bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal diffusivity of rods, tubes, and spheres by the flash method
Authors: Salazar Agustín , Garrido Florencio , Celorrio Ricardo
Published: April 2006

The flash method is the most used technique to measure the thermal diffusivity of solid samples. It consists of heating the front face of an opaque slab by a short light pulse and detecting the temperature evolution at its rear surface, from which the thermal diffusivity is obtained. In this paper, we extend the classical flash method to be used with rods, tubes, and spheres. First, the temperature evolution of the back surface of solid cylinders, hollow cylinders, and spheres is calculated. Then, experimental measurements of the thermal diffusivity on a set of stainless steel samples confirm the validity of the method.
A reaction model for plasma coating of nanoparticles by amorphous carbon layers
Authors: Yarin A. L. , Rovagnati B. , Mashayek F. , Matsoukas T.
Published: April 2006

A detailed chemical kinetics scheme of the reactions occurring in a CH4∕H2 plasma, namely, electron-neutral, ion-neutral, and neutral-neutral reactions, is implemented for the prediction of the species fluxes toward the surface of a submicron particle in a low-pressure environment. Surface reactions at the particle surface are also accounted for. Kinetic theory is applied in the collisionless region within a distance of one mean free path away from the particle, while continuum theory is implemented to solve for species transport in the outer region where reactive-diffusive phenomena occur. These regions are bounded by appropriate boundary conditions. The self-consistent electric field is obtained by solving the Poisson’s equation in the continuum region. The charged and neutral species distributions are calculated and the growth rate of the amorphous carbon layer at the particle surface, as well as particle charging, are predicted. The predicted growth rate is within the range of experimental data from literature for similar conditions. This shows that the model reflects rather accurately the complicated physicochemical phenomena occurring in real systems.
Application of Fokker-Planck-Kramers equation treatment for short-time dynamics of diffusion-controlled reaction in supercritical Lennard-Jones fluids over a wide density range
Authors: Ibuki Kazuyasu , Ueno Masakatsu
Published: April 2006

The validity of a Fokker-Planck-Kramers equation (FPKE) treatment of the rate of diffusion-controlled reaction at short times [K. Ibuki and M. Ueno, J. Chem. Phys. 119, 7054 (2003)] is tested in a supercritical Lennard-Jones fluid over a wide density range by comparing it with the Langevin dynamics and molecular dynamics simulations and other theories. The density n range studied is 0.323nc⩽n⩽2.58nc and the temperature 1.52Tc, where nc and Tc are the critical density and temperature, respectively. For the rate of bimolecular reactions, the transition between the collision-limited and diffusion-limited regimes is expected to take place in this density range. The simulations show that the rate constant decays with time extensively at high densities, and that the magnitude of decay decreases gradually with decreasing density. The decay profiles of the rate constants obtained by the simulations are reproduced reasonably well by the FPKE treatment in the whole density range studied if a continuous velocity distribution is used in solving the FPKE approximately. If a discontinuous velocity distribution is used instead of the continuous one, the FPKE treatment leads to a rate constant much larger than the simulation results at medium and low densities. The rate constants calculated from the Smoluchowski-Collins-Kimball (SCK) theory based on the diffusion equation are somewhat smaller than the simulation results in medium and low densities when the intrinsic rate constant is chosen to adjust the steady state rate constant in the low density limit to that derived by the kinetic collision theory. The discrepancy is relatively small, so that the SCK theory provides a useful guideline for a qualitative discussion of the density effect on the rate constant.
Surface stress control using ultraviolet light irradiation of plasma-polymerized thin films
Authors: Igarashi Shinichi , Itakura Akiko N. , Kitajima Masahiro , Chifen Anye N. , Förch Renate , Berger Rüdiger
Published: April 2006

We investigated the surface stress change of plasma-polymerized allylamine films on 2μm thick silicon micromechanical cantilever substrates induced by ultraviolet light (UV) irradiation. Compressive surface stress was generated during the UV irradiation of the plasma-polymerized films in a dry environment, whereas tensile stress was measured in a humid environment. Fourier transform infrared spectroscopic analysis indicated two mechanisms taking place depending on the environmental conditions. These were attributed to crosslinking and oxidation reactions of the plasma polymer. UV irradiation of plasma polymerized allylamine films at defined humidity suggests a feasible method for achieving tensile and compressive surface stress patterning.
Density functional calculations of surface free energies
Authors: Fox H. , Horsfield A. P. , Gillan M. J.
Published: April 2006

We propose a general method of thermodynamic integration to find the free energy of a surface, where our integration parameter is taken to be the strain on the unit cell of the system (which in the example presented in this paper is simply the extension of the unit cell along the normal to the surface), and the integration is performed over the thermal average stress from a molecular dynamics run. In order to open up a vacuum gap in a continuous and reversible manner, an additional control interaction has been introduced. We also use temperature integration to find a linear relation for the temperature dependence of the free surface energy. These methods have been applied to the titanium dioxide (110) surface, using first principles density functional theory. A proof of principle calculation for zero temperature shows excellent agreement between the integral calculation and the difference in energy calculated by the DFT program. Calculations that have been performed at 295 and 1000K give excellent agreement between the two integration methods.
Nucleation of AgInSbTe films employed in phase-change media
Authors: Ziegler Stefan , Wuttig Matthias
Published: April 2006

In phase-change technology small volumes of a chalcogenide material are switched between amorphous and crystalline states by local heating with a short laser or current pulses. AgInSbTe is an alloy frequently used in optical data storage, which could also be applied in electronic data storage. For those applications it is crucial to understand the reliability and reproducibility of the switching process. In this work the first crystallization of an AgInSbTe alloy has been studied on a microsecond time scale using a focused laser beam. The experiments show that nucleation is a process governed by statistics. A correlation between the success of a nucleation event with the probability of nucleation is established. By measuring the nucleation probability as a function of laser pulse duration, the incubation time is determined to 11μs. The results are compared to measurements of the growth velocity of this material. The analysis of the temperature dependence of the growth velocity explains why AgInSbTe shows growth-dominated recrystallization. The implications of these findings to the application of such growth-dominated materials in electronic data storage are discussed.
Organic light-emitting diode driven by organic thin film transistor on plastic substrates
Authors: Tsukagoshi Kazuhito , Tanabe Jun , Yagi Iwao , Shigeto Kunji , Yanagisawa Keiichi , Aoyagi Yoshinobu
Published: April 2006

A method for fabricating an organic light-emitting diode (OLED) connected to an organic thin film transistor (OTFT) on plastic substrates without heating is proposed. A three-dimensional pixel structure consisting of an OLED and an OTFT is prepared by the proposed method, and the characteristics of the device are tuned by refinement of structural parameters. By room-temperature fabrication, the OTFT with passivation film can be formed on a poly(ethylene naphthalate) plastic substrate, and the transparent anode of the OLED can be fabricated on the passivation film directly. OLED emission is thus generated directly by the current flowing through the OTFT, and the emission intensity is fully controllable by the gate voltage.
Structure of Zn–Se–Te system with submonolayer insertion of ZnTe grown by migration enhanced epitaxy
Authors: Gong Y. , Yan Hanfei F. , Kuskovsky I. L. , Gu Y. , Noyan I. C. , Neumark G. F. , Tamargo M. C.
Published: April 2006

We here report results of high resolution x-ray diffraction, x-ray reflectivity (XRR), as well as optical absorption and reflection measurements on ZnSe samples grown by molecular beam epitaxy, with insertion of planar (δ-) regions of both N as an acceptor dopant and Te as a “co-dopant” to facilitate a p-type doping. We note that to enhance the surface diffusion of Te, migration enhanced epitaxy was adopted in the growth of the “δ-layers;” i.e., Te is deposited in the absence of Zn flux. Structural parameters were extracted by simulating the experimental x-ray diffraction curves using a dynamical model. The results show that only the “δ-layers” (with submonolayer thickness) are rich in ZnTe, while the nominally undoped “spacers” have only a low Te concentration. Moreover, the morphology of the surface and interfaces are studied by XRR. Furthermore, the optical absorption and reflection results show that our samples largely preserve the optical properties of the host material (ZnSe). We note that our results, in particular those on the Te concentration, explain the observed good p-type doping of such samples.
Superconformal symmetry in the interacting theory of (2,0) tensor multiplets and self-dual strings
Authors: Arvidsson Pär
Published: April 2006

We investigate the concept of superconformal symmetry in six dimensions, applied to the interacting theory of (2,0) tensor multiplets and self-dual strings. The action of a superconformal transformation on the superspace coordinates is found, both from a six-dimensional perspective and by using a superspace with eight bosonic and four fermionic dimensions. The transformation laws for all fields in the theory are derived, as well as general expressions for the transformation of on-shell superfields. Superconformal invariance is shown for the interaction of a self-dual string with a background consisting of on-shell tensor multiplet fields, and we also find an interesting relationship between the requirements of superconformal invariance and those of a local fermionic κ-symmetry. Finally, we try to construct a superspace analogue of the Poincaré dual to the string world-sheet and consider its properties under superconformal transformations.
Statistical properties of vortical structures with spanwise vorticity in zero pressure gradient turbulent boundary layers
Authors: Camussi R. , Di Felice F.
Published: April 2006

Turbulent boundary layers at large Reynolds numbers (up to Reθ=17 500) are obtained in a very large recirculating water tunnel and are analyzed through PIV measurements in streamwise–wall–normal planes. Vortical structures in the outer region are tracked using a wavelet based technique. The adopted method, which can be applied also to time series obtained from pointwise measurements, provides the separation of coherent structures from the background flow and the measure of their length scale and of other relevant quantities. The range of Reθ under test is extended by analyzing also a PIV database obtained in a different laboratory flow (public domain data provided by Adrian and co-workers) at lower Reθ (1015 and 7700). In this way, statistical properties of the spanwise coherent structures are parametrically studied in terms of Reθ. The analysis of conditional vortices demonstrates the capability of the identification method to correctly track the spanwise vortical structures, to determine their length scales and, at low Reθ, to evidence the formation of vortex packets. The probability distribution functions of relevant quantities (such as the length scale, the local energy, and the vorticity of the educed vortices) are shown to collapse well when normalized with respect to low order statistical quantities (mean and variance). Analytical approximations useful for extrapolating the observed statistical properties at a large Reynolds number are also presented and discussed.
Energy spectra in microbubbly turbulence
Authors: van den Berg Thomas H. , Luther Stefan , Lohse Detlef
Published: April 2006

Microbubbles (R0=100μm) are injected in fully developed turbulence (Reλ=200) up to a volume concentration of 0.3%. An enhancement of the energy on small scales and a reduction on the large scales is observed, confirming theoretical prediction by I. Mazzitelli, D. Lohse, and F. Toschi [Phys. Fluids 15, L5 (2003)]. The result is a (nonuniversal) less steep slope than −5∕3 in the power spectrum.
Speed of sound from shock fronts in granular flows
Authors: Amarouchene Yacine , Kellay Hamid
Published: April 2006

We show, in two different experiments on stationary flow past an obstacle, that several features such as Mach cones and shock wave detachment usually observed in supersonic molecular fluids under extreme conditions are also observed for granular fluids. By pursuing this analogy, we measure the speed of sound in these experiments and find it in agreement with predictions from granular kinetic theories. Surprisingly, and in spite of this agreement, measured velocity distributions are far from being Gaussian and display algebraic tails.
A relaxation kinetic model for transport phenomena in a reactive flow
Authors: Kremer Gilberto M. , Pandolfi Bianchi Miriam , Jacinta Soares Ana
Published: April 2006

A gaseous mixture of four constituents undergoing a reversible bimolecular reaction is modeled by means of a Bhatnagar, Gross, and Krook (BGK)-type equation in a flow regime close to chemical equilibrium. In the proposed relaxation method, elastic and chemistry collision terms are approximated separately, introducing different reference distribution functions which assure the correct balance laws. A Chapman-Enskog procedure is applied in order to provide explicitly the transport coefficients of diffusion, shear viscosity and thermal conductivity in dependence on elastic and reactive collision frequencies, mass concentrations of each species and temperature of the whole mixture. The closure of the balance equations is performed at the Navier-Stokes level and plane wave solutions are characterized. For the (H2,Cl,HCl,H) system, transport coefficients, as well as the Prandtl number of the mixture, are represented as functions of the temperature and compared with the inert case in order to discuss the influence of chemical reaction. Moreover, the thermal conductivity for nondiffusive and homogeneous mixtures are compared. For the problem of longitudinal wave propagation the phase velocity, attenuation coefficient and affinity are analyzed as functions of the wave frequency.
Quasiharmonic models for the calculation of thermodynamic properties of crystalline silicon under strain
Authors: Zhao H. , Tang Z. , Li G. , Aluru N. R.
Published: April 2006

Quasiharmonic models with Tersoff [Phys. Rev. B 38, 9902 (1988)] interatomic potential are used to study the thermodynamic properties of crystalline silicon. It is shown that, compared to the molecular dynamics simulation data, the reciprocal space quasiharmonic model accurately predicts the thermal properties for temperatures up to 800K. For higher temperatures, anharmonic effects become significant. With a significantly higher computational cost, the results from the real space quasiharmonic model approach the results from the reciprocal space quasiharmonic model as the number of atoms increases. The local quasiharmonic model does not accurately describe the thermal properties as it neglects the vibrational coupling of the atoms. We also investigate the effect of the strain on the thermodynamic properties. The variation of the thermodynamic properties with temperature under a tension, compression, and a shear deformation state is computed.
Three-dimensional isotropic perfect lens based on LC-loaded transmission lines
Authors: Alitalo Pekka , Maslovski Stanislav , Tretyakov Sergei
Published: April 2006

An isotropic three-dimensional flat lens of subwavelength resolution (“perfect lens”), based on the cubic meshes of interconnected transmission lines and bulk loads is proposed. The lens is formed by a slab of a loaded mesh placed between two similar unloaded meshes. The dispersion equations and the characteristic impedances of the eigenwaves in the meshes are derived analytically, with an emphasis on generality. This allows the designing of transmission-line meshes with desired dispersion properties. The required backward-wave mode of operation in the lens is realized with simple inductive and capacitive loads. An analytical expression for the transmission through the lens is derived and the amplification of evanescent waves is demonstrated. The factors that influence the enhancement of evanescent waves in the lens are studied and the corresponding design criteria are established. A possible realization of the structure is outlined.
Acoustoelectric coupling for direct electrical characterization of semiconductor devices
Authors: Ravat Cyril , Absil Émilie , Holé Stéphane , Lewiner Jacques
Published: April 2006

In this paper, the electrical characterization of semiconductor structure by acoustoelectric couplings (pressure-wave-propagation method) is theoretically studied and experimentally tested. Estimated signals for a Schottky diode structure fit very well the experimental measurements. Information on the screening length or on the voltage barrier can be directly obtained from the measurements.
Pulsed-field ionization electron spectroscopy of group 6 metal (Cr, Mo, and W) bis(benzene) sandwich complexes
Authors: Sohnlein Bradford R. , Yang Dong-Sheng
Published: April 2006

Group 6 metal bis(benzene) sandwich complexes (M–bz2: M=Cr, Mo, and W and bz=C6H6) were produced with laser vaporization molecular beam techniques and studied by pulsed-field ionization zero electron kinetic energy spectroscopy and density functional theory calculations. Each sandwich complex is in a D6h eclipsed configuration with A1g1 and A1g2 as the neutral and cationic ground electronic states, respectively. The adiabatic ionization energies for Cr–, Mo–, and W–bz2 are measured to be 44 081(7), 44 581(10), and 43634(7)cm−1, respectively. The metal-benzene stretch and benzene torsion frequencies of the ion are measured to be 264, 277, and 370cm−1 and 11, 21, and 45cm−1 for Cr–, Mo–, and W–bz2, respectively. In addition, a C–H out-of-plane bending mode is measured to be 787cm−1 for the Cr+–bz2 complex, while a C–C in-plane bending mode is measured to be 614cm−1 for the W+–bz2 complex. The unusual trend in the ionization energy and metal-benzene stretch frequency indicates strong relativistic effects on tungsten binding.
Magnetoacoustic tomography with magnetic induction for imaging electrical impedance of biological tissue
Authors: Li Xu , Xu Yuan , He Bin
Published: April 2006

An experimental feasibility study was conducted on magnetoacoustic tomography with magnetic induction (MAT-MI). It is demonstrated that the two-dimensional MAT-MI system can detect and image the boundaries between regions of different electrical conductivities with high spatial resolution. Utilizing a magnetic stimulation coil, MAT-MI evokes magnetically induced eddy current in an object which is placed in a static magnetic field. Because of the existence of Lorenz forces, the eddy current in turn causes acoustic vibrations, which are measured around the object in order to reconstruct the electrical impedance distribution of the object. The present experimental results from the saline and gel phantoms are promising and suggest the merits of MAT-MI in imaging electrical impedance of biological tissue with high spatial resolution.
Modeling the influence of charge traps on single-layer organic light-emitting diode efficiency
Authors: Konezny S. J. , Smith D. L. , Galvin M. E. , Rothberg L. J.
Published: April 2006

We investigate theoretically the role of carrier trapping on the efficiency of single-layer organic light-emitting diodes (OLEDs) by incorporating traps into the OLED device model of Davids et al. [J. Appl. Phys. 82, 6319 (1997)]. Carrier trapping directly affects the density and mobility balance between electrons and holes through its effects on injection and mobility. In addition, trap-mediated changes in density alter recombination rates and spatial profiles of recombination that become important when excited state quenching at metallic contacts is considered. We illustrate these various influences of traps on device efficiency through computations on a series of model devices. Good agreement is obtained with previous experiments by Menon et al. [Chem. Mater. 14, 3668 (2002)], where energetic disorder from transport traps was shown to reduce device efficiency. Our model, however, predicts circumstances where traps will improve device efficiency as well and can assist with selection of contacts to realistic organic materials.
Flow-induced migration of polymers in dilute solution
Authors: Usta O. Berk , Butler Jason E. , Ladd Anthony J. C.
Published: April 2006

We investigate the lateral migration of a confined polymer under pressure driven and uniform shear flows. We employ a hybrid algorithm which couples point particles to a fluctuating lattice-Boltzmann fluid. We observe migration in both uniform shear and pressure driven flows, supporting the idea that migration is driven by a combination of shear and hydrodynamic interactions with the wall, rather than by the shear gradient. Recent numerical and theoretical investigations have suggested that polymers migrate toward the centerline when hydrodynamic interactions are included, but our simulations show that in sufficiently narrow channels there is a reversal of direction and the polymers move toward the wall.
Spherical cloud of point particles falling in a viscous fluid
Authors: Ekiel-Jeżewska M. L. , Metzger B. , Guazzelli É.
Published: April 2006

Statistical mechanics is applied to calculate ensemble-averaged particle and fluid velocity fields of a spherical cloud of point particles sedimenting at a low Reynolds number. The analogy with the fall of a liquid drop in another lighter fluid is discussed.
A convergent multipole expansion for 1,3 and 1,4 Coulomb interactions
Authors: Rafat M. , Popelier P. L. A.
Published: April 2006

Traditionally force fields express 1,3 and 1,4 interactions as bonded terms via potentials that involve valence and torsion angles, respectively. These interactions are not modeled by point charge terms, which are confined to electrostatic interactions between more distant atoms (1,n where n>4). Here we show that both 1,3 and 1,4 interactions can be described on the same footing as 1,n (n>4) interactions by a convergent multipole expansion of the Coulomb energy of the participating atom pairs. The atomic multipole moments are generated by the theory of quantum chemical topology. The procedure to make the multipole expansion convergent is based on a “shift procedure” described in earlier work [L. Joubert and P. L. A. Popelier, Molec. Phys. 100, 3357 (2002)].
Reactive spreading and recoil of oil on water
Authors: van Nierop Ernst A. , Ajdari Armand , Stone Howard A.
Published: April 2006

Droplets of oil containing oleic acid were observed to spread, then recoil, on an aqueous solution of sodium hydroxide. Surfactant is produced at the interface during spreading, and for reagent concentrations of order O(1mM) spreading is observed to be much faster than in the absence of a chemical reaction [radius R(t)∝tα with 0.64<α<0.89]. After t∼10s, drops reach a maximum radius Rmax∼3–5 times the initial radius. Spreading is faster and Rmax is larger for higher concentrations of reagents. The drops are then observed to recoil (with apparent power-law behavior −0.34<α<−0.14), due to diffusion of surfactant away from the oil/water interface, with the rate of recoil being controlled by the NaOH concentration.
Evaluation of titanium silicon nitride as gate electrodes for complementary metal-oxide semiconductor
Authors: Luan H. , Alshareef H. N. , Harris H. R. , Wen H. C. , Choi K. , Senzaki Y. , Majhi P. , Lee B.- H.
Published: April 2006

The effect of deposition temperature and film thickness on the work function of TiSiN gate electrodes has been studied. It is shown that the work function of TiSiN can be tuned from 4.28–4.74eV on SiO2, 4.40–4.79eV on HfO2, and 4.44–4.83eV on HfSiOx. For high-k dielectrics, the work function can be tuned by 200meV on each side of the band gap, making it a suitable electrode for fully depleted silicon-on-insulator devices. Furthermore, TiSiN deposition at high temperature increases the work function to 4.87eV while Si implantation increases it to 4.93eV, making TiSiN a good p-type metal candidate.
Subcritical flow past a circular cylinder surrounded by a porous layer
Authors: Sobera M. P. , Kleijn C. R. , Van den Akker H. E. A.
Published: April 2006

A study of the flow at subcritical Re=3900 around a circular cylinder, surrounded at some fixed small distance by a porous layer with a hydraulic resistance typical for that of textile materials, has been performed by means of direct numerical simulations. The flow in the space between the porous layer and the solid cylinder was found to be laminar and periodic, with a frequency locked to that of the vortex shedding in the wake behind the cylinder. Time averaged flow velocities underneath the porous material were in good agreement with experimental data from laser Doppler anemometry.
Rough-pipe flows and the existence of fully developed turbulence
Authors: Gioia G. , Chakraborty Pinaki , Bombardelli Fabián A.
Published: April 2006

It is widely believed that at high Reynolds number (Re) all turbulent flows approach a limiting state of “fully developed turbulence" in which the statistics of the velocity fluctuations are independent of Re. Nevertheless, direct measurements of the velocity fluctuations have failed to yield firm empirical evidence that even the second-order structure function becomes independent of Re at high Re, let alone structure functions of higher order. Here we relate the friction coefficient (f) of rough-pipe flows to the second-order structure function. Then we show that in light of experimental measurements of f our results yield unequivocal evidence that the second-order structure function becomes independent of Re at high Re, compatible with the existence of fully developed turbulence.
Hydrogen storage and desorption properties of Ni-dispersed carbon nanotubes
Authors: Lee Jung Woo , Kim Hyun Seok , Lee Jai Young , Kang Jeung Ku
Published: April 2006

We report that the H2 storage method using Ni-mediated CNTs is a viable candidate for fuel cell applications. It is demonstrated that a single Ni coated on the carbon nanotubes’ (CNT) surfaces can store up to 5 H2. In this respect, at high Ni-coverage, Ni-dispersed single-walled CNTs are considered to be capable of releasing ∼10wt.% H2 at around room temperature. Moreover, the H2 desorption barrier of 0.26eV∕H2, corresponding to the desorption temperature of 328K, is ideal for fuel cell applications.
Effect of Te precipitates on the performance of CdZnTe detectors
Authors: Carini G. A. , Bolotnikov A. E. , Camarda G. S. , Wright G. W. , James R. B. , Li L.
Published: April 2006

Measurements using the National Synchrotron Light Source provided a detailed comparisons of the microscale detector response and infrared microscopy images for CdZnTe Frisch-ring x-ray and gamma detectors. Analysis of the data showed conclusively that local deteriorations of the electron charge collection and x-ray device response fully correlate with the presence of Te precipitates as seen in the IR images. Effects of the surface processing conditions on the detector performance were also clearly observed.
Laser trapping of ice crystals
Authors: Taji Kazuki , Tachikawa Maki , Nagashima Kazushige
Published: April 2006

Toward application to crystal physics, we demonstrate optical trapping of ice crystals as well as supercooled water droplets using counterpropagating laser beams. Confinement of an ice crystal is evidenced by the angular distribution of laser light deflected from the crystal faces. The average trap time, limited by air currents, is 5s for ice crystals and much longer for water drops.
Single-walled carbon nanotubes as shadow masks for nanogap fabrication
Authors: De Poortere E. P. , Stormer H. L. , Huang L. M. , Wind S. J. , O’Brien S. , Huang M. , Hone J.
Published: April 2006

We describe a technique for fabricating nanometer-scale gaps in Pt wires on insulating substrates, using individual single-walled carbon nanotubes as shadow masks during metal deposition. More than 80% of the devices display current-voltage dependencies characteristic of direct electron tunneling. Fits to the current-voltage data yield gap widths in the 0.8–2.3nm range for these devices, dimensions that are well suited for single-molecule transport measurements.
Cesium vapor laser pumped by a volume-Bragg-grating coupled quasi-continuous-wave laser-diode array
Authors: Wang You , Kasamatsu Tadashi , Zheng Yujin , Miyajima Hirofumi , Fukuoka Hirotake , Matsuoka Shinichi , Niigaki Minoru , Kubomura Hiroyuki , Hiruma Teruo , Kan Hirofumi
Published: April 2006

The experimental demonstration of a broad-area Quasi-continuous-wave (QCW) laser-diode array pumped cesium vapor laser is reported in this letter according to our experimental results. We used a volume-Bragg grating to narrow the spectral linewidth for acquirement of enough resonance transitions. A glass cylindrical cell filled with cesium/buffer gas was set in an end-pumped flat-concave cavity and the gas pressure was set lower than 1atm. Using the QCW drive mode with the repetitive rate and pulse width of 1kHz and 50μs, respectively, 13.45μJ pulse energy has been achieved with the slope efficiency of about ∼1.8%.
Intrinsic nonlinearity probed by intermodulation distortion microwave measurements on high quality MgB2 thin films
Authors: Cifariello G. , Aurino M. , Di Gennaro E. , Lamura G. , Andreone A. , Orgiani P. , Xi X. X. , Villégier J.-C.
Published: April 2006

The two-tone intermodulation distortion arising in MgB2 thin films synthesized by hybrid physical-chemical vapor deposition is studied in order to probe the influence of the two bands on the nonlinear response of this superconductor. The measurements are carried out by using a dielectrically loaded copper cavity operating at 7GHz. Microwave data on samples having critical temperatures above 41K, very low resistivity values, and residual resistivity ratio larger than 10 are shown. The dependence of the nonlinear surface losses and of the third order intermodulation products on the power feeding the cavity and on the temperature is analyzed. At low power, the signal arising from distortion versus temperature shows the intrinsic s-wave behavior expected for this compound. Data are compared with measurements performed on Nb and YBa2Cu3O7−δ thin films using the same technique.
Electrical properties of n-type GaPN grown by molecular-beam epitaxy
Authors: Furukawa Yuzo , Yonezu Hiroo , Wakahara Akihiro , Yoshizumi Yusuke , Morita Yoshiro , Sato Atsushi
Published: April 2006

We have investigated electrical properties of n-GaPN layers grown by molecular-beam epitaxy with an rf-plasma source using sulfur and tellurium as dopants. The electron concentration in n-GaPN was about 10 times lower than that in n-GaP. Desorption of dopants from the grown surface by impinging N atoms may be one of the possible causes for the reduced electron concentration. In addition, electron mobilities in GaPN were restricted by ionized impurity scattering even at room temperature (RT). N atoms at N-related levels could trap the electrons, and these ionized N could act as a Columb scattering center for free electrons even at RT.
Dynamic range of ultrabroadband terahertz detection using GaAs photoconductors
Authors: Hussain A. , Andrews S. R.
Published: April 2006

Electromagnetic transients with frequency components spanning the far and midinfrared are coherently detected by means of the polarization current induced in an electron-hole plasma optically excited in As implanted GaAs. The impulse response is governed by the frequency dependence of the photocarrier mobility and density and the lattice contribution to the dielectric constant. Compared with electro-optic sampling using thin ZnTe crystals, photoconductive detection can yield a comparable or greater dynamic range up to 40THz.
Room-temperature ferromagnetism in zinc-blende and deformed CrAs thin films
Authors: Bi J. F. , Zhao J. H. , Deng J. J. , Zheng Y. H. , Li S. S. , Wu X. G. , Jia Q. J.
Published: April 2006

We try to clarify the controversy about the origin of room-temperature ferromagnetism in a CrAs compound. Two kinds of CrAs thin films were grown on GaAs by molecular-beam epitaxy. Structural analyses confirm that the as-grown CrAs film is a pure zinc-blende phase. Magnetic measurements suggest that room-temperature ferromagnetism exists in zinc-blende CrAs. In contrast, the CrAs film turns into a mixture of zinc-blende and deformed CrAs after annealing. A ferromagnetic signal measured at room temperature demonstrates that zinc-blende CrAs remains room-temperature ferromagnetism even when it is partly deformed into a non-zinc-blende phase.
Coherent acoustic phonons in strain engineered InAs∕GaAs quantum dot clusters
Authors: Bogaart E. W. , van Lippen T. , Haverkort J. E. M. , Nötzel R. , Wolter J. H.
Published: April 2006

Coherent excitation of the quasilongitudinal and quasitransverse acoustic phonon mode in strain engineered InAs∕GaAs quantum dot (QD) clusters grown on (311)B GaAs is monitored by means of time-resolved differential reflection spectroscopy. Carrier capture within the ordered QD clusters initiate coherent acoustic phonon excitation, which induces a transient modulation of the local strain-induced piezoelectric field within the QD clusters. The excited acoustic phonons then modulate the optical properties of the QDs through the quantum-confined Stark effect, causing distinct oscillations of the differential reflection signal.
Scanning near-field optical microscopy images of microradiographs stored in lithium fluoride films with an optical resolution of λ∕12
Authors: Ustione Alessandro , Cricenti Antonio , Bonfigli Francesca , Flora Francesco , Lai Antonella , Marolo Tiziana , Maria Montereali Rosa , Baldacchini Giuseppe , Faenov Anatoly , Pikuz Tatiana , Reale Lucia
Published: April 2006

Here we show a new, simple method to observe soft x-ray microradiographs of biological material. A thin film of lithium fluoride (LiF) works as image detector, storing the microradiograph obtained exposing biological samples to extreme ultraviolet and soft x-ray radiations. To read the stored image, collecting the optically stimulated visible luminescence emitted by the LiF active color centers locally produced by the x rays, a scanning near-field optical microscope is used with an optical aperture of 50nm, i.e., λ∕12, where λ is the wavelength of the collected photoluminescence.
Comparison of free surface polarization of NiMnSb and Co2MnSi
Authors: Miyoshi Y. , Bugoslavsky Y. , Syed M. H. , Robinson T. , Cohen L. F. , Singh L. J. , Barber Z. H. , Grigorescu C. E. A. , Gardelis S. , Giapintzakis J. , Van Roy W.
Published: April 2006

We present a systematic study of the polarization of the transport current from a variety of NiMnSb and Co2MnSi thin films and bulk material using point contact Andreev reflection spectroscopy. The simple analysis suggests that the free surface polarization of NiMnSb is within error 10% lower than that of Co2MnSi. In either material the measured polarization is rather insensitive to key physical and material properties. We use a two channel model to rule out the influence that stray magnetic field from the ferromagnet might have on the measurements presented.
Effect of hydrogen on the growth of thin hydrogenated amorphous carbon films from thermal energy radicals
Authors: Neyts E. , Bogaerts A. , van de Sanden M. C. M.
Published: April 2006

Molecular dynamics simulations have been performed to investigate the growth of thin hydrogenated amorphous carbon (a-C:H) films from radical species with thermal energy. It is found that the incorporation of H into the film increases the mass density. The maximum mass density is reached for a H flux of about 10%. The atom density of the films reaches a maximum at a H flux of about 30%. It is shown that these effects are a result of the change in microstructure of the films, including a H-induced sp to sp2 to sp3 shift. These results are important for thin a-C:H film deposition techniques where chemisorption of radical species is the main growth mechanism.
Localized excitation of InGaAs quantum dots by utilizing a photonic crystal nanocavity
Authors: Nomura Masahiro , Iwamoto Satoshi , Nakaoka Toshihiro , Ishida Satomi , Arakawa Yasuhiko
Published: April 2006

We have studied excitation wavelength dependence of light emission from InGaAs quantum dots (QDs) embedded in high-quality-factor photonic crystal nanocavities. The light emission of the cavity mode around 1μm was very weak with below-band-gap excitation in the InGaAs wetting layer. However, the emission of the lowest-order cavity mode was strongly enhanced when the excitation wavelength was resonant with higher-order cavity modes. This phenomenon can be attributed to the local intensity enhancement of the excitation light which couples with the cavity mode. The on-resonant excitation technique selectively and efficiently excites only the QDs in the cavity without undesirable background emission.
Nitrogen-induced hindering of In incorporation in InGaAsN
Authors: Rubini S. , Bais G. , Cristofoli A. , Piccin M. , Duca R. , Nacci C. , Modesti S. , Carlino E. , Martelli F. , Franciosi A. , Bisognin G. , De Salvador D. , Schiavuta P. , Berti M. , Drigo A. V.
Published: April 2006

We compare the In content of quaternary InxGa1−xAs1−yNy and ternary InxGa1−xAs layers grown by plasma-assisted molecular beam epitaxy in similar conditions. Indium incorporation is found to decrease monotonically with increasing nitrogen content. The magnitude of the reduction strongly depends on N concentration, reaching about 20% of the nominal In content for N concentrations of y=0.044.
Variable optical reflectance of a self-supported Si grating
Authors: Hane Kazuhiro , Kobayashi Takashi , Hu Fang-Ren , Kanamori Yoshiaki
Published: April 2006

Variable reflectance of a self-supported Si grating mirror is reported. A grating suspended in air consisted of an array of 300nm wide, 300nm thick, and 20μm long beams. The period of the grating was varied with an electrostatic microactuator from 600to720nm. A broadband reflection in the wavelength longer than the grating period was observed, which was caused by a resonant interference of the light wave propagating along the grating similar to the guided-mode resonant gratings. Increasing the period of the grating with a microactuator, the reflection spectrum changed. The results were explained by the theoretical calculations based on rigorous coupled-wave analysis.
Cryogenic two-photon laser photolithography with SU-8
Authors: Lee Kwan H. , Green Alex M. , Taylor Robert A. , Sharp David N. , Turberfield Andrew J. , Brossard Frederic S. F. , Williams David A. , Briggs G. Andrew D.
Published: April 2006

We have shown that photolithography can be used to create alignment markers on a semiconductor substrate at cryogenic temperatures. The epoxy resist SU-8 can be exposed effectively by two-photon absorption at a temperature of 4K. By this means a spectroscopy apparatus can be used to find the positions of randomly distributed structures at low temperatures, such as InGaAs∕GaAs quantum dots, and mark their positions. We present a systematic study of the optical exposure parameters for cryogenic two-photon laser photolithography with SU-8.
Robust, scalable self-aligned platinum silicide process
Authors: Zhang Z. , Zhang S.-L. , Östling M. , Lu J.
Published: April 2006

A robust, scalable PtSix process is developed. The process consists of two consecutive annealing steps in a single run; the first is silicidation of Pt films on Si substrates carried out in N2, whereas the second is surface oxidation of the resultant PtSix in O2. By adequately adjusting the temperature during the oxidation step, a protective SiOx hard mask forms on PtSix of different thicknesses and compositions. Such a surface oxidation is absent for Pt on SiO2 isolation, which is crucial for the subsequent selective wet etch for a self-aligned process. Ultralong PtSix nanowires are fabricated using this robust self-aligned process.
Band offsets in the Sc2O3∕GaN heterojunction system
Authors: Chen J.-J. , Gila B. P. , Hlad M. , Gerger A. , Ren F. , Abernathy C. R. , Pearton S. J.
Published: April 2006

The Sc2O3∕GaN interface shows low trap densities and has been used both to demonstrate inversion in gated metal-oxide-semiconductor diodes and to mitigate current collapse in AlGaN∕GaN heterostructure transistors but little is known of the band offsets at this interface. We measured the energy discontinuity in the valence band (ΔEv) of Sc2O3∕GaN heterostructures using x-ray photoelectron spectroscopy. A value of ΔEv=0.42±0.07eV was obtained using the Ga 3d energy level as a reference. With the experimental band gap of 6.0eV for the Sc2O3 grown by this method, this implies that the conduction band offset ΔEC is 2.14eV in this system.
Current-assisted magnetization switching in a mesoscopic NiFe ring with nanoconstrictions of a wire
Authors: Lu Zhengqi , Zhou Yun , Du Yuqing , Moate Roy , Wilton David , Pan Genhua , Chen Yifang , Cui Zheng
Published: April 2006

A mesoscopic NiFe ring with nanoconstrictions of a wire was fabricated by electron beam lithography and lift-off techniques. Magnetic switching and reversal process have been measured by magnetoresistance as a function of the applied current. It is shown that the applied current has an effect on the switching fields and finally affects the reversal process. The decrease or increase in the switching field from the vortex state to the onion state depends on the electron flow with respect to the direction of domain propagation. The spin in the ring switches from an onion state to the opposite onion state in the low applied current via the double switching process. However, the spin in the ring switches directly from an onion state to the opposite due to the spin torque effect when the applied current is higher than the critical current density (of 107A∕cm2).
Aquifers: the ultimate groundwater-dependent ecosystems
Authors: Humphreys William F.
Published: April 2006

Australian aquifers support diverse metazoan faunas comprising obligate groundwater inhabitants, largely crustaceans but also including insects, worms, gastropods, mites and fish. They typically comprise short-range endemics, often of relictual lineages and sometimes widely vicariant from their closest relatives. They have been confined to subterranean environments from a range of geological eras and may contain information on the deep history of aquifers. Obligate groundwater fauna (stygobites) occurs in the void spaces in karst, alluvial and fractured rock aquifers. They have convergent morphologies (reduction or loss of eyes, pigment, enhanced non-optic senses, vermiform body form) and depend on energy imported from the surface except in special cases of in situ chemoautotrophic energy fixation. In Australia, many stygofaunas in arid areas occur in brackish to saline waters, although they contain taxa from lineages generally restricted to freshwater systems. They may occur alongside species belonging to taxa considered typical of the marine littoral although far removed in space and time from marine influence. The ecological attributes of stygofauna makes them vulnerable to changes in habitat, which, combined with their taxonomic affinities, makes them a significant issue to biodiversity conservation. The interaction of vegetation and groundwater ecosystems is discussed and, in places, there are conservation issues common to both.
Impacts of tree plantations on groundwater in south-eastern Australia
Authors: Benyon Richard G. , Theiveyanathan S. , Doody Tanya M.
Published: April 2006

In some regions dependent on groundwater, such as the lower south-east of South Australia in the Green Triangle, deep-rooted, woody vegetation might have undesirable hydrological impacts by competing for finite, good-quality groundwater resources. In other regions, such as the Riverina in south-central New South Wales, where rising watertables and associated salinisation is threatening the viability of agriculture, woody vegetation might have beneficial hydrological impacts. In response to a growing need to better understand the impacts of tree plantations on groundwater, annual evapotranspiration and transpiration were measured at 21 plantation sites in the Green Triangle and the Riverina. Sources of tree water uptake from rainfall and groundwater were determined by measurements of evapotranspiration and soil water over periods of 2–5 years. In the Green Triangle, under a combination of permeable soil over groundwater of low salinity (<2000 mg L–1) at 6-m depth or less, in a highly transmissive aquifer, annual evapotranspiration at eight research sites in Pinus radiata D.Don and Eucalyptus globulus Labill. plantations averaged 1090 mm year–1 (range 847–1343 mm year–1), compared with mean annual precipitation of 630 mm year–1. These plantation sites used groundwater at a mean annual rate of 435 mm year–1 (range 108–670 mm year–1). At eight other plantation sites that had greater depth to the watertable or a root-impeding layer, annual evapotranspiration was equal to, or slightly less than, annual rainfall (mean 623 mm year–1, range 540–795 mm year–1). In the Riverina, where groundwater was always present within 3 m of the surface, Eucalyptus grandis Hill ex Maiden trees at three sites with medium or heavy clay, alkaline, sodic, saline subsoils used little or no groundwater, whereas E. grandis and Corymbia maculata (Hook.) K.D.Hill and L.A.S.Johnson trees at a site with a neutral sandy soil and groundwater of low salinity used 380 and 730 mm year–1 of groundwater (respectively 41 and 53% of total annual evapotranspiration). We conclude that commonly grown Eucalyptus species and P. radiata are able to use groundwater under a combination of light- or medium-textured soil and shallow depth to a low-salinity watertable.
Categorical Langlands correspondence for 𝑆𝑂_{𝑛,1}(ℝ)
Authors: Halupczok Immanuel
Published: April 2006

In the context of the local Langlands philosopy for

R

\mathbb {R}

, Adams, Barbasch and Vogan describe a bijection between the simple Harish-Chandra modules for a real reductive group

G
(

R

)

G(\mathbb {R})

and the space of “complete geometric parameters”—a space of equivariant local systems on a variety on which the Langlands-dual of

G
(

R

)

G(\mathbb {R})

acts. By a conjecture of Soergel, this bijection can be enhanced to an equivalence of categories. In this article, that conjecture is proven in the case where

G
(

R

)

G(\mathbb {R})

is a generalized Lorentz group

SO

n
,
1

⁡
(

R

)

\operatorname {SO}_{n,1}(\mathbb {R})

.