bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic field of the cardiac conduction system (invited)
Authors: Tripp J. H. , Farrell D. E.
Published: February 2003

An overview is given of recent progress in our understanding of the magnetic field of the human cardiac conduction system. This field, of the order of 0.5 pT, has been mapped with a first-order SQUID gradiometer in a rural location having the very low overall noise level of 6×10−3 pT/√Hz. Measurements of similar sensitivity in an ordinary clinical environment have not yet been attempted but we discuss a new approach to noise reduction which should permit this to be achieved. A theoretical model, based on an electrophysiological description of the nerve fibers of the cardiac conduction system accounts quantitatively for the principal features of the existing observations. This constitutes a first step toward the extraction of clinically useful information from magnetic measurements of the conduction system. An extension of this approach is discussed, which promises to supply useful information on abnormal as well as normal subjects.
Formation of iron clusters in a mucus-like medium
Authors: Reinstein Lawrence E. , Robinson Lisa , Glicksman Arvin S.
Published: February 2003

In a recent paper based upon repeated magnetization studies done on the lungs of smokers and non-smokers who have inhaled small quantities of iron oxide power, Cohen et al. claim that the dust clearance ability of the cigarette smoker’s lung is markedly impaired. A re-interpretation of this data which casts doubt on the logic of Cohen’s conclusion was suggested by Sterling and is based upon the hypothesis that during the magnetization phase of Cohen’s experiment, iron oxide ’’clusters’’ were preferentially formed in the highly mucus-filled environment of the smoker’s lung. In order to test the plausibility of this hypothesis, in-vitro experiments have been performed to measure the mean ’’cluster’’ diameter of iron oxide powder in a mucus-like liquid medium (methylcellulose) during and after magnetization as functions of the solution viscosity. Results of these measurements will be presented.
Analysis of mosaic structure of {100} molybdenum
Authors: Bhattacharya P. K.
Published: February 2003

Rutherford backscattering (RBS) measurements are reported of the mosaic structure of vacuum deposited, thermally grown crystals of 1-μm-thick{100} on MgO substrates. RBS <100≳ axail minimum yields were found at 2 MeV on assorted mosaic spread crystals to assess their quality for channeling and blocking effect investigations. Three different mosaic spreads of 9.6, 13.4, and 16.8 min, as determined by x-ray reflection full widths at half maximum over Bragg reflection, were selected. Minimum yields were found to have a linear dependence on mosaic spread at room temperature, having a cutoff value equal to Lindhard’s theoretical estimate. The empirical relationship Δϑ0 = (3.7χmin −6.12) min provides a criteria of characterization of ideal thin {100} Mo crystals for channeling purposes and also permits using the technique to identify faulted and unfaulted crystals.
Phase transitions at 462 and 495 K in barium nitrite
Authors: Abrahams S. C. , Gallagher P. K. , O′Bryan H. M. , Liminga R.
Published: February 2003

New phase transitions at 462 and 495 K have been found in Ba(NO2)2. The increase in entropy at each transition is about 13 J mol−1 K−1. A gain of two orientations per independent NO−2 ion at each transition corresponds to an entropy increase of 11.5 J mol−1 K−1. The crystal melts at 516 K. The high-temperature phase I is metastably retained at 298 K on rapid solidification, reverting to phase III on reheating above 350 K. Phase III is orthorhombic with lattice constants at 298 K of a = 7.657, b = 8.355, and c = 6.742 Å and four Ba(NO2)2 in the unit cell. The linear thermal expansion coefficients are 30.7, 14.0, and −5.9×10−6 Å K−1 for the a, b, and c axes, respectively. The powder pattern for phase II has not been indexed. Phase I may be fitted by a monoclinic unit cell with a = 6.692, b = 7.052, and c = 9.638 Å and β = 104.61° at 507 K with four Ba(NO2)2 in the unit cell. A dielectric anomaly is observed at 468 K in the frequency range 0.1–1 MHz: dielectric losses obscure the anomaly at lower frequencies.
An ultrasonic interface-wave method for predicting the strength of adhesive bonds
Authors: Rokhlin S. I. , Hefets M. , Rosen M.
Published: February 2003

A thin adhesive film, located between two bonded adherents, is capable of localizing the energy of elastic waves in the form of an interface wave. Under study are the phase velocity and transmission losses of the interface wave which were measured during the entire course of polymerization of the adhesive. It is shown that the phase velocity of the interface wave and the effective shear modulus of the interface film, calculated from the velocity data, are related to the strength of the adhesive bonds. The general transmission loss factor, which is a function of the relaxation maximum of losses arising during the course of polymerization of the adhesive, is another parameter correlated with the strength. The shear strength of the joint was determined on a special specimen in the form of a lap joint, which was also used for acoustic measurements.
Platinum silicide formation under ultrahigh vacuum and controlled impurity ambients
Authors: Crider C. A. , Poate J. M. , Rowe J. E. , Sheng T. T.
Published: February 2003

The thin-film Pt-Si silicide system has been investigated under clean, well controlled conditions. A (UHV) ultrahigh vacuum apparatus for this study is described which allows preparation of atomically clean Si surfaces and subsequent evaporation of Pt films in vacuo 10−9 Torr. Samples are annealed and characterized with in situ (RBS) Rutherford backscattering and (AES) Auger electron spectroscopy and later examined with (TEM) transmission electron microscopy and (SEM) scanning electron microscopy techniques. Impurity-free Pt films deposited on clean, room-temperature Si substrates react initially to form Pt2Si and then PtSi with diffusivities one to three orders of magnitude higher than previously reported in the 200–325 °C temperature range. However, the observed activation energies of 1.3±0.2 eV and 1.5±0.2 eV are in reasonable agreement with previous reports. No differences in PtSi-Si interface width, PtSi surface character, growth rates, and phase growth progression are observed between extremely clean, well controlled UHV processed samples and samples prepared with normal wet and dry device processing cleanliness levels provided that the Pt films are impurity-free. The presence of oxygen in the deposited Pt film is crucial in determining reaction rates and the phase growth sequence. Increasing impurity concentrations in the initial metal film or at the Pt-Si interface cause macroscopically nonplanar PtSi-Si interfaces and PtSi surfaces. Diffusivities for both Pt2Si and PtSi formation are observed to be strongly dependent upon oxygen contamination in the initial Pt film over a wide range; excessive contamination alters the phase growth sequence. This behavior would tend to indicate that Pt-silicide growth occurs by grain boundary diffusion at these temperatures.
Theory of continuously distributed trap states at Si-SiO2 interfaces
Authors: Sakurai T. , Sugano T.
Published: February 2003

A calculation method to treat the electronic structures of crystalline Si-amorphous SiO2 interfaces with or without microstructural defects is developed based on semiempirical tight-binding Hamiltonians and the Green’s function formulation, and applied for calculation of the energy level of the trap states between amorphous SiO2 and the Si substrate with (111) orientation. The major results are (i) the perfect interface does not have any states in the forbidden gap of Si although the Si-O-Si bonding angle at the interface is varied in the range between 120° and 180°, and neither does the interface with oxygen dangling bonds have any; (ii) trap states due to a Si dangling bond appear at about the middle of the Si band gap; and (iii) O-vacancy and Si-Si weak bonds at the interface produce trap states at the energy range higher than the midgap, whereas Si-O weak bonds at the interface produces trap states at the energy range lower than the midgap. The energy level of these trap states varies with changing bonding parameters such as bond lengths and bond angles. These energy levels caused by Si-Si weak bonds and Si-O weak bonds are possible origins of the interface states continuously distributed in energy. The reduction of trap states in the Si forbidden gap by bonding H, OH, Cl, and F atoms to Si dangling bonds is also discussed.
Electrical and dielectric behavior of a zinc oxide composite
Authors: Bhushan Bharat , Kashyap Subhash C. , Chopra K. L.
Published: February 2003

Room-temperature studies of I-V characteristics and variation of both the dielectric constant and dielectric loss with frequency are presented for ZnO-Bi2O3 samples having different compositions and prepared by sintering at different temperatures. The nonlinearity parameter, dc resistivity, dielectric constant, and dielectric loss depend on the composition and sintering temperature. These parameters have been optimized for obtaining maximum nonlinearity and dielectric constant. The occurrence of a loss peak is, however, seen to be independent of the composition and sintering temperature. The present study, supported by a scanning electron microscope analysis, confirms the necessity of a two-phase structure in the composite for its nonlinearity and high dielectric constant. The variation in the dielectric constant and nonlinearity parameter with sintering temperature for samples of different compositions has been explained on the basis of change in barrier height of Schottky barriers; the presence of these barriers has been inferred by the observed behavior of capacitance variation with bias.
Optical properties of Nd3+ in tellurite and phosphotellurite glasses
Authors: Weber M. J. , Myers J. D. , Blackburn D. H.
Published: February 2003

Optical-absorption and emission spectra and fluorescence lifetimes were measured for Nd3+ in tellurite glasses containing various alkali and higher valence state cations and in a series of new phosphotellurite glasses. Judd-Ofelt intensity parameters were determined and used to calculate radiative lifetimes and stimulated emission cross sections for 4F3/2→4I11/2 and 4F3/2→4I13/2 transitions. Cross sections for several of the glasses are the largest obtained for any pure oxide glass. The dependence of the spectroscopic properties on composition and the application of tellurite glasses for lasers are discussed.
A contribution to the theory of high-temperature vaporization and electron emission: Application to neodymium hexaboride and lanthanum hexaboride
Authors: Storms E. K.
Published: February 2003

The thermionic emission properties of polycrystalline NdB6 have been determined as a function of surface composition throughout its single-phase region. the equation log I = 1.673−15637/T+2 log T−0.0042 T/{exp[0.07X/(X−6)]+1} describes the relationship between emitted current flux I (A/cm2), temperature T (K), and surface composition X (B/Nd) between 1200 and 1600 K. The effective work function at 1500 K is 3.22 eV for NdB6.0 and 4.04 eV for NdB8.0. Previous measurements of the LaB6 phase were fit by the equation log I = 2.533−15330/T+2 log T−0.5T exp[−0.11X/(X−6)]. This information was used to determine the density of states for the two hexaborides and make predictions about the behavior of various ternary systems.
Thermionic emission and atom vaporization of the Gd-B system
Authors: Storms E. K. , Mueller B. A.
Published: February 2003

Thermionic emission, vapor composition, chemical activity, and weight loss have been measured over a range of compositions in the Gd-B system. Values are reported for various compositions in the GdB4 phase and for one composition in the GdB6 phase. The congruently vaporizing composition at 1700 K was found to be GdB4.03 , with an effective work function of 3.27 eV. The work function of GdB6 is near 4.02 eV. At congruency, the Gd-B system loses mass approximately twice as fast as the La-B system.
Morphological stability of the planar solid-liquid interface
Authors: Holmes Douglas E. , Gatos Harry C.
Published: February 2003

An experimental investigation of the morphological stability of the planar solid-liquid interface was carried out in which, for the first time, all pertinent solidification parameters were determined quantitatively and the effect of convenction was evaluated. The microscopic growth rate and interface morphology were determined through solidification by interface demarcation; thermal characterization of the melt was achieved by direct probing, and compositional profiles were obtained by single point spreading resistance. solidification was carrried out in a stationary vertical Bridgman-type apparatus designed for minimal convective interference. It was found that the interface morphology at the onset of instability is characterized by near-sinusoidal undulations with amplitudes that increase exponentially with time and undergo harmonic distortion as instability develops. Compositional maxima and minima at depressions and protrusions, respectively, across the unstable interface were observed consistent with steady-state equilibrium behavior. When the tangent to the unstable interface became parallel to 〈111〉 planes, microfaceting took place which effectively arrested the development of the instability in the light of current theoretical models, it was concluded that dynamic rather than equilibrium (thermodynamic) criteria control the stability-to-instability transition. Measured dynamic parameters, i.e., the wavelength of the fastest growing perturbation and the time constant, were found to be in very good agreement with theory. However, an inconsistency between experimental and theoretical values of the diffusivity parameter was found which indicates delocalized rather than localized initial perturbations not appropriately described by approximate theory. The heat of fusion and the difference in thermal conductivity of the solid and liquid were shown to promote morphological stability in the presence of constitutional supercooling. The development of a transient instability superimposed on the original instability not described by existing linear or nonlinear theories was attributed to the growth of a second harmonic undulation.
Reactive ion etching induced corrosion of Al and Al-Cu films
Authors: Lee Wen-Yaung , Eldridge J. M. , Schwartz G. C.
Published: February 2003

Aluminum and Al-Cu conductor lines etched with a Cl containing plasma in low-pressure diode systems corroded rapidly upon atmospheric exposure. The mechanisms underlying this corrosion problem were investigated using Auger electron and x-ray photoelectron spectroscopies. Reactive ion etching resulted in a nonprotective oxide layer and thus rendered the etched samples more susceptible to atmospheric corrosion. Factors contributing to the increased reactivity of etched samples includes C and Cl contamination, radiation damage, and for Al-Cu alloys, Cu enrichment. A thermal oxidation treatment at temperatures of ∼300–350 °C and l atm O2 pressure for ≳30–45 min was found to be effective in restoring the protective oxide layer and thus improving the corrosion resistance of etched samples.
I-V characteristics of thin-film transistors
Authors: Chen I. , Luo F. C.
Published: February 2003

A mathematical theory has been formulated for the steady-state I-V characteristics of thin-film transistors, taking into account explicitly the unique properties of this device, namely, the existence of bulk and interface localized states, and the small semiconductor thickness. An excellent agreement has been obtained between the theory and the experimental data. The electronic properties of the semiconductor, i.e., the free carrier density, and the densities of surface and the bulk localized states can be determined by direct comparison of the calculated and experimental I-V characteristics. The two-dimensional theory predicts the current saturation without an ad hoc model. The charge distribution in the semiconductor and the sensitivity of the gain to various parameters are discussed.
Time domain measurement of dielectric spectra of aqueous polyelectrolyte solutions at low frequencies
Authors: Nakamura Haruki , Husimi Yuzuru , Wada Akiyoshi
Published: February 2003

Dielectric measurements of aqueous solutions at low frequencies below 104–105 Hz have always been accompanied by two problems, which have made it difficult to obtain precise results; they are (i) the electrode polarization and (ii) the thermal drift of electric dc conductivity. For the former, adoption of a four-electrode cell has been proven to be effective in suppressing the electrode polarization. For the latter problem, a time domain measurement of the dielectric spectra is adequate. A combination of a four-electrode method with a time domain spectrometry using a Fourier synthesized pseudorandom noise (FSPN) method gave precise dielectric spectra at low frequencies, which were difficult to obtain by previous methods, with an adequate reproducibility for aqueous solutions of biological molecules, DNA, and polyglutamic acid. A precise description of the combined system is mentioned and the precision of the measurement is discussed.
Stimulated emission cross sections of Nd:YVO4 and Nd:La2Be2O5 (BeL)
Authors: Tucker Armin W. , Birnbaum Milton , Fincher Curtis L.
Published: February 2003

The stimulated emission cross sections σ of the 4F3/2→4I11/2 transitions have been measured for a-axis Nd:YVO4 (1064.1 nm, σ = 19.0×10−19 cm2), x-axis Nd:BeL (1079.2 nm, σ = 1.54×10−19 cm2), and y-axis Nd:BeL (1070.1 nm, σ = 2.31×10−19 cm2).
Origin of high-frequency disperision of G
p/ω of metal-oxide semiconductor capacitors
Authors: Knoll M. , Fahrner W. R.
Published: February 2003

The high-frequency maximum of Gp/ω vs ω curves is shown to result from bulk series resistance contrary to conclusions of Morita et al.
Determination of the thermal-conductivity tensor and the heat capacity of insulating solids with the transient hot-strip method
Authors: Gustafsson Silas E. , Karawacki Ernest , Khan M. Naushad
Published: February 2003

The recently described transient hot-strip method has been developed for the study of solids with direction dependent thermal conductivity. By making three independent measurements, with the hot-strip properly oriented, information can be obtained about the thermal conductivities along the principal directions and also about the specific heat capacity per unit volume. To demonstrate the versatility of the method, crystalline quartz was studied over the temperature range 230–340 K and the results are in good agreement with earlier reported data.
Confinement of ions created externally in a quadrupole ion trap operated in the combined Penning and radio-frequency mode
Authors: O Chun-Sing , Schuessler Hans. A.
Published: February 2003

The use of a quadrupole ion trap to catch ions in flight and to trap them for extended periods of time was investigated. The numerical results obtained that storage of ions produced externally is possible in the combined mode, in which suitable radio-frequency, dc-electric, and magnetic fields are applied simultaneously. Equations describing the dynamics of the ion motion have been derived and optimum injection conditions were obtained.
Effect of random aperiodicity on threshold gain of a distributed feedback semiconductor laser
Authors: Hsieh H. C. , Stewart R. W.
Published: February 2003

The effect of a small perturbation such as an irregularity in spatial periodicity in the periodic structure of a distributed feedback semiconductor laser is studied. The threshold condition, which takes into account the presence of this perturbation, is derived with the aid of a linearized one-dimensional solution of the wave equation by the truncated Floquet-Bloch approach. To illustrate the effect of a small random perturbation, variations of mean gain and mean phase parameters, with the coupling parameter τ = (κL) and the perturbation parameter ρ0, are investigated with the aid of approximate expressions obtained by using a truncated MacLaurin series and the first-order stationary Gauss-Markov process. For example, it is shown that when the device is operated in the region of moderate coupling, e.g., 0.1<(κL)<6, the effect of perturbation on the effective gain parameter can be significant. Here, κ and L denote the coupling coefficient and the length of periodic structure, respectively.
Effect of preionization uniformity on a KrF laser
Authors: Sumida Shin , Kunitomo Kouichi , Kaburagi Masahiro , Obara Minoru , Fujioka Tomoo , Sato Kounosuke
Published: February 2003

Our investigation has revealed that the preionization electron density and the spatial distribution of the preionization electrons could play an important role for the scaling of discharge pumped lasers. The KrF laser energy, pulse width, and laser output burn pattern were strongly dependent on the preionization electron density. The spatial uniformity of the preionization in parallel to the electric field affected the discharge uniformity. A more efficient power deposition was obtained in the stronger preionized region of the laser gas mixture.
Measurement of vibrational populations in low-pressure hydrogen plasma by coherent anti-Stokes Raman scattering
Authors: Pealat M. , Taran J. P. E. , Taillet J. , Bacal M. , Bruneteau A. M.
Published: February 2003

Coherent anti-Stokes Raman scattering (CARS) has been applied to the measurement of vibrational populations in a low-pressure H2 plasma. We describe the plasma generator and give some particulars of the optical arrangement. For an electron density of 2×1011 cm−3 and a total pressure of 0.13 mbar, the rotational temperature is found to be 475 K. The populations of vibrational states v = 0, 1, and 2 have also been measured. Their distribution is non-Boltzmann. The influence of pressure and discharge parameters is briefly discussed. The instrument detection sensitivity for a given rovibrational state is about 1012 cm−3.
Holographic x-ray gratings generated with synchrotron radiation
Authors: Csonka Paul L.
Published: February 2003

It is shown that gratings of up to about 105 lines per mm could be manufactured holographically by setting up an interface pattern of x-ray photons emitted from electron storage rings (e.g., SPEAR at Stanford). Such a grating may be used as an optical element for x rays; as a miniaturized circuit; or as a tool in solid-state research, e.g., to observe Bloch oscillations, to study the fine structure of Landau levels, or to construct two-dimensional ’’crystals’’ in which the potential strength and unit cell shape and size are all adjustable.
Transmission of a transient electromagnetic wave obliquely incident on a compressible plasma halfspace
Authors: Stanić Božidar V. , Petrović Zoran Lj.
Published: February 2003

The closed-form solution for the transmitted electromagnetic, impulsive, transverse magnetic plane wave obliquely incident on the compressible plasma halfspace has been obtained using a first-order perturbation theory. The ratio of the electron acoustic velocity and the speed of light a = v/c plays the role of a small parameter. Similar to the reflected waveform, the effects of the shift along the ωpt axis (angle of incidence ϑ<45°) and the change of the amplitude (ϑ?45°) have been observed. Implications of these results for the possible plasma diagnostics are discussed, and further investigations are suggested.
A critique of methods for calculating the dielectric strength of gas mixtures
Authors: Chantry P. J. , Wootton R. E.
Published: February 2003

Three currently available methods for predicting the dielectric strength of gas mixtures are discussed and compared. All are based on the common principle of linear addition of some property of the individual gases in proportion to their concentration in the mixture. The simplest approach uses a weighted sum of the dielectric strengths of the separate gases. The other approaches are based on predicting the limiting reduced field (E/N)*m at which the net ionization coefficient of the mixture (ᾱ/N)m = 0. Wieland’s approximation for ᾱm involves a weighted sum of the ᾱ’s for the separate gases, and requires a knowledge of these over the range (E/N)*w<(E/N)<(E/N)*s, where w and s refer to the weakest and strongest gas involved. It is shown that this approach in general gives a mixture strength which varies monotonically with the fractional concentrations and lies within the above range of E/N. The simplest approach, using weighted linear addition of strengths, and the empirical rule proposed earlier by Takuma et al., are shown to be special cases of the Wieland approximation. The third and most physically realistic approach uses linear proportional addition of all the relevant electron-molecule collision cross sections of the component gases. It requires a knowledge of the electron energy distribution in the mixture, which can be obtained by numerical solution of the Boltzmann equation. In some mixtures the presence of special ’’mixture processes’’, such as Penning ionization, can be anticipated and included in this third approach. The underlying assumption in the Wieland approximation is examined in the framework of the more exact formalism, and the overall hierarchy of approximations involved in the various approaches is identified. The concept of η̄ synergism is introduced as a suitable indicator of the presence of interesting mixture effects contributing to the mixture’s dielectric strength. Comparison of the Wieland formula predictions with experimental data, or the results of more exact calculations, provides an appropriate test for η̄ synergism.
Photoreceptor of a-Si:H with diodelike structure for electrophotography
Authors: Shimizu Isamu , Shirai Shigeru , Inoue Eiichi
Published: February 2003

Charging and photodischarging characteristics were investigated for the photoreceptors of amorphous silicon prepared by rf glow discharge of silane. For the positive corona, a sufficient charge retention was attained in the photoreceptor providing a thin layer of a-silicon doped with boron between the photosensitive Si:H film and the conductive substrate to prohibit the injection of carriers from the substrate. The photoconductivity gain of unity was attained in the photoreceptor when it was illuminated with visible light. A range-limited photocurrent flow was observed in the photoreceptor with a thick a-Si:H layer and the value of 2×10−8 cm2/V was estimated as μτ product of photoholes. The space-charge perturbed photocurrent was observed in the photoreceptor for the negative corona. The structure of the photoreceptor is intrinsic a-Si:H/n-type of a-silicon on a conductive substrate. In this case, the photocurrent flow was effectively perturbed by a space charge that accumulated in the photoconductor owing to the incomplete blocking.
Interaction of surface acoustic waves with current carriers in discontinuous metal films
Authors: Harnik E. , Sadar E.
Published: February 2003

A model of the interaction of surface acoustic waves with current carriers in discontinuous ultrathin metal films is developed on the basis of a simplified theory of electrical conduction advanced by Neugebauer and Webb. It is shown that the attenuation, change in phase velocity, and acoustoelectric current depend on a parameter, associated with a relaxation process inherent in the conduction mechanism, which is determined by the structural characteristics of the film. The model is in reasonable agreement with experimental results, except in inhomogeneous films, where complications may arise.
Probe layer measurements of electroluminescence excitation in ac thin-film devices
Authors: Marrello V. , Samuelson L. , Onton A. , Reuter W.
Published: February 2003

It is found that Mn electroluminescence (EL) efficieny varies widely with the position of a Mn-doped probe layer in a double dielectric thin-film ZnS ac EL device. TbF3-and Ag-doped layers exhibit a more uniform EL efficiency. The results are consistent with impact excitation of Mn in an electric field that varies in the ZnS due to space charge. The more uniform EL efficiency probed in TbF3, in contrast, suggests that the excitation mechanisms of Tb is not primarily by hot-electron impact in our devices.
Chemical vapor deposition of amorphous silicon prepared from SiF2 gas
Authors: Janai M. , Weil R. , Levin K. H. , Pratt B. , Kalish R. , Braunstein G. , Teicher M. , Wolf M.
Published: February 2003

A new chemical vapor deposition (CVD) method for the production of amorphous silicon films from SiF2 gas is described. About 1% (atomic) fluorine is incorporated in the film, its concentration decreasing with increasing deposition temperature. Optical, electronic, and structural properties of the films are reported.
The photoconductivity of polycrystalline semiconductors
Authors: Card H. C.
Published: February 2003

It is shown that, unlike in crystalline semiconductors, the photoconductivity in polycrystalline semiconductors can be principally a majority carrier phenomenon. This occurs when the majority carrier dark current is limited by transport across the grain boundaries, and the only effect of the minority carriers is in the modification, by the optical illumination, of the barrier height at these boundaries, through Shockley-Read-Hall capture/emission processes. The photoconductivity is predicted to be proportional to Gphd2, where Gph is the (uniform) photogeneration rate and d is the (cubic) grain size, over a considerable range of d.
The inverse problem of the conductivity and permeability profiles of a plane stratified medium
Authors: Coen Shimon
Published: February 2003

A transverse electric plane wave is obliquely incident upon a plane stratified medium in which the displacement currents are negligible. It is shown that the conductivity and permeability profiles of the medium can be uniquely reconstructed from the surface impedance at two angles of incidence and at all frequencies.
Determination of lifetime and diffusion constant of minority carriers by a phase-shift technique using an electron-beam-induced current
Authors: Fuyuki T. , Matsunami H.
Published: February 2003

The lifetime and diffusion constant of minority carriers in Si have been determined by a phase-shift technique using an electron-beam-induced current (EBIC). The phase of an EBIC is shifted because of the recombination of minority carriers in a material when the intensity-modulated electron beam is used in the line scan method of EBIC. The phase shift between the electron beam and the EBIC is clarified theoretically by solving the three-dimensional time-dependent diffusion equation. The phase shift increases linearly with the scanning distance. The relation between the phase shift and lifetime τ was found to be expressed using the approximated solutions of the one-dimensional diffusion equation with empirical correction factors. The normalized phase shift (i.e., the amount of the phase shift when the beam scans over one diffusion length) becomes a function of only ωτ (ω = 2πf, where f is modulation frequency). With the aid of a curve of the normalized phase shift vs ωτ, the lifetime and diffusion constant can be determined without any restriction for modulation frequency. Experimental results in Si showed good agreement with the theory.
Behavior of the drift mobility in the glass transition region of some hole-transporting amorphous organic films
Authors: Abkowitz M. , Stolka M. , Morgan M.
Published: February 2003

Drift mobility in prototypical hole-transporting organic glasses is observed to undergo a relatively abrupt, but fully reversible, decrease in activation energy during rate heating near Tg. Sensitivity of charge transport to the dynamic phenomena peculiar to the glass transition process is therefore indicated. No significant hysteresis of the drift mobility is observed during rate heating and subsequent rate cooling through the Tg region. The latter contrasts sharply with the behavior observed in amorphous chalcogenides. It is suggested that absence of mobility hysteresis is a consequence of the fact that electonic states which control transport arise from incorporated chemical species and not, as in the chalcogenides, from structural defects.
Positive and negative charging of thermally grown SiO2 induced by Fowler-Nordheim emission
Authors: Itsumi Manabu
Published: February 2003

Charging properties of thermally grown SiO2 associated with Fowler-Nordheim (F-N) emission have been investigated using a metal-oxide-silicon structure. Shifts in flatband voltage are induced by the F-N current with positive or negative dc gate voltage. The number (Ntrapped) of charges trapped in the SiO2 film is calculated from the flatband voltage shift. The number (Ninjected) of electrons injected into the SiO2 film is calculated from the F-N current. The relationship between Ntrapped and Ninjected is discussed. Charge trapping is marked when current density through the SiO2 film is more than 1×10−6 A/cm2, regardless of the polarity of gate voltage. Both positive charges, trapped under negative gate voltage, and negative charges, trapped under positive gate voltage, are found to depend basically on Ninjected and not on the gate voltage. These trapped charges are located near or at the Si-SiO2 interface, Charge trapping efficiency η, defined as η = ∂Ntrapped/∂Ninjected, is found to decrease with increasing Ninjected and to vary inversely with Ninjected for values of Ninjected over 1018 /cm2. The trapping efficiency of negative charge is found to be lower than that of positive charge. A simple quantitative model derived from the F-N characteristic is presented to account for these behaviors. Relatively good agreement between this model and experimental findings is shown.
Surface controlled InP-MIS (metal-insulator-semiconductor) triodes
Authors: Hirota Yukihiro , Okamura Masamichi , Yamaguchi Eiichi , Nishioka Takashi , Shinoda Yukinobu , Kobayashi Takeshi
Published: February 2003

Surface controlled InP-MIS (metal-insulator-semiconductor) triodes were fabricated and applied as efficient surface luminescence devices and as a more direct measurement of the surface inversion charge density. Sufficient surface luminescence was obtained under an applied pulse gate bias as low as a few volts. The radiation intensity was in proportion to the pulse repetition frequency (0.2–4 MHz). From measurement of the surface controlled MIS current, the surface inversion charge density was estimated more directly. The inversion charge density was closely correlated with the surface-state density Nss, which was deduced to be ∼1013/cm2 eV from comparison of the experimental results with a simple analysis.
Chemical composition of the SiO2/InSb interface as determined by x-ray photoelectron spectroscopy
Authors: Vasquez R. P. , Grunthaner F. J.
Published: February 2003

The chemical composition of the interface formed between deposited SiO2 films and single-crystal InSb substrates is investigated using high-resolution x-ray photoelectron spectroscopy (XPS) in conjunction with a relatively benign chemical depth-profiling technique. The SiO2 films are deposited by the thermal decomposition of silane in the presence of oxygen in a chemical-vapor-deposition (CVD) reactor. Thermal oxidation of the InSb occurs in the reactor resulting in an In-rich oxide and elemental Sb at the native oxide/InSb interface. The native oxide was found to be primarily composed of In2O3 and Sb2O3 in a 3:1 ratio. Reduction of the native oxide by silane forms a thin layer of elemental In at the SiO2/native oxide interface. These results are derived from intensity analysis of XPS spectra and are consistent with thermodynamic considerations.
The ac Josephson effect in hysteretic junctions: Range and stability of phase lock
Authors: Kautz R. L.
Published: February 2003

The rf-induced constant voltage steps generated by the ac Josephson effect are studied within the context of the Stewart-McCumber model. Simulations are used to determine the range of current bias over which phase lock occurs for model parameters appropriate to hysteretic tunnel junctions. The effect of noise on phase lock is also considered. The results are applied to a zero-bias voltage standard proposed by Levinsen et al.
Magnetic and magneto-optical properties of amorphous A1−xFex alloys (A = B, Ge, and Sn)
Authors: Buschow K. H. J. , van Engen P. G.
Published: February 2003

Amorphous alloys of the type A1−xFex, where A represents B, Ge, or Sn, were prepared by two-source coevaporation in the ranges 0.3⩽x⩽0.9, 0.30⩽x⩽0.65, and 0.45⩽x⩽0.64. The magneto-optical properties of these alloys were examined by means of the polar Kerr effect. The magnetic properties of the alloys with B and Ge were also studied. The concentration dependence of the Fe moments in the Fe metalloid alloys is analyzed in terms of a model in which due account is taken of the fact that the variation of the heat of alloying in the various iron metalloid alloys entails a variable degree of intrinsic compositional short-range order.
Magnetic and recording properties of noncrystalline FeN films
Authors: Heiman Neil , Kazama N. S.
Published: February 2003

We have prepared noncrystalline films of FeXN1−x in the range of 0.40⩽X⩽0.75. These films had large coercivities, some in excess of 600 Oe. The films were corrosion resistant and stable against annealing below 200 °C. Films with large Hc could not be produced with thicknesses less than ∼5000 Å or with 4πMS ≲ 8000 G. The usefullness of these films as recording media is thus limited by the large MRt product.
Radiation effects in crystalline SiO2: The role of aluminum
Authors: Halliburton L. E. , Koumvakalis N. , Markes M. E. , Martin J. J.
Published: February 2003

Electron spin resonance (ESR) and infrared absorption (IR) experiments have provided information about the role of aluminum in the radiation response of commercially available high-quality synthetic quartz. Samples obtained from two separate sources were investigated, and identical radiation responses were found for the two materials. Interstitial ions such as H+, Li+, and Na+ as well as radiation-induced holes trapped at oxygen ions act as charge compensators for the ever-present substitutional aluminum ions. Usually the charge compensator is located adjacent to the aluminum, and this gives rise to Al-OH−, Al-Li+, Al-Na+, and [Ale+]0 centers. Absolute concentrations of these compensated aluminum centers have been determined as a function of irradiation and annealing temperature for a variety of samples, both swept and unswept. The various treatments simply exchange one type of compensator for another at the aluminum sites, and within experimental error, the sum of the aluminum centers remains constant for a given sample. This direct accountability of all the aluminum ions in hydrogen-swept samples strongly suggests that the 3306- and 3367-cm−1 infrared bands are associated with the Al-OH− center. Also, the ESR and IR results show that the aluminum content of randomly selected bars of high-quality quartz can vary by an order of magnitude.
Laser-initiated channels for ion transport: Breakdown and channel evolution
Authors: Olsen J. N. , Baker Louis
Published: February 2003

The electrical breakdown and discharge evolution in CO2 laser-heated molecular gases has been studied. With the laser tuned to a vibrational mode of NH3, C2H4, CH2CHCN, or CH3OH the breakdown potential decreases as much as 10-fold for laser pulse energies up to 35 J/cm2. The subsequent 50–142-cm discharges are straight, stable, and reproducible. Analogous tests in D2 and air yield only a small alteration of breakdown potential and do not cause a straight discharge. The expansion of the initial laser-heated gas has been modeled by the CHARTB hydrocode with the addition of the NH3 equation of state in tabular and analytic form to that code. The breakdown characteristics and initial expansion stage confirm the earlier calculation of laser heating to 1900–2100 °K. Experimental observations of the discharge evolution in NH3 have measured (1) the radial expansion velocity by streak-camera photography of the Hβ emission zone, (2) the plasma temperature by the Niv/Niii line-ratio method, and (3) the electron-density profile by holographic interferometry. The central zone of the channel is heated to 5.5 eV and expands with a radial velocity of 1.0–1.2 mm/μs for the case of a 27-kA discharge in 20 Torr of NH3. Preliminary hydrocode simulations of the discharge show qualitative agreement with observations.
Thermal stability of amorphous Zr-Cu alloys
Authors: Buschow K. H. J.
Published: February 2003

By means of differential scanning calorimetry we have studied the glass transition and crystallization in various amorphous Zr1−xCux alloys in the concentration range 0.25 ? × ?0.90. Included in this investigation are several amorphous alloys of Cu and either Hf, La, Gd, Dy, Er, or Y. A linear relationship is observed when the crystallization temperatures are plotted versus the energy neeeded to create a hole the size of a Cu atom in the various alloys. Experimental values for the activation energies of the crystallization processes were dervived by studying these processes with different heating rates. These activation energies are in general larger than the hole-formation enthalpies.
A comparative study of thermal stress induced dislocation generation in pulled GaAs, InP, and Si crystals
Authors: Jordan A. S. , Caruso R. , VonNeida A. R. , Nielsen J. W.
Published: February 2003

We have extended the recently developed quasisteady-state heat transfer/thermal stress model for glide dislocation generation in Czochralski pulled GaAs to InP and Si. The calculated results are displayed by means of (a) dislocation density contour lines for {100} wafers and (b) a novel ambient temperature (Ta) stability diagram. The latter representation explicitly shows the progressive elimination of dislocation-free regions with decreasing Ta in GaAs, InP, and Si. It is predicted that unless the diameter is unusually small (∼1 cm), glide dislocations appear at the periphery of both GaAs and InP grown by LEC at a Ta which is only ∼10 °K below their respective melting points. With decreasing Ta the dislocations rapidly spread throughout the interior. In contrast, an 8-cm-diam Si crystal is dislocation-free even at a Ta about 40 °K below the melting point. At this critical Ta glide dislocations which are confined to the circumference begin to generate. Thus, in accord with current crystal growth experience, Si exhibits a decisive advantage over the compounds in its resistance to thermal stress-induced slipping. This is likely to be due to the elemental solid’s large critical resolved shear stress and thermal conductivity.
Ion implantation and sputtering in the presence of reactive gases: Bombardment-induced incorporation of oxygen and related phenomena
Authors: Wach W. , Wittmaack K.
Published: February 2003

Medium energy backscattering spectrometry has been used to investigate ion impact-induced incorporation of oxygen in silicon. The sample was first exposed to 20-keV Xe bombardment at base pressure (oxygen-to-xenon flux density ratio ν̇(O2)/Φ̇(Xe)⩽0.5, beam incidence ∼10° off normal). Having arrived at the steady-state level in xenon content, bombardment was continued at deliberately enhanced oxygen partial pressures in the target chamber (5⩽ν̇/Φ̇⩽500). This resulted in significant beam-induced incorporation of oxygen which manifests itself not only in a corresponding signal in the backscattering spectra (aligned geometry) but also in an enhanced reemission of xenon and a reduction in the erosion rate of the substrate (up to a factor of 5). The impact-induced oxygen incorporation efficiency α can become very large. At low (added) fluences and for ν̇/Φ̇≳100 we found α0 = (3±1) atoms/ion. This result is supported by sputtering yield measurements on SiO2 and oxygen-exposed silicon, which indicate that the steady-state partial sputtering yield of oxygen at high flux density ratios is Yp,O = (4.3±0.5) atoms/ion. It is suggested that oxygen incorporation and subsequent migration to larger depths is essentially a defect-controlled process. The high incorporation efficiency is thus due to the large (average) number of defects arriving at the surface after impact of a single ion. Analysis of the experimental data suggests that ion-induced desorption sets an upper limit to the incorporation efficiency. Oxygen reduces the xenon retention capacity of the substrate at all concentration levels. The most pronounced effects are observed near the surface where incorporation of oxygen causes drastic reemission of xenon. The steady-state xenon content of an oxidized sample is controlled by the oxygen concentration and the erosion rate.
Temperature variation of some combinations of third-order elastic constants of silicon between 300 and 3 °K
Authors: Philip Jacob , Breazeale M. A.
Published: February 2003

The ultrasonic harmonic generation technique has been used to determine the nonlinearity parameters of silicon between room temperature and 3 °K. By measuring the amplitude of the second harmonic of an initially sinusoidal longitudinal ultrasonic wave propagating along the three principal directions, the temperature dependence of three linear combinations of third-order elastic (TOE) constants of silicon have been studied. Between room temperature and 77 °K, the magnitude of the TOE constants does not vary much as a function of temperature. Between 77 and 3 °K, C111 changes by 3.5%, C112+4C166 changes by 11.7%, and C123+6C144+8C456 changes by −207%. All these combinations are negative at room temperature as well as at low temperatures except C123+6C144+8C456 which is positive below 8 °K. Room-temperature values of the strain generalized Grüneisen parameters of silicon have been calculated from measured nonlinearity parameters and are compared with existing values. Complete sets of third-order elastic constants at 298, 77, and 4 °K have been calculated by combining our nonlinearity parameters with pressure derivatives of elastic constants measured by Beattie and Schirber [Phys. Rev. B 1, 1548 (1970)].
Optical interferometric measurement of the thermal expansion of NdP5O14
Authors: Barch W. E. , Chinn S. R. , Zwicker W. K.
Published: February 2003

The anisotropic thermal expansion coefficients of NdP5O14, a stoichiometric laser material, have been measured by an optical interferometric method. The expansion coefficients are αa = (10.0±1.3)×10−6,αb = (9.5±1.1)×10−6, and αc = (8.3±1.0)×10−6.
The equivalence of quasistatic flow in fluid-saturated porous media and Biot’s slow wave in the limit of zero frequency
Authors: Chandler Richard N. , Johnson David Linton
Published: February 2003

We have established in a simple and straightforward fashion that the analysis of quasistatic flow in fluid-saturated porous media due to Rice and Cleary is derivable from the low-frequency limit of Biot’s slow compressional/diffusive mode. The single material parameter of the problem, the diffusivity, is simply related to the bulk and shear moduli and permeability of the skeletal frame and to the viscous and elastic properties of the constitutive media. Since this common theory treats fluid and solid displacements on an equal footing, it is the most general linearized description of the problem; other treatments are special cases. These latter include the rigid frame approximation used in the petroleum industry and the weak frame approximation used by De Gennes to describe the motion of polymer gels.