bluuebunny/crossref_metadata_2025 huggingface dataset:
Water-induced ethanol dewetting transition
Authors: Ren Xiuping , Zhou Bo , Wang Chunlei
Published: July 2012

The dewetting transitions of two hydrophobic plates immersed in pure water, aqueous ethanol solutions with concentrations from 25% to 90%, and pure ethanol were investigated by molecular dynamics simulations, where the dewetting transition was analogous to a first-order phase transition from liquid to vapor. It was found that the dewetting transitions occurred except that in the pure ethanol system. Although the ethanol molecules prefer to locate in the vicinity of the two plates, the inter-plate region is unfavorable for water molecules, due to losing more than one hydrogen bond. Moreover, each inter-plate water molecule forms hydrogen bonds on average with about two ethanol molecules. These intermolecular hydrogen bonds cause water and ethanol to cooperatively fill or exit the inter-plate region. Thus, water molecules play a more important role in the inter-plate filling/empty process, and induce the ethanol dewetting transition. Our results provide insight into the effect of water on the ethanol dewetting phenomena.
Directional whispering gallery mode emission from Limaçon-shaped electrically pumped quantum dot micropillar lasers
Authors: Albert F. , Hopfmann C. , Eberspächer A. , Arnold F. , Emmerling M. , Schneider C. , Höfling S. , Forchel A. , Kamp M. , Wiersig J. , Reitzenstein S.
Published: July 2012

We experimentally demonstrate directional far field emission from whispering gallery modes (WGMs) in electrically driven quantum dot micropillar lasers. In-plane directionality of whispering gallery mode emission is obtained by patterning micropillars with Limaçon-shaped cross-section and an upper air-bridge contact for current injection. The micropillar lasers with radii R0 down to 4.5 μm show Q-factors of 40 000 and threshold currents of 40 μA at low temperature. We achieved a far field divergence of about 30° and a directionality of 1.67 ± 0.15 for an optimal Limaçon deformation factor ɛ ≈ 0.5. Parameter dependent studies of the directional emission as a function of ɛ reveal good qualitative agreement with theoretical predictions.
Microwave Doppler reflectometer system in LHD
Authors: Tokuzawa T. , Ejiri A. , Kawahata K. , Tanaka K. , Yamada I. , Yoshinuma M. , Ida K. , Suzuki C.
Published: July 2012

In order to measure the poloidal rotation velocity, a Doppler reflectometer has been developed in Large Helical Device (LHD). A remotely controlled antenna tilting system has been installed in an LHD vacuum vessel. A synthesizer is used as the source, and the operation microwave frequency ranges are ka-band and V-band. In LHD last experimental campaign we obtained the Doppler shifted signal, which was consistent with CXRS measurements.
Demonstration of laser induced magnetization reversal in GdFeCo nanostructures
Authors: Le Guyader L. , El Moussaoui S. , Buzzi M. , Chopdekar R. V. , Heyderman L. J. , Tsukamoto A. , Itoh A. , Kirilyuk A. , Rasing Th. , Kimel A. V. , Nolting F.
Published: July 2012

Magnetization switching by a single femtosecond laser heat pulse is demonstrated for out-of-plane domains with sizes down to 200 nm in GdFeCo nanostructures. A complex magnetic domain configuration was revealed with a photoemission electron microscope employing x-ray magnetic circular dichroism at the Fe L3 edge and consisted of in-plane magnetized rims and out-of-plane domains, which results from the structuring process. No influence of this complex domain pattern on the switching efficiency of the structures was detected, constituting an important step towards the application of laser induced magnetization switching in storage devices.
Oscillator strengths between low-lying ro-vibrational states of hydrogen molecular ions
Authors: Tian Quan-Long , Tang Li-Yan , Zhong Zhen-Xiang , Yan Zong-Chao , Shi Ting-Yun
Published: July 2012

It is important for experimental design to know the transition oscillator strengths in hydrogen molecular ions. In this work, for HD+, HT+, and DT+, we calculate the ro-vibrational energies and oscillator strengths of dipole transitions between two ro-vibrational states with the vibrational quantum number ν = 0−5 and the total angular momentum L = 0−5. The oscillator strengths of HT+ and DT+ are presented as supplementary material.
Four-domain twisted nematic structure with enhanced liquid crystal alignment stability and fast response time
Authors: Moon Yeon-Kyu , Lee You-Jin , Yu Chang-Jae , Uk Heo Jeong , Park Jae-Hong , jin Lee Hyeok , Tae Shin Sung , Kim Jae-Hoon
Published: July 2012

In this paper, we propose a stable four-domain twisted nematic structure with wide viewing angle characteristics and a fast response time. A stable structure was realized by introducing a high pre-tilt angle approach incorporating stacked planar and vertical alignment layers. The response time and thermal stability of the proposed device were dramatically improved by the addition of UV-curable reactive mesogen (RM) mixed with a vertical alignment material. Polymerized RMs along the liquid crystal (LC) director increased the polar anchoring energy and reduced back-flow phenomena. A wide viewing angle and fast response time characteristics were achieved over all gray levels.
Effect of Y-doping on the electrical transport properties of nanocrystalline BiFeO3
Authors: Mukherjee A. , Basu S. , Chakraborty G. , Pal M.
Published: July 2012

Effect of yttrium doping on the electrical transport properties of sol-gel prepare nanocrystalline BiFeO3 was investigated. A comprehensive state-of-the art sophisticated instruments like x-ray diffraction, differential thermal analyzer, field emission scanning electron microscope, and HRTEM were utilized to characterize the BiFeO3 nanoparticles. It was observed that the values of dc activation energy calculated from Arrhenius relation increase with increase of yttrium content. The variation of ac conductivity with frequency and temperature exhibits a correlated barrier hopping conduction mechanism. The dielectric permittivity of the sample reveals an increasing tendency with the concentration of yttrium and depends on both the grain and the interfacial grain boundary resistance. The activation energies for the dielectric relaxation estimated from the modulus spectra were found to be reasonably good agreement with those obtained from dc conductivity study.
Effect of quenched size polydispersity on the ordering transitions of hard polyhedral particles
Authors: Agarwal Umang , Escobedo Fernando A.
Published: July 2012

Monodisperse polyhedral nanocrystals with Oh (octahedral) symmetry self-assemble into various mesophases and crystal structures at intermediate and high concentrations. In this work, the effect of quenched size polydispersity on phase and jamming behavior has been studied via molecular simulations for three representative Oh polyhedral shapes; namely, cubes, cuboctahedrons, and truncated octahedrons. Polydispersity is set by the standard deviation “δ” of an underlying Gaussian distribution of particle sizes, and is “quenched” in that it is fixed in a given uniphase sample. Quenched polydisperse states are relevant to: (i) equilibrium behavior for small enough δ when phase segregation does not occur, and (ii) actual experimental behavior for arbitrary δ when dense states are reached at a rate faster than the relaxation of slow diffusion-driven fractionation modes. Space-filling polyhedrons (cubes and truncated octahedrons) are found to be more robust with respect to the nucleation of orientational and translational order at high polydispersities compared to the non-space-filling cuboctahedron, with the former shapes exhibiting an onset of jamming behavior at a critical polydispersity δt that is about twice larger than that for the latter (δt ≈ 0.08). Further, the orientational ordering in cubes is found to be highly resilient to polydispersity, leading to the formation of a dense, orientationally aligned, and translationally jammed state. Overall, increasing size polydispersity enhances the range of pressures where the mesophases occur.
Optimal rates of decay in 2-d thermoelasticity with second sound
Authors: Fernández Sare Hugo D. , Muñoz Rivera Jaime E.
Published: July 2012

We consider a linear thermoelastic plate system where the heat flux is given by Cattaneo's model. We show that the resulting system is exponentially stable if and only if the rotational inertia coefficient μ is positive. On the other hand, for μ = 0, we establish polynomial stability results giving optimal rates of decay for initial data in the domain of the infinitesimal generator of the thermoelastic semigroup.
Magnetic field effect in fluorescence of excited fluorophore equilibrated with exciplex that reversibly dissociates into radical-ion pair undergoing the spin conversion
Authors: Dodin Dmitry V. , Ivanov Anatoly I. , Burshtein Anatoly I.
Published: July 2012

The fluorescence of the photoexcited electron acceptor, 1A*, and the exciplex, 1[D+δA−δ] formed at contact of 1A* with an electron donor 1D, is known to be very sensitive to a magnetic field, assisting the spin conversion in the resulting geminate radical ion pair (RIP), 1, 3[D+…A−]. The relative increase of the fluorescence in the highest magnetic field compared to the lowest one, known as the magnetic field effect, crucially depends on the dielectric constant of the solvent, ɛ. This phenomenon first studied experimentally is at first reproduced here theoretically by means of the so called integral encounter theory. It was shown to be very sensitive to the position of the exciplex energy level relative to the levels of exciplex precursors and the charged products of its dissociation. The results obtained strongly depend on the dielectric properties of the solvents as well as on the exciplex and RIP formation rates.
Communication: Rate coefficients from quasiclassical trajectory calculations from the reverse reaction: The Mu + H2 reaction re-visited
Authors: Homayoon Zahra , Jambrina Pablo G. , Aoiz F. Javier , Bowman Joel M.
Published: July 2012

In a previous paper [P. G. Jambrina et al., J. Chem. Phys. 135, 034310 (2011)10.1063/1.3611400] various calculations of the rate coefficient for the Mu + H2 → MuH + H reaction were presented and compared to experiment. The widely used standard quasiclassical trajectory (QCT) method was shown to overestimate the rate coefficients by several orders of magnitude over the temperature range 200–1000 K. This was attributed to a major failure of that method to describe the correct threshold for the reaction owing to the large difference in zero-point energies (ZPE) of the reactant H2 and product MuH (∼0.32 eV). In this Communication we show that by performing standard QCT calculations for the reverse reaction and then applying detailed balance, the resulting rate coefficient is in very good agreement with the other computational results that respect the ZPE, (as well as with the experiment) but which are more demanding computationally.
Bonding and diffusion of nitrogen in the InSbN alloys fabricated by two-step ion implantation
Authors: Wang Y. , Zhang D. H. , Chen X. Z. , Jin Y. J. , Li J. H. , Liu C. J. , Wee A. T. S. , Zhang Sam , Ramam A.
Published: July 2012

We report bonding and diffusion behavior of nitrogen incorporated into InSb wafer by two-step implantation. Three nitrogen-containing regions, i.e., a surface accumulation region, a uniform region, and a tail region, were observed in the samples after post annealing. X-ray photoelectron spectroscopy measurements at different depths reveal that majority of the nitrogen forms In-N bonds in the uniform region but exists as interstitial defects in the tail region. The diffusion coefficients of nitrogen in InSb were obtained by fitting the modified Fick’s law with experimental data and the activation energy of 0.55 ± 0.04 eV extracted confirms the interstitial dominating diffusion of nitrogen in the InSb wafer.
Ga1−xMnxN epitaxial films with high magnetization
Authors: Kunert G. , Dobkowska S. , Li Tian , Reuther H. , Kruse C. , Figge S. , Jakiela R. , Bonanni A. , Grenzer J. , Stefanowicz W. , Borany J. von , Sawicki M. , Dietl T. , Hommel D.
Published: July 2012

We report on the fabrication of pseudomorphic wurtzite Ga1−xMnxN grown on GaN with Mn concentrations up to 10% using molecular beam epitaxy. According to Rutherford backscattering, the Mn ions are mainly at the Ga-substitutional positions, and they are homogeneously distributed according to depth-resolved Auger-electron spectroscopy and secondary-ion mass-spectroscopy measurements. A random Mn distribution is indicated by transmission electron microscopy, and no Mn-rich clusters are present for optimized growth conditions. A linear increase of the c-lattice parameter with increasing Mn concentration is found using x-ray diffraction. The ferromagnetic behavior is confirmed by superconducting quantum-interference measurements showing saturation magnetizations of up to 150 emu/cm3.
Strain induced phase transition in CdSe nanowires: Effect of size and temperature
Authors: Mandal Taraknath
Published: July 2012

Using all-atom molecular dynamics simulation, we have studied the effect of size and temperature on the strain induced phase transition of wurtzite CdSe nanowires. The wurtzite structure transforms into a five-fold coordinated structure under uniaxial strain along the c axis. Our results show that lower temperature and smaller size of the nanowires stabilize the five-fold coordinated phase which is not a stable structure in bulk CdSe. High reversibility of this transformation with a very small heat loss will make these nanowires suitable for building efficient nanodevices.
Asymmetric Fano resonance in eye-like microring system
Authors: Qiu Chen , Yu Ping , Hu Ting , Wang Fan , Jiang Xiaoqing , Yang Jianyi
Published: July 2012

In this paper, the Fano resonance in the “eye-like” microring resonator system (EMRS) is theoretically and experimentally investigated. The asymmetric Fano-resonance line shape of EMRS is generated by adding a microring inside and coupling with the outer ring to produce a nonlinear phase shift. The EMRS was fabricated on silicon-on-insulator wafer by the complementary metal-oxide-semiconductor compatible process. Compared to the conventional single-stage microring add-drop filter structure, the maximum sharpness of the transmission of the drop port is enhanced 3 times, and the drop port extinction ratio is increased by about 20 dB. The experimental results are in good agreement with the theoretical analysis.
Enhanced electrical and dielectric properties of polymer covered silicon nanowire arrays
Authors: Rasool Kamran , Rafiq M. A. , Li C. B. , Krali E. , Durrani Z. A. K. , Hasan M. M.
Published: July 2012

We investigate DC and AC electrical characteristics of ∼40 μm long p-type silicon nanowire (SiNW) arrays, prepared by metal assisted chemical etching and filled with polyacrylic acid (PAA). PAA diluted to different concentrations with deionized (DI) water is incorporated into the arrays in three steps, yielding polymer filling to the bottom of the arrays. DC and AC electrical measurements show that PAA reduces the array resistance. The AC conductivity increases up to ∼1000 times, and the real part of the overall dielectric constant (ɛ′) by ∼100. We attribute these effects to the formation of acceptor-like states at nanowire/polymer interface.
Pressure effects on the magnetic properties of FeCuZr studied by x-ray magnetic circular dichroism: Evidence of weakening of ferromagnetism in FeCuZr alloys
Authors: Martínez A. , Romero J. J. , Bartolomé F. , García L. M. , Baudelet F. , Hernando A. , Crespo P.
Published: July 2012

The room temperature changes of the magnetic behavior under pressure of an invar alloy of nominal composition (Fe0.5Cu0.5)87Zr13 (at. %) has been studied by K-edge x-ray magnetic circular dichroism (XMCD) and x-ray absorption near edge spectroscopy (XANES). The Curie temperature, as determined from low field magnetization measurements, is (255 ± 15)K. However XMCD shows a non negligible signal above this temperature. In addition, the XMCD signal decreases upon increasing pressure indicating a pressure-induced collapse of the magnetic moment. These results evidence the itinerant character of FeCuZr alloys as well as the occurrence of magnetovolume effects characterized by a strong dependence of the 3d band on the Fe-Fe nearest neighbor distances.
Adsorption of silicon on Au(110): An ordered two dimensional surface alloy
Authors: Enriquez Hanna , Mayne Andrew , Kara Abdelkader , Vizzini Sébastien , Roth Silvan , Lalmi Boubekeur , Seitsonen Ari P , Aufray Bernard , Greber Thomas , Belkhou Rachid , Dujardin Gérald , Oughaddou Hamid
Published: July 2012

We report on experimental evidence for the formation of a two dimensional Si/Au(110) surface alloy. In this study, we have used a combination of scanning tunneling microscopy, low energy electron diffraction, Auger electron spectroscopy, and ab initio calculations based on density functional theory. A highly ordered and stable Si-Au surface alloy is observed subsequent to growth of a sub-monolayer of silicon on an Au(110) substrate kept above the eutectic temperature.
Performance improvement in nanoparticle-assisted stimulated-emission-depletion nanoscopy
Authors: Sivan Yonatan
Published: July 2012

We revisit stimulated-emission-depletion (STED) nanoscopy theory for the case when metal nanoparticles are used to improve the nanoscope’s performance. We show that the improved performance can be estimated in a simple way with no need for heavy computations. We then systematically study the dependence of the improved performance on the field and decay rate enhancements, as well as on the STED pulse and time-gating durations.
The transient behavior of Peltier junctions pulsed with supercooling
Authors: Mao J. N. , Chen H. X. , Jia H. , Qian X. L.
Published: July 2012

There exists the transient thermoelectric supercooling effect that can be enhanced by keeping on increasing the Peltier cooling effect to compensate for the Joule heating effect and Fourier heat conduction effect arriving at the cold junction, in which a transient cold spike can be produced by superimposing an additional shaped current pulse of a large magnitude on the original steady-state optimum value. Most previous work on the transient supercooling mainly focused on the minimum supercooling temperature achievable and separately analyzed the beneficial or detrimental effects on the transient supercooling performance, which was not clarified quantitatively to what extent the interactional effects were on the enhancement of the transient supercooling performance. In this work, we systematically investigate a numerical solution involving time-dependent imposed voltage pulse and time-dependent thermal boundary conditions on the transient supercooling behavior as well as the response of characteristic time and cold-junction temperature distribution to the pulse operation parameters during the periods of pulse start-up, pulse-on time, and pulse-off time, which is served as a theoretical basis for exploiting the coupling interaction of the thermoelectric effects on the heat diffusion from or to the cold junction interrelated with the amount of the availably electrical conversion in the short time scale. Additionally, the advantage of certain pulse forms over others is described. The results indicate that Peltier supercooling capacity shows a decreasing monotonic trend in proportion to the total amount of electrical conversion, and the maximum coefficient of performance for cooling state is about 0.5 to be achieved at steady state. Taking advantage of the temporary Peltier effect focused electrical conversion as the additional cooling for a period long enough against the earlier arrival of the excessively Joule heating dominated heat accumulation is the key parameter for the significant level of thermal enhancement on the pulse supercooling. The discussions may be attractive for compact thermal system coupled with pulsed Peltier supercooling to come up to the localized cooling level of high power packaging.
First-order light-induced orientation transition in nematic liquid crystal in the presence of low-frequency electric field
Authors: Budagovsky I. A. , Pavlov D. S. , Shvetsov S. A. , Smayev M. P. , Zolot’ko A. S. , Boiko N. I. , Barnik M. I.
Published: July 2012

Director deformation in a planar nematic liquid crystal (NLC) with negative optical nonlinearity (director rotates away from the light field) has been studied. First-order orientation transition and a wide hysteresis loop were observed at changing the light intensity in the presence of an ac field that is non-perpendicular to the undistorted director of liquid crystal due to pretilt. The theory of light beam interaction with NLC under ac field was constructed.
Strength and equation of state of fluorite phase CeO2 under high pressure
Authors: Liu Lei , Song Hong X. , Wang Zhigang , Geng Hua Y. , Jing Qiumin , Zhang Yi , Liu Shenggang , Xiang Shikai , Bi Yan , Xu Jian , Li Yanchun , Li Xiaodong , Liu Jing
Published: July 2012

Fluorite phase CeO2 is compressed non-hydrostatically up to 27 GPa using a diamond anvil cell until the transition to α-PbCl2 phase occurred. The compressive strength (t) of CeO2 as a function of pressure is determined by the line width analysis of the high pressure angle dispersive x-ray diffraction patterns. The strength of CeO2 increases quickly below 3.30 GPa and reaches a plateau region at high pressures. A procedure combined the line width analysis and the line shift analysis together, based on the non-hydrostatic data to obtain the corresponding lattice parameter under hydrostatic pressures, is proposed and applied to the case of CeO2 sample. The bulk modulus and its pressure derivative of fluorite phase CeO2 (K0 = 235 (18) GPa, K0′ = 3.67) are obtained by fitting the P-V results into Vinet equation of state. A discussion of the pressure dependence of α, which determines the relative weights of the isostress and isostrain conditions across the grain boundary in an actual case, is presented.
Noise and transport characterization of single molecular break junctions with individual molecule
Authors: Sydoruk V. A. , Xiang D. , Vitusevich S. A. , Petrychuk M. V. , Vladyka A. , Zhang Y. , Offenhäusser A. , Kochelap V. A. , Belyaev A. E. , Mayer D.
Published: July 2012

We studied the noise spectra of molecule-free and molecule-containing mechanically controllable break junctions. Both types of junctions revealed typical 1/f noise characteristics at different distances between the contacts with square dependence of current noise power spectral density on current. Additional Lorentzian-shape (1/f2) noise components were recorded only when nanoelectrodes were bridged by individual 1,4-benzenediamine molecule. The characteristic frequency of the revealed 1/f2 noise related to a single bridging molecule correlates with the lock-in current amplitudes. The recorded behavior of Lorentzian-shape noise component as a function of current is interpreted as the manifestation of a dynamic reconfiguration of molecular coupling to the metal electrodes. We propose a phenomenological model that correlates the charge transport via a single molecule with the reconfiguration of its coupling to the metal electrodes. Experimentally obtained results are in good agreement with theoretical ones and indicate that coupling between the molecule metal electrodes is important aspect that should be taken into account.
Plasmon coupling in circular-hole dimers: From separation- to touching-coupling regimes
Authors: Zhang Yong , Han Mei , Huang Cheng-ping
Published: July 2012

The optical properties of a metal film perforated with periodic circular-hole dimers have been studied and the role of plasmon coupling between the dimer holes has been analyzed. For light polarization perpendicular to the dimer axis, the resonance is sensitive to the hole distance, especially when the dimer holes are nearly touching. Depending on whether the holes are touching or not, two coupling regimes have been explored, where different coupling mechanisms and behaviors are involved. In the separation-coupling regime, the coupling of dimer holes is mainly mediated by the surrounding current or magnetic dipoles. Accordingly, the coupling mode blue-shifts with an increase of hole separation. In the touching-coupling regime, instead, the coupling is mainly governed by two apexes, which carry opposite surface charges and behave as electric dipoles. With the increase of hole distance or approaching of two apexes, the mode shifts drastically to the longer wavelength. The hole touching can also set a cutoff for the current near the apexes, thus, producing a strong circulating current (or magnetic field) around (or inside) the dimer holes. Such a strong magnetic field is not present for single circular holes. In addition, for light polarization parallel to the dimer axis, no obvious shifts of the plasmon mode can be observed. The structure may be employed to boost light-matter interactions via the enhanced electric or magnetic fields and filter light with the desired wavelength or polarization.
Atomic packing and short to medium range order in a U-Fe metallic glass
Authors: Zhang Y. , Mattern N. , Liang T. X. , Huang Q. , Eckert J.
Published: July 2012

The atomic structure of the U85.7Fe14.3 metallic glasses is studied in terms of topological short range order, chemical short range order and medium range order using reverse Monte Carlo simulations. The existence of solute-centered clusters and Fe-enriched clusters clearly demonstrates a strong chemical short range order in both glasses. Two major types of medium range order are detected, one is the Fe-enriched super-clusters and the other is the close packing of the solute-centered clusters. Nevertheless, no existing model can be employed to fully describe the medium range order in U-based metallic glasses, indicating the structural complexity of these metallic glasses.
Transmission enhancement of acoustic waves through a thin hard plate embedded with elastic inclusions
Authors: Hao Rui , Qiu Chunyin , Ye Yangtao , Li Chunhui , Jia Han , Ke Manzhu , Liu Zhengyou
Published: July 2012

We study the transmission response of acoustic waves through a water-immersed thin hard plate embedded with elastic inclusions. The transmission spectra show a striking peak at the subwavelength region, whose position is almost irrelevant with the incident angle. Our study states that the transmission enhancement stems from the resonant excitation of the localized bending mode in the inclusion. Different from the well-known Fabry-Perot effect, here the resonant frequency reduces rapidly as the sample is thinned down. The theory is further validated by experiment. Potential applications of the abnormal transmission effect produced by such thin plate structures can be anticipated.
Lifetime imaging of radiative and non-radiative fluorescence decays on nanoplasmonic surface
Authors: Ranjan Gartia Manas , Eichorst John P. , Clegg Robert M. , Logan Liu G.
Published: July 2012

We report the fluorescence lifetime imaging and quantum yield measurement of five different fluorescence dyes spanning different quantum yield and excitation wavelength ranges in solution as well as on irregular nanoplasmonic substrate surface. Due to a distribution of dye molecules at random distances and orientation to the metal nanoplasmonic structure, the dyes showed multi-component lifetime decays on the surface. We have simulated the distribution of lifetime on the surface based on fractional intensity relative to steady-state value and derived an average lifetime with species fraction. From the quantum yield and fluorescence lifetime measurements we calculated the modified radiative and non-radiative decay rates for the dyes due to energy coupling on the substrate. We measured up to 100 fold fluorescence enhancement on nanoplasmonic substrate, and all molecule fluorescence showed not only considerably higher radiative decay rate but also higher non-radiative decay rate.
Ultrafast room temperature wiping-rubbing fabrication of graphene nanosheets as flexible transparent conductive films with high surface stability
Authors: Yu Yan , Jiang Shenglin , Zhou Wenli , Miao Xiangshui , Zeng Yike , Zhang Guangzu , Zhang Yangyang , Zhang Qingfeng , Zhao Han
Published: July 2012

In this letter, we developed an original innovative wiping-rubbing method to fabricate flexible transparent conductive films (TCFs) based on graphene nanosheets. We achieved this by using only commercial graphite block and polycarbonate film as raw materials, through a cost effective and ultrafast room temperature wiping-rubbing process (within 2 min). The properties of our flexible TCFs were competitive when comparing with literature reported graphene TCFs. Our flexible TCFs showed enough surface stability under a series of surface destructive treatments. The physical mechanism aspects of wiping-rubbing processes and surface stability were discussed.
Structural, dynamical, and electronic properties of transition metal-doped Ge2Sb2Te5 phase-change materials simulated by ab initio molecular dynamics
Authors: Skelton J. M. , Lee T. H. , Elliott S. R.
Published: July 2012

Doping has been widely employed as a means to improve the properties of Ge-Sb-Te (GST) phase-change materials for application in digital storage devices. However, there has been little investigation into how these dopants influence the structure and atomic dynamics of the host material. We have performed ab initio molecular-dynamics simulations of the complete phase-change cycle in undoped and Mn/Zn-doped model systems of Ge2Sb2Te5. Our findings shed valuable light on how transition-metal atoms behave within and influence a GST host matrix, and might be used predictively to select future transition metal dopants for tuning the material properties for non-volatile memory applications.
Nanostructured nickel oxide film for application to fish freshness biosensor
Authors: Yadav Surendra K. , Singh Jay , Agrawal Ved Varun , Malhotra B. D.
Published: July 2012

Xanthine oxidase (XOx) has been physisorbed onto nanostructured nickel oxide (n-NiO, ∼41 nm), electrophoretically deposited onto indium-tin-oxide (ITO) glass substrate using poly-ethylene glycol via co-precipitation. The electrochemical response studies of the XOx/n-NiO/ITO bioelectrode show linear response in the xanthine concentration range as 10–200 μM (R2 = 0.9989), sensitivity as 0.6214 μA/μM cm2, detection limit as 2.989 μM, standard deviation as 0.6192 μA, response time of 15 s with the stability of 100 days. The observed low value (0.0306 mM) Michaelis–Menten constant (Km) indicates high affinity of XOx towards xanthine.
Intermolecular hydrogen-bonded organic semiconductors—Quinacridone versus pentacene
Authors: Daniel Głowacki Eric , Leonat Lucia , Irimia-Vladu Mihai , Schwödiauer Reinhard , Ullah Mujeeb , Sitter Helmut , Bauer Siegfried , Serdar Sariciftci Niyazi
Published: July 2012

Quinacridone is a five-ring hydrogen-bonded molecule analogous in structure and size to the well-known organic semiconductor pentacene. Unlike pentacene, quinacridone has limited intramolecular π-conjugation and becomes highly colored in the solid state due to strong intermolecular electronic coupling. We found that quinacridone shows a field-effect mobility of 0.1 cm2/V·s, comparable to mobilities of pentacene in similarly prepared devices. Photoinduced charge generation in single-layer quinacridone metal-insulator-metal diodes is more than a hundred times more efficient than in pentacene devices. Photoinduced charge transfer from quinacridone to C60 is not effective, as evidenced by measurements in heterojunctions with C60. Hydrogen-bonded organic solids may provide new avenues for organic semiconductor design.
Piezoelectrically actuated time-averaged atomic microtraps
Authors: West A. D. , Wade C. G. , Weatherill K. J. , Hughes I. G.
Published: July 2012

We present a scheme for creating tight and adiabatic time-averaged atom-traps through the piezoelectric actuation of nanomagnetic structures. We show that potentials formed by the circular translation of magnetic structures have several advantages over conventional rotating-field techniques, particularly for high trap frequencies. As the magnitude of the actuation is changed, the trapping potential can be changed adiabatically between harmonic 3D confinement and a toroidal trap.
Evidence of temperature dependent domain wall dynamics in hard lead zirconate titanate piezoceramics
Authors: Garcia J. E. , Ochoa D. A. , Gomis V. , Eiras J. A. , Pérez R.
Published: July 2012

This work presents a study of the domain wall dynamics in Pb(Zr1−xTix)O3 (PZT)-based piezoceramics by means of the temperature dependence non-linear dielectric response and hysteresis loop measurements. In soft PZT, non-linear response gradually increases as the temperature is raised. A similar response is displayed by hard PZT at low temperatures. However, rather more complex behavior is detected at temperatures above 200 K. The anomalous response, which is very marked at room temperature, becomes even greater when the electric field is increased. The non-linear dielectric response is analyzed in the framework of the Rayleigh model. The results suggest a clear change in the domain wall dynamics in hard PZT, which is not observed in soft PZT. Observation of the hysteresis loops confirms that a strong effect of domain wall pinning emerges near room temperature. The change in domain wall dynamics appears as the main cause of the dielectric response difference between both kinds of materials at room temperature.
Space charge induced electroluminescence spectra shift in organic light-emitting diodes
Authors: Xiao J. , Zhu H. , Wang X. X. , Gao X. , Yang Z. H. , Zhang X. H. , Wang S. D.
Published: July 2012

The electroluminescence spectra of organic light-emitting diodes can be tuned by controlling the space charge density in the emission layer, and both red and blue shifts in the electroluminescence spectra are realized. The origin of the space charge induced spectra shift is ascribed to the space charge redistribution as response to the dipole moment variation of the organic emitters at excitation and ground states. The space charge density in the emission layer can be controlled by simply designing the device structure and layer configuration, which may have potential for optimizing the color coordinates of organic light-emitting diodes.
Singularities for solutions to Schrödinger equations with asymptotically constant magnetic fields
Authors: Mao Shikuan
Published: July 2012

This paper studies Schrödinger equations with variable coefficients and magnetic potentials. We suppose the perturbation is short-range type in a sense similar to the work of Nakamura [“Wave front set for solutions to Schrödinger equations,” J. Funct. Anal. 256, 1299–1309 (2009)]10.1016/j.jfa.2008.06.007. We characterize the wave front set of the solutions to the equation in terms of the classical scattering data and the propagator of the unperturbed constant magnetic operator.
Intra-jet shocks in two counter-streaming, weakly collisional plasma jets
Authors: Ryutov D. D. , Kugland N. L. , Park H.-S. , Plechaty C. , Remington B. A. , Ross J. S.
Published: July 2012

Counterstreaming laser-generated plasma jets can serve as a test-bed for the studies of a variety of astrophysical phenomena, including collisionless shock waves. In the latter problem, the jet’s parameters have to be chosen in such a way as to make the collisions between the particles of one jet with the particles of the other jet very rare. This can be achieved by making the jet velocities high and the Coulomb cross-sections correspondingly low. On the other hand, the intra-jet collisions for high-Mach-number jets can still be very frequent, as they are determined by the much lower thermal velocities of the particles of each jet. This paper describes some peculiar properties of intra-jet hydrodynamics in such a setting: the steepening of smooth perturbations and shock formation affected by the presence of the “stiff” opposite flow; the role of a rapid electron heating in shock formation; ion heating by the intrajet shock. The latter effect can cause rapid ion heating which is consistent with recent counterstreaming jet experiments by Ross et al. [Phys. Plasmas 19, 056501 (2012)].
Effect of electron density profile on power absorption of high frequency electromagnetic waves in plasma
Authors: Xi Yan-Bin , Liu Yue
Published: July 2012

Considering different typical electron density profiles, a multi slab approximation model is built up to study the power absorption of broadband (0.75–30 GHz) electromagnetic waves in a partially ionized nonuniform magnetized plasma layer. Based on the model, the power absorption spectra for six cases are numerically calculated and analyzed. It is shown that the absorption strongly depends on the electron density fluctuant profile, the background electron number density, and the collision frequency. A potential optimum profile is also analyzed and studied with some particular parameters.
Bare-tether cathodic contact through thermionic emission by low-work-function materials
Authors: Chen Xin , Sanmartín J. R.
Published: July 2012

A new material, C12A7:e- electride, which might present a work function as low as 0.6 eV and moderately high temperature stability, was recently proposed as coating for floating bare tethers. Arising from heating under space operation, current is emitted by thermionic emission along a thus coated cathodic segment. A preliminary study on the space-charge-limited (SCL) double layer in front of the cathodic segment is presented using Langmuir’s SCL electron current between cylindrical electrodes and orbital-motion-limited ion-collection sheath. A detailed calculation of current and bias profiles along the entire tether length is carried out with ohmic effects and the transition from SCL to full Richardson-Dushman emission included. Analysis shows that in the simplest drag mode, under typical orbital and tether conditions, thermionic emission leads to a short cathodic section and may eliminate the need for an active cathodic device and its corresponding gas feed requirements and power subsystem, which results in a truly “propellant-less” tether system for such basic applications as de-orbiting low earth orbit satellites.
Generation of kinetic Alfvén waves by beam-plasma interaction in non-uniform plasma
Authors: Hong M. H. , Lin Y. , Wang X. Y.
Published: July 2012

This work reports a novel mechanism of the generation of kinetic Alfvén waves (KAWs) using a two-dimensional hybrid simulation: the KAWs are generated by ion beam-plasma interaction in a non-uniform plasma boundary layer, in which the bulk velocity of the ion beam is assumed to be parallel to the ambient magnetic field. As a result of the beam-plasma interaction, strong shear Alfvén waves as well as fast mode compressional waves are first generated on the side of the boundary layer with a high density and thus a low Alfvén speed, propagating along the background magnetic field. Later, Alfvén waves also form inside the boundary layer with a continuous spectrum. As the perpendicular wave number k⊥ of these unstably excited waves increases with time, large-amplitude, short wavelength KAWs with k⊥ ≫ k‖ clearly form in the boundary layer. The physics for the generation of KAWs is discussed.
Numerical modeling of plasma plume evolution against ambient background gas in laser blow off experiments
Authors: Patel Bhavesh G. , Das Amita , Kaw Predhiman , Singh Rajesh , Kumar Ajai
Published: July 2012

Two dimensional numerical modelling based on simplified hydrodynamic evolution for an expanding plasma plume (created by laser blow off) against an ambient background gas has been carried out. A comparison with experimental observations shows that these simulations capture most features of the plasma plume expansion. The plume location and other gross features are reproduced as per the experimental observation in quantitative detail. The plume shape evolution and its dependence on the ambient background gas are in good qualitative agreement with the experiment. This suggests that a simplified hydrodynamic expansion model is adequate for the description of plasma plume expansion.
Manipulating spin injection into organic materials through interface engineering
Authors: Yue F. J. , Shi Y. J. , Chen B. B. , Ding H. F. , Zhang F. M. , Wu D.
Published: July 2012

The correlation of spin injection efficiency and interfacial resistance is investigated in La0.67Sr0.33MnO3 (LSMO)/Alq3/Co organic spin-valve devices. When a thin layer of copper phthalocyanine (CuPc) is inserted between LSMO and Alq3, the magnetoresistance (MR) of the device decrease to only ∼0.4% at 50 K, in sharp contrast to ∼6% MR ratio at the same bias voltage for the device without CuPc interlayer. Meanwhile, the electrical resistance decreases by one order of magnitude, indicating that the interface barrier height is reduced. These results reflect that a strong correlation between the significant decrease of spin injection efficiency at LSMO/CuPc interface and the reduced interfacial resistance. The findings indicate that the conductivity mismatch problem is applicable to organic materials and the interfacial resistance has important impact on the spin injection efficiency.
Magnetovoltaic effect in a quantum dot undergoing Jahn-Teller transition
Authors: Bose Shyamalendu M. , Ndengeyintwali Didier , Behera Surjyo N. , Entel Peter
Published: July 2012

A model is proposed to study the electrical transport properties of a quantum dot capable of undergoing a structural phase transition driven by the Jahn-Teller mechanism. The dot attached to two metallic leads is described by the single impurity Anderson model Hamiltonian to which a term describing the Jahn-Teller distortion and another term to include the possibility of the presence of a magnetic field are added. Calculation of the electrical conductance and Jahn-Teller order parameter reveals several interesting features the most striking of which is the new phenomenon of “magnetovoltaic effect.”
Nanostructure Ag dots for improving thermal stability of Ag reflector for GaN-based light-emitting diodes
Authors: Jeon Joon-Woo , Yum Woong-Sun , Oh Semi , Kim Kyoung-Kook , Seong Tae-Yeon
Published: July 2012

We report the improved thermal stability of Ag reflectors for GaN-based light-emitting diodes (LEDs) using Ag nano-dots (∼65–∼190 nm in size). The nano-dot Ag samples show much higher reflectance than the Ag only samples. The annealed nano-dot Ag samples exhibit a smoother surface, where the grains contain numerous micro-twins. 〈111〉 texture becomes more dominantly evolved in the nano-dot Ag samples than in the Ag only samples after annealing. LEDs with the 300 °C-annealed nano-dot Ag reflectors exhibit 15%–36% higher output power (at 20 mA) than LEDs with the 300 and 400 °C-annealed Ag only reflectors.
Network analyzer measurements of spin transfer torques in magnetic tunnel junctions
Authors: Xue Lin , Wang Chen , Cui Yong-Tao , Katine J. A. , Buhrman R. A. , Ralph D. C.
Published: July 2012

We demonstrate a simple network-analyzer technique to make quantitative measurements of the bias dependence of spin torque in a magnetic tunnel junction. We apply a microwave current to exert an oscillating spin torque near the ferromagnetic resonance frequency of the tunnel junction’s free layer. This produces an oscillating resistance that, together with an applied direct current, generates a microwave signal that we measure with the network analyzer. An analysis of the resonant response yields the strength and direction of the spin torque at non-zero bias. We compare to measurements of the spin torque vector by time-domain spin-torque ferromagnetic resonance.
Factors influencing the microwave pulse duration in a klystron-like relativistic backward wave oscillator
Authors: Xiao Renzhen , Zhang Xiaowei , Zhang Ligang , Li Xiaoze , Zhang Lijun
Published: July 2012

In this paper, we analyze the factors that affect the microwave pulse duration in a klystron-like relativistic backward wave oscillator (RBWO), including the diode voltage, the guiding magnetic field, the electron beam collector, the extraction cavity, and the gap between the electron beam and the slow wave structure (SWS). The results show that the microwave pulse duration increases with the diode voltage until breakdown occurs on the surface of the extraction cavity. The pulse duration at low guiding magnetic field is generally 5–10 ns smaller than that at high magnetic field due to the asymmetric electron emission and the larger energy spread of the electron beam. The electron beam collector can affect the microwave pulse duration significantly because of the anode plasma generated by bombardment of the electron beam on the collector surface. The introduction of the extraction cavity only slightly changes the pulse duration. The decrease of the gap between the electron beam and the SWS can increase the microwave pulse duration greatly.
Study of applied magnetic field magnetoplasmadynamic thrusters with particle-in-cell code with Monte Carlo collision. I. Computation methods and physical processes
Authors: Tang Hai-Bin , Cheng Jiao , Liu Chang , York Thomas M.
Published: July 2012

A two-dimensional axisymmetric electromagnetic particle-in-cell code with Monte Carlo collision conditions has been developed for an applied-field magnetoplasmadynamic thruster simulation. This theoretical approach establishes a particle acceleration model to investigate the microscopic and macroscopic characteristics of particles. This new simulation code was used to study the physical processes associated with applied magnetic fields. In this paper (I), detail of the computation procedure and results of predictions of local plasma and field properties are presented. The numerical model was applied to the configuration of a NASA Lewis Research Center 100-kW magnetoplasmadynamic thruster which has well documented experimental results. The applied magnetic field strength was varied from 0 to 0.12 T, and the effects on thrust were calculated as a basis for verification of the theoretical approach. With this confirmation, the changes in the distributions of ion density, velocity, and temperature throughout the acceleration region related to the applied magnetic fields were investigated. Using these results, the effects of applied field on physical processes in the thruster discharge region could be represented in detail, and those results are reported.
Microfluidic impedance spectroscopy as a tool for quantitative biology and biotechnology
Authors: Sabuncu Ahmet C. , Zhuang Jie , Kolb Juergen F. , Beskok Ali
Published: July 2012

A microfluidic device that is able to perform dielectric spectroscopy is developed. The device consists of a measurement chamber that is 250 μm thick and 750 μm in radius. Around 1000 cells fit inside the chamber assuming average quantities for cell radius and volume fraction. This number is about 1000 folds lower than the capacity of conventional fixtures. A T-cell leukemia cell line Jurkat is tested using the microfluidic device. Measurements of deionized water and salt solutions are utilized to determine parasitic effects and geometric capacitance of the device. Physical models, including Maxwell-Wagner mixture and double shell models, are used to derive quantities for sub-cellular units. Clausius-Mossotti factor of Jurkat cells is extracted from the impedance spectrum. Effects of cellular heterogeneity are discussed and parameterized. Jurkat cells are also tested with a time domain reflectometry system for verification of the microfluidic device. Results indicate good agreement of values obtained with both techniques. The device can be used as a unique cell diagnostic tool to yield information on sub-cellular units.