bluuebunny/crossref_metadata_2025 huggingface dataset:
Elementary pinning force of normal precipitates in a superconductor
Authors: Matsushita T.
Published: February 2003

The elementary pinning force of a small normal precipitate is calculated by using the phenomenological Ginzburg–Landau equations. The resultant elementary pinning force is almost the same as or slightly larger than that of a void of the same size. This contradicts the theoretical result of Kramer and Freyhardt that the elementary pinning force of the normal precipitate smaller than the coherence length is significantly smaller than that of the void due to the proximity effect. It is pointed out that the normal precipitate was incorrectly regarded as an inherent weak superconductor in the theory of Kramer and Freyhardt. The present theoretical result is compared with the result of a previous experiment and satisfactory agreement is obtained.
Production of electronically excited bismuth in a supersonic flow
Authors: Herbelin J. M. , Giedt R. R. , Bixler H. A.
Published: February 2003

Emission signals at 8758 Å were observed when bismuth atom vapor was introduced into a supersonic flow of electronically excited nitrogen fluoride, NF (a1Δ). A correlation of thermal and pressure data with the appearance of the chemiluminescence, along with a computer analysis of the IRTV observations at two wavelengths, is presented. On the basis of an analysis of these data, it is concluded that the observed emission results from the production of an excited-state bismuth atom density, Bi(2D3/2), on the order of >1013 atoms cm−3 by collisional transfer with NF (a1Δ).
Charge injection and transport in high voltage water/glycol capacitors
Authors: Zahn Markus , Voldman Steven , Takada Tatsuo , Fenneman David B.
Published: February 2003

A water/ethylene glycol mixture to be operated at temperatures below 0 °C is being investigated for use as the high permittivity, low loss dielectric in pulse forming lines for pulsed power applications. High voltage open circuit decay curves show a dielectric relaxation time that decreases with initial voltage at room temperature, while at −10 °C, the open circuit decay has a negative second derivative with time in contrast to the expected exponential decay which always has a positive second derivative. It is hypothesized that this anomalous behavior is due to space-charge injection which increases the ohmic conductivity σ to σ+q μ, where q is the time and space dependent net charge density with mobility μ. A drift dominated conduction model is used to solve for the electric field and charge density distributions and the terminal voltage-current behavior of a lossy capacitor where one electrode injects charge proportional to the instantaneous local electric field. The specific case studied is of a parallel plate capacitor rapidly charged to an initial voltage and quickly open circuited. The calculated open circuit voltage decay curves show good agreement with measurements and yield experimental values for the charge injection parameter and the high field mobility of the injected charge. The value of mobility for the best fit of experimental data to the theory agrees with the value for the hydronium ion. Preliminary Kerr electro-optic field mapping measurements in highly purified water without glycol, confirm positive charge injection.
Strong photoinduced infrared absorption in GaP
Authors: Huber C. A. , Nurmikko A. V.
Published: February 2003

Photoinduced infrared absorption spectra, excited by an Argon laser, have been measured from 2.5 to 15 μm in high-quality bulk GaP at liquid helium and room temperatures. The broad spectra, together with photoluminescence and photoconductivity data, show how transitions from donor and acceptor levels to the adjacent bands by trapped nonequilibrium electrons and holes dominate the induced absorption at low temperature in the unintentionally doped material.
Photoluminescence and photoluminescence excitation spectroscopy of the EL2 emission band in GaAs
Authors: Shanabrook B. V. , Klein P. B. , Swiggard E. M. , Bishop S. G.
Published: February 2003

Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy have been performed on the 0.635-eV emission band in GaAs. Recently, this band has become of increased importance as a consequence of having been associated with the main electron trap (EL2) in GaAs. All samples studied exhibit a strong peak in the PLE at 1.5 eV, whose characteristics indicate that this emission band arises from deep donor-acceptor pair recombination. We also observe a related PL band at 0.68 eV which does not exhibit the 1.5-eV peak in the PLE and is attributed to recombination between a deep level and a hole in the valence band. The PLE spectra for both of these emission bands exhibit oscillations resulting from the resonance cooling of hot electrons by the emission of LOΓ phonons. This phenomenon, which has apparently never before been reported for such a deep level, suggests that an intermediate shallow donor state is involved in the recombination processes for both of these PL bands. We will discuss the relationship between our measurements and various microscopic models which have been proposed to describe the EL2 defect center.
The Green’s function along the microstrip substrate from a horizontal magnetic dipole
Authors: Fang D. G. , Chow Y. L.
Published: February 2003

As an aid to the study of coupling microstrip structures, this paper analyzes and computes the radial dependence, along the dielectric substrate, of the magnetic field Green’s function of a horizontal magnetic dipole. The analysis is based on the contour integration of the exact spectral Green’s function. From the results, it is observed that the radial dependence can easily be approximated by the corresponding free-space Green’s function with a small correction term.
The effect of implantation on explosively crystallized a-Si
Authors: Bensahel D. , Auvert G.
Published: February 2003

Implantation in deposited a-Si lowers the threshold temperature of the explosive phenomena. We observe interaction between solid- and liquid-phase explosive crystallization. In the solid-phase explosive crystallization mode, an implanted layer crystallizes independently of the underlying a-Si.
Explosive crystallization in single-crystal silicon amorphized by implantation
Authors: Bensahel D. , Auvert G. , Dupuy M.
Published: February 2003

Both solid- and liquid-phase explosive crystallization occur in mono-Si amorphized by implantation, in addition to solid-phase epitaxy (SPE). As in deposited a-Si, the two corresponding furnacelike crystallization regimes are observed when the dwell time is too short for a complete SPE.
Nuclear-reactor pumped lasers excited by ion-ion neutralization
Authors: Kushner M. J.
Published: February 2003

A class of nuclear pumped lasers (excited by reactor-produced thermal neutrons) in which the laser levels are populated by negative ion-positive ion neutralization is proposed and an analysis of two particular systems, 3He/N2O/O2 and 3He/N2O/N2, is performed. Laser action is predicted in atomic oxygen and nitrogen as a result of O−-O+ and O−-N+ neutralizations. The source of negative ions is dissociative attachment to N2O. A threshold neutron flux of ≊1015cm−2 s−1, peak power of >500 W/cm2, and a fission power to laser power conversion efficiency of ≊0.4% may be possible in these systems. This is as a result of efficient utilization of the large thermal electron density in the attachment process, and the highly selective nature of the ion-ion neutralization in producing product-excited states.
Miscibility gaps and spinodal decomposition in III/V quaternary alloys of the type A
x
B
y
C1−x−y
D
Authors: Stringfellow G. B.
Published: February 2003

Thermodynamic concepts have been developed for the calculation of solid-phase miscibility gaps and spinodal decomposition in quaternary alloys of the type AxByC1−x−yD. These concepts have been applied to the analysis of III/V quaternary alloys using the delta-lattice-parameter (DLP) solution model. In addition, the effects of coherency strain energy have been included in the calculation. Results are presented for the systems AlxGayIn1−x−yP, AlxGayIn1−x−yAs, InPxAsySb1−x−y, and GaPxAsySb1−x−y. Even though these systems all have miscibility gaps, they are shown to be stable against spinodal decomposition at all temperatures due to the elastic strain energy inherent in coherent decomposition of single crystalline alloys.
Semiconductor surface characterization using transverse acoustoelectric voltage versus voltage measurements
Authors: Davari B. , Das P. , Bharat R.
Published: February 2003

An alternative to capacitance-voltage (C-V) measurement is experimentally demonstrated. This technique measures the transverse acoustoelectric voltage (TAV) as a function of applied dc voltage across the semiconductor. The technique is nondestructive and is applied to uniformly doped Si samples. Surface properties such as the flat-band voltage, oxide charge, and the zero bias surface condition are determined.
Potential tritium isotope separation method using resonance radiation
Authors: Stangeby P. C. , Allen J. E.
Published: February 2003

A method for separating hydrogenic isotopes particularly directed at separating tritium from deuterium in the civilian energy context is outlined. An atomically dissociated deuterium/tritium flow—the feedstock—is subject to radiation from an electrical discharge containing pure tritium gas. The tritium atoms in the feedstock selectively absorb line radiation from the discharge light source, are excited to high lying levels and are subsequently ionized. The tritium ions are then trapped in solids present within the light-absorption zone—either as wires or as entrained particles— and are removed from the system. Energy requirements for separation of tritium from deuterium for a typical fusion feedstock are found to be on the order of approximately 300 eV/T.
Quantitative microanalysis of individual particulates. I. Electron probe microanalysis of NBS-glass particulates
Authors: Obori Kenichi , Shimizu Ryuichi , Oura Takahiko , Ichimura Shingo
Published: February 2003

The applicability of the Monte Carlo calculation technique for quantitative analysis of particulate samples with an electron probe microanalyzer was verified through comparison between theoretical and experimental results for an NBS K-411 series of glass particulates. Good agreement between theory and experiment suggests that the Monte Carlo calculation technique will be a useful tool for performing quantitative electron probe microanalysis of individual particulate samples.
On a new type of negative deuterium ion source using a silicon semiconductor
Authors: Akimune H.
Published: February 2003

A new type of negative deuterium ion source for the neutral particle injection in the fusion research is proposed. The element of the ion source is made of a bilayer of vanadium or palladium metal and a silicon semiconductor. The D− ions are formed with the cascade processes which involve the dissociation of D2’s when they are dissolved into the element, the electronic resonance transition from the Si surface to D(1s) diffusing through the element, and the detachment of the resultant D− ion from the surface. The estimations show that in an ideal case, the obtainable current density of D− ions is about 27 mA/cm2 and that the neutral component leaving the surface is about 18.5% of the D− ion current.
Fracture statistics: A comparison of the normal, Weibull, and Type I extreme value distributions
Authors: Doremus R. H.
Published: February 2003

The fit of fracture strengths of glass to the normal, Weibull, and Type I extreme value distributions is compared. For abraded glass, the Type I distribution fits much better than the other two. Both the normal and Weibull distributions fit strengths of as-received glass well. There seems to be no reason to use the maximum-likelihood method for calculating Weibull parameters, although it is preferred by statisticians. Evidence for preferring the normal to the Weibull distribution for fracture strengths and log fatigue times is described. Extreme values of fracture strengths fit the normal, as well as the Weibull, distribution.
Concentration-dependent diffusivity: Hydrogen percolation in WO3
Authors: Vértes Ákos , Schiller Robert
Published: February 2003

The diffusivity of H in a thin layer of WO3 was measured optically through the visible optical absorption of the H-containing substance. Microdensitometry and the photoresist technique made a 1-μm lateral resolution available. When the data were evaluated by Boltzmann’s method, the diffusion coefficient, as low as about Dm ≊10−11 cm2/sec at high H concentrations, was shown to increase sharply with decreasing H content. This behavior was quantitatively understood in terms of a percolation model modified by assuming H atoms to jam fast channels. The extreme low-concentration diffusion coefficient D0 was evaluated by virtue of this model and gave D0≊10−9 cm2/sec.
Studies of a glow discharge electron beam
Authors: Yu Zeng qi , Rocca Jorge J. , Collins George J.
Published: February 2003

The energy spectrum of a kilovolt electron beam, generated by a helium glow discharge at pressures between 0.15 and 0.8 Torr, was measured with an electrostatic energy analyzer. An abrupt increase in the energy spread of the electron beam was observed to be coincident with an increase in the luminosity of the electron beam created plasma, and with the onset of intense microwave radiation. The relevance of these phenomena in cw electron beam pumped ion lasers is discussed.
Inversion of Abel’s integral equation for experimental data
Authors: Deutsch Moshe , Beniaminy Israel
Published: February 2003

A stable high-accuracy method for calculating the inverse of Abel’s integral equation for experimentally derived data is presented. The method employs a piece-wise cubic spline function, least-squares fitted to the data, to represent the function as inverted. Three formulas, two of which are based on the well-known analytic inverses of Abel’s equation and a new one, which was recently developed by the authors and does not contain an explicit derivative, are given for calculating the inverse numerically. The results of numerical tests performed using these formulas on simulated data are presented and compared with the results obtained using other published methods. The comparative study indicates that our method, employing piece-wise least-squares cubic splines, accurately reproduces the inverse function, regardless of the inversion formula employed. It yields markedly better results than do all the other methods compared in this study, when highly error free, sparse, or very noisy data are inverted. The errors at the ends of the data interval (‘‘termination errors’’) are also shown to be smaller than those of the other methods compared in this study.
Theory and experiment on the surface-photovoltage diffusion-length measurement as applied to amorphous silicon
Authors: Moore Arnold R.
Published: February 2003

The collection-efficiency theory for low-mobility solar cells proposed by Reichman has been adapted to the analysis of the surface-photovoltage experiment in amorphous silicon. From measurement of the apparent diffusion length at low- and high-bias light intensity the ambipolar diffusion length and space-charge width can be obtained. In order to fit experimental observations to the theory it was necessary to assume that the positive space-charge density in the surface barrier increases with the light level. This was independently confirmed by capacitance measurements.
Rare gas-oxygen effects on the rf sputter deposition of platinum
Authors: Aita C. R. , Tran Ngoc C.
Published: February 2003

Thin Pt films were sputter deposited on Si substrates using Ar and Ne rf glow discharges containing 0%–6% O2. Significant differences in electrical resistivity, crystallography, and Pt suboxide formation were found to depend upon the type of rare gas used for a given nominal O2 partial pressure. Several reasons for this behavior are proposed.
Phosphorus redistribution in P-doped polycrystalline silicon/tantalum silicide system during high temperature sintering
Authors: Luryi S. , Lifshitz N.
Published: February 2003

We studied redistribution of phosphorus between layers of P-doped polycrystalline silicon and TaSi2 during sintering of the silicide at 900 °C. Because of the loss of phosphorus to the silicide, the sheet resistivity of polysilicon layers is increased. We attempted a systematic study of this effect using polysilicon layers of varying thicknesses (from less than 1000 to more than 6000 Å). The experimental results are in excellent agreement with our model which regards the concentrations of phosphorus in both polysilicon and silicide as dilute solutions and assumes that during sintering of the silicide these solutions come to equilibrium. From the equilibrium condition of uniform chemical potential with respect to the solute, we were able to determine the distribution coefficient of P between the two solvents.
Aging effects in n-type semiconducting WO3 films
Authors: Spichiger-Ulmann Martine , Augustynski Jan
Published: February 2003

Photocurrent spectra of the polycrystalline, n-type WO3 film photoanodes are shown to undergo a profound transformation following aging in a photoelectrolysis cell containing an aqueous acidic electrolyte. The observed significant improvement of the photocurrent efficiency of the WO3 photoanodes is assigned to a decrease of the initial defect concentration in the depletion layer, due to electromigration of interstitial W6+ and W5+ ions toward the semiconductor/electrolyte interface. The durable character of this modification of the photoresponse is pointed out.
Influence of semiconductor barrier tunneling on the current-voltage characteristics of tunnel metal-oxide-semiconductor diodes
Authors: Nielsen Otto M.
Published: February 2003

Current–voltage characteristics have been examined for Al–SiO2–pSi diodes with an interfacial oxide thickness of δ≊20 Å. The diodes were fabricated on 〈100〉 and 〈111〉 oriented substrates with an impurity concentration in the range of NA=1014–1016 cm−3. The results show that for low forward voltages, the diode current is increased with increased NA, but for higher forward voltages, the diode current is decreased as NA is increased. For the diodes examined in this work, the results presented lead to the conclusion that the diode current should be treated as a superposition of multistep tunneling recombination current and injected minority carrier diffusion current. This can explain the observed values of the diode quality factor n. The results also show that the voltage drop across the oxide Vox is increased with increased NA, with the result that the lowering of the minority carrier diode current Jmin is greater than in the usual theory. The conclusion drawn is that the increase in Vox and lowering of Jmin is due to multistep tunneling of majority carriers through the semiconductor barrier.
Macroscopic and microscopic models of i
n s
i
t
u superconductors
Authors: Carr W. J.
Published: February 2003

It is argued that a macroscopic formalism similar to that for continuous filament material can be applied to in situ superconductors, providing an elongated volume element is used for averaging over the microscopic fields and currents. The difference between in situ and continuous filament materials is found in the constitutive equations. For an in situ tape these consist of a specification of three critical current densities for the macroscopic superconducting state, together with three conductivities for the nonsuperconducting state, and, under some conditions, three magnetization components. The interesting region of the nonsuperconducting state occurs when the material is macroscopically nonsuperconducting, but superconducting microscopically. A microscopic model based on the proximity effect is developed for computing the constitutive equations. For calculating the axial current density the model assumes that chains of filaments run through the conductor. When the superconducting proximity layers surrounding a pair of chains overlap, the chains can carry macroscopic supercurrent. In general, a conductor can be superconducting in one, two, or three directions. The critical current densities are expected to be highly anisotropic.
The electrical behavior of i
n s
i
t
u superconductors with large filament separation
Authors: Carr W. J.
Published: February 2003

The electrical properties of in situ superconductors are calculated for the case where the average filament separation is large compared with the range of the proximity effect. The calculations are based on a model recently described by the author, where chains of filaments run through the length of the conductor. The distribution of the chains is assumed to be nonuniform and described by a distribution function f(s), where s is the separation between neighboring chains. The critical temperature Tc for superconductivity in a filament is also assumed to be a function of s. At any given temperature some filaments, as a result of the proximity effect, have a superconducting connection with their neighboring filaments, and others are superconducting but with a resistive connection, while others are normal. The first category of filaments determines the critical current Ic, while the first two categories determine another critical current I*c. Both Ic and I*c are functions of the magnetic field and temperature. For a fixed current I the equations I=Ic and I=I*c define two critical temperatures T1 and T2, which together with the highest value of Tc describe the features of the electrical behavior. The results compare favorably with some published measurements. The value of the proximity length obtained from the model with the aid of the measurements is in good agreement with previous estimates.
Structure and magnetic properties of samarium–alnico pseudobinary alloys
Authors: Chang Y. H. , Weng C. I. , Chen H. S.
Published: February 2003

Ten alloys of the samarium–alnico system containing 10–19 at. % Sm were investigated. It has been found that the structure of the high temperature phases changes with varying samarium content. Seven phases including 1:5 and 2:17 and those designated R1, R2, K, U1, and U2 are identified by the x-ray Debye–Scherrer method. The 1:5 and 2:17 phases correspond to the CaCu5 and Th2Zn17 structures, respectively. The R1 and R2 phases are assumed to be the superlattices of the 2:17 phase and the K phase the superlattice of R2. The maximum saturation magnetic moment is 89.6 emu/g for the alloy containing 10.7 at. % samarium. Curie temperatures of the R1 and 2:17 phases are 697 and 694 °K, respectively. The unknown phase U1 which is analyzed containing little Sm has a magnetic order temperature up to 1146 °K. The intrinsic coercivity of these alloys never exceeds one thousand oersted. The easy magnetization directions of the 1:5 and R phases are found to persist along the c axis even though the atomic ratio of Fe to Co is as high as two. The behavior of reaching maxima in intrinsic coercivity and remanence versus temperature curves below room temperature is due to the corresponding variation of anisotropy field with temperature.
Analytical prediction of the magnetization curve and the ferromagnetic hysteresis loop
Authors: Escobar M. A. , Valenzuela R. , Magaña L. F.
Published: February 2003

We have obtained theoretical expressions for the ferromagnetic magnetization curve and hysteresis loop using an extension of the general ideas of the Globus model for polycrystalline ferrimagnets. In this work we take into account the force which results from the variation of the total energy (magnetic energy plus surface energy) in order to find the value of the critical field. Our theoretical magnetization curve agrees well with the experimental curve and our hysteresis loop has the general qualitative features of the corresponding experimental loops.
Triboluminescence of glasses and quartz
Authors: Chapman G. N. , Walton Alan J.
Published: February 2003

The triboluminescent spectra of a variety of glasses and of crystalline quartz were measured while specimens were cut with a rotating diamond-impregnated saw blade. The spectra, which resemble the emission of a blackbody radiator, were recorded using an image-intensifier spectrograph. The data were intensity-corrected before being fitted to blackbody emission curves. Emission temperatures of around 1850 K for armor plate glass, 2100 K for Pyrex glass, 2400 K for soda lime glass, 2300 K for high-density lead glass, and 2800 K for cut quartz were obtained. It was found that the blackbody temperatures could be accounted for by a model in which a rectangular-shaped high-temperature zone, uniformly heated by energy released by plastic deformation near the crack tip, is supposed to propagate with the crack velocity [R. Weichert and K. Schonert, Q. J. Mech. Appl. Math. 31, 363-379 (1978)]. The measured blackbody temperatures imply zone widths of around 1×10−9 m. The spectrum from impact-fractured quartz was also measured; it was found to have a photoluminescent origin.
Spectroscopic study of excited-state densities in a Zn vacuum-arc plasma
Authors: Goldsmith S. , Bresler Y. , Boxman R. L.
Published: February 2003

A spectroscopic study of the excited-state densities in the interelectrode plasma of a Zn multi-cathode-spot vacuum arc is presented. The plasma was produced by a 1.2-kA peak current, 0.65-ms full-width half-amplitude discharge between Zn butt electrodes, 14 mm in diameter, spaced 4-mm apart. Absolute time and space resolved line intensities were measured using a calibrated lens-monochromator-photomultiplier system. Peak excited-state densities ranging from 1013 to 1017 m−3 were calculated from absolute peak line intensities. The derived Zn i and Zn ii excited state densities could not be fitted to a Boltzmann-like distribution. The observed intensity of some Zn iii lines at the discharge midplane reached its maximum at about 0.25 ms, prior to the attainment of the arc peak current at t=0.28 ms, while the intensity of Zn ii and Zn i spectral lines observed also at the discharge midplaned peaked 0.45 and 1.3 ms after arc initiation, respectively. Thus lines of neutral zinc atoms reached their maxima at the decaying phase of the discharge. At the early phase of the discharge, line intensity as a function of the distance from the cathode surface z generally decreased. However, for each ionic species this trend was reversed (or at least no decrease with z was noted) after a certain time had passed from arc onset. The times at which the line intensity began to increase with z were inversely related to the degree of ionization of the radiating atom. Thus, at t=0.28 ms, time of peak current, Zn iii increased with z, while Zn ii and Zn iii lines decreased.
Ultrasonic measurement of the critical exponent β for the spin glass C
uMn
Authors: Huang F. S.
Published: February 2003

Ultrasonic measurements are presented providing direct measurement of the critical exponent β for a spin glass. Sound velocity measurements were made on Cu0.95Mn0.05 and Cu0.976Mn0.024 single crystals which exhibited the characteristic spin glass cusp in low-field ac susceptibility. A sound velocity anomaly was observed in the vicinity of the susceptibility peak temperature. We attribute this anomaly to critical fluctuations. Using perturbation theory we show that for a spin glass such as CuMn, the critical part of sound velocity is related to that of the Edwards–Anderson spin glass order parameter q. We are able to determine the critical exponent β associated with this order parameter by fitting the theory to the measured critical change in sound velocity in CuMn samples. By combining our values of β with the values of α′ associated with the critical change in specific heat below the spin glass transition temperature, and Suzuki’s scaling laws,we find the values of exponent γ, αs, and γs, associated with the zero field susceptibility, the magnetic field dependent part of specific heat, and the field dependent part of susceptibility.
A theoretical model for multiple-pulse laser-induced damage to metal mirrors
Authors: Lee C. S. , Koumvakalis N. , Bass M.
Published: February 2003

In this paper, we present a phenomenological model based on laser-induced thermoelasticity, which shows that the threshold intensity required to initiate plastic deformation of metal surfaces increases with laser beam size for spots larger than the thermal diffusion length during the pulse. The results are consistent with previous experimental observations.
A scanning electron microscopy/transmission electron microscopy study of the photocrystallization of amorphous silicon
Authors: Prasad A. , Ebihara K. , John P. K. , Tong B. Y. , Wong S. K. , Chik K. P.
Published: February 2003

It has been recognized that the kinetics of crystal growth under rapid solidification conditions opens up a new regime of crystal growth. Photocrystallization of amorphous silicon leads to explosive crystallization under certain conditions. This is true for both laser and incoherent light radiation. The explosive crystallization yields three regions, i.e., a pure yellow region, a reddish brown region, and an ochre-colored region. Till now the amorphous nature or crystallinity of the recrystallized film has been established solely by color judgment. In this communication we report on a study made by using optical, transmission electron, and scanning electron microscopy of the photocrystallized films which correlates the color changes with electron diffraction patterns. The more quantitative measurements indicate that the overwhelmingly larger optical absorption coefficient of amorphous silicon, and the presence of thin overlayers can lead to erroneous judgments of the crystallinity of the regions when made solely by color discrimination. It is also established that for explosive crystallization brought about by incoherent radiation a spherulitic growth in both its branched and unbranched forms is present. The nucleii of the spherulites have been identified as barium. In a second region of crystallization which has no defined nucleus, the dominant crystal orientations have been established.
Alloy scattering potential in p-type Ga1−xAlxAs
Authors: Masu Kazuya , Tokumitsu Eisuke , Konagai Makoto , Takahashi Kiyoshi
Published: February 2003

The two-band transport model is expanded in order to analyze the Hall mobility of p-type III–V compound semiconductors. Using this model, the drift and the Hall mobilities can be calculated separately. The alloy scattering as an additional scattering mechanism in alloy semiconductor systems is assumed and the Hall mobility of p-type Ga1−xAlxAs is analyzed. By comparing the theoretically calculated Hall mobility with the reported Hall mobility data of high purity p-GaAs, the acoustic phonon deformation potential and the optical phonon deformation potential were found to be 7.0 and 11.5 eV, respectively. Theoretical calculations showed that the acoustic and nonpolar optical phonon scattering are more prominent than the polar optical phonon scattering at 300 K in the entire Al compositional range. The alloy scattering potential was determined comparing the theoretically calculated values with the Hall mobility of liquid phase epitaxial p-type Ga1−xAlxAs. Best agreement in the compositional variation at room temperature and the temperature variation was found with the alloy scattering potential of 0.7 eV.
Charge transport and trapping phenomena in off-stoichiometric silicon dioxide films
Authors: DiMaria D. J. , Dong D. W. , Falcony C. , Theis T. N. , Kirtley J. R. , Tsang J. C. , Young D. R. , Pesavento F. L. , Brorson S. D.
Published: February 2003

The electrical characteristics of off-stoichiometric silicon dioxide films have been investigated. The off-stoichiometric oxide films studied had an excess atomic silicon (Si) content in the range of 1%–6%. Raman spectroscopy and photoconductivity measurements indicate that the excess Si is present as amorphous Si islands or small crystallites embedded in silicon dioxide (SiO2) forming a two-phase material. These films differ in structure from previously reported films where dual dielectric layers of stoichiometric SiO2 and Si-rich SiO2 with ≥13% excess atomic Si were used. These dual dielectric films were observed to produce electron injection from contacting electrodes via the Si-rich SiO2 layer into the SiO2 at lower average electric fields. This injection mechanism was believed to be due to localized electric field enhancement near the SiO2–Si-rich SiO2 interface caused by the curvature of the tiny Si islands in the SiO2 matrix. The current versus voltage characteristics of the off-stoichiometric oxide films which will be discussed here were found to be highly nonohmic, showing an increase in conductivity with increasing excess silcion content in the material. At low fields (≲1 MV/cm), these films have a very small conductance with leakage current densities smaller than 10−11 A/cm2 at room temperature. Furthermore, the effect of permanent charge trapping was observed to decrease in these films with increasing Si content. It is proposed that the electron transport across the film is controlled primarily by tunneling between the silicon islands with a reversible space charge region ≲150 Å in extent near the injecting contact, limiting the current measured in the external circuit. It is also proposed that the decrease in permanent electron trapping is associated with this conduction mechanism and/or the possibility of trapped electrons in the SiO2 phase tunneling to the Si islands. With the incorporation of these off-stoichiometric oxides into electrically-alterable read-only-memory devices, extended write/erase cycling (by at least four orders of magnitude) beyond that normally observed for equivalent devices using stoichiometric SiO2 layers is demonstrated due to the reduction in permanent electron trapping in the oxide layer and its effect on the electric fields.
Threshold switching polycrystalline NbO2: Decay and recovery of the on state at room and low temperatures and its relationship to trapping centers
Authors: Vezzoli G. C. , Levy S. , Lalevic B. , Shoga M.
Published: February 2003

Double pulse switching experiments, performed on polycrystalline NbO2 at 300 and 15 K, reveal properties strongly associated with electronic, nonthermal, threshold switching. The data indicate a trapped carrier lifetime of 200 ns, agreeing with our previous measurements on polycrystalline NbO2 devices (data that had been obtained by a different method). The study also shows the functional increase of on-state lifetime with increasing overvoltage and the effect of overvoltage on the on-state I-V characteristics during fast polarity reversal. These results, coupled to previous work, are explicable in terms of a trap-limited transition to a metal-like state induced by a critical electric field and carrier concentration.
Propagation of crazing in viscoelastic media
Authors: Zhang Z. D. , Chern S. S. , Hsiao C. C.
Published: February 2003

Up to now, the growth rate of a craze has been considered either constant or inversely proportional to time. By taking into consideration the effect of the surrounding population of crazes, it is found that the craze growth rate is affected by the local effective stress acting in the vicinity of the craze. Measured data of craze length as a function of time are found to be greatly affected by local interactions.
Study of polyacetylene and composites of polyacetylene/polyethylene by electron nuclear double resonance, electron nuclear nuclear triple resonance, and electron spin echo spectroscopies
Authors: Dalton L. R. , Thomann H. , Morrobel-Sosa A. , Chiu C. , Galvin M. E. , Wnek G. E. , Tomkiewicz Y. , Shiren N. S. , Robinson B. H. , Kwiram A. L.
Published: February 2003

Composites of trans-polyacetylene (t-(CH)x) and low density polyethylene (LDPE) have been studied by Electron Nuclear Double Resonance (ENDOR), Electron Nuclear Nuclear Triple Resonance (TRIPLE), and Electron Spin Echo (ESE) spectroscopies. The results are compared with analogous studies conducted on pure t-(CH)x films and on samples containing mixtures of cis/trans isomers. ENDOR measurements indicate that the paramagnetic electron in all materials studied resides in a pure π molecular orbital. The measured spin densities at carbon of ‖0.06 and ‖0.02‖ for two inequivalent 13C nuclei along the polyene backbone imply that the defect spin density is spread over a polyene segment length on the order of 70 Å. The absolute magnitude of the spin densities, +0.06 and −0.02, obtained by TRIPLE indicate the existence of electron Coulomb correlation effects. Detailed analysis of ENDOR spectra places strict limits on the allowable soliton diffusion coefficient. ENDOR, ESE phase memory (TM), and ESE spin-lattice (T1e) relaxation times are observed to be a function of t-(CH)x concentration in the host material. The importance of other dynamic processes such as electron Heisenberg spin exchange, electron dipolar interactions, and nuclear spin diffusion, are considered as mechanisms for obtaining the observed spectral responses. The analysis indicates the need for caution in interpreting electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) data in terms of models which consider the only active dynamic process to be soliton diffusion.
Axisymmetric magnetic plasma divertors which preserve beam divergence
Authors: Savas Stephen E.
Published: February 2003

We present axisymmetric magnetic field configurations which divert low energy electrons and ions to a wall while allowing passage of a higher energy charged particle beam without increasing its divergence. We give calculated on-axis magnetic field dependence for several values of the beam diameter increase. Also given is a plot of the dependence of a dimensionless parameter α≡[(vb)/ (Ω0Zc)] on the diameter increase of the beam which allows scaling of the beam speed and field.
High efficiency cw laser-pumped tunable alexandrite laser
Authors: Lai Shui T. , Shand Michael L.
Published: February 2003

High efficiency cw alexandrite laser operation has been achieved. With longitudinal pumping by a krypton laser in a nearly concentric cavity, a 51% output power slope efficiency has been measured. Including the transmission at the input coupler mirror, a quantum yield of 85% has been attained above threshold. Tunability from 726 to 802 nm has also been demonstrated. The low loss and good thermal properties make alexandrite ideal for cw laser operation.
High efficiency mid-IR generation by Raman down conversion in liquid nitrogen
Authors: Marquardt C. L. , Storm M. E. , Schneider I. , Esterowitz L.
Published: February 2003

Radiation at 3.92 μm was generated by focusing a 2.05-μm Ho:YLF laser in a single-pass liquid nitrogen Raman cell. The 3.92-μm pulses (∼10 mJ, ∼10 ns) were Gaussian, ≥90% linearly polarized, and approximately diffraction limited. Photon conversion efficiency exceeding 95% was achieved.
Diffraction of ultrasonic waves from periodically rough liquid–solid surface
Authors: Claeys J. M. , Leroy Oswald , Jungman Alain , Adler Laszlo
Published: February 2003

Theoretical and experimental results concerning diffraction of ultrasonic waves on periodic liquid–elastic solid interfaces are presented. A general system of linear equations is established and solved numerically for triangular surfaces. Theoretical results are in good agreement with measurements obtained by a broadband pulse-echo system in the region where the wavelength is of the same order of magnitude as the period and much greater than the depth of the grating. In the spectrum of the reflection coefficient frequency minima are identified as the surface waves excited along the periodic surface.
The effect of flow on the miscibility of a polymer blend
Authors: Mazich K. A. , Carr S. H.
Published: February 2003

Results indicating the extent to which flow in a miscible polymer blend can displace the phase separation temperature are reported. Data were obtained on the system, polystyrene/poly (vinyl methyl ether), in the temperature ranges where it undergoes exsolution upon heating. The theoretical framework for the observed flow-induced miscibility is described.
Monte Carlo modeling of kinetics of polymer crystal growth: Regime III and its implications on chain morphology
Authors: Guttman Charles M. , DiMarzio Edmund A.
Published: February 2003

A Monte Carlo simulation of polymer crystal growth from the melt is presented. This two-dimensional model approximates growth by laying down crystal stems one at a time. The Monte Carlo simulation of various geometric models of the crystal surface yields Regime I and Regime II growth similar to that predicted by Lauritzen and Frank. The analytical expression of Frank is shown to be accurate. A recent prediction by Hoffman of a low temperature region (Regime III) with properties similar to Regime I has been verified. Regime III is lattice dependent. Specifically the solid-on-solid model commonly used to model monatomic systems yields Regime III but is not space filling. The hexagonal lattice yields correctly formed crystals but does not show Regime III as long as we require that the crystals grow on one plane. On the hexagonal lattice, if we allow growth on more than one growth plane, we obtain both space filling crystals and Regime III growth. There are no regimes of growth other than the three discussed here.
Effects of 0.5-MeV electrons on the interlaminar shear and flexural strength properties of graphite fiber composites
Authors: Wolf K. W. , Memory J. D. , Gilbert R. D. , Fornes R. E.
Published: February 2003

Composite samples of graphite fibers in both an epoxy matrix and a polyimide matrix have been prepared with different fiber arrangements and irradiated with 0.5-MeV electrons up to 104 Mrad. Interlaminar shear strengths decreases significantly with radiation dosage while little change was observed in the flexural strengths and moduli. The results indicate that radiation causes significant degradation at the interface but not much change in the fiber or matrix.
Quantum efficiency measurement of a photodiode based on a calorimetric method
Authors: Inoue T. , Yamamura K.
Published: February 2003

Measurement of the internal quantum efficiency of a photodiode by a calorimetric method is described. Using the photodiode itself as the thermal load of a calorimeter, the internal quantum efficiency was determined from the output current and the heat loss of the photodiode. The method has several advantages: it needs no radiant power meter, or reflectivity measurement, and it does not depend on wavelength.
An x-ray diffraction study on the microstructures of cold-worked face centered cubic Cu–Sn–Zn alloys. II. Role of addition of 1 wt. % Sn
Authors: Ghosh S. K. , Sen Gupta S. P.
Published: February 2003

In continuation with our earlier work with Cu–Ni–Zn (Paper I) [Halder, De, and Sen Gupta, J. Appl. Phys. 48, 3560 (1977)], the role of addition of nontransitional solute tin (Sn) in the dilute range (∼1 wt. %) to alpha-brass alloys having compositions 5.0–34.0 wt. %Zn [present experiment concerns initial range, i.e., 5–24 wt. % Zn, and 24–34 wt. % Zn have been studied earlier by Halder, De, and Sen Gupta, Ind. J. Pure Appl. Phys. 17, 492 (1979)] has been examined in the light of x-ray diffraction methods of analyses dealing with peak shift, peak asymmetry, and peak broadening. Unlike the binary system, it has been interestingly observed that the addition of solute element tin in near dilute range of 1 wt. % to alpha-brass system increases the net-stacking fault concentration initially and has an arresting effect on all the microstructural parameters (namely, deformation stacking faults, coherent domain size, rms strains, density of dislocations, stacking fault energy, etc.), which do not change significantly with increasing zinc concentration up to ∼20 wt. %. However, the change is gradual and close to the binary system beyond 20 wt. %Zn where the addition of solute (Sn or Ni, as in Paper I) hardly fails to create any significant change.
Etching of gallium arsenide and indium phosphide in rf discharges through mixtures of trichlorofluoromethane and oxygen
Authors: Burton Randolph H. , Hollien Cathy L. , Marchut Leslie , Abys Susan M. , Smolinsky Gerald , Gottscho Richard A.
Published: February 2003

Optical emission, mass spectrometry, and Auger electron spectroscopy were used to study the kinetics of etching GaAs and InP in a 55-KHz discharge through mixtures of CCl3F and O2. Etching rates increase with increasing O2 concentration (peaking at about 60%), rf power, and residence time. However, at oxygen concentrations greater than 60%, oxide formation competes favorably with etching. Formation of nonvolatile group III fluorides does not appear to be an important process. Gallium arsenide etching shows a weak loading effect and forms an oxide more readily than does InP. Indium phosphide etching shows a stronger loading effect and seems more sensitive to ion bombardment than does GaAs. Above a 60% oxygen concentration, there is little evidence of carbon polymer deposition. This results from oxidation of halocarbon species in the discharge. Both InP and GaAs form thick oxides. The oxide for the latter appears to consist primarily of Ga2O3 while that for the former is most likely InPO4. At long residence times (∼1 sec) and high rf power densities (∼0.38 W/cm2), fast etching rates are obtained for both GaAs (∼12 μm/min) and InP (∼19 μm/min). These results are compared with similar studies of the etching of GaAs and InP in rf discharges through CCl4 and O2.
Amorphous silicon solar cells with graded boron-doped active layers
Authors: Sichanugrist Porponth , Kumada Masatoshi , Konagai Makoto , Takahashi Kiyoshi , Komori Koichiro
Published: February 2003

The effect of graded boron doping in the actives (i layers) of hydrogenated amorphous silicon p-i-n solar cells was investigated. It was found that the cell characteristics strongly depend on the doping profile. A high conversion efficiency of 9.45% was obtained by gradually doping the i layer with boron in order to achieve a linear profile from the p/i to i/n interface. The best fill factor observed was 0.72.
Double heterojunction GaAs/AlxGa1−xAs bipolar transistors prepared by molecular beam epitaxy
Authors: Su S. L. , Fischer R. , Lyons W. G. , Tejayadi O. , Arnold D. , Klem J. , Morkoç H.
Published: February 2003

Double heterojunction AlGaAs/GaAs bipolar junction transistors (DHBJT’s) grown by molecular beam epitaxy (MBE) were fabricated and tested. The incorporation of a graded base-collector junction improved the dc performance of a DHBJT over that obtained with an abrupt base-collector junction. Maximum current gains of 500, 900, and 1650 were obtained using graded collector and emitter junctions and base widths of 0.05, 0.2, and 0.1 μm, respectively. The reduction in current gain in going from a 0.1-μm base width to a 0.05-μm base width is attributed to a lowering of the electron lifetime resulting from the high base doping level used. The value of 1650 is comparable to the current gains obtained from liquid phase epitaxy (LPE)-grown HBJT’s and is the best obtained from MBE-grown HBJT’s. Common-emitter transistor turn-on voltages were found to correspond to a difference in the collector and emitter junction turn-on voltages. High collector growth temperature improved dc performance with 700 °C as the optimum growth temperature. Preliminary results from DHBJT’s with superlattice interfaces have shown that the current gain is almost constant through a wide range of collector current levels.
Calculation of magnetic field due to a conical deflection coil
Authors: Dasgupta Basab B.
Published: February 2003

An analytical calculation of the magnetic field produced by a deflection coil in the shape of an infinitely long cone is presented. The results are compared with the corresponding results obtained from an infinitely long cylindrical model of the coil.
Comment on ‘‘Friction in capillary systems’’
Authors: Parlange J.-Y.
Published: February 2003

A recent model relating friction in capillary systems to contact angle is reexamined. It is shown that the result can be greatly simplified without loss of generality, indicating that friction can be taken proportional to the frictional angle consistently with the limitations of the model. It is also shown that the exact dependence of friction on contact angle represents an additional assumption of the model.