bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of structural defects in annealed silicon containing oxygen
Authors: Maher D. M. , Staudinger A. , Patel J. R.
Published: February 2003

Transmission electron microscopy has been used to characterize the crystallography of structural defects observed in a Czochralski-grown silicon crystal after a two-step annealing treatment. The defect population is complex and consists of precipitates, perfect-dislocation loops, single and double stacking-fault loops, microprecipitate colonies on stacking faults, and imperfect/perfect dislocation-loop pairs. Extensive diffraction-contrast experiments have been carried out in order to evaluate the nature of these defects. The results indicated that all the observed defects place the surrounding silicon matrix in a comprehensive state (i.e., they are of the so-called interstitial type). It is clear from the electron-microscopy observations that perfect-dislocation loops are generated at the precipitate/matrix interface by prismatic punching. However, the structure and elemental nature of the precipitates is unknown. The role that oxygen may play in the formation of precipitates, perfect-dislocation loops, and the mechanisms of formation of stacking faults with their associated microprecipitates is discussed. Additional experimental work in the earlier stages of defect formation is required to clarify this picture.
Simultaneous determination of structure, absolute surface coverage, and nucleation kinetics: Cd on Ge(111)
Authors: Matysik K. J.
Published: February 2003

The feasibility of performing simultaneous RHEED–mass-spectrometric-molecular-beam experiments is demonstrated with a study of the nucleation of Cd on a contaminated Ge(111) surface. The crossed-beam experimental geometry and the scheme for determining absolute adatom density is described. The nucleation mechanism is found to have the appearance of a two-dimensional gas-solid phase transformation. The critical adatom density was found to be dependent on the level of contamination. The onset of clustering was found to correlate well with the MSMB spectra and clusters approaching critical dimensions were observed.
Measurement of piezoelectric ceramics using autocorrelation analysis to avoid history-dependent effects
Authors: Wilhelm Ralph V. , Hsu Hwei P. , McLaren Malcolm G.
Published: February 2003

Piezoelectric materials often undergo material degradation with the application of severe stress. Consequently, repetitive testing with single samples can be very misleading if the interval between increasing stress levels is too small. In this paper, the autocorrelation analysis technique is used to determine a proper stress increment such that single sample testing is uncorrelated with previous stress exposure, consequently insuring an accurate material evaluation. Five piezoelectric materials were evaluated with electric field to 6.0 kV/cm and hydrostatic pressure to 34.5 MPa (5000 psi). Autocorrelation analysis of the data showed that electric field increments of 1.6 kV/cm and pressure increments of 5.5 MPa (800 psi) were adequate to guarantee valid results while minimizing the number of samples required. It is expected that this autocorrelation analysis technique can be used in other applications where successive measurements are being made and history-dependent behavior is suspected or known.
Propagation of elastic waves in a thick water layer between solid plates
Authors: Thomas G. , Komoriya Goh , Parekh J. P.
Published: February 2003

The experimental results for the delay time of a signal propagating through a thick fluid layer as a function of thickness is given. A theoretical analysis of the interference of the normal modes of a thick layer is presented and it is shown that the observations of delayed ’’modes’’ are, in reality, beats between many normal modes.
Strain-rate dependence of acoustic-emission power and spectra in aluminum alloys
Authors: Hatano Hajime
Published: February 2003

Strain-rate dependence of acoustic-emission power and spectra for deformation of aluminum alloys is investigated over a wide frequency range of 100 kHz to 4 MHz. In case of Al-Cu-Mg alloy (2024) and pure aluminum (1100), it is found that acoustic-emission power is proportional to the first power of the plastic strain rate times the gauge length of the specimen. Normalized acoustic-emission power spectra show no significant change at a given strain depending on the strain rate, though they vary with the strain in early stages of deformation. In case of Al-Mg alloy (5056), repeated bursts of acoustic emission are recorded accompanied by repeated discontinuous yielding. The mode of inhomogeneous deformation and the pattern of acoustic emission vary with the strain rate.
Mechanism for negative-ion production in the surface-plasma negative-hydrogen-ion source
Authors: Hiskes J. R. , Karo A. , Gardner M.
Published: February 2003

The system parameters and surface adsorption conditions of the surface-plasma negative-hydrogen-ion source are reviewed. A mechanism is developed for the production of negative ions by incident energetic hydrogen atoms backscattering from a cesiated tungsten surface. The active electronic level during the course of the collision is approximated as the sum of the negative electron affinity of the cesium hydride negative molecular ion and the image potential. The model predicts negative-ion formation for atomic collisions with all alkali-coated surfaces for alkalis from sodium through cesium. In the case of lithium, the model does not apply due to the breakdown of the image potential approximation close to the surface. Negative-ion formation is also expected to occur for incident positive ions which backscatter from the substrate tungsten as neutrals. The energy thresholds for incident atoms are established.
Experimental study of a liquid cathode arc and comparison with a cathode sheath model
Authors: Fabry M. , Thiell G. , Georges J. C.
Published: February 2003

An investigation of an arc generated from a liquid-potassium cathode in an inert gas (argon) at a pressure between 0.16 and 6 Torr is given. A theoretical description of the phenomena arising in the vicinity of the cathode leads us to a model which allows the construction of an existence diagram of the arc. As predicted by the theory, the cathode fall potential is about 7 V. By means of Langmuir probe measurements, it is shown that the voltage reduction mainly occurs in the cathode fall region. A comparison has been made of excitation and electron temperatures, as derived from spectroscopic measurements using spectral lines from the alkali-metal vapor, with the theoretical results and verified that LTE prevails under the conditions of our experiments. The measured electron densities are higher than 3×1015 cm−3 and link up with the electron temperature if Saha equilibrium is assumed in the plasma just above the cathode spots.
Electron microscope observations of 〈100〉 tungsten single-crystal emitters operated in the TF mode
Authors: Mee Peter B.
Published: February 2003

Some problems associated with the fabrication and shaping of mechanically zirconiated and ’’built-up’’ 〈100〉 tungsten emitters are discussed. Observations of geometrical end form changes were made during operation in the TF mode and resulting failure mechanisms catalogued. An anomalous (low δ) contrast was observed in SEM images of faceted and remolded cathodes thought to result from surface oxidation (WO3) and channeling effects.
Recombination in an expanding laser-produced plasma
Authors: Goforth R. R. , Hammerling P.
Published: February 2003

A simple model of three-body recombination in a freely expanding plasma which is initially isothermal but whose initial density decreases with radius leads to a variation of ion charge state within the ion flow, in qualitative agreement with that observed in laser-produced plasma experiments.
Analysis of grain-boundary diffusion in thin films: Chromium in gold
Authors: Holloway P. H. , Amos D. E. , Nelson G. C.
Published: February 2003

The application for surface sensitive analytic techniques to the study of grain boundary diffusion in thin films is described. Two common experimental configurations, sputter profiling and permeation analysis, are described, as are solutions for data reduction. Analytic solutions are difficult to use, even with simplifying assumptions. Rather, a versatile numerical method for data reduction, the method of lines, is used to analyze concentration profiles and surface accumulation concentrations. Both analytic and numerical calculations are compared to data for chromium diffusing in gold and the grain boundary half-width times diffusion coefficient (cm3/sec) is shown to be 8.6 ×10−11 exp(−25000/RT).
Electron-irradiation-induced divacancy in lightly doped silicon
Authors: Evwaraye A. O. , Sun Edmund
Published: February 2003

Two electron traps—A2 and A3—produced in n-type silicon by 1.5-MeV-electron irradiation are characterized by deep level transient spectroscopy. Activation energies of trapped majority carriers and capture cross sections for majority carriers at these levels are reported. From their production rates and annealing behaviors, they have been identified as different charge states of the same defect. Detailed annealing studies show that their annealing kinetics is first order with an activation energy of 1.47 eV. It is suggested that the defect is the divacancy and that dissociation is the likely process for its removal in these devices.
Grain-boundary diffusion in thin films: I. The isolated grain boundary
Authors: Gilmer G. H. , Farrell H. H.
Published: February 2003

Diffusion through grain boundaries in thin films is analyzed using a model with a single high-diffusivity plane perpendicular to the film. One surface of the film is maintained at unit concentration of the diffusing species, and a zero-flux boundary condition is applied at the other surface. It is shown that the region of the film where the diffusion species is supplied primarily by grain-boundary diffusion has a far smaller concentration gradient than that predicted by a similar model with semi-infinite geometry. As a result, calculations of grain-boundary diffusion coefficients in thin films based on the semi-infinite model may be in error by several orders of magnitude. Two methods for the analysis of thin-film diffusion data are described that should provide accurate values of grain-boundary diffusion coefficients.
Low-temperature diffusion of copper through gold
Authors: Tompkins H. G. , Pinnel M. R.
Published: February 2003

Low-temperature (75–150 °C) diffusion of copper through gold is studied with Auger electron spectroscopy. Grain-boundary or pipe diffusion measurements and calculations are discussed with boundary-value-problem assumptions. Electroplated cobalt-hardened gold on electroplated copper printed-wiring-board fingers is used. In addition, contact-resistance data is presented for different heating times and temperatures and a plot of CR values versus amount of surface film is shown. Chlorine, which evolves from the board material upon heating, reacts with copper which has diffused to the surface. This reaction provides a much better sink for the copper than oxidation. Diffusion coefficients are estimated which are several orders of magnitude larger than those previously reported for the Au-Cu system and reasons are discussed. Because of the chlorine emanating from the board, data from accelerated tests, in which the printed wiring board is also heated to elevated temperatures, may give erroneous predictions when extrapolated using an Arrhenius plot. Results demonstrate that diffusion via the defect structure is not the rate-controlling step in the accumulation of copper and/or copper compounds on the gold surface when exposed to normal atmospheres. The surface accumulation is limited by the growth kinetics of the surface film.
Temperature and velocity profiles and energy balances for an inductively coupled plasma discharge in nitrogen
Authors: Barnes Ramon M. , Nikdel Seifollah
Published: February 2003

Modification of a mathematical model described originally by Miller and Ayen to predict radial and axial temperature profiles in an inductively coupled plasma discharge was developed and applied to nitrogen. The modified model incorporates an updated description of three-concentric gas-flow patterns now common in spectrochemical applications. Temperature and velocity profiles and energy-balance distributions were demonstrated for a variety of input power levels and central flow rates. These results parallel similar results for well-characterized argon discharges. The modified plasma model depends upon the application of a weighted average of previous and current computed temperature values in achieving a stable numerical solution.
Magnetic fields for surface containment of plasmas
Authors: Forrester A. T. , Busnardo-Neto J.
Published: February 2003

Magnetic fields produced by a periodic array of rectangular bars magnetized perpendicular to their lengths have proven to be useful boundaries for plasma containment. Convenient formulas are developed for the computation of the magnetic fields for any choice of parameters. These formulas include not only the configuration which has commonly been used, but some alternate arrangements which can be advantageous for certain applications.
Current transport in Schottky-barrier diodes
Authors: Baccarani G.
Published: February 2003

Current transport in Schottky diodes is examined by solving the Boltzmann equation within the semiconductor. The effect of the metal is taken into account by imposing suitable boundary conditions to the above solution, and it is shown that the usual drift-diffusion equation is not correct in the vicinity of the junction. Generalized transport equations are derived, and the current-voltage characteristic is determined. A thermionic-emission velocity twice as large as that derived in the T-D theory is obtained, in accordance with a previous Monte Carlo simulation of the M-S device.
Magnetic field of two toroidal shells
Authors: Rolicz Pawel/ , Purczyǹski Jan , Sikora Ryszard
Published: February 2003

In this paper we investigate the magnetic field of two toroidal shells lying symmetrically on a torus and carrying a steady current. Throughout the work allowances are made for variable current density.
Investigation of semi-insulating GaAs using infrared-modulated cathodoluminescence and specimen current
Authors: Lin W. N. , Wittry D. B.
Published: February 2003

Investigations of the infrared (ir) -induced modulation of cathodoluminescence Ic and specimen current Is in semi-insulating Cr-doped GaAs and undoped as-grown semi-insulating GaAs have been made at 104 and 300 °K. Deep energy levels in the band gap were deduced from the spectra of ΔIc and ΔIs. The observed change ΔIc is due mainly to ir-induced changes in carrier-recombination mechanisms. ΔIs is caused by ir photoconductivity which results in a change of secondary-electron yield due to a change in specimen charging potential and electron-beam landing energy. The dependence of ΔIc and ΔIs on beam voltages and beam current shows that in order to have high sensitivity of modulation, the beam voltages and beam current should be kept as low as possible.
Magnetic properties of amorphous Fe-Si thin films
Authors: Shimada Yutaka , Kojima Hiroshi
Published: February 2003

Magnetic properties of Fe1−xSix sputtered films were investigated in the range 0⩽x⩽0.43. The films were found to be amorphous for the compositions x⩾0.20. The magnetic moment change upon crystallization depends on x. The magnetostriction seems to be a predominant factor in determing the hysteresis loops. The films in the amorphous state are magnetically soft. An in-plane uniaxial anisotropy was observed. The direction of the easy axis depends upon x.
Magnetic field of a current ring
Authors: Sometani Taro , Hasebe Kenroku
Published: February 2003

An expression for a magnetic field of a current ring is presented. The current distribution in the cross section of a thin current ring is expressed as a two-dimensional delta function and is substituted in Poisson’s equation for vector potential. The expression, derived from the solution of the equation, is given in the form of an integral with respect to a parameter. The expression is applied to the problem of the magnetization current on the surface of an iron core and to the problem of the self-inductance of an air-core coil.
Interference effects in microwave ferrite structures
Authors: Mueller R. S.
Published: February 2003

Plane polarized electromagnetic waves directed through a microwave system consisting of a polarizer, magnetized ferrite plate, focusing lens, and analyzer produce interference patterns. These patterns are defined analytically by using isochromatic surfaces. A biasing magnetic field for the ferrite plate can control its electromagnetic propagation characteristics and thereby vary the interference patterns. A scientific instrument that uses birefringent interference phenomena is a polarizing interferometer. Variable phase difference, angular splitting, and interference are explained for interferometers with Wollaston prisms made of transversely magnetized ferrite.
Magnetic domain wall bowing in a perfect metallic crystal
Authors: Carr W. J.
Published: February 2003

From the equation of motion for a domain wall in a perfect crystalline sheet, expressions for the steady-state mobility, power loss, and wall profile are calculated in terms of the magnetic eddy current field acting on the wall. An exact expression for the eddy current field for a given wall shape is derived, and an iteration procedure is used to obtain approximate results. At low wall velocity (0.16MsHAd/ε somewhat smaller than unity, where Ms is the saturation magnetization, HA is the applied field, d is the sheet thickness and ε is the wall energy per unit area) the equation for the wall profile, x=xw(y), is approximately xw= (MsHAd2/πε) [(𝒥m=1,3,5... 1/m3)−1 𝒥m=1,3,5... [sin(mπ/2) m−4](1−cosmπy/d) −(πy2/d2)], where the x axis is normal to the wall and the y axis is normal to the sheet, with the origin at the middle of the sheet. At some critical velocity, or applied field, which in rough approximation is given by 0.16MsHAd/ε equal to unity, no steady-state solution exists. Severe wall bowing cannot occur except near this critical field, just before instability occurs.
Isothermal equation of state for sodium chloride by the length-change-measurement technique
Authors: Chhabildas Lalit C. , Ruoff Arthur L.
Published: February 2003

The change in length of a 1-m-long NaCl single crystal has been determined as a function of hydrostatic pressure up to 7.5 kbar and at temperatures of 29.5 and 40.4 °C, to an accuracy of 500 Å using a Fabry-Perot–type He-Ne laser interferometer. The best values of the isothermal bulk modulus and its pressure derivative at atmospheric pressure and at 29.5 °C are B0=237.7±0.3 kbar, B′0 =5.71±0.25, and B″0=−0.10±0.05 kbar−1, respectively. These are the averages of the values obtained by a least-squares fit of several different equations of state to the present isothermal data. From these low-pressure measurements along, it is not possible to conclude which one of these equations provides a better fit to the data than the others. However, when other high-pressure data are taken into account, it appears that Keane’s equation best represents the measurements. When Keane’s equation is fitted to the data, and the published lattice parameter of NaCl at the Bi-III-V transition and at the NaCl B1-B2 transition are used, the respective transition pressures are found to be 75.8 kbar, within 1.2 kbar of the presently accepted value and 262 kbar, respectively. Considering the precision of the experiment the values of B0, B′0, and B″0 represent the best measurements so far. The determination of B″0 isothermally represents the first measurement of its kind.
Direct comparison of Auger electron spectroscopy and ESCA sensitivities
Authors: Brillson L. J. , Ceasar Gerald P.
Published: February 2003

The relative sensitivities of Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS or ESCA) have been compared for 54 elements, using the same electron analyzer under identical experimental conditions in ultrahigh vacuum. Signal-noise ratios derived from N (E) ESCA spectra and dN (E)/dE AES spectra showed that AES is a more sensitive technique for most elements, particularly those of low atomic number. These ratios of AES and ESCA detectabilities, which varied over a range more than 2 orders in magnitude, can be used as a guide for selecting the more sensitive technique for a particular element.
Refractive index of ion-implanted GaAs
Authors: Kachare A. H. , Spitzer W. G. , Fredrickson J. E.
Published: February 2003

Room-temperature near-infrared reflection and transmission measurements on GaAs ion implanted at 2.7 MeV with a fluence of 6.4×1016 P+/cm2 showed amplitude-modulated interference fringes. The reflection fringes were analyzed by using a simple model in which the implanted material is approximated by two partially absorbing layers on a nonabsorbing substrate. The analysis results indicate that the effective layer thicknesses are comparable with those predicted by the projected ion range and the width of the Gaussian ion distribution. The implantation-induced damage produces an increase in the refractive indices. The observed increase in the absorption is similar to that previously reported for GaAs which has been implanted at lower energy.
Low-temperature interdiffusion between aluminum thin films and GaAs
Authors: Christou A. , Day H. M.
Published: February 2003

Al-GaAs interdiffusion at temperatures between 250 and 450 °C has been studied using Auger electron spectroscopy. Ga has been observed to migrate through 2000-Å Al films at 250 °C and 24 h vacuum anneal. Schottky barrier height φB increases approximately 0.10 eV as a result of annealing at 250 °C. However, φB remains constant between 250 and 450 °C.
Prediction of conditions for a single pulse discharge
Authors: Sherman P. M.
Published: February 2003

An empirical method is presented for the prediction of conditions necessary to obtain a single pulse discharge with no oscillation, no restrike, and no residual energy stored with zero current and zero voltage at the end of the pulse. An LRC circuit with a 14.7-μF capacitor charged to voltages between 2000 and 20 000 V and discharging through wires of different metals was employed to obtain the necessary conditions. It is found to be highly anisotropic and are concluded to be the cause of the varying density in these structures. Statistical data appropriate to Fe-P and Pd-Si glasses are analyzed and discussed for the compositional range from TM73 M27 to TM100. Certain structural features appear only near the 80/20 (atomic percentages) composition common to numerous stable glasses.
Shock waves and acoustoelectric domains in piezoelectric semiconductors
Authors: McCarthy M. F. , Tiersten H. F.
Published: February 2003

The theory of shock waves is applied to the one-dimensional version of the general nonlinear electroelastic equations for deformable semiconductors employed in a recent acceleration wave analysis of acoustoelectric domains in piezoelectric semiconductors. Consequently, the mechanical and dielectric nonlinearities are included in the shock wave analysis as well as the semiconduction nonlinearity. Equations are derived for both the propagation velocity and the amplitude of the shock wave as a function of the jumps in certain variables across, and the state of the material immediately ahead of, the wave front. Expressions are obtained for the jumps in other variables across the shock front, such as the electric field, in terms of the amplitude of the shock. Some physical information concerning the evolutionary behavior of certain simplified types of shock is extracted from the rather complicated shock amplitude equation. When the analysis is specialized to the case of infinitesimal shocks, the results reduce to those obtained in the aforementioned analysis of acceleration waves in piezoelectric semiconductors with linear piezoelectric response.
Effects of shock loading on the Young’s modulus of alloy 2024 Al
Authors: Sinha P. , Singh I. P. , Ma C. H.
Published: February 2003

The effects of shock loading on the Young’s modulus of alloy 2024 Al in two differently heat-treated conditions in the shock pressure range of 58–178 kbar were examined. It was found that while the effects of shock loading are to cause an increase on Young’s modulus at one heat-treated condition, the effects of shock loading are to cause a decrease in Young’s modulus in the other heat-treated condition. These seemingly opposite effects are explained in terms of the defect modulus theory of Mott and Friedel.
Luminescence in warming and cooling from γ-irradiated polyethylene
Authors: Nakamura Shuhei , Ieda Masayuki , Sawa Goro
Published: February 2003

Anomalous luminescence during warming and cooling has been found in previously oxidized polyethylene following γ irradiation in air at room temperature. During warming, one of the thermoluminescence peaks appears at about 384 °K, close to the crystallite melting temperature. Further luminescence during a subsequent cooling appears, rising abruptly at about 370 °K near the recrystallization temperature. Such a luminescence is observable by repeating the warming and cooling cycle, although the luminescence intensity decreases with successive cycles. It appears that the presence of crystallites is essential for an appearance of the luminescence, and an existence of some long-lived trapped electrons above the melting temperature is suggested.
Reshock and release of shock-compressed 6061-T6 aluminum
Authors: Lipkin J. , Asay J. R.
Published: February 2003

The release and reshock behavior of aluminum from an initial shock stress of 2 GPa (20 kbar) has been examined. It is found that a two-wave structure characterizes both release and recompression, although a definite elastic-plastic structure is not obtained in either case. The velocity of the initial disturbance for both recompression and release agrees with the extrapolated ultrasonic longitudinal velocity, which implies initial elastic response from the precompressed state. The present results are discussed in terms of a rate-independent model which incorporates a distribution of yield states in the precompressed material. Reasonable agreement with experimental reshock and release wave profiles is obtained with this model. A brief discussion of rate effects estimated from an acceleration wave analysis is also presented.
An analytic degradation spectrum for H2
Authors: Garvey R. H. , Porter H. S. , Green A. E. S.
Published: February 2003

Using a discrete-energy-bin energy-apportionment method in conjunction with a detailed atomic cross-section approach, we obtain the degradation spectrum of H2 for a range of nonrelativistic incident-electron energies extending from threshold energies up to 50 000 eV. We fit the results so obtained with an analytic function of the incident energy and the energy variable. This representation exceeds in accuracy that achievable with simple scaling. We show that the various excited-state populations obtained using our analytic representation of the degradation spectrum agree closely with the corresponding values obtained directly from the discrete-energy-bin approach. Thus, by specifying the relevant cross sections and parameters in our two-dimensional fit to the degradation spectrum, we can solve all the nonspatial aspects of the initial stages of the nonrelativistic degradation problem of H2.
Plasma confinement by high-power excitation in a waveguide
Authors: Sodha M. S. , Tewari D. P. , Tripathi V. K. , Patheja Bansi Lal
Published: February 2003

Under TE20 mode excitation, the electric field in a rectangular waveguide is minimum at the center and has two intensity maxima at intermediate points. Consequently, the plasma electrons experience a strong ponderomotive force and are redistributed to assemble around intensity minima. A self-consistent solution of the wave equation for this problem reveals that the plasma density around intensity minima may be enhanced by a factor of 10 for accessible rf power. It also suggests that the electromagnetic waves of frequency less than the plasma frequency ωp can penetrate a dense plasma. In a collisional plasma, the redistribution of electrons is predominantly caused by their inhomogeneous heating by the wave. The confinement in this case may be attained at much lower powers.
Observations on the intermittent electron emission in liquefied nitrogen
Authors: Murooka Y.
Published: February 2003

The prebreakdown mechanism in liquefied nitrogen has been studied by using a modified optical Schlieren system. The present method has the advantage of observing the drift velocity of the disturbance in liquids and the prebreakdown mechanism by using a small disk instead of a knife edge. Thus the disturbance occurring due to the charge carriers can be recorded on the screen with an intensity which is proportional to the rate of the refractive index change. The mobilities of the negatively charged carriers derived from the drift velocity of the disturbance fall in the range of 1.1×10−2–1.85×10−1 cm2/V sec at an electric field strength of 9.7×104 V/cm. This value is distinctly larger than that of ions (2.94×10−3 cm2/V sec) in liquefied nitrogen, and also that of the quasifree electrons localized in the tiny bubbles (7.95×10−4 cm2/V sec) as calculated theoretically.
Infrared reflectance studies of bulk and epitaxial-film n-type GaAs
Authors: Holm R. T. , Gibson J. W. , Palik E. D.
Published: February 2003

The reflectance spectra of n-type GaAs samples with carrier densities from 3×1016 to 3×1018 cm−3 have been measured in the spectral range 55–1000 cm−1. Except for slight discrepancies in the vicinity of the reflectance minima, the classical Drude model provides an excellent description of the free-carrier effects in the reflectance. The discrepancies may be accounted for by a depletion layer at the surface or by a quantum-mechanical scattering theory. Inhomogeneities in the carrier density are measured by scanning the surface of the sample with a small aperture at a fixed frequency. The effect of mechanical polishing on the reflectance is analyzed in terms of a damaged layer. Reflectance measurements are also used to characterize samples consisting of epitaxial films of GaAs on GaAs substrates.
Surface-wave harmonic generation on y-z, x-z, and 41 1/2-x lithium niobate
Authors: Vella P. J. , Stegeman G. I. , Ristic V. M.
Published: February 2003

Optical probing was used to evaluate the coefficient for surface-wave harmonic generation on three high-coupling cuts of lithium niobate, namely, y-z, x-z, and 41 1/2-x. Surface-wave attenuation and acoustic beam diffraction profiles of the fundamental and second harmonic were also measured.
Work function and secondary emission studies of various Cu crystal faces
Authors: Haas G. A. , Thomas R. E.
Published: February 2003

The work function and its temperature dependence has been measured for the 〈100〉, 〈110〉, 〈111〉, 〈112〉 as well as 13 other Cu crystal planes. The results, obtained with two types of incident electron beam techniques in this experiment, are in good agreement with recent photoelectric and contact potential difference results reported on ion-sputter-cleaned surfaces. Variation in secondary emission for different crystal faces was found to be determined primarily by the work function changes of the different crystals and not so much by the bulk lattice orientation. It was also observed that the secondary electrons are not as dependent on the velocity constraints imposed by the Bragg condition as are the electrons having thermal energies.
Photoacoustic measurements of spatially varying optical absorption in solids: A theoretical treatment
Authors: Afromowitz Martin A. , Yeh Pen-Shu , Yee Sinclair
Published: February 2003

The effect of a spatially varying optical-absorption coefficient on the photoacoustic signal of a solid sample is discussed. A procedure is described for calculating the spatial variation of the optical-absorption function from the frequency dependence of the photoacoustic signal.
Comments on ’’Generalized criterion for feasibility of controlled fusion and its application to nonideal D-D systems’’
Authors: Chen F. F. , Dawson J. M. , Fried B. D. , Furth H. P. , Rosenbluth M. N.
Published: February 2003

The criticism of Lawson’s nτ criterion in a recent paper is based on a misunderstanding of conventional definitions of the confinement time τ. In attempting to ’’generalize’’ the Lawson criterion, the authors introduce errors of physics that lead them to draw incorrect conclusions about the feasibility of controlled fusion and the relative advantages of various reactor concepts.
On the step structures of alkali halide surfaces
Authors: Yacamán M. José , Ocaña Z. T.
Published: February 2003

The steps created during cleavage, on the surface of an alkali halide, are analyzed. It is concluded that their step height is biatomic rather than monoatomic. This characteristic is discussed in terms of the electrical neutrality of the crystal that must be maintained after cleavage.
Effect of quadratic electron-phonon interaction on band shapes
Authors: Bieg K. W. , Drickamer H. G.
Published: February 2003

A series of empirical relationships have been presented between the measured asymmetry of an optical absorption or emission peak and the configuration coordinate parameters which define the excitation. In this paper we show that these parameters can be derived with no need for empiricism.
Effect of illumination on mobilities in semi-insulating GaAs
Authors: Theodorou D. E. , Euthymiou P. C.
Published: February 2003

The minority-carrier mobility μn and the Hall mobility μH of Cr-doped semi-insulating p-type GaAs crystals were investigated as a function of the wavelength λ of illumination in the region of 400–900 nm, at room temperature. The mobilities were determined by combining photomagnetoresistance and photo-Hall measurements. All the mobility (as a function of wavelenth) curves had the same characteristic form with a minimum at 700 nm. This form is explained by using the variation of the light penetration depth with the wavelength and the existence of two kinds of holes.
Effect of repeated various surface treatments on the surface recombination velocity of n-InSb
Authors: Skountzos P. A. , Euthymiou P. C.
Published: February 2003

The surface recombination velocity of n-type InSb is investigated upon cyclic α bombardment and etching. We observe two clearly distinguished behaviors of the specimens after each treatment. We try to explain the above observation through a model for the structure of the material near the surface of the specimen and for the density distribution of the recombination centers after the various surface treatments.
New analysis of a high-voltage vertical multijunction solar cell
Authors: Hu Chenming , Carney James K. , Frank Robert I.
Published: February 2003

We present an analysis and a model for a vertical multijunction solar cell with covering lens, for which a 21% efficiency has been predicted previously. It is shown that the maximum conversion efficiency is in fact about 0.3%. The present analysis confirms our belief that back-to-back diodes should be designed into a solar cell only with great caution.
Oxidation induced stacking faults in n- and p-type (100) silicon
Authors: Murarka S. P. , Quintana G.
Published: February 2003

The formation of stacking faults during thermal oxidation of silicon has been investigated. The length and the density of stacking faults, in both n- and p-type 5-cm-diam (100) silicon wafers obtained from various manufacturers, were determined as a function of time and temperature of oxidation in dry and steam ambients. There appeared to be two categories of stacking faults. In the first category, the length of the stacking fault was given by L= (const) tn exp(−Q/kT), where n and Q are, respectively, 0.85 and 2.55 eV for dry oxidation and 0.66 and 2.37 eV for steam oxidation. This length was independent of the type (p or n) of the wafer. In the second category, the length of the stacking faults varied randomly across the wafer surface. The number of such faults was only about 5% of the total. For a given oxidation condition, the density of the stacking faults was an order of magnitude or more higher in n-type wafers than that in p-type wafers. Except for the very short periods of oxidation (<20 min) the density was found to be nearly independent of time or temperature of oxidation.
Rotation sensing through electromagnetic-surface-acoustic-wave transduction
Authors: Frost H. M. , Sethares J. C. , Szabo T. L.
Published: February 2003

Rotation rates ranging from two rotations per day to one rpm have been measured by a novel but simple rotation sensor; rotary position can also be measured. This device utilizes a surface-acoustic-wave (SAW) standing-wave pattern on the circumferential surface of a rotating cylinder. The standing-wave nodes and antinodes are stationary in the rotating cylinder frame as they move past a separate sensing transducer. Electromagnetic transducers are used for the contactless transduction of SAW’s. The device sensitivity is effectively several orders of magnitude greater than for earlier SAW sensor designs. In addition, we foresee measurements of rotation rates of up to thousands of rpm and down to less than 0.1°/h. Design considerations and alternate sensor designs are discussed.
Amplified spontaneous emission and gain-saturation nonlinearity in high-gain optical amplifiers: The biased amplifier
Authors: Moreno J. B. , Fisk G. A. , Hoffman J. M.
Published: February 2003

The systematics of amplified spontaneous emission and gain-saturation nonlinearity in high-gain optical amplifiers are explored. It is shown that of all the variations of the several dimensionless parameters that occur, only a reduction of the small-signal gain-length product can simultaneously minimize these two problems. Furthermore, of the various possible changes of the dimensional quantities that make up the gain-length product, increasing the saturation intensity achieves the highest overall gain for a given measure of distortion, and the least distortion for a given value of overall gain. This leads to the concept of the biased amplifier, one version of which is then treated in detail numerically.
Threshold characteristics of mirrorless lasers
Authors: Casperson Lee W.
Published: February 2003

Detailed analytical expressions are developed for the output power and spectral characteristics of high-gain mirrorless laser amplifiers. With regard to intensity variations and spectral narrowing, such lasers are similar in behavior to conventional laser oscillators. A threshold transition region is apparent as saturation sets in, and spectral rebroadening occurs in inhomogeneously broadened laser systems. These solutions take full account of saturation by both the right and left propagating radiation, and the results agree with experiments that have been reported.
Mercury-cesium vacuum-uv laser using charge-exchange pumping
Authors: Seely John F.
Published: February 2003

A mercury-cesium laser using the charge-exchange pumping mechanism is analyzed. The particle and photon rate equations are solved analytically and numerically, and peak laser intensity of order 100 W/cm2 at 1849 Å is calculated.
Measurement of thickness and diffusion length of thin epitaxial layers of GaP
Authors: Stupp E. H. , Milch A.
Published: February 2003

A nondestructive photoelectronic technique for determining the thickness and minority-carrier diffusion length of thin epitaxial layers of GaP is described. The method is useful over a thickness range of about one to ten diffusion lengths. The diffusion lengths can be rapidly measured to within 0.25 μm when the diffusion length of the substrate is known. The accuracy of the thickness measurement is about 0.5 μm. The measurements are independent of the supporting substrate thickness.
SEM observation of dopant striae in silicon
Authors: de Kock A. J. R. , Ferris S. D. , Kimerling L. C. , Leamy H. J.
Published: February 2003

Dopant striae in high-resistivity [?1000Ω cm n- and p-type crystals as well as phosphorus-doped (2–0.1Ω cm)] floating-zone silicon crystals have been investigated in the scanning electron microscope by Schottky barrier charge collection microscopy. The variation of (residual) dopant concentration (striae) produce a spatial variation in the collected current. The sensitivity of this technique for striation detection is found to increase with decreasing doping level. For doped material, good agreement exists between this technique and others (e.g., preferential etching). For resistivities below 0.1Ω cm striation contrast is absent. Striae contrast formation and its dependence on doping level and imaging conditions may be understood by consideration of the charge collection process and its dependence upon the diode depletion layer width.
Trapping effects in silver-doped mercuric iodide crystals
Authors: Hyder S. B.
Published: February 2003

Electrical and photoelectrical characteristics of silver-doped mercuric iodide crystals were investigated with a view to study the trapping phenomena in these crystals. Trapping parameters were determined by thermally-stimulated-current measurements, photoluminescence spectra, spectral response, and photoconductive decay measurements. The effects of temperature on pulse height under uniform illumination was measured in the temperature range of −100 to +100 °C. Resistivity changes and I-V characteristics are also discussed. Results of the experiments indicate a strong possibility for the existence of at least two main impurity levels in silver-doped HgI2—one, a hole trapping acceptor level at 0.73 eV above the valence band, and another, possibly a donor level, at 0.26 eV below the conduction band. The effect of a compensated acceptor level on polarization is also shown.
Growth and continuous compositional grading of GaAs1−x−zSbxPz by liquid phase epitaxy
Authors: Nahory R. E. , Pollack M. A. , DeWinter J. C.
Published: February 2003

The liquid phase epitaxial growth of GaAs1−x−zSbxPz mixed crystals is described. Layers have been continuously graded from a composition with the lattice constant of GaAs to a composition suitable for subsequent growth of a GaAs1−xSbx double-heterostructure laser. The details of the grading are discussed in terms of a phase-diagram calculation.
The conduction mechanism in silicon nitride films
Authors: Svensson C. M.
Published: February 2003

A simple analytical model for the conduction mechanism in silicon nitride films is proposed. The model is based on double injection, trap space-charge-limited current, and internal recombination. The Poole-Frenkel behavior arises from the Frenkel behavior of one of the traps responsible for the space charge. The model was shown to agree with experimental results on the thickness dependence of the current-voltage characteristic, to be compatible with MNOS device models, and to agree with observations of two-carrier conduction at the negative electrode.
Photoelectromagnetic properties of HgI2
Authors: Adduci F. , Cingolani A. , Ferrara M. , Lugarà M. , Minafra A.
Published: February 2003

The photoelectromagnetic effect and photoconductivity measurements at room temperature in HgI2 single crystals are reported for the first time. The sublinear dependence of these effects on the incident light intensity suggests the occurrence of trapping effects; this is taken into account by modifying the already developed calculations and introducing an ’’effective lifetime’’ τ* and an ’’effective diffusion length’’ L*. These two parameters are related to the electron and hole lifetimes. τ* and L* are calculated by the experimental data and they are dependent on the incident light intensity with a −1/3 power dependence; at an incident photon flux of 1015 photon cm−2 sec−1 we found τ*=9×10−8 sec and L*=6×10−5 cm.
High-field drift velocity of silicon inversion layers—a Monte Carlo calculation
Authors: Basu P. K.
Published: February 2003

This paper presents an accurate Monte Carlo calculation of the high-field drift velocity of carriers in the p- and n-channel inversion layers of silicon. The results are then compared with the results obtained by Hess and Sah by assuming a Maxwellian distribution of carriers. The models used in both these calculations are, however, the same as used by Hess and Sah. For the (100) surface of the n-channel device, the electric subband expected to have the largest population at high fields is considered. For the p channel, only the lowest subband is taken and scalar effective mass is assumed. Lattice scattering mechanism alone is assumed to exist. It is found that the Monte Carlo calculation differs from the Maxwellian calculation. Also, the agreement between the former and the experiment of Fang and Fowler and of Sato et al. is not satisfactory. Possible origin of this discrepancy with the experiment is discussed.
Low drive stripe head velocity in bubble garnet material
Authors: Zimmer G. J. , Gál L. , Humphrey F. B.
Published: February 2003

By observing the motion of an unpinned stripe head with a sampling optical microscope, domain wall motion in Y1.57Eu0.78Tm0.65Ga1.05Fe3.95O12 bubble garnet has been investigated at constant drive in the low field range from well below the Slonczewski critical field, through the Walker critical field, and up to the region previously investigated by radial expansion. A low field mobility of 400 cm/sec Oe was measured compared to 1020 cm/sec Oe predicted theoretically. The velocity increases smoothly as the drive field increases with no evidence of any peak velocity as predicted theoretically. A saturation velocity of about 7 m/sec was observed in good agreement with the radial expansion data considering the large difference in the mode of motion. Overshoot was observed in the stripe head motion which varied somewhat with drive and seemed to be essentially constant for the long propagations involved. Since the overshoot could easily be made less than 10% of the total distance, stripe head propagation is a good method for materials characterization.
MOPS, a magneto-optic-photoconductor sandwich for optical information storage
Authors: Krumme J.-P. , Heitmann H. , Mateika D. , Witter K.
Published: February 2003

A magneto-optic photoconductor sandwich, called MOPS, has been assessed as a memory medium for optical information storage. The present version of MOPS is composed of an epitaxial (Gd,Bi)3 (Fe,Ga)5O12 film and a Cu-doped CdS photoconductor film between coplanar In2O3/SnO2 electrodes. The chip contains 1.4×105 bits, requires 1 μW of optical power at 6328 Å for switching a memory cell in a magnetic field of 100 Oe and electric field of 1.2×104 V/cm, exhibits a read-out contrast of 21 : 1 at a read-out efficiency of 0.1%, and has a cycle time of ∼100 μs. MOPS has not been degraded by 107 switching cycles of arbitrary memory cells. No cross talk between neighboring bit sites has been observed.
The physics of zinc oxide varistors
Authors: Emtage P. R.
Published: February 2003

This paper presents a physical description of the action of ZnO varistors, which are complex ceramic bodies of ZnO grains sintered in an oxide flux; their conductivity is very low at low voltage, but becomes high after a certain breakdown voltage is reached. It is found that depletion layers in the ZnO adjacent to the intergranular layers of oxide flux are the principal barrier to conduction at low voltage. These depletion layers are formed because electron traps in the intergranular layer absorb electrons from the ZnO, and the oxide flux itself is found to be more conductive than the neighboring barriers; conduction within the flux is observed at low temperatures. Electrical breakdown is associated with the completion of trap filling in thin regions of the intergranular layer. This model is supported by a wide range of physical phenomena.