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2008 (with abstract)
	▼ Ordered by first author

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1.    A. Aharony, O. Entin-Wohlman, Y. Tokura, and S. Katsumoto

            "Spin filtering by a periodic spintronic device"

            Physical Review B 78 (12), 125328 (2008).

 

            ABSTRACT: For a linear chain of diamondlike elements, we show that the Rashba spin-orbit interaction (which can be tuned by a perpendicular gate voltage) and the Aharonov-Bohm flux (due to a perpendicular magnetic field) can combine to select only one propagating ballistic mode, for which the electronic spins are fully polarized along a direction that can be controlled by the electric and magnetic fields and by the electron energy. All the other modes are evanescent. For a wide range of parameters, this chain can serve as a spin filter.

 

2.    T. Akasaka, Y. Kobayashi, and M. Kasu

            "Anisotropic in-plane strains in nonpolar AlN and AlGaN (11(2)over-bar0) films grown on SiC (11(2)over-bar0) substrates"

            Applied Physics Letters 93 (16), 161908 (2008).

 

            ABSTRACT: Nonpolar Al1-xGaxN (0 <= x <= 0.196) (11 (2) over bar0) films were grown on 4H-SiC (11 (2) over bar0) substrates by metal organic vapor phase epitaxy. Al1-xGaxN (0 <= x <= 0.057) films grew almost pseudomorphically on the substrates due to balanced in-plane stresses along [0001] and [1 (1) over bar 00], while Al1-xGaxN (0.057 < x) films were strained along [0001] but partially relaxed along [1 (1) over bar 00] due to the absence of the balance. The crystal tilts of the films toward [0001] decreased monotonically with increasing Ga composition due to the correspondence between the (0001) plane distances of the films and the (0002) plane distance of substrates and due to a decrease in the in-plane strain along [0001]. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2995994]

 

3.    T. Akazaki, M. Yamaguchi, K. Tsumura, S. Nomura, and H. Takayanagi

            "Negative photoconductivity in In0.52Al0.48As/In0.7Ga0.3As heterostructures"

            Physica E-low-dimensional Systems & Nanostructures 40 (5)1341-1343 (2008).

 

            ABSTRACT: We investigated the transport of a two-dimensional electron gas (2DEG) in an In0.52Al0.48As/In0.7Ga0.3As heterostructure when exposed to light from infrared laser diodes (lambda = 0.78, 1.3 mu m) by means of both Shubnikov-de Haas and Hall-effect measurements. We observed negative photoconductivity due to a reduction in the number of electrons in the 2DEG when they were illuminated by photons at lambda = 1.3 mu m. We speculate that the negative photoconductivity originates from the diffusion and trapping of photo-induced hot electrons at deep impurity levels in the InAlAs barrier layer near the InAlAs/InGaAs interface. (C) 2007 Elsevier B.V. All rights reserved.

 

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

            "Stress dependence of oxidation reaction at SiO2/Si interfaces during silicon thermal oxidation"

            Japanese Journal Of Applied Physics 47 (9)7089-7093 (2008).

 

            ABSTRACT: The microscopic processes of interfacial reaction of O-2 molecules involving compressive stress normal to SiO2/Si(001) interface are investigated by first-principles total-energy calculations. It is found that the energy barrier height for the O-2 reaction increases with residual stress at the interface. This is because the energy of the transition state structure for O-2 diffusion before O-2 insertion into the Si substrate is higher than that for the stress-free interface. The calculated activation volume (7.9 angstrom(3)) is comparable to those obtained by numerical simulations using exporimental data, implying that the effects of interfacial stress on the reaction of O-2 molecules play important roles during thermal oxidation of silicon nanostructures.

 

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

            "Impact of oxidation-induced strain on microscopic processes related to oxidation reaction at the SiO2/Si(100) interface"

            Physical Review B 77 (11), 115356 (2008).

 

            ABSTRACT: The reaction of oxygen molecules at the SiO2/Si(100) interface in the presence of oxidation-induced strain is investigated using total-energy electronic-structure calculations within the density-functional theory. It is found that the calculated effective barrier height for the O-2 reaction at the interface with strained oxide layers less than 2 monolayer (ML) thick is almost identical to that at the strain-released interface. On the other hand, it increases significantly when the strained oxide layer reaches 2 ML. This is because the energy of the O-2 near the strained oxide layer in the 2 ML oxidized interface is higher than that in the strain-released region. Given our result that the oxidation-induced strain should become large enough to prevent the oxidation reaction and the knowledge that oxide formation with smooth interface is continuous, we conclude that there must be some strain-release mechanism that is present during silicon thermal oxidation.

 

6.    S. Amaha, T. Hatano, T. Kubo, Y. Tokura, D. G. Austing, and S. Tarucha

            "Fabrication and characterization of a laterally coupled vertical triple quantum dot device"

            Physica E-low-dimensional Systems & Nanostructures 40 (5)1322-1324 (2008).

 

            ABSTRACT: Laterally coupled vertical triple quantum dots (tQDs) are newly fabricated and their transport properties are investigated. Our device consists of three pillars, each with a separate gate electrode, fabricated from a double-barrier structure and arranged in an equilateral triangular arrangement, with a common source and drain electrodes. The measured conductance on sweeping the two gate voltages shows three series of Coulomb oscillations and this indicates that the tQDs in our device are formed in the intended manner. (C) 2007 Elsevier B.V. All rights reserved.

 

7.    S. Anantathanasarn, Y. Barbarin, N. I. Cade, P. J. van Veldhoven, E. A. Bente, Y. S. Oei, H. Kamada, M. K. Smit, and R. Notzel

            "Wavelength tunable InAs/InP(100) quantum dots in 1.55-mu m telecom devices"

            Materials Science And Engineering B-solid State Materials For Advanced 147 (2-3)124-130 (2008).

 

            ABSTRACT: This paper reviews the growth, characterization and device applications of self-assembled InAs/InP(100) quantum dots (QDs) formed by MOVPE. The problematic As/P exchange reaction during QD growth is suppressed by the insertion of a GaAs interlayer together with optimum growth conditions. This produces QDs with continuously tunable emission over the 1.55-mu m wavelength region for fiber-based telecom applications. Device quality of these QDs is proven by continuous wave lasing at room temperature from the as-cleaved facets of Fabry-Perot narrow ridge-waveguide lasers implementing widely stacked QDs as gain medium. The low transparency current density of 6 A/cm(2) per QD layer and low loss of 4.2 cm(-1) are accompanied by a 80-nm wide gain spectrum. The deeply etched QD lasers possess similar threshold current densities as the shallowly etched ones and do not deteriorate with time, revealing that device performance does not suffer from sidewall recombination. This allows the fabrication of mono-mode and more compact devices with small bending radii, as demonstrated by the operation of a QD ring laser with 40-GHz free spectral range. Unpolarized emission from the cleaved side, important for the realization of polarization insensitive semiconductor optical amplifiers, is obtained by close stacking of QDs due to vertical electronic coupling. Sharp exciton-biexciton emission from a single QD around 1.55 mu m is observed with clearly resolvable peaks above 70 K, which is required for single photon sources working at liquid nitrogen temperature for fiber-based quantum cryptography systems. (C) 2007 Elsevier B.V. All rights reserved.

 

8.    W. R. Clarke, C. E. Yasin, A. R. Hamilton, A. P. Micolich, M. Y. Simmons, K. Muraki, Y. Hirayama, M. Pepper, and D. A. Ritchie

            "Metallic behavior in low-disorder two-dimensional hole systems in the presence of long- and short-range disorder"

            Physica E-low-dimensional Systems & Nanostructures 40 (5)1599-1601 (2008).

 

            ABSTRACT: We compare directly the metallic behavior of high-quality, two-dimensional hole systems (2DHSs) in two GaAs device structures-one dominated by short-range disorder and the other by long-range disorder. We find that the type of disorder strongly affects the metallic behavior of the 2DHSs. In particular, we find that metallic behavior is enhanced in 2D systems with a high proportion of large-angle scattering events. (C) 2007 Elsevier B.V. All rights reserved.

 

9.    W. R. Clarke, C. E. Yasin, A. R. Hamilton, A. P. Micolich, M. Y. Simmons, K. Muraki, Y. Hirayama, M. Pepper, and D. A. Ritchie

            "Impact of long- and short-range disorder on the metallic behaviour of two-dimensional systems"

            Nature Physics 4 (1)55-59 (2008).

 

            ABSTRACT: Two-dimensional (2D) electronic systems can exhibit dramatic drops in resistivity, rho(xx), as the temperature T -> 0, which has renewed debate as to whether 2D systems may have a metallic ground state. The metallic behaviour is only observed in low-disorder systems, where interactions between the carriers are strong. However, the strength of the metallic behaviour is not universal, with decreases in resistivity ranging from a few per cent to an order of magnitude as T -> 0. Here, we compare the metallic behaviour in 2D systems dominated by long-and short-range disorder. We thereby highlight the pivotal role played by the type of disorder in determining the strength of metallic behaviour in these systems. In doing so, we resolve recent confusion in the literature that has arisen from the application of interaction-based theories of metallic behaviour to 2D systems whose disorder environments are inconsistent with the assumptions made by these theories.

 

10.    M. Curty, K. Tamaki, and T. Moroder

            "Effect of detector dead times on the security evaluation of differential-phase-shift quantum key distribution against sequential attacks"

            Physical Review A 77 (5), 052321 (2008).

 

            ABSTRACT: We investigate limitations imposed by detector dead times on the performance of sequential attacks against a differential-phase-shift (DPS) quantum key distribution (QKD) protocol with weak coherent pulses. In particular; we analyze sequential attacks based on unambiguous state discrimination of the signal states emitted by the source and we obtain ultimate upper bounds on the maximal distance achievable by a DPS QKD scheme both for the case of calibrated and uncalibrated devices, respectively.

 

11.    F. Deppe, M. Mariantoni, E. P. Menzel, A. Marx, S. Saito, K. Kakuyanagi, H. Tanaka, T. Meno, K. Semba, H. Takayanagi, E. Solano, and R. Gross

            "Two-photon probe of the Jaynes-Cummings model and controlled symmetry breaking in circuit QED"

            Nature Physics 4 (9)686-691 (2008).

 

            ABSTRACT: Superconducting qubits(1,2) behave as artificial two-level atoms and are used to investigate fundamental quantum phenomena. In this context, the study of multiphoton excitations(3-7) occupies an important role. Moreover, coupling superconducting qubits to onchip microwave resonators has given rise to the field of circuit quantum electrodynamics(8-15) (QED). In contrast to quantum-optical cavity QED (refs 16-19), circuit QED offers the tunability inherent to solid-state circuits. Here, we report on the observation of key signatures of a two-photon-driven Jaynes-Cummings model, which unveils the upconversion dynamics of a superconducting flux qubit(20) coupled to an on-chip resonator. Our experiment and theoretical analysis show clear evidence for the coexistence of one-and two-photon-driven level anticrossings of the qubit-resonator system. This results from the controlled symmetry breaking of the system hamiltonian, causing parity to become a not-well-defined property(21). Our study provides fundamental insight into the interplay of multiphoton processes and symmetries in a qubit-resonator system.

 

12.    H. L. Dong, H. X. Li, E. J. Wang, H. Nakashima, K. Torimitsu, and W. P. Hu

            "Phototransistors of a Rigid Rod Conjugated Polymer"

            Journal Of Physical Chemistry C 112 (49)19690-19693 (2008).

 

            ABSTRACT: Phototransistors of a rigid-rod conjugated polymer, a derivative of poly(para-phenylene ethynylene)s with thioacetyl end groups (TA-PPE), were investigated. The phototransistors exhibited high photo-response properties with responsivity at 36 mA/W and switch ratio up to 3.3 x 10(3), indicating the potential applications of the phototransistors in optoelectronic devices. Moreover, the photoresponse mechanism of the transistors was examined. Two effects-photoconductive and photovoltaic effects-were both observed in the same transistors depending on the gate bias. With gate bias the polymer phototransistors were dominated by photovoltaic effect, while without gate bias the devices were decided by photoconductive effect.

 

13.    K. Edagawa, S. Kanoko, and M. Notomi

            "Photonic amorphous diamond structure with a 3D photonic band gap"

            Physical Review Letters 100 (1), 013901 (2008).

 

            ABSTRACT: We report that a full three-dimensional (3D) photonic band gap (PBG) is formed in a photonic amorphous structure in spite of complete lack of lattice periodicity. It is numerically shown that the structure "photonic amorphous diamond" possesses a sizable 3D PBG (18% of the center frequency for Si-air dielectric contrast) and that it can confine light at a defect as strongly as conventional photonic crystals can. These findings present important new insight into the origin of 3D PBG formation and open new possibilities in developing 3D PBG materials.

 

14.    S. Etaki, M. Poot, I. Mahboob, K. Onomitsu, H. Yamaguchi, and H. S. van der Zant

            "Motion detection of a micromechanical resonator embedded in a d.c. SQUID"

            Nature Physics 4 (10)785-788 (2008).

 

            ABSTRACT: Superconducting quantum interference devices (SQUIDs) are the most sensitive detectors of magnetic flux(1) and are also used as quantum two-level systems (qubits)(2). Recent proposals have explored a novel class of devices that incorporate micromechanical resonators into SQUIDs to achieve controlled entanglement of the resonator ground state and a qubit(3) as well as permitting cooling and squeezing of the resonator modes and enabling quantum-limited position detection(4-10). In spite of these intriguing possibilities, no experimental realization of an on-chip, coupled mechanical-resonator-SQUID system has yet been achieved. Here, we demonstrate sensitive detection of the position of a 2 MHz flexural resonator that is embedded into the loop of ad.c. SQUID. We measure the resonator's thermal motion at millikelvin temperatures, achieving an amplifier-limited displacement sensitivity of 10 fm Hz(-1/2) and a position resolution that is 36 times the quantum limit.

 

15.    T. Fujisawa, G. Shinkai, and T. Hayashi

            "Spin-conserved single-electron transport between Zeeman sublevels in a few-electron quantum dot"

            Japanese Journal Of Applied Physics 47 (4)3107-3110 (2008).

 

            ABSTRACT: The spin-conserved single-electron transport between Zeeman sublevels is investigated in a few-electron quantum dot in the single-electron tunneling regime. The differential conductance or transconductance for the ground state shows Zeeman splitting (doublet structure) in a magnetic field when the total spin is raised by adding an electron, but shows no splitting when it is lowered. Although the characteristics of such transport do not depend solely on the actual spin degeneracy, the spin state can be identified by consecutively investigating the change of the spin from a known spin state. We also discuss Zeeman splitting when the electron-spin g-factor depends on electron number.

 

16.    A. Fujiwara, K. Nishiguchi, and Y. Ono

            "Nanoampere charge pump by single-electron ratchet using silicon nanowire metal-oxide-semiconductor field-effect transistor"

            Applied Physics Letters 92 (4), 042102 (2008).

 

            ABSTRACT: Nanoampere single-electron pumping is presented at 20 K using a single-electron ratchet comprising silicon nanowire metal-oxide-semiconductor field-effect transistors. The ratchet features an asymmetric potential with a pocket that captures single electrons from the source and ejects them to the drain. Directional single-electron transfer is achieved by applying one ac signal with the frequency up to 2.3 GHz. We find anomalous shapes of current steps which can be ascribed to nonadiabatic electron capture. (c) 2008 American Institute of Physics.

 

17.    A. Fukuda, M. Morino, K. Iwata, D. Terasawa, S. Kozumi, N. Kumada, Y. Hirayama, Z. F. Ezawa, and A. Sawada

            "Anisotropic magnetotransport by the pseudospin soliton in the bilayer v = 1 quantum Hall system(vol 40, pg 1255, 2008)"

            Physica E-low-dimensional Systems & Nanostructures 40 (10)3199-3200 (2008).

 

            ABSTRACT:

 

18.    A. Fukuda, M. Morino, K. Iwata, D. Terasawa, S. Kozumi, N. Kumada, Y. Hirayama, Z. F. Ezawa, and A. Sawada

            "Anisotropic magnetotransport by the pseudospin soliton in the bilayer nu=1 quantum Hall system"

            Physica E-low-dimensional Systems & Nanostructures 40 (5)1255-1257 (2008).

 

            ABSTRACT: We investigate the bilayer quantum Hall state at total Landau level filling factor nu = 1, which is the best system to study the pseudospin ferromagnetism, where pseudospin represents the layer degree of freedom. We found an anisotropic magnetoconductivity near the commensurate-incommensurate phase transition point, which is induced by an in-plane magnetic field. We attribute this anisotropy to the formation of a stripe-shaped domain structure of pseudospins called soliton lattice phase. We also discuss dissipation mechanism in terms of the thermodynamics of pseudospin solitons. (C) 2007 Elsevier B.V. All rights reserved.

 

19.    A. Fukuda, K. Iwata, T. Sekikawa, T. Arai, N. Kumada, Y. Hirayama, Z. F. Ezawa, and A. Sawada

            "Activation study of the bilayer nu=1/3 quantum Hall state"

            Physica E-low-dimensional Systems & Nanostructures 40 (5)1261-1263 (2008).

 

            ABSTRACT: We investigated the bilayer fractional quantum Hall state (FQHS) at total Landau level filling factor nu = 1/3, which is interpreted as the bilayer nu = 1 integer quantum Hall state (IQHS) of composite fermions. We carried out detailed magnetotransport experiments of the bilayer nu = 1/3 FQHS in tilted magnetic field. The data are compared with reported data of the bilayer nu = 1 IQHS. We found that the commensurate-incommensurate phase transition, which occurs in the bilayer nu = 1 IQHS, is missing in the bilayer nu = 1/3 FQHS. (C) 2007 Elsevier B.V. All rights reserved.

 

20.    A. Fukuda, D. Terasawa, M. Morino, K. Iwata, S. Kozumi, N. Kumada, Y. Hirayama, Z. F. Ezawa, and A. Sawada

            "Pseudospin soliton in the nu=1 bilayer quantum Hall state"

            Physical Review Letters 100 (1), 016801 (2008).

 

            ABSTRACT: We investigate a domain structure of pseudospins, a soliton lattice in the bilayer quantum Hall state at total Landau level filling factor nu=1, in a tilted magnetic field, where the pseudospin represents the layer degree of freedom. An anomalous peak in the magnetoresistance R-xx appears at the transition point between the commensurate and incommensurate phases. The R-xx at the peak is highly anisotropic for the angle between the in-plain magnetic field B-parallel to and the current, and indicates a formation of the soliton lattice aligned parallel to B-parallel to. The temperature dependence of the R-xx peak reveals that the dissipation is caused by thermal fluctuations of pseudospin solitons. We also study a phase diagram of the bilayer nu=1 system, and the effects of density imbalance between the two layers.

 

21.    D. Fukuoka, T. Yamazaki, N. Tanaka, K. Oto, K. Muro, Y. Hirayama, N. Kumada, and H. Yamaguchi

            "Spin dynamics of two-dimensional electrons in a quantum Hall system probed by time-resolved Kerr rotation spectroscopy"

            Physical Review B 78 (4), 041304 (2008).

 

            ABSTRACT: Time-resolved Kerr rotation spectroscopy under the radio frequency field to depolarize dynamic nuclear polarization reveals the intrinsic spin-relaxation time (T-2(*)) and g factor of two-dimensional electrons in a quantum Hall system. Out-of-plane magnetic field increases the spin coherence drastically through the Landau level quantization. T-2(*) is enhanced strongly around odd filling factors where a quantum Hall ferromagnet is formed. Collapse of spin coherence and appearance of an anomalous Kerr signal observed around nu=1 are discussed in the relation to the formation of Skyrmions.

 

22.    K. Furukawa, H. Nakashirna, Y. Kashimura, and K. Torimitsu

            "Novel "Lipid-Flow Chip" configuration to determine donor-to-acceptor ratio-dependent fluorescence resonance energy transfer efficiency"

            Langmuir 24 (3)921-926 (2008).

 

            ABSTRACT: We report on the determination of fluorescence resonance energy transfer (FRET) efficiency, which is dependent on the donor-to-acceptor (D-A) ratio, by using a new type of microchannel device called a "lipid-flow chip". The chip comprises two supported lipid bilayers (SLBs) that self-spread from either side of 10 mu m wide straight lines and carry molecules embedded in them. We first show that the diffusion process that occurs when the two SLBs collide with each other in the channel and form a unified SLB can be expressed by a one-dimensional diffusion equation. Next we describe a method for determining the FRET efficiency between NBD (donor) and Texas Red (acceptor) from observations using the lipid-flow chip by employing a one-dimensional diffusion model. The advantages of our method are that all the D-A ratios are achieved in one chip, and a large number of data are recorded in one chip. The FRET efficiency varies depending on the D-A ratio under conditions whereby the concentration of the sum of the donors and acceptors is constant. The Forster radius is also estimated from our,results using a known model describing two-dimensional FRET systems, which yields a radius consistent with the previously reported value for NBD and Texas Red.

 

23.    P. Giudici, K. Muraki, N. Kumada, Y. Hirayama, and T. Fujisawa

            "Spin-dependent phase diagram of the nu(T)=1 bilayer electron system"

            Physical Review Letters 100 (10), 106803 (2008).

 

            ABSTRACT: We show that the spin degree of freedom plays a decisive role in the phase diagram of the nu(T)=1 bilayer electron system using an in-plane field B-parallel to in the regime of negligible tunneling. We observe that the phase boundary separating the quantum Hall and compressible states at d/center dot(B)=1.90 for B-parallel to=0 (d: interlayer distance, center dot(B): magnetic length) steadily shifts with B-parallel to before saturating at d/center dot(B)=2.33 when the compressible state becomes fully polarized. Using a simple model for the energies of the competing phases, we can quantitatively describe our results. A new phase diagram as a function of d/center dot(B) and the Zeeman energy is established and its implications as to the nature of the phase transition are discussed.

 

24.    K. Grove-Rasmussen, H. I. Jorgensen, T. Hayashi, P. E. Lindelof, and T. Fujisawa

            "A triple quantum dot in a single-wall carbon nanotube"

            Nano Letters 8 (4)1055-1060 (2008).

 

            ABSTRACT: A top-gated single-wall carbon nanotube is used to define three coupled quantum dots in series between two electrodes. The additional electron number on each quantum dot is controlled by top-gate voltages allowing for current measurements of single, double, and triple quantum dot stability diagrams. Simulations using a capacitor model including tunnel coupling between neighboring dots captures the observed behavior with good agreement. Furthermore, anticrossings between indirectly coupled levels and higher order cotunneling are discussed.

 

25.    A. R. Hamilton, R. Danneau, O. Klochan, W. R. Clarke, A. P. Micolich, L. H. Ho, M. Y. Simmons, D. A. Ritchie, M. Pepper, K. Muraki, and Y. Hirayama

            "The 0.7 anomaly in one-dimensional hole quantum wires"

            Journal Of Physics-condensed Matter 20 (16), 164205 (2008).

 

            ABSTRACT: In this paper we study the anomalous 0.7 structure in high quality ballistic one-dimensional hole systems. Hole systems are of interest because of their large effective mass, strong spin - orbit coupling, as well as having spin 3/2 compared to spin 1/2 for electrons. We observe remarkably clean conductance quantization in a variety of different samples, and a strong feature at similar to 0.7 x 2e(2)/h, which shows a similar temperature and density dependence to the 0.7 feature observed in electron systems. In contrast to the case for electrons, the strong spin - orbit coupling results in an anisotropic Zeeman splitting, which we use to probe the 0.7 feature and the associated zero-bias anomaly. Our results indicate that the 0.7 feature and the zero-bias anomaly are related, and both are suppressed by spin polarization. These results place valuable constraints on models of the microscopic origins of the 0.7 feature.

 

26.    A. R. Hamilton, O. Klochan, R. Danneau, W. R. Clarke, L. H. Ho, A. P. Micolich, M. Y. Simmons, M. Pepper, D. A. Ritchie, K. Muraki, and Y. Hirayama

            "Quantum transport in one-dimensional GaAs hole systems"

            International Journal Of Nanotechnology 5 (2-3)318-330 (2008).

 

            ABSTRACT: In many advanced semiconductor devices, the physical dimensions are sufficiently small that quantum physics becomes important in determining the device behaviour. A celebrated example is the quantum wire, where in the absence of scattering the conductance is quantised in units of 2e(2)/h. Although electron quantum wires have been studied extensively for almost two decades, the development of bole quantum wires has been a significant challenge, limiting studies of hole-based devices. Here we review our recent work on hole quantum wires, and show how they can be used to probe the spin properties of hole systems. The ability to fabricate ballistic quantum wires, and control their spin properties using electrical gate biases, may have implications for future spintronic devices.

 

27.    K. Harada, H. Takesue, H. Fukuda, T. Tsuchizawa, T. Watanabe, K. Yamada, Y. Tokura, and S. Itabashi

            "Generation of high-purity entangled photon pairs using silicon wire waveguide"

            Optics Express 16 (25)20368-20373 (2008).

 

            ABSTRACT: We observed high-purity correlated and entangled photon pairs generated through spontaneous four-wave mixing (SFWM) in a silicon wire waveguide (SWW). Employing a nano-scale silicon waveguide with a low loss mode size converter, we obtained a high coincidence to accidental coincidence ratio (CAR) of around 200 that was larger than that of cooled dispersion shifted fiber (DSF) by a factor 3.2, and observed the two-photon interference fringe of time-bin entangled photons with > 95% visibility without subtracting the accidental coincidences. (C) 2008 Optical Society of America

 

28.    D. Hashimotoa, and K. Shimizu

            "Cooling an optical fiber to 4.5 K by indirect thermal contact with a liquid-helium flow and spectroscopic temperature measurements"

            Review Of Scientific Instruments 79 (9), 093102 (2008).

 

            ABSTRACT: We have made it possible to cool a 10-m-long optical fiber to 4.5 K in a compact helium-flow cryostat. The cryostat is vacuum loaded and the cooling principle is based on thermal contact with a copper holder cooled by the liquid-helium flow. To measure the temperature directly, we employed two different spectroscopic methods depending on the temperature regions. One was photon-counting Raman spectroscopy and the other was Brillouin spectroscopy. We used certain devices to improve the cooling efficiency and confirmed that the fiber was uniformly cooled to 4.5 K. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2976681]

 

29.    T. Hatano, S. Amaha, T. Kubo, Y. Tokura, Y. Nishi, Y. Hirayama, and S. Tarucha

            "Manipulation of exchange coupling energy in a few-electron double quantum dot"

            Physical Review B 77 (24), 241301 (2008).

 

            ABSTRACT: We have used a hybrid vertical-lateral double quantum dot to study the excitation energy spectrum for one- and two-electron states, which are effectively formed on top of a certain core shell. We have observed bonding and antibonding states, and exchange coupled singlet and triplet states for the one- and two-electron states, respectively, and derived the interdot tunnel coupling and exchange coupling energies for various parameters of interdot level detuning, central gate voltage and magnetic field. The obtained exchange coupling energy is consistently reproduced by calculation using the Hund-Mulliken method.

 

30.    T. Hatano, Y. Tokura, S. Amaha, T. Kubo, and S. Tarucha

            "Observation of anti-bonding excited state in charging diagram of a few-electron double dot"

            Physica E-low-dimensional Systems & Nanostructures 40 (5)1238-1240 (2008).

 

            ABSTRACT: We fabricated a unique hybrid vertical-lateral double dot device with two dots coupled in parallel to study the excitation energy spectra with the number of electrons in each dot and inter-dot level detuning as parameters. We measured the charging diagram for a finite bias voltage and observed the tunnel-coupled bonding state and anti-bonding state. The separation between the two states is a direct measure of the inter-dot tunnel coupling energy. We use this energy and other characteristic energies derived from the charging diagram to characterize the exchange interaction energy. (C) 2007 Elsevier B.V. All rights reserved.

 

31.    N. Hayashi, K. Tsumura, S. Nomura, M. Yamaguchi, H. Tamura, T. Akazaki, and Y. Hirayama

            "Optical mapping of properties of two-dimensional electron system in magnetic fields"

            Physica E-low-dimensional Systems & Nanostructures 40 (5)1533-1535 (2008).

 

            ABSTRACT: Real-space mappings of a Hall photovoltage are performed by local laser excitation using optical microscope setup with a spatial resolution of about 2 mu m. The obtained images of broad and narrow strips presumably reflect the diffusion of the optically created electrons in the bulk and the edge states. The image near a current contact is considered to reflect the potential gradient near the contact. (C) 2007 Elsevier B.V. All rights reserved.

 

32.    T. Hayashi, and T. Fujisawa

            "Voltage-pulse-induced electromigration"

            Nanotechnology 19 (14), 145709 (2008).

 

            ABSTRACT: We propose and demonstrate a voltage-pulse-induced electromigration technique, in which electromigration in a gold nanowire is induced for a short period of about 10 mu s by applying a voltage pulse. A local temperature analysis and a controlled electromigration experiment in the presence of voltage pulses indicate successful control of this voltage-pulsed-induced electromigration. We also measured the current-voltage characteristics of the nanowire after the application of each single voltage pulse to investigate the stochastic behavior of electromigration. A pulse duration shorter than the thermal relaxation time of the nanowire would allow us to separately control the local temperature and driving force for electromigration.

 

33.    Y. Hayashi, K. Tanaka, T. Akazaki, M. Jo, H. Kumano, and I. Suemune

            "Superconductor-based light emitting diode: Demonstration of role of cooper pairs in radiative recombination processes"

            Applied Physics Express 1 (1), 011701 (2008).

 

            ABSTRACT: A light emitting diode with superconducting Nb electrodes was fabricated to investigate the contribution of cooper pairs to radiative recombination in a semiconductor. Electroluminescence observed from the active layer in which electron cooper pairs and normal holes are injected was drastically enhanced at the temperature lower than the superconducting transition temperature of the Nb electrodes. This is the first experimental evidence that cooper pairs enhance radiative recombinations by the superradiance effect. (c) 2008 The Japan Society of Applied Physics.

 

34.    H. Hibino, H. Kageshima, F. Z. Guo, F. Maeda, M. Kotsugi, and Y. Watanabe

            "Two-dimensional emission patterns of secondary electrons from graphene layers formed on SiC(0001)"

            Applied Surface Science 254 (23)7596-7599 (2008).

 

            ABSTRACT: We used spectroscopic photoemission and low-energy electron microscopy to measure two-dimensional (2D) emission patterns of secondary electrons (SEs) emitted from graphene layers formed on SiC(0 0 0 1). The 2D SE patterns measured at the SE energies of 0-50 eV show energy-dependent intensity distributions in the 6-fold symmetry. The SE patterns exhibit features ascribed to energy band structures of 2D free electrons, which would prove that electrons are partially confined in thin graphene layers even above the vacuum level. (c) 2008 Elsevier B.V. All rights reserved.

 

35.    H. Hibino, H. Kageshima, and M. Uwaha

            "Instability of steps during Ga deposition on Si(111)"

            Surface Science 602 (14)2421-2426 (2008).

 

            ABSTRACT: We demonstrate that deposition of foreign atoms can induce step wandering. Low-energy electron microscopy and atomic force microscopy were used to investigate step shape changes during Ga deposition on Si(1 1 1). Dramatic step wandering occurs during the root 3 x root 3-to-6.3 x 6.3 transition. Due to the difference in the Si atom density between the root 3 x root 3 and 6.3 x 6.3 structures, steps advance during the phase transition. Because the 6.3 x 6.3 structure is preferentially formed at the lower side of the steps, more Si atoms are incorporated into the steps from the lower side than from the upper side. This asymmetry causes the step wandering. (C) 2008 Elsevier B.V. All rights reserved.

 

36.    H. Hibino, H. Kageshima, F. Maeda, M. Nagase, Y. Kobayashi, and H. Yamaguchi

            "Microscopic thickness determination of thin graphite films formed on SiC from quantized oscillation in reflectivity of low-energy electrons"

            Physical Review B 77 (7), 075413 (2008).

 

            ABSTRACT: Low-energy electron microscopy (LEEM) was used to measure the reflectivity of low-energy electrons from graphitized SiC(0001). The reflectivity shows distinct quantized oscillations as a function of the electron energy and graphite thickness. Conduction bands in thin graphite films form discrete energy levels whose wave vectors are normal to the surface. Resonance of the incident electrons with these quantized conduction band states enhances electrons to transmit through the film into the SiC substrate, resulting in dips in the reflectivity. The dip positions are well explained using tight-binding and first-principles calculations. The graphite thickness distribution can be determined microscopically from LEEM reflectivity measurements.

 

37.    T. Honjo, S. W. Nam, H. Takesue, Q. Zhang, H. Kamada, Y. Nishida, O. Tadanaga, M. Asobe, B. Baek, R. Hadfield, S. Miki, M. Fujiwara, M. Sasaki, Z. Wang, K. Inoue, and Y. Yamamoto

            "Long-distance entanglement-based quantum key distribution over optical fiber"

            Optics Express 16 (23)19118-19126 (2008).

 

            ABSTRACT: We report the first entanglement-based quantum key distribution (QKD) experiment over a 100-km optical fiber. We used superconducting single photon detectors based on NbN nanowires that provide high-speed single photon detection for the 1.5-mu m telecom band, an efficient entangled photon pair source that consists of a fiber coupled periodically poled lithium niobate waveguide and ultra low loss filters, and planar lightwave circuit Mach-Zehnder interferometers (MZIs) with ultra stable operation. These characteristics enabled us to perform an entanglement-based QKD experiment over a 100-km optical fiber. In the experiment, which lasted approximately 8 hours, we successfully generated a 16 kbit sifted key with a quantum bit error rate of 6.9% at a rate of 0.59 bits per second, from which we were able to distill a 3.9 kbit secure key. (C) 2008 Optical Society of America

 

38.    K. Inoue, T. Ohashi, T. Kukita, K. Watanabe, S. Hayashi, T. Honjo, and H. Takesue

            "Differential-phase-shift quantum secret sharing"

            Optics Express 16 (20)15469-15476 (2008).

 

            ABSTRACT: A quantum secret sharing (QSS) protocol based on a differential-phase-shift scheme is proposed, which quantum mechanically provides a full secret key to one party and partial keys to two other parties. A weak coherent pulse train is utilized instead of individual photons as in conventional schemes. Compared with previous QSS protocols, the present one features a simple setup, is suitable for fiber transmission, and offers the possibility for a high key creation rate. An experiment is also carried out to demonstrate the operation. (C) 2008 Optical Society of America

 

39.    T. Ishibashi, T. Kawata, A. Tsukada, H. Shibata, M. Naito, and K. Sato

            "Magneto-optical observation of magnetic flux in patterned MgB2 films"

            Physica C-superconductivity And Its Applications 468 (15-20)1313-1315 (2008).

 

            ABSTRACT: MgB2 films grown by molecular beam epitaxy method were investigated by means of magneto-optical (MO) method. Circular and square patterns of 100-500 mu m in size prepared by a photolithography and a chemical etching process were measured by quantitative MO imaging technique using polarization modulation technique and Bi substituted yttrium iron garnet film prepared by metal-organic decomposition method. A uniform flux penetration from edges of the patterns without any dendrite structures was observed, suggesting magnetic stability of the MgB2 films. Current distributions were calculated from the MO images, from which a current density as high as 6 x 10(7) A/cm(2) was deduced. (C) 2008 Elsevier B.V. All rights reserved.

 

40.    K. Ishikawa, N. Yamamoto, K. Tateno, and Y. Watanabe

            "Characterization of Individual GaAs/AlGaAs Self-Standing Nanowires by Cathodoluminescence Technique using Transmission Electron Microscope"

            Japanese Journal Of Applied Physics 47 (8)6596-6600 (2008).

 

            ABSTRACT: Cathodoluminescence (CL) spectra and monochromatic CL images of GaAs/AlGaAs self-standing nanowires were observed using a transmission electron microscope combined with a CL detection system. Individual nanowires were resolved in monochromatic CL images, and the CL spectra taken from those wires by focused beam illumination showed emission peaks at different energies. Double peaks were sometimes observed to appear in the CL. spectrum from a single nanowire. From the line-scan spectrum measurement and CL image observation of tilled angle illumination, it was found that a quantum-dot-like structure is formed along the nanowire.

 

41.    A. Ishizawa, T. Nishikawa, S. Aozasa, A. Mori, O. Tadanaga, M. Asobe, and H. Nakano

            "Demonstration of carrier envelope offset locking with low pulse energy"

            Optics Express 16 (7)4706-4712 (2008).

 

            ABSTRACT: We demonstrate a carrier-envelope-offset (CEO)-locked frequency comb with 230-pJ fiber coupling pulse energy by using a passively mode-locked Er-fiber amplifier laser. For the generation of an octave-bandwidth spectrum in a highly nonlinear fiber and the second harmonic in a self-referenced interferometer with the lower pulse energy, we use a tellurite photonic crystal fiber and a direct-bonded quasi-phase-matched LiNbO3 ridge waveguide, respectively. Our method is feasible for locking the CEO with a lower pulse energy to obtain a low-noise and high-accuracy optical frequency comb at telecommunications wavelengths. (c) 2008 Optical Society of America.

 

42.    T. Ito, W. Shichi, Y. Nishioka, M. Ichida, H. Gotoh, H. Kamada, and H. Ando

            "Dependence of electron spin g-factor on magnetic field in quantum wells"

            Journal Of Luminescence 128 (5-6)865-867 (2008).

 

            ABSTRACT: The dependence of electron spin g-factor on magnetic field has been investigated in GaAs/AlGaAs quantum wells. We have estimated the electron g-factor from spin precession frequency in time-resolved photoluminescence measurements under a magnetic field in different configurations; the magnetic field perpendicular (g(perpendicular to)) and parallel (g(parallel to)) to the quantum confinement direction. When the angle between the magnetic field and the confinement direction is 45 degrees, we have found that g-factor varies depending on the direction of magnetic field and the circular polarization type of excitation light (sigma(+) or sigma(-)). These dependences of g-factor exhibit main features of Overhauser effect that nuclear spins react back on electron spin precession. The value of g(perpendicular to) and g(parallel to) corrected for the nuclear effects agree well with the results of four-band k . p perturbation calculations. (c) 2007 Elsevier B.V. All rights reserved.

 

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

            "Effects of in-plane magnetic field direction on the nuclear-spin relaxation in the nu=2/3 quantum Hall state"

            Physica E-low-dimensional Systems & Nanostructures 40 (5)1175-1177 (2008).

 

            ABSTRACT: We investigated effects of the direction of in-plane magnetic field B-parallel to on the phase transition in the quantum Hall ferromagnet at Landau-level filling factor v = 2/3 by the nuclear-spin relaxation measurements. We controlled the angle phi between the direction of B-parallel to and a current I, when B-parallel to is parallel (perpendicular) to I, phi = 0 degrees (phi = 90 degrees). We found that the nuclear spin relaxation rate T-1(-1) at phi = 0 degrees is about twice as much as that at phi = 90 degrees. We discuss the anisotropic behavior of T-1(-1) in term of a suppression of low-frequency electron spin fluctuations by B-parallel to at phi = 90 degrees. (C) 2007 Elsevier B.V. All rights reserved.

 

44.    M. Jo, T. Kaizawa, M. Arita, A. Fujiwara, K. Yamazaki, Y. Ono, H. Inokawa, Y. Takahashi, and J. B. Choi

            "Silicon nanodot-array device with multiple gates"

            Materials Science In Semiconductor Processing 11 (5-6)175-178 (2008).

 

            ABSTRACT: We fabricated a nanodot-array device with multiple input gates on a silicon-on-insulator (SOI) wafer by using a pattern-dependent oxidation method with multiple input gates, which embodies a new concept of a flexible single-electron device. Although the device can generate many logic functions owing to the capacitive coupling between dots and many gates, the complicated structural configuration makes it difficult to confirm the formation of the nanodot array. For further investigation of this kind of device to achieve higher functionality, it is important to demonstrate experimentally that the dot array is actually formed. We analyzed the oscillation-peak shift caused by the gate voltage change, and successfully determined the location of the dots that contributed to the experimentally observed oscillations. (C) 2008 Elsevier Ltd. All rights reserved.

 

45.    H. Kageshima, and A. Fujiwara

            "First-principles study on inversion layer properties of double-gate atomically thin silicon channels"

            Applied Physics Letters 93 (4), 043516 (2008).

 

            ABSTRACT: The inversion layer properties of double-gate atomically thin silicon channels are studied based on the first-principles enforced Fermi energy difference method. The calculated results indicate that the atomic-scale thickness of the channel significantly affects the inversion layer capacitance as well as the inversion layer carrier properties. They also indicate that the first-principles approach is essential and practical for studying the device physics of the field effect transistors with nanometer-scale channels. (c) 2008 American Institute of Physics.

 

46.    H. Kamada, and T. Kutsuwa

            "Broadening of single quantum dot exciton luminescence spectra due to interaction with randomly fluctuating environmental charges"

            Physical Review B 78 (15), 155324 (2008).

 

            ABSTRACT: We studied line broadening of single-dot exciton emissions in terms of fluctuating interaction between the quantum dot (QD) exciton and environmental charges. We examined two types of QD excitons: one accompanied by trapped charge whereby the exciton line redshifts under the trapped charge population and the other nearly free from trapped charges. To avoid population decay of exciton-which results from multiple-carrier capture into the QDs, thereby leading to line broadening-and to highlight the effect of the fluctuating charges, we selected QDs that reject the capture of carriers in the barrier material. Interferometric correlation measurements of the single-dot emissions uncover the importance of the trapped charges near the QDs: The fluctuation of the Coulomb field caused by the trapping or detrapping of charges in point defects changes the autocorrelation function into Gaussian decay. A model dealing with the dynamics of the charge occupation driven by the thermally activated carrier capture and photoinduced carrier emissions is constructed consistent with the experiment. Upon temperature rise, the rate of the phase decoherence prevails over that of the charge fluctuation, and the autocorrelation function thereby turns to exponential. In contrast, in the QD nearly free from the trapped nearby charges, the autocorrelation decay obeys a simple exponential function, which is consistent with the absence of the fluctuating charge perturbation. Under an intense excitation, another decoherence due to the exciton or biexciton transition opens. We finally discuss the autocorrelation function in terms of the zero-phonon line and the phonon sideband.

 

47.    H. Kamada, M. Asobe, T. Honjo, H. Takesue, Y. Tokura, Y. Nishida, O. Tadanaga, and H. Miyazawa

            "Efficient and low-noise single-photon detection in 1550 nm communication band by frequency upconversion in periodically poled LiNbO3 waveguides"

            Optics Letters 33 (7)639-641 (2008).

 

            ABSTRACT: We demonstrate 1500 nm band single-photon detection with low dark-count noise and a potentially high efficiency, which may allow long distance and high-bit-rate quantum key distribution. By developing frequency upconversion devices based on periodically poled lithium niobate waveguides, which are specifically designed to use a pump wavelength longer than that of communication-band photons, we completely eliminate the dark-count noise caused by parasitic nonlinear processes in the waveguide. We observed an internal conversion efficiency as high as 40% and demonstrated scaling down to the single photon level while maintaining a background dark-count rate of 10(2) S-1. (C) 2008 Optical Society of America.

 

48.    Y. Kashimura, J. Durao, K. Furukawa, and K. Torimitsu

            "Self-spreading behavior of supported lipid bilayer through single sub-100-nm gap"

            Japanese Journal Of Applied Physics 47 (4)3248-3252 (2008).

 

            ABSTRACT: We report on the self-spreading behavior of a supported lipid bilayer passing through a sub-100-nm gap (nanogap). For this purpose, a device with a nanogap in a microchannel on a silicon substrate was designed and fabricated by electron beam lithography and photolithography. Fluorescence images of the lipid bilayer labeled with dye-conjugated lipids were observed by using a confocal laser scanning microscope. The time evolution of the self-spreading lipid bilayer passing through the nanogap was investigated at first. In the device, the lipid bilayer successfully passed through the nanogap without any stagnation. An analysis of the velocity of an advancing lipid bilayer showed no significant effect before or after passage though the nanogap. The effects of dye-conjugated lipid molecules and the size of the nanogap on the self-spreading behavior were examined next. We observed an abrupt decrease in the fluorescence intensity in the vicinity of the nanogap with Texas Red-DHPE and fluorescein-DHPE. It was revealed that the decrease depends on nanogap size as well as bulkiness of the dye molecule. The results suggest that bulkier dye molecules experience interference when they pass through narrower nanogaps.

 

49.    M. Kasu, K. Ueda, H. Kageshima, and Y. Yamauchi

            "RF equivalent-circuit analysis of p-type diamond field-effect transistors with hydrogen surface termination"

            Ieice Transactions On Electronics E91C (7)1042-1049 (2008).

 

            ABSTRACT: On the basis of the RF characteristics of p-type diamond field-effect transistors (FETs) with hydrogen surface termination, we establish an equivalent circuit (EQC) model. From comparisons of three cases we reveal that to represent the device performance in the EQC, the source, gate, and drain resistance should be considered but that the gate-source and gate-drain resistance can be ignored. The features of diamond FETs are (1) a plateau of the gate capacitance in a certain gate voltage range. (2) maximum f(T) and f(MAX) cut-off frequencies near the threshold gate voltage, and (3) a high f(MAX)/f(T) ratio similar to 3.8. We discuss these features in terms of the energy barrier between the gate metal and the two-dimensional hole channel and drift region below the gate.

 

50.    M. Kasu, K. Ueda, H. Kageshima, and Y. Yamauchi

            "Gate interfacial layer in hydrogen-terminated diamond field-effect transistors"

            Diamond And Related Materials 17 (4-5)741-744 (2008).

 

            ABSTRACT: Cross-sectional transmission microscopy images of hydrogen-terminated diamond field-effect transistor reveal interfacial layers between the metal and hydrogen-terminated diamond layer. Especially interesting is that an interfacial layer between Al and H-terminated diamond is clearly seen. This layer corresponds to the energy barrier, which we confirmed from an RF analysis of a diamond FET. During growth, an amorphous-like subsurface layer with vacancies has already formed on H-terminated diamond, and during subsequent metal evaporation, metal diffuses through vacancies into the subsurface layer, and eventually the interfacial layer forms. (C) 2008 Elsevier B.V. All rights reserved.

 

51.    O. Kazakova, J. C. Gallop, D. C. Cox, E. Brown, A. Cuenat, and K. Suzuki

            "Optimization of 2DEG InAs/GaSb Hall Sensors for Single Particle Detection"

            Ieee Transactions On Magnetics 44 (11)4480-4483 (2008).

 

            ABSTRACT: Magnetic sensors having high spatial and stray field resolutions are key elements in many biomedical applications. One promising magnetic detector is a microsized Hall sensor. We present our first results in realising a measurement system based on a Hall sensor made of an asymmetric 2DEG InAs/GaSb-based heterostructure. The work aims to investigate magnetotransport properties of such Hall sensors and optimize their performance. In particular, we focus on examining noise characteristics of the sensor as it allows us to determine and improve the device sensitivity. We show that in investigated devices a magnetic field sensitivity of better than 0.5 mu T/Hz(1/2) (corresponding to a magnetization detection threshold of 2 X 10(5) mu(B)/HZ(1/2)) should be readily achievable at room temperature and at a frequency of around 3 kHz.

 

52.    N. Y. Kim, C. W. Lai, S. Utsunomiya, G. Roumpos, M. Fraser, H. Deng, T. Byrnes, P. Recher, N. Kumada, T. Fujisawa, and Y. Yamamoto

            "GaAs microcavity exciton-polaritons in a trap"

            Physica Status Solidi B-basic Solid State Physics 245 (6)1076-1080 (2008).

 

            ABSTRACT: We present a simple method to create an in-plane lateral potential in a semiconductor microcavity using a metal thin-film. Two types of potential are produced: a circular aperture and a one-dimensional (ID) periodic grating pattern. The amplitude of the potential induced by a 24 nm - 6 nm Au/Ti film. is on the order of a few hundreds of mu eV measured at 6-8 K. Since the metal layer makes the electromagnetic fields to be close to zero at the metal-semiconductor interface, the photon mode is confined more inside of the cavity. As a consequence, the effective cavity length is reduced under the metalfilm, and the corresponding cavity resonance is blue-shifted. Our experimental results are in a good agreement with theoretical estimates. In addition, by applying a DC electric voltage to the metal film, we are able to modify the quantum well exciton mode due to the quantum confined Stark effect, inducing a similar to 1 meV potential at similar to 20 kV/cm. Our method produces a controllable in-plane spatial trap potential for lower exciton-polaritons (LPs), which can be a building block towards 1D arrays and 2D lattices of LP condensates.

 

53.    Y. Kobayashi, and T. Akasaka

            "Hexagonal BN epitaxial growth on (0001) sapphire substrate by MOVPE"

            Journal Of Crystal Growth 310 (23)5044-5047 (2008).

 

            ABSTRACT: Hexagonal boron nitride (h-BN) epitaxial films were successfully grown on (000 1) sapphire substrate by metalorganic vapor phase epitaxy (MOVPE). BN films were grown using triethylboron and ammonia (NH3) at various V/III ratios ranging from 210 to 2100. BN films grown at high V/III ratios above 1280 showed two X-ray diffraction (XRD) peaks, one from the (0 0 0 2) plane and the other from the (0 0 0 4) plane of h-BN, and exhibited a clear peak at 1366 cm(-1) of the first h-BN Raman mode as well. In contrast, XRD revealed that structures in BIN films grown at low V/III ratios below 640 were turbostratic. These results indicate that the structure of the BN film grown on sapphire substrate by MOVPE strongly depends on the V/III ratio and that the BN growth under a high V/III ratio could lead to the growth of (0 0 0 1) h-BN epitaxial films on (0 0 0 1) sapphire substrates. (C) 2008 Elsevier B.V. All rights reserved.

 

54.    Y. Kobayashi, T. Akasaka, and T. Makimoto

            "Hexagonal boron nitride grown by MOVPE"

            Journal Of Crystal Growth 310 (23)5048-5052 (2008).

 

            ABSTRACT: Hexagonal boron nitride (h-BN) has a potential for optical device applications in the deep ultraviolet spectral region. For several decades, only amorphous and turbostratic boron nitride (BN) films had been grown by chemical vapor deposition and metalorganic vapor phase epitaxy. By introducing flow-rate modulation epitaxy (FME), which enables us to reduce parasitic reactions and lower the optimal growth temperature, we have succeeded in growing single-phase h-BN epitaxial films on nearly lattice-matched (1 1 1) Ni substrates. The h-BN epitaxial films exhibit near-band-gap ultraviolet luminescence at a wavelength of 227 nm in cathodoluminescence at room temperature. The combination of FME and the lattice-matched substrate paves the way for the epitaxial growth of high-quality h-BN. (C) 2008 Elsevier B.V. All rights reserved.

 

55.    T. Kodera, K. Ono, S. Amaha, Y. Tokura, Y. Arakawa, and S. Tarucha

            "Singlet-triplet transition induced by Zeeman energy in weakly coupled vertical double quantum dots"

            Physica E-low-dimensional Systems & Nanostructures 40 (5)1139-1141 (2008).

 

            ABSTRACT: We use Pauli-spin blockade (P-SB) in a vertical double quantum dot to study the interplay between the nuclear spin effect and exchange interaction. We observe a specific P-SB lifting, reflecting coexistence of singlet-triplet admixing due to fluctuating nuclear spin field and singlet-triplet transition induced by the Zeeman effect when the exchange energy and the fluctuating nuclear field energy are comparable. From measurement of the Zeeman-induced P-SB lifting, we derive the exchange energy as a function of inter-dot level detuning. We confirm enhancement of exchange energy by resonance, and use Hubbard model calculation to account for it. (C) 2007 Elsevier B.V. All rights reserved.

 

56.    Y. Krockenberger, J. Kurian, M. Naito, and L. Alff

            "Epitaxial Growth of Superconducting Eu2-xCexCuO4 Thin Films"

            Japanese Journal Of Applied Physics 47 (8)6307-6309 (2008).

 

            ABSTRACT: We have grown (00l)-oriented thin films of Eu2-xCexCuO4 on (001) SrTiO3 with cerium composition in the range 0 <= x <= 0.22 by reactive molecular beam epitaxy and characterized them by X-ray diffraction and transport measurements. A systematic change in the c-axis length upon cerium doping was observed indicating that single-phase films were obtained for the whole doping range up to the solubility limit at x = 0.22. Superconductivity appeared within a cerium concentration of 0.14 <= x <= 0.19. Compared to other electron doped cuprates. the superconducting phase space and maximal critical temperature is reduced. and the point of optimal doping is shifted to a higher doping level.

 

57.    Y. Krockenberger, J. Kurian, A. Winkler, A. Tsukada, M. Naito, and L. Alff

            "Superconductivity phase diagrams for the electron-doped cuprates R2-xCexCuO4 (R=La, Pr, Nd, Sm, and Eu)"

            Physical Review B 77 (6), 060505 (2008).

 

            ABSTRACT: The superconductivity phase diagrams of electron-doped cuprates of the form R2-xCexCuO4 (with R=La, Pr, Nd, Sm, and Eu) have been determined for cerium compositions 0 < x < 0.36 in a consistent series of epitaxial thin films grown by reactive molecular beam epitaxy. The use of epitaxial thin films allows the growth of materials away from thermodynamical equilibrium expanding the accessible phase space beyond the availability of bulk material. The superconducting phase space systematically increases with the rare-earth ionic size. The doping concentration where the maximal transition temperature occurs in La-2 (-) xCexCuO4 is considerably shifted to lower doping (x similar to 0.09) compared to La-2 (-) xSrxCuO4 (x similar to 0.15). At the same time, the width of the superconducting region is broadened.

 

58.    T. Kubo, Y. Tokura, and S. Tarucha

            "Coherent pseudo-spin dynamics in Aharonov-Bohm interferometer containing laterally coupled double quantum dots"

            Physica E-low-dimensional Systems & Nanostructures 40 (5)1243-1245 (2008).

 

            ABSTRACT: We theoretically study the coherent pseudo-spin dynamics in Aharonov-Bohm interferometer containing laterally coupled double quantum dots (DQDs). We propose a novel blockade mechanism in laterally coupled DQDs suffering from a quantum interference effect. The leakage current due to the coherent pseudo-spin dynamics under such a blockade condition is examined using the non-equilibrium Green's function method. (C) 2007 Elsevier B.V. All rights reserved.

 

59.    T. Kubo, Y. Tokura, and S. Tarucha

            "Exotic pseudospin Kondo effect in laterally coupled double quantum dots"

            Physical Review B 77 (4), 041305 (2008).

 

            ABSTRACT: We study the pseudospin Kondo effect in laterally coupled double quantum dots using the slave-boson mean-field theory. We find that the exotic pseudospin Kondo effect appears when a coherent indirect coupling with parameter alpha is present through the common reservoirs. When 0

 

60.    N. Kumada, T. Kamada, S. Miyashita, Y. Hirayama, and T. Fujisawa

            "Electric field induced nuclear spin resonance mediated by oscillating electron spin domains in GaAs-based semiconductors"

            Physical Review Letters 101 (13), 137602 (2008).

 

            ABSTRACT: We demonstrate an alternative nuclear spin resonance using a radio frequency (rf) electric field [nuclear electric resonance (NER)] instead of a magnetic field. The NER is based on the electronic control of electron spins forming a domain structure. The rf electric field applied to a gate excites spatial oscillations of the domain walls and thus temporal oscillations of the hyperfine field to nuclear spins. The rf power and burst duration dependence of the NER spectrum provides insight into the interplay between nuclear spins and the oscillating domain walls.

 

61.    N. Kumada, K. Iwata, K. Tagashira, Y. Shimoda, K. Muraki, Y. Hirayama, and A. Sawada

            "Modulation of bilayer quantum Hall states by tilted-field-induced subband-Landau-level coupling"

            Physical Review B 77 (15), 155324 (2008).

 

            ABSTRACT: We study effects of tilted magnetic fields on energy levels in a double-quantum-well (DQW) system, focusing on the coupling of subbands and Landau levels (LLs). The subband-LL coupling induces anticrossings between LLs directly manifested in the magnetoresistance. The anticrossing gap becomes larger than the spin splitting at the tilting angle theta similar to 20 degrees and larger than the cyclotron energy at theta similar to 50 degrees, demonstrating that the subband-LL coupling exerts a strong influence on quantum Hall states even at a relatively small theta and plays a dominant role for larger theta. We also find that when the DQW potential is asymmetric, LL coupling occurs even within a subband. Calculations including higher-order coupling reproduce the experimental results quantitatively well.

 

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

            "NMR study of a canted antiferromagnet in a bilayer quantum Hall system"

            Physica E-low-dimensional Systems & Nanostructures 40 (5)937-941 (2008).

 

            ABSTRACT: We investigate static and dynamic properties of electron spins in the bilayer quantum Hall system at total Landau level filling factor nu = 2 by using current-pumped and resistively detected nuclear magnetic resonance (NMR). The measured Knight shift, K-S, of As-75 nuclei reveals continuous variation of the out-of-plane electronic spin polarization P-z between nearly full and zero as a function of density imbalance between the two layers. Nuclear spin relaxation rate 1/T-1 indicates that the in-plane spin order accompanied by a gapless low-frequency mode (i.e., the Goldstone mode) develops when P-z varies. These results provide direct information on the spin configuration and the low-energy collective excitations in the canted anti ferromagnetic state. (C) 2007 Elsevier B.V. All rights reserved.

 

63.    M. Kumagai, A. Taguchi, T. Takagahara, T. Ohno, and K. Yakubo

            "Topological aspects of excitons in artificial structure"

            Solid State Communications 145 (3)154-158 (2008).

 

            ABSTRACT: The exciton properties of thin nanotube structures are investigated theoretically. Anisotropic size dependencies have been found in the exciton binding energy, the kinetic energy for the relative motions of an electron and a hole, and the wavefunction. These anisotropies arise from the different boundary conditions in the tube-length and circumferential directions, namely, the topological features of nanotubes. We also found that it is possible to change the topology of exciton wavefunctions by varying the tube-length and the tube-radius. These findings suggest that the optical properties of nanotubes such as oscillator strength or nonlinear susceptibilities can be controlled by tuning the structural parameters, thus yielding a novel guiding principle for designing optical functional materials. (c) 2007 Elsevier Ltd. All rights reserved.

 

64.    K. Kumakura, and T. Makimoto

            "High performance pnp AlGaN/GaN heterojunction bipolar transistors on GaN substrates"

            Applied Physics Letters 92 (15), 153509 (2008).

 

            ABSTRACT: We fabricated pnp AlGaN/GaN heterojunction bipolar transistors (HBTs) with various emitter areas on GaN substrates and investigated their common-emitter current-voltage and high-power characteristics at room temperature. The HBTs with an emitter area of 30x50 mu m(2) exhibited a high performance: a maximum current gain of 85 at a collector current of 30 mA and a maximum collector current density of 7.3 kA/cm(2) at a collector-emitter voltage of 30 V, which corresponds to the maximum power dissipation density of 219 kW/cm(2). The current gain and the collector current density increased compared to those on sapphire substrates. For the HBT with the emitter area of 270x450 mu m(2), the current gain was still as high as 47 and the maximum collector current reached as high as 1 A, and this single HBT showed a high-power dissipation of 30 W. This high performance of the HBTs is ascribed to the low dislocation density and relatively high thermal conductivity of the GaN substrate. Although the emitter crowding and self-heating effects remain, the obtained values are highest among pnp nitride-based HBTs. (C) 2008 American Institute of Physics.

 

65.    E. Kuramochi, H. Taniyama, T. Tanabe, A. Shinya, and M. Notomi

            "Ultrahigh-Q two-dimensional photonic crystal slab nanocavities in very thin barriers"

            Applied Physics Letters 93 (11), 111112 (2008).

 

            ABSTRACT: We demonstrate that width-modulated line-defect nanocavities in photonic crystals with long air slots on either side can maintain an ultrahigh Q even with very thin in-plane photonic crystal (only several rows of air holes). Although it is commonly believed that high-Q photonic crystal nanocavities require relatively thick in-plane barriers, surprisingly these nanocavities fabricated in silicon photonic crystals exhibit an ultrahigh Q (> 10(6)) even with very thin barriers. This design may be useful for various nanocavity applications. (C) 2008 American Institute of Physics.

 

66.    N. Lambert, I. Mahboob, M. Pioro-Ladriere, Y. Tokura, S. Tarucha, and H. Yamaguchi

            "Electron-spin manipulation and resonator readout in a double-quantum-dot nanoelectromechanical system"

            Physical Review Letters 100 (13), 136802 (2008).

 

            ABSTRACT: We demonstrate how magnetically coupling a nanomechanical resonator to a double quantum dot confining two electrons can enable the manipulation of a single electron spin and the readout of the resonator's natural frequency. When the Larmor frequency matches the resonator frequency, the electron spin in one of the dots can be selectively and coherently flipped by the magnetized oscillator. By simultaneously measuring the charge state of the two-electron double quantum dots, this transition can be detected thus enabling the natural frequency and displacement of the mechanical oscillator to be determined.

 

67.    Y. Li, Y. D. Wang, F. Xue, and C. Bruder

            "Quantum theory of transmission line resonator-assisted cooling of a micromechanical resonator"

            Physical Review B 78 (13), 134301 (2008).

 

            ABSTRACT: We propose a quantum description of the cooling of a micromechanical flexural oscillator by a one-dimensional transmission line resonator via a force that resembles cavity radiation pressure. The mechanical oscillator is capacitively coupled to the central conductor of the transmission line resonator. At the optimal point, the micromechanical oscillator can be cooled close to the ground state, and the cooling can be measured by homodyne detection of the output microwave signal.

 

68.    H. W. Liu, T. Fujisawa, H. Inokawa, Y. Ono, A. Fujiwara, and Y. Hirayama

            "A gate-defined silicon quantum dot molecule"

            Applied Physics Letters 92 (22), 222104 (2008).

 

            ABSTRACT: We report electron transport measurements of a silicon double dot formed in multigated metal-oxide-semiconductor structures with a 15-nm-thick silicon-on-insulator layer. Tunable tunnel coupling enables us to observe an excitation spectrum in weakly coupled dots and an energy level anticrossing in strongly coupled ones. Such a quantum dot molecule with both charge and energy quantization provides the essential prerequisite for future implementation of silicon-based quantum computations. (C) 2008 American Institute of Physics.

 

69.    H. W. Liu, T. Fujisawa, Y. Ono, H. Inokawa, A. Fujiwara, K. Takashina, and Y. Hirayama

            "Pauli-spin-blockade transport through a silicon double quantum dot"

            Physical Review B 77 (7), 073310 (2008).

 

            ABSTRACT: We present measurements of resonant tunneling through discrete energy levels of a silicon double quantum dot formed in a thin silicon-on-insulator layer. In the absence of piezoelectric phonon coupling, spontaneous phonon emission with deformation-potential coupling accounts for inelastic tunneling through the ground states of the two dots. Such transport measurements enable us to observe a Pauli spin blockade due to effective two-electron spin-triplet correlations, evident in a distinct bias-polarity dependence of resonant tunneling through the ground states. The blockade is lifted by the excited-state resonance by virtue of efficient phonon emission between the ground states. Our experiment demonstrates considerable potential for investigating silicon-based spin dynamics and spin-based quantum information processing.

 

70.    F. Maeda, H. Hibino, S. Suzuki, and F. Z. Guo

            "Oxide-mediated formation of alpha-FeSi2 on Si(001) studied by X-ray adsorption near edge structure analysis using SPELEEM"

            Surface And Interface Analysis 40 (13)1747-1750 (2008).

 

            ABSTRACT: To investigate the effect of the oxide layer on the oxide-mediated growth in solid phase epitaxy for the formation of a single-phase iron disilicides, the annealing processes were analyzed using spectroscopic photoemission and low-energy electron microscopy for a special surface where oxide areas and clean substrate areas (voids) coexist closely in a micrometer-order view. From the analysis of high-resolution X-ray adsorption near edge structure (XANES), we found that a pure alpha phase of FeSi2 was obtained in the oxide area after annealing at 720 degrees C, although a mixture of its alpha and beta phases was obtained in the void area. This indicates that the oxide layer effectively worked and a single-phase alpha-FeSi2 was successfully formed by the oxide-mediated growth. Copyright (C) 2008 John Wiley & Sons, Ltd.

 

71.    I. Mahboob, and H. Yamaguchi

            "Parametrically pumped ultrahigh Q electromechanical resonator"

            Applied Physics Letters 92 (25), 253109 (2008).

 

            ABSTRACT: The spectral purity of an electromechanical resonance (quality factor Q) can be enhanced by more than one order of magnitude to similar to 2.5 x 10(6) by parametrically exciting the fundamental mode via double frequency modulations to the spring constant mediated by the piezoelectric effect. We theoretically demonstrate that this Q enhancement is an intrinsic property of the parametric resonator by solving the equation of motion for this system. The Q enhancement demonstrated here results in smaller perturbations in the resonance (similar to 0.05 Hz) becoming visible which enables the charge sensitivity of the electromechanical oscillator to improve by a factor equal to the Q enhancement. (C) 2008 American Institute of Physics.

 

72.    I. Mahboob, and H. Yamaguchi

            "Bit storage and bit flip operations in an electromechanical oscillator"

            Nature Nanotechnology 3 (5)275-279 (2008).

 

            ABSTRACT: The Parametron was first proposed as a logic-processing system almost 50 years ago(1). In this approach the two stable phases of an excited harmonic oscillator provide the basis for logic operations(2-6). Computer architectures based on LC oscillators were developed for this approach, but high power consumption and difficulties with integration meant that the Parametron was rendered obsolete by the transistor. Here we propose an approach to mechanical logic based on nanoelectromechanical systems(7-9) that is a variation on the Parametron architecture and, as a first step towards a possible nanomechanical computer(10-12), we demonstrate both bit storage and bit flip operations.

 

73.    I. Mahboob, and H. Yamaguchi

            "Piezoelectrically pumped parametric amplification and Q enhancement in an electromechanical oscillator"

            Applied Physics Letters 92 (17), 173109 (2008).

 

            ABSTRACT: The frequency response of an electromechanical oscillator was measured while being parametrically pumped by double frequency modulations to the effective spring constant via the piezoelectric effect. A 13 dB gain in the resonance amplitude was observed by increasing the pump power where further increase was limited by parametric excitation of the fundamental mode. Concurrently, the coherent amplification resulted in the quality factor of the resonance also being enhanced by similar to 2.5 times. The on-chip degenerate piezoelectric parametric amplification demonstrated here could be implemented in nanoelectromechanical oscillators to bypass the detrimental effects of size minimization. (c) 2008 American Institute of Physics.

 

74.    D. V. Melnikov, T. Fujisawa, D. G. Austing, S. Tarucha, and J. P. Leburton

            "Many-body excitations in the tunneling current spectra of a few-electron quantum dot"

            Physical Review B 77 (16), 165340 (2008).

 

            ABSTRACT: Inherent asymmetry in the tunneling barriers of few-electron quantum dots induces intrinsically different tunneling currents for forward and reverse source-drain biases in the nonlinear transport regime. We demonstrate that in addition to spin selection rules, overlap matrix elements between many-body states are crucial for the correct description of tunneling transmission through quantum dots at large magnetic fields. Signatures of excited (N-1)-electron states in the transport process through the N-electron system are clearly identified in the measured transconductances. Overall, the computed current spectra are found to be in very good agreement with the experimental data.

 

75.    T. Minegishi, A. Ishizawa, J. Kim, D. Kim, S. Ahn, S. Park, J. Park, I. Im, D. C. Oh, H. Nakano, K. Fujii, H. Jeon, and T. Yao

            "Fabrication of periodically polarity-inverted ZnO films"

            Journal Of Vacuum Science & Technology B 26 (3)1120-1123 (2008).

 

            ABSTRACT: One-dimensional periodically polarity-inverted (PPI) structures of ZnO for nonlinear optical devices are fabricated on c-plane Al2O3 substrates. To do so, corrugated MgO buffer layers are fabricated by etching after patterning, which is followed by the growth of ZnO layers by plasma-assisted molecular beam epitaxy. The polarity-inverted structures are confirmed by scanning piezoresponse microscopy and atomic-force microscopy. PPI structures with submicron periodicity are fabricated to satisfy the quasiphase matching condition for second harmonic generation of light. (C) 2008 American Vacuum Society.

 

76.    S. Miyamoto, K. Nishiguchi, Y. Ono, K. M. Itoh, and A. Fujiwara

            "Escape dynamics of a few electrons in a single-electron ratchet using silicon nanowire metal-oxide-semiconductor field-effect transistor"

            Applied Physics Letters 93 (22), 222103 (2008).

 

            ABSTRACT: Transport dynamics of a few electrons in a quantum dot are investigated in a single-electron ratchet using silicon nanowire metal-oxide-semiconductor field-effect transistors. Time-resolved measurements in a nanosecond regime are carried out to determine the escape times of the first, second, and third electrons from the quantum dot originally containing three electrons. The escape time strongly depends on the number of electrons due to the single-electron charging effect in the quantum dot, which makes it possible to achieve selective ejection of a desired number of electrons.

 

77.    M. Nagase, H. Hibino, H. Kageshima, and H. Yamaguchi

            "In-plane conductance measurement of graphene nanoislands using an integrated nanogap probe"

            Nanotechnology 19 (49), 495701 (2008).

 

            ABSTRACT: The in-plane conductance of individual graphene nanoislands thermally grown on SiC substrate was successfully measured using an integrated nanogap probe without lithographic patterning. A Pt nanogap electrode with a 30 nm gap integrated on the cantilever tip of a scanning probe microscope enables us to image a conductance map of graphene nanoislands with nanometer resolution. Single- and double-layer graphene islands are clearly distinguished in the conductance image. The size dependence of the conductance of the nanoislands suggests that the band gap opening is due to the lateral confinement effect.

 

78.    A. Nakamura, K. Okamatsu, T. Tawara, H. Gotoh, J. Temmyo, and Y. Matsui

            "Dot-height dependence of photoluminescence from ZnO quantum dots"

            Japanese Journal Of Applied Physics 47 (4)3007-3009 (2008).

 

            ABSTRACT: We report on the optical properties of ZnO nanodots and how they are influenced by the height of the dot configuration. The nanodots were grown on SiO2/Si substrates by remote-plasma enhanced metalorganic chemical vapor deposition (RPE-MOCVD). The dot configuration was regulated by controlling the growth time. The photoluminescence (PL) spectra of nanodots having average dot height of 2.5, 3.5, and 4.5 nm grown on SiO2/Si substrates were measured at 16 K. A blue shift in the excitonic emission was observed for shorter dots due to a larger quantum confinement effect. The fractional-dimensional space model was used to estimate a dimensionality of 2.35 for ZnO nano dots with an average dot height of 2.5 nm.

 

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

            "Self-assembly of gold nanorods induced by intermolecular interactions of surface-anchored lipids"

            Langmuir 24 (11)5654-5658 (2008).

 

            ABSTRACT: Surface-modified gold nanorods (Au NRs) with 1,2-dipalmitoyl-sn-glycero-3-phosphothioethanol (DPPTE) were synthesized, and their self-assembled structures on a silicon substrate were observed using a scanning electron microscope (SEM). The An NR-DPPTE complex formed characteristic one- and two-dimensional self-assemblies induced by intermolecular interactions of surface-anchored lipids via simple drying process.,The interparticle distance between neighboring NRs was uniform at around 5.0 nm, which was consistent with the thickness of the lipid bilayer. Furthermore, we observed the anisotropic configurations of the NR complex, preferentially oriented in a lateral or perpendicular fashion, in a two-dimensional assembled structure dependent on the interfacial hydrophilicity or hydrophobicity of the silicon surface.

 

80.    K. Nishiguchi, C. Koechlin, Y. Ono, A. Fujiwara, H. Inokawa, and H. Yamaguchi

            "Single-Electron-Resolution Electrometer Based on Field-Effect Transistor"

            Japanese Journal Of Applied Physics 47 (11)8305-8310 (2008).

 

            ABSTRACT: An electrometer based oil field-effect transistors (FETs) wits fabricated oil a silicon-on-insulator substrate (SOI), The electrometer has a nanometer-scale small channel and a capacitively coupled node, where single electrons are stored. We discuss the dependence of the charge sensitivity of the electrometer on its structure and on its operation condition and gives guides for achieving the higher charge sensitivity. The device optimization based on this dependence allows the demonstration of the electrometer with extremely high charge sensitivity. 0.0013 e/root Hz at 1 Hz, at room temperature.

 

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

            "Stochastic data processing circuit based on single electrons using nanoscale field-effect transistors"

            Applied Physics Letters 92 (6), 062105 (2008).

 

            ABSTRACT: A circuit utilizing single electrons is demonstrated at room temperature using a silicon-on-insulator metal-oxide-semiconductor field-effect transistor (MOSFET). Individual electrons randomly passing through the nanoscale MOSFET, which are the origin of shot noise, are monitored by an electrometer in real time. This random behavior of single electrons is used as a random number for a stochastic associative memory for image-pattern matching, in which the most preferable pattern is extracted with the largest probability. The use of electron transport in the MOSFET provides high controllability of the randomness as well as fast generation of random numbers. The present result promises single-electron applications using nanoscale MOSFETs. (c) 2008 American Institute of Physics.

 

82.    K. Nishiguchi, M. Nagase, T. Yamaguchi, A. Fujiwara, and H. Yamaguchi

            "Low-energy electron emission from an electron enversion layer of a Si/SiO2/Si cathode for nano-decomposition"

            Japanese Journal Of Applied Physics 47 (6)5106-5108 (2008).

 

            ABSTRACT: We fabricated an electron-emission cathode with a Si/SiO2/Si structure using metal-oxide-semiconductor field-effect transistor (MOSFET) fabrication technology. Electrons travel from an electron-source Si layer to a thin polycrystalline Si (poly-Si) through a thin SiO2 and some of them with high energy, i.e., hot electrons, are emitted from the poly-Si surface. By utilizing an electron-inversion layer as the electron source, high efficiency and stability of electron emission were achieved. Material decomposition at a depth of a few nanometers was also demonstrated using a low-energy-electron irradiation from the cathode operated in a low vacuum condition.

 

83.    A. Nishikawa, K. Kumakura, M. Kasu, and T. Makimoto

            "High-temperature characteristics of AlxGa1-xN-based vertical conducting"

            Japanese Journal Of Applied Physics 47 (4)2838-2840 (2008).

 

            ABSTRACT: We investigated the high-temperature characteristics for AlxGa1-xN-based (x = 0-0.57) vertical conducting diodes. In the forward current-voltage (I-V) characteristics, the offset voltage decreases with temperature because of the reduction of the built-in potential due to the decrease in the bandgap energy with temperature. In spite of an increase in SiC substrate resistance with temperature because of a decrease in the electron mobility, the on-state resistance of the diode with Al0.22Ga0.78N is as low as 1.45 m Omega cm(2) even at 250 degrees C because of the reduced resistance of the p-InGaN layer due to an increase in the hole concentration. In the reverse I-V characteristics, the breakdown voltage increases with increasing Al composition, x, of AlxGa1-xN layer because the higher the Al composition of the AlxGa1-xN layer is, the higher the critical electric field becomes. Although the reverse leakage current of AlxGa1-xN-based diodes increases with increasing temperature, the breakdown voltage at elevated temperatures is similar to that at room temperature. These features indicate the feasibility of AlxGa1-xN-based diodes for high-temperature operation.

 

84.    J. Nitta, and T. Bergsten

            "Spin interference controlled by electric field: Ensemble average effect on AAS and AB oscillation amplitudes"

            Physica E-low-dimensional Systems & Nanostructures 40 (5)973-977 (2008).

 

            ABSTRACT: Time reversal symmetric Al'tshuler-Aronov-Spivak (AAS) oscillations are measured in an array of InGaAs mesoscopic loops. We confirm that gate voltage dependence of h/2e period oscillations is due to spin interference from the effect of ensemble average on the AAS and Aharonov-Bohm (AB) amplitudes. This spin interference is based on the time reversal Aharonov-Casher (AC) effect. The AC interference oscillations are controlled over several periods. This result shows evidence for electrical manipulation of the spin precession angle in an InGaAs two-dimensional electron gas channel. We control the precession rate in a precise and predictable way with an electrostatic gate. (C) 2007 Elsevier B.V. All rights reserved.

 

85.    S. Nomura, M. Yamaguchi, T. Akazaki, H. Tamura, T. Maruyama, S. Miyashita, and Y. Hirayama

            "Density dependent electron effective mass probed by photo luminescence down to dilute electron density limit"

            Physica E-low-dimensional Systems & Nanostructures 40 (5)1467-1469 (2008).

 

            ABSTRACT: We report on results of determination of the electron effective mass and the reduced mass as functions of the electron density (n(s)) at about 100 mK in perpendicular magnetic fields in the range between 1.5 < r(s) < 6 by magneto-photoluminescence measurements. We find that the obtained effective masses increase with decrease in n(s) at n(s) < 1 x 10(11) cm(-2). (c) 2007 Elsevier B.V. All rights reserved.

 

86.    K. Nonaka, K. Tamaru, M. Nagase, H. Yamaguchi, S. Warisawa, and S. Ishihara

            "Height dependence of Young's modulus for carbon nanopillars grown by focused-ion-beam-induced chemical vapor deposition"

            Japanese Journal Of Applied Physics 47 (6)5116-5119 (2008).

 

            ABSTRACT: We investigated the height dependence of the Young's modulus for carbon nanopillars grown by focused-ion-beam-induced chemical vapor deposition (FIB-CVD) using phenanthrene gas as a source material. Carbon nanopillars of different heights were grown by FIB-CVD at various growth times and a fixed ion-beam focal point. The growth heights ranged from 3.6 to 35.6 mu m. The diameters at the bottoms of the pillars were nearly the same, 100 nm, and it increased as the growth progressed. Young's modulus of the carbon nanopillars was evaluated from resonant frequency for mechanical vibration using uniform and nonuniform models. Young's moduli differed for different growth heights for both of the models.

 

87.    M. Notomi, E. Kuramochi, and T. Tanabe

            "Large-scale arrays of ultrahigh-Q coupled nanocavities"

            Nature Photonics 2 (12)741-747 (2008).

 

            ABSTRACT: Coupled microresonators are expected to play a key role in slow-light engineering and various types of light-matter interaction enhancement, especially if they are based on small and high-Q cavities. Although rapid progress has been made on microresonator performance, large-scale arrays of coupled resonators based on high-Q wavelength-sized cavities have not yet been realized. Here, we show large-scale (N > 100) ultrahigh-Q coupled nanocavity arrays based on photonic crystals. This is the first demonstration of large-scale coupled resonator arrays based on wavelength-sized cavities, in which tight-binding sinusoidal dispersion is seen. We confirm that an ultrahigh value of Q (similar to 1 x 10(6)) is maintained, even when N is large, and the resonators exhibit very low loss characteristics with regard to light propagation. The ultrahigh value of Q and small size has enabled us to achieve ultraslow light pulse propagation with a group velocity well below 0.01c and a long group delay.

 

88.    M. Notomi, and H. Taniyama

            "On-demand ultrahigh-Q cavity formation and photon pinning via dynamic waveguide tuning"

            Optics Express 16 (23)18657-18666 (2008).

 

            ABSTRACT: We show that ultrahigh-Q wavelength-sized cavities can be reconfigurably formed by local refractive index tuning of photonic-crystal mode-gap waveguides. We have found that Q can be extraordinarily high (similar to 5x10(9)), which is much higher than that of structure-modulated mode-gap cavities. Furthermore, the required index modulation is extremely small (Delta n/n similar to 10(-3)), which enables dynamic cavity formation by fast optical nonlinearity. We numerically show that traveling photons in a waveguide can be pinned by fast local index tuning. (c) 2008 Optical Society of America

 

89.    M. Notomi, E. Kuramochi, and H. Taniyama

            "Ultrahigh-Q nanocavity with 1D photonic gap"

            Optics Express 16 (15)11095-11102 (2008).

 

            ABSTRACT: Recently, various wavelength-sized cavities with theoretical Q values of similar to 10(8) have been reported, however, they all employ 2D or 3D photonic band gaps to realize strong light confinement. Here we numerically demonstrate that ultrahigh-Q (2.0 x 10(8)) and wavelength-sized (V-eff similar to 1.4(lambda/n)(3)) cavities can be achieved by employing only 1D periodicity. (C) 2008 Optical Society of America.

 

90.    H. Ohno, D. Takagi, K. Yamada, S. Chiashi, A. Tokura, and Y. Homma

            "Growth of vertically aligned single-walled carbon nanotubes on alumina and sapphire substrates"

            Japanese Journal Of Applied Physics 47 (4)1956-1960 (2008).

 

            ABSTRACT: The synthesis of vertically aligned carbon nanotubes with submillimeter-order heights was performed using ethanol chemical vapor deposition with Co catalysts supported on Al2O3 substrates. The effects of Al2O3 in the form of amorphous alumina and single-crystalline sapphire were investigated through a characterization of the Co catalyst particles on the substrates. An important effect of Al2O3 was found to be the production of highly dense and nanosized Co particles, owing to a low surface diffusivity.

 

91.    S. Ohno, Y. Oba, S. Yabuuchi, T. Sato, and H. Kageshima

            "Magnetism of Single-Walled Carbon Nanotube with Pd Nanowire"

            Journal Of The Physical Society Of Japan 77 (10), 104713 (2008).

 

            ABSTRACT: Magnetism of single-walled carbon nanotubes (SWNTs) filled with Pd in pseudo one-dimension is investigated based on the electronic structure obtained using the first-principle calculation. In addition. the stability of Pd nanowire inside SWNT is evaluated through the calculation of binding energy. The Pd monostrand nanowire with the inter-atomic distance of 2.49 angstrom, which shows ferromagnetism in the freestanding state, has the ferromagnetic moment also in the armchair type SWNTs with the diameter lager than 6.9 angstrom although the magnetic moment is smaller than that of the corresponding free-standing Pd nanowire. The pseudo one-dimensional fcc Pd nanowire with the cross section of the (111) plane in the (14, 0) SWNT has ferromagnetic moment, where the inter-atomic distance is elongated by 28% along the longitudinal axis of SWNT compared with the equilibrium distance, so as to adjust the unit cell size of SWNT. However. the Pd(100) nanowire in (8,8) SWNT does not show ferromagnetism although it has almost the same inter-atomic distance as that of the (111) nanowire in (14, 0) SWNT. This can be interpreted by means of the magnetism of planar Pd clusters whose laminating composes the nanowire.

 

92.    Y. Ono, M. A. Khalafalla, K. Nishiguchi, K. Takashina, A. Fujiwara, S. Horiguchi, H. Inokawa, and Y. Takahashi

            "Charge transport in boron-doped nano MOSFETs: Towards single-dopant electronics"

            Applied Surface Science 254 (19)6252-6256 (2008).

 

            ABSTRACT: We investigate the hole transport in p-channel field-effect transistors doped with boron, at low temperatures (6 - 28 K). In transistors with a relatively large dimension, we observe the acceptor-mediated hopping and carrier freezeout, both of which are strongly influenced by the gate bias. In nanoscale transistors, these features turn into single-charge tunneling, i.e., the trapping/detrapping of single holes by/from individual acceptors. The statistics of the appearance of the modulation in a few ten samples indicates that the number of acceptors is small, or even just one, indicating that what we have observed is single-charge-transistor operation by a single-acceptor quantum dot. (C) 2008 Elsevier B. V. All rights reserved.

 

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

            "Silicon single-charge transfer devices"

            Journal Of Physics And Chemistry Of Solids 69 (2-3)702-707 (2008).

 

            ABSTRACT: The single-electron device (SED) enables the control of electron motion on the level of an elementary charge. Single-charge transfer devices are special SEDs that enable single-electron transfer,,ynchronized with the gate clock. They have the potential for extremely low transfer error rates and are expected to be building blocks for future information processing and electrical metrology. We have been pursuing the fabrication of Si-based SEDs using CMOS technology with the help of electron-beam lithography and have recently demonstrated the single-charge transfer devices. The devices are composed of one Si quantum dot sandwitched between two tiny MOS gates and can operate at much higher temperatures than those of former metal-based and compound-semiconductor-based devices. This opens up the possibility of the practical use of clocked single-charge transfer. (C) 2007 Elsevier Ltd. All rights reserved.

 

94.    T. Ota, N. Kumada, G. Yusa, S. Miyashita, T. Fujisawa, and Y. Hirayama

            "Coherence time of nuclear spins in GaAs quantum well probed by submicron-scale all-electrical nuclear magnetic resonance device"

            Japanese Journal Of Applied Physics 47 (4)3115-3117 (2008).

 

            ABSTRACT: We study the coherence time of nuclear spins of As-75 nuclei in a GaAs quantum well using a submicron-scale all-electrical nuclear magnetic resonance (NMR) device. We estimate the extrinsic transverse relaxation time T-2(*) and intrinsic transverse relaxation time T-2 of nuclear spins using different pulse sequences to measure the decay of spin-echo signals. We significantly improve the coherence time from 0.05 to 1.4ms by eliminating the spatial field inhomogeneity and temporal fluctuation of surrounding electrons and nuclei with the aid of heteronuclear and electron-nuclear spin decoupling techniques. By analyzing the data, we extract individual sources of decoherence in GaAs. We discuss the relationship between the obtained T-2(*) and the peak width of the NMR spectra.

 

95.    H. Oyanagi, A. Tsukada, and M. Naito

            "Local structure study of T ' cuprate superconductors"

            Journal Of Physics And Chemistry Of Solids 69 (9)2307-2310 (2008).

 

            ABSTRACT: Undoped T-type cuprates are believed to be charge transfer (Mott-Hubbard) insulators. Recent observation of undoped superconducting T'-type cuprates suggests half-filling weakly correlated metallic electron states (Tsukada et al.), which is against the fundamental picture. Here we report the local structures of uncloped T'-(La3+,Y3+)(2)CuO4 and doped T-(La3+,Ce4+)(2)CuO4 thin-film single crystals by polarized extended X-ray absorption fine structure (EXAS). The in-plane (Ellab) polarized Cu K-EXAFS data shows a remarkable Cu-O bond distance displacement. The broadened Cu-O distribution suggests a large local lattice distortion in T-type structures, which might influence the electronic structure. (C) 2008 Elsevier Ltd. All rights reserved.

 

96.    S. Perraud, K. Kanisawa, Z. Z. Wang, and T. Fujisawa

            "Bound states induced by a single donor in a semiconductor quantum well: A scanning tunneling spectroscopy study"

            Physica E-low-dimensional Systems & Nanostructures 40 (5)1418-1420 (2008).

 

            ABSTRACT: Low-temperature scanning tunneling spectroscopy under ultrahigh vacuum was used to investigate an In0.53Ga0.47As surface quantum well (QW) grown by molecular beam epitaxy. The electronic local density of states (LDOS) was probed with nanometer-scale resolution around native point defects located at the QW surface. In LDOS spectra acquired in the vicinity of a single point defect, a sharp peak was observed near each subband minimum, which indicates the formation of donor bound states. The LDOS peak intensity was measured as a function of distance from the point defect in order to estimate the Bohr radius of the donor bound states. (c) 2007 Elsevier B.V. All rights reserved.

 

97.    S. Perraud, K. Kanisawa, Z. Z. Wang, and T. Fujisawa

            "Direct measurement of the binding energy and bohr radius of a single hydrogenic defect in a semiconductor quantum well"

            Physical Review Letters 100 (5), 056806 (2008).

 

            ABSTRACT: Low-temperature scanning tunneling spectroscopy under ultrahigh vacuum was used to study donor point defects located at the epitaxial surface of an In0.53Ga0.47As quantum well. The electronic local density of states was measured with nanoscale resolution in the vicinity of single defects. In this way, both the binding energy and the Bohr radius of the defects could be determined. The binding energy and the Bohr radius were found to be functions of the quantum well thickness, in quantitative agreement with variational calculations of hydrogenic impurity states.

 

98.    T. Picot, A. Lupascu, S. Saito, C. J. Harmans, and J. E. Mooij

            "Role of relaxation in the quantum measurement of a superconducting qubit using a nonlinear oscillator"

            Physical Review B 78 (13), 132508 (2008).

 

            ABSTRACT: We analyze the relaxation of a superconducting flux qubit during measurement. The qubit state is measured with a nonlinear oscillator driven across the threshold of bifurcation, acting as a switching dispersive detector. This readout scheme is of quantum nondemolition type. Two successive readouts are used to analyze the evolution of the qubit and the detector during the measurement. We introduce a simple transition rate model for characterizing the qubit relaxation and the detector switching process. Corrected for qubit relaxation the readout fidelity is at least 95%. Qubit relaxation strongly depends on the driving strength and the state of the oscillator.

 

99.    M. Pioro-Ladriere, T. Obata, Y. Tokura, Y. S. Shin, T. Kubo, K. Yoshida, T. Taniyama, and S. Tarucha

            "Selective Manipulation of Electron Spins with Electric Fields"

            Progress Of Theoretical Physics Supplement (176)322-340 (2008).

 

            ABSTRACT: We develop a micro-magnet technique to manipulate single electron spins electrically with a large potential for scalability. We demonstrate that the technique works by rotating independently two electron spins in a double quantum dot circuit integrating a micrometersize ferromagnet. We find that it is the stray magnetic field of the micro-magnet that enables the electrical control and spin selectivity. Based on these results, we propose a scalable architecture for quantum information processing with electron spins using a tailored split micro-magnet geometry.

 

100.    M. Pioro-Ladriere, T. Obata, Y. Tokura, Y. S. Shin, T. Kubo, K. Yoshida, T. Taniyama, and S. Tarucha

            "Electrically driven single-electron spin resonance in a slanting Zeeman field"

            Nature Physics 4 (10)776-779 (2008).

 

            ABSTRACT: The rapid rise of spintronics and quantum information science has led to a strong interest in developing the ability to coherently manipulate electron spins(1). Electron spin resonance(2) is a powerful technique for manipulating spins that is commonly achieved by applying an oscillating magnetic field. However, the technique has proven very challenging when addressing individual spins(3-5). In contrast, by mixing the spin and charge degrees of freedom in a controlled way through engineered non-uniform magnetic fields, electron spin can be manipulated electrically without the need of high-frequency magnetic fields(6,7). Here we report experiments in which electrically driven addressable spin rotations on two individual electrons were realized by integrating a micrometre-size ferromagnet into a double-quantum-dot device. We find that it is the stray magnetic field of the micromagnet that enables the electrical control and spin selectivity. The results suggest that our approach can be tailored to multidot architecture and therefore could open an avenue towards manipulating electron spins electrically in a scalable way.

 

101.    V. T. Renard, O. A. Tkachenko, V. A. Tkachenko, T. Ota, N. Kumada, J. C. Portal, and Y. Hirayama

            "Boundary-mediated electron-electron interactions in quantum point contacts"

            Physical Review Letters 100 (18), 186801 (2008).

 

            ABSTRACT: An unusual increase of the conductance with temperature is observed in clean quantum point contacts for conductances larger than 2(e(2)/h). At the same time, a positive magnetoresistance arises at high temperatures. A model accounting for electron-electron interactions mediated by boundaries (scattering on Friedel oscillations) qualitatively describes the observation. It is supported by a numerical simulation at zero magnetic field.

 

102.    V. T. Renard, O. A. Tkachenko, V. A. Tkachenko, T. Ota, N. Kumada, J. C. Portal, and Y. Hirayama

            "Electron-electron interactions in clean quantum point contacts in the large conductance regime"

            Physica E-low-dimensional Systems & Nanostructures 40 (5)1684-1686 (2008).

 

            ABSTRACT: We report an unusual increase with temperature of the conductance of clean quantum point contact at large conductance and B = 0 T. Numerical simulation including electron-electrons interactions qualitatively explains this observation. Besides, a positive magneto-resistance that could also be related to electron-electron interactions is measured. (c) 2007 Elsevier B.V. All rights reserved.

 

103.    S. Sasaki, H. Tamura, S. Miyashita, T. Maruyama, T. Akazaki, Y. Hirayama, and H. Takayanagi

            "Interplay between electrostatic and tunnel couplings in an independently contacted double quantum dot-quantum wire coupled device"

            Physica E-low-dimensional Systems & Nanostructures 40 (5)1292-1294 (2008).

 

            ABSTRACT: We have studied low temperature transport characteristics of an independently contacted double quantum dot-quantum wire coupled system. Each quantum dot is connected to three leads; source, drain and wire. Fano resonances associated with one dot appear in the conductance of the other dot, which are gradually suppressed as the inter-dot tunnel coupling via the wire is reduced. When the dot-wire tunnel coupling is lost, conductance modulation similar to the Fano, resonances reappear, which is ascribed to purely inter-dot electrostatic coupling effect. (C) 2007 Elsevier B.V. All rights reserved.

 

104.    H. Sato

            "Thickness dependence of superconductivity and resistivity in La1.85Sr0.15CuO4 films"

            Physica C-superconductivity And Its Applications 468 (13)991-995 (2008).

 

            ABSTRACT: The temperature dependence of resistivity was measured for (001), (100) and (110)-oriented La1.85Sr0.15Cu4 (LSCO) thin films with thickness between 1 and 90 nm on LaSrAlO4 (LSAO) substrates. As thickness increases, superconductivity appears for (001) films at 3 nm, whereas it appears for (100) and (110) films at 23 nm. The difference is explained by compressive strain in the c-axis direction for (100) and (110) films caused by a smaller c-axis length in LSAO than in LSCO. It is suggested that small lengths of Cu-O bonds perpendicular to CuO2 planes degrade superconductivity in this system. (c) 2008 Elsevier B.V. All rights reserved.

 

105.    T. Sato, T. Okino, K. Yamanouchi, A. Yagishita, F. Kannari, K. Yamakawa, K. Midorikawa, H. Nakano, M. Yabashi, M. Nagasono, and T. Ishikawa

            "Dissociative two-photon ionization of N-2 in extreme ultraviolet by intense self-amplified spontaneous emission free electron laser light"

            Applied Physics Letters 92 (15), 154103 (2008).

 

            ABSTRACT: Dissociative multiple ionization processes of N-2 were investigated by irradiating N-2 with an intense extreme ultraviolet (XUV) light at 50.3 nm generated by a compact self amplified spontaneous emission free electron laser light source. From the analysis of the momentum distribution of N+ ejected through the Coulomb explosion of N-2 and by the single-shot correlation between the yields of N-2(+) and N+, it was confirmed that double ionization of N-2 occurred by the two-photon absorption of the XUV light. (C) 2008 American Institute of Physics.

 

106.    H. Shibata, T. Maruyama, T. Akazaki, H. Takesue, T. Honjo, and Y. Tokura

            "Photon detection and fabrication of MgB2 nanowire"

            Physica C-superconductivity And Its Applications 468 (15-20)1992-1994 (2008).

 

            ABSTRACT: We report the fabrication of MgB2 nanowire and its optical response. A 10-nm-thick MgB2 thin film with the superconducting transition temperature T-c = 21 K was synthesized by using molecular-beam epitaxy. The film was processed into a nanowire with a width of 300 nm and a length of 10 pm using e-beam lithography and Ar-ion milling. With a dc bias current applied close to the critical current (I-c), the nanowire showed an electrical signal when illuminated by a laser pulse at the telecommunications wavelength. (C) 2008 Elsevier B.V. All rights reserved.

 

107.    Y. Shinozaki, A. M. Siitonen, K. Sumitomo, K. Furukawa, and K. Torimitsu

            "Effect of Ca2+ on vesicle fusion on solid surface: An in vitro model of protein-accelerated vesicle fusion"

            Japanese Journal Of Applied Physics 47 (7)6164-6167 (2008).

 

            ABSTRACT: Lipid Vesicle fusion is an important reaction in the cell. Calcium ions (Ca2+) participate in various important biological events including the fusion of vesicles with cell membranes in cells. We studied the effect of Ca2+ on the fusion of ego yolk phosphatidylcholine/brain phosphatidylserine (eggPC/brainPS) lipid vesicles on a mica substrate with fast scanning atomic force microscopy (AFM). When unattached and unfused lipid vesicles on mica were rinsed away, discrete patches of fused vesicles were observed under high Ca2+ concentrations. At 0 mM Ca2+, lipid vesicles were fused on mica and formed Continuous Supported lipid bilayers (SLBs) covering almost the entire mica surface. The effect of Ca2+ on SLB fort-nation was offset by a Ca2+ chelating agent. When lipid vesicles were added during AFM observation, vesicles fused oil mica and covered almost all areas even under high Ca2+ concentrations. These results indicate that force between AFM tip and vesicles overcomes the Ca2+-reduced fusion of lipid vesicles.

 

108.    A. Shinya, S. Matsuo, Yosia, T. Tanabe, E. Kuramochi, T. Sato, T. Kakitsuka, and M. Notomi

            "All-optical on-chip bit memory based on ultra high Q InGaAsP photonic crystal"

            Optics Express 16 (23)19382-19387 (2008).

 

            ABSTRACT: We demonstrate all-optical bit memory operation with photonic crystal (PhC) nanocavities based on an InGaAsP substrate with a band gap at a wavelength of about 1.3 mu m. The optical bistability is based on a refractive index modulation caused by carrier-plasma dispersion. The operating energy required for switching is only 30 fJ, and the minimum optical bias power for bistability is 40 mu W, which is about one hundred times less than that required for laser based bistable memories. (C) 2008 Optical Society of America

 

109.    K. Shoda, H. Kohno, Y. Kobayashi, D. Takagi, and S. Takeda

            "Feasibility study for sidewall fluorination of SWCNTs in CF4 plasma"

            Journal Of Applied Physics 104 (11), 113529 (2008).

 

            ABSTRACT: Fluorination of single-wall carbon nanotubes (SWCNTs) was performed by using the CF4 radio-frequency plasma technique. The structural and bonding properties of the plasma- processed SWCNTs were investigated by transmission electron microscopy, x-ray photoelectron spectroscopy, and Raman spectroscopy. The plasma parameters, i.e., self-biased voltage, plasma ion density, and ion dose, substantially affected the structural and bonding properties of plasma- processed SWCNTs. We show that sidewall fluorination of SWCNTs occurs in CF4 plasma at low self-biased voltages. Plasma conditions for the sidewall fluorination of SWCNTs are discussed. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3040700]

 

110.    A. M. Siitonen, K. Sumitomo, C. S. Ramanujan, Y. Shinozaki, N. Kasai, K. Furukawa, J. F. Ryan, and K. Torimitsu

            "Elastic modulus of suspended purple membrane measured by atomic force microscopy"

            Applied Surface Science 254 (23)7877-7880 (2008).

 

            ABSTRACT: We have probed the mechanical properties of purple membrane (PM) in a physiological environment using the atomic force microscope (AFM). By suspending PM over nano-trenches, the elastic properties of PM can be evaluated free from the interaction with the substrate. Force-displacement curves were obtained on the suspended membrane and the data was compared to that of a simple model of a thin film over a trench. By fitting the data to the model, the elastic modulus of PM was estimated to be 8 MPa. When the membrane is repeatedly indented, we observed a change in the force-distance data consistent with damage to the two-dimensional crystal of PM. In this paper we demonstrate that the AFM allows us to evaluate the mechanics of biological membranes in their native conditions. (C) 2008 Elsevier B.V. All rights reserved.

 

111.    I. Suemune, T. Akazaki, K. Tanaka, M. Jo, K. Uesugi, M. Endo, H. Kumano, and E. Hanamura

            "Role of Cooper pairs for the generation of entangled photon pairs from single quantum dots"

            Microelectronics Journal 39 (3-4)344-347 (2008).

 

            ABSTRACT: Generation of entangled photon pairs from semiconductor quantum dots (QDs) is highly desirable for realizing practical solid-state photon sources for quantum information processing and quantum cryptography. However, the energy splitting of exciton states in QDs almost prevent the generation of entangled photon pairs. This paper discusses the new possibility with the injection of electron as well as hole Cooper pairs into QDs. (C) 2007 Published by Elsevier Ltd.

 

112.    K. Suzuki, K. Kanisawa, S. Perraud, and T. Fujisawa

            "Spatial imaging of valence band electronic structures in a GaSb/InAs quantum well"

            Applied Surface Science 254 (23)7889-7892 (2008).

 

            ABSTRACT: We measure local density of states (LDOS) for GaSb/InAs heterostructures with quantum wells in the valence band by scanning tunneling spectroscopy (STS) on the cleaved surface. Clear standingwave patterns of LDOS corresponding to the holes confined in the quantum wells are observed. (C) 2008 Elsevier B.V. All rights reserved.

 

113.    S. Suzuki, J. I. Hashimoto, T. Ogino, and Y. Kobayashi

            "Electric property control of carbon nanotubes by defects"

            Japanese Journal Of Applied Physics 47 (4)3292-3295 (2008).

 

            ABSTRACT: Effects of local low-energy irradiation on the electric properties of metallic single-walled carbon nanotubes were studied. Defects formed by 20 keV-electron irradiation in an electron beam lithography system converted the room-temperature electric properties to p-type or ambipolar semiconducting. Coulomb oscillation was also observed at room temperature. The results also suggest that electric measurements are inconclusive for distinguishing whether a nanotube is metallic or semiconducting.

 

114.    S. Suzuki, and Y. Kobayashi

            "Threshold energy of low-energy irradiation damage in single-walled carbon nanotubes"

            Japanese Journal Of Applied Physics 47 (4)2040-2043 (2008).

 

            ABSTRACT: Low-energy electron and photon irradiation cause damage in single-walled carbon nanotubes. In this work, irradiation effects of photons (hv < 20eV) in an ultra-high vacuum were systematically studied. The threshold energy of the low-energy irradiation damage was evaluated to be about 6 eV. Less damage was observed at 8 eV, which seems to be due to a small optical absorption coefficient at that energy.

 

115.    I. Sychugov, H. Omi, and Y. Kobayashi

            "On the role of substrate in light-harvesting experiments"

            Optics Letters 33 (16)1807-1809 (2008).

 

            ABSTRACT: An analysis of the emitted light distribution for a single emitter located at the planar interface of two optical media was performed. The interface of a varying refractive index substrate with air was considered, which is a common case in luminescence microscopy (spectroscopy) experiments. A modification of the radiative recombination rate induced by the variation of the substrate together with the emitted radiation spatial redistribution were taken into account. Simulation results show that the collection efficiency of the emitted light can vary several times depending on the substrate choice and the emitter intrinsic quantum efficiency. (C) 2008 Optical Society of America.

 

116.    I. Sychugov, H. Omi, T. Murashita, and Y. Kobayashi

            "Modeling tip performance for combined STM-luminescence and aperture-SNOM scanning probe: Spatial resolution and collection efficiency"

            Applied Surface Science 254 (23)7861-7863 (2008).

 

            ABSTRACT: Finite-element simulations of the performance of the tip intended for use in combined aperture-SNOM and the scanning tunneling microscope (STM)-luminescence microscopy are presented. Tip geometry and the role of the opening in the protective metal coating were addressed. It is shown that the tip shape can affect transmittance for the excitation SNOM mode by nearly two orders of magnitude and the metal coating can enhance collection efficiency for the STM-luminescence mode. Desired tip configuration can be chosen based on the interplay between the improving collection efficiency and the deteriorating spatial resolution with increasing opening size. (C) 2008 Elsevier B.V. All rights reserved.

 

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

            "Mechanism of gold-catalyzed carbon material growth"

            Nano Letters 8 (3)832-835 (2008).

 

            ABSTRACT: We demonstrate that nanosized Au particles have carbon solubility. Au-catalyzed carbon material growth by chemical vapor deposition undergoes a structural change, either a carbon nanowire or a single-walled carbon nanotube, depending on the catalyst particle size. This carbon material growth from Au is derived by the formation of Au - C eutectic nianosized alloy.

 

118.    H. Takesue

            "Erasing Distinguishability Using Quantum Frequency Up-Conversion"

            Physical Review Letters 101 (17), 173901 (2008).

 

            ABSTRACT: The frequency distinguishability of two single photons was successfully erased using single photon frequency up-conversion. A frequency nondegenerate photon pair generated via spontaneous four-wave mixing in a dispersion shifted fiber was used to emulate two telecom-band single photons that were in the same temporal mode but in different frequency modes. The frequencies of these photons were converted to the same frequency by using the sum-frequency generation process in periodically poled lithium niobate waveguides, while maintaining their temporal indistinguishability. As a result, the two converted photons exhibited a nonclassical dip in a Hong-Ou-Mandel quantum interference experiment. The present scheme will add flexibility to networking quantum information systems that use photons with various wavelengths.

 

119.    H. Takesue, H. Fukuda, T. Tsuchizawa, T. Watanabe, K. Yamada, Y. Tokura, and S. I. Itabashi

            "Generation of polarization entangled photon pairs using silicon wire waveguide"

            Optics Express 16 (8)5721-5727 (2008).

 

            ABSTRACT: We report the experimental generation of polarization entangled photon pairs based on spontaneous four-wave mixing in a silicon waveguide. Using a nano-scale silicon wire waveguide placed in a fiber loop, we obtained 1.5-mu m band polarization entanglement with two-photon interference visibilities of >83%. (C) 2008 Optical Society of America.

 

120.    A. Tallaire, M. Kasu, and K. Ueda

            "Thick diamond layers angled by polishing to reveal defect and impurity depth profiles"

            Diamond And Related Materials 17 (4-5)506-510 (2008).

 

            ABSTRACT: Diamond layers were grown top a thickness of 25 to 35 mu m either on type-Ib synthetic or type-IIa natural diamond substrates by using high or low microwave-power densities. To evaluate defects and impurities depth profiles, the samples were angled by polishing and characterized by cathodoluminescence. The first important finding is that boron, nitrogen and structural defects seem to be concentrated in a 7-10-mu m-thick region near the substrate/layer interface, as evidenced by strong defect or impurity-related luminescences and a weak free-exciton peak. The diamond quality is thus much improved in the bulk or near the surface, especially when high microwave-power densities are used, due to the inhibition of unepitaxial crystals formation. The second important finding is that using type-IIa natural substrates, which contain extremely low levels of impurities, results in a strong decrease in the amount of boron and the intensity of the nitrogen-related peak both in the bulk and at the interface of the CVD layer. These results suggest that most impurities in our CVD layers could originate from the substrate itself (C) 2008 Elsevier B.V. All rights reserved.

 

121.    A. Tallaire, M. Kasu, K. Ueda, and I. Makimoto

            "Origin of growth defects in CVD diamond epitaxial films"

            Diamond And Related Materials 17 (1)60-65 (2008).

 

            ABSTRACT: Three types of growth defects commonly found epitaxial diamond films grown by chemical vapour deposition (CVD), namely unepitaxial crystals (UCs), hillocks with flat top (FHs) and pyramidal hillocks (PHs), were etched using hydrogen/oxygcn plasma to discuss their origin. UCs formed at random locations on the grown layer without any apparent relation with the substrate. Their nucleation might be due to contaminants and their development controlled by the growth conditions in the plasma. In contrast, dislocations formed from impurities segregated at the interface between the substrate and the CVD layer, were found to be the origin of the FHs and the PHs. A simple crystal model that involves micro-faceting or twinning at an intrinsic stacking fault originating from the dislocation core is proposed to explain the formation and the evolution of the growth defects. (C) 2007 Elsevier B.V. All rights reserved.

 

122.    K. Tamaki

            "Unconditionally secure quantum key distribution with relatively strong signal pulse"

            Physical Review A 77 (3), 032341 (2008).

 

            ABSTRACT: We propose an unconditionally secure quantum key distribution protocol, which uses a relatively strong signal pulse. While our protocol shares similar security bases as the Bennett 1992 protocol with a strong reference pulse, our scheme uses a smaller number of detectors and it is robust against Rayleigh scattering in an optical fiber. We derive a lower bound of secret key generation rate of our protocol and show that our protocol can cover relatively long distances, assuming precise phase modulations and stable interferometers.

 

123.    T. Tanabe, H. Taniyama, and M. Notomi

            "Carrier diffusion and recombination in photonic crystal nanocavity optical switches"

            Journal Of Lightwave Technology 26 (9-12)1396-1403 (2008).

 

            ABSTRACT: Carrier dynamics in silicon photonic crystal (PhC) nanocavities are studied numerically. The results agree well with previous experimental demonstrations. It is shown that the presence of carrier diffusion makes fast switching possible, which is an advantage of nanocavity switches over other types of larger carrier based nonlinear optical switches. In particular, diffusion is effective in PhC nanocavity switches, which makes the switching recovery time even faster than that of silicon waveguide-based optical switches. In addition, calculations suggest that the thermo-optic effect can be reduced if the carriers are extracted within a few 100 ps by introducing a p-i-n structure.

 

124.    H. Taniyama, M. Notomi, E. Kuramochi, T. Yamamoto, Y. Yoshikawa, Y. Torii, and T. Kuga

            "Strong radiation force induced in two-dimensional photonic crystal slab cavities"

            Physical Review B 78 (16), 165129 (2008).

 

            ABSTRACT: Radiation force induced by an electromagnetic field stored in a two-dimensional photonic crystal slab is examined. We considered two different types of photonic crystal cavities, namely, double-layer slab cavity structures and air-slot cavity structures. With double-layer structures, induced force is attractive or repulsive depending on the spatial symmetry of the stored electromagnetic field profile. For air-slot structures, we showed that a horizontal attractive force is induced between slabs, and it could be stronger than that for double-layer structures in the case considered here. The induced force on a photonic crystal slab is so strong that it can be detected experimentally with the microelectromechanical systems technique. A simple physical model based on a coupled-resonator well describes these results.

 

125.    H. Taniyamaa, and M. Notomi

            "S-matrix calculation of radiation characteristics from dipole oscillation in two-dimensional photonic crystal slabs"

            Journal Of Applied Physics 103 (8), 083115 (2008).

 

            ABSTRACT: The effects of the photonic band structure on the radiation from a dipole moment placed within photonic crystal (PC) slabs are investigated. Radiation above the slab surface and coupling with the slab's propagating mode are calculated for frequencies above and below the light line of air cladding. The strongly enhanced emission from the surface and coupling with propagating modes and its polarization vector dependence are explained in terms of the photonic band of the PC slab structures. The emitted electromagnetic field is mainly extracted through coupling with the leaky modes of PC slabs. (C) 2008 American Institute of Physics.

 

126.    Y. Taniyasu, and M. Kasu

            "Aluminum nitride deep-ultraviolet light-emitting p-n junction diodes"

            Diamond And Related Materials 17 (7-10)1273-1277 (2008).

 

            ABSTRACT: This paper reviews our work on aluminum nitride (AlN) p-n junction light-emitting diodes (LEDs). N-type AlN was obtained by Si doping, By reducing dislocation density in n-type Si-doped AlN, we achieved a room-temperature electron mobility of 426 cm(2) V-1 s(-1). We analyzed the temperature dependence of the electron mobility and how the electron mobility is limited by specific scattering mechanisms. p-type AlN was obtained by Mg doping and its acceptor ionization energy was estimated to be 630 meV. We fabricated AlN p-n junction LEDs and observed electroluminescence (EL) with a wavelength of approximately 210 nm, the shortest wavelength ever observed among semiconductors. The EL was assigned to the near-band-edge emission of AlN. (C) 2008 Elsevier B.V. All rights reserved.

 

127.    K. Tateno, G. Q. Zhang, and H. Nakano

            "Growth of GaInAs/AlInAs Heterostructure Nanowires for Long-Wavelength Photon Emission"

            Nano Letters 8 (11)3645-3650 (2008).

 

            ABSTRACT: We investigated the growth of GaInAs/AlInAs heterostructure nanowires on InP(111)B and Si(111) substrates in a metalorganic vapor phase epitaxy reactor. Au colloids were used to deposit Au catalysts 20 and 40 nm in diameter on the substrate surfaces. We obtained vertical GaInAs and AlInAs nanowires on InP(111)B surfaces. The GaInAs nanowires capped with GaAs/AlInAs layers show room-temperature photoluminescence. The peak exhibits a blue-shift when the Ga content in the core GaInAs nanowire is increased. For the GaInAs/AlInAs heterostructure growth, it is possible to change the Ga content sharply but Al also exists in the GaInAs layer regions. We also found that the ratios of Ga and Al contents to In content tend to increase and the axial growth rate to decrease along the nanowire toward the top. We were also able to make vertical GaInAs nanowires on Si(111) surfaces after a short growth of GaP and InP.

 

128.    K. Tateno, G. Zhang, and H. Nakano

            "InP nanostructures formed in GaP-based nanowires grown on Si(111) substrates"

            Journal Of Crystal Growth 310 (12)2966-2969 (2008).

 

            ABSTRACT: Two types of InP growth in GaP-based nanowires have been reported. The nanowires were grown by the vapor-liquid-solid method using An particles of around 20-nm diameter as catalysts. For GaP/InP/GaP nanowire growth, InP egg-like structures were formed when the InP growth temperature was higher than the GaP growth one. Successively, the second GaP nanowire could be grown on these InP structures. Transmission electron microscopy and energy dispersive X-ray spectroscopy analyses indicated that these InP nanostructures were grown in both the axial and radial directions and that the edge of the first GaP nanowires was partly covered with InP, which formed a core-shell structure. For InP capping growth, which was performed after the growth of two-times-alternated GaP/GaAs on GaP nanowires, selective InP growth on the two GaAs parts was confirmed. (c) 2008 Elsevier B.V. All rights reserved.

 

129.    T. Tawara, H. Kamada, Y. H. Zhang, T. Tanabe, N. I. Cade, D. Ding, S. R. Johnson, H. Gotoh, E. Kuramochi, M. Notomi, and T. Sogawa

            "Quality factor control and lasing characteristics of InAs/InGaAs quantum dots embedded in photonic-crystal nanocavities"

            Optics Express 16 (8)5199-5205 (2008).

 

            ABSTRACT: We demonstrate lasing action with a high spontaneous emission factor and temperature insensitivity in InAs/InGaAs quantum dots (QD) embedded in photonic crystal nanocavities. A quality factor (Q) of over 10,000 was achieved by suppressing the material absorption by QDs uncoupled to the cavity mode. High Q cavities exhibited ultra low threshold lasing with a spontaneous emission factor of 0.7. Less frequent carrier escape from the QDs, which was primarily favored by high potential barrier energy, enabled low threshold lasing up to 90 K. (C) 2008 Optical Society of America.

 

130.    L. Tiemann, J. G. Lok, W. Dietsche, K. von Klitzing, K. Muraki, D. Schuh, and W. Wegscheider

            "Investigating the transport properties of the excitonic state in quasi-Corbino electron bilayers"

            Physica E-low-dimensional Systems & Nanostructures 40 (5)1034-1037 (2008).

 

            ABSTRACT: We investigate two closely spaced 2D electron systems in a quasi-Corbino geometry with independent contacts to both layers. Magneto-transport and drag experiments show that at the systems total filling factor 1 the drive current diminishes with increasing interlayer interaction (parameterized by the ratio of layer separation and magnetic length) while voltages of equal magnitude build up over both the drive and the drag layer. The identity of both voltages is resilient to thermal perturbations which contrasts markedly to the behavior observed in Hall bars. (C) 2007 Elsevier B.V. All rights reserved.

 

131.    L. Tiemann, J. G. Lok, W. Dietsche, K. von Klitzing, K. Muraki, D. Schuh, and W. Wegscheider

            "Exciton condensate at a total filling factor of one in Corbino two-dimensional electron bilayers"

            Physical Review B 77 (3), 033306 (2008).

 

            ABSTRACT: Magnetotransport and drag measurements on a quasi-Corbino two-dimensional electron bilayer at a total filling factor of 1 (nu(T)=1) reveal a drag voltage that is equal in magnitude to the drive voltage as soon as the two layers begin to form the expected nu(T)=1 exciton condensate. The identity of both voltages remains present even at elevated temperatures of 0.25 K. The conductance of the drive layer vanishes only in the limit of strong coupling between the two layers and at T -> 0 K which suggests the presence of an excitonic circular current.

 

132.    A. Tokura, F. Maeda, Y. Teraoka, A. Yoshigoe, D. Takagi, Y. Homma, Y. Watanabe, and Y. Kobayashi

            "Hydrogen adsorption on single-walled carbon nanotubes studied by core-level photoelectron spectroscopy and Raman spectroscopy"

            Carbon 46 (14)1903-1908 (2008).

 

            ABSTRACT: We have investigated the adsorption of atomic hydrogen on vertically aligned carbon nanotube (CNT) films using in situ synchrotron-radiation-based core-level (CL) photoelectron spectroscopy and Raman spectroscopy. From C 1s CL spectra, we identified a CL peak component due to C-H bonds of carbon atoms in single-walled carbon nanotubes (SWCNTs). We also found the suppression of pi-plasmon excitation, indicating that the hydrogen adsorption deforms the bonding structure. Raman spectra of the SWCNT film indicated that the radial-breathing-mode intensities of SWCNTs decreased due to the adsorption-induced bonding-structure deformation. Moreover, the decrease for small-diameter SWCNTs was more severe than that for large-diameter SWCNTs. Our results strongly suggest that the hydrogen adsorption, which induces the structure deformation from sp(2) to sp(3)-like bonding, depends on the diameter of SWCNTs. (C) 2008 Elsevier Ltd. All rights reserved.

 

133.    Y. Tokura, T. Kubo, S. Amaha, T. Kodera, and S. Tarucha

            "Phonon induced coherence in multi-level quantum dot system"

            Physica E-low-dimensional Systems & Nanostructures 40 (5)1690-1692 (2008).

 

            ABSTRACT: The effect of electron-phonon scattering is studied for the resonant tunneling processes through series double quantum dots. When one of the dots facilitates multiple quantum levels within the transport window, the electron-phonon scattering process in this dot affects the resonant current. In most cases, inelastic processes predominates but phonon induced coherent process is shown to be possible under certain conditions. We find that inter-dot resonance can be strongly modified by this phonon-induced coherent process, and propose it as one of the origins for the peculiar magnetic field dependence of the resonant current peaks, observed in the experiments of the vertical quantum dots. (c) 2007 Elsevier B.V. All rights reserved.

 

134.    K. Tsubaki, and H. Yamaguchi

            "Magnetic field induced by the carbon nanotubes current by magnetic force microscopy"

            Physica E-low-dimensional Systems & Nanostructures 40 (6)2220-2221 (2008).

 

            ABSTRACT: Recently carbon nanotubes (CNTs) are reported to be able to generate large magnetic field because of their nanometer-size-diameter [K. Tsubaki, H. Yamaguchi, J. Phys. C 38 (2006) 49]. The magnetic fields around CNTs current path are investigated by magnetic force microscopy (MFM). Under the consideration of the magnetic properties of magnetically coated tip of MFM, tip heights, current directions, and background magnetic field, etc., the magnetic field distribution are analyzed. The distribution of the magnetic field generated by the CNTs current is found to be asymmetric, and its distribution anomaly is found to be a kind of hysteresis effect of the MFM cantilever materials. (C) 2007 Elsevier B.V. All rights reserved.

 

135.    T. Tsurumaru, and K. Tamaki

            "Security proof for quantum-key-distribution systems with threshold detectors"

            Physical Review A 78 (3), 032302 (2008).

 

            ABSTRACT: In this paper, we rigorously prove the intuition that in security proofs for the Bennett-Brassard 1984 (BB84) protocol, one may regard an incoming signal to Bob as a qubit state. From this result, it follows that all security proofs for BB84 protocol based on a virtual qubit entanglement distillation protocol, which was originally proposed by Lo and Chau [Science 283, 2050 (1999)] and by Shor and Preskill [Phys. Rev. Lett. 85, 441 (2000)], are all valid even if Bob's actual apparatus cannot distill a qubit state explicitly. As a consequence, especially, the well-known result that a higher bit error rate of 20% can be tolerated for BB84 protocol by using two-way classical communications is still valid even when Bob uses threshold detectors. Using the same technique, we also prove the security of Bennett-Brassard-Mermin 1992 (BBM92) protocol where Alice and Bob both use threshold detectors.

 

136.    T. Uchida, M. Tazawa, H. Sakai, A. Yamazaki, and Y. Kobayashi

            "Radial breathing modes of single-walled carbon nanotubes in resonance Raman spectra at high temperature and their chiral index assignment"

            Applied Surface Science 254 (23)7591-7595 (2008).

 

            ABSTRACT: Radial breathing modes (RBMs) in resonance Raman spectra from single-walled carbon nanotubes (SWCNTs) on a SiO2/Si (0 0 1) substrate are studied between 25 and 720 degrees C. A change in the relative intensity of each RBM peak with temperature is observed, which originates from the temperature dependence of the resonance condition of nanotubes. For 25 degrees C, each RBM peak is reasonably assigned on the basis of data in the literature [J. Maultzsch, H. Telg, S. Reich, F. Hennrich, C. Thomsen, Phys. Rev. B 72 (2005) 205438]. By taking into account the temperature-dependent behavior of the relative intensity of the RBM peaks, each RBM peak is successfully assigned even for 720 degrees C. It is found that most of the observed RBM peaks for a laser excitation energy of E-exc = 1.96 eV are from chiral SWCNTs. These results make it possible to discuss further details of the chirality-dependent growth behavior observed for in situ Raman spectroscopy. (c) 2008 Elsevier B.V. All rights reserved.

 

137.    K. Ueda, and A. Kasu

            "High-pressure and high-temperature annealing of diamond ion-implanted with various elements"

            Diamond And Related Materials 17 (7-10)1269-1272 (2008).

 

            ABSTRACT: We tried to dope various ions (B, Al, Ga, Mg, and Be) into diamond films by combining ion-implantation and high-pressure and high-temperature annealing. In cathodoluminescence spectra of Be-implanted films, previously unreported emissions appeared at 4.843, 4.687, 4.533 eV. These emissions were only observed from Be-implanted films, and they were not observed from B, Al, Ga, and Mg-implanted ones. The 4.843-eV line is assigned to zero phonon line, and the 4.687- and 4.533-eV lines are its phonon replicas because the energy difference between each peak is close to the optical phonon energy of diamond (similar to 0.15 eV). The temperature dependence of the 4.843-eV line is similar to that of bound excitons. (C) 2008 Elsevier B.V. All rights reserved.

 

138.    K. Ueda, and M. Kasu

            "High-pressure and high-temperature annealing effects of boron-implanted diamond"

            Diamond And Related Materials 17 (4-5)502-505 (2008).

 

            ABSTRACT: We show that high-pressure and high-temperature (HPHT) annealing of ion-implanted diamond is efficient as a doping technique. The HPHT annealing condition is located in the thermodynamically stable region for diamond. The HPHT annealing is highly effective for the recovery of damage induced by ion implantation. In the entire annealing temperature range, the HPHT annealing is more efficient than conventional thermal annealing methods such as vacuum annealing. At 1400 degrees C, we obtained the highest boron doping efficiency of 7.1%, which is ten times higher than that by vacuum annealing. (C) 2007 Elsevier B.V. All rights reserved.

 

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

            "Terahertz images of biological molecules: Frequency dependence of spatial resolution using a tunable terahertz laser source"

            Japanese Journal Of Applied Physics 47 (2)1315-1320 (2008).

 

            ABSTRACT: The spatial resolution of transmitted terahertz (THz) images of metal slits and protein [myoglobin (Mb)] thin films was analyzed at 1.40, 1.63, and 2.55THz by using continuous THz waves from a tunable gas laser. The resolution of the THz images of the metal slit was 0.40, 0.35, and 0.45mm at 2.55, 1.63, and 1.40THz, respectively. The spatial resolution is determined not only by the diffraction limit of the wavelength of the THz wave but also by other experimental conditions such as laser power. The resolution of the THz images of Mb thin films was 0.55 and 0.60 mm at 2.55 and 1.63 THz, respectively. The approximately twofold stronger THz wave absorption of Mb film at 2.55 THz than at 1.63 THz provides the better resolution. By using a THz wave with a frequency at which the target sample has strong absorption we can obtain a THz image with good resolution.

 

140.    Y. Ueno, and K. Ajito

            "Analytical terahertz spectroscopy"

            Analytical Sciences 24 (2)185-192 (2008).

 

            ABSTRACT: Recent progress in analytical terahertz (THz) spectroscopy is reviewed with illustrative examples showing that it is an effective method for detecting and identifying intermolecular interactions in chemical compounds, such as hydrogen bonds. The unique and characteristic properties of THz waves, their significance to both science and industry, and the bases of one of the successful fields of analytical THz spectroscopy, namely THz time-domain spectroscopy and THz imaging for chemical analysis, are described. Preliminary quantitative studies are presented to show the potential of THz spectroscopy for the detection and identification of intermolecular hydrogen bonds in unknown mixture samples. The selective detection of intramolecular hydrogen bonds and the detection of intramolecular interactions in ice are also introduced. Some brief remarks are provided on future developments, the main issues, and the prospects for analytical THz spectroscopy.

 

141.    S. Utsunomiya, L. Tian, G. Roumpos, C. W. Lai, N. Kumada, T. Fujisawa, M. Kuwata-Gonokami, A. Loffler, S. Hofling, A. Forchel, and Y. Yamamoto

            "Observation of Bogoliubov excitations in exciton-polariton condensates"

            Nature Physics 4 (9)700-705 (2008).

 

            ABSTRACT: Einstein's 1925 paper predicted the occurrence of Bose-Einstein condensation (BEC) in an ideal gas of non-interacting bosonic particles(1). However, particle-particle interaction and peculiar excitation spectra are keys for understanding BEC and superfluidity physics. A quantum field-theoretical formulation for aweakly interacting Bose condensed systemwas developed by Bogoliubov in 1947, which predicted the phonon-like excitation spectrum(2) in the low-momentum regime. The experimental verification of the Bogoliubov theory on the quantitative level was carried out for atomic BEC3 using the two-photon Bragg scattering technique(4). Exciton-polaritons in a semiconductor microcavity, which are elementary excitations created by strong coupling between quantum-well excitons and microcavity photons, were proposed as a new BEC candidate in solid-state systems(5). Recent experiments with exciton-polaritons have demonstrated several interesting signatures from the viewpoint of polariton condensation, such as quantum degeneracy at non-equilibrium conditions(6-8), the polariton-bunching effect at the condensation threshold(9), long spatial coherence(10-12) and quantum degeneracy at equilibrium conditions(13). The particle-particle interaction and the Bogoliubov excitation spectrum are at the heart of BEC and superfluidity physics, but have only been studied theoretically for exciton-polaritons(14,15). In this letter, we report the first observation of interaction effects on the exciton-polariton condensate and the excitation spectra, which are in quantitative agreement with the Bogoliubov theory.

 

142.    A. Valeille, K. Muraki, and Y. Hirayama

            "Highly reproducible fabrication of back-gated GaAs/AlGaAs heterostructures using AuGeNi ohmic contacts with initial Ni layer"

            Applied Physics Letters 92 (15), 152106 (2008).

 

            ABSTRACT: We show for back-gated GaAs/AlxGa1-xAs heterostructures that a thin Ni layer deposited prior to the standard AuGeNi Ohmic contacts dramatically improves the device yield by keeping the annealed contacts from reaching the back gate 1.2 mu m below the channel. A systematic investigation of the contact resistance and the back-gate characteristics as a function of the initial Ni layer thickness and the annealing temperature demonstrates that back-gated structures with contact resistance below 100 Omega can be obtained with a high yield of 90%. (C) 2008 American Institute of Physics.

 

143.    V. Vedral, and F. Morikoshi

            "Schrodinger's cat meets Einstein's twins: A superposition of different clock times"

            International Journal Of Theoretical Physics 47 (8)2126-2129 (2008).

 

            ABSTRACT: The phenomenon of quantum superposition, which allows a physical system to exist in different states 'simultaneously', is one of the most bizarre notions in physics. Here we illustrate an even more bizarre example of it: a superposed state of a physical system consisting of both an 'older' version and a 'younger' version of that system. This can be accomplished by exploiting the special relativistic effect of time dilation featuring in Einstein's famous twin paradox.

 

144.    M. Wagenknecht, D. Koelle, R. Kleiner, S. Graser, N. Schopohl, B. Chesca, A. Tsukada, S. T. Goennenwein, and R. Gross

            "Phase diagram of the electron-doped La2-xCexCuO4 cuprate superconductor from andreev bound states at grain boundary junctions"

            Physical Review Letters 100 (22), 227001 (2008).

 

            ABSTRACT: We use quasiparticle tunneling across La2-xCexCuO4 grain boundary junctions to probe the superconducting state and its disappearance with increasing temperature and magnetic field. A zero bias conductance peak due to zero energy surface Andreev bound states is a clear signature of the phase coherence of the superconducting state. Hence, such a peak must disappear at or below the upper critical field B-c2(T). For La2-xCexCuO4 this approach sets a lower bound for B-c2(0)approximate to 25 T which is substantially higher than reported previously. The method of probing the superconducting state via Andreev bound states should also be applicable to other cuprate superconductors.

 

145.    Y. D. Wang, K. Semba, and H. Yamaguchi

            "Cooling of a micro-mechanical resonator by the back-action of Lorentz force"

            New Journal Of Physics 10, 043015 (2008).

 

            ABSTRACT: Using a semi-classical approach, we describe an on-chip cooling protocol for a micro-mechanical resonator by employing a superconducting flux qubit. A Lorentz force, generated by the passive back-action of the resonator's displacement, can cool down the thermal motion of the mechanical resonator by applying an appropriate microwave drive to the qubit. We show that this on-chip cooling protocol, with well-controlled cooling power and a tunable response time of passive back-action, can be highly efficient. With feasible experimental parameters, the effective mode temperature of a resonator could be cooled down by several orders of magnitude.

 

146.    S. Yabuuchi, H. Kageshima, Y. Ono, M. Nagase, A. Fujiwara, and E. Ohta

            "Origin of ferromagnetism of MnSi1.7 nanoparticles in Si: First-principles calculations"

            Physical Review B 78 (4), 045307 (2008).

 

            ABSTRACT: The origin of the magnetism of MnSi1.7 nanoparticles in Si is investigated using the first-principles calculations: bulk and interface effects are considered. The bulk magnetic property is expected to be affected by stoichiometry, strain, and charge accumulation. Stoichiometry and charge accumulation induce a ferromagnetic state, and strain stabilizes the ferromagnetic state. Another factor, the MnSi1.7/Si interface formation, is seen as triggering ferromagnetism strongly localized at the interface. These two mechanisms are shown to be related to the experimentally determined hard and soft components, respectively.

 

147.    S. Yabuuchi, Y. Ono, M. Nagase, H. Kageshima, A. Fujiwara, and E. Ohta

            "Ferromagnetism of manganese-silicide nanopariticles in silicon"

            Japanese Journal Of Applied Physics 47 (6)4487-4490 (2008).

 

            ABSTRACT: The annealing-temperature (700-900 degrees C) dependence of the ferromagnetism of manganese-implanted silicon is investigated. In the annealed samples, the manganese-containing nanoparticles, whose mean size was found to get bigger with temperature, are formed and these samples show ferromagnetism. We obtain evidence that the samples annealed at 800-850 degrees C produce two kinds of ferromagnets and that one of them offers a coercivity as high as 2500 Oe, suggesting the possibility of Si-based nanostructures with stable ferromagnetism. The origin of these ferromagnetisms is also discussed in conjunction with the size distribution of the nanoparticles.

 

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

            "First-principles calculations of uniaxial strain effects on manganese in silicon"

            Japanese Journal Of Applied Physics 47 (1)26-30 (2008).

 

            ABSTRACT: Uniaxial strain effects on manganese in silicon are investigated using the first-principles calculations. Manganese doping is shown to enhance the increase rate of vertical strain as a function of lateral strain by similar to 10%. The formation energy of manganese in silicon decreases by 0.1 eV at a lateral strain of 3.3%. The magnetic moments of manganese remain at 3 mu(B) being independent of the strain magnitude. These results are found in both substitutional and interstitial tetrahedral manganese. An analysis of detailed calculation results reveals that these properties are realized by the impact of uniaxial strain on the electronic states of manganese.

 

149.    H. Yamaguchi, K. Kato, Y. Nakai, K. Onomitsu, S. Warisawa, and S. Ishihara

            "Improved resonance characteristics of GaAs beam resonators by epitaxially induced strain"

            Applied Physics Letters 92 (25), 251913 (2008).

 

            ABSTRACT: Micromechanical-beam resonators were fabricated using a strained GaAs film grown on relaxed In0.1Ga0.9As/In0.1Al0.9As buffer layers. The natural frequency of the fundamental mode was increased 2.5-4 times by applying tensile strain, showing good agreement with the model calculation assuming strain of 0.35% along the beam. In addition, the Q factor of 19 000 was obtained for the best sample, which is one order of magnitude higher than that for the unstrained resonator. This technique can be widely applied for improving the performance of resonator-based micro-/nanoelectromechanical devices. (c) 2008 American Institute of Physics.

 

150.    M. Yamaguchi, S. Nomura, T. Maruyama, S. Miyashita, Y. Hirayama, H. Tamura, and T. Akazaki

            "Evidence of a Transition from Nonlinear to Linear Screening of a Two-Dimensional Electron System Detected by Photoluminescence Spectroscopy"

            Physical Review Letters 101 (20), 207401 (2008).

 

            ABSTRACT: We clearly identify single-electron-localization (SEL), nonlinear screening (NLS), and linear screening (LS) regimes of gate induced electrons in a GaAs quantum well from photoluminescence spectra and intergate capacitance. Neutral and charged excitons observed in the SEL regime rapidly lose their oscillator strength when electron puddles are formed, which mark the onset of NLS. A further increase in the density of the electrons induces the transition from the NLS to LS, where the emission of a charged exciton changes to the recombination of two-dimensional electron gas and a hole.

 

151.    T. Yamaguchi, and H. Yamaguchi

            "Two-dimensional patterning of flexible designs with high half-pitch resolution by using block copolymer lithography"

            Advanced Materials 20 (9)1684-+ (2008).

 

            ABSTRACT: A two-dimensional patterning method that allows for flexible designs is demonstrated by combining bottom-up diblock copolymer self-assembly with top-down electron beam lithography (EBL), which increases the applicability of block copolymer lithography to nanodevice fabrication. Both bent lamellae and concentric cylinders (see figure) can be formed between the intentionally designed 2D EBL guiding patterns, and can be successfully transferred to a semiconductor substrate with a 1.6 nm half-pitch resolution.

 

152.    T. Yamaguchi, T. Tawara, H. Kamada, H. Gotoh, H. Okamoto, H. Nakano, and O. Mikami

            "Single-photon emission from single quantum dots in a hybrid pillar microcavity"

            Applied Physics Letters 92 (8), 081906 (2008).

 

            ABSTRACT: We demonstrate 1240 nm single-photon emissions from InAs quantum dots (QDs) embedded in a hybrid pillar microcavity consisting of dielectric and semiconductor distributed Bragg reflectors. The QDs are grown by metal organic chemical vapor deposition. Discrete emission lines corresponding to isolated QDs in the hybrid pillar are observed with a spontaneous emission rate enhanced by a factor of 2. Single-photon emissions are confirmed by antibunching in a second-order photon correlation function. (C) 2008 American Institute of Physics.

 

153.    K. Yamamoto, T. Ohashi, T. Tawara, H. Gotoh, A. Nakamura, and J. Temmyo

            "Photoluminescence lifetime and potential fluctuation in wurtzite Zn1-xCdxO alloy films"

            Applied Physics Letters 93 (17), 171913 (2008).

 

            ABSTRACT: Carrier recombination dynamics in wurtzite Zn1-xCdxO alloy films has been studied by time-resolved photoluminescence (PL) to evaluate the potential fluctuation. Typical PL lifetime tau(2) in Zn1-xCdxO is around 200 ps and gradually increases with a Cd content of up to 0.19. At a Cd content over 0.3, tau(2) becomes roughly 50 ns. The degree of potential fluctuation E-0 is increased from 9 to 157 meV with an increment in Cd content of 0.19. In contrast, at a Cd content over 0.3, E0 decreases to 35 meV with a Cd content of 0.55. This suggests that the potential fluctuation in Zn1-xCdxO with a high Cd content is greatly improved, which is qualitatively supported by the Zimmermann's model [R. Zimmermann, J. Cryst. Growth 101, 346 (1990)]. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3013322]

 

154.    T. Yamamoto, M. Notomi, H. Taniyama, E. Kuramochi, Y. Yoshikawa, Y. Torii, and T. Kuga

            "Design of a high-Q air-slot cavity based on a width-modulated line-defect in a photonic crystal slab"

            Optics Express 16 (18)13809-13817 (2008).

 

            ABSTRACT: We have presented a novel design of a photonic crystal slab (PCS) nanocavity, in which the electric field of the cavity mode is strongly localized in free space. The feature of the cavity is a linear air slot introduced to the center of the mode-gap confined PCS cavity. Owing to the discontinuity of the dielectric constant, the electric field of the cavity mode is strongly enhanced inside the slot, allowing strong matter-field coupling and large interaction volume in free space. Using finite-difference time-domain method, we calculate the properties of the cavity mode as a function of the slot width. The calculated quality factor is still as high as 2 x 10(5) and the mode volume is as small as 0.14 of a cubic wavelength in a vacuum, even if 200-nm-wide slot is introduced to the PCS. (c) 2008 Optical Society of America.

 

155.    K. Yamazaki, and H. Yamaguchi

            "Three-dimensional alignment with 10 nm order accuracy in electron-beam lithography on rotated sample for three-dimensional nanofabrication"

            Journal Of Vacuum Science & Technology B 26 (6)2529-2533 (2008).

 

            ABSTRACT: Three-dimensional (3D) alignment with 10 nm order accuracy in 3D electron-beam (EB) lithography has been achieved by means of highly accurate rotation control and mark location using the transmission electron signal. Accurately aligned EB writing from various directions on micron order resists blocks on a small substrate provides great structural flexibility in the creation of 3D nanostructures. As a demonstration of the accuracy, a 3D hydrogen silsesquioxane nanostructure was made by 3D EB writing and two-step development using different developers. Moreover, a 3D poly(methyl methacrylate) nanostructure was made by repeated 3D EB writing and development to demonstrate 3D nanofabrication with great structural flexibility.

 

156.    K. Yamazaki, and H. Yamaguchi

            "Flexible nanofabrication in three-dimensional electron-beam lithography enhanced by suppression of proximity effect"

            Applied Physics Express 1 (9), 097001 (2008).

 

            ABSTRACT: Nanofabrication of three-dimensional (3D) structures with a high aspect ratio has been achieved using electron-beam (EB) lithography. Although electron scattering, or the proximity effect, on the remaining parts in positive resist is generally serious for repeated EB writing from different 3D directions, we can largely avoid the effect by adding appropriate surrounding buffer regions, which are cut off by the following EB writing and development. This enables us to make a 3D nanostructure in poly(methyl methacrylate) (PMMA), which demonstrates the great structural flexibility obtainable in our EB technique. (C) 2008 The Japan Society of Applied Physics.

 

157.    T. Yamazaki, K. Kuramochi, D. Takagi, Y. Homma, F. Nishimura, N. Hori, K. Watanabe, S. Suzuki, and Y. Kobayashi

            "Ordered fullerene nanocylinders in large-diameter carbon nanotubes"

            Nanotechnology 19 (4), 045702 (2008).

 

            ABSTRACT: A new ordered fullerene phase encapsulated by large-diameter CNTs is systematically investigated by combining a growth technique by chemical vapour deposition, high-resolution transmission electron microscopy and molecular-dynamics simulations. In contrast to fullerenes in smaller (1-2 nm) diameter CNTs, where fullerenes are packed in linear or helical chains, fullerenes form a nanoscale cylinder in double-walled CNTs with diameters of similar to 4 nm. The fullerenes were shown to form a nanocylinder with a side wall that resembled the (111) plane of solid C-60. This ordered phase is different from peapods or fullerene solids known so far, and a result of the interaction between the CNT wall and fullerenes. This finding will open up a new field of fullerene science.

 

158.    G. Zhang, K. Tatenoa, T. Sogawa, and H. Nakano

            "Growth and characterization of GaP nanowires on Si substrate"

            Journal Of Applied Physics 103 (1), 014301 (2008).

 

            ABSTRACT: The integration of III-V semiconductor materials with Si technology is of great interest for optoelectronic integration circuits. We have studied the growth and structural aspects of Gal? nanowires (NWs) grown on Si substrate in a metalorganic vapor phase epitaxy system. Au colloid particles dispersed on Si substrate were used as catalysts to conduct the NW growth. The growth temperature considerably affected the growth rate and shape of Gal? NWs. The growth rate showed a maximum value of 14.69 nm/s at 480 degrees C. When growth temperature increased the radial growth on NW sides was enhanced and the NWs therefore exhibited a tapering shape. Gal? NWs with a uniform diameter could be grown at a growth temperature as low as 420 degrees C using a two-temperature process. The NW diameter could be well controlled by using size-selective Au colloid particles. The growth rate dependence showed that the thin NWs-grew more slowly than thick ones and the V/III source ratio had a significant effect on the growth rate dependence. An analysis of the GaP/Si interface by transmission electron microscopy indicated that the NWs were epitaxially grown on the Si(111) substrate. Based on these experimental results, the growth mechanism of the GaP NWs on Si was discussed. (c) 2008 American Institute of Physics.

 

159.    G. Q. Zhang, K. Tateno, T. Sogawa, and H. Nakano

            "Vertically aligned GaP/GaAs core-multishell nanowires epitaxially grown on Si substrate"

            Applied Physics Express 1 (6), 064003 (2008).

 

            ABSTRACT: We report the core-multishell GaP/GaAs/GaP nanowires grown in a metalorganic vapor phase epitaxy system by a combination of the vapor-liquid-solid growth mode and conventional vapor phase epitaxy method. By growing GaAs sacrificial segments on the core GaP nanowires followed by selective chemical etching, Au particles were removed and top faceted core-shell nanowires were formed after the shell growth. Analysis by transmission electron microscopy indicated that the shell layers were epitaxially grown on the sides of core GaP nanowires. (C) 2008 The Japan Society of Applied Physics.

 

160.    Q. Zhang, H. Takesue, S. W. Nam, C. Langrock, X. P. Xie, B. Baek, M. M. Fejer, and Y. Yamamoto

            "Distribution of Time-Energy Entanglement over 100 km fiber using superconducting single-photon detectors"

            Optics Express 16 (8)5776-5781 (2008).

 

            ABSTRACT: In this letter, we report an experimental realization of distributing entangled photon pairs over 100 km of dispersion-shifted fiber. In the experiment, we used a periodically poled lithium niobate waveguide to generate the time-energy entanglement and superconducting single-photon detectors to detect the photon pairs after 100 km. We also demonstrate that the distributed photon pairs can still be useful for quantum key distribution and other quantum communication tasks. (C) 2008 Optical Society of America.

 

161.    Q. Zhang, C. Langrock, H. Takesue, X. P. Xie, M. Fejer, and Y. Yamamoto

            "Generation of 10-GHz clock sequential time-bin entanglement"

            Optics Express 16 (5)3293-3298 (2008).

 

            ABSTRACT: This letter reports telecom-band sequential time-bin entangled photon-pair generation at a repetition rate of 10 GHz in periodically poled reverse-proton-exchange lithium niobate waveguides based on mode demultiplexing. With up-conversion single-photon detectors, we observed an entangled-photon-pair flux of 313 Hz and a two-photon-interference-fringe visibility of 85.32% without subtraction of accidental noise contributions. (c) 2008 Optical Society of America.

 

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

            "Superconducting proximity effect and reentrant behaviors in random network carbon nanotubes"

            Physica C-superconductivity And Its Applications 468 (7-10)709-713 (2008).

 

            ABSTRACT: We investigated the superconducting proximity effect in a sandwich structure of network-like carbon nanotubes coupled to NbN electrodes. The proximity effect gives rise to multiple Andreev reflection processes and enhanced magnetoconductance fluctuations that are similar to universal conductance fluctuation. Reentrant behavior caused by the proximity effect was observed. The proximity effect correction to the conductance disappears at low temperature and reaches a maximum value at about 8 K, which corresponds to Thouless energy. This reentrant behavior was also observed in the temperature dependance of fluctuation amplitude. These results are compared with theory. (c) 2008 Elsevier B.V. All rights reserved.

 

163.    N. M. Zimmerman, W. H. Huber, B. Simonds, E. Hourdakis, A. Fujiwara, Y. Ono, Y. Takahashi, H. Inokawa, M. Furlan, and M. W. Keller

            "Why the long-term charge offset drift in Si single-electron tunneling transistors is much smaller (better) than in metal-based ones: Two-level fluctuator stability"

            Journal Of Applied Physics 104 (3), 033710 (2008).

 

            ABSTRACT: A common observation in metal-based (specifically, those with AlOx tunnel junctions) single-electron tunneling (SET) devices is a time-dependent instability known as the long-term charge offset drift. This drift is not seen in Si-based devices. Our aim is to understand the difference between these, and ultimately to overcome the drift in the metal-based devices. A comprehensive set of measurements shows that (1) brief measurements over short periods of time can mask the underlying drift, (2) we have not found any reproducible technique to eliminate the drift, and (3) two-level fluctuators (TLFs) in the metal-based devices are not stable. In contrast, in the Si-based devices the charge offset drifts by less than 0.01e over many days, and the TLFs are stable. We also show charge noise measurements in a SET device over four decades of temperature. We present a model for the charge offset drift based on the observation of nonequilibrium heat evolution in glassy materials, and obtain a numerical estimate in good agreement with our charge offset drift observations. We conclude that, while the Si devices are not perfect and defect-free, the defects are stable and noninteracting; in contrast, the interacting, unstable glasslike defects in the metal-based devices are what lead to the charge offset drift. We end by suggesting some particular directions for the improvement in fabrication, and in particular, fabrication with crystalline metal-oxide barriers, that may lead to charge offset drift-free behavior. (c) 2008 American Institute of Physics.