bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical investigation of the relative stability of Na+Hen (n = 2–24) clusters: Many-body versus delocalization effects
Authors: Issaoui Noureddine , Abdessalem Kawther , Ghalla Houcine , Yaghmour Saud Jamil , Calvo Florent , Oujia Brahim
Published: November 2014

The solvation of the Na+ ion in helium clusters has been studied theoretically using optimization methods. A many-body empirical potential was developed to account for Na+–He and polarization interactions, and the most stable structures of Na+Hen clusters were determined using the basin-hopping method. Vibrational delocalization was accounted for using zero-point energy corrections at the harmonic or anharmonic levels, the latter being evaluated from quantum Monte Carlo simulations for spinless particles. From the static perspective, many-body effects are found to play a minor role, and the structures obtained reflect homogeneous covering up to n = 10, followed by polyicosahedral packing above this size, the cluster obtained at n = 12 appearing particularly stable. The cationic impurity binds the closest helium atoms sufficiently to negate vibrational delocalization at small sizes. However, this snowball effect is obliterated earlier than shell completion, the nuclear wavefunctions of 4HenNa+ with n = 5–7, and n > 10 already exhibiting multiple inherent structures. The decrease in the snowball size due to many-body effects is consistent with recent mass spectrometry measurements.
Stability and size of particle pairs in complex plasmas
Authors: Nosenko V. , Ivlev A. V. , Kompaneets R. , Morfill G.
Published: November 2014

Particle pairing in a complex plasma was experimentally studied with the emphasis on pair spatial extent and stability. Micron-size particles were suspended in the (pre)sheath area above the lower electrode in a capacitively coupled radio-frequency discharge in argon. They formed vertical pairs due to the ion wakes created by the flow of ions past particles. We discuss the confinement mechanism for the lower particle, resulting from a combination of the wake field and the field of non-uniform sheath. A model of particle pairs is proposed, which provides good description for the dependence of pair size and stability on experimental parameters.
Complete active space second-order perturbation theory with cumulant approximation for extended active-space wavefunction from density matrix renormalization group
Authors: Kurashige Yuki , Chalupský Jakub , Lan Tran Nguyen , Yanai Takeshi
Published: November 2014

We report an extension of our previous development that incorporated quantum-chemical density matrix renormalization group (DMRG) into the complete active space second-order perturbation theory (CASPT2) [Y. Kurashige and T. Yanai, J. Chem. Phys. 135, 094104 (2011)]. In the previous study, the combined theory, referred to as DMRG-CASPT2, was built upon the use of pseudo-canonical molecular orbitals (PCMOs) for one-electron basis. Within the PCMO basis, the construction of the four-particle reduced density matrix (4-RDM) using DMRG can be greatly facilitated because of simplicity in the multiplication of 4-RDM and diagonal Fock matrix in the CASPT2 equation. In this work, we develop an approach to use more suited orbital basis in DMRG-CASPT2 calculations, e.g., localized molecular orbitals, in order to extend the domain of applicability. Because the multiplication of 4-RDM and generalized Fock matrix is no longer simple in general orbitals, an approximation is made to it using the cumulant reconstruction neglecting higher-particle cumulants. Also, we present the details of the algorithm to compute 3-RDM of the DMRG wavefunction as an extension of the 2-RDM algorithm of Zgid et al. [J. Chem. Phys. 128, 144115 (2008)] and Chan et al. [J. Chem. Phys. 128, 144117 (2008)]. The performance of the extended DMRG-CASPT2 approach was examined for large-scale multireference systems, such as low-lying excited states of long-chain polyenes and isomerization potential of {[Cu(NH3)3]2O2}2+.
Dynamics of intermittent force fluctuations in vesicular nanotubulation
Authors: Ashok B. , Ananthakrishna G.
Published: November 2014

Irregular force fluctuations are seen in most nanotubulation experiments. The dynamics behind their presence has, however, been neither commented upon nor modeled. A simple estimate of the mean energy dissipated in force drops turns out to be several times the thermal energy. This coupled with the rate dependent nature of the deformation reported in several experiments point to a dynamical origin of the serrations. We simplify the whole process of tether formation through a three-stage model of successive deformations of sphere to ellipsoid, neck-formation, and tubule birth and extension. Based on this, we envisage a rate-softening frictional force at the neck that must be overcome before a nanotube can be pulled out. Our minimal model includes elastic and visco-elastic deformation of the vesicle, and has built-in dependence on pull velocity, vesicle radius, and other material parameters, enabling us to capture various kinds of serrated force-extension curves for different parameter choices. Serrations are predicted in the nanotubulation region. Other features of force-extension plots reported in the literature such as a plateauing serrated region beyond a force drop, serrated flow region with a small positive slope, an increase in the elastic threshold with pull velocity, force-extension curves for vesicles with larger radius lying lower than those for smaller radius, are all also predicted by the model. A toy model is introduced to demonstrate that the role of the friction law is limited to inducing stick-slip oscillations in the force, and all other qualitative and quantitative features emerging from the model can only be attributed to other physical mechanisms included in the deformation dynamics of the vesicle.
Small molecule solvation changes due to the presence of salt are governed by the cost of solvent cavity formation and dispersion
Authors: Li Libo , Fennell Christopher J. , Dill Ken A.
Published: November 2014

We are interested in the free energies of transferring nonpolar solutes into aqueous NaCl solutions with salt concentrations upwards of 2 M, the Hofmeister regime. We use the semi-explicit assembly (SEA) computational model to represent these electrolyte solutions. We find good agreement with experiments (Setschenow coefficients) on 43 nonpolar and polar solutes and with TIP3P explicit-solvent simulations. Besides being much faster than explicit solvent calculations, SEA is more accurate than the PB models we tested, successfully capturing even subtle salt effects in both the polar and nonpolar components of solvation. We find that the salt effects are mainly due to changes in the cost of forming nonpolar cavities in aqueous NaCl solutions, and not mainly due to solute-ion electrostatic interactions.
Generalized Korteweg-de Vries equation induced from position-dependent effective mass quantum models and mass-deformed soliton solution through inverse scattering transform
Authors: Ganguly A. , Das A.
Published: November 2014

We consider one-dimensional stationary position-dependent effective mass quantum model and derive a generalized Korteweg-de Vries (KdV) equation in (1+1) dimension through Lax pair formulation, one being the effective mass Schrödinger operator and the other being the time-evolution of wave functions. We obtain an infinite number of conserved quantities for the generated nonlinear equation and explicitly show that the new generalized KdV equation is an integrable system. Inverse scattering transform method is applied to obtain general solution of the nonlinear equation, and then N-soliton solution is derived for reflectionless potentials. Finally, a special choice has been made for the variable mass function to get mass-deformed soliton solution. The influence of position and time-dependence of mass and also of the different representations of kinetic energy operator on the nature of such solitons is investigated in detail. The remarkable features of such solitons are demonstrated in several interesting figures and are contrasted with the conventional KdV-soliton associated with constant-mass quantum model.
Modeling and optimizing of the random atomic spin gyroscope drift based on the atomic spin gyroscope
Authors: Quan Wei , Lv Lin , Liu Baiqi
Published: November 2014

In order to improve the atom spin gyroscope's operational accuracy and compensate the random error caused by the nonlinear and weak-stability characteristic of the random atomic spin gyroscope (ASG) drift, the hybrid random drift error model based on autoregressive (AR) and genetic programming (GP) + genetic algorithm (GA) technique is established. The time series of random ASG drift is taken as the study object. The time series of random ASG drift is acquired by analyzing and preprocessing the measured data of ASG. The linear section model is established based on AR technique. After that, the nonlinear section model is built based on GP technique and GA is used to optimize the coefficients of the mathematic expression acquired by GP in order to obtain a more accurate model. The simulation result indicates that this hybrid model can effectively reflect the characteristics of the ASG's random drift. The square error of the ASG's random drift is reduced by 92.40%. Comparing with the AR technique and the GP + GA technique, the random drift is reduced by 9.34% and 5.06%, respectively. The hybrid modeling method can effectively compensate the ASG's random drift and improve the stability of the system.
A high precision method for mapping phase to amplitude in direct digital synthesis and its hardware implementation
Authors: Cao Zhang , Song Wei , Peng Zhicong , Xu Lijun
Published: November 2014

There exist a number of algorithms to map the phase to amplitude in direct digital synthesis (DDS). For DDS with more than 14 output bits, the Coordinate Rotation Digital Computer (CORDIC) algorithm is well known for its high precision. Also, it is effective in solutions where there is the need of in-phase and quadrature components simultaneously because the algorithm calculates both. In this paper, a Taylor expansion based method was proposed to calculate both in-phase and quadrature at the same time. Numerical simulations for different data format, e.g., double and finite bits, were carried out in Matlab and Quartus, which were followed by the hardware implementation in Field Programmable Gate Array. The results demonstrated that the proposed method possessed higher precision and exhausted less logic elements than the CORDIC algorithm.
Monte Carlo simulation and equation of state for flexible charged hard-sphere chain fluids: Polyampholyte and polyelectrolyte solutions
Authors: Jiang Hao , Adidharma Hertanto
Published: November 2014

The thermodynamic modeling of flexible charged hard-sphere chains representing polyampholyte or polyelectrolyte molecules in solution is considered. The excess Helmholtz energy and osmotic coefficients of solutions containing short polyampholyte and the osmotic coefficients of solutions containing short polyelectrolytes are determined by performing canonical and isobaric-isothermal Monte Carlo simulations. A new equation of state based on the thermodynamic perturbation theory is also proposed for flexible charged hard-sphere chains. For the modeling of such chains, the use of solely the structure information of monomer fluid for calculating the chain contribution is found to be insufficient and more detailed structure information must therefore be considered. Two approaches, i.e., the dimer and dimer-monomer approaches, are explored to obtain the contribution of the chain formation to the Helmholtz energy. By comparing with the simulation results, the equation of state with either the dimer or dimer-monomer approach accurately predicts the excess Helmholtz energy and osmotic coefficients of polyampholyte and polyelectrolyte solutions except at very low density. It also well captures the effect of temperature on the thermodynamic properties of these solutions.
Ideal solar cell equation in the presence of photon recycling
Authors: Lan Dongchen , Green Martin A.
Published: November 2014

Previous derivations of the ideal solar cell equation based on Shockley's p-n junction diode theory implicitly assume negligible effects of photon recycling. This paper derives the equation in the presence of photon recycling that modifies the values of dark saturation and light-generated currents, using an approach applicable to arbitrary three-dimensional geometries with arbitrary doping profile and variable band gap. The work also corrects an error in previous work and proves the validity of the reciprocity theorem for charge collection in such a more general case with the previously neglected junction depletion region included.
Lie bundle on the space of deformed skew-symmetric matrices
Authors: Dobrogowska Alina , Goliński Tomasz
Published: November 2014

We study a Lie algebra \documentclass[12pt]{minimal}\begin{document}$\mathcal {A}_{a_1,\ldots ,a_{n-1}}$\end{document}Aa1,...,an−1 of deformed skew-symmetric n × n matrices endowed with a Lie bracket given by a choice of deformed symmetric matrix. The deformations are parametrized by a sequence of real numbers a1, …, an − 1. Using isomorphism \documentclass[12pt]{minimal}\begin{document}$(\mathcal {A}_{a_1,\ldots ,a_{n-1}})^*\cong L_+$\end{document}(Aa1,...,an−1)*≅L+ we introduce a Lie–Poisson structure on the space of upper-triangular matrices L+. In this way, we generate hierarchies of Hamiltonian systems with bihamiltonian structure.
Non-exponential relaxation, fictive temperatures, and dispersive kinetics in the liquid-glass-liquid transition range of acetaminophen, sulfathiazole, and their mixtures
Authors: Aji D. P. B. , Khouri J. , Johari G. P.
Published: November 2014

To investigate the effects of added molecular heterogeneity on the hysteretic features of liquid-glass-liquid transition, we studied acetaminophen, sulfathiazole, and three of their mixtures by calorimetry, and determined the Tg and the fictive temperature, Tf, from changes in the enthalpy and entropy on the cooling and heating paths, as well as the non-exponential parameter, βcal. We find that, (i) Tf for cooling is within 1–3 K of Tf for heating and both are close to Tg, (ii) the closed loop entropy change in the liquid-glass-liquid range is negligibly small, (iii) Tg and Tf increase on increasing sulfathiazole in the mixture, (iv) βcal first slightly increases when the second component is added and then decreases, and (v) ageing causes deviations from a non-exponential, nonlinear behavior of the glass. In terms of fluctuations in a potential energy landscape, adding a solute heterogeneity would shift the state point to another part of the landscape with a different distribution of barrier heights and a different number of minima accessible to the state point. Part of the change in βcal is attributed to hydrogen-bond formation between the two components. Ageing changes the relaxation times distribution, more at short relaxation times than at long relaxation times, and multiplicity of relaxation modes implied by βcal < 1 indicates that each mode contributing to the enthalpy has its own Tg or Tf. βcal differs from βage determined from isothermal ageing, and the distribution parameter of α-relaxation times would differ from both βcal and βage.
Microscopic properties of lithium, sodium, and magnesium battery anode materials related to possible dendrite growth
Authors: Jäckle Markus , Groß Axel
Published: November 2014

Lithium and magnesium exhibit rather different properties as battery anode materials with respect to the phenomenon of dendrite formation which can lead to short-circuits in batteries. Diffusion processes are the key to understanding structure forming processes on surfaces. Therefore, we have determined adsorption energies and barriers for the self-diffusion on Li and Mg using periodic density functional theory calculations and contrasted the results to Na which is also regarded as a promising electrode material in batteries. According to our calculations, magnesium exhibits a tendency towards the growth of smooth surfaces as it exhibits lower diffusion barriers than lithium and sodium, and as an hcp metal it favors higher-coordinated configurations in contrast to the bcc metals Li and Na. These characteristic differences are expected to contribute to the unequal tendencies of these metals with respect to dendrite growth.
Entropic penalties in circular DNA assembly
Authors: Zoli Marco
Published: November 2014

The thermodynamic properties of DNA circular molecules are investigated by a new path integral computational method which treats in the real space the fundamental forces stabilizing the molecule. The base pair and stacking contributions to the classical action are evaluated separately by simulating a broad ensemble of twisted conformations. We obtain, for two short sequences, a free energy landscape with multiple wells corresponding to the most convenient values of helical repeat. Our results point to a intrinsic flexibility of the circular structures in which the base pair fluctuations move the system from one well to the next thus causing the local unwinding of the helix. The latter is more pronounced in the shorter sequence whose cyclization causes a higher bending stress. The entropic reductions associated to the formation of the ordered helicoidal structure are estimated.
Electronic properties of Si hollow nanowires
Authors: Di Mario Lorenzo , Turchini Stefano , Zema Nicola , Cimino Roberto , Martelli Faustino
Published: November 2014

The electronic and structural properties of amorphous and crystalline silicon hollow nanowires (HNWs) have been investigated by X-ray photoemission (XPS), Raman, and photoluminescence spectroscopies. The HNWs have an internal diameter of about 80 nm and sidewalls with a thickness of 8–15 nm. Crystalline HNWs are obtained by thermal annealing of the amorphous ones. XPS shows that although oxidation is a very important process in these suspended nanostructures, a clear Si 2p signal is detected in the crystalline HNWS, thus indicating that the sidewall surface maintains mainly a pure silicon nature. Raman shows that the thermal annealing gives rise to a very good crystal quality and a weak visible luminescence signal is detected in the crystalline HNWs.
Structural and thermodynamic consideration of metal oxide doped GeO2 for gate stack formation on germanium
Authors: Lu Cimang , Lee Choong Hyun , Zhang Wenfeng , Nishimura Tomonori , Nagashio Kosuke , Toriumi Akira
Published: November 2014

A systematic investigation was carried out on the material and electrical properties of metal oxide doped germanium dioxide (M-GeO2) on Ge. We propose two criteria on the selection of desirable M-GeO2 for gate stack formation on Ge. First, metal oxides with larger cation radii show stronger ability in modifying GeO2 network, benefiting the thermal stability and water resistance in M-GeO2/Ge stacks. Second, metal oxides with a positive Gibbs free energy for germanidation are required for good interface properties of M-GeO2/Ge stacks in terms of preventing the Ge-M metallic bond formation. Aggressive equivalent oxide thickness scaling to 0.5 nm is also demonstrated based on these understandings.
Single-phase Mn1−xZnxFe2O4(x = 0.2, 0.5, 0.8) hollow ceramic microspheres: One-step preparation and electromagnetic properties
Authors: Hongfei Lou , Jianjiang Wang , Baocai Xu , Guanhui Liang , Zhiguang Li , Yongshen Hou , Guoshun Wan , Haitao Gao , Liang Yu
Published: November 2014

Single-phase Mn1−xZnxFe2O4 (x = 0.2, 0.5, 0.8) hollow ceramic microspheres (MnZn-HCMs) was one-step prepared using self-reactive quenching method. Material parameters of three MnZn-HCMs were studied by SEM and XRD, and electromagnetic properties were investigated by vibrating sample magnetometer and vector network analyzer. The results showed that the phase composition of three MnZn-HCMs presents single-phase, with particle size distribution of 20–60 μm; when x was equal to 0.2 or 0.8, the surface of HCMs showed a large number of nano-lamellar crystal with crossing, connecting or laminating each other, and for 0.5, a large quantity of nano-isometric crystal was formed. Thanks to special surface structure and micron-particle size, three MnZn-HCMs exhibited superparamagnetic. With the content of Zn increases, the saturated magnetization (Ms) decreases first and then increases, meanwhile, the coercivity (Hc) decreases gradually. In the 0.1–18 GHz range, due to nano-lamellar structure could enhance the interfacial polarization and space charge polarization, Mn0.8Zn0.2Fe2O4 HCMs and Mn0.2Zn0.8Fe2O4 HCMs have higher real part of permittivity (ε′) value than Mn0.5Zn0.5Fe2O4 HCMs. Owing to higher conductivity, the value of imaginary part of permittivity (ε″) of Mn0.5Zn0.5Fe2O4 HCMs was the highest in 0.1–0.8 GHz range, however, with the frequency increases, the ε″ of Mn0.8Zn0.2Fe2O4 HCMs and Mn0.2Zn0.8Fe2O4 HCMs increased significantly resulting from orientation polarization and interfacial polarization, which was greater than Mn0.5Zn0.5Fe2O4 HCMs. Due to the higher Ms, the value of imaginary part of permeability (μ″) of Mn0.2Zn0.8Fe2O4 HCMs and Mn0.8Zn0.2Fe2O4 HCMs was greater than Mn0.5Zn0.5Fe2O4 HCMs. Moreover, the μ″-f curve reveals a broad resonance peak of Mn0.8Zn0.2Fe2O4 HCMs ranging from 0.1 to 8 GHz, which maybe relate to its thick nano-lamellar crystal.
Note: Calibration of atomic force microscope cantilevers using only their resonant frequency and quality factor
Authors: Sader John E. , Friend James R.
Published: November 2014

A simplified method for calibrating atomic force microscope cantilevers was recently proposed by Sader et al. [Rev. Sci. Instrum. 83, 103705 (2012); Sec. III D] that relies solely on the resonant frequency and quality factor of the cantilever in fluid (typically air). This method eliminates the need to measure the hydrodynamic function of the cantilever, which can be time consuming given the wide range of cantilevers now available. Using laser Doppler vibrometry, we rigorously assess the accuracy of this method for a series of commercially available cantilevers and explore its performance under non-ideal conditions. This shows that the simplified method is highly accurate and can be easily implemented to perform fast, robust, and non-invasive spring constant calibration.
A high velocity impact experiment of micro-scale ice particles using laser-driven system
Authors: Yu Hyeonju , Kim Jungwook , Yoh Jack J.
Published: November 2014

A jet engine for high speed air breathing propulsion is subject to continuous wear as a result of impacts of micro-scale ice particles during a flight in the atmosphere. The inlet duct and compressor blades are exposed to on-coming frozen moisture particles that may result in the surface damage and significantly shorten the designed lifetime of the aircraft. Under such prolonged high-speed impact loading, the performance parameters such as flight instability and power loss of a jet engine can be significantly degraded. In this work, a laser-driven system was designed to accelerate micro-scale ice particles to the velocity up to Mach 2 using a Q-switched Nd:YAG laser beam at 100–600 mJ with 1064 nm wavelength and 9 ns pulse duration. The high speed images (Phantom v711) and double exposure shadowgraphs were used to calculate the average velocity of ice particles and their deceleration. Velocity Interferometer System for Any Reflector measurements were also utilized for the analysis of free surface velocity of a metal foil in order to understand the interfacial dynamics between the impacting particles and accepting metal target. The velocity of our ice particles is sufficiently fast for studying the effect of moisture particle collision on an air-breathing duct of high speed aircraft, and thus the results can provide insight into how minute space debris or micrometeorites cause damage to the orbiting spacecraft at large.
Nonlinear model for thermal effects in free-electron lasers
Authors: Peter E. , Endler A. , Rizzato F. B.
Published: November 2014

In the present work, we extend results of a previous paper [Peter et al., Phys. Plasmas 20, 12 3104 (2013)] and develop a semi-analytical model to account for thermal effects on the nonlinear dynamics of the electron beam in free-electron lasers. We relax the condition of a cold electron beam but still use the concept of compressibility, now associated with a warm beam model, to evaluate the time scale for saturation and the peak laser intensity in high-gain regimes. Although vanishing compressibilites and the associated divergent densities are absent in warm models, a series of discontinuities in the electron density precede the saturation process. We show that full wave-particle simulations agree well with the predictions of the model.
Diffusionless phase transition with two order parameters in spin-crossover solids
Authors: Gudyma Iurii , Ivashko Victor , Linares Jorge
Published: November 2014

The quantitative analysis of the interface boundary motion between high-spin and low-spin phases is presented. The nonlinear effect of the switching front rate on the temperature is shown. A compressible model of spin-crossover solid is studied in the framework of the Ising-like model with two-order parameters under statistical approach, where the effect of elastic strain on interaction integral is considered. These considerations led to examination of the relation between the order parameters during temperature changes. Starting from the phenomenological Hamiltonian, entropy has been derived using the mean field approach. Finally, the phase diagram, which characterizes the system, is numerically analyzed.
Detection of volcanic infrasound with a ring laser interferometer
Authors: Dunn Robert W. , Hosman Ashley R.
Published: November 2014

Over the last 15 years, large horizontally mounted ring lasers have been used to study numerous geophysical phenomena. This paper provides examples of the sensitivity of large active ring laser interferometers to far field infrasound emissions from explosive volcanic eruptions. Volcanic infrasound is reported from representative eruptions of volcanoes Kelut (Kelud), Klyuchevskaya (Kliuchevskoi), Puyehua, Santa Maria, Sakurajima, and Tungurahua. The detected infrasound frequencies are in basic agreement with the far field air wave frequencies from the 1980 eruption of Mount St. Helens and the 1991 eruption of Mount Pinatubo. Cavities of large horizontally mounted active ring lasers contain two counter-propagating waves that in the presence Earth's rotation become traveling waves of slightly different frequencies. The Sagnac or beat frequency due to the difference in the traveling wave frequencies is modulated by geophysical phenomena, in this case volcanic infrasound. Signatures of the infrasound are found in the frequency modulated side bands.
Comprehensive study of Al-induced layer-exchange growth for orientation-controlled Si crystals on SiO2 substrates
Authors: Kurosawa Masashi , Sadoh Taizoh , Miyao Masanobu
Published: November 2014

Orientation-controlled crystalline Si films on insulating substrates are strongly required to achieve high-performance thin-film devices for next-generation electronics. We have comprehensively investigated the layer-exchange kinetics of Al-induced crystallization (AIC) in stacked structures, i.e., amorphous-Si/Al-oxide/Al/SiO2-substrates, as a function of the air-exposure time of Al surfaces (tair: 0–24 h) to form Al-oxide interface-layers, the thickness of Al and Si layers (dAl, dSi: 50–200 nm), the annealing temperature (450–500 °C), and the annealing time (0–50 h). It has been clarified that longer tair (>60 min) and/or thinner dAl and dSi (<50 nm) lead to the (111) oriented growth; in contrast, shorter tair (<60 min) and/or thicker dAl and dSi (>100 nm) lead to the (100) oriented growth. No correlation between the annealing temperature and the crystal orientation is observed. Detailed analysis reveals that the layer-exchange kinetics are dominated by “supply-limited” processing, i.e., diffusion of Si atoms into Al layers through Al-oxide layer. Based on the growth rate dependent Si concentration profiles in Al layers, and the free-energy of Si at Al-oxide/Al or Al/SiO2 interfaces, a comprehensive model for layer-exchange growth is proposed. This well explains the experimental results of not only Si-AIC but also another material system such as gold-induced crystallization of Ge. In this way, a growth technique achieving the orientation-controlled Si crystals on insulating substrates is established from both technological and scientific points of view.
Bending of electromagnetic waves in all-dielectric particle array waveguides
Authors: Savelev Roman S. , Filonov Dmitry S. , Kapitanova Polina V. , Krasnok Alexander E. , Miroshnichenko Andrey E. , Belov Pavel A. , Kivshar Yuri S.
Published: November 2014

We propose and demonstrate experimentally an alternative approach for realizing subwavelength photonic structures, exploiting the waveguiding properties of chains of high-index dielectric disks with both electric and magnetic dipole resonances. We reveal that the electromagnetic energy can be efficiently guided through sharp corners by means of the mode polarization conversion at waveguide bends. We confirm experimentally the guidance through a 90° bend in the microwave frequency range.
Tunneling magnetoresistance phenomenon utilizing graphene magnet electrode
Authors: Hashimoto T. , Kamikawa S. , Soriano D. , Pedersen J. G. , Roche S. , Haruyama J.
Published: November 2014

Using magnetic rare-metals for spintronic devices is facing serious problems for the environmental contamination and the limited material-resource. In contrast, by fabricating ferromagnetic graphene nanopore arrays (FGNPAs) consisting of honeycomb-like array of hexagonal nanopores with hydrogen-terminated zigzag-type atomic structure edges, we reported observation of polarized electron spins spontaneously driven from the pore edge states, resulting in rare-metal-free flat-energy-band ferromagnetism. Here, we demonstrate observation of tunneling magnetoresistance (TMR) behaviors on the junction of cobalt/SiO2/FGNPA electrode, serving as a prototype structure for future rare-metal free TMR devices using magnetic graphene electrodes. Gradual change in TMR ratios is observed across zero-magnetic field, arising from specified alignment between pore-edge- and cobalt-spins. The TMR ratios can be controlled by applying back-gate voltage and by modulating interpore distance. Annealing the SiO2/FGNPA junction also drastically enhances TMR ratios up to ∼100%.
Correlation between the electron-phonon coupling and rectifying performance for poly(3-hexylthiophene)/n-type Si devices
Authors: Lin Yow-Jon , Chin Yi-Min
Published: November 2014

A correlation between the electron-phonon coupling and rectifying performance is identified for poly(3-hexylthiophene) (P3HT)/n-type Si devices and an analysis using the temperature-dependent Hall-effect characteristics is presented. The carrier mobility in the P3HT film exhibits strong temperature dependence, indicating the dominance of tunneling. However, the incorporation of titanium oxide (TiO2) nanoparticles into P3HT leads to the dominance of hopping. The results demonstrate that the incorporation of TiO2 nanoparticles into P3HT influences the electrical property of P3HT/n-type Si devices by the electron-phonon coupling modification and the increased spacing between molecules that serve to enhance the carrier mobility in P3HT.
Amorphization of hard crystalline materials by electrosprayed nanodroplet impact
Authors: Gamero-Castaño Manuel , Torrents Anna , Borrajo-Pelaez Rafael , Zheng Jian-Guo
Published: November 2014

A beam of electrosprayed nanodroplets impacting on single-crystal silicon amorphizes a thin surface layer of a thickness comparable to the diameter of the drops. The phase transition occurs at projectile velocities exceeding a threshold, and is caused by the quenching of material melted by the impacts. This article demonstrates that the amorphization of silicon is a general phenomenon, as nanodroplets impacting at sufficient velocity also amorphize other covalently bonded crystals. In particular, we bombard single-crystal wafers of Si, Ge, GaAs, GaP, InAs, and SiC in a range of projectile velocities, and characterize the samples via electron backscatter diffraction and transmission electron microscopy to determine the aggregation state under the surface. InAs requires the lowest projectile velocity to develop an amorphous layer, followed by Ge, Si, GaAs, and GaP. SiC is the only semiconductor that remains fully crystalline, likely due to the relatively low velocities of the beamlets used in this study. The resiliency of each crystal to amorphization correlates well with the specific energy needed to melt it except for Ge, which requires projectile velocities higher than expected.
Combined effects of Bi deficiency and Mn substitution on the structural transformation and functionality of BiFeO3 films
Authors: Chen Jingyi , Wang Yao , Deng Yuan
Published: November 2014

Mn-doped BiFeO3 films with Mn contents of 5 and 10 mol. % were prepared via a chemical route. A carefully controlled amount of Bi deficiency was introduced to further tune the lattice structure and the functionality of multiferroic BiFeO3. The crystal structure of Bi1−δFe1−xMnxO3 films was investigated by X-ray diffraction and Raman spectra; a rhombohedral-to-orthorhombic phase transition was revealed. The observed double hysteresis loops and two capacitance maxima from polarization vs electric field and capacitance-voltage measurements indicate an antiferroelectric-like behavior. Additionally, the coexistence of ferroelectric (FE) and antiferroelectric (AFE) phases in Bi1−δFe1−xMnxO3 films was revealed from the domain structures obtained by piezoelectric force microscopy. The effects of Mn substitution in conjunction with Bi deficiency on the FE-AFE phase transition and electrical behavior of BiFeO3 films are discussed in detail. Meanwhile, magnetic and photoluminescence measurements on the films illustrate that Mn substitution gives rise to the net magnetic moment and the defects induced by both Bi deficiency and Mn substitution influence the electronic structure of BiFeO3 films. This study thus shows a simple and effective way to control the functionalities of BiFeO3 films.
Communication: Ultrafast time-resolved ion photofragmentation spectroscopy of photoionization-induced proton transfer in phenol-ammonia complex
Authors: Shen Ching-Chi , Tsai Tsung-Ting , Ho Jr-Wei , Chen Yi-Wei , Cheng Po-Yuan
Published: November 2014

Photoionization-induced proton transfer (PT) in phenol-ammonia (PhOH-NH3) complex has been studied using ultrafast time-resolved ion photofragmentation spectroscopy. Neutral PhOH-NH3 complexes prepared in a free jet are photoionized by femtosecond [1+1] resonance-enhanced multiphoton ionization via the S1 state, and the subsequent dynamics occurring in the cations is probed by delayed pulses that result in ion fragmentation. The observed temporal evolutions of the photofragmentation spectra are consistent with an intracomplex PT reaction. The experiments revealed that PT in [PhOH-NH3]+ cation proceeds in two distinct steps: an initial impulsive wave-packet motion in ∼70 fs followed by a slower relaxation of about 1 ps that stabilizes the system into the final PT configuration. These results indicate that for a barrierless PT system, even though the initial PT motions are impulsive and ultrafast, the reaction may take a much longer time scale to complete.
Investigation of effective base transit time and current gain modulation of light-emitting transistors under different ambient temperatures
Authors: Yang Hao-Hsiang , Tu Wen-Chung , Wang Hsiao-Lun , Wu Chao-Hsin
Published: November 2014

In this report, the modulation of current gain of InGaP/GaAs light-emitting transistors under different ambient temperatures are measured and analyzed using thermionic emission model of quantum well embedded in the transistor base region. Minority carriers captured by quantum wells gain more energy at high temperatures and escape from quantum wells resulting in an increase of current gain and lower optical output, resulting in different I-V characteristics from conventional heterojunction bipolar transistors. The effect of the smaller thermionic lifetime thus reduces the effective base transit time of transistors at high temperatures. The unique current gain enhancement of 27.61% is achieved when operation temperature increase from 28 to 85 °C.
2kF-selected conductance oscillations of high-mobility two-dimensional electron gas in Corbino devices
Authors: Liu Xiaoxue , Zhu Yuying , Du Lingjie , Yang Changli , Lu Li , Pfeiffer Loren , West Kenneth , Du Rui-Rui
Published: November 2014

We have observed electrical-field induced magneto-conductivity oscillations measured in Corbino samples made of a GaAs high-mobility two-dimensional electron gas, and found a consistent interpretation based on a semiclassical model of 2kF-selected orbital transitions between N and N + 1, 2, 3,…, Landau levels at respective local potentials, where kF is the Fermi wavevector. From the oscillation period, we deduce an effective mass value, which is consistent with the bare electron band mass of GaAs. In the same devices but with a vanishing electrical field and at elevated temperatures, we observed additional oscillation features, which can be attributed to cyclotron resonance by population of acoustic phonons. We thus demonstrate a method to determine the carrier effective mass and the sound velocity of host crystals by standard electrical transport.
Reversible modulation of electric transport properties by oxygen absorption and releasing on Nb:SrTiO3 surface
Authors: Lu H. X. , Liu Y. B. , Chen Y. S. , Wang J. , Shen B. G. , Sun J. R.
Published: November 2014

Pt Schottky contacts on (001)-orientated Nb-doped SrTiO3 (NSTO) in both ambient air and vacuum were investigated by the conductive atomic force microscope. The co-existed TiO2 and SrO termination layers were identified on the terrace-structured NSTO surface, where the former possessed a higher forward current than the latter. In ambient air, the barrier height of Pt/NSTO Schottky junction exhibited periodical variation with cyclic terrace plane and step sites, whereas it became homogeneous in ambient vacuum. We suggested that the oxygen absorption and releasing of surface dangling bonds were the origin for reversible changes in transport properties, which indicates a feasible approach for the surface modulation and band structure tailoring of NSTO based heterojunctions.
Microstructural analysis of 9.7% efficient Cu2ZnSnSe4 thin film solar cells
Authors: Buffière M. , Brammertz G. , Batuk M. , Verbist C. , Mangin D. , Koble C. , Hadermann J. , Meuris M. , Poortmans J.
Published: November 2014

This work presents a detailed analysis of the microstructure and the composition of our record Cu2ZnSnSe4 (CZTSe)-CdS-ZnO solar cell with a total area efficiency of 9.7%. The average composition of the CZTSe crystallites is Cu1.94Zn1.12Sn0.95Se3.99. Large crystals of ZnSe secondary phase (up to 400 nm diameter) are observed at the voids between the absorber and the back contact, while smaller ZnSe domains are segregated at the grain boundaries and close to the surface of the CZTSe grains. An underlying layer and some particles of CuxSe are observed at the Mo-MoSe2-Cu2ZnSnSe4 interface. The free surface of the voids at the back interface is covered by an amorphous layer containing Cu, S, O, and C, while the presence of Cd, Na, and K is also observed in this region.
Study on matching map for the absorber filled by metallic magnetic particles
Authors: Wang Tao , Xu Fei , Tang Liyun , Qiao Liang , Li Fashen
Published: November 2014

A map displaying the matching characteristics and absorption performance for the metallic carbonyl iron composite in microwave frequency band is developed based on the origin of absorption peaks. In this map, the dependence of matching frequency fm on absorber thickness, input impendence, and absorption peak value is achieved simultaneously from the complex permeability and permittivity spectra without any approximation. From this map, the perfect matching frequency fpm and perfect matching thickness tpm at input impendence Z = 1 can be directly searched. Moreover, the required absorber thickness and the reflection loss value at any expected frequency where the absorption peak locates can be directly observed.
Non-linear mixing in coupled photonic crystal nanobeam cavities due to cross-coupling opto-mechanical mechanisms
Authors: Ramos Daniel , Frank Ian W. , Deotare Parag B. , Bulu Irfan , Lončar Marko
Published: November 2014

We investigate the coupling between mechanical and optical modes supported by coupled, freestanding, photonic crystal nanobeam cavities. We show that localized cavity modes for a given gap between the nanobeams provide weak optomechanical coupling with out-of-plane mechanical modes. However, we show that the coupling can be significantly increased, more than an order of magnitude for the symmetric mechanical mode, due to optical resonances that arise from the interaction of the localized cavity modes with standing waves formed by the reflection from thesubstrate. Finally, amplification of motion for the symmetric mode has been observed and attributed to the strong optomechanical interaction of our hybrid system. The amplitude of these self-sustained oscillations is large enough to put the system into a non-linear oscillation regime where a mixing between the mechanical modes is experimentally observed and theoretically explained.
Multiple soliton self-frequency shift cancellations in a temporally tailored photonic crystal fiber
Authors: Liu Lai , Kang Zhe , Li Qing , Gao Xuejian , Liao Meisong , Qin Guanshi , Hu Lili , Ohishi Yasutake , Qin Weiping
Published: November 2014

We report the generation of multiple soliton self-frequency shift cancellations in a temporally tailored tellurite photonic crystal fiber (PCF). The temporally regulated group velocity dispersion (GVD) is generated in the fiber by soliton induced optical Kerr effect. Two red-shifted dispersive waves spring up when two Raman solitons meet their own second zero-dispersion-wavelengths in the PCF. These results show how, through temporally tailored GVD, nonlinearities can be harnessed to generate unexpected effects.
Inductive pulsed phase thermography for reducing or enlarging the effect of surface emissivity variation
Authors: Yang Ruizhen , He Yunze , Gao Bin , Tian Gui Yun
Published: November 2014

Emissivity variation introduces illusory temperature inhomogeneity and results in false alarms in infrared thermography, thus, it is important to separate the influence of surface emissivity variation. This letter experimentally demonstrates the advantages of phase information to reduce or enlarge the effect of surface emissivity variation with inductive pulsed phase thermography, where inductive excitation is emissivity-independent and avoids the effect of emissivity variation in heating process. The directly heated area and the indirectly heated area are divided in the phasegrams. The emissivity variation is removed or enlarged perfectly at the specific frequency and defect detectability is improved remarkably.
Enhancing the photo-currents of CdTe thin-film solar cells in both short and long wavelength regions
Authors: Paudel Naba R. , Yan Yanfa
Published: November 2014

The recent increases in the record efficiency of CdTe thin-film solar cell technology largely benefited from enhancements in short circuit current densities (JSC) in the short-wavelength regions by reducing the thicknesses of CdS window layers. Here, we report that the JSC can be enhanced in both short and long wavelength regions by using CdSe as the window layer. Comparing to CdS, CdSe has a higher solubility in CdTe, resulting in stronger interdiffusion at the CdSe/CdTe interface and the formation of CdTe1−xSex alloys with high x values. Due to bowing effects, the CdTe1−xSex alloys exhibit narrower band gaps than CdTe, enhancing the JSC in the CdTe-based solar cells for long-wavelengths. We further report that the use of combined CdS/CdSe window layers can realize high open circuit voltages and maintain the JSC enhancements. Our results suggest a viable approach to improve the performance of CdTe thin-film solar cells.
Experimental evidence on removing copper and light-induced degradation from silicon by negative charge
Authors: Boulfrad Yacine , Lindroos Jeanette , Wagner Matthias , Wolny Franziska , Yli-Koski Marko , Savin Hele
Published: November 2014

In addition to boron and oxygen, copper is also known to cause light-induced degradation (LID) in silicon. We have demonstrated previously that LID can be prevented by depositing negative corona charge onto the wafer surfaces. Positively charged interstitial copper ions are proposed to diffuse to the negatively charged surface and consequently empty the bulk of copper. In this study, copper out-diffusion was confirmed by chemical analysis of the near surface region of negatively/positively charged silicon wafer. Furthermore, LID was permanently removed by etching the copper-rich surface layer after negative charge deposition. These results demonstrate that (i) copper can be effectively removed from the bulk by negative charge, (ii) under illumination copper forms a recombination active defect in the bulk of the wafer causing severe light induced degradation.
Additional magnetoelectric effect in electrode-arrayed magnetoelectric composite
Authors: Pan D. A. , Zuo Z. J. , Zhang S. G. , Liu B. , Qiao L. J. , Volinsky A. A.
Published: November 2014

An electrode-arrayed magnetoelectric (ME) composite was proposed, in which the positive and negative electrodes of the PZT-5H plate (Pb(Zr0.52Ti0.48)O3) were equally divided into a 2 × 5 array, while the PZT plate remained intact. The ME voltage coefficients of these 10 sections were measured individually and in parallel/series modes. The magnetoelectric coefficient is doubled compared with un-arrayed condition, when the 10 sections are connected in parallel/series using an optimized connecting sequence derived from the charge matching rule. This scheme can also be applied to other types of layered magnetoelectric composites to obtain additional magnetoelectric effect from the original composite structure.
Electron Momentum Spectroscopy of Valence Orbitals of n-Propyl Iodide: Spin-Orbit Coupling Effect and Intramolecular Orbital Interaction
Authors: Wang En-liang , Shi Yu-feng , Shan Xu , Yang Hong-jiang , Zhang Wei , Chen Xiang-jun
Published: November 2014

The binding energy spectrum and electron momentum distributions for the outer valence orbitals of n-propyl iodide molecule have been measured using the electron momentum spectrometer employing non-coplanar asymmetric geometry at impact energy of 2.5 keV plus binding energy. The ionization bands have been assigned in detail via the high accuracy SAC-CI general-R method calculation and the experimental momentum profiles are compared with the theoretical ones calculated by Hartree-Fock and B3LYP/aug-cc-pVTZ(C,H)6-311G** (I). The spin-orbit coupling effect and intramolecular orbital interaction have been analyzed for the outermost two bands, which are assigned to the iodine 5p lone pairs, using NBO method and non-relativistic as well as relativistic calculations. It is found that both of the interactions will lead to the observed differences in electron momentum distributions. The experimental results agree with the relativistic theoretical momentum profiles, indicating that the spin-orbit coupling effect dominates in n-propyl iodide molecule.