bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of secondary phase precipitation on grain boundary electrical activity in Cu2ZnSnS4 (CZTS) photovoltaic absorber layer material
Authors: Mendis Budhika G. , Goodman Max C. J. , Major Jonathan D. , Taylor Aidan A. , Durose Ken , Halliday Douglas P.
Published: December 2012

Cathodoluminescence is used to measure the recombination velocity of the heterointerfaces between Cu2ZnSnS4 (CZTS) and CuxSnySz, SnS secondary phases precipitated along the grain boundaries as well as ZnS precipitated within the CZTS grain interiors. The CZTS/CuxSnySz and CZTS/ZnS heterointerfaces had recombination velocities smaller than the bulk carrier diffusion velocity while the opposite is true for the CZTS/SnS heterointerface. Secondary phases having crystal structures compatible with CZTS (e.g., ZnS, Cu2SnS3) are likely to form heterointerfaces with small misfit strain and hence low interfacial recombination velocity. The precipitation of such secondary phases along grain boundaries in CZTS provides a novel mechanism for grain boundary passivation. However, it is not known if grain boundary passivating secondary phases would necessarily increase the overall photovoltaic device efficiency since other factors, such as the band gap of the secondary phase compared to the Shockley-Queisser ideal value and the nature of the heterointerface between CZTS (i.e., type-I vs type-II), also affect device operation and must therefore be taken into consideration.
Wood anomaly transmission enhancement in fishnet-based metamaterials at terahertz frequencies
Authors: Soltani N. , Lheurette É. , Lippens D.
Published: December 2012

On the basis of a fishnet-like structure, we analyze a metamaterial design involving dimer aperture arrays. It is shown that this approach leads to very strong Fano resonances within the transmission spectrum. The role of the Wood anomaly in the enhancement of the magnetic field is pointed out in order to explain this transmission characteristic. A sensitivity numerical analysis of this resonant feature is carried out. A figure of merit, defined as the ratio between the sensitivity and the width at half maximum of the resonance, as high as 830, is obtained. To our knowledge, this value is greater than the ones reported so far in literature using the inter-particle electromagnetic induced transparency principle. This property is of great interest for environment control applications, especially for sensing of highly diluted media, such as gaseous phase pollutants, as a complement to conventional spectroscopy techniques.
Charge carrier relaxation and effective masses in silicon probed by terahertz spectroscopy
Authors: Engelbrecht S. G. , Reichel A. J. , Kersting R.
Published: December 2012

Charge transport in silicon is investigated on a metal-oxide-semiconductor structure, which is driven into depletion, accumulation, or inversion. Terahertz electromodulation spectroscopy provides momentum relaxation times as well as conductivity effective masses of electrons and holes. At room temperature the conductivity effective masses of electrons and holes are close to those values reported for cryogenic temperatures.
Time-averaged heat generation in a quantum dot driven by an alternating current bias
Authors: Pei Wei , Sun Qing-feng
Published: December 2012

We theoretically study the time-averaged heat generation in a quantum dot over one period of an ac bias. By tuning the frequency ω of the ac bias, it is shown that for the definite ω=ωq/k, where ωq is the frequency of the phonon mode and k is an integer number, there appears an sharp resonant energy transfer from the electron subsystem to the phonon subsystem. Such a phenomenon can be interpreted as a consequence of the indirect coupling between the electric oscillation and the nanomechanical vibration via the tunnelling electrons. Moreover, this feature is susceptive to the parameters of transport, by change of which the heat generation will be limited or enhanced as we desire.
Very low 1/f barrier noise in sputtered MgO magnetic tunnel junctions with high tunneling magnetoresistance
Authors: Feng J. F. , Chen J. Y. , Kurt H. , Coey J. M. D.
Published: December 2012

Low frequency 1/f barrier noise has been investigated in sputtered MgO magnetic tunnel junctions (MTJs) with a tunneling magnetoresistance ratio of up to 330% at room temperature. The lowest normalized noise parameter α of the tunnel barrier reaches 2.5 × 10−12–2.1 × 10−11 μm2, which is comparable to that found in MTJs with the MgO barrier grown by MBE or electron–beam evaporation. This normalized barrier noise is almost bias independent in the voltage range of up to ±1.2 V. The low noise level and high voltage stability may reflect the high quality of the sputtered MgO with a uniform distribution of defects in the MgO layer.
Ultrananocrystalline diamond nano-pillars synthesized by microwave plasma bias-enhanced nucleation and bias-enhanced growth in hydrogen-diluted methane
Authors: Chu Yueh-Chieh , Tu Chia-Hao , Liu Chuan-pu , Tzeng Yonhua , Auciello Orlando
Published: December 2012

Bias-enhanced nucleation and growth of ultrananocrystalline diamond (UNCD) nano-pillars on silicon substrates by low-pressure microwave plasma chemical vapor deposition in a hydrogen-rich gas mixture with methane is reported. Direct-current biasing of the substrate in a constant-current mode is applied to substrates, which are pre-heated to 800 °C, to result in a negative bias voltage of greater than 350 V throughout the nucleation and growth process. Self-masking by UNCD clusters, angle dependent sputtering of UNCD clusters, and ion-assisted chemical vapor deposition by bias enhanced bombardment of energetic ions are attributed to the formation of UNCD nano-pillars. High-resolution transmission electron microscopy analysis indicates that an interfacial layer exists between the silicon substrate and the UNCD nano-pillars. The porous UNCD film with high-density nano-pillars exhibits excellent optical anti-reflectivity and improved electron field emission characteristics compared to smooth and solid UNCD films.
Dependence of charge transfer phenomena during solid–air two-phase flow on particle disperser
Authors: Tanoue Ken-ichiro , Suedomi Yuuki , Honda Hirotaka , Furutani Satoshi , Nishimura Tatsuo , Masuda Hiroaki
Published: December 2012

An experimental investigation of the tribo-electrification of particles has been conducted during solid-air two-phase turbulent flow. The current induced in a metal plate by the impact of polymethylmethacrylate (PMMA) particles in a high-speed air flow was measured for two different plate materials. The results indicated that the contact potential difference between the particles and a stainless steel plate was positive, while for a nickel plate it was negative. These results agreed with theoretical contact charge transfer even if not only the particle size but also the kind of metal plate was changed. The specific charge of the PMMA particles during solid-air two-phase flow using an ejector, a stainless steel branch pipe, and a stainless steel straight pipe was measured using a Faraday cage. Although the charge was negative in the ejector, the particles had a positive specific charge at the outlet of the branch pipe, and this positive charge increased in the straight pipe. The charge decay along the flow direction could be reproduced by the charging and relaxation theory. However, the proportional coefficients in the theory changed with the particle size and air velocity. Therefore, an unexpected charge transfer occurred between the ejector and the branch pipe, which could not be explained solely by the contact potential difference. In the ejector, an electrical current in air might have been produced by self-discharge of particles with excess charge between the nickel diffuser in the ejector and the stainless steel nozzle or the stainless steel pipe due to a reversal in the contact potential difference between the PMMA and the stainless steel. The sign of the current depended on the particle size, possibly because the position where the particles impacted depended on their size. When dual coaxial glass pipes were used as a particle disperser, the specific charge of the PMMA particles became more positive along the particle flow direction due to the contact potential difference between the PMMA and the stainless steel. Furthermore, the current in air using the dual coaxial glass pipes was less than that using the ejector.
The effect of nanostructuring on thermoelectric transport properties of p-type higher manganese silicide MnSi1.73
Authors: Norouzzadeh Payam , Zamanipour Zahra , Krasinski Jerzy S. , Vashaee Daryoosh
Published: December 2012

Higher manganese silicide (HMS) alloys have a complex band structure with multiple valleys close to the conduction and valence band edges, which complicates the analysis of their electronic transport properties. We present a semi-classical two-band model that can describe the charge carrier and phonon transport properties of p-type HMS in crystalline and bulk nanostructured forms. The effect of grain boundaries is modeled with an interface potential scattering for charge carriers and diffusive and refractive scattering for phonons. A unique set of effective masses and acoustic phonon deformation potentials are introduced that can explain both electrical and thermal transport properties versus temperature. The acoustic phonon and ionized impurity scatterings for charge carriers and phonon-phonon, point defect, and electronphonon scattering mechanisms for phonons are included in the model. The simplicity of the presented model would be valuable especially for practical purposes. The thermoelectric transport properties of nanostructured HMS were calculated versus grain size and it was shown that even though bulk nanostructuring of HMS enhances thermoelectric performance, it is not sufficient to enhance considerably the figure-of-merit.
Coupled electromagnetic TE-TM wave propagation in a layer with Kerr nonlinearity
Authors: Smirnov Yury G. , Valovik Dmitry V.
Published: December 2012

Coupled polarized electromagnetic wave propagation in a nonlinear dielectric layer filled with lossless, nonmagnetic, and isotropic medium is considered. The layer is located between two half-spaces with constant permittivities. The permittivity in the layer is described by Kerr law. Considered coupled wave is formed of transverse electric (TE) and transverse magnetic (TM) polarized waves. This nonlinear coupled wave is called coupled TE-TM wave. The analysis is reduced to the nonlinear two-parameter eigenvalue problem. We look for coupled eigenvalues of the problem and reduce the question to the analysis of the corresponding system of two dispersion equations. Existence and uniqueness of solution to the two-parameter eigenvalue problem is proved. It is shown that a new regime for coupled TE and TM wave propagation exists in a layer with Kerr nonlinearity.
Vibrational properties of LaPO4 nanoparticles in mid- and far-infrared domain
Authors: Savchyn P. , Karbovnyk I. , Vistovskyy V. , Voloshinovskii A. , Pankratov V. , Cestelli Guidi M. , Mirri С. , Myahkota O. , Riabtseva A. , Mitina N. , Zaichenko A. , Popov A. I.
Published: December 2012

Nanopowders of LaPO4 have been grown by sedimentation-micellar method. As-prepared LaPO4 nanoparticles with the average grain size of about 8 nm have a single-phase hydrated hexagonal structure. After thermal annealing at 600 and 800 °C, the average size of nanoparticles increases up to ∼35 and ∼50 nm, respectively, and the structure transforms into single-phase monoclinic. IR spectra of LaPO4 nanoparticles of different size were investigated in the wide range of wavenumbers from 130 to 5000 cm−1 in the 20–300 K temperature region. Differences between IR spectra of the bulk material and nanoparticles as well as the temperature behavior of the vibrational properties are discussed.
Flipping, scooping, and spinning: Drift of rigid curved nonchiral fibers in simple shear flow
Authors: Wang Jianghui , Tozzi Emilio J. , Graham Michael D. , Klingenberg Daniel J.
Published: December 2012

The motion of isolated, rigid, neutrally-buoyant, non-Brownian, curved, nonchiral fibers in simple shear flow of an incompressible Newtonian fluid at low Reynolds number is studied by computer simulation. For some initial orientations, fibers with small curvature drift steadily in the gradient direction without external forces or torques. The average drift velocity and direction depend on the fiber aspect ratio, curvature, and initial orientation. The drift results from the coupling of rotational and translational dynamics, and the combined effects of flipping, scooping, and spinning motions of the fiber.
Non-volatile spin switch for Boolean and non-Boolean logic
Authors: Datta Supriyo , Salahuddin Sayeef , Behin-Aein Behtash
Published: December 2012

We show that the established physics of spin valves together with the recently discovered giant spin-Hall effect could be used to construct Read and Write units that can be integrated into a single spin switch with input-output isolation, gain and fan-out similar to complementary metal oxide semiconductor inverters, but with the information stored in nanomagnets making it non-volatile. Such spin switches could be interconnected, with no external amplification, just with passive circuit elements, to perform logic operations. Moreover, since the digitization and storage occur naturally in the magnets, the voltages can be used to implement analog “weighting” for non-Boolean logic.
End station for nanoscale magnetic materials study: Combination of scanning tunneling microscopy and soft X-ray magnetic circular dichroism spectroscopy
Authors: Ueno Tetsuro , Sawada Masahiro , Kishimizu Yusuke , Kimura Akio , Namatame Hirofumi , Taniguchi Masaki
Published: December 2012

We have constructed an end station for nanoscale magnetic materials study at the soft X-ray beamline HiSOR BL-14 at Hiroshima Synchrotron Radiation Center. An ultrahigh-vacuum scanning tunneling microscope (STM) was installed for an in situ characterization of nanoscale magnetic materials in combination with soft X-ray magnetic circular dichroism (XMCD) spectroscopy experiment. The STM was connected to the XMCD experimental station via damper bellows to isolate it from environmental vibrations, thus achieving efficient spatial resolution for observing Si(111) surface at atomic resolution. We performed an in situ experiment with STM and XMCD spectroscopy on Co nanoclusters on an Au(111) surface and explored its practical application to investigate magnetic properties for well-characterized nanoscale magnetic materials.
Infrared absorption of methanethiol clusters (CH3SH)n, n = 2–5, recorded with a time-of-flight mass spectrometer using IR depletion and VUV ionization
Authors: Fu Lung , Han Hui-Ling , Lee Yuan-Pern
Published: December 2012

We investigated IR spectra in the CH- and SH-stretching regions of size-selected methanethiol clusters, (CH3SH)n with n = 2–5, in a pulsed supersonic jet using infrared (IR)-vacuum ultraviolet (VUV) ionization. VUV emission at 132.50 nm served as the source of ionization in a time-of-flight mass spectrometer. Clusters were dissociated with light from a tunable IR laser before ionization. The variations in intensity of methanethiol cluster ions (CH3SH)n+ were monitored as the IR laser light was tuned across the range 2470–3100 cm−1. In the SH-stretching region, the spectrum of (CH3SH)2 shows a weak band near 2601 cm−1, red-shifted only 7 cm−1 from that of the monomer. In contrast, all spectra of (CH3SH)n, n = 3–5, show a broad band near 2567 cm−1 with much greater intensity. In the CH-stretching region, absorption bands of (CH3SH)2 are located near 2865, 2890, 2944, and 3010 cm−1, red-shifted by 3–5 cm−1 from those of CH3SH. These red shifts increase slightly for larger clusters and bands near 2856, 2884, 2938, and 3005 cm−1 were observed for (CH3SH)5. These spectral results indicate that the S–H···S hydrogen bond plays an important role in clusters with n = 3–5, but not in (CH3SH)2, in agreement with theoretical predictions. The absence of a band near 2608 cm−1 that corresponds to absorption of the non-hydrogen-bonded SH moiety and the large width of observed feature near 2567 cm−1 indicate that the dominant stable structures of (CH3SH)n, n = 3–5, have a cyclic hydrogen-bonded framework.
On the competition between linear and perpendicular isomers in photodynamics of cationic argon trimers
Authors: Kalus René , Stachoň Martin , Gadea Florent Xavier
Published: December 2012

Photoabsorption and subsequent photodissociation of two structural isomers of \documentclass[12pt]{minimal}\begin{document}${\rm Ar}_3^+$\end{document} Ar 3+ are studied via semiclassical non-adiabatic dynamics simulations. Several experimental observables are simulated under various plausible experimental conditions with the main emphasis on the differences between the data produced for the two isomers. They include photoabsorption cross section, total kinetic energy released, fragments kinetic energy distributions, and distribution of the total kinetic energy among photofragments represented via Dalitz plots. The ability of the parameters to discriminate between the two isomers is analyzed through a thorough comparison with available experimental data. We show that the recently recorded experimental Dalitz plots [V. Lepère, Y. J. Picard, M. Barat, J. A. Fayeton, B. Lucas, and K. Béroff, J. Chem. Phys. 130, 194301 (2009)10.1063/1.3130974] correspond to a hot mixture of distorted linear-like and perpendicular-like structures where linear-like structures prevail.
Magnetic field mediated low-temperature resistivity upturn in electron-doped La1−xHfxMnO3 manganite oxides
Authors: Guo E. J. , Wang L. , Wu Z. P. , Wang L. , Lu H. B. , Jin K. J. , Gao J.
Published: December 2012

The low-temperature transport properties were systematically studied on the electron-doped polycrystalline La1−xHfxMnO3 (x = 0.2 and 0.3) compounds at the presence of external magnetic fields. The resistivity of all samples exhibits a generally low-temperature resistance upturn behavior under zero magnetic field at the temperature of Tmin, which first shifts towards lower temperature at low magnetic field (H < 0.75 T) and then moves back to higher temperature as magnetic fields increase, which is greatly different with the previous results on the hole-doped manganites. The best fitting of low-temperature resistivity could be made by considering both electron-electron (e-e) interactions in terms of T1/2 dependence and Kondo-like spin dependent scattering in terms of lnT dependence at all magnetic fields. Our results will be meaningful to understand the underlying physical mechanism of low-temperature resistivity minimum behavior in the electron-doped manganites.
Electric-field-induced and spontaneous relaxor-ferroelectric phase transitions in (Na1/2Bi1/2)1 − xBaxTiO3
Authors: Craciun F. , Galassi C. , Birjega R.
Published: December 2012

Complex dielectric susceptibility was used to investigate the relaxor properties and the ferroelectric phase transitions in (Na1/2Bi1/2)1 − xBaxTiO3 (0 ≤ x ≤ 0.08) ceramics. XRD was used to characterize the ground states of poled and unpoled samples. Dielectric susceptibility vs. temperature studies allowed to obtain the relaxor properties and to identify the electric field-induced phase transitions in the morphotropic phase boundary (MPB) compositions (0.06 < x < 0.08) and the spontaneous relaxor-ferroelectric phase transitions in the rhombohedral compositions (x < 0.06). The frequency dispersion of the dielectric maximum at Tm was observed for all compositions, although of decreased extension for lower x. The relaxor properties have been analysed with Vogel-Fulcher law. The activation energy and attempt frequency for the MPB compositions are similar to those of classical relaxors like Pb(Mg1/3Nb2/3)O3, while for rhombohedral compositions, they are similar to relaxor ferroelectrics with spontaneous relaxor-ferroelectric phase transitions, like Pb(Sc1/2Nb1/2)O3. A relationship has been found between the relaxor dispersion degree and the hysteresis of the ferroelectric transition.
Separation of finite electron temperature effect on plasma polarimetry
Authors: Imazawa Ryota , Kawano Yasunori , Kusama Yoshinori
Published: December 2012

This study demonstrates the separation of the finite electron temperature on the plasma polarimetry in the magnetic confined fusion plasma for the first time. Approximate solutions of the transformed Stokes equation, including the relativistic effect, suggest that the orientation angle, θ, and ellipticity angle, ε, of polarization state have different dependency on the electron density, ne, and the electron temperature, Te, and that the separation of ne and Te from θ and ε is possible in principle. We carry out the equilibrium and kinetic reconstruction of tokamak plasma when the central electron density was 1020 m−3, and the central electron temperatures were 5, 10, 20, and 30 keV. For both cases when a total plasma current, Ip, is known and when Ip is unknown, the profiles of plasma current density, jϕ, ne, and Te are successfully reconstructed. The reconstruction of jϕ without the information of Ip indicates the new method of Ip measurement applicable to steady state operation of tokamak.
Free-energy analysis of water affinity in polymer studied by atomistic molecular simulation combined with the theory of solutions in the energy representation
Authors: Kawakami Tomonori , Shigemoto Isamu , Matubayasi Nobuyuki
Published: December 2012

Affinity of small molecule to polymer is an essential property for designing polymer materials with tuned permeability. In the present work, we develop a computational approach to the free energy ΔG of binding a small solute molecule into polymer using the atomistic molecular dynamics (MD) simulation combined with the method of energy representation. The binding free energy ΔG is obtained by viewing a single polymer as a collection of fragments and employing an approximate functional constructed from distribution functions of the interaction energy between solute and the fragment obtained from MD simulation. The binding of water is then examined against 9 typical polymers. The relationship is addressed between the fragment size and the calculated ΔG, and a useful fragment size is identified to compromise the performance of the free-energy functional and the sampling efficiency. It is found with the appropriate fragment size that the ΔG convergence at a statistical error of ∼0.2 kcal/mol is reached at ∼4 ns of replica-exchange MD of the water-polymer system and that the mean absolute deviation of the computational ΔG from the experimental is 0.5 kcal/mol. The connection is further discussed between the polymer structure and the thermodynamic ΔG.
Tunnel conductance in GaN:Mn/AlN/GaN:Mn (0001) junction from first-principles calculations
Authors: Chen GuangWei , Huang GuiQin
Published: December 2012

The tunnel conductance of diluted ferromagnetic semiconductor tunnel junction GaN:Mn/AlN/GaN:Mn is calculated based on the first-principles calculations. The dependence of the conductance on AlN barrier thickness, doping site, and doping concentration of Mn is studied. The contributions from coherent tunneling and resonant tunneling are discussed by combining the complex band structure of AlN barrier layer and the interface states on both sides of the barrier.
Lithium-decorated oxidized porous graphene for hydrogen storage by first principles study
Authors: Huang Shi-han , Miao Ling , Xiu Yu-jie , Wen Ming , Li Cong , Zhang Le , Jiang Jian-jun
Published: December 2012

The first-principles calculations are performed to investigate the geometric stability and the hydrogen storage capacity of lithium-decorated oxidized porous graphene (PG). Due to strong interaction between Li and O atom, two stable Li decorated structures have relatively high Li binding energies of 3.84 and 3.04 eV, which could eliminate the clustering problem for Li atoms on PG surface. One doped Li atom could hold five H2 molecules and the binding energy of each H2 is above 0.2 eV. The interaction of H2 molecules with Li atom results from charge exchange between H2's σ orbital and Li's 2s orbital. In the final structure with two Li-O groups in one carbon pore, a hydrogen storage capacity of 9.43 wt. % could be achieved. By the combination of the advantage of Li decoration and oxidized porous graphene, Li-OPG possesses remarkable geometric stability and high hydrogen storage capacity.
Buckling transitions of an elastic filament in a viscous stagnation point flow
Authors: Guglielmini Laura , Kushwaha Amit , Shaqfeh Eric S. G. , Stone Howard A.
Published: December 2012

The interplay of viscous and elastic stresses is relevant to a number of flow problems involving slender elastic fibers. These range from the swimming of microorganisms to the transport of pulp fibers in processing flow as well as from nanotube and nanocarpet applications to semi-flexible polymer behavior. In some applications, slender fibers are attached to walls where they experience externally applied flows. In this paper, we focus on the model problem of a wall mounted filament in a (compressive) extensional flow and characterize the flow-induced bending and buckling of the fiber. Using a combination of stability analysis and numerical simulations (with the latter based on a discretized beam model), we show that, for a critical value of the ratio between viscous and elastic forces, the filament is susceptible to bending and buckling instabilities at supercritical bifurcation points.
Markovian dissipative coarse grained molecular dynamics for a simple 2D graphene model
Authors: Kauzlarić David , Español Pep , Greiner Andreas , Succi Sauro
Published: December 2012

Based upon a finite-element “coarse-grained molecular dynamics” (CGMD) procedure, as applied to a simple atomistic 2D model of graphene, we formulate a new coarse-grained model for graphene mechanics explicitly accounting for dissipative effects. It is shown that, within the Mori-projection operator formalism, the reversible part of the dynamics is equivalent to the finite temperature CGMD-equations of motion, and that dissipative contributions to CGMD can also be included within the Mori formalism. The CGMD nodal momenta in the present graphene model display clear non-Markovian behavior, a property that can be ascribed to the fact that the CGMD-weighting function suppresses high-frequency modes more effectively than, e.g., a simple center of mass (COM) based CG procedure. The present coarse-grained graphene model is also shown to reproduce the short time behavior of the momentum correlation functions more accurately than COM-variables and it is less dissipative than COM-CG. Finally, we find that, while the intermediate time scale represented directly by the CGMD variables shows a clear non-Markovian dynamics, the macroscopic dynamics of normal modes can be approximated by a Markovian dissipation, with friction coefficients scaling like the square of the wave vector. This opens the way to the development of a CGMD model capable of describing the correct long time behavior of such macroscopic normal modes.
Linear maps preserving maximal deviation and the Jordan structure of quantum systems
Authors: Hamhalter Jan
Published: December 2012

In the algebraic approach to quantum theory, a quantum observable is given by an element of a Jordan algebra and a state of the system is modelled by a normalized positive functional on the underlying algebra. Maximal deviation of a quantum observable is the largest statistical deviation one can obtain in a particular state of the system. The main result of the paper shows that each linear bijective transformation between JBW algebras preserving maximal deviations is formed by a Jordan isomorphism or a minus Jordan isomorphism perturbed by a linear functional multiple of an identity. It shows that only one numerical statistical characteristic has the power to determine the Jordan algebraic structure completely. As a consequence, we obtain that only very special maps can preserve the diameter of the spectra of elements. Nonlinear maps preserving the pseudometric given by maximal deviation are also described. The results generalize hitherto known theorems on preservers of maximal deviation in the case of self-adjoint parts of von Neumann algebras proved by Molnár.
Sign-sensitive determination of heteronuclear dipolar coupling to spin-1 by selective decoupling
Authors: Kharkov B. B. , Chizhik V. I. , Dvinskikh S. V.
Published: December 2012

This paper presents a theoretical and experimental study of nuclear magnetic resonance technique for sign-sensitive determination of the dipolar couplings of rare spins-1/2 to spin-1 with a strong quadrupolar interaction. The technique is based on low-power transition-selective single-quantum decoupling of spin-1 in the presence of high-power decoupling of abundant (proton) spins. Single-transition operator formalism is employed to calculate the time evolution of the density matrix in the presence of low-power irradiation of spin-1. Generally, the sign of dipolar coupling is unavailable from intrinsically symmetric shapes of dipolar-coupled spectra. Asymmetric dipolar multiplets, resulted from selective decoupling, reveal both the signs and magnitudes of the heteronuclear dipolar couplings. The approach is used to develop the experimental strategy for sign-sensitive measurements of short- and long-range heteronuclear dipolar couplings in highly ordered anisotropic samples. The technique is demonstrated for 13C–2H and 13C–14N spin pairs and for 13C–2H2 three-spin system in liquid crystals.
High precision magnetic linear dichroism measurements in (Ga,Mn)As
Authors: Tesařová N. , Šubrt J. , Malý P. , Němec P. , Ellis C. T. , Mukherjee A. , Cerne J.
Published: December 2012

Investigation of magnetic materials using the first-order magneto-optical Kerr effects (MOKEs) is well established and is frequently used. On the other hand, the utilization of the second-order (or quadratic) magneto-optical (MO) effects for the material research is rather rare. This is due to the small magnitude of quadratic MO signals and the fact that the signals are even in magnetization (i.e., they do not change a sign when the magnetization orientation is reversed), which makes it difficult to separate second-order MO signals from various experimental artifacts. In 2005 a giant quadratic MO effect—magnetic linear dichroism (MLD)—was observed in the ferromagnetic semiconductor (Ga,Mn)As. This discovery not only provided a new experimental tool for the investigation of in-plane magnetization dynamics in (Ga,Mn)As using light at normal incidence, but it also motivated the development of experimental techniques for the measurement of second-order MO effects in general. In this paper we compare four different experimental techniques that can be used to measure MLD and to separate it from experimental artifacts. We show that the most reliable results are obtained when we monitor the polarization of reflected light while the magnetization of the sample is rotated by applying an external magnetic field. Using this technique we measure the MLD spectra of (Ga,Mn)As in a broad spectral range from 0.1 eV to 2.7 eV and we observe that MLD has a magnitude comparable to the polar MOKE signals in this material.
Shock structure in shock-turbulence interactions
Authors: Donzis Diego A.
Published: December 2012

The structure of a shock wave interacting with isotropic turbulence is investigated. General principles of similarity scaling show that consistency with known physical limiting behavior requires incomplete similarity solutions where the governing non-dimensional parameters, namely, the Reynolds, convective, and turbulent Mach numbers (Rλ, M, and Mt, respectively), can be combined to reduce the number of similarity parameters that describes the phenomenon. An important parameter is found to be K = Mt/Rλ1/2(M − 1) which is proportional to the ratio of laminar shock thickness to the Kolmogorov length scale. The shock thickness under turbulent conditions, on the other hand, is essentially a random variable. Under a quasi-equilibrium assumption, shown to be valid when K2 ≪ 1, analytical results are obtained for the first and second moments of the turbulent shock thickness, velocity gradient, and dilatation at the shock. It is shown that these quantities exhibit universal behavior in the parameter K with corrections in Mt/(M − 1), for velocity fields with arbitrary statistics. Excellent agreement is observed with available data from direct numerical simulations. Two-point statistics of velocity gradients at the shock show that the distribution of dilatation over the shock surface is determined by transverse structure functions of the incoming turbulence. The regimes of the interaction are also investigated. It is found that the appropriate parameter to delimit the different regimes is Mt/(M − 1). Flow retardation ahead of the shock is suggested as a mechanism for so-called broken shocks.
Setting the post-reaction internal energies in direct simulation Monte Carlo chemistry simulations
Authors: Bird G. A.
Published: December 2012

The application of the direct simulation Monte Carlo, or DSMC, method to chemically reacting flows requires the specification of the post-reaction internal energies of the product molecules. These have generally been set to the distributions that lead to equilibrium in a non-reacting gas and they do not lead to detailed balance for reactions with finite activation energies. Detailed balance requires that the post-reaction distributions match the relevant pre-reaction distributions and it can be enforced only if the pre-reaction distributions are known. The DSMC reaction procedures that are employed in the quantum-kinetic, or Q-K, theory have been used to derive analytical expressions for the vibrationally resolved reaction rates in an equilibrium gas. The post-reaction distributions based on these expressions promote detailed balance and have been implemented in DSMC applications to binary exchange and chain reactions and also to dissociation-recombination reactions. The results from these calculations lead to equilibrium or near equilibrium. On the other hand, similar calculations that employ the traditional procedures lead to large differences between the temperatures based on the individual energy modes.
Magnetic switching driven by nanosecond scale heat and magnetic field pulses: An application of macrospin Landau-Lifshitz-Bloch model
Authors: Kilic U. , Finocchio G. , Hauet T. , Florez S. H. , Aktas G. , Ozatay O.
Published: December 2012

High-temperature (near Curie-point) magnetization-behavior in materials with strong-perpendicular-magnetocrystalline-anisotropy has recently gained importance due to potential applications in thermally/heat-assisted-magnetic-recording (TAR/HAMR) systems. We have implemented a macrospin-model within the Landau-Lifshitz-Bloch formalism for strongly exchange-coupled CoNi/Pd multilayers subject to nanosecond-scale localized-heat and magnetic-field pulses. The temperature dependence of the longitudinal-susceptibility, as determined from a single-fitting-parameter of the experimental coercive-field, is consistent with the previously reported ab initio calculations. We demonstrate that this model is able to predict the full map of switching-speed as a function of magnetic-field and local-temperature providing a robust tool for the evaluation of this and similar material systems in TAR/HAMR applications.
Crystallization to polycrystalline silicon thin film and simultaneous inactivation of electrical defects by underwater laser annealing
Authors: Machida Emi , Horita Masahiro , Ishikawa Yasuaki , Uraoka Yukiharu , Ikenoue Hiroshi
Published: December 2012

We propose a low-temperature laser annealing method of a underwater laser annealing (WLA) for polycrystalline silicon (poly-Si) films. We performed crystallization to poly-Si films by laser irradiation in flowing deionized-water where KrF excimer laser was used for annealing. We demonstrated that the maximum value of maximum grain size of WLA samples was 1.5 μm, and that of the average grain size was 2.8 times larger than that of conventional laser annealing in air (LA) samples. Moreover, WLA forms poly-Si films which show lower conductivity and larger carrier life time attributed to fewer electrical defects as compared to LA poly-Si films.
Three-dimensional analysis of nanoparticles on carbon support using aberration-corrected scanning confocal electron microscopy
Authors: Hashimoto Ayako , Wang Peng , Shimojo Masayuki , Mitsuishi Kazutaka , Nellist Peter D. , Kirkland Angus I. , Takeguchi Masaki
Published: December 2012

We observed Pt nanoparticles on carbon nanohorn aggregates by annular dark-field scanning confocal electron microscopy (ADF-SCEM) with an aberration-corrected microscope for three-dimensional (3D) imaging. The object elongation length along an optical axis that corresponds to the depth resolution was independent of the lateral size. Furthermore, the nanoparticle elongation length was reduced to 34 nm as compared with that by an uncorrected microscope. Hence, aberration-corrected ADF-SCEM provides structural information not only on the nanoparticles but also on the large carbon supports such as projecting nanohorns and hollow structures. Finally, aberration-corrected ADF-SCEM is effective for the 3D analysis of nanoparticle-supported composites.
Extensive study of giant magnetoresistance properties in half-metallic Co2(Fe,Mn)Si-based devices
Authors: Sakuraba Y. , Ueda M. , Miura Y. , Sato K. , Bosu S. , Saito K. , Shirai M. , Konno T. J. , Takanashi K.
Published: December 2012

Fully epitaxial Co2FexMn1−xSi(CFMS)/Ag/Co2FexMn1−xSi current-perpendicular-to-plane giant magnetoresistive devices with various Fe/Mn ratios x and top CFMS layer thicknesses tCFMS were prepared. The highest magnetoresistance (MR) ratios, 58% at room temperature and 184% at 30 K, were observed in the sample with x = 0.4 and tCFMS = 3 nm. Enhancement of interface spin-asymmetry was suggested for x = 0.4 compared with that at x = 0. A MR ratio of 58% was also observed even in a very thin trilayer structure, CFMS(4 nm)/Ag(3 nm)/CFMS(2 nm), which is promising for a next-generation magnetic read sensor for high-density hard disk drives.
Structural and electronic properties of GaAs0.64P0.19Sb0.17 on GaAs
Authors: Chin Yu-Chung , Chen Jyun-Yi , Chen Bo-Han , Tsai Hen-Shen , Huang Ying-Sheng , Lin Hao-Hsiung
Published: December 2012

GaAsPSb is an alloy with strong structural disorder, resulting from internal bond distortion. In this work, we study the structural and electronic properties of GaAs0.64P0.19Sb0.17 grown on GaAs. Results from reciprocal space mapping measurement reveal an unusual large residual strain left in the epilayer. We used the strain and the crystal field splitting determined from piezoreflectance (PzR) to obtain a shear deformation potential b = −1.31 eV. The unstrained energy gap Eg and spin-orbital splitting Δ0 determined from PzR at 300 K are 1.256 eV and 0.442 eV, respectively. The Δ0 of the GaAs0.64P0.19Sb0.17 is higher than that from the linear interpolation of the values of the end-point binaries, 0.363 eV, suggesting that the spin-orbit splitting has a significant negative bowing.
Passivation of trap states in unpurified and purified C60 and the influence on organic field-effect transistor performance
Authors: Olthof Selina , Singh Sanjeev , Mohapatra Swagat K. , Barlow Stephen , Marder Seth R. , Kippelen Bernard , Kahn Antoine
Published: December 2012

We investigate trap-state passivation by addition of ultra-low amounts of n-dopants in organic field-effect transistors (OFET) made of as-received and purified fullerene C60. We find a strong dependence of the OFET threshold voltage (VT) on the density of traps present in the layer. In the case of the unpurified material, VT is reduced from 17.9 V to 4.7 V upon trap passivation by a dopant:C60 ratio of ∼10−3, while the Ion/off current ratio remains high. This suggests that ultra-low doping can be used to effectively compensate impurity and defect-related traps.
Effect of plug-in hybrid electric vehicles charging/discharging management on planning of smart microgrid
Authors: Hakimi S. M. , Moghaddas-Tafreshi S. M.
Published: December 2012

Plug-in hybrid electric vehicles (PHEVs) are recently being widely touted as a viable alternative to conventional vehicles due to their environment friendly and energy-wise features. Assuming that moving into the future, a large number of PHEVs users will exist, the overall influence of charging the on-board energy storage system is non negligible. Instead of charging from grid, renewable energies, such as wind and solar energies, are a potential alternative. This paper explores the potential impact of PHEVs as flexible load in order to increase the penetration rate of renewable energy in smart microgrid and also increase the load factor. In this study, we consider three scenarios for PHEVs charging and discharging. The first scenario to charge these cars is to connect them to grid as a plug and forget demand and they start charging whenever they are connected to grid until their batteries became completely charged. In the second and third scenario, PHEVs are connected as vehicle to grid. Charging and discharging is possible in this interface and an algorithm should be used to manage charge and discharge of these vehicles. This ability can be used in order to improve characteristic of power system like its load factor and increase renewable energy penetration. Customers with flexible charging patterns may be able to use smart charging systems to charge their vehicles when demand is low or renewable energy production is high. This study is performed for Ekbatan residential complex in Tehran, Iran.
Coexistence of mixed mode multipactor
Authors: Kishek R. A.
Published: December 2012

Multipactor is a vacuum discharge based on secondary electron emission, and can manifest in many resonant and non-resonant modes. Where two or more types of multipactor coexist in the same device, it is found analytically that the one with the highest yield or the lowest order dominates.
The penetration limit of poly(4-vinyl phenol) thin films for etching via holes by inkjet printing
Authors: Zhang Y. , Liu C. , Whalley D. C.
Published: December 2012

This paper reports the penetration limit of via holes through dissolving dielectric polymer thin films by inkjet printing. It was found that both the outer diameter of via holes and the polymer thickness affect the penetration depth from the experimental results. Based on this finding, a more accurate relationship between the inner diameter of via holes and the diameter of in-flight droplets for different polymer thicknesses is obtained.
Deviation from exponential decay for spin waves excited with a coplanar waveguide antenna
Authors: Birt Daniel R. , An Kyongmo , Tsoi Maxim , Tamaru Shingo , Ricketts David , Wong Kin L. , Khalili Amiri Pedram , Wang Kang L. , Li Xiaoqin
Published: December 2012

We have investigated the propagation of surface spin waves in a Permalloy thin film excited by an asymmetric coplanar antenna. A surprising oscillatory behavior superimposed on the exponential decay is observed in the spin wave intensity mapped with the micro-Brillouin light scattering technique. The oscillations can be modeled as the interference between a propagating spin wave and a background magnetization with spatially uniform phase. We use a simple closed-form equation that includes both contributions to fit our experimental results. From the fit results, we extract the spin wave propagation length and the spin wave vector in a frequency range limited by the antenna bandwidth.
Band offsets of Al2O3 and HfO2 oxides deposited by atomic layer deposition technique on hydrogenated diamond
Authors: Liu J. W. , Liao M. Y. , Imura M. , Koide Y.
Published: December 2012

High-k oxide insulators (Al2O3 and HfO2) have been deposited on a single crystalline hydrogenated diamond (H-diamond) epilayer by an atomic layer deposition technique at temperature as low as 120 °C. Interfacial electronic band structures are characterized by X-ray photoelectron spectroscopy. Based on core-level binding energies and valence band maximum values, valence band offsets are found to be 2.9 ± 0.2 and 2.6 ± 0.2 eV for Al2O3/H-diamond and HfO2/H-diamond heterojunctions, respectively. Band gaps of the Al2O3 and HfO2 have been determined to be 7.2 ± 0.2 and 5.4 ± 0.2 eV by measuring O 1s energy loss spectra, respectively. Both the Al2O3/H-diamond and HfO2/H-diamond heterojunctions are concluded to be type-II staggered band configurations with conduction band offsets of 1.2 ± 0.2 and 2.7 ± 0.2 eV, respectively.
2.8 μm emission from type-I quantum wells grown on InAsxP1−x/InP metamorphic graded buffers
Authors: Jung Daehwan , Song Yuncheng , Yu Lan , Wasserman Daniel , Larry Lee Minjoo
Published: December 2012

We report 2.8 μm emission from compressively strained type-I quantum wells (QWs) grown on InP-based metamorphic InAsxP1−x step-graded buffers. High quality metamorphic graded buffers showed smooth surface morphology and low threading dislocation densities of approximately 2.5 × 106 cm−2. High-resolution x-ray diffraction scans showed strong satellites from multiple quantum wells grown on metamorphic buffers, and cross-sectional transmission electron microscopy revealed smooth and coherent quantum well interfaces. Room-temperature photoluminescence emission at 2.8 μm with a narrow linewidth (∼50 meV) shows the promise of metamorphic growth for mid-infrared laser diodes on InP.
Three-dimensional Maxwell-Bloch calculation of the temporal profile of a seeded soft x-ray laser pulse
Authors: Tissandier F. , Sebban S. , Gautier J. , Zeitoun Ph. , Oliva E. , Rousse A. , Maynard G.
Published: December 2012

We present three-dimensional modeling of amplification of a high-order harmonic seed by a soft x-ray laser plasma. The time-dependent evolution of the x-ray signal is determined from a fully dynamic Maxwell-Bloch calculation. At high seed intensities, a simplified one-dimensional calculation leads to strong Rabi-like temporal oscillations of the output signal. However, such oscillations have not been observed experimentally. Our calculations demonstrate that this is due to spatial non-uniformities in the plasma gain that cause the Rabi oscillations to dampen dramatically. Large amplitude Rabi-like oscillations are expected to appear only in long and uniform plasma. Such targets require optimized guiding techniques.
Upconversion luminescence, ferroelectrics and piezoelectrics of Er Doped SrBi4Ti4O15
Authors: Peng Dengfeng , Zou Hua , Xu Chaonan , Wang Xusheng , Yao Xi , Lin Jian , Sun Tiantuo
Published: December 2012

Er3+ doped SrBi4Ti4O15 (SBT) bismuth layered-structure ferroelectric ceramics were synthesized by the traditional solid-state method, and their upconversion photoluminescent (UC) properties were investigated as a function of Er3+ concentration and incident pump power. Green (555 nm) and red (670 nm) emission bands were obtained under 980 nm excitation at room temperature, which corresponded to the radiative transitions from 4S3/2, and 4F9/2 to 4I15/2, respectively. The emission color of the samples could be changed with moderating the doping concentrations. The dependence of UC intensity on pumping power indicated a two-photon emission process. Studies on dielectric properties indicated that the introduction of Er increased the ferroelectric-paraelectric phase transition temperature (Tc) of SBT, thus making this ceramic suitable for piezoelectric sensor applications at higher temperatures. Piezoelectric measurement showed that the doped SBT had a relative higher piezoelectric constant d33 compared with the non-doped ceramics. The thermal annealing behaviors of the doped sample revealed a stable piezoelectric property. The doped SBT showed bright UC emission while simultaneously having increased Tc and d33. As a multifunctional material, Er doped SBT ferroelectric oxide showed great potential in application of sensor, future optical-electro integration and coupling devices.