bluuebunny/crossref_metadata_2025 huggingface dataset:
Extended atomic hydrogen dimer configurations on the graphite(0001) surface
Authors: Šljivančanin Ž. , Rauls E. , Hornekær L. , Xu W. , Besenbacher F. , Hammer B.
Published: August 2009

We present density functional theory calculations and scanning tunneling microscopy experiments investigating the structures and kinetics of extended hydrogen dimer configurations on the graphite (0001) surface. We identify several hydrogen dimer structures where surface mediated interactions between the two hydrogen atoms lead to increased binding energy even at interatom separations as large as 7 Å. By modeling the formation of dimers as sequential adsorption of hydrogen atoms, we find that these dimer configurations exhibit decreased barriers to sticking for the second H atom, compared to the sticking barrier of an H atom on the clean surface. According to our calculations, the activation energies for desorption of a single H atom from any of the experimentally observed extended dimers are higher than the barriers for diffusion to the paradimer configuration. Consequently, molecular hydrogen formation out of the extended dimer structures takes place via diffusion over the paradimer configuration.
Photocurrent and photoconductance properties of a GaAs nanowire
Authors: Thunich S. , Prechtel L. , Spirkoska D. , Abstreiter G. , Fontcuberta i Morral A. , Holleitner A. W.
Published: August 2009

We report on photocurrent and photoconductance processes in a freely suspended p-doped single GaAs nanowire. The nanowires are grown by molecular beam epitaxy, and they are electrically contacted by a focused ion beam deposition technique. The observed photocurrent is generated at the Schottky contacts between the nanowire and metal source-drain electrodes, while the observed photoconductance signal can be explained by a photogating effect induced by optically generated charge carriers located at the surface of the nanowire. Both optoelectronic effects are sensitive to the polarization of the exciting laser field, enabling polarization dependent photodetectors.
A compact submicrosecond, high current generator
Authors: Kovalchuk B. M. , Kharlov A. V. , Zorin V. B. , Zherlitsyn A. A.
Published: August 2009

Pulsed current generator was developed for experiments with current carrying pulsed plasma. Main parts of the generator are capacitor bank, low inductive current driving lines, and central load part. Generator consists of four identical sections, connected in parallel to one load. Capacitor bank is assembled from 24 capacitor blocks (100 kV, 80 nF), connected in parallel. It stores 9.6 kJ at 100 kV charging voltage. Each capacitor block incorporates a multigap spark switch, which is able to commute by six parallel channels. Switches operate in dry air at atmospheric pressure. The generator was tested with an inductive load and a liner load. At 17.5 nH inductive load and 100 kV of charging voltage it provides 650 kA of current amplitude with 390 ns rise time with 0.6 Ω damping resistors in discharge circuit of each capacitor block. The net generator inductance without a load was optimized to be as low as 15 nH, which results in extremely low impedance of the generator (∼0.08 Ω). It ensures effective energy coupling with a low impedance load such as Z pinch. The generator operates reliably without any adjustments in 70–100 kV range of charging voltage. Jitter in delay between output pulse and triggering pulse is less than 5 ns at 70–100 kV charging voltage. Operation and handling are very simple, because no oil or purified gases are required for the generator. The generator has dimensions 5.24×1.2×0.18 m3 and total weight about 1400 kg, thus manifesting itself as simple, robust, and cost effective apparatus.
Detection of pesticide effects in human keratinocytes by means of Raman microspectroscopy
Authors: Perna G. , Lasalvia M. , Castro A. , Mezzenga E. , L’Abbate N. , Biagi P. F. , Capozzi V.
Published: August 2009

Biochemical modifications of single cells of human keratinocytes exposed to different concentrations of chlorpyriphos solutions were detected by means of Raman microspectroscopy. The modifications mainly consist of breakdown of amide linkage between aminoacids. Fragmentation of DNA bases and single aminoacids occurs as well. The protein and DNA damage are already detectable at a chlorpyriphos concentration value (10−6M), which is at least three orders of magnitude lower than the concentration estimated as cytotoxic (10−3M). Raman microspectroscopy technique results to be a very sensitive technique to detect molecular changes even in single human cells exposed to toxic pesticide.
Rotating electric fields in complex (dusty) plasmas
Authors: Nosenko V. , Ivlev A. V. , Zhdanov S. K. , Fink M. , Morfill G. E.
Published: August 2009

The rotation of monolayer particle clusters suspended in the sheath of a rf discharge plasma was observed experimentally. The cluster rotation was driven by an electric field that rotated uniformly in the horizontal plane (“rotating wall” technique). No external magnetic field was applied. The cluster rotation velocity depended nonmonotonically on the manipulation field frequency that was much higher than the dust plasma frequency. Mechanisms of rotation are proposed based on the interplay between the electric and ion-drag forces. Possible applications of rotating electric fields in complex plasmas are discussed.
The Richtmyer–Meshkov instability in magnetohydrodynamics
Authors: Wheatley V. , Samtaney R. , Pullin D. I.
Published: August 2009

In ideal magnetohydrodynamics (MHD), the Richtmyer–Meshkov instability can be suppressed by the presence of a magnetic field. The interface still undergoes some growth, but this is bounded for a finite magnetic field. A model for this flow has been developed by considering the stability of an impulsively accelerated, sinusoidally perturbed density interface in the presence of a magnetic field that is parallel to the acceleration. This was accomplished by analytically solving the linearized initial value problem in the framework of ideal incompressible MHD. To assess the performance of the model, its predictions are compared to results obtained from numerical simulation of impulse driven linearized, shock driven linearized, and nonlinear compressible MHD for a variety of cases. It is shown that the analytical linear model collapses the data from the simulations well. The predicted interface behavior well approximates that seen in compressible linearized simulations when the shock strength, magnetic field strength, and perturbation amplitude are small. For such cases, the agreement with interface behavior that occurs in nonlinear simulations is also reasonable. The effects of increasing shock strength, magnetic field strength, and perturbation amplitude on both the flow and the performance of the model are investigated. This results in a detailed exposition of the features and behavior of the MHD Richtmyer–Meshkov flow. For strong shocks, large initial perturbation amplitudes, and strong magnetic fields, the linear model may give a rough estimate of the interface behavior, but it is not quantitatively accurate. In all cases examined the accuracy of the model is quantified and the flow physics underlying any discrepancies is examined.
Combined holographic-mechanical optical tweezers: Construction, optimization, and calibration
Authors: Hanes Richard D. L. , Jenkins Matthew C. , Egelhaaf Stefan U.
Published: August 2009

A spatial light modulator (SLM) and a pair of galvanometer-mounted mirrors (GMM) were combined into an optical tweezers setup. This provides great flexibility as the SLM creates an array of traps, which can be moved smoothly and quickly with the GMM. To optimize performance, the effect of the incidence angle on the SLM with respect to phase and intensity response was investigated. Although it is common to use the SLM at an incidence angle of 45°, smaller angles give a full 2π phase shift and an output intensity which is less dependent on the magnitude of the phase shift. The traps were calibrated using an active oscillatory technique and a passive probability distribution method.
Properties of water along the liquid-vapor coexistence curve via molecular dynamics simulations using the polarizable TIP4P-QDP-LJ water model
Authors: Bauer Brad A. , Patel Sandeep
Published: August 2009

We present an extension of the TIP4P-QDP model, TIP4P-QDP-LJ, that is designed to couple changes in repulsive and dispersive nonbond interactions to changes in polarizability. Polarizability is intimately related to the dispersion component of classical force field models of interactions, and we explore the effect of incorporating this connection explicitly on properties along the liquid-vapor coexistence curve of pure water. Parametrized to reproduce condensed-phase liquid water properties at 298 K, the TIP4P-QDP-LJ model predicts density, enthalpy of vaporization, self-diffusion constant, and the dielectric constant at ambient conditions to about the same accuracy as TIP4P-QDP but shows remarkable improvement in reproducing the liquid-vapor coexistence curve. TIP4P-QDP-LJ predicts critical constants of Tc=623 K, ρc=0.351 g/cm3, and Pc=250.9 atm, which are in good agreement with experimental values of Tc=647.1 K, ρc=0.322 g/cm3, and Pc=218 atm, respectively. Applying a scaling factor correction (obtained by fitting the experimental vapor-liquid equilibrium data to the law of rectilinear diameters using a three-term Wegner expansion) the model predicts critical constants (Tc=631 K and ρc=0.308 g/cm3). Dependence of enthalpy of vaporization, self-diffusion constant, surface tension, and dielectric constant on temperature are shown to reproduce experimental trends. We also explore the interfacial potential drop across the liquid-vapor interface for the temperatures studied. The interfacial potential demonstrates little temperature dependence at lower temperatures (300–450 K) and significantly enhanced (exponential) dependence at elevated temperatures. Terms arising from the decomposition of the interfacial potential into dipole and quadrupole contributions are shown to monotonically approach zero as the temperature approaches the critical temperature. Results of this study suggest that self-consistently treating the coupling of phase-dependent polarizability with dispersion interactions in classical water force fields may be an important effect for the extension of polarizable water force fields to reproduce properties along the liquid-vapor coexistence envelope as well as near critical conditions. More importantly, the present study demonstrates the rather remarkable transferability of a water model parametrized to a single state point to other thermodynamic states. Further studies are recommended.
Dielectric relaxations in ribose and deoxyribose supercooled water solutions
Authors: Pagnotta S. E. , Cerveny S. , Alegría A. , Colmenero J.
Published: August 2009

The relaxation dynamic of ribose and deoxyribose water solutions at different concentrations has been studied by broadband dielectric spectroscopy and differential scanning calorimetry in the temperature range of 150–250 K. Two relaxation processes are observed for all the hydration levels; the slower (process I) is related to the relaxation of the whole solution whereas the faster one (process II) is associated with the reorientation of water molecules in the mixture. As for other polymeric water solutions, dielectric data for process II indicate the existence of a critical water concentration above which water mobility is less restricted. According to these results, attenuated total reflectance Fourier transform infrared spectroscopy measurements of the same sugar solutions showed an increment in the intensity of the OH stretching sub-band close to 3200 cm−1 as water content increases.
Tunable ferromagnetism by oxygen vacancies in Fe-doped In2O3 magnetic semiconductor
Authors: Xing P. F. , Chen Y. X. , Yan Shi-Shen , Liu G. L. , Mei L. M. , Zhang Z.
Published: August 2009

Fe-doped In2O3 films with well defined bcc (440) texture were grown on r-cut sapphire at different oxygen pressures by pulsed laser deposition. Nonmonotonic dependence of ferromagnetism on oxygen pressure has been observed. Under optimal deposition conditions, the saturation magnetization can reach 2.5μB/Fe atom. Moreover, the ferromagnetism can be reversed between the higher magnetization state and the lower magnetization state by alternate annealing in vacuum and in air. All these features are well explained by a modified model of F-center mediated ferromagnetism.
Conduction-atomic force microscopy study of H2 sensing mechanism in Pd nanoparticles decorated TiO2 nanofilm
Authors: Kumar Manippady Krishna , Tan Lee Kheng , Gosvami Nitya Nanda , Gao Han
Published: August 2009

In situ conduction-AFM is used to observe room temperature hydrogen gas response mechanism of Pd nanoparticles decorated TiO2 nanofilm. The response mechanism is due to chemical and electronic sensitization of the nanofilm. The nanofilm with thickness ∼5 nm, in range of the wall thickness of a typical TiO2 nanotube, is prepared by atomic layer deposition. For the mechanism study and also for hydrogen sensor applications, this nanofilm with electrical conduction switching from the order of picoampere in air, to ∼0.30 μA in 1000 ppm H2 is an alternative to TiO2 nanotube/nanostructures.
Effect of laser fluence on yeast cell viability in laser-assisted cell transfer
Authors: Lin Yafu , Huang Yong , Wang Gaoyan , Tzeng Tzeng-Rong J. , Chrisey Douglas B.
Published: August 2009

Matrix-assisted pulsed-laser evaporation direct-write (MAPLE DW) has been emerging as a promising biological construct fabrication technique. The post-transfer cell viability in MAPLE DW depends on various operation conditions such as the applied laser fluence; unfortunately, the effect of laser fluence on the post-transfer cell viability has not been well elucidated. This work aims to study the effect of laser fluence on the post-transfer cell viability and the cell recovery ability in MAPLE DW of yeast cells (Saccharomyces cerevisiae). It has been observed that (1) yeast cell viability decreases as the laser fluence increases from 85 to around 1500mJ∕cm2 and (2) some of the MAPLE DW process-induced cell damage is reversible. The post-transfer yeast cell recovery is a function of laser fluence; however, this dependence relationship is not monotonic. Future work is needed to better understand the physical and chemical mechanisms of the above observations.
Broadband blue superluminescent light-emitting diodes based on GaN
Authors: Feltin E. , Castiglia A. , Cosendey G. , Sulmoni L. , Carlin J.-F. , Grandjean N. , Rossetti M. , Dorsaz J. , Laino V. , Duelk M. , Velez C.
Published: August 2009

We report on the achievement of III-nitride blue superluminescent light-emitting diodes on GaN substrates. The epitaxial structure includes an active region made of In0.12Ga0.88N quantum wells in a GaN/AlGaN waveguide. Superluminescence under cw operation is observed at room temperature for a current of 130 mA and a current density of 8 kA/cm2. The central emission wavelength is 420 nm and the emission bandwidth is ∼5 nm in the superluminescence regime. A peak optical output power of 100 mW is obtained at 630 mA under pulsed operation and an average power of 10 mW is achieved at a duty cycle of 20%.
A note on the neutral stochastic functional differential equation with infinite delay and Poisson jumps in an abstract space
Authors: Ren Yong , Chen Li
Published: August 2009

In this note, we prove the existence and uniqueness of the solution to neutral stochastic functional differential equation with infinite delay and Poisson jumps in the phase space B with non-Lipschitz coefficients. The known results that appeared in the studies by Ren and Xia [Appl. Math. Comput. 210, 72 (2009); Ren and XiaAppl. Math. Comput. 214, 457 (2009)] and Xu and Hu [Acta Appl. Math. (unpublished)] are generalized and improved. An example is provided to illustrate the theory.
Induced ferromagnetism in Mn3N2 phase embedded in Mn/Si3N4 multilayers
Authors: Céspedes E. , Román E. , Huttel Y. , Chaboy J. , García-López J. , de Andrés A. , Prieto C.
Published: August 2009

Room temperature ferromagnetism has been obtained for different sets of Mn/Si3N4 multilayers prepared by sputtering. In order to find the most suitable conditions to stabilize the ferromagnetic ordering in this system, the evolution of the magnetic properties has been studied for films in which the Si3N4 layer thickness was maintained constant while that of the Mn layer was varied, [Mn(tm)/Si3N4(3.4 nm)]n, and conversely, in [Mn(0.7 nm)/Si3N4(tsn)]43 samples, in which the Mn layer thickness was kept constant while varying the Si3N4 layer thickness. Structural, compositional, electronic and magnetic characterizations have been performed by means of x-ray reflectometry, Rutherford backscattering spectrometry, x-ray photoemission spectroscopy, x-ray absorption, and superconducting quantum interference device for further knowledge of the magnetic-structural relationship in this system. Our results show that the peculiar magnetic behavior of these films is mainly related to the stabilization of a slightly distorted Mn3N2 phase that is induced by the Si3N4 at the interfaces. For samples with larger Mn layer thickness, metallic Mn and Mn3N2 phases coexist, which leads to a reduction of the total magnetization per Mn atom due to the presence of metallic Mn. For small Mn layer thickness (tm<0.86 nm), where noncontinuous Mn3N2 layers are formed, the magnetization decreases noticeably due to the superparamagnetic size limit. It has been found that the best conditions for the stabilization of the ferromagnetism in this system occur when both, the manganese-rich and the silicon nitride layers, are continuous and with similar thickness, close to 3.5 nm.
Influence of Ni silicide phases on effective work function modulation with Al-pileup in the Ni fully silicided gate/HfSiON system
Authors: Tsuchiya Yoshinori , Yoshiki Masahiko , Koga Junji , Nishiyama Akira , Koyama Masato
Published: August 2009

Influences of Ni silicide phases on the effective work function (Φeff) modulation effect with Al incorporation has been investigated in the Ni silicide/HfSiON systems. We formed metal-insulator-semiconductor capacitors with Al incorporated Ni silicide (NiSi, Ni2Si, and Ni3Si) gates on HfSiON by Al solid-phase diffusion (Al-SPD) process or Al ion implantation (I/I) process. In the Al-SPD process, Al is deposited on Ni silicide gate. In the Al-I/I process, Al ions were doped in the upper part of Ni silicide layer. In both cases, we performed Al drive-in annealing under the condition of 450 °C for 30 min in N2 ambient. It is found that the flat-band voltage (Vfb) values of Al incorporated NiSi and Ni2Si gates shift negatively and identical independent of Al incorporation processes. A highly concentrated Al piled-up layer, which induces Φeff modulation to Al-Φeff value, seems to correspond to the Vfb modulation. On the other hand, Al incorporation has little influence on Φeff at the Ni3Si/HfSiON interface. We revealed that a lower Al diffusion coefficient in Ni3Si phase reduces the Al interface density at the Ni3Si/HfSiON interface. In addition, Al piled-up layer is inherently unstable at the Ni3Si/HfSiON interface, which is confirmed from the detailed investigation about thermal stability of Al piled-up layer by using phase change process from NiSi to Ni3Si phase.
Time dependent dielectric breakdown of amorphous ZrAlxOy high-k dielectric used in dynamic random access memory metal-insulator-metal capacitor
Authors: Zhou Dayu , Schroeder U. , Jegert G. , Kerber M. , Uppal S. , Agaiby R , Reinicke M. , Heitmann J. , Oberbeck L.
Published: August 2009

Reliability is of serious concern for high-k dielectrics used in advanced memory applications. In this study, the time dependent dielectric breakdown behavior is investigated for metal-insulator-metal capacitors with amorphous ZrAlxOy thin films as insulator and TiN as electrodes. Constant voltage stress measurements over seven orders of magnitude in time show that the power-law model is appropriate for lifetime extrapolation. The voltage acceleration parameter increases with decreasing temperature, and the thermal activation energy, Ea, increases with decreasing stress voltage, both translating to a gain in lifetime under product operation conditions.
Left-handed behavior of strontium-doped lanthanum manganite in the millimeter waveband
Authors: Khodzitsky M. K. , Kalmykova T. V. , Tarapov S. I. , Belozorov D. P. , Pogorily A. M. , Tovstolytkin A. I. , Belous A. G. , Solopan S. A.
Published: August 2009

Left-handed behavior of strontium-doped lanthanum manganite was revealed in the millimeter waveband. The bulk specimen of La1−xSrxMnO3, was used as a boundary medium for one-dimensional photonic crystal. In the absence of magnetic field known Tamm peak appears in the forbidden zone of photonic crystal indicating that manganite is a single negative medium (negative permittivity). In the presence of external magnetic field somewhat above frequency of ferromagnetic resonance the additional (field sensitive) transparency peak appears in photonic crystal forbidden zone, indicating that manganite becomes double negative medium (negative permittivity and permeability). Model theoretical calculations corroborate the experimental findings.
Extrinsic interface formation of HfO2 and Al2O3∕GeOx gate stacks on Ge (100) substrates
Authors: Seo H. , Bellenger F. , Chung K. B. , Houssa M. , Meuris M. , Heyns M. , Lucovsky G.
Published: August 2009

The extrinsic interfaces present at the HfO2∕GeOx∕Ge and Al2O3∕GeOx∕Ge gate stacks are investigated. The effective trapped charge density, estimated from hysteresis in capacitance-voltage characteristics, is higher for HfO2 than for Al2O3, implying qualitatively different charge trapping sources in each dielectric. Spectroscopic ellipsometry and medium energy ion scattering measurements reveal that HfO2 deposition induces the formation of a thicker germanate (intermixed) layer at the HfO2∕GeOx interface, where nonstoichiometric Ge-rich GeOx having significantly low bandgap (∼1.8eV) is present. In contrast, Al2O3 deposition leads to an abrupt and thinner O-rich GeOx interfacial layer without Ge-rich GeOx phase. The proposed band alignment indicates that Ge-rich GeOx layer at HfO2∕GeOx arises a significant band potential well trapping, while O-rich GeOx layer in Al2O3∕GeOx is responsible for a relatively lower charge trapping at band potential well. The combined results strongly suggest that the control of the GeOx interface layers is crucial to reduce the high charge trapping at high-κ∕GeOx∕Ge gate stacks.
Temperature-dependent study of photocurrent signal in CdGa2Se4 layers
Authors: You S. H. , Hong K. J. , Jeong T. S. , Youn C. J.
Published: August 2009

The photoconductive CdGa2Se4 layer has been investigated using photocurrent (PC) spectroscopy as a function of temperature. Three peaks corresponding to the band-to-band transitions were observed in the PC spectra for all temperature ranges. From the relations of peak position and temperature, the temperature dependence of the band-gap energy is precisely discussed. Also, contrary to our expectation, the PC intensities decreased with decreasing temperatures. From the relation of log Jph versus 1/T, where Jph is the PC density, two dominant levels by the exponential variation in the PC with varying temperature were observed, one at high temperatures and the other at low temperatures.
Energy band alignment of SiO2/ZnO interface determined by x-ray photoelectron spectroscopy
Authors: You J. B. , Zhang X. W. , Song H. P. , Ying J. , Guo Y. , Yang A. L. , Yin Z. G. , Chen N. F. , Zhu Q. S.
Published: August 2009

Thin SiO2 interlayer is the key to improving the electroluminescence characteristics of light emitting diodes based on ZnO heterojunctions, but little is known of the band offsets of SiO2/ZnO. In this letter, energy band alignment of SiO2/ZnO interface was determined by x-ray photoelectron spectroscopy. The valence band offset ΔEV of SiO2/ZnO interface is determined to be 0.93±0.15 eV. According to the relationship between the conduction band offset ΔEC and the valence band offset ΔEV: ΔEC=EgSiO2−EgZnO−ΔEV, and taking the room-temperature band-gaps of 9.0 and 3.37 eV for SiO2 and ZnO, respectively, a type-I band-energy alignment of SiO2/ZnO interface with a conduction band offset of 4.70±0.15 eV is found. The accurate determination of energy band alignment of SiO2/ZnO is helpful for designing of SiO2/ZnO hybrid devices and is also important for understanding their carrier transport properties.
Microscopic theory of relaxation processes in systems of particles interacting with the hydrodynamic medium
Authors: Nikolayenko S. O. , Slyusarenko Yu. V.
Published: August 2009

Our work considers spatially nonuniform states of particles, weakly interacting with a hydrodynamic medium. We developed a microscopic theory, describing such systems involving Bogolubov’s reduced description method. It was shown that such systems have both kinetic and hydrodynamic stages of evolution. At the kinetic stage of evolution the one-particle distribution function is a reduced description parameter for particles, and, therefore, a medium is described by five hydrodynamic parameters (density, temperature, and velocity). The coupled system of equations of motion describing the system on the kinetic stage of evolution was obtained on the basis of Bogolubov’s reduced description method. The transition from the kinetic to hydrodynamic stage of evolution for particles interacting with the medium was also studied within the reduced description method. It was shown that on the hydrodynamic stage the only description parameter of particles is their density, although the medium is still described by five hydrodynamic variables. Consequently, a coupled system of equations, which completely describe the evolution of the system under consideration on the hydrodynamic stage, including dissipation processes, was obtained. These equations were used to study the propagation of acoustic waves in our system. Also the influence of particles on relaxation processes was discussed. The obtained equations, for example, may be used to describe the neutrons propagating in a hydrodynamic medium without multiplication and capture.
Heating rate of ions via nonresonant interaction with turbulent Alfvén waves with ionization and recombination
Authors: Wang Bin , Wang C. B.
Published: August 2009

Ion heating due to turbulent Alfvén waves via nonresonant wave-particle interaction is discussed to complement a preceding work. We claim that newborn ions can get extra energy from turbulent Alfvén waves. Since in plasmas newborn ions are created continuously and intrinsically via ionization and recombination, heating associated with these newborn ions may be significant. The heating rate is proportional to the creation rate of newborn ions and the total wave field energy density without dependence on the profile of the wave spectrum. Based on observed nonthermal velocities, we estimate the energy density of the wave field and the corresponding heating rate in the solar atmosphere. The results show that such a heating process could be significant in the upper chromosphere and transition region of the sun.
Widely tunable lifetimes for donor-acceptor pair states created by displacing an intrinsic atom in photonic crystals
Authors: Nojima S. , Nakahata M.
Published: August 2009

This paper theoretically investigates the formation processes of intrinsic defect states in two-dimensional photonic crystals. We observe two types of defect states—what could be called the donor and acceptor states—created simultaneously by merely displacing a single rod atom from its regular site. The localization of light in the vicinity of these states is reasonably explained in terms of the stability of light around them. Finally, we demonstrate that the lifetimes of light trapped at these states can be tuned in a wide range by adjusting the position of the displaced rod appropriately.
Characterization of current injection mechanism in Schottky-barrier metal-oxide-semiconductor field-effect transistors
Authors: Choi Sung-Jin , Han Jin-Woo , Jang Moongyu , Choi Cheljong , Choi Yang-Kyu
Published: August 2009

We discuss the carrier injection mechanism from source/drain to a channel in the on/off-state of Schottky-barrier silicon-on-insulator (SOI) metal-oxide-semiconductor field-effect transistor by developing a refined extraction method for estimation of the Schottky-barrier height. This method is applied to validate the suggested mechanism by utilizing the dummy-gate in an underlap device with a thicker spacer and applying back-gate bias to SOI wafer. The results clearly show that the tunneled carriers from the drain side drive the off-state leakage current. In contrast with the conventional leakage path, the leakage current flows along the interfacial surface of the channel rather than a path underneath the channel.
Shock and release wave speed of an alumina epoxy composite
Authors: Neel Christopher , Thadhani Naresh
Published: August 2009

A filled epoxy with 43% by volume of disk-shaped Al2O3 particles is used to investigate the effect of high-aspect ratio (4:1) particle shape on composite shock and release response. Stress profiles are recorded during a symmetric impact experiment performed at an impact velocity of 569 m/s. The shock and release velocities are respectively observed to be 3511 and 5685 m/s, which agrees with data previously reported, indicating that particle shape has no effect on the Hugoniot or the isentrope. However, the high-aspect ratio particles are found to increase the acoustic wave speeds, especially in shear, and also to increase shock wave dispersion, as indicated by the measured rise time of the stress profile.
Structures and magnetic properties of p-type Mn:TiO2 dilute magnetic semiconductor thin films
Authors: Li Xinyu , Wu Shuxiang , Hu Ping , Xing Xiangjun , Liu Yajing , Yu Yunpeng , Yang Mei , Lu Jingquan , Li Shuwei , Liu Wen
Published: August 2009

The behavior of p-type conductivity in Mn-doped TiO2 films grown on LaAlO3 substrates by plasma-assisted molecular beam epitaxy has been investigated. Raman scattering, x-ray photoelectron spectroscopy, and x-ray diffraction studies indicate that the films are single phase, and Mn is successfully doped into the TiO2 matrix. Semiconducting behavior with p-type carriers was confirmed by Hall-effect measurements. The structural and electrical investigations demonstrate that the ferromagnetism observed at room temperature is an intrinsic property of the Mn:TiO2 films, and does not originate from any secondary phase. The magnetic properties of Ti1−xMnxO2 might be related to the formation of acceptor bound magnetic polarons, in which the spins of the holes and manganese are aligned via exchange interaction.
Thermally activated domain wall depinning in thin strips with high perpendicular magnetocrystalline anisotropy
Authors: Martinez E. , Lopez-Diaz L. , Alejos O. , Torres L.
Published: August 2009

A theoretical analysis on domain wall dynamics along thin ferromagnetic strips with high perpendicular magnetocrystalline anisotropy driven by both magnetic fields and spin-polarized currents is reported. The domain wall depinning from a constriction is characterized both at zero and at room temperature for different values of the nonadiabatic parameter. The results indicate that engineering of pinning sites in thin strips of high perpendicular anisotropy provides an efficient pathway to achieve both high stability against thermal fluctuations and low current-induced domain wall depinning and, therefore, it can find application on designing memory devices driven by static currents.
PbTe and SnTe quantum dot precipitates in a CdTe matrix fabricated by ion implantation
Authors: Kaufmann E. , Schwarzl T. , Groiss H. , Hesser G. , Schäffler F. , Palmetshofer L. , Springholz G. , Heiss W.
Published: August 2009

We present rock-salt IV-VI semiconductor quantum dots fabricated by implantation of Pb+, Te+, or Sn+ ions into epitaxial zinc-blende CdTe layers. PbTe and SnTe nanoprecipitates of high structural quality are formed after implantation by thermal annealing due to the immiscibility of dot and matrix materials. For samples implanted only with Pb+, intense continuous-wave photoluminescence peaked at 1.6 μm at 300 K is found. In contrast, for PbTe quantum dots fabricated by coimplantation of Pb+ and Te+, the 300 K emission peak is observed at 2.9 μm, indicating luminescence from much larger dots.
Surface deformation of Ar+ ion collision process via molecular dynamics simulation with comparison to experiment
Authors: Satake Shin-ichi , Momota Sadao , Yamashina Shun , Shibahara Masahiko , Taniguchi Jun
Published: August 2009

Molecular dynamics simulations of Ar ion collision on a Si surface using an optimized potential function were carried out in the case of the acceleration voltages of 50keV for Ar ions. A hillock structure was formed by the Ar ion impact on the Si surface. The height of the structure calculated by the simulations corresponded to those of the experiments. The height of the structure was found to be proportional to the fluence of Ar ions. The amorphous structural region was expanded by the progress of the interface region between the amorphous structure and the crystalline structure with increasing the fluence in the depth direction.
Magnetic properties of sonochemically synthesized CoCr2O4 nanoparticles
Authors: Dutta Dimple P. , Manjanna J. , Tyagi A. K.
Published: August 2009

Cobalt chromite (CoCr2O4) is a potential multiferroic material. In order to understand the temperature dependent magnetic transitions on particle morphology, here we prepared CoCr2O4 nanoparticles by sonochemical technique. We used powder x-ray diffraction, transmission electron microscopy, selected area electron diffraction, superconducting quantum interference device magnetometer, and ac susceptibility measurement techniques for characterization. The low-temperature magnetic behavior of CoCr2O4 nanoparticles have been investigated in more detail. While the bulk CoCr2O4 exhibits two magnetic transitions viz., Tc≈98 K and Ts≈26 K, the nanoparticles here showed a Tc≈84 K and Ts≈25 K. We tentatively attribute this shift in Tc to finite size effects.
Electric-field effects on Fano resonances and transmission phase through quantum wires
Authors: Vargiamidis Vassilios , Fessatidis Vassilios , Horing Norman J. M.
Published: August 2009

The effect of a transverse electric field on Fano line shapes in electronic transport through a quantum wire is investigated via a Feshbach three-channel model. The coupling between channels is provided by an attractive short-range scatterer with lateral extent. It is shown that the resonance structure in a particular subband is sensitive on the electric field strength and direction. In particular, collapse of a Fano profile either in the first or the second subband may occur, depending on whether the electric field points in the negative or positive direction, respectively. This is due to the vanishing coupling between the bound states and the conduction ones which, in turn, is a consequence of the electric field-induced shift of the confining potential. This tunability of Fano resonances may prove experimentally useful in ballistic transport through narrow channels. The results in the first subband are compared with those obtained from a two-channel model. A detailed account of the transmission phase is also given, and the abrupt phase shift by π is shown to occur whenever the energy of the transmitted electron crosses the energy of the transmission zero.
Stability of the valence anion of cytosine is governed by nucleobases sequence in the double stranded DNA π-stack: A computational study
Authors: Kobyłecka Monika , Leszczynski Jerzy , Rak Janusz
Published: August 2009

The stabilities of the valence anion of cytosine (C−) in model trimers of complementary base pairs that possess the B-DNA geometry but differ in base sequence are reported. In order to estimate the energetics of electron attachment to the middle cytosine incorporated in the trimer, a thermodynamic cycle employing all possible two-body interaction energies in the neutral and anionic duplex as well as the adiabatic electron affinity of isolated cytosine were developed. All calculations were carried out at the MP2 level of theory with the aug-cc-pVDZ basis set. We have demonstrated that contrary to the literature reports, concerning single stranded DNA, the sequence of nucleic bases has a profound effect on the stability of the cytosine valence anion. The anionic 3′-CCC-5′ complex is the most stable configuration (EA=0.399 eV) and the 3′-GCG-5′ trimer anion is the most unstable species (EA=−0.193 eV). Moreover, with the energetic correction for the presence of sugar-phosphate backbone all possible double stranded DNA sequences lead to the stable C−. The predicted electron affinities of the cytosine anion have been compared to the results of analogous studies on the thymine anion published recently [M. Kobyłecka et al., J. Am. Chem. Soc. 130, 15683 (2008)]. The consequences of low-energy barrier proton transfer in the GC anion have been discussed in the context of induced by electrons DNA single strand breaks. The DNA sequences that should dramatically differ in their vulnerability to be damaged by low energy electrons have been proposed.
Raman spectra of GexAsySe1−x−y glasses
Authors: Wang R. P. , Smith A. , Prasad A. , Choi D. Y. , Luther-Davies B.
Published: August 2009

Various Ge–As–Se glasses spanning a mean coordination number (MCN) from 2.2 to 2.94 have been investigated using differential scanning calorimetry and Raman spectroscopy. The glass transition temperature Tg was found to increase with increasing MCN, except for those glasses located within the nanoscale phase-separated region of the phase diagram. The evolution of Raman features at wavenumbers from 150 to 350 cm−1 exhibits two transitionlike features. Merging of the 225 and 250 cm−1 modes at MCN=2.5 is a symbol of the extinction of Se–Se bonds. Additionally, the appearance of two modes at 280–290 and 170 cm−1 at MCN>2.7 come from the defect modes of ethanelike Ge2Se6/2. The increase in the scattering from these defects is an important factor leading to enhanced optical loss in the glasses with high MCN.
Effects of surface alloying and orientation on work function of MoTa metal gate
Authors: Xu Guigui , Wu Qingyun , Chen Zhigao , Huang Zhigao , Feng Yuan Ping
Published: August 2009

Work functions of sub- and monolayers Mo on metal Ta of various orientations are investigated using first-principles methods based on density functional theory. The calculated results reveal that the work function has strongly orientation dependence. However, for a given surface orientation, the work function is insensitive to distributions of Ta/Mo atoms in the surface layer. Moreover, it is found that work functions of the (100) and (111) surfaces increase with increasing Mo composition in the surface layer but those of the (110) decrease. By analysis of surface dipole density, it is found that the metal work function is mainly determined by surface orientation and surface charge redistribution.
The effect of Nd substitution on the electrical properties of Bi3NbTiO9 Aurivillius phase ceramics
Authors: Zhang Hongtao , Yan Haixue , Reece Michael J.
Published: August 2009

The effect of Nd substitution on the microstructures and electrical properties of Aurivillius phase ferroelectric Bi3NbTiO9-based ceramics has been studied. All of the Bi3−xNdxNbTiO9 (0≤x≤1) ceramics are ferroelectrics. The Curie point TC decreased with increasing Nd doping content x. The Bi3−xNdxNbTiO9 ceramics exhibited a sharp ferroelectric-paraelectric phase transition at small x values (x≤0.6), whereas a diffuse phase transition was observed at higher x values (x≥0.8). Both the piezoelectric constant d33 and the dc electrical resistivity of Bi3NbTiO9 ceramics were greatly enhanced by Nd substitution on the A sites. The improved properties can be attributed to the fact that Nd substitution depressed the generation of oxygen vacancies. A combination of high d33 values, high resistivity, and high TC points (>700 °C) suggests that the Bi3−xNdxNbTiO9 ceramics with x≤0.6 could be good candidates for high-temperature piezoelectric applications.
Viscous nonpolar liquids in confinement studied by mechanical solvation
Authors: Wen Wen , Richert Ranko
Published: August 2009

Using surface selective triplet state solvation techniques, we study the relaxation behavior of nonpolar liquids near their glass transition in confinement to porous glass with 4 nm pore diameter. As specific liquid-surface interactions are not expected for alkanes, we ask whether a substantial frustration of the dynamics is a general phenomenon for such liquids, and how the effects change with surface silanization. We find that interfacial dynamics display relaxation times that are increased by orders of magnitude for several nonpolar molecular liquids. Silanization removes this frustration effect almost entirely. Regarding the comparison of native versus silanized pore surfaces, it is concluded that the strong adhesive forces involved in alkanes wetting silica can explain the sluggish interfacial dynamics. The findings are not consistent with finite size effects.
Partition function of the eight-vertex model with domain wall boundary condition
Authors: Yang Wen-Li , Zhang Yao-Zhong
Published: August 2009

We derive the recursive relations of the partition function for the eight-vertex model on an N×N square lattice with domain wall boundary condition. Solving the recursive relations, we obtain the explicit expression of the domain wall partition function of the model. In the trigonometric/rational limit, our results recover the corresponding ones for the six-vertex model.
Counter-rotating coupled drift-acoustic vortices in the presence of sheared ion flows in electron-ion quantum magnetoplasmas
Authors: Masood W. , Mirza Shahid M. , Mirza Arshad M.
Published: August 2009

Nonlinear equations governing the dynamics of finite amplitude drift acoustic waves are derived by taking into account sheared ion flow perpendicular to the ambient magnetic field in a quantum magnetoplasma comprising of ions and electrons. It is shown that stationary solution of the nonlinear equations can be represented in the form of a counter-rotating vortex for a particular choice of the equilibrium profile. The counter-rotating vortices are, however, observed to form on very short scales, i.e., of the order of ion Larmor radius ρi in quantum plasmas. The relevance of the present investigation with regard to dense astrophysical environments is also pointed out.
Free alignment defect, low driving voltage of half-V ferroelectric liquid crystal device
Authors: Chen Huang-Ming P. , Lin Chi-Wen
Published: August 2009

The horizontal chevron alignment defect in half-V mode ferroelectric liquid crystal (FLC) cell can be reduced by asymmetrical alignment hybrid cell. The low free energy level generated from the interaction between spontaneous polarization and opposite polar alignment surfaces was found. As a result, uniformly aligned FLC cell can be achieved without applied external voltage. The R3206 FLC material is applied as model compound. The contrast ratio of R3206–70 is greatly enhanced from 76 to 780 with 1.0 ms response time under 5 V.
Overcoming gain-bandwidth product constraint in slow light Raman amplification with the use of light-stopping schemes
Authors: Sandhu Sunil , Povinelli Michelle L. , Fan Shanhui
Published: August 2009

We show that a light-stopping system with Raman amplification can overcome the gain-bandwidth constraint of slow light Raman amplification systems. The gain scales linearly with the time the pulse spends in the stopped state and is thus much larger than the gain experienced in a slow light system of the same length and operating bandwidth. We present a theoretical analysis of Raman amplification in such a light-stopping system and verify the results using numerical simulations.
N
2
band oscillator strengths at near-threshold energies
Authors: Huber Klaus P. , Chan Man-Chor , Stark Glenn , Ito Kenji , Matsui Takashi
Published: August 2009

Band oscillator strengths for 58 bands in the near-threshold region of N2, i.e., from 116 200 to 125 400 cm−1, are derived from measured band-integrated optical depths. The complexity of the absorption spectrum demands that the measurements be carried out on rotationally cold supersonic jet expansions. The column density N in the absorbing path of the jet cannot be measured directly. Instead, the room temperature f values of selected calibration bands are used to convert the band-integrated optical depths of the jet-cooled calibration bands to preliminary column densities [N], which, plotted as a function of jet reservoir pressure p, scatter around a straight line passing through the origin of the graph. From the slope of the line, first estimates of the effective column density N can be derived for any value of p. Second estimates are obtained by repeating the same procedure using ab initio calculated f values based on the work of Spelsberg and Meyer [J. Chem. Phys. 115, 6438 (2001)]. Depending on the jet configuration, the two estimates differ by 3%–15%; their average is accepted as the best approximation to N. The derived band oscillator strengths are compatible with ab initio results of Spelsberg and Meyer and reproduce the observations reasonably well, even where two or more transitions combine in the formation of complex band structures. They also clarify the analysis of the absorption spectrum in the region of the 7p(0) complex [Jungen, Huber, Jungen, and Stark, J. Chem. Phys. 118, 4517 (2003)] and lead to a plausible interpretation of the spectrum in the 124 680−124 880 cm−1 range. As a result, the lowest three vibronic levels of both the 3′d′σ and the 4′s′σ core excited states have now been identified.
Electrical properties of ZnO–BaTiO3–ZnO heterostructures with asymmetric interface charge distribution
Authors: Voora V. M. , Hofmann T. , Brandt M. , Lorenz M. , Ashkenov N. , Grundmann M. , Schubert M.
Published: August 2009

We report on capacitance-voltage, current-voltage, Sawyer–Tower, and transient current switching measurements for a ZnO–BaTiO3–ZnO heterostructure deposited on (001) silicon by using pulsed laser deposition. The triple-layer structure reveals asymmetric capacitance- and current-voltage hysteresis and cycling-voltage dependent Sawyer–Tower polarization drift. We explain our findings by coupling of the ferroelectric (BaTiO3) and piezoelectric (ZnO) interface charges and parallel polarization orientation of the ZnO layers causing asymmetric space charge region formation under positive and negative bias. The transient current characteristics suggest use of this structure as nonvolatile memory device.
Photocurrent generation in random networks of multiwall-carbon-nanotubes grown by an “all-laser” process
Authors: El Khakani M. A. , Le Borgne V. , Aïssa B. , Rosei F. , Scilletta C. , Speiser E. , Scarselli M. , Castrucci P. , De Crescenzi M.
Published: August 2009

We report photocurrent generation in entangled networks of multiwall-carbon nanotubes (MWCNTs) grown on TiN/Si substrates by an all-laser process. By integrating these MWCNTs into planar devices, we demonstrate that they generate photocurrent over all the visible and near-ultraviolet range, with maximum efficiency around 420 nm. Photocurrent is obtained even at zero applied voltage, pointing to a true photovoltaic (PV) effect. The extracted photocurrent as a function of applied voltage exhibits nonlinear behavior for voltages ≥2 V, suggesting that the devices do not behave as pure photoresistances. Other mechanisms (e.g., Schottky barriers imbalance) are invoked to describe current flow in these PV devices.