bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of a photon assisted field emission device
Authors: Jensen K. L. , Lau Y. Y. , McGregor D. S.
Published: July 2002

A field emitter array held at the threshold of emission by a dc gate potential from which current pulses are triggered by the application of a laser pulse on the backside of the semiconductor may produce electron bunches (“density modulation”) at gigahertz frequencies. We develop an analytical model of such optically controlled emission from a silicon tip using a modified Wentzel–Kramers–Brillouin and Airy function approach to solving Schrödinger’s equation. Band bending and an approximation to the exchange-correlation effects on the image charge potential are included for an array of hyperbolic emitters with a distribution in tip radii and work function. For a simple relationship between the incident photon flux and the resultant electron density at the emission site, an estimation of the tunneling current is made. An example of the operation and design of such a photon-assisted field emission device is given.
Plasma generation and confinement in a toroidal magnetic cusp
Authors: Egedal J. , Fasoli A. , Porkolab M. , Tarkowski D.
Published: July 2002

The first measurements of plasma parameters in a discharge created by electron cyclotron resonance heating in a toroidal cusp configuration are discussed along with the predictions of particle orbits and confinement from a guiding center model. The configuration appears to be suitable for basic investigations of the physics of plasma flows and instabilities around a magnetic null, hence of magnetic reconnection.
Importance sampling and theory of nonequilibrium solvation dynamics in water
Authors: Geissler Phillip L. , Chandler David
Published: July 2002

We have devised a novel importance sampling method for nonequilibrium processes. Like transition path sampling, the method employs a Monte Carlo procedure to confine or bias the search through trajectory space. In this way, molecular dynamics trajectories consistent with the nonequilibrium dynamics of interest are generated efficiently. Using results of this sampling, we demonstrate that statistics of the energy gap between a solute’s electronic states are Gaussian throughout the dynamics of nonequilibrium solvation in water. However, these statistics do change in time, reflecting linear response that is nonstationary. Discrepancies observed between the dynamics of nonequilibrium relaxation and of equilibrium fluctuations are thus explained. We analyze a simple Gaussian field theory that accounts for this nonstationary response.
Lie algebraic approach to the construction of (2+1)-dimensional lattice-field and field integrable Hamiltonian equations
Authors: Błaszak Maciej , Szum Andrzej
Published: July 2002

Two different methods for the construction of (2+1)-dimensional integrable lattice-field and field Hamiltonian dynamical systems are presented. The first method is based on the so-called central extension procedure applied to the Lie algebra of shift operators and the Lie algebra of pseudodifferential operators. The second method is the so-called operand formalism. Both methods allow a construction of some new integrable nonlinear Hamiltonian lattice-field and field equations in (2+1)-dimensional space.
Do grain boundaries assist S diffusion in polycrystalline CdS/CdTe heterojunctions?
Authors: Yan Y. , Albin D. , Al-Jassim M. M.
Published: July 2002

We report on a transmission electron microscopy and energy-dispersive x-ray spectroscopy study of S diffusion in polycrystalline CdS/CdTe heterojunctions. We find that grain boundaries significantly assist S diffusion in the CdTe layer when the CdTe is grown without the presence of oxygen, i.e., the S diffuses more easily along the grain boundaries than in the grains. However, grain boundaries do not enhance the S diffusion in CdTe when it is grown in the presence of oxygen. The reason is likely to be the formation of Cd–O bonds at the grain boundaries, which are resistance to the S diffusion.
Effective mobilities in pseudomorphic Si/SiGe/Si p-channel metal-oxide-semiconductor field-effect transistors with thin silicon capping layers
Authors: Palmer M. J. , Braithwaite G. , Grasby T. J. , Phillips P. J. , Prest M. J. , Parker E. H. C. , Whall T. E. , Parry C. P. , Waite A. M. , Evans A. G. R. , Roy S. , Watling J. R. , Kaya S. , Asenov A.
Published: July 2002

The room-temperature effective mobilities of pseudomorphic Si/Si0.64Ge0.36/Si p-metal-oxidesemiconductor field effect transistors are reported. The peak mobility in the buried SiGe channel increases with silicon cap thickness. It is argued that SiO2/Si interface roughness is a major source of scattering in these devices, which is attenuated for thicker silicon caps. It is also suggested that segregated Ge in the silicon cap interferes with the oxidation process, leading to increased SiO2/Si interface roughness in the case of thin silicon caps.
Fractional differential forms
Authors: Cottrill-Shepherd Kathleen , Naber Mark
Published: July 2002

A generalization of exterior calculus is considered by allowing the partial derivatives in the exterior derivative to assume fractional orders. That is, a fractional exterior derivative is defined. This is found to generate new vector spaces of finite and infinite dimension, fractional differential form spaces. The definitions of closed and exact forms are extended to the new fractional form spaces with closure and integrability conditions worked out for a special case. Coordinate transformation rules are also computed. The transformation rules are different from those of the standard exterior calculus due to the properties of the fractional derivative. The metric for the fractional form spaces is given, based on the coordinate transformation rules. All results are found to reduce to those of standard exterior calculus when the order of the coordinate differentials is set to one.
Axial high-temperature superconducting-quantum-interference-device gradiometer composed of magnetometers with a monolithic feedback and compensation coil
Authors: Yokosawa Koichi , Oyama Hiroshi , Kuriki Shinya , Suzuki Daisuke , Tsukada Keiji
Published: July 2002

A first-order axial gradiometer has been constructed using two high-critical-temperature superconducting-quantum-interference-device magnetometers having a double-pickup loop configuration on bicrystal substrates. The magnetometer, which had a slot-type structure but no weak links on the pickup loops, can be operated steadily in an unshielded environment after in situ cooling. The gradiometer was formed by connecting the feedback and the compensation coils of the two magnetometers in series using a normal conductive wire. Sufficiently high noise reduction (31 dB at 1 Hz) was achieved without any need for adjustments and low-noise magnetocardiograms were obtained with the gradiometer in a moderately magnetically shielded room.
Equations of State for Cu, Ag, and Au for Wide Ranges in Temperature and Pressure up to 500 GPa and Above
Authors: Holzapfel W. B. , Hartwig M. , Sievers W.
Published: July 2002

New constraints on the volume dependence of the Grüneisen parameter (γ(V)) are derived from a comparison of earlier shock wave data with more recent ultrasonic data for the bulk modulus K0 and its pressure derivative K0′ in the frame of a rigorous Mie–Grüneisen model. This model uses a specially “Modified pseudo-Debye–Einstein model” for an accurate representation of the thermal energy and pressure. Within this framework, previous discrepancies between shock wave and static data concerning the equations of state for various reference materials (like Cu, Ag, and Au) are resolved, the corresponding pressure scale is refined, and the uncertainties in this scale are estimated.
Optical signal coupling in microchannel plate detectors with a subnanosecond performance
Authors: Wurz Peter , Schletti Reto
Published: July 2002

For an application in high-performance mass spectrometry we adapted our recent design of a fast microchannel plate detector such that the signal output when registering a single particle is realized via optical impulses which are then forwarded to the data acquisition system. The charge impulse collected at the anode of the detector is converted to a light impulse using a vertical cavity surface emitting laser diode. Such an assembly has the advantage that the electrical circuitry at the anode is very small and thus high signal quality is achieved even in the gigahertz frequency range. Furthermore, such a detector can easily be operated at high electric potentials without the need for capacitive signal coupling.
Rate of diffusion-limited reactions in a cluster of spherical sinks
Authors: Tsao Heng-Kwong , Lu Shin-Yuan , Tseng Chin-Yao
Published: July 2002

The reaction rate is calculated for a cluster of perfectly absorbing, stationary spherical sinks in a medium containing a mobile reactant. The diffusive interactions are accurately taken into account by employing the first-passage technique. The configurations of the clusters include three spheres, four spheres, regular polygons, linear chains, squares, and finite cubic arrays. For a given number of sinks, the reaction rate is decreased with increasing the compactness of the structure due to the screening effect. For a specified configurations, the asymptotic expressions for the reaction rate varying with the number of sinks are confirmed. By comparing results with these “exact” data, the method of multipole expansions up to the dipole level, which is suitable for a finite system of many sinks, proved to be an excellent approximation.
Low-temperature formation of an interfacial buffer layer using monomethylsilane for 3C–SiC/Si(100) heteroepitaxy
Authors: Nakazawa Hideki , Suemitsu Maki
Published: July 2002

By using monomethylsilane (MMS:H3Si–CH3), we have formed a Si1−xCx interfacial buffer layer for 3C–SiC/Si(100) heteroepitaxy at substrate temperature Tf of as low as 450–650 °C, which is compared to the conventional carbonization temperature of 900 °C or higher. The buffer layer allows the subsequent growth of high-quality single-crystalline 3C–SiC films at 900 °C without formation of voids in the Si substrate at the interface. The grown 3C–SiC films degrade for Tf<450 or >650 °C. The low processing temperature as well as the suppressed Si outdiffusion can be related to the inclusion of both Si–H and Si–C bonds within the MMS molecule.
Spatially resolved photoluminescence of inversion domain boundaries in GaN-based lateral polarity heterostructures
Authors: Schuck P. J. , Mason M. D. , Grober R. D. , Ambacher O. , Lima A. P. , Miskys C. , Dimitrov R. , Stutzmann M.
Published: July 2002

Intentionally grown GaN inversion domain boundaries (IDBs) of lateral polarity heterostructures have been spectroscopically imaged at low temperature using high spatial resolution photoluminescence. It is shown that the IDBs are not only optically active, but are more than an order of magnitude brighter than the GaN bulk material. Our findings are in agreement with calculations predicting that IDBs should not adversely affect near-band-gap photoluminescence due to the absence of midgap electronic states. Typical linewidths are on the order of 10–20 meV, however, features less than 0.6 meV are observed. The boundary emission is found to be neither spectrally nor spatially uniform. Also, a strong polarization dependence of the IDB photoluminescence is measured and determined to be oriented parallel to the boundary between GaN of N- or Ga-face polarity.
Effects of vibrational energy relaxation and reverse reaction on electron transfer kinetics and fluorescence line shapes in solution
Authors: Denny R. Aldrin , Bagchi Biman , Barbara Paul F.
Published: July 2002

The existing theoretical formulations of electron transfer reactions (ETR) neglect the effects of vibrational energy relaxation (VER) and do not include higher vibrational states in both the reactant and the product surfaces. Both of these aspects can be important for photo-induced electron transfer reactions, particularly for those which are in the Marcus inverted regime. In this article, a theoretical formulation is presented which describes the two aspects. The formalism requires an extension of the hybrid model introduced earlier by Barbara et al. [Science 256, 975 (1992)]. We model a general electron transfer as a two-surface reaction where overlap between the vibrational levels of the two surfaces create multiple, broad reaction windows. The strength and the accessibility of each window is determined by many factors. We find that when VER and reverse transfer are present, the time dependence of the survival probability of the reactant differs significantly (from the case when they are assumed to be absent) for a large range of values of the solvent reorganization energy (λX), quantum mode reorganization energy (λq), electronic coupling constant (Vel) and vibrational energy relaxation rate (kVER). Several interesting results, such as a transient rise in the population of the zeroth vibrational level of the reactant surface, a Kramers (or Grote–Hynes) type recrossing due to back reaction and a pronounced role of the initial Gaussian component of the solvation time correlation function in the dynamics of electron transfer reaction, are observed. Significant dependence of the electron transfer rate on the ultrafast Gaussian component of solvation dynamics is predicted for a range of values of Vel, although dependence on average solvation time can be weak. Another result is that, although VER alters relaxation dynamics in both the product and the reactant surfaces noticeably, the average rate of electron transfer is found to be weakly dependent on kVER for a range of values of Vel; this independence breaks down only at very small values of Vel. In addition, the hybrid model is employed to study the time resolved fluorescence line shape for the electron transfer reactions. It is found that VER can have a significant influence on the fluorescence spectrum. The possibility of vibrational state resolved spectra is investigated.
Extraordinary elevation of the glass transition temperature of thin polymer films grafted to silicon oxide substrates
Authors: Tate Ranjeet S. , Fryer David S. , Pasqualini Silvia , Montague Martha F. , de Pablo Juan J. , Nealey Paul F.
Published: July 2002

We used local thermal analysis and ellipsometry to measure the glass transition temperatures (Tg) of supported thin films of poly(4-hydroxystyrene) (PHS) and hydroxy terminated polystyrene (PS-OH). The films were spuncast from solution onto silicon oxide substrates and annealed under vacuum at elevated temperatures to graft the polymer to the substrate. Grafting was verified and characterized in terms of the thickness of and the advancing contact angle of water on the residual layer after solvent extraction. For PHS, each segment of the polymer chain was capable of grafting to the substrate. The thickness of the residual layer increased with increasing annealing temperature. For this polymer the critical thickness below which the Tg of the film deviated from the bulk value was nearly 200 nm after annealing at the highest temperature (190 °C); the Tg of films 100 nm thick or less were elevated by more than 50 °C above the bulk value. For PS-OH films the polymer was only capable of grafting at one chain end, forming a brush layer at the substrate interface. The critical thicknesses for PS-OH films and the Tg elevations were substantially higher than for ungrafted PS films, but were not as large as for PHS. The film thickness dependence of Tg for PHS and PS-OH were well described as piecewise linear, consistent with a “dual-mechanism” model.
Extraction of highly charged ions (up to 90+) from a high-energy electron-beam ion trap
Authors: McDonald J. W. , Bauer R. W. , Schneider D. H. G.
Published: July 2002

The extraction of high-Z high-charge-state ions up to U90+ from a high-energy electron-beam ion trap, the SuperEBIT at Lawrence Livermore National Laboratory, is reported. The SuperEBIT provides a 240 mA electron beam with up to 200 keV of energy. Depending on the operating conditions (pulsed, continuous) and charge state, the number of ions extracted from the SuperEBIT varies between 102 and 105 ions per second under the tested conditions. The ions produced in SuperEBIT are extracted at potentials ranging from 0.5 to 20 keV (continuously variable) to provide highly charged low-emittance ion beams with energies between a few keV and several MeV. The performance of the SuperEBIT as an ion source is described and aspects for future developments and potential applications are discussed.
Snowplow-like behavior in the implosion phase of wire array Z pinches
Authors: Lebedev S. V. , Beg F. N. , Bland S. N. , Chittenden J. P. , Dangor A. E. , Haines M. G.
Published: July 2002

The effect of discrete wires on the implosion dynamics of wire array Z-pinch experiments at ∼1 MA current level is discussed. The data show that the formation of a core–corona structure leads to gradual radial redistribution of mass by precursor plasma flow from the stationary wire cores during the first ∼80% of the implosion time. This phase ends with the formation of gaps in the wire cores, which occurs due to the nonuniformity of ablation rate along the wires. The final phase of the implosion starting at this time occurs as a rapid snowplow-like implosion of the plasma, previously injected into the interior of the array. The density distribution of the precursor plasma being peaked on the array axis could be a key factor providing stability of the wire array implosions operating in the regime of discrete wires. The implications of this implosion scenario to the operation of nested wire arrays and foam targets on the array axis are also discussed.
Optical and structural studies of films grown thermally on zirconium surfaces
Authors: Morgan J. M. , McNatt J. S. , Shepard M. J. , Farkas N. , Ramsier R. D.
Published: July 2002

Variable angle IR reflection spectroscopy and atomic force microscopy are used to determine the thickness and morphology of films grown thermally on Zr surfaces in air. The density and homogeneity of these films increases with temperature in the range studied (773–873 K) and growth at the highest temperature follows cubic rate law kinetics. We demonstrate a structure-property relationship for these thermally grown films and suggest the application of IR reflectivity as an inspection method during the growth of environmentally passive films on industrial Zr components.
Effects of postmetallization annealing on ultrathin SiO2 layer properties
Authors: Asuha  , Yuasa Toshiro , Maida Osamu , Kobayashi Hikaru
Published: July 2002

Observation of both longitudinal optical and transverse optical phonons of ∼1.3 nm ultrathin silicon dioxide (SiO2) layers formed by immersion in nitric acid shows that the SiO2 density increases by 16% after postoxidation annealing (POA) at 900 °C. For the SiO2 layers without POA, postmetalization annealing (PMA) greatly decreases the SiO2 thickness from 1.3 to 0.2 nm, the effect of which is attributable to the reaction of aluminum with SiO2 to form a metallic mixture of aluminum oxide and Si. For SiO2 layers with POA, PMA decreases the SiO2 thickness to a lesser extent (from 1.4 to 0.9 nm), because of the suppression of aluminum diffusion into SiO2 due to its dense structure. PMA is found to decrease the interface state density but increase the leakage current density.
Stages of chaotic synchronization
Authors: Tang D. Y. , Dykstra R. , Hamilton M. W. , Heckenberg N. R.
Published: July 2002

In an experimental investigation of the response of a chaotic system to a chaotic driving force, we have observed synchronization of chaos of the response system in the forms of generalized synchronization, phase synchronization, and lag synchronization to the driving signal. In this paper we compare the features of these forms of synchronized chaos and study their relations and physical origins. We found that different forms of chaotic synchronization could be interpreted as different stages of nonlinear interaction between the coupled chaotic systems.
Quark-based description of nuclear matter with simulated annealing
Authors: Frichter George M. , Piekarewicz J.
Published: July 2002

The ground-state properties of a many-quark system in the string-flip model using variational Monte Carlo methods are calculated. The many-body potential energy of the system is determined by finding the optimal grouping of quarks into hadrons. This (optimal) assignment problem is solved by using the stochastic optimization technique of simulated annealing. Results are presented for the energy and length-scale for confinement as a function of density. These results show how quarks clustering decreases with density and characterize the nuclear- to quark-matter transition. The results are compared to a previously published work with a similar model which uses, instead, a pairing approach to the optimization problem.
Visualization of resonant absorption in solar coronal loops by simulation of soft x-ray images
Authors: Beliën A. J. C. , Poedts S. , Spoelder H. J. W. , Leenders R. , Goedbloed J. P.
Published: July 2002

One of the proposed mechanisms to explain the heating of the solar corona is resonant absorption of magnetic Alfvén waves. Numerical studies of this mechanism often involve large scale computations and produce large amounts of data that need to be visualized. In this article we present a method to visualize numerically calculated density and temperature evolutions of heating calculations by simulating the soft x-ray observations of the soft x-ray telescope aboard the Yohkoh satellite. The visualization method is applied to two different model calculations of the heating of coronal magnetic loops by the resonant absorption of Alfvén waves. For these two cases, information on the variations of temperature and density can be extracted conveniently from the generated images. The resulting images reveal features that are characteristic of the resonant absorption process. This suggests that signatures of resonant absorption can be extracted from real soft x-ray observations of coronal loops. By varying the parameters of the models and visualizing the results the effects of the parameters on the simulated soft x-ray images will become known. In turn, this information can be used to identify the heating mechanism in real observations. © 1996 American Institute of Physics.
Higher-order variable-step algorithms adapted to the accurate numerical integration of perturbed oscillators
Authors: Vigo-Aguiar Jesús , Ferrándiz José M.
Published: July 2002

In this article we introduce a predictor–corrector pair of multistep algorithms adapted to the accurate and efficient numerical integration of perturbed oscillators, since the truncation error comes exclusively from the perturbation terms. They are the first such methods that can achieve a high order while allowing step-size and order variations. © 1998 American Institute of Physics.
Holographic photoelectrochemical etching of diffraction gratings in n-InP and n-GaInAsP for distributed feedback lasers
Authors: Lum R. M. , Glass A. M. , Ostermayer F. W. , Kohl P. A. , Ballman A. A. , Logan R. A.
Published: July 2002

Direct photoelectrochemical (PEC) etching of diffraction gratings on n-InP and n-GaInAsP in a 2-M HF/0.5-M KOH solution has been demonstrated using laser interference holography. Development of a maskless technique for producing gratings has potential application in the fabrication of distributed feedback lasers which are currently made by a multistep photoresist process. Submicron diffraction gratings having a period of 0.5 μm, corresponding to second-order feedback in GaInAsP at λ=1.55 μm, have been achieved. Measurements were obtained on the exposure characteristics, diffraction efficiency, and PEC etching sensitivity of gratings produced in InP and GaInAsP as a function of the writing beam intensity, laser wavelength, material doping level, and grating spatial frequency. For grating frequencies greater than 100 mm−1 the sensitivity was observed to decrease approximately as the inverse square of the spatial frequency. In addition, undoped InP and GaInAsP exhibited significantly lower sensitivities than n-doped material.
Determining photothermally the thickness of a buried layer
Authors: Baumann J. , Tilgner R.
Published: July 2002

The conventional thermal-wave treatment following the Rosencwaig–Gersho theory is used to analyze the manner in which the properties of a layer buried within a sample influence the amplitude and the phase of surface-temperature oscillation during periodic heating by chopped light. This method can be applied to evaluate materials nondestructively in a manner similar to eddy current testing of electrically conductive layered samples: First experimental results on determining the thickness of a thin layer between an aluminum block and a 0.5-mm-thick blackened aluminum sheet are presented.
Photoluminescence of neodymium-implanted gallium phosphide and gallium arsenide
Authors: Müller H. D. , Ennen H. , Schneider J. , Axmann A.
Published: July 2002

Characteristic intra 4f-shell luminescence spectra of Nd3+(4f3) have been observed from neodymium-implanted gallium phosphide and gallium arsenide. The luminescent centers were found to occupy different types of noncubic lattice sites, presumably formed by association of the neodymium implants with radiation damage centers. The relative intensities of the neodymium luminescent centers were found to depend critically on the conditions of postimplantation thermal annealing.
Solution of the nonlinear Poisson equation of semiconductor device theory
Authors: Mayergoyz I. D.
Published: July 2002

A new iterative method for solving the discretized nonlinear Poisson equation of semiconductor device theory is presented. This method has two main advantages. First, it converges for any initial guess (global convergence). Secondly, the values of electric potential are updated at each mesh point by means of explicit formulas (that is, without the solution of simultaneous equations). The first property makes this method quite robust, while the second allows for the implementation of the method on computers with small RAMs. Some numerical results obtained by this method are reported.
Free-electron density and transit time in a finite superlattice
Authors: Jogai B. , Wang K. L. , Brown K. W.
Published: July 2002

In this paper we have calculated the free-electron density in a finite superlattice. Resonant tunneling causes a buildup of particle density in the well regions, giving rise to an accumulation of electrons in those regions. Using our results, we have estimated the change in barrier heights and well depths caused by the electrostatic force. A negligible change is found for a double-well structure having well widths of 40 Å and barrier widths of 20 Å. Our approach could be extended to calculate the tunneling current self-consistently. Additionally we have used a time-dependent solution of Schrödinger’s equation to estimate the trapping time of the electrons due to the resonant effect. The results show that the probability density oscillates several times between the two wells, leaking out gradually at each step. After about 2.4×10−13 s, most of the waves centered about the resonant energies have been transmitted.
Perpendicular anisotropy in Pd/Co multilayers
Authors: Draaisma H. J. G. , den Broeder F. J. A. , de Jonge W. J. M.
Published: July 2002

The anisotropy values in polycrystalline Pd/Co multilayers with [111] texture as determined from magnetization measurements, torque measurements, and ferromagnetic resonance are compared. It is concluded that the most reliable value is obtained from the area between the magnetization curves measured with the field parallel and perpendicular to the plane of the film. The anisotropy is made up of a volume and an interface contribution. In a pair interaction model for the interface anisotropy it is shown that the latter is very sensitive to the precise distribution of Co and Pd at the interfaces. From the experimental data we derive a lower bound value of 0.2 meV per Co atom for the energy change with the direction of the magnetic moment. The temperature dependence of the magnetization indicates a long-range interaction across the Pd layers up to 15–25 Å.
Influence of metallic electrodes on electrical tree initiation in polyethylene
Authors: Vijh Ashok K. , Crine Jean-Pierre
Published: July 2002

The nature of electrical tree initiation in polyethylene is treated with a focus on the influence of the nature of metallic electrodes on the initiation voltage. It is shown that the latter parameter varies linearly with the work function of the oxide-covered metallic electrode. This suggests that charge injection in polymers depends on the oxide layer at the metal-polymer interface.
Theoretical analysis of the electrode sheath in rf discharges
Authors: Riemann K.-U.
Published: July 2002

Starting from a previous kinetic theory of the plasma boundary layer (charge exchange model of the presheath), we investigate a collisionless planar electrode sheath of a capacitively coupled rf discharge in the frequency range between the ionic and electronic plasma frequencies (ωp+≪ω≪ωp−). The resulting model equations are evaluated in an approximation based on thick-sheath assumptions. We calculate the current-voltage characteristics of the sheath and analyze the voltage distribution in a two-electrode system.
Stoichiometric effects on the optical properties of LiInSe2
Authors: Smith Cecily J. , Lowe Calvin W.
Published: July 2002

We have measured the diffuse reflectance of LiInSe2 between 0.67 and 3.54 eV. The Kubelka–Munk theory was used to obtain the absorption coefficient from the data. The band gap in our samples is located at approximately 1.6 eV. The In and Se content of the samples was determined from atomic absorption measurements. We observed absorption peaks at 0.890 and 0.896 eV, which are correlated, respectively, to the selenium and indium deficiencies in our samples.
Triggering in trigatron spark gaps: A fundamental study
Authors: Williams P. F. , Peterkin F. E.
Published: July 2002

The trigatron has been in widespread use as a demand-triggered, high-voltage switch for more than 40 years. In spite of the popularity and maturity of the technology, there persists an uncertainty over the basic physical mechanism(s) responsible for triggering breakdown in the devices. We present the results of an empirical study of trigatrons that directly demonstrates that breakdown is initiated by a streamer launched from the trigger pin, independent of the trigger spark. We compare our results with those of previous workers, and discuss the generality of our conclusions.
Guided waves in a bonded plate: A parametric study
Authors: Xu P.-C. , Datta S. K.
Published: July 2002

Dispersion of elastic waves in a bonded plate has been analyzed using the exact solution as well as by two approximate models: a spring model that neglects the inertia effects and a density model that does not account for the finite stiffness of the bond layer. It is shown that the two model predictions agree with the exact solution in two overlapped regions of the density and stiffness ratios. However, they fail to predict the actual behavior in certain regions of the parameter domain.
Irreversible phase transitions and wave propagation in silicate geologic materials
Authors: Swegle J. W.
Published: July 2002

Shock and unloading experiments on quartz and silicate rocks indicate that the release adiabats lie below the Hugoniot. The hysteresis and energy dissipation inherent in this situation have important wave propagation implications. On loading, there is a pressure-induced transition to the stishovite phase which does not occur under conditions of thermodynamic equilibrium, in that the Hugoniot passes through a metastable mixed-phase region for several tens of GPa. One interpretation of the unloading data is that the transition is not reversible, and the phase mixture remains frozen on unloading. However, material strength may also play a role. A complete thermodynamically consistent equation of state which includes phase transitions and strength effects has been developed and used to examine shock and release data on quartz and silicate rocks in order to quantify the kinetics of the reverse transition and to separate the hysteretic effects due to reverse phase transition kinetics from those due to material strength. The model allows quantitative determination of the effect of reverse transition kinetics on ground shock propagation in silicate materials.
Iron overlayer polarization enhancement technique for spin-polarized electron microscopy
Authors: VanZandt T. , Browning R. , Landolt M.
Published: July 2002

Thin iron overlayers on ferromagnetic samples are shown to be nonintrusive probes of the magnetization of the underlying sample when using spin-polarized secondary-electron emission for domain microscopy. Domain images of the iron overlayer show that the local magnetization direction is indicative of that in the sample. The magnitude of the spin polarization, however, reflects the magnetization of the iron overlayer. Thus, for materials with low spin polarization, the iron overlayer provides a large signal enhancement. The method is also applicable to oxidized transition-metal surfaces. The iron film is found to be exchange coupled to the substrate across oxide layers on the sample surface. These points are demonstrated in experiments with an Fe〈100〉 whisker and with a Co-Ni alloy magnetic disk.
The frequency dependence of ac coercivity of ultrathin, low magnetostriction Co-based amorphous ribbons
Authors: Piotrowski C. , Yagi M. , Sawa T.
Published: July 2002

The dynamic (ac) coercivity of zero magnetostriction Co-based ultrathin amorphous ribbons from the [(Co0.95Fe0.05)0.95Cr0.05]75Si15B10 family was measured over the frequency range of 20 Hz to 20 kHz. Ribbons with thicknesses between 5.3 and 18 μm, and widths held constant at approximately 6 mm, were studied. The results are well fit by a power law dependence of the coercivity Hc on frequency f. The exponent which characterizes the best fit to the data depends on ribbon thickness. Within experimental uncertainty, the exponent increases linearly with ribbon thickness, varying between 0.18 and 0.32 for the ribbons studied. In contrast, simple phenomenological models predict a constant value of 0.5 for the exponent. The origins of the deviations from this simple phenomenological dependence of coercivity on frequency are discussed.
Fabrication, characterization, and theoretical analysis of high-T
c Y-Ba-Cu-O superconducting films prepared by a chemical sol gel method
Authors: Hussain A. A. , Sayer M.
Published: July 2002

Thin films of Y1Ba2Cu3O7−x have been produced on MgO substrates by a chemical sol gel method. X-ray diffraction data indicate that the annealed films have the characteristic orthorhombic structure with lattice constants which are nearly the same as the values reported for the bulk specimen of Y1Ba2Cu3O7−x. Auger electron spectroscopy depth profiling measurements indicate that the films are uniform in thickness and composition. Measurements of electrical resistance of films 1–4.7 μm in thickness have been carried out between 12 and 300 K using a standard four-probe geometry. The films are superconducting with an onset temperature around 95 K and a full transition temperature as high as 79.5 K, and a critical current density of 2700 A/cm2 at 20 K. A theoretical analysis of the critical current density in Y1Ba2Cu3O7−x as a function of temperature has been made in order to determine the characteristics of the junctions between the superconducting grains. Theoretical models which describe the dependence of the critical current density on temperature have been presented and agreement has been found between these models and experimental values for sol gel films. The critical transport current has a temperature dependence which is characteristic of superconductor-normal metal-superconductor (S-N-S) type junctions. The magnitude of the resistance and thickness of the junctions has been determined from the theoretical models. Information regarding calculation of the oxygen content in Y1Ba2Cu3O7−x films is also presented.
Cross-sectional transmission electron microscopic study of Au/GaP and Au/InP contacts
Authors: Pécz B. , Veresegyházy R. , Radnóczi G. , Barna A. , Mojzes I. , Geszti O. , Vincze Gy.
Published: July 2002

Au(80 nm)/GaP(111) samples were heat treated in forming gas in the temperature range of 450–550 °C. Very thin elongated α-Au(Ga) grains were grown into the GaP at 475 °C as a result of the interface reaction between Au and GaP. A surface (interface) energy driven grain growth in Au-Ga solid solution was observed after annealing at 500 °C. At 525 °C long, flat grains were formed from the thin elongated ones of α-Au(Ga). At 550 °C the metallization melted due to its high Ga content. During the solidification the shape of drops was preserved, and the metallization consisted of Au2Ga and Au7Ga2 grains. Au(100 nm)/InP(111) samples were annealed at 375 and 400 °C in forming gas for 10 min. Elongated crystals grown into the InP substrate due to the interaction between gold and InP were observed. Au9In4 grains are situated in these pits in the matrix of the Au2P3 monoclinic phase.
Elastic properties of TiN/(VxNb1−x)N superlattices measured by Brillouin scattering
Authors: Mirkarimi P. B. , Shinn M. , Barnett S. A. , Kumar Sudha , Grimsditch M.
Published: July 2002

Brillouin scattering measurements have been carried out on single-crystal lattice-matched TiN/(V0.6Nb0.4)N and mismatched TiN/NbN superlattices. Measured surface wave velocities were found to be independent of superlattice wavelength over the entire range investigated, 1.5–30 nm, and were averages of the measured velocities of pure homogeneous TiN, NbN, and (V0.6Nb0.4)N. These results indicate that there is no anomaly in the C44 elastic constant. X-ray diffraction results from the superlattices indicated that the average lattice spacing did not vary with wavelength. This is consistent with previous observations where elastic anomalies were related to changes in lattice spacing. The absence of a correlation between the C44 elastic constant and previously reported hardness enhancements indicates that the latter are not caused by anomalies in C44; they could, however, be correlated with other elastic moduli.
Transition from a capacitive to a resistive regime in a silane radio frequency discharge and its possible relation to powder formation
Authors: Boeuf J. P. , Belenguer Ph.
Published: July 2002

Self-consistent fluid and particle-in-cell models of radiofrequency glow discharges have been used to analyze the existence of different regimes experimentally observed in silane discharges. The discharge ionization mechanism changes from a situation where the ionization occurs during the expansion of the sheath to a situation where the bulk plasma plays a major role. We suggest that the transition is consistent with powder formation with increasing power. This leads to supplementary losses of electrons and then to an increase in the plasma electric field.
Phase separation during film growth
Authors: Atzmon M. , Kessler D. A. , Srolovitz D. J.
Published: July 2002

A diffusion equation describing phase separation during co-deposition of a binary alloy is derived, and solved in the limit of dominant surface diffusion. Linear stability analysis yields results similar to bulk spinodal decomposition, except that long, and possibly all, wavelength are stabilized. Decomposition into two phases is investigated by solving the diffusion equation for lamellar and cylindrical symmetry. For the lamellar geometry, typically observed for near-equal volume fractions, the diffusion equation does not yield wavelength selection criteria. These can be obtained if free energy minimization is assumed. For the cylindrical geometry, solutions for small volume fractions yield domain dimensions proportional to the deposition-rate dependent surface diffusion length.
Random field effects at the spin-flop transition of diluted and mixed (K1−xRbx)2Fe1−yIny(Cl1−zBrz)5⋅H2O
Authors: Becerra C. C. , Paduan-Filho A. , Palacio F. , Barbeta V. B.
Published: July 2002

The magnetization of the diluted and mixed low anisotropy antiferromagnets (K1−xRbx)2Fe1−yIny(Cl1−zBrz)5H2O was measured as a function of an applied magnetic field 0≤H≤4.0 T in the temperature range 1.5≤T≤15 K. The focus of this work is on the effects that random fields, generated by an external field applied along the easy axis, have on the spin-flop transition. The sharp first order transition that occurs in K2FeCl5H2O has its width increased by almost an order of magnitude when substitution is introduced in any of the K, Fe, or Cl sites. In K2Fe1−yInyCl5H2O and K2Fe(Cl1−zBrz)5H2O hysteseris is also observed. Hysteresis is not observed in (K1−xRbx)2FeCl5H2O.
The role of hydride coverage in surface-limited thin-film growth of epitaxial silicon and germanium
Authors: Eres Gyula , Sharp J. W.
Published: July 2002

The connection between the hydride coverage and thin-film growth rate was investigated by a kinetic model consisting of the elementary reaction steps of source gas chemisorption and hydrogen desorption in silicon and germanium epitaxial thin-film growth from silanes and germanes. A generalized form of the model for steady-state conditions was used to extract the kinetic parameters of the elementary reaction steps from experimental film growth data in the literature. Three-dimensional plots of the growth rate as a function of the substrate temperature and the source gas flux were used to summarize the trends in steady-state surface-limited thin-film growth using the kinetic parameters extracted by the model. The three-dimensional plots show that: (1) each of the elementary reaction steps is dominantly dependent only on a single external growth parameter, and (2) in the transition region where neither of the elementary steps is clearly dominant the growth rates exhibit a complex dependence on the growth parameters. The kinetic parameters for the elementary reaction steps are found to be in good agreement with the values obtained by independent (nonfilm growth) surface studies. The insight gained by modeling the hydride coverage in thin-film growth led to development of digital epitaxy, an alternative growth method to atomic layer epitaxy of group IV materials. Digital epitaxy is accomplished through cyclic repetition of alternating chemisorption and hydrogen desorption stages.
Growth and structure of IrSi3 on Si(111)
Authors: Lange Davis A. , Gibson Gary A. , Falco Charles M.
Published: July 2002

Molecular-beam epitaxy has been used to grow films that are almost entirely IrSi3 by codeposition of Si and Ir in a 3:1 ratio on Si(111) substrates. Bragg–Brentano and Seemann–Bohlin x-ray diffraction reveal that polycrystalline IrSi3 films form as low as 490 °C, the lowest temperature yet reported for growth of this iridium silicide phase. Above 580 °C this hexagonal phase becomes textured, with as many as seven preferred growth orientations on Si(111). Samples codeposited on Si(111) between 680 and 780 °C consist almost entirely of IrSi3 with its c axis perpendicular to the substrate’s surface. At higher substrate temperatures, near 830 °C growth of IrSi3 with its c axis in the plane of the substrate dominates. Atomic force microscopy shows that there is a difference in the surface morphology of the c-axis in-plane and perpendicular growth modes. Transmission electron microscope diffraction and in situ low-energy electron diffraction verify that both of these IrSi3 growth modes are epitaxially registered with their substrates. To check the quality of this epitaxy ion-beam channeling and x-ray rocking curves were used. The data from the epitaxial samples have channeling χmin ratios as low as 0.64. The x-ray rocking curves for these IrSi3 films are narrow, with full-width-at- half-maxima of as little as 0.07°.
Two-photon laser induced fluorescence and amplified spontaneous emission atom concentration measurements in O2 and H2 discharges
Authors: Amorim J. , Baravian G. , Touzeau M. , Jolly J.
Published: July 2002

Multiphoton laser-induced fluorescence (LIF) and amplified spontaneous emission (ASE) are used to detect ground-state atoms in oxygen and hydrogen glow discharge plasmas. Experimental results and modeling are analyzed to establish the validity criteria for the use of LIF and ASE as diagnostic probes in the measurements of ground-state atom concentrations. An absolute calibration of the LIF signals is obtained by vacuum ultraviolet absorption experiments, either on the 130 nm resonant line of the atomic oxygen, or the 125 nm resonant line of the hydrogen atom. Under typical operating conditions of dc glow discharges, that is, for gas pressure between 0.5 and 5.0 Torr and discharge current from 1 to 50 mA, the densities of the atomic species are measured in the range 1013 cm−3–1015 cm−3. Under the same conditions the hydrogen atom temperature varies from (336±43) K to (1580±90) K.
Photovoltaic performance of a-Si:H homojunction p-i-n solar cells: A computer simulation study
Authors: Chatterjee Parsathi
Published: July 2002

A first principles computer model for simulating the performance of amorphous semiconductor solar cells has been developed. With a suitable choice of parameters, the calculated results for the illuminated J-V characteristics and solar cell quantum efficiencies are shown to agree well with experiments. The model has been used in this paper to study the sensitivity of the light J-V characteristics to various device and material parameters in p-i-n homojunction solar cells. The single most important factor controlling the open circuit voltage, short circuit current, fill factor, and cell efficiency is the transparent conducting oxide/p-a-Si:H contact barrier height φbo, when φbo is less than a certain critical value. Also shown is that practically no improvement in cell performance can be achieved by decreasing the dangling-bond midgap state density, described by Gaussian distribution functions, to lower than 1016 cm−3, unless the valence-band tail states are also reduced. Moreover, results indicate that light-induced defect states have neutral capture cross sections of 10−15 cm2, which is at least one order of magnitude higher than the corresponding quantity for the gap states in annealed materials. Finally, low band microscopic carrier mobilities are found to have a strong detrimental influence on solar cell performance.
Evaluating the effects of optical and carrier losses in etched-post vertical cavity lasers
Authors: Thibeault B. J. , Strand T. A. , Wipiejewski T. , Peters M. G. , Young D. B. , Corzine S. W. , Coldren L. A. , Scott J. W.
Published: July 2002

We demonstrate the combined effects of optical scattering loss and surface recombination (or carrier diffusion) on the performance and scalability of etched-post vertical cavity lasers (VCLs). The size dependence of optical losses and threshold gain are determined from pulsed measurements of external quantum efficiency. Deeper etch depths result in a stronger radial dependence of the threshold gain, which quickly increases the threshold current density. With optical loss accounted for, pulsed threshold current density measurements give the extra information needed for evaluating carrier loss. Surface recombination or carrier diffusion also results in threshold current density increases, but scalability is ultimately limited by the ability of the active region to provide enough gain for smaller size, higher optical loss devices. Even with these losses, three-quantum-well VCLs with shallow etches have threshold currents as low as 420 μA.