bluuebunny/crossref_metadata_2025 huggingface dataset:
Photo-induced mass transfer in metal nanocluster doped glasses under continuous wave laser irradiation
Authors: Kaganovskii Yu. , Rosenbluh M.
Published: April 2011

Mass transfer accompanying continuous wave optical recording in glasses with embedded silver nanoclusters has been studied using optical microscopy, STEM and AFM. Recording was carried out by two crossed laser beams (514 nm), which created a periodic intensity distribution on the illuminated surface of the glass-silver composites. The quality of the recorded gratings was found to be independent of the light polarization. It was determined that laser irradiation induces two mass transfer processes: diffusion coalescence of nanoclusters and redistribution of silver between illuminated and nonilluminated interference lines. The temperature profile under the illuminated surface has been calculated, as well as the kinetics of the mass redistribution.
Design guideline of high efficiency crystalline Si thin film solar cell with nanohole array textured surface
Authors: Wang Fei , Yu Hongyu , Li Junshuai , Wong Shemein , Sun Xiao Wei , Wang Xincai , Zheng Hongyu
Published: April 2011

Silicon thin film with a nanohole (NH) array textured surface is systematically studied via simulation for solar energy harvesting and compared with a nanopillar (NP) array textured one. It is found that for the same thickness and optimized structure parameters, the NH array shows superior light trapping capability and thus, higher power conversion efficiency than its NP counterpart. The requirement for efficient cells at the optically optimized NH and NP geometries are studied in terms of minority carrier diffusion length, emitter doping level, and the emitter junction depth after considering the impact of surface recombination velocity. The results provide a practical guideline to design and fabricate high efficiency and cost effective NH textured Si thin film solar cells.
Some experimental methods and tricks
Authors: Dolgopolov V. T.
Published: April 2011

A wide range of experimental methods are used in the study of two-dimensional electronic systems. Each of these methods is rather simple by itself and has, in principle, been known for along time. Nevertheless, most of them have not become part of daily practice, partly because of considerable difficulties in their use and partly because they have not become popular enough. This article is a brief review of these potentially useful methods and outlines the areas where they can be used.
Acoustic switching of quantum states in semiconductors
Authors: Averkiev N. S. , Rozhansky I. V. , Tarasenko S. A. , Lifshits M. B.
Published: April 2011

The interaction between solitary elastic strain pulses (acoustic solitons) and localized holes in low-dimensional silicon structures is studied theoretically. It is shown that a soliton propagating through a region of hole localization converts it from one quantum state to another characterized by a different projection of the angular momentum. This effect originates in splitting of the ground hole state, which is degenerate in the absence of a perturbation, by the elastic strain. A detailed microscopic calculation of the acoustic switching of quantum mechanical states is carried out for holes localized at a quantum dot or at a shallow impurity acceptor in a quantum well. It is shown that the acoustic soliton amplitude required for complete reversal of the projected angular momentum of a hole corresponds to the amplitude of typical experimentally produced strain pulses.
Anomalous low-temperature contribution to the heat capacity from hybridized electronic states on transition element impurities
Authors: Okulov V. I. , Lonchakov A. T. , Govorkova T. E. , Okulova K. A. , Podgornykh S. M. , Paranchich L. D. , Paranchich S. Yu.
Published: April 2011

An anomalous nonmonotonic contribution to the temperature dependence of the electron heat capacity of mercury selenide is detected. This is explained in terms of hybridized electronic states on donor impurities. The observed effect is described by a theory of electron heat capacity based on a quantum Fermi-liquid approach including localization and electron-electron interactions. A quantitative interpretation of the experimental dependences yields values for the parameters of the hybridized states that are consistent with those known from other experiments. A new parameter characterizing the electron-electron interaction in the hybridized states is also found.
Temperature-dependent forward gate current transport in atomic-layer-deposited Al2O3/AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor
Authors: Liu Z. H. , Ng G. I. , Arulkumaran S. , Maung Y. K. T. , Zhou H.
Published: April 2011

The mechanisms of the temperature-dependent forward gate current transport in the atomic-layer-deposited Al2O3/AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MISHEMT) were investigated. In contrast to the conventional Schottky-gate AlGaN/GaN HEMT, thermionic field emission was found not to be the dominant transport mechanism for the Al2O3/AlGaN/GaN MISHEMT. Fowler–Nordheim tunneling was found to be dominant at low temperature (T<0 °C) and high electrical filed, whereas trap assistant tunneling was found to be dominant at medium electrical field and high temperature (T>0 °C).
Plasma plume propagation characteristics of pulsed radio frequency plasma jet
Authors: Liu J. H. , Liu X. Y. , Hu K. , Liu D. W. , Lu X. P. , Iza F. , Kong M. G.
Published: April 2011

A 4 cm long helium cold atmospheric pressure plasma jet with pulsed radio frequency (rf) excitation was obtained by a copper electrode inside a quartz tube. The plasma bullet propagation characteristics common to the microseconds direct current pulse and kilohertz plasma jet is not observed in this case. The space-, time-, and wavelength-resolved optical emission profiles suggest the pulsed rf plasma channel out of the tube was strengthened by ions and metastables with longer life time than the rf period, and the plasma propagation was actually an illumination of the plasma channel caused by energetic electrons accelerated along the channel.
A simulation test of the optical Kerr mechanism for laser-induced nucleation
Authors: Knott Brandon C. , Doherty Michael F. , Peters Baron
Published: April 2011

Recent experiments have demonstrated that intense, nanosecond laser pulses can induce crystal nucleation from supersaturated solutions that are transparent at the incident wavelengths, a phenomenon termed nonphotochemical laser-induced nucleation (NPLIN). Previous work has proposed that this effect is due to the alignment of solute molecules in solution due to the electric field of the applied laser light, promoting crystalline order. We have used simulations of NPLIN to examine how an orientational bias in solution affects nucleation with Monte Carlo simulations of a Potts lattice gas model. We examine this effect within both a classical, one-step nucleation framework as well as in the context of two-step nucleation. Our results indicate that an orientational bias can reduce the free energy barrier to nucleation within the one-step picture as well as promote the crystallization of amorphous precritical nuclei (the rate-determining step in the two-step picture). However, these effects are only present with field strengths that are much greater than those used in experiments.
Improved threshold of buried heterostructure InAs/GaInAsP quantum dot lasers
Authors: Franke D. , Moehrle M. , Sigmund A. , Kuenzel H. , Pohl U. W. , Bimberg D.
Published: April 2011

The parameters for reducing the threshold current density of InAs/InGaAsP/InP quantum-dot (QD) lasers suitable for high temperature operation are studied. The structures were grown using metalorganic vapor phase epitaxy. Increasing the number of QD layers leads to a substantial improvement of the optical confinement and a markedly reduced threshold per dot layer in broad area devices. A reduction of the spacer thickness between the QD layers was not found to significantly affect device characteristics. Depending upon the device length, an optimum number of QD layers was deduced. Based upon optimized QD stacks, buried-heterostructure lasers with a medium device length emitting at 1.5 μm were fabricated. Laterally single-mode devices show promising low threshold currents near 10 mA and good thermal stability with a characteristic temperature of 65 K up to 90 °C.
Experimental demonstration of dielectric-loaded plasmonic waveguide disk resonators at telecom wavelengths
Authors: Randhawa Sukanya , Krasavin Alexey V. , Holmgaard Tobias , Renger Jan , Bozhevolnyi Sergey I. , Zayats Anatoly V. , Quidant Romain
Published: April 2011

Dielectric-loaded plasmonic waveguide disk resonators (WDRs) operating at telecom wavelengths are fabricated and investigated. Disks resonators of various radii coupled to a straight waveguide are studied both numerically and experimentally. For each disk radius, the gap between the disk and the waveguide is varied from 0 to 300 nm. Performance of the fabricated WDRs is characterized in the wavelength range of 1500–1620 nm using near-field optical microscopy. Wavelength selectivity and efficiency of the WDRs are evaluated and are in good agreement with numerical results.
Influence of nanowires length on performance of crystalline silicon solar cell
Authors: Li Haofeng , Jia Rui , Chen Chen , Xing Zhao , Ding Wuchang , Meng Yanlong , Wu Deqi , Liu Xinyu , Ye Tianchun
Published: April 2011

Silicon-nanowire (Si-NW) array, prepared by an electroless chemical-etching method, shows excellent optical antireflection property over a wide spectral bandwidth. The influence of the wire length on the optical antireflection property and the solar cell performance were studied for both the Si-NW array solar cells and the planar solar cells. The reflectance of NWs solar cells is almost invariable and much lower than that of the planar solar cells but the performance of planar solar cells is the best. Results show the performance of NWs solar cells is strongly affected by some other factors such as surface passivation and electrode-contact property.
Electronic structures of graphane sheets with foreign atom substitutions
Authors: Wang Yanli , Ding Yi , Shi Siqi , Tang Weihua
Published: April 2011

Using first-principles calculations, we investigate the electronic structures of the recently synthesized hydrogenated graphene, called graphane, with substitutional B, N, P, and Al atoms. We find that both the n-type and p-type substitutions can cause the semiconductor-to-metal transitions in graphane sheets. The substitutional B and Al atoms induce magnetic moments of nearby carbon atoms. Moreover, the B-substituted graphane sheets have the concentration-dependent magnetic properties, while the Al-substituted ones exhibit robust half-metallic behaviors. Our studies demonstrate that the substituted graphane sheets have potential applications in nanoelectronics and spintronics.
Density scaling of the transport properties of molecular and ionic liquids
Authors: López Enriqueta R. , Pensado Alfonso S. , Comuñas María J. P. , Pádua Agílio A. H. , Fernández Josefa , Harris Kenneth R.
Published: April 2011

Casalini and Roland [Phys. Rev. E 69, 062501 (2004); J. Non-Cryst. Solids 353, 3936 (2007)] and other authors have found that both the dielectric relaxation times and the viscosity, η, of liquids can be expressed solely as functions of the group (TV γ), where T is the temperature, V is the molar volume, and γ a state-independent scaling exponent. Here we report scaling exponents γ, for the viscosities of 46 compounds, including 11 ionic liquids. A generalization of this thermodynamic scaling to other transport properties, namely, the self-diffusion coefficients for ionic and molecular liquids and the electrical conductivity for ionic liquids is examined. Scaling exponents, γ, for the electrical conductivities of six ionic liquids for which viscosity data are available, are found to be quite close to those obtained from viscosities. Using the scaling exponents obtained from viscosities it was possible to correlate molar conductivity over broad ranges of temperature and pressure. However, application of the same procedures to the self-diffusion coefficients, D, of six ionic and 13 molecular liquids leads to superpositioning of poorer quality, as the scaling yields different exponents from those obtained with viscosities and, in the case of the ionic liquids, slightly different values for the anion and the cation. This situation can be improved by using the ratio (D/T), consistent with the Stokes–Einstein relation, yielding γ values closer to those of viscosity.
Time-dependent approaches for the calculation of intersystem crossing rates
Authors: Etinski Mihajlo , Tatchen Jörg , Marian Christel M.
Published: April 2011

We present three formulas for calculating intersystem crossing rates in the Condon approximation to the golden rule by means of a time-dependent approach: an expression using the full time correlation function which is exact for harmonic oscillators, a second-order cumulant expansion, and a short-time approximation of this expression. While the exact expression and the cumulant expansion require numerical integration of the time correlation function, the integration of the short-time expansion can be performed analytically. To ensure convergence in the presence of large oscillations of the correlation function, we use a Gaussian damping function. The strengths and weaknesses of these approaches as well as the dependence of the results on the choice of the technical parameters of the time integration are assessed on four test examples, i.e., the nonradiative S1 \documentclass[12pt]{minimal}\begin{document}$\leadsto$\end{document}⇝ T1 transitions in thymine, phenalenone, flavone, and porphyrin. The obtained rate constants are compared with previous results of a time-independent approach. Very good agreement between the literature values and the integrals over the full time correlation functions are observed. Furthermore, the comparison suggests that the cumulant expansion approximates the exact expression very well while allowing the interval of the time integration to be significantly shorter. In cases with sufficiently high vibrational density of states also the short-time approximation yields rates in good agreement with the results of the exact formula. A great advantage of the time-dependent approach over the time-independent approach is its excellent computational efficiency making it the method of choice in cases of large energy gaps, large numbers of normal modes, and high densities of final vibrational states.
Magnetocardiography with sensors based on giant magnetoresistance
Authors: Pannetier-Lecoeur M. , Parkkonen L. , Sergeeva-Chollet N. , Polovy H. , Fermon C. , Fowley C.
Published: April 2011

Biomagnetic signals, mostly due to the electrical activity in the body, are very weak and they can only be detected by the most sensitive magnetometers, such as Superconducting Quantum Interference Devices (SQUIDs). We report here biomagnetic recordings with hybrid sensors based on Giant MagnetoResistance (GMR). We recorded magnetic signatures of the electric activity of the human heart (magnetocardiography) in healthy volunteers. The P-wave and QRS complex, known from the corresponding electric recordings, are clearly visible in the recordings after an averaging time of about 1 min. Multiple recordings at different locations over the chest yielded a dipolar magnetic field map and allowed localizing the underlying current sources. The sensitivity of the GMR-based sensors is now approaching that of SQUIDs and paves way for spin electronics devices for functional imaging of the body.
Omnifocus video camera
Authors: Iizuka Keigo
Published: April 2011

The omnifocus video camera takes videos, in which objects at different distances are all in focus in a single video display. The omnifocus video camera consists of an array of color video cameras combined with a unique distance mapping camera called the Divcam. The color video cameras are all aimed at the same scene, but each is focused at a different distance. The Divcam provides real-time distance information for every pixel in the scene. A pixel selection utility uses the distance information to select individual pixels from the multiple video outputs focused at different distances, in order to generate the final single video display that is everywhere in focus. This paper presents principle of operation, design consideration, detailed construction, and over all performance of the omnifocus video camera. The major emphasis of the paper is the proof of concept, but the prototype has been developed enough to demonstrate the superiority of this video camera over a conventional video camera. The resolution of the prototype is high, capturing even fine details such as fingerprints in the image. Just as the movie camera was a significant advance over the still camera, the omnifocus video camera represents a significant advance over all-focus cameras for still images.
Geometric and magnetic properties of Pt clusters supported on graphene: Relativistic density-functional calculations
Authors: Błoński Piotr , Hafner Jürgen
Published: April 2011

The geometric and magnetic structures of small Ptn clusters (n = 1 − 5) supported on a graphene layer have been investigated using ab initio density functional calculations including spin-orbit coupling. Pt–Pt interactions were found to be much stronger than the Pt–C interactions promoting the binding to the support. As a consequence, the equilibrium structure of the gas-phase clusters is preserved if they are deposited on graphene. However, the clusters bind to graphene only via at most two Pt–C bonds: A Pt2 dumbbell prefers an upright position, the larger clusters are bound to graphene only via one edge of the planar cluster (Pt3 and Pt5) or via two terminal Pt atoms of a bent Pt4 rhombus. Evidently, the strong buckling of the graphene layer induced by the Pt–C bonds prevents the formation of a larger number of cluster-support bonds. As the local spin and orbital magnetic moments are quenched on the Pt atoms forming Pt–C bonds, the magnetic structure of the supported clusters is much more inhomogeneous as in the gas-phase. This leads to noncollinear magnetic structures and a strongly reduced magnetic anisotropy energy.
Diffusion of spherical particles in microcavities
Authors: Imperio A. , Padding J. T. , Briels W. J.
Published: April 2011

The diffusive motion of a colloidal particle trapped inside a small cavity filled with fluid is reduced by hydrodynamic interactions with the confining walls. In this work, we study these wall effects on a spherical particle entrapped in a closed cylinder. We calculate the diffusion coefficient along the radial, azimuthal, and axial direction for different particle positions. At all locations the diffusion is smaller than in a bulk fluid and it becomes anisotropic near the container's walls. We present a simple model which reasonably well describes the simulation results for the given dimensions of the cylinder, which are taken from the recent experimental work.
Structural dynamics of supercooled water from quasielastic neutron scattering and molecular simulations
Authors: Qvist Johan , Schober Helmut , Halle Bertil
Published: April 2011

One of the outstanding challenges presented by liquid water is to understand how molecules can move on a picosecond time scale despite being incorporated in a three-dimensional network of relatively strong H-bonds. This challenge is exacerbated in the supercooled state, where the dramatic slowing down of structural dynamics is reminiscent of the, equally poorly understood, generic behavior of liquids near the glass transition temperature. By probing single-molecule dynamics on a wide range of time and length scales, quasielastic neutron scattering (QENS) can potentially reveal the mechanistic details of water's structural dynamics, but because of interpretational ambiguities this potential has not been fully realized. To resolve these issues, we present here an extensive set of high-quality QENS data from water in the range 253–293 K and a corresponding set of molecular dynamics (MD) simulations to facilitate and validate the interpretation. Using a model-free approach, we analyze the QENS data in terms of two motional components. Based on the dynamical clustering observed in MD trajectories, we identify these components with two distinct types of structural dynamics: picosecond local (L) structural fluctuations within dynamical basins and slower interbasin jumps (J). The Q-dependence of the dominant QENS component, associated with J dynamics, can be quantitatively rationalized with a continuous-time random walk (CTRW) model with an apparent jump length that depends on low-order moments of the jump length and waiting time distributions. Using a simple coarse-graining algorithm to quantitatively identify dynamical basins, we map the Newtonian MD trajectory on a CTRW trajectory, from which the jump length and waiting time distributions are computed. The jump length distribution is Gaussian and the rms jump length increases from 1.5 to 1.9 Å as the temperature increases from 253 to 293 K. The rms basin radius increases from 0.71 to 0.75 Å over the same range. The waiting time distribution is exponential at all investigated temperatures, ruling out significant dynamical heterogeneity. However, a simulation at 238 K reveals a small but significant dynamical heterogeneity. The macroscopic diffusion coefficient deduced from the QENS data agrees quantitatively with NMR and tracer results. We compare our QENS analysis with existing approaches, arguing that the apparent dynamical heterogeneity implied by stretched exponential fitting functions results from the failure to distinguish intrabasin (L) from interbasin (J) structural dynamics. We propose that the apparent dynamical singularity at ∼220 K corresponds to freezing out of J dynamics, while the calorimetric glass transition corresponds to freezing out of L dynamics.
Velocity map imaging of HBr photodissociation in large rare gas clusters
Authors: Fedor J. , Kočišek J. , Poterya V. , Votava O. , Pysanenko A. , Lipciuc M. L. , Kitsopoulos T. N. , Fárník M.
Published: April 2011

We have implemented the velocity map imaging technique to study clustering in the pulsed supersonic expansions of hydrogen bromide in helium, argon, and xenon. The expansions are characterized by direct imaging of the beam velocity distributions. We have investigated the cluster generation by means of UV photodissociation and photoionization of HBr molecules. Two distinct features appear in the hydrogen atom photofragment images in the clustering regime: (i) photofragments with near zero kinetic energies and (ii) “hot” photofragments originating from vibrationally excited HBr molecules. The origin of both features is attributed to the fragment caging by the cluster. We discuss the nature of the formed clusters based on the change of the photofragment images with the expansion parameters and on the photoionization mass spectra and conclude that single HBr molecule encompassed with rare gas “snowball” is consistent with the experimental observations.
Diffusion amid random overlapping obstacles: Similarities, invariants, approximations
Authors: Novak Igor L. , Gao Fei , Kraikivski Pavel , Slepchenko Boris M.
Published: April 2011

Efficient and accurate numerical techniques are used to examine similarities of effective diffusion in a void between random overlapping obstacles: essential invariance of effective diffusion coefficients (Deff) with respect to obstacle shapes and applicability of a two-parameter power law over nearly entire range of excluded volume fractions (ϕ), except for a small vicinity of a percolation threshold. It is shown that while neither of the properties is exact, deviations from them are remarkably small. This allows for quick estimation of void percolation thresholds and approximate reconstruction of Deff (ϕ) for obstacles of any given shape. In 3D, the similarities of effective diffusion yield a simple multiplication “rule” that provides a fast means of estimating Deff for a mixture of overlapping obstacles of different shapes with comparable sizes.
Interpolated model-matrix optoacoustic tomography of the mouse brain
Authors: Jetzfellner Thomas , Rosenthal Amir , Englmeier K.-H. , Dima Alexander , Caballero Miguel Ángel Araque , Razansky Daniel , Ntziachristos Vasilis
Published: April 2011

Neuroscience investigations may significantly benefit from the availability of accurate imaging methods of brain parameters in small animals. In this letter, we investigate the imaging performance of the recently introduced interpolated model-matrix inversion (IMMI), in quantitative optoacoustic imaging of the mouse head. We compare the findings of the method against back-projection inversion methods that have more commonly been considered. We find that cross-sectional images of the mouse head accurately match anatomical structures seen on cryosliced head images serving as the gold standard. Moreover, superior imaging performance is found for IMMI compared to previously reported optoacoustic imaging of the mouse head.
Low-resistance Ni/Al Ohmic contacts applied to a nonpolar a-plane n-type GaN
Authors: Kim Dong Ho , Kim Su Jin , Seo Yu Jeong , Kim Tae Geun , Hwang Sung Min
Published: April 2011

The authors report upon a low-resistance Ni/Al Ohmic contact to a nonpolar n-type a-plane GaN with respect to the annealing temperature. The Schottky behavior of the Ni/Al contact changes to a linear Ohmic behavior at a 700 °C annealing, at which the specific contact resistivity of the Ni/Al contact became as low as 5.8×10−5 whereas that of a typical Ti/Al contact was 1.6×10−3 Ω cm2. This improvement is attributed to a lowering of the Schottky barrier height via a Ni–Al interdiffused layer, formed at the interface between the metal and the nonpolar a-plane n-type GaN during the annealing process.
Terahertz sources based on intracavity frequency mixing in mid-infrared quantum cascade lasers with passive nonlinear sections
Authors: Adams Robert W. , Vizbaras Augustinas , Jang Min , Grasse Christian , Katz Simeon , Boehm Gerhard , Amann Markus C. , Belkin Mikhail A.
Published: April 2011

We report the design and performance of terahertz quantum cascade laser sources based on intracavity difference frequency generation in dual-wavelength mid-infrared quantum cascade lasers with a passive nonlinear section at the exit facet, designed for giant second-order nonlinear susceptibility. These devices operate in the mid-infrared at λ1=8.4 μm and λ2=9.5 μm, with terahertz output at the difference frequency, λ3≈73 μm. Terahertz output of approximately 100 nW was observed up to a heat sink temperature of 210 K.
Manipulation of confined bubbles in a thin microchannel: Drag and acoustic Bjerknes forces
Authors: Rabaud David , Thibault Pierre , Raven Jan-Paul , Hugon Olivier , Lacot Eric , Marmottant Philippe
Published: April 2011

Bubbles confined between the parallel walls of microchannels experience an increased drag compared to freestanding bubbles. We measure and model the additional friction from the walls, which allows the calibration of the drag force as a function of velocity. We then develop a setup to apply locally acoustic waves and demonstrate the use of acoustic forces to induce the motion of bubbles. Because of the bubble pulsation, the acoustic forces—called Bjerknes forces—are much higher than for rigid particles. We evaluate these forces from the measurement of bubble drift velocity and obtain large values of several hundreds of nanonewtons. Two applications have been developed to explore the potential of these forces: asymmetric bubble breakup to produce very well controlled bidisperse populations and intelligent switching at a bifurcation.
A geometry for optimizing nanoscale magnetic resonance force microscopy
Authors: Xue Fei , Peddibhotla P. , Montinaro M. , Weber D. P. , Poggio M.
Published: April 2011

We implement magnetic resonance force microscopy (MRFM) in an experimental geometry, where the long axis of the cantilever is normal to both the external magnetic field and the rf microwire source. Measurements are made of the statistical polarization of H1 in polystyrene with negligible magnetic dissipation, gradients greater than 105 T/m within 100 nm of the magnetic tip, and rotating rf magnetic fields over 12 mT at 115 MHz. This geometry could facilitate the application of nanometer-scale MRFM to nuclear species with low gyromagnetic ratios and samples with broadened resonances, such as In spins in quantum dots.
Si nanoparticle–Er3+ coupling through contact in as-deposited nanostructured films
Authors: Núñez-Sánchez S. , Roque P. M. , Serna R. , Petford-Long A. K.
Published: April 2011

The efficient excitation of Er3+ ions through contact with Si nanoparticles (NPs) is demonstrated. A nanostructured doping process has been developed that leads to contact between Si NPs formed in situ and optically-active Er3+ ions embedded in Al2O3. This is achieved by independent and consecutive deposition of the dopants and matrix. The Si NP–Er3+ contact regime enhances the probability of efficient interaction due to the local spatial overlap of the electronic states of the Er3+ and of the Si NP exciton, enabling energy transfer by interband exciton recombination. This leads to up to 53% of the Er3+ ions being excited in as-deposited films.
Excellent crystalline silicon surface passivation by amorphous silicon irrespective of the technique used for chemical vapor deposition
Authors: Schüttauf Jan-Willem A. , van der Werf Karine H. M. , Kielen Inge M. , van Sark Wilfried G. J. H. M. , Rath Jatindra K. , Schropp Ruud E. I.
Published: April 2011

Crystalline silicon surface passivation by amorphous silicon deposited by three different chemical vapor deposition (CVD) techniques at low (T∼130 °C) temperatures is compared. For all three techniques, surface recombination velocities (SRVs) are reduced by two orders of magnitude after prolonged thermal annealing at 200 °C. This reduction correlates with a decreased dangling bond density at the amorphous-crystalline interface, indicating that dangling bond saturation is the predominant mechanism. All three deposition methods yield excellent surface passivation. For a-Si:H layers deposited by radio frequency plasma enhanced CVD, we obtain outstanding carrier lifetimes of 10.3 ms, corresponding to SRVs below 1.32 cm/s.
Bound magnetic polarons and p-d exchange interaction in ferromagnetic insulating Cu-doped ZnO
Authors: Tian Yufeng , Li Yongfeng , He Mi , Putra Irwan Ade , Peng Haiyang , Yao Bin , Cheong Siew Ann , Wu Tom
Published: April 2011

A systematic study on the magnetic and electrical transport properties of single-phase wurtzite Zn1−xCuxO is performed. Efros variable range hopping dominates the conduction, which is accompanied by a ferromagnetic order up to 700 K for x>1%. Both the first-principles calculations and Cu/Al co-doping experiments suggest that the spontaneous spin polarization originates from the p-d exchange interaction between O 2p and Cu 3d orbitals. Furthermore, our results are consistent with the scenario that the intrinsic ferromagnetism is established through indirect interactions between bound magnetic polarons mediated by magnetic impurities.
Time-temperature dependence of positive gate bias stress and recovery in amorphous indium-gallium-zinc-oxide thin-film-transistors
Authors: Chowdhury Md Delwar Hossain , Migliorato Piero , Jang Jin
Published: April 2011

We have analyzed the time-temperature dependence of positive bias stress (PBS) and recovery in amorphous indium-gallium-zinc-oxide (a-IGZO) Thin-film-transistors (TFTs) incorporating SiO2 back channel passivation. The data are fitted to stretched exponentials, yielding the time constant τ and stretch parameter β as fitting parameters. As-fabricated samples and samples annealed in vacuum at 250 °C 200 h are compared. The time constant for room temperature stress increases fivefold with the 200 h anneal to the value τ=1.3×106 s. The dependence of τ from stress temperature is well described by an Arrhenius plot, with activation Eτ=0.95 eV. Stress and recovery show very similar activation energies, supporting the defect formation in the bulk or at the gate insulator/a-IGZO interface as the mechanism responsible for PBS.
Environment-dependent thermal instability of sol-gel derived amorphous indium-gallium-zinc-oxide thin film transistors
Authors: Chung Wan-Fang , Chang Ting-Chang , Li Hung-Wei , Chen Shih-Ching , Chen Yu-Chun , Tseng Tseung-Yuen , Tai Ya-Hsiang
Published: April 2011

The environment-dependent electrical performances as a function of temperature for sol-gel derived amorphous indium-gallium-zinc-oxide (a-IGZO) thin film transistors are investigated in this letter. In the ambients without oxygen, thermal activation dominates and enhances device performance. In oxygen-containing environments, mobility and drain current degrades and the threshold slightly increase as temperature increases. We develop a porous model for a-IGZO film relating to the drain current and mobility lowering due to film porosity and oxygen adsorption/penetration. It also relates to the threshold voltage recovery at high temperature owing to the varying form of adsorbed oxygen and the combination of oxygen and vacancies.
Surface plasmon dispersion engineering via double-metallic Au/Ag layers for III-nitride based light-emitting diodes
Authors: Zhao Hongping , Zhang Jing , Liu Guangyu , Tansu Nelson
Published: April 2011

Double-metallic Au/Ag layers deposited on top of InGaN/GaN quantum wells (QWs) are used to tune the Purcell peak enhancement of the radiative recombination rate for nitride light-emitting diodes. By modifying the Au/Ag thicknesses, the Purcell factor can be widely tuned between the surface plasmon frequencies of Au/GaN and Ag/GaN. Photoluminescence studies demonstrated the concept of the Purcell factor tuning by using the double-metallic Au/Ag layers.
Light-driven manipulation of picobubbles on a titanium oxide phthalocyanine-based optoelectronic chip
Authors: Yang Shih-Mo , Yu Tung-Ming , Huang Hang-Ping , Ku Meng-Yen , Tseng Sheng-Yang , Tsai Che-Liang , Chen Hung-Po , Hsu Long , Liu Cheng-Hsien
Published: April 2011

Microbubbles have a variety of applications in science and biological technology. Here, we demonstrate the manipulation of the picoliter gas bubble (picobubble) based on the optoelectronic-mechanism. The organic photoconductive material, titanium oxide phthalocyanine (TiOPc), was developed to make the light-sensitive substrate of this optoelectronic chip. The virtual electrodes are formed by projecting the dynamic light pattern onto TiOPc layer for generating the desired nonuniform electric field. The picobubble suspended in silicone oil can be manipulated with the velocity of 40–50 μm/s. The driving force up to 160 pico-Newtons could be generated for manipulating a gas bubble of 300 picoliters.
Size tunable visible and near-infrared photoluminescence from vertically etched silicon quantum dots
Authors: Walavalkar Sameer S. , Homyk Andrew P. , Hofmann Carrie E. , Henry M. David , Shin Claudia , Atwater Harry A. , Scherer Axel
Published: April 2011

Corrugated etching techniques were used to fabricate size-tunable silicon quantum dots that luminesce under photoexcitation, tunable over the visible and near infrared. By using the fidelity of lithographic patterning and strain limited, self-terminating oxidation, uniform arrays of pillar containing stacked quantum dots as small as 2 nm were patterned. Furthermore, an array of pillars, with multiple similar sized quantum dots on each pillar, was fabricated and tested. The photoluminescence displayed a multiple, closely peaked emission spectra corresponding to quantum dots with a narrow size distribution. Similar structures can provide quantum confinement effects for future nanophotonic and nanoelectronic devices.
Luminescence dynamics in Ga(AsBi)
Authors: Imhof Sebastian , Wagner Christian , Thränhardt Angela , Chernikov Alexej , Koch Martin , Köster Niko S. , Chatterjee Sangam , Koch Stephan W. , Rubel Oleg , Lu Xianfeng , Johnson Shane R. , Beaton Daniel A. , Tiedje Thomas
Published: April 2011

The temporal evolution of the spectrally resolved luminescence is measured for a Ga(AsBi) sample at low temperatures. The results are analyzed with the help of kinetic Monte Carlo simulations incorporating two disorder scales attributed to alloy disorder and Bi- clustering. An average time of 5 ps is identified as the upper limit for carrier capture into the Bi clusters whereas the extracted hopping rate associated with alloy fluctuations is much faster than the transitions between the individual cluster sites.
Direct observation of photonic Fermi surfaces by plasmon tomography
Authors: Regan C. J. , Krishnan A. , Lopez-Boada R. , Grave de Peralta L. , Bernussi A. A.
Published: April 2011

Light propagation in dielectric plasmonic crystals with different parameters and symmetries was investigated by plasmon tomography. We show that the photonic Fermi surfaces at the crystal’s reciprocal lattice space can be observed directly from the Fourier plane images. Directional gaps were observed where the isofrequency wavevectors of the propagating surface plasmon mode intersect the first Brillouin zone of the plasmonic crystal structures. We determined that the angular magnitude of the directional gaps depends strongly on the crystal symmetry and the lattice period.
Second-order post-Hartree–Fock perturbation theory for the electron current
Authors: Dzhioev Alan A. , Kosov D. S.
Published: April 2011

Based on the super-fermion representation of quantum kinetic equations we develop nonequilibrium, post-Hartree–Fock many-body perturbation theory for the current through a region of interacting electrons. We apply the theory to out of equilibrium Anderson model and discuss practical implementation of the approach. Our calculations show that nonequilibrium electronic correlations may produce significant quantitative and qualitative corrections to mean-field electronic transport properties.
Electrolyte-gated organic field-effect transistors for sensing applications
Authors: Buth F. , Kumar D. , Stutzmann M. , Garrido J. A.
Published: April 2011

We report on the electrolytic gating of α-sexithiophene thin film transistors, in which the organic semiconductor is in direct contact with an electrolyte. Due to the large capacitance of the electrical double layer at the electrolyte/semiconductor interface, modulation of the channel conductivity via an electrical field effect is achieved at low voltages. The transistors are stable for several hours and are sensitive to variations in the pH resulting from a pH-dependent surface charge, which modulates the threshold voltage. The response to different ion concentrations is described by the influence of the ions on the mobility and an electrostatic screening effect.
Optimization of the nanolens consisting of coupled metal nanoparticles: An analytical approach
Authors: Sun G. , Khurgin J. B.
Published: April 2011

Using a simple and intuitive analytical approach, we perform optimization of a nanolens composed of coupled metal nanoparticles capable of subwavelength focusing of light inside the narrow gap separating the particles. Specifically, we optimize the structure of two nanospheres of different sizes to achieve maximum field enhancement at an off-center position in the gap. We demonstrate that the nanolens of two or more spheres acts simultaneously as an efficient antenna with large dipole and an efficient cavity with small effective volume.
The cold and atmospheric-pressure air surface barrier discharge plasma for large-area sterilization applications
Authors: Wang Dacheng , Zhao Di , Feng Kecheng , Zhang Xianhui , Liu Dongping , Yang Size
Published: April 2011

This letter reports a stable air surface barrier discharge device for large-area sterilization applications at room temperature. This design may result in visually uniform plasmas with the electrode area scaled up (or down) to the required size. A comparison for the survival rates of Escherichia coli from air, N2 and O2 surface barrier discharge plasmas is presented, and the air surface plasma consisting of strong filamentary discharges can efficiently kill Escherichia coli. Optical emission measurements indicate that reactive species such as O and OH generated in the room temperature air plasmas play a significant role in the sterilization process.
How Little Do We Need for 3-D Shape Perception?
Authors: Nandakumar Chetan , Torralba Antonio , Malik Jitendra
Published: April 2011

How little do we need to perceive 3-D shape in monocular natural images? The shape-from-texture and shape-from-shading perspectives would motivate that 3-D perception vanishes once low-level cues are disrupted. Is this the case in human vision? Or can top – down influences salvage the percept? In this study we probe this question by employing a gauge-figure paradigm similar to that used by Koenderink et al (1992, Perception & Psychophysics52 487 – 496). Subjects were presented degraded natural images and instructed to make local assessments of slant and tilt at various locations thereby quantifying their internal 3-D percept. Analysis of subjects' responses reveals recognition to be a significant influence thereby allowing subjects to perceive 3-D shape at high levels of degradation. Specifically, we identify the ‘medium-blur’ condition, images approximately 32 pixels on a side, to be the limit for accurate 3-D shape perception. In addition, we find that degradation affects the perceived slant of point-estimates making images look flatter as degradation increases. A subsequent condition that eliminates texture and shading but preserves contour and recognition reveals how bottom – up and top – down cues can combine for accurate 3-D shape perception.
The Paddle Move Commonly Used in Magic Tricks as a Means for Analysing the Perceptual Limits of Combined Motion Trajectories
Authors: Hergovich Andreas , Gröbl Kristian , Carbon Claus-Christian
Published: April 2011

Following Gustav Kuhn's inspiring technique of using magicians' acts as a source of insight into cognitive sciences, we used the ‘paddle move’ for testing the psychophysics of combined movement trajectories. The paddle move is a standard technique in magic consisting of a combined rotating and tilting movement. Careful control of the mutual speed parameters of the two movements makes it possible to inhibit the perception of the rotation, letting the ‘magic’ effect emerge—a sudden change of the tilted object. By using 3-D animated computer graphics we analysed the interaction of different angular speeds and the object shape/size parameters in evoking this motion disappearance effect. An angular speed of 540° s−1 (1.5 rev. s−1) sufficed to inhibit the perception of the rotary movement with the smallest object showing the strongest effect. 90.7% of the 172 participants were not able to perceive the rotary movement at an angular speed of 1125° s−1 (3.125 rev. s−1). Further analysis by multiple linear regression revealed major influences on the effectiveness of the magic trick of object height and object area, demonstrating the applicability of analysing key factors of magic tricks to reveal limits of the perceptual system.
“It's Time to Take a Stand”: Depicting Crosshairs Can Indeed Promote Violence
Authors: Schoormans Jan P L , Carbon Claus-Christian , Gattol Valentin
Published: April 2011

There is abundant evidence that people derive meaning from signs (Krippendorff, 1989 Design Issues5 9 – 39) and that signs influence attitudes (Landau et al, 2010 Psychological Bulletin136 1045 – 1067). We put to a test whether the use of crosshairs in a map can be viewed as representing violence. In a fictive scenario describing a plague of foxes, members of a Dutch household panel were confronted with a map that showed inflicted areas either by crosshairs or by neutral markers (plain circles). Respondents indicated the extent to which they favoured two solutions: killing-by-shooting or capturing-and-relocating. The results show that crosshairs indeed shape people's attitudes more towards the violent solution of shooting the foxes. Therefore, especially when used in heated public debates, the possibly violence-inducing effect of such visual metaphors should not be underestimated.
Wood Protection Properties of Quaternary Ammonium Spiroborate Esters Derived from Alkyl Tartrates
Authors: Carr Jenny M. , Duggan Peter J. , Humphrey David G. , Platts James A. , Tyndall Edward M.
Published: April 2011

Four new tetra-n-butylammonium spiroborates derived from dimethyl, diethyl, di-iso-propyl and di-n-butyl esters of l-tartaric acid have been prepared and their potential as environmentally benign wood protectants investigated. These compounds showed good activity in a no-choice cellulose paper bioassay with Coptotermes acinaciformis termites. The hydrolytic stability of these spiroborates is not high relative to other spiroborates, yet the tetra-n-butylammonium spiroborate derived from di-iso-propyl-l-tartrate showed remarkable permanence in timber in a demanding leaching test.
O - H Bond Dissociation Energies
Authors: Chan Bun , Morris Michael , Radom Leo
Published: April 2011

High-level composite, ab initio and density functional theory (DFT) procedures have been employed to study O–H bond dissociation energies (BDEs), as well as radical stabilization energies (RSEs) in the oxygen-centred radicals that are formed in the dissociation of the O–H bonds. Benchmark values are provided by Wn results up to W3.2 and W4.x. We are able to recommend revised BDE values for FO–H (415.6 ± 3 kJ mol–1), MeC(O)O–H (459.8 ± 6 kJ mol–1) and CF3CH2O–H (461.9 ± 6 kJ mol–1) on the basis of high-level calculations. We find that Gn-type procedures are generally reliable and cost-effective, and that some contemporary functionals and double-hybrid DFT procedures also provide adequate O–H BDEs/RSEs. We note that the variations in the O–H BDEs are associated with variations in the stabilities of not only the radicals but also the closed-shell precursor molecules. Most substituents destabilize both species, with σ-electron-withdrawing groups having larger destabilizing effects, while π-electron acceptors are stabilizing. Although there is little correlation between the stabilizing/destabilizing effects of the substituents and the RSEs, we present some general patterns in the RSEs that emerge from the present study.
A story of attitudes and aptitudes?
Authors: Rosiers Alexandra , Eyckmans June , Bauwens Daniel
Published: April 2011

Unlike in the early days of interpreter training, most student interpreters nowadays are still in the process of acquiring their target language(s), which raises questions as to which skills — linguistic as well as non-linguistic — may be required at the outset of interpreter training. This study focuses on individual difference variables and how these relate to interpreting students’ performance. It aims to investigate the ways in which the profiles of translation and interpreting students differ by obtaining information regarding their self-perceived communication competence, self-perception of language skills, anxiety levels and integrative motivation. These profiles are then related to the students’ sight translation performances, arguably a hybrid activity between translating and interpreting that is as cognitively demanding as simultaneous and consecutive interpreting. The students’ performances were assessed by a ‘blind judge’ along two parameters: (1) overall interpreting performance and (2) fluency. The results suggest that the two groups indeed differ significantly with regard to some of the individual difference variables. However, no significant correlations between these variables and students’ sight translation performance were found.