude. This result suggests that the Si-Si atomic distance expanded and structural disordering occurred as a result of the production of liquid Si. (c) 2005 American Institute of Physics.

 

95.    J. Ohe, M. Yamamoto, T. Ohtsuki, and J. Nitta

            "Mesoscopic Stern-Gerlach spin filter by nonuniform spin-orbit interaction"

            Physical Review B 72 (4), 041308 (2005).

 

            ABSTRACT: A spin filtering in a two-dimensional electron system with nonuniform spin-orbit interactions (SOI) is theoretically studied. The strength of SOI is modulated perpendicular to the charge current. A spatial gradient of effective magnetic field due to the nonuniform SOI causes the Stern-Gerlach-type spin separation. The direction of the polarization is perpendicular to the current and parallel to the spatial gradient. Almost 100% spin polarization can be realized even without applying any external magnetic fields and without attaching ferromagnetic contacts. The spin polarization persists even in the presence of randomness.

 

96.    Y. Ohminami, S. Suzuki, N. Matsudaira, T. Nomura, W. J. Chun, K. Ijima, M. Nakamura, K. Mukasa, M. Nagase, and K. Asakura

            "Preparation and characterization of a microfabricated oxide-on-oxide catalyst of alpha-Sb2O4/VSbO4"

            Bulletin Of The Chemical Society Of Japan 78 (3)435-442 (2005).

 

            ABSTRACT: We have prepared microfabricated alpha-Sb2O4 thin films on VSbO4 by electron lithography. The VSbO4 thin films were prepared on a Si substrate by a sol-gel method combined with a spin coating. The size, separation and arrangement of the alpha-Sb2O4 overlayer were controlled by electron-beam lithography. We could successfully draw 0.5 mu m wide lines with a separation of 2 pm. A preliminary study on the catalysis showed an enhancement of the selectivity in a propene conversion reaction to acrolein on a microfabricated alpha-Sb2O4/VSbO4.

 

97.    H. Okamoto, T. Yamada, H. Miyazaki, T. Nakanishi, K. Takeda, K. Usui, I. Obataya, H. Mihara, H. Azehara, W. Mizutani, K. Hashimoto, H. Yamaguchi, and Y. Hirayama

            "Difference in self-assembling morphology of peptide nanorings"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 44 (11)8240-8248 (2005).

 

            ABSTRACT: We synthesized the peptide nanorings of cyclo[-(D-Ala-L-Gln)(3)], cyclo[-(D-CyS-L-Gln)(3)], CyC10[-D-Cys-L-HiS-D-Ala-L-Asn-Gly-L-Gln-1 and Cyc1o[-(L-Gln)(5)], and studied the way in which the difference in the type and/or number of component amino acid residues changes the self-assembling morphology of the nanorings on gold substrates by atomic force microscopy. The study revealed that CyClo[-(D-Ala-L-Gln)(3)] formed nanotube bundles through inter-ring hydrogen bonds, while the nanorings of CyC10[-(D-CyS-L-Gln)3] adhered to the gold surface directly due to the high affinity of thiol to gold. In contrast, a random amino acid sequence of cyclo[-D-CyS-L-HiS-D-Ala-L-Asn-GlY-L-Gln-] resulted in many isolated nanotubes, which were first observed in the present study. While the D,L-peptide nanotubes have very straight forms, the homo-L-peptide of cyclo[-(L-Gln)(5)] formed interesting randomly branching nanotubes that were entwined and grew on the substrate. Scanning tunneling microscopy was also performed and high-resolution images of both the peptide nanotubes and the nanotube bundles were obtained.

 

98.    H. Okamoto, T. Akazaki, M. Ueki, and H. Yamaguchi

            "Strongly enhanced sensitivity of piezoresistive cantilevers by utilizing the superconducting proximity effect"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 44 (28-32)L893-L895 (2005).

 

            ABSTRACT: We fabricated a novel piezoresistive cantilever that integrates a superconductor-semiconductor-superconductor (S-Sm-S) junction. The cantilever was processed from an InAs/AlGaSb heterostructure and a submicron-size niobium gap was patterned to form a Nb-InAs-Nb junction, at which the deflection of the cantilever can be detected as resistance change, i.e., piezoresistance. The resulting piezoresistance at similar to 2K strongly depends on the bias current, and we confirmed that the piezoresistance is enhanced by two orders of magnitude at the critical current, where transition between superconducting state and normal state occurs in the S-Sm-S junction. This indicates that S-Sm-S junctions can be applied for highly sensitive displacement and force sensors.

 

99.    H. Omi, and Y. Homma

            "Self-ordering on vicinal Si(111) during molecular beam epitaxy"

            Physical Review B 72 (19), 195322 (2005).

 

            ABSTRACT: Surface patterns on vicinal Si(111) miscut toward the [112] direction during homoepitaxial step-flow molecular beam epitaxy were investigated by atomic force microscopy and cross-sectional transmission electron microscopy as a function of growth thickness, miscut angle, and growth temperature. We found a one-dimensional universal periodicity of surface patterns after about 200-nm-thick homoepitaxial growth on the vicinal surface at the growth temperature between 700 and 780 degrees C, which is independent of miscut angle. We discuss the possibility that the growth induced long-range ordering caused by faceting through a energetic balance between (7x7) terraces and (1x1) step-bunched quasifacets on the growing surface.

 

100.    H. Omi, Y. Homma, V. Tonchev, and A. Pimpinelli

            "New types of unstable step-flow growth on Si(111)-(7 x 7) during molecular beam epitaxy: Scaling and universality"

            Physical Review Letters 95 (21), 216101 (2005).

 

            ABSTRACT: New types of unstable homoepitaxial growth of vicinal Si(111)-(7 x 7) surfaces are studied using ex situ atomic force microscopy. The growth features are two types of step bunching with straight step edges between 700 and 775 degrees C and one type of simultaneous bunching and meandering at 800 degrees C. The results of a quantitative size scaling analysis of the straight steps are discussed from the perspective of universality classes in bunching theory.

 

101.    H. Omi, T. Kawamura, S. Fujikawa, Y. Tsusaka, Y. Kagoshima, and J. Matsui

            "In-plane strain distribution in the surface region of thin silicon overlayers on insulator"

            Applied Physics Letters 86 (26), 263112 (2005).

 

            ABSTRACT: A thin silicon nano-overlayer (SNOL) fabricated by oxidation and etchback in a separation by implantation of oxygen wafer was investigated by grazing incident x-ray diffraction at incident angles between 0.01 degrees and 0.1 degrees below the critical angle of total reflection (0.18 degrees). We measured {220} reflections by probing the sample in depth and found that the SNOL has finite domains under strain close to the surface. We also found that annealing the sample up to 1000 degrees C significantly reduced inhomogeneous in depth strain and increased the size of the domains in the surface region of the SNOL. (c) 2005 American Institute of Physics.

 

102.    Y. Ono, K. Nishiguchi, H. Inokawa, S. Horiguchi, and Y. Takahashi

            "Charge-state control of phosphorus donors in silicon-on-insulator metal-oxide-semiconductor field-effect transistor"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 44 (4B)2588-2591 (2005).

 

            ABSTRACT: The drain current vs gate-voltage characteristics of a phosphorus-doped n-channel silicon-on-insulator metal-oxide-semiconductor field-effect transistor have been investigated. It was shown that, by controlling the voltage to the substrate at 20 K, the charge states of phosphorus donors can be changed in a controlled manner. Most of the donors are neutralized for the substrate voltage of around 0V, while a major portion of the donors is ionized for a positive or negative voltage. Such a change can be detected by monitoring the change in the threshold voltage of the transistor. This is an experimental demonstration of the systematic control and monitoring of donor charge states in silicon.

 

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

            "Manipulation and detection of single electrons for future information processing"

            Journal Of Applied Physics 97 (3), 031101 (2005).

 

            ABSTRACT: The ultimate goal of future information processing might be the realization of a circuit in which one bit is represented by a single electron. Such a challenging circuit would comprise elemental devices whose tasks are to drag, transfer, and detect single electrons. In achieving these tasks, the Coulomb blockade, which occurs in tiny conducting materials, plays an important role. This paper describes the current status of research on such single-charge-control devices from the viewpoints of circuit applications. (C) 2005 American Institute of Physics.

 

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

            "Spatially separated Mn and Be doping for high hole concentration in GaMnAs by using MEE"

            Journal Of Crystal Growth 278 (1-4)699-703 (2005).

 

            ABSTRACT: The spatially separated doping of Mn and Be in GaAs is successfully performed to increase the total hole concentration and thus to improve the ferromagnetic transition temperature without creating undesirable complex defects. All the layers are grown with low-temperature migration-enhanced epitaxy. The layer structure composed of delta-doped Be and Mn layers separated by 3-monolayer undoped GaAs is found to be useful to increase the hole concentration without creating Mn-Be complex defects. The Mn-Be spatially separated doping samples show considerably improved hole concentration and other electrical transport characteristics compared with those grown by simultaneous Mn-Be co-doping. They also show much better magnetization characteristics than those with only Mn delta-doped samples, indicating that the holes supplied from the spatially separated Be-doped layers are effective to improve the magnetic properties of GaMnAs. (c) 2004 Published by Elsevier B.V.

 

105.    H. Oyanagi, N. L. Saini, A. Tsukada, and M. Naito

            "Lattice anomalies in (La,Sr)(2)CuO4 under epitaxial strain probed by polarized X-ray absorption spectroscopy"

            Journal Of Superconductivity 18 (5-6)731-735 (2005).

 

            ABSTRACT: Local lattice anomalies in optimally doped T-(La,Sr)(2)CuO4 single crystal like thin films (T-c = 43.4 K) grown by molecular-beam epitaxy have been studied by the in-plane polarized Cu K-edge extended X-ray absorption fine structure (EXAFS). The results indicate temperature-dependent local atomic displacements which are anomalous at the Tc and below a higher temperature T-s as demonstrated by a change in the mean square relative displacement of the Cu-O bond sigma(2)(Cu-O), i.e.. a sharp drop at the T-c and a gradual deviation from a noncorrelated Debye-like behavior below T, where the spatial inhomogeneity appears. We find that the magnitude of the Cu-O displacement changes at the T-c, Delta sigma(2)(Cu-O) is enhanced by compressive strain while the tendency of charge segregation is suppressed. The results suggest that the uniaxial pressure effects stabilize the system by decreasing the onset temperature and magnitude of spatial heterogeneity.

 

106.    V. Peano, M. Thorwart, A. Kasper, and R. Egger

            "Nanoscale atomic waveguides with suspended carbon nanotubes"

            Applied Physics B-lasers And Optics 81 (8)1075-1080 (2005).

 

            ABSTRACT: We propose an experimentally viable setup for the realization of one-dimensional ultracold atom gases in a nanoscale magnetic waveguide formed by single doubly-clamped suspended carbon nanotubes. We show that all common decoherence and atom loss mechanisms are small, guaranteeing a stable operation of the trap. Since the extremely large current densities in carbon nanotubes are spatially homogeneous, our proposed architecture allows for creation of a very regular trapping potential for the atom cloud. Adding a second nanowire allows creation of a double-well potential with a moderate tunneling barrier which is desired for tunneling and interference experiments with the advantage of tunneling distances being in the nanometer regime.

 

107.    A. Richter, K. Matsuda, T. Akazaki, T. Saku, H. Tamura, Y. Hirayama, and H. Takayanagi

            "Transport properties of a lateral semiconductor quantum dot defined by a single connected metallic front-gate"

            Physica E-low-dimensional Systems & Nanostructures 25 (4)472-478 (2005).

 

            ABSTRACT: We present studies on the electric transport in a lateral GaAs/AlGaAs quantum dot defined by a patterned single connected metallic front-gate. This gate design allows to easily couple a large number of quantum dots and therefore holds high potential in the design of new materials with tailor-made band structures based on quantum dot superlattices of controlled shape. Clear Coulomb diamond structures and well pronounced tunneling peaks observed in experiment indicate that single-electron control has been achieved. However, the dependence on electron density in the heterostructure embedding the dot, which is controlled by an additional back-gate, reveals that transport characteristics are strongly influenced supposedly by potential fluctuations in the dot and lead regions. (C) 2004 Elsevier B.V. All rights reserved.

 

108.    T. Sakata, H. Ishii, Y. Okabe, M. Nagase, T. Kamei, K. Kudou, M. Yano, and K. Machida

            "Anti-sticking effect of organic dielectric formed by electrodeposition in microelectromechanical-system structures"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 44 (7B)5732-5735 (2005).

 

            ABSTRACT: In microelectromechanical-system (MEMS) structures, selective encapsulation with an organic dielectric using electrodeposition can prevent sticking. Selective electrodeposition characteristics were investigated on a gold surface using sulfonium cations with epoxy groups as a source material. We observed an incubation period in the initial stage of the deposition. X-ray photoelectron spectroscopy revealed that the cause of the incubation period is the removal of oxygen adsorbed on the gold surface. Applying this technique to the encapsulation of MEMS structures confirmed the anti-sticking effect between an actuator and a gold electrode selectively coated with an organic dielectric.

 

109.    S. Sasaki, T. Fujisawa, T. Hayashi, and Y. Hirayama

            "Electrical pump-and-probe study of spin singlet-triplet relaxation in a quantum dot"

            Physical Review Letters 95 (5), 056803 (2005).

 

            ABSTRACT: Spin relaxation from a triplet excited state to a singlet ground state in a semiconductor quantum dot is studied by employing an electrical pump-and-probe method. Spin relaxation occurs via cotunneling when the tunneling rate is relatively large, confirmed by a characteristic square dependence of the relaxation rate on the tunneling rate. When cotunneling is suppressed by reducing the tunneling rate, the intrinsic spin relaxation is dominated by spin-orbit interaction. We discuss a selection rule of the spin-orbit interaction based on the observed double-exponential decay of the triplet state.

 

110.    S. Sasaki, and S. Tarucha

            "The Kondo effect enhanced by state degeneracy"

            Journal Of The Physical Society Of Japan 74 (1)88-94 (2005).

 

            ABSTRACT: The Kondo effect associated with state degeneracy is studied for a two-dimensional harmonic quantum dot. State degeneracies between a spin singlet and triplet states, between two spin doublet states, and between a spin doublet and quadruplet states are induced by magnetic field. For the first two degenracies, strong enhancement of the Kondo effect is observed. The estimated Kondo temperature for the "doublet-doublet" degeneracy with an odd electron number is similar to that for the "singlet-triplet" degeneracy with an even electron number, indicating that a total of four-fold spin and orbital degeneracy for both cases accounts for the similar enhancement of the Kondo temperature. The Kondo effect generally gives rise to enhanced conductnace and a zero-bias peak of differential conductance in the Coulomb valley. In contrast, enhacned conductance but a zero-bias dip is observed for the third "doublet-quadruplet" degeneracy. This can be due to Zeeman splitting but no clear interpretation is reached yet.

 

111.    H. Sato, and J. Kurian

            "Superconducting bandpass filters on thin films of NdBa2Cu3O7"

            Physica C-superconductivity And Its Applications 4261616-1621 (2005).

 

            ABSTRACT: For possible application to microwave filters, we examined high-quality superconducting films of NdBa2Cu3O7 (NBCO), whose Tc is higher than that for YBa2Cu3O7 (Y-BCO). We fabricated bandpass filters on NBCO films and characterized them with measurements of the scattering parameters and third-order intermodulation. The results indicate that utilizing MBE-grown films of NBCO is effective in obtaining filters with high-power-handling capability. The filters made from NBCO films yielded higher values for the third-order intercept, IP3, than filters made from YBCO films, which has been widely used for microwave applications of high-temperature superconductivity so far. For the filters of NBCO, we also investigated the effects of oxygen annealing and passband width on the power-handling capability. (c) 2005 Elsevier B.V. All rights reserved.

 

112.    T. Shimura, K. Yasutake, M. Umeno, and M. Nagase

            "X-ray diffraction measurements of internal strain in Si nanowires fabricated using a self-limiting oxidation process"

            Applied Physics Letters 86 (7), 071903 (2005).

 

            ABSTRACT: We demonstrate x-ray diffraction measurements of internal strain in Si nanowires that were fabricated using a self-limiting oxidation process. Rod-shaped scattering around the 111 Bragg point due to interference effects from the Si nanowires were observed, which are robust reflections for incoherent displacement of the wires. From the shifts of the scattering in reciprocal space, the strain was estimated to be 1.0-1.5 x 10(-3) for the sample oxidized at 800degreesC for 300 min. (C) 2005 American Institute of Physics.

 

113.    A. Shinya, S. Mitsugi, E. Kuramochi, and M. Notomi

            "Ultrasmall multi-channel resonant-tunneling filter using mode gap of width-tuned photonic-crystal waveguide"

            Optics Express 13 (11)4202-4209 (2005).

 

            ABSTRACT: We have devised an ultra-small multi-channel drop filter based on a two-port resonant tunneling system in a two-dimensional photonic crystal with a triangular air-hole lattice. This filter does not require careful consideration of the interference process to achieve a high dropping efficiency. First we develop three-port systems based on a two-port resonant tunneling filter. Next we devise a multi-port channel drop filter by cascading these three-port systems. In this paper, we demonstrate a ten-channel drop filter with an 18 mu m device size by 2D-FDTD calculation, and a three-port resonant tunneling filter with 65 +/- 20% dropping efficiency by experiment. (C) 2005 Optical Society of America.

 

114.    S. Suzuki, and Y. Kobayashi

            "Conductivity decrease in carbon nanotubes caused by low-acceleration-voltage electron irradiation"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 44 (46-49)L1498-L1501 (2005).

 

            ABSTRACT: Effects of low-acceleration-voltage (20kV) electron irradiation damage in single-walled carbon nanotubes (SWNTs) were studied by in-situ electric measurements. The irradiation drastically decreased the conductivity for both metallic and semiconducting nanotubes due to the irradiation-induced damage. Intensive electron irradiation made the SWNTs almost insulating. This phenomenon could be utilized to fabricate nanotube-based electric networks.

 

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

            "Photoemission electron microscopy of individual single-walled carbon nanotubes"

            Journal Of Electron Spectroscopy And Related Phenomena 144357-360 (2005).

 

            ABSTRACT: Individual suspended single-walled carbon nanotubes were observed by means of C Is and secondary electron photoemission electron microscopy. No band bending was observed in the images, suggesting that the depletion width near the catalytic Fe/nanotube or substrate Si/nanotube contact is comparable to the spatial resolution of 40 nm or less. 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. (c) 2005 Elsevier B.V. All rights reserved.

 

116.    S. Suzuki, H. Yamamoto, F. Maeda, Y. Watanabe, K. Yamada, and T. Kiyokura

            "Beamline for angle-resolved photoemission spectroscopy at low-temperature constructed at NTT Atsugi R&D Center"

            Journal Of Electron Spectroscopy And Related Phenomena 1441109-1112 (2005).

 

            ABSTRACT: A vacuum ultra-violet beamline for in situ angle-resolved photoemission spectroscopy of MBE-grown high-T-c superconductors at low temperature has been constructed at beamline ABL-6B of the normal-conducting ring in the synchrotron radiation facility of the NTT Atsugi R&D Center. The constant-deviation-angle varied-line-spacing plane grating monochromator covers the energy range of 20-200 eV by using two gratings. A photon flux of the order of 10(11) s(-1) with a resolving power of 2000 or more was achieved in the whole energy range. The endstation is equipped with an angle-resolved photoelectron spectrometer, an rf-stimulated He discharge lamp, a custom-designed sample manipulator for low-temperature measurements and a loadlock system for in situ measurements. Total energy resolution of about 13 meV has been obtained for the photoemission spectrum of the Au Fermi edge, in spite of the bending-magnet light source of a second-generation synchrotron radiation ring. (c) 2005 Elsevier B.V. All rights reserved.

 

117.    S. Suzuki, D. Takagi, Y. Homma, and Y. Kobayashi

            "Selective removal of carbon nanotubes utilizing low-acceleration-voltage electron irradiation damage"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 44 (1-7)L133-L135 (2005).

 

            ABSTRACT: A simple method for spatially selective removal of single-walled carbon nanotubes is demonstrated. This method is based on low-acceleration-voltage electron irradiation damage and consists of local electron irradiation of nanotubes and annealing in air. The irradiation damage seems to follow excitation of valence electrons.

 

118.    A. Taguchi

            "First-principles investigations of Ga and As adsorption properties on a GaAs(110) surface"

            Compound Semiconductors 2004, Proceedings 184345-348 (2005).

 

            ABSTRACT: We investigated adsorption properties of Ga and As atoms on a GaAs(110) surface by using first-principles calculations. It was found that both Ga and As adatoms do not form strong bonds with the substrate atoms, and then diffusion barrier heights are rather low. It was also found that the most stable sites of the adatoms are not the lattice sites. These results suggest that the epitaxial growth mechanism on GaAs(110) surface is similar to that on GaAs(111)A surface.

 

119.    A. Taguchi

            "First-principles investigations of surface reconstructions of an InAs(111)B surface"

            Journal Of Crystal Growth 278 (1-4)468-472 (2005).

 

            ABSTRACT: We investigated the stable atomic configurations and surface reconstructions of InAs(l I I)B surface by first-principles calculations. We considered three kinds of surface reconstructions, which are full-coverage, As-vacancy, and As-trimer reconstructions. Although 1 x 1 periodicity has been observed in experiments, the present calculation results imply that clean surface has 2 x 2 periodicity. We also estimated relative stability of the reconstructions by taking account of the chemical potential of As. The obtained relative stability among the reconstructions is quite similar to that of the GaAs(111)B surface. The calculation results indicate that the As-trimer reconstruction is the most stable under high As-pressure condition. Although this reconstruction has not been observed, it would be found on the InAs(111)B surface, as on the GaAs(111)B surface. © 2005 Elsevier B.V. All rights reserved.

 

120.    A. Taguchi, H. Kageshima, and K. Wada

            "First-principles investigations of nitrogen-doping effects on defect aggregation processes in Czochralski Si"

            Journal Of Applied Physics 97 (5), 053514 (2005).

 

            ABSTRACT: We theoretically investigated the nitrogen (N)-doping effect on vacancy aggregation and oxygen precipitation processes in Czochralski Si. By using first-principles calculations, we investigated stable atomic configurations and formation energies of various complexes formed by vacancies (V), oxygen (O), and N. It was found that V and O form stable complexes, but some O capture processes are endothermic, suggesting that the V aggregation preferentially occurs, resulting in void growth. It was also found that the {N-2-V-2} complex, which is already known as the most stable complex among N and V complexes, effectively captures several O atoms, and then forms stable {N-2-V-2-O-n} complexes. The stable {N-2-V-2-O-n} complexes may become the heterogeneous nucleation sites of the O precipitates, suggesting that the N doping drives the aggregation of O. This is consistent with the experimentally observed enhancement of O precipitate formation due to N doping. The experimentally observed shape change of the void may be due to anisotropic void growth originating from the N and N-O involved in void formation during the growth. (C) 2005 American Institute of Physics.

 

121.    A. Taguchi, and K. Shiraishi

            "Surface reconstructions and stabilizing mechanism of the GaAs(311)A surface"

            Physical Review B 71 (3), 035349 (2005).

 

            ABSTRACT: We investigated various surface reconstructions of a GaAs(311)A surface by using first-principles calculations. The relative stability of the reconstructions was compared by estimating the formation energy taking into account the chemical potentials of Ga and As. We found many metastable reconstructions. Moreover, we found that the electron counting model is not so effective for this surface, although it is a strong guiding principle for determining the stable surface reconstruction of GaAs(100). Further investigations suggested that sp(2)-like bond formation effectively works on the (311)A surface. Competition between the sp(2)-like bond formation and the conventional stabilization mechanism of As-dimer formation would explain why the (311)A surface has many metastable surface reconstructions.

 

122.    D. Takagi, Y. Homma, S. Suzuki, and Y. Kobayashi

            "Vertical growth of individual single-walled carbon nanotubes on silicon and SiO2 substrates"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 44 (4A)1564-1568 (2005).

 

            ABSTRACT: Individually isolated single-walled carbon nanotubes (SWNTs) have been successfully grown vertically on a substrate by chemical vapor deposition with methane and Fe or Co catalysts. Vertical growth is obtained when the growth temperature was high, 900-1000 degrees C, and the tube diameter is large, 2-5 nm. Vertically grown SWNTs are short, ranging from several tens to 300 nm, which are useful for use as, tips of a field emission or probe microscope. Fullerene encapsulation has been achieved directly in vertical SWNTs on a substrate.

 

123.    H. Takesue, E. Diamanti, T. Honjo, C. Langrock, M. M. Fejer, K. Inoue, and Y. Yamamoto

            "Differential phase shift quantum key distribution experiment over 105km fibre"

            New Journal Of Physics 7, 232 (2005).

 

            ABSTRACT: We report a quantum key distribution experiment based on the differential phase shift keying (DPSK) protocol with a Poissonian photon source, in which secure keys were generated over > 100 km fibre for the first time. We analysed the security of the DPSK protocol and showed that it is robust against strong attacks by Eve, including a photon number splitting attack. To implement this protocol, we developed a new detector for the 1.5 mu m band based on frequency up-conversion in a periodically poled lithium niobate waveguide followed by an Si avalanche photodiode. The use of detectors increased the sifted key generation rate up to > 1 Mbit s(-1) over 30 km fibre, which is two orders of magnitude larger than the previous record.

 

124.    H. Takesue, and K. Inoue

            "Generation of 1.5-mu m band time-bin entanglement using spontaneous fiber four-wave mixing and planar light-wave circuit interferometers"

            Physical Review A 72 (4), 041804 (2005).

 

            ABSTRACT: This paper reports 1.5-mu m band time-bin entanglement generation. We employed a spontaneous four-wave mixing process in a dispersion shifted fiber, with which correlated photon pairs with very narrow bandwidths were generated efficiently. To observe two-photon interference, we used planar lightwave circuit based interferometers that were operated stably without feedback control. As a result, we obtained coincidence fringes with 99% visibilities after subtracting accidental coincidences, and successfully distributed entangled photons over 20-km standard single-mode fiber without any deterioration in the quantum correlation.

 

125.    H. Takesue, and K. Inoue

            "1.5-mu m band quantum-correlated photon pair generation in dispersion-shifted fiber: suppression of noise photons by cooling fiber"

            Optics Express 13 (20)7832-7839 (2005).

 

            ABSTRACT: Spontaneous four-wave mixing in a dispersion-shifted fiber (DSF) is a promising approach for generating quantum-correlated photon pairs in the 1.5 mu m band. However, it has been reported that noise photons generated by the spontaneous Raman scattering process degrade the quantum correlation of the generated photons. This paper describes the characteristics of quantum-correlated photon pair generation in a DSF cooled by liquid nitrogen. With this technique, the number of noise photons was sufficiently suppressed and the ratio of true coincidence to accidental coincidence was increased to similar to 30. (c) 2005 Optical Society of America.

 

126.    H. Takesue, K. Inoue, O. Tadanaga, Y. Nishida, and M. I. Asobe

            "Generation of pulsed polarization-entangled photon pairs in a 1.55-mu m band with a periodically poled lithium niobate waveguide and an orthog onal polarization delay circuit"

            Optics Letters 30 (3)293-295 (2005).

 

            ABSTRACT: We report a scheme for generating pulsed polarization-entangled photon pairs based on conversion from time-bin entanglement to polarization entanglement by use of an orthogonal polarization delay circuit and post-selection. We have experimentally demonstrated the scheme, using a periodically poled lithium niobate waveguide, and successfully obtained polarization entanglement in the 1.55-mum telecom wavelength band. (C) 2005 Optical Society of America.

 

127.    H. Tamura, and L. Glazman

            "Tunable Kondo screening in a quantum dot device"

            Physical Review B 72 (12), 121308 (2005).

 

            ABSTRACT: We consider electron transport along a single-mode channel which is in contact, via tunnel junctions in its walls, with two quantum dots. Electron tunneling to and from the dots contributes to the electron backscattering, and thus modifies the channel conductance. If the dots carry spin, the channel conductance becomes temperature dependent due to the Kondo effect. The two-dot device geometry allows for a formation of S=1 localized spin due to the indirect exchange interaction, called Ruderman-Kittel-Kasuya-Yosida interaction. This device offers a possibility to study the crossover between fully screened and underscreened Kondo impurity. We investigate the manifestation of such crossover in the channel conductance.

 

128.    T. Tanabe, M. Notomi, S. Mitsugi, A. Shinya, and E. Kuramochi

            "All-optical switches on a silicon chip realized using photonic crystal nanocavities"

            Applied Physics Letters 87 (15), 151112 (2005).

 

            ABSTRACT: We demonstrate all-optical switching in the telecommunication band, in silicon photonic crystals at high speed (similar to 50 ps), with extremely low switching energy (a few 100 fJ), and high switching contrast (similar to 10 dB). The devices consist of ultrasmall high-quality factor nanocavities connected to input and output waveguides. Switching is induced by a nonlinear refractive-index change caused by the plasma effect of carriers generated by two-photon absorption in silicon. The high-quality factor and small mode volume led to an extraordinarily large reduction in switching energy. The estimated internal switching energy in the nanocavity is as small as a few tens of fJ, indicating that further reduction on the operating energy is possible. (C) 2005 American Institute of Physics.

 

129.    T. Tanabe, M. Notomi, S. Mitsugi, A. Shinya, and E. Kuramochi

            "Fast bistable all-optical switch and memory on a silicon photonic crystal on-chip"

            Optics Letters 30 (19)2575-2577 (2005).

 

            ABSTRACT: We demonstrate extremely low-power all-optical bistability by utilizing silicon photonic crystal nanocavities, based on the plasma effect of carriers generated by two-photon absorption. Owing to the high quality factor and the small volume of the nanocavities, the photon density inside the cavity becomes extremely high, which leads to a large reduction in operation power. Optical bistable operation in a single nanocavity permits optical read-write memory operation, which opens the possibility of an integrated optical logic circuit on a single chip, based on photonic crystals. The demonstrated bistable threshold power is 0.4 mW with a set pulse energy of 74 fJ, at a switching speed of < 100 ps. (c) 2005 Optical Society of America.

 

130.    H. Taniyama, M. Notomi, and Y. Yoshikuni

            "Propagation characteristics of one-dimensional photonic crystal slab waveguides and radiation loss"

            Physical Review B 71 (15), 153103 (2005).

 

            ABSTRACT: We present a type of slab waveguide structure, which is composed of one-dimensional photonic crystal. We calculated the dispersion relations and radiative loss ratio for air-bridge and SiO2 cladding waveguide structures. The calculations show that the dispersion relations of the proposed waveguide are greatly different from those of the usual index-guided waveguide structure, and then predict the existence of small-group velocity modes. Although the small-group velocity modes are above the light line, the numerical results indicate that they have a small radiation-loss rate for large slab thicknesses, even above the light line of cladding material.

 

131.    K. Tateno, H. Gotoh, and H. Nakano

            "Nanoholes formed by Au particles digging into GaAs and InP substrates by reverse vapor-liquid-solid mechanism"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 44 (50-52)L1553-L1555 (2005).

 

            ABSTRACT: Under a CBr4 gas supply, Au nanoparticles dig into GaAs and InP substrates to form nanoholes through the reverse vapor-liquid-solid mechanism. The nanohole formation tends to proceed in the [111]B direction. For GaAs, straight holes sometimes appear in the [011] and [211]B directions. This is due to the stable {111}B facets, which block the etching. For InP, many straight holes are seen in the [111]B direction. For both materials, direct etching of the surface also occurs. It is therefore necessary to find the optimum etching conditions for high selectivity to fabricate nanoholes.

 

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

            "Nanoholes in InP and C-60 layers on GaAs substrates by using AlGaAs nanowire templates"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 44 (12-15)L428-L431 (2005).

 

            ABSTRACT: As one of the nano-scale fabrication techniques, free-standing nanowires are promising. We have developed a new method for nanohole fabrication using nanowire templates; that is, etching the exposed wires selectively after the layer growth. We have demonstrated nanoholed array in InP and C-60 layers on GaAs substrates. For the metalorganic vapor phase epitaxy of InP, (111)B facets tend to form so that the AlGaAs nanowires are easily removed. Tilted nanowires and nanoholes are possible by using (311)B substrates. As another holed layer case, a C-60 layer was tried. We found that this method can also be applied to the fragile material like C-60.

 

133.    D. Terasawa, S. Kozumi, A. Fukuda, A. Sawada, Z. F. Ezawa, N. Kumada, and Y. Hirayama

            "Pseudospin domain of v=1 double-layer quantum Hall state near commensurate-incommensurate transition"

            Journal Of Physics And Chemistry Of Solids 66 (8-9)1560-1562 (2005).

 

            ABSTRACT: We investigate the quantum Hall (QH) state at the total Landau level filling factor v = 1 in double layer systems around the commensurate (C)-incommensurate (IC) transition point. We find a broad maximum in the magnetoresistance (R-xx) between the C and IC phases. The temperature dependence of R-xx shows that the maximum remains finite when the data are extrapolated down to 0 K. This fact suggests that there is a dissipative phase between the C and IC phases such as the theoretically predicted soliton lattice phase. (c) 2005 Elsevier Ltd. All rights reserved.

 

134.    Y. Tokunaga, T. Yamamoto, M. Koashi, and N. Imoto

            "Simple experimental scheme of preparing a four-photon entangled state for the teleportation-based realization of a linear optical controlled-NOT gate"

            Physical Review A 71 (3), 030301 (2005).

 

            ABSTRACT: We propose a simple experimental scheme of preparing a four-photon entangled state, which is a useful resource for two-qubit quantum operations, e.g., the controlled-NOT gate. The scheme can successfully postselect the events of the desired four-photon entangled state in the coincidence basis and can be constructed with four photons from parametric down conversion, linear optical devices, and conventional photon detectors, all of which are available in current technology. We also show an experimental scheme for a controlled-NOT gate based on teleportation with the prepared four-photon state.

 

135.    M. Tsuda, H. Arai, M. Takahashi, H. Ohtsuka, Y. Sakurai, K. Sumitomo, and H. Kageshima

            "Electrode performance of layered LiNi0.5Ti0.5O2 prepared by ion exchange"

            Journal Of Power Sources 144 (1)183-190 (2005).

 

            ABSTRACT: A layered Li-Ni-Ti oxide including divalent nickel and tetravalent titanium with a Ni2+/Ti4+ ratio of almost I was obtained by the ion exchange of a layered Na-Ni-Ti oxide precursor. By using various nickel and titanium sources, we obtained samples with different specific surface areas. Sample with larger specific surface areas had larger first charge capacities. However, a large irreversible capacity and poor cyclability were observed for all the samples when measured at room temperature. However, when we set the ambient temperature at 55 degrees C, the cyclability improved. This suggests that the lithium diffusion rate strongly affects the electrode performance of layered Li-Ni-Ti oxide. We also employed a first-principles calculation of the LiNi0.5Ti0.5O2/Ni0.5Ti0.5O2 system to evaluate its structural and voltage characteristics. (c) 2005 Elsevier B.V. All rights reserved.

 

136.    A. Tsukada, H. Yamamoto, and M. Naito

            "Ce doping in T-La2CuO4 films: Broken electron-hole symmetry for high-T-c superconductivity"

            Physica C-superconductivity And Its Applications 426454-458 (2005).

 

            ABSTRACT: We attempted Ce doping in La2CuO4 with the K2NiF4 (T) structure by molecular beam epitaxy. At low growth temperature and with an appropriate substrate choice, we found that Ce can be incorporated into the K2NiF4 lattice up to x similar to 0.06, which had not yet been realized in bulk synthesis. The doping of Ce makes T-La2-xCexCuO4 more insulating, which is in sharp contrast to Cc doping in La2CuO4 with the Nd2CuO4 structure, which makes the compounds superconducting. The observed smooth increase in resistivity from hole-doped side (T-La2-xSrxCuO4) to electron-doped side (T-La2-xCexCuO4) indicates that electron-hole symmetry is broken in the T-phase materials. (c) 2005 Elsevier B.V. All rights reserved.

 

137.    A. Tsukada, M. Noda, H. Yamamoto, and M. Naito

            "Role of impurity oxygen in superconductivity of "non-doped" T '-(La, RE)(2)CuO4"

            Physica C-superconductivity And Its Applications 426459-463 (2005).

 

            ABSTRACT: We have systematically investigated the effect of oxygen non-stoichiometry in a nominally undoped superconductor T'-(La,Y)(2)CuO4+y. In the experiments, the reduction condition was changed after the sample growth by MBE. The superconductivity is very sensitive to the reduction condition. With systematically increasingly reduced atmospheres, resistivity shows a continuous drop and no discontinuity is observed even until the appearance of superconductivity. The absence of the highly insulating state expected for Mott insulators around y similar to 0 suggests that T'-(La,Y)(2)CuO4 has intrinsic carriers. The role of residual apical oxygen, which is detrimental to superconductivity, is also discussed based on the resistivity-temperature characteristics in insufficiently reduced samples. (c) 2005 Elsevier B.V. All rights reserved.

 

138.    A. Tsukada, Y. Krockenberger, M. Noda, H. Yamarnoto, D. Manske, L. Alff, and M. Naito

            "New class of T '-structure cuprate superconductors"

            Solid State Communications 133 (7)427-431 (2005).

 

            ABSTRACT: High-temperature superconductivity has been discovered in La2-xBaxCuO4 [J.G. Bednorz, K.A. Muller, Z. Phys. B 64 (1986) 189. [1]], a compound that derives from the undoped La2CuO4 crystallizing in the perovskite T-structure. In this structure oxygen octahedra surround the copper ions. It is common knowledge that charge carriers induced by doping in such an undoped antiferromagnetic Mott-insulator lead to high-temperature superconductivity [V.J. Emery, Phys. Rev. Lett. 58 (1987) 2794; C. M. Varma, S. Schmitt-Rink, E. Abrahams, Solid State Commun. 62 (1987) 68 1; E. Dagotto, Rev. Mod. Phys. 66 (1994) 763. [2-4]]. The undoped material La2CuO4 is also the basis of the electron-doped cuprate superconductors [Y. Tokura, H. Takagi, S. Uchida, Nature (London) 337 (1989) 345. [5]] of the form La2-xCexCuO4+y [M. Naito, M. Hepp, Jpn. J. Appl. Phys. 39 (2000) L485; A. Sawa, M. Kawasaki, H. Takagi, Y. Tokura, Phys. Rev. B 66 (2002) 014531. [6,7]] which, however, crystallize in the so-called V-structure, i.e. without apical oxygen above or below the copper ions of the CuO2-plane. It is well known that for La2-xCexCuO4+y the undoped V-structure parent compound cannot be prepared due to the structural phase transition back into the T-structure occurring around x similar to 0.05. Here, we report that if La is substituted by RE = Y, Lu, Sm, Eu, Gd, or Tb, which have smaller ionic radii but have the same valence as La, nominally undoped La2-xRExCuO4 can be synthesized by molecular beam epitaxy in the T'-structure. The second important result is that all these new T'-compounds are superconductors with fairly high critical temperatures up to 21 K. For this new class of cuprates La2-xRExCuO4, which forms the T'-parent compounds of the La-based electron doped cuprates, we have not been able to obtain the Mott-insulating ground state for small x before the structural phase transition into the T-structure takes place. (C) 2004 Elsevier Ltd. All rights reserved.

 

139.    K. Uchida, H. Kageshima, and H. Inokawa

            "Charge-injection effects in a single 4,4 ''-terphenyldithiol molecule"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 44 (12)8759-8763 (2005).

 

            ABSTRACT: The effects of charge injections into a single 4,4"-terphenyldithiol molecule were investigated using density-functional calculations. It is shown that the atomic structures of the molecule are remarkably modified by electron or hole injections into it. Strengthening and weakening of the C-C and C-S pi-bonds brought about by the charge injections are closely associated with these structural modifications. Analyses of the wave functions of the highest occupied molecular orbital (HOMO) and the lowest un-occupied molecular orbital (LUMO), especially those on the arrangements of the nodes and loops of them, help our understanding of such modulations of the bond orders. It is also shown that the energies required for charging the molecule are considerably affected by these deformations. These results suggest the importance of the electron-lattice interactions in the current conduction due to the single-electron tunneling through the 4,4"-terphenyldithiol molecular single-electron island.

 

140.    K. Ueda, S. Saito, K. Sernba, T. Makimoto, and M. Naito

            "All-MgB2 Josephson tunnel junctions"

            Applied Physics Letters 86 (17), 172502 (2005).

 

            ABSTRACT: Sandwich-type all-MgB2 Josephson tunnel junctions (MgB2/AlOx/MgB2) have been fabricated with as-grown MgB2 films formed by molecular-beam epitaxy. The junctions exhibit substantial superconducting current (IcRN product similar to 0.8 mV at 4.2 K), a well-defined superconducting gap (Delta = 2.2-2.3 mV), and clear Fraunhofer patterns. The superconducting gap voltage of Delta agrees well with the smaller gap in the multigap scenario. The results demonstrate that MgB2 has great promise for superconducting electronics that can be operated at T similar to 20 K. (c) 2005 American Institute of Physics.

 

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

            "Effect of nitrogen on diffusion in silicon oxynitride"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 44 (11)7756-7759 (2005).

 

            ABSTRACT: The effect of nitrogen (N) on diffusion in silicon oxynitride was investigated through the simulation of silicon oxynitridation. We assumed that the incorporation of N reduces the SiO diffusivity in SiO2 because oxynitride layers retard B penetration, or B diffusion, which is enhanced by SiO. In order to validate this assumption, we simulated the thickness of thermally grown oxynitride. The simulation was based on our oxidation model in which SiO molecules emitted to the oxide during oxidation modulate the oxidation rate. The assumption that the SiO diffusivity exponentially decreases with increasing N concentration was introduced to our oxidation model. The simulation results fit the experimental oxynitride thickness, and this indicates the validity of our assumption of the N effect on diffusion. During oxynitridation, the diffusion of SiO molecules generated at the interface is strongly retarded by the N atoms, which are incorporated and piled up at the interface. This retardation increases the SiO concentration in SiO2 near the interface as oxynitridation proceeds, which decreases the oxynitridation rate with time. The formation of Si-3&3bond; N bonds, which should block the reconstruction of Si-O bonds, is most likely the cause of the retardation of SiO diffusion in SiO2.

 

142.    M. Uematsu

            "Self-diffusion and impurity diffusion in silicon dioxide"

            Journal Of Phase Equilibria And Diffusion 26 (5)547-554 (2005).

 

            ABSTRACT: We present experimental and simulation results of silicon (Si) self-diffusion and boron (B) diffusion in silicon dioxide (SiO2), and examine the effect of nitrogen (N) on diffusion in SiO2 . To elucidate the point defect that mainly governs the diffusion in SiO2, the diffusion of implanted Si-30 in thermally grown (SiO2)-Si-28 is investigated. The experimental results show that Si self-diffusivity increases with decreasing distance between the Si-30 and Si-SiO2 interface. We propose a model in which SiO molecules generated at the interface and diffusing into SiO2 enhance Si self-diffusion, and the simulation results fit the experimental results. The B diffusivity also increases with decreasing the distance, which indicates that B diffusion is enhanced by SiO. In addition, we investigate the effects of B and N on SiO diffusion in SiO2. We show that the existence of B increases SiO diffusivity and hence decreases the viscosity of SiO2. On the other hand, the incorporation of N decreases SiO diffusivity, which reduces B diffusion in SiO2 and increases the viscosity.

 

143.    M. Uematsu

            "Unified simulation of diffusion in silicon and silicon dioxide"

            Diffusion In Materials: Dimat 2004, Pt 1and 2 237-24038-49 (2005).

 

            ABSTRACT: We present a unified simulation of diffusion in silicon (Si) and silicon dioxide (SiO2) that is based on the diffusing dopant species and point defects that primarily contribute to the diffusion. We first present the simulation of phosphorus (P) diffusion in Si based on the integrated diffusion model that we have developed and elucidate the mechanism of the appearance of the anomalous P in-diffusion profile. The vacancy mechanism governs P diffusion in the plateau region, while the kick-out mechanism governs it in the deeper region, where Si self-interstitials dominate in the kink region and P interstitials dominate in the tail region. Next, we present the simulation of boron (B) diffusion and Si self-diffusion in SiO2. We examined the co-diffusion of implanted B and Si-30 in thermally grown (SiO2)-Si-28, which shows increasing diffusivities with decreasing distance between the diffusers and Si/SiO2 interface and with higher B concentration in SiO2- We propose a model in which SiO molecules generated at the interface and diffusing into SiO2 enhance both B diffusion and Si self-diffusion. The simulation showed that the SiO diffusion is so slow that the SiO concentration at the B and 30Si region critically depends on the distance from the interface. In addition, the simulation predicts the possibility of time-dependent diffusivities for B and Si because more SiO molecules should be arriving from the interface with time, and this time dependence was experimentally observed. Moreover, based on the B concentration dependence, the simulation result indicates that B and Si atoms in SiO2 diffuse correlatively via SiO; namely, the enhanced SiO diffusion by the existence of B enhances B diffusion and Si self-diffusion.

 

144.    A. Vijayaraghavan, K. Kanzaki, S. Suzuki, Y. Kobayashi, H. Inokawa, Y. Ono, S. Kar, and P. M. Ajayan

            "Metal-semiconductor transition in single-walled carbon nanotubes induced by low-energy electron irradiation"

            Nano Letters 5 (8)1575-1579 (2005).

 

            ABSTRACT: We report the effect of low-energy (1 keV) electron beam irradiation on gated, three-terminal devices constructed from metallic single-walled carbon nanotubes. Pristine devices, which exhibited negligible gate voltage response at room temperature and metallic single-electron transistor characteristics at low temperatures, when exposed to an electron beam, exhibited ambipolar field effect transistor (room temperature) and single-electron transistor (low temperature) characteristics. This metal-semiconductor transition is attributed to inhomogeneous electric fields arising from charging during electron irradiation.

 

145.    C. X. Wang, N. Maeda, M. Hiroki, T. Tawara, T. Makimoto, T. Kobayashi, and T. Enoki

            "Comparison of AlGaN/GaN insulated gate heterostructure field-effect transistors with ultrathin Al2O3/Si3N4 bilayer and Si3N4 single layer"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 44 (4B)2735-2738 (2005).

 

            ABSTRACT: Device performances have been compared between two types of AlGaN/GaN metal-insulator-semiconductor heterostructure field effect transistors (MIS-HFETs) with Al2O3/Si3N4 bilayers and a Si3N4 single layer. Al2O3/Si3N4 bilayer-based MIS-HFETs have much lower gate current leakage than Si3N4-based MIS devices by more than 3 orders of magnitude under reverse gate biases. An ultralow gate leakage of 1 x 10(-11) A/mm at -15 V has been achieved in the Al2O3/Si3N4 bilayer-based MIS devices though higher maximum drain-source current has been obtained in the Si3N4-based MIS devices. A maximum transconductance of more than 180 mS/mm with ultra-low gate leakage has been achieved in the ultrathin Al2O3/Si3N4 bilayer-based MIS-HFET device with a gate length of 1.5 mu m, which is much higher than that of less than 130 mS/mm in the Si3N4-based MIS devices. The reduction in the transconductance of Al2O3/Si3N4 bilayer-based devices was much smaller than that in the Si3N4-based MIS devices due to the employment of ultrathin bilayers with a large dielectric constant. This work demonstrates that an Al2O3/Si3N4 bilayer insulator is a superior candidate for nitride-based MIS-HFET devices.

 

146.    H. Yamaguchi, A. K. Das, A. Ney, T. Hesjedal, C. Pampuch, D. M. Schaadt, and R. Koch

            "From ferro- to antiferromagnetism via exchange-striction of MnAs/GaAs(001)"

            Europhysics Letters 72 (3)479-485 (2005).

 

            ABSTRACT: We investigated the stress evolution in single-crystal MnAs films on GaAs(001) upon applying high external magnetic fields in the alpha/beta phase transition regime (10-40 degrees C) and beyond. Our stress measurements reveal large field-induced lattice distortions at temperatures, where beta-MnAs is present, even well above the phase transition (> 40 degrees C). A quantitative comparison with the field-induced increase of magnetization reveals that the changes in the lattice dimensions can be fully explained by the (reversible) back-transformation of beta-MnAs to alpha-MnAs. Our direction-dependent experiments identify the structural distortions at the phase transition as a volume magnetostriction effect and -due to the persisting magnetocrystalline anisotropy above 40 degrees C-strongly support an antiferromagnetic state for beta-MnAs.

 

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

            "Force/displacement detection using quantum effects in InAs/Al0.5Ga0.5Sb two-dimensional electron systems"

            Compound Semiconductors 2004, Proceedings 184187-192 (2005).

 

            ABSTRACT: We have fabricated micromechanical piezoresistive InAs/AI(0.5)Ga(0.5)Sb cantilevers and the piezoresitace was measured at liquid helium temperature under a magnetic field. Depending on the electron mobility of the InAs films, we observed conductance fluctuation and Schbnikov-de Haas oscillation, which was caused by the quantum effects, in the piezoresistance. At appropriately choosing the magnetic field, we obtained enhanced force and displacement sensitivity of 10(-12)N/root Hz and 10(-11)m/root Hz, respectively.

 

148.    H. Yamaguchi, Y. Hirayama, S. Miyashita, and S. Ishihara

            "Force/displacement detection using quantum transport in InAs/AlGaSb two-dimensional heterostructures"

            Applied Physics Letters 86 (5), 052106 (2005).

 

            ABSTRACT: We fabricated a piezoresistive microelectromechanical cantilever that contains an InAs/Al0.5Ga0.5Sb quantum well and measured the piezoresistance as a function of perpendicular magnetic field at 2.0 K. The magneto-piezoresistance shows the feature of Schvnikov-de Haas oscillation, indicating a strong quantum effect on the piezoresistance. At the magnetic field that gives the largest piezoresistance, displacement and force sensitivities of 10(-11) m/rootHz and 10(-12) N/rootHz, respectively, were obtained. (C) 2005 American Institute of Physics.

 

149.    M. Yamaguchi, S. Nomura, D. Sato, T. Akazaki, H. Tamura, and H. Takayanagi

            "Photoluminescence measurements in Be-delta-doped back-gated quantum well"

            Surface Science 583 (1)94-99 (2005).

 

            ABSTRACT: We measured the photoluminescence (PL) spectra of a two-dimensional electron system induced in a Be-delta-doped GaAs/AlGaAs quantum well (QW) with a back gate. The electron density is controlled by means of the back-gate voltage. We estimated the electron density using the magneto-optical method and the PL linewidth, and also by undertaking transport measurements. We show that a uniform 2DES as large as 1 mm(2) is induced by the back-gate operation from 2.5 x 10(10) cm(-2). This experiment indicates that optical measurement with a back-gated QW is advantageous for studying the low-density 2DES. (c) 2005 Elsevier B.V. All rights reserved.

 

150.    T. Yamaguchi, and H. Namatsu

            "Graphoepitaxy of diblock copolymer on micropatterned substrates"

            Journal Of Photopolymer Science And Technology 18 (3)421-423 (2005).

 

            ABSTRACT:

 

151.    M. Yamamoto, J. Ohea, T. Ohtsuki, J. Nitta, and B. Kramer

            "Spin-polarization in a 3-terminal conductor induced by Rashba spin-orbit coupling"

            Physica E-low-dimensional Systems & Nanostructures 29 (3-4)490-494 (2005).

 

            ABSTRACT: We investigate numerically the spin polarization of the current in the presence of Rashba spin-orbit interaction (RSOI) in a 3-terminal conductor. We use equation-of-motion method to simulate the time evolution of the wave packet and focus on single-channel transport. A T-shaped conductor with uniform RSOI proposed by Kiselev and Kim and a Y-shaped conductor with nonuniform RSOI are considered. In the T-shaped conductor, the strength of RSOI is assumed to be uniform. We have found that the spin polarization becomes nearly 100% with little loss of conductance for sufficiently strong spin-orbit coupling. This is due to the spin-dependent group velocity of electrons at the junction which causes the spin separation. In the Y-shaped conductor, the strength of RSOI is modulated perpendicular to the charge Current. A spatial gradient of effective magnetic field due to the nonuniform RSOI causes the Stern-Gerlach type spin separation. The direction of the polarization is perpendicular to the Current and parallel to the spatial gradient. Again almost 100% spin polarization can be realized by this spin separation. (c) 2005 Elsevier B.V. All rights reserved.

 

152.    T. Yamazaki, S. Ohmi, S. Morita, H. Ohri, J. Murota, M. Sakuraba, H. Omi, and T. Sakai

            "Separation by bonding Si islands (SBSI) for advanced CMOS LSI applications"

            Ieice Transactions On Electronics E88C (4)656-661 (2005).

 

            ABSTRACT: We have developed separation by bonding Si islands (SBSI) process for advanced CMOS LSI applications. In this process, the Si islands that become the SOI regions are formed by selective etching of the SiGe layer in the Si/SiGe stacked layers, and those are bonded to the Si substrate with the thermal oxide layers by furnace annealing. The etching selectivity for SiGe/Si and surface roughness after the SiGe etching were found to be improved by decreasing the HNO3 concentration in the etching solution. The thicknesses of the fabricated Si island and the buried oxide layer also became uniform by decreasing the HNO3 concentration. In addition, it was found that the space formed by SiGe etching in the Si/SiGe stacked layers was able to be filled with the thermal oxide layer without furnace annealing.

 

153.    T. Yamazaki, S. Ohmi, S. Morita, H. Ohri, J. Murota, M. Sakuraba, H. Omi, Y. Takahashi, and T. Sakai

            "Separation by bonding Si islands (SBST) for LSI applications"

            Materials Science In Semiconductor Processing 8 (1-3)59-63 (2005).

 

            ABSTRACT: We propose and describe a novel method called separation by bonding Si islands (SBSI) that can be used to form silicon-on-insulator (SOI) and isolation regions simultaneously. The Si islands are formed by selectively etching the SiGe layer of Si/SiGe stacked layers grown by chemical vapor deposition (CVD). Thin oxide layers are formed at the surface of the Si islands and the Si substrate by using thermal oxidation, and the Si islands are bonded to the Si substrate with the oxide layers. We obtained a uniform Sol layer and a smooth interface between the Sol and buried oxide (BOX) layers. The thicknesses of the Sol and BOX layers observed with cross-sectional transmission electron microscopy (TEM) were 18.2 and 23.5nm, respectively. (C) 2004 Elsevier Ltd. All rights reserved.

 

154.    R. Yano, and H. Gotoh

            "Tunable terahertz electromagnetic wave generation using birefringent crystal and grating pair"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 44 (12)8470-8473 (2005).

 

            ABSTRACT: We generated frequency-tunable terahertz (THz) waves with stable carrier-envelope phases (CEPs) by exciting a photoconductive antenna with intensity-modulated laser pulses. The modulation of a laser pulse by using a birefringent crystal and a grating pair produced two chirped laser pulses with a fixed time separation, or in other words, an intensity-modulated laser pulse. The stability of the CEP of the THz waves was governed by the stability of the time separation of the two laser pulses generated by the birefringent crystal. Because the crystal thickness was fixed, the CEP of the THz wave was stable and not affected by the mechanical vibration of the optical components. We also demonstrated the CEP control of the THz wave.

 

155.    R. Yano, H. Gotoh, Y. Hirayama, S. Miyashita, Y. Kadoya, and T. Hattori

            "Terahertz wave detection performance of photoconductive antennas: Role of antenna structure and gate pulse intensity"

            Journal Of Applied Physics 97 (10), 103103 (2005).

 

            ABSTRACT: We studied the receiver performance of two photoconductive antennas (bow tie and dipole antennas) fabricated on the same low-temperature-grown GaAs substrate to clarify the effect of the antenna structure and gate pulse intensity on terahertz wave detection. We observed the gate pulse intensity dependence of the temporal profiles of the terahertz waves or terahertz spectra. For both antennas, the sensitivity in the low-frequency regime (< 0.5 THz) was enhanced compared to that in the high-frequency regime for large gate pulse intensities. This is because the carrier trap time increased due to the saturation of the GaAs defect levels. We also observed that the peak-to-peak amplitude of the terahertz wave detected by one antenna was not always larger than that detected by the other antenna, and the peak-to-peak amplitude of the bow tie antenna was larger (smaller) than that of the dipole antenna when the gate pulse intensity was high (low). This was explained by the gate pulse intensity dependence of the frequency-dependent detection sensitivity and also by the resonance frequency of the antenna structure. (c) 2005 American Institute of Physics.

 

156.    H. T. Ye, H. X. Yan, and R. B. Jackman

            "Dielectric properties of single crystal diamond"

            Semiconductor Science And Technology 20 (3)296-298 (2005).

 

            ABSTRACT: LCR measurements have been performed on type IIa and type Ib single crystal diamonds, in an attempt to identify any differences in their dielectric characteristics. It is found that the type IIa diamond, which contains little nitrogen, behaves as an ideal insulator, with the dielectric loss appearing to be frequency independent at low temperatures, whilst assuming a frequency dependence at high temperatures. In contrast, the type Ib diamond samples exhibited a dielectric loss peak in the temperature-dependent data, from which a thermal activated process with an E-a of 1.67 eV can be determined using a simple Debye law relationship. However, the data suggests that a dielectric relaxation constant (nitrogen-induced dipole) of 10(17) Hz is evident in the Ib system, which is much higher than that predicted by the Debye model, as such it is unlikely due to the dipole moment itself. A possible physical mechanism responsible for this phenomena is simply the ionization of a nitrogen centre with a defect level lying at 1.7 eV below the conduction band.

 

157.    A. Yokoo, and S. Sasaki

            "Oxidation patterning of GaAs by nanoelectrode lithography"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 44 (2)1119-1122 (2005).

 

            ABSTRACT: Nanoelectrode lithography, which transfers patterns from a nanoelectrode to a target via an electrochemical reaction, is employed for patterning GaAs. Gallium oxide and arsenic oxide are produced by the anodic oxidation of GaAs. A-400-nm pitch line and space (L/S) pattern and a closely packed hexagonal pattern with a 500 nm pitch are successfully transferred. For the 400-nm-pitch L/S pattern, a patterned area of 6 x 8 mm(2) is obtained with a reaction time of 30 s. The fabricated pattern can be directly used as an etching mask. Structures with depths of approximately 70 and 10 nm are obtained by wet and dry etchings, respectively. In addition, it is confirmed that multiple patterning is also possible on a GaAs substrate.

 

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

            "Resistance oscillations by electron-nuclear spin coupling in microscopic quantum Hall devices"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 44 (4B)2669-2671 (2005).

 

            ABSTRACT: We study electron -n uc lear spin coupled systems implemented in microscopic fractional quantum Hall (FQH) devices. We find that the longtitudinal resistance in such systems oscillates with a period of about similar to 200 s and is driven by a constant voltage instead of a constant current. This 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 spill Coupled systems.

 

159.    G. Yusa, K. Muraki, K. Takashina, K. Hashimoto, and Y. Hirayama

            "Controlled multiple quantum coherences of nuclear spins in a nanometre-scale device"

            Nature 434 (7036)1001-1005 (2005).

 

            ABSTRACT: The analytical technique of nuclear magnetic resonance (NMR1,2) is based on coherent quantum mechanical superposition of nuclear spin states. Recently, NMR has received considerable renewed interest in the context of quantum computation and information processing(3-11), which require controlled coherent qubit operations. However, standard NMR is not suitable for the implementation of realistic scalable devices, which would require all-electrical control and the means to detect microscopic quantities of coherent nuclear spins. Here we present a self-contained NMR semiconductor device that can control nuclear spins in a nanometre-scale region. Our approach enables the direct detection of (otherwise invisible) multiple quantum coherences between levels separated by more than one quantum of spin angular momentum. This microscopic high sensitivity NMR technique is especially suitable for probing materials whose nuclei contain multiple spin levels, and may form the basis of a versatile multiple qubit device.

 

160.    B. Y. Zhang, G. S. Solomon, M. Pelton, J. Plant, C. Santori, J. Vuckovic, and Y. Yamamoto

            "Fabrication of InAs quantum dots in AlAs/GaAs DBR pillar microcavities for single photon sources"

            Journal Of Applied Physics 97 (7), 073507 (2005).

 

            ABSTRACT: We report the molecular beam epitaxy growth of low-density strain-induced InAs quantum dots (QD) embedded in an AlAs/GaAs distributed Bragg reflector structure for a triggered photon source. By optimal selection of growth temperature, InAs deposited thickness and other experimental parameters, it is possible to grow low density (10/mu m(2)) InAs quantum dots with a suitable emission wavelength for a triggered photon source. The empirical formulas for the refractive indices of AlAs and GaAs materials at high temperature over a wide wavelength range are constructed by combining high resolution x-ray diffraction, dynamic optical reflectivity, and optical reflectivity spectrum techniques. Utilizing the electron-beam lithography and electron-cyclotron-resonance plasma etching techniques, a micropost microcavity with the top diameter of 0.6 mu m and the post height of 4.2 mu m has been fabricated. Narrow, spectrally limited single QD emission embedded in a micropost microcavity is observed in the photoluminescence. (C) 2005 American Institute of Physics.

 

161.    Z. H. Zhang, K. Sumitomo, and F. Lin

            "Observation of B segregation on Si(113) by scanning tunneling microscopy"

            Ultramicroscopy 105 (1-4)16-21 (2005).

 

            ABSTRACT: We implanted B atoms in Si(113) and annealed the samples to make B segregate to the surface. A series of Si(113)-3 x 1:B surfaces with different B-induced features have been observed by scanning tunneling microscopy. It is demonstrated that on a Si(113) surface B is favorable to be self-interstitials underneath a type of surface reconstructing blocks called pentamers and such pentamers can be boronized with different numbers of B atoms and therefore appear at different levels of electronic states. (c) 2005 Elsevier B.V. All rights reserved.

 

162.    Z. H. Zhang, and K. Sumitomo

            "Boronizing structures of Si(113) surfaces"

            Surface Science 576 (1-3)83-88 (2005).

 

            ABSTRACT: With the help of scanning tunneling microscopy observations and first-principles calculations, we demonstrate that B preferential occupation at self-interstitial sites of Si(113) induces 3 x 1:B surfaces made up of adatoms and interstitial pentamers. The B atoms may serve as adatoms, while the interstitial pentamers may be boronized with different numbers of B atoms owing to the self-interstitial effects of B atoms. Our findings indicate that a Si(113) surface may be doped with B to an extremely high level. (C) 2004 Elsevier B.V. All rights reserved.