bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion beam generation in a diode with a ferroelectric anode
Authors: Chirko K. , Krasik Ya. E. , Felsteiner J.
Published: July 2002

In this article experimental results of the application of a ferroelectric anode for the generation of ion beams are presented. The ferroelectric anode was made of a solid solution of Sr, Ba, Ti, Nb, Pb, and O. Its front side was covered by a grounded Cu strip electrode. The ion beam generation was studied in a planar diode powered by a high-voltage generator with accelerating voltage ⩽300 kV and pulse duration ⩽400 ns. The source of the ion beam was found to be the plasma which was formed on the front anode surface. This plasma was formed by a driving pulse with an amplitude ⩽18 kV and pulse duration of ∼400 ns which was applied to the rear Cu disk electrode prior to the application of the accelerating pulse. The generation of ion beams with current amplitude up to 150 A was demonstrated in the plasma prefilled mode of the diode operation. It was found that the generated ion beam consists of light (H+,C+,O+) and heavy (Ti+,Cu+,Sr+) ions. In addition, it was shown that the application of a reflex triode scheme with a negative grid cathode allowed us to separate effectively the light ions from the generated ion beam.
Effect of Ga content on defect states in CuIn1−xGaxSe2 photovoltaic devices
Authors: Heath J. T. , Cohen J. D. , Shafarman W. N. , Liao D. X. , Rockett A. A.
Published: July 2002

Defects in the band gap of CuIn1−xGaxSe2 have been characterized using transient photocapacitance spectroscopy. The measured spectra clearly show response from a band of defects centered around 0.8 eV from the valence band edge as well as an exponential distribution of band tail states. Despite Ga contents ranging from Ga/(In+Ga)=0.0 to 0.8, the defect bandwidth and its position relative to the valence band remain constant. This defect band may act as an important recombination center, contributing to the decrease in device efficiency with increasing Ga content.
Deterministic chaos in the Belousov–Zhabotinsky reaction: Experiments and simulations
Authors: Zhang Dongmei , Györgyi László , Peltier William R.
Published: July 2002

An account of the experimental discovery of complex dynamical behavior in the continuous-flow, stirred tank reactor (CSTR) Belousov–Zhabotinsky (BZ) reaction, as well as numerical simulations based on the BZ chemistry are given. The most recent four- and three-variable models that are deduced from the well-accepted, updated chemical mechanism of the BZ reaction and which exhibit robust chaotic states are summarized. Chaos has been observed in experiments and simulations embedded in the regions of complexities at both low and high flow rates. The deterministic nature of the observed aperiodicities at low flow rates is unequivocally established. However, controversy still remains in the interpretation of certain aperiodicities observed at high flow rates.
Don’t bleach chaotic data
Authors: Theiler James , Eubank Stephen
Published: July 2002

A common first step in time series signal analysis involves digitally filtering the data to remove linear correlations. The residual data is spectrally white (it is ‘‘bleached’’), but in principle retains the nonlinear structure of the original time series. It is well known that simple linear autocorrelation can give rise to spurious results in algorithms for estimating nonlinear invariants, such as fractal dimension and Lyapunov exponents. In theory, bleached data avoids these pitfalls. But in practice, bleaching obscures the underlying deterministic structure of a low-dimensional chaotic process. This appears to be a property of the chaos itself, since nonchaotic data are not similarly affected. The adverse effects of bleaching are demonstrated in a series of numerical experiments on known chaotic data. Some theoretical aspects are also discussed.
Nonlinear waves, chaos and patterns in microwave electronic devices
Authors: Trubetskov D. I. , Mchedlova E. S. , Anfinogentov V. G. , Ponomarenko V. I. , Ryskin N. M.
Published: July 2002

We discuss some problems, concerning the application of nonlinear dynamics methods and ideas to vacuum microwave electronics. We consider such phenomena as solitons, deterministic chaos and pattern formation in different models of electron flows and devices. Our results reveal that microwave electronics is an interesting field of application of nonlinear dynamics.
On the generation of solitons and breathers in the modified Korteweg–de Vries equation
Authors: Clarke Simon , Grimshaw Roger , Miller Peter , Pelinovsky Efim , Talipova Tatiana
Published: July 2002

We consider the evolution of an initial disturbance described by the modified Korteweg–de Vries equation with a positive coefficient of the cubic nonlinear term, so that it can support solitons. Our primary aim is to determine the circumstances which can lead to the formation of solitons and/or breathers. We use the associated scattering problem and determine the discrete spectrum, where real eigenvalues describe solitons and complex eigenvalues describe breathers. For analytical convenience we consider various piecewise-constant initial conditions. We show how complex eigenvalues may be generated by bifurcation from either the real axis, or the imaginary axis; in the former case the bifurcation occurs as the unfolding of a double real eigenvalue. A bifurcation from the real axis describes the transition of a soliton pair with opposite polarities into a breather, while the bifurcation from the imaginary axis describes the generation of a breather from the continuous spectrum. Within the class of initial conditions we consider, a disturbance of one polarity, either positive or negative, will only generate solitons, and the number of solitons depends on the total mass. On the other hand, an initial disturbance with both polarities and very small mass will favor the generation of breathers, and the number of breathers then depends on the total energy. Direct numerical simulations of the modified Korteweg–de Vries equation confirms the analytical results, and show in detail the formation of solitons, breathers, and quasistationary coupled soliton pairs. Being based on spectral theory, our analytical results apply to the entire hierarchy of evolution equations connected with the same eigenvalue problem.
Excimer laser ablation and thermal coupling efficiency to polymer films
Authors: Dyer P. E. , Sidhu J.
Published: July 2002

Thermal coupling and etch rate measurements are reported for polyethylene terephthalate and polyimide films irradiated at excimer laser wavelengths of 193, 248, and 308 nm. Thermal energy balance is observed up to a threshold fluence but above this the energy absorbed remains approximately constant, the excess energy being carried away by the ablated material. The ablated material appears to have a temperature >103 K as determined by calculations based on the thermal energy loading and relaxation time estimated from IR measurements. These results provided useful information on the interaction mechanism.
Survey of chaos in the rf-biased Josephson junction
Authors: Kautz R. L. , Monaco R.
Published: July 2002

Chaotic behavior in the rf-biased Josephson junction is studied through digital simulations of the Steward–McCumber model. Chaotic states are characterized by Poincare sections, Liapunov exponents, and power spectra. Models are presented which explain some features of the chaotic spectra. The parameter range over which chaotic behavior occurs is determined empirically for a broad range of dc bias, rf bias, and hysteresis parameters for a fixed rf frequency. It is shown that chaos does not occur if either the dc bias or the rf bias is very large. An attempt is made to explain the boundaries of the chaotic region in terms of simple models for chaotic behavior.
Parametric analysis of isotope enrichment in a vacuum-arc centrifuge
Authors: Krishnan Mahadevan , Prasad Rahul R.
Published: July 2002

Centrifugal separation of isotopes occurs in a magnetized, rotating column of plasma. An analysis is presented of the dependence of the net enrichment of a given isotope upon the radius of the column, its rotation frequency, and the number of successive stages of separation. Three different cases are considered: 48Ca, in which the heaviest isotope is collected at the outer edge of the column; 203Tl, in which the lighter isotope is collected in the core of the column; and 68Zn, in which an intermediate-mass isotope is collected in an annular region within the column. For the particular case of Gaussian radial distributions of the isotopes in the rotating column, a multifluid model of the enrichment reveals that staging provides no benefit for collection of the heaviest isotope. For collection of the lightest species in the core, multistaging of the enrichment significantly reduces the required column radius and rotation frequency. Experimental measurements in a laboratory-scale centrifuge yielded typical values for the rotation frequency and column radius. With these values it is shown that vacuum-arc centrifuges are capable of providing enriched stable isotopes of use in nuclear physics and nuclear medicine.
Reactively magnetron sputtered Hf-N films. I. Composition and structure
Authors: Johansson B. O. , Helmersson U. , Hibbs M. K. , Sundgren J.-E.
Published: July 2002

Thin films of Hf-N, covering the entire composition range from pure Hf to overstoichiometric HfN, have been prepared by reactive magnetron sputtering. The structure of the films has been investigated by x-ray diffraction, transmission electron microscopy, and scanning electron microscopy and the composition has been determined using Auger electron spectroscopy. A solubility of ≊30 at. % nitrogen is found in the α-Hf region. Above 30 at. % N a multiphase structure consisting of α-Hf, HfN, Hf3N2, and/or Hf4N3 is found, which is not in agreement with the equilibrium structure. In the mononitride region a lattice parameter of ≊4.53 Å is observed. This value is slightly higher than reported bulk values due to intrinsic stress in the films. Increasing the nitrogen content above 50 at. % causes a distortion of the cubic symmetry of the lattice. This is first observed as an increase in the (111) interplanar spacing while other spacings decrease. Also a splitting of some reflections occurs at higher nitrogen contents. This phase transition is suggested to be due to a successive change from a cubic to a rhombohedral structure.
Use of spatially dependent electron capture to profile deep-level densities in Schottky barriers
Authors: Gombia E. , Ghezzi C. , Mosca R.
Published: July 2002

A new procedure to profile deep-level densities within the space-charge region of Schottky barriers is presented. The method takes advantage of the spatial dependence of the time constant for the free-electron capture by deep-donor traps. The amplitude of the slow component of the capture capacitance transient following a negative reverse voltage pulse is simply related to the trap density at the point where the Fermi level crosses the trap level itself. The density profile of a given trap can be achieved by measuring the slow-component transient signal as a function of the reverse voltage at a suitably chosen constant temperature. The estimated spatial resolution of the method was near 50 Å in a practical case. Experimental density profiles for EL14, EL8, EL3, and the EC−ET =0.37 eV level in Cr/GaAs and Al/GaAs Schottky barriers are presented and discussed. The procedure is expected to be also applicable to the case of trap densities comparable with the shallow-donor density without introducing large errors.
Hydrogen impurities in quantum well wires
Authors: Brown Jerry W. , Spector Harold N.
Published: July 2002

The binding energy of hydrogenic impurites in a quantum well wire has been calculated as a function of the width of the quantum well wire and the location of the impurity with respect to the axis of the wire. The calculations have been preformed using a variational wave function which takes into account the confinement of the carriers in the wire. For the confining potential used in our calculations, we have used the models of either an infinite potential well or a finite potential well whose depth is detemined by the discontinuity of the band gas in the quantum well wire and the cladding. For the infinite potential well model, the binding energy continues to increase as the radius of the wire decreases while in the finite potential well model, the binding energy reaches a peak value as the wire radius decreases and then decreases to a value characteristic of the cladding. The binding energy also depends upon the location of the impurity in the wire and is a maximum when the impurity is located on the axis of the wire.
Fields and gradients in multipolar magnets
Authors: Sotgiu Antonello
Published: July 2002

This paper describes the two-dimensional field generated by an M pole electromagnet of cylindrical symmetry. By individually controlling the currents on each pole, it is possible to rotate the direction of the field around the axis of the cylinder. Gradients of any order can also be generated. The dependence of the power on the physical dimensions of the whole magnet and on the gap region is also discussed.
An air flow sensor based on interface thermal wave propagation
Authors: Lambert David K. , Harrington Charles R.
Published: July 2002

An air flow sensor that uses a flow-induced change of temperature oscillation phase at an air-solid interface is described and analyzed. The sensor is fabricated on silicon coated with polyimide. The source and detector of temperature oscillations are integrated on the same substrate but spatially separated. A narrow strip of metal film driven by ac is the source. A PbTe thin-film thermocouple is the detector. Device operation in still air is analyzed and compared with experiment. The temperature oscillation amplitude and phase on an interface with an oscillating strip heat source is derived for interface thermal resistance and for a layered substrate. Interference between thermal oscillations propagating from source to detector through the solid and through the air is predicted and observed with a 53-μm-thick polymide layer. In contrast, with a 16-μm-thick polyimide layer, interference that varies with frequency is not seen, also in agreement with theory. Experimental demonstration of flow response is also reported. Qualitative agreement with the predictions of a time-of-flight model of flow response is found.
Influence of ion effects on high-current relativistic diodes
Authors: Choi Eun H. , Shin Hee M. , Choi Duk I. , Uhm Han S.
Published: July 2002

Properties of bipolar electron and ion flow in a relativistic planar diode are investigated within the framework of the cold-fluid-Poisson equations. Defining the parameter q by q=(Ji/Je) [(mi/2Zme)]1/2, the electron current density Je is expressed in terms of the diode voltage, the anode-cathode gap, and the parameter q satisfying q≤qs=(γ0+1)1/2/2. Here me is the rest mass of electrons, Z and mi are the charge state and the rest mass, respectively, of ions, Ji is the ion current density, γ0 is the relativistic mass ratio of electrons at the anode, and the extreme value q=qs represents the space-charge limited ion flow. From the analysis, it is found that presence of the ions in the diode significantly enhances the electron current, although the ion current is less than few percent of the electron current. In an appropriate physical parameter regime, the electron current with counterstreaming ions is more than twice of that without ions.
Semiconductor bridge: A plasma generator for the ignition of explosives
Authors: Benson D. A. , Larsen M. E. , Renlund A. M. , Trott W. M. , Bickes R. W.
Published: July 2002

Small metal bridgewires are commonly used to ignite energetic powders such as pyrotechnics, propellants, and primary or secondary explosives. In this paper we describe a new means for igniting explosive materials using a semiconductor bridge (SCB). When driven with a short (20 μs), low-energy pulse (less than 3.5 mJ), the SCB produces a hot plasma that ignites explosives. The SCB, a heavily n-doped silicon film, typically 100 μm long by 380 μm wide by 2 μm thick, is 30 times smaller in volume than a conventional bridgewire. SCB devices produce a usable explosive output in a few tens of microseconds and operate at one-tenth the input energy of metal bridgewires. In spite of the low energies for ignition, SCB devices are explosively safe. We describe SCB processing and experiments evaluating SCB operation. Also discussed are the SCB vaporization process, plasma formation, optical spectra from the discharge, heat transfer mechanisms from the SCB to the explosive powders, and SCB device applications.
Electrical and optical properties of P- and As-doped Cd1−xMnxTe
Authors: Becla P. , Kaiser D. , Giles N. C. , Lansari Y. , Schetzina J. F.
Published: July 2002

The introduction of phosphorus and arsenic dopants into bulk Cd1−xMnxTe crystals grown by the Bridgman–Stockbarger technique has been studied with respect to the resulting electrical and optical properties. Uncompensated acceptor concentrations as high as 1015–1016 cm−3 are obtained. Samples with a Mn composition in the range 0.10<x<0.30, both as-grown and annealed, are studied. Hall-effect and resistivity measurements are used to determine carrier concentrations, mobilities, and acceptor activation energies. A combination of room-temperature transmittance and reflectance measurements over the spectral range from the ultraviolet to the far infrared has been used to gain information concerning structural quality and point defects. Low-temperature photoluminescence measurements (1.6–5 K) are used to determine optical quality and excitonic energies. The effect of alloy broadening on luminescence linewidth is calculated and compared with measured values.
Low-temperature spin waves in amorphous Fe90−xNixZr10
Authors: Fernandez-Baca J. A. , Lynn J. W. , Rhyne J. J. , Fish G. E.
Published: July 2002

Inelastic neutron scattering measurements have been performed on rapid-quenched ribbons of Fe90−xNixZr10 (x=1,5,10) to measure the small wave-vector spin-wave spectrum. At all three concentrations a quadratic dispersion relation typical of an isotropic ferromagnet is observed, but with anomalous properties at low temperatures. For x=5 and 10 the excitations are found to broaden considerably for temperatures ≤0.3 Tc. For x=1 the spin waves not only broaden for T≤0.5Tc, but the spin-wave energies decrease monotonically with decreasing temperature while a resolution-limited quasielastic component of the scattering develops. These results are consistent with a picture of competing ferromagnetic and antiferromagnetic interactions, with reentrant spin-glass behavior evident if the frustration is sufficiently strong.
Interface roughness of GaAs-AlAs quantum wells grown by molecular-beam epitaxy:  Misorientation effects
Authors: Tanaka Masaaki , Sakaki Hiroyuki
Published: July 2002

We have studied the atomic steps and/or terraces at the interfaces of GaAs-AlAs quantum wells (QWs) grown by molecular-beam epitaxy on slightly misoriented GaAs substrates from (001) toward [110] with various off angles α=0°, 0.5°, 1°, 2°, and 5°. It was found that the terrace edges at the surface/interface on the misoriented substrates are either randomly spaced or kinked, leading to the broadening of the photoluminescence (PL) linewidth. We have explained the PL data by considering the diffusion length Ldiff of Ga and Al atoms on the growth front, and the average terrace width Loff due to the misorientation, in relation to the exciton size Dex in QWs. Unlike the case of (001) flat substrates, growth interruption has little effect on the reduction of PL linewidth of the QWs on misoriented substrates.
Phase formation of NiAl3 on lateral diffusion couples
Authors: Liu Joyce C. , Mayer J. W. , Barbour J. C.
Published: July 2002

The kinetics of NiAl3 phase growth is studied on lateral diffusion couples in the temperature range from 375 to 450 °C. The lateral diffusion couple consists of an Al-rich source on a Ni2 Al3 thin film. Analytical electron microscopy is used to determine the crystal structures and chemical compositions of the growing phases. The results show that: (1) Al is the dominant moving species in the growing NiAl3 phase; (2) an equilibrium concentration of Al is established during the growth; and (3) the growth has a parabolic dependence on the annealing time. The study of NiAl3 growth kinetics on lateral diffusion couples bridges the gap between bulk and thin-film diffusion couples in terms of reaction temperatures. The activation energy of NiAl3 growth is 1.2±0.2 eV.
Measurements of swarm parameters and derived electron collision cross sections in methane
Authors: Davies D. K. , Kline L. E. , Bies W. E.
Published: July 2002

A pulsed drift tube has been used to measure the electron drift velocity in methane over the range of E/N from 10 to 1000 Td. In addition, measurements of the positive ion mobility and ionization coefficient have been made over the range of E/N from 80 to 1000 Td. Within the experimental sensitivity, no evidence of attachment has been observed in this range. A set of electron collision cross sections has been assembled and used in Monte Carlo simulations to predict values of swarm parameters. The cross-section set includes a momentum transfer cross section which is based primarily on the present and previous drift velocity measurements, cross sections for vibrational excitation and ionization based on published experimental cross-section measurements, and a cross section for dissociation into neutral products obtained by subtracting a measured dissociative ionization cross section from a measured total dissociation cross section. Isotropic scattering is assumed for all types of collisions in the Monte Carlo simulations. Good agreement between the predicted and measured values of swarm parameters is obtained without making any adjustments to these cross sections. A two-term Boltzmann equation method has also been used to predict swarm parameters using the same cross sections as input. The two-term results are in poor agreement with experiment and confirm the well-known inadequacy of two-term methods in the case of methane.
Magnetic properties of Fe/Co, Fe/CoFe, and (Fe/Co)/SiO2 multilayer films
Authors: Senda Masakatsu , Nagai Yasuhiro
Published: July 2002

This paper reports on the systematical investigation into the magnetic properties of Fe/Co, Fe/CoFe, and (Fe/Co)/SiO2 multilayer films. Magnetostriction in Fe/Co and Fe/CoFe films can be controlled by changing the thicknesses of the layers. The Fe/Co film (10/0.5 nm) shows saturation magnetization of more than 2 T and hard-axis coercivity of 1.5 Oe for magnetostriction near zero. The hard-axis coercivity is decreased to 0.8 Oe by 300 °C annealing. A magnetic domain structure suitable for a thin-film head is also established for this film. Additionally, a hard-axis coercivity of less than 1 Oe, a relative permeability of 2000, and a saturation magnetization of approximately 2 T are achieved in (Fe/Co)/SiO2 film [(15/0.5)/5 nm] with no annealing. A controlled domain structure consisting of extended 180° walls is observed in this film.
NiAl3 formation in Al/Ni thin-film bilayers with and without contamination
Authors: Ma E. , Nicolet M-A. , Nathan M.
Published: July 2002

The interfacial reactions induced by vacuum furnace annealing and rapid thermal annealing in sequentially deposited Al/Ni bimetallic thin-film diffusion couples have been investigated with MeV 4He+ backscattering spectrometry, cross-sectional transmission electron microscopy, and Auger electron spectroscopy. Upon annealing, NiAl3 is the first aluminide phase to grow. In uncontaminated samples, the NiAl3 growth proceeds in uniform planar fashion, governed by diffusion-limited kinetics. The kinetics data fit well with those for NiAl3 growth on large-grained Al substrates, yielding a common kinetics law of x2=kt, where x is the thickness of the NiAl3 grown at the interface, t is the annealing duration, and k is the growth constant, which is given by k=2.24(cm2/s) exp(−1.5±0.1 eV/kBT), in which T is the annealing temperature and kB is the Boltzmann constant. Microscopic examination reveals slight nonuniformity at the Al/NiAl3 interface resulting from shallow local protrusions of NiAl3 grains into the Al layer at grain boundaries. When either the Al film or the Al/Ni interface is purposely contaminated during sample preparation, the roughness at this Al/NiAl3 interface becomes very pronounced, and the reaction rate is significantly reduced. Meanwhile, Ni motion becomes appreciable as NiAl3 grains and/or Ni severely penetrate the Al layer. In contrast, the NiAl3/Ni interface remains sharp in all samples. The irregular morphology and nonuniform reaction cannot be attributed uniquely to the presence of grain boundaries in the Al film, but rather are a combined effect of impurities and Al grain boundaries. Short-term rapid thermal annealing at elevated temperatures appreciably alleviates the nonuniformity at the Al/NiAl3 interface in contaminated samples.
Raman characterization of molecular-beam-epitaxy-grown GaAlSb on GaSb and GaAs substrates
Authors: Haines Miles , Kerr T. , Newstead S. , Kirby P. B.
Published: July 2002

The optic phonons of Ga1−xAlxSb layers with 0≤x≤1 grown by molecular-beam epitaxy on GaAs and GaSb substrates have been studied using Raman spectroscopy. The phonon energies are interpreted using a modified random element isodisplacement model to allow accurate composition determination. A comparison between the layers grown on GaAs and GaSb substrates is made in terms of strain and anharmonicity effects and related to x-ray and transmission electron microscopy measurements.
The scattering of x rays from nonideal multilayer structures
Authors: Stearns D. G.
Published: July 2002

A general theory is developed for the scattering of x rays from a single nonideal interface between two dielectric media. It is then extended to describe the scattering of x rays from a multilayer structure composed of many nonideal interfaces. The most unique feature of this theory is that there are no constraints on the physical structure of the interfaces; the interfaces can have any form of roughness or compositional inhomogeneity. A simple analytical expression is derived for both the near and far radiation field to first order, assuming that the scattering is weak. The theory is valid for arbitrary polarization and at all angles of incidence (measured from the normal) less than the critical angle for total external reflection. Finally, the results are applied to study the effect of different interface structures on the performance of multilayer x-ray optics.
Properties and characterization of codeposited boron nitride and carbon materials
Authors: Moore A. W. , Strong S. L. , Doll G. L. , Dresselhaus M. S. , Spain I. L. , Bowers C. W. , Issi J. P. , Piraux L.
Published: July 2002

The physical properties of carbon-boron nitride (C-BN) prepared from mixtures of BCl3, NH3, and selected hydrocarbons by codeposition methods have been investigated using x-ray diffraction, electron diffraction, transmission electron spectroscopy, x-ray photoelectron spectroscopy, Raman scattering, optical reflectivity, thermal conductivity, thermopower, and electrical resistivity. Taken collectively, the results of these experiments indicate that the compression-annealed C-BN materials studied here consist of separated domains of pyrolytic boronated graphite and pyrolytic boron nitride, while as-deposited samples may possibly be a single-phase mixture of C, B, and N. As-deposited materials containing more than 20% carbon were found to be more highly oriented than unannealed pyrolytic graphite, and the crystallinity of these materials was greatly enhanced by uniaxial compression annealing. Results of the thermal conductivity, thermopower, and electrical resistivity measurements are consistent with a network of turbostratic graphite BN domains with some conduction paths for charge carrier transport between the domains. Increasing the carbon concentration from 20% to 60% leads to an increased linkage between the conducting domains and a percolation conducting network is established.
Liquid junctions for characterization of electronic materials. I. The potential distribution at the Si/methanol interface
Authors: Fantini M. C. A. , Shen Wu-Mian , Tomkiewicz Micha , Gambino J. P.
Published: July 2002

Photoelectrochemical cells consisting of n-type 〈100〉-Si wafers in methanolic solutions of ferrocene derivatives with LiClO4 as the supporting electrolyte have been analyzed using a complementary set of impedance spectroscopy, electroreflectance, and current-voltage measurements. The results were interpreted in terms of charge accumulation modes correlated with junction parameters such as space-charge layer, surface states, Fermi-level pinning, and the possible presence of an insulating layer at the interface. The impedance of these junctions is interpreted in terms of an equivalent circuit. The Fermi level is partially pinned at a potential about 0.2 eV below the conduction band and is completely pinned at potentials positive to midgap. The electroreflectance results agree well with the impedance. The effect of an HF etching on the properties of the cells will be discussed. We have also compared the results in the methanolic solution with an aqueous electrolyte. The potential distribution obtained in this case is very similar to the ferrocene solution.
Chemical processes promoted by CO2 laser-assisted decomposition of silane on silica substrates
Authors: Tonneau D. , Pauleau Y. , Auvert G.
Published: July 2002

Microstructures were produced on silica substrates by localized deposition or etching via cw CO2 laser-induced decomposition of silane. Silicon dots having a Gaussian profile were deposited at SiH4 pressures above 1 Torr for laser-induced surface temperature at the center of the irradiated zone above 850 °C. With SiH4 pressures below 1 Torr, ring-shaped Si microstructures were produced while the temperature at the center of the irradiated zone was varied from 950 to 1050 °C. The absence of deposition in the center of the hot spot may be attributed to a decrease in nucleus density of Si clusters. At temperatures above 1050 °C, silica substrates were attacked since the interaction between SiO2 and Si atoms produced by decomposition of silane led to the formation of volatile SiO. The etching kinetics was governed by the decomposition kinetics of SiH4 molecules in the hot zone irradiated with the cw CO2 laser beam.
An analysis of the anomalous high-current cathode emission in pseudospark and back-of-the-cathode lighted thyratron switches
Authors: Hartmann W. , Dominic V. , Kirkman G. F. , Gundersen M. A.
Published: July 2002

An analysis of the anomalously large cathode emission recently observed in the superdense glow of pseudospark and back-lighted thyratrons is presented. These switches are low-pressure (27 Pa H2) glow-discharge pulsed-power devices. After operating at peak discharge currents of 6–8 kA and pulse durations of 0.5–1 μs, the surface surrounding the cathode hole was found to have been homogeneously melted within a radius of ≊4 mm indicating that the discharge is a superdense glow discharge, not an arc, with a cross-sectional area on the order of 1 cm2. This conclusion is also supported by streak camera measurements. The current density at the cathode surface under these conditions is 5–10 kA/cm2, several orders of magnitude larger than that of thermionic cathodes in common thyratrons. This high-current density is explained by intense cathode heating from a high-current density ion ‘‘beam’’ produced in the cathode fall during the initial stage of current buildup. The surface heating resulting from this ‘‘beam’’ yields a significant field-enhanced thermionic emission of electrons.
Properties and structure of PbO-PbF2-B2O3 glasses
Authors: Gressler Carole A. , Shelby James E.
Published: July 2002

Glasses containing as little as 5 mol % B2O3 have been made in the ternary system PbO-PbF2-B2O3. Glass transformation and crystallization temperatures, thermal expansion behavior, and electrical conductivity of these glasses have been measured. The lead fluoroborate glasses appear to be anion conductors, with conductivities among the highest ever reported for fluorine-conducting glasses. A model for the structural role of fluorine in these glasses is proposed.
Elevated temperature reactive ion etching of GaAs and AlGaAs in C2H6/H2
Authors: Pearton S. J. , Hobson W. S.
Published: July 2002

The etch rate, surface morphology and atomic composition, and depth of hydrogen passivation of Si dopants in n-type GaAs and AlGaAs have been examined as a function of the temperature of the sample during reactive ion etching in C2H6/H2. While there is no temperature dependence of the etch rate of AlGaAs over the range 50–350 °C, the etching of GaAs shows an increase of a factor of 2 between 150 and 250 °C, decreasing at higher temperatures. The As-to-Ga ratio in the near-surface region of GaAs remains unchanged over the whole temperature range investigated and there is no polymer deposition. The etched surface morphology is smooth for both GaAs and AlGaAs for all temperatures while the depth of Si dopant passivation by hydrogen shows an increase with increasing substrate temperature during the etching treatment.
Dependence of the nonlinear transmission properties of fused silica fibers on excimer laser wavelength
Authors: Brimacombe Robert K. , Taylor R. S. , Leopold K. E.
Published: July 2002

The nonlinear transmission properties of commercially available fused silica fibers have been determined as a function of excimer laser wavelength. Accurate two-photon absorption coefficients have been measured and the influence of color center formation is discussed. Two-photon absorption and color center formation dominate the ArF and KrF transmission at high intensities while both of these effects are negligible at the XeCl and XeF laser wavelengths.
Magnetization reversal of cobalt-modified γ-Fe2O3 particles
Authors: Schabes Manfred E. , Bertram H. Neal
Published: July 2002

A micromagnetic study of the effects of cobalt modification on the magnetization reversal of elongated γ-Fe2O3 particles is presented. Equilibrium states and irreversible switching are computed numerically. The undoped particle core is identified as the site for the initial irreversible processes. For certain material parameters this can lead to a core-reversed state. The enhancement and the saturation of the enhancement of the switching field are explained as a function of doping level. Extrapolation of the numerical results suggests that approximately one monolayer of cobalt-ferrite is sufficient to yield significant enhancement of the coercivity.
Heavily-doped n-type InP and InGaAs grown by metalorganic chemical vapor deposition using tetraethyltin
Authors: Pinzone C. J. , Gerrard N. D. , Dupuis R. D. , Ha N. T. , Luftman H. S.
Published: July 2002

Heavily doped n-type InP and InGaAs epitaxial layers have been grown by metalorganic chemical vapor deposition at atmospheric pressure using tetraethyltin (TESn) as a dopant source. Sn-doped InP and InGaAs layers have been grown with doping concentrations as high as n300K∼3.3×1019 cm−3 and n300 K∼6.1×1019 cm−3, respectively. Hall measurements of Nd-Na at 300 and 77 K indicate that the Sn is uncompensated up to these concentrations. Analysis of the Sn concentration in InP:Sn and InGaAs:Sn layers using secondary ion mass spectrometry, shows that all of the Sn is ionized in InP and InGaAs until a limit is reached that corresponds to the electrical limits. SIMS profiles also show that the use of TESn for the growth n+ InP and InGaAs layers results in no severe memory effects and that abrupt Sn doping profiles can be achieved.
Phosphorus coimplantation effects on optimum annealing temperature in Si-implanted GaAs
Authors: Sugitani Suehiro , Hyuga Fumiaki , Yamasaki Kimiyoshi
Published: July 2002

Phosphorus (P) coimplantation raises the optimum annealing temperature, providing maximum sheet carrier concentration in Si-implanted GaAs active layers. 3×1013 cm−2 coimplanted P raises the optimum annealing temperature for channel layers from 920 to 990 °C, the same temperature for contact layers. Photoluminescence measurement reveals that this is due to suppression of GaAs and SiAs acceptor generations up to about 1000 °C by P coimplantation. These features indicate that P coimplantation helps to achieve GaAs integrated circuits with high performance.
Electron-wave quarter-wavelength quantum well impedance transformers between differing energy-gap semiconductors
Authors: Gaylord T. K. , Glytsis E. N. , Brennan K. F.
Published: July 2002

Impedance transformers for ballistic (collisionless) electron waves traveling between dissimilar energy-gap semiconductors are designed as a series of quarter (electron) wavelength layers in the form of a compositional superlattice. The quantitative analogies that have been previously established [J. Appl. Phys. 65, 814 (1989)] between electron-wave propagation in semiconductors and electromagnetic-wave propagation in dielectrics are used. For the design energy, the electron wave would be totally transmitted and the structure is analogous to an antireflection coating in electromagnetic optics. Practical constraints on the impedance transformer layers are (1) their compositions must be within the usable compositional range and (2) their thicknesses must be integer multiples of a monolayer thickness. These constraints are included in the design process. Procedures for designing narrow-band, maximally flat (Butterworth), and equal-ripple (Chebyshev) impedance transformers of arbitrary spectral bandwidth are presented. Example practical single-layer and three-layer transformers for connecting GaAs and Ga0.8Al0.2As are presented.
Rechargeable E′ centers in silicon-implanted SiO2 films
Authors: Kalnitsky A. , Ellul J. P. , Poindexter E. H. , Caplan P. J. , Lux R. A. , Boothroyd A. R.
Published: July 2002

Implantation of Si in does of 1015–1016 cm−2 into dry thermal oxides on silicon wafers produces a three-state MOS memory device. For both positive- and negative-going traps, gate voltage stress up to ±10 MV/cm−1 generates stable (±) oxide charge near the gate and (∓) charge near the substrate. Electron paramagnetic resonance (EPR) measurement on corona-field (≤11 MV/cm) stressed oxides reveals E′ centers in regions of positive charge, which may be recycled between the EPR-visible (+) state and the invisible neutral state. The correspondence of charge and EPR indicates a composite or Feigl-Fowloer-Yip E′ center, O3 3/4 Si:...+Si 3/4 O3, arising from nonstoichiometric Si fused into the SiO2 lattice. Upon trapping an electron, the center rebonds to yield O3 3/4 SiSi 3/4 O3. The charging parameters of the E′ center suggest tunneling of an electron from the (0→+) state, and are consistent with the theoretical prediction of the energy level and Franck–Condon relaxation. The three types of E′ centers observed in this and related studies are compared with the E′α, Eβ and E′γ variants of bulk amorphous silica.
Analysis of viscoplasticity in 6061-T6 aluminum
Authors: Rubin M. B.
Published: July 2002

Results from a previous analysis of experimental data on 6061-T6 aluminum have been used to determine values for material parameters in constitutive equations for viscoplasticity and hardening. In contrast to previous work, the present model includes the continued hardening observed in Hopkinson bar tension experiments and predicts the wave structure measured in plate impact experiments reasonably well. An interesting conclusion of the present work is that the structure of the unsteady portions of weak shocks measured in plate impact experiments can provide a sensitive measure of hardening near the onset of plasticity.
Micromechanical fracture strength of silicon
Authors: Ericson Fredric , Schweitz Jan-Åke
Published: July 2002

In order to test the statistical influence of some process and micromachining parameters on the fracture strength of silicon microelements, arrays of identical microsized cantilever beams were bulk micromachined in single-crystalline silicon wafers. The beams were exposed to various surface treatments (diamond polishing with different grades, oxidization, stripping of oxide) in different combinations. The influence on fracture strength was investigated by bending the beams to fracture in a micromanipulator mounted in situ in a scanning electron microscope while registering force-versus-deflection curves. Average fracture strengths, standard deviations, Weibull moduli, crack-initiating flaw sizes, and in some cases elastic moduli were evaluated. Diamond polishing was found to decrease the fracture strength drastically, but polishing followed by oxidization not only restored the original strength, but actually increased it, due to crack healing. Polishing, oxidization, and subsequent stripping of oxide resulted in fracture strengths slightly higher than the original strength. The Weibull modulus was diminished from 10 to 6–9 by the polishing. The initiating flaw sizes were theoretically evaluated, and found to agree with previous results of cross-sectional transmission electron microscopy studies of polished silicon surfaces. The elastic moduli determined were significantly lower (30%–40%) than the corresponding module of pure, single-crystalline silicon, probably due to high dopant contents in the specimens investigated here.
Anisotropy of piezoresistance in n-channel inversion layers of metal-oxide-semiconductor transistors on (001)Si
Authors: Maruyama T. , Zaima S. , Koide Y. , Kanda Y. , Yasuda Y.
Published: July 2002

The crystallographic orientation dependence of piezoresistance of n-channel inversion layers in metal-oxide-semiconductor field-effect transistors on p-type (001)Si has been studied by using a diaphragm at room temperature. The experimental results have been compared with self-consistent calculations based on a surface quantization effect. The main feature of the crystallographic orientation dependence can be explained by an electron repopulation effect induced by applied strain and an effective mass anisotropy. It can be found that the difference between longitudinal and transverse piezoresistance in the devices nearly along the [110] directions is mainly due to an orthorhombic distortion of Si, and the shear deformation coefficients Ξu is determined to be 5.8 eV from comparing the experimental results with the calculated ones. An expression of the shear piezoresistance component π44 is also derived.
Theoretical treatment of rf discharges in CO2 waveguide lasers
Authors: Schröder K.
Published: July 2002

Theoretical investigations have been performed to describe the discharges in rf-excited CO2 waveguide lasers. Especially, the formation of boundary layers has been considered as these regions are not yet understood completely. As characterization of the plasma, the spatial distributions of electron density and electric field have been calculated as these two quantities are suitable to describe the electrical properties of the discharge as well as the optical behavior. The electric-field strength is split up into the rf field and a static field which forms as a consequence of ambipolar diffusion.
Pressure effect on magnetic transition temperature and magnetic phase diagram of Mn2−xCoxSb
Authors: Kanomata T. , Hasebe Y. , Ito T. , Yoshida H. , Kaneko T.
Published: July 2002

Pressure effects on spin-flop transition temperature (Tsf) of Mn2−xCoxSb have been measured in order to study the nature of spin-flop phase transitions. The magnetic phase diagrams for Tsf versus concentration and for Tsf versus pressure have been determined. Tsf increases with increasing applied pressure (dTsf/dp=2.9 K/kbar for x=0.05, dTsf/dp=3.7 K/kbar for x=0.10, dTsf/dp=3.3 K/kbar for x=0.15, and dTsf/dp=2.7 K/kbar for x=0.20). On the other hand, Tsf decreases slowly with x up to ≂0.05 and increases rapidly under further increasing x at normal atmospheric pressure. On the basis of these results, the microscopic origin of the magnetic anisotropy of Mn2−xCoxSb is discussed.
Substrate temperature dependence of electrical properties of ZnO:Al epitaxial films on sapphire (12̄10)
Authors: Igasaki Yasuhiro , Saito Hiromi
Published: July 2002

ZnO:Al films were deposited on (12̄10) oriented sapphire substrates heated up to 400 °C by rf magnetron sputtering from a ZnO target mixed with Al2O3 of 2 wt%. Films deposited on a substrate heated to a temperature in the range 50–350 °C were (0001) oriented single crystals but those grown at 400 °C consisted of crystallites with the (0001) and (11̄01) orientation. The former films had relatively smooth surfaces whereas the latter exhibited very rough surfaces. Electrical properties such as resistivity, carrier concentration, and the Hall mobility were measured as a function of substrate temperature. The carrier concentration decreased as the substrate temperature was increased up to 300 °C, although the Al content remained unchanged in this temperature range. From these measurements, it was found that the native donors were important as a source of carriers, even in ZnO:Al films. However, it was found that the Hall mobilities for films with a thickness of more than 200 nm experienced minor changes over a growth temperature range from 50 to 350 °C. The minimum resistivity obtained was about 1.5×10−4Ω cm, a value comparable to that for indium tin oxide film.
Improved interface state density function in metal-semiconductor junctions by deep-level transient spectroscopy
Authors: Halder N. C. , Kim H. W. , D’Souza K. M. , Barnes D. E. , Hartson S. E. , Mohapatra R.
Published: July 2002

Deep-level transient spectroscopy (DLTS) measurements have been made to obtain the activation energy and capture cross section in Schottky diodes. Previous theories for interface state density (ISD) functions, which are derived for metal-semiconductor junctions, made approximations that were inappropriate. This paper derives improvements to the previous analysis and calculates ISD using the measured DLTS data. As for examples, Schottky diodes of Si, GaAs, and AlxGa1−xAs have been investigated with both methods. It has been found that the previously used method overestimated both the peak maximum position and peak height of the ISD.
On a method to calculate the demagnetizing field in a micromagnetic structure
Authors: Bagnérés-Viallix A. , Baras P.
Published: July 2002

The simultaneous minimization of demagnetizing, exchange, anisotropy, and Zeeman energies in a micromagnetic structure is a difficult problem. The way it has been handled by previous investigators has often involved long running times or full matrices. In this paper, we take the demagnetizing energy into account by calculating the scalar potential φ associated with the demagnetizing field. This involves the calculation of another unknown φ in a problem which already has three unknowns: the components of the magnetization. By using φ, the problem is now uncoupled and the sparsity of the matrices is preserved. The magnetic structures studied here are thin slabs. We want to perform the calculations only on a small part of the slab. Since φ is defined in the whole space, the problem reduces to determining boundary conditions. By assuming that each unknown is periodic within the two directions in the plane of the slab, the domain of the problem reduces to a rectangular cell. The equations given in Ref. 1 are discretized by the finite-element method and boundary elements are taken on the upper and lower surface to evaluate the scalar potential. This paper will outline the steps of the calculation of φ.