bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaction potential and infrared absorption of endohedral H2 in C60
Authors: Ge Min , Nagel U. , Hüvonen D. , Rõõm T. , Mamone S. , Levitt M. H. , Carravetta M. , Murata Y. , Komatsu K. , Chen J. Y.-C. , Turro N. J.
Published: February 2011

We have measured the temperature dependence of the infrared spectra of a hydrogen molecule trapped inside a C60 cage, H2@C60, in the temperature range from 6 to 300 K and analyzed the excitation spectrum by using a five-dimensional model of a vibrating rotor in a spherical potential. The electric dipole moment is induced by the translational motion of endohedral H2 and gives rise to an infrared absorption process where one translational quantum is created or annihilated, ΔN = ±1. Some fundamental transitions, ΔN = 0, are observed as well. The rotation of endohedral H2 is unhindered but coupled to the translational motion. The isotropic and translation–rotation coupling part of the potential are anharmonic and different in the ground and excited vibrational states of H2. The vibrational frequency and the rotational constant of endohedral H2 are smaller than those of H2 in the gas phase. The assignment of lines to ortho- and para-H2 is confirmed by measuring spectra of a para enriched sample of H2@C60 and is consistent with the earlier interpretation of the low temperature infrared spectra [Mamone et al., J. Chem. Phys. 130, 081103 (2009)].
Vibration based on liquid surface tension
Authors: Yang Xing , Ren Xiao Yan , Li Dan , Ren Man Rui , Yang Jia Rui , Zhou Zhao Ying , Zheng Quan Shui
Published: February 2011

In this paper, vibration based on liquid surface tension is reported. A prototype vibrator composed of a water film sandwiched between two plates is fabricated and tested. The free and the continuous vibrations (electromagnetic drive) of the proposed vibrator are demonstrated. The mechanical model of the vibrator is also presented. Theoretical analysis and experiments prove the surface tension, which has the advantages of the no-mechanical parts, simple-structure, and self-lubrication, is effective for driving. The liquid surface tension vibrator demonstrates the potential applications in resonating sensors, precision actuator, and mechanical switch.
Composition and strain in thin Si1−xGex virtual substrates measured by micro-Raman spectroscopy and x-ray diffraction
Authors: Perova T. S. , Wasyluk J. , Lyutovich K. , Kasper E. , Oehme M. , Rode K. , Waldron A.
Published: February 2011

Micro-Raman spectroscopy was employed for the determination of the germanium content, x and strain, ε, in ultrathin SiGe virtual substrates grown directly on Si by molecular beam epitaxy. The growth of highly relaxed SiGe layers was achieved by the introduction of point defects at a very low temperature during the initial stage of growth. SiGe virtual substrates with thicknesses in the range 40–200 nm with a high Ge content (up to 50%) and degree of relaxation, r, in the range 20%–100% were investigated using micro-Raman spectroscopy and x-ray diffraction (XRD) techniques. The Ge content, x, and strain, ε, were estimated from equations describing Si–Si, Si–Ge, and Ge–Ge Raman vibrational modes, modified in this study for application to thin SiGe layers. The alteration of the experimentally derived equations from previous studies was performed using independent data for x and r obtained from XRD reciprocal space maps. A number of samples consisting of a strained-silicon (s-Si) layer deposited on a SiGe virtual substrate were also analyzed. The stress value for the s-Si varied from 0.54 to 2.75 GPa, depending on the Ge-content in the virtual substrates. These results are in good agreement with theoretically predicted values.
Thermoelectric transport in the coupled valence-band model
Authors: Ramu Ashok T. , Cassels Laura E. , Hackman Nathan H. , Lu Hong , Zide Joshua M. O. , Bowers John E.
Published: February 2011

The Boltzmann transport equation (BTE) is applied to the problem of thermoelectric transport in p-type semiconductors whose valence band-structure is describable in terms of two bands degenerate at the Γ point. The Seebeck coefficient and mobility are calculated from the solution to two coupled BTEs, one for each band, with interband scattering and scattering by inelastic mechanisms treated exactly by the application of an algorithm developed by the authors in an earlier work. Most treatments of this problem decouple the two bands by neglecting certain terms in the BTE, greatly simplifying the mathematics: the error in the Seebeck coefficient and mobility introduced by this approximation is quantified by comparing with the exact solution. Degenerate statistics has been assumed throughout, and the resulting formalism is therefore valid at high hole concentrations. Material parameters are used that have been deduced from optical, strain and other experiments often not directly related to hole transport. The formulations in this work thus do not use adjustable or fitting parameters. The transport coefficients of heavily doped gallium antimonide, a typical high-efficiency p-type thermoelectric material, are calculated and agreement to experimentally determined values is found to be satisfactory.
Nonequilibrium simulations of filled polymer networks: Searching for the origins of reinforcement and nonlinearity
Authors: Raos Guido , Casalegno Mosè
Published: February 2011

We present nonequilibrium dissipative particle dynamics (DPD) simulations of cross-linked elastomers containing solid filler particles at 30% volume fraction. We study systematically the effect of the morphology (dispersed or aggregated particles) and of the effective particle–particle interactions. In addition, we have experimented by replacing the standard harmonic DPD bonds with other potential functions, conceived to deal with the finite extensibility of the polymer chains and the possibility of a slow equilibrium between strongly and weakly adsorbed chains at the rubber-filler interface. The simulation results shed some light on the basic mechanisms of rubber reinforcement, including the nonlinearity and history dependence commonly known as “Payne effect” and “Mullins effect.”
Structural and elemental characterization of high efficiency Cu2ZnSnS4 solar cells
Authors: Wang Kejia , Shin Byungha , Reuter Kathleen B. , Todorov Teodor , Mitzi David B. , Guha Supratik
Published: February 2011

We have carried out detailed microstructural studies of phase separation and grain boundary composition in Cu2ZnSnS4 based solar cells. The absorber layer was fabricated by thermal evaporation followed by post high temperature annealing on hot plate. We show that inter-reactions between the bottom molybdenum and the Cu2ZnSnS4, besides triggering the formation of interfacial MoSx, results in the out-diffusion of Cu from the Cu2ZnSnS4 layer. Phase separation of Cu2ZnSnS4 into ZnS and a Cu–Sn–S compound is observed at the molybdenum-Cu2ZnSnS4 interface, perhaps as a result of the compositional out-diffusion. Additionally, grain boundaries within the thermally evaporated absorber layer are found to be either Cu-rich or at the expected bulk composition. Such interfacial compound formation and grain boundary chemistry likely contributes to the lower than expected open circuit voltages observed for the Cu2ZnSnS4 devices.
Raman scattering analysis of silicon dioxide single crystal treated by direct current plasma discharge
Authors: Popovic D. M. , Milosavljevic V. , Zekic A. , Romcevic N. , Daniels S.
Published: February 2011

Low-k materials such as silicon dioxide (SiO2) play an important role in the semiconductor industry. Plasma has become indispensable for advanced materials processing. In this work a treatment of SiO2 single crystal by direct current plasma discharge is studied in detail. Offline metrology is conducted for silicon dioxide wafers by Raman scattering, energy-dispersive x-ray spectroscopy, and ellipsometry. Broad Raman peak at around 2800 cm−1 is observed for the treated SiO2 wafers. Effects of plasma treatment on position of this peak are reported in the paper. An analysis of this correlation could be a framework for creating virtual etch rate sensors, which might be of importance in managing plasma etching processes.
Static and dynamic observation of supermolecular protein, ferritin, using high-speed atomic force microscope
Authors: Yamamoto S.-I. , Okada T. , Uraoka Y. , Yamashita I. , Hasegawa S.
Published: February 2011

We have studied the behavior of ferritin molecules using a high-speed atomic force microscope (high-speed AFM), which uses a miniaturized cantilever and scan stage to reduce the mechanical response time of the cantilever and to prevent the onset of resonant motion at high scan speeds. Using this instrument, we were able to achieve scan rates of up to 1 frame per second for pure fluids. A conventional AFM can visualize the ferritin molecule-substrate interaction directly at the single-molecule level. The conventional AFM can dynamically visualize the process of the ferritin molecule interacting with the substrate; however, it cannot dynamically visualize the adsorption of ferritin molecules on the substrate, which occurs in a fraction of a second, because of its very low scan speed. In this study, we used a novel high-speed AFM to dynamically visualize the behavior of the ferritin molecule-substrate reaction at the single-ferritin-molecule level by real time.
IR studies of the impact of Ge doping on the successive conversion of VOn defects in Czochralski-Si containing carbon
Authors: Londos C. A. , Andrianakis A. , Sgourou E. N. , Emtsev V. V. , Ohyama H.
Published: February 2011

We report infrared absorption studies of oxygen-related defects in electron-irradiated Ge-doped Czochralski-Si. Our investigation was mainly focused on the reaction channel leading to the formation of VOn (1≤n≤6) defects. The VOn defects form mainly upon annealing, as a result of the successive aggregation of oxygen atoms in the initial VO defect produced by the irradiation: (VO+Oi→VO2+Oi→VO3+Oi→VO4,…). It was found that the ratio of the conversion of VOn to VOn+1 defects is sensitive to the Ge content of the material. In particular, the ratio of the conversion of the VO to the VO2 defects was found to decrease with the increase in Ge concentration of the samples, although the opposite trend was observed for the VO3 to VO4 conversion. However, the VO2 to VO3 conversion changes only slightly with Ge content, being practically unaffected for Ge concentrations up to 2×1020 cm−3. In the case of VO2 formation, the phenomenon was attributed to the elastic strains induced in the lattice due to the Ge presence which affects the balance between the reactions VO+Oi→VO2, VO+SiI→Oi, mainly involved in the decay of the VO and the growth of the VO2 defects. In the case of VO4 formation, the phenomenon was discussed by taking into account the enhancement of the diffusivity of the Oi atoms in the Ge-doped Si, which could lead to an enhancement of the rate of the reaction VO3+Oi→VO4. For the VO3 formation this effect is practically negligible due to the fact that at the temperatures of VO2 to VO3 conversion oxygen diffusivity is quite small. The exhibited behavior in the conversion of the VOn to VOn+1 defects (n=1,2,3) was similar in Ge-doped samples with low carbon content ([Cs]<2×1016 cm−3) and in Ge-doped samples with high carbon content ([Cs]≥1×1017 cm−3). The impact of C as well as its role in the conversion efficiency of VO to VO2 was studied by comparing the spectra in low carbon and high carbon Ge free Si material. Furthermore, a pair of bands at (1037,1051 cm−1) was attributed to the VO5 defect. The origin of another pair of bands (967,1005 cm−1) was discussed and tentatively correlated with a VOnCs structure. The role of Ge and C in the formation of the latter two pairs of bands was discussed.
Molecular beam epitaxial growth of metamorphic AlInSb/GaInSb high-electron-mobility-transistor structures on GaAs substrates for low power and high frequency applications
Authors: Loesch R. , Aidam R. , Kirste L. , Leuther A.
Published: February 2011

We report on molecular beam epitaxial growth of AlInSb/GaInSb metamorphic high-electron-mobility-transistor structures for low power, high frequency applications on 4 in. GaAs substrates. The structures consist of a Ga0.4In0.6Sb channel embedded in Al0.4In0.6Sb barrier layers which are grown on top of an insulating metamorphic buffer, which is based on the linear exchange of Ga versus In and a subsequent exchange of As versus Sb. Precise control of group V fluxes and substrate temperature in the Al0.4In0.6As1−xSbx buffer is essential to achieve high quality device structures. Good morphological properties were achieved demonstrated by the appearance of crosshatching and root mean square roughness values of 2.0 nm. Buffer isolation is found to be >100 kΩ/◻ for optimized growth conditions. Hall measurements at room temperature reveal electron densities of 2.8×1012 cm−2 in the channel at mobility values of 21.000 cm2/V s for single-sided Te volume doping and 5.4×1012 cm−2 and 17.000 cm2/V s for double-sided Te δ-doping, respectively.
Mechanically stiffened and thermally softened bulk modulus of BaXO3(X=Ti,Zr,Nb) cubic perovskites
Authors: Liu X. J. , Pan L. K. , Sun Z. , Wang X. H. , Zhou J. , Li L. T. , Sun Chang Q.
Published: February 2011

Although the physics behind the bulk modulus, B(T,P), as a function of temperature (T) and pressure (P), has been intensively investigated, an atomic scale understanding of this attribute remains a high challenge. Here, we show that the B(T,P) for BaXO3 (X=Ti,Zr,Nb) can be established by connecting the B directly to the bond length and bond energy and their response to the applied T and P in the form of binding energy density, B[E/d3(T,P)]. Besides an estimation of the Debye temperature and single bond energy, outcomes clarified that the thermally softened B arises from bond expansion and bond weakening due to lattice vibration and the mechanically stiffened B results from bond compression and bond strengthening due to mechanical work hardening.
Global existence and uniform stabilization of a generalized dissipative Klein–Gordon equation type with boundary damping
Authors: Zhang Zai-yun , Liu Zhen-hai , Miao Xiu-jin , Chen Yue-zhong
Published: February 2011

In this paper, we prove the existence, uniqueness, and uniform stability of strong and weak solutions of the nonlinear generalized Klein-Gordon equation (1.1)_1 (see Sec. I) in bounded domains with nonlinear damped boundary conditions given by (1.1)_3 (see Sec. I) with some restrictions on function f(u), h(∇u), g(ut), and b(x), we prove the existence and uniqueness by means of nonlinear semigroup method and obtain the uniform stabilization by using the multiplier technique.
Influence of nano-Cu additive on MgB2 phase formation, processing temperature, and transport properties
Authors: Varghese Neson , Vinod K. , Rahul S. , Devadas K. M. , Thomas Syju , Pradhan S. , Syamaprasad U.
Published: February 2011

Pure and nano-Cu doped MgB2/Fe superconducting wires were prepared by in situ powder-in-tube method at different temperatures (550–675 °C). The phase formation, microstructure, and transport critical current density of the wires were investigated as a function of the heat-treatment temperature. A small amount of nano-Cu addition (2.5 wt %) was found to dramatically decrease the reaction temperature of magnesium and boron, forming MgB2 without any degradation in the transport critical current. From x-ray diffraction and scanning electron microscopy analyses, it was found that the added Cu form a reacted phase Mg2Cu with Mg which melts at around 550 °C. This liquid phase helps the formation of MgB2 at a significant lower temperature with improved grain connectivity, grain size, and density. All Cu doped samples heat treated in the range of 550–650 °C exhibited a transport JC quite comparable to that of the pure sample processed at 650 °C, which shows that high quality MgB2 conductors can be produced even at 550 °C with minor Cu doping.
Impact of type of crystal defects in multicrystalline Si on electrical properties and interaction with impurities
Authors: Takahashi Isao , Usami Noritaka , Mizuseki Hiroshi , Kawazoe Yoshiyuki , Stokkan Gaute , Nakajima Kazuo
Published: February 2011

We investigated impact of type of crystal defects in multicrystalline Si (mc-Si) on electrical properties and their change after gettering process of impurities. A bundle of dislocations gives negative impact on the gettering process, while Σ3 grain boundaries does not affect at all. In addition, we categorized random grain boundaries in mc-Si by the contact angle between adjacent dendrite crystals to form the grain boundary. Change in the contrast of photoluminescence intensity around the grain boundary was found to systematically vary by the contact angle, which showed good correlation with calculated interface energy of the grain boundary. Grain boundaries with low interface energy are concluded to be preferable to weaken recombination activity by the gettering process and improvement of solar cell performance based on mc-Si.
Highly accurate determination of the electron affinity of ${\rm SF}_{6}$ SF 6 and analysis of structure and photodetachment spectrum of ${\rm SF}^{-}_{6}$ SF 6−
Authors: Eisfeld Wolfgang
Published: February 2011

The title system is thoroughly investigated by high-level electronic structure techniques and nuclear quantum dynamics calculations. Equilibrium geometries and harmonic frequencies are determined by coupled-cluster singles doubles [CCSD(T)] calculations with large AO basis sets. A \documentclass[12pt]{minimal}\begin{document}$C_{4v}$\end{document}C4v distorted geometry is found for the anion in contrast to previous assumptions. This is explained by the bonding situation in the electronic ground state and possible vibronic interactions with higher electronic states. The computed adiabatic electron affinity of 0.73 eV is considerably lower than the currently recommended value. Analysis of the electronic states of the anion shows that the \documentclass[12pt]{minimal}\begin{document}$\sigma ^*$\end{document}σ* ground state at equilibrium position corresponds to a highly excited state at the neutral's geometry where the ground state is either a very weakly bound or scattering state. If the electron is captured by this latter state, a nonadiabatic transition to the \documentclass[12pt]{minimal}\begin{document}$\sigma ^*$\end{document}σ* state followed by internal vibrational redistribution could explain the formation of a stable anion. The \documentclass[12pt]{minimal}\begin{document}$C_{4v}$\end{document}C4v distortion of the equilibrium geometry is essential for the explanation of recently measured photodetachment spectra. Since the distortion leads to six equivalent minima with very low barriers, an anharmonic potential energy surface (PES) of the four relevant vibrational modes is constructed and fitted to CCSD(T) computed energies. The remaining 11 modes are treated as harmonic oscillators. The vibrational dynamics of the anion is studied by diagonalization of the Hamiltonian in the basis of the neutral's eigenstates. The computed photoelectron spectra are in good agreement with recent experiments and demonstrate the quality of the PES and that \documentclass[12pt]{minimal}\begin{document}$C_{4v}$\end{document}C4v distortion is responsible for the observed irregularities. However, thermal effects play a significant role for the shape of the spectra because many low-lying initial states are populated.
Effect of polarization on the solubility of gases in molten salts
Authors: Simonin Jean-Pierre
Published: February 2011

The solubility of noble gases and water in molten salts is predicted by developing an analytical parameter-free description in terms of polarizable hard sphere (the gas particle) in a medium composed of charged hard spheres of comparable size (the salt). The chemical potential of solute contains contributions from excluded volume, polarization, and dispersion forces. The polarization of the gas particle is calculated explicitly within the framework of the mean spherical approximation for the ion–dipole mixture. An additional contribution originating from the polarization of the salt is proposed. This effect has been overlooked in previous theoretical studies. Its magnitude is estimated in an approximate way. The description is found to give predictions that are in good agreement with experimental solubility data for noble gases and water in molten KCl and RbCl. The results suggest that volume exclusion and salt polarization may constitute the main two opposing factors affecting this phenomenon.
A generalization of Gudder–Nagy's theorem with numerical ranges of operators
Authors: Du Hong-Ke , Dou Yan-Ni , Zhang Hai-Yan , Shen Ling-Min
Published: February 2011

In this paper, we prove that, for A, B, C, which are bounded linear operators on a separable complex Hilbert space \documentclass[12pt]{minimal}\begin{document}$\mathcal {H}$\end{document}H, (Ax, x)(Bx, x) = (Cx, x) for all \documentclass[12pt]{minimal}\begin{document}$x\in \mathcal {H}$\end{document}x∈H with ∥x∥ = 1, if and only if there exists a complex number \documentclass[12pt]{minimal}\begin{document}$c\in \mathbb {C}$\end{document}c∈C, such that A = cI and C = cB or B = cI and C = cA.
Generalizations of the Fuoss approximation for ion pairing
Authors: Zhu P. , You X. , Pratt L. R. , Papadopoulos K. D.
Published: February 2011

An elementary statistical observation identifies generalizations of the Fuoss approximation for the probability distribution function that describes ion clustering in electrolyte solutions. The simplest generalization, equivalent to a Poisson distribution model for inner-shell occupancy, exploits measurable interionic correlation functions, and is correct at the closest pair distances whether primitive electrolyte solutions models or molecularly detailed models are considered, and for low electrolyte concentrations in all cases. With detailed models, these generalizations include nonionic interactions and solvation effects. These generalizations are relevant for computational analysis of bimolecular reactive processes in solution. Comparisons with direct numerical simulation results show that the simplest generalization is accurate for a slightly supersaturated solution of tetraethylammonium tetrafluoroborate in propylene carbonate ([tea][\documentclass[12pt]{minimal}\begin{document}${\rm BF}_4$\end{document} BF 4]/PC), and also for a primitive model associated with the [tea][\documentclass[12pt]{minimal}\begin{document}${\rm BF}_4$\end{document} BF 4]/PC results. For [tea][\documentclass[12pt]{minimal}\begin{document}${\rm BF}_4$\end{document} BF 4]/PC, the atomically detailed results identify solvent-separated nearest-neighbor ion-pairs. This generalization is examined also for the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][\documentclass[12pt]{minimal}\begin{document}${\rm BF}_4$\end{document} BF 4]) where the simplest implementation is less accurate. In this more challenging situation an augmented maximum entropy procedure is satisfactory, and explains the more varied near-neighbor distributions observed in that case.
Orbifolds, the A, D, E family of caustic singularities, and gravitational lensing
Authors: Aazami A. B. , Petters A. O. , Rabin J. M.
Published: February 2011

We provide a geometric explanation for the existence of magnification relations for the \documentclass[12pt]{minimal}\begin{document}$A_n (n \ge 2), D_n (n \ge 4), E_6, E_7, E_8$\end{document}An(n≥2),Dn(n≥4),E6,E7,E8 family of caustic singularities, which were established in recent work. In particular, it was shown that for families of general mappings between planes exhibiting any of these caustic singularities, and for any noncaustic target point, the total signed magnification of the corresponding preimages vanishes. As an application to gravitational lensing, it was also shown that, independent of the choice of a lens model, the total signed magnification vanishes for a light source anywhere in the four-image region close to elliptic and hyperbolic umbilic caustics. This is a more global and higher order analog of the well-known fold and cusp magnification relations. We now extend each of these mappings to weighted projective space, which is a compact orbifold, and show that magnification relations translate into a statement about the behavior of these extended mappings at infinity. This generalizes multidimensional residue techniques developed in previous work, and introduces weighted projective space as a new tool in the theory of caustic singularities and gravitational lensing.
Origin of line tension for a Lennard-Jones nanodroplet
Authors: Weijs Joost H. , Marchand Antonin , Andreotti Bruno , Lohse Detlef , Snoeijer Jacco H.
Published: February 2011

The existence and origin of line tension has remained controversial in literature. To address this issue, we compute the shape of Lennard-Jones nanodrops using molecular dynamics and compare them to density functional theory in the approximation of the sharp kink interface. We show that the deviation from Young’s law is very small and would correspond to a typical line tension length scale (defined as line tension divided by surface tension) similar to the molecular size and decreasing with Young’s angle. We propose an alternative interpretation based on the geometry of the interface at the molecular scale.
A molecular dynamics study of ethanol–water hydrogen bonding in binary structure I clathrate hydrate with CO2
Authors: Alavi Saman , Ohmura Ryo , Ripmeester John A.
Published: February 2011

Guest–host hydrogen bonding in clathrate hydrates occurs when in addition to the hydrophilic moiety which causes the molecule to form hydrates under high pressure–low temperature conditions, the guests contain a hydrophilic, hydrogen bonding functional group. In the presence of carbon dioxide, ethanol clathrate hydrate has been synthesized with 10% of large structure I (sI) cages occupied by ethanol. In this work, we use molecular dynamics simulations to study hydrogen bonding structure and dynamics in this binary sI clathrate hydrate in the temperature range of 100–250 K. We observe that ethanol forms long-lived (>500 ps) proton-donating and accepting hydrogen bonds with cage water molecules from both hexagonal and pentagonal faces of the large cages while maintaining the general cage integrity of the sI clathrate hydrate. The presence of the nondipolar CO2 molecules stabilizes the hydrate phase, despite the strong and prevalent alcohol–water hydrogen bonding. The distortions of the large cages from the ideal form, the radial distribution functions of the guest–host interactions, and the ethanol guest dynamics are characterized in this study. In previous work through dielectric and NMR relaxation time studies, single crystal x-ray diffraction, and molecular dynamics simulations we have observed guest–water hydrogen bonding in structure II and structure H clathrate hydrates. The present work extends the observation of hydrogen bonding to structure I hydrates.
Sources of the deficiencies in the popular SPC/E and TIP3P models of water
Authors: Kiss Péter T. , Baranyai András
Published: February 2011

Motivated by the results of Vega et al. [J. Phys. Condens. Matter 20, 153101 (2008)] about the phase diagram of water, and by the results of Kiss and Baranyai [J. Chem. Phys. 131, 204310 (2009)] about the properties of gas-phase clusters, we carried out a comparative study of the structure modeled by SPC/E and TIP3P interactions in ambient liquid water. The gas-phase clusters of SPC/E and TIP3P models show erroneous structures, while TIP4P-type models, either polarizable or not, provide qualitatively correct results. The trimers of SPC/E and TIP3P are planar in gas phase, contrary to experimental and TIP4P-type models. The aim of this study was to see whether traces of these false geometries characteristic to SPC/E and TIP3P in gas phase can also be found in the liquid phase. For this purpose we selected trimers formed by adjacent neighbors of water molecules in the liquid and calculated their geometrical features. We determined angles formed by the HO bonds of the molecules with OO vectors and with the normal vector of the OOO plane in the selected trimers. Our results showed that, despite high temperature, the SPC/E and TIP3P water contains larger number of planar arrangements than other TIP4P-type models. Although structural differences presented in this study are small, they are accurately detectable. These results weaken the reliability of studies obtained by the SPC/E or TIP3P models even in the liquid phase.
Light absorption in textured thin film silicon solar cells: A simple scalar scattering approach versus rigorous simulation
Authors: Rockstuhl C. , Fahr S. , Lederer F. , Haug F.-J. , Söderström T. , Nicolay S. , Despeisse M. , Ballif C.
Published: February 2011

Rigorous diffraction theory is a reliable tool to quantify the absorption enhancement in textured thin film solar cells. We provide a line of arguments that make the insights from such an involved analysis accessible to a broader community by using a scalar approach. We show that the scattering response from a textured surface as calculated by a simple scalar model can be related to the measured external quantum efficiency of a solar cell and double-check this model by rigorous calculations. This approach allows estimating the performance of a textured thin film to a certain extent without any sophisticated numerical analysis.
Functional gate metal-oxide-semiconductor field-effect transistors using tunnel injection/ejection of trap charges enabling self-adjustable threshold voltage for ultralow power operation
Authors: Nakajima Anri , Kudo Takashi , Ito Takashi
Published: February 2011

Metal-oxide-semiconductor field-effect transistors (MOSFETs) with a functional gate, which enables self-adjustment of threshold voltage (Vth), were proposed for ultralow power operation and fabricated with conventional complementary metal-oxide-semiconductor (CMOS) technology. In the on-current state of fabricated nMOSFETs, electron ejection from the charge trap layer by direct tunneling makes Vth low and increases on-current further. In the off-current state, electron injection into the charge trap layer makes Vth high and suppresses subthreshold leakage current. Although the characteristic time of electron transfer of the functional gate from on-current state to off-current state is fairly long, the logic mode operating principle has been verified with the experimental device. Reduction of tunnel oxide thickness (Tox) will reduce the time, which will lead to the practical use of the proposed device for CMOS logic application.
Effect of vanadium deficiency on properties of polycrystalline LaVO3
Authors: Gharetape S. Jamali , Singh M. P. , Razavi F. S. , Crandles D. A. , Zhao L. Y. , Leung K. T.
Published: February 2011

We report the influence of V deficiency on structure, transport, and magnetic properties of polycrystalline LaVO3. Up to 10% V-deficient samples were synthesized using standard solid state chemistry route. Structural and spectroscopic studies show that it intricately modifies lattice parameters and oxidation states of V. Further temperature dependent resistivity data reveal that V deficiency induces an enhancement in the resistivity and activation energy. The paramagnetic moment of these samples depends on net V composition while all samples exhibit a paramagnetic-to-antiferromagnetic transition at about 140 K. These distinct properties are understood owing to the presence of multiple oxidations states of V, predominantly V3+ and V4+, in nonstoichiometric LaVO3.
Detecting single nanomagnet dynamics beyond the diffraction limit in varying magnetostatic environments
Authors: Liu Z. , Brandt R. , Yahagi Y. , Hansen B. , Harteneck B. , Bokor J. , Hawkins A. R. , Schmidt H.
Published: February 2011

As areal bit density increases, characterizing individual magnetic bits within dense arrays becomes difficult with diffraction-limited optics. We demonstrate that dynamic magneto-optical detection breaks this diffraction limit if the characteristic behavior of a nanomagnet is sufficiently different from its neighbors’. We use far-field time-resolved Kerr microscopy to resolve the high-frequency magnetization dynamics of a single, small (Ø150 nm) nanomagnet within a low-frequency background from an array of large (Ø500 nm) magnets. We use this technique to observe and quantify the effects of magnetostatic interactions on the single magnet dynamics as the intermagnet spacing is varied.
Improved power conversion efficiency of InP solar cells using organic window layers
Authors: Li Ning , Lee Kyusang , Renshaw Christopher K. , Xiao Xin , Forrest Stephen R.
Published: February 2011

We employ the organic semiconductor 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) as a nanometer thick window layer for p-InP/indium tin oxide (ITO) Schottky barrier diode solar cells. The power conversion efficiency is enhanced compared to ITO/InP cells lacking the PTCDA window layer, primarily due to neutralizing InP surface state charges via hole injection from the PTCDA. This leads to an increased ITO/p-InP Schottky barrier height, and hence to an increased open circuit voltage. The power conversion efficiency of the cells increases from 13.2±0.5% for the ITO/InP cell to 15.4±0.4% for the ITO/4 nm PTCDA/p-InP cell under 1 sun, AM1.5G simulated solar illumination. The PTCDA window layer is also shown to contribute to the photocurrent by light absorption followed by exciton dissociation at the organic/inorganic semiconductor interface.
Ultimate performance of polymer:fullerene bulk heterojunction tandem solar cells
Authors: Kotlarski J. D. , Blom P. W. M.
Published: February 2011

We present the model calculations to explore the potential of polymer:fullerene tandem solar cells. As an approach we use a combined optical and electrical device model, where the absorption profiles are used as starting point for the numerical current-voltage calculations. With this model a maximum power efficiency of 11.7% for single cells has been achieved as a reference. For tandem structures with a ZnO/poly(3,4-ethylenedioxythiophene)/poly(styrenesulphonic acid) middle electrode an ultimate efficiency of 14.1% has been calculated. In the optimum configuration the subcell with the narrowest band gap is placed closest to the incoming light. Consequently, tandem structures are expected to enhance the performance of optimized single cells by about 20%.
Direct observation of the spin configurations of vertical Bloch line
Authors: Kim JinBae , Akinaga Hiro , Kim Jongryoul
Published: February 2011

We observed the spin configurations of Bloch lines in a ferromagnetic MnAs film on GaAs(001) by conventional magnetic force microscopy (MFM) and tilt-scanning (TS)-MFM. Due to the high lateral resolution of conventional MFM measurements, we were able to demonstrate the out-of-plane magnetic components within the Bloch line. Through vertical stray magnetic field mapping, the TS-MFM operation was shown to enable the detailed measurement and visualization of the spin configurations of the Bloch lines. This direct observation method of the spin configurations of vertical Bloch line structures allowed us to visualize antiparallel domain structure on the out-of-plane rotation of magnetization.
Hysteresis and intermittency in direct-current superconducting quantum interference device with nanobridges fabricated on a thin membrane
Authors: Segev Eran , Suchoi Oren , Shtempluck Oleg , Xue Fei , Buks Eyal
Published: February 2011

This study examined the voltage response of nanobridge-based direct-current superconducting quantum interference devices (dc-SQUIDs) fabricated on a Si3N4 membrane. Such a configuration may help in reducing 1/f noise, which possibly originates from substrate fluctuating defects. Results showed that the poor thermal coupling between the dc-SQUID and the substrate leads to a strong hysteretic response of the superconducting quantum interference device (SQUID) even though it is biased by an alternating current. In addition, when the dc-SQUID is biased near a threshold of spontaneous oscillations, the measured voltage has an intermittent pattern, which depends on the applied magnetic flux threading the loop of the SQUID.
Large converse magnetoelectric effect in Metglas FeCoBSi and 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 laminated composite
Authors: Xuan H. C. , Wang L. Y. , Ma S. C. , Zheng Y. X. , Cao Q. Q. , Wang D. H. , Du Y. W.
Published: February 2011

Converse magnetoelectric (CME) effect is investigated in a FeCoBSi/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 laminated composite by using induction method within different frequencies. A large CME coefficient of 3.05 G/V is observed at the resonance frequency of 76.5 kHz under a low bias magnetic field of 50 Oe. The CME coefficient of the heterostructure is almost constant and exhibits a relatively high value in a wide frequency span of 1–64 kHz. The origin of large CME effect and the advantages of Metglas acting as ferromagnetic layer are discussed in the present paper.
Theoretical study on tethered polymers with explicit grafting points in Θ-solvent
Authors: Suo Tongchuan , Yan Dadong
Published: February 2011

Systematic studies on the polymers chemically grafted onto a solid substrate with various grafting densities are presented based on the self-consistent mean-field theory (SCMFT). The distribution of the grafting points is explicitly included and all the three coordinates of each grafting point are fixed during the calculations. The existence of solvent molecules is also explicitly considered in the model and the case of Θ-solvent is investigated. The structure of the system is derived by solving the SCMFT equations in three-dimensional space. For the cases of low grafting density, the system is highly inhomogeneous and typical mushroom-like structures are derived. On the other hand, when the grafting density is high enough, the system is nearly homogeneous along the substrate and the polymer concentration profile is consistent with the numerical results of one dimensional SCMFT calculations. The crossover between “mushroom” regime and polymer brush is obtained by tuning the grafting density. In addition, in brush limit, while the root-mean-squared thickness of the brush is linearly dependent on the degree of polymerization, its dependency on the grafting density is in general more complicated than a simple power law.
Ferromagnetic carbon materials prepared from polyacrylonitrile
Authors: Saito Tetsuji , Nishio-Hamane Daisuke , Yoshii Shunsuke , Nojima Tsutomu
Published: February 2011

We report a ferromagnetic carbon material that is attracted by a permanent magnet. The ferromagnetic carbon material was prepared by pyrolysis of polyacrylonitrile at 1273 K for 1 h. Chemical analysis combined with an energy-dispersive x-ray analysis revealed that the carbon material did not contain any transition metals. The metal-free ferromagnetic carbon material exhibited a saturation magnetization of 1.22 emu/g at room temperature.
Memory-bit selection and recording by rotating fields in vortex-core cross-point architecture
Authors: Yu Young-Sang , Jung Hyunsung , Lee Ki-Suk , Fischer Peter , Kim Sang-Koog
Published: February 2011

In one of our earlier studies S.-K. Kim et al., [Appl. Phys. Lett. 92, 022509 (2008)], we proposed a concept of robust information storage, recording, and readout, which can be implemented in nonvolatile magnetic random-access memories and is based on the energetically degenerated twofold ground states of vortex-core magnetizations. In the present study, we experimentally demonstrate reliable memory-bit selection and recording in vortex-core cross-point architecture, specifically using a two-by-two vortex-state disk array. In order to efficiently switch a vortex core positioned at the intersection of crossed electrodes, two orthogonal addressing electrodes are selected, and then two Gaussian pulse currents of optimal pulse width and time delay are applied. Such tailored pulse-type rotating magnetic fields which occur only at the selected intersection are a prerequisite for a reliable memory-bit selection and low-power-consumption recording of information in the existing cross-point architecture.
Streaming potential generated by a pressure-driven flow over superhydrophobic stripes
Authors: Zhao Hui
Published: February 2011

The streaming potential generated by a pressure-driven flow over a weakly charged slip-stick surface [the zeta potential of the surface is smaller than the thermal potential (25 mV)] with an arbitrary double layer thickness is theoretically studied by solving the Debye–Huckel equation and Stokes equation. A series solution of the streaming potential is derived. Approximate expressions for the streaming potential in the limits of thin double layers and thick double layers are also given in excellent agreement with the full solution. To understand the impact of the slip, the streaming potential is compared against that over a homogeneously charged smooth surface. Our results indicate that the streaming potential over a superhydrophobic surface can only be enhanced under certain conditions. Moreover, as the double layer thickness increases, the advantage of the superhydrophobic surface diminishes. In addition, the Onsager relation which directly relates the magnitude of electro-osmotic effect to that of the streaming current effect has been explicitly proved to be valid for thin and thick double layers and homogeneously charged superhydrophobic surfaces. Comparisons between the streaming current and electro-osmotic mobility for an arbitrary electric double layer thickness under various conditions indicate that the Onsager relation seems applicable for arbitrary weakly charged superhydrophobic surfaces although there is no general proof. Knowledge of the streaming potential over a slip-stick surface can provide guidance for designing novel and efficient microfluidic energy-conversion devices using superhydrophobic surfaces.
Measurement of relative biological effectiveness of protons in human cancer cells using a laser-driven quasimonoenergetic proton beamline
Authors: Yogo A. , Maeda T. , Hori T. , Sakaki H. , Ogura K. , Nishiuchi M. , Sagisaka A. , Kiriyama H. , Okada H. , Kanazawa S. , Shimomura T. , Nakai Y. , Tanoue M. , Sasao F. , Bolton P. R. , Murakami M. , Nomura T. , Kawanishi S. , Kondo K.
Published: February 2011

Human cancer cells are irradiated by laser-driven quasimonoenergetic protons. Laser pulse intensities at the 5×1019 W/cm2 level provide the source and acceleration field for protons that are subsequently transported by four energy-selective dipole magnets. The transport line delivers 2.25 MeV protons with an energy spread of 0.66 MeV and a bunch duration of 20 ns. The survival fraction of in vitro cells from a human salivary gland tumor is measured with a colony formation assay following proton irradiation at dose levels of up to 8 Gy, for which the single bunch dose rate is 1×107 Gy/s and the effective dose rate is 0.2 Gy/s for 1 Hz repetition of irradiation. Relative biological effectiveness at the 10% survival fraction is measured to be 1.20±0.11 using protons with a linear energy transfer of 17.1 keV/μm.
Conductance of kinked nanowires
Authors: Cook B. G. , Varga K.
Published: February 2011

The conductance properties of kinked nanowires are studied by first-principles transport calculations within a recently developed complex potential framework. Using prototypical examples of monoatomic Au chains as well as small diameter single-crystalline silicon nanowires we show that transmission strongly depends on the kink geometry and one can tune the conductance properties by the kink angle and other geometrical factors. In the case of a silicon nanowire the presence of a kink drastically reduces the conductance.
Charge transport in fibrous/not fibrous α3-helical and (5Q,7Q)α3 variant peptides
Authors: Bezerril L. M. , Fulco U. L. , Oliveira J. I. N. , Corso G. , Albuquerque E. L. , Freire V. N. , Caetano E. W. S.
Published: February 2011

Although differing only by the Ala→Gln substitution at the fifth or seventh position of the α3-peptide amino acid sequence (Leu-Glu-Thr-Leu-Ala-Lys-Ala)3, the 5Qα3 variant forms fibrous assemblies more attenuated than those of the α3-peptide, while the 7Qα3 variant does not form fibrils. A tight-binding transport modeling was performed to obtain their current-voltage patterns, with hopping energies of the dipeptides calculated within the density functional theory framework. Beyond the semiconductor character, we obtain that the current pattern can be used to distinguish them, suggesting that it can be useful for the development of devices as diagnostics tools for amyloidosislike diseases.
Freestanding piezoelectric rings for high efficiency energy harvesting at low frequency
Authors: Massaro Alessandro , De Guido Stefano , Ingrosso Ilaria , Cingolani Roberto , De Vittorio Massimo , Cori Marco , Bertacchini Alessandro , Larcher Luca , Passaseo Adriana
Published: February 2011

Energy harvesting at low frequency is a challenge for microelectromechanical systems. In this work we present a piezoelectric vibration energy harvester based on freestanding molybdenum (Mo) and aluminum nitride (AlN) ring-microelectromechanical-system (RMEMS) resonators. The freestanding ring layout has high energy efficiency due to the additional torsional modes which are absent in planar cantilevers systems. The realized RMEMS prototypes show very low resonance frequencies without adding proof masses, providing the record high power density of 30.20 μW mm−3 at 64 Hz with an acceleration of 2g. The power density refers to the volume of the vibrating RMEMS layout.
Dependence of nonlocal Gilbert damping on the ferromagnetic layer type in ferromagnet/Cu/Pt heterostructures
Authors: Ghosh A. , Sierra J. F. , Auffret S. , Ebels U. , Bailey W. E.
Published: February 2011

We have measured the size effect in the nonlocal Gilbert relaxation rate in ferromagnet (FM) (tFM)/Cu(3nm)[/Pt(2nm)]/Al(3nm) heterostructures, FM={Ni81Fe19,Co60Fe20B20,pureCo}. A common behavior is observed for three FM layers where the additional relaxation obeys both a strict inverse power law dependence ΔG=Ktn, n=−1.04±0.06 and a similar magnitude K=224±40MHz⋅nm. As the tested FM layers span an order of magnitude in spin diffusion length λSD, the results are in support of spin diffusion rather than nonlocal resistivity as the origin of the effect.
Time-dependent current-voltage curves during the forming process in unipolar resistance switching
Authors: Lee S. B. , Yoo H. K. , Chang S. H. , Gao L. G. , Kang B. S. , Lee M.-J. , Kim C. J. , Noh T. W.
Published: February 2011

We investigated the time-dependent current-voltage curves of the forming process in unipolar resistance switching. We applied triggered-voltage triangular-waveform (pulse-waveform) signals with varied sweep rate (amplitude) to Pt/SrTiOx/Pt capacitors. By investigating their temperature dependences, we found that the forming process was driven by two different mechanisms, depending on the sweep rate (amplitude): a purely electrical dielectric breakdown and a thermally assisted dielectric breakdown. For the latter process, we observed precursory changes in the current I(t) before the forming process. By fitting the time-dependent precursory changes with I(t)=Io−A exp(−t/τ), we suggest that the thermally activated migration of oxygen vacancies/ions could help the thermally assisted dielectric breakdown.