bluuebunny/crossref_metadata_2025 huggingface dataset:
LaAlO3/Si capacitors: Comparison of different molecular beam deposition conditions and their impact on electrical properties
Authors: Pelloquin Sylvain , Saint-Girons Guillaume , Baboux Nicolas , Albertini David , Hourani Waël , Penuelas Jose , Grenet Geneviève , Plossu Carole , Hollinger Guy
Published: January 2013

A study of the structural and electrical properties of amorphous LaAlO3 (LAO)/Si thin films fabricated by molecular beam deposition (MBD) is presented. Two substrate preparation procedures have been explored namely a high temperature substrate preparation technique—leading to a step and terraces surface morphology—and a chemical HF-based surface cleaning. The LAO deposition conditions were improved by introducing atomic plasma-prepared oxygen instead of classical molecular O2 in the chamber. An Au/Ni stack was used as the top electrode for its electrical characteristics. The physico-chemical properties (surface topography, thickness homogeneity, LAO/Si interface quality) and electrical performance (capacitance and current versus voltage and TunA current topography) of the samples were systematically evaluated. Deposition conditions (substrate temperature of 550 °C, oxygen partial pressure settled at 10−6 Torr, and 550 W of power applied to the O2 plasma) and post-depositions treatments were investigated to optimize the dielectric constant (κ) and leakage currents density (JGate at |VGate| = |VFB − 1|). In the best reproducible conditions, we obtained a LAO/Si layer with a dielectric constant of 16, an equivalent oxide thickness of 8.7 Å, and JGate ≈ 10−2A/cm2. This confirms the importance of LaAlO3 as an alternative high-κ for ITRS sub-22 nm technology node.
Adsorption of single polymer molecules in shear flow near a planar wall
Authors: Dutta Sarit , Dorfman Kevin D. , Kumar Satish
Published: January 2013

Adsorption of homopolymers from a dilute solution to a planar wall in the presence of shear flow is studied using a bead-spring dumbbell model. The bead-bead and bead-wall interactions are described by generalized Lennard-Jones potentials. A kinetic theory incorporating bead-wall hydrodynamic interaction is developed in order to obtain an analytical expression for the steady-state dumbbell concentration profile. The concentration profile exhibits an exclusion zone in the immediate vicinity of the wall, is followed by a peak, and finally approaches the bulk concentration far away from the wall. Using the analytical expression, the amount adsorbed and the equivalent film thickness are studied as a function of flow strength and the parameters characterizing the bead-wall interaction potential. Shear flow causes migration of the dumbbells due to bead-wall hydrodynamic interaction, which leads to desorption. On increasing the flow strength, the quantity adsorbed and the film thickness decrease until complete desorption occurs. The dependence of the flow strength required for desorption on the model parameters is also studied and a scaling law is derived for the strong-interaction limit. Brownian dynamics simulations are performed to verify the predictions from the kinetic theory. Although the theory makes a number of simplifying assumptions, it captures many of the key features seen in the simulations.
Comment on “Three-dimensional numerical investigation of electron transport with rotating spoke in a cylindrical anode layer Hall plasma accelerator” [Phys. Plasmas 19, 073519 (2012)]
Authors: Ellison C. L. , Matyash K. , Parker J. B. , Raitses Y. , Fisch N. J.
Published: January 2013

The oscillation behavior described by Tang et al. [Phys. Plasmas 19, 073519 (2012)] differs too greatly from previous experimental and numerical studies to claim observation of the same phenomenon. Most significantly, the rotation velocity by Tang et al. [Phys. Plasmas 19, 073519 (2012)] is three orders of magnitude larger than that of typical “rotating spoke” phenomena. Several physical and numerical considerations are presented to more accurately understand the numerical results of Tang et al. [Phys. Plasmas 19, 073519 (2012)] in light of previous studies.
Response to “Comment on ‘Three-dimensional numerical investigation of electron transport with rotating spoke in a cylindrical anode layer Hall plasma accelerator’” [Phys. Plasmas 20, 014701 (2013)]
Authors: Tang D. L. , Geng S. F. , Qiu X. M. , Chu Paul K.
Published: January 2013

The numerical simulation described in our paper [D. L. Tang et al., Phys. Plasmas 19, 073519 (2012)] shows a rotating dense plasma structure, which is the critical characteristic of the rotating spoke. The simulated rotating spoke has a frequency of 12.5 MHz with a rotational speed of ∼1.0 × 106 m/s on the surface of the anode. Accompanied by the almost uniform azimuthal ion distribution, the non-axisymmetric electron distribution introduces two azimuthal electric fields with opposite directions. The azimuthal electric fields have the same rotational frequency and speed together with the rotating spoke. The azimuthal electric fields excite the axial electron drift upstream and downstream due to the additional Eθ x B field and then the axial shear flow is generated. The axial local charge separation induced by the axial shear electron flow may be compensated by the azimuthal electron transport, finally resulting in the azimuthal electric field rotation and electron transport with the rotating spoke.
A modulated gradient model for scalar transport in large-eddy simulation of the atmospheric boundary layer
Authors: Lu Hao , Porté-Agel Fernando
Published: January 2013

As a simple alternative to the standard eddy-diffusivity closure, a nonlinear subgrid-scale (SGS) flux model is introduced and implemented in simulations of a neutral atmospheric boundary layer and a stable atmospheric boundary layer. The new model computes the structure of the SGS flux (relative magnitude of the vector components) based on the normalized gradient vector, which is derived from the Taylor expansion of the exact SGS flux. The SGS magnitude is computed as the product of a SGS velocity scale and a SGS scalar concentration scale, which are estimated based on the local-equilibrium hypothesis. To resolve the instability issue of the original gradient model and ensure numerical stability, we adopt a clipping procedure to avoid local negative SGS dissipation rate of the scalar variance. The model formulation, using constant coefficients, is assessed through a systematic comparison with well-established theoretical predictions and reference results of various flow statistics. Simulation results obtained with the use of this new model show good agreement with the reference results and an evident improvement over results obtained using traditional eddy-diffusivity models. For instance, the new model can deliver the expected surface-layer similarity scalar profile and power-law scaling of the power spectrum of scalar fluctuation.
Six-site polarizable model of water based on the classical Drude oscillator
Authors: Yu Wenbo , Lopes Pedro E. M. , Roux Benoît , MacKerell Alexander D.
Published: January 2013

A polarizable water model, SWM6, was developed and optimized for liquid phase simulations under ambient conditions. Building upon the previously developed SWM4-NDP model, additional sites representing oxygen lone-pairs were introduced. The geometry of the sites is assumed to be rigid. Considering the large number of adjustable parameters, simulated annealing together with polynomial fitting was used to facilitate model optimization. The new water model was shown to yield the correct self-diffusion coefficient after taking the system size effect into account, and the dimer geometry is better reproduced than in the SWM4 models. Moreover, the experimental oxygen-oxygen radial distribution is better reproduced, indicating that the new model more accurately describes the local hydrogen bonding structure of bulk phase water. This was further validated by its ability to reproduce the experimental nuclear magnetic shielding and related chemical shift of the water hydrogen in the bulk phase, a property sensitive to the local hydrogen bonding structure. In addition, comparison of the liquid properties of the SWM6 model is made with those of a number of widely used additive and polarizable models. Overall, improved balance between the description of monomer, dimer, clustered, and bulk phase water is obtained with the new model compared to its SWM4-NDP polarizable predecessor, though application of the model requires an approximately twofold increase on computational resources.
Quantized phonon modes in loaded polymer films
Authors: Farmer David J. , Akimov Andrey V. , Sharp James S. , Kent Anthony J.
Published: January 2013

We study the spectrum of quantized hypersonic vibrations in gold coated polymer films deposited on crystalline silicon substrates. Gold films with thickness values in the range 2.5 nm to 30 nm were deposited onto supported polystyrene films and shifts in the resonant frequency of coated areas were observed relative to the bare polymer films. The experimental results and analysis based on solving the elastic equation with various boundary conditions show that supported polymer films have a potential for application in mass sensing and studies of the nanomechanical response of ultrathin adsorbed layers of material.
Relaxation of surface tension in the free-surface boundary layer of simple Lennard-Jones liquids
Authors: Lukyanov A. V. , Likhtman A. E.
Published: January 2013

In this paper we use molecular dynamics to answer a classical question: how does the surface tension on a liquid/gas interface appear? After defining surface tension from the first principles and performing several consistency checks, we perform a dynamic experiment with a single simple liquid nanodroplet. At time zero, we remove all molecules of the interfacial layer, creating a fresh bare interface with the bulk arrangement of molecules. After that the system evolves towards equilibrium, and the expected surface tension is re-established. We found that the system relaxation consists of three distinct stages. First, the mechanical balance is quickly re-established. During this process the notion of surface tension is meaningless. In the second stage, the surface tension equilibrates, and the density profile broadens to a value which we call “intrinsic” interfacial width. During the third stage, the density profile continues to broaden due to capillary wave excitations, which does not however affect the surface tension. We have observed this scenario for monatomic Lennard-Jones (LJ) liquid as well as for binary LJ mixtures at different temperatures, monitoring a wide range of physical observables.
Experimental study of temperature fluctuations in forced stably stratified turbulent flows
Authors: Eidelman A. , Elperin T. , Gluzman I. , Kleeorin N. , Rogachevskii I.
Published: January 2013

We study experimentally temperature fluctuations in stably stratified forced turbulence in air flow. In the experiments with an imposed vertical temperature gradient, the turbulence is produced by two oscillating grids located nearby the side walls of the chamber. Particle image velocimetry is used to determine the turbulent and mean velocity fields, and a specially designed temperature probe with sensitive thermocouples is employed to measure the temperature field. We found that the ratio \documentclass[12pt]{minimal}\begin{document}$\big [(\ell _x \nabla _x \overline{T})^2 + (\ell _y \nabla _y \overline{T})^2 + (\ell _z \nabla _z \overline{T})^2\big ] / \langle \theta ^2 \rangle$\end{document}(ℓx∇xT¯)2+(ℓy∇yT¯)2+(ℓz∇zT¯)2/⟨θ2⟩ is nearly constant, is independent of the frequency of the grid oscillations, and has the same magnitude for both, stably and unstably stratified turbulent flows, where ℓi are the integral scales of turbulence along x, y, z directions, \documentclass[12pt]{minimal}\begin{document}$\overline{T}$\end{document}T¯ and θ are the mean and turbulent fluctuations components of the fluid temperature. We demonstrated that for large frequencies of the grid oscillations, the temperature field can be considered as a passive scalar, while for smaller frequencies the temperature field behaves as an active field. The theoretical predictions based on the budget equations for turbulent kinetic energy, turbulent potential energy (∝ ⟨θ2⟩), and turbulent heat flux, are in a good agreement with the experimental results. Detailed comparison with experimental results obtained previously in unstably stratified forced turbulence is performed.
Combinatorial exploration of rare-earth-free permanent magnets: Magnetic and microstructural properties of Fe-Co-W thin films
Authors: Gao T. R. , Wu Y. Q. , Fackler S. , Kierzewski I. , Zhang Y. , Mehta A. , Kramer M. J. , Takeuchi I.
Published: January 2013

We have investigated the magnetic and structural properties of Fe-Co-W films using a composition spread technique. From the magnetometry measurements, large magnetization (900  emu/cm3) and enhanced perpendicular coercive fields (2–3 kOe) of low W concentration films were observed. The synchrotron diffraction results show a structural transition from a crystalline to an amorphous state and the crystallization onset increases with increasing W concentration. The SEM and TEM characterizations show that the films with low W concentrations have vertically standing platelet-like grain structures which is ascribed to the enhanced coercive fields. Magnetometry studies indicate that as the W concentration increases, microstructural change results in evolution of magnetization reversal mechanism.
The effect of degree of reduction on the electrical properties of functionalized graphene sheets
Authors: Punckt Christian , Muckel Franziska , Wolff Svenja , Aksay Ilhan A. , Chavarin Carlos A. , Bacher Gerd , Mertin Wolfgang
Published: January 2013

We study the effect of carbon to oxygen ratio (C/O) on the electrical resistance of functionalized graphene sheets prepared by thermal exfoliation and reduction of graphite oxide at various temperatures. Using a 2-probe technique in conjunction with Kelvin probe force microscopy, we observe a transition from high-resistance (>400 kΩ/sq) nonlinear current/voltage characteristics at low C/O to low-resistance (<10 kΩ/sq) linear behavior at high C/O, indicating a transition from hopping to diffusive electron transport. Simultaneously, the metal-graphene contacts change from high-resistance Schottky-type behavior to nearly non-invasive metal-metal contact characteristics.
Dynamics of semiflexible regular hyperbranched polymers
Authors: Fürstenberg Florian , Dolgushev Maxim , Blumen Alexander
Published: January 2013

We study the dynamics of semiflexible Vicsek fractals (SVF) following the framework established by Dolgushev and Blumen [J. Chem. Phys. 131, 044905 (2009)10.1063/1.3184797], a scheme which allows to model semiflexible treelike polymers of arbitrary architecture. We show, extending the methods used in the treatment of semiflexible dendrimers by Fürstenberg et al. [J. Chem. Phys. 136, 154904 (2012)10.1063/1.3703757], that in this way the Langevin-dynamics of SVF can be treated to a large part analytically. For this we show for arbitrary Vicsek fractals (VF) how to construct complete sets of eigenvectors; these reduce considerably the diagonalization problem of the corresponding equations of motion. In fact, such eigenvector sets arise naturally from a hierarchical procedure which follows the iterative construction of the VF. We use the obtained eigenvalues to calculate the loss moduli G″(ω) of SVF for different degrees of stiffness of the junctions. Finally, we compare the results for SVF to those found for semiflexible dendrimers.
Strain assisted inter-diffusion in GaN/AlN quantum dots
Authors: Leclere C. , Fellmann V. , Bougerol C. , Cooper D. , Gayral B. , Proietti M. G. , Renevier H. , Daudin B.
Published: January 2013

The structural and optical properties of high temperature-annealed superlattices of GaN quantum dots embedded in AlN barrier have been studied by a combination of X-ray techniques (reciprocal space mapping, multiwavelength anomalous diffraction, and diffraction anomalous fine structure), high resolution transmission electron microscopy, and photoluminescence spectroscopy. Taking advantage of the disentangling of the chemical and structural information provided by the simultaneous use of X-ray absorption and diffraction data obtained in a synchrotron environment, we provide quantitative determination of strain and composition for each different region of the nanostructures. Eventually, it is shown that strain driven dot/barrier intermixing is present, mostly on top of the dots. These observations have been confirmed by high resolution electron microscopy. A blue shift of photoluminescence peak has been furthermore observed and assigned to GaN/AlN intermixing suggesting a new path for engineering the emission wavelength of such heterostructures.
Relaxation processes in liquids: Variations on a theme by Stokes and Einstein
Authors: Shi Zane , Debenedetti Pablo G. , Stillinger Frank H.
Published: January 2013

We investigate numerically the temperature and density dependence of the Stokes-Einstein ratio, Dη/T, and of two commonly-used variants thereof, Dτ and Dτ/T, where D is a diffusivity, η the shear viscosity, and τ a structural relaxation time. We consider a family of atomic binary mixtures with systematically-softened repulsive interactions, and the Lewis-Wahnström model of ortho-terphenyl (OTP). The three quantities grow significantly as the temperature decreases in the supercooled regime, a well-known phenomenon. At higher temperatures, Dτ exhibits negative violations of Stokes-Einstein behavior, i.e., decrease upon cooling, for the atomic systems, though not for OTP. We consider two choices for the relaxation time, one based on the decay of the self-intermediate scattering function, and the other on the integral of the stress autocorrelation function. The instantaneous shear modulus exhibits appreciable temperature dependence for the two classes of systems investigated here. Our results suggest that commonly-invoked assumptions, such as τ ∼ η and τ ∼ η/T, should be critically evaluated across a wide spectrum of systems and thermodynamic conditions. We find the Stokes-Einstein ratio, Dη/T, to be constant across a broad range of temperatures and densities for the two classes of systems investigated here.
Molecular diffusion between walls with adsorption and desorption
Authors: Levesque Maximilien , Bénichou Olivier , Rotenberg Benjamin
Published: January 2013

The time dependency of the diffusion coefficient of particles in porous media is an efficient probe of their geometry. The analysis of this quantity, measured, e.g., by nuclear magnetic resonance, can provide rich information pertaining to porosity, pore size distribution, permeability, and surface-to-volume ratio of porous materials. Nevertheless, in numerous if not all practical situations, transport is confined by walls where adsorption and desorption processes may occur. In this article, we derive explicitly the expression of the time-dependent diffusion coefficient between two confining walls in the presence of adsorption and desorption. We show that they strongly modify the time-dependency of the diffusion coefficient, even in this simple geometry. We finally propose several applications, from sorption rates measurements to the use as a reference for numerical implementations for more complex geometries.
Forming-free resistive switching memories based on titanium-oxide nanoparticles fabricated at room temperature
Authors: Verrelli E. , Tsoukalas D. , Normand P. , Kean A. H. , Boukos N.
Published: January 2013

In this work, we present symmetric metal-insulator-metal bipolar memristors based on room-temperature deposition of charged titanium-oxide nanoparticles formed in vacuum by a physical process. One of the most striking features of these devices is that they do not require a forming step, which is to be related to protrusions of the top electrode material inside the intrinsically porous nanoparticle films. Furthermore, we report that deposition under substrate biasing conditions strongly affects the structural and electrical properties of the produced titanium oxide nanoparticle films including their bipolar switching behaviour.
Distribution of melting times and critical droplet in kinetic Monte Carlo and molecular dynamics
Authors: Lemarchand C. A.
Published: January 2013

A kinetic Monte Carlo model on a lattice, based on a reaction-like mechanism, is used to investigate the microscopic properties of the homogeneous melting of a metastable crystal. The kinetic Monte Carlo model relies on nearest-neighbors interactions and a few relevant dynamical parameters. To examine the reliability of the model, careful comparison with molecular dynamics simulations of a hard sphere crystal is drawn. A criterion on the critical nature of a microscopic configuration is deduced from the bimodal character of the probability density function of melting time. For kinetic Monte Carlo simulations with dynamical parameter values which fit the molecular dynamics results, the number of liquid sites of the critical droplet is found to be smaller than 300 and the ability of the critical droplet to invade the entire system is shown to be independent of the droplet shape as long as this droplet remains compact. In kinetic Monte Carlo simulations, the size of the critical droplet is independent of the system size. Molecular dynamics evidences a more complex dependence of melting time on system size, which reveals non-trivial finite size effects.
Temporal instability analysis of inviscid compound jets falling under gravity
Authors: Mohsin Muhammad , Uddin Jamal , Decent Stephen P. , Afzaal Muhammad F.
Published: January 2013

Compound liquid jets can be used in a variety of industrial applications ranging from capsule production in pharmaceutics to enhance printing methods in ink-jet printing. An appreciation of how instability along compound jets can lead to breakup and droplet formation is thus critical in many fields in science and engineering. In this paper, we perform a theoretical analysis to examine the instability of an axisymmetric inviscid compound liquid jet which falls vertically under the influence of gravity. We use a long-wavelength, slender-jet asymptotic expansion to reduce the governing equations of the problem into a set of one-dimensional partial differential equations, which describe the evolution of the leading-order axial velocity of the jet as well as the radii of both the inner and the outer interfaces. We first determine the steady-state solutions of the one-dimensional model equations and then we perform a linear temporal instability analysis to obtain a dispersion relation, which gives us useful information about the maximum growth rate and the maximum wavenumber of the imposed wave-like disturbance. We use our results to estimate the location and qualitative nature of breakup and then compare our results with numerical simulations.
Dependence of the width of the glass transition interval on cooling and heating rates
Authors: Schmelzer Jürn W. P. , Tropin Timur V.
Published: January 2013

In a preceding paper [J. W. P. Schmelzer, J. Chem. Phys. 136, 074512 (2012)10.1063/1.3685510], a general kinetic criterion of glass formation has been advanced allowing one to determine theoretically the dependence of the glass transition temperature on cooling and heating rates (or similarly on the rate of change of any appropriate control parameter determining the transition of a stable or metastable equilibrium system into a frozen-in, non-equilibrium state of the system, a glass). In the present paper, this criterion is employed in order to develop analytical expressions for the dependence of the upper and lower boundaries and of the width of the glass transition interval on the rate of change of the external control parameters. It is shown, in addition, that the width of the glass transition range is strongly correlated with the entropy production at the glass transition temperature. The analytical results are supplemented by numerical computations. Analytical results and numerical computations as well as existing experimental data are shown to be in good agreement.
Nernst-Planck model of photo-triggered, pH–tunable ionic transport through nanopores functionalized with “caged” lysine chains
Authors: Nasir Saima , Ramirez Patricio , Ali Mubarak , Ahmed Ishtiaq , Fruk Ljiljana , Mafe Salvador , Ensinger Wolfgang
Published: January 2013

We describe the fabrication of asymmetric nanopores sensitive to ultraviolet (UV) light, and give a detailed account of the divalent ionic transport through these pores using a theoretical model based on the Nernst-Planck equations. The pore surface is decorated with lysine chains having pH-sensitive (amine and carboxylic acid) moieties that are caged with photo-labile 4,5-dimethoxy-2-nitrobenzyl (NVOC) groups. The uncharged hydrophobic NVOC groups are removed using UV irradiation, leading to the generation of hydrophilic “uncaged” amphoteric groups on the pore surface. We demonstrate experimentally that polymer membranes containing single pore and arrays of asymmetric nanopores can be employed for the pH-controlled transport of ionic and molecular analytes. Comparison between theory and experiment allows for understanding the individual properties of the phototriggered nanopores, and provides also useful clues for the design and fabrication of multipore membranes to be used in practical applications.
Band gap bowing and band offsets in relaxed and strained Si1−xGex alloys by employing a new nonlinear interpolation scheme
Authors: Sant Saurabh , Lodha Saurabh , Ganguly Udayan , Mahapatra Souvik , Heinz Frederik O. , Smith Lee , Moroz Victor , Ganguly Swaroop
Published: January 2013

We present nonlocal empirical pseudopotential calculations for SiGe alloys employing a novel nonlinear interpolation scheme. Our interpolation scheme is able to correctly model for the first time the band gap bowing observed in relaxed SiGe alloys. The valence-band-edge and conduction-band-edge energies in relaxed Si1−xGex for arbitrary x, which are difficult to obtain by experimental techniques, have been evaluated using pseudopotential calculations. We have also calculated the band energies of pseudomorphic [100]-strained Si1−xGex alloys grown over unstrained Si1−yGey substrates. The energy gaps, valence and conduction band offsets, effective masses, and strain induced splittings in pseudomorphic SiGe layers are calculated for the whole range of alloy compositions x and y.
Internal detection of surface plasmon coupled chemiluminescence during chlorination of potassium thin films
Authors: Becker Felix , Krix David , Hagemann Ulrich , Nienhaus Hermann
Published: January 2013

The interaction of chlorine with potassium surfaces is a prototype reaction with a strong non-adiabatic energy transfer leading to exoemission and chemiluminescence. Thin film K/Ag/p-Si(111) Schottky diodes with 8 nm potassium on a 5−200 nm thick Ag layer are used as 2π-photodetectors for the chemiluminescence during chlorination of the K film at 110 K. The observed photocurrent shows a sharp maximum for small exposures and decreases gradually with the increasing chloride layer. The time dependence can be explained by the reaction kinetics, which is governed initially by second-order adsorption processes followed by an electric field-assisted diffusion. The detector current corresponds to a yield of a few percent of elementary charge per reacting chlorine molecule and is orders of magnitude larger than for external detection. The photoyield can be enhanced by increasing the Ag film thickness. For Ag films of 30 and 50 nm, the yield exhibits a maximum indicating surface plasmon coupled chemiluminescence. Surface plasmon polaritons in the Ag layer are excited by the reaction and decay radiatively into Si leading to the observed currents. A model calculation for the reverse process in attenuated total reflection is applied to explain the observed current yield maxima.
A novel photonic Doppler velocimetry for transverse velocity measurement
Authors: Chen Guanghua , Wang Detian , Liu Jun , Meng Jianhua , Liu Shouxian , Yang Qingguo
Published: January 2013

A fiber interferometry for transverse velocity measurement has been developed. This diagnostic is similar to photonic Doppler velocimetry in the way in which laser propagates and couples. The interferometer mainly consists of a fiber coupler, an emitting probe, and two receiving probes. A pair of scattered laser beams mix in the coupler and generates fringes with frequency proportional to transverse velocity. Measurement of transverse velocity is independent of longitudinal velocity. The feasibility of the technique has been verified by rotating wheel experiment and shock loading experiment.
Laser heating and detection of bilayer microcantilevers for non-contact thermodynamic measurements
Authors: Burke Brian G. , LaVan David A.
Published: January 2013

We describe a method for optical detection (frequency and position) and heating of bilayer microcantilevers (BMCs) to high temperatures at fast heating rates (106 °C/s to 109 °C/s) for non-contact thermodynamic measurements of small quantities of materials in the femtogram range. The current experimental apparatus with a 2 μm × 10 μm BMC achieves a deflection sensitivity of 0.1 Å, heating rate of 3.0 × 106 °C/s, and heat sensitivity of 18 pJ in a 3 kHz bandwidth in air. By measuring the resonant frequency shift after sample loading, we achieve a mass resolution of 2.67 fg.
Note: Network random walk model of two-state protein folding: Test of the theory
Authors: Berezhkovskii Alexander M. , Murphy Ronan D. , Buchete Nicolae-Viorel
Published: January 2013

We study two-state protein folding in the framework of a toy model of protein dynamics. This model has an important advantage: it allows for an analytical solution for the sum of folding and unfolding rate constants [A. M. Berezhkovskii, F. Tofoleanu, and N.-V. Buchete, J. Chem. Theory Comput. 7, 2370 (2011)10.1021/ct200281d] and hence for the reactive flux at equilibrium. We use the model to test the Kramers-type formula for the reactive flux, which was derived assuming that the protein dynamics is described by a Markov random walk on a network of complex connectivity [A. Berezhkovskii, G. Hummer, and A. Szabo, J. Chem. Phys. 130, 205102 (2009)10.1063/1.3139063]. It is shown that the Kramers-type formula leads to the same result for the reactive flux as the sum of the rate constants.
Deposition of (WO3)3 nanoclusters on the MgO(001) surface: A possible way to identify the charge states of the defect centers
Authors: Zhu Jia , Lin Shujuan , Wen Xingwei , Fang Zhenxing , Li Yi , Zhang Yongfan , Huang Xin , Ning Lixin , Ding Kaining , Chen Wenkai
Published: January 2013

Periodic density functional theory calculations have been performed to study the most stable structure of the (WO3)3 nanocluster deposited on the MgO(001) surface with three kinds of FS centers (FS0, FS+, and FS2+). Our results indicate that the configuration of (WO3)3 cluster, including the cyclic conformation and the heights of three W atoms, and the oxidation states are sensitive to the charge state of the FS center. It is interesting that the electron-riched FS0 vacancy on the MgO(001) surface can act as a promoting site to enhance the W–W interaction and the W3O3 cyclic conformation is maintained, while the skeleton of cluster becomes flexible when (WO3)3 is adsorbed on the electron-deficient vacancy (FS+ and FS2+). Accordingly, three FS-centers exhibit different arrangements of X-ray photoelectron spectra, the scanning tunneling microscopy images, and the vibrational spectra after depositing (WO3)3 cluster. Present results reveal that the (WO3)3 cluster may be used as a probe to identify the different FS centers on the MgO(001) surface.
Nonlinear thermal conductance in single-wall carbon nanotubes: Negative differential thermal resistance
Authors: Ai Bao-quan , An Meng , Zhong Wei-rong
Published: January 2013

Nonlinear thermal conductance in single-wall carbon nanotubes (CNTs) is investigated by applying the large temperature difference. From the classical molecular dynamics simulations, we observe the occurrence of negative differential thermal resistance (NDTR) in CNTs, namely, there exist a region of temperature difference, where the heat flux decreases as the applied temperature difference increases. Double NDTRs even occur in some CNTs with special diameters. When the length of CNTs increases, NDTR regime reduces and vanishes in the thermodynamic limit. CNTs with NDTR may be the good candidate materials for designing thermal devices such as thermal transistors, thermal logic gates, and thermal memory.
Electromagnetic waves destabilized by runaway electrons in near-critical electric fields
Authors: Kómár A. , Pokol G. I. , Fülöp T.
Published: January 2013

Runaway electron distributions are strongly anisotropic in velocity space. This anisotropy is a source of free energy that may destabilize electromagnetic waves through a resonant interaction between the waves and the energetic electrons. In this work, we investigate the high-frequency electromagnetic waves that are destabilized by runaway electron beams when the electric field is close to the critical field for runaway acceleration. Using a runaway electron distribution appropriate for the near-critical case, we calculate the linear instability growth rate of these waves and conclude that the obliquely propagating whistler waves are most unstable. We show that the frequencies, wave numbers, and propagation angles of the most unstable waves depend strongly on the magnetic field. Taking into account collisional and convective damping of the waves, we determine the number density of runaways that is required to destabilize the waves and show its parametric dependences.
Phase transitions and thermal expansion in pyroelectric energy conversion
Authors: McKinley Ian M. , Pilon Laurent
Published: January 2013

This paper elucidates dynamic effects of phase transitions and thermal expansion on pyroelectric energy conversion. The Olsen cycle was performed on [001]-oriented 0.72PbMg1/3Nb2/3O3−0.28PbTiO3 (PMN-28PT) single crystals at different frequencies with electric field cycled between 0.2 and 0.75 MV/m and temperature between 22 and 140 ∘C. The measured energy density more than doubled as frequency increased from 0.0173 to 0.0211 Hz. This was attributed to secondary pyroelectric effect caused by thermal expansion. At 0.0211 Hz, the samples transitioned from pseudocubic to highly polarized tetragonal phase during cooling. At lower frequency, it underwent additional phase transition from tetragonal to less polarized monoclinic phase.
Intrinsic bandgap of cleaved ZnO(112¯) surfaces
Authors: Sabitova A. , Ebert Ph. , Lenz A. , Schaafhausen S. , Ivanova L. , Dähne M. , Hoffmann A. , Dunin-Borkowski R. E. , Förster A. , Grandidier B. , Eisele H.
Published: January 2013

The existence of intrinsic surface states, the position of the Fermi level, and the size of the surface bandgap of the non-polar ZnO(112¯0) cleavage surfaces were investigated by scanning tunneling microscopy and spectroscopy. The comparison of spectroscopic measurements performed on atomically flat and stepped surfaces reveals the absence of intrinsic surface states within the fundamental bulk bandgap, but shows the occurrence of step-induced gap states. These states lead to a pinning of the Fermi level at the surface within the bandgap and generate a significant defect-related tunnel current, narrowing the measured apparent bandgap.
Structure and thermodynamic properties of BeO: Empirical corrections in the quasiharmonic approximation
Authors: Luo Fen , Cheng Yan , Cai Ling-Cang , Chen Xiang-Rong
Published: January 2013

The equilibrium lattice parameters, bulk modulus, and phase transition of BeO are investigated by using the density functional theory with the Perdew-Burke-Ernzerhof (PBE) and Perdew and Zunger (PZ) functionals. With two different exchange-correlation functionals, we predict the similar results that BeO is stable in hexagonal wurtzite (B4) phase up to pressure of 100 GPa and then transforms directly into the rocksalt (B1) phase. The calculated phonon dispersion curves of the B4 phase BeO are in excellent agreement with the experimental data. Under compression, the phonon dispersion curves of BeO in the B4 phase do not show any anomaly or instability. Within the quasiharmonic approximation (QHA) plus empirical energy corrections (EEC) calculations, the thermal equation of state and thermodynamic properties of BeO are obtained. The EECs improve the systematic deviations of PBE and PZ functionals and reproduce the experimental results in the range of the validity of the QHA. Moreover, the effect of EECs on the phase stability has been investigated.
Near resonant and nonresonant third-order optical nonlinearities of colloidal InP/ZnS quantum dots
Authors: Wang Y. , Yang X. , He T. C. , Gao Y. , Demir H. V. , Sun X. W. , Sun H. D.
Published: January 2013

We have investigated the third-order optical nonlinearities of high-quality colloidal InP/ZnS core-shell quantum dots (QDs) using Z-scan technique with femtosecond pulses. The two-photon absorption cross-sections as high as 6.2 × 103 GM are observed at 800 nm (non-resonant regime) in InP/ZnS QDs with diameter of 2.8 nm, which is even larger than those of CdSe, CdS, and CdTe QDs at similar sizes. Furthermore, both of the 2.2 nm and 2.8 nm-sized InP/ZnS QDs exhibit strong saturable absorption in near resonant regime, which is attributed to large exciton Bohr radius in this material. These results strongly suggest the promising potential of InP/ZnS QDs for widespread applications, especially in two-photon excited bio-imaging and saturable absorbing.
An 8-bit carry look-ahead adder with 150 ps latency and sub-microwatt power dissipation at 10 GHz
Authors: Herr Anna Y. , Herr Quentin P. , Oberg Oliver T. , Naaman Ofer , Przybysz John X. , Borodulin Pavel , Shauck Steven B.
Published: January 2013

Reciprocal quantum logic combines the speed and power-efficiency of single-flux quantum superconductor devices with design features that are similar to CMOS. We have demonstrated an 8-bit carry look-ahead adder in the technology using combinational gates with fanout of four and non-local interconnect. Measured power dissipation of the fully active circuit is only 510 nW at 6.2 GHz. Latency is only 150 ps at a clock rate of 10 GHz.
Tunable topological electronic structures in Sb(111) bilayers: A first-principles study
Authors: Chuang Feng-Chuan , Hsu Chia-Hsiu , Chen Chia-Yu , Huang Zhi-Quan , Ozolins Vidvuds , Lin Hsin , Bansil Arun
Published: January 2013

Electronic structures and band topology of a single Sb(111) bilayer in the buckled honeycomb configuration are investigated using first-principles calculations. A nontrivial topological insulating phase can be induced by tensile strain, indicating the possibility of realizing the quantum spin Hall state for Sb thin films on suitable substrates. The presence of buckling provides an advantage in controlling the band gap through an out-of-plane external electric field, making a topological phase transition with six spin-polarized Dirac cones at the critical point. With a tunable gap and reversible spin polarization, Sb thin films are promising candidates for spintronic applications.
Leaky and bound modes in terahertz metasurfaces made of transmission-line metamaterials
Authors: Hon Philip W. C. , Liu Zhijun , Itoh Tatsuo , Williams Benjamin S.
Published: January 2013

Prism coupling and reflection spectroscopy are used to characterize bound modes within composite right/left handed terahertz metamaterial waveguides. The cavity antenna model is used to understand the polarization dependence of the radiative coupling to TM00 and TM01 waveguide modes. Furthermore, the cavity model along with transmission-line theory is used to derive a surface impedance model for a waveguide array metasurface. Qualitative agreement with the experiment is observed, including a mode splitting for p-polarized surface waves at the light line and the existence of s-polarized magnetic spoof surface plasmons.
Cation and magnetic orders in MnFe2O4 from density functional calculations
Authors: Huang Jhih-Rong , Cheng Ching
Published: January 2013

MnFe2O4 generally crystallizes in a mixed phase consisting of both the normal and inverse spinel structures with the fitted experimentally determined saturation moments of 5 and 3 μB per formula, respectively. Employing the density-functional methods with the generalized gradient approximation for the exchange-correlation energy functional and the on-site Coulomb effect (GGA+U), we have studied this material through exploring various cation distributions and magnetic orders of the system. We demonstrate that the magnetic moment can be accounted for by the high-spin Mn2+ cations at the tetrahedral site in the normal spinel structure and by the intermediate-spin Mn2+ cations at the octahedral site in the inverse spinel structure. That is, the results support the single-valence state for this material. The corresponding energetics, exchange interactions, and electronic properties are also presented and discussed.
Enhancement of room temperature dislocation-related photoluminescence of electron irradiated silicon
Authors: Xiang Luelue , Li Dongsheng , Jin Lu , Wang Shuming , Yang Deren
Published: January 2013

In this paper, we have investigated the room temperature dislocation-related photoluminescence of electron irradiated silicon. It is found that high temperature annealing can enhance the D1 line emission measured at room temperature. The abnormal peak shift of D1 line on the dependence of temperatures reveals the reconstruction of D1 luminescence center. It is suggested that the high temperature annealing could cause the transformation of the dislocation-point defect structure, so that the D1 luminescence is enhanced and stabilized.
Decoupling free-carriers contributions from oxygen-vacancy and cation-substitution in extrinsic conducting oxides
Authors: Lin Y. H. , Liu Y. S. , Lin Y. C. , Wei Y. S. , Liao K. S. , Lee K. R. , Lai J. Y. , Chen H. M. , Jean Y. C. , Liu C. Y.
Published: January 2013

The intrinsic oxygen-vacancies and the extrinsic dopants are two major fundamental free-carrier sources for the extrinsic conducting oxides, such as Sn-doped In2O3. Yet, the individual contributions of the above two free-carrier sources to the total carrier concentrations have never been unraveled. A carrier-concentration separation model is derived in this work, which can define the individual contributions to the total carrier concentration from the intrinsic oxygen-vacancies and the extrinsic dopants, separately. The individual contributions obtained from the present carrier-concentration separation model are verified by the two-state trapping model, photoluminescence, and positron annihilation lifetime (PAL) spectroscopy. In addition, the oxygen-vacancy formation energy of the Sn:In2O3 thin film is determined to be 0.25 eV by PAL spectroscopy.
Sensitivity of thermal conductivity of carbon nanotubes to defect concentrations and heat-treatment
Authors: Park Jungkyu , Bifano Michael F. P. , Prakash Vikas
Published: January 2013

In the present work, we use reverse non-equilibrium molecular dynamics with adaptive intermolecular reactive empirical bond order interatomic potential to investigate sensitivity of thermal conductivity in (6, 6) single-walled carbon nanotubes (SWCNTs) to side-wall defects and high temperature heat- treatment. Effects of two side-wall defect types and their concentrations are evaluated: chemisorbed hydrogen adatoms on the SWCNT side wall and point vacancy defects. The results of the simulations indicate that the degree of hydrogenation and vacancy concentrations have very similar detrimental effects on the thermal conductivity of (6, 6) SWCNTs. Vacancy repair is evident with heat treatment, and heat-treatment temperatures of 3000 °C for up to 22 ns are found to transform point vacancies into various non-hexagonal side-wall defects. The vacancy repair is accompanied by an approximately 10% increase in thermal conductivity. In addition, thermal conductivity measurements in both heat-treated and non-heat treated chemical vapor deposition grown multi-walled carbon nanotubes (MWCNTs) are reviewed. The results of the study suggest that thermal conductivity of carbon nanotubes (CNTs) can be drastically increased if measures are taken to remove common defects from the carbon nanotube side-walls.
Impact of hydrogen radical-injection plasma on fabrication of microcrystalline silicon thin film for solar cells
Authors: Abe Yusuke , Kawashima Sho , Fukushima Atsushi , Lu Ya , Takeda Keigo , Kondo Hiroki , Ishikawa Kenji , Sekine Makoto , Hori Masaru
Published: January 2013

A plasma-enhanced chemical deposition system with hydrogen radical-injection (RI) is proposed for the fabrication of hydrogenated microcrystalline silicon (μc-Si:H) thin films. The plasma parameters and resultant growth characteristics obtained with the RI-capacitively coupled plasma (RI-CCP) system excited with 60 MHz power were compared with those obtained using a conventional CCP (C-CCP) system. The absolute density of hydrogen (H) radicals was measured by vacuum ultraviolet laser absorption spectroscopy (VUVLAS) to evaluate the effect of RI for controlling the H radical density. A higher density of H radicals was achieved with RI-CCP than with C-CCP by H RI. The crystallinity factor, preferential orientation, defect density, microstructure, and post-deposition oxidation of Si thin films deposited using C-CCP and RI-CCP were investigated. Crystallinity factor of 0.6 was realized with high deposition rate of about 2 nm/s even under a low plasma density using RI-CCP. The defect density of μc-Si:H thin films prepared using RI-CCP was lower than that in thin films prepared using C-CCP. In addition, post-deposition oxidation of the films with RI-CCP was lower than that with C-CCP. The high performance of RI-CCP for the fabrication of μc-Si:H thin films for solar cell devices is also demonstrated.
Room temperature reversible tuning of magnetism of electrolyte-gated La0.75Sr0.25MnO3 nanoparticles
Authors: Mishra A. K. , Darbandi Azad J. , Leufke Philipp M. , Kruk Robert , Hahn Horst
Published: January 2013

Reversible control of magnetization and Curie temperature (TC) by electrostatic modulation of the surface charge carrier density is presented for the strongly correlated La0.75Sr0.25MnO3 (LSMO) system. The nanoparticulate LSMO was synthesized by spray pyrolysis. A controlled post annealing was carried out to obtain a sharp magnetic transition slightly above room temperature along with favorable surface-to-volume ratios. Resulting nanoporous LSMO was electrostatically charged using a non-aqueous electrolyte with applied voltage limited within the purely capacitive window. The electrostatic charging effect on magnetization was investigated around TC for varying temperatures and applied magnetic fields. The resultant magnetization modulation upon charging is discussed in terms of the reversible electrostatic hole doping.
Effect of tunneling transfer on thermal redistribution of carriers in hybrid dot-well nanostructures
Authors: Mazur Yu. I. , Dorogan V. G. , Marega E. , Guzun D. , Ware M. E. , Zhuchenko Z. Ya. , Tarasov G. G. , Lienau C. , Salamo G. J.
Published: January 2013

The thermally induced redistribution of carriers between quantum well (QW) and quantum dot (QD) layers in a hybrid dot-well system composed of InAs QDs and an InGaAs QW is studied by means of photoluminescence (PL) spectroscopy. This redistribution significantly affects the QD and QW PL intensities depending both on the dot-well barrier thickness and height. For comparatively thin barriers, the interplay between tunnel and thermal carrier fluxes becomes crucial, governing the exciton dynamics in a tunnel injection dot-well structure at elevated temperatures. For a sufficiently thick spacer, it is shown that exciton localization within the QW, apparently induced by QD strain fields, has a profound influence on the transfer dynamics at low temperatures.