1.    T. Akasaka, H. Gotoh, Y. Kobayashi, H. Nakano, and T. Makimoto

            "InGaN quantum wells with small potential fluctuation grown on InGaN underlying layers"

            Applied Physics Letters 89 (10), 101110 (2006).

 

            ABSTRACT: A series of InGaN quantum wells (QWs) emitting blue-green, blue, violet, or ultraviolet light was grown on InGaN underlying layers (ULs). The potential fluctuation in these InGaN QWs was carefully measured using time-resolved photoluminescence, taking several steps to reduce the quantum confinement Stark effect. The potential fluctuation of InGaN QWs on InGaN ULs was smaller than that on conventional GaN ULs with the identical emission wavelength. A violet-light-emitting diode using an InGaN UL had the electroluminescence intensity approximately five times higher than the one using a conventional GaN UL under the low injection-current conditions, indicating that an InGaN UL effectively eliminates the nonradiative recombination centers in the InGaN QWs. (c) 2006 American Institute of Physics.

 

2.    T. Akasaka, and T. Makimoto

            "Flow-rate modulation epitaxy of wurtzite AlBN"

            Applied Physics Letters 88 (4), 041902 (2006).

 

            ABSTRACT: Wurtzite AlBN thin films were fabricated using flow-rate modulation epitaxy (FME), wherein group-III and group-V sources are alternatively supplied to the growing surface. A 350-nm-thick wurtzite Al1-xBxN (x similar to 0.015) film grown by FME exhibited a single sharp peak in the omega-2 theta scan of x-ray diffraction, a smooth surface with the root-mean-square roughness of 3.4 nm, and a sharp epitaxial interface with SiC(0001) substrate, whereas that prepared by conventional metalorganic chemical vapor deposition contained faceted columnar AlBN(11_01) crystallites several ten nanometers in width in an AlBN(0001) matrix. FME is useful for fabricating high-quality wurtzite AlBN thin films, because it suppresses polycrystallization through enhancement of the surface migration of boron atoms. (c) 2006 American Institute of Physics.

 

3.    T. Akiyama, K. Kawamoto, H. Kageshima, M. Uematsu, K. Nakamura, and T. Ito

            "A first-principles study of O-2 incorporation and its diffusion in compressively strained high-density silicon oxides"

            Thin Solid Films 508 (1-2)311-314 (2006).

 

            ABSTRACT: The microscopic mechanisms of O-2 diffusion in compressively strained high-density silicon oxides are investigated based on first-principles total-energy calculations. It is found that, both in high-density alpha-quartz and in alpha-cristobalite, the calculated incorporation energies and energy barriers increase with increase of oxide density. Independent of the structure of oxides, the calculated activation energies increase with increasing density. Furth en-no re, the calculated activation volumes suggest that the oxidation retardation by the oxidation-induced strain is due to the retardation of O-2 diffusion in the high-density region, qualitatively consistent with experimental results. (c) 2005 Elsevier B.V. All fights reserved.

 

4.    T. Bergsten, T. Kobayashi, Y. Sekine, and J. Nitta

            "Experimental demonstration of the time reversal Aharonov-Casher effect"

            Physical Review Letters 97 (19), 196803 (2006).

 

            ABSTRACT: We demonstrate the time reversal Aharonov-Casher (AC) effect in small arrays of mesoscopic semiconductor rings. By using an electrostatic gate we can control the spin precession rate and follow the AC phase over several interference periods. We show that we control the precession rate in two different gate voltage ranges; in the lower range the gate voltage dependence is strong and linear and in the higher range the dependence in almost an order of magnitude weaker. We also see the second harmonic of the AC interference, oscillating with half the period. We finally map the AC phase to the spin-orbit interaction parameter alpha and find it is consistent with Shubnikov-de Haas analysis.

 

5.    N. I. Cade, H. Gotoh, H. Kamada, H. Nakano, S. Anantathanasarn, and R. Notzel

            "Optical characteristics of single InAs/InGaAsP/InP(100) quantum dots emitting at 1.55 mu m"

            Applied Physics Letters 89 (18), 181113 (2006).

 

            ABSTRACT: The authors have studied the emission properties of individual InAs quantum dots (QDs) grown in an InGaAsP matrix on InP(100) by metal-organic vapor-phase epitaxy. Low-temperature microphotoluminescence spectroscopy shows emission from single QDs around 1550 nm with a characteristic exciton-biexciton behavior and a biexciton antibinding energy of more than 2 meV relative to the exciton. Temperature-dependent measurements reveal negligible optical phonon induced broadening of the exciton line below 50 K, and emission from the exciton state clearly persists above 70 K. These results are encouraging for the development of a controllable photon source for fiber-based quantum information and cryptography systems. (c) 2006 American Institute of Physics.

 

6.    N. I. Cade, H. Gotoh, H. Kamada, H. Nakano, and H. Okamoto

            "Fine structure and magneto-optics of exciton, trion, and charged biexciton states in single InAs quantum dots emitting at 1.3 mu m"

            Physical Review B 73 (11), 115322 (2006).

 

            ABSTRACT: We present a detailed investigation into the optical characteristics of individual InAs quantum dots (QDs) grown by metalorganic chemical vapor deposition, with low temperature emission in the telecoms window around 1300 nm. Using microphotoluminescence (PL) spectroscopy we have identified neutral, positively charged, and negatively charged exciton and biexciton states. Temperature-dependent measurements reveal dot-charging effects due to differences in carrier diffusivity. We observe a pronounced linearly polarized splitting of the neutral exciton and biexciton lines (similar to 250 mu eV) resulting from asymmetry in the QD structure. This asymmetry also causes a mixing of the excited trion states which is manifested in the fine structure and polarization of the charged biexciton emission; from this data we obtain values for the ratio between the anisotropic and isotropic electron-hole exchange energies of Delta(1)/Delta(0) approximate to 0.2-0.5. Magneto-PL spectroscopy has been used to investigate the diamagnetic response and Zeeman splitting of the various exciton complexes. We find a significant variation in g factor between the exciton, the positive biexciton, and the negative biexciton; this is also attributed to anisotropy effects and the difference in lateral extent of the electron and hole wave functions.

 

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

            "Fabrication of induced two-dimensional hole systems on (311)A GaAs"

            Journal Of Applied Physics 99 (2), 023707 (2006).

 

            ABSTRACT: We demonstrate a method for fabricating induced two-dimensional hole devices in (311)A GaAs. The method uses a metallic p(+)-GaAs capping layer as an in situ top gate that pins the Fermi energy close to the valence band, thereby allowing very small gate biases to be used to induce a two-dimensional hole system at a AlGaAs/GaAs interface. We present transport data from devices with different levels of background impurities. Modeling the mobility as a function of hole density gives a quantitative measure of the level of disorder and indicates that these systems can be used for a systematic study of the effects of disorder in strongly interacting low-dimensional systems. (c) 2006 American Institute of Physics.

 

8.    N. Clement, H. Inokawa, and Y. Ono

            "Studies on metal-oxide-semiconductor field-effect transistor low-frequency noise for electrometer applications"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 45 (4B)3606-3608 (2006).

 

            ABSTRACT: We studied the low-frequency noise of n-channel silicon-on-insulator metal-oxide-semiconductor field-effect transistors (SOI MOSFETs) fabricated by a foundry process to evaluate their charge sensitivity at 8 K. Measurements were performed for conventionally doped and undoped (channel-implantation-free) MOSFETs mainly under surface-channel condition. For conventionally doped MOSFETs, we observed, in the frequency range of 0.1 Hz-100 kHz a Lorentzian spectrum with a cutoff frequency of approximately 200 Hz. This spectrum is linked to a peculiar multilevel random telegraph signal (RTS) related to multiple traps with nearly identical time constants. The origin of this noise, related to dopants, is discussed. We also found that the MOSFETs without channel dopant implantation exhibit a 1/f-like spectrum and have-a smaller noise at 8 K with a charge noise spectral density of 7.8 x 10(-3) e/Hz(1/2) at 10 Hz, which is smaller than that of the specially designed GaAs FET reported in the literature.

 

9.    A. R. Dedigama, D. Deen, S. Q. Murphy, N. Goel, J. C. Keay, M. B. Santos, K. Suzuki, S. Miyashita, and Y. Hirayama

            "Current focusing in InSb heterostructures"

            Physica E-low-dimensional Systems & Nanostructures 34 (1-2)647-650 (2006).

 

            ABSTRACT: We report transverse electron focusing in a symmetrically doped, InSb-based two-dimensional electron system. In a focusing device, the application of a perpendicular magnetic field steers the electron current from an injecting quantum point contact into a collector quantum point contact whenever the diameter of the cyclotron orbit corresponds to an integer fraction of the injector to collector spatial separation. In low-temperature measurements of in-plane gated devices, we observe peaks in the collector voltage at magnetic fields where focusing is expected. The first peak displays substructure which is preserved at temperatures as high as 10 K and under a variety of gating conditions. We speculate that this substructure originates from spatially distinct paths for electrons with different spin polarizations arising from the large Dresselhaus effect expected for InSb-based electron systems. (c) 2006 Elsevier B.V. All rights reserved.

 

10.    E. Diamanti, H. Takesue, C. Langrock, M. M. Fejer, and Y. Yamamoto

            "100 km differential phase shift quantum key distribution experiment with low jitter up-conversion detectors"

            Optics Express 14 (26)13073-13082 (2006).

 

            ABSTRACT: We present a quantum key distribution experiment in which keys that were secure against all individual eavesdropping attacks allowed by quantum mechanics were distributed over 100 km of optical fiber. We implemented the differential phase shift quantum key distribution protocol and used low timing jitter 1.55 mu m single-photon detectors based on frequency up-conversion in periodically poled lithium niobate waveguides and silicon avalanche photodiodes. Based on the security analysis of the protocol against general individual attacks, we generated secure keys at a practical rate of 166 bit/s over 100 km of fiber. The use of the low jitter detectors also increased the sifted key generation rate to 2 Mbit/s over 10 km of fiber. (c) 2006 Optical Society of America.

 

11.    E. Diamanti, C. Langrock, M. M. Fejer, Y. Yamamoto, and H. Takesue

            "1.5 mu m photon-counting optical time-domain reflectometry with a single-photon detector based on upconversion in a periodically poled lithium niobate waveguide"

            Optics Letters 31 (6)727-729 (2006).

 

            ABSTRACT: Optical time-domain reflectometry (OTDR) is one of the most powerful tools in the characterization of optical fiber links. We demonstrate a photon-counting OTDR system at 1.5 mu m with a single-photon detector, which combines frequency upconversion in a periodically poled lithium niobate waveguide and a silicon avalanche photodiode. The system exhibits high sensitivity, good spatial resolution, and short measurement time. (c) 2006 Optical Society of America.

 

12.    T. Fujisawa, T. Hayashi, R. Tomita, and Y. Hirayama

            "Bidirectional counting of single electrons"

            Science 312 (5780)1634-1636 (2006).

 

            ABSTRACT: A bidirectional single-electron counting device is demonstrated. Individual electrons flowing in forward and reverse directions through a double quantum dot are detected with a quantum point contact acting as a charge sensor. A comprehensive statistical analysis in the frequency and time domains and of higher order moments of noise reveals antibunching correlation in single-electron transport through the device itself. The device can also be used to investigate current flow in the attoampere range, which cannot be measured by existing current meters.

 

13.    T. Fujisawa, T. Hayashi, and S. Sasaki

            "Time-dependent single-electron transport through quantum dots"

            Reports On Progress In Physics 69 (3)759-796 (2006).

 

            ABSTRACT: We describe time-dependent single-electron transport through quantum dots in the Coulomb blockade regime. Coherent dynamics of a single charge qubit in a double quantum dot is discussed with full one-qubit manipulation. Strength of decoherence is controlled with the applied voltage, but uncontrolled decoherence arises from electron-phonon coupling and background fluctuations. Then energy-relaxation dynamics is discussed for orbital and spin degree of freedom in a quantum dot. The electron-phonon interaction and spin-orbit coupling can be investigated as the dissipation problem. Finally, charge detection measurement is presented for statistical analysis of single-electron tunnelling transitions and for a sensitive qubit read-out device.

 

14.    A. Fujiwara, H. Inokawa, K. Yamazaki, H. Namatsu, Y. Takahashi, N. M. Zimmerman, and S. B. Martin

            "Single electron tunneling transistor with tunable barriers using silicon nanowire metal-oxide-semiconductor field-effect transistor"

            Applied Physics Letters 88 (5), 053121 (2006).

 

            ABSTRACT: We have achieved the operation of single-electron tunneling (SET) transistors with gate-induced electrostatic barriers using silicon nanowire metal-oxide-semiconductor field-effect transistor (MOSFET) structures. The conductance of tunnel barriers is tunable by more than three orders of magnitude. By using the flexible control of the tunable barriers, the systematic evolution from a single charge island to double islands was clearly observed. We obtained excellent reproducibility in the gate capacitances: values on the order of 10 aF, with the variation smaller than 1 aF. This flexibility and controllability both demonstrate that the device is highly designable to build a variety of SET devices based on complementary metal-oxide-semiconductor technology. (c) 2006 American Institute of Physics.

 

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

            "Quantum transport study of canted antiferromagnetic phase in the v=2 bilayer quantum Hall state"

            Physica E-low-dimensional Systems & Nanostructures 34 (1-2)77-80 (2006).

 

            ABSTRACT: We examine the v = 2 bilayer quantum Hall (QH) state in clean two-dimensional electron systems (2DESs) to study effects due to not only the layer degree of freedom called pseudospin but also the real spin degree of freedom. The novel canted antiferromagnetic phase (CAF phase) has been predicted to emerge from subtle many-body electron interactions between the singlet (S) and ferromagnet (F) phases. Though several experiments indicate an onset of the CAF phase, a systematic transport study is not yet to be demonstrated. We have carried out magnetotransport measurements of the v = 2 bilayer QH state using a sample with tunneling energy Delta(SAS) = 11 K. Activation energy was precisely measured as a function of the total density of the 2DES and the density difference between the two layers. Results support an appearance of the CAF phase between the S and F phases. (c) 2006 Elsevier B.V. All rights reserved.

 

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

            "Magnetotransport study of the canted antiferromagnetic phase in bilayer nu=2 quantum Hall state"

            Physical Review B 73 (16), 165304 (2006).

 

            ABSTRACT: Magnetotransport properties are investigated in the bilayer quantum Hall state at the total filling factor nu=2. We measured the activation energy elaborately as a function of the total electron density and the density difference between the two layers. Our experimental data demonstrate clearly the emergence of the canted antiferromagnetic (CAF) phase between the ferromagnetic phase and the spin-singlet phase. The stability of the CAF phase is discussed by the comparison between experimental results and theoretical calculations using a Hartree-Fock approximation and an exact diagonalization study. The data reveal also an intrinsic structure of the CAF phase divided into two regions according to the dominancy between the intralayer and interlayer correlations.

 

17.    K. Furukawa, H. Nakashima, Y. Kashimura, and K. Torimitsu

            "Microchannel device using self-spreading lipid bilayer as molecule carrier"

            Lab On A Chip 6 (8)1001-1006 (2006).

 

            ABSTRACT: We propose a microchannel device that employs a surface-supported self-spreading lipid bilayer membrane as a molecule carrying medium. The device has a micropattern structure fabricated on a SiO2 surface by photolithography, into which a self-spreading lipid bilayer membrane is introduced as the carrier medium. This system corresponds to a microchannel with a single lipid bilayer membrane height of similar to 5 nm, compared with conventional micro-fluidic channels that have a section height and width of at least several mm. The device is beneficial for detecting intermolecular interactions when molecules carried by the self-spreading lipid bilayer collide with each other in the microchannel. The validity of the device was confirmed by observing the fluorescence resonance energy transfer (FRET) between two dye molecules, coumarin and fluorescein.

 

18.    T. Goto, K. Degawa, H. Inokawa, K. Furukawa, H. Nakashima, K. Sumitomo, T. Aoki, and K. Torimitsu

            "Molecular-mediated single-electron devices operating at room temperature"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 45 (5A)4285-4289 (2006).

 

            ABSTRACT: We report the electrical characteristics of gold nanogap devices modified by conjugated molecules with thiol endgroups. Gold nanogap electrodes with a nominal gap distance of between 1-2 nm were fabricated by double oblique deposition from opposite directions. The electrodes were then immersed in 4,4'-p-terphenyldithiol (TPDT) solutions to enhance conductance. Using the substrate as a gate electrode, we observed a large Coulomb diamond at room temperature with a charging energy as large as 0.25 eV. The characteristics of the device can be explained on the basis of a multi-metallic-island system. It is considered that ultra small gold islands are formed during the metal deposition and that the molecules bridging metallic islands and electrodes work as tunnel junctions.

 

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

            "Effects of nonradiative centers on localized excitons in InGaN quantum well structures"

            Applied Physics Letters 89 (22), 222110 (2006).

 

            ABSTRACT: The authors report the effects of nonradiative recombination on the properties of spatially localized excitons in InGaN quantum well structures studied using a microphotoluminescence (PL) technique. Sharp PL lines (linewidth of less than 1 meV) are clearly obtained by combining the PL and nanolithographic techniques. The PL originates from localized excitons induced by quantum-dot-like local potential minima where indium is accumulated. A systematic study with various kinds of samples reveals that suppressing the density of the nonradiative centers is crucially important in terms of observing the exciton localization effects rather than increasing the effects of indium accumulation. (c) 2006 American Institute of Physics.

 

20.    H. Gotoh, H. Sanada, H. Kamada, H. Nakano, S. Hughes, H. Ando, and J. Temmyo

            "Detecting coupled excitons with microphotoluminescence techniques in bilayer quantum dots"

            Physical Review B 74 (11), 115322 (2006).

 

            ABSTRACT: The coupling effects between excitons are examined in a pair of quantum dots to probe coupled excitons in optical measurements. The exciton photoluminescence (PL) and absorption spectrum are measured with the micro-PL excitation (micro-PLE) technique in bilayer InGaAs quantum dots. The PL peaks from the coupled exciton have similar PLE spectra for a weak excitation, which agree well with a theoretical prediction. Additional PL peaks appear for a strong excitation. A sum rule in four PL peaks is satisfied due to the energy conservation rule in the case of two exciton creation. A simple control of the coupling effect is also demonstrated using a two-color excitation technique. The coupling energy can be controlled by the intensity of a second laser. These results provide good guidelines for finding PL peaks from coupled excitons, which are crucially important to demonstrate scalable quantum gates and quantum computing with quantum dots.

 

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

            "Detecting spatially localized excitons in InGaN quantum well structures with a micro-photoluminescence technique"

            Solid State Communications 138 (12)590-593 (2006).

 

            ABSTRACT: Spatially localized excitons are observed in InGaN quantum well structures at 4 K by using a micro-photo luminescence (PL) technique. By combining PL and nano-lithographic techniques, we are able to detect PL signals with a 0.2 mu m spatial resolution. A sharp PL line (linewidth of < 0.4 meV) is clearly obtained, which originates from a single localized exciton induced by a quantum dot like a local potential minimum position. Sharp PL spectra detected in three QWs with different indium compositions confirm that there are exciton localization effects in quantum wells in the blue-green (about 2.60 eV, 477 nm) to purple (about 3.05 eV, 406 nm) regions. (c) 2006 Elsevier Ltd. All rights reserved.

 

22.    T. Hayashi, T. Fujisawa, R. Tomita, and Y. Hirayama

            "Real-time observation of charge states and energy relaxation in a double quantum dot"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 45 (4B)3629-3632 (2006).

 

            ABSTRACT: We performed real-time observation of charge states in a double quantum dot (QD) by monitoring the current passing through an adjacent quantum point contact (QPC). The position of the QPC was chosen in such a way that the Coulomb coupling of the QPC to one QD is made stronger than to the other QD, so that the QPC current can clearly resolve the charge states of the double QD. With a response time of similar to 200 mu s, we also investigated the energy relaxation time T-1 of the double QD by applying rectangular voltage pulses to the double QD. We confirmed that T-1 can be made sufficiently longer than the response time of the QPC.

 

23.    H. Hibino, M. Uematsu, and Y. Watanabe

            "Void growth during thermal decomposition of silicon oxide layers studied by low-energy electron microscopy"

            Journal Of Applied Physics 100 (11), 113519 (2006).

 

            ABSTRACT: Low-energy electron microscopy (LEEM) has been used to investigate void growth during thermal decomposition of 1-2-nm-thick silicon oxide on Si substrates. Real-time LEEM observations clarify that the void size (square root of the void area) grows linearly with time. The temperature dependence of the growth rate reveals that the activation energy of the void growth is about 4.0 eV. We also find that the void density increases at faster rates in later stages of the oxide decomposition. This suggests that the nucleation is not initiated by a random single event. Additionally, we demonstrate that the voids become shallower because the void shape changes during the growth. (c) 2006 American Institute of Physics.

 

24.    Y. Hirayama, G. Yusa, and S. Sasaki

            "Electron spin and nuclear spin manipulation in semiconductor nanosystems"

            Physica Status Solidi B-basic Solid State Physics 243 (14)3764-3772 (2006).

 

            ABSTRACT: Manipulations of electron spin and nuclear spin have been studied in AlGaAs/GaAs semiconductor nanosystems. Non-local manipulation of electron spins has been realized by using the correlation effect between localized and mobile electron spins in a quantum dot- quantum wire coupled system. Interaction between electron and nuclear spins was exploited to achieve a coherent control of nuclear spins in a semiconductor point contact device. Using this device, we have demonstrated a fully coherent manipulation of any two states among the four spin levels of Ga and As nuclei. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

 

25.    Y. Hirayama, A. Miranowicz, T. Ota, G. Yusa, K. Muraki, S. K. Ozdemir, and N. Imoto

            "Nanometre-scale nuclear-spin device for quantum information processing"

            Journal Of Physics-condensed Matter 18 (21)S885-S900 (2006).

 

            ABSTRACT: We have developed semiconductor point contact devices in which nuclear spins in a nanoscale region are coherently controlled by all-electrical methods. Different from the standard nuclear-magnetic resonance technique, the longitudinal magnetization of nuclear spins is directly detected by measuring resistance, resulting in ultra-sensitive detection of the microscopic quantity of nuclear spins. All possible coherent oscillations have been successfully demonstrated between two levels from four nuclear spin states of I = 3/2 nuclei. Quantum information processing is discussed based on two fictitious qubits of an I = 3/2 system and methods are described for performing arbitrary logical gates both on one and two qubits. A scheme for quantum state tomography based on M-z-detection is also proposed. As the starting point of quantum manipulations, we have experimentally prepared the effective pure states for the I = 3/2 nuclear spin system.

 

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

            "Suspended architecture formation process of single-walled carbon nanotubes"

            Applied Physics Letters 88 (2), 023115 (2006).

 

            ABSTRACT: The formation processes of suspended structures and bundles of single-walled carbon nanotubes (SWNTs) are directly observed by in situ scanning electron microscopy during chemical vapor deposition of SWNTs on a patterned specimen. SWNTs exhibit lively movements during extension from micropillar patterns, resulting in bridging, bundling, merging, and debundling. Fluctuation of the extension direction of a SWNT cantilever is observed. Swing of the SWNT cantilever is the reason for the enhanced-nearest-neighbor interconnection.

 

27.    T. Honjo, K. Inoue, A. Sahara, E. Yamazaki, and H. Takahashi

            "Quantum key distribution experiment through a PLC matrix switch"

            Optics Communications 263 (1)120-123 (2006).

 

            ABSTRACT: Quantum key distribution (QKD) is being studied as a way to provide unconditionally secure communications. Several experiments have shown its feasibility. However, most experiments have used a point-to-point occupied optical link. In order to use QKD for secure communications on a real network, it is preferable to be able to change parties on demand and to have quantum transmission and ordinary optical transmission share the optical network. In this work, QKD, through a silica-based planar lightwave circuit (PLC) 8 x 8 nonblocking matrix switch was investigated. We found that an interferometer type switch can work even for a single-photon-level light and that a multi-user QKD network can be constructed using a silica-based PLC 8 x 8 non-blocking matrix switch. In addition, single-photon-level transmission and ordinary optical transmission can share the same 8 x 8 non-blocking matrix switch, so which shows the possibility of sending quantum signals through current optical networks. (c) 2006 Elsevier B.V. All rights reserved.

 

28.    T. Honjo, and K. Inoue

            "Differential-phase-shift quantum key distribution with an extended degree of freedom"

            Optics Letters 31 (4)522-524 (2006).

 

            ABSTRACT: Differential-phase-shift quantum key distribution (DPS-QKD) with an extended degree of freedom of measurement is proposed. Extending the degree of freedom makes it possible to strengthen the DPS-QKD scheme against intercept-and-resend attacks. The feasibility of this idea is experimentally demonstrated. (c) 2006 Optical Society of America.

 

29.    S. Hosoi, K. Nakajima, M. Suzuki, K. Kimura, Y. Shimizu, S. Fukatsu, K. M. Itoh, M. Uematsu, H. Kageshima, and K. Shiraishi

            "Observation of Si emission during thermal oxidation of Si(001) with high-resolution RBS"

            Nuclear Instruments & Methods In Physics Research Section B-beam 249390-393 (2006).

 

            ABSTRACT: An epitaxially grown- Si isotope heterostructure, Si-28(2nM)/Si-30(1 nM)/Si-nat, was used to study the behavior of Si atoms during oxidation. The change in the Si-isotope profiles during the oxidation was observed using high-resolution Rutherford backscattering spectroscopy. A significant oxidation-enhanced diffusion of Si-30 into the (SiO)-Si-nat layer was observed in the oxidation at 800 degrees C, while the concentration of emitted Si-30 into the (SiO2)-Si-28 layer was found to be less than 5 at.% in the oxidation at 1100 degrees C. (c) 2006 Elsevier B.V. All rights reserved.

 

30.    W. P. Hu, H. Nakashima, E. J. Wang, K. Furukawa, H. X. Li, Y. Luo, Z. G. Shuai, Y. Kashimura, Y. Q. Liu, and K. Torimitsu

            "Advancing conjugated polymers into nanometer-scale devices"

            Pure And Applied Chemistry 78 (10)1803-1822 (2006).

 

            ABSTRACT: In this article, we review the possibility of combining conjugated polymers with nanometer-scale devices (nanodevices), in order to introduce the properties associated with conjugated polymers into such nanodevices. This approach envisages combining the highly topical disciplines of polymer electronics and nanoelectronics to engender a new subdirection of polymer nanoelectronics, which can serve as a tool to probe the behavior of polymer molecules at the nanometer/molecular level, and contribute to clarifying transport mechanisms in conjugated polymers. In this study, we exemplify this combination, using a family of linear and conjugated polymers, poly(p-phenylene-ethynylene)s (PPEs) with thiolacetate-functionalized end groups.

 

31.    W. P. Hu, J. Jiang, H. Nakashima, Y. Luo, Y. Kashimura, K. Q. Chen, Z. Shuai, K. Furukawa, W. Lu, Y. Q. Liu, D. B. Zhu, and K. Torimitsu

            "Electron transport in self-assembled polymer molecular junctions"

            Physical Review Letters 96 (2), 027801 (2006).

 

            ABSTRACT: A molecular junction of a poly(p-phenyleneethynylene)s derivative with thioacetate end groups (TA-PPE) was fabricated by self-assembling. Nanogap electrodes made by electroplating technique was used to couple thiol end groups of TA-PPE molecules. Room temperature current-voltage characteristics of the molecular junction exhibited highly periodic, repeatable, and identical stepwise features. First-principles calculations suggest that one possibility for the equidistant step is due to the opening of different conducting channels that corresponds to the unoccupied molecular orbitals of the polymer in the junction. It is interesting to see that an 18 nm long polymer is of quantized electronic structures and behaves like a quantum transport device.

 

32.    S. Hughes, H. Gotoh, and H. Kamada

            "Classical and quantum optical correlation effects between single quantum dots: The role of the hopping photon"

            Physical Review B 74 (11), 115334 (2006).

 

            ABSTRACT: We present a theoretical study of photon-coupled single quantum dots in a semiconductor. A series of optical effects are demonstrated, including a subradiant dark resonance, superradiance, reversible spontaneous emission decay, and pronounced exciton entanglement. Both classical and quantum optical approaches are presented using a self-consistent formalism that treats real and virtual photon exchange on an equal footing and can account for different quantum dot properties, surface effects, and retardation in the dipole-dipole coupling, all of which are shown to play a non-negligible role.

 

33.    K. Inoue

            "Quantum key distribution technologies"

            Ieee Journal Of Selected Topics In Quantum Electronics 12 (4)888-896 (2006).

 

            ABSTRACT: Since it was noted that quantum computers could break public key cryptosystems based on number theory, extensive studies have been undertaken on quantum cryptography (QC), which offers unconditionally secure communication based on quantum mechanics. This paper describes QC technologies, introduces a typical and widely used QC protocol BB84 and then describes a recently proposed scheme called the differential-phase-shift protocol.

 

34.    K. Inoue, and H. Takesue

            "Quantum key distribution using entangled-photon trains with no basis selection"

            Physical Review A 73 (3), 032332 (2006).

 

            ABSTRACT: Conventional quantum key distribution (QKD) protocols include a basis selection process for providing a secure secret key. In contrast, this paper proposes an entanglement-based QKD with no basis selection procedure. Entangled-photon pulse trains with an average photon number less than one per pulse are sent to two legitimate parties, from which a secret key is created utilizing the entanglement nature. Eavesdropping on a transmission line is prevented by a condition of less than one photon per pulse, and sending classically correlated coherent pulses instead of quantum correlated ones is revealed by monitoring coincident count rates.

 

35.    A. Ishizawa, and H. Nakano

            "Measurement of the true value of the carrier-envelope phase of a few-cycle laser pulse by the interference between second and third harmonics from the surface of a solid"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 45 (5A)4087-4089 (2006).

 

            ABSTRACT: We demonstrate a measurement that provides the true value of the carrier-envelope phase using, a few-cycle laser pulse. The measurement is based on the interference between the second and third harmonics from the surface of a solid. The interference intensity is sensitive to the carrier-envelope phase. This result for low-energy Pulses will lead to a new technique for measuring the carrier-envelope phase.

 

36.    T. Ito, T. Tawara, H. Yamaguchi, M. Ueki, K. Tateno, S. Mitsugi, H. Gotoh, E. Kuramochi, and M. Notomi

            "Enhanced emission of single quantum dot formed by interface fluctuations in photonic-crystal microcavities"

            Photonics And Nanostructures-fundamentals And Applications 4 (2)89-93 (2006).

 

            ABSTRACT: We fabricated photonic-crystal (PhC) microcavities tuned to GaAs quantum dots (QDs) formed by interface fluctuation for the first time and observed the spontaneous emission enhancement in a weak coupling regime. A QD is a very thin GaAs quantum Well (QW), and its interface steps exhibit quantum dot-like behavior. The emission intensity front the PhC cavity was stronger than that from the area Where no PhC pattern was fabricated and the overall shape of the photoluminescence (PL) agreed with the cavity mode calculated with the three-diniensional (3D) finite-difference time domain (FDTD) method. The spontaneous emission enhancement factor was 10. (c) 2006 Elsevier B.V. All rights reserved.

 

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

            "Behavior of catalytic nanoparticles during chemical vapor deposition for carbon nanotube growth"

            Chemical Physics Letters 422 (1-3)83-88 (2006).

 

            ABSTRACT: The change in the size of iron nanoparticles before and after single-walled carbon nanotubes (SWNTs) growth was systematically investigated for the first time using atomic force microscopy and transmission electron microscopy. In contrast to the conventional growth model of SWNTs, we found that thin SWNTs grow from large catalytic nanoparticles and all particles are finally embedded in SiO2 substrates after thermal chemical vapor deposition. The present results provide useful information for achieving diameter-con trolled growth of SWNTs. (c) 2006 Elsevier B.V. All rights reserved.

 

38.    J. Johansson, S. Saito, T. Meno, H. Nakano, M. Ueda, K. Semba, and H. Takayanagi

            "Vacuum Rabi oscillations in a macroscopic superconducting qubit LC oscillator system"

            Physical Review Letters 96 (12), 127006 (2006).

 

            ABSTRACT: We have observed the coherent exchange of a single energy quantum between a flux qubit and a superconducting LC circuit acting as a quantum harmonic oscillator. The exchange of an energy quantum is known as the vacuum Rabi oscillation: the qubit is oscillating between the excited state and the ground state and the oscillator between the vacuum state and the first excited state. We also show that we can detect the state of the oscillator with the qubit and thereby obtained evidence of level quantization of the LC circuit. Our results support the idea of using oscillators as couplers of solid-state qubits.

 

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

            "Theoretical study of nitrogen-doping effects on void formation processes in silicon crystal growth"

            Journal Of Applied Physics 100 (11), 113513 (2006).

 

            ABSTRACT: Nitrogen-doping effects in silicon crystal growth have been theoretically studied using thermodynamical simulation based on first-principles calculation results. The results show that the densities of various complexes are determined in the balance between the enthalpy effects and the entropy effects. They also show that about one order larger density of doped nitrogen is required in Czochralski silicon to obtain a void suppression effect similar to that in float-zone silicon. This is because oxygen itself has a weak void suppression effect due to the formation of vacancy-oxygen complexes around the void formation temperature. Competition between nitrogen and oxygen in trapping vacancies around the void formation temperature weakens the nitrogen-doping effect to suppress the void formation in Czochralski silicon. Since doped nitrogen preferentially forms nitrogen-vacancy-oxygen complexes at lower temperatures, the high density nitrogen doping enhances the oxygen precipitate density in Czochralski silicon. (c) 2006 American Institute of Physics.

 

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

            "Oxygen trap hypothesis in silicon oxide"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 45 (10A)7672-7674 (2006).

 

            ABSTRACT: A hypothesis on the atomic structure of silicon oxide is proposed to explain the discrepancy between theoretical and experimental studies on the oxygen diffusion and the interfacial reaction during the thermal silicon oxidation process. The hypothesis says that silicon oxide contains "oxygen traps", in which the molecular oxygen can be located with almost 0 dissolving enthalpy. The density of the "traps" is similar to 10(16) cm(-3). A possible local structure is also proposed based on the first-principles calculations.

 

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

            "Mechanism of oxide deformation during silicon thermal oxidation"

            Physica B-condensed Matter 376407-410 (2006).

 

            ABSTRACT: Mechanisms of oxide deformation during silicon thermal oxidation are studied by investigating the energetics of intrinsic point defects in the bulk silicon oxide and in the oxide film of the silicon oxide/silicon interface with first-principles calculations. The results suggest that the SiO2 and the SiO interstitials are thought to relate to the deformation of the silicon oxide. Especially, during the silicon oxidation, the SiO interstitial is suggested to be important because it can be formed in the oxide film neighboring to the interface and can enhance the deformation of the oxide films. (c) 2005 Elsevier B.V. All rights reserved.

 

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

            "Transport mechanism of interfacial network forming atoms during silicon oxidation"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 45 (2A)694-699 (2006).

 

            ABSTRACT: A first-principles study on the energetics of the structural transformation a, the interface, revealed that oxygen vacancies can accompany the high density oxide regions formed during the silicon oxidation. The vacancies can also promote the effective out-migration of these regions, which allows the easier oxide viscous flow to release the interfacial strain. Compared with this mechanism, self-interstitials are rarely formed in the silicon substrate. These results also suggest defect formation mechanisms around the interfaces.

 

43.    S. Karimoto, H. Sato, and T. Makimoto

            "Influence of impurity of MgO substrates on properties of molecular beam epitaxy-grown superconducting NdBa2CU3O7-delta thin films"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 45 (12-16)L419-L421 (2006).

 

            ABSTRACT: We prepared various MgO substrates cut from various ingots with different impurity-Ca concentrations and deposited NdBa2Cu3O7-delta (NBCO) thin-films on them by using molecular beam epitaxy (MBE). As a result, we found that the room temperature resistivity (rho(RT)) of NBCO thin-films and the Ca concentration in an MgO substrate are quantitatively correlated. Moreover we clarified the permissible impurity-Ca concentration in MgO substrates in terms of practical microwave applications.

 

44.    N. Kasai, A. Shimada, N. Tobias, and K. Torimitsu

            "Fabrication of an electrochemical sensor array for 2D H2O2 imaging"

            Electrochemistry 74 (8)628-631 (2006).

 

            ABSTRACT: To achieve accurate real-time 2D H2O2 distribution imaging, we fabricated an H2O2 sensor array by dispensing small quantities of enzyme solution very accurately onto electrodes in an electrode array. We confirmed the accuracy of the dispensing technique. We then investigated the responses of each sensor to H2O2 injection using a 64-channel multipotentiostat and found they varied by 20%. Real-time 2D H2O2 imaging was therefore successfully realized by using our flow cell system. This sensor array will be useful for the non-invasive, real-time monitoring of the H2O2 distribution in biological samples.

 

45.    M. Kasu, K. Ueda, H. Ye, Y. Yamauchi, S. Sasaki, and T. Makimoto

            "High RF output power for H-terminated diamond FETs"

            Diamond And Related Materials 15 (4-8)783-786 (2006).

 

            ABSTRACT: We report great improvement of RF output power for H-terminated diamond field-effect transistors (FETs). For the FET device with a gate width of 1 mm and a gate length of 0.4 mu m, the maximum output power (P-out) is 1.26 W, the maximum power gain is 23.2 dB, and the power added efficiency (PAE) is 56.3%. The increase in the device temperature when output power is 0.84 W is only similar to 0.6 degrees C. This is due to diamond having the highest thermal conductivity. (c) 2006 Elsevier B.V. All rights reserved.

 

46.    T. Kimura, S. Tsuchiya, M. Yamashita, and S. Kurihara

            "Superfluid-mott insulator transition of spin-1 bosons in optical lattice under magnetic field"

            Journal Of The Physical Society Of Japan 75 (7), 074601 (2006).

 

            ABSTRACT: We study the first- and second-order superfluid-Mott insulator transitions of spin-1 bosons in an optical lattice under a magnetic field by the Gutzwiller approximation. We find that, in contrast to previous perturbative studies, the phase boundary curve continuously changes as a function of magnetic field. We also find a sharp cusp structure on the phase boundary curve under some circumstances. When the phase boundary curve deviates from that obtained with the perturbative studies, the phase transition is a first-order one. We further clarify the specific features of the phase transition in the present system. The order parameters exactly at the boundary point, where the transition changes from first to second order, remain finite under a finite magnetic field and continuously vanish as the magnetic field approaches zero.

 

47.    O. Klochan, W. R. Clarke, R. Danneau, A. P. Micolich, L. H. Ho, A. R. Hamilton, K. Muraki, and Y. Hirayama

            "Ballistic transport in induced one-dimensional hole systems"

            Applied Physics Letters 89 (9), 092105 (2006).

 

            ABSTRACT: The authors have fabricated and studied a ballistic one-dimensional p-type quantum wire using an undoped AlGaAs/GaAs heterostructure. The absence of modulation doping eliminates remote ionized impurity scattering and allows high mobilities to be achieved over a wide range of hole densities and, in particular, at very low densities where carrier-carrier interactions are strongest. The device exhibits clear quantized conductance plateaus with highly stable gate characteristics. These devices provide opportunities for studying spin-orbit coupling and interaction effects in mesoscopic hole systems in the strong interaction regime where r(s)>10. (c) 2006 American Institute of Physics.

 

48.    Y. Kobayashi, and T. Makimoto

            "Growth of boron nitride on 6H-SiC substrate by flow-rate modulation epitaxy"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 45 (4B)3519-3521 (2006).

 

            ABSTRACT: Boron nitride (BN) layers on 6H-SiC substrate were grown by metalorganic vapor phase epitaxy (MOVPE) using triethylboron (TEB) and ammonia (NH3). The growth rate of the BN decreased as the NH3 flow rate increased, indicating that a strong parasitic reaction occurred between TEB and NH3. Flow-rate modulation epitaxy (FME), which is based on alternating the gas Supply, was applied to the BN growth for the first time and it was found that the parasitic reactions could be effectively reduced. The Structural properties of BN grown by FME were also investigated by X-ray diffraction (XRD) and transmission electron microscopy. In contrast with amorphous BN layers grown by MOVPE. the BN structure crown by FME was turbostratic with a weakly preferred orientation to the c-axis.

 

49.    T. Koga, Y. Sekine, and J. Nitta

            "Experimental realization of a ballistic spin interferometer based on the Rashba effect using a nanolithographically defined square loop array"

            Physical Review B 74 (4), 041302 (2006).

 

            ABSTRACT: We succeeded in observing gate-controlled electron spin interference in nanolithographically defined square loop arrays that were fabricated in In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As quantum wells (QWs). In this experiment, we demonstrated electron spin precession in ballistic channels within the QW that is caused by the Rashba effect. It turned out that the spin precession angle theta was gate controllable by more than 0.75 pi for a length of 1.5 mu m. Thus, the demonstration of the large controllability of theta by the applied gate voltage was carried out in a more direct way using spin interference of an electron wave function than the conventional beating analysis of the Shubnikov-de Haas oscillations.

 

50.    T. Kubo, Y. Tokura, T. Hatano, and S. Tarucha

            "Electron transport through Aharonov-Bohm interferometer with laterally coupled double quantum dots"

            Physical Review B 74 (20), 205310 (2006).

 

            ABSTRACT: We theoretically investigate electron transport through an Aharonov-Bohm interferometer containing laterally coupled double quantum dots. We introduce the indirect coupling parameter alpha, which characterizes the strength of the coupling via the reservoirs between two quantum dots. vertical bar alpha vertical bar=1 indicates the strongest coupling, where only a single mode contributes to the transport in the system. Two conduction modes exist in a system where vertical bar alpha vertical bar not equal 1. The interference effects such as the Fano resonance and the Aharonov-Bohm oscillation are suppressed as the absolute value of the parameter alpha decreases from 1. The linear conductance does not depend on the flux when alpha=0 since it corresponds to independent coupling of the dots to the reservoir modes.

 

51.    N. Kumada, K. Muraki, and Y. Hirayama

            "Nuclear-spin-lattice relaxation in a v=1 bilayer quantum Hall system"

            Physica E-low-dimensional Systems & Nanostructures 34 (1-2)164-167 (2006).

 

            ABSTRACT: We examined the electron spin degree of freedom around the total Landau-level filling factor v = 1 in a bilayer system via nuclear spins. In a balanced bilayer system, nuclear-spin-lattice relaxation rate 1/T-1, which probes low-energy electron spin fluctuations, increases gradually as the system is driven from the quantum Hall (QH) state through a phase transition to the compressible state. This result demonstrates that the electron spin degree of freedom is not frozen either in the QH or compressible states. Furthermore, as the density difference between the two layers is increased from balanced bilayer to monolayer configurations, I/T-1 around v = I shows a rapid yet smooth increase. This suggests that pseudospin textures around the bilayer v = 1 system evolves continuously into the spin texture for the monolayer system. (c) 2006 Elsevier B.V. All rights reserved.

 

52.    N. Kumada, K. Muraki, and Y. Hirayama

            "Low-frequency spin dynamics in a canted antiferromagnet"

            Science 313 (5785)329-332 (2006).

 

            ABSTRACT: Resistively detected nuclear spin relaxation measurements in closely separated two-dimensional electron systems reveal strong low-frequency electron-spin fluctuations in the quantum Hall regime. As the temperature is decreased, the spin fluctuations, manifested by a sharp enhancement of the nuclear spin-lattice relaxation rate 1/T-1, continue to grow down to the lowest temperature of 66 millikelvin. The observed divergent behavior of 1/T-1 signals a gapless spin excitation mode and is a hallmark of canted antiferromagnetic order. Our data demonstrate the realization of a two-dimensional system with planar broken symmetry, in which fluctuations do not freeze out when approaching the zero temperature limit.

 

53.    K. Kumakura, and T. Makimoto

            "Growth of GaN on sapphire substrates using novel buffer layers of ECR-plasma-sputtered Al2O3/graded-AlON/AlN/Al2O3"

            Journal Of Crystal Growth 292 (1)155-158 (2006).

 

            ABSTRACT: We proposed and demonstrated GaN growth on sapphire substrates by metalorganic vapor phase epitaxy using novel buffer layers of Al2O3/graded-AlON/AlN/Al2O3. The buffer layers were deposited by electron cyclotron resonance plasma sputtering at room temperature. The total thickness of the buffer layers was around 20 nm. The cross-sectional bright-field transmission electron microscope observation showed that the dislocations were bent at the initial stage of the growth, indicating the enhancement of lateral growth. Typical dislocation density in the GaN layer was 6.5 x 10(8) cm(-2). We obtained high electron mobility of 640 cm(2)/Vs at the electron concentration of 2.0 x 10(17) cm(-3) for Si-doped GaN. We also obtained high electron mobility of 1760 cm(2)/Vs at a sheet electron concentration of 8.3 x 10(12) cm(-2) for an AlGaN/GaN heterostructure. These results indicate that the quality of the epitaxial layer grown on sapphire substrates using the electron cyclotron resonance plasma sputtered buffer is comparable or superior to that of GaN layers using the conventional low-temperature buffer layer. (c) 2006 Elsevier B.V. All rights reserved.

 

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

            "Ultrahigh-Q photonic crystal nanocavities realized by the local width modulation of a line defect"

            Applied Physics Letters 88 (4), 041112 (2006).

 

            ABSTRACT: We propose an ultrahigh quality factor (Q) photonic crystal slab nanocavity created by the local width modulation of a line defect. We show numerically that this nanocavity has an intrinsic Q value of up to 7x10(7). Transmission measurements for fabricated Si photonic-crystal-slab nanocavities directly coupled to input/output waveguides have exhibited a loaded Q value of similar to 800 000. These theoretical and experimental Q values are very high for photonic crystal nanocavities. In addition, we demonstrate that simply shifting two holes away from a line defect is sufficient to achieve an ultrahigh Q value both theoretically and experimentally. (c) 2006 American Institute of Physics.

 

55.    H. M. Lee, K. Muraki, E. Y. Chang, and Y. Hirayama

            "Electronic transport characteristics in a one-dimensional constriction defined by a triple-gate structure"

            Journal Of Applied Physics 100 (4), 043701 (2006).

 

            ABSTRACT: We investigate the electronic transport characteristics of a one-dimensional (1D) narrow constriction defined in a GaAs/AlxGa1-xAs heterostructure by a simple triple-gate structure consisting of a pair of split gates and an additional surface Schottky gate (center gate) between them. Comparison between devices with and without a center gate reveals that the center gate, even when zero biased (V-CG=0 V), significantly modifies the surface potential and facilitates the 1D confinement in a deep two-dimensional electron system. The pinch-off voltages at V-CG=0 V for various channel widths W (=0.4-0.8 mu m) and lengths L (=0.2-2 mu m) are well described by the analytical formula based on the pinned-surface model [J. H. Davies , J. Appl. Phys. 77, 4504 (1995)]. Nonlinear transport spectroscopy with an additional dc bias shows that the lowest 1D subband energy separation (Delta E-1,E-2) changes linearly with V-CG and can be enhanced by 70% for V-CG=0.8 V. A simple model assuming an infinitely long channel and no self-consistent potential well reproduces the overall behavior of the measured Delta E-1,E-2. In addition, effects of impurities, occasionally found for long-channel devices (L >= 1 mu m), are found to be greatly reduced by applying positive V-CG and thereby enhancing Delta E-1,E-2. Data are also presented for the transport anomaly below the first conductance plateau, the so-called "0.7 anomaly," demonstrating that the triple-gate structure is useful for the study of density-dependent phenomena in a 1D system. (c) 2006 American Institute of Physics.

 

56.    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 and vortex glass transition in La1.87Y0.13CuO4"

            Physica B-condensed Matter 378-80447-448 (2006).

 

            ABSTRACT: The angular dependence of the critical current density (J(c)(theta)) and the vortex glass transition temperature (T-g(theta)) in La1.87Y0.13;CuO4 were measured at different fields and temperatures. Both J(c)(theta) and T-c(theta) showed a strong angular variation, which is typical for anisotropic superconductors. The angular variation could be described by using the anisotropic three-dimensional Ginzburg-Landau theory. From our analysis, we were able to estimate the anisotropy ratio. (c) 2006 Elsevier B.V. All rights reserved.

 

57.    Y. C. Lin, E. Y. Chang, H. Yamaguchi, Y. Hirayama, X. Y. Chang, and C. Y. Chang

            "Device linearity comparison of uniformly doped and delta-doped In0.52Al0.48As/In0.6Ga0.4As metamorphic HEMTs"

            Ieee Electron Device Letters 27 (7)535-537 (2006).

 

            ABSTRACT: The uniformly doped and the delta-doped In0.52Al0.48As/In0.6Ga0.4As metamorphic high-electron mobility transistors (MHEMTs) were fabricated, and the dc characteristics and the third-order intercept point (IP3) of these devices were measured and compared. Due to more uniform electron distribution in the quantum-well region, the uniformly doped MHEMT exhibits a flatter transconductance (G(m)) versus drain-to-source current (I-DS) curve and much better linearity with higher IP3 and higher IP3-to-P-dc. ratio as compared to the delta-doped MHEMT, even though the delta-doped device exhibits higher peak transconductance. As a result, the uniformly doped MHEMT is more suitable for communication systems that require high linearity operation.

 

58.    P. Liu, T. Okino, Y. Furukawa, T. Ichikawa, R. Itakura, K. Hoshina, K. Yamanouchi, and H. Nakano

            "Three-body sequential Coulomb explosions of CH3OD3+ induced by intense laser fields"

            Chemical Physics Letters 423 (1-3)187-191 (2006).

 

            ABSTRACT: Three-body Coulomb explosion of triply charged methanol-d (CH3OD3+), CH3OD3+ -> H+ + H-2(+) + COD+ induced by a laser field of (approximate to 2 x 10(14) W/cm(2)), is investigated by. the coincidence momentum imaging (CMI) method. It is securely identified that the explosion proceeds in a stepwise manner and that there are two types of sequential pathways: one is a pathway in which H+ is ejected first, and the other is a pathway in which H-2(+) is ejected first. Dynamical information on the two types of explosion processes is extracted from the analysis of CMI correlation maps. (c) 2006 Elsevier B.V. All rights reserved.

 

59.    X. F. Ma, C. H. Fung, F. Dupuis, K. Chen, K. Tamaki, and H. K. Lo

            "Decoy-state quantum key distribution with two-way classical postprocessing"

            Physical Review A 74 (3), 032330 (2006).

 

            ABSTRACT: Decoy states have recently been proposed as a useful method for substantially improving the performance of quantum key distribution (QKD) protocols when a coherent-state source is used. Previously, data postprocessing schemes based on one-way classical communications were considered for use with decoy states. In this paper, we develop two data postprocessing schemes for the decoy-state method using two-way classical communications. Our numerical simulation (using parameters from a specific QKD experiment as an example) results show that our scheme is able to extend the maximal secure distance from 142 km (using only one-way classical communications with decoy states) to 181 km. The second scheme is able to achieve a 10% greater key generation rate in the whole regime of distances. We conclude that decoy-state QKD with two-way classical postprocessing is of practical interest.

 

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

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

            Physica Status Solidi A-applications And Materials Science 203 (7)1861-1865 (2006).

 

            ABSTRACT: Al2O3/Si3N4 insulated-gate AlGaN/GaN heterostructure field-effect transistors (HFETs) have been fabricated, where the regrown ohmic structure was incorporated to reduce the contact resistance. Excellent DC and RF characteristics have been obtained together with the low gate leakage current as the result of employing the metal-insulator-semiconductor (MIS) structure. An HFET with a gate length (L-g) of 0.1 mu m has exhibited a drain current density (I-d) and a transconductance (g(m)) of 1.30 A/mm and 293 mS/mm, respectively, with a reduced contact resistance of 0.3 Omega mm. The gate leakage current (I-g) was as low as 1 x 10(-8) A/mm in the reverse vias region, and only 4 x 10(-5) A/mm even at a forward bias voltage of +3 V. In this device, the cutoff frequency (f(T)) and maximum oscillation frequency (f(max)) were estimated to be 70 and 90 GHz, respectively. In the HFETs with longer L-g of 0.7 and 1.0 mu m, f(T) and f(max) were 20 and 48 GHz (L-g = 0.7 mu m), respectively; and 14 and 35 GHz (L-g = 1.0 mu m), respectively. Thus, the Al2O3/Si3N4 MIS HFETs have proved to also exhibit excellent RF characteristics. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

 

61.    I. Mahboob, H. Okamoto, M. Ueki, and H. Yamaguchi

            "Electron phase modulation in a suspended InAs/AlGaSb nanomechanical beam"

            Applied Physics Letters 89 (19), 192106 (2006).

 

            ABSTRACT: The magnetopiezoresistance in a quasi one-dimensional electron system incorporated into an InAs/AlGaSb nanomechanical suspended beam was measured while the beam was at mechanical resonance. The magnetopiezoresistance showed reproducible highly periodic resistance oscillations which arise via strain induced electron phase modulation. The Fourier transform of the magnetopiezoresistance indicates that mechanical activation of the beam affects only a few electron trajectories and the electron interference in only a single electron loop gives rise to the resistance oscillations in the magnetopiezoresistance.

 

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

            "Influence of lattice constants of GaN and InGaN on npn-type GaN/InGaN heterojunction bipolar transistors"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 45 (4B)3395-3397 (2006).

 

            ABSTRACT: We investigated the a- and c-axis lattice constants of GaN buffer and 180-nm-thick p-InGaN layers grown on SiC and sapphire substrates using reciprocal space mapping of the X-ray diffraction intensity. It was found that the a-axis lattice constant of the GaN buffer layer on a SiC substrate is larger than those of unstrained GaN and a GaN buffer layer on a sapphire substrate. As a result, the p-InGaN layer oil GaN/SiC is fully strained even at the In mole fraction of 9.0% where that on GaN/sapphire is relaxed. This result means that fewer defects are generated in p-InGaN on GaN/SiC at higher In mole fractions. This is another advantage of SiC Substrate for npn-type GaN/InGaN heterojunction bipolar transistors, in addition to its high thermal conductivity. The collector current density dependence of current gain shows the ideality factor of 2 for GaN/ InGaN HBTs on both SiC and sapphire substrates. This is ascribed to the recombination current at the emitter-base interface, which arises from the threading dislocations generated at the interface between the substrate and nitride buffer layer.

 

63.    T. Makimoto, and K. Kumakura

            "Growth of nitride semiconductors and its application to heterojunction bipolar transistors"

            Electronics And Communications In Japan Part Ii-electronics 89 (3)20-25 (2006).

 

            ABSTRACT: Nitride heterojunction bipolar transistors (HBTs) are promising for high-power and high-temperature applications. However, two major issues for nitride HBTs have been low current gains and large offset voltages. Recently, to resolve these two issues, we developed a technique for extrinsic base regrowth of p-InGaN which led to the successful fabrication of Npn-type GaN/InGaN HBTs with high current gains and low offset voltages. These GaN/InGaN HBTs have a low-resistivity p-InGaN base and wide-bandgap n-GaN collector. We demonstrated their high breakdown voltage characteristics as well as high current density characteristics. These characteristics indicate that GaN/InGaN HBTs are favorable for high-power electronic devices. (c) 2006 Wiley Periodicals, Inc.

 

64.    T. Matsuoka, Y. Kobayashi, H. Takahata, T. Mitate, S. Mizuno, A. Sasaki, M. Yoshimoto, T. Ohnishi, and M. Sumiya

            "N-polarity GaN on sapphire substrate grown by MOVPE"

            Physica Status Solidi B-basic Solid State Physics 243 (7)1446-1450 (2006).

 

            ABSTRACT: N-polar GaN was grown on (0001) sapphire using two-step growth technique by MOVPE. In the growth, the key points were the controlling of the density of nuclei in a buffer layer and promoting lateral growth at high temperature. The grown GaN films had mirror-like smooth surfaces and were proved to have N-polarity using convergent-beam electron diffraction and coaxial impact-collision ion spectroscopy. The FWHM of this GaN in the co-scan was also much narrower than the previous reports. The density of threading dislocations was much less than for usual Ga-polar GaN grown with a GaN or AlN buffer layer by MOVPE and MBE. In PL at room temperature, the strong edge emission was observed as Ga-polarity. The p-type conduction in Mg-doped GaN was also realized by the same methods as for Ga-polarity.

 

65.    Z. Ming, K. Nakajima, M. Suzuki, K. Kimura, M. Uematsu, K. Torii, S. Kamiyama, Y. Nara, and K. Yamada

            "Si emission from the SiO2/Si interface during the growth of SiO2 in the HfO2/SiO2/Si structure"

            Applied Physics Letters 88 (15), 153516 (2006).

 

            ABSTRACT: HfO2/SiO2/Si(001) structures were annealed in dry oxygen, and compositional depth profiles were measured by high-resolution Rutherford backscattering spectroscopy. Growth of the interfacial SiO2 layer and simultaneous surface accumulation of Si were observed. The observed result indicates that silicon species are emitted from the SiO2/Si interface to release the stress induced by oxidation as was predicted by recent theoretical studies. (c) 2006 American Institute of Physics.

 

66.    S. Moreau, M. Byszewski, M. L. Sadowski, M. Potemski, S. A. Studenikin, G. Austing, A. S. Sachrajda, T. Saku, and Y. Hirayama

            "Optically detected cyclotron resonance in a high mobility 2D electron gas"

            Physica E-low-dimensional Systems & Nanostructures 32 (1-2)203-206 (2006).

 

            ABSTRACT: We study the properties of high mobility GaAs/GaAlAs quantum well structure by monitoring the microwave induced changes in the low-temperature photoluminescence of the 2DEG as a function of the external magnetic field. The most pronounced changes are observed at cyclotron resonance conditions, but weak features are also visible at cyclotron resonance replicas. Possible observation of microwave induced shift in the Landau-level structure of magneto-photoluminescence is reported in addition to the effects of carrier heating which are conventionally bracketed together with microwave irradiation. (c) 2006 Elsevier B.V. All rights reserved.

 

67.    F. Morikoshi

            "Information-theoretic temporal Bell inequality and quantum computation"

            Physical Review A 73 (5), 052308 (2006).

 

            ABSTRACT: An information-theoretic temporal Bell inequality is formulated to contrast classical and quantum computations. Any classical algorithm satisfies the inequality, while quantum ones can violate it. Therefore, the violation of the inequality is an immediate consequence of the quantumness in the computation. Furthermore, this approach suggests a notion of temporal nonlocality in quantum computation.

 

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

            "Anisotropic magneto transport near the v=2/3 quantum Hall state"

            Physica E-low-dimensional Systems & Nanostructures 34 (1-2)152-155 (2006).

 

            ABSTRACT: We report experimental results on an anisotropic magnetotransport of a bilayer electron system at the Landau level filling factor v = 2/3 under tilted magnetic fields. We find that the magnetoresistance changes when the direction of applied in-plane field B-vertical bar vertical bar is changed with respect to the direction of the current while keeping the strength of B-vertical bar vertical bar fixed. This anisotropy only appears at the ground state where interlayer electron tunneling is permitted. Therefore, this phenomenon indicates that bilayer systems at v =2/3 with interlayer tunneling inherently have a dissipation mechanism related to the direction of the in-plane field. (c) 2006 Elsevier B.V. All rights reserved.

 

69.    W. J. Naber, T. Fujisawa, H. W. Liu, and W. G. van der Wiel

            "Surface-acoustic-wave-induced transport in a double quantum dot"

            Physical Review Letters 96 (13), 136807 (2006).

 

            ABSTRACT: We report on nonadiabatic transport through a double quantum dot under irradiation of surface acoustic waves generated on chip. At low excitation powers, absorption and emission of single and multiple phonons are observed. At higher power, sequential phonon assisted tunneling processes excite the double dot in a highly nonequilibrium state. The present system is attractive for studying electron-phonon interaction with piezoelectric coupling.

 

70.    M. Nagase, K. Nakamatsu, S. Matsui, H. Namatsu, and H. Yamaguchi

            "Carbon multiprobe on a Si cantilever for pseudo-metal-oxide-semiconductor field-effect-transistor"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 45 (3B)2009-2013 (2006).

 

            ABSTRACT: A newly developed scanning probe microscopy system with multiple probes has been applied to measurements of local electrical properties of semiconductor films. Carbon multiprobes fabricated by focused ion beam deposition oil a Si cantilever were used for source and drain electrodes on a pseudo-siticon-on-insulator (SOI) metal-oxide-semiconductor (MOS) field-effect-transistor (FET) on which the Si substrate and buried oxide (BOX) act as a gate electrode and gate insulator, respectively. The pseudo-MOSFET characteristics of a 10-nm-thick Si layer oil an SOI Substrate were Successfully measured using the multiprobe. Furthermore, a carbon film deposited by electron cyclotron resonance (ECR) plasma sputtering oil a Si substrate with an oxide layer was confirmed as a semiconductor for the first time, using the pseudo-FET method with a carbon multiprobe. The results clearly demonstrate that this multiprobe system can be a powerful and widely applicable tool for measuring local device characteristics of electrical materials.

 

71.    K. Nakamatsu, J. Igaki, M. Nagase, T. Ichihashi, and S. Matsui

            "Mechanical characteristics of tungsten-containing carbon nanosprings grown by FIB-CVD"

            Microelectronic Engineering 83 (4-9)808-810 (2006).

 

            ABSTRACT: Tungsten-containing carbon (WC) nanosprings fabricated by focused-ion-beam chemical vapor deposition (FIB-CVD) using a source gas mixture of phenanthrene (C14H10) and tungsten hexacarbonyl (W(CO)(6)) showed unique characteristics they could expand and contract as flexibly as macro-scale springs. The large micro-scale displacements of the WC nanosprings were measured through optical microscope observation. In addition, we found that the spring constants of the springs rose as the W content increased. Moreover, the WC springs with a W content higher than 3% had an estimated Young's modulus of more than 200 GPa; this value exceeds Young's modulus of diamond-like carbon springs grown by FIB-CVD and is feasible for nanoelectromechanical applications. (c) 2006 Elsevier B.V. All rights reserved.

 

72.    K. Nakarnatsu, K. Tone, H. Namatsu, and S. Matsui

            "Room-temperature nanocontact printing using soft template"

            Journal Of Vacuum Science & Technology B 24 (1)195-199 (2006).

 

            ABSTRACT: Direct pattern transfer technology by room-temperature nanocontact printing using hydrogen silsesquioxane (HSQ) and Ag paste, which takes advantage of adhesion properties of these transfer materials, has been developed. The use of poly(ethylene) laminated on poly (methylmethacrylate) sheet has been proposed as the soft template for the contact printing. The HSQ transferred pattern with 35 nm linewidth was obtained onto Si surface. In addition, 1,mu m linewidth, and 2 mu m pitch Ag patterns were successfully transferred from the soft template to the SiO2/Si substrate. The transferred Ag wiring with 1 mu m linewidth showed good conduction characteristic, resistivity to be 1.7 X 10(-7) Omega M. (c) 2006 American Vacuum Society.

 

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

            "Room-temperature-operating data processing circuit based on single-electron transfer and detection with metal-oxide-semiconductor field-effect transistor technology"

            Applied Physics Letters 88 (18), 183101 (2006).

 

            ABSTRACT: A single-electron-based circuit, in which electrons are transferred one by one with a turnstile and subsequently detected with a high-charge-sensitivity electrometer, was fabricated on a silicon-on-insulator substrate. The turnstile, which is operated by opening and closing two metal-oxide-semiconductor field-effect transistors alternately, allows single-electron transfer at room temperature owing to electric-field-assisted shrinkage of the single-electron box. It also achieves fast single-electron transfer (less than 10 ns) and extremely long retention (more than 10(4) s). We have applied these features to a multilevel memory and a time-division weighted sum circuit for a digital-to-analog converter. (c) 2006 American Institute of Physics.

 

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

            "Critical electric fields of AlGaN in AlGaN-based vertical conducting diodes on n-SiC substrates"

            Superlattices And Microstructures 40 (4-6)332-337 (2006).

 

            ABSTRACT: We have succeeded in obtaining high critical electric fields from AlGaN layers using the p-InGaN/i-AlxGa1-xN/n-AlxGa1-xN (x = 0-0.22) vertical conducting diodes grown on n-SiC substrates by low-pressure metalorganic vapor phase epitaxy (MOVPE). The breakdown voltage (V-B) increases with increasing Al composition of the AlGaN layer. The corresponding critical electric fields are calculated to be 2.4 MV/cm for GaN and 3.5 MV/cm for Al0.22Ga0.78N. The critical electric field is proportional to the bandgap energy to a power of 2.5. This bandgap energy dependence is much stronger than that in the empirical expression proposed by Sze and Gibbons. The figure of merit, (V-B)2/R-on, increases with increasing Al composition, indicating the AlGaN-based p-i-n diodes are promising for high-power and high-temperature electronic device applications. (c) 2006 Elsevier Ltd. All rights reserved.

 

75.    A. Nishikawa, K. Kumakura, and T. Makimoto

            "High breakdown voltage with low on-state resistance of p-InGaN/n-GaN vertical conducting diodes on n-GaN substrates"

            Applied Physics Letters 89 (15), 153509 (2006).

 

            ABSTRACT: p-InGaN/n-GaN vertical conducting diodes were grown on freestanding n-GaN substrates by metal organic vapor phase epitaxy. The homoepitaxial growth produced a high-quality GaN layer, as evidenced by the full width at half maximum of the (0002) x-ray rocking curve is as low as 34 arc sec. For a diode with a 3.6-mu m-thick n-GaN layer, a high breakdown voltage (V-B) of 571 V is obtained with a low on-state resistance (R-on) of 1.23 m Omega cm(2), leading to the figure of merit, (V-B)(2)/R-on, of 265 MW/cm(2). This is the highest value among those previously reported for GaN-based vertical conducting Schottky and p-n junction diodes. (c) 2006 American Institute of Physics.

 

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

            "p-InGaN/n-GaN vertical conducting diodes on n(+)-SiC substrate for high power electronic device applications"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 45 (4B)3387-3390 (2006).

 

            ABSTRACT: We have investigated the current-voltage (I-V) characteristics of p-InGaN/n-GaN vertical conducting diodes grown on n(+)- SiC substrates by low-pressure metal organic vapor phase epitaxy (MOVPE). The breakdown voltage (V-B) of 250 V was obtained with a low on-state resistance (R-on) of 1.28 m Omega cm(2) when the n-GaN layer thickness was increased to 1800 nm, leading to the high figure-of-merit, (V-B)(2)/R-on, of 49 MW/cm(2). With increasing measurement temperature from room temperature (RT) to 520 K, the on-state resistance decreased due to the reduced contact resistance of the p-InGaN layer, while the breakdown voltage remained almost constant because of fewer defects in the n-GaN layer. These I-V characteristics are preferable for high-power and high-temperature electronic device applications.

 

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

            "High critical electric field of AlxGa1-xN p-i-n vertical conducting diodes on n-SiC substrates"

            Applied Physics Letters 88 (17), 173508 (2006).

 

            ABSTRACT: We report the current-voltage characteristics of AlxGa1-xN (x=0-0.22) p-i-n vertical conducting diodes grown on n-SiC substrates by low-pressure metal organic vapor phase epitaxy. An increase in the breakdown voltage was experimentally demonstrated with increasing Al composition. The corresponding critical electric fields were calculated to be 2.4 MV/cm for GaN and 3.5 MV/cm for Al0.22Ga0.78N. The critical electric field is proportional to the band gap energy to a power of 2.5. The forward voltage drop also increases with increasing Al composition but it is still as low as 5.2 V even in the case of the Al0.22Ga0.78N p-i-n diode. (c) 2006 American Institute of Physics.

 

78.    S. Nomura, M. Yamaguchi, T. Akazaki, H. Tamura, H. Takayanagi, and Y. Hirayama

            "Electron-hole states in the fractional quantum Hall regime probed by photoluminescence"

            Physica E-low-dimensional Systems & Nanostructures 34 (1-2)292-295 (2006).

 

            ABSTRACT: The electron-hole states in the fractional quantum Hall regime is investigated with a back-gated undoped quantum well by photoluminescence in magnetic fields. The evolution of the photoluminescence spectra is discussed depending on the electron density. We find anomalies of the photoluminescence at the integer as well as the fractional filling factors. (c) 2006 Elsevier B.V. All rights reserved.

 

79.    M. Notomi, H. Taniyama, S. Mitsugi, and E. Kuramochi

            "Optomechanical wavelength and energy conversion in high-Q double-layer cavities of photonic crystal slabs"

            Physical Review Letters 97 (2), 023903 (2006).

 

            ABSTRACT: We demonstrate that ultrasmall double-layer photonic-crystal-slab cavities exhibit a very high-Q value for a wide range of the layer spacing, which enables us to realize unique optomechanical coupling. By mechanically varying the separation, we can achieve extraordinarily large wavelength conversion. In addition, the light stored in the cavity can generate a large radiation force. We show that this system exhibits extremely high energy conversion efficiency between optical and mechanical energy, leading to a novel approach for the optomechanical control of light and matter.

 

80.    M. Notomi, and S. Mitsugi

            "Wavelength conversion via dynamic refractive index tuning of a cavity"

            Physical Review A 73 (5), 051803 (2006).

 

            ABSTRACT: We demonstrate numerically that the wavelength conversion of light is possible by the simple dynamic refractive index tuning of an optical cavity in a photonic crystal. We also clarify the mechanism and conservation rule for this conversion process. In addition, we discuss the observability of this phenomenon in realistic cavities. Our results indicate that this linear adiabatic wavelength conversion process can be observed for various high-Q microcavities.

 

81.    H. Okamoto, T. Akazaki, M. Ueki, H. Yamaguchi, and H. Namatsu

            "A piezoresistive cantilever integrating an InAs-based semiconductor-superconductor junction"

            Physica E-low-dimensional Systems & Nanostructures 32 (1-2)512-515 (2006).

 

            ABSTRACT: Targeting highly sensitive displacement and force sensors, we fabricated a piezoresistive cantilever that integrates a superconductor-semiconductor-superconductor (S-Sm-S) junction based on an InAs/AlGaSb heterostructure. The S-Sm-S junction is composed of a submicron Nb gap patterned on the InAs thin film, and a deflection of the cantilever is detected as a resistance change at the junction. We confirmed that the resistance change caused by induced strain (i.e., piezoresistance) has a strong dependence on bias current. When the maximum Josephson current (I-c) is biased to the junction, the resistance change is significantly enhanced by more than a factor of 10 compared to that at the bias current above I-c (the resistive state). The resulting maximum resistance change is 3.9 m Omega, which is three orders of magnitude larger than that obtained for our preliminary sample. This large piezoresistance at the S-Sm-S junction will lead to highly sensitive self-detective sensors. (c) 2006 Elsevier B.V. All rights reserved.

 

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

            "Observation of femtosecond-laser-induced ablation plumes of aluminum using space- and time-resolved soft x-ray absorption spectroscopy"

            Applied Physics Letters 89 (22), 221502 (2006).

 

            ABSTRACT: The dynamics of the laser ablation plume expansion of aluminum was investigated by using space- and time-resolved soft x-ray absorption spectroscopy. Blueshifts of the Al L-shell photoabsorption edge indicating the state of aluminum were observed in the plumes, which were generated by irradiating an aluminum target with 120 fs near-infrared pulses at an intensity of 10(14) W/cm(2). The spatiotemporal evolution of the plumes exhibited a multilayer structure consisting of vaporized aluminum and condensed aluminum particles, following the expansion of plasma, with expansion velocities of 10(4) m/s for the atomic state and 10(3) m/s for the condensed state. (c) 2006 American Institute of Physics.

 

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

            "Soft x-ray imaging system for picosecond time-resolved absorption spectroscopy using a femtosecond-laser-plasma source"

            Review Of Scientific Instruments 77 (4), 046105 (2006).

 

            ABSTRACT: We have developed an imaging system for time-resolved soft x-ray absorption spectroscopy. The system consists of a femtosecond-laser-plasma x-ray source for time-resolved measurements and an x-ray microscope with critical illumination for imaging. The temporal and spatial resolutions were 23 ps and better than 12.5 mu m, respectively. We applied this system to the measurement of an aluminum ablation plume induced by irradiation with a 120 fs laser pulse. The shift of the L-shell photoabsorption edge in the expanding plume was observed in the spatiotemporally resolved absorbance spectrum. The space- and time-resolved x-ray absorption spectrum of an expanding laser ablation plume was clearly obtained using the developed system. (c) 2006 American Institute of Physics.

 

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

            "Spatial distribution of soft x-ray line emissions from aluminum plasma excited by a pair of femtosecond-laser pulses"

            Journal Of Applied Physics 99 (6), 063302 (2006).

 

            ABSTRACT: We measured the time-integrated, spatially resolved spectra of soft x rays emitted from laser-induced aluminum plasma to characterize its spatial features. The plasma was excited by an intense femtosecond-laser pulse with a controlled artificial prepulse at intensities of 9.9x10(15) and 6.4x10(14) W/cm(2), respectively. The dependence of the spectra on the time intervals between the main pulse and the prepulse was obtained for delay times of 0-3 ns. The strongest emissions in soft x-ray range occurred in a narrow region less than 50 mu m from the target surface. In contrast to the continuum spectrum, the prepulse technique causes the Al(3+)2p(6)-2p(5)3s emission to extend more than 600 mu m from the target surface. We showed that the line emission can be separated spatially from the other continuum component of the emission spectra and that the extension length increased with increases in the pulse-separation time. (c) 2006 American Institute of Physics.

 

85.    T. Okino, Y. Furukawa, P. Liu, T. Ichikawa, R. Itakura, K. Hoshina, K. Yamanouchi, and H. Nakano

            "Ejection dynamics of hydrogen molecular ions from methanol in intense laser fields"

            Journal Of Physics B-atomic Molecular And Optical Physics 39 (13)S515-S521 (2006).

 

            ABSTRACT: The ejection of hydrogen molecular ions from two-body Coulomb explosion processes of methanol (CH3OH, CD3OH and CH3OD) in an intense laser field (800 nm, 60 fs, 0.2 PW cm(-2)) is investigated by a coincidence momentum imaging method. From the coincidence momentum maps, the ejection processes of hydrogen molecular ions, CH3OH2+. H-m(+) + CH(3-m) OH+ (m = 2, 3), CD3OH2+ -> D-m(+) + CH(3-m)OH+ (m = 2,3) and CH3OD2+. H-m(+) + CH(3-m) OD+(m = 2, 3), are identified. Based on the results obtained with isotopically substituted methanol, the isotope effect on the ejection process of hydrogen molecular ions is discussed. Furthermore, the ejection of H/D exchanged hydrogen molecular ions (HD+, HD2+ and H2D+) is identified, and the timescales for the H/D exchanging processes are estimated from the extent of anisotropy in the ejection directions.

 

86.    T. Okino, Y. Furukawa, P. Liu, T. Ichikawa, R. Itakura, K. Hoshina, K. Yamanouchi, and H. Nakano

            "Coincidence momentum imaging of ultrafast hydrogen migration in methanol and its isotopomers in intense laser fields"

            Chemical Physics Letters 423 (1-3)220-224 (2006).

 

            ABSTRACT: Two-body Coulomb explosion processes of methanol (CH3OH, CD3OH, CH3OD) in an intense laser field (0.2 pW/cm(2), 60 fs) are investigated by the coincidence momentum imaging method. The dissociation pathways with hydrogen/deuterium migration or hydrogen/deuterium exchange prior to the C-O bond breaking are securely identified. From the anisotropic angular distributions and the relative yields of the fragment ions, it is revealed that the hydrogen migration process is terminated within the period of an intense ultrashort laser pulse. A comparison of the results obtained for CH3OH and those for the isotopomers shows that the hydrogen migration is decelerated by the isotope substitution. (c) 2006 Elsevier B.V. All rights reserved.

 

87.    T. Okino, Y. Furukawa, P. Liu, T. Ichikawa, R. Itakura, K. Hoshina, K. Yamanouchi, and H. Nakano

            "Coincidence momentum imaging of ejection of hydrogen molecular ions from methanol in intense laser fields"

            Chemical Physics Letters 419 (1-3)223-227 (2006).

 

            ABSTRACT: Two-body Coulomb explosion processes of methanol (CH3OH) in an intense laser field (0.2 pW/cm(2), 60 fs) are investigated by the coincidence momentum imaging method. In the coincidence momentum images, the hydrogen ejection processes, CH3OH2+ ->, H-m(+) + CH(3-m)OH+ (m = 1-3), are securely identified. From the anisotropy in the angular distributions of the fragment ions, the lifetimes of the corresponding precursor ions CH3OH2+ are estimated to be 70-290 fs for the H+ ejection, 110-550 fs for the H-2(+) ejection, and much longer than 1.4 ps for the H-3(+) ejection. (c) 2005 Elsevier B.V. All rights reserved.

 

88.    H. Omi, H. Kageshima, and M. Uematsu

            "Scaling and universality of roughening in thermal oxidation of Si(001)"

            Physical Review Letters 97 (1), 016102 (2006).

 

            ABSTRACT: By analyzing atomic force microscopy images, we derive a continuum equation that quantitatively explains the roughening at the Si(001)-SiO2 interface during thermal oxidation at the temperature at 1200 degrees C in an Ar atmosphere containing a small fraction of O-2. We also show that there is a phase transition in the universality class from a disordered to step-terrace structure at the interface at oxidation temperatures between 1150 and 1380 degrees C with the miscut angle of the substrate as the scaling parameter.

 

89.    Y. Ono, J. F. Morizur, K. Nishiguchi, K. Takashina, H. Yamaguchi, K. Hiratsuka, S. Horiguchi, H. Inokawa, and Y. Takahashi

            "Impurity conduction in phosphorus-doped buried-channel silicon-on-insulator field-effect transistors at temperatures between 10 and 295 K"

            Physical Review B 74 (23), 235317 (2006).

 

            ABSTRACT: We investigate transport in phosphorus-doped buried-channel metal-oxide-semiconductor field-effect transistors at temperatures between 10 and 295 K. We focus on transistors with phosphorus donor concentrations higher than those previously studied, where we expect conduction to rely on donor electrons rather than conduction-band electrons. In a range of doping concentration between around 2.1 and 8.7x10(17) cm(-3), we find that a clear peak emerges in the conductance versus gate-voltage curves at low temperature. In addition, temperature dependence measurements reveal that the conductance obeys a variable-range-hopping law up to an unexpectedly high temperature of over 100 K. The symmetric dual-gate configuration of the silicon-on-insulator we use allows us to fully characterize the vertical-bias dependence of the conductance. Comparison to computer simulation of the phosphorus impurity band depth profile reveals how the spatial variation of the impurity-band energy determines the hopping conduction in transistor structures. We conclude that the emergence of the conductance peak and the high-temperature variable-range hopping originate from the band bending and its change by the gate bias. Moreover, the peak structure is found to be strongly related to the density of states (DOS) of the phosphorus impurity band, suggesting the possibility of performing a spectroscopy for the DOS of phosphorus, the dopant of paramount importance in Si technology, through transport experiments.

 

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

            "Local structure of (La,Sr)(2)CuO4 under uniaxial strain studied by polarized X-ray absorption spectroscopy"

            Journal Of Physics And Chemistry Of Solids 67 (9-10)2154-2158 (2006).

 

            ABSTRACT: Local structure of optimally doped T-(La,Sr)(2)CuO4 (LSCO) single-crystal thin films grown by molecular-beam epitaxy on LaSrCuO4 and SrTiO3 substrates was studied by the in-plane polarized Cu K-edge extended X-ray absorption fine structure (EXAFS). The results of data analysis show that the local structure (CuO6 octahedra) of LSCO thin films is strained by ca. 5 x 10(-3) in accordance with the crystallographic data. Although the planar and apical oxygen displacements Delta R-CuO are related to the critical temperature in a simple relation, the magnitude of strain-induced oxygen displacements (leading to anti-Jahn-Tell or Jahn-Teller distortion) is less than 0.1% of the equilibrium bond length. This suggests that the strain dependence of electronic states involves a different mechanism than a purely electronic model in a homogeneous conducting plane. The fact that LSCO thin films under tensile strain have a large local distortion of planar oxygens indicates that inhomogeneity may affect the critical temperature rather than the apical oxygen displacement. (c) 2006 Elsevier Ltd. All rights reserved.

 

91.    H. Oyanagi, A. Tsukada, M. Naito, N. L. Saini, M. O. Lampert, D. Gutknecht, P. Dressler, S. Ogawa, K. Kasai, S. Mohamed, and A. Fukano

            "Fluorescence X-ray absorption spectroscopy using a Ge pixel array detector: application to high-temperature superconducting thin-film single crystals"

            Journal Of Synchrotron Radiation 13314-320 (2006).

 

            ABSTRACT: A Ge pixel array detector with 100 segments was applied to fluorescence X-ray absorption spectroscopy, probing the local structure of high-temperature superconducting thin-film single crystals (100 nm in thickness). Independent monitoring of pixel signals allows real-time inspection of artifacts owing to substrate diffractions. By optimizing the grazing-incidence angle theta and adjusting the azimuthal angle phi, smooth extended X-ray absorption fine structure (EXAFS) oscillations were obtained for strained (La,Sr)(2)CuO4 thin-film single crystals grown by molecular beam epitaxy. The results of EXAFS data analysis show that the local structure (CuO6 octahedron) in (La,Sr)(2)CuO4 thin films grown on LaSrAlO4 and SrTiO3 substrates is uniaxially distorted changing the tetragonality by similar to 5 x 10(-3) in accordance with the crystallographic lattice mismatch. It is demonstrated that the local structure of thin-film single crystals can be probed with high accuracy at low temperature without interference from substrates.

 

92.    S. Perraud, K. Kanisawa, Z. Z. Wang, and Y. Hirayama

            "Unpinning of the Fermi level at (111)A clean surfaces of epitaxially grown n-type In0.53Ga0.47As"

            Applied Physics Letters 89 (19), 192110 (2006).

 

            ABSTRACT: Low-temperature scanning tunneling spectroscopy under ultrahigh vacuum was employed to investigate the (111)A clean surface of n-type In0.53Ga0.47As, grown by molecular beam epitaxy on lattice-matched InP substrates. It was found that the surface Fermi level is located in the conduction band, close to the bulk Fermi level, and can be controlled by varying the dopant concentration in the bulk. This observation was confirmed by determining the dispersion relation of electron standing waves resulting from scattering interferences. Such an unpinning of the surface Fermi level strongly contrasts with the pinning phenomenon observed at the (001) clean surface.

 

93.    K. Prabhakaran, S. Gotzinger, K. V. Shafi, A. Mazzei, S. Schietinger, and O. Benson

            "Ultrafine luminescent structures through nanoparticle self-assembly"

            Nanotechnology 17 (15)3802-3805 (2006).

 

            ABSTRACT: We report the fabrication of ultrafine structures consisting of regular arrays of nanoemitters through the self-assembly of luminescent nanoparticles on a silicon wafer. Nanoparticles of yttrium aluminium garnet (YAG) doped with Eu3+ ions were synthesized by a sonochemical technique. These particles, suspended in ethanol, are introduced onto a pre-patterned silicon wafer, covered with a thin oxide layer. On annealing the sample in an ultrahigh-vacuum chamber, the nanoparticles self-assemble along the pattern. We demonstrate this 'chemical lithography' by assembling the nanoparticles along a variety of patterns. We believe that such self-organized nanopatterning of functional structures is important for the realization of nanodevices.

 

94.    R. Rungsawang, Y. Ueno, I. Tomita, and K. Ajito

            "Angle-dependent terahertz time-domain spectroscopy of amino acid single crystals"

            Journal Of Physical Chemistry B 110 (42)21259-21263 (2006).

 

            ABSTRACT: The measurement of absorption spectra using angle-dependent terahertz (THz) time-domain spectroscopy for amino acid single crystals of L-cysteine and L-histidine is reported for the first time. Linearly polarized THz radiation enables us to observe angle-dependent far-infrared absorption spectra of amino acid single crystals and determine the direction of the oscillating dipole of the molecules in the 20-100 cm(-1) range. By comparing the THz spectra of a single crystal and powder, we found that there was a clear hydrogen-bond peak in the crystal spectrum as a result of the larger hydrogen-bond network. The low-temperature THz spectra of amino acid microcrystals showed more intermolecular vibrational modes than those measured at room temperature. An ab initio frequency calculation of a single amino acid molecule was used to predict the intramolecular vibrational modes. The validity of the calculation models was confirmed by comparing the results with experimentally obtained data in the Raman spectral region.

 

95.    R. Rungsawang, Y. Ueno, I. Tomita, and K. Ajito

            "Terahertz notch filter using intermolecular hydrogen bonds in a sucrose crystal"

            Optics Express 14 (12)5765-5772 (2006).

 

            ABSTRACT: We propose a THz notch filter that uses the absorption of the intermolecular hydrogen bonds in a molecular crystal such as sucrose. Terahertz ( THz) time-domain spectroscopy was used to investigate the absorption characteristics of a rotationally oriented sucrose single crystal in the 0.3-3.0 THz frequency range. The crystal was set so that the ( 100) face ( cleavage) was normal to the THz propagation direction. The two lowest frequency intermolecular hydrogen bonding bands clearly exist at room temperature and at 1.45 and 1.64 THz when the b-axis of the crystal is parallel and perpendicular to the THz polarization, respectively. In contrast, they disappear when the b-axis is reversed. This absorption feature means that it would be possible to utilize a sucrose crystal as a notch filter with a 1.45-THz band center for the 0.1-1.7 THz range and with a 1.64-THz band center for the 0.1-1.9 THz range. When the crystal is rotated, the transmitted intensities of the frequency components near the absorption bands alternate as a sine function against angle. The spectroscopic properties of the sucrose filter were confirmed by continuous THz wave imaging. (c) 2006 Optical Society of America.

 

96.    S. Saito, T. Meno, M. Ueda, H. Tanaka, K. Semba, and H. Takayanagi

            "Parametric control of a superconducting flux qubit"

            Physical Review Letters 96 (10), 107001 (2006).

 

            ABSTRACT: Parametric control of a superconducting flux qubit has been achieved by using two-frequency microwave pulses. We have observed Rabi oscillations stemming from parametric transitions between the qubit states when the sum of the two microwave frequencies or the difference between them matches the qubit Larmor frequency. We have also observed multiphoton Rabi oscillations corresponding to one- to four-photon resonances by applying single-frequency microwave pulses. The parametric control demonstrated in this work widens the frequency range of microwaves for controlling the qubit and offers a high quality testing ground for exploring nonlinear quantum phenomena of macroscopically distinct states.

 

97.    S. Sasaki, S. Kang, K. Kitagawa, M. Yamaguchi, S. Miyashita, T. Maruyama, H. Tamura, T. Akazaki, Y. Hirayama, and H. Takayanagi

            "Spin manipulation in a double quantum-dot-quantum-wire coupled system"

            Journal Of Vacuum Science & Technology B 24 (4)2024-2028 (2006).

 

            ABSTRACT: We have studied spin correlation in a double quantum-dot-quantum-wire coupled device revealed in low-temperature transport characteristics. We demonstrate nonlocal control of the Kondo effect in one dot by manipulating the spin states of the other. The modulation of the local density of states in the wire region due to the Fano-Kondo antiresonance and the Ruderman-Kittel-Kasuya-. Yoshida exchange interaction are the two possible mechanisms underlying the observed features. When the dot states are indirectly probed in the side-coupled geometry, double suppression of the wire conductance is observed due to the Fano-Kondo antiresonance involving both dots. (c) 2006 American Vacuum Society.

 

98.    S. Sasaki, S. Kang, K. Kitagawa, M. Yamaguchi, S. Miyashita, T. Maruyama, H. Tamura, T. Akazaki, Y. Hirayama, and H. Takayanagi

            "Nonlocal control of the Kondo effect in a double quantum dot-quantum wire coupled system"

            Physical Review B 73 (16), 161303 (2006).

 

            ABSTRACT: We have performed low-temperature transport measurements on a double quantum dot-quantum wire coupled device and demonstrated nonlocal control of the Kondo effect in one dot by manipulating the electronic spin states of the other. We discuss the modulation of the local density of states in the wire region due to the Fano-Kondo antiresonance, and the Ruderman-Kittel-Kasuya-Yoshida exchange interaction as the mechanisms responsible for the observed features.

 

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

            "Many-body interactions in Bi-based high-T-c cuprates studied by angle-resolved photoemission spectroscopy"

            Journal Of Physics And Chemistry Of Solids 67 (1-3)628-631 (2006).

 

            ABSTRACT: Systematic angle-resolved photoemission spectroscopy (ARPES) has been performed on Bi2Sr2Can-1CunO2n+4 (n = 1-3). For n = 2 and 3, the dispersion kink becomes pronounced on approaching (pi, 0) below T-c, while a kink appears only around the nodal direction above T-c. This indicates that the coupling of electrons with magnetic resonance mode plays a dominant role in the superconducting state for multi-layered cuprates. Ultrahigh-resolution (Delta E = 1.3 meV) ARPES result for n = 2 indicates that spectra around (pi, 0) below T-c is understood in terms of (1) the coupling of electrons with the resonance mode, (2) the real-space inhomogeneity, and (3) the impurity states in the vicinity of E-F. (c) 2005 Elsevier Ltd. All rights reserved.

 

100.    Y. Sawai, B. Takimoto, H. Nabika, K. Ajito, and K. Murakoshi

            "Control of near-infrared optical response of metal nano-structured film on glass substrate for intense Raman scattering"

            Faraday Discussions 132179-190 (2006).

 

            ABSTRACT: Near-infrared SERS activity of the Ag film under electric polarization was evaluated in aqueous solution containing 1 mM glutamic acid. Spectra were obtained in situ from the near infrared laser Raman microscope system with an excitation wavelength of 785 nm. Intensity of the SERS increased significantly upon application of an external electric field to the film. Empirical signal enhancement factor, which was determined from the peak integration ratio of the SERS vibration to the unenhanced signal from the solution of a defined sample concentration, was estimated to be in the range between 10(5) and 10(9). The evolution of the scattering signal was not observed in the absence of an applied external field. Under the present conditions, the SERS intensity was fully controlled by the applied field and the time. Relatively strong enhancement observed at the present system could be attributable to closed-packed particulate structure characterized by the diameters of approximately 20 - 90 nm on the Ag film. Raman images prove that the scattering signals are highly localized at the specific sites on the films showing possible achievement of relatively larger enhancement more than 10(12). Importance of the control of the size and inter-particle distance for intense Raman scattering was proved by the preparation of the well-ordered chained Ag dot array showing stronger SERS signals than those at the Ag films.

 

101.    H. Shibata, S. Karimoto, A. Tsukada, and T. Makimoto

            "Growth of (Cu,C)Ba2Ca((n-1))CunOy thin films by molecular-beam epitaxy"

            Physica C-superconductivity And Its Applications 445862-864 (2006).

 

            ABSTRACT: We report the growth of (Cu,C)Ba(2)Ca((n-1))Cu(n)Oy (n = 2,4) thin films on NdGaO3(100) and LaSrGaO4(001) substrates by molecular-beam epitaxy (MBE). For n = 2, we synthesize superconducting films with T-c(on) similar to 85 K and T-c(zero) similar to 50 K on NdGaO3. The film is a-axis oriented with 90 degrees domains, and the lattice parameters are a = 3.894 angstrom and c = 11.634 angstrom. We also obtained a-axis oriented superconducting films for n = 4 with T-c(on) similar to 105 K and T-c(zero) similar to 53 K. (c) 2006 Elsevier B.V. All rights reserved.

 

102.    K. Shimizu, and A. Kawaguchi

            "Approach to the quantum phase transition of spin chains in terms of pair-wise entanglement"

            Physics Letters A 355 (3)176-179 (2006).

 

            ABSTRACT: The Lewenstein-Sanpera decomposition of a two-qubit density matrix rho provides us with a clear understanding of the entanglement properties in S 1/2 quantum Ising spin chains undergoing quantum phase transition (QPT). By decomposing p into a separable part Lambda rho(s) and an inseparable part (1-Lambda)rho(e), we can evaluate the concurrence C(rho), a measure of pair-wise entanglement, as a product of 1-Lambda and the concurrence C(rho(e)). By analyzing 1-Lambda and C(rho(e)), we can interpret the reported singular behavior of C(rho) in the conventional QPT framework. The behavior of C(rho(e)) and 1-Lambda at the critical point indicates the singular maximization of quantum spin fluctuation and the divergence in the spin correlation length, respectively. (c) 2006 Elsevier B.V. All rights reserved.

 

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

            "Ultrasmall multi-port channel drop filter in two-dimensional photonic crystal on silicon-on-insulator substrate"

            Optics Express 14 (25)12394-12400 (2006).

 

            ABSTRACT: We demonstrate ultrasmall five-port channel drop filters (CDFs) based on a two-dimensional photonic crystal slab. We combine seven photonic crystals with different lattice constants and use light reflections at the different photonic crystal boundaries to control the interference process and achieve a high dropping efficiency. We operate the CDFs in two modes; one requires careful control of the interference process, whereas the other does not. The former can output a narrower signal spectrum than the latter, and CDF design is easier with the latter. Both CDFs achieve a high dropping efficiency and can function in the CL-band. (c) 2006 Optical Society of America.

 

104.    A. Shinya, S. Mitsugi, T. Tanabe, M. Notomi, I. Yokohama, H. Takara, and S. Kawanishi

            "All-optical flip-flop circuit composed of coupled two-port resonant tunneling filter in two-dimensional photonic crystal slab"

            Optics Express 14 (3)1230-1235 (2006).

 

            ABSTRACT: We propose an optical flip-flop circuit composed of two-port resonant-tunneling filters based on a two-dimensional photonic crystal slab with a triangular air-hole lattice. This circuit can function as an optical digital circuit that synchronizes input data with a clock. In this report, we demonstrate that this circuit can achieve a fast operating speed with a response time of about 10 ps and a low operating power of 60 mW by employing a two-dimensional FDTD calculation. (c) 2006 Optical Society of America.

 

105.    I. Suemune, T. Akazaki, K. Tanaka, M. Jo, K. Uesugi, M. Endo, H. Kumano, E. Hanamura, H. Takayanagi, M. Yamanishi, and H. Kan

            "Superconductor-based quantum-dot light-emitting diodes: Role of Cooper pairs in generating entangled photon pairs"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 45 (12)9264-9271 (2006).

 

            ABSTRACT: The realization of solid-state photon sources that are capable of on-demand generation of an entangled single-photon pair at a generating an entangled time is highly desired for quantum information processing and communication. A new method of single-photon pair at a time is proposed employing Cooper-pair-related radiative recombination in a quantum dot (QD). Cooper pairs are bosons and the control of their number states is difficult. Pauli's exclusion principle on quasiparticles in a discrete state of a QD regulates the number state of the generated photon pairs in this scheme. The fundamental heterostructures for constructing superconductor-based quantum-dot light-emitting diodes (SQ-LEDs) and the fundamental operation conditions of SQ-LED will be discussed. The experimental studies on Cooper-pair injection into the related semiconductor structures will be also discussed.

 

106.    W. Suhara, M. Kobayashi, H. Sagara, K. Hamada, T. Goto, I. Fujimoto, K. Torimitsu, and K. Mikoshiba

            "Visualization of inositol 1,4,5-trisphosphate receptor by atomic force microscopy"

            Neuroscience Letters 391 (3)102-107 (2006).

 

            ABSTRACT: Inositol 1,4,5-trisphosphate (IP3) receptor (IP3R) acts as a ligand-gated channel that mediates neuronal signals by releasing Ca2+ from the endoplasmic reticulum. The three-dimensional (3D) structure of tetrameric IP3R has been demonstrated by using electron microscopy (EM) with static specimens; however, the dynamic aspects of the IP3R structure have never been visualized in a native environment. Here we attempt to measure the surface topography of IP3R in solution using atomic force microscopy (AFM). AFM revealed large protrusions extending similar to 4.3 nm above a flat membrane prepared from Spodoptera frugiperda (Sf9) cells overexpressing mouse type 1 IP3R (Sf9-IP(3)R1). The average diameter of the large protrusions was similar to 32 nm. A specific antibody against a cytosolic epitope close to the IP3-binding site enabled us to gold-label the Sf9-IP(3)R1 membrane as confirmed by EM. AFM images of the gold-labeled membrane revealed 7.7-nm high protrusions with a diameter of similar to 30 nm, which should be IP(3)R1-antibody complexes. Authentic IP(3)R1 immumo-purified from mouse cerebella had approximately the same dimensions as those of the IP3R-like protrusions on the membrane. Altogether, these results suggest that the large protrusions on the Sf9-IP(3)R1 membrane correspond to the cytosolic domain of IP(3)R1. Our study provides the first 3D representation of individual IP(3)R1 particles in an aqueous solution. (C) 2005 Elsevier Ireland Ltd. All rights reserved.

 

107.    S. Suzuki, Y. Watanabe, and S. Heun

            "Photoelectron spectroscopy and microscopy of carbon nanotubes"

            Current Opinion In Solid State & Materials Science 10 (2)53-59 (2006).

 

            ABSTRACT: In this review we will focus our attention on the characterization of carbon nanotubes by X-ray photoelectron spectroscopy. In contrast to other spectroscopic techniques, photoelectron spectroscopy allows to obtain information on the overall electronic structure of the sample in a wide energy range, which makes it a unique technique. We will discuss the most recent and the most significant results on the intrinsic electronic properties of carbon nanotubes obtained with photoelectron spectroscopy. Furthermore, we will discuss in detail the application of photoelectron microscopy, i.e. photoelectron spectroscopy with high lateral resolution, to the study of carbon nanotubes. This technique allows to obtain laterally resolved spectroscopic information from ensembles of carbon nanotubes, but it even allows to perform photoelectron spectroscopy on single carbon nanotubes. (c) 2006 Elsevier Ltd. All rights reserved.

 

108.    S. Suzuki, and Y. Kobayashi

            "Diameter dependence of low-energy electron and photon irradiation damage in single-walled carbon nanotubes"

            Chemical Physics Letters 430 (4-6)370-374 (2006).

 

            ABSTRACT: Low-energy photon irradiation in an ultra-high vacuum, as well as low-energy electron irradiation, was found to damage single-walled carbon nanotubes, meaning that electronic excitations are solely responsible for the defect formation. The formation and healing of the defects were found to strongly depend on nanotube diameter; that is, thinner nanotubes are more easily damaged and hardly recovered. The results mean that the irradiation damage is prominent in a rolled up graphene sheet, but not in a planar one. The curvature-induced strain energy seems to be essentially important for the damage. (c) 2006 Elsevier B.V. All rights reserved.

 

109.    A. Taguchi, and K. Kanisawa

            "Stable reconstruction and adsorbates of InAs(111)A surface"

            Applied Surface Science 252 (15)5263-5266 (2006).

 

            ABSTRACT: We investigated the surface properties of InAs(111)A by low-temperature scanning tunneling microscopy (LT-STM) with atomic resolution and first-principles calculation. Very clear atom image was observed, showing that the surface reconstruction is an In-vacancy structure. We also observed two kinds of adsorbates on the surface. The first-principles calculations indicate that the In-vacancy structure is the most stable surface reconstruction under any experimental conditions, which is consistent with the LT-STM observation. Investigations of adsorption properties of an In atom, an As atom, and an As-2 molecule by the first-principles calculations imply that the observed adsorbates are an In atom and an As-2 molecule. (c) 2006 Elsevier B.V. All rights reserved.

 

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

            "Theoretical study of vacancy supersaturation during silicon crystal growth and nitrogen-doping effects"

            Physica B-condensed Matter 376130-132 (2006).

 

            ABSTRACT: We performed thermodynamical simulations of the vacancy supersaturation during silicon crystal growth and investigated nitrogen-doping effects on the suppression of void formation and the enhancement of oxygen precipitates. Although the mechanism with the N2V complex has been proposed to explain the suppression, we found that it cannot reproduce the suppression even with nitrogen density as high as 1020 cm(-3). On the other hand, the mechanism with the N2V2 complex can reproduce the suppression with about 10,5 cm(-3) Of nitrogen, which is consistent with the experiments. It also explains the enhancement of oxygen precipitates. Therefore, the N2V2 complex plays the dominant role in the vacancy aggregation process. (c) 2005 Elsevier B.V. All rights reserved.

 

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

            "In situ scanning electron microscopy of single-walled carbon nanotube growth"

            Surface And Interface Analysis 38 (12-13)1743-1746 (2006).

 

            ABSTRACT: We have developed an in situ observation technique for chemical vapor deposition (CVD) of single-walled carbon nanotubes (SWNTs) using a scanning electron microscope (SEM). The growth of SWNTs in the SEM is achieved by employing low-pressure ethanol vapor as the carbon source and cobalt as the catalyst. The time evolution of SWNT growth is successfully traced by alternate CVD growth in low vacuum and SEM observation in high vacuum. By limiting the nanotube growth areas, individual SWNT growth could be observed. Copyright (C) 2006 John Wiley & Sons, Ltd.

 

112.    D. Takagi, Y. Homma, H. Hibino, S. Suzuki, and Y. Kobayashi

            "Single-walled carbon nanotube growth from highly activated metal nanoparticles"

            Nano Letters 6 (12)2642-2645 (2006).

 

            ABSTRACT: We demonstrate that any metal, even gold, silver, and copper, can act as a catalyst for SWCNT synthesis in chemical vapor deposition (CVD). Metal nanoparticles 3 nm or less in diameter, introduced into CVD ambience immediately after heat treatment at 800-950 degrees C in air, produce SWCNTs. The activation method is effective for copper and various noble metals as well as for iron-family elements. This implies that any metal particle may produce SWCNTs when its size becomes 1-3 nm. In other words, carbon atoms can form SWCNTs in a self-assembling fashion on nanoparticles without the specific functions of iron-family elements.

 

113.    K. Takashina, R. J. Nicholas, B. Kardynal, N. J. Mason, D. K. Maude, and J. C. Portal

            "Current-driven breakdown of the quantized Hall states of a broken-gap 2D electron-hole system"

            Semiconductor Science And Technology 21 (12)1758-1763 (2006).

 

            ABSTRACT: We report results from experimental studies on the current driven breakdown of the quantum Hall effect in an InAs/GaSb-based electron-hole system. We find that the critical currents observed in this system are typically much smaller than those reported for single carrier-type systems. Width dependence measurements show two regimes of behaviour. For sufficiently wide samples, the critical current has a linear dependence on the channel width, while for narrower samples, the critical current has a strong tendency to be vastly reduced. There is a critical width at which this crossover occurs, which is found to depend on the magnetic field, Fermi energy and the ratio between the electron and hole concentrations. We refer to the two regimes as the 'linear regime' and the 'fragile regime'. For samples in the linear regime, critical electric fields or macroscopic critical current densities can be defined. Although the absolute values seem small compared to single carrier-type systems, the values are found to be comparable when scaled by the activation energies. In the fragile regime, the critical current is disproportionately small compared with single carrier-type systems.

 

114.    K. Takashina, Y. Ono, A. Fujiwara, Y. Takahashi, and Y. Hirayama

            "Intersubband scattering in double-gate MOSFETs"

            Ieee Transactions On Nanotechnology 5 (5)430-435 (2006).

 

            ABSTRACT: Quantum mechanical features of even the most basic of semiconductor components can be expected to become of paramount importance for future nanoelectronics and quantum information technology. Here, we show that the conductivity of even a two-dimensionally extended double-gate silicon-on-insulator metal-oxide-silicon field-effect transistor can develop a distinct peak structure in its top-gate voltage dependence at low temperatures, due to the discreteness of sub-band edges resulting from quantum mechanical confinement in the vertical gating direction. Our findings are confirmed using low-temperature magnetic field measurements.

 

115.    K. Takashina, Y. Ono, A. Fujiwara, Y. Takahashi, and Y. Hirayama

            "Valley polarization in Si(100) at zero magnetic field"

            Physical Review Letters 96 (23), 236801 (2006).

 

            ABSTRACT: The valley splitting, which lifts the degeneracy of the lowest two valley states in a SiO2/Si(100)/SiO2 quantum well, is examined through transport measurements. We demonstrate that the valley splitting can be observed directly as a step in the conductance defining a boundary between valley-unpolarized and -polarized regions. This persists to well above liquid helium temperature and shows no dependence on magnetic field, indicating that single-particle valley splitting and valley polarization exist in (100) silicon even at zero magnetic field.

 

116.    H. Takesue, E. Diamanti, C. Langrock, M. M. Fejer, and Y. Yamamoto

            "1.5-mu m single photon counting using polarization-independent up-conversion detector"

            Optics Express 14 (26)13067-13072 (2006).

 

            ABSTRACT: We report a 1.5-mu m band polarization independent single photon detector based on frequency up-conversion in periodically poled lithium niobate (PPLN) waveguides. To overcome the polarization dependence of the PPLN waveguides, we employed a polarization diversity configuration composed of two up-conversion detectors connected with a polarization beam splitter. We experimentally confirmed polarization independent single photon counting using our detector. We undertook a proof-of-principle differential phase shift quantum key distribution experiment using the detector, and confirmed that the sifted key rate and error rate remained stable when the polarization state was changed during single photon transmission. (c) 2006 Optical Society of America.

 

117.    H. Takesue, E. Diamanti, C. Langrock, M. M. Fejer, and Y. Yamamoto

            "10-GHz clock differential phase shift quantum key distribution experiment"

            Optics Express 14 (20)9522-9530 (2006).

 

            ABSTRACT: This paper reports the first quantum key distribution experiment implemented with a 10-GHz clock frequency. We used a 10-GHz actively mode-locked fiber laser as a source of short coherent pulses and single photon detectors based on frequency up-conversion in periodically poled lithium niobate waveguides. The use of short pulses and low-jitter upconversion detectors significantly reduced the bit errors caused by detector dark counts even after long-distance transmission of a weak coherent state pulse. We employed the differential phase shift quantum key distribution protocol, and generated sifted keys at a rate of 3.7 kbit/s over a 105 km fiber with a bit error rate of 9.7%. (c) 2006 Optical Society of America

 

118.    H. Takesue, and K. Inoue

            "Quantum secret sharing based on modulated high-dimensional time-bin entanglement"

            Physical Review A 74 (1), 012315 (2006).

 

            ABSTRACT: We propose a scheme for quantum secret sharing (QSS) that uses a modulated high-dimensional time-bin entanglement. By modulating the relative phase randomly by {0,pi}, a sender with the entanglement source can randomly change the sign of the correlation of the measurement outcomes obtained by two distant recipients. The two recipients must cooperate if they are to obtain the sign of the correlation, which is used as a secret key. We show that our scheme is secure against intercept-and-resend (IR) and beam splitting attacks by an outside eavesdropper thanks to the nonorthogonality of high-dimensional time-bin entangled states. We also show that a cheating attempt based on an IR attack by one of the recipients can be detected by changing the dimension of the time-bin entanglement randomly and inserting two "vacant" slots between the packets. Then, cheating attempts can be detected by monitoring the count rate in the vacant slots. The proposed scheme has better experimental feasibility than previously proposed entanglement-based QSS schemes.

 

119.    H. Takesue, T. Honjo, and H. Kamada

            "Differential phase shift quantum key distribution using 1.3-mu m up-conversion detectors"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 45 (7)5757-5760 (2006).

 

            ABSTRACT: We report a differential phase shift quantum key distribution (DPS-QKD) experiment in the 1.3-mu m band that uses single photon detectors based on a frequency up-conversion technique. By combining a fast-clock DPS-QKD and up-conversion detectors operated in a non-gated mode, we have achieved a sifted key rate of 180kbit/s over 10km of fiber, which is one order of magnitude larger than a previously reported 1.3-mu m band result.

 

120.    H. Takesue, N. Yoshimoto, Y. Shibata, T. Ito, Y. Tohmori, and T. Sugie

            "Wavelength channel data rewriter using semiconductor optical aturator/modulator"

            Journal Of Lightwave Technology 24 (6)2347-2354 (2006).

 

            ABSTRACT: A wavelength channel data rewriter (WCDR) a device that erases the data on an incoming signal by utililing the saturation characteristic of a semiconductor optical amplifier (SOA) and then modulates it with new data to generate an upstream signal. This paper describes a theoretical and experimental investigation designed to improve the performance of the WCDR. Through numerical calculations, this paper shows that an SOA with a long waveguide with a large small-signal gain better suppresses optical bit patterns. This paper also uses calculated and experimental results to show that the amplified-spontaneous emission noise in the SOA input signal degrades the bit-pattern suppression. This paper then describes the semiconductor optical saturator/modulator (SOSM), which this paper has developed for use in the WCDR based on the results of the author's theoretical investigations. This paper outlines the SOSM specifications and provides experimental results that confirm the improved WCDR performance obtained using the SOSM.

 

121.    H. Takesue

            "Long-distance distribution of time-bin entanglement generated in a cooled fiber"

            Optics Express 14 (8)3453-3460 (2006).

 

            ABSTRACT: This paper reports the first demonstration of the generation and distribution of time-bin entangled photon pairs in the 1.5-mu m band using spontaneous four-wave mixing in a cooled fiber. Noise photons induced by spontaneous Raman scattering were suppressed by cooling a dispersion shifted fiber with liquid nitrogen, which resulted in a significant improvement in the visibility of two-photon interference. By using this scheme, time-bin entangled qubits were successfully distributed over 60 km of optical fiber with a visibility of 76%, which was obtained without removing accidental coincidences. (c) 2006 Optical Society of America.

 

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

            "Increased electron mobility in n-type Si-doped AlN by reducing dislocation density"

            Applied Physics Letters 89 (18), 182112 (2006).

 

            ABSTRACT: For n-type Si-doped AlN with a low Si doping concentration of 3x10(17) cm(-2), a high room-temperature electron mobility of 426 cm(2) V-1 s(-1) was achieved, and at 220 K the mobility reached 730 cm(2) V-1 s(-1), the highest value ever reported for AlN. At Si doping concentrations lower than 10(18) cm(-3), dislocation scattering is the most dominant scattering mechanism, and the mobility can therefore be increased significantly by reducing the dislocation density. (c) 2006 American Institute of Physics.

 

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

            "An aluminium nitride light-emitting diode with a wavelength of 210 nanometres"

            Nature 441 (7091)325-328 (2006).

 

            ABSTRACT: Compact high-efficiency ultraviolet solid-state light sources(1) such as light-emitting diodes (LEDs) and laser diodes - are of considerable technological interest as alternatives to large, toxic, low-efficiency gas lasers and mercury lamps. Microelectronic fabrication technologies and the environmental sciences both require light sources with shorter emission wavelengths: the former for improved resolution in photolithography and the latter for sensors that can detect minute hazardous particles. In addition, ultraviolet solid-state light sources are also attracting attention for potential applications in high-density optical data storage, biomedical research, water and air purification, and sterilization. Wide-bandgap materials, such as diamond(2) and III - V nitride semiconductors (GaN, AlGaN and AlN; refs 3 - 10), are potential materials for ultraviolet LEDs and laser diodes, but suffer from difficulties in controlling electrical conduction. Here we report the successful control of both n-type and p-type doping in aluminium nitride ( AlN), which has a very wide direct bandgap(11) of 6 eV. This doping strategy allows us to develop an AlN PIN (p-type/intrinsic/n-type) homojunction LED with an emission wavelength of 210 nm, which is the shortest reported to date for any kind of LED. The emission is attributed to an exciton transition, and represents an important step towards achieving exciton-related light-emitting devices as well as replacing gas light sources with solid-state light sources.

 

124.    K. Tateno, H. Hibino, H. Gotoh, and H. Nakano

            "Vertical GaP nanowires arranged at atomic steps on Si(111) substrates"

            Applied Physics Letters 89 (3), 033114 (2006).

 

            ABSTRACT: We report vertical GaP nanowires self-arranged in lines formed from Au islands that were initially arranged at single-layer steps on Si(111) substrates. These Au islands are spontaneously arranged by controlling the deposition. There are three aspects to the growth of vertical GaP wires: the cosupply of TMGa and PH3, two growths at different temperatures, and a low PH3 flow rate. The grown wires are quite ordered in lines of several micrometers. Electrical measurement confirmed selective current flow at the wires and we confirmed photoluminescence from the wires. This bottom-up technique is promising for nano-hetero-device integration on Si circuits. (c) 2006 American Institute of Physics.

 

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

            "Multi-quantum structures of GaAs/AlGaAs free-standing nanowires"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 45 (4B)3568-3572 (2006).

 

            ABSTRACT: Free-standing semiconductor nanowires are promising for future nano-scale devices. We have investigated the growth and photoluminescence characteristics of AlGaAs-capped nanowires containing multi-quantum structures. Using small Au particles of around 20 nm diameter, we were able to form many columnar-like GaAs nanostructures in capped wire structures by means of vapor-liquid-solid growth for the wire cores and metalorganic vapor phase epitaxy for the capping. In order to investigate photoluminescence characteristics, we performed scanning near-field optical microspectrometer measurements at about 20 K. Many sharp luminescence peaks were observed around 700 nm. By mapping each peak, we could obtain some wire images. We found one wire had several luminescence peaks, which originated from localized excitons in the one-dimensional potential.

 

126.    T. Tawara, T. Ito, T. Tanabe, K. Tateno, E. Kuramochi, M. Notomi, and H. Nakano

            "Highly selective ZEP/AlGaAs etching for photonic crystal structures using Cl-2/HI/Xe mixed plasma"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 45 (33-36)L917-L919 (2006).

 

            ABSTRACT: We demonstrate the highly selective etching of AlGaAs photonic crystal (PhC) structures with electron beam (EB) resist masks by using Cl-2/HI/Xe mixed plasma. We found that the Cl-2/HI plasma etches the AlGaAs layer while suppressing EB mask etching, and the addition of Xe eliminates damage to the EB mask caused by radicals. With this balanced approach, we achieved a 3-fold increase in the etching selectivity of the etching rate ratio of AlGaAs/resist. Moreover, using these conditions we successfully fabricated an AlGaAs PhC slab with a fine structure and very small air holes that had a radius of 48 nm and a lattice constant of 240 nm.

 

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

            "Stability of soliton lattice phase in the v=1 bilayer quantum Hall state under tilted magnetic fields"

            Physica E-low-dimensional Systems & Nanostructures 34 (1-2)81-84 (2006).

 

            ABSTRACT: The bilayer quantum Hall (QH) state at the filling factor v = 1 shows various fascinating quantum phenomena due to the layer degree of freedom called 'pseudospin'. We report an experimental evidence of the soliton lattice (SL) phase, which is a domain structure of pseudospin, by the appearance of a local maximum of magneto resistance near the v = I QH state. We investigate the stability of the SL phase by changing B-vertical bar vertical bar and the total electron density n(T). Detailed magnetotransport measurements under tilted magnetic fields were carried out to obtain a B-vertical bar vertical bar-n(T) plane phase diagram containing the C, IC and SL phases. We found the SL phase is only stable at low nT region. Namely, the C-SL-IC phase transition occurs only at low nT region as B-vertical bar vertical bar increases. On the contrary, the C-IC phase transition directly occurs without passing through the SL phase at high nT region. (c) 2006 Elsevier B.V. All rights reserved.

 

128.    Y. Tokura, W. G. van der Wiel, T. Obata, and S. Tarucha

            "Coherent single electron spin control in a slanting Zeeman field"

            Physical Review Letters 96 (4), 047202 (2006).

 

            ABSTRACT: We consider a single electron in a 1D quantum dot with a static slanting Zeeman field. By combining the spin and orbital degrees of freedom of the electron, an effective quantum two-level (qubit) system is defined. This pseudospin can be coherently manipulated by the voltage applied to the gate electrodes, without the need for an external time-dependent magnetic field or spin-orbit coupling. Single-qubit rotations and the controlled-NOT operation can be realized. We estimated the relaxation (T-1) and coherence (T-2) times and the (tunable) quality factor. This scheme implies important experimental advantages for single electron spin control.

 

129.    I. Tomita, M. Asobe, H. Suzuki, J. Yumoto, and Y. Yoshikuni

            "Broadband quasi-phase-matched second-harmonic generation in a nonlinear photonic crystal"

            Journal Of Applied Physics 100 (2), 023120 (2006).

 

            ABSTRACT: We analyze the properties of quasi-phase-matched second-harmonic generation (SHG) from a defect waveguide in photonic-crystal (PhC) slabs embedded in a periodically chi((2)) inverted material with a collinear beam configuration. We show that by controlling the material dispersion with the structural dispersion of a defect waveguide in PhC slabs of infinite height, it is possible to realize a much wider frequency range for quasi-phase-matched SHG than without the PhC structure. Also, taking the fabrication of actual devices into consideration, we examine the case for PhC slabs of finite height and show that, although guided modes are index confined in the vertical direction (while they are confined by the PhC structure in the horizontal direction), the effect that the PhC structure has on the broadening of the frequency range remains and that the broadened range can be comparable to that for the PhC slabs of infinite height if appropriate structural parameters are taken. (c) 2006 American Institute of Physics.

 

130.    I. Tomita, and A. Suzuki

            "A note on electron confinement to a two-dimensional quantum disk"

            Journal Of Applied Physics 99 (12), 126104 (2006).

 

            ABSTRACT: The confinement properties of an electron to a two-dimensional quantum disk surrounded with a finite-height potential barrier are investigated. It is shown that since the confining barrier is distorted by a centrifugal potential arising from nonzero electron angular momentum, the electron can tunnel out through a thin part of the distorted barrier, which takes place when the radius of the disk is smaller than a critical radius. It is found that since the barrier for zero electron angular momentum is deformed by a centripetal potential characteristic of two dimensions, although no electron leaks out at any radii, bound-energy levels ascend as the disk radius decreases and become tied up at the top of the confining potential well, resulting in high density of states. Some experimental methods are outlined to observe those leaky and confining phenomena. (c) 2006 American Institute of Physics.

 

131.    I. Tomita, H. Suzuki, H. Ito, H. Takenouchi, K. Ajito, R. Rungsawang, and Y. Ueno

            "Terahertz-wave generation from quasi-phase-matched GaP for 1.55 mu m pumping"

            Applied Physics Letters 88 (7), 071118 (2006).

 

            ABSTRACT: We have realized a terahertz (THz)-wave source employing difference frequency generation (DFG) from a quasi-phase-matched GaP stack pumped at 1.55 mu m. We observed THz waves with enhanced power by quasi-phase matching (QPM) in the < 110 > direction of GaP with a < 111 > polarization direction for the incidence of two pump lights with the same propagation and polarization directions. We obtained THz-wave power proportional to the product of two pump-light powers due to DFG. We also confirmed that power peaks appeared at around 1 and 2.6 THz reflecting the first- and the third-order QPM, respectively.

 

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

            "Doping of Ce in T-La2CuO4: Rigorous test for electron-hole symmetry for high-T-c superconductivity"

            Physical Review B 74 (17), 174515 (2006).

 

            ABSTRACT: We report that Ce doping was achieved in La2CuO4 with the K2NiF4 (T) structure for the first time by molecular beam epitaxy. A synthesis temperature of as low as similar to 630 degrees C and an appropriate substrate choice, i.e., (001)LaSrGaO4 (a(s)=3.843 A), enabled us to incorporate Ce into the K2NiF4 lattice and to obtain Ce-doped T-La2-xCexCuO4 up to x similar to 0.06. The doping of Ce makes T-La2CuO4 more insulating, which is in sharp contrast to Sr (or Ba) doping in T-La2CuO4, which makes the compound metallic and superconducting. The observed smooth increase in resistivity from the hole-doped side (T-La2-xSrxCuO4) to the electron-doped side (T-La2-xCexCuO4) indicates that the electron-hole symmetry is broken in the T-phase materials.

 

133.    A. Tsukada, H. Shibata, M. Noda, H. Yamamoto, and M. Naito

            "Charge transfer gap for T '-RE2CuO4 and T-La2CuO4 as estimated from Madelung potential calculations"

            Physica C-superconductivity And Its Applications 44594-96 (2006).

 

            ABSTRACT: T '-RE2CUO4 (RE: rare-earth element), after appropriate "reduction", has fairly high conductivity and also exhibits clear Fermi edge in photoemission spectroscopy. To clarify the origin of conductivity in the T ' mother compounds, we evaluated the unscreened charge-transfer gap (Delta(0)) for T '-RE2CUO4 and T-La2CuO4. The Delta(0) value for T '-compounds almost linearly decreases with increasing the ionic radius of RE from 12.24 eV for T '-Tm2CuO4 to 9.90 eV for T '-La2CuO4. The results qualitatively explain metallic conductivity in T '-RE2CuO4 for large RE. (c) 2006 Published by Elsevier B.V.

 

134.    K. Tsumura, S. Nomura, T. Akazaki, and J. Nitta

            "Infrared magneto-photoluminescence spectra and electron-hole g-factor of an InAs-inserted channel InGaAs/InAlAs heterostructure"

            Physica E-low-dimensional Systems & Nanostructures 34 (1-2)315-317 (2006).

 

            ABSTRACT: We performed infrared magneto-photoluminescence (PL) spectroscopy on an InAs-inserted-channel InGaAs/InAlAs heterostructure. Series of Landau levels were clearly observed in the infrared PL spectra. From the energy separation between sigma+ and sigma- components of PL, the electron-hole g-factor in each Landau level were determined. We discuss the obtained Landau fan-diagram from the points that nonparabolicity of conduction band structure and penetration of electron wavefunction into InGaAs layer. (c) 2006 Elsevier B.V. All rights reserved.

 

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

            "Quantum effects in the capacitance between a pair of thin and slightly separated SrTiO3 slabs: A first-principles study"

            Physical Review B 74 (3), 035408 (2006).

 

            ABSTRACT: We calculated the capacitance between a pair of thin and slightly separated SrTiO3 slabs (electrodes) by using first-principles approaches with the enforced Fermi-energy difference method. The calculated capacitance exhibited several quantum effects, which were successfully understood by relating them to the density of states of the electrodes and the effective and variable interelectrode distance. The present work is an indispensable step towards exhaustive and systematic first-principles investigations of the capacitors whose electrodes are composed of a series of transition-metal oxides.

 

136.    K. Ueda, M. Kasu, A. Tallaire, and T. Makimoto

            "High-pressure and high-temperature annealing effects on CVD homoepitaxial diamond films"

            Diamond And Related Materials 15 (11-12)1789-1791 (2006).

 

            ABSTRACT: High-pressure and high-temperature (HPHT) annealing effects on the chemical vapor-deposited (CVD) homoepitaxial diamond films were investigated. By the HPHT annealing, the intensity of free-exciton (FE)-related emission was increased by - 2 times and the luminescence bands from 270 to 320 min, which originate from 5RL and 2BD bands, were almost completely eliminated in the cathodoluminescence (CL) spectrum. The CL intensity of band-A emission, which is related to crystal defects in diamond, was also decreased. The hole mobility at room temperature was increased from 826 to 1030 cm(2)/Vs by HPHT annealing. These results suggest that HPHT annealing decreases the crystalline defects and improves the optical and electronic properties of homoepitaxial diamond films. (c) 2006 Elsevier B.V. All rights reserved.

 

137.    K. Ueda, M. Kasu, Y. Yamauchi, T. Makimoto, M. Schwitters, D. J. Twitchen, G. A. Scarsbrook, and S. E. Coe

            "Characterization of high-quality polycrystalline diamond and its high FET performance"

            Diamond And Related Materials 15 (11-12)1954-1957 (2006).

 

            ABSTRACT: We characterized high-quality polycrystalline diamond with large grains and fabricated polycrystalline diamond field effect transistors (FETs). The polycrystalline diamond had (110) preferred orientation, and its typical grain size was similar to 100 mu m. Well-resolved free exciton related emissions were observed at room temperature in cathodoluminescence. The FETs showed extremely high DC and RF performance. The cut-off frequency for current gain (f(T)) and power gain (f(max)) were 45 and 120 GHz, respectively. The maximum drain current (I-DS) was 550 mA/mm. These values are the highest among diamond FETs, including those fabricated from single-crystal diamond. These results suggest that high-quality polycrystalline diamond, whose maximum size is 4 in., is very promising for diamond electronic devices. (c) 2006 Elsevier B.V. All rights reserved.

 

138.    K. Ueda, and T. Makimoto

            "Low-temperature growth of MgB2 thin films with T-c above 38 K"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 45 (7)5738-5741 (2006).

 

            ABSTRACT: MgB2 thin films with the T-c above 38 K have been fabricated using molecular beam epitaxy (NIBE) at the growth temperature below 300 degrees C. The T-c of 38.2 K was obtained in 1.3-mu m-thick MgB2 films formed on SiC substrates with AIN buffer layers. The T-c is comparable to those of MgB2 single crystals and the highest among MgB2 films fabricated below 500 degrees C. Increase of the film thickness of MgB2 above 1 mu m was the key point to obtain high-quality films at low growth temperature.

 

139.    K. Ueda, M. Kasu, Y. Yamauchi, T. Makimoto, M. Schwitters, D. J. Twitchen, G. A. Scarsbrook, and S. E. Coe

            "Diamond FET using high-quality polycrystalline diamond with f(T) of 45 GHz and f(max) of 120 GHz"

            Ieee Electron Device Letters 27 (7)570-572 (2006).

 

            ABSTRACT: Using high-quality polycrystalline chemical-vapor-deposited diamond films with large grains (similar to 100 mu m), field effect transistors (FETs) with gate lengths of 0.1 mu m were fabricated. From the RF characteristics, the maximum transition frequency f(T) and the maximum frequency of oscillation f(max) were similar to 45 and similar to 120 GHz, respectively. The fT and f(max) values are much higher than the highest values for single-crystalline diamond FETs. The dc characteristics of the FET showed a drain-current density-I-DS of 550 mA/mm at gate-source voltage V-GS of -3.5 V and a maximum transconductance g(m) of 143 mS/mm at drain voltage V-DS of -8 V. These results indicate that the high-quality polycrystalline diamond film, whose maximum size is 4 in at present, is a most promising substrate for diamond electronic devices.

 

140.    M. Uematsu, H. Kageshima, S. Fukatsu, K. M. Itoh, K. Shiraishl, M. Otani, and A. Oshiyama

            "Enhanced Si and B diffusion in semiconductor-grade SiO2 and the effect of strain on diffusion"

            Thin Solid Films 508 (1-2)270-275 (2006).

 

            ABSTRACT: We present experimental and simulation results of Si self-diffusion and B diffusion in SiO2 formed directly on Si substrates by thermal oxidation. We show that both Si and B diffusion in SiO2 are enhanced by SiO generated at the Si/SiO2 interface and diffusing into SiO2. We also show that the existence of high-concentration B in SiO2 enhances SiO diffusion, which enhances both Si self-diffusion and B diffusion. This correlated diffusion of Si and B in SiO2 is consistent with the first-principles calculation results, which show that B diffuses via a complex of BSiO with frequent bond exchanges in the SiO2 network. Furthermore, based on the results, the enhancement of Si self-diffusion and B diffusion in SiO2 by compressive strain and their retardation by tensile strain are suggested. (c) 2005 Elsevier B.V. All rights reserved.

 

141.    Y. Ueno, R. Rungsawang, I. Tomita, and K. Ajito

            "Terahertz time-domain spectra of inter- and intramolecular hydrogen bonds of fumaric and maleic acids"

            Chemistry Letters 35 (10)1128-1129 (2006).

 

            ABSTRACT: The inter- and intramolecular hydrogen-bonding modes of two steric isomers, namely fumaric acid and maleic acid, are observed by using terahertz time-domain spectroscopy (THz-TDS). The intermolecular modes observed with fumaric acid crystals are inactivated by incorporating the molecules in the nano-sized pores of a mesoporous silicate (SBA-16) due to the separation of the molecules, whereas the intramolecular modes of maleic acid of the crystal and the incorporated samples are similar.

 

142.    Y. Ueno, R. Rungsawang, I. Tomita, and K. Ajito

            "Quantitative measurements of amino acids by terahertz time-domain transmission spectroscopy"

            Analytical Chemistry 78 (15)5424-5428 (2006).

 

            ABSTRACT: The quantitative analysis of amino acids by terahertz (THz) time-domain absorption spectroscopy is demonstrated. The optical densities of the amino acids were found to be linearly proportional to the concentration. The molar absorption coefficients of L-glutamic acid (L-Glu), L-glutamic acid sodium salt ( Na- L-Glu), L- glutamic acid hydrochloric salt (HCl-L-Glu), L- cysteine (L-Cys), and L- histidine ( L- His) were calculated by averaging the THz spectra of the amino acids at several different concentrations in approximately the 0.2-1.0 mol L-1 range. The concentrations of L-Glu, L-Cys, and L- His mixed samples were successfully calculated with errors of less than 11% and 20% when their concentrations were higher than 0.45 and 0.22 mol L-1, respectively, by using the obtained molar absorption coefficient.

 

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

            "Spin-orbit induced interference of ballistic electrons in polygon structures"

            Physical Review B 73 (23), 235315 (2006).

 

            ABSTRACT: We investigate the spin-orbit induced spin-interference pattern of ballistic electrons traveling along any regular polygon. It is found that the spin interference depends strongly on the Rashba and Dresselhaus spin-orbit constants as well as on the sidelength and alignment of the polygon. We derive the analytical formulas for the limiting cases of either zero Dresselhaus or zero Rashba spin-orbit coupling, including the result obtained for a circle. We calculate the nonzero Dresselhaus and Rashba case numerically for the square, triangle, hexagon, and circle and discuss the observability of the spin interference which can potentially be used to measure the Rashba and Dresselhaus coefficients.

 

144.    A. Vijayaraghavan, S. Kar, S. Rumyantsev, A. Khanna, C. Soldano, N. Pala, R. Vajtai, K. Kanzaki, Y. Kobayashi, O. Nalamasu, M. S. Shur, and P. M. Ajayan

            "Effect of ambient pressure on resistance and resistance fluctuations in single-wall carbon nanotube devices"

            Journal Of Applied Physics 100 (2), 024315 (2006).

 

            ABSTRACT: We report low-frequency resistance fluctuation (noise) measurements in semiconducting and metallic Ti/Au-contacted single-wall carbon nanotube devices. In both types of devices, the noise power spectra has a "1/f" dependence, and is proportional to the squared current. Semiconducting devices were found to have three orders of magnitude higher noise levels compared to the metallic ones. In vacuum, the resistance increases but noise decreases by over an order of magnitude for both metallic and semiconducting devices. The resistance and noise levels recover to their original values when the samples are brought back to atmospheric pressure. Both noise and resistance change simultaneously when the chamber is evacuated. However, when the chamber is brought back to atmospheric pressure, the noise level takes several tens of hours longer to recover. (c) 2006 American Institute of Physics.

 

145.    E. Waks, H. Takesue, and Y. Yamamoto

            "Security of differential-phase-shift quantum key distribution against individual attacks"

            Physical Review A 73 (1), 012344 (2006).

 

            ABSTRACT: We derive a proof of security for the differential-phase-shift quantum key distribution protocol under the assumption that Eve is restricted to individual attacks. The security proof is derived by bounding the average collision probability, which leads directly to a bound on Eve's mutual information on the final key. The security proof applies to realistic sources based on pulsed coherent light. We then compare individual attacks to sequential attacks and show that individual attacks are more powerful.

 

146.    E. Waks, E. Diamanti, and Y. Yamamoto

            "Generation of photon number states"

            New Journal Of Physics 8, 4 (2006).

 

            ABSTRACT: The visible light photon counter (VLPC) has the capability to discriminate photon number states, in contrast to conventional photon counters which can only detect the presence or absence of photons. We use this capability, along with the process of parametric down-conversion, to generate photon number states. We experimentally demonstrate generation of states containing 1, 2, 3 and 4 photons with high fidelity. We then explore the effect the detection efficiency of the VLPC has on the generation rate and fidelity of the created states.

 

147.    C. X. Wang, N. Maeda, M. Hiroki, H. Yokoyama, N. Watanabe, T. Makimoto, T. Enoki, and T. Kobayashi

            "Mechanism of superior suppression effect on gate current leakage in ultrathin Al2O3/Si3N4 bilayer-based AlGaN/GaN insulated gate heterostructure field-effect transistors"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 45 (1A)40-42 (2006).

 

            ABSTRACT: On the basis of the thin barrier surface (TSB) model, the mechanism of gate current leakage under reverse gate-source bias in nitride-based heterostructure field effect transistors (HFETs) and metal-insulator-semiconductor (MIS) HFETs with an ultrathin (1 nm/0.5 nm) Al2O3/Si3N4 bilayer has been investigated. The simulations show that the electron tunneling through the Schottky barrier is the dominant mechanism for gate current in conventional HFETs due to the high density of donor like defects on the surface. An Al2O3/Si3N4 bilayer insulator can substantially reduce the donor like surface defect density and then significantly suppress the gate current leakage in nitrides-base MIS-HFET devices.

 

148.    S. Yabuuchi, E. Ohta, H. Kageshima, and A. Taguchi

            "First-principles study of strain effects on Mn in Si"

            Physica B-condensed Matter 376672-676 (2006).

 

            ABSTRACT: The effects of strain on Mn impurities in Si were investigated by using first-principles calculations. It is shown that substitutional Mn is stabilized and that the magnetic moment is maintained when a tensile strain is given. This suggests that the tensile strain is effective for improving the crystallinity of epitaxial films. Under high Mn concentration conditions, the substitutional Min complex can cause a structural change and decrease the lattice constant of the crystal. Thus.. the formation of shrinked epitaxial films can cause a structural change related to the substitutional Mn complexes, which might make it impossible to obtain the ferromagnetic property. (c) 2006 Elsevier B.V. All rights reserved.

 

149.    H. Yaguchi, K. Takizawa, M. Kawamura, N. Kikugawa, Y. Maeno, T. Meno, T. Akazaki, K. Semba, and H. Takayanagi

            "Tunnelling spectroscopy of the interface between Sr2RuO4 and a single Ru micro-inclusion in eutectic crystals"

            Journal Of The Physical Society Of Japan 75 (12), 125001 (2006).

 

            ABSTRACT:

 

150.    M. Yamaguchi, S. Nomura, K. Miyakoshi, H. Tamura, T. Akazaki, and H. Takayanagi

            "Controlling electric field and electron density in a double-gated GaAs/AlGaAs quantum well"

            Journal Of Applied Physics 100 (11), 113523 (2006).

 

            ABSTRACT: We demonstrate that the vertical electric field and the electron density of a two-dimensional electron system (2DES) can be controlled in a double-gated GaAs/AlGaAs quantum well (QW). Photoluminescence (PL) spectra from the recombination of an electron with a hole bound to a beryllium acceptor atom are measured as functions of gate biases applied to front and back gates. By comparing the measured spectra with theoretical models, we analyze the effect of the potential gradient in the QW on the PL energy for different electron filling. While a photoexcited electron recombines with a bound hole in an empty QW, a layer of 2DES is induced when the conduction band bottom of the QW lowers below the Fermi energy by the back-gate bias. In this case, a simple capacitor model gives a good estimation of the electron density. When we increase the front-gate bias, another electron layer is formed on the other side of the QW. These two electron layers screen the electric field inside the QW where the PL energy is insensitive to the gate bias. (c) 2006 American Institute of Physics.

 

151.    M. Yamaguchi, S. Nomura, K. Miyakoshi, T. Akazaki, H. Tamura, and H. Takayanagi

            "Electric-field control of electron-hole wave functions in a wide quantum well"

            Physica E-low-dimensional Systems & Nanostructures 34 (1-2)300-303 (2006).

 

            ABSTRACT: The electric field dependence of the electron/hole wave function and the radiation energy of an exciton in a Be-delta-doped 80 nm quantum well (QW) is studied experimentally and compared it with variational calculation. The photoluminescence (PL) spectra show Stark shifts depending on the gate electric field and PL intensity of the exciton of the first excited state has a dip in the electric-field dependence which reflects the node of the electron wave function. (c) 2006 Elsevier B.V. All rights reserved.

 

152.    T. Yamaguchi, and H. Yamaguchi

            "Resist-pattern guided self-assembly of symmetric diblock copolymer"

            Journal Of Photopolymer Science And Technology 19 (3)385-388 (2006).

 

            ABSTRACT:

 

153.    M. Yamamoto, M. Stopa, Y. Tokura, Y. Hirayama, and S. Tarucha

            "Negative Coulomb drag in a one-dimensional wire"

            Science 313 (5784)204-207 (2006).

 

            ABSTRACT: We observed negative Coulomb drag for parallel coupled quantum wires, in which electrons flow in the opposite directions between the wires. This only occurred under the conditions of strong correlation in the wires, that is, low density, high magnetic field, and low temperature, and cannot be addressed by a standard theory of momentum transfer. We propose a Coulomb drag model in which formation of a Wigner crystal state in the drag wire and a particle-like state in the drive wire is taken into account.

 

154.    N. Yamamoto, S. Bhunia, and Y. Watanabe

            "Polarized cathodoluminescence study of InP nanowires by transmission electron microscopy"

            Applied Physics Letters 88 (15), 153106 (2006).

 

            ABSTRACT: Cathodoluminescence (CL) spectra and polarized monochromatic CL images of InP nanowires were studied using a transmission electron microscope combined with a CL detection system. Emission spectra from individual nanowires showed a broad single peak with a peak energy of 1.6 eV, which is higher than expected from the quantum confinement effect for an average nanowire with a diameter of 20 nm. An individual nanowire could be resolved in the monochromatic CL images. The emission is highly polarized along the wire axis with a degree of polarization of more than 50%.

 

155.    T. Yamashita, N. Kawakami, and M. Yamashita

            "Fermionic atoms trapped in a one-dimensional optical superlattice with harmonic confinement"

            Physical Review A 74 (6), 063624 (2006).

 

            ABSTRACT: We study the ground-state properties of spin-1/2 fermionic atoms confined in a one-dimensional optical superlattice with harmonic confinement by using the density-matrix renormalization group method. For this purpose, we consider an ionic Hubbard model that has superlattice potentials with two-site periodicity. We find that several different types of insulating regimes coexist even if the number of atoms at each site is not an integer, but its average within the unit cell is an integer or half integer. This is contrasted to the coexisting phase of the metallic and Mott-insulating regimes known for the ordinary Hubbard model in an optical lattice. The phase characteristics are elucidated by investigating the profiles of the atom density, the local density (spin) fluctuations, the double occupation probability, and the spin correlations in detail.

 

156.    K. Yamazaki, and H. Namatsu

            "Three-dimensional resist-coating technique and nanopatterning on a cube using electron-beam lithography and etching"

            Japanese Journal Of Applied Physics Part 2-letters & Express Letters 45 (12-16)L403-L405 (2006).

 

            ABSTRACT: A new resist-coating technique for three-dimensional substrates keeps a substrate in a quasi-static ambient of very fine mist of resist solution, so that a resist can be uniformly coated on each face of the substrate. We found that the temperature of the substrate has to be carefully controlled to obtain a smooth resist surface. A polymethylmethacrylate resist was coated with good uniformity on an oxidized Si cube, and patterns delineated on different faces by electron-beam lithography were similar. The resolution was confirmed to be 50 nm or less by observing dense line patterns etched in the oxide film on the cube.

 

157.    R. Yano, T. Hattori, and H. Shinojima

            "Improvement of signal-to-noise ratio of terahertz electromagnetic waves by bias field modulation of photoconductive antenna"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 45 (11)8714-8716 (2006).

 

            ABSTRACT: Inversion of the direction of the DC bias field applied to a photoconductive (PC) antenna produces a terahertz wave with its sign changed. We succeeded in increasing the signal amplitudes of the terahertz electromagnetic waves emitted from a pc antenna by a factor of 2 by modulating the polarization of the bias field applied to the PC antenna in the lock-in detection scheme. By this method, we were able to increase the signal-to-noise ratio of the terahertz electromagnetic waves by a factor of 2.

 

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

            "Synthesis of terahertz electromagnetic wave pulses using amplitude-and-phase masks"

            Chemical Physics 326 (2-3)577-582 (2006).

 

            ABSTRACT: In the conventional terahertz (THz) electromagnetic emission and detection scheme using a semiconductor as a THz wave emitter and a photoconductive antenna as a THz wave receiver, we generated THz electromagnetic waves having various temporal waveforms by inserting simple plastic plates between off-axis parabolic mirrors. We simulated the observed waveforms using a simple model, where the THz field is expressed by the summation of fields passing through each sub-section of the whole cross-section of the collimated THz beam. The results show a new simple method to shape THz pulses with complicated temporal waveforms. (c) 2006 Elsevier B.V. All rights reserved.

 

159.    H. Ye, M. Kasu, K. Ueda, Y. Yamauchi, N. Maeda, S. Sasaki, and T. Makimoto

            "Temperature dependent DC and RF performance of diamond MESFET"

            Diamond And Related Materials 15 (4-8)787-791 (2006).

 

            ABSTRACT: This paper reports the first Studies on temperature dependent DC and RF characteristics of diamond metal-semi conductor field-effect transistors along with circular-transmission-like-method measurements on hydrogen-terminated diamond surface. In general, the device under study is thermally stable up to 100 degrees C as it does not deteriorate at higher temperatures with the cut-off frequency for current gain maintained at 8 similar to 9 GHz. It is found that the sheet resistance is almost totally independent of temperature, contact resistance is negligible, and channel conductance underneath the gate decreases with increasing temperature. The threshold voltage for the device is found to shift to the negative side with increasing temperature. A small-signal equivalent circuit analysis reveals that both transconductance and gate-source capacitance decrease with increasing temperature,. which results in the almost constant cut-off frequency for current gain. The experimental results call be explained by the fact that with increasing temperature, the band near the Al/H-terminated diamond surface bends upward more weakly, which leads to a decrease of buffer capacitance. At the same time the mobility decreases and the transconductance therefore decreases. (c) 2006 Elsevier B.V. All rights reserved.

 

160.    H. T. Ye, M. Kasu, K. Ueda, Y. Yamauchi, N. Maeda, S. Sasaki, and T. Makimoto

            "RF performance of diamond metel-semiconductor field-effect transistor at elevated temperatures and analysis of its equivalent circuit"

            Japanese Journal Of Applied Physics Part 1-regular Papers Brief 45 (4B)3609-3613 (2006).

 

            ABSTRACT: Temperature dependent DC and RF characteristics of p-type diamond metal-semiconductor field-effect transistors (MESFETs) on hydrogen-terminated surfaces are investigated. The device is thermally stable up to 100 degrees C. because it does not deteriorate at all at higher temperatures. Temperature coefficients of transconductance (g(m)), drain conductance (g(ds)), gate-source capacitance (C-gs), gate-drain capacitance (C-gd), cut-off frequency (f(T)), and maximum drain current (I-ds) were obtained from small-signal equivalent circuit analysis. The cut-off frequency (fT) is almost totally independent of temperature. Intrinsic g(m), g(ds), and C-gs decrease with increasing temperature. C-gd is almost totally independent of temperature. The threshold voltage shifts to the negative side with increasing temperature. We propose a band model of an Al-gate contact/H-terminated diamond to explain the temperature dependence of these components.

 

161.    Z. H. Zhang, Z. H. Liu, K. Sumitomo, and X. Zhu

            "Multistable features of boronized interstitial-pentamers on Si(113) surfaces"

            Surface And Interface Analysis 38 (6)1078-1082 (2006).

 

            ABSTRACT: On Si(113) surfaces there exists a peculiar type of reconstructing blocks called pentamers, which are stabilized by self-interstitial atoms at the subsurface. Here, we demonstrate that such interstitial-pentamers (IP) can be boronized with different numbers of B atoms and therefore behave as differently stable blocks. The multistable features of the blocks are presented by images of scanning tunneling microscopy and investigated by ab initio calculations, which revealed the surface energy as a function of the number of B atoms in an IP and a minimum of the surface energy for three B atoms in each block. Copyright (C) 2006 John Wiley & Sons, Ltd.

 

162.    Y. L. Zhong, T. Akazaki, K. Kanzaki, Y. Kobayashi, and H. Takayanagi

            "Superconducting proximity effect in single-walled carbon nanotubes between NbN electrodes"

            Science And Technology Of Advanced Materials 7S78-S82 (2006).

 

            ABSTRACT: We have fabricated network-like single-walled carbon nanotubes with superconducting NbN electrodes. The single-wall carbon nanotubes were synthesized on SiO2 substrates by the thermal chemical vapor deposition technique using Co catalyst. We obtained sufficiently good contact characteristics between the single-walled carbon nanotubes and the NbN electrodes by infrared annealing at heater temperature 700 degrees C for similar to 15 min in vacuum. We observed multiple Andreev reflection by measuring differential resistance as a function of applied voltage below 7K. This multiple Andreev reflection is due to the proximity effect between NbN electrodes. The superconducting energy gap of NbN, 2 Delta, is about 6meV. The multiple Andreev reflection processes occur around the dips, i.e. +/- 2 Delta/e and +/-Delta/e. On the other hand, at above 8 K, the curves of different resistance are changed from dip to peak at zero bias voltage. This behavior is similar to reentrant behavior that has a maximum conductance corresponding to the correlation energy (Thouless energy) below superconducting critical temperature T-c. This reentrant behavior has been studied in normal metal or two-dimensional gas of semiconductor heterostructures coupled to superconductor. (c) 2006 NIMS and Elsevier Ltd. All rights reserved.

 

163.    N. M. Zimmerman, A. Fujiwara, H. Inokawa, and Y. Takahashi

            "Electrostatically gated Si devices: Coulomb blockade and barrier capacitance"

            Applied Physics Letters 89 (5), 052102 (2006).

 

            ABSTRACT: Using a device resembling a nano-charge-coupled-device and measuring the Coulomb blockade, we show how the Coulomb blockade degrades with increasing barrier conductance. To explain this behavior, we identify a new parameter, the "barrier capacitance." This parameter can be used to elucidate information about the energy barrier under a gate with a size of a few tens of nanometers. (c) 2006 American Institute of Physics.