bluuebunny/crossref_metadata_2025 huggingface dataset:
Inverted xerographic depletion discharge mechanism for the dark decay of electrostatic surface potential on amorphous semiconductors
Authors: Kasap S. O.
Published: July 2002

Recently, the xerographic depletion discharge (XDD) model has been applied extensively to chemically modified a-Se, a-Se1−xTex alloys, and a-As2Se3 as well as to a-Si:H films to study the nature of charge carrier generation from deep mobility gap states which control the dark decay of the electrostatic surface potential on a corona charged amorphous semiconductor. In the normal XDD model, the dark discharge involves bulk thermal generation of a mobile carrier of the same sign as the surface charge and its subsequent sweep out from the sample leaving behind an ionized center of opposite charge. It is shown that an ‘‘inverted depletion discharge’’ mechanism, which involves the thermal generation of a mobile charge carrier of the opposite sign to the surface charge and its subsequent drift to the surface and the resulting surface charge neutralization there, results in a dark discharge rate which has identical features as the normal XDD mechanism. In the normal XDD mechanism, the neutral region develops after the depletion time from the grounded electrode, whereas in the inverted XDD mechanism the neutral region grows from the surface. Furthermore, during inverted depletion discharge the surface charge is actually dissipated by neutralization, whereas in the normal depletion discharge model there is no such requirement over the time scale of the experiment. It is concluded that xerographic dark decay experiments alone cannot determine the sign of the thermally generated mobile carrier and that of the bulk space charge. Chemically modified amorphous selenium case is discussed as an example of surface potential decay resulting from bulk space-charge buildup.
Application of multiscattering theory to impurity bands in Si:As
Authors: Lowney Jeremiah R.
Published: July 2002

Impurity bands in arsenic-doped silicon have been calculated for doping densities of 3.3×1017, 1.2×1018, and 8.0×1018 cm−3. A multiscattering approach is used with a model potential which provides both electronic screening and the proper bound-state energy for the isolated center. The results are in good agreement with previous calculations based on electron hopping among hydrogenic centers. An advantage of the multiscattering approach is that it treats the conduction-band states as well and shows the loss of these states to the formation of the impurity band. This is a new result and affects the density for the Mott transition. Calculations are also performed for the states associated with the binding of an extra electron to unionized arsenic centers, the so-called D− band. The overall results are in good agreement with the observed Mott transition in Si:As near 8×1018 cm−3.
Experimental study of the surface photoelectric effect in cesiated thin silver films
Authors: Goudonnet J. P. , Chabrier G. , Vernier P. , Arakawa E. T.
Published: July 2002

We have measured the photoyield Y of thin silver films as a function of the angle of incidence for polarized light in the attenuated total reflection geometry. For s polarization a pure volume effect can explain the variation of the yield Ys. For p polarization the experimental photoyield Yp is much larger than that calculated by the volume process. The excess yield is attributed to the surface effect and a parameter K/p0 accounting for the structures observed in Yp has been calculated.
Diffusion in three different dislocations in an fcc crystal
Authors: Stark J. P. , Lee D. Y. , Vaughn Leslie
Published: July 2002

A theoretical study is made of dislocation pipe self-diffusion in an fcc crystal for three differing dislocation structures to ascertain the correlation factor, diffusivity, and mobility in an electric field. The three structures may be described as a pure edge dislocation with the usual Burgers vector b=a/2[110]. The other two are mixed dislocations with b=a[01̄0] and either a line sense of ξ=a[100] or ξ=a[101]. The latter two are similar to an edge-type dislocation and are formed by the removal of one-half of a (010) plane of atoms whose edge follows these directions. It is found that very little difference exists in the transport processes in these three structures. Thus, although the latter two dislocations have a major screw character in the sense of a mixed dislocation, the transport is dominated by the edge character which in turn is controlled by the binding energy of the vacancy to the core. Additionally, the ratio of the mobility to diffusivity in an electric field is proportional to the reciprocal of the correlation factor as found in the past for other self-diffusion situations, and these authors conclude that such a result is an unprovable axiom of correlated crystalline transport.
Lattice relaxation in silicon doped with 4d and 5d transition metals
Authors: Mayo Santos , Lowney Jeremiah R.
Published: July 2002

Photoionization cross-section spectra from deep centers in silicon doped with technologically important 4d and 5d transition elements were analyzed by the Ridley and Amato lattice coupling model to determine threshold energy and lattice relaxation parameters corresponding to optically induced transitions involving either band. The average optic phonon energy is 50 meV. Electron transitions to the conduction band from the silver, platinum, and gold acceptor centers have, respectively, threshold energies (in meV) ET0 =550,226, and 570. For silver and gold, the Huang–Rhys parameter S could not be determined because of a mixture of both allowed and forbidden transitions; for platinum, S=0.3. Hole transitions from the valence band to the same centers have, respectively, ET0 =580, 905, 590, and S=1.3, 0.5, 0.8. Hole transitions from the valence band to the donor centers of these elements are, respectively, ET0 =340, 320, 335 and S=1.2, 1.4, 0.4. ET0, and S values are uncertain to within ±5 meV and ±0.05, respectively. Electron transition data from the donor centers of these elements to the conduction band are not available or insufficient to allow analysis of the threshold region.
Comment on ‘‘Noncontact doping level determination in GaAs using photoreflectance spectroscopy’’ [J. Appl. Phys. 6
2, 4558 (1987)]
Authors: Bottka N. , Gaskill D. K.
Published: July 2002

It is pointed out that it is inappropriate to use the third-derivative functional form derived by Aspnes [Surf. Sci. 37, 418 (1973)] to fit the photoreflectance data of GaAs at the fundamental absorption edge when the low-field condition is not satisfied. Instead, the Franz–Keldysh oscillations can be used to determine the carrier concentration of the material.
Reply to ‘‘Comment on ‘Noncontact doping level determination in GaAs using photoreflectance spectroscopy’ ’’ [J. Appl. Phys. 6
2, 4558 (1987)]
Authors: Theis W. M. , Peters L. , Phaneuf L. , Kapitan L. W.
Published: July 2002

Compliance to the low electric field regime necessary for application of the third derivative functional form formalism is demonstrated for ion-implanted samples used to determine the doping level by photoreflectance spectroscopy. Due to field and doping inhomogeneity, the proper line shape is speculated to be described by a superposition of Franz–Keldysh oscillations.
Parametric study of a room-temperature metal vapor laser
Authors: Anders A. K. , Tobin R. C.
Published: July 2002

We have demonstrated laser operation at room temperature on the Cui (511,578 nm) and Aui (312,628 nm) transitions and obtained specific pulse energies for the Cui 511 nm and Aui 628 nm lines of about 5 and 2 μJ cm−3, respectively, from a single-section tube. A simple theoretical model has been used to show that the reduced outputs for the Cui 578 nm and Aui 312 nm lines are due to the significantly smaller fraction of the working volume in saturation in each case. The metal vapor column of length 20 cm and local ground-state concentration in the 1014–1015 cm−3 range is produced on demand in a single-section tube in less than 10 ms. The highest output power obtained is for a 90% He in an Ar/He mixture at a total flowrate of 1.8 ℓ min−1, the tube pressure being 20 mbar. A specific sputtering discharge energy of approximately 600 mJ cm−3 is needed to obtain a peak power of 1 kW on either the Cui 511 nm or Aui 628 nm lines.
A power-squared sensor for two-photon spectroscopy and dispersion of second-order coherence
Authors: Jones Richard D. , Callis Patrik R.
Published: July 2002

A method using second harmonic generation from potassium dihydrogen phosphate (KDP) powder was developed and used as a normalizing reference to obtain accurate relative two-photon fluorescence excitation spectra of naphthalene and several related compounds in the range 550–650 nm. The method removes almost all uncertainty in matching overlapping spectra obtained from different dyes when using a dye laser pumped by a pulsed YAG laser second harmonic. The resulting naphthalene spectrum, which was corrected for the dispersion of the second harmonic generation efficiency, differs only slightly from most previously reported two-photon spectra which used linearly responding references. The distortions introduced in the latter method during single dye scans due to the increase of second-order coherence in the low gain extremes of the tuning curve were verified as resulting mainly from shortening of the pulse width. Spatial changes in the beam profile as a function of wavelength were found to make a smaller, but significant contribution to the dispersion of the second-order coherence.
Degenerate four-wave mixing from a waveguide with guided wave pump beams
Authors: Stegeman G. I. , Wright E. M. , Seaton C. T.
Published: July 2002

We have analyzed the problem of degenerate four-wave mixing in which a probe beam is incident from above onto a thin-film waveguide pumped by two oppositely propagating guided waves. Four-wave mixing signals are obtained both on reflection from the film surface and on transmission into the substrate supporting the film. Analytical formulae are evaluated for a number of different cases which compare nonlinearities in the film versus the substrate.
Axis shielding in cylindrical nuclear-reactor-pumped lasers
Authors: Torczynski J. R. , Gross R. J.
Published: July 2002

A numerical study of the motion of the gaseous medium in nuclear-reactor-pumped lasers with cylindrical geometry has revealed the existence of an axis-shielding phenomenon—the spatial nonuniformity of the fission-fragment energy deposition forces the gas to redistribute itself in a way that causes the on-axis power density to vanish. The nondimensional parameters that govern the energy deposition and the gas motion are derived, and the region of parameter space in which axis shielding occurs is determined.
Ultraviolet photoelectron spectroscopic study of perfluorinated carboxylic acid monomolecular films prepared by vacuum deposition
Authors: Mitsuya Munehisa , Seki Kazuhiko , Inokuchi Hiroo
Published: July 2002

Ultraviolet photoelectron spectra have been measured for monomolecular films of perfluorinated carboxylic acids prepared by vacuum deposition. Their threshold ionization potentials were determined to be 8.5 eV and their work functions larger than those for other organic compounds. The escape depth of photoelectrons through the perfluorocarbon chain was evaluated at 2.3 nm. These results are interpreted in relation to the large electronegativity of constituent fluorine atoms.
Three-fluid simulation of the plasma-erosion-opening switch
Authors: Mason Rodney J. , Jones Michael E. , Grossmann John M. , Ottinger Paul F.
Published: July 2002

The dynamics of the plasma-erosion-opening switch is characterized with the aid of 2D three-fluid simulation using the anthem implicit simulation code, for plasma fill densities ranging from 1012 to 6×1013 cm−3 with 45-ns pulse rise times. The switch behavior is found to depend sensitively on the threshold for electron emission at the cathode, on the detailed structure of the anode with its injection holes, and on the possible action of anomalous resistivity in the fill plasma. Closest agreement with NRL GAMBLE I experimental results is obtained with the combination of zero electric field threshold emission at the cathode, an ‘‘open’’ anode, and modest anomalous resistivity.
A Markov treatment of the self-diffusion dyadic in homogeneous crystals
Authors: Mullins W. W.
Published: July 2002

Expressions are derived for the drift velocity V and the self-diffusion dyadic D⇊ of a particle in a macroscopically homogeneous multicomponent crystal based on two related finite Markov descriptions. In the first or system state description, the Markov states, αβγ⋅⋅⋅, correspond to configurational states of a crystal with periodic boundary conditions. To each Markov transition α→β is assigned the vector rαβ equal to the displacement, if any, of the particle during that transition. In the second or jump description, the Markov states ijk⋅⋅⋅ correspond to the type of jump executed by the particle. To each Markov state i is assigned the vector ri equal to the displacement of the particle executing the ith type of jump. The parameters of the second description are derived in terms of those of the first. The treatment extends previous ones in the following ways: (1) It is three dimensional; (2) it gives a rigorous derivation of D⇊ when correlation and bias (i.e., nonzero V) effects are simultaneously present; (3) new expressions for D⇊ are given that are equivalent to but formally simpler than previous results; (4) the general form of the results is independent of the geometrical details of the system.
The growth and structure of Cd0.95Fe0.05Te thin films grown by radio-frequency sputtering
Authors: Alvarez-Fregoso O. , Mendoza-Alvarez J. G. , Sánchez-Sinencio F. , Huanosta A.
Published: July 2002

The growth and structure properties of Cd1−xFexTe thin films prepared by rf sputtering were studied. Films with thicknesses in the range 0.75–2.45 μm were grown onto Corning glass substrates at temperatures between 50 and 300 °C in an argon atmosphere at a pressure of 3 mTorr. The deposition rate was determined by film thickness profile analysis. Transmission electron microscopy and x-ray diffractometry techniques were used to evaluate the structure, grain size, and orientation of the films. These properties were found to be related to the substrate deposition temperature.
Investigation of the bubble formation mechanism in a-Si:H films by Fourier-transform infrared microspectroscopy
Authors: Mishima Y. , Yagishita T.
Published: July 2002

The formation of bubbles and holes in hydrogenated amorphous silicon (a-Si:H) films after isochronal annealing has been investigated. The internal stress of the bubble in an a-Si:H film has been determined by the relationship between the diameter and height of a bubble. In addition, the internal stress of the bubble has also been investigated based on the difference in hydrogen concentration between the flat and bubble areas determined by Fourier-transform infrared microspectroscopy. Consistent results are obtained from both methods regarding the magnitude of the internal stress. These results indicate that the bubble is formed by molecular hydrogen evolving from the a-Si:H film.
Theory of high-field electronic transport in bulk ZnS and ZnSe
Authors: Brennan Kevin
Published: July 2002

We present ensemble Monte Carlo calculations of electron transport in bulk ZnSe and ZnS under conditions of high applied electric field strengths. The calculations include the full details of the first two conduction bands as well as the full-order treatment of the electron-phonon scattering mechanisms. The steady-state electron drift velocities as a function of applied electric field are determined for each material system as well as the total electron-phonon scattering rates. In addition, the high-field probability distribution function is presented for both ZnS and ZnSe. As expected, based on the values of the optical-phonon energy, the electron distribution is much cooler in bulk ZnS than in bulk ZnSe at comparable electric field strengths even in the absence of significant impact ionization in either material. Consequently, carrier heating to comparable energies is more difficult to achieve in ZnS than in ZnSe. This has relevance to the operation of electroluminescent devices made from these materials.
Phase-amplitude imaging: The fully automated analysis of megagauss magnetic field measurements in laser-produced plasmas
Authors: Kalal Milan , Luther-Davies Barry , Nugent Keith A.
Published: July 2002

This paper describes the application of phase-amplitude imaging to the measurement of self-generated magnetic fields in laser-produced plasmas. The magnitude of the magnetic field is determined by polarimetry and the plasma density profile by interferometry. Both pieces of information are recorded on a single interferogram in a form that can be analyzed automatically using computer-based image processing. We describe a method for successfully determining the magnetic field profile in plasmas generated by 70-ps Nd laser pulses at high intensity on planar targets when plasma motion or turbulence introduces an additional difficulty by reducing the visibility of the fringes.
Doping dependence of the specific contact resistance of NiSi2 on (100) n-Si
Authors: Sasse E. , König U.
Published: July 2002

Nickel disilicide (NiSi2 ) was formed on (100) oriented n-type Si-molecular beam epitaxial layers (Si-MBE) of various doping levels between 2×1016 and 13×1018 cm−3 and on substrates of 2×1019 cm−3 . Very low contact resistances were found and a low Schottky barrier of φBn =0.49 V was derived. A comparison with other commonly used contact materials shows NiSi2 to be highly favorable in this doping range.
Nonlinear effects in hot-electron transport
Authors: Zanette D. H. , Barrachina R. O. , Garibotti C. R.
Published: July 2002

A method to compute the solution of the nonlinear Boltzmann equation for a one-dimensional hot-electron system is presented. Nonlinear terms rising from the electron exchange interaction determine a nonmonotonic space dependence of the stationary electron distribution in the presence of an electric field. We show that the effective temperature approximation is only valid for the high-energy tail of the distribution.
Thin-skin electromagnetic fields around surface-breaking cracks in metals
Authors: Lewis A. M. , Michael D. H. , Lugg M. C. , Collins R.
Published: July 2002

There has been a long history of the use of two electromagnetic techniques to measure surface-breaking cracks in metals. Both the alternating current potential drop (ACPD) technique and the eddy current technique have given good agreement with experimental results, even though the theoretical models on which their interpretations are based use contrasting assumptions for the boundary condition on the metal surface. The model for the ACPD technique assumes that the magnetic scalar potential satisfies the 2D Laplace equation, while eddy current modeling assumes an approximation of Born type in which the surface field is unperturbed by the presence of the crack. This paper considers a general model matching the thin-skin electromagnetic field around a surface-breaking crack to that in the free space above and shows that the two contrasting boundary conditions are extremes of a more general one. The Laplace approximation is valid for high permeability materials such as mild steel, while the Born approximation is appropriate for materials of low permeability and high conductivity such as aluminum. Experimental investigations of the magnetic fields near semielliptical cracks in mild steel and aluminum show quantitative agreement with the theory.
Magnetic bubble collapse in the presence of a microwave field
Authors: Dong J. L. , Artman J. O. , Charap S. H.
Published: July 2002

A bubble collapse experiment has been done on a garnet sample with the composition Y1.92Sm0.1Ca0.98Fe4.02Ge0.98O12 both with and without an applied local microwave field. To explain the experimental results, the analysis of bubble domain wall motion by Callen and Josephs has been modified by introducing a nonlinear velocity-drive characteristic. In the case of no microwave excitation, a good fit between the theory and the experimental data is then obtained. A bubble collapse model in the presence of a microwave field which includes contributions from microwave-produced ‘‘dipolar pressure’’ and ‘‘intrinsic pressure’’ has been made. While some discrepancies exist between theory and experiment, nevertheless these results may be helpful in understanding the observations of microwave bubble generation reported by a number of research groups.
The effect of interposing thin oxide layers on the photovoltaic properties of a-Si:H solar cells II between the middle n and p layers of a tandem-type cell
Authors: Sakai Yuichi , Fukuyama Keiichi , Matsumura Michio , Nakato Yoshihiro , Tsubomura Hiroshi
Published: July 2002

The properties of the p/n junction of hydrogenated amorphous silicon (a-Si) were studied by use of some kinds of a-Si cells. It was concluded that the photoelectromotive force generated at the p/n junction reduces the photovoltage of the tandum-type solar cells, and the rate of the electron-hole recombination lowers their fill factor. However, by interposing a 2-nm-thick TiO2 layer between p and n layers of the tandem-type solar cells, the open-circuit photovoltage was raised from 1.50 to 1.64 V, the fill factor from 0.705 to 0.775, and the energy conversion efficiency was improved ∼10%. Among the metal oxides examined i.e., V2O5, TiO, TiOx, TiO2, NiO, WO3, ITO, Fe2O3, and SiO2, the TiOx (x=1.7) layer showed the best result. In addition, it was observed that the thickness of the p and n layers, which was necessary to form the p/n junction, could be reduced by interposing a metal-oxide layer.
On dose correction in electron beam lithography
Authors: Deshmukh P. R. , Khokle W. S.
Published: July 2002

Ideal proximity exposure compensation is shown to occur when the dose correction factors are obtained by considering the electron energy dissipation distribution at the lowest plane in the resist. In such an ideal situation, the simulation of resist profiles in line patterns shows that the resist edge slope becomes nearly equal to what can be obtained with a single beam line.
The effect of chemical and mechanical treatment on the stability of Zr76Fe24 metallic glass
Authors: Radliński A. P. , Calka A.
Published: July 2002

We demonstrate that mechanical grinding and chemical etching dramatically reduce the thermal stability of the eutectic Zr76Fe24 metallic glasses. Using differential scanning calorimetry and x-ray diffractometry, it is shown that this effect is due to the activation of a surface crystallization process associated with out-diffusion of zirconium and subsequent formation of a Zr2Fe+αZr crystalline layer. The kinetics and bulk crystallization are analyzed in detail for the etched samples using the concept of the local value of the Avrami exponent.
Trap suppression by isoelectronic In or Sb doping in Si-doped n-GaAs grown by molecular-beam epitaxy
Authors: Li A. Z. , Kim H. K. , Jeong J. C. , Wong D. , Schlesinger T. E. , Milnes A. G.
Published: July 2002

The effects of isoelectronic doping of GaAs by In or Sb on the electron deep levels in n-GaAs grown by molecular-beam epitaxy have been investigated in the growth temperature range 500–600 °C for Si doping levels of 4–7×1016 cm−3 and As-stabilized conditions. The two dominant traps M3 and M6 are drastically reduced in concentration by up to three orders of magnitude for M3 (from 1015 cm−3 down to <1012 cm−3) and two and a half orders of magnitude for M6 by introducing 0.2–1 at.% In or Sb and increasing growth temperatures from 500 to 550 °C. The trap concentrations of M3 and M6 were also significantly reduced by increasing the growth temperature to 600 °C without In or Sb doping and by decreasing the growth rate from 1.0 to 0.3 μm/h. The incorporation coefficients of In and Sb have been measured and are found to decrease with increasing growth temperature. The growths with high M3 and M6 trap densities are shown to have short minority-carrier diffusion lengths. Indium isoelectronic doping, which is presumed to take place on a gallium sublattice site, and Sb doping, which is expected to take place on an arsenic sublattice site, appear to have rather similar effects in suppressing the concentration of the M3 and M6 electron traps. This suggest that both of these traps are in some way related to (VAsVGa) complexes or (VAsXVGa) complexes where X is different for M3 and M6 and might be interstitial or impurity related.
Oxide degradation during selective epitaxial growth of silicon
Authors: Friedrich J. A. , Neudeck G. W.
Published: July 2002

A derivative of selective epitaxial growth and epitaxial lateral overgrowth, has been devised to create single-crystal silicon on insulator structures. The effect of conditions present in selective epitaxial growth and epitaxial lateral overgrowth on the electrical characteristics of the insulating masking oxides has been studied. It was determined that thin (<150 nm) oxides were attacked by the ambient employed in selective epitaxy. The rate of degradation increased with decreasing oxide thickness and with the addition of silicon-containing species to the gas phase. The observed defect formation may be related to the oxide decomposition during annealing in oxygen-free ambients and the undercutting of masking oxide at the Si-SiO2 interface during the in situ preclean step used in epitaxial processes.
Study on the early stage of photochemical vapor deposition of amorphous silicon from disilane on a SiO2 substrate
Authors: Kawasaki Mitsuo , Tsukiyama Yoshio , Hada Hiroshi
Published: July 2002

The nucleation in the very early stage of photochemical vapor deposition of amorphous silicon on a SiO2 substrate from disilanes was studied by using a chemical amplification technique to detect the small Si nuclei. Phenomena characteristics of the nucleation process were observed and the effects of some fundamental deposition parameters on the nucleation revealed interesting features of the nucleation chemistry. In particular, we found two different regions of substrate temperature; in the low-temperature region up to about 150 °C the initial nucleation rate decreased as a whole with substrate temperature, while above 150 °C the tendency was apparently reversed, suggesting a change of nucleation mechanism. Information about the production, transportation, and identity of active species serving as nucleation precursors was obtained from the effects of gas pressure and addition of nitric oxide as a radical scavenger upon the nucleation efficiency. Based on the known chemistry of silanes and related species, basic surface reactions possibly involved in the nucleation step are discussed.
Electron transport in SiO2 under a strongly inhomogeneous electric field
Authors: Sano Nobuyuki , Fukai J.
Published: July 2002

Monte Carlo simulations have been performed to study the electron transport in SiO2 subject to a strongly inhomogeneous electric field produced by a hyperboloid needle and plate assembly. The dominant scattering mechanism (the polar electron-phonon interaction) in a regime of electric field (≲3×106 V/cm) is treated with the Fröhlich–Hamiltonian formalism [Proc. R. Soc. London A 160, 230 (1937)]. The spatial evolutions of the electron energy distribution and the average electron energy are presented. A characteristic overheating due to the nonuniform high electric field near the needle tip is observed and its relevance to the initiation of dielectric breakdown is pointed out.
Demonstration of the linear electro-optic effect in a thermopoled polymer film
Authors: Hill J. R. , Pantelis P. , Abbasi F. , Hodge P.
Published: July 2002

We describe an interdigital linear electro-optic modulator produced from a novel polymer. The polymer was formed into a thin phase grating by simultaneous application of heat and a periodic electric field. The first maximum generated by diffraction of 633-nm HeNe laser light passing through the grating was electrically modulated to a depth of over 17%. The performance of the modulator is compared with a quadratic electro-optic modulator having the same electrode structure but where the polymer was replaced by nitrobenzene. It is estimated that the application of a thermopoling field strength of 20 V/μm to the polymer would impart a linear electro-optic coefficient of about 30 pm/V, which is comparable to the largest coefficient of lithium niobate.
Oxygen incorporation in molecular-beam epitaxial silicon doped using a boric oxide source
Authors: Tuppen C. G. , Prior K. A. , Gibbings C. J. , Houghton D. C. , Jackman T. E.
Published: July 2002

Oxygen incorporation in epitaxial silicon produced by molecular-beam epitaxy and boron doped by coevaporation of boric oxide has been investigated. The concentration of oxygen in the deposited layers was measured using secondary-ion mass spectrometry and shown to depend on a number of growth parameters. A reaction mechanism is proposed and is quantitatively modeled using a thermodynamic approach. A simple expression is given for determining the onset of oxygen incorporation.
Intensities of backscatter Mössbauer spectra
Authors: Mei Z. , Fultz B. , Morris J. W.
Published: July 2002

The intensities of γ-ray and x-ray backscatter Mössbauer spectra of 57Fe nuclei in different matrix materials were studied theoretically and experimentally. A previous analysis by J. J. Bara [Phys. Status Solidi A 58, 349 (1980] showed that negative peak intensities occur in backscatter γ-ray spectra when the 57Fe nuclei are in a matrix of light elements. We report a confirmation of this work and offer a simple explanation of the phenomenon. The present paper extends Bara’s analysis to the case of conversion x-ray spectra; expressions for the intensity of conversion x-ray spectra as a function of absorber thickness and absorber material parameters are presented. We show that negative peak intensities are expected in conversion x-ray spectra when the 57Fe nuclei are in a matrix of heavy elements.
X-ray standing wave determination of Mn sublattice occupancy in a Cd1−xMnxTe mosaic crystal
Authors: Durbin Stephen M.
Published: July 2002

An x-ray standing wave investigation of the structure of a high-quality mosaic crystal of Cd0.725Mn0.275Te reveals that the Cd and Mn cations occupy the same sublattice in this zinc-blende material, as expected. This conclusion is made by inspection of the data obtained from a simple measurement made at the Cornell high energy synchrotron source. Furthermore, these data clearly indicate that the two cations have slightly different positions within the cation sublattice. Fitting these data to a simple model using x-ray dynamical diffraction theory shows that these distinct cation positions are consistent with the bimodal CdTe and MnTe bond lengths previously observed with extended x-ray absorption fine structure spectroscopy [A. Balzarotti, M. Czyzyk, A. Kisiel, N. Motta, M. Podgorny, and M. Zimnal-Starnawska, Phys. Rev. B 30, 2295 (1984)], but contradict the assertion that the cation sublattice is undistorted. This application of the standing wave technique to a mosaic crystal demonstrates that dynamical diffraction methods can produce important structural information from a much larger class of crystals than previously considered.
Remote monitoring of thermal conductivity of a powder by a flash radiometry technique
Authors: Leung W. P. , Tam A. C.
Published: July 2002

We study the dependence of the thermal conductivity of a carbon-loaded epoxy powder on its porosity using a noncontact flash radiometry technique. The thermal conductivity is found to be very small when the porosity of the sample is higher than a critical value. Below the critical porosity Pcrit, thermal conductivity increases linearly with packing density. This phenomenon can be explained by a two-phase model; the powder exhibits continuous thermal conduction paths only when the porosity is less than Pcrit.
Generalization of the metal-oxide-semiconductor charge-sheet model to two dimensions
Authors: Sanchez Julian J. , DeMassa Thomas A.
Published: July 2002

The metal-oxide-semiconductor field-effect transistor (MOSFET) model is extended to two dimensions using a generalized form of the charge-sheet model. This generalized form is obtained by way of conformal mapping techniques that empirically extend the modeling capabilities to allow solutions for a wider class of problems. The physical structure of the device can be incorporated in these conformal maps, allowing individual tailoring of the device shape for a given process. Since the charge-sheet model produces continuous I-V characteristics for all regimes, electrical characteristics such as threshold, gate swing voltage, surface punchthrough, and other such parameters can be evaluated. In this paper the characteristics of the generalized model are explored by examining a nonrecessed small-width structure. This structure is simple and provides an accurate assessment of the model’s capability.
Thermoelectret state in polyvinyl chloride : polyethylene polyblends
Authors: Tripathi Anita , Tripathi A. K. , Pillai P. K. C.
Published: July 2002

Thermoelectrets of polyvinyl chloride (PVC)–polyethylene blends were prepared and their thermally stimulated discharge current was studied. The results are discussed in terms of space charge that leads to induced dipole formation. The results indicate that the contribution of PVC dipoles to the total polarization of polyblend thermoelectrets is either insignificant, or is masked by the space-charge polarization that leads to induced dipole formation.
Some characteristics of granular superconductivity in GdBa2Cu3O7−y ceramics
Authors: Zhao Yong , Sun Shifang , Zhang Qirui
Published: July 2002

The behavior of granular superconductivity of single-phase GdBa2Cu3O7−y ceramics has been studied systematically by measuring the crystal structure, superconductivity, magnetoresistance, I-V characteristics, etc. The grain-boundary Josephson effect, the behavior of the current-carrying resistive state, and the percolation nature, etc., have been observed. Based on the three-dimensional network model of Josephson junctions, the phenomena noted above are explained satisfactorily.
Effective scattering angle of relativistic electron beams injected through an anode foil
Authors: Vijayan T. , Gupta G. P. , Rohatgi V. K.
Published: July 2002

The values of the effective scattering angle 〈θ〉 of a relativistic electron beam injected through an anode foil are analyzed by different methods in the light of reported values for various beam-plasma heating experiments. Wide variations in calculated 〈θ〉 are noted depending on the method used. It is argued that the 〈θ2〉1/2 expression corrected for Molière screening and the (1/e) equivalent from the Monte Carlo code give nearly the same average scattering angle and one of them should be used to determine 〈θ〉. It is also seen that a small variation in 〈θ〉 alters significantly the plasma temperature estimate.
Growth of (111) GaAs on (111) Si using molecular-beam epitaxy
Authors: Radhakrishnan G. , Liu J. , Grunthaner F. , Katz J. , Morkoç H. , Mazur J.
Published: July 2002

(111) GaAs layers have been grown epitaxially on (111) Si wafers, both on-axis as well as 3° off-axis towards the 11̄0 direction, using molecular-beam epitaxy. The grown layers have been characterized by scanning electron microscopy, x-ray diffraction, and transmission electron microscopy.
Comment on ‘‘A new model of the rapid initial oxidation of silicon’’
Authors: Lu Y. Z. , Cheng Y. C.
Published: July 2002

The basic assumptions of a recent model of the rapid initial oxidation of silicon by Schafer and Lyon are examined. It is found that the hypothesis is inconsistent with existing experimental data. Instead, our previous model on initial oxidation is used to satisfactorily explain their experimental data. The charge density at the interface and the equilibrium concentration of oxygen in the oxide are estimated based on this model, which agrees well with measured results. These comparisons suggest that our previous model of oxidation gives an overall satisfactory picture of the rapid initial thermal oxidation of silicon.
Equitemporal x-ray optics (time compression of x-ray pulses)
Authors: Csonka Paul L.
Published: July 2002

Equitemporal optics is a dynamical optical method that makes it possible to reduce the pulse duration of an x-ray beam without making any changes in the source generating the photons. The total number of photons in a pulse is not significantly reduced by the method. The SPEAR and PEP electron storage rings at Stanford are considered as examples. Time compression factors of one or two orders of magnitude seem feasible, more if the planned emittance reduction is implemented in PEP. In general, x-ray pulse lengths down to 0.1 ps appear feasible with emittances available today, using conventional materials. This may be reduced another order of magnitude by employing single-crystal materials.
Microwave and millimeter-wave power generation in silicon carbide avalanche devices
Authors: Mehdi I. , Haddad G. I. , Mains R. K.
Published: July 2002

Silicon carbide (SiC), due to its thermal and electronic properties, has long been considered an excellent device material for microwave and millimeter-wave power generation. Numerical simulations were performed to study the typical power generating capabilities of SiC impact avalanche transit-time (IMPATT) diodes utilizing the recent experimental data available. Operating characteristics of double-drift IMPATT devices at 10, 35, 60 and 94 GHz are compared. Both pulsed mode and continuous-wave (cw) mode operation are studied. Finally, a comparison among SiC, Si, and GaAs double-drift IMPATT devices is made at various frequencies. It is shown that, for the pulsed mode of operation, SiC double-drift IMPATT devices can produce significantly higher powers than Si and GaAs devices at comparable frequencies. In the cw mode of operation, SiC devices can produce significantly more power than GaAs devices at all frequencies. However, a comparison at 94 GHz indicates that SiC IMPATT diodes in the cw mode of operation produce power levels comparable to Si IMPATT devices. At lower frequencies the performance of SiC diodes operating in the cw mode is expected to be better than the performance of Si devices due to the better thermal conductivity of SiC.
Thermal-resistive instability and magnetic insulation breakdown in ion diodes
Authors: Litwin Christof , Maron Yitzhak
Published: July 2002

A cathode plasma instability is suggested as an origin of electron bursts observed in a recent experiment. The instability leads to a local increase of the plasma temperature and increased ionization. It is argued that this causes an appearance of a plasma protrusion in the diode and the breakdown of the magnetic insulation. Time and length scales of the instability are analyzed and found to be in general agreement with observations.
Influence of annealing and substrate orientation on metalorganic chemical vapor deposition GaAs on silicon heteroepitaxy
Authors: Kaliski R. W. , Ito C. R. , McIntyre D. G. , Feng M. , Kim H. B. , Bean R. , Zanio K. , Hsieh K. C.
Published: July 2002

GaAs layers grown on misoriented silicon substrates are examined for defect reduction as a function of thermal annealing and degree of misorientation. These GaAs layers (3–4 μm) are grown by a two-step metalorganic chemical vapor deposition process on Si substrates misoriented 1°, 1.5°, 2°, 3°, 4°, and 6° from (100) toward [011]. Annealing takes place in an open tube furnace under an arsine ambient at 850 °C for one or two 30-min cycles. Double-crystal x-ray rocking measurements and plan-view and cross-section transmission electron microscopy are used to evaluate the resulting crystal quality. Prior to annealing, all cases exhibit approximately equal defect densities with the average size of the microtwins being a function of misorientation. There also exists an anisotropy in the microtwin variant distribution in the layers. After annealing, however, the defect density is found to be dependent on the misorientation. The 1° and 2° layers, which have smaller microtwins, exhibit a greater reduction in defect density after thermal cycling than the 4° and 6° layers. The annealed 4° and 6° layers instead exhibit larger microtwins on average than the as-grown layers. These data indicate that smaller microtwins are more likely to be annihilated through thermal cycling. In addition to the change in the microtwin structures, thermal cycling produces elongated dislocations in the 1° and 2° layers and dislocation tangles associated with the remaining microtwins in the 4° and 6° layers.
Phosphorus redistribution during nickel silicide formation
Authors: Kikuchi Akira
Published: July 2002

Nickel silicide was formed by heat treating Ni film on a single-crystal Si(100) substrate. The Schottky barrier height of Ni silicide was examined in relation to the phosphorus dose implanted into the Si substrate. The reduction of the Schottky barrier height during the Ni silicide formation indicates phosphorus redistribution.
Effects of minority carriers on conductance measurement for metal/SiO2/p-Si structure
Authors: Hung K. K. , Cheng Y. C.
Published: July 2002

Conductance measurement on metal/SiO2/p-Si structure reveals that the interface-trap response at weak inversion is dominated by minority-carrier transitions in contrast to the usual behavior observed in metal/SiO2/n-Si structure. The phenomenon can be explained in terms of the lateral flow of minority carriers from the permanent inversion layer beyond the gate region which drastically reduces the minority-carrier response time.
Measurement of surface acoustic wave slowness curves with a scanning laser acoustic microscope
Authors: Robbins William P. , Rudd Eric P.
Published: July 2002

The measurement of the velocity and power flow angle of surface acoustic waves (SAWs) using a scanning laser acoustic microscope is described. Data obtained from a single scan by the microscope and from a single direction of insonification are Fourier transformed from the spatial domain into the spatial frequency domain. The incident cw surface waves scatter from the sides of the sample into all possible wave vectors. Thus, the Fourier transform in the spatial frequency domain is the inverse velocity or slowness curve for surface waves propagating on the material. From this curve, the phase velocity, group velocity, and power flow angle versus propagation direction can be obtained. Experimental results for YZ lithium niobate, ST quartz, and (111) silicon are in good agreement with theoretical calculations.
The switching mechanism in V2O5 gel films
Authors: Zhang J. G. , Eklund P. C.
Published: July 2002

We report the first explanation of the novel electrical switching in two-terminal devices based on thin V2O5⋅1.6H2O gel films. The switching is shown to be associated with the existence of a current-induced channel between the contacts. The data demonstrate that the switching between the ‘‘on’’ and ‘‘off’’ states of the device is driven by the joule heating of a metal-insulator (MI) transition in the channel material (or filaments in the channel). Resistivity data on the channel exhibit a sharp MI transition at T=334 K which is also the temperature at which the device is observed to stop switching. The signature of the MI transition in the channel is very similar to that observed in VO2(TMI=341 K), suggesting the channel may contain VO2−x conduction paths.
A new growth model of thin silicon oxide in dry oxygen
Authors: Wong H. , Cheng Y. C.
Published: July 2002

This paper presents a new growth kinetic model for thermal oxidation of silicon in dry oxygen, taking into account the effect of charged oxygen on the growth rate. Two parallel oxidizing species are assumed to be transported during oxidation, i.e., neutral ones via interstitial sites and charged ones through the network. The kinetic model has sufficient physical justifications and agrees with a recent dry oxidation study using 18O/16O sequential treatment. The model is found to correlate very well with experimental data at an O2 pressure of 1 atm in the temperature range 850–1000 °C in dry oxygen for both 〈100〉 and 〈111〉 silicon. Special emphasis is placed on the thin initial regime (10–300 Å) where this model is in excellent agreement with the experiments. The maximum error does not exceed 0.2 Å/min in the curve fitting.
Interdiffusion in ZnSe-ZnTe strained-layer superlattices
Authors: Imai Akira , Kobayashi Masakazu , Dosho Shiro , Kongai Makoto , Takahashi Kiyoshi
Published: July 2002

A detailed study has been made of interdiffusion in ZnSe-ZnTe strained-layer superlattices (SLSs) grown by molecular-beam epitaxy (MBE) at a growth temperature of 320 °C. In x-ray diffraction measurements, the satellite peak intensities relative to the zero-order peak intensity decreased with annealing time. The interdiffusion coefficient D was calculated assuming a linear diffusion model. The values of D=3.6×10−21 to 2.2×10−19 cm2/s at an annealing temperature of 500 °C were obtained for the ZnSe-ZnTe SLSs. In the high-resolution transmission electron microscopy (HRTEM) image of as-grown SLSs, the presence of fine superlattice structures was seen, but for interdiffused samples stripes due to the periodic superlattice structures were not visible and many dislocation lines were observed. These results suggest that the structure of SLSs is significantly modulated by thermal annealing at a temperature higher than the growth temperature.
A case study of degeneracy in quantum statistics. II.
Authors: Barker William A. , Raney Daniel , Sy John
Published: July 2002

In an earlier paper, classical and weak degeneracy, with the activity parameter r between 0 and 1, are investigated. In this paper, intermediate and strong degeneracy, with r>1, are studied. Coefficients for the Joyce–Dixon-type series are calculated for bosons as well as fermions in one, two, and three dimensions, for either nonrelativistic or ultrarelativistic particles. The theory is applied to the electrons and Cooper pairs in mercury at four temperatures.
Multiple-short-pulse stimulated Brillouin scattering
Authors: Corvo Antonio , Gavrielides Athanasios
Published: July 2002

Stimulated Brillouin scattering characteristics are formulated for the case of a multiple-short-pulse pump. Simplified stimulated Brillouin scattering equations in the small- and large-gain limits are solved for the Stokes intensity giving the dependence on the pulse width and delay, and pulse number. Coherent and incoherent intensities were also calculated and a quadratic versus linear dependence, respectively, on the pulse number was found. It is shown that the gain is largely unaffected by the appearance of a pulsed pump; however, the intensity is roughly reduced by the ratio τp/Δ, where τp is the pulse width and Δ is the sum of the pulse width and separation.
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u x-ray photoemission studies of the oxidation of Y-Ba-Cu films
Authors: Price R. J. , Jackman R. B. , Foord J. S.
Published: July 2002

X-ray photoemission has been used to investigate the formation of Y-Ba-Cu films on Si(100) and as an in situ probe of their subsequent oxidation to yield the associated oxide ceramic. The layers are prepared by coevaporation of the metallic components under ultrahigh vacuum, and pure alloy phases can be deposited at 300 K; reaction with the underlying substrate resulting in loss of Cu and incorporation by Si in the film takes place, however, at higher temperatures. Room-temperature oxidation stabilizes the film against this interaction and results in the preferential oxidation and surface segregation of barium at the expense of Cu. This segregation process becomes even more apparent during higher temperature (∼600 K) oxidation reactions. Chemical shifts and associated effects in x-ray photoelectron spectra are used to infer information on the chemical changes that occur in the film as oxidation proceeds. The thin-film phases prepared in situ in this work reveal a very similar surface composition to bulk superconducting samples prepared ex situ. This suggests that the surface segregation in bulk samples does not simply result from reaction with species such as water vapor, but instead may represent an equilibrium state of the oxide-oxygen interface.