bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of hard transparent B–C–N–H thin films formed by plasma chemical-vapor deposition at room temperature
Authors: Montasser Kadry , Hattori S. , Morita S.
Published: July 2002

B–C–N–H thin films were deposited by plasma chemical-vapor deposition with an external capacitively coupled reactor at an rf frequency of 13.56 MHz. The films were formed from a gas mixture of B2H6 (5.25 vol % in N2), methane, and argon or nitrogen as carrier gases. The deposition was carried out at room temperature and without heating the substrate. The films were transparent in the range of 10 000–2000-Å wavelengths. The Knoop microhardnesses were 1825–3324 kg/mm2 and the refractive index was 1.3–1.6. An extensive discussion of the effect of the deposition conditions on both microhardness and film composition is given. In addition, the interrelation between the microhardness and composition is illustrated.
Čerenkov maser operation at lower-mm wavelengths
Authors: Garate E. , Cook R. , Heim P. , Layman R. , Walsh J.
Published: July 2002

The basic operating principles of Čerenkov maser oscillators are briefly reviewed and the experimental performance of a 3-mm device is discussed. A power level of approximately 100 kW was achieved at 88 GHz and voltage tuning from 84 to 128 GHz on the fundamental TM01 mode was observed. Operation on higher-order modes at frequencies up to 300–320 GHz was demonstrated, and a two-stage buncher-amplifier configuration was investigated.
Ion cluster emission and deposition from liquid gold ion sources
Authors: D’Cruz C. , Pourrezaei K. , Wagner A.
Published: July 2002

The emission and deposition of molten gold droplets from needle-tip liquid metal ion sources was investigated. The Taylor cone was identified as the source of droplet emission. An upper limit of 8 μm for the virtual source size was measured. Gold films were deposited on silicon substrates. The deposited gold spots showed a peaked, axially symmetric, distribution with a half angle for droplet emission of ∼2° which was considerably smaller than the ion emission angle of ∼45°. Typical deposition fluxes were ∼5×105 μm3/s/sr with total deposition rates of ∼3×103 μm3/s and on an average droplet diameter of ∼1 μm at an emission current of 150 μA. Smaller diameter droplets are produced with decreasing emission current and angle. Gold films with a fine textured morphology suitable for submicron patterning were obtained at emission currents less than ∼135 μA.
Magnetic properties, microstructure, and domain structure of SmCo3.25Cu1.75
Authors: Mitchell R. K. , McCurrie R. A.
Published: July 2002

A study of the magnetic properties, microstructure, and domain structure of a cast and annealed alloy of SmCo3.25Cu1.75 has been made with the object of relating the magnetic properties, and in particular the mechanism of magnetization reversal, to the microstructure by using the techniques of magnetometry, the Kerr magneto-optic effect, scanning electron microscopy, and electron probe microanalysis. It has been concluded that in the cast alloy, the coercivity is principally determined by domain-wall nucleation with subsequent weak pinning at the grain boundaries. In the annealed alloy, the coercivity is principally determined by domain-wall pinning by the two-phase microstructure within the grains.
Radiation from and force acting on a point charge moving through a cylindrical hole in a conducting medium
Authors: De Zutter D. , De Vleeschauwer D.
Published: July 2002

The radiation from and the force acting on a point charge, moving with relativistic velocity through a cylindrical hole in a conducting medium, is determined. It is shown that a Cerenkov effect occurs if the conductivity of the medium is sufficiently small. Explicit results are given for the time dependence of the field demonstrating the existence of a Cerenkov cone. The dragging force on the moving particle due to radiation losses is examined in detail. The proposed method also applies to dispersive media.
Enhanced diffusion of antimony within a heavily phosphorus-doped layer
Authors: Nishi Kenji , Sakamoto Kouichi , Ueda Jun
Published: July 2002

Antimony diffusion within a heavily phosphorus-doped silicon layer has been studied. Enhanced diffusion of antimony has been found within a heavily phosphorus-doped layer, which contrasts with the retarded diffusion below such layers reported elsewhere. Antimony diffusivity increases in proportion to a certain power of electron concentration when carriers are given by phosphorus, and resembles the behavior of phosphorus diffusivity. These results indicate that the increase of charged vacancies due to Fermi-level effect within heavily phosphorus-doped layers coexists with vacancy undersaturation below the layer.
Discrete spatial filtering with SQUID gradiometers in biomagnetism
Authors: Bruno A. C. , Costa Ribeiro P. , von der Weid J. P. , Symko O. G.
Published: July 2002

First-, second-, and third-order gradiometers used in detecting biomagnetic signals are analyzed as spatial filters. Their transfer functions independent of the source to be measured are presented and both the magnitude and phase characteristics of the transfer functions are analyzed. The distortion introduced by the gradiometer can be estimated from these characteristics. In order to treat the signal in that approach, the spatial Fourier transform of a magnetic signal produced by a current dipole at a given distance is discussed.
Ionization of methane and ethane by x rays: Effect of fluid density on energy absorption (dosimetry)
Authors: György István , Freeman Gordon R.
Published: July 2002

When a fluid contained in a glass or steel cell is irradiated with x rays, the energy absorbed by the fluid is not a linear function of the fluid density over the range 1–1000 kg/m3. A semiempirical model is presented to estimate the absorbed energy as a function of density. The model is based on the energy distribution and ranges of secondary electrons at different densities. The dose measured in air at 1 atm pressure and 298 K is used as a reference. The model is tested against data on the ionization of air at densities 1–5 kg/m3, methane at 12–453 kg/m3, and ethane at 28–571 kg/m3. The yields of ionization estimated with the model increase at high densities, in agreement with an earlier theory of ionization in dense fluids.
Epitaxial growth of Cd1−xMnxTe films by ionized-cluster beams and their magneto-optical properties
Authors: Koyanagi Tsuyoshi , Matsubara Kakuei , Takaoka Hiroshi , Takagi Toshinori
Published: July 2002

Epitaxial growth of Cd1−xMnxTe films with x ranging from 0 to 0.76 has been investigated on sapphire (0001) substrates using the ionized-cluster beam method. Magneto-optical properties of the films are discussed using Kramers–Kronig relation. Epitaxial films in the form of a single crystal can be obtained at low substrate temperatures up to 300 °C by the reactive composing of an accelerated CdTe cluster beam and a neutral MnTe cluster beam. When CdTe clusters are only ionized and accelerated, the composition of grown films varies largely, depending on the acceleration voltage. Faraday rotation for Cd1−xMnxTe films represents a band-edge dispersion, and the intensity increases as Mn concentration x increases; for the film with x=0.76, the maximum value of the Verdet constant was 0.72 °/cm G, which was two orders of magnitude larger than that of a CdTe (x=0) film. The magneto-optical figure of merit θF/α (H=5 kOe) for a Cd1−xMnxTe (x=0.76) epitaxial film was estimated to be about 400 ° at 660 nm.
Electron transfer between adjacent channels simulated by ensemble Monte Carlo methods
Authors: Kizilyalli I. C. , Hess K. , Iafrate G. J.
Published: July 2002

The transfer of electrons between two channels, which are viewed as constituents of a ‘‘generic device’’ is studied. A many-particle Monte Carlo model with self-consistent electric fields is used for this analysis. The study has been performed to assess switching speeds associated with various novel devices, such as velocity modulation transistors and dual-channel high-electron mobility transistors. Typical switching time constants for a 1-μm device (0.4-μm gate length) are 3.5 ps for the longitudinal (source-to-drain) switch on, and 0.2 ps for the transport perpendicular to the interfaces between the two channels.
Synchronizable, injection-locked, Q-switched, mode-locked, and cavity-dumped ten-atmosphere CO2 laser
Authors: Houtman H. , Meyer J.
Published: July 2002

A novel, active, mode-locking scheme for producing single, line-tunable, high-power ultrashort CO2-laser pulses is described. Using an auxiliary grating-tuned cw CO2 laser for injection locking on the 9R(16) line, the Q-switched, mode-locked, and cavity-dumped 10-atm CO2 laser produces single, detection-limited (<500 ps) pulses of 5-mJ energy at λ=9.29 μm. Details are given on the traveling-wave GaAs Pockels cells, both of which are controlled by a single, ultraviolet (UV) triggered spark gap. The time-locked output pulse is delayed by precisely 300.7 ns with <±50 ps jitter against the UV triggered spark gap, so the laser pulse is synchronizable to an external event to <±250 ps. To drive the transverse-electric (TE) 10-atm amplifier section, instead of the conventional Marx bank or inductance-capacitance (LC) generator, a new type of circuit is used. The automatically preionized, double-sided LC inversion circuit uses only one spark gap, and a detailed description with operating characteristics is provided.
Electron traps in AlGaAs grown by molecular-beam epitaxy
Authors: Yamanaka K. , Naritsuka S. , Kanamoto K. , Mihara M. , Ishii M.
Published: July 2002

Using deep-level transient capacitance spectroscopy we have investigated deep electron traps in n-AlGaAs grown by molecular-beam epitaxy (MBE). The thermal activation energies of seven traps, labeled ME1–ME7, observed in this study increase with increasing Al content(x) up to the direct-indirect crossover point (x∼0.42), but show only a small change with further increases in Al content. Traps ME4–ME7 are dominant in samples with x≤0.2. Traps ME4–ME6 strongly depend on the growth ambient. The concentration of ME7 is almost independent of the ambient in the growth chamber but decreases rapidly with increasing growth temperature. ME7 is a native defect and can almost certainly be identified with the trap EL2 observed in bulk and vapor-phase epitaxially grown GaAs. Traps ME4–ME6 are probably formed by impurities involving oxygen such as CO, H2O, and AsO in the growth ambient. All of the traps, ME5–ME7 are clearly responsible for a decrease in the photoluminescence intensity of MBE grown AlGaAs.
Transient photoconductive response of InP:Fe
Authors: Iverson A. Evan , Smith D. L. , Paulter N. G. , Hammond R. B.
Published: July 2002

We present experimental transient response data for iron-doped indium phosphide (InP:Fe) photoconductors subject to impulse and rectangular-pulse excitation over a wide range of excitation intensities. The detector response shape is observed to depend strongly on the excitation intensity. We present a model for bulk-material response based on the dynamics of electron and hole trapping and recombination on the deep-level iron impurities. The model qualitatively reproduces the observed experimental behavior.
Fabrication of high-gain inertial fusion targets using gas jet cooling and intensity-graded laser illumination
Authors: Kim K. , Krahn D. L.
Published: July 2002

A new method, which is particularly suitable for fabricating a uniformly thick solid- or liquid-fuel layer inside an inertial confinement fusion target, is described. The method employs a cold helium-gas-jet shower to uniformly cool a target and an intensity-graded laser illumination to create a desired thermal gradient across the target. The net result is a thermally induced fuel migration inside the target, which precisely counterbalances the gravity-induced fuel sagging, bringing about a uniform layer of fuel condensate on the target interior. This new method is significant for the following reasons: First, it allows for fabrication of both solid- and liquid-fuel layers. Second, it is a noncontact method. Third, it requires either none or very little cryogenic shielding. Fourth, it is simple to implement. Fifth, it allows for easy diagnostic access to the target. Details of the apparatus and results showing the capabilities of the method are presented.
Coupled electron and excited-state kinetics in a nitrogen afterglow
Authors: Gorse C. , Capitelli M.
Published: July 2002

The coupling between the metastable state N2(A3Σ+u) and the electron energy distribution function (EDF) as well as the vibrational distribution N2(X,v) of the ground state in a nitrogen afterglow has been studied by simultaneously solving the Boltzmann equation for the EDF and the rate equations describing the kinetics of N2(A) and N2(X,v). The results show that in the decaying plasma, the presence of N2(A) strongly affects both the EDF and N2(X,v). In particular, superelastic electronic collisions produce a broad maximum in the EDF which follows the temporal evolution of the N2(A) concentration, while bimolecular reactions involving N2(A) create a N2(X,v) distribution characterized by a plateau which decays with time.
Experimental identification of the energy level of substitutional manganese in silicon
Authors: Haider M. , Sitter H. , Czaputa R. , Feichtinger H. , Oswald J.
Published: July 2002

A combination of deep level transient spectroscopy (DLTS) and electron spin resonance (ESR) measurements was used to determine the energy level of substitutional manganese in silicon. Samples of p-type silicon were subjected to a copper-manganese codiffusion. Successfully prepared samples show the typical ESR signal of substitutional manganese with a single positive charge. The Hamiltonian parameters g=2.029 and A=−62.7×10−4 cm−1 are different from those for negatively charged interstitial manganese. The DLTS measurements reveal an energy level of M1=0.39 eV above the valence-band edge for the substitutional manganese. Because of the codiffusion of Cu also the previously reported levels C1=0.098 eV, C2=0.22 eV, and C3=0.41 eV were found. The combination of ESR and DLTS results allowed a conclusive identification of the defect level M1 and provided no evidence for ordinary amphoteric or negative U behavior in the lower half of the band gap. Furthermore, isothermal and isochronal annealing experiments were performed which support the conclusion that the defect level M1 orginates from substitutional manganese in p-type silicon.
Conductivity variations induced by water vapor adsorption in granular metal films
Authors: Nannini A. , Bagnoli P. E. , Diligenti A. , Neri B. , Pugliese S.
Published: July 2002

The resistance variations induced by relative humidity (RH) changes were measured on Pd/Al2O3 and Au/(C2F4)n granular films in the RH range 0%–97% at room temperature. It was verified that the contact-film interface has no influence on the observed phenomena. A maximum ΔR/R0=26% was detected for the Au/(C2F4)n system.
Phototriggering of a 1-J excimer laser using either UV or x rays
Authors: Lacour B. , Vannier C.
Published: July 2002

Photoswitching of a homogeneous 1-l discharge has been tested on a specially designed excimer laser by using either an x-ray beam or a KrF laser beam as a photoionization source. With x rays, a 1.4-J, 4×4-cm2, XeCl laser beam has been obtained with 1.7% efficiency and an impedance-matched 50-ns pulse-forming line directly connected to the electrodes. Since the output energy seems to rise monotonically as a function of electron–ion pair initial density, even better performances should be attainable with a more intense photoionization source.
Effects of neutron irradiation on the critical current of bronze processed multifilamentary Nb3Sn superconducting composites
Authors: Okada T. , Fukumoto M. , Katagiri K. , Saito K. , Kodaka H. , Yoshida H.
Published: July 2002

The influence of fast neutron irradiation on critical current Ic and its strain dependence in a bronze processed fine multifilamentary Nb3Sn superconducting composite has been investigated. The neutron irradiation has been performed in a fission reactor at the reactor ambient temperature (≂355 K) up to the neutron fluence φt=3.6×1019 n/cm2 (E>0.1 MeV). The effects of annealing after irradiation have also been investigated. From the measurement of Ic at various magnetic fields, the scaling law for the change in dose has been found to be held in a certain range of neutron dose. The strain sensitivity of Ic under common ratio of applied magnetic field to bulk upper critical field B*c2 is affected slightly by irradiation up to φt=1.5×1019 n/cm2 but remarkably by annealing after irradiation to 3.6×1019 n/cm2. The strain scaling law has been found to be the specimen irradiated to 1.5×1019 n/cm2 and also to the one annealed (723 K, 2 h) after 3.6×1019 n/cm2 irradiation. The exponent value for B*c2 in pinning force density vs B*c2 relation deviated from unity which is applied for many types of Nb3Sn conductors.
Photoreflectance, absorption, and nuclear resonance reaction studies of AlxGa1−x As grown by molecular-beam epitaxy
Authors: Huang D. , Ji G. , Reddy U. K. , Morkoç H. , Xiong F. , Tombrello T. A.
Published: July 2002

The photoreflectance (PR) spectra of bulk AlxGa1−xAs alloys with x≤0.45 were studied. The observed line shapes from different samples suggest that the PR technique is very sensitive to the material quality, surface condition, and the background impurities. The energy gap derived from the PR spectra compared well to that obtained from the absorption spectra. The relationship between the energy gap and the Al mole fraction value x was established through the nuclear resonance reaction analysis. The electric field near the surface was calculated from the periodicity of Franz–Keldysh oscillations observed in many of the samples. From our analysis, we believe that the number of oscillations shown in PR spectra corresponds to sample quality, in general. We also believe that the low-field-like line shape is mainly caused by the fluctuation of Al distribution along the growth direction. An additional feature related to the impurity transition was also observed in the spectra.
The effect of microstructure on the height of potential energy barriers in porous tin dioxide gas sensors
Authors: Romppainen P. , Lantto V.
Published: July 2002

A theoretical study is made on the height of potential energy barriers formed at intergranular contacts in porous tin dioxide. Expressions are derived for the height of barriers in a one-dimensional case when the donor concentration is constant and also when there is a concentration gradient in the surface. Expressions are also derived for the case when the intergranular contact is in the shape of a cylinder. The treatment in this case, together with the application of Fermi–Dirac statistics, leads to a conclusion of the existence of a distribution of the height of barriers. The potential barrier on the center line of the cylinder vanishes above a critical radius. The effect of the distribution of the height of barriers on the activation energy of the conductance of porous tin dioxide is discussed on the basis of a random barrier network model.
Theory of circularly polarized x-ray absorption by ferromagnetic Fe
Authors: Ebert H. , Strange P. , Gyorffy B. L.
Published: July 2002

A description of the absorption of circularly polarized x rays based on a spin-polarized version of relativistic multiple scattering theory is presented. The approach treats all relativistic effects and spin polarization on equal footing, permitting us to study the difference in absorption of left and right circularly polarized x rays. Results obtained for ferromagnetic Fe are presented and compared with experiment.
Low-temperature (350 °C) growth of AlGaAs/GaAs laser diode by migration enhanced epitaxy
Authors: Asai M. , Sato F. , Imamoto H. , Imanaka K. , Shimura M.
Published: July 2002

Migration enhanced epitaxy, in which group III and group V elements are deposited onto the substrate alternately under ultrahigh vacuum, has been employed to reduce AlGaAs growth temperature. By optimizing growth conditions of AlGaAs, molecular-beam intensities, and substrate temperatures between 600 and 250 °C, an AlGaAs/GaAs single-quantum-well laser diode has been fabricated successfully at very low temperature of 350 °C for the first time. A broad area laser diode emitting at 780 nm shows the threshold current density of 2.5 kA/cm2 at room temperature under the pulsed operation.
Mechanisms of sputtering of Si in a Cl2 environment by ions with energies down to 75 eV
Authors: Oostra D. J. , Haring A. , van Ingen R. P. , de Vries A. E.
Published: July 2002

Sputtering of Si in a Cl2 environment by Ar+ and Xe+ ions with energies down to 75 eV has been investigated. Mass spectra and time-of-flight distributions of the sputtered species have been measured. Under 75-eV Ar+-ion bombardment of the Si target, SiCl, SiCl2, SiCl3, and/or SiCl4 are sputtered. When increasing the ion energy the SiCl4 contribution decreases in comparison with SiCl. This is caused by the fact that the newly formed Si-Cl compounds are sputtered at a high rate compared to the rate of SiCl4 formation. Time-of-flight distributions indicate that under 100-eV Ar+-ion bombardment the species are not sputtered by a collision-cascade mechanism. The spectra can be fitted by Maxwell–Boltzmann distributions at a high (>2000 K) temperature. Increasing the Ar+-ion energy to approximately 250 eV the time-of-flight spectra of the sputtered species change from Maxwell–Boltzmann-like into spectra as expected for a collision-cascade mechanism. For low-energy Xe+ ion bombardment the sputtered species also show Maxwell–Boltzmann time-of-flight distributions. The change from Maxwell–Boltzmann to collision-cascade distributions occurs at higher ion energies than for Ar+-ion bombardment. The results obtained for low ion energies are discussed in terms of evaporation from an ion-induced hot spot.
Flow-enhanced corona discharge: The corona torch
Authors: Maezono I. , Chang Jen-Shih
Published: July 2002

An experimental investigation has been conducted to enhance and control corona discharge in two small diameter cylindrical hollow electrodes by an external gas flow. The results show that the time-averaged corona current for fixed discharge voltages increases with increasing gas flowrate of pure nitrogen, and pressure drop is not significantly influenced by corona discharge currents.
On the kinetics of solid phase regrowth and dopant activation during rapid thermal annealing of implantation amorphized silicon
Authors: Adekoya W. O. , Hage-Ali M. , Muller J. C. , Siffert P.
Published: July 2002

We have studied the solid phase epitaxial regrowth (SPER) of implantation [31P+,11B+(73Ge+ preamorphized)] amorphized silicon in the temperature range 500–600 °C induced by rapid thermal annealing (RTA), using Rutherford backscattering (RBS) and channeling measurements. Our results show rate enhancements (≂3.5–6.5) of the velocities of regrowth in all cases studied with respect to values reported in the literature for furnace-induced epitaxy. The measured SPER activation energies (2.7 and 2.6 eV for 31P+ and 11B+ implantations, respectively) while being comparable to literature reported values, were nevertheless higher than the energy required for the activation of these dopants, ≂1.55–2.45 eV. Also, the ratio VB/VP (velocity of regrowth in the presence of boron with respect to phosphorus) gives a value of approximately 3 in both RTA and furnace-induced kinetics. These results are explained by a model which takes into account the role of electrically active interfacial defect sites during SPER.
Electrical and interfacial properties of metal-polyimide-silicon structures
Authors: Hahn B. R. , Yoon D. Y.
Published: July 2002

The electrical and interfacial properties of gold-polyimide-silicon structures were studied experimentally by measuring the capacitance-voltage (C-V) characteristics. Two different polyimides of PMDA-ODA (synthesized from pyromellitic dianhydride and oxydianiline) and BTDA-ODA (from benzophenone tetracarboxylic dianhydride and oxydianiline), respectively, were employed. Polyimide coatings on n-type silicon (with a doping level N=5×1014 cm−3) were prepared by spin coating followed by thermal cure to range from 0.4 to 2.1 μm in thickness. The resulting high frequency C-V plots of these structures were well defined and could be described by the basic theory on metal-insulator-semiconductor (MIS) devices. Distinct differences in the C-V characteristics were observed, depending upon the polyimides. PMDA-ODA dielectrics resulted in C-V hysteresis, believed to be caused by charge injection. On the other hand, BTDA-ODA showed much smaller hysteresis, but some stretch-out in the C-V curve. These differences are attributed to the different interfacial properties of these polyimides in contact with silicon substrates.
Surface studies relevant to silicon carbide chemical vapor deposition
Authors: Stinespring C. D. , Wormhoudt J. C.
Published: July 2002

Experimental studies of C2 H4, C3 H8, and CH4 reactions on the Si(111) surface and C2 H4 reaction on the Si(100) surface have been performed for surface temperatures in the range of 1062–1495 K. These studies used x-ray photoelectron spectroscopy and related ultrahigh vacuum procedures to identify the reaction products, characterize the solid-state transport mechanisms, determine the surface nucleation mechanisms and growth kinetics, and assess the effects of surface orientation. The reaction product was found to be essentially carbidic throughout the course of the reaction, although the surface layer may contain partially hydrogenated C adspecies. The dominant transport process was shown to be Si out-diffusion rather than C in-diffusion. The Si adspecies produced by out-diffusion react at the gas-surface interface with C adspecies to form the SiC film via a two-dimensional nucleation and layer-by-layer growth mechanism. The reaction efficiency for C2 H4 on the Si(111) and Si(100) surfaces was shown to be ∼10−3. The reaction efficiency for C3 H8 and CH4 on the Si(111) surface was shown to be ∼10−5. For growth temperatures above 1395 K, Si diffusion limitations and sublimation from the SiC surface were found to limit the availability of Si for the SiC growth process. In the absence of Si adspecies, the adlayer formed by the reaction of C2 H4 on SiC appeared to passivate the surface with respect to further C2 H4 reaction. When combined with previously reported modeling studies of the associated gas phase chemistry, these results provide the basis for a mechanistic model of the β-SiC chemical vapor deposition process.
Dopant redistribution in heavily doped silicon: Confirmation of the validity of the vacancy-percolation model
Authors: Mathiot D. , Pfister J. C.
Published: July 2002

This communication discusses the physical origin of the diffusion enhancement observed by various authors at high doping levels during the annealing of dopant-implanted silicon. It is shown that the experimental results can be accounted for by the percolation model previously developed for high-concentration phosphorus diffusion. A quantitative treatment is given in the case of the diffusion of implanted Sb in heavily doped n-type silicon.
Secondary ion mass spectrometry depth profiling of proton-exchanged LiNbO3 waveguides
Authors: Wilson R. G. , Novak S. W. , Zavada J. M. , Loni A. , De La Rue R. M.
Published: July 2002

Simultaneous depth profiles for H and Li have been measured in proton-exchanged lithium niobate crystals (LiNbO3) by the use of charge-compensated secondary ion mass spectrometry (SIMS). Electron flooding of the insulator during sputtering permits accurate depth profiling through the exchanged region and into the substrate. Four samples of z-cut proton-exchanged LiNbO3 were analyzed using SIMS, and were used in optical waveguiding experiments. In each sample, the H distribution is in the shape of a plateau that extends from the surface to a depth that is in good agreement with the results of the optical waveguiding measurements.The Li profiles show reduced concentrations within the regions of high H concentration, that is, within the waveguiding regions. Based on SIMS data, the proton-exchange process appears to stabilize at a value of 0.4<x<0.5 for the Li1−xHxNbO3 compound.
Anisotropic defect distribution in ZnSe/ZnS epitaxial layers grown by metalorganic vapor-phase epitaxy on (001)-oriented GaAs
Authors: Brown P. D. , Russell G. J. , Woods J.
Published: July 2002

Epitaxial layers of ZnSe/ZnS have been grown by metalorganic vapor-phase epitaxy on (001)-oriented GaAs. A microstructural study of the defect content of these layers was performed using the combined techniques of scanning electron microscopy, reflection high-energy electron diffraction, transmission electron microscopy, and microdiffraction. Investigation of the epilayers in the [110] and [11̄0] orientations highlighted the strong anisotropy in the defect content of these ZnSe/ZnS layers. Microtwins were found exclusively in the [11̄0] sample orientation, while examination of the same layers along the orthogonal [110] projection revealed only misfit dislocations. The influence of the differential motion of α and β dislocations in the sphalerite structure is discussed in connection with these observations.
Analysis of solid phase crystallization in amorphized polycrystalline Si films on quartz substrates
Authors: Nakamura Akira , Emoto Fumiaki , Fujii Eiji , Yamamoto Atsuya , Uemoto Yasuhiro , Senda Kohji , Kano Gota
Published: July 2002

The solid phase crystallization of amorphized Si films on quartz substances is studied by means of the transmission electron microscope observation of grain growth. The amorphous Si films are prepared by Si ion implantation into polycrystalline Si films deposited by low-pressure chemical vapor deposition. It has been found that the twin formation in grains at the early stage of the crystallization accelerates the growth rate preferentially in a 〈112〉 direction. During the twin growth about a given 〈112〉 direction, other twins also grow from the twin boundary dendritically in some other 〈112〉 directions, leading to the formation of a large grain of dendritic structure.
Spallation studies in aluminum targets using shock waves induced by laser irradiation at various pulse durations
Authors: Cottet F. , Boustie M.
Published: July 2002

The conditions of laser-driven shock wave loading lead to the study of the dynamic fracture in an unusual range of stress and strain rates: 20–200 GPa and more than 107 s−1. A cumulative damage criterion for the spallation process has been included in a one-dimensional finite difference hydrodynamic code. Numerical studies show the effect of different parameters: laser-pulse duration, peak induced pressure related to the incident intensity, and target thickness. The simulation results are in agreement with spallation shock-laser experiments on aluminum targets of various thicknesses irradiated by laser pulses of durations between 0.6 and 25 ns with an incident intensity of about 1012 W/cm2 .
Interpretation of the magnetization mechanism in Terfenol-D using Barkhausen pulse-height analysis and irreversible magnetostriction
Authors: Jiles D. C. , Hariharan S.
Published: July 2002

The ternary alloy Dy0.7Tb0.3Fe1.9, known as Terfenol-D, is a highly magnetostrictive alloy with magnetostriction coefficients along the principal crystallographic directions of λ111=1640×10−6 and λ100≤100(±30)×10−6. The bulk magnetostriction λ is dependent on the state of magnetization M, on the original domain configuration, and on the texture of the material. This paper reports on Barkhausen measurements and magnetostriction. The pulse-height distribution of Barkhausen emissions revealed events occurring at a specific amplitude which were stress dependent. The magnetostriction results gave a saturation magnetostriction in excess of 2000 μ strain.
Effect of size and dimensionality on the magnetic moment of transition metals
Authors: Liu Feng , Khanna S. N. , Jena P.
Published: July 2002

The effect of size and dimensionality on the magnetic moments of Fe, Co, and Ni have been studied theoretically by confining the atoms to various structural forms such as chains, surfaces, and thin films. The size of these systems is controlled by limiting the number of atoms. A new first-principles theory is developed that enables us to study the electron spin density of states and moments of atoms in clusters containing two to a few thousand atoms. The theory is based upon the elementary principles governing the tight binding and linear combination of atomic orbitals formulations. It contains no adjustable parameters and can be applied to systems with or without topological symmetry. We have discovered quantum size effects on the magnetic moments of linear chains and these effects disappear when the chains contain more than 20 atoms. We have also found distinct effects of the local environment on the magnetic moment. For example, the moments increase with decreasing coordination number and increasing interatomic distance. Our results will be compared with available experimental and theoretical results.
Vacancy-type defects in Si+ -implanted GaAs and its effects on electrical activation by rapid thermal annealing
Authors: Lee Jong-Lam , Uedono Akira , Tanigawa Shoichro , Lee Jeong Yong
Published: July 2002

The depth distributions of vacancy-type defects in Si+ -implanted and thermally activated GaAs were studied by a slow positron beam technique and were compared with the results observed with a transmission electron microscope. In as-implanted GaAs, the concentration of vacancy-type defects decreased monotonically with increasing depth below the surface and the generation of point defects was demonstrated by the lattice image of transmission electron microscopy. The vacancy concentration is not dependent upon activation conditions; however, the electrical activation coefficiency obtained from Hall measurements is enhanced with increasing activation annealing time. This indicates that the electrical activation of Si+ -implanted GaAs is proceeding by the exchange of interstitial Si with substitutional Ga rather than the recombination of interstitial Si into Ga-related vacancies. The maximum number of extrinsic-type stacking faults was observed at 70–80 nm below the surface after the activation annealing, which is compared with that of vacancy-type defects, at 25–35 nm, obtained by the slow positron beam technique. This discrepancy in both of the damage distributions could originate in different types of defects existing along the depth below the surface, which was discussed with the high-energy recoil theory.
GaAs-on-Si: Improved growth conditions, properties of undoped GaAs, high mobility, and fabrication of high-performance AlGaAs/GaAs selectively doped heterostructure transistors and ring oscillators
Authors: Chand Naresh , Ren F. , Macrander A. T. , van der Ziel J. P. , Sergent A. M. , Hull R. , Chu S. N. G. , Chen Y. K. , Lang D. V.
Published: July 2002

Improved growth conditions by molecular-beam epitaxy (MBE) and fabrication of state-of-the-art AlGaAs/GaAs selectively doped heterostructure transistors (SDHTs) and ring oscillators on Si substrates are reported. In MBE growth, use of minimum As4:Ga flux ratio during initial nucleation combined with in situ thermal cycles gave a marked improvement in material quality. With this method, FWHM of x-ray rocking curves was measured as low as 135 arcsec for a 3.5-μm-thick GaAs layer on Si. Although 3-μm-thick undoped GaAs buffer layers on p-type Si substrates were fully depleted under a Schottky contact, a parallel n-type conduction path confined in a thin region (<0.1 μm) near the GaAs/Si interface was sometimes observed whose sheet density (1012–1013 cm−2) and mobility (600–900 cm2 V−1 s−1) were independent of temperature between 300 and 77 K. This parallel conduction was successfully prevented by doping 0.1 μm GaAs with 5–10×1016 cm−3 Be atoms near the interface. In AlGaAs/GaAs selectively doped heterostructures, for a sheet density of 1012 cm−2, a mobility as high as 53 500 cm2 V−1 s−1 at 77 K was obtained, as against a mobility of ∼70 000 cm2 V−1 s−1 for a similar structure on GaAs substrates. For 1-μm-gate-length SDHTs, maximum transconductances of 220 and 365 mS/mm were measured at 300 and 77 K, respectively. A minimum propagation delay time τd of 28 ps/stage was measured at 300 K for ring oscillators at 1.1 mW/stage power dissipation. τd decreased to 17.6 ps/stage at 77 K. From microwave S-parameter measurements at 300 K, current gain and power gain cutoff frequencies of 15 and 22 GHz, respectively, were measured. These results are comparable to that of SDHT technology on GaAs substrates.
Investigation on the oxide field dependence of hole trapping and interface state generation in SiO2 layers using homogeneous nonavalanche injection of holes
Authors: Schwerin A. V. , Heyns M. M. , Weber W.
Published: July 2002

Homogeneous injection of holes into the gate oxide of metal-oxide-semiconductor (MOS) devices was obtained using p-channel MOS transistors under illumination conditions. Because gate hole currents could be measured the dependence of the hole trapping on the oxide electric field and on the energy of the holes at the injection point could be investigated. In contrast to results recently reported for electron injection no evidence for the generation of traps during hole injection was found. Only a small dependence of the capture cross section on the oxide field was observed. The study of the interface state generation during hole injection at various fields revealed that the amount of interface states directly generated by the injected holes is less than 5% of the number of trapped holes. For longer times a transformation process occurs and a correlation is found between the detrapping of holes and the generation of interface states.
Analysis of the device performance of quantum interference transistors utilizing ultrasmall semiconductor T structures
Authors: Subramaniam S. , Bandyopadhyay S. , Porod W.
Published: July 2002

We present a theoretical study of a recently proposed class of quantum interference transistors that utilize quantum interference effects in ultrasmall semiconductor T structures. Our analysis reveals that the attractive features of these transistors are the very low power-delay product and multifunctionality; whereas the major drawbacks are extreme sensitivity of the device characteristics to slight structural variations, low gain, and low extrinsic switching speed in digital circuits caused by a large resistance-capacitance (RC) time constant arising from an inherently low current-carrying capability. The low switching speed of the transistors can however be improved dramatically by switching the device optically rather than electronically, using virtual charge polarization caused by optical excitation. This mode of switching (which is possible because of the small value of the threshold voltage) eliminates the RC time constant limitation on the switching time and results in an ultrafast optoelectronic switch.
Comparison of model predictions with detailed species kinetic measurements of XeCl laser mixtures
Authors: Kannari F. , Kimura W. D. , Ewing J. J.
Published: July 2002

Detailed measurements of the time-dependent electron density, xenon excited-state densities, and total HCl depletion have been recently made in electron-beam- (e-beam-) pumped XeCl. This paper presents the results of extensive computer modeling of these experiments and detailed comparisons with the measured results. The model used includes updated HCl reaction cross sections and an enlarged xenon excited-state manifold. A reduced Boltzmann equation is used to calculate the high-energy electron-energy distribution function, and the low-energy distribution function assumes a quasi-Maxwellian distribution. These changes are upgrades to prior models. The model accurately predicts the total HCl depletion, the time-dependent electron density for initial HCl concentrations ≥0.16% (4.8 Torr), and the time-dependent xenon excited-state densities for lean (≂0.04%) initial HCl concentration cases. The model tends to underpredict the rate of electron-density growth after the electron density begins to run away. Since depletion of HCl is a key factor in understanding the kinetics data, possible mechanisms that can contribute to this process are also discussed.
Hydrogen-passivated amorphous gallium arsenide thin films
Authors: Manorama Vardhireddy , Dighe P. M. , Bhoraskar S. V. , Rao V. J. , Singh Prabhat , Belhekar A. A.
Published: July 2002

Conditions have been developed for the deposition of stoichiometric thin films of amorphous gallium arsenide by the technique of flash evaporation. Structural properties of as-deposited and annealed thin films of a-GaAs have been studied using x-ray diffraction and transmission electron microscopy techniques. The as-deposited films are noncrystalline, structural ordering starts at about 200 °C, and the film becomes crystalline at about 400 °C with the structure matching with that of polycrystalline GaAs. The as-deposited a-GaAs thin films have been passivated using hydrogen plasma under different conditions. The influence of hydrogenation on these a-GaAs films has been studied using Fourier transform infrared absorption spectroscopy. These data are explained in terms of the various types of hydrogen bondings and the results are in excellent agreement with the earlier investigations on a-GaAs:H.
X-ray photoelectron spectroscopy studies of the reaction of N+2 -ion beams with niobium and tantalum metals
Authors: Badrinarayanan S. , Sinha S.
Published: July 2002

I n situ nitrogen-ion implantation of polycrystalline niobium and tantalum was performed and the surface was characterized by x-ray photoelectron spectroscopy (XPS). The XPS chemical shifts indicated the formation of metal nitride. The chemical shift values are calculated theoretically and compared with the experimental values.
MnFe structure-exchange anisotropy relation in the NiFe/MnFe/NiFe system
Authors: Kung Kenneth T.-Y. , Louie Libby K. , Gorman Grace L.
Published: July 2002

The relation between the MnFe structure and the exchange anisotropy in the Ni80Fe20/Mn50Fe50/Ni80Fe20 system has been investigated. The samples have a layered structure of glass/NiFe(600 Å)/MnFe(40–400 Å)/NiFe(300 Å)/Ta(200 Å). For the lower interface, NiFe(600 Å)/MnFe, the anisotropy energy falls in the range of 0.00–0.06 erg/cm2 and the critical temperature in the range of 120–160 °C; both increase initially with the MnFe thickness but become essentially constant for MnFe thicknesses beyond 80 and 160 Å, respectively. For the upper interface, MnFe/NiFe(300 Å), the anisotropy energy falls in the range of 0.00–0.16 erg/cm2 and the critical temperature in the range of 110–190 °C; again, both increase initially with the MnFe thickness but decrease for MnFe thickness beyond 120 and 360 Å, respectively. The correlations between the exchange anisotropy and the MnFe structure determined by x-ray diffraction are identified.
Simultaneous in-plane Kerr effects in Fe/GaAs (110) thin films
Authors: Florczak J. M. , Dahlberg E. Dan , Kuznia J. N. , Wowchak A. M. , Cohen P. I.
Published: July 2002

For many materials that can be magnetized, part of the magnetization process may be attributed to a rotation of the magnetization vector. In this context, a combination of the longitudinal and transverse magneto-optical Kerr effects are used to detect two orthogonal magnetization components in single-crystal Fe/GaAs (110) thin films. Hysteresis curves obtained by this magneto-optical technique are presented for fields along the in-plane [001], [11̄0], and [11̄1] crystal directions. For those curves that show signs of rotation, these data are simulated using a coherent rotation mechanism for the magnetization process and Fresnel reflection coefficients for the two Kerr effects. From the experimental data, it is found that the [11̄1] curves have shapes that are indicative of a rotational process. On the other hand, both the [001] and [11̄0] have magnetization curves that do not follow a simple rotation. From the coherent rotation model, there is qualitative agreement between the modeled and experimental data for the [11̄1].
Simultaneous generation of the 7.6-eV optical absorption band and F2 molecule in fluorine doped silica glass under annealing
Authors: Awazu Koichi , Kawazoe Hiroshi , Muta Ken-ichi
Published: July 2002

We examined chemical state of fluorine doped silica glasses and its thermal behavior. Almost all of the fluorine atoms were found to have the ≡SiF structure with Raman spectroscopy. No optical absorption in the region of 3–9 eV was detected in the glass. When the glasses were annealed in a He atmosphere at 1000 °C, absorption bands peaking at 7.6 and 4.3 eV appeared. These two bands are attributed to the ≡SiSi≡ structure and to F2 molecules, respectively. We proposed a thermal decomposition reaction expressed as ≡SiF+FSi≡→≡SiSi≡+F2. The concentrations of the reaction products, ≡SiSi≡ and F2, estimated from the absorption cross sections were equal to each other within the errors of measurements. We also examined the radiation damage with γ ray. The concentration of E′ center was almost the same for the same dose in silica glasses having different concentrations of FSi≡ and ≡SiSi≡. We suggest that FSi≡ and ≡SiSi≡ were found to be stable for γ-irradiation at room temperature.
Neutron-induced defects in high-purity germanium
Authors: Fourches N. , Walter G. , Bourgoin J. C.
Published: July 2002

Fast neutron-induced defects have been studied in high-purity n- and p-type germanium using capacitance techniques. Capacitance versus voltage has been applied to monitor the total defect introduction rate. The defects introduced by low-temperature (10 K) and room-temperature irradiations, as well as the native defects present in the As-grown materials, are characterized by deep level transient spectroscopy. The restrictions of these techniques when applied to a material having a low-free-carrier concentration are pointed out. The previous knowledge of the annealing behavior and introduction rates of defects created by electron irradiation allowed some information about the microscopic origin of the point defects observed to be obtained. The dominant defects induced by the irradiation are vacancy or divacancy related. The study of the stable traps at low temperature provides a reasonable understanding of the primary defects and their annealing behavior up to room temperature. The characteristics of the secondary defects created after low-temperature irradiation and annealing are compared with those created directly by room-temperature irradiation. The origin of the Ev+0.07 eV level present in dislocation-free high-purity germanium is also discussed.
Microstructure and orientation effects in diamond thin films
Authors: DeNatale J. F. , Harker A. B. , Flintoff J. F.
Published: July 2002

The microstructure and orientation of diamond thin films grown by plasma assisted chemical vapor deposition have been studied as functions of growth temperature, substrate identity, and substrate pre-treatment. Results indicate that for growth temperatures below 650 °C, competition between film growth and etching can lead to preferential (110) oriented films on a variety of substrate materials. This orientation can be globally sustained during growth by the occurrence of (111) planar defects.
Probability wave theory of the atomic configuration for multicomponent crystal structures and its application to the ordered structure of complex perovskite materials
Authors: Gu Binglin , Ni Jun , Zhang Xiaowen
Published: July 2002

The probability wave of the atomic configuration is used to study the occupation probabilities of different kinds of atoms at lattice sites in multicomponent solid solutions and predict the crystal structures of multicomponent solid solutions. The theory of the probability wave of atomic configuration is applied to study the atomic configuration of the most stable superlattices formed in the complex perovskite structure. Seven basic ordered structures are deduced theoretically; these have been compared with the experiment results.