bluuebunny/crossref_metadata_2025 huggingface dataset:
Variational transition state theory evaluation of the rate constant for proton transfer in a polar solvent
Authors: McRae Robin P. , Schenter Gregory K. , Garrett Bruce C. , Svetlicic Zoran , Truhlar Donald G.
Published: July 2002

Variational transition state theory (VTST) is used to calculate rate constants for a model proton transfer reaction in a polar solvent. We start from an explicit description of the reacting solute in a solvent, and we model the effects of solvation on the reaction dynamics by a generalized Langevin equation (GLE) for the solute. In this description, the effects of solvation on the reaction energetics are included in the potential of mean force, and dynamical, or nonequilibrium, solvation is included by solvent friction. The GLE solvation dynamics are approximated by a collection of harmonic oscillators that are linearly coupled to the coordinates of the reacting system. This approach is applied to a model developed by Azzouz and Borgis [J. Chem. Phys. 98, 7361 (1993)] to represent proton transfer in a phenol-amine complex in liquid methyl chloride. In particular, semiclassical VTST, including multidimensional tunneling contributions, is applied to this model with three explicit solute coordinates and a multioscillator GLE description of solvation to calculate rate constants. We compare our computed rate constants and H/D kinetic isotope effects to previous calculations using other approximate dynamical theories, including approaches based on one-dimensional models, molecular dynamics with quantum transitions, and path integrals. By examining a systematic sequence of 18 different sets of approximations, we clarify some of the factors (such as classical vibrations, harmonic approximations, quantum character of reaction-coordinate motion, and nonequilibrium solvation) that contribute to the different predictions of various approximation schemes in the literature.
Spin-polarized transport in GaMnAs multilayers
Authors: Loureiro da Silva L. , Boselli M. A. , da Cunha Lima I. C. , Wang X. F. , Ghazali A.
Published: July 2002

The spin-dependent mobility for the lateral transport of the hole gas in a GaMnAs/GaAs heterostructure containing several metallic-like ferromagnetic layers is calculated. The electronic structure is obtained self-consistently taking into account the direct Coulomb Hartree and exchange-correlation terms, besides the sp–d exchange interaction with the Mn magnetic moments.
Ultraviolet light-emitting diodes at 340 nm using quaternary AlInGaN multiple quantum wells
Authors: Adivarahan V. , Chitnis A. , Zhang J. P. , Shatalov M. , Yang J. W. , Simin G. , Khan M. Asif , Gaska R. , Shur M. S.
Published: July 2002

An ultraviolet light-emitting diode with peak emission wavelength at 340 nm is reported. The active layers of the device were comprised of quaternary AlInGaN/AlInGaN multiple quantum wells, which were deposited over sapphire substrates using a pulsed atomic-layer epitaxy process that allows precise control of the composition and thickness. A comparative study of devices over sapphire and SiC substrates was done to determine the influence of the epilayer design on the performance parameters and the role of substrate absorption.
Covariant localizations in the torus and the phase observables
Authors: Cassinelli Gianni , De Vito Ernsesto , Lahti Pekka , Pellonpää Juha-Pekka
Published: July 2002

We describe all the localization observables of a quantum particle in a one-dimensional box in terms of sequences of unit vectors in a Hilbert space. An alternative representation in terms of positive semidefinite complex matrices is furnished and the commutative localizations are singled out. As a consequence, we also get a vector sequence characterization of the covariant phase observables.
Linking the photoelectron and infrared spectroscopies of the (H2O)6− isomers
Authors: Kelley Jude A. , Weddle Gary H. , Robertson William H. , Johnson Mark A.
Published: July 2002

We report a novel photoelectron spectroscopy variation of population labeling spectroscopy and apply it to assign the isomeric carrier of the strong autodetaching OH stretching vibrational resonances reported previously [J. Phys. Chem. 100, 16782 (1996) and J. Chem. Phys. 108, 444 (1998)] for a mixed ensemble of (H2O)6− isomers. The vibrational bands are traced to the isomer with the higher vertical electron detachment energy (VDE). This result indicates that resonances are most readily observed for vibrational bands which lie below the VDE of the parent species.
Guided ion beam studies of the reactions of Vn+ (n=2–13) with D2: Cluster–deuteride bond energies as a chemical probe of cluster electronic structure
Authors: Liyanage Rohana , Conceição J. , Armentrout P. B.
Published: July 2002

The kinetic energy dependencies of the reactions of Vn+ (n=2–13) with D2 are studied in a guided ion beam tandem mass spectrometer. Products observed are VnD+ for all clusters and VnD2+ for n=4–13. All reactions are observed to exhibit thresholds, except for formation of VnD2+ for n=4,5,7,9,11–13. The enhanced reactivity of the odd-sized clusters towards D2 chemisorption is nicely correlated with the D0(Vn+–V) bond energies. The odd-number clusters are less stable and more reactive, suggesting that they are open shell, whereas the even-number clusters, which are more stable and less reactive, appear to be closed shell. Threshold analyses of the endothermic reactions lead to Vn+–D binding energies (n=1–13), which reach values comparable to the bulk phase for larger clusters. The Vn+–D bond energies show odd–even oscillations anticorrelated with D0(Vn+–V) for n<5, but roughly parallel with D0(Vn+–V) for n>5. Magnitude differences in the two series of bond energies suggest that the metal–metal bonding has appreciable 3d–3d contributions. The variation in the Vn+–D bond energies with cluster size is explained using promotion energy arguments.
Electron beams and Z-pinches as plasma strippers and lens for low-energy heavy ions
Authors: Hershcovitch A. , Johnson B. M. , Patton F. , Rostoker N. , VanDrie A. , Wessel F. J.
Published: July 2002

Numerous approaches to the production of intense beams of highly charged heavy ions are compared and contrasted. The competing processes of ionization and electron capture are described and evaluated to explore ways to further improve upon the encouraging recent results from electron-beam (E-MEVVA) and low-impedance Z-discharge (LIZ-MeV) variations on the venerable metal vapor vacuum arc (MEVVA) ion source.
Investigating a link between all-atom model simulation and the Ising-based theory on the helix–coil transition: Equilibrium statistical mechanics
Authors: Takano Mitsunori , Nagayama Kuniaki , Suyama Akira
Published: July 2002

To describe the polypeptide helix–coil transition, while the Ising-based theory has been playing the principal role for 40 years, we can now make use of computer simulation using the so-called “all-atom model” that is far more precise than the Ising-based model. In this study, by conducting molecular dynamics (MD) simulations of helix–coil transition exhibited by a short polyalanine chain, we investigated how the MD simulation results and the Ising-based theoretical values coincide with each other, placing a focus on their equilibrium statistical mechanical properties. Several important physical properties, such as temperature-dependent helix ratio, distribution of the helix-residue number, position-dependent helix ratio, and pair-correlation between residue states were taken up as the proving grounds on which we made a comparison between the all-atom model simulation and the Ising-based theory. As an overall trend, we realized that the Ising-based theoretical results agreed with the all-atom simulation results at least qualitatively, suggesting that the Ising-based model, though very simple, extracts the essence of the phenomenon with respect to the equilibrium properties. On the other hand we found some quantitative disagreements between them. The origins of the observed disagreements are discussed by going into details of the all-atom model.
Structures of polymer field-effect transistor: Experimental and numerical analyses
Authors: Roichman Y. , Tessler N.
Published: July 2002

We compare two basic organic field-effect transistor structures both experimentally and theoretically. By using time-resolved analysis, we gain insight into the mechanisms affecting the performance of these structures. Using a two-dimensional numerical model, we focus on the top contact structure and analyze the difference between the two structures.
Off-center donor impurity in multilayered quantum wires
Authors: Hsieh Cheng-Ying
Published: July 2002

The binding energies of a hydrogenic impurity located at the center and off-center of a multilayered quantum wire (MLQW) are studied within the framework of the effective-mass approximation. The MLQW consists of a GaAs core wire coated by a AlxGa1−xAs cylindrical shell and embedded in the bulk AlyGa1−yAs. It is found that for a small wire radius, the ground state binding energy of hydrogenic impurity located at the center of a MLQW behaves very differently from that of a single-layered QW. Our calculation shows that the binding energy depends on the potential profiles, potential barrier height, impurity position, shell thickness and the difference between the Al concentration contained in the shell region and bulk regions. Our trial function is also used to reproduce the binding energies of a hydrogenic impurity located at the center of a single-layered QW. Good agreement with the previous results is obtained. Therefore, our trial wave function is suitable for single-layered and multilayered QW systems.
Nonlinear oscillations in dusty plasmas with variable charges on dust particles
Authors: Tribeche M. , Houili H. , Zerguini T. H.
Published: July 2002

Recent analysis of the excitation of dust Bernstein–Greene–Kruskal modes [Tribeche et al., Phys. Plasmas 7, 4013 (2000)] is extended to include self-consistently the dust charge variation. The grain charge becomes a new self-consistent dynamical variable, leading to some new and interesting results such as threshold lowering, mode damping, and spatially localized nonlinear structures.
Magnitude and orientation dependence of intermolecular interaction between perfluoroalkanes: High level ab initio calculations of CF4 and C2F6 dimers
Authors: Tsuzuki Seiji , Uchimaru Tadafumi , Mikami Masuhiro , Urata Shingo
Published: July 2002

Intermolecular interaction energies of eight orientation CF4 dimers and seven orientation C2F6 dimers were calculated with electron correlation correction by the second-order Møller–Plesset perturbation (MP2) method. The D3d CF4 dimer and C2h C2F6 dimer have the largest binding energies. Electron correlation correction increases the attraction considerably, while the effects of electron correlation beyond MP2 are small. Electrostatic and induction energies are not large in all cases. This indicates that dispersion interaction is mainly responsible for the attraction. The calculated binding energy of the CF4 dimer (0.69 kcal/mol) is about 60% larger than that of the CH4 dimer (0.44 kcal/mol), while the binding energy of the C2F6 dimer (1.02 kcal/mol) is close to that of the C2H6 dimer (0.90 kcal/mol). The intermolecular separations (C⋯C distance) in the CF4 and CH4 dimers at the potential minima are close (4.0 and 3.8 Å, respectively), while the separation in the C2F6 dimer (4.8 Å) is appreciably larger than that in the C2H6 dimer (4.0 Å). The larger intermolecular separation in the C2F6 dimer reduces dispersion energy. Therefore the binding energies of the C2F6 and C2H6 dimers are not largely different. The molar volume of C2F6 is substantially larger than that of C2H6 due to bulky fluorine atoms. The small difference of the binding energies suggests that the large molecular volume of perfluoroalkanes is the cause of their small heats of vaporization per volume.
Spectral measurements of Rayleigh–Taylor mixing at small Atwood number
Authors: Wilson Peter N. , Andrews Malcolm J.
Published: July 2002

Temperature measurements have been made in a buoyancy driven mixing layer created by an unstable temperature gradient in water. Experiments were performed with a temperature difference of 5 °C, with a corresponding Atwood number of 7.5×10−4. Two types of analyses were used to determine density fluctuation correlations. The first analysis determined density fluctuation correlations from the mean density profiles, which is sufficient for a two-fluid distribution of the density where there was no molecular mixing. The second analysis used measurements taken from a continuous distribution of density, and thus included molecular mixing associated with heat diffusion. The thermocouples used for temperature measurements enabled the collection of large sample sizes and thus a detailed examination of molecular mix fractions, spectral properties of the density fluctuations, and probability distributions of the density through the mixing layer.
Ultraviolet photoresponse of porous ZnO thin films prepared by unbalanced magnetron sputtering
Authors: Sharma Parmanand , Mansingh Abhai , Sreenivas K.
Published: July 2002

Fast ultraviolet photoresponse is observed in ZnO thin films prepared by unbalanced magnetron sputtering. Films with a porous microstructure and a mixed (100), (002) and (101) crystallographic orientation exhibit photoresponse with good linearity and minimal aging effects. A fast rise time of 792 ms and a fall time of 805 ms are observed under low intensity (9.5 mW/cm2, λ=365 nm) ultraviolet light.
Polarization properties of ultrafast white-light continuum generated in condensed media
Authors: Midorikawa Katsumi , Kawano Hiroyuki , Suda Akira , Nagura Chihiro , Obara Minoru
Published: July 2002

Polarization properties of a white-light continuum generated by 392 nm femtosecond laser pulses in transparent condensed media is investigated. Self-induced polarization change of the generated white-light continuum is observed in an isotropic material with a cubic crystal structure such as CaF2 and LiF. The experimental observation is explained by considering self-induced birefringence.
A new interpretation of the CrO− photoelectron detachment spectra
Authors: Bauschlicher Charles W. , Gutsev G. L.
Published: July 2002

Complete active space self-consistent field/multireference configuration interaction calculations are performed on CrO− and CrO. The ground state of CrO− is identified as Π4, not Σ+6, as recently suggested. We assign the experimental detachment features to the seven one-electron processes arising from the two ion states.
Surface morphology and crystal quality of low resistive indium tin oxide grown on yittria-stabilized zirconia
Authors: Ohta Hiromichi , Orita Masahiro , Hirano Masahiro , Hosono Hideo
Published: July 2002

Highly electrically conductive (resistivity: 1×10−4 Ω cm) indium tin oxide (ITO) thin films were grown heteroepitaxially on (111) and (100) surfaces of yttria-stabilized zirconia (YSZ) at a growth temperature of 900 °C using a pulsed-laser deposition technique, and their crystal quality and surface morphology were evaluated by using high-resolution x-ray diffraction and an atomic force microscope. Higher growth temperature, the use of a cleaved surface as a substrate, and an increase in oxygen pressure are essential to fabricate an ITO thin film with an atomically flat surface. The full width at half maximum of out-of-plane x-ray rocking curves of ITO (222) grown on YSZ (111) and of ITO (400) on YSZ (100) were 54 and 720 arcseconds, respectively, which indicates that (111)-oriented ITO films exhibited higher crystal quality than (100)-oriented ITO films. The ITO film was grown on YSZ (111) by the three-dimensional spiral growth mode, with flat terraces and steps corresponding to (222) plane spacing of 0.293 nm, and the grain size was reduced with increasing oxygen pressure during ITO film growth, to improve overall surface flatness. On the other hand, only a columnar structure was observed in the (100)-oriented ITO film surface.
Thermal magnetic noise and spectra in spin valve heads
Authors: Zhu Jian-Gang
Published: July 2002

In this article we present a quantitative micromagnetic modeling analysis of thermally activated magnetic noise in spin valves heads at deep submicron track widths. It is found that, for these spin valve heads, the thermal magnetic noise is at a magnitude that is comparable to that of the head’s Johnson noise. Reducing the sensor track width by keeping the same aspect ratio and film layer thickness will not necessarily yield an increase of thermal magnetic noise, which is attributed to the accompanying increase of the demagnetization field within the sensing layer. However, both the magnitude of noise and the noise spectra are strong functions of the sensor stripe height. An excessive stripe height will yield significantly higher thermal magnetic noise.
The molecular origins of the two-dimensional Raman spectrum of an atomic liquid. II. Instantaneous-normal-mode theory
Authors: Ma Ao , Stratt Richard M.
Published: July 2002

One of the most direct outcomes one could have envisioned from the two-dimensional (fifth-order) nonresonant Raman spectroscopy of liquids would have been a verdict on usefulness of instantaneous normal modes (INMs) as a basis for describing ultrafast liquid dynamics. Seeing the echo predicted by standard INM theory would have been persuasive evidence that this dynamics could really be thought of in terms of independent harmonic intermolecular vibrations. However, molecular dynamics calculations on liquid Xe show that there is no echo, implying that dynamical anharmonicities can have qualitative consequences even on ultrafast time scales—a notion seemingly inimical to the entire INM concept. What we show in this paper is that the fifth-order Raman spectrum can be understood within the confines of INM ideas, and from a fully molecular perspective, simply by including the contributions of the pure dephasing undergone by each INM mode. We show, in particular, that this dephasing stems from the adiabatic variation of the INM frequencies and of the cubic anharmonicity along each mode, and that lack of an echo can be understood from the magnitudes of the instantaneous anharmonicities alone. The resulting detailed picture of fifth-order Raman spectroscopy allows us, at least for liquid Xe, to assign a definitive mechanism for the origin of the signal; the spectrum is largely a measure of the liquid’s dynamical anharmonicities and not of any nonlinear coupling of the liquid dynamics to the polarizability.
Intermittency, current flows, and short time diffusion in interacting finite sized one-dimensional fluids
Authors: Pal Subrata , Srinivas Goundla , Bhattacharyya Sarika , Bagchi Biman
Published: July 2002

Long time molecular dynamics simulations of one-dimensional Lennard-Jones systems reveal that while the diffusion coefficient of a tagged particle indeed goes to zero in the very long time, the mean-square displacement is linear with time at short to intermediate times, allowing the definition of a short time diffusion coefficient [Lebowitz and Percus, Phys. Rev. 155, 122 (1967)]. The particle trajectories show intermittent displacements, surprisingly similar to the recent experimental results [Wei et al., Science 287, 625 (2000)]. A self-consistent mode coupling theory is presented which can partly explain the rich dynamical behavior of the velocity correlation function and also of the frequency dependent friction. The simulations show a strong dependence of the velocity correlation function on the size of the system, quite unique to one dimensional interacting systems. Inclusion of background noise leads to a dramatic change in the profile of the velocity time correlation function, in agreement with the predictions of Percus [Phys. Rev. A 9, 557 (1974)].
Excess low-frequency noise in AlGaN/GaN-based high-electron-mobility transistors
Authors: Vitusevich S. A. , Danylyuk S. V. , Klein N. , Petrychuk M. V. , Sokolov V. N. , Kochelap V. A. , Belyaev A. E. , Tilak V. , Smart J. , Vertiatchikh A. , Eastman L. F.
Published: July 2002

The low-frequency 1/f noise characteristics of AlGaN/GaN high-electron-mobility transistors with gate length scaled down to 150 nm grown on sapphire by metalorganic chemical vapor deposition have been studied. Certain features of the 1/f noise have been revealed in these short-gate transistors. The low-frequency noise spectra show drastically different behavior depending on the gate voltage VG in the range of low (VGt⩽VG⩽0) and high (VG<VGt) biases. The noise spectra-gate bias dependences allow one to distinguish a spatial redistribution of effective noise sources in the transistor channel. The Hooge parameter has been deduced separately for the ungated region, αHp≃10−3, and for the gated region, αHa≃2×10−4, of the transistor channel. These values are as low as those previously observed in nitride heterostructures grown on silicon carbide substrates.
Local fluorescent probes for the fluorescence resonance energy transfer scanning near-field optical microscopy
Authors: Shubeita G. T. , Sekatskii S. K. , Dietler G. , Letokhov V. S.
Published: July 2002

We present fluorescence resonance energy transfer (FRET) images of donor dye molecule clusters recorded using a local fluorescence probe for scanning near-field optical microscopy (SNOM): standard apertured SNOM fiber tip coated with the 30–100-nm-thick polymer layer stained with the acceptor dye molecules. The tip works as a “self-sharpening pencil”: the apical layers of the FRET-active tip coating are mechanically worn out during scanning thus continuously exposing a fresh active apex to continue imaging. Only a few tens of acceptor molecules are used to form the optical images, and using such an approach spatial resolution better than the size of the aperture is achievable.
Plasma parameter limits of magnetically confined low temperature plasmas from a combined particle and power balance
Authors: Lechte Carsten , Stöber Jennifer , Stroth Ulrich
Published: July 2002

A global particle and power balance calculation is carried out to assess the accessible plasma parameter range in a toroidal confined low temperature plasma. Power and particle sources and sinks are calculated from the relevant atomic processes. The balance is fulfilled for hyperbolic-like curves in the temperature–density plane. They constitute an upper limit accessible for plasmas at a given heating power, neutral density, and sort of gas. The calculations are compared with results from the TJ-K torsatron [N. Krause, C. Lechte, U. Stroth, S. Niedner, J. Stöber, R. Westphal, E. Ascasibar, and J. Alonso, “The Torsatron TJ-K, a toroidal plasma experiment for low-temperature plasma research,” Rev. Sci. Instrum. (in press).
Quantum information geometry and standard purification
Authors: Jenčová Anna
Published: July 2002

We investigate relations between Uhlmann’s parallelism, monotone Riemannian metrics and dual affine connections on the space of density matrices.
Normal-incidence voltage-tunable middle- and long-wavelength infrared photoresponse in self-assembled InAs quantum dots
Authors: Chen Zhonghui , Kim Eui-Tae , Madhukar Anupam
Published: July 2002

We report the realization of electron intraband absorption based middle- (∼5.6 μm) and long- (∼10 μm) wavelength infrared (IR) photoresponse for normally incident radiation on InGaAs-capped GaAs(001)/InAs quantum dots (QDs) in a n–i(QD)–n structure. The relative photoresponse in this dual-wavelength structure is tunable up to two orders of magnitude with bias. The full width at half maximum of the long-wavelength IR intraband photocurrent peak at 80 K is as narrow as 8.2 meV.
Mechanisms affecting the photoluminescence spectra of GaInNAs after post-growth annealing
Authors: Tournié E. , Pinault M.-A. , Guzmán A.
Published: July 2002

We have investigated by photoluminescence spectroscopy and x-ray diffraction the influence of ex situ postgrowth annealing on the properties of a series of dedicated Ga(In)(N)As ternary and quaternary quantum wells (QWs) confined by various barrier layers. We show that the low growth temperature and not N per se, is largely responsible for the low radiative efficiency of Ga(In)NAs QWs. Furthermore, postgrowth annealing induces a blueshift of the photoluminescence line in the case of quaternary GaInNAs QWs only, while x-ray diffraction reveals the absence of compositional change. We conclude with the occurrence of a local reorganization of the N-bonding configuration within the GaInNAs quaternary material during annealing.
Relation between distribution of states and the space-charge-region capacitance in semiconductors
Authors: Balberg I.
Published: July 2002

In contrast with recent suggestions we show that frequency dependent capacitance-voltage (C-V) characteristics can yield information on the state distribution in the forbidden gap of semiconductors which have a continuous state distribution there. For this purpose we have applied an analysis which is based on the solution of the Poisson equation in various sections of the space-charge region. Then, by using a new recursion approach we found new general expressions for the frequency and temperature dependence of the C-V characteristics. The present work yields analytic results and a transparent physical picture so that clear correlation is obtained between features of the above characteristics and features of the state distribution. In particular, it is shown that under deep depletion the well-known linear 1/C2 vs V relation is maintained regardless of the state distribution. This enables the use of the frequency, or temperature, dependence of the corresponding slope for the evaluation of the state distribution from experimental data.
Reaction of atomic fluorine with silicon
Authors: Ninomiya Ken , Suzuki Keizo , Nishimatsu Shigeru , Okada Osami
Published: July 2002

The etch rate of Si with F atoms was measured by the use of F2 microwave plasma over a range of discharge pressures between 2.7×10−2 and 17 Pa. Fluorine atom concentration in the plasma was determined over the same pressure range by means of both gas-phase titration and actinometry using Ar gas. A Si surface etched at 1.0×10−1, 5.3×10−1, 1.3, and 5.3 Pa was analyzed with XPS without exposing the surface to room air. A linear relation was obtained between the Si etch rate and the F atom concentration at discharge pressures between 2.7×10−2 and 2.7 Pa. The reaction probability of F atoms with Si to yield SiF4 was determined from the linear relation to be 0.1 for a Si surface at about 300 K. When the discharge pressure was higher than 1.3 Pa, the surface became rather strongly oxidized by O atoms resulting from residual gases. This surface oxidation results in a slight saturation of the Si etch rate at about 10 Pa.
New method for vitrifying water and other liquids by rapid cooling of their aerosols
Authors: Mayer Erwin
Published: July 2002

A method for the vitrification of pure liquid water and dilute aqueous solutions is described which is the only one without a liquid cryomedium for heat transfer: rapid cooling of aqueous aerosol droplets on a solid cryoplate. This method is not limited to water and aqueous solutions, but can be used for the vitrification of any liquid aerosol, the only impurity being some codeposited vapor. The method can be applied in diverse fields such as cryobiology, cryomicroscopy, and low-temperature spectroscopy of water and dilute aqueous solutions to avoid the formation of crystalline ice.
Interpretation of capacitance versus voltage measurements in the presence of a high density of deep levels
Authors: Shiau Jeng-Jye , Fahrenbruch Alan L. , Bube Richard H.
Published: July 2002

We present a detailed discussion of the physical significance of measurements of capacitance as a function of applied bias voltage to a Schottky barrier when the semiconductor involved contains not only shallow levels but also deep levels. Whether deep levels are affecting the capacitance can be determined by measuring the capacitance versus voltage as a function of frequency or of temperature, and observing the frequency or temperature dependence of the slope of a plot of inverse capacitance as a function of voltage compared to the frequency or temperature dependence of the slope of a plot of inverse squared capacitance as a function of voltage. The slope of the inverse capacitance as a function of voltage should not be a function of frequency or temperature regardless of whether deep levels are significant or not, whereas the slope of the inverse squared capacitance as a function of voltage should depend on frequency and/or temperature if deep levels are significant. Examples of this behavior are given from measurements on CdTe single crystals and thin films.
Epitaxial growth and the crystallographic, dielectric, and pyroelectric properties of lanthanum-modified lead titanate thin films
Authors: Iijima Kenji , Takayama Ryoichi , Tomita Yoshihiro , Ueda Ichiro
Published: July 2002

Using an rf-magnetron sputtering method, highly c-axis-oriented La-modified PbTiO3 (PLT) thin films with compositions of Pb1−xLaxTi1−x/4O3, where x=0.05, 0.10, and 0.15, have been obtained on MgO single-crystal and epitaxial Pt thin-film substrates under conditions of low gas pressure and low deposition rate. The degree of c-axis orientation of the PLT films decreases, and the tetragonality of PLT becomes smaller with increasing La content. The Curie point of the films decreases at a rate of 18 °C/at. % of La with an increase of La content. D-E hysteresis loops were observed, and these became slim and symmetric with increasing La. It was found that significant pyroelectric currents are detected on all as-grown specimens even without a poling treatment, and the directions are the same in all specimens. Relative dielectric constant εr decreases, and pyroelectric coefficient γ increases with increasing degree of c-axis orientation. εr and γ became large with increase of La content in the films. Considering the figure of merit for pyroelectric infrared detection and the temperature coefficient of γ, it was concluded that PLT films with x=0.10 were good material for pyroelectric infrared detectors.
Influence of Cd vacancies on the photoluminescence of CdTe
Authors: Figueroa Juan M. , Sánchez-Sinencio F. , Mendoza-Alvarez J. G. , Zelaya O. , Vázquez-López C. , Helman J. S.
Published: July 2002

Cd vacancies are identified as responsible for both the 1.55-eV narrow band and the 1.591-eV bound exciton peak of the CdTe photoluminescence spectrum. The characteristic 1.44-eV broadband does not seem to be related to luminescent centers involving those vacancies.
TbxNdy(FeCo)1−x−y: Promising materials for magneto-optical storage?
Authors: Reim W. , Gambino R. J. , Ruf R. R. , Plaskett T. S.
Published: July 2002

A systematic study of the pseudoternary system TbxNdy(FeCo)1−x−y is presented focusing on key parameters for magneto-optical storage applications. For compositions with perpendicular anisotropy at room temperature (x>0.08; 0.4>z+y>0.15) the Kerr rotation (λ=633 nm) increases with FeCo concentration for a given x/y ratio and increases also with the Nd concentration for a given FeCo concentration. The latter effect is more pronounced at λ=420 nm than at λ=800 nm. Room-temperature compensation is found at x=0.2 for all of these compounds indicating a Nd moment parallel and, in magnitude, similar to the FeCo moment. The high-temperature magneto-optical measurements revealed a significant lowering of the anisotropy constant at elevated temperatures with Nd concentration, which leads to a loss of square loops already 100 K below TC for certain compounds.
Maxwell–Wagner–Silars relaxations due to glass occlusions in a thermoset composite
Authors: Aldrich P. D. , McGee R. L. , Yalvaç S. , Bonekamp J. E. , Thurow S. W.
Published: July 2002

Maxwell–Wagner–Silars (MWS) dielectric relaxations have been studied in thermoset composites made with hollow glass microspheres and reinforced with aramid fiber. Over the temperature range reported (140–230 °C) the glass microspheres show a conductivity of 10−10–10−5 (Ω cm)−1 so that MWS loss peaks fall in the 102–105 Hz frequency range. The apparent activation energy for the relaxation is about 20 kcal/mole. The observed MWS relaxation times depend only on temperature and not on volume fraction of microspheres as predicted by MWS theory. Also, the enhancement of activation energy for the relaxation over the activation energy for conduction of the glass seems to be explainable from the standpoint of the frequency and temperature dependence of the glass dielectric constant.
GaAs films grown by vacuum chemical epitaxy using thermally precracked trimethyl-arsenic
Authors: Fraas L. M. , McLeod P. S. , Weiss R. E. , Partain L. D. , Cape J. A.
Published: July 2002

Trimethyl-arsenic (TMAs) is used as a source of arsenic for GaAs film growth. In the process used, vacuum chemical epitaxy, TMAs is thermally decomposed into arsenic upstream in a hot cracker furnace. The arsenic and stable hydrocarbons are then transported in vacuum without condensation to the epitaxial growth zone. The hole carrier concentration and carbon content in grown films are studied via Hall, electrochemical profile, and secondary ion mass spectroscopy as a function of cracker furnace design. It is shown that when the TMAs decomposition efficiency is poor, the carbon content can be as high as 1019/cm3 but for a more efficient cracker, the carbon content can be reduced into the 1016/cm3 range. Toxic injury hazards can be reduced substantially by substituting TMAs for the more widely used arsine in GaAs growth systems.
Evidence for field-assisted thermal emission of holes from deep mobility gap states in amorphous semiconductors from xerographic dark discharge measurements
Authors: Kasap S. O. , Baxendale M. , Juhasz C.
Published: July 2002

The xerographic depletion discharge model describing the dark decay of the surface potential on a corona or capacitively charged amorphous semiconductor film is further developed by including an electric field enhanced charge carrier emission probability from deep mobility gap states via a Poole–Frenkel type of coulombic potential barrier lowering. An expression is derived for the dependence of the xerographic depletion time on the initial charging voltage. Xerographic dark discharge experiments carried out on vacuum-deposited a-Se:Te alloy photoconductor films show good agreement with the theory and indicate that the field-assisted hole emission occurs from an exponential distribution of midgap localized states.
Band-gap narrowing in semi-insulating gallium arsenide
Authors: Hrivnák Ľubomír
Published: July 2002

A model of energy band-gap narrowing in SI GaAs crystals doped by chromium is proposed in order to explain the higher values of intrinsic carrier densities deduced from galvanomagnetic measurements in some Cr-doped SI GaAs crystals by various authors. This model is based on the screening of electron-hole interaction due to the chromium Cr2⇄Cr3+ state transitions. Also some other possible reasons for band-gap narrowing in SI GaAs are discussed.
Growth and characterization of lattice-matched CaxSr1−xF2 on GaAs(100)
Authors: Sinharoy S. , McMullin P. G. , Greggi J. , Lin Y. F.
Published: July 2002

The epitaxial growth and characterization of the structural, morphological, interfacial, and electrical properties of lattice-matched Ca0.43Sr0.57F2 on GaAs(100) are reported here. The ∼200 nm films were grown at 500 °C on the GaAs(100) substrates that had been cleaned by annealing at 600 °C. Nomarski optical microscopy, transmission electron microscopy (TEM), scanning electron microscopy, and reflection high-energy electron diffraction results showed that the films were smooth and crackfree, with good crystalline quality. TEM showed evidence of two general types of extended defects in the film which occur at or near the film/substrate interface region. Film resistivity was found to be (3.6±0.75)×1013 Ω cm, and the breakdown field strength was (5.8±1.4)×105 V/cm. However, the breakdown in this case represented a nondestructive conduction process, as opposed to the catastrophic and irreversible change observed in previous studies. The dielectric constant of the films was measured to be 7.43±0.22. Capacitance-voltage measurements indicated that there could be a high density of surface states at the interface that pin the Fermi level within the gap region.
Ion transit through capacitively coupled Ar sheaths: Ion current and energy distribution
Authors: Greene W. M. , Hartney M. A. , Oldham W. G. , Hess D.W.
Published: July 2002

The ion current and ion energy distribution (IED) of Ar+ and ArH+ impinging on a grounded surface immersed in capacitively coupled Ar plasmas have been measured as a function of pressure, applied rf voltage amplitude (Vrf), interelectrode gap, and sampling orifice size. A maximum in ion current occurs at high Vrf and intermediate electrode spacing. rf modulation of the collisionless IED occurs at high pressure and high Vrf and is caused by reduction of the sheath dimension under these conditions. Collisional shift to lower ion energy is also noted at high pressure. A low-energy peak at ∼10 eV is observed under high pressure and ion current conditions. Larger orifice sizes increase the collisions occurring downstream from the orifice as indicated by collisional energy shifts in the IED and a decrease in ion current density.
Microstructure of sputtered garnet films for magneto-optical recording media
Authors: Shono K. , Kano H. , Koshino N. , Ogawa S.
Published: July 2002

Sputtered garnet films have a high potential for use as a magneto-optical recording medium. However, the medium noise is thought to be large because of its crystal boundaries. We investigated the microstructure of films on GGG substrate, using TEM and SEM. The film crystallized by postannealing shows a rectangular hysteresis loop with high coercivity, and has an uneven surface. This is because the direction and size of each crystallite is not uniform. However, the film crystallized during deposition has quite a smooth surface, but does not have magnetic properties suitable for use in magneto-optical recording. This film has a mosaiclike structure, in which all crystallites are uniformly oriented. We found that ion implantation of Ne+ and successive annealing of the film crystallized during deposition improved the magnetic properties without roughening the surface.
Piezoelectric effects in strained-layer superlattices
Authors: Smith D. L. , Mailhiot C.
Published: July 2002

Because zinc-blende structure semiconductors are piezoelectric, polarization fields can be generated in the constituent materials of strained-layer superlattices by lattice-mismatch-induced strain. The orientation of the polarization fields depends on the superlattice growth axis. Because one of the constituent layers of the superlattice is in biaxial tension and the other is in biaxial compression, the sign of the polarization field is opposite in the two constituent layers making up the superlattice period. Thus, sheets of divergence of polarization occur at the interface for a longitudinal induced polarization and sheets of curl of polarization occur at the interface for a transverse induced polarization. For a [111] growth axis, the induced polarization is purely longitudinal; for a [110] growth axis, the induced polarization is purely transverse. For a general growth axis the induced polarization has both longitudinal and transverse components. The sheets of divergence of polarization generate internal electric fields and the sheets of curl of polarization generate internal electric displacement fields. The internal electric fields are always purely longitudinal and the internal electric displacement fields are always purely transverse. The magnitude of these fields can be very large.
A field-effect quantum-well laser with lateral current injection
Authors: Ahn D. , Chuang S. L.
Published: July 2002

Polarization-dependent gain switching in a field-effect quantum-well laser with lateral current injection is studied. We use the k⋅p method for the optical dipole matrix and take into account the intraband relaxation. Gain switching is achieved by the field effect from a gate terminal in a lateral current injection quantum-well laser structure. It is shown that the peak gain exhibits a red shift and the peak-gain amplitude decreases with an increasing electric field for the TE mode. The TM mode is less affected by the external field.
Photochemical vapor deposition of amorphous silica films using disilane and perfluorosilanes: Defect structures and deposition mechanism
Authors: Nonaka Hidehiko , Arai Kazuo , Fujino Yoshiyuki , Ichimura Shingo
Published: July 2002

Amorphous silicon dioxide films were deposited from oxygen, disilane (Si2H6), and perfluorosilanes (Si2F6 or SiF4) by photochemical vapor deposition using a deuterium lamp at a substrate temperature of as low as 200 °C. It was found that by mixing Si2F6, defects such as H and OH in the films were effectively removed with an enhancement in the growth rate and a slight doping of fluorine into the films, while SiF4 had no effect except a little doping of fluorine. The generation and extinction of defects including H, OH, and SiSi were investigated quantitatively by measuring infrared spectra and vacuum ultraviolet absorptions at the optical band edge. The model on the deposition process was proposed that photodissociated F-containing radicals eliminate H and activate the growing surface, resulting in enhancing the deposition rate.
Copper-catalyzed etching of silicon by F2: Kinetics and feature morphology
Authors: Selamoglu Nur , Mucha John A. , Flamm Daniel L. , Ibbotson Dale E.
Published: July 2002

The copper-catalyzed fluorination of silicon is first order in [F2] and in [Cu]s until the coverage reaches ∼4 monolayers. Above ∼4 monolayers the reaction rate is zero order in copper, suggesting a limited number of catalytically active Cu/Si sites. Copper islands form at high coverages, above saturation, and provide a reservoir of catalyst. The limited rate of surface diffusion of copper leads to anisotropic etching and feature size-dependent etch depths. The copper compounds, CuF2 and CuO, and copper silicides, Cu5Si and Cu3Si, all catalyzed the F2-Si reaction which suggests that they are all converted to the same active species. The results can be explained by mechanisms involving copper fluorides or copper silicides as active intermediates.
Electrostrictions in high-power soliton generator
Authors: Ikezi H. , Lin-Liu Y. R. , Ohkawa T. , deGrassie J. S.
Published: July 2002

Electrostriction effects are considered in a high power dielectric loaded transmission line designed to generate solitons. The Čerenkov emission of elastic waves from the metal-dielectric interface produces the largest strain among the strain producing mechanisms. The expression for strain as a function of electric field strength is found. The signal loss due to the emission of elastic waves is shown to be insignificant.
Thermomagnetic mechanical heat engines
Authors: Solomon Dan
Published: July 2002

Thermomagnetic heat engines that convert thermal energy into mechanical energy are described. These heat engines utilize the thermomagnetic effect which is a property of ferromagnetic materials whereby their magnetization changes with temperature. A computer model is developed from which the performance of the device can be determined. Design curves are included which give the overall dimension, operating parameters, and thermal efficiency of thermomagnetic heat engines operating between a thermal source of 90, 150, or 225 °C and a thermal sink of 25 °C.
Model calculations of the angular dependence of the switching field of imperfect ferromagnetic particles with special reference to barium ferrite
Authors: Richter H. J.
Published: July 2002

Based on a one-dimensional model of an infinite material with a slab in which the magnetocrystalline anisotropy is zero [A. Aharoni, Phys. Rev. 119, 127 (1960)], the angular dependence of the switching field is calculated. The results are compared with experimental data of barium ferrite. It is found that for small defect regions the predictions agree well with experimental data, but for bigger ones considerable differences occur. The shape anisotropy effect as well as the effects of inhomogeneous reversals in ideal specimens are also discussed.
Role of strained layer superlattices in misfit dislocation reduction in growth of epitaxial Ge0.5Si0.5 alloys on Si(100) substrates
Authors: Hull R. , Bean J. C. , Leibenguth R. E. , Werder D. J.
Published: July 2002

We investigate the role of strained layer superlattices in threading dislocation reduction in the growth of Ge0.5Si0.5 alloys on Si(100) substrates by molecular-beam epitaxy. Several superlattice structures are studied with zero, negative, and positive net strains with respect to a Ge0.5Si0.5 buffer layer. Control samples consisting of uniform strained layers are also grown for each superlattice structure. Transmission electron microscopy analysis of defect densities is found to be hampered by defect losses from thin foils, particularly in the plan view geometry. It is found that although strained interfaces are effective at deflecting threading dislocations into the interfacial plane, little surface threading dislocation density reduction is observed as a function of the presence of the superlattices for dislocation densities of the order 108 cm−2. This observation may be understood in terms of threading dislocation propagation at strained interfacial planes, and a simple predictive model is developed for defect interaction probabilities.
Optical and electrical properties of isotype crystalline molecular organic heterojunctions
Authors: Forrest S. R. , Leu L. Y. , So F. F. , Yoon W. Y.
Published: July 2002

We have studied the electrical and optical characteristics of isotype p-P organic heterojunctions (HJ) consisting of CuPc (copper phthalocyanine) and PTCDA (3,4,9,10-perylenetetracarboxylic dianhydride). It is found that the charge-transport properties of the heterojunction are limited by thermionic emission of holes over the energy barrier at the CuPc/PTCDA heterojunction at low forward and reverse bias, and by series resistance at high voltage. The heterojunction energy barrier at the CuPc/PTCDA valence-band edge was measured using both current-voltage and capacitance-voltage analysis and was found to be ΔEvC,P=0.48±0.05 eV. Similar measurements made for HJs consisting of CuPc and PTCDA in combination with another perylene-based material, 3, 4, 9, 10-perylenetetracarboxylic-bis-benzimidazole (PTCBI), suggest that the band offsets for these three materials follow a transitive relationship. That is, ΔEvC,P=ΔEvC,B−ΔEvB,P, where subscripts C, P, and B refer to CuPc, PTCDA, and PTCBI, respectively. The results are discussed in terms of energy-band and molecular energy-level models.
Development of a bulk microdefect analyzer for Si wafers
Authors: Moriya Kazuo , Hirai Katsuyuki , Kashima Kazuyoshi , Takasu Shin’ichiro
Published: July 2002

A new inspection system using laser scattering was developed to characterize bulk microdefects in intrinsic gettering processed Si wafers. The density profiles of bulk microdefects and the width of the denuded zone in Si wafers were measured by this system without any etching treatment. The minimum size observed, as a particle, was estimated at several tens of nm in diameter by comparing a scattering image with a transmission electron microscope observation. From an analysis of the scattering intensity, differences of up to 10% in diameter were recognizable.