1.    H. Aikawa, S. Takaoka, K. Oto, K. Murase, T. Saku, Y. Hirayama, S. Shimomura, and S. Hiyamizu

            "In-plane magnetic field dependence of cyclotron resonance in two-dimensional electron system"

            Physica E-low-dimensional Systems & Nanostructures 12 (1-4)578-580 (2002).

 

            ABSTRACT: The in-plane magnetic field dependence of cyclotron resonance is measured both in single and double layer 2DES. In particular. we observe that the in-plane dependence of cyclotron mass in single-layer 2DES changes with carrier density and perpendicular magnetic field in the low electron density sample, which cannot be explained by the semiclassical calculation. (C) 2002 Elsevier Science B.V. All rights reserved.

 

2.    K. Ajito, and K. Torimitsu

            "Laser trapping and Raman spectroscopy of single cellular organelles in the nanometer range"

            Lab On A Chip 2 (1)11-14 (2002).

 

            ABSTRACT: The laser trapping technique combined with near-infrared Raman (NIR) spectroscopy was used for the analysis of single cellular organelles in the nanometer range. The samples were synaptosomes, nerve-ending particles (about 500-700 nm in diameter) isolated from a neuron in a rat brain, dispersed in the phosphate buffer solution. The NIR laser Raman trapping (NIR-LRT) system trapped a single synaptosome without photochemical damage and provided a Raman spectrum of the sample with less fluorescence background. After the background subtraction from the Raman spectrum, two large peaks appeared, which are attributed to the peaks of the CH2 deformation mode and the amide I mode. This indicates the laser-trapped synaptosomes include some types of lipids and proteins. The result demonstrates that the NIR-LRT system can determine biological molecules in single cellular organelles in the nanometer range. Further improvement of the detection sensitivity will enable us to get detailed information about the functions of single cellular organelles in the brain, which will be valuable for neuroscience.

 

3.    K. Ajito, and K. Torimitsu

            "Single nanoparticle trapping using a Raman tweezers microscope"

            Applied Spectroscopy 56 (4)541-544 (2002).

 

            ABSTRACT: We have obtained a Raman spectrum of single nanometer-sized particles (nano-particles) trapped by laser tweezers for the first time. The microscope used in this study is a new version of our Raman tweezers microscope (RTM); it contains an oil-immersed objective lens with high numerical aperture to increase the force of the optical radiation pressure of the near-infrared laser beam to trap single organic and biological nanoparticles and provides sufficient sensitivity for the Raman measurement of the trapped nanoparticles. The confocal arrangement in the system completely eliminates the Raman signal of the oil under the objective lens. The RTM provides a Raman spectrum of a single poly styrene latex bead about 40 nm in diameter with an exposure time of 3 s and allows us to determine its molecular species. Furthermore, the RTM enables us to count the number of nanoparticles in the focal spot of the laser beam from the Raman spectra of trapped nanoparticles.

 

4.    A. A. Andreev, J. Limpouch, A. B. Iskakov, and H. Nakano

            "Enhancement of x-ray line emission from plasmas produced by short high-intensity laser double pulses"

            Physical Review E 65 (2), 026403 (2002).

 

            ABSTRACT: Femtosecond laser-produced plasmas are bright ultrafast line x-ray sources potentially suitable fur different applications including material science and biology. The conversion efficiency of the laser energy incident onto a solid target into the x-ray emission is significantly enhanced when a laser prepulse precedes the main pulse. The details of x-ray line emission from solid targets irradiated by a pair of ultrashort laser Pulse, are investigated both theoretically and experimentally. Insight into spatial and temporal characteristics of the line x-ray source is provided by numerical simulations and a simplified analytical model. Optimal time separation of the laser pulses is searched for in order to reach the maximum conversion of laser energy into the emission of selected x-ray lines. We deduced how the optimal pulse separation scales with laser and target parameters.

 

5.    T. Asayama, Y. Tokura, S. Miyashita, M. Stopa, and S. Tarucha

            "1D Bragg reflector in the Tomonaga-Luttinger liquid regime and Fermi liquid regimes"

            Physica E-low-dimensional Systems & Nanostructures 12 (1-4)186-189 (2002).

 

            ABSTRACT: Employing an array of shallow etched trenches aligned transverse to current flow. we have fabricated long (1-2 mum) split-gate quantum wires with weak periodic potential modulation on a GaAs/AlGaAs 2DEG wafer, thereby realizing a 1D Bragg reflector at a very low temperature. In the presence of the first and second edge states, i.e. in the Fermi liquid regime, we observe two groups of conductance dips due to the spin-separate reflection resonances. On the other hand, in the weak magnetic field range. we observe a dip of conductance with temperature as a signature of the Tomonaga-Luttinger liquid effects. (C) 2002 Elsevier Science B.V. All rights reserved.

 

6.    D. G. Austing, S. Sasaki, K. Muraki, K. Ono, S. Tarucha, M. Barranco, A. Emperador, M. Pi, and F. Garcias

            "Influence of mismatch on the addition energy spectra of vertical diatomic artificial molecules"

            Physica E-low-dimensional Systems & Nanostructures 12 (1-4)896-899 (2002).

 

            ABSTRACT: We investigate the dissociation of few-electron circular vertical semiconductor double quantum dot artificial molecules at 0 T as a function of interdot distance. Slight mismatch introduced in the fabrication of the artificial molecules from materials with nominally identical constituent quantum wells induces localization. This offsets the energy levels in the quantum dots by up to 2 meV, and can play a crucial role in the appearance of the addition energy spectra as a function of coupling strength particularly in the weak coupling limit. (C) 2002 Elsevier Science B.V. All rights reserved.

 

7.    S. Bhunia, T. Kawamura, Y. Watanabe, S. Fujikawa, K. Uchida, S. Nozaki, H. Morisaki, J. Matsui, Y. Kagoshima, and Y. Tsusaka

            "Real-time observation of step-flow limited metal organic vapor phase epitaxial growth of InP and their characteristics"

            Compound Semiconductors 2001 (170)647-652 (2002).

 

            ABSTRACT: Using our recently developed technique of near-grazing angle x-ray surface reflection, we have studied the real-time atomic surface kinetics during metal organic vapor phase epitaxy of InP by monitoring the monolayer scale roughness during the growth. The evolution of the surface roughness for various group III and group V precursor flows has been reported. The step-flow mode of growth was observed at the growth temperatures of 550 degreesC and 525 degreesC and their characteristics have been discussed in details.

 

8.    V. V. Borovkov, J. M. Lintuluoto, H. Sugeta, M. Fujiki, R. Arakawa, and Y. Inoue

            "Supramolecular chirogenesis in zinc porphyrins: Equilibria, binding properties, and thermodynamics"

            Journal Of The American Chemical Society 124 (12)2993-3006 (2002).

 

            ABSTRACT: Complexation mechanism, binding properties and thermodynamic parameters of supramolecular chirality induction in the achiral host molecule, syn (face-to-face conformation) ethane-bridged bis(zinc porphyrin), upon interaction with chiral monoamine and monoalcohol guests have been studied by means of the UV-vis, CD, H-1 NMR, and ESI MS techniques. It was found that the chirogenesis process includes three major equilibria steps: the first guest ligation to a zinc porphyrin subunit of the host (K-1), syn to anti conformational switching (K-s), and further ligation by a second guest molecule to the remaining ligand-free zinc porphyrin subunit (K-2), thus forming the final bis-ligated species possessing supramolecular chirality. The validity of this equilibria model is confirmed by the excellent match between the calculated and experimentally observed spectral parameters of the bis-ligated species. The second ligation proceeds in a cooperative manner as K-2 > K-1 for all supramolecular systems studied, regardless of the structure of the chiral ligand used. The binding properties are highly dependent on the nature of the functional group (amines are stronger binders than alcohols) and on the structure of the chiral guests (primary and aliphatic amines have overall binding constant values greater than those of secondary and aromatic amines, respectively).

 

9.    D. J. Bottomley, H. Omi, Y. Kobayashi, M. Uematsu, H. Kageshima, and T. Ogino

            "Origin of self-assembled step and terrace formation at the Si(001)-SiO2 interface"

            Physical Review B 66 (3), 035301 (2002).

 

            ABSTRACT: We demonstrate that >1 mum lateral scale atomic height range steps and terraces can be formed at the Si(001)-SiO2 interface by annealing at high temperatures, such as 1325 degreesC, in an Ar atmosphere containing a small fraction of O-2. The kinetics of the step-terrace morphology formation are quantitatively consistent with a model in which Si is emitted from the interface during the annealing, diffuses in the oxide, and returns. The step-terrace morphology is a logical consequence of recent theoretically proposed ordered interfacial structures at this interface, supporting the structures' existence.

 

10.    D. J. Bottomley

            "Thermo-piezochemistry of InAs on GaAs(001)"

            Applied Physics Letters 80 (25)4747-4749 (2002).

 

            ABSTRACT: We show that the large biaxial epitaxial stress (-5.3 GPa) of InAs on GaAs(001) strongly affects the chemical reaction between elemental In and As on the GaAs(001) surface at temperatures between 200 and 500 degreesC. In contrast to the reaction in the bulk at zero stress, solid InAs is not the sole reaction product, but rather a mixture of elemental and compound phases including liquid In and liquid InAs result. This view differs radically from the conventional view that solid InAs is the sole stable reaction product formed at the growing surface on a GaAs(001) substrate. (C) 2002 American Institute of Physics.

 

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

            "Impedance analysis of a radio-frequency single-electron transistor"

            Applied Physics Letters 81 (17)3257-3259 (2002).

 

            ABSTRACT: We investigate rf transport through an AlGaAs/GaAs single-electron transistor (SET). The presented rf-SET scheme provides a transmission coefficient proportional to the admittance of the device, which is desirable for impedance analysis as well as for high-sensitivity charge detection. The impedance of a SET, including the small tunneling capacitance, is successfully analyzed at the high frequency of 643 MHz, and is compared with a simple model. The ability to measure the impedance of a SET would expand the measurable regime of single-electron tunneling behavior. (C) 2002 American Institute of Physics.

 

12.    S. De Franceschi, R. Hanson, W. G. van der Wiel, J. M. Elzerman, J. J. Wijpkema, T. Fujisawa, S. Tarucha, and L. P. Kouwenhoven

            "Out-of-equilibrium Kondo effect in a mesoscopic device"

            Physical Review Letters 89 (15), 156801 (2002).

 

            ABSTRACT: We study the nonequilibrium regime of the Kondo effect in a quantum dot laterally coupled to a narrow wire. We observe a split Kondo resonance when a finite bias voltage is imposed across the wire. The splitting is attributed to the creation of a double-step Fermi distribution function in the wire. Kondo correlations are strongly suppressed when the voltage across the wire exceeds the Kondo temperature. A perpendicular magnetic field enables us to selectively control the coupling between the dot and the two Fermi seas in the wire. Already at fields of order 0.1 T only the Kondo resonance associated with the strongly coupled reservoir survives.

 

13.    H. Deng, G. Weihs, C. Santori, J. Bloch, and Y. Yamamoto

            "Condensation of semiconductor microcavity exciton polaritons"

            Science 298 (5591)199-202 (2002).

 

            ABSTRACT: A phase transition from a classical thermal mixed state to a quantum-mechanical pure state of exciton polaritons is observed in a GaAs multiple quantum-well microcavity from the decrease of the second-order coherence function. Supporting evidence is obtained from the observation of a nonlinear threshold behavior in the pump-intensity dependence of the emission, a polariton-like dispersion relation above threshold, and a decrease of the relaxation time into the lower polariton state. The condensation of microcavity exciton polaritons is confirmed.

 

14.    G. Feve, W. D. Oliver, M. Aranzana, and Y. Yamamoto

            "Rashba effect within the coherent scattering formalism"

            Physical Review B 66 (15), 155328 (2002).

 

            ABSTRACT: The influence of spin-orbit coupling in two-dimensional systems is investigated within the framework of the Landauer-Buttiker coherent scattering formalism. After a short review of the features of spin-orbit coupling in two-dimensional electron gases, we define the creation and annihilation operators for the stationary states of the Rashba spin-orbit coupling Hamiltonian and use them to calculate the current operator within the Landauer-Buttiker formalism. The current is expressed as it is in the standard spin-independent case, but with the spin label replaced by a new label, which we call the spin-orbit coupling label. The spin-orbit coupling effects can then be represented in a scattering matrix that relates the spin-orbit coupling stationary states in different leads. As an example, we calculate the scattering matrix in the case of a four-port beam splitter, and it is shown to mix states with different spin-orbit coupling labels in a manner that depends on the angle between the leads. A noise measurement after the collision of spin-polarized electrons at an electron beam splitter provides an experimental means to measure the Rashba parameter alpha. It is also shown that the degree of electron bunching in an entangled-electron collision experiment is reduced by the spin-orbit coupling according to the beam splitter lead angle.

 

15.    P. Finnie, and Y. Homma

            "Epitaxy: the motion picture"

            Surface Science 500 (1-3)437-457 (2002).

 

            ABSTRACT: The engineering of many modern electronic devices demands control over a crystal down to the thickness of a single layer of atoms and future demands will be even more challenging. Such control is achieved by the method of crystal growth known as epitaxy, and that makes this method the subject of intense study. More than that, recent advances are revolutionizing our knowledge of how surfaces grow. In fact, growing surfaces show a beautifully rich variety of phenomena, many of which are only now beginning to be uncovered. In the past few years many surface imaging techniques have been used to give us a close look at how crystals grow-while they are growing. The purpose of this article will be to illustrate some of the ways real surfaces grow and change as revealed by some of the latest in situ microscopic imaging technologies. It is often said that crystal growth is more of an art than a science. Here we will show that it is emphatically both. Crown Copyright (C) 2001 Published by Elsevier Science B.V. All rights reserved.

 

16.    K. J. Friedland, R. Hey, O. Bierwagen, H. Kostial, Y. Hirayama, and K. H. Ploog

            "Conductance anisotropy of high-mobility, modulation-doped GaAs single quantum wells"

            Physica E-low-dimensional Systems & Nanostructures 13 (2-4)642-645 (2002).

 

            ABSTRACT: The conductance in high-mobility and high-density, modulation-doped GaAs single quantum wells on GaAs(001) substrates with thin spacer layers is strongly anisotropic with a 2-3 times higher mobility in the [(1) over bar 1 0] than that in the [1 1 0] direction. We show that the anisotropic scattering potential is strongly influenced by additional X-like electrons in the barriers formed by short-period superlattices. The X-electrons are able to considerably smooth the flucuations of the potential thus. increasing the correlation length of the fluctuations. We investigate the correlation length of the potential fluctuations by oscillations in the low-field magnetoresistance. (C) 2002 Elsevier Science B.V. All rights reserved.

 

17.    T. Fujii, I. Terasaki, T. Watanabe, and A. Matsuda

            "In-plane anisotropy on the transport properties in the modulated Bi2O2-based conductors Bi-2212 and Bi-Sr-Co-O"

            Physica C-superconductivity And Its Applications 378182-186 (2002).

 

            ABSTRACT: We investigated the in-plane anisotropy on the resistivity and thermopower of the Bi2Sr2CaCu2O8+delta (Bi-2212) and Bi-Sr-Co-O (BiCo) single crystals. In Bi-2212, the b-axis resistivity is higher than the a-axis resistivity, and is expressed as a sum of the a-axis resistivity and an additional residual resistivity. A downward deviation due to pseudogap is observed below a characteristic temperature T* which is isotropic in the form of conductivity. These results suggest that the modulation structure along the b-axis works as an anisotropic scattering center, but does not affect the pseudogap formation. On the other hand, the anisotropy of the resistivity and the thermopower in Pb-doped BiCo is substantial, probably owing to the misfit structure between the hexagonal CoO2 layer and the rock-salt Bi2O2 layer. However, the anisotropy in the resistivity in Pb-free BiCo is very small, suggesting that the inplane anisotropy is averaged by the modulation structure, whose direction is tilted by 45degrees from the a- and b-axis. (C) 2002 Elsevier Science B.V. All rights reserved.

 

18.    T. Fujii, I. Terasaki, T. Watanabe, and A. Matsuda

            "Large in-plane anisotropy on resistivity and thermopower in the misfit layered oxide Bi2-xPbxSr2Co2Oy"

            Japanese Journal Of Applied Physics Part 2-letters 41 (7A)L783-L786 (2002).

 

            ABSTRACT: We investigated the in-plane anisotropy on the resistivity and thermopower of Bi2-xPbxSr2Co2Oy single crystals, which have a misfit structure between the hexagonal CoO2 layer and the rock salt Bi2Sr2O4 layer. The resistivity and thermopower show significant anisotropy, which exceeds two at maximum. This anisotropy is thought to arise from the anisotropic pseudogap formation enhanced by the misfit structure. The thermopower changes with Pb doping to take a maximum at x = 0.4. The misfit structure improves the thermoelectric properties through chemical pressure. The power factor is as large as 9 muW/cm(.)K(2) at 100 K for x = 0.6, which is the highest value obtained for thermoelectric oxides at 100 K.

 

19.    T. Fujii, I. Terasaki, T. Watanabe, and A. Matsuda

            "Doping dependence of anisotropic resistivities in the trilayered superconductor Bi2Sr2Ca2Cu3O10+delta"

            Physical Review B 66 (2), 024507 (2002).

 

            ABSTRACT: The doping dependence of the thermopower, in-plane resistivity rho(ab)(T), out-of-plane resistivity rho(c)(T), and susceptibility has been systematically measured for high-quality single crystal Bi2Sr2Ca2Cu3O10+delta. We found that the transition temperature T-c and pseudogap formation temperature T-rhoc(*), below which rho(c) shows a typical upturn, do not change from their optimum values in the "overdoped" region, even though doping actually proceeds. This suggests that, in overdoped region, the bulk T-c is determined by the always underdoped inner planes, which have a large superconducting gap, while the carriers are mostly doped in the outer planes, which have a large phase stiffness.

 

20.    T. Fujisawa, D. G. Austing, Y. Tokura, Y. Hirayama, and S. Tarucha

            "Allowed and forbidden transitions in artificial hydrogen and helium atoms"

            Nature 419 (6904)278-281 (2002).

 

            ABSTRACT: The strength of radiative transitions in atoms is governed by selection rules that depend on the occupation of atomic orbitals with electrons(1). Experiments have shown(2-5) similar electron occupation of the quantized energy levels in semiconductor quantum dots-often described as artificial atoms. But unlike real atoms, the confinement potential of quantum dots is anisotropic, and the electrons can easily couple with phonons of the material(6). Here we report electrical pump-and-probe experiments that probe the allowed and 'forbidden' transitions between energy levels under phonon emission in quantum dots with one or two electrons (artificial hydrogen and helium atoms). The forbidden transitions are in fact allowed by higher-order processes where electrons flip their spin. We find that the relaxation time is about 200 mus for forbidden transitions, 4 to 5 orders of magnitude longer than for allowed transitions. This indicates that the spin degree of freedom is well separated from the orbital degree of freedom, and that the total spin in the quantum dots is an excellent quantum number. This is an encouraging result for potential applications of quantum dots as basic entities for spin-based quantum information storage.

 

21.    T. Fujisawa, Y. Tokura, D. G. Austing, Y. Hirayama, and S. Tarucha

            "Spin-dependent energy relaxation inside a quantum dot"

            Physica B-condensed Matter 314 (1-4)224-229 (2002).

 

            ABSTRACT: We employ pulse excitation measurements in order to investigate spin-dependent energy relaxation inside a quantum dot. A fast pulse signal is applied to a gate electrode in order to excite a quantum dot, and the induced transient current is analyzed in terms of energy relaxation. We describe transient current measurements on a lateral quantum dot, in which the tunneling rates are controllable with gate voltages, and on a vertical quantum dot, in which the total number of electrons and total spin can be well identified. The spin-conservation rule during energy relaxation is clearly identified. (C) 2002 Elsevier Science B.V. All rights reserved.

 

22.    T. Fujisawa, D. G. Austing, Y. Tokura, Y. Hirayama, and S. Tarucha

            "Nonequilibrium transport through a vertical quantum dot in the absence of spin-flip energy relaxation"

            Physical Review Letters 88 (23), 236802 (2002).

 

            ABSTRACT: We investigate nonequilibrium transport in the absence of spin-flip energy relaxation in a few-electron quantum dot artificial atom. Novel nonequilibrium tunneling processes involving high-spin states, which cannot be excited from the ground state because of spin blockade, and other processes involving more than two charge states are observed. These processes cannot be explained by orthodox Coulomb blockade theory. The absence of effective spin relaxation induces considerable fluctuation of the spin, charge, and total energy of the quantum dot. Although these features are revealed clearly by pulse excitation measurements, they are also observed in conventional dc current characteristics of quantum dots.

 

23.    A. Fujiwara, and Y. Takahashi

            "Si nano-devices using an electron-hole system"

            Journal De Physique Iv 12 (PR3)85-92 (2002).

 

            ABSTRACT: Si nano-devices consisting of a Si quantum wire with fine gates are described. Storage and detection of single charges are enabled based on the electron-hole (e-h) system in the Si wire. Due to the electric field applied across the Si wire, electrons and holes are spatially separated within the Si wire so that they do not recombine soon. Stored charges in the Si wire can be sensed by the current of the other type of charges flowing nearby. Based on this technique, the charge-coupled device that can manipulate a single charge is realized.

 

24.    A. Fujiwara, and Y. Takahashi

            "Mechanism of single-charge detection using electron-hole system in Si-wire transistors"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 41 (3A)1209-1213 (2002).

 

            ABSTRACT: We demonstrate and investigate a method of single-charge detection in Si-wire metal-oxide-semiconductor field-effect transistors (MOSFETs) fabricated on a silicon-on-insulator (SOI) wafer. The method is based on an electron-hole (e-h) system in the Si wire, which is formed by applying a large electric field across the Si wire and thereby making electrons and holes separated and localized at two opposite Si/SiO2 interfaces. Photogenerated holes, which are accumulated at the front interface, are sensed by the electron current flowing at the back interface. The phenomenon can be regarded as a kind of floating-body effect in SOI-MOSFETs. With the use of a nanometer-sized wire channel, the scheme has sensitivity of the elementary charge. A unique recombination dynamics in the e-h system is found to enable the selective storage of the single hole; the recombination lifetime is strongly dependent on the number of stored holes due to the resultant change in the electron current.

 

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

            "Detection of single charges and their generation-recombination dynamics in Si nanowires at room temperature"

            Applied Physics Letters 80 (24)4567-4569 (2002).

 

            ABSTRACT: Detection of single electrons and single holes is demonstrated at room temperature in Si nanowire transistors using an electron-hole (e-h) system. Photogenerated carriers are stored in a quantum dot electrically formed in a Si wire by a front gate. The stored charges affect the current of the other type of carriers that flow along the bottom of the Si wire. The linear photoresponce of single-charge generation is observed. It is revealed that the recombination occurs by a bimolecular process, suggesting that it is due to the e-h interband transition. These results open up the possibility of developing single-photon devices with this system. (C) 2002 American Institute of Physics.

 

26.    K. Furukawa, and K. Ebata

            "Conformational transition of end-grafted poly(di-n-hexylsilane) in solventless conditions"

            Macromolecules 35 (2)327-329 (2002).

 

            ABSTRACT:

 

27.    T. Greibe, M. Hepp, and M. Naito

            "Role of substrates in molecular beam epitaxy growth of superconducting T '-La2-xCexCuO4 films"

            Physica C-superconductivity And Its Applications 3721082-1086 (2002).

 

            ABSTRACT: We report the molecular beam epitaxy growth of the electron-doped 30-K superconductor, T'-La-2 Ce3CuO4. T'-La2-xCexCuO4 with a very limited range of x can be prepared by bulk synthesis using rather complicated techniques. In contrast, this compound is very easy to prepare by thin film synthesis, The key factor in thin film growth to stabilize T'-La2-xCexCuO4 is a low synthesis temperature below 700 degreesC. The use of appropriate substrates further stabilizes T' formation by an epitaxial effect. In this work, we examined various substrates for the growth of T'-La2-xCe3CuO4. Based on the experimental results, we discuss the roles of iubstrates. (C) 2002 Elsevier Science B.V. All rights reserved.

 

28.    M. P. Halsall, H. Omi, and T. Ogino

            "Optical properties of self-assembled Ge wires grown on Si(113)"

            Applied Physics Letters 81 (13)2448-2450 (2002).

 

            ABSTRACT: We report photoluminescence and Raman scattering measurements of Ge wires formed by self-assembly on Si(113) substrates. The samples were grown at a growth temperature of 500 degreesC on Si(113) substrates by solid-source molecular-beam epitaxy. Atomic force microscopy results clearly show the formation of coherent wire-shaped islands elongated in the [33-2] direction, some with lengths exceeding 500 nm. Micro-Raman measurements indicate that at this low growth temperature intermixing of the silicon and germanium is restricted with an average Ge fraction exceeding 0.7. Capping of the wires with a 20 nm Si epilayer enables the observation of low-temperature photoluminescence. A series of samples with increasing Ge coverage were studied and the onset of Ge islanding is observed to occur at a coverage of 5 monolayers. Wire formation occurs at coverages of 6 monolayers or greater. The observed emission band from the wires has a line shape quite different from that observed from Ge islands on Si[100], being substantially narrower in energy. A stochastic calculation based on idealized quantum wires is presented which reproduces the observed photoluminescence line shape well. (C) 2002 American Institute of Physics.

 

29.    O. Hanaizumi, M. Saito, Y. Ohtera, S. Kawakami, S. Yano, Y. Segawa, E. Kuramochi, T. Tamamura, S. Oku, and A. Ozawa

            "Introducing CdS into two- and three-dimensional photonic crystals"

            Optical And Quantum Electronics 34 (1-3)71-77 (2002).

 

            ABSTRACT: SiO2/air three-dimensional (3D) periodic structures were fabricated by removing Si layers partially from Si/SiO2 3D photonic crystals (PhCs) formed by using autocloning. CdS/SiO2 3D periodic structures were formed by introducing CdS into the SiO2/air structures by the TEA method and photoluminescence (PL) was observed from the introduced CdS. TiO2/air/CdS two-dimensional (2D) PhCs were also fabricated by introducing CdS into the voids of TiO2/air 2D periodic structures, in which SiO2 layers were partially etched out from TiO2/SiO2 2D PhCs fabricated by using autocloning. PL radiating normal to the surface was measured and large polarization dependence was observed.

 

30.    Y. Harada, S. Jensen, T. Akazaki, and H. Takayanagi

            "Anomalous magnetic flux periodicity of supercurrent in mesoscopic SNS Josephson junctions"

            Physica C-superconductivity And Its Applications 367 (1-4)229-233 (2002).

 

            ABSTRACT: We measure the magnetic flux dependence of the supercurrent in diffusive Nb/n-InAs/Nb mesoscopic SNS Josephson junctions with junction length ranging from 220 to 720 nm. In the longer junctions, the modulation periodicity of the maximum supercurrent by magnetic flux is a quantum flux, Phi(0) = h/2e as usual. However, we find that the magnetic flux periodicity becomes twice or 2Phi(0) = h/e when the junction lengths are shorter than 400 urn. (C) 2002 Elsevier Science B.V. All rights reserved.

 

31.    H. Hasegawa, D. Okada, Y. Horikoshi, and T. Saitoh

            "Growth of GaAs/InAs antidot structure by solid-source MBE"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 41 (4B)2505-2507 (2002).

 

            ABSTRACT: Area selective epitaxy of antidot structures of GaAs/InAs heterostructures on GaAs substrates masked by SiO2 has been investigated by solid-source molecular beam epitaxy. 100-nanometer-scale antidot structures have successfully been grown by a migration-enhanced deposition sequence. When the diameter of a SiO2-covered hole is larger than 150 nm, the sidewalls exhibit triangular shapes because of the formation of inclined {110} facets. However, when the diameter is reduced below this value, the {110} facets disappear from the sidewall Instead, facet-free vertical sidewalls appear, implying the importance of surface tension during growth on small-diameter holes. Longitudinal resistance in Hall-bar samples with the antidot structure shows prominent fluctuation in the magnetic field between 0 and 2 T.

 

32.    K. Hashimoto, K. Muraki, T. Saku, and Y. Hirayama

            "Electrically controlled nuclear spin polarization and relaxation by quantum-Hall states"

            Physical Review Letters 88 (17), 176601 (2002).

 

            ABSTRACT: We study interactions between electrons and nuclear spins by using the resistance (R-xx ) peak which develops near the Landau-level filling factor nu = 2/3 as a probe. Temporarily tuning nu to a different value, nu(temp) , with a gate demonstrates that the R-xx peak regenerates even after complete depletion (nu(temp) = 0 ), while it rapidly relaxes on either side of nu(temp) = 1 . This indicates that the nu = 2/3 domain morphology is memorized by the nuclear spins which can be rapidly depolarized by Skyrmions. An additional enhancement in the nuclear spin relaxation around nu = 1/2 and 3/2 suggests a Fermi sea of partially polarized composite fermions.

 

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

            "Measuring the energy levels and wave functions in a single quantum dot"

            Physica E-low-dimensional Systems & Nanostructures 13 (2-4)634-637 (2002).

 

            ABSTRACT: We use an array of gate electrodes to select an individual self-assembled quantum dot from an ensemble. In combination with magneto-tunnelling spectroscopy this allows us to measure the energy levels and wave functions associated with the ground and excited state of the selected quantum dot. (C) 2002 Elsevier Science B.V. All rights reserved.

 

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

            "Controlling the electron tunneling through InAs self-assembled dots"

            Journal Of Applied Physics 91 (5)3474-3476 (2002).

 

            ABSTRACT: We investigate electron tunneling through GaAs/(AlGa)As/GaAs, single-barrier tunnel diodes in which a layer of self-assembled InAs quantum dots is incorporated onto the center plane of the (AlGa)As tunnel barrier. We study the effect on the electrical conduction of substrate orientation and of the inclusion of thin GaAs cladding layers on either side of the dot layer. We find that the presence of the cladding layers increases the conduction. We attribute this to a raising of the energy of the electron states, probably due to the diffusion of Ga into the dots. Photoluminescence measurements confirm this hypothesis. We show that this effect can be used to tailor the transport characteristics for specific applications. (C) 2002 American Institute of Physics.

 

35.    A. Hirata, T. Nagatsuma, R. Yano, H. Ito, T. Furuta, Y. Hirota, T. Ishibashi, H. Matsuo, A. Ueda, T. Noguchi, Y. Sekimoto, M. Ishiguro, and S. Matsuura

            "Output power measurement of photonic millimetre-wave and sub-millimetre-wave emitter at 100-800GHz"

            Electronics Letters 38 (15)798-800 (2002).

 

            ABSTRACT: A photonic millimetre-wave and sub-millimetre-wave emitter (PME) that uses a log-periodic antenna and a uni-travelling carrier photodiode has been fabricated and tested. The output power and spectra of the PME were measured with a Fourier transform spectrometer and a bolometer at 100-800 GHz in a low-power excitation condition. The extrapolated output power with 15 mA photocurrent is several tens of microWatts in the 300-600 GHz range.

 

36.    M. Hiroki, N. Maeda, and N. Kobayashi

            "Metalorganic vapor phase epitaxy growth of AlGaN/GaN heterostructures on sapphire substrates"

            Journal Of Crystal Growth 237956-960 (2002).

 

            ABSTRACT: AlGaN/GaN heterostructures were grown on (0 0 0 1) sapphire substrates by metalorganic vapor phase epitaxy. The dependences of electrical properties on the SiH4 flow rate, and the At composition and thickness of the AlxGa1-xN layer were studied. For Al compositions less than or equal to 15%, sheet electron densities were proportional to the SiH4 flow rate. At ail At compositions of 15%, a mobility of 1220 cm(2)/Vs (sheet electron densities 5.2 x 10(12) cm(-2)) was obtained, indicating the formation of high-quality AlGaN/GaN hetero-interfaces. Sheet electron densities continue to increase in proportion to the At composition. Even when the AlGaN was undoped, sheet electron density as high as 2.6 x 10(13) cm(-2) was obtained at an At composition of 45%. This is due to the effect of piezoelectric and spontaneous polarizations. When the AlGaN layer thickness exceeds the critical thickness, the sheet electron density decreased, because the piezoelectric polarization was also reduced by the relaxation. The dependence of sheet carrier density on the At composition can be explained by the polarization at the heterointerface and the effect of relaxation. The critical thickness estimated by Xray diffraction was higher than the theoretical calculation, implying that the elastic properties might be affected by the presence of high-density dislocations. (C) 2002 Elsevier Science B.V. All rights reserved.

 

37.    Y. Homma, T. Yamashita, Y. Kobayashi, and T. Ogino

            "Interconnection of nanostructures using carbon nanotubes"

            Physica B-condensed Matter 323 (1-4)122-123 (2002).

 

            ABSTRACT: We propose a novel application of carbon nanotubes as a wiring materials for self-assembling nano-interconnections. We investigated nanotube growth on patterned silicon substrates as a model for interconnectional growth. The growth was performed by methane chemical vapour deposition with an iron-oxide nanoparticle catalyst. Nanotubes originating from the top of a mesa grew laterally, bridging one mesa after another. A nanotube network was seen among an array of mesas. These results demonstrate the possibility of self-assembled wiring. (C) 2002 Published by Elsevier Science B.V.

 

38.    Y. Homma, Y. Kobayashi, T. Ogino, and T. Yamashita

            "Growth of suspended carbon nanotube networks on 100-nm-scale silicon pillars"

            Applied Physics Letters 81 (12)2261-2263 (2002).

 

            ABSTRACT: We investigated carbon nanotube growth by means of methane chemical vapor deposition on ultrafine silicon patterns prepared by synchrotron-radiation lithography. Grown nanotubes formed suspended bridges between pillars when pillar spacing was comparable to pillar height. Network-like interconnections were obtained on pillar arrays. Nearest-neighbor bridging accounted for more than 80% of all the bridging nanotubes. The self-directed growth between neighboring pillars may be explained by the swing of the nanotube cantilever which contacts a catalyst particle in liquid phase as the nanotube grows. These results confirm the possibility of self-assembled wiring of nanostructures. (C) 2002 American Institute of Physics.

 

39.    Y. Homma, and P. Finnie

            "Step dynamics on growing silicon surfaces observed by ultrahigh vacuum scanning electron microscopy"

            Journal Of Crystal Growth 23728-34 (2002).

 

            ABSTRACT: The motion of atomic steps on Si(1 1 1) "1 x 1" is studied using in situ scanning electron microscopy to observe ultraflat Si(1 1 1) substrates that have flat terraces of 100 mum width. Atomic steps are revealed by (7 x 7)-domain decoration. Step-flow growth and sublimation processes are compared for single-step-high islands and holes. The step motion is highly symmetric for growth in comparison with Sublimation. and for islands in comparison with holes. The step motion fits well with the simple model by Burton, Cabrera and Frank. No clear asymmetry in step kinetics is observed for upper terraces in comparison with lower terraces. However, by introducing an asymmetry in the relative terrace sizes on either side of a step, the adatom flux balance is tilted, and the result is a morphological instability in step flow. (C) 2002 Elsevier Science B.V. All rights reserved.

 

40.    Y. Homma

            "Summary of ISO/TC 201 Standard: II ISO 14237 : 2000 - Surface chemical analysis - Secondary ion mass spectrometry - Determination of boron atomic concentration in silicon using uniformly doped materials"

            Surface And Interface Analysis 33 (4)361-362 (2002).

 

            ABSTRACT: This International Standard specifies a secondary ion mass spectrometric method for the determination of boron atomic concentration in single crystalline silicon using uniformly doped materials calibrated by a certified reference material implanted with boron. This method is applicable to uniformly doped boron in the concentration range 1 X 10(16)-1 X 10(20) atoms cm(-3). Copyright (C) 2002 John Wiley Sons, Ltd.

 

41.    Y. Homma, T. Yamashita, P. Finnie, M. Tomita, and T. Ogino

            "Single-walled carbon nanotube growth on silicon substrates using nanoparticle catalysts"

            Japanese Journal Of Applied Physics Part 2-letters 41 (1AB)L89-L91 (2002).

 

            ABSTRACT: We investigated the growth of carbon nanotubes (CNT) directly on silicon substrates by nanoparticle-catalyst-assisted chemical vapor deposition, Single-walled CNTs were almost selectively obtained when methane was used in combination with Fe2O3 nanoparticles at the growth temperature of around 950degreesC. In the growth of single-walled CNTs, this temperature is essential in order to avoid silicidation of the catalyst. The growth direction was parallel to the substrate surface, which is useful for device applications. For Fe-metal nanoparticles, grown nanotubes always contained thick multiwalled CNTs. The selective single-walled CNT growth for Fe2O3 nanoparticles is attributed to the fact that the particles remain small even after the chemical vapor deposition (CVD) process.

 

42.    T. Hong, M. W. Jack, M. Yamashita, and T. Mukai

            "Enhanced Kerr nonlinearity for self-action via atomic coherence in a four-level atomic system"

            Optics Communications 214 (1-6)371-380 (2002).

 

            ABSTRACT: Enhancement of optical Kerr nonlinearity for self-action by electro-magnetically induced transparency in a four-level atomic system including dephasing between the ground states is studied in detail by solving the density matrix equations for the atomic levels. We discern three major contributions, from energy shifts of the ground states induced by the probe light, to the third-order susceptibility in the four-level system. In this four-level system with the frequency-degenerate probes, quantum interference amongst the three contributions can, not only enhance the third-order susceptibility more effectively than in the three-level system with the same characteristic parameters, but also make the ratio between its real and imaginary part controllable. Due to dephasing between the two ground states and constructive quantum interference, the most effective enhancement generally occurs at an offset that is determined by the atomic transition frequency difference and the coupling Rabi frequency. (C) 2002 Elsevier Science B.V. All rights reserved.

 

43.    Y. Hoshino, T. Nishimura, Y. Taki, Y. Asami, K. Sumitomo, and Y. Kido

            "Structure change of Ni(1 ML)/Si(111) by post-annealing observed by atomic force microscopy, ion scattering and photoelectron spectroscopy"

            Surface Science 511 (1-3)112-120 (2002).

 

            ABSTRACT: Structure change of Ni(1 ML: 7.83 x 10(14) atoms/cm(2))/Si(1 1 1) by post-annealing was observed by reflection high energy electron diffraction, atomic force microscopy (AFM), medium energy ion scattering (MEIS) and photoelectron spectroscopy. The AFM observation showed dramatic change of the surface morphology after the Ni deposition at room temperature (RT) followed by annealing at 400, 600, 700 and 800 degreesC for 2 min in an ultrahigh vacuum. MEIS using 70 keV He+ ions analyzed the depth profiles of Ni and the crystallographic structure of the Ni-composites formed by annealing. The valence band and the Si-2p and Ni-3p core level analyses using synchrotron-radiation light showed that the NiSi phase appeared by 1 ML-Ni deposition at RT and both NiSi and NiSi, islands were formed by annealing at 400 degreesC. Annealing at 600 and 700 degreesC led to growth of the B-type NiSi2 islands with height of four and six Si-Ni-Si triple layers. After annealing at 800 degreesC three-fourth of the deposited Ni atoms were dissipated from the surface and the dominant surface structure was the I x I-ring clusters accompanied by a small amount of root19 x root19 phase. The present analysis clearly showed the structure change of Ni (1 ML)/Si(1 1 1) by post-annealing and provided the information about the kinetics for the Ni-Si system. (C) 2002 Published by Elsevier Science B.V.

 

44.    C. M. Hu, J. Nitta, A. Jensen, J. B. Hansen, H. Takayanagi, T. Matsuyama, D. Heitmann, and U. Merkt

            "Spin injection across a hybrid heterojunction: Theoretical understanding and experimental approach (invited)"

            Journal Of Applied Physics 91 (10)7251-7255 (2002).

 

            ABSTRACT: Spin injection across a hybrid ferromagnet/semiconductor junction has proven to be difficult, unlike in an all-metal junction used in giant magnetoresistance devices. The difference responsible is highlighted in a simple model. We perform spin-injection-detection experiments on devices with two ferromagnetic contacts on a two-dimensional electron gas confined in an InAs quantum well. We demonstrate that spin injection allows the hybrid device to combine both the advantage of the ferromagnet as well as that of the semiconductor. (C) 2002 American Institute of Physics.

 

45.    C. M. Hu, J. Nitta, A. Jensen, J. B. Hansen, H. Takayanagi, T. Matsuyama, D. Grundler, G. Meier, D. Heitmann, and U. Merkt

            "Spin injection into a two-dimensional electron gas using inter-digital-ferromagnetic contacts"

            Physica E-low-dimensional Systems & Nanostructures 12 (1-4)395-398 (2002).

 

            ABSTRACT: We present a model that describes the spin injection across a single interface with two electrodes. The spin-injection rate across a typical hybrid junction made of ferromagnet (FM) and a two-dimensional electron gas (2DEG) is found at the percentage level. We perforin spin-injection-detection experiment on devices with two ferromagnetic contacts on a 2DEG confined in an InAs quantum well. A spin-injection rate of 4.5% is estimated from the measured magnetoresistance. (C) 2002 Elsevier Science B.V. All rights reserved.

 

46.    R. Huang, Y. Yamamoto, R. Andre, J. Bleuse, M. Muller, and H. Ulmer-Tuffigo

            "Exciton-polariton lasing and amplification based on exciton-exciton scattering in CdTe microcavity quantum wells"

            Physical Review B 65 (16), 165314 (2002).

 

            ABSTRACT: We describe experiments demonstrating an exciton-polariton laser and amplifier based on an incoherent exciton-polariton reservoir in CdTe microcavity quantum wells. The gain mechanism is real excited exciton-exciton scattering, in which excitons created at large in-plane wave vectors are thermalized and accumulate at the bottleneck lower polariton states at smaller in-plane wave vectors. Because the exciton-exciton scattering rate for CdTe at the saturation density is higher than that for GaAs, the threshold for spontaneous polariton lasing is more easily reached in the case of CdTe with respect to GaAs. We demonstrate a high-gain amplification of bottleneck lower polaritons close to the lasing threshold. By performing a pulsed pump and probe experiment, we observe unambiguous evidence of real excited exciton-exciton scattering gain in the form of exp(const N-exc(2)), where N-exc is the exciton-polariton reservoir population. This result is in sharp contrast to the recently demonstrated parametric polariton amplifier based on virtual coherent four wave mixing, in which gain is proportional to exp(const N-exc).

 

47.    Y. Igaku, S. Matsui, H. Ishigaki, J. Fujita, M. Ishida, Y. Ochiai, H. Namatsu, M. Komuro, and H. Hiroshima

            "Room temperature nanoimprint technology using hydrogen silsequioxane (HSQ)"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 41 (6B)4198-4202 (2002).

 

            ABSTRACT: Room-temperature nanoimprint lithography (RT-NIL) technology has been developed to overcome critical dimensions and pattern placement error due to thermal expansion in the conventional nanoimprint lithography (NIL) process, We propose RT-NIL using hydrogen silsequioxane (HSQ) instead of PMMA used in conventional NIL, and demonstrate HSQ replicated patterns with 90nm hole diameter and 50nm linewidth realized by room-temperature replications. We performed step-and-repeat replications using HSQ on a 1.5 in. wafer and evaluated the uniformity of the imprinted HSQ patterns.

 

48.    H. Inokawa, A. Fujiwara, and Y. Takahashi

            "A merged single-electron transistor and metal-oxide-semiconductor transistor logic for interface and multiple-valued functions"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 41 (4B)2566-2568 (2002).

 

            ABSTRACT: A merged single-electron transistor and metal-oxide-semiconductor transistor logic is introduced that features large voltage gain and output amplitude that far exceed the limits of Cg/Cd and e/C-Sigma inherent to a single-electron transistor (SET), where C-g, C-d, e, and C-Sigma are gate capacitance, drain capacitance. elemental charge, and the total capacitance around the Coulomb island, respectively. The operation of the proposed logic is verified with devices fabricated by the complementary metal-oxide-semiconductor (CMOS)-compatible pattern-dependent oxidation process. The proposed logic is not only suitable for a SET-to-CMOS inter-face circuit, but is also useful as a basic element for multiple-valued functions.

 

49.    K. Inoue, and T. Mukai

            "Experimental study on noise characteristics of a gain-saturated fiber optical parametric amplifier"

            Journal Of Lightwave Technology 20 (6)969-974 (2002).

 

            ABSTRACT: A fiber optical parametric amplifier (OPA) has a unique saturation property such that, with increase in signal input, the signal output power increases, reaches a peak. level, then decreases. Around the output peak condition, a negative feedback mechanism works to suppress intensity fluctuations in the signal output. This paper experimentally studies noise characteristics of such a gain-saturated fiber OPA. Two kinds of incident signals are injected into a fiber OPA. One is intentionally fluctuated light with large excess noise and the other is excess-noise-free (or shot-noise-limited) light. It is demonstrated that the noise suppression has an effect both on the excess noise and on beat noise due to amplified spontaneous emission generated inside the amplifier.

 

50.    K. Inoue, E. Waks, and Y. Yamamoto

            "Differential phase shift quantum key distribution"

            Physical Review Letters 89 (3), 037902 (2002).

 

            ABSTRACT: A novel quantum cryptography scheme is proposed, in which a single photon is prepared in a linear superposition state of three basis kets. A photon split to three pulses is sent from Alice to Bob, where the phase difference between sequential two pulses carries bit information. Bob measures the phase difference by passive differential phase detection. This scheme is suitable for fiber transmission systems and offers a key creation efficiency higher than conventional fiber-based BB84.

 

51.    T. Isa, T. Fukase, M. Sasaki, M. Koyano, N. Taniguchi, T. Kimura, Y. Isobe, and H. Negishi

            "Mid-gap state formed inside Mott gap of 1T-TaS2 single crystals and metal-insulator transition"

            Journal Of Low Temperature Physics 127 (1-2)63-79 (2002).

 

            ABSTRACT: We have measured electrical resistivity, Hall coefficient, thermoelectric power, and magnetization for charge-density, wave (CDW) material 1T-TaS2 single crystals grown by varying the excess sulfur content x(es). We have revealed that a small mid-gap state is joined inside the Mott gap and that anomalous low, temperature transport is not governed by the Mott gap state itself but by the mid-gap state, The electric properties of the mid-gap state are modified by increasing x, (or hole doping), and we have found the insulator-metal transition occurs by hole doping below 60 K.

 

52.    T. Ishiyama, M. Nagase, and Y. Omura

            "Evolution of step-terrace structure at Si-SiO2 interface in SIMOX substrate during annealing"

            Applied Surface Science 190 (1-4)16-19 (2002).

 

            ABSTRACT: The step-terrace structures at the interface between the Si layer and the buried SiO2 layer of a Separation by IMplanted OXygen substrate has been observed by using atomic force microscopy (AFM) after removing the SiO2, and Si layers. The time evolution of the Si-SiO2 interface roughness during high-temperature annealing was analyzed by the scaling analysis of AFM data. The correlation length exhibited a nice correspondence to the size of square domain structures. Decreasing in the index of the length scale indicates that the growth mechanism changes as the annealing proceeds. (C) 2002 Published by Elsevier Science B.V.

 

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

            "Measurements of blue shifts due to collisionless absorption in harmonic generation from subpicosecond laser-produced plasmas"

            Physical Review E 66 (2), 026414 (2002).

 

            ABSTRACT: Harmonic generation from solid surface plasmas is studied using a subpicosecond Nd:glass laser system. For a 45degrees angle of incidence, the speculars up to the fifth harmonics are blue shifted when the laser intensity exceeds 2x10(16) W cm(-2). The second harmonic is blueshifted by similar to16 Angstrom, and the fifth harmonic is blue shifted by similar to51 Angstrom for p polarization at the intensity of 1x10(17) W cm(-2). We observed the blue shift of the fifth harmonics and found that the magnitude of blue shift is higher compared with that for the second harmonics. The blue shift is interpreted as a collisionless absorption due to the anomalous skin effect. It is also found that the divergence of harmonics preserves a smaller divergence when using a shorter pulse length for the driving laser.

 

54.    T. Iwamoto, Y. Jimbo, and K. Aihara

            "Extracting temporal firing patterns of neurons from noisy data"

            Ieice Transactions On Fundamentals Of Electronics Communications And E85A (4)892-902 (2002).

 

            ABSTRACT: We propose a novel method for analysis of time-related neuronal activities. This method can he used for the detection of firing patterns in the presence of noise, which is inevitable in physiological experiments. This method is also useful for probability density estimation. because it enables precise information quantification from a small amount of data.

 

55.    M. W. Jack

            "Decoherence due to three-body loss and its effect on the state of a Bose-Einstein condensate"

            Physical Review Letters 89 (14), 140402 (2002).

 

            ABSTRACT: A Born-Markov master equation is used to investigate the decoherence of the state of a macroscopically occupied mode of a cold atom trap due to three-body loss. In the large-number limit only coherent states remain pure for times longer than the decoherence time: the time it takes for just three atoms to be lost from the trap. For large numbers of atoms (N>10(4)) the decoherence time is found to be much faster than the phase-collapse time caused by intratrap atomic collisions.

 

56.    M. Jetter, V. Perez-Solorzano, Y. Kobayashi, M. Ost, F. Scholz, and H. Schweizer

            "Photoluminescence studies on InGaN/GaN quantum dots"

            Physica Status Solidi A-applied Research 192 (1)91-96 (2002).

 

            ABSTRACT: InGaN/GaN quantum dots are currently of major interest in basic research and for device application. If material of sufficient quality is available, light emission from blue to green is already possible in this system. We report here on our InGaN/GaN quantum dots grown by metalorganic vapour phase epitaxy (MOVPE). The dot formation was examined using atomic force microscopy (AFM). This work is focused on photoluminescence (PL) and cathodoluminescence (CL) measurements of these InGaN dots. To prove the existence of quantum dots in capped samples we have performed power-dependent PL and found evidence of state filling, which is typical for quantum dots. These results were confirmed with CL measurements on structured samples.

 

57.    H. Kamada, H. Gotoh, J. Temmyo, H. Ando, and T. Takagahara

            "Exciton Rabi oscillation in single isolated quantum dots"

            Physica Status Solidi A-applied Research 190 (2)485-490 (2002).

 

            ABSTRACT: The Rabi population oscillation of a single excitonic two-level system in an isolated InxGa1-xAs quantum dot was examined by quantum wave function interferometry in the time domain. The corresponding energy splitting was also confirmed in an energy-domain measurement. Two-pulse dipole interference on an excited excitonic state revealed a long-lived coherence of zero-dimensional excitonic states and demonstrated coherent population flopping under a strong optical field.

 

58.    A. A. Kaminskii, T. Kaino, T. Taima, A. Yokoo, K. Ueda, K. Takaichi, J. Hulliger, H. J. Eichler, J. Hanuza, J. Fernandez, R. Balda, M. Moczka, and G. M. Gad

            "Monocrystalline 2-adamantylamino-5-nitropyridine (AANP) - a novel organic material for laser Raman converters in the visible and near-IR"

            Japanese Journal Of Applied Physics Part 2-letters 41 (6A)L603-L605 (2002).

 

            ABSTRACT: We have open up new nonlinear-laser potential in polar C15H19N3O2 (AANP) single crystal. At room temperature under one-micron picosecond laser excitation high-order stimulated Raman scattering (SRS) and self-sum-frequency generation effects in this organic material were observed. All their registered lasing components were identified and put in relation with the SRS-active vibration modes (omega(SRS) approximate to 1280 cm(-1))., The investigated crystal is classified a as promising X chi((2)) + chi((3)) medium for laser-frequency converters and Raman lasers in the visible and near-IR.

 

59.    Y. Kangawa, T. Ito, Y. S. Hiraoka, A. Taguchi, K. Shiraishi, and T. Ohachi

            "Theoretical approach to influence of As-2 pressure on GaAs growth kinetics"

            Surface Science 507285-289 (2002).

 

            ABSTRACT: The newly developed first-principles calculation based computational method incorporating chemical potential of As-2 gas is applied to understand the influence of As-2 pressure on GaAs growth kinetics under the molecular beam epitaxy growth conditions with high As-2 pressures where the c(4 x 4) reconstructed structure appears on the surface. The calculated results suggest that the chemical potential of As-2 gas increases with As-2 pressure, which suppresses As-2 (As-dimer) desorption or extends As-2 surface lifetime. This induces the decrease of GaAs growth rate, because GaAs layer-by-layer growth does not proceed without As-2 desorption on the As-rich c(4 x 4) surface. (C) 2002 Elsevier Science B.V. All rights reserved.

 

60.    Y. Kangawa, T. Ito, A. Taguchi, K. Shiraishi, and T. Ohachi

            "Empirical interatomic potential calculations for relative stability of Ga adatom on GaAs(100) and (n11)A surfaces"

            Journal Of Crystal Growth 237223-226 (2002).

 

            ABSTRACT: Relative stability of Ga adatom on GaAs(1 0 0)-(2 x 4)beta2 and GaAs(n11)A (n = 2, 3 and 4) surfaces are investigated by empirical interatomic potential calculations. The calculated results suggest that Ga on (3 1 I)A is the most stable amongst all (n I I)A surfaces because the strain around the Ga adatom on (3 1 I)A is the smallest in the systems. Moreover, we studied the temperature dependence of Ga sticking coefficient on each surface using calculated Ga adsorption energy and chemical potential of atomic Ga in the vapor phase. The results imply that Ga sticking coefficient on (10 0)-(2 x 4)beta2 and (4 1 I)A decreases with increase of temperature T at T > 850 K, while it is almost unity on (2 1 1)A and (3 1 1)A around this temperature range. (C) 2002 Elsevier Science B.V. All rights reserved.

 

61.    Y. Kangawa, T. Ito, A. Taguchi, K. Shiraishi, T. Irisawa, and T. Ohachi

            "Monte Carlo simulation for temperature dependence of Ga diffusion length on GaAs(001)"

            Applied Surface Science 190 (1-4)517-520 (2002).

 

            ABSTRACT: Diffusion length of Ga on the GaAs(0 0 1)- (2 x 4) beta2 is investigated by a newly developed Monte Carlo-based computational method. The new computational method incorporates chemical potential of Ga in the vapor phase and Ga migration potential on the reconstructed surface obtained by ab initio calculations; therefore we can investigate the adsorption, diffusion and desorption kinetics of adsorbate atoms on the surface. The calculated results imply that Ga diffusion length before desorption decreases exponentially with temperature because Ga surface lifetime decreases exponentially. Furthermore, Ga diffusion length L along [1 (1) over bar 0] and [1 1 0] on the GaAs(0 0 1)-(2 x 4) beta2 are estimated to be L[(1 (1) over bar 0]) congruent to 700 nm and L-[1 1 0] congruent to 200 nm, respectively, at the incorporation-desorption transition temperature (T similar to 860 K). (C) 2062 Elsevier Science B.V. All rights reserved.

 

62.    K. Kanzaki, T. Yamaguchi, M. Nagase, K. Yamazaki, and H. Namatsu

            "Resist thinning effect on nanometer-scale line-edge roughness"

            Japanese Journal Of Applied Physics Part 2-letters 41 (11B)L1342-L1344 (2002).

 

            ABSTRACT: The thickness dependence of the roughness of ultrathin (less than or equal to 100 nm) electron-beam resist (ZEP520) was investigated using an atomic force microscope (AFM). The roughness (linewidth fluctuations of line patterns) increased with decreasing resist thickness, especially below 30 nm. On the other hand, polymer aggregates, which are well observed in conventional resists, existed in compressed form even in this ultrathin film. In addition, the dissolution rate of the resist tended to be faster with thickness reduction. Both the existence of polymer aggregates and the fast dissolution of the entire resist polymer possibly caused the larger roughness in the ultrathin resist films.

 

63.    S. Karimoto, K. Ueda, M. Naito, and T. Imai

            "Superconducting thin films of electron-doped infinite-layer Sr1-xLaxCuO2 grown by molecular beam epitaxy"

            Physica C-superconductivity And Its Applications 378127-130 (2002).

 

            ABSTRACT: We grew single-crystalline Sr1-xLaxCuO2 thin films of electron-doped infinite-layer compounds by molecular beam epitaxy. Crucial to our success was the use of KTaO3 substrates. The best film showed T-c(onset) = 41.5 K and T-c(zero) = 39.0 K. The resistivity of the optimum-doped films exhibited metallic temperature dependence with a low resistivity of 320 muOmega cm. at room temperature and 120 muOmega cm. just above T-c. Such excellent electrical properties have not previously been reported for this system with either thin films or bulk polycrystalline specimens. (C) 2002 Elsevier Science B.V. All rights reserved.

 

64.    N. Kasai, Y. Jimbo, and K. Torimitsu

            "Electrochemical monitoring of glutamate release at multiple positions in a rat hippocampal slice"

            Analytical Sciences 18 (12)1325-1327 (2002).

 

            ABSTRACT: The continuous monitoring of the distribution of glutamate (Glu), a neurotransmitter released at synaptic terminals, is important in terms of understanding the signal transfer mechanism in the brain. In this study, we monitored the concentration of Glu released at multiple positions in a hippocampal slice continuously, and obtained an approximate Glu distribution by using our electrochemical glutamate sensor array. After confirming our sensor's high sensitivity to Glu, we placed a slice on the array, and measured the currents at selected electrodes in the array. When we stimulated a specific position in the slice electrically, the glutamate concentration increased in different areas after several tens of seconds. The presence of glutamate receptor blockers suppressed these increases. This suggests that the electrical signal was transferred along with neurons through synapses and stimulated the Glu release. Our multichannel glutamate sensor should be a powerful tool to determining the distribution of real-time glutamate non-invasively for the studies using biological samples.

 

65.    M. Kasu, and N. Kobayashi

            "High field-emission current density from heavily Si-doped AlN and AlxGa1-xN"

            Compound Semiconductors 2001 (170)39-44 (2002).

 

            ABSTRACT: From measurements of the electric field strength (E-FE) necessary for a field emission (FE) current, we found that AlN showed the lowest EFE among AlxGa1-xN (0.38less than or equal toxless than or equal to1) and that as the Si dopant density (N-Si) increases EFE decreases in the range 5x10(18) < N-Si < 1x10(21) cm(-3). Heavy Si doping induces spontaneous formation of ridges having nanometer-order sharpness and decreases the energy barrier height in FE. From heavily Si-doped (Nsi: 1x10(21) cm(-3)) AlN, we obtained an FE current density of 0.22 A/cm(2).

 

66.    M. Kasu, and N. Kobayashi

            "High hole mobility (1300 cm(2)/V s) at room temperature in hydrogen-terminated (001) diamond"

            Applied Physics Letters 80 (21)3961-3963 (2002).

 

            ABSTRACT: We have obtained high hole mobility of 1300 cm(2)/V s at room temperature in a hydrogen-terminated homoepitaxial diamond (001) layer grown at 766 degreesC and with the thickness of 6.5 mum. Above room temperature, the hole sheet density increased proportionally as the homoepitaxial-layer thickness increased. We discuss the mechanism for the high hole mobility near room temperature assuming parallel conduction in the homoepitaxial layer and on (or near) the surface. (C) 2002 American Institute of Physics.

 

67.    A. Kawaharazuka, T. Saku, C. A. Kikuchi, Y. Horikoshi, and Y. Hirayama

            "Study of free GaAs surfaces using a back-gated undoped GaAs/AlGaAs heterostructure"

            Physica E-low-dimensional Systems & Nanostructures 13 (2-4)663-666 (2002).

 

            ABSTRACT: We study the free GaAs surface by using a back-gated undoped AlGaAs/GaAs heterostructure. This structure is suitable for investigating this surface since a two-dimensional electron gas is induced by the back-gate bias in the undoped heterostructure. We compare the channel depth dependence of the transport characteristics with two different models of the free GaAs: the,mid-gap pinning model', which assumes a constant surface Fermi level, and an alternative approach called the 'frozen surface model', which assumes a constant surface charge density. The experimental results indicate that the frozen surface model appropriately describes free GaAs surfaces at low temperature in spite of the fact that the characteristics deviate from this model at higher temperature or for a shallow channel. (C) 2002 Elsevier Science B.V. All rights reserved.

 

68.    T. Kawamura, Y. Watanabe, S. Fujikawa, S. Bhunia, K. Uchida, J. Matsui, Y. Kagoshima, and Y. Tsusaka

            "Real-time observation of surface morphology of indium phosphide MOVPE growth with using X-ray reflectivity technique"

            Journal Of Crystal Growth 237398-402 (2002).

 

            ABSTRACT: The results of real-time X-ray reflectivity measurements of MOVPE grown indium phosphide surface are presented. At the low growth temperature of 450degreesC, large decreases of reflectivity were observed. Suggesting the formation of indium islands. At higher growth temperature of 550degreesC, only small changes were observed at high growth rate, indicating the step-flow growth mode. Oscillations longer than mono-layer growth were also observed at 500degreesC and 550degreesC, and roughness changes obtained from these oscillations were less than 0.01-nm suggesting small islands formation on the terrace or step-edge fluctuation during the growth. (C) 2002 Elsevier Science B.V. All rights reserved.

 

69.    T. Kimura, H. Tamura, K. Kuroki, K. Shiraishi, H. Takayanagi, and R. Arita

            "Superconductivity in quantum dot superlattices composed of quantum wire networks"

            Physical Review B 66 (13), 132508 (2002).

 

            ABSTRACT: Based on calculations using the local density approximation, we propose quantum wire networks with square and plaquette-type lattice structures that form quantum dot superlattices. These artificial structures are well described by the Hubbard model. Numerical analysis reveals a superconducting ground state with transition temperatures T-c of up to 90 mK for the plaquette, which is more than double the value of 40 mK for the square lattice type and is sufficiently high to allow for the experimental observation of superconductivity.

 

70.    T. Kimura

            "Breathing modes of Bose-Einstein condensates in highly asymmetric traps"

            Physical Review A 66 (1), 013608 (2002).

 

            ABSTRACT: The breathing mode collective-excitation frequency of a Bose-Einstein condensate is studied in a highly asymmetric (two- or one-dimensional) trap by using a sum-rule method and a time-dependent variational method. The collective-excitation frequency of the breathing mode in the Thomas-Fermi limit for a purely two- or one-dimensional trap is reproduced by a general result for a three-dimensional trap. In the case of a two- or one-dimensional trap, we obtain the lowest-order correction for the excitation frequency due to the finiteness of the trap frequency in the tightly trapped direction or the finiteness of the number of atoms.

 

71.    T. Kimura, H. Tamura, K. Shiraishi, and H. Takayanagi

            "Magnetic field effects on the ferromagnetism and transport properties of Kagome dot superlattices"

            Physica E-low-dimensional Systems & Nanostructures 12 (1-4)197-199 (2002).

 

            ABSTRACT: Magnetic field effects on a Kagome dot superlattice are studied. The Hofstadter butterfly has wide gap structures where a wide quantized Hall plateau should be observable in experiments. A magnetic-field-induced ferromagnetic-paramagnetic transition and a metal-insulator one are predicted. All of these magnetic field effects should be observable in small magnetic fields (of the order of 0.1 T). (C) 2002 Elsevier Science B.V. All rights reserved.

 

72.    T. Kimura, H. Tamura, K. Shiraishi, and H. Takayanagi

            "Magnetic-field effects on a two-dimensional Kagome lattice of quantum dots"

            Physical Review B 65 (8), 081307 (2002).

 

            ABSTRACT: Magnetic-field effects on the energy spectrum (Hofstadter butterfly) and the flat-band ferromagnetism: are studied on a. two-dimensional Kagome lattice of quantum dots. Application of a perpendicular magnetic field destroys the flat-band ferromagnetism and induces a metal-insulator transition because the flat band has a finite dispersion. In the half-filled flat band, the ferromagnetic-paramagnetic transition and the metal-insulator one occur simultaneously at a magnetic field when the Coulomb interaction is strong. These phenomena can be observed in experiment under reasonable magnetic fields in artificial quantum dot superlattices.

 

73.    Y. Kobayashi, V. Perez-Solorzano, J. Off, B. Kuhn, H. Grabeldinger, H. Schweizer, and F. Scholz

            "Investigations of growth of self-assembled GaInN-GaN islands on SiC substrate by metalorganic vapor phase epitaxy"

            Journal Of Crystal Growth 243 (1)103-107 (2002).

 

            ABSTRACT: Processes involved in the formation of self-assembled GaInN/GaN islands without a surfactant on (0 0 0 1) 6H-SiC substrates have been investigated by atomic force microscopy (AFM). The GaInN islands were grown by metalorganic vapor phase epitaxy using triethylgallium (TEGa), trimethylindiurn (TMIn) and ammonia. Island formation could be confirmed by AFM only for growth temperatures below 670degreesC. At low growth rates, dot formation could only be observed for a large vapor phase ratio, TMIn/(TMIn + TEGa). There was no such limitation for larger growth rates, and the dot density increased with increasing vapor phase ratio at 670degreesC up to 1 x 10(9) cm(-2). Even larger densities of 1 x 10(10) cm(-2) were obtained when the substrate temperature was decreased to 625degreesC, which can be explained by the higher In incorporation coefficient at lower temperatures. These results indicate that the density of self-assembled GaInN-GaN islands increases with increasing strain in GaInN, i.e., increasing In incorporation. GaInN islands are found to exhibit a Stranski-Krastanow growth mode with a critical wetting layer thickness of about 2.5 ML. (C) 2002 Elsevier Science B.V. All rights reserved.

 

74.    T. Koga, J. Nitta, T. Akazaki, and H. Takayanagi

            "Rashba spin-splitting energies probed by anti-weak-localization analysis in symmetric and asymmetric InGaAs/InAlAs quantum wells"

            Physica E-low-dimensional Systems & Nanostructures 13 (2-4)542-546 (2002).

 

            ABSTRACT: The values of the zero-field spin-splitting energy Delta(o) in InAlAs InGaAs InAlA, heterostructures are investigated using anti-weak-localization analysis. The obtained values for A, are compared with Value, that were theoretically predicted assuming Rashba spin-orbit coupling (denoted by Delta(R)) The good agreement between Delta(o) and Delta(R) and their dependence on quantum,kell asymmetry suggest that our approach provides a useful tool for designing future spintronics devices using Rashba spin-orbit coupling. (C) 2002 Elsevier Science B.V. All rig its reserved.

 

75.    T. Koga, J. Nitta, T. Akazaki, and H. Takayanagi

            "Rashba spin-orbit coupling probed by the weak antilocalization analysis in InAlAs/InGaAs/InAlAs quantum wells as a function of quantum well asymmetry"

            Physical Review Letters 89 (4), 046801 (2002).

 

            ABSTRACT: We have investigated the values of the Rashba spin-orbit coupling constant alpha in In-0.52 Al-0.48 As/In Ga-0.53 As-0.47/In Al-0.52 As-0.48 quantum wells using the weak antilocalization (WAL) analysis as a function of the structural inversion asymmetry (SIA) of the quantum wells. We have found that the deduced alpha values have a strong correlation with the degree of SIA of the quantum wells as predicted theoretically. The good agreement between the theoretical and experimental values of alpha suggests that our WAL approach for deducing alpha values provides a useful tool in designing future spintronics devices that utilize the Rashba spin-orbit coupling.

 

76.    T. Koga, J. Nitta, T. Akazaki, and H. Takayanagi

            "Conditions for the spin rectification phenomena predicted for semiconducting triple barrier structures in the presence of the Rashba spin-orbit coupling"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 41 (4B)2501-2504 (2002).

 

            ABSTRACT: We propose the fabrication of a spin rectifying diode that utilizes the Rashba spin-orbit coupling, by the application of semiconducting triple barrier structures. This spin diode makes use of spin-dependent resonant tunneling levels that are formed in the triple barrier structures. We found that, for a certain emitter-collector bias voltage, it is possible to engineer the structure in such a way that a resonant level formed within the first quantum well matches that of the second quantum well only for a selected spin state, thus realizing an electronic spin rectifier. The calculated spin-filter efficiency of the transmitted current through the device, which is defined as [I-up arrow - I-down arrow]/(I-up arrow + I-down arrow), is found to be higher than 99.9%.

 

77.    T. Koga, J. Nitta, and H. Takayanagi

            "Spin-filter device based on the Rashba effect using a nonmagnetic resonant tunneling diode"

            Physical Review Letters 88 (12), 126601 (2002).

 

            ABSTRACT: We propose an electronic spin-filter device that uses a nonmagnetic triple barrier resonant tunneling diode (TB-RTD). This device combines the spin-split resonant tunneling levels induced by the Rashba spin-orbit interaction and the spin blockade phenomena between two regions separated by the middle barrier in the TB-RTD. Detailed calculations using the InAlAs/InGaAs material system reveal that a splitting of a peak should be observed in the I-V curve of this device as a result of the spin-filtering effect. The filtering efficiency exceeds 99.9% at the peak positions in the I-V curve.

 

78.    N. Kumada, D. Terasawa, Y. Shimoda, H. Azuhata, A. Sawada, Z. F. Ezawa, K. Muraki, T. Saku, and Y. Hirayama

            "Phase diagram of interacting composite fermions in the bilayer nu=2/3 quantum Hall effect"

            Physical Review Letters 89 (11), 116802 (2002).

 

            ABSTRACT: We study the phase diagram of composite fermions (CFs) in the presence of spin and pseudospin degrees of freedom in the bilayer nu=2/3 quantum Hall (QH) state. Activation studies elucidate the existence of three different QH states with two different types of hysteresis in the magnetotransport. While a noninteracting CF model provides a qualitative account of the phase diagram, the observed renormalization of tunneling gap and a non-QH state at high densities are not explained in the noninteracting CF model, and are suggested to be manifestations of interactions between CFs.

 

79.    N. Kumada, D. Terasawa, Y. Shimoda, H. Azuhata, A. Sawada, Z. F. Ezawa, K. Muraki, T. Saku, and Y. Hirayama

            "Various phase transitions in v=2/3 bilayer quantum Hall states"

            Physica E-low-dimensional Systems & Nanostructures 12 (1-4)32-35 (2002).

 

            ABSTRACT: We measured the magnetoresistance in bilayer quantum Hall (QH) state at fractional filling factor v Surprisingly, for different QH areas and two types of hysteresis were observed by controlling the total electron density and the density difference in two layers. Two QH areas and one type of hysteresis are novel characteristic of bilayer systems. (C) 2002 Elsevier Science B.V. All rights reserved.

 

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

            "Pnp AlGaN/GaN heterojunction bipolar transistors operating at 300 degrees C"

            Physica Status Solidi A-applied Research 194 (2)443-446 (2002).

 

            ABSTRACT: We have fabricated Pnp AlGaN/GaN heterojunction bipolar transistors and investigated their common-emitter current-voltage (I-V) characteristics at the temperatures from room temperature to 300 degreesC. Good saturation properties were observed in their common-emitter I-V characteristics. The current gain of 20 at room temperature increased with elevating the temperature. The maximum current gain was as high as 71 at 300 degreesC with the collector current from 20 to 200 muA. This increase in current gain is ascribed to the enhancement in the hole injection efficiency from the p-AlGaN emitter to the n-GaN base as well as the reduction of the device resistance and the improved Ohmic characteristics of the subcollector. These results indicate that Pup HBTs have the potential for high temperature operation.

 

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

            "Common-emitter current-voltage characteristics of a Pnp AlGaN/GaN heterojunction bipolar transistor with a low-resistance base layer"

            Applied Physics Letters 80 (20)3841-3843 (2002).

 

            ABSTRACT: We fabricated a Pnp AlGaN/GaN heterojunction bipolar transistor and investigated its common-emitter current-voltage characteristics. The device structures were grown by metalorganic vapor phase epitaxy on a sapphire substrate. The Al mole fraction in an AlGaN emitter layer was 0.18. The thickness of the GaN base layer was 0.12 mum and its Si doping concentration was as high as 1x10(19) cm(-3), so its base resistance decreased two orders of magnitude compared with the reported Npn nitride heterojunction bipolar transistors. The transistor showed good saturation current-voltage characteristics and the maximum common-emitter current gain of 28 was obtained for collector current of -2x10(-5) A at room temperature. (C) 2002 American Institute of Physics.

 

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

            "Common-emitter current-voltage characteristics of a pnp GaN bipolar junction transistor"

            Applied Physics Letters 80 (7)1225-1227 (2002).

 

            ABSTRACT: We fabricated a pnp GaN bipolar junction transistor and investigated its common-emitter current-voltage characteristics. The device structures were grown by metalorganic vapor phase epitaxy on a sapphire substrate. The base thickness was 0.12 mum and its doping concentration was estimated to be lower than mid-10(17) cm(-3). We have obtained a maximum common-emitter current gain of 50 at room temperature for collector current ranging from -10(-5) to -10(-4) A. (C) 2002 American Institute of Physics.

 

83.    E. Kuramochi, M. Notomi, T. Kawashima, J. Takahashi, C. Takahashi, T. Tamamura, and S. Kawakami

            "A new fabrication technique for photonic crystals: Nanolithography combined with alternating-layer deposition"

            Optical And Quantum Electronics 34 (1-3)53-61 (2002).

 

            ABSTRACT: We propose two photonic crystal structures that can be created by combining nanolithography with alternating-layer deposition. Photonic band calculations suggest that a drilled alternating-layer photonic crystal combining two-dimensional (2D) alternating multilayers and an array of vertically drilled holes may achieve a full photonic bandgap. In addition, a 3D/2D/3D cross-dimensional photonic crystal, which sandwiches a 2D photonic crystal slab between three-dimensional (3D) alternating-layer photonic crystals, should provide better vertical confinement of light than a conventional index guiding slab. Fabrication techniques based on existing technologies (electron beam lithography, bias sputtering, and low-pressure ECR etching) require very few process steps. Our preliminary fabrication suggests that, by refining these technologies, we will be able to realize photonic crystals.

 

84.    J. Kurian, Y. Takahashi, T. Amemura, T. Suzuki, and T. Morishita

            "The growth and characterization of epitaxial Ba2NdTaO6 dielectric ceramic thin films on (100) SrTiO3"

            Journal Of Physics D-applied Physics 35 (22)3002-3006 (2002).

 

            ABSTRACT: Ba2NdTaO6 (BNTO) dielectric ceramic thin films were grown on (100) SrTiO3 by pulsed laser deposition technique. The optimum growth conditions for the epitaxial growth of BNTO on single crystal SrTiO3 have been established. The BNTO films were characterized by theta-2theta, omega-scan and phi-scan measurements using a four-axis x-ray diffractometer and the surface morphology studied by atomic force microscopy. The films grown under the optimized conditions were epitaxial with (00l) orientation and were in-plane aligned. The BNTO films grown under the optimized deposition condition were smooth with a root mean square roughness of 2 nm for a 2 mum x 2mum area. The dielectric properties of the BNTO films measured using impedance analyser show that the dielectric constant and loss factor values agree with the values reported for the bulk BNTO in the literature.

 

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

            "Studies of advanced soft X-ray laser and coherent higher harmonic generation using intense subpicosecond laser produced high density plasma"

            Journal Of Luminescence 100 (1-4)291-300 (2002).

 

            ABSTRACT: Current activities on our research of soft X-ray lasers and higher harmonic generations using intense, subpicosecond lasers are reviewed. Especially for soft X-ray lasers we experimentally demonstrate that by longitudinally pumping 2-mm-long molybdenum preformed plasma with high-intensity 475 fs duration laser pulse, a highly directive soft-X-ray laser at 18.9 nm wavelength is generated. The divergence of the beam is evaluated to be of the submilliradian order, and only requires pump laser energy of 150 mJ. Simulations show that the pedestal in the main pump pulse can generate electron density and gain profiles with large spatial gradients, which result in the selective amplification of low-order transverse modes. The present result is the demonstration of an efficient and alternative method of improving the spatial coherence of X-ray lasers with amplified spontaneous emission medium, with possibilities of becoming an excellent tool to explore various application experiments. In higher harmonic generation, topics related to observation of blue shift due to collisionless absorption process is described. (C) 2002 Published by Elsevier Science B.V.

 

86.    H. Kuroda, T. Ozaki, A. Ishizawa, T. Kanai, K. Yamamoto, R. Li, and J. Zhang

            "Coherent short wavelength radiation via picosecond Nd : glass lasers"

            Laser And Particle Beams 20 (1)59-65 (2002).

 

            ABSTRACT: The generation of coherent soft X rays is studied using a terawatt picosecond Nd:glass laser system. Two different methods are investigated as candidates for efficient generation of such radiation, namely, longitudinally pumped transient collisional excitation nickel-like molybdenum X-ray laser, and high-harmonic generation from solid-vacuum interfaces. In the course of experiments on longitudinally pumped X-ray lasers, unexpected jetlike structures are observed in the visible emission of the molybdenum plasma, extending over a length of several millimeters. An interesting characteristic of this phenomena is that clear jets are observed only for longitudinal pump intensities between 5 x 10(14) and 7 x 10(14) W/cm(2). The effects of a finite scale length density gradient on surface harmonics is also investigated. The efficiency of harmonic generation from near-solid density plasma is found to increase by a factor of 2 to 3 when using prepulses. The scale length of the preplasma is simulated using a one-dimensional hydrodynamic code, and the increase in efficiency is verified to be in accordance with particle-in-cell simulation results.

 

87.    K. Kuroki, T. Kimura, R. Arita, Y. Tanaka, and Y. Matsuda

            "dx2-y2- versus dxy- like pairings in organic superconductors kappa-(BEDT-TTF)(2)X"

            Physical Review B 65 (10), 100516 (2002).

 

            ABSTRACT: Pairing symmetry in kappa-(BEDT-TTF)(2)X is reexamined by applying the fluctuation exchange method to the Hubbard model on the original four-band lattice. Our study is motivated by the discrepancy between recent thermal conductivity/tunneling spectroscopy experiments and the previous theories based on the effective single or two-band model. In contrast to the previous theories, we find that d(x)2-(y)2-like pairing dominates over d(xy) in agreement with recent experiments. Our study provides a general lesson that even if the Fermi surface seems to be reproduced by an effective model, the pairing symmetry can be different from that of the original system.

 

88.    T. D. Ladd, J. R. Goldman, F. Yamaguchi, Y. Yamamoto, E. Abe, and K. M. Itoh

            "All-silicon quantum computer"

            Physical Review Letters 89 (1), 017901 (2002).

 

            ABSTRACT: A solid-state implementation of a quantum computer composed entirely of silicon is proposed. Qubits are Si-29 nuclear spins arranged as chains in a Si-28 (spin-0) matrix with Larmor frequencies separated by a large magnetic field gradient. No impurity dopants or electrical contacts are needed. Initialization is accomplished by optical pumping, algorithmic cooling, and pseudo-pure state techniques. Magnetic resonance force microscopy is used for ensemble measurement.

 

89.    K. T. Liu, A. Fujiwara, Y. Takahashi, K. Murase, and Y. Horikoshi

            "Voltage gain of Si single-electron transistor and analysis of performance of n-metal-oxide-semiconductor type inverter with resistive load"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 41 (2A)458-463 (2002).

 

            ABSTRACT: Voltage gain of Si single-electron transistors (SETs) fabricated by the pattern-dependent oxidation (PADOX) method was investigated. It was experimentally demonstrated that the structural parameters of the SET, such as Si wire length and gate oxide thickness, are important parameters to be optimized for obtaining high voltage gain. Moreover, the performance of the n-metal-oxide-semiconductor (nMOS) type inverter with resistive load was investigated by simulation based on the measured characteristics of the Si-SET. It was found that the simulated result significantly differs from the simulation using ideal SET characteristics derived from the orthodox theory; we discuss the voltage gain, response times, power consumption and logic swing voltage.

 

90.    Y. X. Liu, A. Miranowicz, M. Koashi, and N. Imoto

            "Realization of symmetric sharing of entanglement in semiconductor microcrystallites coupled hy a cavity field"

            Physical Review A 66 (6), 062309 (2002).

 

            ABSTRACT: The entanglement of excitonic states in a system of N spatially separated semiconductor microcrystallites is investigated. The interaction among the different microcrystallites is mediated by a single-mode cavity field. It is found that the symmetric sharing of the entanglement (measured by the concurrence) between any pair of the excitonic state with N qubits defined by the number states (vacuum and a single-exciton states) or the coherent states (odd and even coherent states) can be prepared by the cavity field for this system.

 

91.    Y. X. Liu, N. Imoto, S. K. Ozdemir, G. R. Jin, and C. P. Sun

            "Semiconductor-cavity QED in high-Q regimes: Detuning effect"

            Physical Review A 65 (2), 023805 (2002).

 

            ABSTRACT: The nonresonant interaction between the high-density excitons in a quantum well and a single-mode cavity field is investigated. An analytical expression for the physical spectrum of the excitons is obtained. The spectral properties of the excitons, which are initially prepared in the number states or the superposed states of the two different number states by the resonant femtosecond pulse pumping experiment, are studied. A numerical study of the physical spectrum is carried out and a discussion of the detuning effect is presented.

 

92.    T. Machida, T. Yamazaki, S. Komiyama, K. Muraki, and Y. Hirayama

            "Dynamic nuclear-spin polarization induced by scattering between fractional quantum Hall edge channels"

            Microelectronic Engineering 63 (1-3)63-68 (2002).

 

            ABSTRACT: We find spin-dependent enhancement/suppression of scattering between fractional quantum Hall (FQH) edge channels (ECs), which originates from the hyperfine interaction between electron spins and nuclear spins. Nuclear magnetic resonance is detected via the FQH-EC transport, indicating the relevance of dynamic nuclear polarization (DNP). Spin polarizations of FQH ECs are inferred from the DNP. (C) 2002 Elsevier Science B.V. All rights reserved.

 

93.    T. Machida, S. Ishizuka, T. Yamazaki, S. Komiyama, K. Muraki, and Y. Hirayama

            "Spin polarization of fractional quantum Hall edge channels studied by dynamic nuclear polarization"

            Physical Review B 65 (23), 233304 (2002).

 

            ABSTRACT: We find that the scattering between unequally populated fractional quantum Hall (FQH) edge channels (EC's) polarizes nuclear spins through the hyperfine interaction. This dynamic nuclear polarization (DNP) is evidenced by the nuclear magnetic resonance detected via the transport through FQH EC's. Spin polarizations of different FQH EC's are inferred from the polarity of DNP.

 

94.    T. Machida, S. Ishizuka, and K. Muraki

            "Spin polarization in fractional quantum Hall edge channels"

            Physica E-low-dimensional Systems & Nanostructures 12 (1-4)76-79 (2002).

 

            ABSTRACT: The derivative Hall resistance in quantum Hall systems shows a hysteretic nonlinearity in the presence of the unequal population between fractional quantum Hall edge channels. The hysteresis is ascribed to spin-dependent enhancement, suppression of the inter-edge-channel scattering. which we suggest to originate from the hyperfine interaction between electron spins and nuclear spins. (C) 2002 Elsevier Science B.V. All rights reserved.

 

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

            "Two-dimensional electron gas transport properties in AlGaN/GaN heterostructure field-effect transistors with high Al compositions"

            Compound Semiconductors 2001 (170)107-112 (2002).

 

            ABSTRACT: In order to clarify the effect of the Al composition on the two-dimensional electron gas (2DEG) transport properties in Si-doped AlGaN/GaN heterostructure field-effect transistors (HFETs), the 2DEG mobility has been examined as the function of the 2DEG density for the Al composition up to 0.3 below and above room temperature. Above room temperature (up to 400degreesC), the 2DEG mobility for the same 2DEG density has been shown to increase with increasing the Al composition as the result of the increased polarization-induced electrons. For a very high 2DEG density of 2x10(13) cm(-2), the HFET with the Al composition of 0.3 has exhibited high 2DEG mobilities more than 1000 cm(2)/Vs at room temperature and about 140 cm(2)/Vs at 400degreesC. Thus the HFETs with high At compositions are promising from the viewpoint of both the 2DEG mobility and the 2DEG density.

 

96.    P. C. Main, A. Patane, R. J. Hill, A. Levin, L. Eaves, M. Henini, D. G. Austing, S. Tarucha, Y. V. Dubrovskii, and E. E. Vdovin

            "Mapping the wave functions in quantum dots"

            Physica E-low-dimensional Systems & Nanostructures 12 (1-4)794-801 (2002).

 

            ABSTRACT: We use magneto-tunnelling spectroscopy to investigate the form of the wave functions of the confined electron states in InAs self-assembled quantum dots. We are able to observe the wave functions corresponding to the ground and the two lowest excited states for dots grown on (100)- and (311)B-oriented GaAs substrates. For both orientations. the wave functions are found to have a biaxial symmetry in the growth plane. with axes parallel to main crystallographic directions. In addition, we have performed magneto-tunnelling spectroscopy measurements on tunnel diodes that incorporate gate electrodes. By observing how the energies of particular states vary with gate bias, we are able to identify the states associated with an individual dot. This allows us to measure quantitatively both the energy levels and wave functions of the dot states. (C) 2002 Elsevier Science B.V. All rights reserved.

 

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

            "Npn InGaN/GaN double heterojunction bipolar transistors with high common-emitter current gains"

            Compound Semiconductors 2001 (170)33-38 (2002).

 

            ABSTRACT: Npn InGaN/GaN double heterojunction bipolar transistors have been fabricated using p-type InGaN and n-type GaN as base and collector layers, respectively. The In mole fraction in the base layer and its thickness were 0.06 and 100 nm, respectively. The Mg doping concentration in the base layer was 1 x 10(19) cm(-3) corresponding to a hole concentration of 5x10(18) cm(-3) at room temperature. The common-emitter I-V characteristics showed good saturation characteristics and the maximum current gain of 20 was obtained at room temperature. Using this current gain, a minority carrier diffusion length for electrons was calculated to be 0.32 mum in the p-InGaN base layer. The corresponding minority carrier lifetime was 400 ps. These results mean the good crystal quality of p-InGaN.

 

98.    T. Makimoto, K. Kumakura, T. Nishida, and N. Kobayashi

            "Valence-band discontinuities between InGaN and GaN evaluated by capacitance-voltage characteristics of p-InGaN/n-GaN diodes"

            Journal Of Electronic Materials 31 (4)313-315 (2002).

 

            ABSTRACT: Valence-band discontinuities between InGaN and GaN were evaluated using the capacitance-voltage characteristics of p-InGaN/n-GaN heterojunction diodes with high hole concentrations in p-InGaN. This capacitance-voltage method is effective to evaluate valence-band discontinuities because the influence of the piezoelectric charges at the heterojunction is ignored due to high acceptor concentrations. The built-in potential obtained from the capacitance-voltage measurements decreased with the In mole fraction of p-InGaN. This result indicates that the valence-band discontinuity (DeltaE(V)) increases with the In mole fraction (x) and is expressed as DeltaE(V) (eV) = 0.85x for xless than or equal to0.28. The DeltaE(V) value obtained in this work is about 50% lower than that reported previously using the photoluminescence (PL) method.

 

99.    P. Matagne, J. P. Leburton, D. G. Austing, and S. Tarucha

            "Hund's first rule and addition energy spectra of cylindrical quantum dots"

            Physica E-low-dimensional Systems & Nanostructures 13 (2-4)679-682 (2002).

 

            ABSTRACT: We discuss various spin sequences occurring during the charging of realistic vertical quantum dots with emphasis on three-dimensional (3D) effects. Our analysis is based on a combined theoretical-3D) density functional model-experimental approach. In the third shell, a clear dip at N = 7 electrons followed by a peak at N = 8 or 9 is the signature of maximum spin alignment at half-shell filling. (C) 2002 Elsevier Science B.V. All rights reserved.

 

100.    P. Matagne, J. P. Leburton, D. G. Austing, and S. Tarucha

            "Shell charging and spin-filling sequences in realistic vertical quantum dots"

            Physical Review B 65 (8), 085325 (2002).

 

            ABSTRACT: For nominally high-symmetry cylindrical-shaped vertical quantum dots, we show that Hund's first rule is not violated if maxima appear in the 0-T addition energy spectra at positions other than when the shell is half filled. For the third shell, a minimum at N=7 electrons followed by a maximum at N=8 or 9 electrons is the only clear signature of sequential spin alignment up to half shell occupation. We demonstrate that the filling of this shell and the consequent spectral shape for realistic dots are quite rich and varied.

 

101.    K. Matsuda, N. Hatakenaka, H. Takayanagi, and T. Sakuma

            "Tunable single-photon source using Korteweg-de Vries solitons"

            Applied Physics Letters 81 (15)2698-2700 (2002).

 

            ABSTRACT: We describe the quantum transport of electrons by solitary waves and use it as the basis for a scheme for generating a single photon with highly nonclassical nature. A concave soliton acting as an attractive potential can capture an electron in its only eigenstate and the captured electron can be transported by soliton propagation. A single photon is generated by a transition between eigenstates in the interacting soliton potential when a soliton with a captured electron interacts with an empty soliton with a lower eigenstate. (C) 2002 American Institute of Physics.

 

102.    T. Matsuoka, H. Okamoto, M. Nakao, H. Harima, and E. Kurimoto

            "Optical bandgap energy of wurtzite InN"

            Applied Physics Letters 81 (7)1246-1248 (2002).

 

            ABSTRACT: Wurtzite InN films were grown on a thick GaN layer by metalorganic vapor phase epitaxy. Growth of a (0001)-oriented single crystalline layer was confirmed by Raman scattering, x-ray diffraction, and reflection high energy electron diffraction. We observed at room temperature strong photoluminescence (PL) at 0.76 eV as well as a clear absorption edge at 0.7-1.0 eV. In contrast, no PL was observed, even by high power excitation, at similar to1.9 eV, which had been reported as the band gap in absorption experiments on polycrystalline films. Careful inspection strongly suggests that a wurtzite InN single crystal has a true bandgap of 0.7-1.0 eV, and the discrepancy could be attributed to the difference in crystallinity. (C) 2002 American Institute of Physics.

 

103.    A. Miranowicz, S. K. Ozdemir, Y. X. Liu, M. Koashi, N. Imoto, and Y. Hirayama

            "Generation of maximum spin entanglement induced by a cavity field in quantum-dot systems"

            Physical Review A 65 (6), 062321 (2002).

 

            ABSTRACT: Equivalent-neighbor interactions of the conduction-band electron spins of quantum dots in the model of Imamoglu [Phys. Rev. Lett. 83, 4204 (1999)] are analyzed. An analytical solution and its Schmidt decomposition are found and applied to evaluate how much the initially excited dots can be entangled with the remaining dots if all of them are initially disentangled. It is demonstrated that perfect maximally entangled states (MES's) can only be generated in systems of up to six dots with a single dot initially excited. It is also shown that highly entangled states, approximating the MES's with good accuracy, can still be generated in systems of odd numbers of dots with almost half of them excited. A sudden decrease of entanglement is observed on increasing the total number of dots in a system with a fixed number of excitations.

 

104.    N. Miura, H. Nakagawa, T. Sekitani, M. Naito, H. Sato, and Y. Enomoto

            "High-magnetic-field study of high-T-c cuprates"

            Physica B-condensed Matter 319 (1-4)310-320 (2002).

 

            ABSTRACT: We present our recent studies of high-T-c superconductors in very high pulsed magnetic fields exceeding 100T (megagauss fields). In YBa2Cu3O7-delta, the super to normal transition was observed in transport measurements for B\ c under short pulse fields up to 120 T. A plot of the upper critical field H,2 as a function of temperature demonstrates that the curve obeys the conventional relation well established in other type-11 superconductors in the dirty limit. From the resistivity versus temperature curve at high magnetic fields above the super to normal transition, it was found that the hole system shows a metallic temperature dependence for B\ c. In Nd2-xCexCuO4 as electron-doped cuprate, a large magneto-resistance was observed above the transition field. It was also found that the temperature dependence of the resistivity above the critical field is insulator-like showing a prominent logarithmic up-turn at low temperatures. A similar logarithmic up-turn was observed in several other cuprates such as La2-xSrxCuO4 (LSCO), La2-xCexCuO, and Pr2-xCexCuO4. The experimental results for thin-film samples of LSCO with different strains suggest that the Kondo effect plays an important role in these materials. A new phase diagram of LSCO is proposed on the basis of a viewpoint of the interplay between superconductivity and the Kondo effect. (C) 2002 Published by Elsevier Science B.V.

 

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

            "Activation studies of pseudospin quantum Hall ferromagnets in double quantum wells"

            Physica E-low-dimensional Systems & Nanostructures 12 (1-4)8-11 (2002).

 

            ABSTRACT: We study pseudospin quantum Hall ferromagnets realized in a strongly coupled double-quantum-well structure. The pseudospin dependence of the Coulomb interactions leads to magnetic anisotropy. Activation energies measured as a function of the single-particle gap, i.e. the pseudospin Zeeman energy. reveal a striking difference between the easy-axis and easy-plane ferromagnets. In the limit of zero single-particle gap, we observe a novel low-energy excitation, reminiscent of Skyrmions, for the v = 4 easy-axis ferromagnet. We discuss the reduced gap in terms of topological charge excitations in the domain walls. (C) 2002 Elsevier Science B.V. All rights reserved.

 

106.    A. Nagase, S. Horiguchi, A. Fujiwara, Y. Ono, K. Yamazaki, H. Namatsu, and Y. Takahashi

            "Single-electron devices formed by pattern-dependent oxidation: microscopic structural evaluation"

            Applied Surface Science 190 (1-4)144-150 (2002).

 

            ABSTRACT: The embedded Si structure formed by pattern-dependent oxidation (PADOX) in single-electron device (SED) is analyzed by novel microscopic methods using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface charge imaging SEM reveals the outline of the embedded Si nanowire of the electrically-measured SED. The size of the wire in the device is small enough to make a potential barrier caused by the quantum mechanical size effect. The result of the Si height in the oxidized structure estimated by AFM indicates that the huge stress induced by oxidation is applied to the narrow Si wire. The experimental results support the theoretical model of the SED fabricated by PADOX that the potential profile responsible for the SED operation is produced by two effects, the quantum mechanical size effect and the strain-induced bandgap reduction. (C) 2002 Elsevier Science B.V. All rights reserved.

 

107.    M. Naito, S. Karimoto, and A. Tsukada

            "Epitaxy-stabilized n-type superconducting cuprates"

            Superconductor Science & Technology 15 (12)1663-1668 (2002).

 

            ABSTRACT: We report the growth of n-type superconducting T'-(La,Ce)(2)CuO4 and infinite-layer (IL) (Sr,La)CuO2 thin films by means of molecular beam epitaxy (MBE). The bulk synthesis of T-(La,Ce)(2)CuO4 and IL-(Sr,La)CuO2 requires complicated techniques: synthesis at low temperatures below 600 degreesC for the former and at high pressures above 3 GPa for the latter. This makes it difficult to grow bulk single crystals. We have found, however, that high-quality single-crystalline films of both compounds can be rather easily prepared by thin-film processes. Single-phase T'-(La,Ce)(2)CuO4 films can be obtained for a wide range of x (0.0 less than or equal to x less than or equal to similar to0.4). The best T-c(end) is over 30 K, which is the highest in the T' family. For IL-(SrLa)CuO2, by using KTaO3 substrates, high T-c(end) over 39 K and also metallic resistivity were achieved for the first time to our knowledge. We describe the key parameters in the growth and the properties of the resultant films.

 

108.    T. Nakanishi, H. Okamoto, Y. Nagai, K. Takeda, I. Obataya, H. Mihara, H. Azehara, Y. Suzuki, W. Mizutani, K. Furukawa, and K. Torimitsu

            "Synthesis and atomic force microscopy observations of the single-peptide nanotubes and their micro-order assemblies"

            Physical Review B 66 (16), 165417 (2002).

 

            ABSTRACT: Hexa-peptide nanotubes (cyclo[-(L-Gln-D-Ala)(3)]) and octa-peptide nanotubes (cyclo[-(L-Gln-D-Ala)(4)]) were synthesized by a solid-phase method using Fmoc chemistry. We investigated their morphology by atomic force microscopy (AFM) and observed the single straight nanotube forms. We also obtained AFM images of the nano-order and/or micro-order assemblies on the same substrates. The assembled forms were rather different between the hexa-peptide nanotubes and the octa-peptide nanotubes. While the former produce nanobundles or microbundles, the latter form micro-order aggregated bundles.

 

109.    H. Nakano, and H. Takayanagi

            "Proximity-induced Cooper-pair in a very small normal-metal island"

            Physica C-superconductivity And Its Applications 367 (1-4)211-217 (2002).

 

            ABSTRACT: We analyzed the electronic states in a very small normal-metal (N)/insulator (I)/superconductor (S) tunneling junction, taking into account the charging effect generated with the charge transfer through the insulator. This junction has the microscopic (quasiparticle) and the macroscopic (Cooper-pair) aspects at the same time even if the relevant energies (eV, k(B)T) are much lower than the superconducting gap energy in the S electrode. By using the expression with Andreev reflection and Cooperon for the proximity effect, both the aspects (micro/macro) can be treated consistently. The results show that if the charging energy E-C is comparable to or smaller than the Thouless energy of the N region, a proximity-induced gap appears in the quasiparticle density of states and a Cooper-pair exists in the N region. However, the Cooper-pair does not oscillate between N and S regions. This behavior is quite different from the Cooper-pair in the single Cooper-pair box. (C) 2002 Elsevier Science B.V. All rights reserved.

 

110.    H. Namatsu

            "Supercritical drying for nanostructure fabrication"

            Journal Of Photopolymer Science And Technology 15 (3)381-388 (2002).

 

            ABSTRACT: Supercritical drying has been developed for the fabrication of nanostructures made of silicon or resist. Pattern collapse, which is a very serious problem in the fabrication of fine patterns, is related to the spacing, the aspect ratio and the surface tension of rinse solution. Among them, reducing the surface tension is the most effective way to suppress pattern collapse, because it does not affect pattern size. The use of supercritical carbon dioxide, which has no surface tension, as a final rinse, has enabled the formation of fine silicon patterns without collapse. For resists, preventing water contamination is the key to suppressing pattern deformation during supercritical drying. On the other hand, for water-rinsed resist systems, the use of a surfactant, which acts as a bridge between rinse water and supercritical fluid, is the most important technique that makes supercritical resist drying feasible. Thus, a drying technique that produces resist patterns without collapse or deformation has been developed; and a special dryer, which holds one wafer on a hot holder, has been constructed.

 

111.    K. G. Nath, F. Maeda, S. Suzuki, and Y. Watanabe

            "Passivation-mediated growth of Co on Se, S and O rich GaAs surfaces: A potential approach to control interface crystallinity and magnetic continuity"

            Journal Of Applied Physics 91 (6)3943-3945 (2002).

 

            ABSTRACT: Passivation-mediated growth was used to control the interface crystalline order and the magnetic continuity in epitaxial Co films on several GaAs(001) surfaces. Using Se, S, and O passivated layers on GaAs before Co deposition, we observed a variety of interface structures depending on the substrate condition. With the help of transmission electron microscopy (TEM) images, we show that a perfect and well-ordered crystalline growth at the initial stage of deposition for Co/Se/GaAs ensures a better growth for thicker film. The magnetic properties of Co overlayers on all the substrates were studied by magnetic linear dichroism in angular distribution (MLDAD) in photoemission and found to be different depending on the film crystallinity. By combining the TEM and MLDAD results, we conclude that Co film on Se/GaAs, which has an ordered interface, is a good candidate for use as a spin filter from the viewpoint of spin-injection mechanism. (C) 2002 American Institute of Physics.

 

112.    M. Nishida, N. Hatakenaka, and S. Kurihara

            "Supercurrent through hybrid junctions with anisotropic Cooper-pair condensates"

            Physical Review Letters 88 (14), 145302 (2002).

 

            ABSTRACT: general formula for the supercurrent between different internal structures in a wide class of hybrid junctions is derived on the basis of the Andreev-reflection picture. The formula extends existing formulas and also enables us to analyze novel B-phase/A-phase/B-phase junctions in super fluid He-3 systems. We propose a mechanism for pi states due to the (l) over cap texture in the A phase of the junction, which could elucidate major features of the pi states with higher critical current (H states) discovered in super fluid 3 He weak links. The bistability of the pi states is also discussed.

 

113.    T. Nishida, and N. Kobayashi

            "Characteristics of AlGaN quantum well light emitting diodes under large current operation"

            Compound Semiconductors 2001 (170)231-235 (2002).

 

            ABSTRACT: AlGaN-based ultraviolet light emitting diodes (LED) are characterized. The devices consist of an Al0.06Ga0.94N (2 nm) / Al0.12Ga0.88N single quantum well active layer sandwiched by Al0.3Ga0.7N carrier blocking layers and cladding layers of an Al0.16Ga0.84N (1.5 nm)/Al0.2Ga0.8N (1.5 nm) short-period alloy superlattice grown on bulk GaN substrate. Efficient conversion to UV light is confirmed, which indicates a high-quality active layer, effective suppression of carrier overflow, and transparency of conductive cladding layers. Radiative recombination dominantly occurs in the quantum well at injection current density lower than 0.25 kA/cm(2). Further dense injection leads to enhancement of the radiative recombination in the barrier layer. This clarifies the importance of the design of the active layer for high-power application.

 

114.    J. Nitta, T. Schapers, H. B. Heersche, T. Koga, Y. Sato, and H. Takayanagi

            "Investigation of ferromagnetic microstructures by local Hall effect and magnetic force microscopy"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 41 (4B)2497-2500 (2002).

 

            ABSTRACT: We have investigated the magnetization process of NiFe micro-magnets, using fringing field induced local Hall effect (LHE) and magnetic force microscopy (MFM), Although the LHE reflects information only from the edge of micro-magnets, the MFM observation supports the conclusion that a rapid jump in the Hall resistance implies a sharp switching of the magnetization. The width dependence of coercive field H-c for NiFe micro-magnets obtained from LHE measurement is well reproduced by numerical calculations. The good agreement between the LHE experiment and the model calculation shows that a LHE device provides useful information on the magnetization process in micro-magnets.

 

115.    J. Nitta, T. Koga, and H. Takayanagi

            "Interference of Aharonov-Bohm ring structures affected by spin-orbit interaction"

            Physica E-low-dimensional Systems & Nanostructures 12 (1-4)753-757 (2002).

 

            ABSTRACT: Gate-controlled Aharonov-Bohm (AB) experiments are performed with two AB-ring samples with different ring diameters in the presence of spin-orbit interaction. For the larger AB-ring, the magnetoresistance at zero magnetic field [R(B = 0)] shows minima in the whole gate voltage range. In both larger and smaller AB-rings, R(B = 0) shows oscillatory behaviors as a function of the gate voltage. The possible reason for this oscillation can be attributed to the phase interference induced by the spin-orbit interaction. (C) 2002 Elsevier Science B.V. All rights reserved.

 

116.    S. Nojima

            "Recurrent-photon feedback in two-dimensional photonic-crystal lasers"

            Physical Review B 65 (7), 073103 (2002).

 

            ABSTRACT: Theoretical studies are carried out for the close-to-lasing two-dimensional finite-size photonic crystals. On the basis of the simulations on the field-intensity distributions and the photon-energy flux distributions, this paper demonstrates the occurrence of a different type of positive feedback of light, which can be called recurrent-photon feedback. This feedback mechanism can be construed as an extension of the feedback mechanism in ordinary one-dimensional distributed-feedback lasers.

 

117.    M. Notomi, A. Shinya, K. Yamada, J. Takahashi, C. Takahashi, and I. Yokohama

            "Structural tuning of guiding modes of line-defect waveguides of silicon-on-insulator photonic crystal slabs"

            Ieee Journal Of Quantum Electronics 38 (7)736-742 (2002).

 

            ABSTRACT: We experimentally demonstrate the structural tuning of the waveguiding modes of line defects in photonic crystal (PC) slabs. By tuning the defect widths, we realized efficient single-mode waveguides that operate within photonic band gap frequencies in silicon-on-insulator PC slabs. The observed waveguiding characteristics agree very well with three-dimensional finite difference time-domain calculations. We also directly measured the propagation loss of the line defect waveguides and obtained a value of 6 dB/mm.

 

118.    M. Notomi, A. Shinya, E. Kuramochi, I. Yokohama, C. Takahashi, K. Yamada, J. Takahashi, T. Kawashima, and S. Kawakami

            "Si-based photonic crystals and photonic-bandgap waveguides"

            Ieice Transactions On Electronics E85C (4)1025-1032 (2002).

 

            ABSTRACT: We studied various types of 2D and 3D Si-based photonic crystal structures that are promising for future photonic integrated circuit application. With regard to 2D SOI photonic crystal slabs, we confirmed the formation of a wide photonic bandgap at optical communication wavelengths, and used structural tuning to realize efficient single-mode line-defect waveguides operating within the bandgap. As regards 3D photonic crystals, we used a combination of lithography and the autocloning deposition method to realize complicated 3D structures. We used this strategy to fabricate 3D full-gap photonic crystals and 3D/2D hybrid photonic crystals.

 

119.    M. Notomi

            "Negative refraction in photonic crystals"

            Optical And Quantum Electronics 34 (1-3)133-143 (2002).

 

            ABSTRACT: We demonstrate that light propagation in strongly modulated 2D/3D photonic crystals (PhCs) becomes refraction-like in the vicinity of the photonic bandgap, which is contrary to the fact that light propagation in weakly modulated PhCs is very different from refraction and thus the definition of refraction index becomes meaningless. Such a crystal behaves like a material having an effective refractive index controllable by the band structure. This situation is analogous to the effective-mass approximation in electron-band theory. The propagation states having a negative effective index exhibit unusual properties, such as mirror-like imaging effect, image-transfer effect. These properties are confirmed by finite-difference time-domain simulations.

 

120.    R. Nuryadi, Y. Ishikawa, Y. Ono, and M. Tabe

            "Thermal agglomeration of single-crystalline Si layer on buried SiO2 in ultrahigh vacuum"

            Journal Of Vacuum Science & Technology B 20 (1)167-172 (2002).

 

            ABSTRACT: Thermal agglomeration of an ultrathin Si layer in silicon-on-insulator structures with a thickness ranging from 1 to 15 nm has been studied by atomic force microscopy. We found that the size of Si islands formed by agglomeration depends on the initial thickness of the Si layer, i.e., the height and the lateral size of Si islands increase with increasing Si thickness. Because the critical temperature for the agglomeration, however, is lower for thinner Si, the thickness dependence of Si island features is accompanied by a temperature effect. A calculation model based on both strain energy and surface free energy qualitatively explains most of the observed agglomeration phenomena, i.e., island formation and ordering. (C) 2002 American Vacuum Society.

 

121.    T. Ogino, Y. Homma, Y. Kobayashi, H. Hibino, K. Prabhakaran, K. Sumitomo, H. Omi, S. Suzuki, T. Yamashita, D. J. Bottomley, F. Ling, and A. Kaneko

            "Design of Si surfaces for self-assembled nano architecture"

            Surface Science 514 (1-3)1-9 (2002).

 

            ABSTRACT: The final goal of nanostructure integration based on self-assembly is full-wafer design of whole atomic-level structures. Toward this goal, we must first be able to control atomic steps, reconstructed domains, surface strain, and atomic species. Atomic steps can be rearranged artificially in a large area using lithographic technique and we are now close to achieving complete control of step positions. Patterns of reconstructed domain regions can be ordered by self-organization. In nanostructure self-assembly, such as the coherently grown Ge quantum nanostructures on Si(0 0 1) and Si(1 1 3) surfaces, strain engineering is important for controlling position, shape, and distribution. Ordered Ge-island chains on Si(0 0 1) show that artificial strain distribution design is a powerful tool for nanostructure integration. Surface composition on SiGe mixed surfaces can be reversibly changed by hydrogen adsorption and desorption. These approaches to designing surface structures show that the bottom-up approach is a promising alternative in semiconductor integration technology. (C) 2002 Elsevier Science B.V. All rights reserved.

 

122.    Y. Ohtera, T. Kawashima, Y. Sakai, T. Sato, I. Yokohama, A. Ozawa, and S. Kawakami

            "Photonic crystal waveguides utilizing a modulated lattice structure"

            Optics Letters 27 (24)2158-2160 (2002).

 

            ABSTRACT: We experimentally demonstrate a new class of optical waveguide consisting of alpha-Si/SiO2 autocloned photonic crystals with modulated lattice structure. The waveguide utilizes the macroscopic form birefringence of photonic crystals and confines light by the difference in the effective refractive index. A monopole modal field with spot diameters of 6.9 mum X 6.5 mum was observed at a wavelength of 1.55 mum. The propagation loss of the waveguide at the wavelength was found to be similar to4.2 dB/mm at most. (C) 2002 Optical Society of America.

 

123.    W. D. Oliver, F. Yamaguchi, and Y. Yamamoto

            "Electron entanglement via a quantum dot"

            Physical Review Letters 88 (3), 037901 (2002).

 

            ABSTRACT: This Letter presents a method of electron entanglement generation. The system under consideration,,e is a single-level quantum dot with one input and two output leads. The leads are arranged such that the dot is empty, single-electron tunneling is suppressed by energy conservation, and two-electron virtual cotunneling, is allowed. Such a configuration effectively filters the singlet-state portion of a two-electron input, yielding a nonlocal spin-singlet state at the output leads. Coulomb interaction mediates the entanglement generation, and, in its absence, the singlet state vanishes. This approach is a four-wave mixing process analogous to the photon entanglement generated by a chi((3)) parametric amplifier.

 

124.    H. Omi, D. J. Bottomley, Y. Homma, T. Ogino, S. Stoyanov, and V. Tonchev

            "Shape of atomic steps on Si(111) under localized stress"

            Physical Review B 66 (8), 085303 (2002).

 

            ABSTRACT: Localized elastic strain in Si crystal is artificially produced by buried silicon oxide inclusions formed beneath a lithographically defined area by oxygen implantation. The Si crystal with local strain is annealed at 1180-1260 degreesC, and the shape of atomic steps at a vicinal Si(111) surface is observed by in situ ultrahigh-vacuum secondary-electron microscopy and ex situ atomic force microscopy. The step shape is determined by the balance between the elastic stress at the surface and the Gibbs-Thomson effect-the decrease of the chemical potential mu related to the step curvature. The shape analysis enables us to estimate the strain-related contribution to the Gibbs free energy density DeltaG/A=8.3x10(-5) J/m(2).

 

125.    H. Omi, D. J. Bottomley, and T. Ogino

            "Strain distribution control on the silicon wafer scale for advanced nanostructure fabrication"

            Applied Physics Letters 80 (6)1073-1075 (2002).

 

            ABSTRACT: Looking to the long-term future of Si semiconductor technology, we propose, fabricate, and demonstrate strain distribution control on the planar Si wafer scale for advanced nanostructure self-assembly. Oxygen ions are implanted through patterned layers on the Si wafer; the sample is then annealed at 1325 degreesC to produce bulk oxide inclusions which yield a strain distribution. Strained epitaxial growth of Ge on the Si(001) substrate surface at 550 degreesC in ultrahigh vacuum produces three-dimensional islands whose location and size distribution are well controlled. The degree of localization control is in agreement with simulations of the elastic strain distribution. (C) 2002 American Institute of Physics.

 

126.    K. Ono, D. G. Austing, Y. Tokura, and S. Tarucha

            "Current rectification by Pauli exclusion in a weakly coupled double quantum dot system"

            Science 297 (5585)1313-1317 (2002).

 

            ABSTRACT: We observe spin blockade due to Pauli exclusion in the tunneling characteristics of a coupled quantum dot system when two same-spin electrons occupy the lowest energy state in each dot. Spin blockade only occurs in one bias direction when there is asymmetry in the electron population of the two dots, leading to current recti cation. We induce the collapse of the spin blockade by applying a magnetic field to open up a new spin-triplet current-carrying channel.

 

127.    K. Ono, D. G. Austing, Y. Tokura, and S. Tarucha

            "Angular momentum selectivity in tunneling between two quantum dots"

            Physica B-condensed Matter 314 (1-4)450-454 (2002).

 

            ABSTRACT: We measure the current-voltage characteristics of a single-electron transistor containing two vertically coupled circular-disk-shaped quantum dots in a magnetic field applied perpendicular to the disks, and observe current peaks associated with elastic tunneling through the two dots. The magnetic field dependence of the peak positions follows that of the Fock-Darwin states, and the peak height becomes smaller as the difference in angular momentum of the states of the two dots increase. We use a sequential tunneling model to account for this result. (C) 2002 Elsevier Science B.V. All rights reserved.

 

128.    Y. Ono, H. Inokawa, and Y. Takahashi

            "Binary adders of multigate single-electron transistors: Specific design using pass-transistor logic"

            Ieee Transactions On Nanotechnology 1 (2)93-99 (2002).

 

            ABSTRACT: We describe how to construct area-efficient adders using single-electron transistors (SETs). The design is based on pass-transistor logic and multigate SETs are used as pass transistors. The proposed design enables us to construct a full adder using only six SETs. We also show that multibit binary adders can be built using cascaded SET structures without any long wires. The small number of transistors and no-metal-interconnection configuration significantly reduces the circuit area and capacitance to be charged. A Monte Carlo simulation shows that even when the inter-SET-node capacitances are reduced and consequently the carry signal level terribly fluctuates in its path due to single-electron charging effects, the carry can correctly propagate as long as the final output node capacitance is sufficiently large. This proves that the area reduction and speed improvement are compatible in our design. We also discuss the possibility of large-scale integration, touching on the random-offset-charge issue.

 

129.    Y. Ono, K. Yamazaki, M. Nagase, S. Horiguchi, K. Shiraishi, and Y. Takahashi

            "Fabrication of single-electron transistors and circuits using SOIs"

            Solid-state Electronics 46 (11)1723-1727 (2002).

 

            ABSTRACT: The paper describes the fabrication of single-electron transistors and circuits using silicon-on-insulators (SOIs). We first point out that control of the oxidation of Si is quite important and could be the key to the fabrication of quantum devices including single-electron devices. We then introduce our technique for making single-electron transistors, which uses special phenomena that occur during the oxidation of SOIs, and show that the technique enables us to realize primary single-electron circuits as a result of its high controllability, reproducibility and thermal stability. (C) 2002 Elsevier Science Ltd. All rights reserved.

 

130.    Y. Ono, and Y. Takahashi

            "Observation and circuit application of negative differential conductance in silicon single-electron transistors"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 41 (4B)2569-2573 (2002).

 

            ABSTRACT: A conductance anomaly displaying large negative differential conductance (NDC) has been observed in a drain current vs. drain voltage curve of Si single-electron transistors (SETs) at 27 K. The NDC appears, mainly in the single-electron-tunneling regime, in such a way that it aligns parallel to the edges of Coulomb diamonds, strongly suggesting that it reflects the discrete nature of the dot states. We show that high-gain SETS, i.e., SETs with gate capacitance that is well larger than the junction capacitances, enable us to regulate the appearance of NDC and to accentuate the tunneling conditions only at the drain side because of the asymmetric sharing of the source-drain voltage between the two junctions. We also show, using high-gain SETS, that the NDC results in a hysteresis loop of drain output voltage as a function of gate voltage for a constant drain-current bias. This enables us to use the SET as a Schmitt-trigger with excellent noise immunity.

 

131.    K. Onomitsu, A. Kawaharazuka, T. Okabe, T. Makimoto, H. Saito, and Y. Horikoshi

            "Field effect of photoluminescence from excitons bound to nitrogen atom pairs in GaAs"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 41 (9)5503-5506 (2002).

 

            ABSTRACT: Field effect of photoluminescence due to excitons bound to nitrogen atom pairs in GaAs has been investigated for uniformly doped and atomic-layer-doped samples grown on (00 1) GaAs substrates. The intensities of excitonic photoluminescence lines due to distant nitrogen atom pairs decrease much more rapidly than those from closer pairs when the electric field is increased. In addition, photoluminescence clue to tile nearest neighbor pairs in atomic-layer-doped samples exhibits much more stable characteristics than that Of Uniformly doped samples against an applied electric field, This stability is observed only when the electric field is applied in either the [110] or [(1) over bar 10] direction. This anomalous field effect can be explained by considering the electron trapping process to the isoelectric N traps modulated by the electric field.

 

132.    K. Onomitsu, A. Kawaharazuka, T. Okabe, T. Makimoto, H. Saito, and Y. Horikoshi

            "Modulation of PL recombination processes in N doped GaAs/Al0.33Ga0.67As SQW by electric field"

            Compound Semiconductors 2001 (170)407-411 (2002).

 

            ABSTRACT: Radiative recombination rate of excitons bound to nitrogen atom pairs in the AlGa-As/GaAs single quantum wells is investigated by comparing the recombination process between the quantized levels by using nitrogen atomic layer doped samples. When the nitrogen-doped layer is located at the center of the well, photoluminescence due to the quantized levels almost vanishes. The quantum well photoluminescence appears when the nitrogen-doped layer is shifted from the center of the well toward the heterojunction. It is found that the recombination process can be relatively modulated by changing the spatial distance of the nitrogen-doped layer from the heterojunction or, by applying an electric field in the direction perpendicular to the well.

 

133.    T. Ozaki, K. Yamamoto, T. Kanai, and H. Kuroda

            "Jetlike structures in the visible emission of plasma pumped by an obliquely incident picosecond laser"

            Journal Of The Physical Society Of Japan 71 (12)2963-2968 (2002).

 

            ABSTRACT: The observation of millimeter-long jetlike structures in the visible emission from laser-produced plasma is reported, which is produced by longitudinal pumping of preformed plasma with high-intensity 2 ps duration Nd:phosphate glass laser pulse. Clear jets are observed only for a relatively narrow range of the longitudinal pump intensity, from 5 x 10(14) W/cm(2) to 7 x 10(14) W/cm(2). Spectral observation of the jets reveal that the spectrum is dominated by line emission, and not by the continuum. The dominant lines in the visible region originate from neutral and singly-ionized molybdenum ions. The decay time of the jetlike emission is found to be comparable to the typical radiative decay time of the line emission. The present observations are compared with those of plasma bullets by Vogel and Kochan [Phys. Rev. Lett. 86 (2001) 232] is discussed.

 

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

            "Highly directive 18.9 nm nickel-like molybdenum X-ray laser operating at 150 mJ pump energy"

            Physical Review Letters 89 (25), 253902 (2002).

 

            ABSTRACT: We experimentally demonstrate that by longitudinally pumping 2 mm long molybdenum preformed plasma with high-intensity 475 fs duration laser pulse, a highly directive soft-x-ray laser at 18.9 nm wavelength is generated. The divergence of the beam is evaluated to be of the submilliradian order, and only requires a pump laser energy of 150 mJ.

 

135.    T. Ozaki, H. Nakano, and H. Kuroda

            "Effects of pump propagation and absorption on the gain distribution of longitudinally pumped Ni-like molybdenum x-ray lasers"

            Physical Review E 66 (4), 047402 (2002).

 

            ABSTRACT: We reveal from simulations that in longitudinally pumped Ni-like Mo x-ray lasers, deformation of the temporal gain profile can occur, causing the x-ray laser pulse to have a steep rising edge. This is shown to be due to the rapid change in the inverse bremsstrahlung absorption when the main picosecond pulse pumps the cold preplasma.

 

136.    T. Ozaki, H. Nakano, and H. Kuroda

            "Prepulse-produced plasma waveguide for longitudinally pumped nickellike molybdenum x-ray lasers"

            Journal Of The Optical Society Of America B-optical Physics 19 (6)1335-1341 (2002).

 

            ABSTRACT: A novel method is proposed by which multiple prepulses are used to generate a waveguidelike density profile for longitudinally pumped transient collisional excitation x-ray lasers. It is shown that a high-density waveguide with subcritical densities can be produced with this method, which requires a typical total prepulse energy of only 200 mJ. A multipulse pumping configuration to achieve the optimal plasma condition and also to completely confine the longitudinal pump beam within the waveguide is proposed. Gain calculations along the waveguide reveal the conditions necessary for saturated operation of the 18.9-nm nickellike molybdenum x-ray laser. (C) 2002 Optical Society of America.

 

137.    S. K. Ozdemir, A. Miranowicz, M. Koashi, and N. Imoto

            "Pulse-mode quantum projection synthesis: Effects of mode mismatch on optical state truncation and preparation"

            Physical Review A 66 (5), 053809 (2002).

 

            ABSTRACT: Quantum projection synthesis can be used for phase-probability-distribution measurement and optical-state truncation and preparation. The method relies on interfering optical light beams, which is a major challenge in experiments performed by pulsed light sources. In the pulsed regime, the time frequency overlap of the interfering light beams has a major impact on the efficiency of the method. In this paper, the pulse-mode projection-synthesis approach is developed, the mode structures of interfering light beams are characterized, and the effect of this overlap on the fidelity of optical-state truncation and preparation is investigated. By introducing the positive-operator-valued measure for the detection events in the scheme, the effect of mode mismatch between the photon-counting detectors and the incident light beams is also presented.

 

138.    S. K. Ozdemir, A. Miranowicz, M. Koashi, and N. Imoto

            "Optical qubit generation by state truncation using an experimentally feasible scheme"

            Journal Of Modern Optics 49 (5-6)977-984 (2002).

 

            ABSTRACT: Generation of arbitrary superposition of vacuum and one-photon states using a quantum scissors device (QSD) is studied. The device allows the preparation of states by truncating an input coherent light. Optimum values of the intensity of the coherent light for the generation of any desired state using the experimentally feasible QSD scheme are found.

 

139.    A. Patane, R. J. Hill, L. Eaves, P. C. Main, M. Henini, M. L. Zambrano, A. Levin, N. Mori, C. Hamaguchi, Y. V. Dubrovskii, E. E. Vdovin, D. G. Austing, S. Tarucha, and G. Hill

            "Probing the quantum states of self-assembled InAs dots by magnetotunneling spectroscopy"

            Physical Review B 65 (16), 165308 (2002).

 

            ABSTRACT: We describe how magnetotunneling spectroscopy can be used to investigate the spatial form of the wave function of confined electron states in self-assembled InAs quantum dots grown on (100)- and (311)B-oriented GaAs substrates. For both orientations, the wave function is found to have a biaxial symmetry in the growth plane, with axes parallel to the main crystallographic directions. We also present magnetotunneling spectroscopy measurements in a multiple-terminal resonant-tunneling device, which incorporates a series of gate electrodes. The gates allow us to address an individual dot electrostatically, and to identify and measure its energy levels and associated wave functions. The limitations and possible future applications of the technique are also discussed.

 

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

            "Efficient source of single photons: A single quantum dot in a micropost microcavity"

            Physical Review Letters 89 (23), 233602 (2002).

 

            ABSTRACT: We have demonstrated efficient production of triggered single photons by coupling a single semiconductor quantum dot to a three-dimensionally confined optical mode in a micropost microcavity. The efficiency of emitting single photons into a single-mode traveling wave is approximately 38%, which is nearly 2 orders of magnitude higher than for a quantum dot in bulk semiconductor material. At the same time, the probability of having more than one photon in a given pulse is reduced by a factor of 7 as compared to light with Poissonian photon statistics.

 

141.    M. Pelton, C. Santori, G. S. Solomon, O. Benson, and Y. Yamamoto

            "Triggered single photons and entangled photons from a quantum dot microcavity"

            European Physical Journal D 18 (2)179-190 (2002).

 

            ABSTRACT: Current quantum cryptography systems are limited by the attenuated coherent pulses they rise as light sources: a security loophole is opened up by the possibility of multiple-photon pulses. By replacing the source with a single-photon emitter, transmission rates of secure information call be improved. We have investigated the use of single self-assembled InAs/GaAs quantum dots as such single-photon sources, and have seen a tenfold reduction in the multi-photon probability as compared to Poissonian pulses. An extension of our experiment should also allow for the generation of triggered, polarization-entangled photon pairs. The utility of these light sources is currently limited by the low efficiency with which photons are collected. However, by fabricating an optical microcavity containing a single quantum dot, the spontaneous emission rate into a single mode can be enhanced. Using this method, we have seen 78% coupling of single-dot radiation into a single cavity resonance. The enhanced spontaneous decay should also allow for higher photon pulse rates, up to about 3 GHz.

 

142.    M. Pelton, J. Vuckovic, G. S. Solomon, A. Scherer, and Y. Yamamoto

            "Three-dimensionally confined modes in micropost microcavities: Quality factors and Purcell factors"

            Ieee Journal Of Quantum Electronics 38 (2)170-177 (2002).

 

            ABSTRACT: We present detailed calculations of the mode structure of distributed-Bragg-reflector micropost microcavities. Two methods are used: a first-principles, finite-difference time-domain model, and an approximate, heuristic model based on the separation of variables. We calculate modal quality factors, as well as enhancement of spontaneous emission rates, from single quantum dots in the microcavities. Both ideal and realistic post shapes are considered. The two methods give similar results, and are capable of accurately predicting experimentally measured values.

 

143.    V. Perez-Solorzano, Y. Kobayashi, M. Jetter, H. Schweizer, F. Scholz, E. Hahn, and D. Gerthsen

            "Initial experiments to obtain self-assembled GaInN quantum islands by MOVPE"

            Physica Status Solidi A-applied Research 192 (2)412-416 (2002).

 

            ABSTRACT: GaInN/GaN islands have been grown by metalorganic vapor phase epitaxy (MOVPE) on SiC substrates. We report on the influence of different growth parameters, such as growth temperature, growth rate or the quantity of deposited material on the growth of such dots. The characterisation of these structures has been done by using atomic force microscopy (AFM) and transmission electron microscopy (TEM). Up to now, the maximum density obtained is 10(10) dots/cm(2) at 660 degreesC at a growth rate of 4 ML/min.

 

144.    A. Pimenov, A. V. Pronin, A. Loidl, A. Tsukada, and M. Naito

            "Peak in the far-infrared conductivity of strongly anisotropic cuprates"

            Physical Review B 66 (21), 212508 (2002).

 

            ABSTRACT: We investigate the far-infrared and submillimeter-wave conductivity of electron-doped La2-xCexCuO4 tilted 1degrees off from the ab-plane. The effective conductivity measured for this tilt angle reveals an intensive peak in the normal-state at finite frequency (nusimilar to50 cm(-1)) due to a mixing of the in-plane and out-of-plane responses. The peak disappears for the pure in-plane response and transforms into a pure Drude-like contribution. A comparative analysis of the mixed and the in-plane spectra allows us to extract the c-axis conductivity which shows a Josephson plasma resonance at nusimilar or equal to11.7 cm(-1) in the superconducting state.

 

145.    K. Prabhakaran, H. Hibino, and T. Ogino

            "Ultrafine and well-defined patterns on silicon through reaction selectivity"

            Advanced Materials 14 (19)1418-1421 (2002).

 

            ABSTRACT:

 

146.    K. Prabhakaran, K. V. Shafi, Y. Yamauchi, K. Tsubaki, A. Ulman, Y. Homma, and T. Ogino

            "Nanoparticle-induced multi-functionalization of silicon: A plug and play approach"

            Applied Surface Science 190 (1-4)161-165 (2002).

 

            ABSTRACT: Here, we demonstrate a "plug and play" approach to achieve multi-functionalization of Si. In this approach, externally synthesized functional nanoparticles are introduced onto device quality Si wafers and the surface chemical bonds are manipulated. Sonochemically synthesized Fe2O3 nanoparticles are introduced onto Si from an alcohol suspension. On annealing this sample in ultra-high vacuum, the oxygen atoms change the bonding partner from Fe to Si and desorb as SiO at similar to750 degreesC. This results in the formation of nanoparticles of Fe on the surface and exhibits ferromagnetic behavior. Deposition of a thin layer (2 nm) of Si onto the sample containing the metallic Fe nanoparticles followed by annealing at 560 degreesC leads to optically active Si. Photoluminescence measurements show that this sample emits light at three different wavelengths, namely 1.57, 1.61 and 1.63 mum, when excited by He-Ne or Ar lasers. Oxidation of this material results in the formation of a selective capping layer of SiO2. Thus we obtain multi-functional Si in an "all in one" form and we believe that this approach is universal. (C) 2002 Elsevier Science B.V. All rights reserved.

 

147.    K. Prabhakaran, K. V. Shafi, A. Ulman, P. M. Ajayan, Y. Homma, and T. Ogino

            "Low-temperature, carbon-free reduction of iron oxide"

            Surface Science 506 (1-2)L250-L254 (2002).

 

            ABSTRACT: We report here that iron oxide can be reduced completely to elemental iron, through a carbon-free and low-temperature reaction. Nanoparticles of Fe2O3. are completely reduced. resulting in the formation of nanoparticles of Fe, on the surfaces of Si or Ge, at similar to740 and similar to440 degreesC respectively. We show that this phenomenon is due to the oxygen atoms changing the bonding partner from Fe to Si or Ge, followed by the desorption of the respective monoxides. Therefore, the reduction temperature is dictated by the desorption temperatures of SiO or GeO molecules. The nanoparticles thus formed are magnetic and are of uniform size and shape. On graphite surfaces, however. Fe2O3 retains the original stoichiometry even after annealing at higher temperatures. (C) 2002 Elsevier Science B.V. All rights reserved.

 

148.    S. Saito, H. Tanaka, H. Nakano, M. Ueda, and H. Takayanagi

            "pi-phase jump of magnetic-field dependence of retrapping current in dc SQUID's"

            Physical Review B 66 (13), 134522 (2002).

 

            ABSTRACT: We measured the retrapping current of a small-capacitance underdamped dc superconducting quantum interference device (SQUID) at low temperatures as a function of magnetic field. We found that the relative phase relation between the magnetic-field dependence of the retrapping current and that of the switching current jumped from 0 to pi at E(J)similar toE(C), where E-J and E-C are the Josephson energy and the charging energy of a Cooper pair. This phenomenon cannot be reproduced by a model that approximates the SQUID as a single junction with a controllable switching current. It can be explained phenomenologically by taking into account two kinds of dissipation that arise from ac currents flowing through the lead and along the SQUID's loop.

 

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

            "Indistinguishable photons from a single-photon device"

            Nature 419 (6907)594-597 (2002).

 

            ABSTRACT: Single-photon sources have recently been demonstrated using a variety of devices, including molecules(1-3), mesoscopic quantum wells(4), colour centres(5), trapped ions(6) and semiconductor quantum dots(7-11). Compared with a Poisson-distributed source of the same intensity, these sources rarely emit two or more photons in the same pulse. Numerous applications for single-photon sources have been proposed in the field of quantum information, but most-including linear-optical quantum computation(12)-also require consecutive photons to have identical wave packets. For a source based on a single quantum emitter, the emitter must therefore be excited in a rapid or deterministic way, and interact little with its surrounding environment. Here we test the indistinguishability of photons emitted by a semiconductor quantum dot in a microcavity through a Hong-Ou-Mandel-type two-photon interference experiment(13,14). We find that consecutive photons are largely indistinguishable, with a mean wave-packet overlap as large as 0.81, making this source useful in a variety of experiments in quantum optics and quantum information.

 

150.    C. Santori, G. S. Solomon, M. Pelton, and Y. Yamamoto

            "Time-resolved spectroscopy of multiexcitonic decay in an InAs quantum dot"

            Physical Review B 65 (7), 073310 (2002).

 

            ABSTRACT: The multiexcitonic decay process in a single InAs quantum dot is studied through high-resolution time-resolved spectroscopy. A cascaded emission sequence involving three spectral lines is seen that is described well over a wide range of pump powers by a simple model. The measured biexcitonic decay rate is about 1.5 times the single-exciton decay rate. This ratio suggests the presence of selection rules, as well as a significant effect of the Coulomb interaction on the biexcitonic wave function.

 

151.    S. Sasaki, Y. Kitamura, W. Izumida, K. Ono, and S. Tarucha

            "The Kondo effect in a one- and two-electron quantum dot"

            Physica E-low-dimensional Systems & Nanostructures 12 (1-4)806-809 (2002).

 

            ABSTRACT: We study the Kondo effect in a vertical quantum dot holding only one- or two-electrons. We observe clear Kondo features in the temperature and bias voltage dependence of the conductance when there is only one electron in the dot (spin S = 1, 2). The estimated Kondo temperature is much higher than in previous reports due to large dot-lead tunnel coupling on the order of 800 mueV. We also observe a Kondo enhancement of the conductance when the two-electron ground state makes a transition from a spin singlet (S = 0) to a triplet (S = 1) at a magnetic field of 3.2 T. The bias voltage dependence of the differential conductance at this transition field shows weak features that may be related to the Zeeman splitting of the triplet state. (C) 2002 Published by Elsevier Science B.V.

 

152.    T. Sato, H. Matsui, S. Nishina, T. Takahashi, T. Fujii, T. Watanabe, and A. Matsuda

            "Low energy excitation and scaling in Bi2Sr2Can-1CunO2n+4 (n=1-3): Angle-resolved photoemission spectroscopy"

            Physical Review Letters 89 (6), 067005 (2002).

 

            ABSTRACT: Angle-resolved photoemission spectroscopy (ARPES) has been performed on the single- to triple-layered Bi-family high-T (c) superconductors (Bi2Sr2Can-1CunO2n+4, n=1-3). We found a sharp coherent peak as well as a pseudogap at the Fermi level in the triple-layered compound. Comparison among three compounds has revealed a universal rule that the characteristic energies of superconducting and pseudogap behaviors are scaled with the maximum T-c.

 

153.    T. Sato, K. Terao, A. Teramoto, and M. Fujiki

            "On the composition-driven helical screw-sense inversion of chiral-achiral random copolymers"

            Macromolecules 35 (14)5355-5357 (2002).

 

            ABSTRACT:

 

154.    T. Sato, K. Terao, A. Teramoto, and M. Fujiki

            "Conformational fluctuations of helical poly(dialkyl silylene)s in solution"

            Macromolecules 35 (6)2141-2148 (2002).

 

            ABSTRACT: On the basis of the broken wormlike chain model, the persistence length q of helical polymers is formulated in terms of the internal rotation potential E(phi), probabilities p(P) and p(M) of the right- and left-handed helical states, the average length 1 of a helix sequence, and the kink angle thetav at the helix reversal. Here, p(P), p(M), and (l) can be calculated from the free energy difference 2DeltaG(h) between the right- and left-handed helical states and the free energy DeltaG(r) of the helix reversal; 2DeltaG(h) can be calculated from E(phi). With assumption of an empirical functional form of E(phi) along with using DeltaG(r) determined experimentally, q and 2DeltaG(h) are calculated for two optically active polysilylenes, poly [n-hexyl-(S)-3-methylpentylsilylone] (polysilylene 1) and poly[(R)-3,7-dimethyloctyl-(S)-3-methylpentylsilylene] (polysilylene 2), and the results are compared with experimental data obtained in previous work to determine parameters in E(phi) and thetav. From the E(phi) determined, standard deviations ((phi - phi(0))(2))(1/2) of the torsional fluctuation in the dihedral angle are estimated for the two polysilylene chains in solution. The considerably flexible polysilylene 1 has larger theta(y) and ((phi - phi(0))(2))(1/2) than the rigid polysilylene 2. While the chain flexibility of polysilylene 2 is mainly determined by the torsional fluctuation, both kink due to the helix reversal and torsional fluctuation are important in the chain flexibility of polysilylene 1. The potential E(phi) determined is compared with a result of molecular mechanics. It is shown that the ultraviolet absorption spectrum of polysilylene correlates not to the torsional fluctuation but to the helix reversal (or (l)).

 

155.    T. Sato, K. Miura, N. Ishino, Y. Ohtera, T. Tamamura, and S. Kawakami

            "Photonic crystals for the visible range fabricated by autocloning technique and their application"

            Optical And Quantum Electronics 34 (1-3)63-70 (2002).

 

            ABSTRACT: We fabricate photonic crystals for the visible range by the 'autocloning' technique, in which multilayers are stacked by an appropriate combination of sputter deposition and sputter etching. TiO2/SiO2 and Ta2O5/SiO2 are chosen as materials since they are transparent in the range and give a high contrast of refractive indices. The fabrication technique has flexibility regarding materials and size and is very reliable and reproducible even if the pitch is less than 0.2 mum. We also study the application of photonic crystals to birefringent elements such as waveplates and polarization selective gratings and experimentally verify that they are useful for optical pick-up systems.

 

156.    T. Schapers, J. Nitta, H. B. Heersche, and H. Takayanagi

            "Model for ballistic spin-transport in ferromagnet/two-dimensional electron gas/ferromagnet structures"

            Physica E-low-dimensional Systems & Nanostructures 13 (2-4)564-567 (2002).

 

            ABSTRACT: The spin dependent conductance of a ferromagnet/two-dimensional electron gas ferromagnet structure is theoretically examined in the ballistic transport regime. It is shown that the spin signal can be improved considerably by making use of the spin filtering effect of a barrier at the ferromagnet two-dimensional electron gas interface, For sufficiently short semiconductor layers interference effects can result in an additional increase of the spin signal. (C) 2002 Elsevier Science B.V. All rights reserved.

 

157.    S. Seki, Y. Matsui, Y. Yoshida, S. Tagawa, J. R. Koe, and M. Fujiki

            "Dynamics of charge carriers on poly[bis(p-alkylphenyl)silane]s by electron beam pulse radiolysis"

            Journal Of Physical Chemistry B 106 (27)6849-6852 (2002).

 

            ABSTRACT: The degree of electron delocalization along polymer skeletons was discussed for ion radicals of poly[bis(palkylphenyl)silane]s by electron beam pulse radiolysis: The degree of delocalization of negative charges on the Si chains strongly depended on the substitution position of the alkyl groups (n- and tert-butyl) on the phenyl rings, though relatively small effects were observed for holes. The empirical relationship between oscillator strength and the degree of delocalization (n(del)) gave the value of n(del) as similar to36 Si units for excess electrons on poly [bis(p-n-butylphenyl)silane] in contrast to the value of n(del) = 14 for poly [bis(p-t-butylphenyl)silane], which was similar to that for poly(methylphenylsilane). The oscillator strength of the cation radicals of poly[bis(p-alkylphenyl)silane]s (f(.+) > 0.65) was similar to2 times higher than that of poly(methylphenylsilane) (f(.+) = 0.35): Positive charges gave a higher degree of delocalization in poly [bis(p-alkylphenyl)silane]s in comparison with that in poly(methylphenylsilane), suggesting that the Si skeleton of poly [bis(p-alkylphenyl)silane]s should be good conducting paths for holes.

 

158.    T. Sekitani, H. Sato, M. Naito, and N. Miura

            "High-field magnetotransport in strained (La,Sr)(2)CuO4 films"

            Physica C-superconductivity And Its Applications 378195-198 (2002).

 

            ABSTRACT: We report high-field magnetotransport properties of strained La1.85Sr0.15CuO4 (LSCO) thin films. The measurements were performed on two LSCO films with identical chemical composition but with different epitaxial strain. One film was compressively strained in plane, and had T-c similar to 44 K. The other film was strained in the opposite way, and had T-c similar to 26 K. These films show a striking contrast in the normal-state transport: the latter has a prominent low-temperature upturn while the former has not. The low-temperature upturn can be explained on the basis of Kondo scattering due to Cu2+ local spins. The results suggest the epitaxial strain seems to regulate the strength of the Kondo interaction and thereby to affect the superconducting temperature T-c. (C) 2002 Elsevier Science B.V. All rights reserved.

 

159.    T. Sekitani, N. Miura, and M. Naito

            "High-field transport properties of T'-Ln(2-x)Ce(x)CuO(4) (Ln=Nd, Pr, La)"

            International Journal Of Modern Physics B 16 (20-22)3216-3219 (2002).

 

            ABSTRACT: We report low-temperature magnetotransport in the normal state of the electron-doped superconductors, Nd2-xCexCuO4, Pr2-xCexCuO4, and La2-xCexCuO4, by suppressing the superconductivity with high magnetic fields. The normal state rho - T curve shows an up-turn at low temperatures. which has a log T dependence with saturation at lowest temperatures. The up-turn is gradually suppressed with increasing magnetic field, resulting in negative magnetoresistance. We discuss these findings on the basis of the Kondo scattering originating from the magnetic moments of Cu2+ ions.

 

160.    T. Sekitani, M. Naito, N. Miura, and K. Uchida

            "Kondo effect in the normal state of T '-Ln(2-x)Ce(x)CuO(4) (Ln = La, Pr, Nd)"

            Journal Of Physics And Chemistry Of Solids 63 (6-8)1089-1092 (2002).

 

            ABSTRACT: We have measured low-temperature magnetotransport in the normal state of the electron-doped superconductors, Nd2-xCexCuO4, Pr2-xCexCuO4, and La2-xCeCuO4, by suppressing the superconductivity with high magnetic fields. The normal state rho-T curve shows an up-turn at low temperatures, which has a log T dependence with saturation at lowest temperatures. The up-turn is gradually suppressed by increasing the magnetic field, resulting in negative magnetoresistance. We discuss these findings on the basis of the Kondo scattering originating from the magnetic moments of Cu2+ ions. (C) 2002 Elsevier Science Ltd. All rights reserved.

 

161.    K. Semba, M. Mukaida, and A. Matsuda

            "Characteristic transport properties observed in underdoped YBa2Cu3O6+x"

            Physica B-condensed Matter 31274-76 (2002).

 

            ABSTRACT: By annealing under the equilibrium oxygen pressure, we have succeeded in obtaining YBa2Cu3O6+x with any doping level. Both in bulk and film samples, the doping driven superconductor-to-insulator (S-I) transition has been observed at rho(ab) similar or equal to 0.8 mOmega cm which corresponds to the universal resistance h/4e(2) per CuO2 bi-layer. The observed critical carrier density is n(H)(SI) similar or equal to 3 x 10(20) cm(-3). Within the critical region of the S-I transition, using a thin film sample, we have succeeded in observing the resistivity scaling as a function of doping. The carrier density obeys the relation n(H) proportional to x - 0.2 in the underdoped region (0.2 less than or equal to x less than or equal to 0.5), where the conductivity is substantially small and transport properties show weaker temperature dependence. The quantum effects are considered to be more important e.g., the quantum phase fluctuation in superconductors with small superfluid density. (C) 2002 Elsevier Science B.V. All rights reserved.

 

162.    H. Shibata

            "Josephson plasma in RuSr2GdCu2O8"

            Physical Review B 65 (18), 180507 (2002).

 

            ABSTRACT: Josephson plasma in RuSr2GdCu2O8, Ru1-xSr2GdCu2+xO8 (x=0.3), and RuSr2Eu2-xCexCu2O10 (x=0.5) compounds is investigated by the sphere resonance method. The Josephson plasma is observed in a low-frequency region (around 8.5 cm(-1) at T

 

163.    H. Shibata

            "Optical study of the Josephson plasma in high-T-c superconductors"

            Physica C-superconductivity And Its Applications 367 (1-4)360-364 (2002).

 

            ABSTRACT: Josephson plasma in various high-T-c superconductors is studied, The plasma frequencies of most cuprates are distributed between a few GHz to the THz region. and can be detected by many optical measurement methods. Among these methods. the sphere resonance method is the easiest way to observe the plasma. and can estimate the c-axis penetration depth from the ceramic sample. Various types of the Josephson plasma. such as the double Josephson plasma mode. transverse Josephson plasma mode. and the plasma in ferromagnetic superconductor are also discussed. (C) 2002 Elsevier Science B.V. All rights reserved.

 

164.    K. Shimizu, and N. Imoto

            "Communication channels analogous to one out of two oblivious transfers based on quantum uncertainty"

            Physical Review A 66 (5), 052316 (2002).

 

            ABSTRACT: This paper proposes a cryptographic quantum communication scheme analogous to one out of two oblivious transfers based on quantum conjugate coding defined in a four-dimensional Hilbert space. The quantum uncertainty principle ensures that our scheme can satisfy the following two conditions: (i) a sender, Bob, can encode two bits of information Xis an element of{0,1} and Yis an element of{0,1}, but a receiver, Alice, can only obtain either X or Y dependent on her choice; and (ii) honest Bob, who attempts to encode (X,Y), cannot reveal Alice's choice. By contrast, when malicious Bob tries to reveal her choice, honest Alice can detect malicious Bob with a finite probability. Moreover, by using our proposed scheme many times, we can construct a protocol for quantum bit commitment (QBC) from Alice to Bob. Contrary to common belief, the security of our QBC protocol may not be violated by the well-known no-go theorem of QBC. This is because our QBC protocol does not meet the assumptions in which the no-go theorem holds.

 

165.    K. Shimizu, and N. Imoto

            "Fault-tolerant simple quantum-bit commitment unbreakable by individual attacks"

            Physical Review A 65 (3), 032324 (2002).

 

            ABSTRACT: This paper proposes a simple scheme for quantum-bit commitment that is secure against individual particle attacks, where a sender is unable to use quantum logical operations to manipulate multiparticle entanglement for performing quantum collective and coherent attacks. Our scheme employs a cryptographic quantum communication channel defined in a four-dimensional Hilbert space and can be implemented by using single-photon interference. For an ideal case of zero-loss and noiseless quantum channels, our basic scheme relies only on the physical features of quantum states. Moreover, as long as the bit-flip error rates are sufficiently small (less than a few percent), we can improve our scheme and make it fault tolerant by adopting simple error-correcting codes with a short length. Compared with the well-known Brassard-Crepeau-Jozsa-Langlois 1993 (BCJL93) protocol, our scheme is mathematically far simpler, more efficient in terms of transmitted photon number, and better tolerant of bit-flip errors.

 

166.    A. Shinya, M. Notomi, I. Yokohama, C. Takahashi, J. I. Takahashi, and T. Tamamura

            "Two-dimensional Si photonic crystals on oxide using SOI substrate"

            Optical And Quantum Electronics 34 (1-3)113-121 (2002).

 

            ABSTRACT: Two-dimensional photonic crystals (2D-PhCs) on oxide can be easily incorporated into photonic integrated circuits. Although an asymmetrical structure (air/PhC/oxide) is advantageous in terms of ease of fabrication, it has been pointed out that such a structure may have no photonic band gap (PBG). To clarify the characteristics of the asymmetrical structure, we calculated the band structure using the three-dimensional (3D) FDTD method and measured the transmission characteristics of a fabricated 2D Si-PhC on oxide. The calculations show that we can use a quasi-PBG even in an asymmetrical structure when the PhC thickness satisfies the single-mode condition. The measured transmission characteristics correspond to the calculated band structure and reveal the existence of a quasi-PBG. These results show that the asymmetrical 2D Si-PhC-on-oxide structure can be applied to various optical devices.

 

167.    K. Shiraishi, N. Oyama, K. Okajima, N. Miyagishima, K. Takeda, H. Yamaguchi, T. Ito, and T. Ohno

            "First principles and macroscopic theories of semiconductor epitaxial growth"

            Journal Of Crystal Growth 237206-211 (2002).

 

            ABSTRACT: We discuss the relation between microscopic mechanism and macroscopic growth behavior. First, we introduce a macroscopic theory of growth behavior in semiconductor heteroepitaxy that includes the effects of the formation of Stranski-Krastanov islands and the misfit dislocations. This theory can reproduce the various types of' growth behavior observed in heteroepitaxial growth. Next, we have formulated a procedure for determining the phenomenological parameters that includes atomistic informations. The critical thickness of' InAs/GaAs(110) heteroepitaxy obtained by this procedure is in good agreement with the scanning tunneling microscopy (STM) observations. (C) 2002 Elsevier Science B.V. All rights reserved.

 

168.    J. A. Skinta, T. R. Lemberger, T. Greibe, and M. Naito

            "Evidence for a nodeless gap from the superfluid density of optimally doped Pr1.855Ce0.145CuO4-y films"

            Physical Review Letters 88 (20), 207003 (2002).

 

            ABSTRACT: We present measurements of the ab -plane magnetic penetration depth, lambda(T) , in five optimally doped Pr-1.855 Ce-0.145 CuO4-y films for 1.6 Kless than or equal toTless than or equal toT(c)similar to24 K . Low resistivities, high superfluid densities n(s)(T)proportional tolambda(-2)( T) , high T-c 's, and small transition widths are reproducible and indicative of excellent film quality. For all five films, lambda(-2)(T)/lambda(-2)( 0) at low T is well fitted by an exponential temperature dependence with a gap, Delta(min) , of 0.85k(B)T(c) . This behavior is consistent with a nodeless gap and is incompatible with d -wave superconductivity.

 

169.    J. A. Skinta, M. S. Kim, T. R. Lemberger, T. Greibe, and M. Naito

            "Evidence for a transition in the pairing symmetry of the electron-doped cuprates La2-xCexCuO4-y and Pr2-xCexCuO4-y"

            Physical Review Letters 88 (20), 207005 (2002).

 

            ABSTRACT: We present measurements of the magnetic penetration depth, lambda(-2)(T) , in Pr2-xCe xCuO4-y and La2-xCe xCuO4-y films at three Ce doping levels, x , near optimal. Optimal and overdoped films are qualitatively and quantitatively different from underdoped films. For example, lambda(-2)(0) decreases rapidly with underdoping but is roughly constant above optimal doping. Also, lambda(-2)(T) at low T is exponential at optimal and overdoping but is quadratic at underdoping. In light of other studies that suggest both d - and s -wave pairing symmetry in nominal optimally doped samples, our results are evidence for a transition from d - to s -wave pairing near optimal doping.

 

170.    G. S. Solomon, M. Pelton, and Y. Yamamoto

            "Single optical mode coupling of single quantum dot spontaneous emission"

            Compound Semiconductors 2001 (170)493-500 (2002).

 

            ABSTRACT: Experiments conducted in the early 1980s showed that the spontaneous emission from single atoms can be modified using electromagnetic cavities in the microwave regime. In a condensed matter analogy, we demonstrate that the spontaneous emission from an isolated InAs quantum dot can be coupled with high efficiency to a single, polarization-degenerate cavity mode using an all-epitaxial compact structure. The quantum dot is embedded in a planar epitaxial microcavity, which is processed into a post of sub-micron diameter. The single quantum dot spontaneous emission lifetime is reduced from the noncavity value of 1.3ns to 280ps, resulting in a single-mode spontaneous emission coupling efficiency of 78%. It is believed that this structure will useful in triggered photons sources for quantum cryptography.

 

171.    M. Stopa

            "Charging ratchets: Coulomb blockade and rectification"

            Applied Physics A-materials Science & Processing 75 (2)247-252 (2002).

 

            ABSTRACT: Discrete ratchets describe directed motion of a 'reaction coordinate' through a cycle of states in response to some varying external parameter. Such systems, in the simple, history-independent case, are described by a Markov process which in turn leads to a master equation with a transition matrix. Thus the ratchet property is reduced to a characteristic of the parameter-dependent symmetry of matrices. In the standard model of tunneling through a set of quantum dots in the Coulomb-blockade regime, a master equation is also used to describe the evolution through states in 'dot-occupancy space', leading to transport of electrons from a source to a drain. The symmetry of the transition matrix in this case is also a function of external parameters, notably the applied gate voltages and source-drain voltage, as well as depending on the configuration of dots and their tunnel couplings. We show that rectification and other ratchet behavior is a common feature of tunneling transport in the Coulomb-blockade regime. We also show that specific arrangements of dots and their tunnel couplings can be designed to enhance the ratchet effect. Finally, we show that the strong rectification of Coulomb-blockaded systems results from the reduction in phase space accessible to the system as it traverses the states in the reaction cycle.

 

172.    A. Sugimoto, I. Iguchi, T. Miyake, and H. Sato

            "Diamagnetic precursor state in high-T-c oxide superconductors near optimal doping using scanning superconducting quantum interference device microscopy"

            Japanese Journal Of Applied Physics Part 2-letters 41 (5A)L497-L499 (2002).

 

            ABSTRACT: Magnetic images of high-T-c La1.85Sr0.15CuO4 (LSCO) and YBa2Cu3O7-y (YBCO) thin films near optimal doping observed by scanning superconducting quantum interference device (SQUID) microscopy are presented in the temperature range both below and above the transition temperature T-c. While the quantized vortices were observable below T-c, local diamagnetic domains that led to the Meissner state were found in the narrow limited temperature range above T-c. The result provides evidence that local diamagnetic domains are closely related to the pseudogap state and the d-wave superconductivity.

 

173.    K. Sumitomo, Z. Zhang, H. Omi, D. J. Bottomley, and T. Ogino

            "Proof of kinetic influence in Ge nanowire formation on Si(113)"

            Journal Of Crystal Growth 2371904-1908 (2002).

 

            ABSTRACT: Based on scanning tunneling microscopy observations, we have investigated the formation and self-stabilization of Ge nanowires on Si(1 1 3) during Ge deposition. Under zero Ge flux, we observed a shape transition from nanowires to dot-like islands by annealing at 430degreesC, which is a favorable temperature for nanowire formation during deposition. The nanowires are, therefore, metastable and are formed Under a kinetically limited growth condition. We find that the strain of the nanowire is relaxed anisotropically. During growth the nanowire shape is effectively self-stabilizing. which leads to elongated growth of the islands. (C) 2002 Elsevier Science B.V. All rights reserved.

 

174.    N. Susa

            "Large absolute and polarization-independent photonic band gaps for various lattice structures and rod shapes"

            Journal Of Applied Physics 91 (6)3501-3510 (2002).

 

            ABSTRACT: Despite the considerable amount of research undertaken on various lattice structures, the photonic band gap (PBG) for a triangular lattice remains the largest both in the transverse magnetic (TM) and transverse electric (TE) modes. The PBG for a square lattice can be doubled by using square air holes rather than air cylinders. Reducing the symmetry was effective in terms of a honeycomb lattice in that the PBG can be increased 40% by deforming the lattice and using oval dielectric rods instead of cylindrical rods. The PBGs for all the examined structures increase monotonously as the refractive index is increased. The overlap PBG between the TM and TE gaps (polarization-independent PBG) is the largest for a triangular lattice of circular air rods. The overlap PBG for a hybrid square lattice of air rods is the next largest, and is twice as large as that for the well-known honeycomb lattice consisting of dielectric cylinders. When the refractive index of a dielectric material is increased to more than 3.50, the magnitude of the overlap PBG for almost all the photonic crystals that exhibit an overlap PBG saturates or decreases, except for the largest and next largest overlap PBG's mentioned above. (C) 2002 American Institute of Physics.

 

175.    K. Suzuki, S. Miyashita, and Y. Hirayama

            "Transport properties in back-gated InAS/GaSb heterostructures"

            Compound Semiconductors 2001 (170)339-344 (2002).

 

            ABSTRACT: In InAs/GaSb heterostructures, electrons in the InAs layer and holes in the GaSb layer coexist proximately. The structures show a compensated-quantum-Hall-effect, where the Hall resistance is quantized by the subtraction between the electron and the hole integer-Landau-level-filling-factors. We made an InAs/GaSb heterostructure sandwiched between AlGaSb barriers grown on a conductive InAs substrate as a back-gate, and succeeded in controlling the hole density, keeping the electron density constant. The transport characteristics clearly show the transition from the electron-hole coexisting system to the simple two-dimensional electron system applying the gate-voltage. The quantum-Hall-effect of the coexisting systems emerges along the integer-filling-factors of the electrons excess of holes and is not directly dependent on the Landau-quantization of holes, which suggests the exciton coupling of electrons and holes in the incompressive state of the electron quantum-Hall-effect regions.

 

176.    S. Suzuki, Y. Watanabe, T. Ogino, S. Heun, L. Gregoratti, A. Barinov, B. Kaulich, M. Kiskinova, W. Zhu, C. Bower, and O. Zhou

            "Extremely small diffusion constant of Cs in multiwalled carbon nanotubes"

            Journal Of Applied Physics 92 (12)7527-7531 (2002).

 

            ABSTRACT: The Cs intercalation process in multiwalled carbon nanotubes (MWNTs) was studied by cross-sectional scanning photoemission microscopy. Cs atoms initially deposited on the tips of aligned nanotubes diffused toward their roots. The Cs diffusion constant for the MWNTs at room temperature was evaluated from the Cs distribution measured along the axes of the tubes. The value of 2x10(-12) cm(2)/s obtained is seven orders of magnitude smaller than that in graphite, although the local atomic structure of an intercalated MWNT is very similar to that of intercalated graphite. (C) 2002 American Institute of Physics.

 

177.    S. Suzuki, Y. Watanabe, T. Kiyokura, K. G. Nath, T. Ogino, S. Heun, W. Zhu, C. Bower, and O. Zhou

            "Effects of air exposure and Cs deposition on the electronic structure of multiwalled carbon nanotubes"

            Surface Review And Letters 9 (1)431-435 (2002).

 

            ABSTRACT: Electronic structural changes in multiwalled carbon nanotubes caused by adsorbates and Cs deposition were studied by photoemission spectroscopy. The adsorbates formed by air exposure slightly increased the work function. The increased work function is considered to be due to the surface dipole moment induced by the negatively charged adsorbates. On the other hand, the Cs deposition followed by the intercalation drastically decreased the work function. The results suggest that field emission current enhancement induced by adsorbates and by Cs deposition are based on essentially different mechanisms; that is, the former is associated with the formation of localized electronic states and the latter is mainly due to the work function decrease.

 

178.    S. Suzuki, Y. Watanabe, T. Ogino, S. Heun, L. Gregoratti, A. Barinov, B. Kaulich, M. Kiskinova, W. Zhu, C. Bower, and O. Zhou

            "Electronic structure of carbon nanotubes studied by photoelectron spectromicroscopy"

            Physical Review B 66 (3), 035414 (2002).

 

            ABSTRACT: The electronic structure of multiwalled carbon nanotubes aligned perpendicularly on a Si substrate was studied by means of photoelectron spectromicroscopy. The valence band and the C 1s spectra, measured systematically from spatially selected regions along the tube axes, were the fingerprint for lateral variations in the electron density of states and in the band bending, respectively. It was found that the tips have a larger density of states near the Fermi level than the sidewalls, whereas band bending, which would explain such a spectral difference, was not observed. It is suggested that the different density of states near the Fermi level is due to a larger dangling bond density at the tips.

 

179.    Y. Takahashi, Y. Ono, A. Fujiwara, and H. Inokawa

            "Silicon single-electron devices"

            Journal Of Physics-condensed Matter 14 (39)R995-R1033 (2002).

 

            ABSTRACT: Single-electron devices (SEDs) are attracting a lot of attention because of their capability of manipulating just one electron. For their operation, they utilize the Coulomb blockade (CB), which occurs in tiny structures made from conductive material due to the electrostatic interactions of confined electrons. Metals or III-V compound semiconductors have so far been used to investigate the CB and related phenomena from the physical point of view. However, silicon is preferable from the viewpoint of applications to integrated circuits because, on a silicon substrate, SEDs can be used in combination with conventional complementary metal-oxide-semiconductor (CMOS) circuits. In addition, the well established fabrication technologies for CMOS large-scale integrated circuits (LSIs) can be applied to making such small structures. LSI applications of the silicon SEDs can be categorized into two fields: memory and logic. Many kinds of device structure and fabrication process have been proposed and tested for these purposes. This paper introduces the current status of silicon-based SED studies for LSI applications.

 

180.    H. Takayanagi, H. Tanaka, S. Saito, and H. Nakano

            "Readout of the qubit state with a dc-SQUID"

            Superlattices And Microstructures 32 (4-6)221-229 (2002).

 

            ABSTRACT: The states of a flux qubit with three Josephson junctions were observed with a dc-SQUID. The qubit is an aluminium superconductor loop surrounded by a dc-SQUID for readout. It has two states, which have persistent currents flowing in opposite directions. The system potentially offers the advantage of allowing single-shot/single-system measurements of macroscopic superposition of the two states. We have developed a highly sensitive, low-noise, single-shot detection system, and here we report the first direct observation of a macroscopic quantum superposition. The measured ground and the first excited state showed the same behaviour as the theoretical ones. We also showed that the measured behaviour of the switching current in a dc-SQUID was the same as that of the quantum-mechanically expected value of the switching current in the qubit. (C) 2003 Elsevier Ltd. All rights reserved.

 

181.    H. Takayanagi, H. Tanaka, S. Saito, and H. Nakano

            "Observation of qubit state with a dc-SQUID and dissipation effect in the SQUID"

            Physica Scripta T10295-102 (2002).

 

            ABSTRACT: Two states of a flux qubit with three Josephson junctions were shown in a single measurement with a dc-SQUID. The qubit is an aluminum superconductor loop surrounded by a dc-SQUID for readout. It has two states, which have persistent currents flowing in opposite directions. The readout data for three samples with different junction sizes suggest that the probability distribution for the double-well potential depends on the ratio of E-J/E-C,where E-J is the Josephson energy and E-C is the charging energy The probability distribution was estimated by calculating the wavefunctions and energy levels for the measured samples. We measured the retrapping current of a dc-SQUID without the qubit as a function of the magnetic field. It was found that the relative phase relation for the magnetic field dependence of the retrapping current jumped from 0 to pi at E-J approximate to E-C. This jump can be explained phenomenologically by taking into account the two kinds of dissipation arising from ac currents flowing through the lead and along the SQUID loop. The fact that the jump occurred at E-J approximate to E-C strongly suggests that the quantum nature of the electromagnetic environment needs to be taken into account in order to understand the origin of the dissipation.

 

182.    H. Takayanagi, T. Akazaki, M. Kawamura, Y. Harada, and J. Nitta

            "Superconducting junctions using AlGaAs/GaAs heterostructures with high H-c2 NbN electrodes"

            Physica E-low-dimensional Systems & Nanostructures 12 (1-4)922-926 (2002).

 

            ABSTRACT: We investigated a superconductor-semiconductor-superconductor junction formed by two superconducting NbN electrodes and a two-dimensional electron gas (2DEG) in an AlGaAs/GaAs heterostructure. We obtained a good ohmic contact between NbN/AuGeNi electrodes and 2DEG by annealing them at 450degreesC for 1 min in an N-2 atmosphere. We observed a decrease in the resistance caused by Andreev reflection (AR) within the superconducting energy gap voltage in a zero magnetic field in this structure. We found that the peculiar features of the magnetoresistance in the transition region can be qualitatively explained by considering the existence of the AR in high magnetic fields. (C) 2002 Elsevier Science B.V. All rights reserved.

 

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

            "Reflectionless tunneling due to Andreev reflection in a gated superconductor-semiconductor junction"

            Physica C-superconductivity And Its Applications 367 (1-4)204-210 (2002).

 

            ABSTRACT: We have studied the differential resistance in a gated superconductor-semiconductor junction in the ballistic transport regime. The zero-bias resistance shows a minimum as a function of the gate voltage. while the junction normal resistance measured at a high bias voltage shows a monotonic increase. This is explained as follows: the conductance enhancement due to coherent Andreev reflection is controlled by the gate voltage which changes the transparency of the gate barrier. We have also fabricated a two-gated junction with a high transparency at the superconductor-semiconductor interface and measured its resistance as functions of two gate voltages. An increase in one gate voltage results in the resistance minimum as a function of the other gate voltage. The obtained results agree well with the so-called reflectionless tunneling theory. (C) 2002 Elsevier Science B.V. All rights reserved.

 

184.    H. Tamura, K. Shiraishi, T. Kimura, and H. Takayanagi

            "Flat-band ferromagnetism in quantum dot superlattices"

            Physical Review B 65 (8), 085324 (2002).

 

            ABSTRACT: The possibility of flat-band ferromaganetism in quantum dot arrays is theoretically discussed. By using a quantum dot as a building block, quantum dot superlattices are possible. We consider dot arrays on Lieb and kagome lattices known to exhibit flat-band ferromagnetism. By performing an exact diagonalization of the Hubbard Hamiltonian, we calculate the energy difference between the ferromagnetic ground state and the paramagnetic excited state, and discuss the stability of the ferromagnetism against the second-nearest-neighbor transfer. We calculate the dot-size dependence of the energy difference in a dot model and estimate the transition temperature of the ferromaganetic-paramagnetic transition, which is found to be accessible within the present fabrication technology. We point out advantages of semiconductor ferromagnets and suggest other interesting possibilities of electronic properties in quantum dot superlattices.

 

185.    H. Tanaka, Y. Sekine, S. Saito, and H. Takayanagi

            "DC-SQUID readout for qubit"

            Physica C-superconductivity And Its Applications 368 (1-4)300-304 (2002).

 

            ABSTRACT: Two states of flux quantum bit (qubit) with three Josephson junctions are confirmed by a single measurement with a DC-SQUID (superconducting quantum interference device). This qubit is an aluminum superconductor loop surrounded by a DC-SQUID for measurement. The qubit has two states. which have persistent currents flowing in opposite directions. These two states are the around state of the qubit. The qubit is controlled by changing the external magnetic field. We reduced the external noise to improve the DC-SQUID's sensitivity. The switching current distribution of a DC-SQUID is sufficiently narrow to allow us to distinguish between the two ground states of the qubit. Although quantum coherence stability is required for full qubit operation. the readout values clearly show the possibility of single shot measurement. (C) 2001 Elsevier Science B.V. All rights reserved.

 

186.    S. Tanda, T. Tsuneta, Y. Okajima, K. Inagaki, K. Yamaya, and N. Hatakenaka

            "Crystal topology: A Mobius strip of single crystals - A crystalline ribbon of niobium and selenium can be coaxed into a novel topology."

            Nature 417 (6887)397-398 (2002).

 

            ABSTRACT:

 

187.    H. Z. Tang, M. Fujiki, and T. Sato

            "Thermodriven conformational transition of optically active poly [2,7-{9,9-bis[(S)-2-methyloctyl]}fluorene] in solution"

            Macromolecules 35 (16)6439-6445 (2002).

 

            ABSTRACT: We report the first solution state circular dichroism (CD) spectroscopic properties of a newly designed polyfluorene (PF) featuring highly enantiopure beta-branched chiral alkyl side chains, poly[2,7-{9,9-bis [(S)-2-methyloctyl]} fluorenel (PFMO), in dilute THF solution. Upon cooling the solution temperature, the single positive-sign CD band at 380 nm at +50 degreesC gradually changed into an apparent bisignate CD signal with two extrema of 403 and 355 nm at -80 degreesC, while the broad UV-vis band centered at 380 nm changed into a major intense band at 399 nm with a shoulder around 380 nm. On the basis of these data combined with photoluminescence (PL) studies and viscometric measurement, we concluded that PFMO in THF solution underwent a certain thermodriven, order-disorder conformational transition around 0 degreesC. It was considered that, upon cooling, the randomly twisted local PF backbone motifs in the wormlike PF backbone at higher temperature were transformed into a highly ordered PF backbone motif, possibly a P-5(2) helix (the P-handedness is assumed here corresponding to the negative-sign CD band, and vice versa), and other unclear local backbone motifs with the opposite screw sense at lower temperature.

 

188.    H. Z. Tang, H. Miura, and Y. Kawakami

            "Enantiopure spiro[3-3]heptane-2.6-dicarboxylic acid"

            Enantiomer 7 (1)5-9 (2002).

 

            ABSTRACT: Using chiral HPLC and C-13 NMR analyses, the optical purity of (+)-spiro[3.3]heptane-2,6-dicarboxylic acid (1) obtained by the known diastereomer method with brucine was first clarified to be 90% e.e., which was conventionally considered to be 100% e.e. Among the ester derivatives synthesized, dicinnamyl spiro[3.3]heptane-2,6-dicarboxylate (2) was found to show high optical separation ability on the chiral HPLC with cellulose phenyl carbamate stationary phase eluting with hexane/2-propanol (10/1, v/v) at a flow rate of 0.4 ml/min at 3 5 C (separation factor, alpha, 1.14), and the isolated optically pure (+)- and (-)-2 show [alpha](D)(26) of + 1.84degrees (c = 1.74, CHCl3) and -1.84degrees (c = 1.74, CHCl3), respectively. Acidic hydrolysis of optically pure (+)-/(-)-2 without racemization yielded optically pure exhibiting [phi](405)(27) = +21.1degrees ([phi](D)(27) = +9.1degrees) (c = 5.33, acetone) and [phi](405)(27) = -21.1degrees ([phi](D)(27) = -9.1degrees) (c = 5.32, acetone), respectively.

 

189.    Y. Taniyasu, M. Kasu, and N. Kobayashi

            "Intentional control of n-type conduction for Si-doped AlN and AlxGa1-xN with high Al content"

            Physica Status Solidi B-basic Research 234 (3)845-849 (2002).

 

            ABSTRACT: N-type conductive Si-doped AlN and AlxGa1-xN with high Al content have been obtained by intentionally controlling the Si dopant density [Si]. Self-compensation plays an important role at higher [Si] and determines the upper doping limit of Si. The Si-doped AlN showed n-type conduction when [Si] was less than 3 x 10(19) cm(-3). When [Si] was more than 3 x 10(19) cm-, it became highly resistive due to the self-compensation of Si donors, For x > 0.49, the ionization energy of Si donors increased sharply with increasing Al content. This resulted in a sharp decrease in the highest obtainable electron concentration with increasing Al content for the Si-doped AlxGa1-xN.

 

190.    Y. Taniyasu, M. Kasu, and N. Kobayashi

            "Compositional and structural characterization of novel Al1-xSi1-xN ternary alloy"

            Compound Semiconductors 2001 (170)819-824 (2002).

 

            ABSTRACT: Formation of a solid solution of Al1-xSixN ternary alloy was confirmed in the range of 0 < x less than or equal to 0.12. As Si atomic density increased, Al atomic density decreased by the same amount, and the N atomic density stayed constant. This indicates that Si atoms mainly substitute for Al atoms. The lattice constants were obtained from X-ray reciprocal lattice map measurements, taking the residual strain into account. The a-axis and c-axis lattice constants of the strain-free Al1-xSixN linearly decreased with the Si content as a(0)=3.1113-0.1412x (Angstrom) and c(0)=4.9814-0.2299x (Angstrom).

 

191.    Y. Taniyasu, M. Kasu, and N. Kobayashi

            "Intentional control of n-type conduction for Si-doped AlN and AlxGa1-xN (0.42 <= x < 1)"

            Applied Physics Letters 81 (7)1255-1257 (2002).

 

            ABSTRACT: We have obtained n-type conductive Si-doped AlN and AlXGa1-XN with high Al content (0.42less than or equal tox<1) in metalorganic vapor phase epitaxy by intentionally controlling the Si dopant density, [Si]. Si-doped AlN showed the n-type conduction when [Si] was less than 3x10(19) cm(-3). When [Si] was more than 3x10(19) cm(-3), it became highly resistive due to the self-compensation of Si donors. This indicates that the self-compensation plays an important role at higher [Si] and determines the upper doping limit of Si for the AlN and AlXGa1-XN. For xgreater than or equal to0.49, the ionization energy of Si donors increased sharply with increasing Al content. These resulted in a sharp decrease in the highest obtainable electron concentration with increasing Al content for the Si-doped AlXGa1-XN. (C) 2002 American Institute of Physics.

 

192.    T. Tateno, A. Kawana, and Y. Jimbo

            "Analytical characterization of spontaneous firing in networks of developing rat cultured cortical neurons"

            Physical Review E 65 (5), 051924 (2002).

 

            ABSTRACT: We have used a multiunit electrode array in extracellular recording to investigate changes in the firing patterns in networks of developing rat cortical neurons. The spontaneous activity of continual asynchronous firing or the alternation of asynchronous spikes and synchronous bursts changed over time so that activity in the later stages consisted exclusively of synchronized bursts. The spontaneous coordinated activity in bursts produced a variability in interburst interval (IBI) sequences that is referred to as "form." The stochastic and nonlinear dynamical analysis of IBI sequences revealed that these sequences reflected a largely random process and that the form for relatively immature neurons was largely oscillatory while the form for the more mature neurons was Poisson-like. The observed IBI sequences thus showed changes in form associated with both the intrinsic properties of the developing cells and the neural response to correlated synaptic inputs due to interaction between the developing neural circuits.

 

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

            "Self-organized quantum disks for a two-state system"

            Materials Science And Engineering B-solid State Materials For Advanced 88 (2-3)153-157 (2002).

 

            ABSTRACT: We mainly discuss the self-organization in a strained InGaAs/AlGaAs system on a GaAs(311)B surface. This self-organizing growth mode in metal-organic-vapor phase epitaxy automatically produces very small confined nanostructure of quantum disks during growth interruption under a high growth temperature. The micro-photoluminescence (micro-PL) and PL excitation spectroscopies exhibit very narrow excitonic emission and absorption lines. These results indicate that the self-organized quantum disk is a zero-dimensional nanostructure and discrete excitonic states in the zero-dimensional disk may be applicable to a two-state quantum system. (C) 2002 Elsevier Science B.V. All rights reserved.

 

194.    Y. Tokura, and A. Khaetskii

            "Towards a microscopic theory of the 0.7 anomaly"

            Physica E-low-dimensional Systems & Nanostructures 12 (1-4)711-714 (2002).

 

            ABSTRACT: A microscopic mechanism for the so-called 0.7 anomaly is proposed, The exchange interactions in a constriction develop electron spin fluctuations with decreasing carrier density. For non-adiabatic transmission, this spin fluctuation causes additional electron backscattering. The position of the anomaly and its shape are explained by the energy dependence of the transmission probability through the static potential, The temperature dependence is also given by our model. (C) 2002 Elsevier Science B.V. All rights reserved.

 

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

            "Gate voltage dependence of subband structure in a two-dimensional electron gas in AlGaN/GaN heterostructures"

            Physica E-low-dimensional Systems & Nanostructures 13 (2-4)1111-1114 (2002).

 

            ABSTRACT: AlGaN/GaN heterostructure devices have recently been attracting much attention because of their potential for microwave applications. Therefore, the electronic properties of a two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructures have recently been discussed. In this paper, we have studied the subbands of the 2DEG in AlGaN/GaN heterostructures by magnetoresistance measurements for the backgate voltages between 0 and -20 V up to 8 T. Since two kinds of periodic oscillations are observed, the existence of two subbands, the ground-subband and the first-excited-subband, is confirmed. The gate-voltage dependence of the electron concentration in each subband exhibits similar behaviour to the gate-voltage dependence of the electron concentration in AlGaAs/GaAs heterostructures. (C) 2002 Elsevier Science B.V. All rights reserved.

 

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

            "Spin splitting in modulation-doped AlGaN/GaN two-dimensional electron gas"

            Applied Physics Letters 80 (17)3126-3128 (2002).

 

            ABSTRACT: AlGaN/GaN heterostructure devices have recently been attracting much attention because of their potential for high-performance microwave applications. Therefore, the electronic properties of a two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructures have recently been discussed. We studied the magnetoresistance oscillation of the 2DEG at 0.4 K for various backgate voltages, and observed multiple oscillations resulting from spin splitting. The magnetoresistance shows clear beating due to the superposition of three oscillations. The frequency interval between the first and second largest frequencies is proportional to the total electron concentration and the measured spin-orbit interaction parameter agrees with the theoretical one. Therefore, the first and second largest frequencies are found to correspond to spin splitting by the spin-orbit interaction. (C) 2002 American Institute of Physics.

 

197.    A. Tsukada, T. Greibe, and M. Naito

            "Phase control of La2CuO4 in thin film synthesis"

            Physical Review B 66 (18), 184515 (2002).

 

            ABSTRACT: The lanthanum copper oxide, La2CuO4, which is an end member of the prototype high-T-c superconductors (La,Sr)(2)CuO4 and (La,Ba)(2)CuO4, crystallizes in the K2NiF4 structure in high-temperature bulk synthesis. The crystal chemistry, however, predicts that La2CuO4 is at the borderline of the K2NiF4 stability and that it can crystallize in the Nd2CuO4 structure at low synthesis temperatures. In this article we demonstrate that low-temperature thin-film synthesis actually crystallizes La2CuO4 in the Nd2CuO4 structure. We also show that the phase control of K2NiF4-type La2CuO4 versus Nd2CuO4-type La2CuO4 can be achieved by varying the synthesis temperature and using different substrates.

 

198.    K. Ueda, H. Yamamoto, and M. Naito

            "Synthesis and photoemission study of as-grown superconducting MgB2 thin films"

            Physica C-superconductivity And Its Applications 378225-228 (2002).

 

            ABSTRACT: As-grown superconducting thin films of MgB2 were prepared by molecular beam epitaxy (MBE), and studied by X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS). Only films prepared at temperatures between 150 and 320 degreesC showed superconductivity. The best T-c(onset) of 36 K was obtained with a sharp transition width of similar to1 K although the film crystallinity was poor. The in situ photoelectron spectra obtained on the surfaces of the MBE grown MgB2 films were free from dirt peaks. The XP spectra revealed the binding energy of the Mg 2p levels in MgB2 is close to that of metallic Mg and the binding energy of B 1s is close to that of transition-metal diborides. The valence UP spectra showed a clear Fermi edge although the density of states at E-F is low and the major components of the valence band are located between 5 and 11 eV. (C) 2002 Elsevier Science B.V. All rights reserved.

 

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

            "Microscopic mechanism of thermal silicon oxide growth"

            Computational Materials Science 24 (1-2)229-234 (2002).

 

            ABSTRACT: The atomistic mechanism of silicon oxidation is investigated by a combination of first-principles calculations and macroscopic approaches. The results of first-principles calculations show that oxidation-induced strain accumulates at the interface as oxidation proceeds, which indicates the emission of a large number of Si atoms to release the accumulated strain. Further calculations to investigate the favorable location of the emitted Si atoms indicate that most of them diffuse into the oxide layer and are oxidized there. Based on these results, we propose a model that the emitted Si atoms in the oxide govern the oxidation rate due to their high concentration. Next, based on the model, we construct the macroscopic diffusion equations, which include Si diffusion species in addition to oxidant species, and we successfully simulate the whole range of oxide thickness, including the thin film regime, in a wide range of oxidation conditions. In addition, combined with the elastic continuum theory, we show that the strain release by the Si emission can explain the recent observations of Si layer-by-layer oxidation together with the formation of many small oxide islands. (C) 2002 Elsevier Science B.V. All rights reserved.

 

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

            "Interfacial silicon emission in dry oxidation - the effect of H and Cl"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 41 (4B)2455-2458 (2002).

 

            ABSTRACT: The effect of H and Cl on the interfacial silicon emission has been investigated by the simulation of dry oxidation with the addition of small amounts (less than or equal to 10%) of water (H2O) and chlorine (Cl-2). The simulation results for the oxide thickness indicate that the interfacial silicon emission rate is decreased and the equilibrium concentration of the oxygen in the oxide is increased by the addition of these species, as expected from the interfacial Si emission model. From these results, we show that the model is effective for describing oxidation processes.

 

201.    Y. Ueno, K. Ajito, and Y. Y. Maruo

            "Study of reactor-NO2-gas diffusion in a porous glass chip by near-infrared Raman spectroscopy"

            Physical Chemistry Chemical Physics 4 (11)2341-2345 (2002).

 

            ABSTRACT: We have used near-infrared (NIR) Raman spectroscopy to study a coloration reaction that occurs in nano-sized pores in a porous glass chip. This coloration reaction is a modified Saltzman reaction that produces an azo dye by selective reaction with nitrogen dioxide gas (NO2). Neither the details of the reaction mechanisms in the nano-sized pores nor the interaction between the products and the pore surface have previously been investigated. We analyzed the mechanism by measuring the Raman intensity of the azo dye produced in the pores. We found that, in the early stages of NO2 exposure, the NO2 gas reacts at the surface of the porous glass chip, while in the later stages more NO2 gas diffuses into deeper areas without reacting with the reagent. We estimated the limit of the NO2 gas diffusion distance to be about 500 m We also analyzed the interaction between the azo dye and the surface of the pores by comparing the Raman spectrum in the porous glass chip with that in a bulk d(4)-methanol solution. The azo dye is mainly adsorbed as a result of hydrogen bonding between the pi-electrons of the phenyl group and the silanol of the glass surface. We also determined that the azo dye has a trans-conformation molecular structure by calculating the total steric energy. The interaction between the azo group and the silanol is weaker in the adsorbed state than in bulk, due to the steric effect of the bulky substituents around the azo group. Our proposed geometry for the azo dye adsorbed on the surface of the pores has a flatter orientation.

 

202.    J. M. Ulloa, L. Borruel, J. M. Tijero, J. Temmyo, I. Esquivias, I. Izpura, and J. L. Sanchez-Rojas

            "Spontaneous emission study of (111) InGaAs/GaAs quantum well lasers"

            Microelectronics Journal 33 (7)589-593 (2002).

 

            ABSTRACT: Spontaneous emission spectra of (111) and (100) InGaAs/GaAs QW lasers with high In content are measured up to high injection levels and compared with the theoretical results of our own model. Piezoelectric effects are investigated in (111) devices, finding significant contribution of forbidden transitions and a strong blue shift due to carrier screening of piezoelectric field. Band gap renormalization (BGR) in (111) QW lasers is estimated from the measured broadening of the low energy side of the spectrum comparing with model, and corrected by a fundamental band edge. It is also theoretically calculated, including screening effects of the coulomb interaction, in order to explain the estimated results. BGR is found to be higher in (111) samples than in (100) ones, the difference being mainly due to the hole contribution. (C) 2002 Elsevier Science Ltd. All rights reserved.

 

203.    E. Waks, C. Santori, and Y. Yamamoto

            "Security aspects of quantum key distribution with sub-Poisson light"

            Physical Review A 66 (4), 042315 (2002).

 

            ABSTRACT: The security of quantum key distribution with sub-Poisson light sources is investigated. It is shown that a quantitative analysis of the security, of such sources requires only two measured values, the efficiency and second-order correlation. These two numbers represent figures of merit, which characterize the performance of such light sources. We show that sub-Poisson light sources can offer significant improvements in communication rate over Poisson light in the presence of realistic experimental imperfections. We also investigate the amount of channel loss that can be tolerated for secure communication to be possible, and show that this only depends on the second-order correlation, provided the device efficiency exceeds a critical value. If this critical efficiency is exceeded, an inefficient source can perform as well as an efficient one at sufficiently high channel losses.

 

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

            "Secure communication: Quantum cryptography with a photon turnstile"

            Nature 420 (6917)762-762 (2002).

 

            ABSTRACT:

 

205.    E. Waks, A. Zeevi, and Y. Yamamoto

            "Security of quantum key distribution with entangled photons against individual attacks"

            Physical Review A 65 (5), 052310 (2002).

 

            ABSTRACT: We investigate the security of quantum key distribution with entangled photons, focusing on the two-photon variation of the Bennett-Brassard 1984 (BB84) protocol proposed in 1992 by Bennett, Brasard, and Mermin (BBM92). We present a proof of security which applies to realistic sources, and to untrustable sources which can be placed outside the labs of the two receivers. The proof is restricted to individual eavesdropping attacks, and assumes that the detection apparatus is trustable. We find that the average collision probability for the BBM92 protocol is the same as that of the BB84 protocol with an ideal single-photon source. This indicates that there is no analog in BBM92 to photon splitting attacks, and that the source can be placed between the two receivers without changing the form of the collision probability. We then compare the communication rate of both protocols as a function of distance, and show that BBM92 has potential for much longer communication distances, up to 170 km, in the presence of realistic experimental imperfections. Finally, we propose a scheme based on entanglement swapping that can lead to even longer distance communication. The limiting factor in this scheme is the channel loss, which imposes very slow communication rates at longer distances.

 

206.    H. L. Wang, M. Kumagai, T. Tawara, T. Nishida, T. Akasaka, N. Kobayashi, and T. Saitoh

            "Fabrication of an InGaN multiple-quantum-well laser diode featuring high reflectivity semiconductor/air distributed Bragg reflectors"

            Applied Physics Letters 81 (25)4703-4705 (2002).

 

            ABSTRACT: High-quality deeply-etched GaN-based semiconductor/air distributed Bragg reflectors (DBRs) have been fabricated. A 50% reduction relative to the value for reflectors of Fabry-Perot type in the threshold pump intensity was realized by the introduction of such DBRs at the ends of the laser cavity. The reflectivity of the grating was evaluated between 44% and 62%. Finite-difference time-domain simulation had earlier been used to obtain a design for the semiconductor/air DBRs, which provides high values for reflectivity despite a significant inclination from the vertical of the sidewalls of the structure. (C) 2002 American Institute of Physics.

 

207.    H. L. Wang, T. Tawara, M. Kumagai, T. Saftoh, and N. Kobayashi

            "Novel design to fabricate high reflectivity GaN-Based semiconductor/air distributed bragg reflector with the tilt of vertical sidewall"

            Japanese Journal Of Applied Physics Part 2-letters 41 (6B)L682-L684 (2002).

 

            ABSTRACT: High reflectivity can be reached with the proper design of a GaN-based semiconductor/air distributed Bragg reflector (DBR) structure even with a large vertical sidewall tilt. Finite-difference time-domain simulations show that vertical sidewall tilt is a crucial concern for obtaining a high-reflectivity DBR in a conventional design. A tilt of only 3degrees reduces die reflectivity to similar to 30%. Experimentally, it is difficult to etch vertical sidewalls of GaN-based materials. So, the novel design to obtain high reflectivity is important for the application of the GaN-based semiconductor/air DBR structure in waveguide lasers.

 

208.    K. Yamada, M. Notomi, A. Shinya, C. Takahashi, J. Takahashi, and H. Morita

            "Singlemode lightwave transmission in SOI-type photonic-crystal line-defect waveguides with phase-shifted holes"

            Electronics Letters 38 (2)74-75 (2002).

 

            ABSTRACT: Singlemode lightwave transmission was observed in novel line-defect photonic-crystal (PC) waveguides. The waveguide structure is constructed by adding phase-shifted holes in an ordinary missing-hole line detect. This device permits a fine singlemode lightwave transmission even though the waveguide structure is fabricated on silicon-on-insulator (SOI) substrate. which seriously promote, off-plane leakage of waveguiding modes.

 

209.    F. Yamaguchi, and Y. Yamamoto

            "Quantum simulation of the t-J model"

            Superlattices And Microstructures 32 (4-6)343-345 (2002).

 

            ABSTRACT: zComputer simulation of a many-particle quantum system is bound to reach the inevitable limits of its ability as the system size increases. The primary reason for this is that the memory size used in a classical simulator grows polynomially whereas the Hilbert space of the quantum system does so exponentially. Replacing the classical simulator by a quantum simulator would be an effective method of surmounting this obstacle. The prevailing techniques for simulating quantum systems on a quantum computer have been developed for purposes of computing numerical algorithms designed to obtain approximate physical quantities of interest. The method suggested here requires no numerical algorithms; it is a direct isomorphic translation between a quantum simulator and the quantum system to be simulated. In the quantum simulator, physical parameters of the system, which are the fixed parameters of the simulated quantum system, are under the control of the experimenter. A method of simulating a model for high-temperature superconducting oxides, the t-J model, by optical control, as an example of such a quantum simulation, is presented. (C) 2003 Elsevier Ltd. All rights reserved.

 

210.    H. Yamaguchi, and Y. Hirayama

            "Novel fabrication method of semiconductor nano-electromechanical structures using controlled surface step distribution"

            Compound Semiconductors 2001 (170)335-338 (2002).

 

            ABSTRACT: We selectively etched a GaAs sacrificial layer under InAs wires preferentially grown on bunched steps on misoriented GaAs (110) surfaces, which led to the successful formation of InAs nanoscale cantilevers with a length of 50-100 nm, width of 20-50 nm, and thickness of 5-10 nm. This is a novel fabrication technique for nano-scale electromechanical structures, which can serve as an alternate to state-of-the-art electron-beam lithography.

 

211.    H. Yamaguchi, R. Dreyfus, S. Miyashita, and Y. Hirayama

            "Fabrication and elastic properties of InAs freestanding structures based on InAs/GaAs(111)A heteroepitaxial systems"

            Physica E-low-dimensional Systems & Nanostructures 13 (2-4)1163-1167 (2002).

 

            ABSTRACT: InAs semiconducting freestanding structures, such as beams, Hall bars and cantilevers, were successfully fabricated based on InAs/GaAs( 1 1 1)A heteroepitaxial systems with extremely high slenderness ratios (length/thickness) of up to 10(3). Without any intentional doping, the structures showed clear n-type electric conductivity with increased carrier concentration and mobility in comparison with similarly grown heterostructure samples, The mechanical motion of cantilevers was electrically activated and clear resonance characteristics confirmed, indicating that these structures are promising for the application in the field of micro/nano electromechanical systems. (C) 2002 Elsevier Science B.V. All rights reserved.

 

212.    H. Yamaguchi, and Y. Hirayama

            "Fabrication of conductive single-crystal semiconductor nanoscale electromechanical structures"

            Applied Physics Letters 80 (23)4428-4430 (2002).

 

            ABSTRACT: As an application of the self-organization growth technique to the fabrication of nanoscale mechanical structures, we selectively etched a GaAs sacrificial layer under InAs wires preferentially grown on bunched steps on misoriented GaAs (110) surfaces, which led to the formation of single-crystal InAs nanoscale cantilevers. Their lengths, widths and thickness are typically 50-300, 20-100 and 10-30 nm, respectively. The structures are expected to be electrically conductive and to be promising for use in fabricating single-crystal nanoelectromechanical systems. (C) 2002 American Institute of Physics.

 

213.    H. Yamaguchi, R. Dreyfus, S. Miyashita, and Y. Hirayama

            "Application of InAs freestanding membranes to electromechanical systems"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 41 (4B)2519-2521 (2002).

 

            ABSTRACT: We have fabricated freestanding InAs membranes by selectively etching the sacrificial GaAs layer in InAs/GaAs heterostructures and characterized their electrical and mechanical properties. The membranes show n-type conductivity without any intentional doping because of native electron accumulation in the near-surface region. The use of focused ion beam implantation makes it possible to cut the membrane into the desired shapes with the accuracy of 150 nm. With these processing techniques, we have fabricated single and coupled cantilevers whose mechanical motion can be electrically activated.

 

214.    T. Yamaguchi, and H. Namatsu

            "Binary-solvent developer for cross-linked positive-tone resists"

            Japanese Journal Of Applied Physics Part 1-regular Papers Short Notes & 41 (6B)4217-4221 (2002).

 

            ABSTRACT: A new binary-solvent developer has been developed for a cross-linked positive-tone resist called suppressed aggregate extraction development (SAGEX) resist. It is composed of a good solvent and a poor solvent that does not produce swelling in the resist polymer. Hydrocarbon. such as n-hexane, was used as a poor solvent in this study because alcohol, which is conventionally used as a poor solvent, was not effective. A hydrocarbon, which causes little swelling of the base polymer, reduces the dissolution of lightly exposed SAGEX resist in a good solvent. As a result, with this developer, a high contrast can be obtained and resist residue can be eliminated at the same time. In addition, this developer has been shown to be effective in reducing resist roughness; that is, it helps reduce the line-edge roughness of resist patterns to 1 nm or less.

 

215.    H. Yamamoto, K. Aoki, and M. Naito

            "Synthesis of superconducting FeSr2YCu2Oy thin films"

            Physica C-superconductivity And Its Applications 37852-55 (2002).

 

            ABSTRACT: We report the thin-film synthesis of the superconducting FeSr2YCu2Oy (Fe-1212) discovered recently by Shimoyama et al. (Physica C 341-348 (2000) 563). The superconducting phase was obtained by an ex situ three-step process that essentially follows the bulk synthesis process. The resultant Fe-1212 films are c-axis oriented and the lattice constants are c(0) = 11.45 and 11.33 A before and after oxygen loading, both of which are close to the bulk values. The best film shows T-c(onset) similar to 40 K, T-c(end) similar to 10 K, and p(300 K) similar to 3 mOmegacm. Attempts at in situ molecular beam epitaxy growth with atomic oxygen or ozone were unsuccessful since Fe4+, unlike the Fe3+ required, is stable in activated oxygen. (C) 2002 Elsevier Science B.V. All rights reserved.

 

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

            "Coulomb drag between quantum wires: magnetic field effects and negative anomaly"

            Physica E-low-dimensional Systems & Nanostructures 12 (1-4)726-729 (2002).

 

            ABSTRACT: We have measured the drag resistance R-D between parallel. split gate quantum wires fabricated on an n-GaAs/GaAs 2DEG heterostructure in magnetic fields B from zero up to the edge state regime. We find that a peak in R-D associated with the alignment of the Fermi wave vectors in the drive and drag wires at B = 0 vanishes in the edge state regime of the drag-wire conductance. This effect is attributed to suppressed backscattering. By contrast, when the conductance of both wires is appreciably below the first plateau, a peak in R-D which occurs for B = 0 is enhanced by an order of magnitude in the strong field, This behavior appears to emerge from the quasi-singular nature of the density of states at the bottom of a Landau band. Finally, for both zero and non-zero fields, we observe negative Coulomb drag when the drive-wire density is driven close to pinch off and it is high enough. The negative drag can be explained in terms of the response of a 1D Fermi liquid to a sliding Wigner crystal in the drive wire. (C) 2002 Elsevier Science B.V. All rights reserved.

 

217.    A. Yokoo, M. Notomi, H. Suzuki, M. Nakao, T. Tamamura, and H. Masuda

            "Emission from functional-polymer-injected point defects in two-dimensional photonic crystals"

            Ieee Journal Of Quantum Electronics 38 (7)938-942 (2002).

 

            ABSTRACT: We consider the selective injection of active material into a 2-D photonic crystal. Using an alumina nanohole array as a base photonic crystal, we fabricated a positional-selective through-hole in the array with a focused ion beam. The active material, a polythiophen derivative, was then injected into the through-hole. As a result, a positional-selective polythiophen-injected alumina nanohole array was fabricated. The calculation predicts that the defect level is introduced into the photonic bandgap of the alumina nanohole array by selective injection of polythiophen. Optical measurement shows a sharp emission peak corresponding to the defect level. This demonstrates that a functional point in an alumina nanohole array can be successfully fabricated by selective polymer injection and proves that the defect level is introduced into the photonic bandgap by the selective polymer injection.

 

218.    M. Yuda, T. Sasaki, J. Temmyo, M. Sugo, and C. Amano

            "High-power, highly reliable 1.05 mu m InGaAs strained quantum well laser diodes as pump sources for thulium-doped fibre amplifiers"

            Electronics Letters 38 (1)45-46 (2002).

 

            ABSTRACT: High output power of about 500 mW in chips without kink and having stable operation for over 5500 h under auto-power-control of 225 mW at 50 degreesC have been achieved in 1.05 mum InGaAs strained quantum well laser diodes for pump sources of thulium-doped fibre amplifiers. Low-temperature growth of the InGaAs well layer enabled the lasing wavelength to be extended to 1.05 mum.

 

219.    Z. B. Zhang, M. Fujiki, H. Z. Tang, M. Motonaga, and K. Torimitsu

            "The first high molecular weight poly (N-alkyl-3,6-carbazole)s"

            Macromolecules 35 (6)1988-1990 (2002).

 

            ABSTRACT:

 

220.    Z. B. Zhang, M. Fujiki, M. Motonaga, H. Nakashima, K. Torimitsu, and H. Z. Tang

            "Chiroptical properties of poly{3,4-bis[(S)-2-methyloctyl]lthiophene}"

            Macromolecules 35 (3)941-944 (2002).

 

            ABSTRACT: The circular dichroism (CD) of a polythiophene in the molecularly dispersed state was observed for the first time. The polythiophene possesses two chiral alkyl side chains (poly{3,4-bis[(S)-2-methyloctyl]thiophene}, PDMOT). The chiroptical properties of this polymer in solution, aggregate, and thin solid film states were investigated. A chirally distorted main-chain conformation in a single molecule of PDMOT accounts for the observed CD spectra in solution and could also be considered as a novel chiral motif in an optically active polymer, besides the highly ordered, intramolecular helical structure and the chiral superstructure resulting from intermolecular pi-pi stacking. Significant temperature and solvent effects on the CD were also observed in the spectra.

 

221.    Z. H. Zhang, K. Sumitomo, H. Omi, T. Ogino, J. Nakamura, and A. Natori

            "Atomic structures of the Ge/Si(113)-(2X2) surface"

            Physical Review Letters 88 (25), 256101 (2002).

 

            ABSTRACT: Based on scanning tunneling microscopy observations of the epitaxial growth of Ge on Si(113) and first-principles total energy and band calculations, we demonstrate that the Ge/Si(113)-(2 X 2) surface is made up of alternating [(1) over bar 10]-oriented rows of rebonded atoms and tilted pentamers of five atoms, where each pentamer is stabilized by an interstitial atom at the subsurface. From the existence of stacking defects in rows of tilted pentamers observed at room temperature, we have deduced that at epitaxial temperatures the pentamers frequently change their tilting orientations between two minimum energy states.

 

222.    Z. H. Zhang, K. Sumitomo, H. Omi, and T. Ogino

            "Influences of the Si(113) anisotropy on Ge nanowire formation and related island shape transition"

            Surface Science 497 (1-3)93-99 (2002).

 

            ABSTRACT: Based on the scanning tunneling microscopy observations of Ge coherent growth on Si(113), we demonstrate that the anisotropy of substrate stiffness is responsible for the anisotropic relaxation of islands, which leads to island elongation perpendicular to the softer direction of the substrate surface. The transition from wire-like islands to dot-like islands indicates that relaxation of islands tends to become isotropic as the size of the islands increase. Island volume measurements reveal that the material grown on the substrate, including the wetting layer, is continuously rebuilt during island formation and transition. (C) 2001 Elsevier Science B.V. All rights reserved.