bluuebunny/crossref_metadata_2025 huggingface dataset:
Transmission electron microscopy studies on the lateral growth of nickel silicides
Authors: Chen S. H. , Zheng L. R. , Carter C. B. , Mayer J. W.
Published: July 2002

Transmission electron microscopy (TEM) has been utilized to study the nickel-silicide growth in self-supported lateral-diffusion, thin-film couples by overlapping deposited layers of Ni and Si between two silicon oxide deposited films. Energy-dispersive x-ray spectroscopy, microdiffraction, and selected area diffraction were used to identify the Ni-silicide phases and their crystal structures. Long-grain growth of Ni2Si, as a result of phase-boundary migration induced by diffusion, was observed during in situ annealing between 500 and 750 °C in TEM. No preferred orientation or particular crystallographic relationship was found among the long grains.
Hole transport equation analysis of photoelectrochemical etching resolution
Authors: Ostermayer F. W. , Kohl P. A. , Lum R. M.
Published: July 2002

A theoretical model that predicts the spatial resolution for grating formation on n-type semiconductors by photoelectrochemical etching has been developed. The ratio of the amplitude of the grating to the average depth etched by a sinusoidal spatial variation of light intensity was determined from a model that takes into account the drift and two-dimensional diffusion of the photogenerated holes and their rate of reaction at the surface. Experimental measurements of the growth of gratings agree with the predictions of the theory for the dependence on the period of the grating, the carrier concentration of the semiconductor, and the wavelength of the light. Fitting the experimental data to the theory provides a novel method for determining the reaction velocities of the decomposition reaction in different electrolytes. The theory predicts that large improvements in the resolution would be possible if electrolytes giving higher reaction velocities could be found.
Photoluminescence and stimulated emission in Si- and Ge-disordered AlxGa1−xAs-GaAs superlattices
Authors: Kaliski R. W. , Gavrilovic P. , Meehan K. , Gavrilovic J. , Hsieh K. C. , Jackson G. S. , Holonyak N. , Coleman J. J. , Burnham R. D. , Thornton R. L. , Paoli T. L.
Published: July 2002

Photoluminescence and absorption data are presented on AlxGa1−xAs-GaAs superlattices (SLs) disordered into bulk-crystal AlyGa1−yAs (0≤y≤x) by Si or Ge diffusion. The bulk-crystal AlyGa1−yAs produced by impurity-induced disordering (by Al-Ga interchange) is determined by transmission electron microscopy, absorption measurements, and photoluminescence to be homogeneous, with an alloy composition (y) that agrees with the average Al concentration of the SL. For low enough Al concentration (y≊0.23<yc =0.44, the direct-indirect crossover), in absorption the Ge- or Si-disordered SL exhibits (4.2 and 77 K) the bulk-crystal exciton, which is characteristic of homogeneous alloy (AlyGa1−yAs). Stimulated emission (4.2 and 77 K) in bulk-crystal AlyGa1−yAs is observed ΔE≤50 meV below the band edge via photopumping for both Si- and Ge-disordered SLs of Al concentration yielding y∼0.23 and y∼0.39. Shallow hydrogenlike donor or acceptor states are characteristic of AlxGa1−xAs-GaAs SLs disordered with Ge or with Si. For the Si impurity (i.e., an AlxGa1−xAs-GaAs SL disordered with Si), however, much deeper states (transitions) are observed that saturate at higher photoexcitation levels. These states are attributed to nearest-neighbor or extended Si-Si pairs since similarly disordered AlxGa1−xAs-GaAs SLs doped with Ge do not exhibit deeper states.
Capacitance transient analysis of configurationally bistable defects in semiconductors
Authors: Levinson M.
Published: July 2002

Configurationally bistable defects can exist in either of two different structural configurations for the same charge state. Each configuration exhibits distinct optical and electronic properties. Here a framework is presented for the use and interpretation of deep level capacitance transient spectroscopy measurements in the study of these defects. Examples are presented for the MFe center in InP, a bistable A-center-related defect in Si, and the EL2 center in GaAs.
Elastic waveforms using laser generation and electromagnetic acoustic transducer detection
Authors: Hutchins D. A. , Wilkins D. E.
Published: July 2002

A Q-switched, frequency-doubled ruby laser has been used to generate wide bandwidth ultrasonic transients in aluminum and steel plates. Both longitudinal and shear waves were generated, resultant waveforms being dependent upon the irradiation conditions. Various designs of electromagnetic acoustic transducers were then used to detect these waveforms at the opposite side of the plate. The result is a method of ultrasonic inspection with potential in noncontact applications.
Velocity profiles in a rarefied argon plasma stream by crossed electrostatic probes
Authors: Poissant G. , Dudeck M.
Published: July 2002

This paper describes experimental measurements of flow velocity, electron temperature, and density performed in a steady, rarefied, free jet of argon plasma. The plasma jet is generated by an arc discharge. The axial profiles of the flow velocity, electron temperature and density, and ion saturation currents are determined over a length of 60 cm starting from the nozzle exit. The radial profiles of these quantities are measured in the subsonic zone of the plasma flow. The electron temperature and density are deduced from the characteristic of a single, cylindrical electrostatic probe. The experimental conditions are such that the Debye length λD ≪ probe diameter φ ≪ mean free path. The velocity of the flowing plasma is determined from the ion saturation currents of two mutually perpendicular probes. The method of Kanal is used without a correction factor on the ion current collected by the perpendicular probe.
Analysis of light-induced degradation in amorphous silicon alloy p-i-n solar cells
Authors: Hack M. , Shur M.
Published: July 2002

We present results of computer simulations of the characteristics of amorphous silicon alloy p-i-n solar cells in both undegraded and degraded conditions for illumination through the n+ or p+ layers. Changes in device performance upon degradation correlate well with realistic changes in the minority carrier diffusion length of the intrinsic layer. The results of our model are in good agreement with experimental data and lead us to conclude that the observed degradation in the electronic properties of amorphous silicon alloys are only consistent with the observed increases in the localized state density if the photoinduced metastable defects have larger capture cross sections than the localized states in as-deposited material. The analysis of recombination losses shows that upon degradation, primarily because of the decrease in the minority carrier diffusion length, cells illuminated through the n+ layer exhibit a loss of short-wavelength response whereas those illuminated through the p+ layer exhibit a loss of long-wavelength response.
Measurement of the electron density and the attachment rate coefficient in silane/helium discharges
Authors: Fleddermann C. B. , Beberman J. H. , Verdeyen J. T.
Published: July 2002

Measurements of the electron density in dc and pulsed silane/helium discharges show that the addition of silane to the gas mixture causes a large reduction in the electron density. By monitoring the electron decay time in the afterglow, it is found that the dominant electron loss mechanism in silane/helium is not ambipolar diffusion to the walls, but instead is a volumetric loss process, most likely dissociative attachment of electrons to a product of the silane dissociation. A lower bound for the rate coefficient for this loss process has been determined to be 2.65×10−10 cm3/sec.
Epitaxial growth of high quality ZnSe on Si substrates by molecular beam epitaxy and application to dc electroluminescent cells
Authors: Mino Naoki , Kobayashi Masakazu , Konagai Makoto , Takahashi Kiyoshi
Published: July 2002

ZnSe thin films were grown on (100) and (111) oriented Si substrates by molecular beam epitaxy. The single-crystalline ZnSe films were obtained in the substrate temperature range of 300–450 °C. The epitaxial layers were evaluated by reflection high-energy electron diffraction, x-ray diffraction, etch pit density, photoluminescence, and Hall effect measurements. Etch pit density was estimated to be 3×105 cm−2. The carrier concentration and electron mobility of the epitaxial ZnSe layers at room temperature are 1.3×1017–2.8×1017 cm−3 and 170–250 cm2/V s, respectively. These epitaxial films were applied to Au/ZnSe:Mn/Si dc-operated electroluminescent cells. The maximum quantum efficiency of 2.2×10−2 (30.4 V, 6.3×10−5 A/cm2) was achieved.
Reactive sputtering of polyphosphide thin films by plasma cracking of P4
Authors: Schachter R. , Viscogliosi M. , Baumann J. , Raccah P. M.
Published: July 2002

For the first time, we are reporting on the sputter deposition of amorphous-polyphosphide thin films from a compound target. We demonstrated that the growth rate of this compound semiconductor is determined by the metal flux, and the stoichiometry is determined by the phosphorus flux. The amount of excess phosphorus required to maintain the stoichiometry of the growing film was calculated. A new technique was used to provide the excess phosphorus, namely the generation of reactive phosphorus (P) species from P4 molecules injected into the plasma via an Ar carrier from an external P4 delivery system. The sticking coefficient of K is found to be independent of substrate temperature while that of the P species changes from 1 at 23 °C to 0.25 at 250 °C. The plasma-cracking efficiency is measured to be almost 100%. The effect of plasma on the P4 chemistry has implications for polyphosphide deposition and for the growth of other compound semiconductors containing Group V elements.
Formation of AsGa antisite defects in electron-irradiated GaAs
Authors: von Bardeleben H. J. , Bourgoin J. C.
Published: July 2002

The anion antisite AsGa formation in electron-irradiated GaAs of various compositions and dopings has been studied by electron paramagnetic resonance. The results are interpreted in a new model based on carrier recombination enhanced mobile arsenic interstitials exchanging sites with gallium-substituted impurities.
Moderate-power cw chemical oxygen-iodine laser capable of long duration operation
Authors: Wiswall C. E. , Bragg S. L. , Reddy K. V. , Lilenfeld H. V. , Kelley J. D.
Published: July 2002

Design and operation of a cw, transverse-flow oxygen-iodine chemical laser are reported. Reactant recirculation in the O2(1Δ) chemical generator allows long duration (up to 2 h) operation. Peak powers of 460 W, and stable outputs of 80 W have been demonstrated. Power extraction efficiencies of up to 65% were measured for 80-W operation, and the implications of this observation for the I2 dissociation mechanism are discussed.
Temperature dependence of the dielectric constant of InP
Authors: Meiners L. G.
Published: July 2002

Low-frequency capacitance measurements were used to determine the dielectric constant of InP from 100 to 300 K. A value of 12.56±0.2 was obtained at 300 K and an extrapolated value of 11.93±0.2 was obtained at 77 K. Below about 220 K the temperature dependence can be expressed by the relationship ε0=11.76(1+2.26×10−4 T).
Influence of transmission resonance on carrier collection in a semiconductor quantum well
Authors: Zohta Yasuhito
Published: July 2002

It is pointed out that carrier collection in a quantum well becomes very effective when the quantum well thickness satisfies a transmission resonance condition. This is attributable to the fact that an electron wave dwells on the quantum well for a long time under resonance condition.
Correlation of GaAs lattice parameter to growth and annealing conditions
Authors: Kuwamoto H. , Holmes D. E.
Published: July 2002

The dependence of the lattice parameter of GaAs grown by the liquid-encapsulated-Czochralski technique has been investigated as a function of melt stoichiometry during growth and As overpressure during annealing. The lattice parameter decreases as the As composition in the melt increases. By annealing under an As overpressure, the lattice parameter of Ga-rich-grown crystals was found to decrease to that of As-rich-grown crystals, while As-rich-grown crystals show no lattice parameter change. The lattice parameter is uniform within experimental error both across and along individual crystals.
Improved GaAs/AlGaAs quantum-well heterostructures by organometallic vapor-phase epitaxy
Authors: Schaus C. F. , Shealy J. R. , Eastman L. F. , Cooman B. C. , Carter C. B.
Published: July 2002

The properties of GaAs/AlGaAs quantum-well heterostructures have been investigated using transmission electron microscopy (TEM) together with photoluminescence. Modifications to the reactor are described which allow abrupt interfaces (∼5 Å) and strong optical emission to be obtained up to 300 K from single layers <40 Å thick. TEM and Raman scattering have been used to characterize heterostructures, which has resulted in an optimized gas handling system for precise control of reactant fluxes in a low-pressure apparatus. The effects of pressure transients, gas-flow recirculation, and residual aluminum incorporation in thin GaAs films grown over AlGaAs are presented.
Conversion electron Mössbauer spectroscopy and x-ray photoemission spectroscopy studies of thermal oxidation of Fe67Co18B14Si1 metallic glass
Authors: Bhandarkar Y. V. , Kanetkar S. M. , Ogale S. B. , Ghaisas S. V. , Bhide V. G. , Prabhawalkar P. D.
Published: July 2002

The oxidation kinetics and associated structural and chemical transformations in the Fe67Co18B14Si1 metallic glass have been investigated by using the techniques of conversion electron Mössbauer spectroscopy (CEMS) and x-ray photoemission spectroscopy (XPS). The as-quenched as well as vacuum-annealed samples of the metallic glass have been subjected to thermal treatment in air at 100, 300, and 390 °C for 1/2 h in each case. The information regarding the structural transformations and chemical reactions has been obtained by deconvoluting the complex CEMS spectra and analyzing the contributions of various elements to the XPS spectra. It is shown that oxygen incorporation in the glass initiates the process of recrystallization of the glassy state at a temperature which is lower as compared to its temperature of recrystallization in vacuum. The oxygen-coordinated phases in the oxide scale and the other phases precipitated due to the reactive thermal treatment have been identified and the physical mechanisms underlying the observed effects have been commented upon. Experiments have also been performed to examine the transformations occurring in the metallic glass upon its prolonged thermal treatment in air at a typical temperature (∼100 °C) within the recommended temperature range (25–125 °C) for its use in applications. It has been demonstrated that the surface layers of the as-received glass are affected by such a treatment, though the sample preannealed at 300 °C remains relatively unaffected. The observations made on the basis of CEMS and XPS studies have been supported by x-ray diffraction and resistance-annealing measurements.
Calculation of magnetic shielding and ohmic losses from finite thickness Faraday shields used in rf heating of plasmas
Authors: Smithe D. N. , Kashuba R. J. , Kammash T.
Published: July 2002

Metallic Faraday shields commonly in use in many ion cyclotron resonance heating experiments have been shown to have two adverse effects on the antenna-plasma coupling properties: magnetic shielding of the antenna current and possibly significant ohmic losses. The purpose of this paper is to investigate these two effects for shields of finite thickness using a detailed analysis of the fringing fields induced by the Faraday shields. Naturally, the extension to finite thickness introduces the question of shield cross-section shape. Considerable attention is given to this point through two case studies of a square-edged and a rounded-edge shield. It is shown that magnetic shielding properties of a given cross section can be characterized by a single parameter, dependent only on cross-section shape and dimensions. Ohmic losses are seen to be 30%–40% less for a cross section with rounded edges than for the square-edged cross section. Also of interest is a minimum in the ohmic loss versus thickness relation for the round cross section, indicating the existence of an optimum ohmic loss design with respect to shield thickness.
Spectroscopic study of the wall corrosion in super high-pressure sodium discharge lamps
Authors: Reints Bok W.
Published: July 2002

In 30-W sodium discharge lamps with Na pressures up to 1 atm a chemical reaction takes place between Na and the vessel, consisting of sintered polycrystalline Al2O3 (PCA), leading to the formation of β-aluminates and Al. From emission measurements at the 396-nm line the Al pressure in operating lamps is derived. The transmission of the PCA wall and the plasma temperature, which are necessary in the Al pressure derivation, are determined by additional measurements on the 436- and 818-nm emission lines of Hg and Na, respectively. The Al pressure is axially dependent, with a maximum in the center being about 10−6 atm at a lamp power of 32 W. When the lamp power is increased by 25% the central Al pressure increases by a factor of 5. The central Al pressure depends exponentially upon lamp power. The linear shape of the axial pressure profiles near the ends of the lamp indicates that Al production takes place mainly in the center of the lamp. Using a diffusion model the production rate of Al atoms is estimated to be 4×1011 atoms/s at 32 W. The experimentally determined pressures are higher than pressures calculated by equilibrium thermodynamics.
Self-consistent T-matrix solution and computer-simulated velocity averaging approaches for the effective elastic constants of monoclinic polycrystals
Authors: Paul Mala , Middya T. R. , Basu A. N.
Published: July 2002

The self-consistent T-matrix solution envisaged by the effective-medium approach [R. Zeller and P. H. Dederichs, Phys. Status Solidi B 55, 831 (1973)] has, in general, led to a considerable clarification of our understanding of the mechanical properties of a variety of disorder systems including polycrystals. Specifically, the relevant formulations have been developed for cubic polycrystals by Zeller and Dederichs, and for hexagonal, tetragonal, trigonal, and orthorhombic polycrystals by T. R. Middya and A. N. Basu [J. Appl. Phys. 59, 2368 (1986)]. The present work on monoclinic polycrystals is a sequel to our previous work. We have developed the complete set of equations within the framework of the effective medium theory which delivers in a self-consistent manner the effective elastic constants of a monoclinic polycrystal in terms of those of the single crystal data. For comparison we have also evaluated the same quantities for each polycrystal by the computer simulation employing the velocity averaging process developed by T. R. Middya, A. N. Basu, and S. Sengupta [J. Appl. Phys. 57, 1844 (1985)]. Finally the results obtained by the above approaches for eight different polycrystals are compared with each other and also with other existing theoretical calculations.
Possibility of measuring shear waves in oblique-impact experiments with in-material piezoresistance gauges
Authors: Rosenberg Z. , Bless S. J.
Published: July 2002

We suggest the use of in-material piezoresistance gauges to record shear waves in oblique-impact experiments. The advantages of the proposed technique are discussed in detail and possible candidates for shear gauges are suggested. A preliminary oblique-impact experiment, with a manganin gauge embedded in an alumina target, is described. The gauge record shows the arrival of two waves with the expected time interval as calculated from the longitudinal and shear velocities for alumina.
One-dimensional collisions of two similar flat elastic solids
Authors: Coltharp David R. , Jones Gordon E.
Published: July 2002

An analysis of elastic waves is used to predict the final velocity of a flat metal plate that is struck by a second plate made of the same material. The loss of kinetic energy of the system is also calculated. Three examples corresponding to different mass ratios are considered, and it is seen that solutions for the ratio of the final velocity of the second plate to the initial velocity of the first plate, and for the ratio of the final kinetic energy to the initial kinetic energy, always lie between the solutions that correspond to perfectly elastic and perfectly inelastic collisions. One interesting result is that rebound never occurs, even if the mass of the projectile plate is less than that of the target.
Low-temperature annealing characteristics of chemical vapor deposited WSi2 film
Authors: Togei R.
Published: July 2002

Resistivity annealing characteristics of tungsten silicide films made by the chemical vapor deposition technique at 0.3 Torr and 275–425 °C has been investigated paying particular attention to their low temperature annealing behavior. The Si-to-W atomic ratio was controlled in the range of 2.1–4.1 by means of a substrate temperature. Resistivity of the annealed sample with the lower atomic ratio is shown to increase initially in the temperature range below about 500 °C. It was concluded that this increase is explained neither by impurity effect nor by compositional change of Si and W as detected by Rutherford backscattering spectroscopy and secondary ion mass spectroscopy. X-ray diffraction analysis shows that this phenomenon is rather well correlated with the formation of hexagonal phase of WSi2.
Dopant redistribution during titanium silicide formation
Authors: Amano Jun , Merchant P. , Cass T. R. , Miller J. N. , Koch Tim
Published: July 2002

For advanced metal-oxide-semiconductor structures it is highly desirable to have a self-aligned silicide structure on source and drain regions as well as on the gate in order to simplify lithography while reducing parasitic resistances. The reproducible formation of metal silicides on highly doped n+ and p+ regions with shallow junctions is required for those structures. Therefore, it is essential to understand the dopant behavior, silicide phase formation, and grain growth during high-temperature annealing. Titanium silicides were formed on arsenic and boron difluoride implanted and annealed Si substrates. Arsenic atoms showed a significant redistribution and loss during titanium silicide formation. Arsenic atoms diffused out of the silicide surface with an activation energy of 0.95 eV. Boron atoms segregated to the silicide surface, and some boron atoms were lost from the surface; on the other hand, fluorine atoms were retained in the silicide layer. After prolonged 900 °C annealing, the thin titanium disilicide layers were converted into discontinuous structures.
Effects of dislocation generation at surfaces and subgrain boundaries on precursor decay in high-purity LiF
Authors: Meir G. , Clifton R. J.
Published: July 2002

In plate impact experiments, the elastic precursor is attenuated as it propagates through the shocked specimen due to plastic straining at the shock front. However, the plastic strain rates required to explain the observed precursor decay are much higher than the strain rates that are predicted for known initial dislocation densities in the unshocked specimen, regarded as homogeneous. This anomaly, which poses a significant difficulty for the acceptance of the micromechanical theory of plasticity, has motivated this investigation of the effects of dislocation generation at surfaces and subgrain boundaries on precursor decay in single crystals of high-purity LiF. Surface damage effects have been minimized by preparing damage-free surfaces and by using fluid layers to protect the specimen surfaces during impact. These precautions reduce the precursor decay significantly compared to the decay measured for lapped crystals impacted directly (normal stresses of 5 kbars). However, computer simulation of the experiments based on subsonic dislocation motion, a linear viscous drag model, and nonlinear elasticity (assuming a homogeneous specimen), does not predict the measured wave profiles within experimental uncertainty. When dislocation generation at the surfaces is included in the computation, the calculated precursor amplitudes are comparable with measurements only for thin (3-mm) specimens. Reexamination of recovered specimens from plate impact experiments suggests that subgrain boundaries are important sources for dislocation generation in precursor decay experiments. When subgrain boundaries are included as additional sources for dislocation generation, the computed velocity-time profiles at 3 and 6.6 mm are in good agreement with measured profiles. Thus, it appears that the inclusion of dislocation generation at impact surfaces and subgrain boundaries provides a means for explaining the precursor decay anomaly, at least for high-purity LiF.
First observation of two-dimensional hole gas in a Ga0.47In0.53As/InP heterojunction grown by metalorganic vapor deposition
Authors: Razeghi M. , Maurel P. , Tardella A. , Dmowski L. , Gauthier D. , Portal J. C.
Published: July 2002

We report the observation of a two-dimensional (2D) hole gas in Ga0.47In0.53As/InP heterojunction grown by metalorganic chemical-vapor deposition. In a sample with a total hole density ptot =7.6×1011 cm−2 a Hall mobility μH =10 500 cm2/V s was reached at 4.2 K. Angle-dependent Shubnikov–de Haas measurements as well as quantized Hall effect observations confirmed the two-dimensionality of the system. In contrast to the case of the 2D hole gas in GaAs/AlGaAs, low-temperature persistent photoconductivity was observed, significantly increasing the hole density at the interface.
Selective self-optical compensation effect for a newly discovered acceptor-associated emission in Zn+ ion-implanted GaAs
Authors: Ohnishi Nobukazu , Makita Yunosuke , Irie Katsuhiro , Kudo Kazuhiro , Nomura Toshio , Tanaka Hideki , Mori Masahiko , Mitsuhashi Yoshinobu
Published: July 2002

Photoluminescence measurements were carried out at 2 K for Zn+ ion-implanted GaAs, where the concentration of Zn was widely varied from 3×1016 to 1×1021 cm−3. Two Zn+-associated emissions were formed. One emission is at 1.512 eV, g, and the other emission [g-g] is just below g and this moves towards the lower energy level with increasing Zn concentration, [Zn]. The intensity of [g-g] was enhanced with increasing [Zn], up to [Zn]=3×1017 cm−3, and was gradually suppressed for [Zn] beyond that concentration. This selective self-optical compensation effect (SSOC) for [g-g] was found to occur for moderately heavy ion acceptor species such as Zn and Cd, although [g-g] is a common emission among many other acceptor impurities. In addition two new emissions were observed between g and [g-g] at certain [Zn]. Preliminary theoretical explanations are presented for this SSOC effect.
Deep-level transient spectroscopy study of a thermal conversion layer on semi-insulating GaAs grown by the liquid-encapsulated Czochralski method
Authors: Chan Y. J. , Lin M. S.
Published: July 2002

A thermal conversion mechanism of semi-insulating GaAs with a SiOxNy cap was studied. Both SiO- and SiN-rich cap films exhibit n-type conductivity after thermal annealing, and a newly discovered level Ec−0.91 eV is present in these converted samples found by deep-level transient spectroscopy measurements. This conversion phenomenon may be attributed to Ga out-diffusion through the cap layer during thermal annealing.
Investigation of OH dynamics in the argon sensitized pulse radiolysis of water vapor
Authors: Bera Ranajit K. , Hanrahan Robert J.
Published: July 2002

Reactions of OH radical were studied in systems containing 650-Torr Ar and from 0.5 to 9-Torr H2O using the method of pulse radiolysis-absorption spectroscopy. It was found that initial concentrations of OH radical increased and the half-life for its loss decreased at higher water pressures. Dependence of OH half-life on OH concentrations occurs because homogeneous OH loss processes are second order in reaction intermediates, whose concentration increases with added H2O. A contribution by water in chaperoning OH/OH and OH/H combination is also important. The kinetic scheme was examined with a Gear integrator. A good fit of the experimental rate data was obtained using literature values for rate constants of OH+OH, OH+H, and H+H reactions, when experimental zero-time absorbance values were converted to OH concentrations based on an extinction coefficient of 6.37×104 l mol−1 cm−1 at 309.5 nm. Using the same extinction coefficient, an alternative empirical reduction of rate data gives k (apparent bimolecular) for loss of OH at 650-Torr Ar pressure of 5.06×10−11 cm3 molec−1 s−1, consistent with literature rate constants within 10%. Dependence of OH yield on water concentration is interpreted on a two state model for argon precursor, involving short-lived (resonance state) Ar* (1P1 and 3P1) and longer-lived (metastable) Ar** (3P2 and 3P0). Adjustment of assumed initial Ar* and Ar** concentrations allowed prediction of measured OH concentrations within experimental error at all water pressures studied.
A magnetic field-effect transistor
Authors: Mannhart J. , Huebener R. P.
Published: July 2002

The magnetic control of the filamentary current flow during avalanche breakdown in a semiconductor at low temperatures represents an interesting new principle of a magnetic field-effect transistor. The power losses in such a device are minimized by using superconducting lines for the generation of the magnetic control field and for the interconnections. For such a hybrid concept, implementing semiconducting and superconducting components, the important performance characteristics are evaluated.
Piezoelectric copolymer jacketed single-mode fibers for electric-field sensor application
Authors: Imai M. , Tanizawa H. , Ohtsuka Y. , Takase Y. , Odajima A.
Published: July 2002

Characteristics of a piezoelectric copolymer jacketed optical fiber are presented. The jacket consisting of a copolymer of vinylidene fluoride and trifluoroethylene was made piezoactive by corona poling. The performance of the fiber as an optical-phase modulator was demonstrated over a frequency range of 20 Hz–5 kHz. An electric field-induced phase shift of 1.5×10−7 rad/(V/m) per meter of fiber was measured in the low-frequency (axially unconstrained) region. Several resonance peaks in optical phase shift were observed and discussed in conjunction with piezoelectricity in polymer jackets.
Eliminating interference effects in picosecond photoinduced absorption decays: Application to intrinsic hydrogenated amorphous silicon
Authors: Roberts Dale M. , Palmer Joseph F. , Gustafson Terry L.
Published: July 2002

We measure picosecond photoinduced absorption in a low-defect sample of intrinsic hydrogenated amorphous silicon. Our results indicate that both the imaginary and real parts of the complex index of refraction contribute to the observed decay of the induced transmittance. We present methods for obtaining the undistorted decay of the induced absorption. We show that the decay of the induced absorption depends strongly on the peak carrier density and the repetition rate of the excitation source. The photoinduced absorption decays are consistent with the model for dispersive transport in amorphous materials.
GaAs (110)–oxygen interaction: A study of electronic properties
Authors: Ismail A. , Palau J. M. , Lassabatere L.
Published: July 2002

The modifications of the electronic properties of cleaved GaAs (110) surfaces induced by the oxygen adsorption have been studied by contact potential difference measurement. The oxygen exposure induces acceptor and donor surface states which pin the surface Fermi level at approximately 0.45 and 0.7 eV above the valence band for n- and p-doped samples, respectively. Noticeable modifications Δχ of the electronic affinity are also produced. The features of the states and the possible origins of Δχ are discussed.
A transmission line model for magnetic waves on a thin film
Authors: Seshadri S. R.
Published: July 2002

The magnetic wave interactions on a thin film with interfaces having the profile of a periodic array of rectangular grooves are investigated. The film is assumed to be magnetized uniformly normal to the midplane. The technique is based on a transmission line model which is valid even for large relative depths of variation of the film thickness. When specialized to small relative depths of variation of the film thickness, the spectral characteristics of the power reflection coefficient determined by this large-amplitude theory are in good agreement with those predicted by the existing small-amplitude theories. The present large-amplitude theory shows that the small-amplitude theory gives the maximum of the power reflection coefficient reasonably correctly but overestimates the center frequency, the error increasing with the increasing values of the relative depth of variation of the film thickness. The investigation of the characteristics of the first two band gaps with the help of the present large-amplitude theory reveals interesting features in the behavior of the band gaps as the relative depth of variation of the film thickness becomes large.
A revised fringe equation for the hook method in anomalous dispersion
Authors: Bayha William T.
Published: July 2002

A revised fringe equation is proposed for the hook method in anomalous dispersion for the case of thick plate compensation. The derivation is based on the equality of transit times through the interferometer arms, which results in a revised expression for the optical path difference of the plate. As a result, an apparent fringe order inconsistency in the traditional derivation is resolved, and the interpretation of the hook constant is clarified.
Coherent curvature radiation pulse duration
Authors: Buschauer Robert
Published: July 2002

Simple expressions are derived for the duration of the coherent curvature radiation pulse that is emitted toward a fixed distant observer by a column of relativistic charged particles as they move along adjacent curved trajectories. The duration is found to depend on the coherence length of the column, the energy of the radiating particles, and the radius of the particle trajectories. A simple physical picture is presented to elucidate the fundamental ideas involved and suggestions are made for using this information as a diagnostic to characterize the emitting system.
Electroreflectance study of Hg1−xMnxTe in the E1 and E1+Δ1 energy regions
Authors: Wrobel J. M. , Bassett L. C. , Aubel J. L. , Sundaram S. , Becla P.
Published: July 2002

We report electrolyte electroreflectance studies of the ternary semimagnetic semiconductor Hg1−xMnxTe for compositions below x=0.2. The dependence of E1 and E1+Δ1 transition energies on the composition was determined on the basis of the low field approximation. The present results are compared and discussed in relation to experimental data obtained previously and the theoretical predictions reported in the literature.
Experimental and theoretical studies of nuclear generation of ozone from oxygen and oxygen–sulfur hexafluoride mixtures
Authors: Elsayed-Ali H. E. , Miley G. H.
Published: July 2002

A series of experimental measurements of the yield of O3 in nuclear-induced O2 and O2-SF6 discharges are reported. The discharges were created by bombardment with energetic particles from the 10B(n,α)7Li reaction. Continuous irradiation at dose rates of 1015–1017 eV cm−3 s−1 and pulsed irradiation (∼10 ms FWHM) at a peak dose rate of ∼1020 eV cm−3 s−1 were conducted. At the lower dose rates, the addition of SF6 generally increased the ozone yield due to the slowing of ozone destruction by negative oxygen and ozone ions. In contrast, at the high dose rates, the ozone concentration decreased due to SF6 suppression of atomic oxygen formation by ion–ion recombination. A numerical model was developed and tested against experimental conditions. This model indicates that the steady-state ozone concentration was limited by the reaction O−3+O3→2O2+O−2 with a rate coefficient of ∼1×10−12 cm3 s−1. In addition to dose rate effects, pressure and temperature effects on ozone production are discussed and methods for increasing the ozone yield are suggested.
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u ion implantation for quantitative secondary ion and sputtered neutral mass spectrometry analysis
Authors: Gnaser H.
Published: July 2002

The primary ion beam column of a combined secondary ion/sputtered neutral mass spectrometer is used for in situ ion implantation of precise amounts of a given species superimposed as an internal standard upon its residual concentration. Subsequent depth profile analysis is done in the instrument after switching to another primary projectile. It is shown that concentrations can be determined with an accuracy of 4% from the known in situ implanted fluence by comparing the original and the added amounts. In this way, the helium concentration in a silicon sample (produced by external implantation) and the interfacial oxygen concentration between an amorphous and crystalline Si layer are determined quantitatively.
Self-biased Josephson junctions
Authors: Hyun O. B. , Finnemore D. K.
Published: July 2002

Transport currents in one leg of a cross strip superconducting-normal metal-superconducting Josephson junction have been used to bias the current-voltage characteristics of the junction, and hence use the junction as a control element. The bias current creates a magnetic field in the junction, which in turn modulates the Josephson currents. As the bias current causes successive flux quanta to enter the junction, the Josephson critical current shows current-voltage curves similar to the resistively shunted junction model and a normal Fraunhofer pattern. Values of the bias are relatively small because the junctions are so thick. A detailed study of the junction voltage as a function of bias current shows reentrant superconductivity as successive vortices enter the junction.
Thin-film gallium arsenide homojunction solar cells on recrystallized germanium and large-grain germanium substrates
Authors: Chu Shirley S. , Chu T. L. , Han Y. X.
Published: July 2002

Polycrystalline gallium arsenide films of 10-μm thickness deposited on tungsten/graphite substrates by the reaction between gallium, hydrogen chloride, and arsine have been used for the fabrication of thin-film homojunction solar cells. The major problem associated with polycrystalline gallium arsenide thin-film cells is the grain-boundary shunting effect. In order to prepare solar cells with conversion efficiency higher than 10%, gallium arsenide films with large grains are necessary. Unlike gallium arsenide, germanium films can be easily recrystallized to enhance the grain size. Thin-film gallium arsenide solar cells of the p+/n configuration with an AM1 efficiency of about 10% have been prepared using recrystallized germanium and large-grain germanium substrates.
Modeling of the optically controlled semiconductor switch
Authors: Weiner M. , Bovino L. , Youmans R. , Burke T. , Dollak F.
Published: July 2002

Closed-form solutions for the transient conductivity and the electric field in optically controlled semiconductors have been obtained. The one-dimensional calculations include important effects such as field-independent electrode injection efficiency, displacement current, space charge, carrier trapping, and the influence of trapped charge on the field. The model is restricted to linear phenomena so that, for example, the carrier-velocity dependence upon electric field is neglected. Despite such limitations, the model provides much insight into the operation of the semiconductor switch and is particularly applicable under conditions of low carrier generation rate and velocity saturation. A significant result of the model reveals that even for small departures of the electrode injection efficiency from unity, nonuniform and very intense electric fields will develop, particularly near the electrodes. These large fields may be exaggerated, however, since the onset of a field-dependent injection efficiency will tend to limit such fields. A preliminary comparison of the theory and experiment for the current pulse was conducted for the case of a GaAs target, under conditions of low carrier generation rate. The comparison shows that the linear model is capable of explaining the observed current waveform under such conditions.
The influence of growth conditions on sulfur and selenium incorporation in Ga1−xAlxAs grown by molecular-beam epitaxy
Authors: Andrews D. A. , Heckingbottom R. , Davies G. J.
Published: July 2002

An electrochemical cell Pt/AgI/Ag2 X/Pt (X=S,Se) has been used as a highly controllable source of chalcogen dimers for n-type doping of Ga1−xAlxAs grown by molecular-beam epitaxy (MBE). The incorporation behavior has been investigated as a function of alloy composition, growth temperature, and arsenic overpressure. At low temperatures, <600 °C, sulfur and selenium are incorporated into Ga1−xAlxAs in a facile manner. At higher temperatures, where loss of chalcogen dopant from GaAs has previously been observed, sulfur shows an enhanced stability in the aluminum-containing alloys. Excess As4 is shown to hinder the loss further. The behavior is modelled in terms of the relative stabilities of the volatile and involatile gallium and aluminum chalcogenides under MBE growth conditions.
Density of midgap states and Urbach edge in chemically vapor deposited hydrogenated amorphous silicon films
Authors: Hegedus Steven S. , Rocheleau R. E. , Cebulka J. M. , Baron B. N.
Published: July 2002

Intrinsic or lightly boron-doped amorphous silicon films were produced by chemical vapor deposition (CVD) from disilane at temperatures from 380 to 460 °C and at growth rates from 0.1 to 40 Å/s. The density of states (DOS) near the middle of the mobility gap was determined by space-charge-limited conduction on n-i-n structures and by steady-state capacitance-temperature spectroscopy on p-i-n structures. Very close agreement was found between the two techniques for intrinsic layers deposited under similar conditions. The DOS distribution is rather flat from 0.60 to 0.75 eV from the conduction-band edge and has a range of 1–6×1017 cm−3 eV−1 for intrinsic films, with the minimum occurring for depositions at 440 °C independent of growth rate or contaminants in the disilane. Diborane levels from 9 to 18 ppm in the gas phase reduces the DOS at 440 °C to 3–6×1016 cm−3 eV−1. The exponential absorption below the band edge in the range 1.4–1.6 eV was determined from primary photocurrent spectra of p-i-n structures. The Urbach edge parameter E0 ranged from 0.048 to 0.056 eV with the minimum also occurring for depositions at 440 °C, independent of growth rate and boron content. Comparison to glow-discharge a-Si:H films indicates that CVD a-Si:H films have a similar amount of structural disorder, determined from E0, but an inherently larger DOS deep in the gap. A model is proposed in which boron reduces the high midgap dangling bond density caused by insufficient weakly bonded hydrogen in the film as a consequence of the high deposition temperatures. The model is consistent with other measurements, such as hole collection width.
Electrical circuit modeling of conductors with skin effect
Authors: Kerst D. W. , Sprott J. C.
Published: July 2002

The electrical impedance of a lossy conductor is a complicated function of time (or frequency) because of the skin effect. By solving the diffusion equation for magnetic fields in conductors of several prototypical shapes, the impedance can be calculated as a function of time for a step function of current. The solution suggests an electrical circuit representation that allows calculation of time-dependent voltages and currents of arbitrary waveforms. A technique using an operational amplifier to determine the current in such a conductor by measuring some external voltage is described. Useful analytical approximations to the results are derived.
A chemical and mechanistic view of reaction profiles in laser direct-write metallization in metallo-organic films. Gold.
Authors: Gross M. E. , Appelbaum A. , Schnoes K. J.
Published: July 2002

Laser direct-write metallization in metallo-organic films involves complex thermal profiles and changes in optical properties that affect the spatial resolution, chemical purity, and electrical properties of the resulting features. Compositional profiles of the metal features, determined by scanning Auger electron spectroscopy, are reported and correlated with the chemistry of the laser-initiated thermal reaction and the observed feature structure. Studies of the changes in optical properties of the films by conventional thermal decomposition offer important insights into the reaction mechanisms. We also report an optimized development procedure for the laser-exposed samples.
Effect of the dissolved oxygen concentration on the growth of thin oxide films on silicon
Authors: Murali V. , Murarka S. P.
Published: July 2002

Silicon (100) wafers with different dissolved oxygen concentrations were oxidized to form thin oxide films in a conventional furnace and in a rapid thermal processing system. In all cases, silicon with higher dissolved oxygen concentration oxidized at a slightly (but significantly) lower rate as compared to the silicon with lower dissolved oxygen concentration. These results clearly indicate that the oxide growth rate, in the thin-film (0<200 Å) range, depends strongly on the nature of the substrate (including its oxygen concentration), as predicted by the recently proposed reaction zone model.
Noise characteristics of a dc SQUID with a resistively shunted inductance. II. Optimum damping
Authors: Enpuku K. , Yoshida K. , Kohjiro S.
Published: July 2002

Effects of a damping resistance on noise characteristics of a dc SQUID are studied theoretically, where the damping resistance is in shunt with a loop inductance of the SQUID. An analytical expression for the energy resolution of the SQUID is obtained, with which the relation between the damping resistance and the energy resolution is studied in detail. It is shown that an optimum value of the damping resistance exists, which is determined by the tradeoff between the improvement of the transfer function and the additional noise due to the damping resistance. Optimum values of the damping resistance are about twice the shunt resistance of the SQUID and vary slightly with SQUID modulation parameter β. For optimum damping, the energy resolution is improved, compared with the case without the damping resistance. This means that the SQUID with large β can be used without significant degradation of the performance, i.e., the previous restriction of β=1 can be loosened. The analytical results agree quantitatively with numerical ones.
Calculation of Hugoniot values from atomic properties
Authors: Walker Franklin E. , Walker F. Gary , Walker J. Bruce
Published: July 2002

A relatively simple equation is presented for use in calculating the Hugoniot values of any condensed element from its atomic weight, atomic radius, and density. Calculations from the equation are compared with data for many elements, and a discussion of the development and utility of the equation is included. The equation also appears to be useful for the gaseous elements when they are in condensed phases.
Micropores and the role of ring structures at the Si–SiO2 interface
Authors: Devine R. A. B.
Published: July 2002

The results of nuclear magnetic resonance and photoemission studies on SiO2, SiOx, and the Si–SiO2 interface are combined to examine the role of ring structures in dry oxides. It is demonstrated that the rings, manifesting their presence through charge transfer effects resulting from Si–O–Si bond angle variations, do modify the photoemission spectra. It is further argued that rings, preferentially oriented parallel to the substrate near the SiO2 interface, when stacked up constitute the micropores invoked to explain enhanced O2 diffusion and oxidation rates in thin, dry oxides. The role of OH as a ring inhibitor in wet oxides is discussed.