bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparative Study of Photoluminescence in Ordered and Disordered Ga0.5In0.5P Alloys under Hydrostatic Pressure
Authors: Shoji Masataka , Kobayashi Toshihiko , Deol Rajpal S. , Nakahara Jun' ichiro
Published: March 2014

We have measured the photoluminescence (PL) spectra of ordered GaInP alloys grown by organometallic vapor phase epitaxy (OMVPE) at three different growth temperatures (Tg = 600, 650, and 700 °C) as a function of pressure up to about 4.0 GPa at a temperature of 300 K. We have also done similar measurements on a disordered (bulk) alloy for comparison. We find that the band-gap energy Eo, derived from the PL perk spectra, of ordered alloys shows a sublinear pressure dependence and is significantly different from that of the disordered sample. The overall shift of Eo with pressure up to 3.5 GPa for the ordered sample grown at 700 °C is smaller than for both the ordered material grown at 600 °C and the disordered sample studied. The observed behavior of Eo can be related to the existence of a CuPt-type ordered structure in which the degree of ordering depends on Tg and between Γ-folded states affects the band-gap energy.
Hydrostatic Pressure Dependence of the Fundamental Absorption Edges of CdInCaS4 and ZnIn2S4
Authors: Toyoda Taro , Sorazawa Mitsumasa , Nakanishi Hisayuki , Endo Saburo , Irie Taizo
Published: March 2014

The optical absorption of CdInGaS4 and ZnIn2S4 single crystals has been measured over a hydrostatic pressure range up to 35 kbar in the 1.6 - 3.5 eV photon energy range at room temperature. The interband gap for indirect allowed transition of CdInGaS4 was found to have a
pressure coefficient, dEg/dP, of (+4.1±0.3)×10-6 eV/bar, and that for direct allowed transition in ZnIn2S4 was found to have (+4.9±0.6)×10-6 eV/bar.
Nonlinear Refractive Index of Organic Materials under High Pressure
Authors: Hiraga Takashi , Tanaka Norio , Moriya Tetsuo
Published: March 2014

High pressure measurements on the nonlinear refractive indices(n2) of 2-methyl-4-nitroaniline (MNA) are investigated. A Fabry-Perot interferometer(FP) constructed with a pair of diamond anvil (DA) culets coated with a dielectric substance is used. The n2 irradiated by 10 nsec laser light pulses increases with pressure increasing up to 3.3 GPa. Further measurements on n2 by using shorter than nsec laser light pulses are discussed.
Pressure Effects on CdS Microcrystals Embedded in Germanate Glasses
Authors: Arai Toshihiro , Inokuma Takao , Makino Toshiharu , Onari Seinosuke
Published: March 2014

We measured the absorption edge, photo-luminescence and Raman scattering spectra of CdS microcrystals embedded in germanate glasses under high hydrostatic pressure. We found that the one L0 phonon frequency shifts to the higher energy side with the increase of the pressure. The Raman shift with pressure variation is rather insensitive to the size of the CdS microcrystal and the change of its value with pressure is approximately equal to that of the bulk material. This strongly suggests that the stress induced by the glass medium is small. We also found that the absorption edge energy increases with the increase of the pressure. The bulk CdS shows a phase transition at 2.7 GPa pressure, however, the microcrystals exhibit no drastic change in the measured pressure range. The dependence of the luminescence on the pressure was also measured. The surface emission, which is in the lower energy part of the edge emission luminescence spectra, shifts to the higher energy side and disappears gradually with the Increase of the pressure.
Dynamic Behaviors of Protons and Deuterons in Squaric Acid Crystal as Investigated by High-Pressure Raman Spectroscopy
Authors: Moritomo Yutaka , Tokura Yshinori
Published: March 2014

Effects of hydrostatic pressure on the Raman spectra for a prototypical hydrogen-bonded molecular solid, the isotopically mixed crystal of squaric acid ((H1-xDx)2C404; x=0.4), have been investigated. Pressure-enhanced back-and-forth motion of the protons (deuterons) induces a symmetry change of the constituent squaric molecules from the asymmetric (C1h) to centrosymmetric (C4h) form around 3GPa at 300K. Furthermore, the critical pressure (PS) for the symmetry change is found to increase with decreasing temperature. Based on these results, dynamic behaviors of the protons as well as deuterons under pressures are discussed.
Fourier Transform Spectroscopy at Diamond Anvil Cell Pressures
Authors: Holmes S. N. , Li M. , Weinstein B. A. , McCombe B. D.
Published: March 2014

The high pressure diamond anvil cell can be used for Fourier Transform Magneto-Spectroscopy of impurity levels in semiconductors at far infrared wavelengths. The performance of the diamond anvil cell for this type of spectroscopy is evaluated. In the present measurements we investigate the non-metastable impurity states in n-type AlxGa1-xAs materials in the frequency range 80-300 cm-1 up to a maximum pressure of 45 kbar. A shallow to deep transition of an impurity in undoped n-type Al0.03Ga0.97As was observed at approximately 22kbar. This non-metastable state is either non-lattice relaxed or is weakly relaxed and is resonant with the conduction band at atmospheric pressure. In lightly silicon doped n-type GaAs the crossover from the shallow donor state to the non-metastable silicon A1 antibonding level occurred at 25 kbar.
GaP-GaN Pseudobinary System. Crystal Growth of GaN from the Solution in the Liquid GaP
Authors: Grzegory Izabella , Jun Jan , Krukowski Stanislaw , Porowski Sylwester
Published: March 2014

Phase diagram of pseudobinary GaP-GaN system has been calculated using Phillips-Van Vechten theory of solid solutions and Hildebrand theory of nonelectrolytic liquids. Large miscibility gap in the solid phase, was predicted. Solubility of P in GaN is negligible which opens the possibility of GaN crystal growth from the molten GaP. The theoretical results were confirmed by crystal growth of GaN from molten GaP under high N2 pressure. High pressure of nitrogen, 17 - 20 kbar, assures the stability of GaN growing at temperatures exceeding GaP melting. Single crystals of GaN have been grown. As predicted, the presence of phosphorus in GaN was not detected by EDX technique.
The Success of Strained Layer Lasers Elucidated by High Pressure Experiments
Authors: Adams Alfred R. , Hawley Martin , O'reilly Eoin , Ring William
Published: March 2014

The presence of Auger recombination and Intervalance Band Absorption is shown to be greatly reduced in both compressively and tensiley strained multiple quantum well lasers. The differential quantum efficiency of tensiley and compressively strained lasers is demonstrated to be relatively independent of pressure. We present for the first time measurements of the temperature sensitivity of long wavelength lasers as a function of high pressure. Unstrained lasers show a pressure dependent temperature sensitivity whilst tensiley strained lasers do not, over the range of temperatures from 150K to 300K.
On the High Pressure Phases of InSb
Authors: Guo G. Y. , Crain J. , Temmerman W. M.
Published: March 2014

Motivated by a recent X-ray diffraction experiment using the synchrotron radiation source at Daresbury Laboratory, we have re-examined the high pressure structures of InSb by means of the first-principles density functional total energy calculations. In this paper, we present results of our all-electron full-potential linear augmented plane wave (FLAPW) calculations. Among other things, we find that the tetragonal β–Sn structure is unstable compared with the newly proposed body-centred orthorhombic structure and that the calculated structural parameters are in good agreements with the X-ray diffraction experiment.
Phase Diagram of the Three-Dimensional Halogen-Bridged Mixed-Valence Compounds M2Au2X6 (M=Rb, Cs; X=Cl, Br, I) under High Pressure
Authors: Kojima Norimichi , Tanaka Atsushi , Sato Hirohiko , Kitagawa Hiroshi , Kikegawa Takumi , Shimomura Osamu
Published: March 2014

M2AuIAuIIIX6 (M=Rb, Cs; X=Cl, Br, I) are known as three-dimensional halogen-bridged Au mixed-valence compounds. These compounds undergo a semiconductor-to-metal transition under high pressures. From an interest in the relationship between the crystal structure and the Au valence state, we investigated the phase diagram of M2Au2X6 from the structural analysis under high pressures.
Structural Transitions in Iodine-Intercalated Bi2Sr2CaCu2O8+x: X-Ray and Raman Scattering Studies
Authors: Qiu C. H. , Wada N. , Ciszek T. F.
Published: March 2014

Iodine-intercalated Bi2Sr2CaCu2O8+x compounds were investigated as functions of temperature and pressure by x-ray diffraction and Raman scattering. A structural transition from stage 1 (c ≈ 19.0 Å) to “stage 2” (c ≈ 36.6 Å) was found at ∼150 °C. Raman scattering results indicate that the intercalation compounds consist of I3
-, I2 and atomic iodine. The molecular species are more stable at lower temperatures and higher pressures.
FIR Properties of GaAs–GaAlAs Heterojunctions Controlled by Metastable States under Pressure
Authors: Raymond A. , Chaubet C. , Dur D. , Knap W. , Zawadzki W. , Andre J. P.
Published: March 2014

By using the metastable properties of the Si donors in modulation doped GaAs-GaAlAs heterojunctions, we control the 2D electron density under hydrostatic pressure. We perform simultaneously FIR emission experiments (cyclotron emission) as well as transport experiments (ρxx and ρxy parameters). The transport experiments allow us to determine accurate values of the 2D electron density Ns in the conditions of heating of the 2D electrons for the cyclotron emission. The curves of the effective mass (obtained from the FIR emission) versus Ns show a clear linear increase. This behaviour is analysed in terms of nonparabolicity, using a theory of electric and magnetic quantization in narrow gap semiconductors.
Optical Properties of Small Silicon Clusters: Chain, Ladder and Cubic Structures
Authors: Kanemitsu Yoshihiko , Suzuki Katsunori , Kyushin Soichiro , Matsumoto Hideyuki
Published: March 2014

We have studied the luminescence properties of chemically synthesized Si8 clusters with chain, ladder and cubic structures. The optical properties of Si8 clusters depend strongly on the shape of clusters. The luminescence properties of the cubic Si8 cluster are entirely different from those of the chain and ladder Si8 clusters. The unique optical properties of silicon clusters are discussed.
Nonlinear Optical Spectra of the Confined Excitons in Stress Induced Nanostructures in BiI3
Authors: Akai Ichiro , Karasawa Tsutomu , Komatsu Teruo , Iwai Sadayuki , Edamatsu Keiichi , Itoh Tadashi , Yano Satoshi , Goto Takenori
Published: March 2014

We report the optical nonlinear response of the confined excitons in nanostructures induced by external stress in a layered crystal BiI3. The absorption intensity of the confined excitons is saturated by intense laser excitation. We clarify the size dependence of the saturation density which reflects the nanostructure size. The saturation density of the confined exciton in large domains is lower than the the case of small domains. By pump-probe measurements using a sub-picosecond laser pulse, we examine the dynamical process of the confined excitons in the disks with various sizes. From the temporal behavior of the absorption saturation, it becomes clear that the exciton life times in small disks are shorter than the large ones. A new nonlinearly growing luminescence due to the process by a inelastic recoiling of excitons is detected.
Characterization of CoO-Doped SiO2 Nanocomposite Films and Their Optical Transmittance Change by Nitrogen Oxide
Authors: Koshizaki Naoto , Yasumoto Katsuya , Terauchi Shin-ya
Published: March 2014

We developed CoO-doped nanocomposite films which change their optical transmittance by nitrogen oxide using co-sputtering method. Films sputtered from SiO2 target with CoO pellets on at 100W under 0.27 Pa Ar atmosphere showed reversible transmittance change by NO at 350°C in the wavelength range from 400 to 800 nm. Cobalt oxide dots 4-8 nm in diameter were observed in the CoO/SiO2 nanocomposite films by TEM observation. The heat-treated CoO/SiO2 film at 600°C which showed no transmittance change by NO still had cobalt oxide nanoparticles embedded in SiO2 matrix. The sensing properties is considered to be originated from nanostructure composed of functional nanoparticles which change their optical transmittance, nanopores which give paths of gas molecules and transparent matrix,
Visible Light Emission from the Silicon-Doped SiO2 Thin Film Deposited by Sputtering
Authors: Nozaki Shinji , Nakamura Hitoshi , Ono Hiroshi , Morisaki Hiroshi , Ito Nobuo
Published: March 2014

Visible light emission strong enough to be seen with the naked eye was obtained at room temperature from the Si-doped SiO2 thin films deposited on Si substrates by cosputtering of Si and SiO2 when they were annealed in Ar at high temperature. The luminescence model with radiative recombination centers at the surface of a Si nanocrystal and nonradiative recombination centers in SiO2 has been developed to explain the results of the combined x-ray diffraction and photolumines cence measurements.
Magnetic Field Effects in Direct- and Indirect-Gap Semiconductor Quantum Dots
Authors: Nomura Shintaro , Zhao Xinwei , Schoenfeld Olaf , Misawa Kazuhiko , Kobayashi Takayoshi , Segawa Yusaburo , Aoyagi Yoshinobu , Sugano Takuo
Published: March 2014

A magnetic circular dichroism (MCD) measurement is utilized to investigate confined states in direct (CuCl, and CdSxSe1-x) and indirect gap (Si) semiconductor quantum dots (QD's). CuCl and CdSxSe1-x QD's belong to the weak and intermediate confinement regimes, leading to contrastive response to a magnetic field. In CuCl QD's, the enhancement of g-value is observed due to the mixing of the relative and the center-of-mass motions, while (p, P)type transition is observed in CdSxSe1-x QD's. In Si QD's confined states with direct as well as indirect nature are observed that confirms the quantum confinement effects in Si QD's.
Study of Diffusion and Carrier Recombination for Cu2O Ultrafine Particles in Organosols
Authors: Zhang X. Q. , Chen Y. M. , Zhao J. L. , Qin W. P. , Fan X. W. , Huang S. H.
Published: March 2014

The diffusion coefficient and carrier recombination time have been obtained by time-delayed four-wave mixing with incoherent light for Cu2O ultra fine particles in the organosols at room temperature. The results, D=0.011 cm2/s, T

R
=1.2 ns. The diffusion processes was discussed.
Dynamics of Exciton Recombination in II-VI Semiconductor Quantum Wells
Authors: Schülzgen Axel , Runge Erich , Henneberger Fritz , Zimmermann Roland
Published: March 2014

We have studied the temporal evolution of the inhomogeneously broadend exciton emission band to obtain information about the process of exciton localization in ZnCdSe/ZnSe and ZnSe/ZnMnSe quantum well structures. The observed behavior can be described with quantitative agreement by theoretical calculations taking into account the exciton center-of-mass motion in a disordered potential being Gauss distributed and correlated over distances of the exciton Bohr radius. As predicted by the theory a nearly linear increase of the exciton life-time is observed between 5 K and 40 K for the ZnCdSe/ZnSe structure.
Size Effects of Molecular Excitons in Organic-Inorganic Hetero Nanostructures
Authors: Takada Jun
Published: March 2014

Nano boxes and nano sheets composed of organic molecular crystal of copperphthalocyanyne (CuPc) and amorphous ceramics of titanium oxide (TiOx) and silicon dioxide (SiO2) were formed by vacuum thin film technology in order to explore physics in organic-inorganic hetero nanospaces. Quite different phenomena of CuPc molecular exciton between hetero structures of CuPc-SiO2 and CuPc-TiOx have been observed. Molecular excitons of CuPc only in the CuPc-TiOx hetero nanostructures exhibited size effects clearly.
Excitonic Optical Nonlinearity and Optical Bistability in ZnSe–CdZnSe MQWs at Room Temperature
Authors: Shen D. Z. , Zhang J. Y. , Fan X. W. , Sun J. M. , Yang B. J. , Lu Y. M. , Wang S. M.
Published: March 2014

Excitonic optical bistability with picosecond switching time in ZnSe-CdZnSe multiple quantum wells (MQWs) optical bistable device is investigated at room temperature for the first time. The result indicates that the threshold and contrast ratio for the optical bistability in ZnSe-CdZnSe MQWs optical bistable device are about 210 kW/cm2 and 2 : 1, respectively. On the basis of the excitonic nonlinear theories, excitonic absorption and excitonic emission under different excitation intensities in the ZnSe-CdZnSe MQWs obtained here, we attribute the major nonlinear mechanism for the optical bistability in ZnSe-CdZnSe MQWs optical bistable device to the phase space filling of excitonic states and excitonic band broadening due to exciton-exciton interactions.
Magneto-Optical Studies on Cd1-xMnxSe Quantum Dots
Authors: Yanata Kohei , Oka Yasuo
Published: March 2014

Magneto-optical effects of Cd1-xMnxSe quantum dots (QDs) embedded in quartz glass have been investigated in magnetic fields up to 7T. The photoluminescence shows large Zeeman shifts from a few meV up to 30meV depending on the size and Mn mole fraction. The exciton luminescence measured by selective excitation spectroscopy in an applied magnetic field shows the excitonic magnetic polaron (EMP) effect in the Cd1-xMnxSe QDs with the EMP formation energy above 20meV. The transient emission of the QD exciton has also been examined in the picosecond time domain. The lifetime of the QD excitons at the emission peak decreases from 900ps to 400ps in the presence of a magnetic field of 5T.
Exciton Dynamics of Poly(di-n-hexylsilane) Film
Authors: Suto Shozo , Shimizu Makoto , Goto Takenari , Watanabe Akira , Matsuda Minoru
Published: March 2014

We have measured excitation spectra of exciton luminescence and time response of a σ-conjugated one-dimensional polymer, poly(di-n-hexylsilane), film at 2K. The site selective luminescence near 3.36 eV is measured under the excitation of light with energy lower than 3.528 eV. The time-resolved spectra of the luminescence show that the peak energy of 3.369 eV shifts to 3.360 eV within 360 picoseconds. The site-selective luminescence and the peak shift in the picosecond time region are discussed in terms of the disordered segment model.
Femtosecond Dynamics of Frenkel Excitons in Pseudoisocyanine J Aggregates
Authors: Sasaki Fumio , Kobayashi Shunsuke
Published: March 2014

We report results of femtosecond pump-probe and degenerate four-wave mixing (DFWM) experiments in pseudoisocyanine J aggregates at 77 K. In the pump-probe experiments, the spectral oscillatory structure has been observed when the probe pulse precedes the pump pulse. This spectral oscillation is ascribed to the perturbed free induction decay of the J band. From the rise-up of the oscillation and results of DFWM experiments, the relaxation time is estimated from 300 to 600 fs. The time-resolved degenerate four-wave mixing spectroscopy is adopted to measure the coherent polarization decay in the J aggregates. The results clearly shows that the coherent polarization decay of the J band is ascribed to the free induction decay.
Absorption and Photoemission Studies of Au–55 Metal Clusters
Authors: Miyauchi Hiroshi , Taketomi Kuniyasu , Egami Akihiro , Hosoi Shinnya , Fukutani Hirohito
Published: March 2014

Absorption spectra of chemically synthesized Au-55 metal clusters were investigated in the photon energy from 0.5 to 40 eV. Apart from the well-known plasma resonance at 2.4 eV, small but distinct features were found at 4.5 and 5.0 eV. The valence band photoemission spectra were also investigated. The Au-5d band maximum was found at -4.0 eV below Fermi level. We attribute the two features to transitions from the d-band maximum to unoccupied states which arise from the level quantization of Au-6sp electrons confined in Au-55 clusters with 7 A radius.
Raman Scattering Study on a Pure C60 Film in Vacuum
Authors: Kasuya A. , Tanaka W. , Nishitani R. , Saito Y. , Shinohara H. , Nishina Y.
Published: March 2014

The Raman scattering from a pure C60 film has been measured in vacuum under various Ar+ laser irradiataion conditions. The spectral profiles are found to depend on laser intensity and wavelength. The results are interpreted in terms of relative orientation of C60 molecules in the crystal modified by laser irradiation.
Brillouin Scattering from Spin Waves in an Ultrathin Fe Wedge
Authors: Yoshihara Akira , Suzuki Yoshishige , Katayama Toshikazu
Published: March 2014

Collective spin waves in an ultrathin epitaxial bcc Fe (001) wedge have been investigated using Brillouin scattering at room temperature. Spin wave frequencies were determined as a function of the external magnetic field for various Fe thicknesses ranging between 2.6Å and 8.9Å. We found that the stable direction of the magnetization of the wedge under zero magnetic field turns over from the in-plane direction to the surface normal below d≈3Å.
Quantum Wires and Dots Made by Man and by God: A Peek into the Optics Toolbox!
Authors: Merz James L.
Published: March 2014

In this paper a number of examples will be provided which describe the kind of information available from optical investigations of low-dimensional quantum structures. These measurement techniques include photo- and cathodoluminescence, photoluminescence excitation and selective photoluminescence, magnetoluminescence, intensity and time-decay measurements
Magnetic Oscillation of Luminescence Energy in Single Heterostructures
Authors: Tsuchiya Takuma , Katayama Shin'ichi , Ando Tsuneya
Published: March 2014

Magnetic-field dependence of luminescence energy due to recombination of a two-dimensional electron and a photo-excited hole trapped in an acceptor state in n-type GaAs/AlGaAs single hetero-structures is calculated. The luminescence energy shows red shift when the Fermi energy is in an energy gap between adjacent Landau levels. Amplitude of the red shift decreases as the distance between acceptors and the hetero-interface increases. When the distance is larger than a few hundred angstroms, the energy oscillation of electrons becomes dominant. Calculated first moment (center of gravity) of luminescence spectrum reproduces result of a recent experiment quite well.
Optical Properties in ZnCdSe–ZnSe Multiple Quantum Wells
Authors: Fan X. W. , Zhang J. Y. , Shen D. Z. , Yang B. J.
Published: March 2014

The optical properties of Zn1-xCdxSe–ZnSe multiple quantum wells (MQWs) have been investigated. The MQWs samples exhibit five photoluminescence peaks under the 457.9 nm line of an Ar ion laser excitation at 77 K. Three of these bands are attributed to different exciton emission: the n=1 heavy–hole exciton transition, the n=1 light–hole exciton transition and n=1 heavy–hole exciton transition with the emission of two LO phonons. The room–temperature nanosecond switching property has also been studied in Zn1-xCdxSe–ZnSe MQWs F–P–type optical bistable device operation in reflection, in which their switching threshold and contrast ratio are about 47 kW/cm2 and 7:1, respectively. The origin of the major nonlinear mechanism for the optical switching property is due to the change of the refractive index caused by the effect of the excitonic saturating absorption effect in the ZnCdSe–ZnSe MQWs.
Photoluminescence Spectra of “Green” Porous Silicon
Authors: Astrova E. V. , Lebedev A. A. , Remenyuk F. D. , Rud' Yu. V.
Published: March 2014

Photoluminescence spectra (PL) of porous silicon (PS) at 77–440 K have been studied. We have found the transformation of the spectra when as prepared green-emitting PS was subjected to drying in ambient air. We report also the observation of additional peaks on the PL band and pronounced fine structure at rather high temperature 77 K. The temperature quenching of the PL intensity revealed the same activation energy, as the electroconductivity ∼0.3 eV and may be considered to be the ionization energy of radiative center.
Roles of Inter-Molecular Charge Transfer Excitons in Optical Absorption and Photo-Induced Polymerization in C60 Crystal
Authors: Tsubo Tomiyuki , Nasu Keiichiro
Published: March 2014

Optical absorption spectra of a C60 molecule and a fcc type C60 crystal are theoretically studied by using an extended Hubbard model, so as to clarify exciton effects in these π-electron systems. The ground and the excited states are calculated within the Hartree-Fock approximation, reinforced by the first-order perturbation of electron-hole attraction. The calculated results show that exciton effects are very important in both cases of the molecule and the crystal. Only in the case of crystal, the spectral intensity at around 2.5∼2.8 eV is shown to be enhanced greatly by the effect of inter-molecular charge-transfer(CT) exciton. After the lattice relaxation, this CT exciton self-localizes in neighbouring two or three molecules by contracting inter-molecular σ-bonds, and triggers the photo-induced polymerization.
Photoluminescence of Si Nanocrystals Created by Heavy Ion Irradiation of Amorphous SiO Films
Authors: Roditchev Dmitri , Lavallard Philippe , Gandais Madeleine , Dooryhee Eric , Slaoui Abdelilah , Perriere Jacques
Published: March 2014

In order to create Si nanocrystals we have irradiated amorphous films of SiO by high energy heavy ions.The electron microscope images clearly show crystallites of 15-25Å size formed inside ion traces of ∼200Å diameter. The broad luminescence band observed in the visible is attributed to the radiative recombination of photoexcited carriers confined in the Si crystallites. We are able to control the density and the mean size of the nanocrystals by tuning the irradiation parameters.
New Approaches to Obtaining Semiconductor Doped Glasses with Narrow Size Distribution of Nanoparticles
Authors: Onushchenko Aleksei A. , Petrovskii Gurii T.
Published: March 2014

Precipitation process of CuBr nanoparticles (NPs) in silicate glasses has been investigated. Nonstandard preparation procedure was used. Energy shift of exciton lines due to quantum size effect has been found to increase at first then to decrease. This is the case for glass samples that do not contain a great many of nuclei of precipitated phase before heat treatment. The effect can be explained taking into account change of distribution function during precipitation process. Early stages of precipitation process are reasonable for decreasing size dispersion of NPs.
Resonant Tunneling of a Wannier Exciton through a Single Heterobarrier
Authors: Saito Noriko , Kayanuma Yosuke
Published: March 2014

Quantum tunneling of a Wannier exciton through a hetero-barrier structure is studied theoretically by a one-dimensional model. It is predicted that resonance structures will be observed in the transmission spectrum even for a single-barrier tunneling due to the momentary trapping of the exciton at the potential barrier.
Photoreflectance and Resonant Raman Scattering of Above-Barrier Transitions in a GaAs/AlGaAs Superlattice
Authors: Nakayama Masaaki , Sugie Ryuichi , Ohta Hirotaka , Nakashima Shin-ichi
Published: March 2014

We have investigated the energy states above the barrier potential (above-barrier states) in a (GaAs)10/(Al0.3Ga0.7As)10 superlattice using photoreflectance and resonant-Raman scattering spectroscopies. The energies of the photoreflectance signals observed in the above-barrier region higher than the band-gap energy of Al0.3Ga0.7As just agree with the peak energies of the resonant-Raman profiles of the longitudinal-optical phonons. From the miniband energies calculated by an effective-mass approximation, we conclude that the photoreflectance signals and the resonant Raman profiles are caused by the transitions associated with the above-barrier states at the mini-Brillouin-zone edge.
Visible Electroluminescence from Porous Silicon Diodes with Immersed Conducting Polymer Contacts
Authors: Koshida Nobuyoshi , Mizuno Hiroyuki , Koyama Hideki , Collins George J.
Published: March 2014

The visible electroluminescence (EL) from porous silicon (PS) diodes has been studied in relation to the electrical contact problem. As an electrical contact for carrier injection into luminescent PS, conducting polypyrrole (PP) films were electrochemically formed into PS layers. From the results of electrical characterization studies of the fabricated PP/PS interface, including measurements of the EL characteristics, it is demonstrated that the PP films penetrateare into the PS layer and act as an useful large-area electrical contact for the PS light-emitting diode.
Synthesis of σ-π Conjugated Organosilicon Copolymers and Their Optical Properties
Authors: Fang Mao-Ching , Watanabe Akira , Matsuda Minoru
Published: March 2014

A series of σ-π conjugated organosilicon copolymers, -[(SiMe2)m-Z]n-, m=1, 2, 3, 4, and 6, with alternating dimethylsilylene units and unsaturated groups (Z = acetylene, 4,4'-biphenylene, and 9,10-anthranylene) in the polymer main chain were prepared by the reaction of α, ω-dichloropermethylated oligosilanes, Cl-(SiMe2)m-Cl, with the appropriate dilithio compounds. The influence of the chain length of the dimethylsilylene unit, m, in the copolymer backbone on the electronic absorption spectra was investigated. The enhancement of the σ-π conjugation between the dimethylsilylene units and the π-conjugated units with increasing the dimethylsilylene chain length was suggested by the thermochromism.
Second-Harmonic Generation in UV-Poled Glass
Authors: Fujiwara Takumi , Takahashi Masahide , Ikushima Akira J.
Published: March 2014

A remarkably large second-harmonic generation (SHG) in a germanosilicate glass (15.7 GeO2-84.3 SiO2 in mol.%), which was induced by poling with ArF laser irradiation at the wavelength of 193 nm is reported Using the Maker-Fringe technique, the induced SHG coefficient, d, was measured at various poling electric-field strengths. The measured d coefficient value increases with increasing poling field and then saturates around 1.5×105 V/cm. The largest d coefficient value obtained in this experiment, which is 3.4±0.3 pm/V, seems to exceed d
22 of LiNbO3. Furthermore, polarization dependence of the induced SHG indicates an anisotropy of the refractive index.
Second- and Third-Order Nonlinearity of Homogeneous Glasses
Authors: Nasu Hiroyuki
Published: March 2014

Second- and third-order optical nonlinearity was measured by second- and third-harmonic generation of the glass, respectively. Second-order optical nonlinearity can be seen in thermally poled SiO2 glass samples. The intensity of the second-harmonic generation depends on the concentration of some additives such as OH or TiO2. On the other hand, third-order optical nonlinearity can be found all kinds of glasses. The magnitude of third-order optical nonlinearity basically depends on the linear refractive index of the glasses.
Properties of Silica Glass: Effect of Terminal Structures and Granular Structure
Authors: Kuzuu Nobu
Published: March 2014

Silica glass has high optical transmission in a wide wavelength range, high heat resistivity and high radiation resistivity. Most of these properties are related to the “hardness” of the silica glass network which is controlled by terminal structures such as SiOH and SiCl. The properties of fused quartz produced by melting natural quartz powder are not only controlled by these terminal structures but are also affected by the “grain structure” which reflects the trace of the adhesion of the particles of natural quartz powder.
A Theorist's View on Supercooled Liquids and Glass Transitions
Authors: Kawasaki Kyozi
Published: March 2014

The recent attempts to gain the first principle understanding of supercooled liquids and glass transition are explained. The most successful first principle theory to date is an application of the mode coupling theroy (MCT) to this problem, which, however, appears to be limited to the initial stage of freezing prior to glass transition. In the hope of overcoming this limitation a theoretical framework which combines the mode coupling mechanism and the free energy barrier hopping which takes place in the glassy state is proposed.
Silica/Air Photonic Crystal Fibres
Authors: Russell Philip St. , Birks Tim A. , Knight Jonathan C. , Cregan Robert F. , Mangan Brian J. , Sandro Jean-Philippe De
Published: March 2014

We describe the fabrication, characterisation and applications of silica/air photonic crystal fibres with microscopic arrays of air capillaries running along their length.
Processing Induced Defects in Silica Glasses
Authors: Lee Jong-Won , Jr. George H. Sigel,
Published: March 2014

The effects of the fiber drawing process on defects of silica fibers have been investigated. This study has focused on the oxygen deficient centers (ODCs) and E' centers induced by the fiber drawing process in low-OH oxygen deficient silica. The ODCs induced by the fiberization process have been investigated using the optical absorption band at 248 nm. In case of E' centers, optical absorption and electron spin resonance (ESR) have been used. The population of ODCs in the neck-down region has also been investigated. The concentration of ODCs are observed to increase dramatically within the neck-down region.
X-ray Detection Characteristics of Nb-Based Superconducting Tunnel Junctions
Authors: Katagiri Masaki , Kishimoto Maki , Ukibe Masahiro , Nakamura Tatsuya , Kurakado Masahiko , Maehata Keisuke , Ishibashi Kenji , Nakazawa Masaharu
Published: March 2014

Detailed X-ray detection characteristics for Nb-based superconducting tunnel junctions (STJs) were measured with cooled 4-JFETs low noise charge sensitive amplifier that we developed. We studied the detection characteristics for a wide energy range of X-rays and signal production processes for quasiparticles in Nb-based SIS junction and substrate phonons, and phonon detection.
Radiation Hardness of Josephson Devices
Authors: Frunzio Luigi , Cristiano Roberto , Pagano Sergio
Published: March 2014

We have experimentally investigated the effects of intense proton beam irradiation (fluence up to 1016 p/cm2 and dose up to 5 Grad) and ion beam irradiation (fluence up to 1.3×1012 ion/cm2 and dose up to 0.92 Grad) at room temperature on Josephson junctions, junction arrays and RSFQ digital devices. The devices we have studied were realized using state of the art full-Nb technology, employing same materials and thicknesses of common Josephson digital circuit designs. Regarding proton irradiation, evidences of induced radiation damage in the electrodes have been found still allowing all circuits work. The appearance of irradiation induced damages presents a low probability and is proportional to the junction area. After ion irradiation, induced radiation damage in the barrier have been observed such that digital circuits are unable to operate.
Cryogenic Semiconductor Electronics
Authors: Camin Daniel Victor , Pessina Gianluigi , Previtali Ezio
Published: March 2014

The Milan group has centred its activity on cryogenic microelectronics on the use of GaAs MESFET technology. This choice was taken after having found extremely low 1/f noise at 4 K in discrete MESFETs fabricated by NEC and SONY about 20 years ago. Those devices have been discontinued and replaced by equivalent units which nevertheless did not give the same cryogenic performance. A commercial MESFET process has been characterized at cryogenic temperatures, after which FETs and monolithic preamplifier circuits, intended for operation in liquid Helium and liquid Argon, have been designed and fabricated. We will report on our FETs and monolithic preamplifiers which could be of interest for STJ applications. We will briefly review characteristics and results obtained with other technologies which promise new opportunities for the realization of deep cryogenic front-end electronics.
Series Array of Superconducting Tunnel Junctions as Phonon Sensor in a Dark Matter Detector
Authors: Esposito Emanuela.
Published: March 2014

A design of a cryogenic detector for a WIMP dark matter search based on a single crystal absorber using Series Array of Superconducting Tunnel Junctions (SASTJs) as readout sensors has been presented. In order to investigate the behaviour of such a detector the response of two spatially separated Series Arrays of Superconducting Tunnel Junctions (SASTJs) to the non-equilibrium phonons generated in a single crystal of BaF2, by external α–particles has been measured. A strong position dependence in pulse height and pulse shape of the detector response has been observed. The fast time response of the SASTJs permits time resolved measurements of the spatially separated particle interactions in the crystal.
Modeling ecohydrological impacts of land management and water use in the Silver Creek basin, Idaho
Authors: Loinaz Maria C. , Gross Dayna , Unnasch Robert , Butts Michael , Bauer‐Gottwein Peter
Published: March 2014

A number of anthropogenic stressors, including land use change and intensive water use, have caused stream habitat deterioration in arid and semiarid climates throughout the western U.S. These often contribute to high stream temperatures, a widespread water quality problem. Stream temperature is an important indicator of stream ecosystem health and is affected by catchment‐scale climate and hydrological processes, morphology, and riparian vegetation. To properly manage affected systems and achieve ecosystem sustainability, it is important to understand the relative impact of these factors. In this study, we predict relative impacts of different stressors using an integrated catchment‐scale ecohydrological model that simulates hydrological processes, stream temperature, and fish growth. This type of model offers a suitable measure of ecosystem services because it provides information about the reproductive capability of fish under different conditions. We applied the model to Silver Creek, Idaho, a stream highly valued for its world‐renowned trout fishery. The simulations indicated that intensive water use by agriculture and climate change are both major contributors to habitat degradation in the study area. Agricultural practices that increase water use efficiency and mitigate drainage runoff are feasible and can have positive impacts on the ecosystem. All of the mitigation strategies simulated reduced stream temperatures to varying degrees; however, not all resulted in increases in fish growth. The results indicate that temperature dynamics, rather than point statistics, determine optimal growth conditions for fish. Temperature dynamics are influenced by surface water‐groundwater interactions. Combined restoration strategies that can achieve ecosystem stability under climate change should be further explored.
A “breathing” source surface for cycles 23 and 24
Authors: Arden W. M. , Norton A. A. , Sun X.
Published: March 2014

The potential field source surface (PFSS) model is used to represent the large‐scale geometry of the solar coronal magnetic fields. The height of the source surface in this model can be taken as a free parameter. Previous work suggests that varying the source surface height during periods of solar minimum yields better agreement between PFSS models and the measured magnitude of the interplanetary magnetic field (IMF) open flux at 1 AU—in other words, the source surface “breathes” in and out over the course of the solar cycle. We examine the evolution of open flux during all of cycle 23 and the first part of cycle 24 using photospheric magnetic field maps from the Solar and Heliospheric Observatory's Michelson Doppler Imager and Solar Dynamics Observatory's Helioseismic and Magnetic Imager instruments. We determine the value of source surface height that provides a best fit to the IMF open flux at 1 AU (using the OMNI 2 data set) for the time period 1996–2012. The canonical 2.5 Rs source surface matches the measured IMF open flux during periods of solar maximum but needs to be raised by approximately 15–30% in order to match the measured IMF open flux at the periods of solar minimum.
Magnetosheath filamentary structures formed by ion acceleration at the quasi‐parallel bow shock
Authors: Omidi N. , Sibeck D. , Gutynska O. , Trattner K. J.
Published: March 2014

Results from 2.5‐D electromagnetic hybrid simulations show the formation of field‐aligned, filamentary plasma structures in the magnetosheath. They begin at the quasi‐parallel bow shock and extend far into the magnetosheath. These structures exhibit anticorrelated, spatial oscillations in plasma density and ion temperature. Closer to the bow shock, magnetic field variations associated with density and temperature oscillations may also be present. Magnetosheath filamentary structures (MFS) form primarily in the quasi‐parallel sheath; however, they may extend to the quasi‐perpendicular magnetosheath. They occur over a wide range of solar wind Alfvénic Mach numbers and interplanetary magnetic field directions. At lower Mach numbers with lower levels of magnetosheath turbulence, MFS remain highly coherent over large distances. At higher Mach numbers, magnetosheath turbulence decreases the level of coherence. Magnetosheath filamentary structures result from localized ion acceleration at the quasi‐parallel bow shock and the injection of energetic ions into the magnetosheath. The localized nature of ion acceleration is tied to the generation of fast magnetosonic waves at and upstream of the quasi‐parallel shock. The increased pressure in flux tubes containing the shock accelerated ions results in the depletion of the thermal plasma in these flux tubes and the enhancement of density in flux tubes void of energetic ions. This results in the observed anticorrelation between ion temperature and plasma density.
On the identification of time interval threshold in the twin‐CME scenario
Authors: Ding Liu‐Guan , Li Gang , Dong Li‐Hua , Jiang Yong , Jian Yi , Gu Bin
Published: March 2014

Recently it has been suggested that the “twin‐CME” scenario may be a very effective mechanism in causing extreme solar energetic particle (SEP) events and, in particular, ground level enhancement (GLE) events. Ding et al. (2013) performed a statistical examination of the twin‐CME scenario with a total of 126 fast and wide western coronal mass ejections (CMEs). They found that CMEs having a preceding CME with a speed > 300 km/s within 9 h from the same active region have larger probability of leading to large SEP events than CMEs that do not have preceding CMEs. The choice of 9 h being the time lag τ between the preceding CME and the main CME was based on some crude estimates of the decay time of the turbulence downstream of the shock driven by the preceding CME. In this work, we examine this choice. For the 126 fast wide CMEs examined in, we vary the time lag τ from 1 h to 24 h with an increment of 1 h. By considering three quantities whose values depend on the choice of this time lag τ, we show that the choice of 13 h for τ is more appropriate. Our study confirms our earlier result that twin CMEs are more likely to lead to large SEP events than single fast CMEs. The results shown here are of great relevance to space weather studies.
Pyroxenes as tracers of mantle water variations
Authors: Warren Jessica M. , Hauri Erik H.
Published: March 2014

The concentration and distribution of volatiles in the Earth's mantle influence properties such as melting temperature, conductivity, and viscosity. To constrain upper mantle water content, concentrations of H2O, P, and F were measured in olivine, orthopyroxene, and clinopyroxene in mantle peridotites by secondary ion mass spectrometry. Analyzed peridotites are xenoliths (Pali Aike, Spitsbergen, Samoa), orogenic peridotites (Josephine Peridotite), and abyssal peridotites (Gakkel Ridge, Southwest Indian Ridge, Tonga Trench). The comparison of fresh and altered peridotites demonstrates that low to moderate levels of alteration do not affect H2O concentrations, in agreement with mineral diffusion data. Olivines have diffusively lost water during emplacement, as demonstrated by disequilibrium between olivine and coexisting pyroxenes. In contrast, clinopyroxene and orthopyroxene preserve their high‐temperature water contents, and their partitioning agrees with published experiments and other xenoliths. Hence, olivine water concentrations can be determined from pyroxene concentrations using mineral‐mineral partition coefficients. Clinopyroxenes have 60–670 ppm H2O, while orthopyroxenes have 10–300 ppm, which gives calculated olivine concentrations of 8–34 ppm. The highest olivine water concentration translates to an effective viscosity of 6 × 1019 Pa s at 1250°C and ~15 km depth, compared to a dry effective viscosity of 2.5 × 1021 Pa s. Bulk rock water concentrations, calculated using mineral modes, are 20–220 ppm and correlate with peridotite indices of melt depletion. However, trace element melt modeling indicates that peridotites have too much water relative to their rare earth element concentrations, which may be explained by late‐stage melt addition, during which only hydrogen diffuses fast enough for reequilibration.
The influence of slope breaks on lava flow surface disruption
Authors: Glaze Lori S. , Baloga Stephen M. , Fagents Sarah A. , Wright Robert
Published: March 2014

Changes in the underlying slope of a lava flow impart a significant fraction of rotational energy beyond the slope break. The eddies, circulation, and vortices caused by this rotational energy can disrupt the flow surface, having a significant impact on heat loss and thus the distance the flow can travel. A basic mechanics model is used to compute the rotational energy caused by a slope change. The gain in rotational energy is deposited into an eddy of radius R whose energy is dissipated as it travels downstream. A model of eddy friction with the ambient lava is used to compute the time‐rate of energy dissipation. The key parameter of the dissipation rate is shown to be ρR2/μ, where ρ is the lava density and μ is the viscosity, which can vary by orders of magnitude for different flows. The potential spatial disruption of the lava flow surface is investigated by introducing steady state models for the main flow beyond the steepening slope break. One model applies to slow‐moving flows with both gravity and pressure as the driving forces. The other model applies to fast‐moving, low‐viscosity, turbulent flows. These models provide the flow velocity that establishes the downstream transport distance of disrupting eddies before they dissipate. The potential influence of slope breaks is discussed in connection with field studies of lava flows from the 1801 Hualalai and 1823 Keaiwa Kilauea, Hawaii, and 2004 Etna eruptions.
Evaluation of glacier changes in high‐mountain Asia based on 10 year GRACE RL05 models
Authors: Yi Shuang , Sun Wenke
Published: March 2014

In this paper, 10 years of time‐variable gravity data from the Gravity Recovery and Climate Experiment Release 05 have been used to evaluate the glacier melting rate in high‐mountain Asia (HMA) using a new computing scheme, i.e., the Space Domain Inverse method. We find that in HMA area, there are three different kinds of signal sources that should be treated together. The two generally accepted sources, glacier melting and India underground water depletion, are estimated to change at the rate of −35.0 ± 5.8 Gt/yr (0.09 mm/yr sea level rising) and −30.6 ± 5.0 Gt/yr, respectively. The third source is the remarkable positive signal (+30 Gt/yr) in the inner Tibetan Plateau, which is challenging to explain. Further, we have found that there is a 5 year undulation in Pamir and Karakoram, which can explain the controversies of the previous studies on the glacier melting rate here. This 5 year signal can be explained by the influence of Arctic Oscillation and El Niño–Southern Oscillation.