bluuebunny/crossref_metadata_2025 huggingface dataset:
An explicitly correlated local coupled cluster method for calculations of large molecules close to the basis set limit
Authors: Adler Thomas B. , Werner Hans-Joachim
Published: October 2011

A new explicitly correlated local coupled-cluster method with single and double excitations and a perturbative treatment of triple excitations [DF-LCCSD(T0)-F12x (x = a,b)] is presented. By means of truncating the virtual orbital space to pair-specific local domains (domain approximation) and a simplified treatment of close, weak and distant pairs using LMP2-F12 (pair approximation) the scaling of the computational cost with molecular size is strongly reduced. The basis set incompleteness errors as well as the errors due to the domain approximation are largely eliminated by the explicitly correlated terms. All integrals are computed using efficient density fitting (DF) approximations. The accuracy of the method is investigated for 52 reactions involving medium size molecules. A comparison of DF-LCCSD(T0)-F12x reaction energies with canonical CCSD(T)-F12x calculations shows that the errors introduced by the domain approximation are indeed very small. Care must be taken to keep the errors due to the additional pair approximation equally small, and appropriate distance criteria are recommended. Using these parameters, the root mean square (RMS) deviations of DF-LCCSD(T0)-F12a calculations with triple-ζ basis sets from estimated CCSD(T) complete basis set (CBS) limits and experimental data amount to only 1.5 kJ mol−1 and 2.9 kJ mol−1, respectively. For comparison, the RMS deviation of the CCSD(T)/CBS values from the experimental values amounts to 3.0 kJ mol−1. The potential of the method is demonstrated for five reactions of biochemical or pharmacological interest which include molecules with up to 61 atoms. These calculations show that molecules of this size can now be treated routinely and yield results that are close to the CCSD(T) complete basis set limits.
Enhanced thermoelectric figure of merit in SiGe alloy nanowires by boundary and hole-phonon scattering
Authors: Martinez Julio A. , Provencio Paula P. , Picraux S. T. , Sullivan John P. , Swartzentruber B. S.
Published: October 2011

We report the thermoelectric characteristics of individual p-type SiGe alloy nanowires for diameters of 100 to 300 nm and temperatures between 40 to 300 K. A technique that allows for electrical and thermal characterization on the same nanowire was developed in this work. Experimental data provide evidence of the scattering of low-frequency phonons by the boundary of the nanowires. The thermal conductivities for SiGe alloy nanowires with different free carrier concentrations reveal that the long free path phonons are also scattered by hole-phonon interactions. Combined boundary and hole-phonon scattering mechanisms with alloy scattering resulted in thermal conductivities as low as 1.1 W/m-K at 300 K, which is one of the lowest measured for SiGe alloys and is comparable to that of bulk silica. The enhanced thermal properties observed in this work yielded ZT close to 0.18 at 300 K—more than a factor of 2 higher than the bulk SiGe alloy.
Direct imaging of InSb (110)-(1×1) surface grown by molecular beam epitaxy
Authors: Mishima T. D.
Published: October 2011

High-resolution transmission electron microscopy under a profile imaging condition (HR-profile TEM) was employed to determine the structural model for the InSb(110)-(1×1) relaxation surface grown by molecular beam epitaxy (MBE). HR-profile TEM analyses indicate that the chevron model, which is widely accepted for zinc-blende-type III-V(110)-(1×1) surfaces prepared by cleavage, is also applicable to the InSb(110)-(1×1) surface prepared under an Sb-rich MBE condition. The assignment of atomic species (In or Sb) of InSb(110)-(1×1) surfaces was confirmed based on a HR-profile TEM image that captures the connected facets of InSb(110)-(1×1) and InSb(111)B-(2×2). On the basis of the well-known atomic species of InSb(111)B-(2×2), the atomic species of the InSb(110)-(1×1) surface were deduced straightforwardly: the atoms shifted upward and downward at the topmost layer of the InSb(110)-(1×1) surface are Sb and In, respectively. The atomic arrangements of the InSb(110)-(1×1)-InSb(111)B-(2×2) facet determined by HR-profile TEM may represent the atomic arrangements of zinc-blende-type III-V(331)B surfaces.
Free-standing ferroelectric multilayers: Crossover from thin-film to bulk behavior
Authors: Prokhorenko S. , Pertsev N. A.
Published: October 2011

Ferroelectric films usually have phase states and physical properties very different from those of bulk ferroelectrics. Here we propose free-standing ferroelectric-elastic multilayers as a bridge between these two material systems. Using a nonlinear thermodynamic theory, we determine phase states of such multilayers as a function of temperature, misfit strain, and volume fraction φp of passive elastic material. The numerical calculations performed for two classical ferroelectrics—PbTiO3 and BaTiO3—demonstrate that polarization states of multilayers in the limiting cases φp→1 and φp→0 coincide with those of thin films and bulk crystals. At intermediate volume fractions, however, the misfit strain-temperature phase diagrams of multilayers differ greatly from those of epitaxial films. Remarkably, a ferroelectric phase not existing in thin films and bulk crystals can be stabilized in BaTiO3 multilayers. Owing to additional tunable parameter and reduced clamping, ferroelectric multilayers may be superior for a wide range of device applications.
Structural, magnetic and magnetostrictive properties of Co-doped Tb1-xHoxFe2 (0 ≤ x ≤ 1.0) alloys
Authors: Liu J. J. , Wang R. , Ying H. Y. , Liu X. C. , Du J.
Published: October 2011

Structural, magnetic, and magnetostrictive properties of Tb1-xHox(Fe0.8Co0.2)2 (0 ≤ x ≤ 1.0) alloys have been investigated by means of x-ray diffraction, ac initial susceptibility, an alternating gradient magnetometer and a standard strain gauge technique. A single (Tb,Ho)(Fe,Co)2 Laves phase with a cubic MgCu2-type structure is formed when 0.50 ≤ x ≤ 1.0, while the secondary phase with a PuNi3-type structure occurs at higher Tb content for 0 ≤ x ≤ 0.40. The easy direction of magnetization (EMD) is observed toward 〈111〉 when 0 ≤ x ≤ 0.75, accompanied by a rhombohedral distortion with large spontaneous magnetostriction coefficients λ111. The abnormal λ100 of –550 ppm for x = 0 and as larger than 300 ppm for 0.60 ≤ x ≤ 0.75 were observed, which can be ascribed to the filling of the 3d band due to Co substitution for Fe. The 20 at.% Co substitution for Fe moves the anisotropy compensation point to the Tb-rich side, and increases the Curie temperature TC with about 30 K as compared to the Co-free Tb1-xHoxFe2 alloys. The Tb0.25Ho0.75(Fe0.8Co0.2)2 alloy has a large magnetostriction at a relatively low magnetic field and a low anisotropy accompanied by the minimum coercivity, and may make it a promising magnetostrictive material.
Intrinsic frequency doubling in a magnetic tunnel junction–based spin torque oscillator
Authors: Muduli P. K. , Heinonen O. G. , Åkerman Johan
Published: October 2011

We show that the frequency of a magnetic tunnel junction (MTJ)-based spin torque oscillator (STO) can be doubled and the first harmonic entirely suppressed by orienting the free and fixed layer magnetizations in an antiparallel (AP) state. The angular dependence of the harmonics allows us to extract the free layer precession angle, which follows a parabolic decrease from a maximum of 20∘ in the AP state to about 10∘ at 25∘ of misalignment. Frequency-doubling provides both a promising way for increasing the frequency of MTJ-STOs and a means for high-rate frequency shift keying using only a small magnetic field.
Hybrid metallic photonic crystals with higher-order coupling processes
Authors: Pang Zhaoguang , Zhang Xinping , Zhai Tianrui
Published: October 2011

Hybrid metallic photonic crystals (MPCs) combine the orderly arranged grating structures and the disordered gold nanostructures, where the gratings are fabricated by interference lithography on a layer of waveguide and the isolated gold nanoislands arranged randomly in the grating grooves are produced using solution-processible gold nanoparticles. Strong coupling between multiple higher-order resonance modes of the waveguide grating structures and particle plasmon resonance of the isolated gold nanoislands has been observed in the visible spectral range. This technique actually realizes fabrication of the waveguide grating structures and the plasmonic gold nanostructures separately. In this way, the plasmonic resonance of the gold nanostructures is not determined by the dimensions of the grating lines anymore. Thus, the grating structures can be fabricated easily with a period of microns, whereas the size of the gold nanostructures can be controlled flexibly by changing the colloidal concentration and the annealing temperature. Large grating period leads to higher-order coupled modes in the visible. This contributes to the “family” of the MPC fabrication techniques and lowers significantly the rigorous requirements on fabrication method of the large-area nanoscale MPCs.
The low frequency electrical properties of sea ice
Authors: Buchanan S. , Ingham M. , Gouws G.
Published: October 2011

Impedance measurements were performed across the frequency range 40 Hz-1MHz on laboratory grown sea ice using a custom four-electrode capacitive cell. The measurements were performed in-situ, throughout the ice growth in horizontal and vertical orientations. Two-electrode measurements were susceptible to electrode polarization and a four-electrode measurement was required to measure the true electrical properties of the ice. A broadband mathematical model is presented which distinguishes polarization and conduction in the bulk material from space charge polarization at interfaces. The fit of this model to the impedance data gives insight into the relative contribution of these phenomena. The bulk material undergoes a dielectric relaxation and we have examined the temperature dependence of the relaxation time and susceptibility. Aspects of the susceptibility and DC conductivity can be reconciled with a conductive dielectric model in which brine is confined to regular ellipsoids.
Surface transition induced island formation on thin strained InGaN layers on GaN (0001) in metal-organic vapour phase epitaxy
Authors: Pristovsek Markus , Kadir Abdul , Meissner Christian , Schwaner Tilman , Leyer Martin , Kneissl Michael
Published: October 2011

The surfaces of thin strained InGaN layers were investigated in metal-organic vapour phase epitaxy as a function of layer thickness and indium content. Even at layer thickness below 1 nm the surface exhibited 1−2 monolayer high irregular islands with diameters larger than twice the terrace spacing. Such islands are not observed on GaN grown at similar conditions. In-situ ellipsometry indicates a surface transition at the start and end of growth. During growth the surface contains about 1.5 monolayer of metal. We present two models that explain how a surface transition could form these islands.
Nonlinear transverse current response in zigzag graphene nanoribbons
Authors: Wang Bo , Ma Zhongshui , Zhang C.
Published: October 2011

By employing a self-consistent approach, we reveal a number of unique properties of zigzag graphene nanoribbons under crossed electric and magnetic fields: (1) a very strong electrical polarization along the transverse direction of the ribbon, and (2) a strong nonlinear Hall current under a rather moderate electrical field. At the field strength of 5000 V/cm, the ratio of the nonlinear current to the linear current is around 1 under an applied magnetic field of 7.9 T. Our results suggest that graphene nanoribbons are an ideal system to achieve a large electrical polarizability. Our results also suggest that the nonlinear effect in graphene nanoribbons has been grossly underestimated without the self-consistent scheme proposed here.
Association constants and distribution functions for ion pairs in binary solvent mixtures: Application to a cyanine dye system
Authors: Odinokov A. V. , Basilevsky M. V. , Nikitina E. A.
Published: October 2011

The computations of the association constants Kass were performed at the microscopic level for the ion pair Cy+I− composed of the complex cyanine dye cation Cy+ coupled to the negative iodine counterion. The wide array of Kass values is arranged by a variation of the composition of the binary solvent mixtures toluene/dimethylsulfoxide with the accompanying change of the solvent polarity. The potentials of mean force (PMFs) are calculated for a set of interionic separations R in the Cy+I− by a methodology which combines the quantum-chemical techniques for the treatment of the electronic structure of the Cy+I− system with the recent dielectric continuum approach which accounts for the solvation effects. For a given solute/solvent system the probability function P(R), which describes the distribution of interionic separations, is constructed in terms of the PMFs and implemented for the evaluation of the Kass.
Decay kinetics of the excited S1 state of the cyanine dye Cy+I− (thiacarbocyanine iodide): The computation of quantum yields for different pathways
Authors: Odinokov A. V. , Basilevsky M. V. , Petrov N. Kh.
Published: October 2011

This work explains the unordinary solvent effect which was observed in the photochemical decay kinetics for the cyanine dye thiacarbocyanine iodide (Cy+I−) in binary solvent mixtures toluene/dimethylsulfoxide. The interpretation is formulated in terms of the probability density F(R) describing the distribution of interionic distances R in the ion pair Cy+I− and depending on the solvent composition. The proper normalization of this distribution is expressed via the degree of association α for the ion pair in a given solvent mixture. The α values are, in turn, extracted by means of the mass action law from the ionic association constants computed in a separate publication. The detailed kinetic scheme includes the empirical parametrization of the R-dependent kinetic constants for different decay channels. The multiparameter fitting procedure represents, with the reasonable parameter values, the dependence of the observed quantum yields on the solvent composition.
Basis set convergence of explicitly correlated double-hybrid density functional theory calculations
Authors: Karton Amir , Martin Jan M. L.
Published: October 2011

The basis set convergence of explicitly correlated double-hybrid density functional theory (DFT) is investigated using the B2GP-PLYP functional. As reference values, we use basis set limit B2GP-PLYP-F12 reaction energies extrapolated from the aug′-cc-pV(Q+d)Z and aug′-cc-pV(5+d)Z basis sets. Explicitly correlated double-hybrid DFT calculations converge significantly faster to the basis set limit than conventional calculations done with basis sets saturated up to the same angular momentum (typically, one “gains” one angular momentum in the explicitly correlated calculations). In explicitly correlated F12 calculations the VnZ-F12 basis sets converge faster than the orbital A′VnZ basis sets. Furthermore, basis set convergence of the MP2-F12 component is apparently faster than that of the underlying Kohn-Sham calculation. Therefore, the most cost-effective approach consists of combining the MP2-F12 correlation energy from a comparatively small basis set such as VDZ-F12 with a DFT energy from a larger basis set such as aug′-cc-pV(T+d)Z.
Wide depletion width of 1 eV GaInNAs solar cells by thermal annealing
Authors: Sellers I. R. , Tan W.-S. , Smith K. , Hooper S. , Day S. , Kauer M.
Published: October 2011

We present high quality GaInNAs p-i-n solar cells with depletion widths in excess of 1 μm for material absorbing in the practically important 1 eV band gap regime. This is achieved through optimization of post-growth rapid thermal annealing at a temperature of ∼ 910 °C. Despite the improvements in material quality evidenced by a low background impurity concentration and improved minority carrier collection, the external quantum efficiency remains limited to ∼50%. This is attributed to losses due to efficient radiative recombination in the bulk GaInNAs intrinsic region enhanced via localization of carriers in alloy fluctuations.
One-way cloak based on nonreciprocal photonic crystal
Authors: He Cheng , Zhang Xiao-Liu , Feng Liang , Lu Ming-Hui , Chen Yan-Feng
Published: October 2011

We propose a physical concept of non-reciprocal transformation optics, by which a one-way invisible cloak is designed. The one-way invisible cloak is made of a coordinate-transformed nonreciprocal photonic crystal, showing a perfect cloaking for wave incident from one direction but acting as a perfect reflector for wave from the counter direction. The proposed design shows a high promise of applications in military, as protecting the own information to be detected but efficiently grabbing the information from the “enemy” side.
Microphotonic parabolic light directors fabricated by two-photon lithography
Authors: Atwater J. H. , Spinelli P. , Kosten E. , Parsons J. , Van Lare C. , Van de Groep J. , Garcia de Abajo J. , Polman A. , Atwater H. A.
Published: October 2011

We have fabricated microphotonic parabolic light directors using two-photon lithography, thin-film processing, and aperture formation by focused ion beam lithography. Optical transmission measurements through upright parabolic directors 22 μm high and 10 μm in diameter exhibit strong beam directivity with a beam divergence of 5.6°, in reasonable agreement with ray-tracing and full-field electromagnetic simulations. The results indicate the suitability of microphotonic parabolic light directors for producing collimated beams for applications in advanced solar cell and light-emitting diode designs.
Elastic and inelastic low-energy electron collisions with pyrazine
Authors: Mašín Zdeněk , Gorfinkiel Jimena D.
Published: October 2011

We present results of ab-initio scattering calculations for electron collisions with pyrazine using the R-matrix method, carried out at various levels of approximation. We confirm the existing experimental and theoretical understanding of the three well-known π* shape resonances. In addition, we find numerous core-excited resonances (above 4.8 eV) and identify their most likely parent states. We also present differential cross sections, showing high sensitivity to the scattering model chosen at low energies. We make recommendations regarding the selection of models for scattering calculations with this type of targets.
Proximity effect in Nb-Mo layered films: Transition temperature and critical current dependence on period
Authors: Walker A. E. , Veldhorst J. , Myers D. M. , McElrath Z. , Lewis J. B. , Broussard P. R.
Published: October 2011

The behavior of the transition temperature and critical current density for a Mo/Nb repeated bilayer system as a function of the number of periods was explored. The measured values of the transition temperature are compared to the theoretical predictions for the proximity effect in the dirty limit. We find that the transition temperature does not decrease as the number of periods increase. In addition, inductive critical current density measurements also show a scaling that indicates the superconductivity properties are not dependent on the number of bilayers.
Terahertz and infrared studies of antiferroelectric phase transition in multiferroic Bi0.85Nd0.15FeO3
Authors: Goian V. , Kamba S. , Greicius S. , Nuzhnyy D. , Karimi S. , Reaney I. M.
Published: October 2011

High-frequency dielectric studies of Bi0.85Nd0.15FeO3 ceramics performed betweeen 100 and 900 K reveal hardening of most polar phonons on cooling below antiferroelectric phase transition, which occurs near 600 K. Moreover, a strong THz dielectric relaxation is seen in paraelectric phase. Its relaxation frequency softens on cooling towards TC ≈ 600 K, its dielectric strength simultaneously decreases, and finally the relaxation disappears from the spectra below 450 K. Both phonon and dielectric relaxation behavior are responsible for a decrease in the dielectric permittivity at the antiferroelectric phase transition. Origin of unusual strong THz dielectric relaxation in paraelectric phase is discussed. Bi0.85Nd0.15FeO3 structure lies on the phase boundary between polar rhombohedral and non-polar orthorhombic phase and owing to this, the polarization rotation and polarization extension can enhance the piezoelectric response of this system. Similarities and discrepancies with lead-based piezoelectric perovskites, exhibiting morphotrophic phase boundary between two ferroelectric phases, are discussed.
Tunable terahertz-mirror and multi-channel terahertz-filter based on one-dimensional photonic crystals containing semiconductors
Authors: Li Ying , Xiang Yuanjiang , Wen Shuangchun , Yong Junhai , Fan Dianyuan
Published: October 2011

We demonstrate that tunable terahertz-mirrors and multichannel terahertz-filters can be carried out by taking into account the transmission properties of the one-dimensional photonic crystals (1DPCs) containing semiconductor materials with a tunable dielectric constant in the THz frequency range. Using the semiconductor InSb as the components in the 1DPCs, we have designed such a mirror and a filter and identified their tunability. The THz-mirror is tunable by changing the external temperature or the thickness of the components of the 1DPC. The operation frequency of the multichannel-filter can be tuned by changing the temperature and thickness of the component materials in the 1DPC, the channel number of the filter can be controlled by varying the number of the defect layers in the 1DPC, and the transmittance bandwidth can be adjusted by changing the period number of the 1DPC. With thermal tunability, structure controllability and narrow bandwidth, 1DPCs containing semiconductors open a promising way to fabricate tunable terahertz devices for future terahertz communications.
Adsorption of CO and O2 on W2C(0001)
Authors: Aizawa Takashi , Otani Shigeki
Published: October 2011

CO, O2, and H2 adsorption on a clean W2C(0001)\documentclass[12pt]{minimal}\begin{document}$\sqrt{13} \times \sqrt{13}$\end{document}13×13 R ± 13.9° reconstructed surface at room temperature (RT) were investigated using high-resolution electron energy loss spectroscopy (HREELS). The W2C(0001) adsorbs CO molecularly and adsorbs O2 dissociatively, but does not adsorb H2 at RT. In the CO adsorption system, two C–O stretching (antisymmetric CCO stretching) modes were found at 242.3 meV (1954 cm−1) and at 253.0 meV (2041 cm−1). The low-frequency site is occupied at first with subsequent conversion to the high-frequency site with increasing coverage. Additionally, a small peak was apparent at 104.5 meV (843 cm−1), and a middle peak at 50–51 meV (400–410 cm−1), which are assignable to a symmetric stretching mode and a hindered translational mode, respectively, of a CCO (ketenylidene) species. These observations are consistent with the CO adsorption model on top of the surface carbon. For oxygen adsorption, two adsorption states were found at 65.2–68.1 meV (526–549 cm−1) and 73.6 meV (594 cm−1): typical frequencies to oxygen adsorption on metal surfaces. Results suggest that atomic oxygen adsorption occurred on a threefold hollow site of the second W layer.
Investigation of orbital magnetization in inverse spinel cobalt ferrite using magnetic Compton scattering
Authors: Mund H. S. , Tiwari Shailja , Sahariya Jagrati , Itou M. , Sakurai Y. , Ahuja B. L.
Published: October 2011

We present the spin momentum densities of CoFe2O4 measured at 8 and 300 K using magnetic Compton scattering. The magnetic Compton profiles were decomposed into component profiles of constituents namely Fe and Co, to determine their role in the formation of total spin moment. It is seen that the major contribution (about 80%) in the spin moment is from Co, whereas the itinerant electrons show a small reverse polarization. Moreover, it is clearly visualized that the spin moment at Co reduces from 2.55 → 2.35 μB/f.u. while going from 8 → 300 K. The magnetic Compton profiles, when compared with the magnetization data, show about 17% contribution of orbital moment to the total magnetic moment at both temperatures. The origin of the orbital moment is explained on the basis of rotation of hole on t2g orbital of Co+2 ion.
The behavior of nanothermite reaction based on Bi2O3/Al
Authors: Wang L. , Luss D. , Martirosyan K. S.
Published: October 2011

We studied the impact of aluminum particle size and the thickness of surrounding alumina layer on the dynamic pressure discharge of nanothermite reactions in the Bi2O3/Al system. A pressure discharge from 9 to 13 MPa was generated using as-synthesized Bi2O3 nano-particles produced by combustion synthesis and Al nanoparticles with size from 3 μm to 100 nm. The maximum reaction temperature was measured to be ∼2700 °C. The estimated activation energy of the reaction was 45 kJ/mol. A very large (several orders of magnitude) difference existed between the rate of the pressure pulse release by nanothermite reactions and by thermite reactions with large aluminum particles. The maximum observed pressurization rate was 3200 GPa/s. The time needed to reach the peak pressure was 0.01 ms and 100 ms for aluminum particles with diameter of 100 nm and 70 microns, respectively. The discharge pressure was a monotonic decreasing function of the thickness of the surrounding alumina layer.
Mass-analyzed velocity map imaging of doubly charged photofragments from C70
Authors: Katayanagi Hideki , Mitsuke Koichiro
Published: October 2011

The velocity distributions of the fragments produced by dissociative photoionization of C70 have been measured at several photon energies in the extreme UV region, by using a flight-time resolved velocity map imaging (VMI) technique combined with a high-temperature molecular beam and synchrotron radiation. Average kinetic energy release was estimated for the six reaction steps of consecutive C2 emission, starting from C702+ → C682+ + C2 to C602+→ C582+ + C2. The total kinetic energy generated in each step shows a general tendency to increase with increasing hν, except for the first and fifth steps. This propensity reflects statistical redistributions of the excess energy in the transition states for the above fragmentation mechanism. Analysis based on the finite-heat-bath theory predicts the detectable minimum cluster sizes at the end of the C2-emission decay chain. They accord well with the minimum sizes of the observed ions, if the excess energy in the primary C702+ is assumed to be smaller by ∼15 eV than the maximum available energy. The present VMI experiments reveal remarkably small kinetic energy release in the fifth step, in contradiction to theoretical predictions, which suggests involvement of other fragmentation mechanisms in the formation of C602+.
Atomic layer coating of hafnium oxide on carbon nanotubes for high-performance field emitters
Authors: Il Song Young , Yang Cheol-Min , Ku Kwac Lee , Gun Kim Hong , Ahm Kim Yoong
Published: October 2011

Carbon nanotubes coated with hafnium oxide exhibit excellent electron emission characteristics, including a low turn-on voltage, a high field enhancement factor, and exceptional current stability. Their enhanced emission performance was attributed to a decrease in the work function and an increase in the electron density of states at the carbon nanotube Fermi level closest to the conduction band minimum of hafnium oxide. In addition, the enhanced current stability was attributed to the ability of hafnium oxide to protect the carbon nanotubes against ions and free radicals created in the electron field emission process.
Effective Hamiltonian for femtosecond vibrational dynamics
Authors: Barnes George L. , Kellman Michael E.
Published: October 2011

Time propagation of zero-order states of an effective spectroscopic Hamiltonian is tested against femtosecond time dependent dynamics of adiabatic wavepackets evolving on a model potential energy surface for two coupled modes of the radical HO2 with multiple potential wells and above barrier motion. A generalized Hamiltonian which breaks the usual conserved polyad action by including extra resonance couplings (V2:1 and V3:1) successfully describes the time evolution after the further addition of two “ultrafast” couplings. These new couplings are a nonresonant coupling \documentclass[12pt]{minimal}\begin{document}$a_1a_2 + a_1^\dagger a_2^\dagger$\end{document}a1a2+a1†a2† and a resonant coupling V1:1 that functions as an ultrafast term because the system is far from 1:1 frequency resonance.
Mechano-chemical pathways to H2O and CO2 splitting
Authors: Vedadi Mohammad H. , Haas Stephan
Published: October 2011

The shock-induced collapse of CO2-filled nanobubbles is investigated using molecular dynamics simulations based on a reactive force field. The energetic nanojet and high-pressure water hammer shock formed during and after collapse of the nanobubble trigger mechano-chemical H2O-CO2 reactions, some of which lead to splitting of water and formation of O2 molecules. The dominant pathways through which splitting of water molecules occur are identified.
Impact of KCN etching on the chemical and electronic surface structure of Cu2ZnSnS4 thin-film solar cell absorbers
Authors: Bär M. , Schubert B.-A. , Marsen B. , Krause S. , Pookpanratana S. , Unold T. , Weinhardt L. , Heske C. , Schock H.-W.
Published: October 2011

The chemical and electronic surface structure of Cu2ZnSnS4 thin-film solar cell absorbers has been investigated by direct and inverse photoemission. Particular emphasis was placed on the impact of KCN etching, which significantly alters the surface composition and is best explained by a preferred etching of Cu and, to a lesser degree, Sn. As a consequence the surface band gap increased from (1.53 ± 0.15) eV, which agrees with optically derived bulk band gap values, to (1.91 ± 0.15) eV.
Two-dimensional solid solution alloy of Bi-Pb binary films on Rh(111)
Authors: Yuhara J. , Yokoyama M. , Matsui T.
Published: October 2011

We studied the atomic arrangements and phase diagrams of two-dimensional (2D) Bi-Pb binary films on a Rh(111) surface with low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and Auger electron spectroscopy. The 2D binary films exhibited incommensurate (4 × 4) LEED patterns with any compositional ratio of Bi:Pb. Atomically resolved STM images revealed that the binary films formed hexagonal, close-packed structures in a 2D solid solution alloy. We found that the 2D binary films followed the Hume-Rothery rule. The interatomic distance decreased linearly from 0.359 nm to 0.342 nm with increasing proportions of Pb. This indicated that the lattice constant of the 2D binary films followed Vegard’s law.
Electrocaloric effect in relaxor ferroelectrics
Authors: Pirc R. , Kutnjak Z. , Blinc R. , Zhang Q. M.
Published: October 2011

A theoretical model for the electrocaloric effect (ECE) in relaxor ferroelectrics is presented. By solving a self-consistent relation for the ECE temperature change ΔT and minimizing numerically the mean field free energy for relaxors, the field and temperature dependence of ΔT is calculated. The corresponding harmonic Landau coefficient a=a(T), which differs from the ferroelectric case by always being positive, is derived from the spherical random bond-random field model, and the fourth-order coefficient b is treated as a phenomenological parameter, which can be either positive or negative. For b<0, a line of field-induced first-order relaxor-to-ferroelectric phase transitions exists in relaxors, which terminates at a liquid-vapor type critical point ECP,TCP. The critical behavior close to ECP,TCP is analyzed. It is shown that near the first-order phase transition a temperature or field interval or gap formally appears, where ΔT cannot be found. However, domain formation in the coexistence range should restore the continuous behavior of the ECE observed in real systems. Finally, it is shown that the ECE responsivity R1=ΔT/E reaches a maximum near the critical point, in agreement with recent experiments.
Ordered silicon nanocones arrays for label-free DNA quantitative analysis by surface-enhanced Raman spectroscopy
Authors: Xu Ting-Ting , Huang Jian-An , He Li-Fang , He Yao , Su Shao , Lee Shuit-Tong
Published: October 2011

Ordered vertical silicon nanocones arrays coated with silver nanoparticles (AgNPs@SiNCs) are developed as surface-enhanced Raman scattering (SERS)-active substrate, which features good uniformity and reliable reproducibility of SERS signals. Label-free DNA at low concentrations (10−8 M) could be quantitatively analyzed via SERS using the AgNPs@SiNCs. The Raman peak at 732 cm−1 due to adenine breathing mode was selected as an endogenous Raman marker for quantitative detection of label-free DNA. The AgNPs@SiNCs as high-performance SERS-active substrates are attractive for surface enhancement mechanism investigation and biochemical sensing applications.
Multidimensional treatment of stochastic solvent dynamics in photoinduced proton-coupled electron transfer processes: Sequential, concerted, and complex branching mechanisms
Authors: Soudackov Alexander V. , Hazra Anirban , Hammes-Schiffer Sharon
Published: October 2011

A theoretical approach for the multidimensional treatment of photoinduced proton-coupled electron transfer (PCET) processes in solution is presented. This methodology is based on the multistate continuum theory with an arbitrary number of diabatic electronic states representing the relevant charge distributions in a general PCET system. The active electrons and transferring proton(s) are treated quantum mechanically, and the electron-proton vibronic free energy surfaces are represented as functions of multiple scalar solvent coordinates corresponding to the single electron and proton transfer reactions involved in the PCET process. A dynamical formulation of the dielectric continuum theory is used to derive a set of coupled generalized Langevin equations of motion describing the time evolution of these collective solvent coordinates. The parameters in the Langevin equations depend on the solvent properties, such as the dielectric constants, relaxation time, and molecular moment of inertia, as well as the solute properties. The dynamics of selected intramolecular nuclear coordinates, such as the proton donor-acceptor distance or a torsional angle within the PCET complex, may also be included in this formulation. A surface hopping method in conjunction with the Langevin equations of motion is used to simulate the nonadiabatic dynamics on the multidimensional electron-proton vibronic free energy surfaces following photoexcitation. This theoretical treatment enables the description of both sequential and concerted mechanisms, as well as more complex processes involving a combination of these mechanisms. The application of this methodology to a series of model systems corresponding to collinear and orthogonal PCET illustrates fundamental aspects of these different mechanisms and elucidates the significance of proton vibrational relaxation and nonequilibrium solvent dynamics.
Spontaneous polarization and band gap bowing in YxAlyGa1-x-yN alloys lattice-matched to GaN
Authors: Shimada Kazuhiro , Zenpuku Atsuhito , Fujiwara Kazuya , Hazu Kouji , Chichibu Shigefusa F. , Hata Masahiro , Sazawa Hiroyuki , Takada Tomoyuki , Sota Takayuki
Published: October 2011

First-principles calculations are carried out to estimate the spontaneous polarization and the energy band gap bowing in YxAlyGa1-x-yN alloys lattice-matched to GaN. The ground state properties of alloys are computed by using the pseudopotential-planewave method in conjunction with generalized gradient approximation to density functional theory. We find nonlinear behavior of the spontaneous polarization and the band gap energies in YxAlyGa1-x-yN alloys and the values depend on the atomic geometry in the unit cell, especially on that of yttrium.
Raman study on the interlayer interactions and the band structure of bilayer graphene synthesized by alcohol chemical vapor deposition
Authors: Okano Makoto , Matsunaga Ryusuke , Matsuda Kazunari , Masubuchi Satoru , Machida Tomoki , Kanemitsu Yoshihiko
Published: October 2011

We investigated the electronic band structure and interlayer interactions in graphene synthesized by alcohol-chemical vapor deposition (a-CVD) using microprobe Raman spectroscopy and tight-binding band-structure calculations. The number of graphene layers was determined from the spectrally integrated intensity ratios of the G phonon to 2D phonon peaks. We found that the value of the parameter determining interlayer interactions in a-CVD bilayer graphene was less than half that of exfoliated bilayer graphene. The weak interlayer interaction in a-CVD bilayer graphene was attributed to non-AB stacking order.
Characterization of enhancement-mode AlGaN/GaN high electron mobility transistor using N2O plasma oxidation technology
Authors: Chiu Hsien-Chin , Yang Chih-Wei , Chen Chao-Hung , Fu Jeffrey S. , Chien Feng-Tso
Published: October 2011

In this study, an enhancement-mode (E-mode) AlGaN/GaN high electron mobility transistor (HEMT) using N2O plasma oxidation process has been performed. Before the gate metal deposition, the AlGaN barrier layer was treated by 135 W N2O plasma for 240 s. The surface native oxide of AlGaN was removed and a 4 nm high quality Ga2O3/Al2O3 compound insulator was simultaneously formed. The threshold voltage of conventional depletion-mode (D-mode) GaN HEMT was −3.6 V and this value can be shifted to +0.17 after N2O plasma oxidation treatment beneath the gate metal. This 4 nm Ga2O3/Al2O3 compound insulator oxidized by N2O can suppress the polarization charge density for E-mode operation of gate terminal and the gate leakage was also reduced simultaneously.
Spatial distribution of intra-molecular water and polymeric components in polyelectrolyte dendrimers revealed by small angle scattering investigations
Authors: Wu Bin , Li Xin , Do Changwoo , Kim Tae-Hwan , Shew Chwen-Yang , Liu Yun , Yang Jun , Hong Kunlun , Porcar Lionel , Chen Chun-Yu , Liu Emily L. , Smith Gregory S. , Herwig Kenneth W. , Chen Wei-Ren
Published: October 2011

An experimental scheme using contrast variation small angle neutron scattering technique is developed to investigate the structural characteristics of amine-terminated poly(amidoamine) dendrimers solutions. Using this methodology, we present the dependence of both the intra-dendrimer water and the polymer distribution on molecular protonation, which can be precisely adjusted by tuning the pH of the solution. Assuming spherical symmetry of the spatial arrangement of the constituent components of dendrimer, and that the atomic ratio of hydrogen-to-deuterium for the solvent residing within the cavities of dendrimer is identical to that for the solvent outside the dendrimer, the intra-dendrimer water distribution along the radial direction is determined. Our result clearly reveals an outward relocation of the peripheral groups, as well as enhanced intra-dendrimer hydration, upon increasing the molecular protonation and, therefore, allows the determination of segmental backfolding in a quantitative manner. The connection between these charge-induced structural changes and our recently observed progressively active segmental dynamics is also discussed.
Fundamental role of Σ3(1¯11) and Σ3(1¯12) grain boundaries in elastic response and slip transfer
Authors: Tsuru T. , Kaji Y. , Shibutani Y.
Published: October 2011

The techniques of grain boundary engineering are rapidly gaining significance microstructural design. To understand individual grain boundary characteristics, the influence of grain boundaries on the elastic and plastic deformation behaviors of copper bicrystals with Σ3(1¯11) twin and Σ3(1¯12) grain boundaries were investigated by large scale molecular statics simulation. These grain boundaries were chosen as examples of coherent and incoherent grain boundaries. Nanoindentation tests perpendicular to the grain boundary plane were used to investigate local deformation properties. Our results showed that an incoherent boundary experiences a reduction in elastic resistance due to the increase in excess free volume and structure-dependent local indentation modulus, while a coherent boundary has little effect on the elastic deformation. The propagation of plastic deformation is strongly blocked by the dissociation into a displacement shift complete (DSC) lattice dislocation which explains the superficial absorptive ability of a coherent twin boundary. However, plastic deformation of the Σ3(1¯12) indentation demonstrates easy slip transfer across the interface.
Correlation effects on electron tunneling through doubly occupied quantum dots: A study beyond phenomenological models
Authors: Lan Jian , Sheng Weidong
Published: October 2011

Electron transport through doubly occupied quantum dots is studied theoretically. Beyond the semi-classic framework of phenomenological models, a quantum mechanical solution for the cotunneling and sequential tunneling of electrons through a one-dimensional multi-level quantum dot is obtained. Correlation effects are shown to play an important role in inelastic sequential tunneling through the doubly occupied system, which accommodates four single-particle levels. It is revealed that the cotunneling conductance exhibits strong dependence on the spin configuration of the electrons confined inside the dot. Especially for the triplet configuration, the conductance shows an obvious deviation from the well-known quadratic dependence on the applied bias voltage.
Transport and thermal properties of single- and polycrystalline NiZr0.5Hf0.5Sn
Authors: Ouardi Siham , Fecher Gerhard H. , Felser Claudia , Blum Christian G. F. , Bombor Dirk , Hess Christian , Wurmehl Sabine , Büchner Bernd , Ikenaga Eiji
Published: October 2011

The thermoelectric properties of a Heusler compound with NiZr0.5Hf0.5Sn composition were studied. A comparison of the properties of a single crystal and a polycrystal was carried out by measurements of the electrical conductivity, Seebeck coefficient, and thermal conductivity. The transport properties are directly compared to the valence band electronic structure measured by photoelectron spectroscopy. The single crystal shows a higher figure of merit (ZT = 0.1) at room temperature which originates from the high electrical conductivity that is mediated by “in-gap” states observed by photoemission spectroscopy.
Critical optical coupling between a GaAs disk and a nanowaveguide suspended on the chip
Authors: Baker C. , Belacel C. , Andronico A. , Senellart P. , Lemaitre A. , Galopin E. , Ducci S. , Leo G. , Favero I.
Published: October 2011

We report on an integrated GaAs disk/waveguide system. A millimeter-long waveguide is suspended and tapered on the chip over a length of 25 μm to evanescently couple to high Q optical whispering gallery modes of a GaAs disk. The critical coupling regime is obtained both by varying the disk/guide gap distance and the width of the suspended nanoscale taper. Experimental results are in good agreement with predictions from coupled mode theory.
AlGaN/GaN metal-insulator-semiconductor heterostructure field-effect transistor with an in-situ AlN cap layer
Authors: Lee K. H. , Chang P. C. , Chang S. J.
Published: October 2011

In this study, we investigate AlGaN/GaN metal-insulator-semiconductor heterostructure field-effect transistor with an in-situ AlN cap layer with regards to DC-, RF-, and power-performance. This “earlier” passivation by in-situ AlN cap layer protects the surface during processing and neutralizes the charges at the top of AlGaN interface, which leads to a higher electron density of channel and superior device characteristics.
Low-loss unidirectional transducer for high frequency surface acoustic wave devices
Authors: Biryukov S. V. , Martin G. , Schmidt H. , Wall B.
Published: October 2011

A multi-track unidirectional transducer for surface acoustic wave devices is presented. This transducer consists of periodic cells containing in each of the multiple tracks, only two electrodes and two gaps with quarter period width. So the structure has maximal possible dimensions of its elements for a cell period equal to one wavelength. In spite of current technological limitations this permits to implement unidirectional transducers in GHz range. In contrast to known structures with active tracks only, the structure contains alternating both active transducer tracks and passive reflector tracks with different apertures comparable to surface acoustic wave (SAW) wavelength. The tracks strongly interact due to diffraction of waves excited by such electrode structure on a piezoelectric substrate. A structure analysis by means of finite element method shows that complete unidirectionality can be reached. First experimental results are given.
Light confinement-induced antireflection of ZnO nanocones
Authors: Hyun Lee Sang , Earle Jellison Gerald , Duty Chad E. , Xu Jun
Published: October 2011

The antireflective features of aperiodic vertical aligned ZnO nanocones on Si wafer were studied both experimentally and theoretically through comparison with planar ZnO films on Si substrates and bare Si substrates. The measured diffuse reflectance spectra show that the nanocone-based texture reduces the light reflection in a broad spectral range and is much more effective than the planar textures. The numerical simulations exhibit a good agreement with the experimental data and suggest that the light confinement inside nanocones by controlling the diameters can bring further improvement of light absorption into Si.
Effects of (NH4)2S passivation on the off-state performance of 3-dimensional InGaAs metal-oxide-semiconductor field-effect transistors
Authors: Gu J. J. , Neal A. T. , Ye P. D.
Published: October 2011

Planar and 3-dimensional (3D) buried-channel InGaAs metal-oxide-semiconductor field-effect transistors (MOSFETs) have been experimentally demonstrated at deep-submicron gate lengths. The effect of (NH4)2 S passivation with different concentrations (20%, 10%, or 5%) on the off-state performance of these devices has been systematically studied. 10% (NH4)2 S treatment is found to yield the optimized high-k/InP barrier layer interface property, resulting in a minimum subthreshold swing (SS) lower than 100 mV/dec. Moreover, the 3D device structure greatly improves the off-state performance and facilitates enhancement-mode operation. A scaling metrics study has been carried out for 10% (NH4)2 S treated 3D devices with gate lengths down to 100 nm. With the optimized interface passivation, 3D III-V MOSFETs are very promising for future high-speed low-power logic applications.
Synchrotron radiation infrared microscopic study of non-bridging oxygen modes associated with laser-induced breakdown of fused silica
Authors: Matthews Manyalibo J. , Carr Christopher W. , Bechtel Hans A. , Raman Rajesh N.
Published: October 2011

Nanosecond pulse laser-driven optical breakdown at SiO2 surfaces as probed by synchrotron-based Fourier transform infrared (SRFTIR) and photoluminescence (PL) microscopies is presented. SRFTIR mapping of laser damage identified localized non-bridging Si-O vibrational modes at ∼950 cm−1 which became stiffer as 355 nm laser pulse lengths were increased from 5 to 20 ns. The bridging Si-O-Si transverse optic mode frequency varied significantly across damaged regions indicating a wide range of average bond angles, softening slightly with increasing pulse length. 355 nm-excited PL images of laser modified regions could be directly correlated with the structural modifications identified through SRFTIR.
Boundary symmetry-stabilized memory in mono-layered cholesteric capsules
Authors: Lee Ji-Hoon , Lee Burm-Young
Published: October 2011

The bistable memory of a cholesteric liquid crystal often disappears owing to the unstable orientation of the focal conic state. We demonstrated the stabilization of the memory by controlling the boundary symmetry of a mono-layered cholesteric liquid crystal capsules which were fabricated with a membrane filter. It was found that the focal conic memory state with a random orientation of the helical axes became more stable in the capsules with higher boundary symmetry. With the same principle, the planar memory state with a lower symmetric orientation of the helical axes became more stable in the capsules with lower symmetry.