bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Parathyroid Hormone Combined With Gait Training on Bone Density and Bone Architecture in People With Chronic Spinal Cord Injury
Authors: Gordon Keith E. , Wald Michael J. , Schnitzer Thomas J.
Published: April 2013

Objective

To evaluate the response of bone to 2 anabolic stimuli, teriparatide and mechanical loading, in subjects with spinal cord injury.

Design

A pilot study, 1 group, pretest‐posttest.

Setting

A rehabilitation hospital.

Participants

A convenience sample of 12 nonambulatory chronic spinal cord injury subjects.

Methods

The subjects were administered open‐label teriparatide 20 μg/d while undergoing robotic‐assisted stepping 3 times a week for 6 months, followed by 6 months of teriparatide alone.

Main Outcome Measurements

Bone status was evaluated at 3, 6, and 12 months by using dual‐energy x‐ray absorptiometry to calculate bone mineral density (BMD) at the spine and hip, magnetic resonance imaging to assess bone microarchitecture of the distal tibia, and serum bone markers.

Results

Mean (SD) baseline BMD measurements at the spine and the left and right total hip were 1.05 ± 0.162 g/cm2, 0.638 ± 0.090 g/cm2 and 0.626 ± 0.088 g/cm2, respectively. After 6 months of treatment, BMD changed 2.19% ± 3.61%, 0.02% ± 2.21%, and 0.74% ± 2.80% at the spine, and left and right total hip, respectively. These changes were not statistically significant (P > .05 for all). Magnetic resonance imaging supported an anabolic effect after 3 months of treatment with significant (P < .05) changes in trabecular thickness, 4.4% ± 4.06%; surface‐to‐curve ratio, 23.6% ± 22.3%; and erosion index, −17.04% ± 12.9%. Although the trend remained after 6 months, statistical significance was not retained. At 6 months, bone markers indicated an increase in mean levels of bone‐specific alkaline phosphatase, 53.8% ± 62.9%; C‐terminal telopeptides of type I collagen, 137.6% ± 194.6%; and intact amino‐terminal propeptide of type I procollagen, 61.4% ± 99.3%.

Conclusion

In this limited pilot study, teriparatide and mechanical loading resulted in a numerical but not statistically significant increase in lumbar spine BMD and no significant BMD changes at the hip. Magnetic resonance imaging at the distal tibia suggested an anabolic effect, but the high sensitivity offered by this technique was challenged by the limited ability to obtain analyzable data from all the subjects. Further studies that involve longer treatment periods and greater mechanical loading are warranted.
Effects of Lewis number on conditional fluid velocity statistics in low Damköhler number turbulent premixed combustion: A direct numerical simulation analysis
Authors: Chakraborty Nilanjan , Lipatnikov Andrei N.
Published: April 2013

The effects of global Lewis number Le on the statistics of fluid velocity components conditional in unburned reactants and fully burned products in the context of Reynolds Averaged Navier Stokes simulations have been analysed using a Direct Numerical Simulations (DNS) database of statistically planar turbulent premixed flames with a low Damköhler number and Lewis number ranging from 0.34 to 1.2. The conditional velocity statistics extracted from DNS data have been analysed with respect to the well-known Bray-Moss-Libby (BML) expressions which were derived based on bi-modal probability density function of reaction progress variable for high Damköhler number flames. It has been shown that the Lewis number substantially affects the mean velocity and the velocity fluctuation correlation conditional in products, with the effect being particularly pronounced for low Le. As far as the mean velocity and the velocity fluctuation correlation conditional in reactants are concerned, the BML expressions agree reasonably well with the DNS data reported in the present work. Based on a priori analysis of present and previously reported DNS data, the BML expressions have been empirically modified here in order to account for Lewis number effects, and the non-bimodal distribution of reaction progress variable. Moreover, it has been demonstrated for the first time that surface averaged velocity components and Reynolds stresses conditional in unburned reactants can be modelled without invoking expressions involving the Lewis number, as these surface averaged conditional quantities remain approximately equal to their conditionally averaged counterparts in the unburned mixture.
Extension of the Test-Area methodology for calculating solid-fluid interfacial tensions in cylindrical geometry
Authors: Blas Felipe J. , Mendiboure Bruno
Published: April 2013

We extend the well-known Test-Area methodology of Gloor et al. [J. Chem. Phys. 123, 134703 (2005)]10.1063/1.2038827, originally proposed to evaluate the surface tension of planar fluid-fluid interfaces along a computer simulation in the canonical ensemble, to deal with the solid-fluid interfacial tension of systems adsorbed on cylindrical pores. The common method used to evaluate the solid-fluid interfacial tension invokes the mechanical relation in terms of the tangential and normal components of the pressure tensor relative to the interface. Unfortunately, this procedure is difficult to implement in the case of cylindrical geometry, and particularly complex in case of nonspherical molecules. Following the original work of Gloor et al., we perform free-energy perturbations due to virtual changes in the solid-fluid surface. In this particular case, the radius and length of the cylindrical pore are varied to ensure constant-volume virtual changes of the solid-fluid surface area along the simulation. We apply the modified methodology for determining the interfacial tension of a system of spherical Lennard-Jones molecules adsorbed inside cylindrical pores that interact with fluid molecules through the generalized 10-4-3 Steele potential recently proposed by Siderius and Gelb [J. Chem. Phys. 135, 084703 (2011)]10.1063/1.3626804. We analyze the effect of pore diameter, density of adsorbed molecules, and fluid-fluid cutoff distance of the Lennard-Jones intermolecular potential on the solid-fluid interfacial tension. This extension, as the original Test-Area formulation, offers clear advantages over the classical mechanical route of computational efficiency, easy of implementation, and generality.
Unveiling the complex glassy dynamics of square shoulder systems: Simulations and theory
Authors: Das Gayatri , Gnan Nicoletta , Sciortino Francesco , Zaccarelli Emanuela
Published: April 2013

We performed extensive molecular dynamics (MD) simulations, supplemented by Mode Coupling Theory (MCT) calculations, for the square shoulder model, a purely repulsive potential where the hardcore is complemented by a finite shoulder. For the one-component version of this model, MCT predicted [Sperl et al., Phys. Rev. Lett. 104, 145701 (2010)10.1103/PhysRevLett.104.145701] the presence of diffusion anomalies both upon cooling and upon compression and the occurrence of glass-glass transitions. In the simulations, we focus on a non-crystallising binary mixture, which, at the investigated shoulder width, shows a non-monotonic behaviour of the diffusion upon cooling but not upon isothermal compression. In addition, we find the presence of a disconnected glass-glass line in the phase diagram, ending in two higher order singularities. These points generate a logarithmic dependence of the density correlators as well as a subdiffusive behaviour of the mean squared displacement, although with the interference of the nearby liquid-glass transition. We also perform novel MCT calculations using as input the partial structure factors obtained within MD, confirming the simulation results. The presence of two hard sphere glasses, differing only in their hardcore length, is revealed, showing that the simple competition between the two is sufficient for creating a rather complex dynamical behaviour.
Weak Lie symmetry and extended Lie algebra
Authors: Goenner Hubert
Published: April 2013

The concept of weak Lie motion (weak Lie symmetry) is introduced. Applications given exhibit a reduction of the usual symmetry, e.g., in the case of the rotation group. In this context, a particular generalization of Lie algebras is found (“extended Lie algebras”) which turns out to be an involutive distribution or a simple example for a tangent Lie algebroid. Riemannian and Lorentz metrics can be introduced on such an algebroid through an extended Cartan-Killing form. Transformation groups from non-relativistic mechanics and quantum mechanics lead to such tangent Lie algebroids and to Lorentz geometries constructed on them (1-dimensional gravitational fields).
Highly efficient charge transfer in nanocrystalline Si:H solar cells
Authors: Kiriluk K. G. , Fields J. D. , Simonds B. J. , Pai Y. P. , Miller P. L. , Su T. , Yan B. , Yang J. , Guha S. , Madan A. , Shaheen S. E. , Taylor P. C. , Collins R. T.
Published: April 2013

We demonstrate that in nanostructured films of nanocrystalline silicon imbedded in a hydrogenated amorphous silicon matrix, carriers generated in the amorphous region are transported out of this region and therefore do not recombine in the amorphous phase. Electron paramagnetic resonance (EPR) and photoluminescence (PL) measurements show that the EPR and PL from the amorphous phase are rapidly quenched as the volume fraction of Si nanocrystals exceeds about 30 vol. %. We propose the use of similar structures to dramatically increase the open circuit voltages in solar cell devices.
Mapping the phase diagram for neon to a quantum Lennard-Jones fluid using Gibbs ensemble simulations
Authors: Georgescu Ionuţ , Brown Sandra E. , Mandelshtam Vladimir A.
Published: April 2013

In order to address the issue of whether neon liquid in coexistence with its gas phase can be mapped to a quantum Lennard-Jones (LJ) fluid, we perform a series of simulations using Gibbs ensemble Monte Carlo for a range of de Boer quantum parameters \documentclass[12pt]{minimal}\begin{document}$\Lambda =\hbar /(\sigma \sqrt{m\epsilon })$\end{document}Λ=ℏ/(σmε). The quantum effects are incorporated by implementing the variational Gaussian wavepacket method, which provides an efficient numerical framework for estimating the quantum density at thermal equilibrium. The computed data for the LJ liquid is used to produce its phase diagram as a function of the quantum parameter, 0.065 ⩽ Λ ⩽ 0.11. These data are then used to fit the experimental phase diagram for neon liquid. The resulting parameters, ε = 35.68 ± 0.03 K and σ = 2.7616 ± 0.0005 Å (Λ = 0.0940), of the LJ pair potential are optimized to best represent liquid neon in coexistence with its gas phase for a range of physically relevant temperatures. This multi-temperature approach towards fitting and assessing a pair-potential is much more consistent than merely fitting a single data point, such as a melting temperature or a second virial coefficient.
Capturing static and dynamic correlations by a combination of projected Hartree-Fock and density functional theories
Authors: Garza Alejandro J. , Jiménez-Hoyos Carlos A. , Scuseria Gustavo E.
Published: April 2013

This paper explores the possibility of combining projected Hartree-Fock and density functional theories for treating static and dynamic correlations in molecular systems with mean-field computational cost. The combination of spin-projected unrestricted Hartree-Fock (SUHF) with the TPSS correlation functional (SUHF+TPSS) yields excellent results for non-metallic molecular dissociations and singlet-triplet splittings. However, SUHF+TPSS fails to provide the qualitatively correct dissociation curve for the notoriously difficult case of the chromium dimer. By tuning the TPSS correlation parameters and adding complex conjugation symmetry breaking and restoration to SUHF, the right curve shape for Cr2 can be obtained; unfortunately, such a combination is found to lead to overcorrelation in the general case.
Phase space path-integral formulation of the above-threshold ionization
Authors: Milošević D. B.
Published: April 2013

Atoms and molecules submitted to a strong laser field can emit electrons of high energies in the above-threshold ionization (ATI) process. This process finds a highly intuitive and also quantitative explanation in terms of Feynman's path integral and the concept of quantum orbits [P. Salières et al., Science 292, 902 (2001)]10.1126/science.108836. However, the connection with the Feynman path-integral formalism is explained only by intuition and analogy and within the so-called strong-field approximation (SFA). Using the phase space path-integral formalism we have obtained an exact result for the momentum-space matrix element of the total time-evolution operator. Applying this result to the ATI we show that the SFA and the so-called improved SFA are, respectively, the zeroth- and the first-order terms of the expansion in powers of the laser-free effective interaction of the electron with the rest of the atom (molecule). We have also presented the second-order term of this expansion which is responsible for the ATI with double scattering of the ionized electron.
Spectral problem for quasi-uniform nearest-neighbor chains
Authors: Banchi Leonardo , Vaia Ruggero
Published: April 2013

One-dimensional arrays with nearest-neighbor interactions occur in several physical contexts: magnetic chains, Josephson-junction and quantum-dot arrays, 1D boson and fermion hopping models, and random walks. When the interactions at the boundaries differ from the bulk ones, these systems are represented by quasi-uniform tridiagonal matrices. We show that their diagonalization is almost analytical: the spectral problem is expressed as a variation of the uniform one, whose eigenvalues constitute a band. A density of in-band states can be introduced, making it possible to treat large matrices, while few discrete out-of-band localized states can show up. The general procedure is illustrated with examples.
Structure and dynamics of supercooled water in neutral confinements
Authors: Klameth F. , Vogel M.
Published: April 2013

We perform molecular dynamics simulations to study the structure and dynamics of liquid water in neutral nanopores, which are generated by pinning a suitable subset of water molecules in an equilibrium configuration of a bulk system. It is found that such neutral confinement does not disturb the structure of water, in particular, the local tetrahedral order, while it imposes a pronounced spatial inhomogeneity on the dynamics of water. Specifically, when the pore wall is approached, hopping motion sets in and water dynamics slows down. We show that the logarithm of the correlation time is an exponential function of the distance to the wall, indicating a tremendous gradient of water mobility across the confinement. Upon cooling, the length scale associated with this exponential distance dependence and, thus, the range of the wall effect increases, at least down to the critical temperature of mode coupling theory, Tc. Also, the temperature dependence of water dynamics varies across the pore, i.e., fragility is high in the pore center, while it is low near the pore wall. Due to all these effects, time-temperature superposition is violated. Our observations for a neutral confinement reveal that specific interactions at hydrophilic or hydrophobic walls are not the main cause of spatially inhomogeneous dynamics of confined water. In view of similarities with the behavior of Lennard-Jones liquids in neutral confinements, one may rather speculate that the effects observed for confined water are general and result from the existence of a static contribution to the energy landscape, which is imprinted by an immobile environment.
Structural and thermodynamic behavior of alkane chains at the liquid/vapor interface
Authors: Hernandez David Alejandro , Domínguez Hector
Published: April 2013

Computer simulations for several alkane fluids were carried out to study thermodynamics and structural behavior of the molecules at the liquid-vapor interface. Three different models were used to simulate the fluids, one of them was proposed in this work and we obtained a slightly better agreement than the other models with experimental data. The fluid structure at the interface was analyzed at temperatures close to the melting point using the new model and it was found that molecules at the free surface present more order than those at the bulk liquid phase. By calculating the order of the hydrocarbon chains a strong structure of molecules was observed at the interface than those in bulk, moreover, some of those molecules at the interface were aligned perpendicular to the interface. Previous simulations report stronger structures at the interface by the formation of a monolayer of alkane chains, however, those simulations started at very low temperatures and they did not reproduce thermodynamic properties such as the interfacial tension correctly. The model proposed in the present work not only presents good agreement with surface tension data but also shows evidence that the fluid structured as experiments indicated at temperatures close to the melting temperature.
Determination of relative pinning strength of hexagonally arranged composite pinning centers
Authors: Cao Rong , Horng Lance , Wu Tian-Chiuan , Chen Chien-Miao , Wang Jui-Chun , Wu Jong-Ching
Published: April 2013

A method to determine the relative pinning strength of different pinning sites in composite hexagonal pinning arrays is proposed and experimentally realized. Six different samples of superconducting Nb films with composite hexagonal arrays were fabricated and measured. Two types of pinning sites have different sizes. The density of one type of pinning site is twice that of the other. The critical current versus the applied magnetic fields were also measured. The vortex configurations at the matching fields can be deduced from these curves and verified by molecular dynamic simulations. The relative pinning strength of different pinning sites can be determined from these configurations. The method could be extended to decide the optimal pinning size or to compare the pinning strength of pinning sites made of different materials.
Dynamic asymmetry of self-diffusion in liquid ZnCl2 under pressure: An ab initio molecular-dynamics study
Authors: Koura Akihide , Ohmura Satoshi , Shimojo Fuyuki
Published: April 2013

The static and dynamic properties of liquid ZnCl2 under pressure are investigated by ab initio molecular-dynamics simulations. The pressure range covers ambient to approximately 80 GPa. The ZnCl4 tetrahedra, which are rather stable at ambient pressure, are shown to deform and collapse with increasing pressure while maintaining an almost constant nearest-neighbor distance between Zn and Cl atoms. The average coordination number of Cl atoms around Zn atoms increases monotonically with pressure, from four at ambient pressure to seven at approximately 80 GPa. Although the self-diffusion coefficients of Zn and Cl atoms, dZn and dCl, are almost the same at ambient pressure, the difference between them increases with pressure. At around 10 GPa, dZn is about two times larger than dCl. Under further compression, this dynamic asymmetry becomes smaller. The microscopic mechanism of the appearance of the dynamic asymmetry is discussed in relation to the pressure dependence of the local structure.
Competing local orders in liquid and amorphous structures of Ge2Sb2Te5: Influence of exchange-correlation functional
Authors: Yeop Kim Kye , Cho Deok-Yong , Cheong Byung-ki , Kim Dohyung , Horii Hideki , Han Seungwu
Published: April 2013

Liquid and amorphous structures of Ge2Sb2Te5 are theoretically studied with various exchange-correlation functionals. It is found that the balance of competing local orders around Ge atoms is substantially affected by the functional type, and the hybrid functional leads to structures that are in best agreement with experiment. The delocalization error inherent in semilocal functionals results in over-population of octahedral Ge configurations, which is compounded by the limitation of melt-quench processes in identifying the most stable amorphous structure. The present work underscores the importance of functional choice when competing local orders present in disordered systems.
Analysis of the series resistance in pin-type thin-film silicon solar cells
Authors: Müller Thomas C. M. , Pieters Bart E. , Rau Uwe , Kirchartz Thomas
Published: April 2013

The series resistance of microcrystalline hydrogenated silicon thin-film pin-type solar cells is investigated using illumination dependent current/voltage characteristics. We present a simple analytical model describing the total series resistance of low-mobility pin-type solar cells. The model thus provides insight into the influence of the material properties of the intrinsic layer on the series resistance. Our model allows us to separate the voltage dependent internal resistance of the intrinsic layer from the residual, external resistance. We verified our model over a wide range of parameters relevant to thin-film silicon devices by comparison to numerical simulations. Finally, we demonstrate that our model can consistently describe the series resistance of experimental a μc-Si:H pin-type solar cell. Furthermore, the fitting of the model with experimental data yields the external series resistance and information of the carrier mobilities and effective density of states in the bands of the intrinsic layer in the device.
Charge transport in Si nanocrystal/SiO2 superlattices
Authors: Gutsch S. , Laube J. , Hartel A. M. , Hiller D. , Zakharov N. , Werner P. , Zacharias M.
Published: April 2013

Size-controlled silicon nanocrystals in silicon oxynitride matrix were prepared using plasma-enhanced chemical vapor deposition following the superlattice approach. A combination of current transport and charge trapping studies is carried out on a number of samples with varied structural configuration. We demonstrate that at low electric fields, trapping of injected carriers dominates, if the coupling between the silicon nanocrystals is strong. In contrast, we show that at higher electric fields, the charge distribution within the films is essentially governed by charge separation within the superlattice. This effect can be well explained by a two-step electric field ionization of silicon nanocrystals that proceeds via defect-assisted band-to-band tunneling of silicon valence electrons to the conduction band and is mediated by silicon surface dangling bonds. The defects are dominating the charge transport even if the defect density is reduced to a minimum by efficient hydrogen passivation.
Generic model of superexchange effects in magnetoelastic oxides
Authors: Dionne G. F. , Kim D. H. , Bi L. , Ross C. A.
Published: April 2013

Room temperature magnetic properties of tetragonally distorted SrTi1−xMxO3 epitaxial films occur when M = Fe or Co is in a magnetoelastic 4+ valence state. However, these ions can limit the saturation magnetization by magnetic superexchange through M–O–M bonding when the concentration (x) is high enough to create a population of antiferromagnetic (AFM) spin pairs. For moderate concentrations, a random distribution of isolated spin sites is interspersed with AFM-coupled sites below the Neel temperature. Analysis of this model involves the following assumptions: (1) the fraction of unpaired sites with 6 equivalent near neighbors is F = (1 − x)6, leaving (1 − F) as the fraction of paired sites, (2) the variation of saturation magnetization with temperature for the unpaired paramagnetic sites is treated by the orbit-lattice strain model reported previously, and the canted contributions of the antiferromagnetic pairs by a reverse Brillouin function. The model is applied to SrTiO3 compounds containing substitutions of low-spin Co4+ ions that reveal how the exchange-coupled group can become part of the magnetoelastic alignment system as T approaches the effective Neel temperature (TN) of the paired spins. Evidence of this effect in the form of magnetic moment peaks at TN is found in thermomagnetic data from zero-field cooled films in a partially magnetized state.
Spin alignment of surface oxidized CoxNi1–x/Cu(001)
Authors: Shih Ying-Ta , Tsai Chung-Wei , Su Chien-Yu , Pan Wei , Wei Der-Hsin , Chan Yuet-Loy , Chang Hui-Ching
Published: April 2013

We investigated the ferromagnetic (FM)/antiferromagnetic (AF) spin alignment of a 13 monolayer oxidized CoxNi1–x/Cu(001) (x = 0 or 0.05) surface by X-ray magnetic circular dichroism and X-ray magnetic linear dichroism photoemission electron microscopy (XMCD-PEEM and XMLD-PEEM). Surface NiO and the underlying Ni (CoxNi1–x) were found to be AF and FM by analyzing the gray scale of XMLD-PEEM and XMCD-PEEM images; this indicates the spin orientation with respect to the polarization of the incident X-ray. We found both collinear and perpendicular alignment of the FM and AF spins. This suggests that the AF NiO is magnetically random, resulting in coercivity enhancement without exchange bias in the surface-oxidized CoxNi1–x/Cu(001) films.
Metal foil gap switch and its electrical properties
Authors: Lv Junjun , Zeng Qingxuan , Li Mingyu
Published: April 2013

In order to reduce the volume of exploding initiator system, a metal foil spark gap switch was designed and fabricated using magnetron sputter deposition and standard microelectronic technology. The switch constitutes of two main electrodes and a trigger electrode, and stylus profiler was employed to ascertain dimension of the switch. We discussed the discharge characterization of the metal foil spark gap switch under nitrogen atmosphere and at pressure of 0.5 bars, 0.75 bars, 1.0 bar, 1.25 bars, 1.5 bars, and 1.75 bars, respectively. The relationship between self-breakdown voltage of the switch and pressure times distance corresponds to linearity. The switch had short delay time and low time jitter when the operating voltage was between 70% and 90% of its self-breakdown voltage. Compared with a commercial stereo spark gap switch, when it was fired by a conventional capacitive discharge unit, the firing circuit had lower inductance and higher resistance.
X-ray diffraction microscopy of lithiated silicon microstructures
Authors: Fister Tim T. , Goldman Jason L. , Long Brandon R. , Nuzzo Ralph G. , Gewirth Andrew A. , Fenter Paul A.
Published: April 2013

Optically patterned silicon microstructures show great promise as lithium ion battery electrodes as they can balance the high intrinsic charge capacity of silicon with its large volume changes during repeated cycling. Previous scanning electron microscopy showed that lithiation initially occurs at (110)-oriented facets, but was not directly sensitive to the amount of crystalline silicon within the core of each microstructure. Here, we image the extent of the lithiation and the degree of residual crystallinity in individual silicon micro-posts directly using full-field x-ray reflection interfacial microscopy (XRIM). Images of the silicon posts are interpreted using a straightforward model relevant for XRIM images obtained from large scale topological features. This approach should be widely applicable to a broad range of battery materials and for probing the liquid/solid interfaces of complex heterostructures during lithiation reactions.
Electronic properties of graphene nanoribbons stacked on boron nitride nanoribbons
Authors: Yu Jin , Zhang Zhuhua , Guo Wanlin
Published: April 2013

Hexagonal boron nitride sheet has been shown to be the best insulating substrate for graphene electronics. Using first-principles calculations, we here show that BN nanoribbons (BNNRs) can not only serve as a desirable substrate but also bring new properties into the supported graphene nanoribbons (GNRs). In particular, zigzag GNRs on zigzag BNNRs become a spin-relevant semiconductor that can be easily tuned into a half-metal, thanks to polar character of the BNNRs. In contrast, armchair GNRs can basically have all their electronic properties survived from the interaction of armchair BNNRs. Our findings provide helpful guide for developing hybrid BN-graphene nanodevices.
Helium plasma implantation on metals: Nanostructure formation and visible-light photocatalytic response
Authors: Kajita Shin , Yoshida Tomoko , Kitaoka Daiki , Etoh Reo , Yajima Miyuki , Ohno Noriyasu , Yoshida Hisao , Yoshida Naoaki , Terao Yoshitaka
Published: April 2013

It has been found recently that low-energy helium (He) plasma irradiation to tungsten (W) leads to the growth of W nanostructures on the surface. The process to grow the nanostructure is identified as a self-growth process of He bubbles and has a potential to open up a new plasma processing method. Here, we show that the metallic nanostructure formation process by the exposure to He plasma can occur in various metals such as, titanium, nickel, iron, and so on. When the irradiation conditions alter, the metallic cone arrays including nanobubbles inside are formed on the surface. Different from W cases, other processes than growth of fiberform structure, i.e., physical sputtering and the growth of large He bubbles, can be dominant on other metals during irradiation; various surface morphology changes can occur. The nanostructured W, part of which was oxidized, has revealed a significant photocatalytic activity under visible light (wavelength >700 nm) in decolorization of methylene blue without any co-catalyst.
Effect of oxygen and associated residual stresses on the mechanical properties of high growth rate Czochralski silicon
Authors: Youssef Khaled , Shi Meirong , Radue Chantelle , Good Ethan , Rozgonyi George
Published: April 2013

The mechanical properties of Czochralski silicon (Cz-Si) crystals grown in vacancy rich regimes with elevated axial oxygen concentrations ranging from ∼6 × 1017 to ∼12 × 1017 atoms/cm3 have been investigated using nano- and micro-indentation techniques. Both hardness and fracture toughness were found to decrease with increasing oxygen concentration, while major differences in mechanical properties were found between the central core and the edge of the high oxygen concentration wafers. Photoluminescence imaging and Nomarski optical microscopy of high-oxygen wafers revealed the presence of a ring and swirl-like distributions of micro defects, including oxidation induced stacking faults. Micro-Raman analysis was used to measure local residual stress profiles associated with these characteristic defects. These results provide a quantitative understanding of the influence of the oxygen content and the associated defects resulting from the sub-optimal growth regimes within the Cz-Si process.
Optimized amorphous silicon oxide buffer layers for silicon heterojunction solar cells with microcrystalline silicon oxide contact layers
Authors: Ding Kaining , Aeberhard Urs , Finger Friedhelm , Rau Uwe
Published: April 2013

We report on the systematic optimization of the intrinsic amorphous silicon oxide buffer layer in interplay with doped microcrystalline silicon oxide contact layers for silicon heterojunction solar cells using all silicon oxide based functional layers on flat p-type float-zone wafers. While the surface passivation quality is comparably good within a wide range of low oxygen contents, the optical band gap increases and the dark conductivity decreases with increasing oxygen content, giving rise to an inevitable trade-off between optical transparency and electrical conductivity. On the cell level, fill factor FF and short circuit current density Jsc losses compete with the open circuit voltage Voc gains resulting from a thickness increase of the front buffer layers, whereas Jsc and Voc gains compete with FF losses resulting from increasing thickness of the rear buffer layers. We obtained the highest active area efficiency of ηact = 18.5% with Voc = 664 mV, Jsc = 35.7 mA/cm2, and FF = 78.0% using 4 nm front and 8 nm rear buffer layer with an oxygen content of 5%.
Magnetic and self-biased properties of highly oriented M-type barium ferrite films on Pt-coated Si substrate by magnetron sputtering
Authors: Li Yuanxun , Liu Yingli , Li Jie , Yang Kai , Zhang Huaiwu
Published: April 2013

Highly oriented M-type barium ferrite (BaM) thin films were deposited by sputtering on Pt-coated Si Substrate with different substrate temperatures. X-ray diffraction and atomic force microscopy results show that BaM films have crystal texture of c-axis grains perpendicular to film plane with apparent hexagonal morphology. On the other hand, it is clearly observed that the remanent magnetization (Mr) in out-plane is higher than those in in-plane, and the Mr in out-plane increases with increasing the substrate temperature, reaching maximum when substrate temperature (Ts) is 600 °C. The hysteresis curves also indicate that the BaM thin film exhibits nice self-biased property with 4πMr of 3803.04 Gs, squareness ratio (Mr/Ms) of 0.96, and coercivity of 1767.3 Oe. These results make sure that these BaM films have potential for use in self-biasing microwave/millimeter wave magnetic devices such as circulators and isolators.
Surface states and conductivity of silicon nano-wires
Authors: Kumar Bhaskar Umesh , Pardoen Thomas , Passi Vikram , Raskin Jean-Pierre
Published: April 2013

The transport characteristics of low dimensional semiconductors like silicon nano-wires (SiNWs) rarely conform to expectations from geometry and dopant density, exhibiting significant variations as a function of different surface terminations/conditions. The association of these mechanisms with surface states and their exact influence on practical SiNW devices still remains largely unclear. Herein, we report on the influence of surface state charge distributions on SiNW transport characteristics. For this study, p-type SiNW devices with widths of 50, 100, and 2000 nm are fabricated from 25, 50, and 200 nm-thick SOI wafers. A ∼five order difference in effective carrier concentration was observed in the initial SiNWs characteristics, when comparing SiNWs fabricated with and without a thermal oxide. The removal of the surface oxide by a hydrogen fluoride (HF) treatment results in a SiNW conductance drop up to ∼six orders of magnitude. This effect is from a surface depletion of holes in the SiNW induced by positive surface charges deposited as a result of the HF treatment. However, it is observed that this charge density is transient and is dissipated with the re-growth of an oxide layer. In summary, the SiNW conductance is shown to vary by several orders of magnitude, while comparing its characteristics for the three most studied surface conditions: with a native oxide, thermal oxide and HF induced H-terminations. These results emphasize the necessity to interpret the transport characteristics of SiNWs with respect to its surface condition, during future investigations pertaining to the physical properties of SiNWs, like its piezo-resistance. As a sequel, prospects for efficiently sensing an elementary reduction/oxidation chemical process by monitoring the variation of SiNW surface potential, or in practice the SiNW conductance, is demonstrated.
One-dimensional wave-propelled bouncing drop on an oscillating liquid bath
Authors: Chu Hong-Yu , Fei Hsiang-Ting , Ko Chang-Rong
Published: April 2013

We investigate the wave-propelled phenomena of the drop on the oscillating flat surface and on the Faraday wave. With the quasi-one-dimensional setup, we observe the deformations of the oscillating oil surface and the gliding drop on the oil surface. The “glider” drop is found reaching the largest speed while system is driving at 65 Hz, which is consistent with the resonance of the drop and the oscillating surface. The distorted surface wave with different slopes is suspected of being responsible for the acceleration of the traveling drop. Furthermore, for drop traveling on the Faraday wave, the traveling speed is affected by the wavelength and the amplitude of the wave. The drops are found being trapped or slowed down around the nodes of the Faraday wave where the slopes are alternatively changed. The traveling speed of the drop is found decreasing linearly with the increase of the wave amplitude.
Structural, magnetic, and magnetoelastic properties of magnesium substituted cobalt ferrite
Authors: Nlebedim I. C. , Hadimani R. L. , Prozorov R. , Jiles D. C.
Published: April 2013

The effects of substituting Mg on the structural, magnetic, and magnetostrictive properties of cobalt ferrite have been investigated. Comparable values of lattice parameter were obtained for the Mg-substituted samples. Saturation magnetization continuously decreased with increase in Mg concentration. Peak-to-peak magnetostriction amplitude and strain sensitivity had a similar dependence on Mg concentration.
A metal-insulator-metal plasmonic Mach-Zehnder interferometer array for multiplexed sensing
Authors: Zeng Xie , Gao Yongkang , Hu Haifeng , Ji Dengxin , Gan Qiaoqiang , Bartoli Filbert
Published: April 2013

A multi-layered metal-insulator-metal plasmonic Mach-Zehnder interferometer (MZI) is proposed to work as an array for multiplexed sensing. The interference patterns based on wavelength modulation and intensity modulation are modeled analytically and numerically, showing a high figure of merit over 170 for intensity-interrogated sensing. The proposed structure can overcome the one-slit illumination limitation of previously reported single-layered double-slit plasmonic MZI and will enable portable, high-throughput and sensitive biosensing applications.
Coupling and induced depinning of magnetic domain walls in adjacent spin valve nanotracks
Authors: Sampaio J. , O'Brien L. , Petit D. , Read D. E. , Lewis E. R. , Zeng H. T. , Thevenard L. , Cardoso S. , Cowburn R. P.
Published: April 2013

The magnetostatic interaction between magnetic domain walls (DWs) in adjacent nanotracks has been shown to produce strong inter-DW coupling and mutual pinning. In this paper, we have used electrical measurements of adjacent spin-valve nanotracks to follow the positions of interacting DWs. We show that the magnetostatic interaction between DWs causes not only mutual pinning, as observed till now, but that a travelling DW can also induce the depinning of DWs in near-by tracks. These effects may have great implications for some proposed high density magnetic devices (e.g., racetrack memory, DW-based magnetic random access memory (MRAM), or DW logic circuits.)
Bright light emissions with narrow spectral linewidths from single InAs/GaAs quantum dots directly grown on silicon substrates
Authors: Benyoucef M. , Usman M. , Reithmaier J. P.
Published: April 2013

High brightness light emissions from single InAs/GaAs quantum dots (QDs) epitaxially grown directly on silicon substrates are realized for the first time. The grown structures contain a low quantum dot density of about 108 cm−2. Low-temperature spatially resolved photoluminescence (PL) measurements illustrate bright single QD emissions with relatively sharp excitonic lines comparable to PL spectra of near-surface QDs grown on GaAs substrates.
Passive contact guidance of fibroblast cells using consecutive trapezoidal micropatterns
Authors: Don Han Eui , Yoon Sang-Hee , Hee Kim Byeong , Ho Seo Young
Published: April 2013

Cell migration on micropatterned substrates is a complex process regulated by cell-substrate interactions. This paper presents a passive method for guiding the migration of NIH 3T3 fibroblasts using consecutive trapezoidal micropatterns, made of a biocompatible photopolymer (OrmoComp®), to provide tapered micro-features on the cells. The cell migration paths measured from our platforms quantitatively address the dependence of the migratory behavior of the cells on the tapered micro-features. Most of the cells on the micropatterns have moved in a converging direction rather than in a diverging one; migration speed on the micropatterns has been noticeably faster than that on flat substrates.
Experimental observation of plasmons in a graphene monolayer resting on a two-dimensional subwavelength silicon grating
Authors: Zhu Xiaolong , Yan Wei , Uhd Jepsen Peter , Hansen Ole , Asger Mortensen N. , Xiao Sanshui
Published: April 2013

We experimentally demonstrate graphene-plasmon polariton excitation in a continuous graphene monolayer resting on a two-dimensional subwavelength silicon grating. The subwavelength silicon grating is fabricated by a nanosphere lithography technique with a self-assembled nanosphere array as a template. Measured transmission spectra illustrate the excitation of graphene-plasmon polaritons, which is further supported by numerical simulations and theoretical prediction of plasmon-band diagrams. Our grating-assisted coupling to graphene-plasmon polaritons forms an important platform for graphene-based opto-electronics applications.
Quasi-two-dimensional Ag nanoparticle formation in silica by Xe ion irradiation and subsequent Ag ion implantation
Authors: Wang Jun , Jia Guangyi , Mu Xiaoyu , Liu Changlong
Published: April 2013

Ag nanoparticles were fabricated in silica by Xe ion irradiation and subsequent Ag ion implantation, which distributed in a depth range from 4.8 to 14.3 nm, rather than dispersed from surface to a depth of 24.7 nm when no irradiation was made in advance. In addition, the suppression of Ag implants' sputtering loss was also evidenced by a greatly increased Ag content in the prepared sample. These results are mainly due to the defect-enhanced in-beam particle growth. Further, formation of polycrystalline Ag nanoparticles was revealed, whose effect on optical absorption was discussed according to the electron mean-free-path mode.
Tuning of the emission energy of fluorophores using solid state solvation for efficient luminescent solar concentrators
Authors: Green Adam P. , Butler Keith T. , Buckley Alastair R.
Published: April 2013

Solid state solvation is employed to reduce self-absorption, a key loss mechanism in Luminescent Solar Concentrator (LSC) devices. For an example materials system consisting of poly(methylmethacrylate), Camphoric Acid Anhydride, and the laser dye 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7,-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) a substantial shift in DCJTB emission energy of 832.2 cm−1 is observed whilst no decrease in fluorescence quantum yield occurs. When extrapolated to an LSC device a 16.1% relative improvement in efficiency is predicted with a potential for 23.1% when employing stronger dielectric additives. For a range of dicyanomethylene based fluorophores the predicted improvement in LSC efficiency is from 17.5% to 24.4%.
Localized surface plasmon-enhanced propulsion of gold nanospheres
Authors: Li Ying , Hu Yanjun
Published: April 2013

We experimentally demonstrated the enhanced propulsion of 250 nm gold nanospheres using an optical nanofiber decorated with five gold nanoparticles. By tuning the input laser wavelength to 808 nm, the enhanced propulsion phenomenon occurred due to the excitation of local surface plasmon resonance (LSPR) of the gold nanoparticles. Simulated results indicate considerably enhanced optical scattering force on the gold nanospheres provided by LSPR, which lead to enhanced propulsion velocity. The velocity was measured to be about 10 times larger for the LSPR of gold nanoparticles than the conventional evanescent field around the nanofiber.
TiO2 nanoparticle induced space charge decay in thermal aged transformer oil
Authors: Lv Yuzhen , Du Yuefan , Li Chengrong , Qi Bo , Zhong Yuxiang , Chen Mutian
Published: April 2013

TiO2 nanoparticle with good dispersibility and stability in transformer oil was prepared and used to modify insulating property of aged oil. It was found that space charge decay rate in the modified aged oil can be significantly enhanced to 1.57 times of that in the aged oil at first 8 s after polarization voltage was removed. The results of trap characteristics reveal that the modification of nanoparticle can not only greatly lower the shallow trap energy level in the aged oil but also increase the trap density, resulting in improved charge transportation via trapping and de-trapping process in shallower traps.
Optimization of Pt-based spin-Hall-effect spintronic devices
Authors: Ulrichs H. , Demidov V. E. , Demokritov S. O. , Lim W. L. , Melander J. , Ebrahim-Zadeh N. , Urazhdin S.
Published: April 2013

We study experimentally the routes to improve the characteristics of the spin-Hall-effect devices based on permalloy/Pt bilayers by optimization of the Pt layer thickness and by the addition of an antiferromagnetic spin-sinking layer. We experimentally determine the spin-diffusion length in Pt and show that Pt thickness can be reduced down to 2 nm without degradation of the device characteristics caused by the spin accumulation effects, which provides possibilities for significant reduction of the required driving currents. We also show that the addition of a spin-sinking layer results in a non-monotonic dependence of device efficiency on the Pt thickness.
Interband tunneling in two-dimensional crystal semiconductors
Authors: Ma Nan , Jena Debdeep
Published: April 2013

Interband quantum tunneling of electrons in semiconductors is of intense recent interest as the underlying transport mechanism in tunneling field-effect transistors. Such transistors can potentially perform electronic switching with lower energy than their conventional counterparts. The recent emergence of two-dimensional (2D) semiconducting crystals provides an attractive material platform for realizing such devices. In this work, we derive an analytical expression for understanding tunneling current flow in single-layer 2D crystal semiconductors in the k-space. We apply the results to a range of 2D crystal semiconductors, and compare it with tunneling currents in three-dimensional semiconductors. We also discuss the implications for tunneling devices.
Sensitivity analysis of electron leakage in III-nitride light-emitting diodes
Authors: Piprek Joachim , Simon Li Z. M.
Published: April 2013

III-nitride light-emitting diodes (LEDs) suffer from efficiency droop, which is partially attributed to electron leakage into the p-doped layers. Only very few direct measurements of such leakage are published. We here analyze leakage measurements on AlGaN LEDs with an emission wavelength near 260 nm. The electron leakage disappears after insertion of a thin undoped electron blocking layer (EBL). In good agreement with these measurements, we show that the electron blocking effect is extremely sensitive not only to the EBL material composition but also to the conduction band offset and to the net polarization, which are both not exactly known.
Impact of charge impurities on transport properties of graphene nanoribbons
Authors: Smith Christian W. , Katoch Jyoti , Ishigami Masa
Published: April 2013

Previous experimental studies have shown qualitative dependence of transport property of graphene nanoribbons on external charged impurities. We have measured transport properties of a graphene nanoribbon at increasing coverage of charged impurities in an ultra high vacuum environment. We discovered an exact relationship between the source-drain and gate gaps at increasing charged impurity density. In addition, we found that graphene nanoribbons have different electronic screening as compared to bulk graphene. Our study paves the way for controlling transport property of nanoribbons using extrinsic impurities.