bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanism of fast proton transfer in ice: Potential energy surface and reaction coordinate analyses
Authors: Kobayashi Chigusa , Saito Shinji , Ohmine Iwao
Published: July 2002

The mechanism of proton transfer in ice is investigated theoretically by examining the potential energy surfaces and determining the reaction coordinates. It is found to be quite different from that in liquid water. As shown by many authors, proton transfer in liquid water is promoted by the structure fluctuation, creating three-coordinated water molecules in the hydrogen bond network rearrangement, and the excess proton makes transitions among these three-coordinated water molecules as forming a so-called Zundel structure, (H5O2)+. This kind of large structural rearrangement cannot take place in ice. Nevertheless, the proton transfer in ice can be very fast. It is found that the strong constraint on the molecular geometry in ice is the source of the facile proton transfer. This constraint reduces the stabilization of the excess proton state in two ways: (1) as O–O cannot shrink freely, it cannot form a stable Zundel structure in which two water molecules share the excess proton locating at the center of the shortened O–O bond, and (2) as the existence of the repulsive force, an Eigen structure cannot be much stabilized. This repulsive force also contributes to partially shorten the O–O distance and thus facilitating a proton transfer. As the result, the excess proton is not trapped in a deep energy minimum but makes the transfers on small energy barriers. The molecular geometry relaxation along the proton transfer is analyzed; it is found that O–O stretchings/shrinkages at the excess proton moiety are mutually coupled to assist the sequential proton transfers in a concerted fashion. The energetics and geometrical changes along these reaction coordinates are analyzed. The potential energies are found to be fairly flat for different locations of the excess proton. The nature of the excess proton solvation from the surrounding water molecules are analyzed; it is shown that the solvation by even distant shells yields a significant contribution to the potential energy surface of the proton transfer.
Stress calculation in atomistic simulations of perfect and imperfect solids
Authors: Cormier J. , Rickman J. M. , Delph T. J.
Published: July 2002

We analyze a real-space expression for the local stress tensor. This tensor rigorously satisfies conservation of linear momentum. From this expression a coarse-grained tensor is obtained for use in atomistic simulations of solids. Our formulation is then validated by considering both a homogeneously strained crystalline solid and one containing an oversized inclusion. In the latter case a direct comparison is made with results from anisotropic elasticity theory. We find that we are able to obtain good agreement with the suitably averaged continuum solutions in the far-field regime. Moreover, the coarse-grained tensor derived here appears to offer superior accuracy as compared to a stress tensor that has been widely used in atomistic analysis.
IUPAC-NIST Solubility Data Series 71. Nitromethane with Water or Organic Solvents: Binary Systems
Authors: Sazonov Valerii P. , Marsh Kenneth N. , Hefter Glenn T.
Published: July 2002

The mutual solubilities and liquid–liquid equilibrium of nitromethane binary systems with liquid solvents are reviewed. The solvents include water, inorganic compounds, and a variety of organic compounds as hydrocarbons, halogenated hydrocarbons, alcohols, acids, esters, and nitrogen compounds. A total 474 systems published through 1993 are compiled. For 39 systems sufficient data were available to allow critical evaluation. All data are expressed as mass and mole fractions as well as the originally reported units. Similar reviews of gas, liquid, and solid solubilities for other systems were published in the frame of Solubility Data Series.
The origin of the electron distribution in SnO
Authors: Watson Graeme W.
Published: July 2002

Gradient corrected density functional theory calculations have been performed on SnO in the litharge and idealized CsCl structures with the litharge structure in good agreement with experiment. The CsCl structured SnO has a spherical electron density whereas the litharge structured SnO has a nonspherical electron distribution. Such asymmetry is often attributed to a sterically active lone pair formed by the 5s2 electrons which does not take part in chemical bonding. However, analysis of the density of states and band structures indicates that the situation is more complicated. In CsCl structured SnO mixing of the Sn 5s with the oxygen 2p electronic states results in filled bonding and antibonding combinations. The antibonding combinations, at the top of valence band, can interact with Sn 5p to stabilize the structure, only when in the distorted litharge structure resulting in the asymmetric electron density. This is in contrast to the classical theory of hybridization of the tin 5s and 5p orbitals to form a “lone pair” as the asymmetric electron distribution is the result of the tin–oxygen covalent interactions.
Deformation behavior of ion-beam-modified GaN
Authors: Kucheyev S. O. , Bradby J. E. , Williams J. S. , Jagadish C. , Swain M. V. , Li G.
Published: July 2002

The deformation behavior of wurtzite GaN films modified by ion bombardment is studied by nanoindentation with a spherical indenter. Results show that implantation disorder significantly changes the mechanical properties of GaN. In particular, GaN amorphized by ion bombardment exhibits plastic deformation even for very low loads with dramatically reduced values of hardness and Young’s modulus compared to the values of as-grown GaN. Implantation-produced defects in crystalline GaN suppress the plastic component of deformation and significantly change the values of hardness and Young’s modulus. In addition, implantation disorder in crystalline GaN suppresses both “pop-in” events during loading and the appearance of slip traces on the sample surface as a result of indentation. This strongly suggests that slip nucleation (rather than a phase transformation) is the physical mechanism responsible for the pop-in events observed during loading of as-grown crystalline GaN.
Epitaxial growth of orientation-controlled KNbO3 crystal films on MgO using KTaxNb1−xO3 intermediate layer by metalorganic chemical vapor deposition
Authors: Onoe Atsushi , Yoshida Ayako , Chikuma Kiyofumi
Published: July 2002

In this letter, we report a method to obtain an orientation-controlled (010) KNbO3 crystal film on (110) MgO substrate based on the epitaxial growth by the low-pressure metalorganic chemical vapor deposition. In order to control the orientation of the KNbO3 film, an intermediate layer of KTaxNb1−xO3 was used. In the case where the Ta/(Ta+Nb) ratio of the KTaxNb1−xO3 film was over 40%, we could obtain (010)-oriented epitaxial KNbO3 films. Furthermore, the surface morphology of the deposited film, the thickness of which was about 1 μm, was smooth at the Ta/(Ta+Nb) ratio of 60%. The measurement of the refractive index dispersion of the KNbO3 crystal film was also carried out.
Irreducible Brillouin conditions and contracted Schrödinger equations for n-electron systems. I. The equations satisfied by the density cumulants
Authors: Mukherjee Debashis , Kutzelnigg Werner
Published: July 2002

Two alternative conditions for the stationarity of the energy expectation value with respect to k-particle excitations are the k-particle Brillouin conditions BCk and the k-particle contracted Schrödinger equations, CSEk. These conditions express the k-particle density matrices γk in terms of density matrices of higher particle rank. The latter can be eliminated if one expresses the γk in terms of their cumulants λk, but this is not sufficient to make the BCk or CSEk separable (extensive), i.e., they are not expressible in terms of only connected diagrams. However, in a formulation based on the recently introduced general normal ordering with respect to arbitrary wave functions, the irreducible counterparts IBCk and ICSEk of the BCk and CSEk can be defined. They are easily evaluated explicitly in terms of the generalized Wick theorem for arbitrary wave functions, and they lead to equations for the direct construction of the cumulants λk, which are additively separable quantities and which scale linearly with the system size. The IBCk or the ICSEk are necessary conditions for γ and the λk to represent an exact n-fermionic eigenstate of the given Hamiltonian. To specify the desired state, additional conditions must be satisfied as well, e.g., the partial trace relations which relate λ2 to γ and γ2. The particle number and the total spin must be specified and n-representability conditions enter implicitly. While the nondiagonal elements of γ and the λk are determined by the IBCk or the ICSEk, the additional conditions mainly serve to fix the diagonal elements. A hierarchy of k-particle approximations is defined. It is based on the fact that the expansion in terms of cumulants λk can be truncated at any particle rank, which would not be possible for the density matrices γk. For closed-shell states the one-particle approximation agrees with Hartree–Fock.
Emission properties of different cathodes at E⩽105 V/cm
Authors: Krasik Ya. E. , Dunaevsky A. , Krokhmal A. , Felsteiner J. , Gunin A. V. , Pegel I. V. , Korovin S. D.
Published: July 2002

We present results of the investigation of different types of cathodes operating in an electron diode powered by a high-voltage generator (300 kV, 250 ns, 84 Ω, ⩽5 Hz). The cathodes which have the same emitting area of 100 cm2 are made of metal–ceramic, carbon fibers, carbon fabric, velvet, or corduroy. We also tested carbon fibers and carbon fabric cathodes coated by CsI. It was shown that for all types of cathodes the electron emission occurs from the plasma which is formed as a result of a flashover of separate emitting centers. The amount of the emitting centers and the time delay in the electron emission were found to depend strongly on the accelerating electric field growth rate. Experimental data concerning the uniformity of the light emission from the cathode surface and divergence of the generated electron beams are presented. Data related to the general parameters of the diode, namely its impedance, power, and energy are given as well. For all the cathodes investigated the observed diode impedance indicated the existence of a quasistationary cathode plasma boundary for electron current density ⩽20 A/cm2. We present the dependencies of the average emitted electron current density and of the time delay in the electron emission on the number of generator shots. We also present data of the vacuum deterioration as a result of the tested cathodes operation. The obtained data are discussed within the framework of plasma formation as a result of cathode surface flashover.
Ion beam milling fabrication of a small off-axis ellipsoidal mirror, diffraction limited to 1 μm resolution at 14 nm
Authors: Mercier Raymond , Mullot Michel , Lamare Michel , Tissot Gérard
Published: July 2002

One interest of extreme ultraviolet wavelengths is their potentially high optical resolution. Such optics require high precision, low roughness surfaces onto which will be deposed adequate multilayers giving near-normal incidence reflection. For a spatially resolved interferometer, we have manufactured and tested with a reasonable degree of confidence an 8×8 mm off-axis ellipsoidal mirror, below the diffraction limit for a 14 nm wavelength. The ion beam milling technique employed for the fabrication allows to preserve the low roughness of the initial spherical substrate, and although we only achieved a 0.4 nm root-mean-square roughness, better could easily be done. At these precisions, testing is as important and as difficult as the figuring itself. The resulting mirror combines high theoretical resolution (1 μm) over a large object field (∼1 mm in diameter).
A model for layer formation in stably stratified turbulence
Authors: Wunsch Scott , Kerstein Alan
Published: July 2002

Stably stratified turbulent flows are common in geophysics and astrophysics, and frequently exhibit layered structures in which large regions of nearly constant fluid density are separated by sharp density gradients. Experiments have demonstrated that, under suitable conditions, the stirring of a stably stratified fluid generates these layer structures. In this paper, a stochastic one-dimensional model is used to study layer formation in stably stratified turbulence. The results support mixing length arguments previously proposed to describe layers in steady state.
Interparticle coupling effects in nanofabricated substrates for surface-enhanced Raman scattering
Authors: Gunnarsson L. , Bjerneld E. J. , Xu H. , Petronis S. , Kasemo B. , Käll M.
Published: July 2002

Surface-enhanced Raman scattering (SERS) substrates, consisting of arrays of electromagnetically coupled Ag nanoparticles on Si, were manufactured by electron-beam lithography. Substrate Raman efficiency, evaluated from the relative SERS intensities of the adsorbates rhodamine 6G and thiophenol, was found to increase rapidly with decreasing interparticle separation, signaling the importance of strong interparticle coupling effects in SERS. The observed SERS efficiency variation can be qualitatively explained in terms of electrostatic models of coupled metal structures.
Statistical modeling of sprays using the droplet distribution function
Authors: Subramaniam S.
Published: July 2002

The theoretical foundations of a statistical spray modeling approach based on the droplet distribution function (ddf), which was originally proposed by Williams [Phys. Fluids 1, 541 (1958)], are established. The equation governing the ddf evolution is derived using an alternative approach. The unclosed terms in the ddf evolution equation are precisely defined, and the regime of applicability of current models is discussed. The theory of point processes is used to rigorously establish the existence of a disintegration of the ddf in terms of a spray intensity, which is the density of expected number of spray droplets in physical space, and the joint probability density function (jpdf) of velocity and radius conditional on physical location. Evolution equations for the spray intensity and the conditional jpdf of velocity and radius are derived. The intensity evolution equation contains a sink term corresponding to droplet vaporization, hitherto missing in previous derivations of this equation. This sink term is essential in order to correctly represent the vaporization phenomenon. Problems with numerical convergence of computed solutions to the ddf evolution are discussed, and criteria for establishing convergence are proposed. The study also shows how quantities predicted by ddf-based spray models can be compared to experimental measurements.
Homogeneous nucleation of n-pentanol in a laminar flow diffusion chamber
Authors: Lihavainen Heikki , Viisanen Yrjö , Kulmala Markku
Published: July 2002

Nucleation rate isotherms of n-pentanol were measured in laminar flow diffusion chamber. n-pentanol was chosen for nucleating vapor and helium for carrier gas as a part of a world wide joint experiment on homogeneous nucleation. Experimental temperature range was from 260 to 290 K. Experimental nucleation rate range was from 103 to 107 cm−3 s−1. The results were compared to the classical nucleation theory and experimental data found in literature. Experimental results were three orders of magnitude higher than predicted by the theory. The difference was constant over the whole experimental range. The saturation ratio dependency of nucleation rate was well predicted by the theory. The number of molecules in the critical clusters was quite consistent with the theory. The results were in reasonable agreement with data found in literature.
Nonexponentiality of time dependent survival probability and the fractional viscosity dependence of the rate in diffusion controlled reactions in a polymer chain
Authors: Srinivas Goundla , Yethiraj Arun , Bagchi Biman
Published: July 2002

Brownian dynamics (BD) simulations have been carried out for the time dependent survival probability [Sp(t)] of donor–acceptor pairs embedded at the two ends of an ideal polymer chain. Long distance fluorescence resonance energy transfer (FRET) between the donor and the acceptor is assumed to occur via the Forster mechanism, where the transfer rate k(R) is a function of the distance (R) between the donor and acceptor. For the Rouse chain simulated here, k(R) is assumed to be given by k=kF/[1+(R/RF)6], where kF is the rate in the limit of zero separation and RF is the Forster radius. The survival probability displays a strong nonexponential decay for the short to intermediate times when RF is comparable to RM [distance at which the R2P(R) is maximum]. The nonexponentiality is also more prominent in the case of highly viscous polymer solutions. It is predicted that the FRET rate can exhibit a fractional viscosity dependence. This prediction can be tested against experiments. We have also compared the BD simulation results with the predictions of the well-known Wilemski–Fixman (WF) theory at the level of survival probability. It is found that the WF theory is satisfactory for the smaller RF values (where the rate is small). However, the agreement becomes progressively poorer as the Forster radius is increased. The latter happens even at intermediate strengths of kF. The present results suggest the need to go beyond the WF theory.
Breaking the NO bond on Rh, Pd, and Pd3Mn alloy (100) surfaces: A quantum chemical comparison of reaction paths
Authors: Loffreda D. , Delbecq F. , Simon D. , Sautet P.
Published: July 2002

Total energy calculations have been performed within the periodic density-functional theory framework to study the dissociation of molecularly adsorbed nitrogen monoxide NO over three different catalytic surfaces: palladium, rhodium, and palladium-manganese (100). The potential energy surfaces for NO dissociation on these metallic surfaces have been calculated in order to determine the minimal energy paths. The accurate optimizations of the transition states and their characterization with a complete vibrational analysis, including the degrees of freedom of the surface, have been presented. The order of increasing activation energy barrier is Rh, Pd3Mn, and Pd. Two types of reaction paths have been found: one involving a horizontal molecular precursor state and a low activation energy barrier (Rh and Pd3Mn) and the other involving a vertical molecular state and a high activation energy (Pd). Hence the improvement of the catalytic activity for dissociating NO by alloying manganese to palladium has been explained and interpreted. The simulation of the reaction rate constants is fully compatible with the observed catalytic behavior. The differences in catalytic activity have been analyzed with a bond breaking–bond forming energetic decomposition and a Mulliken population analysis.
Quantitative imaging of nanoscale mechanical properties using hybrid nanoindentation and force modulation
Authors: Syed Asif S. A. , Wahl K. J. , Colton R. J. , Warren O. L.
Published: July 2002

In this article, we present a quantitative stiffness imaging technique and demonstrate its use to directly map the dynamic mechanical properties of materials with nanometer-scale lateral resolution. For the experiments, we use a “hybrid” nanoindenter, coupling depth-sensing nanoindentation with scanning probe imaging capabilities. Force modulation electronics have been added, enhancing instrument sensitivity and enabling measurements of time dependent materials properties (e.g., loss modulus and damping coefficient) not readily obtained with quasi-static indentation techniques. Tip–sample interaction stiffness images are acquired by superimposing a sinusoidal force (∼1 μN) onto the quasi-static imaging force (1.5–2 μN), and recording the displacement amplitude and phase as the surface is scanned. Combining a dynamic model of the indenter (having known mass, damping coefficient, spring stiffness, resonance frequency, and modulation frequency) with the response of the tip–surface interaction, creates maps of complex stiffness. We demonstrate the use of this approach to obtain quantitative storage and loss stiffness images of a fiber-epoxy composite, as well as directly determine the loss and storage moduli from the images using Hertzian contact mechanics. Moduli differences as small as 20% were resolved in the images at loads two orders of magnitude lower than with indentation, and were consistent with measurements made using conventional quasi-static depth-sensing indentation techniques.
Yang–Mills field quantization in the factor space
Authors: Manjavidze J. , Sissakian A.
Published: July 2002

The perturbation theory over inverse interaction constant 1/g is constructed for Yang–Mills theory. It is shown that the new perturbation theory is free from the gauge ghosts and Gribov’s ambiguities, and each order over 1/g presents the gauge-invariant quantity. It is remarkable that offered perturbation theory did not contain divergences, at least in the vector fields sector, and no renormalization procedure is necessary for it.
Very-high-efficiency double-heterostructure copper phthalocyanine/C60 photovoltaic cells
Authors: Peumans P. , Forrest S. R.
Published: July 2002

We demonstrate an external power conversion efficiency of (3.6±0.2)% under AM1.5 spectral illumination of 150 mW/cm2 (1.5 suns) with vacuum-deposited copper phthalocyanine/C60 thin-film double-heterostructure photovoltaic cells incorporating an exciton-blocking layer (EBL). We show that the anode work function influences the photocarrier collection characteristics through the built-in electric field. The cell parameters are less sensitive to the cathode work function, which is attributed to cathode-induced defect states in the EBL energy gap. The presence of these defect states also explains the surprisingly low resistance of the EBL to electron transport. We anticipate significant further improvements in power conversion efficiency by employing optimal structures in light-trapping geometries.
Supergeneralization of Duffin–Kemmer–Petiau Algebra and Lie superalgebra osp(N,M)
Authors: Okubo Susumu
Published: July 2002

We will consider a supergeneralization of the Duffin–Kemmer–Petiau algebra. It has been shown to be intimately related to the Lie super algebra osp(N,M). We will also discuss its representations.
Ultrafast dichroism spectroscopy of anthracene in solution. II. Solvation dynamics from a one-dimensional experiment
Authors: Zhang Yunhan , Berg Mark A.
Published: July 2002

Experiments to determine the frequency autocorrelation function of an electronic transition (the “solvation function”) inherently depend on a multidimensional response function. However, a degenerate transient absorption experiment, or “single-wavelength transient hole burning” (SW-THB), provides a one-dimensional cut through this multidimensional space with sufficient information to uniquely determine the desired solvation function. We derive an analytical formula that relates the solvation function to the one-dimensional SW-THB signal. Sample calculations examine the effects of strong versus weak coupling to the solvent, the wavelength of the laser relative to the absorption spectrum and of unresolved fast relaxation components. We conclude that for many systems, SW-THB provides a simpler alternative to multidimensional methods for measuring solvation dynamics.
Discontinuities in Dirac eigenfunction expansions
Authors: Szmytkowski Radosław
Published: July 2002

An expansion, over a finite interval, of a two-component function in a basis of eigenfunctions of a one-dimensional regular Dirac differential operator with separated homogeneous boundary conditions imposed at ends of the interval is considered. It is shown that at the ends of the domain the expansion does not converge to the expanded function unless the latter obeys at these points the same homogeneous boundary conditions as the basis eigenfunctions. General results obtained in the work are illustrated by an analytically solvable example. The problem is related to the R-matrix theory for Dirac particles.
Role of adsorption kinetics in the low-temperature Si growth by gas-source molecular beam epitaxy: In situ observations and detailed modeling of the growth
Authors: Murata Takeshi , Nakazawa Hideki , Tsukidate Yoshikazu , Suemitsu Maki
Published: July 2002

The growth rate and surface hydrogen coverage during Si gas-source molecular beam epitaxy using disilane have been obtained as functions of both the growth temperature and the source-gas pressure. The activation energy of the low-temperature (<600 °C) growth rate was found to increase with the source-gas pressure, indicating a contribution by the adsorption process in these low-temperature growth kinetics. Several growth models have been constructed based on the results, among which the two-site/four-site-adsorption model [M. Suemitsu et al., Jpn. J. Appl. Phys., Part 2 36, L625 (1997)] showed the best fit to both the growth rate and the hydrogen coverage.
Brownian dynamics simulations of ions channels: A general treatment of electrostatic reaction fields for molecular pores of arbitrary geometry
Authors: Im Wonpil , Roux Benoı̂t
Published: July 2002

A general method has been developed to include the electrostatic reaction field in Brownian dynamics (BD) simulations of ions diffusing through complex molecular channels of arbitrary geometry. Assuming that the solvent is represented as a featureless continuum dielectric medium, a multipolar basis-set expansion is developed to express the reaction field Green’s function. A reaction field matrix, which provides the coupling between generalized multipoles, is calculated only once and stored before the BD simulations. The electrostatic energy and forces are calculated at each time step by updating the generalized multipole moments. The method is closely related to the generalized solvent boundary potential [Im et al., J. Chem. Phys. 114, 2924 (2001)] which was recently developed to include the influence of distant atoms on a small region part of a large macromolecular system in molecular dynamics simulations. It is shown that the basis-set expansion is accurate and computationally inexpensive for three simple models such as a spherical ionic system, an impermeable membrane system, and a cylindrical pore system as well as a realistic system such as OmpF porin with all atomic details. The influence of the static field and the reaction field on the ion distribution and conductance in the OmpF channel is studied and discussed.
Atomic Weights of the Elements 1999
Authors: Coplen T. B.
Published: July 2002

The biennial review of atomic-weight, Ar(E), determinations and other cognate data have resulted in changes for the standard atomic weights of the following elements: fromtonitrogen14.006 74±0.000 07¯14.0067±0.0002¯sulfur32.066±0.00632.065±0.005chlorine35.4527±0.000935.453±0.002germanium72.61±0.0272.64±0.01xenon131.29±0.02131.293±0.006erbium167.26±0.03167.259±0.003uranium238.0289±0.0001238.028 91±0.000 03Presented are updated tables of the standard atomic weights and their uncertainties estimated by combining experimental uncertainties and terrestrial variabilities. In addition, this report again contains an updated table of relative atomic mass values and half-lives of selected radioisotopes. Changes in the evaluated isotopic abundance values from those published in 1997 are so minor that an updated list will not be published for the year 1999. Many elements have a different isotopic composition in some nonterrestrial materials. Some recent data on parent nuclides that might affect isotopic abundances or atomic-weight values are included in this report for the information of the interested scientific community.
Lateral profiling of impurity surface concentration in submicron metal–oxide–silicon transistors
Authors: Wang Yih , Sah Chih-Tang
Published: July 2002

Theory and line-shape analysis of carrier recombination current at interfacial electronic traps under a surface controlling gate in metal–oxide–silicon (MOS) structures is investigated using the Shockley–Read–Hall recombination statistics. The theoretical analysis demonstrates the sensitive dependence of the line shape of the peaked basewell-terminal recombination current versus gate/base voltage (IB–VGB) characteristics on the lateral variation of the impurity concentration along the surface channel. An electrical measurement method is presented based on this discovery for extracting the impurity surface concentration profile NIM(x=0, y, z) in the five regions (basewell, drain and source junction and extension) covered by the gate conductor in submicron MOS transistors. Impurity surface concentration profiles in the basewell channel region are then extracted by the analytical theory for MOS transistors fabricated by an advanced 0.13 μm complementary MOS technology. Effects of nitrogen in the gate oxide and current generated in the drain and source extension regions for profiling the NIM in the extension regions are illustrated.
Interpretation of double x-ray diffraction peaks from InGaN layers
Authors: Pereira S. , Correia M. R. , Pereira E. , O’Donnell K. P. , Alves E. , Sequeira A. D. , Franco N.
Published: July 2002

The presence of two, or more, x-ray diffraction (XRD) peaks from an InGaN epilayer is sometimes regarded as an indicator of phase segregation. Nevertheless, detailed characterization of an InGaN/GaN bilayer by a combination of XRD and Rutherford backscattering spectrometry (RBS) shows that splitting of the XRD peak may be completely unrelated to phase decomposition. Wurtzite InGaN/GaN layers were grown in a commercial reactor. An XRD reciprocal space map performed on the (105) plane shows that one component of the partially resolved InGaN double peak is practically aligned with that of the GaN buffer, indicating that part of the layer is pseudomorphic to the GaN template. The other XRD component is shown to have the same indium content as the pseudomorphic component, from a consideration of the effect of strain on the c- and a-lattice constants. The composition deduced from XRD measurements is confirmed by RBS. Depth-resolving RBS channeling angular scans also show that the region closer to the GaN/InGaN interface is nearly pseudomorphic to the GaN substrate, whereas the surface region is almost fully relaxed.
Measurement and analysis of nonhydrostatic lattice strain component in niobium to 145 GPa under various fluid pressure-transmitting media
Authors: Singh Anil K. , Kenichi Takemura
Published: July 2002

The d spacings in niobium have been measured to 145 GPa with a diamond anvil cell using a fluid pressure-transmitting medium [methanol–ethanol–water (MEW) mixture, or helium]. The conventional geometry, wherein the primary x-ray beam passes parallel to the load axis with image plate, has been used to record the diffraction patterns. The analysis of the d spacings using the lattice strain equations indicates the presence of nonhydrostatic stress component (with both MEW and He pressure-transmitting media) in the pressure ranges that are well below the freezing pressure of the pressure-transmitting medium. A method to correct the measured d spacings for the nonhydrostatic pressure effect is suggested. This study clearly emphasizes the need to carefully analyze the data for the nonhydrostatic compression effects even if the experiments are performed with fluid pressure-transmitting medium.
Nanoscale patterning of Si(100) surfaces by scratching through the native oxide layer using atomic force microscope
Authors: Santinacci L. , Djenizian T. , Schmuki P.
Published: July 2002

We demonstrate selective electrodeposition of Cu into nanoscratches produced in native oxide covered p-type and n-type Si(100). Nanosize grooves were produced with a diamond-coated atomic force microscope tip at heavy forces. Onto these grooved surfaces, Cu was electrodeposited from a 0.01 M CuSO4+0.05 M H2SO4 electrolyte under various conditions. The results clearly show that these scratches represent activated sites for metal electrodeposition—the surrounding intact oxide layer acts as a highly efficient mask. After optimization of electrochemical parameters, we were able to achieve the deposition of uniform and well-defined structures with a lateral resolution in the 100 nm range. In general, the process opens alternate perspectives for selective electrodeposition and direct patterning of Si surfaces.
A note on quantum thermodynamic rate theories
Authors: Pollak Eli , Shao Jiushu
Published: July 2002

The relationship between quantum transition state theory, the mixed quantum classical rate theory and the Hansen–Andersen analytic continuation methods is analyzed. We prove that the first three time derivatives of a coordinate dependent operator are the same in quantum and classical mechanics. As a result, the mixed quantum classical theory, in which the quantum projection operator is replaced by the classical, may be considered as a specific case of the Hansen–Andersen methodology. The same holds true for quantum transition state theory for one dimensional systems, where the exact quantum propagator is replaced by its parabolic barrier approximation. In the multidimensional case, quantum transition state theory errs somewhat in the second nonzero time derivative, however it may be reformulated to assure that it too remains exact for the first two nonzero initial time derivatives. Further systematic improvement of the mixed quantum classical theory may be obtained by including higher order terms in the ℏ2 expansion of the Wigner–Liouville equation. An iterative solution of the integral form of the Wigner–Liouville equation is suggested, which is based on propagation of classical trajectories only.
Six-dimensional variational calculation of the bending energy levels of HF trimer and DF trimer
Authors: Wang Xiao-Gang , Carrington Tucker
Published: July 2002

The bending energy levels of HF and DF trimer were calculated variationally using a six-dimensional kinetic-energy operator derived by constraining the stretch degrees of freedom to their equilibrium values. A basis of direct products of spherical harmonics is used to represent the wave function. The symmetry adapted Lanczos method is used to calculate levels of all symmetries from one sequence of matrix-vector products. Two efficient ways of implementing the symmetry-adapted Lanczos method are presented. To determine the concerted hydrogen bond breaking tunneling splitting in HF and DF trimer one needs to use the D3h point group. By doing D3h calculations, we find that the splitting is negligible for the low-lying levels. If the tunneling is unfeasible, the appropriate group is C3h. Our calculation using the most accurate SO-3+HF3BG potential developed by Quack, Stohner, and Suhm indicates that two gas-phase overtone bending bands of HF trimer should be reassigned, and that the noble gas matrix spectra of the bending fundamental bands are significantly shifted from their gas-phase counterparts.
Photodissociation of LiFH and NaFH van der Waals complexes: A semiclassical trajectory study
Authors: Jasper Ahren W. , Hack Michael D. , Chakraborty Arindam , Truhlar Donald G. , Piecuch Piotr
Published: July 2002

The photodissociation of Li⋯FH and Na⋯FH van der Waals complexes is studied using Tully’s fewest-switches surface-hopping and the natural decay of mixing semiclassical trajectory methods for coupled-state dynamics. The lifetimes of the predissociated excited-state complex (exciplex), as well as the branching ratio into reactive and nonreactive arrangements and the internal energy distribution of the products are reported at several excitation energies. The semiclassical trajectory methods agree with each other only qualitatively, and the results are strongly dependent on the choice of electronic representation. In general, the lifetime of the LiFH exciplex is shorter and less dependent on the excitation energy than the lifetime of the NaFH exciplex. The semiclassical dynamics of LiFH and NaFH are interpreted in terms of the features of their coupled potential energy surfaces.
Crystallographic texture and magnetic anisotropy of α-Fe/Nd2Fe14B nanocomposites prepared by controlled melt spinning
Authors: Zhang X. Y. , Guan Y. , Yang L. , Zhang J. W.
Published: July 2002

In this study, α-Fe/Nd2Fe14B nanocomposite magnets with strong crystallographic texture were prepared by controlled melt spinning. For a relatively low wheel speed of 10 m/s, the c-axis texture of the Nd2Fe14B crystals is predominantly perpendicular to the plane of the ribbon, but it switches to parallel to the ribbon plane direction at a higher wheel speed of 20 m/s. The magnets show strong magnetic anisotropy between in and out of the ribbon planes. High remanence of 0.74Ms and a large energy product of 24.3 MGOe were observed parallel to the ribbon plane direction in the magnets prepared at a wheel speed of 20 m/s.
Reference system master equation approaches to condensed phase charge transfer processes. II. Numerical tests and applications to the study of photoinduced charge transfer reactions
Authors: Golosov Andrei A. , Reichman David R.
Published: July 2002

In this paper we test and apply the master equation approaches developed in paper I. We demonstrate that our master equation methods can greatly improve upon the performance of more standard approaches, rendering nearly quantitative agreement compared to numerically exact tests under a variety of conditions. The methods developed in paper I are also demonstrated to be fully capable of handling the effects of nonequilibrium initial preparation, which can be quite prominent at short times. This property is used to study the kinetics of photoinduced charge transfer in a mixed valence compound. For this system, we discuss observed short-time nonexponential behavior, dynamical trapping, and coherence. Last, we discuss the significant computational advantages of our methods in terms of their scaling with the number of discrete states in the system.
Orientation of liquid crystal monolayers on polyimide alignment layers: A molecular dynamics simulation study
Authors: van der Vegt N. F. A. , Müller-Plathe F. , Geleßus A. , Johannsmann D.
Published: July 2002

Detailed atomistic molecular dynamics simulations were performed on monolayers of 4′-n-octyl-4-cyanobiphenyl (8CB) adsorbed onto a surface of poly-m-alkanpyromellitimide (poly-m-APM), where m is the number of CH2 units between the imide moieties. Poly-3-APM and poly-4-APM surfaces served as model surfaces to investigate the influence of microscopic grooves, polar carbonyl groups exposed to the surface, and an anisotropic van der Waals interaction between the liquid crystal (LC) molecules and the polymer chains. A Lennard-Jones fluid was chosen as the bulk phase in order to mimic the bulk LC phase. The fluid lubricates the motion of the LC molecules and increases the molecular tilt angle. While microgrooves dominate the alignment of isolated molecules, an anisotropic van der Waals interaction with the main chain is stronger in the case of entire monolayers.
Auger recombination in low-band-gap n-type InGaAs
Authors: Metzger W. K. , Wanlass M. W. , Ellingson R. J. , Ahrenkiel R. K. , Carapella J. J.
Published: July 2002

We measured the recombination lifetime of degenerate n-InxGa1−xAs for three different compositions that correspond to x=0.53, 0.66, and 0.78 (band gaps of 0.74, 0.60, and 0.50 eV, respectively) over the doping range of 3×1018–5×1019 carriers/cm3. The Auger recombination rate increases slowly with decreasing band gap, and it matches the behavior predicted for phonon-assisted recombination.
On the problem of negative dissipation of fast waves at the fundamental ion cyclotron resonance and the accuracy of absorption estimates
Authors: Castejón F. , Pavlov S. S. , Swanson D. G.
Published: July 2002

Negative dissipation appears when ion cyclotron resonance (ICR) heating at first harmonic in a thermal plasma is estimated using some numerical schemes. The causes of the appearance of such a problem are investigated analytically and numerically in this work showing that the problem is connected with the accuracy with which the absorption coefficient at the first ICR harmonic is estimated. The corrections for the absorption estimation are presented for the case of quasiperpendicular propagation of fast wave in this frequency range. A method to solve the problem of negative dissipation is presented and, as a result, an enhancement of absorption is found for reactor-size plasmas.
1/f
noise in pentacene and poly-thienylene vinylene thin film transistors
Authors: Vandamme L. K. J. , Feyaerts R. , Trefán Gy. , Detcheverry C.
Published: July 2002

We investigate low frequency conductivity noise in the drain-source channel of organic material field-effect transistors by measuring the spectra of current fluctuations for several values of the gate voltage Vgs and drain voltage Vds and find that it is 1/f. The samples are biased in the ohmic range of the applied Vds. The relative current 1/f noise is inversely proportional to the charge carrier numbers N generated by illumination or by varying the gate-source voltage. Hooge’s empirical relation for the 1/f noise is validated for these organic semiconductors with an α≅0.01 for poly-thienylene vinylene and about 100 for pentacene thin film transistors. From geometry dependence of the noise we conclude that series resistance can be ignored for poly-thienylene vinylene field-effect transistors. However, some pentacene samples suffer from a noisy series resistance to the channel resistance. From the 1/f noise dependence on geometry and gate voltage bias we conclude that it can be used as a diagnostic tool for device quality assessment.
Zero field spin splitting in inversion layers on p-InSb: A fully numerical study
Authors: Lamari Saadi
Published: July 2002

Within Kane’s multiband Hamiltonian, the subband spin splitting of electrons in the inversion layer on bulk p-InSb is investigated self-consistently as a function of the electron sheet density Ns. The splitting δk is a nonlinear function of wave vector k, and depends strongly on density Ns and subband ν. The concomitant Rashba spin-orbit parameter αk decreases substantially with k and ν and is maximal for ν=0 as k→0. At the Fermi level the spin splitting δ, the Rashba parameter α and the product m*α computed for each subband in the range 0.14×1012 cm−2 – 3.07×1012 cm−2 increase nonlinearly with Ns except for higher subbands.
Xenon charge exchange cross sections for electrostatic thruster models
Authors: Miller J. Scott , Pullins Steve H. , Levandier Dale J. , Chiu Yu-hui , Dressler Rainer A.
Published: July 2002

Charge exchange between xenon ions and xenon atoms is the source of a detrimental low energy plasma in the vicinity of electrostatic spacecraft thrusters. Proper modeling of charge-exchange induced spacecraft interactions requires knowledge of the respective charge-exchange cross sections. Guided-ion beam measurements and semiclassical calculations are presented for xenon atom charge-exchange collisions with Xe+ and Xe2+ at energies per ion charge ranging from 1 to 300 eV. The present measurements for the symmetric Xe++Xe exchange system are in good agreement with several earlier experimental studies and semiclassical calculations based on the most recently computed Xe2+ interaction potentials. The cross sections are ∼30% higher than predictions by the Rapp and Francis model [D. Rapp and W. E. Francis, J. Chem. Phys. 37, 2631 (1962)]. The present Xe2++Xe symmetric charge exchange measurements are the first to cover the ion energy range from 40 to 600 eV. The cross sections are in good agreement with low-energy drift tube measurements and are significantly lower than previous higher energy measurements. A simple model for symmetric two-electron transfer is proposed that is in good agreement with the present measurements. The onset for the asymmetric charge-exchange process, Xe2++Xe→2Xe+, is observed to be at 10 eV. For this process, a cross section of 2.8±0.9 Å2 is measured for a Xe2+ energy of 600 eV.
Electrical and optical characterization of conducting poly-3-methylthiophene film by THz time-domain spectroscopy
Authors: Jeon Tae-In , Grischkowsky D. , Mukherjee A. K. , Menon Reghu
Published: July 2002

Using THz time-domain spectroscopy (THz-TDS), we have measured the absorption and dispersion of 7.5/(Ω cm) conducting poly-3-methylthiophene film from low frequencies up to 4 THz. From these measurements the complex conductance that increases with increasing frequency was obtained over this frequency range. The results do not follow simple Drude theory and are not comparable with normal metal and semiconductors; the results were well fit by the localization-modified Drude theory.
Polarization reversal study using ultrasound
Authors: Yin Jianhua , Cao Wenwu
Published: July 2002

We found that the sound velocity changes drastically near the coercive field for a 0.955Pb(Zn1/3Nb2/3)O3–0.045PbTiO3 ferroelectric single crystal, which reflects that domain rotation occurred during polarization switching. This velocity change associated with polarization switching provides a powerful method to study the dynamics of polarization reversal process in nontransparent ferroelectric crystals. A complete phase velocity-electric field loop was measured quasi-statically in a switching cycle and compared with the polarization hysteresis loop. In addition, two attenuation peaks were found in the switching cycle, which indicates that two domain switching processes are involved in the polarization reversal.
Organic bistable light-emitting devices
Authors: Ma Liping , Liu Jie , Pyo Seungmoon , Yang Yang
Published: July 2002

An organic bistable device, with a unique trilayer structure consisting of organic/metal/organic sandwiched between two outmost metal electrodes, has been invented. [Y. Yang, L. P. Ma, and J. Liu, U.S. Patent Pending, U.S. 01/17206 (2001)]. When the device is biased with voltages beyond a critical value (for example 3 V), the device suddenly switches from a high-impedance state to a low-impedance state, with a difference in injection current of more than 6 orders of magnitude. When the device is switched to the low-impedance state, it remains in that state even when the power is off. (This is called “nonvolatile” phenomenon in memory devices.) The high-impedance state can be recovered by applying a reverse bias; therefore, this bistable device is ideal for memory applications. In order to increase the data read-out rate of this type of memory device, a regular polymer light-emitting diode has been integrated with the organic bistable device, such that it can be read out optically. These features make the organic bistable light-emitting device a promising candidate for several applications, such as digital memories, opto-electronic books, and recordable papers.
Relativistic N-boson systems bound by oscillator pair potentials
Authors: Hall Richard L. , Lucha Wolfgang , Schöberl Franz F.
Published: July 2002

We study the lowest energy E of a relativistic system of N identical bosons bound by harmonic-oscillator pair potentials in three spatial dimensions. In natural units ℏ=c=1 the system has the semirelativistic (or “spinless-Salpeter”) Hamiltonian, H=∑i=1Nm2+pi2+∑j>i=1Nγ|ri−rj|2, γ>0. We derive the following energy bounds: E(N)=minr>0[N(m2+2(N−1)P2/(Nr2))1/2+(N/2)(N−1)γr2], N⩾2, where P=1.376 yields a lower bound and P=32 yields an upper bound for all N⩾2. A sharper lower bound is given by the function P=P(m) which makes the formula for E(2) exact: with this choice of P, the bounds coincide for all N⩾2 in the Schrödinger limit defined by m→∞.