bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of temperature increments on tunneling barrier height and effective electron mass for plasma nitrided thin SiO2 layer on a large wafer area
Authors: Aygun G. , Roeder G. , Erlbacher T. , Wolf M. , Schellenberger M. , Pfitzner L.
Published: October 2010

Thermally grown SiO2 layers were treated by a plasma nitridation process realized in a vertical furnace. The combination of a pulsed-low frequency plasma and a microwave remote plasma with N2/NH3/He feed gas mixture was used to nitride the thermally grown SiO2 gate dielectrics of MIS structures. Temperature dependency of effective masses and the barrier heights for electrons in pure thermally grown SiO2 as well as plasma nitrided SiO2 in high electric field by means of Fowler–Nordheim regime was determined. It is frequently seen from the literature that either effective electron mass or barrier height (generally effective electron mass) is assumed to be a constant and, as a result, the second parameter is calculated under the chosen assumption. However, in contrast to general attitude of previous studies, this work does not make any such assumptions for the calculation of neither of these two important parameters of an oxide at temperature ranges from 23 to 110 °C for SiO2, and 23 to 130 °C for nitrided oxide. It is also shown here that both parameters are affected from the temperature changes; respectively, the barrier height decreases while the effective mass increases as a result of elevated temperature in both pure SiO2 and plasma nitrided SiO2. Therefore, one parameter could be miscalculated if the other parameter, i.e., effective mass of electron, was assumed to be a constant with respect to variable physical conditions like changing temperature. Additionally, the barrier heights were calculated just by taking constant effective masses for both types of oxides to be able to compare our results to common literature values.
Non-Hermitean Wishart random matrices (I)
Authors: Kanzieper Eugene , Singh Navinder
Published: October 2010

A non-Hermitean extension of paradigmatic Wishart random matrices is introduced to set up a theoretical framework for statistical analysis of (real, complex, and real-quaternion) stochastic time series representing two “remote” complex systems. The first paper in a series provides a detailed spectral theory of non-Hermitean Wishart random matrices composed of complex valued entries. The great emphasis is placed on an asymptotic analysis of the mean eigenvalue density for which we derive, among other results, a complex-plane analog of the Marčenko–Pastur law. A surprising connection with a class of matrix models previously invented in the context of quantum chromodynamics is pointed out.
Simulation of loss mechanisms in organic solar cells: A description of the mesoscopic Monte Carlo technique and an evaluation of the first reaction method
Authors: Groves Chris , Kimber Robin G. E. , Walker Alison B.
Published: October 2010

In this letter we evaluate the accuracy of the first reaction method (FRM) as commonly used to reduce the computational complexity of mesoscale Monte Carlo simulations of geminate recombination and the performance of organic photovoltaic devices. A wide range of carrier mobilities, degrees of energetic disorder, and applied electric field are considered. For the ranges of energetic disorder relevant for most polyfluorene, polythiophene, and alkoxy poly(phenylene vinylene) materials used in organic photovoltaics, the geminate separation efficiency predicted by the FRM agrees with the exact model to better than 2%. We additionally comment on the effects of equilibration on low-field geminate separation efficiency, and in doing so emphasize the importance of the energy at which geminate carriers are created upon their subsequent behavior.
Nonequilibrium alloy formation in the immiscible Cu–Mo system studied by thermodynamic calculation and ion beam mixing
Authors: Bai X. , Wang T. L. , Ding N. , Li J. H. , Liu B. X.
Published: October 2010

For the equilibrium immiscible Cu–Mo system characterized by a positive heat of formation (+19 kJ mol−1), thermodynamic calculation showed that by adding an adequate interfacial free energy, the Gibbs free energy of the Cu–Mo multilayered films could be elevated up to a higher level than the convex-shaped free energy curve of the amorphous phase and supersaturated solid solutions. Accordingly, ion beam mixing of the Cu–Mo multilayered samples did result in forming a unique amorphous phase with an alloy composition around 80 at. % Mo and two supersaturated solid solutions of fcc and bcc structures at around 27 at. % and 90 at. % Mo, respectively, matching well with the thermodynamic calculation.
Experimental study of highly turbulent isothermal opposed-jet flows
Authors: Coppola Gianfilippo , Gomez Alessandro
Published: October 2010

Opposed-jet flows have been shown to provide a valuable means to study a variety of combustion problems, but have been limited to either laminar or modestly turbulent conditions. With the ultimate goal of developing a burner for laboratory flames reaching turbulence regimes of relevance to practical systems, we characterized highly turbulent, strained, isothermal, opposed-jet flows using particle image velocimetry (PIV). The bulk strain rate was kept at 1250 s−1 and specially designed and properly positioned turbulence generation plates in the incoming streams boosted the turbulence intensity to well above 20%, under conditions that are amenable to flame stabilization. The data were analyzed with proper orthogonal decomposition (POD) and a novel statistical analysis conditioned to the instantaneous position of the stagnation surface. Both POD and the conditional analysis were found to be valuable tools allowing for the separation of the truly turbulent fluctuations from potential artifacts introduced by relatively low-frequency, large-scale instabilities that would otherwise partly mask the turbulence. These instabilities cause the stagnation surface to wobble with both an axial oscillation and a precession motion about the system axis of symmetry. Once these artifacts are removed, the longitudinal integral length scales are found to decrease as one approaches the stagnation line, as a consequence of the strained flow field, with the corresponding outer scale turbulent Reynolds number following a similar trend. The Taylor scale Reynolds number is found to be roughly constant throughout the flow field at about 200, with a value virtually independent of the data analysis technique. The novel conditional statistics allowed for the identification of highly convoluted stagnation lines and, in some cases, of strong three-dimensional effects, that can be screened, as they typically yield more than one stagnation line in the flow field. The ability to lock on the instantaneous stagnation line, at the intersection of the stagnation surface with the PIV measurement plane, is particularly useful in the combustion context, since the flame is aerodynamically stabilized in the vicinity of the stagnation surface. Estimates of the ratio of the mean residence time (inverse strain rate) to the vortex turnover time yield values greater than unity. The conditional mean velocity gradient suggests that, in contrast to the existing literature, the highest gradients are around the system centerline, which would result in a higher probability of flame extinction in that region under chemically reacting conditions. The compactness of the domain and the short mean residence time render the system well suited to direct numerical simulation, more so than conventional jet flames.
Note: Tangential x-ray diagnosis for investigating fast MHD events in EAST tokamak
Authors: Li Erzhong , Hu Liqun , Chen Kaiyun , Zhang Jizong , Chen Yiebin , Zhou Ruijie , Gan Kaifu , Liu Yong
Published: October 2010

A tangential x-ray diagnosis has been installed in the experimental advanced superconducting tokamakvacuum vessel for the study of fast magnetohydrodynamics (MHD) events. This system is based on absolute x-ray ultraviolet detectors with a collimator which is processed by laser machine. The first experimental results have proved its ability to measure the small-scale and transient MHD perturbations.
Generation of enhanced evanescent Bessel beam using band-edge resonance
Authors: Rui Guanghao , Lu Yonghua , Wang Pei , Ming Hai , Zhan Qiwen
Published: October 2010

A method for generating enhanced evanescent Bessel beam is reported. When a radially polarized beam is strongly focused onto the last interface of one-dimensional photonic band gap structure, enhanced evanescent J0 type Bessel beam can be generated via the band-edge resonance. Similarly, enhanced evanescent J1 type Bessel beam can be created by reversing the multilayer structure under azimuthally polarized illumination. These enhanced evanescent Bessel fields may have important applications in optical manipulations of nanoparticles.
Effects of AlGaAs energy barriers on InAs/GaAs quantum dot solar cells
Authors: Sablon K. A. , Little J. W. , Olver K. A. , Wang Zh. M. , Dorogan V. G. , Mazur Yu. I. , Salamo G. J. , Towner F. J.
Published: October 2010

We have studied the effects of AlGaAs energy barriers surrounding self-assembled InAs quantum dots in a GaAs matrix on the properties of solar cells made with multiple quantum dot layers in the active region of a photodiode. We have compared the fenced dot samples with conventional InAs/GaAs quantum dot solar cells and with GaAs reference cells. We have found that, contrary to theoretical predictions, the AlGaAs fence layers do not enhance the transport properties of photogenerated carriers but instead suppress the extraction of the carriers excited in the dots by light with wavelengths longer than the cutoff wavelength of the GaAs matrix material. Both the standard quantum dots and the fenced dots were found to give solar cell performance comparable to the GaAs reference cells for certain active region thicknesses but neither showed enhancement due to the longer wavelength absorption or improved carrier transport.
Nonlinear enhancement of plasma density in linear combination of multiple collisional internal inductively coupled plasma sources
Authors: Chen Zhipeng , Li Hong , Li Bin , Luo Chen , Xie Jinlin , Liu Wandong
Published: October 2010

The nonlinear enhancement of plasma density in a combination of two and four collisional internal inductively coupled plasma sources has been experimentally investigated at different mediate gas pressures and radio-frequency powers, where each source can be considered as independent and the combination is linear. In the nonlinear enhancement phenomenon, the plasma density distribution in combination is not only larger than that of every individual source, but also larger than the linear summation of them in most region of the midplane. The nonlinear enhancement effect in the center of the midplane has stronger functional relation to the plasma density and is sensitive to the arrangement method, while it is weakly affected by the neutral particle density. Meanwhile, the electron temperature approximately keeps constant during the antenna’s individual to combinational discharge. Furthermore, a nonlinear diffusion model including the multistep ionization is applied to describe the nonlinear enhancement phenomenon in linear combination, of which the solutions are good consistent with the experimental results.
Ab initio prediction of magnetically dead layers in freestanding γ-Ce(111)
Authors: Jalali Asadabadi S. , Kheradmand F.
Published: October 2010

It is well known that the surface of nonmagnetic α-Ce is magnetically ordered, i.e., γ-like. One then might conjecture, in agreement with previous theoretical predictions, that the γ-Ce may also exhibit at its surfaces even more strongly enhanced γ-like magnetic ordering. Nonetheless, our result shows that the (111)-surfaces of magnetic γ-Ce are neither spin nor orbitally polarized, i.e., α-like. Therefore, we predict, in contrast to the nonmagnetic α-phase which tends to produce magnetically ordered γ-like thin layers at its free surfaces, the magnetic γ-phase has a tendency to form α-like dead layers. This study, which explains the suppressed (promoted) surface magnetic moments of γ-Ce (α-Ce), shows that how nanoscale can reverse physical properties by going from bulk to the surface in isostructural α- and γ-phases of cerium. We predict using our freestanding surface results that a typical unreactive and nondiffusive substrate can dramatically influence the magnetic surface of cerium thin films in contrast to most of the uncorrelated thin films and strongly correlated transition metals. Our result implies that magnetic surface moments of α-Ce(111) can be suddenly disappeared by increasing lattice mismatch at the interface of a typical unreactive and nondiffusive substrate with cerium overlayers.
Laser peen forming induced two way bending of thin sheet metals and its mechanisms
Authors: Hu Yongxiang , Xu Xiaoxia , Yao Zhenqiang , Hu Jun
Published: October 2010

Laser peen forming, is a purely mechanical forming method achieved through the use of laser energy to form complex shapes or modify curvatures. It is flexible and independent of tool inaccuracies that result from wear and deflection. Its nonthermal process makes it possible to form sheet metal without material degradation or even improve them by inducing compressive stress over the target surface. Experimental investigation has been carried out to understand the effect of process parameters such as laser intensity, scanning velocity on the bending deformation of thin sheet metal with different thicknesses. It is found that the sheet metal can be made to bend not only toward but also away from the laser beam depending on the process condition. The bending deformation is found to be varied continuously and smoothly from the concave form to the convex by increasing the sheet thickness or decreasing the laser intensity. There is also a specific thickness for sheet metal to remain flat after laser peen forming. Two mechanisms are proposed to understand all experimental results, which are shock bending mechanism and stress gradient mechanism for bending toward and away from the laser beam, respectively. Due to the coupling effect of two mechanisms, the smoothly switching from one mechanism to the other depending on process conditions makes the laser peen forming to be an easily controlled process for forming complex shapes and high precision curvature modification.
Grain-oriented sodium bismuth titanate-based lead-free piezoelectric ceramics prepared using the pulsed strong magnetic field and template grain growth
Authors: Zhao Jun , Wang Fajun , Li Wen , Li Hui , Zhou Dongxiang , Gong Shuping , Hu Yunxiang , Fu Qiuyun
Published: October 2010

In this paper, 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 (BNBT6) lead-free piezoelectric ceramics have been prepared using the gelcasting technology. The dielectric and piezoelectric properties of these ceramics have been investigated. The specimens were sintered at 1100–1200 °C after grain-oriented under the pulsed strong magnetic field during the solidification of the green bodies. Compared with the BNBT6 samples without applying magnetic field, the ceramics textured by applying 5 T pulsed magnetic field has a coercive field with reduction of 400 V/mm, which makes the polarization process easier. Meanwhile, it is noted that the orientation degree increases with increasing sintering temperature, whereas the piezoelectric constant and electromechanical coupling coefficients are improved. If SrTiO3 seed grain is introduced, the orientation degree can reach 0.70 and the relative density of the sintered ceramics is up to 96%. The dielectric properties are anisotropic in directions vertical and parallel to the applied magnetic field. At around 180 °C, the dielectric constant in the direction vertical to the magnetic field is three times of that in the direction parallel to the magnetic field. And the dielectric loss in the direction vertical to the magnetic field is also higher than that in the direction parallel to the magnetic field.
Elastic moduli of Pu and Ga stabilized δ-Pu: Experimental data and phenomenological behavior at high temperature
Authors: Nadal Marie-Hélène , Bourgeois Ludivine
Published: October 2010

To contribute to the equation of state and constitutive relations of pure plutonium (Tm=913 K) and Ga stabilized δ-plutonium (Pu–2.3 at. %Ga; Tm=928 K), we have determined the elastic moduli (Young modulus E; adiabatic bulk modulus B, and shear modulus G) versus temperature T in the temperature range T∊[300;750] K or T/Tm∊[0.3;0.85]. Using an ultrasonic method as a robust concept despite the radiation damage to transducers, the elastic-waves velocities are described as decreasing for each crystallographic phase. Experimental results are compared to literature.
Constructal structure of nanofluids
Authors: Bai Chao , Wang Liqiu
Published: October 2010

The present work considers the problem of further enhancing nanofluids performance inside practical systems through designing their inside structures. Constructal analysis is performed up to the two-branching level on the classical blade-configured disk-shaped domain with central heat sink, adiabatic periphery and uniform heat generation. Transition point from one-branching-level to two-branching-level blade configuration is found. The effects of thermal conductivity ratio and overall volume fraction of blade material on nondimensional constructal overall temperature difference are found to appear always in the form of their product. The number of tributaries does not affect the system performance. Constructal robustness is also observed. Compared with the dispersed configuration under same conditions, this orderly-arranged blade configuration generates much smaller constructal overall temperature difference and thus performs much better for the heat conduction domain considered. Therefore, searching for better and better heat-flow structure is significant to performance.
The role of hot electron refluxing in laser-generated K-alpha sources
Authors: Neumayer P. , Aurand B. , Basko M. , Ecker B. , Gibbon P. , Hochhaus D. C. , Karmakar A. , Kazakov E. , Kühl T. , Labaune C. , Rosmej O. , Tauschwitz An. , Zielbauer B. , Zimmer D.
Published: October 2010

A study of the contribution of refluxing electrons in the production of K-alpha radiation from high-intensity laser irradiated thin targets has been performed. Thin copper foils both freestanding, and backed by a thick substrate were irradiated with laser pulses of energies around 100 J at intensities ranging from below 1017 to above 1019 W/cm2. At high laser intensities we find a strong reduction in the K-alpha yield from targets backed by the substrate. The observed yield reduction is in good agreement with a simple model using hot electron spectra from particle-in-cell simulations or directly inferred from the measured bremsstrahlung emission and can therefore be interpreted as due to the suppression of hot electron refluxing. The study shows that refluxing electrons play a dominant role in high-intensity laser driven K- alpha generation and have to be taken into account in designing targets for laser driven high-flux K-alpha sources.
Shielding of absorbing objects in collisionless flowing plasma
Authors: Tyshetskiy Yu. , Vladimirov S. V.
Published: October 2010

The electrostatic shielding of a charged absorbing object (dust grain) in a flowing collisionless plasma is investigated by using the linearized kinetic equation for plasma ions with a point-sink term accounting for ion absorption on the object. The effect of absorption on the attractive part of the grain potential distribution in plasma is investigated. For subthermal ion flows, the attractive part of the grain potential in the direction perpendicular to the ion flow can be significantly reduced or completely destroyed, depending on the absorption rate. For superthermal ion flows, however, the effect of absorption on the grain attraction in the direction perpendicular to the ion flow is shown to be exponentially weak. It is thus argued that, in the limit of superthermal ion flows, the effect of ion absorption by the grain on the grain's shielding potential can be safely ignored for typical grain sizes relevant to complex plasmas.
Transport of heat and mass in a two-phase mixture: From a continuous to a discontinuous description
Authors: Glavatskiy K. S. , Bedeaux D.
Published: October 2010

We present a theory that describes the transport properties of the interfacial region with respect to heat and mass transfer. Postulating the local Gibbs relation for a continuous description inside the interfacial region, we derive the description of the Gibbs surface in terms of excess densities and fluxes along the surface. We introduce overall interfacial resistances and conductances as the coefficients in the force-flux relations for the Gibbs surface. We derive relations between the local resistivities for the continuous description inside the interfacial region and the overall resistances of the surface for transport between the two phases for a mixture. It is shown that interfacial resistances depend among other things on the enthalpy profile across the interface. Since this variation is substantial, the coupling between heat and mass flow across the surface is also substantial. In particular, the surface puts up much more resistance to the heat and mass transfer than the homogeneous phases over a distance comparable to the thickness of the surface. This is the case not only for the pure heat conduction and diffusion but also for the cross effects such as thermal diffusion. For the excess fluxes along the surface and the corresponding thermodynamic forces, we derive expressions for excess conductances as integrals over the local conductivities along the surface. We also show that the curvature of the surface affects only the overall resistances for transport across the surface and not the excess conductivities along the surface.
Plasma transport in stochastic magnetic field caused by vacuum resonant magnetic perturbations at diverted tokamak edge
Authors: Park G. , Chang C. S. , Joseph I. , Moyer R. A.
Published: October 2010

A kinetic transport simulation for the first 4 ms of the vacuum resonant magnetic perturbations (RMPs) application has been performed for the first time in realistic diverted DIII-D tokamak geometry [J. Luxon, Nucl. Fusion 42, 614 (2002)], with the self-consistent evaluation of the radial electric field and the plasma rotation. It is found that, due to the kinetic effects, the stochastic parallel thermal transport is significantly reduced when compared to the standard analytic model [A. B. Rechester and M. N. Rosenbluth, Phys. Rev. Lett. 40, 38 (1978)] and the nonaxisymmetric perpendicular radial particle transport is significantly enhanced from the axisymmetric level. These trends agree with recent experimental result trends [T. E. Evans, R. A. Moyer, K. H. Burrell et al., Nat. Phys. 2, 419 (2006)]. It is also found, as a side product, that an artificial local reduction of the vacuum RMP fields in the vicinity of the magnetic separatrix can bring the kinetic simulation results to a more detailed agreement with experimental plasma profiles.
On the nature of Bose–Einstein condensation enhanced by localization
Authors: Jaeck Thomas , Pulé Joseph V. , Zagrebnov Valentin A.
Published: October 2010

In a previous paper we established that for the perfect Bose gas and the mean-field Bose gas with an external random or weak potential, whenever there is generalized Bose–Einstein condensation in the eigenstates of the single particle Hamiltonian, there is also generalized condensation in the kinetic-energy states. In these cases Bose–Einstein condensation is produced or enhanced by the external potential. In the present paper we establish a criterion for the absence of condensation in single kinetic-energy states and prove that this criterion is satisfied for a class of random potentials and weak potentials. This means that the condensate is spread over an infinite number of states with low kinetic-energy without any of them being macroscopically occupied.
Measurements of the fast electron bremsstrahlung emission during electron cyclotron resonance heating in the HL-2A tokamak
Authors: Zhang Y. P. , Liu Yi , Song X. Y. , Yuan G. L. , Chen W. , Ji X. Q. , Ding X. T. , Yang J. W. , Zhou J. , Li X. , Yang Q. W. , Duan X. R. , Pan C. H. , Liu Y.
Published: October 2010

A fast electron bremsstrahlung (FEB) diagnostic technique based on cadmium telluride (CdTe) detector has been developed recently in the HL-2A tokamak for measurements of the temporal evolution of FEB emission in the energy range of 10–200 keV. With a perpendicular viewing into the plasma on the equatorial plane, the hard x-ray spectra with eight different energy channels are measured. The discrimination of the spectra is implemented by an accurate spectrometry. The system also makes use of fast digitization and software signal processing technology. An ambient environment of neutrons, gammas, and magnetic disturbance requires careful shielding. During electron cyclotron resonance heating, the generation of fast electrons and the oscillations of electron fishbone (e-fishbone) have been found. Using the FEB measurement system, it has been experimentally identified that the mode strongly correlates with the electron cyclotron resonance heating produced fast electrons with 30–70 keV.
On the hydration of the phosphocholine headgroup in aqueous solution
Authors: Foglia Fabrizia , Lawrence M. Jayne , Lorenz Christian D. , McLain Sylvia E.
Published: October 2010

The hydration of the phosphocholine headgroup in 1,2-dipropionyl-sn-glycero-3-phosphocholine (C3–PC) in solution has been determined by using neutron diffraction enhanced with isotopic substitution in combination with computer simulation techniques. The atomic scale hydration structure around this head group shows that both the N(CH3)3 and CH2 portions of the choline headgroup are strongly associated with water, through a unique hydrogen bonding regime, where specifically a hydrogen bond from the CH group to water and a strong association between the water oxygen and N+ atom in solution have both been observed. In addition, both PO4 oxygens (P=O) and CO oxygens are oversaturated when compared to bulk water in that the average number of hydrogen bonds from water to both X=O oxygens is about 2.5 for each group. That water binds strongly to the glycerol groups and is suggestive that water may bind to these groups when phosophotidylcholine is embedded in a membrane bilayer.
A compact streak camera for 150 fs time resolved measurement of bright pulses in ultrafast electron diffraction
Authors: Kassier G. H. , Haupt K. , Erasmus N. , Rohwer E. G. , von Bergmann H. M. , Schwoerer H. , Coelho S. M. M. , Auret F. D.
Published: October 2010

We have developed a compact streak camera suitable for measuring the duration of highly charged subrelativistic femtosecond electron bunches with an energy bandwidth in the order of 0.1%, as frequently used in ultrafast electron diffraction (UED) experiments for the investigation of ultrafast structural dynamics. The device operates in accumulation mode with 50 fs shot-to-shot timing jitter, and at a 30 keV electron energy, the full width at half maximum temporal resolution is 150 fs. Measured durations of pulses from our UED gun agree well with the predictions from the detailed charged particle trajectory simulations.
Molecular dynamics simulations for CO2 absorption spectra. I. Line broadening and the far wing of the ν3 infrared band
Authors: Hartmann J.-M. , Boulet C. , Tran H. , Nguyen M. T.
Published: October 2010

Classical molecular dynamics simulations (CMDS) have been carried out for gaseous CO2 starting from the intermolecular potential energy surface. Through calculations for a large number of molecules treated as rigid rotors, various autocorrelation functions (ACFs) are obtained together with probabilities of rotational changes. Those used in the present paper are the ACFs of the center of mass velocity and of the molecular orientation, and the conditional probability of a change of the angular speed. They enable calculations, respectively, of the mass diffusion coefficient, of the infrared (dipolar) band shape including the wings, and of individual line-broadening coefficients. It is shown that these calculations, free of any adjustable parameter, lead to good agreement with measured values. This is expected from previous studies for the mass diffusion coefficient and line-broadening coefficients, but it is, to our knowledge, the first demonstration of the interest of CMDS for the prediction of band wings. The present results thus open promising perspectives for the theoretical treatment of the difficult problem of far wings profiles.
Large deformation and electromechanical instability of a dielectric elastomer tube actuator
Authors: Zhu Jian , Stoyanov Hristiyan , Kofod Guggi , Suo Zhigang
Published: October 2010

This paper theoretically analyzes a dielectric elastomer tube actuator (DETA). Subject to a voltage difference between the inner and outer surfaces, the actuator reduces in thickness and expands in length, so that the same voltage will induce an even higher electric field. This positive feedback may cause the actuator to thin down drastically, resulting in electrical breakdown. We obtain an analytical solution of the actuator undergoing finite deformation when the elastomer obeys the neo-Hookean model. The critical strain of actuation is calculated in terms of various parameters of design. We also discuss the effect of the strain-stiffening on electromechanical behavior of DETAs by using the model of freely joined links.
Local etch control for fabricating nanomechanical devices
Authors: Kim Hyunseok , Kim Chulki , Yu Minrui , Kim Hyun-Seok , Blick Robert H.
Published: October 2010

We report on the fabrication of suspended nanoelectromechanical systems using an etch enhancement technique. Nanoscale beams are defined by conventional electron beam lithography, followed by locally enhanced etching via electron beam exposure. The structures are successfully suspended within the “etch-booster window” by using an HF vapor etch step. The method is simple, does not require a special setup, and allows the spatial and temporal fine-tuning of the underetching process.
Anomalous aggregation state of deuterium molecules in the nanoscale pores of a metal organic framework
Authors: Kanoya Izuru , Furuta Terumi , Sakamoto Ryogo , Hosoe Mitsuya , Ichikawa Masao , Itoh Keiji , Fukunaga Toshiharu
Published: October 2010

The behavior of hydrogen molecules adsorbed onto the nanospace of porous materials is of great interest but is poorly understood. Here we show direct visualization of deuterium molecules adsorbed on isoreticular metal organic frameworks (IRMOF-1) at 77 K using reverse Monte Carlo simulation based on first principle molecular dynamics simulation and neutron diffraction. Results show that the two types of adsorption sites around a ZnO4 cluster are almost fully occupied by the deuterium molecules but that other sites are not fully occupied. Moreover an interesting information about the aggregation state of deuterium molecules was directly obtained from the deuterium–deuterium partial pair distribution function. Namely, the average distance of deuterium molecules adsorbed onto IRMOF-1 is slightly longer than that in a solid state but much shorter than that in the corresponding gas state.
GaN nanostructure design for optimal dislocation filtering
Authors: Liang Zhiwen , Colby Robert , Wildeson Isaac H. , Ewoldt David A. , Sands Timothy D. , Stach Eric A. , García R. Edwin
Published: October 2010

The effect of image forces in GaN pyramidal nanorod structures is investigated to develop dislocation-free light emitting diodes (LEDs). A model based on the eigenstrain method and nonlocal stress is developed to demonstrate that the pyramidal nanorod efficiently ejects dislocations out of the structure. Two possible regimes of filtering behavior are found: (1) cap-dominated and (2) base-dominated. The cap-dominated regime is shown to be the more effective filtering mechanism. Optimal ranges of fabrication parameters that favor a dislocation-free LED are predicted and corroborated by resorting to available experimental evidence. The filtering probability is summarized as a function of practical processing parameters: the nanorod radius and height. The results suggest an optimal nanorod geometry with a radius of ∼50b (26 nm) and a height of ∼125b (65 nm), in which b is the magnitude of the Burgers vector for the GaN system studied. A filtering probability of greater than 95% is predicted for the optimal geometry.
Multiscale three-dimensional simulations of charge gain and transport in diamond
Authors: Dimitrov D. A. , Busby R. , Cary J. R. , Ben-Zvi I. , Rao T. , Smedley J. , Chang X. , Keister J. W. , Wu Q. , Muller E.
Published: October 2010

A promising new concept of a diamond-amplified photocathode for generation of high-current, high-brightness, and low thermal emittance electron beams was recently proposed and is currently under active development. Detailed understanding of physical processes with multiple energy and time scales is required to design reliable and efficient diamond-amplifier cathodes. We have implemented models, within the VORPAL computational framework, to simulate secondary electron generation and charge transport in diamond in order to facilitate the investigation of the relevant effects involved. The models include inelastic scattering of electrons and holes for generation of electron-hole pairs, elastic, phonon, and charge impurity scattering. We describe the integrated modeling capabilities we developed and present results on charge gain and collection efficiency as a function of primary electron energy and applied electric field. We compare simulation results with available experimental data. The simulations show an overall qualitative agreement with the observed charge gain from transmission mode experiments and have enabled better understanding of the collection efficiency measurements.
Ultrahigh sensitivity magnetic field and magnetization measurements with an atomic magnetometer
Authors: Dang H. B. , Maloof A. C. , Romalis M. V.
Published: October 2010

We describe an ultrasensitive atomic magnetometer based on optically pumped potassium atoms operating in a spin-exchange relaxation free regime. We demonstrate magnetic field sensitivity of 160 aT/Hz1/2 in a gradiometer arrangement with a measurement volume of 0.45 cm3 and energy resolution per unit bandwidth of 44ℏ. As an example of an application enabled by such a magnetometer, we describe measurements of weak remnant rock magnetization as a function of temperature with a sensitivity on the order of 10−10 emu/cm3/Hz1/2 and temperatures up to 420°C.
Transitional flow of a non-Newtonian fluid in a pipe: Experimental evidence of weak turbulence induced by shear-thinning behavior
Authors: Esmael A. , Nouar C. , Lefèvre A. , Kabouya N.
Published: October 2010

The present letter is a thorough study of the flow regime where an asymmetry of the mean axial velocity profiles is observed for shear-thinning fluids flow in a pipe. This study is based on a statistical analysis of the axial velocity fluctuations. It is shown that this flow regime exhibits features of a weak turbulence: chaotic in time and regular in space. More precisely, (i) power spectra of axial velocity fluctuations decay following a power law with an exponent very close to −3, (ii) large-scale coherent structures are generated, and (iii) there is essentially no intermittency in this flow regime.
Fusion product diagnostics planned for Large Helical Device deuterium experiment
Authors: Isobe M. , Yamanishi H. , Osakabe M. , Miyake H. , Tomita H. , Watanabe K. , Iwai H. , Nomura Y. , Nishio N. , Ishii K. , Kaneko J. H. , Kawarabayashi J. , Takada E. , Uritani A. , Sasao M. , Iguchi T. , Takeiri Y. , Yamada H.
Published: October 2010

Deuterium experiment on the Large Helical Device (LHD) is now being planned at the National Institute for Fusion Science. The fusion product diagnostics systems currently considered for installation on LHD are described in this paper. The systems will include a time-resolved neutron yield monitor based on neutron gas counters, a time-integrated neutron yield monitor based on activation techniques, a multicollimator scintillation detector array for diagnosing spatial distribution of neutron emission rate, 2.5 MeV neutron spectrometer, 14 MeV neutron counter, and prompt γ-ray diagnostics.
Carbon impurities and the yellow luminescence in GaN
Authors: Lyons J. L. , Janotti A. , Van de Walle C. G.
Published: October 2010

Using hybrid functional calculations we investigate the effects of carbon on the electrical and optical properties of GaN. In contrast to the currently accepted view that C substituting for N (CN) is a shallow acceptor, we find that CN has an ionization energy of 0.90 eV. Our calculated absorption and emission lines also indicate that CN is a likely source for the yellow luminescence that is frequently observed in GaN, solving the longstanding puzzle of the nature of the C-related defect involved in yellow emission. Our results suggest that previous experimental data, analyzed under the assumption that CN acts as a shallow acceptor, should be re-examined.
Random laser action in GaN nanocolumns
Authors: Sakai Masaru , Inose Yuta , Ema Kazuhiro , Ohtsuki Tomi , Sekiguchi Hiroto , Kikuchi Akihiko , Kishino Katsumi
Published: October 2010

We report observations of random laser action in self-organized GaN nanocolumns. We have measured three samples with different filling fractions and investigated the dependence of the lasing property on the random configuration of nanocolumns. Numerical calculations based on a finite-difference time-domain method have also been performed and the comparison with the experimental results shows a clear relationship between the strength of light localization and the occurrence of random laser action.
A Bayesian method for construction of Markov models to describe dynamics on various time-scales
Authors: Rains Emily K. , Andersen Hans C.
Published: October 2010

The dynamics of many biological processes of interest, such as the folding of a protein, are slow and complicated enough that a single molecular dynamics simulation trajectory of the entire process is difficult to obtain in any reasonable amount of time. Moreover, one such simulation may not be sufficient to develop an understanding of the mechanism of the process, and multiple simulations may be necessary. One approach to circumvent this computational barrier is the use of Markov state models. These models are useful because they can be constructed using data from a large number of shorter simulations instead of a single long simulation. This paper presents a new Bayesian method for the construction of Markov models from simulation data. A Markov model is specified by (τ,P,T), where τ is the mesoscopic time step, P is a partition of configuration space into mesostates, and T is an NP×NP transition rate matrix for transitions between the mesostates in one mesoscopic time step, where NP is the number of mesostates in P. The method presented here is different from previous Bayesian methods in several ways. (1) The method uses Bayesian analysis to determine the partition as well as the transition probabilities. (2) The method allows the construction of a Markov model for any chosen mesoscopic time-scale τ. (3) It constructs Markov models for which the diagonal elements of T are all equal to or greater than 0.5. Such a model will be called a “consistent mesoscopic Markov model” (CMMM). Such models have important advantages for providing an understanding of the dynamics on a mesoscopic time-scale. The Bayesian method uses simulation data to find a posterior probability distribution for (P,T) for any chosen τ. This distribution can be regarded as the Bayesian probability that the kinetics observed in the atomistic simulation data on the mesoscopic time-scale τ was generated by the CMMM specified by (P,T). An optimization algorithm is used to find the most probable CMMM for the chosen mesoscopic time step. We applied this method of Markov model construction to several toy systems (random walks in one and two dimensions) as well as the dynamics of alanine dipeptide in water. The resulting Markov state models were indeed successful in capturing the dynamics of our test systems on a variety of mesoscopic time-scales.
Defected graphene nanoribbons under axial compression
Authors: Neek-Amal M. , Peeters F. M.
Published: October 2010

The buckling of defected rectangular graphene nanoribbons when subjected to axial stress with supported boundary conditions is investigated using atomistic simulations. The buckling strain and mechanical stiffness of monolayer graphene decrease with the percentage of randomly distributed vacancies. The elasticity to plasticity transition in the stress-strain curve, at low percentage of vacancies, are found to be almost equal to the buckling strain thresholds and they decrease with increasing percentage of vacancies.
Impact of interfacial dipole on carrier transport in bulk heterojunction poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester blends
Authors: Tsang S. W. , Drolet N. , Tse S. C. , Tao Y. , Lu Z. H.
Published: October 2010

The electron transport properties in various poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) blend films, prepared by various process conditions, were investigated by admittance spectroscopy at different temperatures. It was found that the electron mobility and the dispersive transport behavior showed a strong dependence on the thermal treatment condition; the blend with the fastest growth rate had orders of magnitude reduction in the mobility and a much more dispersive transport. Using the Gaussian disorder model, it was found that the energetic disorder of the density-of-states between blends plays a significant role in the observed phenomena. It is proposed that the difference in the energetic disorder is due to the interfacial dipole effect at the P3HT/PC61BM heterojunctions in the various blend films.
Enhancement of anisotropic conductivity, elastic, and dielectric constants in a liquid crystal-gold nanorod system
Authors: Sridevi S. , Prasad S. Krishna , Nair Geetha G. , D’Britto Virginia , Prasad B. L. V.
Published: October 2010

We report electrical conductivity (σ), dielectric constant (ε) and the elastic constant measurements in a nematic liquid crystal (LC) doped with small concentrations of gold nanorods. This LC-nanoparticle complex, shows not only orders of magnitude higher σ, but also stabilizes its anisotropy. The ε data suggests an increased ordering in the nematic phase, and an improved antiparallel correlation of the molecules in the isotropic phase. Surprisingly, an anisotropic enhancement of the Frank elasticity is also seen. We suggest a possible electro/magnetomechanical conductivity switch and also provide explanations based on the aspect ratio of the nanoparticles vis-à-vis the LC molecules.
p-type conductivity in silicon nanowires induced by heterojunction interface charge transfer
Authors: Yuan G. D. , Ng T. W. , Zhou Y. B. , Wang F. , Zhang W. J. , Tang Y. B. , Wang H. B. , Luo L. B. , Wang P. F. , Bello I. , Lee C. S. , Lee S. T.
Published: October 2010

p-type conductivity in intrinsic silicon nanowires (SiNWs) synthesized by an etching method was achieved via surface coating of MoO3 and tetrafluoro-tetracyanoquinodimethane thin layers. Characterization of field-effect transistors fabricated from single SiNW revealed a decrease in resistivity by six orders of magnitude and an increase in hole concentration by eight orders of magnitude with respect to the original silicon wafers. The enhancement of p-type conduction was demonstrated to originate from the interface charge transfer between inorganic/inorganic and organic/inorganic heterojunctions and the enrichment of hole concentration in SiNW surfaces based on band energy alignment and x-ray photoelectron spectroscopic analysis.
Plasma-enabled growth of separated, vertically aligned copper-capped carbon nanocones on silicon
Authors: Kumar S. , Levchenko I. , Keidar M. , Ostrikov K.
Published: October 2010

The formation of vertically aligned, clearly separated, copper-capped carbon nanocones with a length of up to 500 nm and base diameter of about 150 nm via three-stage process involving magnetron sputtering, N2 plasma treatment, and CH4+N2 plasma growth is studied. The width of gaps between the nanocones can be controlled by the gas composition. The nanocone formation mechanism is explained in terms of strong passivation of carbon in narrow gaps, where the access of plasma ions is hindered and the formation of large CnH2n+2 molecules is possible. This plasma-enabled approach can be used to fabricate nanoelectronic, nanofluidic, and optoelectronic components and devices.
Permalloy-based carbon nanotube spin-valve
Authors: Aurich H. , Baumgartner A. , Freitag F. , Eichler A. , Trbovic J. , Schönenberger C.
Published: October 2010

In this paper we demonstrate that permalloy (Py), a widely used Ni/Fe alloy, forms contacts to carbon nanotubes (CNTs) that meet the requirements for the injection and detection of spin-polarized currents in carbon-based spintronic devices. We establish the material quality and magnetization properties of Py strips in the shape of suitable electrical contacts and find a sharp magnetization switching tunable by geometry in the anisotropic magnetoresistance (AMR) of a single strip at cryogenic temperatures. In addition, we show that Py contacts couple strongly to CNTs, comparable to Pd contacts, thereby forming CNT quantum dots at low temperatures. These results form the basis for a Py-based CNT spin-valve exhibiting very sharp resistance switchings in the tunneling magnetoresistance, which directly correspond to the magnetization reversals in the individual contacts observed in AMR experiments.
Low temperature sintering of Ag nanoparticles for flexible electronics packaging
Authors: Hu A. , Guo J. Y. , Alarifi H. , Patane G. , Zhou Y. , Compagnini G. , Xu C. X.
Published: October 2010

We achieve robust bonding of Cu wires to Cu pads on polyimide with silver nanopaste cured at 373 K. The paste is prepared by simply condensing Ag nanoparticle (NP) solution via centrifuging. The bonding is formed by solid state sintering of Ag NPs through neck growth and direct metallic bonding between clean Ag–Cu interfaces. Both experiment and Monte Carlo simulation confirm that the melting point of joint clusters increases during sintering. This creates improved bonds for use at an elevated operating temperature using Ag NPs.
Quantum dynamics of the S+OH→SO+H reaction
Authors: Jorfi Mohamed , Honvault Pascal
Published: October 2010

First accurate quantum mechanical scattering calculations have been carried out for the S(P3)+OH(X Π2)→SO(X Σ3−)+H(S2) reaction using a recent ab initio potential energy surface for the ground electronic state, X A2″, of HSO. Total and state-to-state reaction probabilities for a total angular momentum J=0 have been determined for collision energies up to 0.5 eV. A rate constant has been calculated by means of the J-shifting approach in the 10–400 K temperature range. Vibrational and rotational product distributions show no specific behavior and are consistent with a mixture of direct and indirect reaction mechanisms.