bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanism for existence of nonmagnetic cerium sites in magnetically ordered cerium compounds
Authors: Kioussis N. , Cooper B. R. , Banerjea A.
Published: July 2002

Hybridization of moderately delocalized f electrons with band electrons gives rise to a highly anisotropic two-ion interaction, which, as Siemann and Cooper first showed, accounts well for the unusual magnetic behavior of CeBi. In the present paper it is shown that the even more unusual magnetic behavior of CeSb with a succession of magnetic structures in which the higher-temperature structures (AFP) involve a periodic stacking of nonmagnetic {001} planes alternating with magnetically ordered {001} planes of [001] moment alignment can be understood on the basis of the same hybridization-mediated interionic interaction in the presence of a cubic crystal field (CF) of comparable strength. The tendency to form nonmagnetic planes, which are indeed paramagnetic in nature (Kramers doublets), is found to increase with increasing CF strength, and the stability of the AFP phases at high temperatures is shown to arise from the reconciliation of the magnetic ordering with the CF interactions. The calculations yield first-order phase transitions from a low-temperature type I antiferromagnetic phase to two high-temperature AFP phases. The possibility of a fully nonmagnetic singlet ground state, which, however, is not Kondo-like, also occurs and will be discussed.
Novel highly sensitive coincidence detection method for resonance ionization signals
Authors: Minowa Tatsuya , Katsuragawa Hidetsugu , Nishiyama Koichi , Shimazu Mitsuyoshi , Inamura Takashi
Published: July 2002

A novel method of highly sensitive detection of pairs of ions and electrons has been developed for resonance ionization spectroscopy and tested for a thallium atomic beam. Only the pairs of ion and electron signals whose time differences corresponded to the time of flight of a thallium ion were detected. The signal-to-noise ratio has been improved by the order of 102 compared with the single detection of electrons or ions. The sensitivity of this method reached the order of thallium density of 102 cm−3.
Effect of argon dilution of silane on persistent photoconductivity in single-layered hydrogenated amorphous silicon
Authors: Choi Suk-Ho , Lee Choochon , Jang Jin
Published: July 2002

The effect of argon dilution of silane on the persistent photoconductivity (PPC) has been studied for single-layered hydrogenated amorphous silicon films prepared by a glow-discharge decomposition. The magnitude of the PPC effect and the columnar-growth morphology increase when the argon-to-silane mixing ratio increases to 10. Above this ratio both the PPC and the columnar pattern decrease. A clear correlation between the magnitude of the PPC and the microstructure has been observed for undoped single-layered films. It is concluded that the PPC effect is not confined to the multilayers and to the compensated films, and that by increasing the microstructure in undoped films through argon dilution the effect can be increased.
Singlet oxygen generator using a porous pipe
Authors: Takehisa K. , Shimizu N. , Uchiyama T.
Published: July 2002

The results of a study of an improved new method for generating O2(1Δ) for use in a chemical oxygen-iodine laser are presented. The generator, using a porous pipe, was found to produce O2(1Δ) with an excitation efficiency of more than 80% and a maximum production of O2 molecules from the unit surface area of 2.2 mmol min−1 cm−2 has been attained.
Effect of elastic strain on the energy band gap in heteroepitaxially grown ZnSe
Authors: Potts J. E. , Cheng H. , Mohapatra S. , Smith T. L.
Published: July 2002

Low-temperature photoluminescence spectra have been measured for a series of ZnSe films of varying thicknesses grown by molecular-beam epitaxy on GaAs, and variations in the spectra have been correlated with changes in the lattice parameter in the epilayer. Elastic strain resulting from in-plane compression of the epilayer is found to cause a displacement of exciton-related photoluminescence features to higher energies with decreasing layer thickness. This behavior reflects an increase in the band gap of ZnSe under increasing strain, similar to the behavior observed in several other zinc-blende semiconductor epilayer systems, but in contrast to the behavior predicted for this particular system by some authors.
Protective coating on the p-n junction of In0.53Ga0.47As/InP p-i-n planar diodes by vacuum-evaporated glass
Authors: Ota Yusuke , Hu Patrick H-S. , Seabury Charles W. , Brown Michael G.
Published: July 2002

A technique for protecting the p-n junction of InGaAs planar diodes using thermally evaporated glass films has been developed. A planar diode with a 90-μm-diam diffused junction protected with the glass film had a reverse current less than 1 nA at −20 V. The diode showed low reverse current even after prolonged high-temperature exposure (≳275 °C for 24 h) in air.
Atomic chlorine concentration and gas temperature measurements in a plasma etching reactor
Authors: Wormhoudt J. , Stanton A. C. , Richards A. D. , Sawin H. H.
Published: July 2002

The technique of diode laser absorption has been used to measure gas temperatures and atomic chlorine concentrations in a Cl2 glow discharge. The infrared transition used is between the 2P1/2←2P3/2 spin-orbit levels and occurs at 882.36 cm−1. The measured atomic chlorine translational temperature was 770±100 K, and was relatively independent of plasma conditions over the range studied. This temperature was confirmed by an analysis of the rotational band shape of nitrogen second-positive emission which yields a nitrogen rotational temperature. Measured atomic chlorine concentrations ranged from 1.8×1014 to 6.6×1014 cm−3, representing atomic chlorine fractions from 3% to 8%. Atomic chlorine concentration increased with both increasing discharge power and pressure.
Strain in self-implanted silicon
Authors: Chami A. C. , Ligeon E. , Danielou R. , Fontenille J. , Eymery R.
Published: July 2002

Direct measurements of perpendicular strain by channeling presented here show that self-implantations (50 keV at 20 K) at dose levels up to amorphization of silicon induce a uniaxial elongation of the lattice parameter. The maximum strain is proportional to the implanted dose up to the amorphous threshold, and the strain varies with depth as the nuclear energy distribution. The relation of such an elongation to the co-existence of disordered amorphous (clusters) and crystalline phases in the implanted layer is discussed.
PtSi contact metallurgy formed by three-temperature annealing sequences and short annealing time
Authors: Chang Chin-An , Segmüller Armin
Published: July 2002

PtSi contact metallurgy has been formed using a wide series of annealing sequences, employing the three-temperature scheme developed earlier but with much shorter annealing durations. Using either 200-300-550 °C or 200-300-450 °C schemes and a total annealing time between 20 and 40 min in forming gas (N2-H2 9:1), all the films show complete reaction between Pt and Si, a necessary condition for high-quality PtSi contact used in devices as determined from earlier studies. The films also show surface passivating oxide layers of good resistance against etching in aqua regia. The results obtained make the three-temperature process a promising one for the fabrication of devices containing PtSi contact metallurgy.
Anomalous magnetic properties of planar bibridged trinuclear copper(II)-halide compounds
Authors: Grigereit T. E. , Willett R. D.
Published: July 2002

The magnetic susceptibilities of five trinuclear pseudoplanar bibridged copper(II) chloride species have been measured from approximately 5 to 300 K. The compounds all show antiferromagnetic intratrimer and generally weaker ferromagnetic intertrimer spin coupling. These compounds show systematic deviations from the susceptibility as calculated from an isotropic Heisenberg Hamiltonian with nearest-neighbor coupling. The deviations arise from intertrimer interactions through the formation of semicoordinate bonds and result in a spin-frustrated state at low temperatures. The results of a phenomenological mean field theory model support spin-frustration occurrence by accurately modeling the non-Boltzmann depopulation of the excited quartet state. Preliminary cluster expansion calculations have not lent support to the postulate but more extended calculations may be necessary to include a sufficient number of intermolecular interactions in order to accurately describe the crystalline state.
Organic ferromagnets: New approaches and new experimental results (abstract)
Authors: Torrance J. B. , Oostra S. , Nazzal A. , Johannsen I. , Bechgaard K.
Published: July 2002

Different models and proposals are reviewed for synthesizing an organic ferromagnet, including a particularly simple and promising new model for making a solid containing ferromagnetically aligned organic radicals. A number of new experimental results are described and compared with these approaches. For example, new polymers based on s-triaminobenzene have been synthesized. These materials appear to show ferromagnetic interactions at room temperature and represent the first organic ferromagnet.
Magnetic investigation of a (Co,Zn)2 W-type hexaferrite (abstract)
Authors: Paoluzi A. , Turilli G. , Licci F. , Rinaldi S.
Published: July 2002

Single-crystal samples of cobalt-zinc W-type hexagonal oxides were flux grown and magnetically investigated over the temperature range 78–700 K. As it is well known cobalt has a large influence on the magnetocrytalline anisotropy of ferromagnetic oxides. With varying the Co concentration and the temperature, the easy direction of magnetization in this system changes from the basal plane to an easy and/or to an easy cone undergoing different spin reorientation transitions. In some cases one also observes first-order magnetization processes (FOMP).1 We will present the magnetic phase diagram of the system CoxZn2−x-W, 0≤x≤2, and the analysis of the magnetization curves, measured for different samples at various temperatures in terms of anisotropy constants up to the sixth order, in the usual power expansion for the anisotropy energy. Also the dependence on the composition of the Curie temperature and saturation magnetization will be reported. The results will be analyzed on the basis of a simple model2 which takes into account the competition between different sublattices anisotropies and exchange.
Effect of deposition parameters on rf sputtered CoZr and CoZrRe thin films for magnetic recording heads
Authors: Guzman J. I. , Kryder M. H.
Published: July 2002

It has been shown by Tago, Nishimura, and Yanagisawa [IEEE Trans. Magn. MAG-21, 2032 (1985)] that addition of small amounts of Re to CoZr produces material with zero magnetostriction. We have prepared CoZr and CoZrRe amorphous films by rf sputtering, producing alloys with soft magnetic characteristics suitable for use in thin-film recording heads. The dependence of coercivity, anisotropy field, and saturation magnetization on sputtering conditions and film composition has been characterized. Co93Zr7 films have been fabricated with 4πMs of 15 kG and Hc less than 0.4 Oe in the as-sputtered state. Similar results were obtained with Co92Zr6Re2 films. The films which exhibited the best soft magnetic properties were deposited at low target bias, 5-mTorr argon pressure, and zero substrate bias. Below 1500-V target bias, low anisotropy field was accompanied by a dispersion factor of up to 4° in CoZr and up to 9.5° in CoZrRe films. Coercivity and anisotropy field both increased with increasing target bias, whereas film dispersion decreased. These effects were accompanied by a decrease in Zr content in both CoZr and CoZrRe films of up to 5 at. % across the range of target biases. It is believed that, at bias greater than 2500 V, substrate heating was also significant in determining film characteristics. Increasing argon pressure increased the coercivity and anisotropy field, which is in agreement with previously published results for CoZr. Applying bias to the substrate also increased the coercivity and anisotropy field, producing films with undesirable magnetic properties. Trends and limitations of the deposition technique are analyzed and discussed.
Vector Preisach modeling
Authors: Wiesen Kurt , Charap S. H.
Published: July 2002

A vector hysteresis model for particulate media has been developed and applied to a two-dimensional, self-consistent simulation of the magnetic recording process. Vector modeling is accomplished using a scalar Preisach model recording process. Vector modeling is accomplished using a scalar Preisach model for each of the two perpendicular directions, with each model responding to the corresponding component of the applied field. The Preisach density function is factored to permit description of hysteretic behavior based solely on the major loop. Each scalar Preisach model is partially demagnetized by the corresponding perpendicular field component. This feature couples the models and provides a substantial degree of reversibility with respect to rotating applied fields. Vector model performance was tested by the degradation of the longitudinal remanent moment as a function of vertical applied field. This model has been successfully used in a recording simulation.
Ion exchange process for fabrication of waveguide couplers for fiber optic sensor applications
Authors: Honkanen S. , Tervonen A. , von Bagh H. , Leppihalme M.
Published: July 2002

Coupling elements for fiber optic vibration/displacement, backscattering, and backreflecting sensors have been fabricated by placing two separate waveguides on top of each other. The waveguides are fabricated by the Ag+-Na+ ion exchange using Ag films as ion sources. The ion exchange process is analyzed accurately in one dimension and approximately in two dimensions. The design considerations of the couplers and the properties of the fabricated waveguides are presented.
Generation of GW VHF power pulses with a magnetically swept e beam and inverse e beam diodes
Authors: Johnson D. J. , Lockner T. R. , Poukey J. W.
Published: July 2002

The concept of converting a multi-kA relativistic e beam into an ultrahigh-power rf pulse with a magnetically swept e-beam switch is studied. Two short VHF pulses are created by rapidly switching a 60-ns, 900-keV, 15-kA e beam between a pair of inverse e-beam diodes. The switching is done by a transverse 500-G, sinusoidal B field, oscillating at 50 MHz. The e-beam pulses are transported 1.6–4.6 cm in vacuum and ballistically or magnetically focused onto the collectors of the inverse diodes. The inverse diodes extract electrical energy from the deflected e-beam pulses and transport the energy to resistive loads that varied between 30 and 130 Ω. Numerical simulations of the e-beam transport with self-electric and magnetic fields are performed that show the sources of electrical inefficiency. These occur because the e beam is near the space-charge limit during transport. Peak unipolar powers of 2.0 and 0.5 GW are coupled to the resistive loads for the ballistically and magnetically transported e-beam geometries, respectively.
Analysis of molecular-beam epitaxially grown ZnSe on GaAs and GaP by means of ion channeling
Authors: Hishida Yuji , Yoneda Kiyoshi , Matsunami Noriaki , Itoh Noriaki
Published: July 2002

Structural disorder at the interface of molecular-beam epitaxially grown ZnSe layers on GaAs and GaP substrates has been investigated by means of the Rutherford backscattering channeling technique. For ZnSe layers grown on GaAs substrates, for which the lattice mismatch is only about 0.25%, high-quality ZnSe layers were obtained independent of the layer thickness with little increase in the minimum yield χmin at the interface. For ZnSe layers grown on GaP substrates, for which the lattice mismatch is about 4%, a disordered layer was found in the vicinity of the interface. The crystalline quality for ZnSe grown on GaP substrate was found to depend on the layer thickness; at a sufficiently great layer thickness, the crystallinity is comparable to the layers grown on GaAs substrates.
Field effect on thermal emission from the 0.85-eV hole level in GaP
Authors: Baber N. , Iqbal M. Zafar
Published: July 2002

Results on the measurements of electric field dependence of thermal emission of holes from the 0.85-eV level in liquid-phase-epitaxial GaP, using deep-level transient spectroscopy, are reported for various temperatures. The observed field dependence is analyzed in terms of Poole–Frenkel emission from the three-dimensional Coulomb and square-well potentials. The field effect is found to be too weak to account for the large spread in the published emission rate data on the 0.85-eV hole level in GaP necessitating a reappraisal of its hitherto presumed origin.
Absorption characteristics of CO2 molecules dissolved in ZrF4-based fluoride glass
Authors: Ohishi Yasutake
Published: July 2002

Absorption characteristics of CO2 molecules dissolved in ZrF4-based glass are measured using a Fourier transform spectral attenuation measurement system. Absorptions due to vibrational modes appear at 2353, 3606, and 3716 cm−1, respectively. The influence of the CO2 impurity on transmission loss is clarified. The interaction between dissolved CO2 molecules and the glass matrix is discussed on the basis of the measured spectra.
Time-of-flight x-ray photoconductivity of HgI2
Authors: Kurtz S. R. , Hughes R. C. , Ortale C. , Schnepple W. F.
Published: July 2002

Time-of-flight photoconductivity measurements were performed on HgI2 using a penetrating, pulsed x-ray source, simulating the operation of photoconductive x-ray detectors. By examining a variety of HgI2 samples, a wide range of electron and hole mobilities were observed, but in all cases hole transport was highly localized, limiting the collection of the photocarriers in HgI2 detectors. The intrinsic photocarrier generation and recombination processes differed from classical Onsager and Langevin mechanisms observed in low-mobility photoconductors.
Multichannel acceleration of intense, low-energy ion beams
Authors: Thomae R. W. , Siebenlist F. , van Amersfoort P. W. , Granneman E. H. A. , Klein H. , Schempp A. , Weis T.
Published: July 2002

We present measurements on multichannel acceleration of intense, low-energy ion beams with a multiple electrostatic quadrupole array linear accelerator. The beam properties are investigated for different transverse and longitudinal focusing strengths, which can be adjusted independently in the accelerator. A maximum He+ ion current of four times 2 mA has been accelerated from 40 to 115 keV with an acceleration efficiency of 50%. Measurements and computer simulations suggest that the current is limited by transverse fields and by mismatch and misalignment of the beams, whereas longitudinal fields are of minor importance. The energy spread in the bunches is roughly three times the gap voltage.
Nonlinear optical properties of the electron-hole plasma in Al0.52Ga0.48As
Authors: Kalt H. , Bohnert K. , Norwood D. P. , Boggess Thomas F. , Smirl Arthur L. , D’Haenens I. J.
Published: July 2002

A dense electron-hole plasma is created in Al0.52Ga0.48As using picosecond excitation with high excess energy. Its properties are studied by time-resolved photoluminescence and transient transmission spectroscopy. Simultaneous emission out of the indirect X and the direct Γ band is observed. Alloy disorder strongly influences the bimolecular recombination by allowing for quasidirect transitions and stimulated emission out of the indirect X band. The electron-hole plasma, whose electrons reside mainly in the X valleys, causes strong optical nonlinearities at the direct absorption edge. A persistent absorption bleaching and large induced refractive-index changes due to band filling of the valence band and induced absorption due to band-gap renormalization are observed.
Characterization of GaAs wafers and epilayers with electron-beam-induced current, etching, and reflected light
Authors: Partain L. D. , Dean S. M. , Berard B. L. , McLeod P. S. , Fraas L. M. , Cape J. A. , Sheldon P.
Published: July 2002

We have used a combination of electron-beam-induced current (EBIC), etching, and optical measurements to show dramatic differences between the minority-carrier transport properties and defect structures in GaAs wafers from two different vendors. We found that the EBIC defects correspond to the traditional ones found with molten KOH etching and optical inspection. However, the EBIC micrographs give a great deal of additional information. The EBIC patterns from the first vendor’s wafer showed diagonal striations and point defects that made the EBIC go to zero and were interconnected by wormlike lines. The second vendor’s wafers showed EBIC point defects that only suppressed the response by 20% and gettered the surrounding material so that it had higher EBIC response. However, this second vendor’s wafer had about a 15% overall lower EBIC response and a much higher density of surface polish defects identified by reflected light. Etching data showed that EBIC defects are bulk material properties and that electrochemical etching with a KOH electrolyte allows the wormlike defects to be seen optically in a Nomarski equipped microscope. Examination of epilayers showed that the wafer defects did not propagate up into a 4-μm-thick layer grown by vacuum chemical epitaxy or a 1.5-μm-thick layer grown by molecular-beam epitaxy.
Observation of a high-resistance to a low-resistance transition in a silicon bicrystal
Authors: Ling C. H.
Published: July 2002

The transition from a high-resistance to a low-resistance state has been observed in a silicon bicrystal. This phenomenon is attributed to the trapping of minority carriers at the grain-boundary interface states. In the low-resistance state, the dc resistance of different samples falls into a narrow range of values, and exhibits, in addition, a positive temperature coefficient.
Plasma-processed Ag/P4Se10 (80° deposited) films as a negative resist
Authors: Gupta P. K. , Chopra K. L.
Published: July 2002

Lithographic properties of Ag/P4Se10 (80° deposited) films exposed to photons and glow-discharge hydrogen plasma have been investigated. It has been observed that the etching rate of the exposed film is lower compared to the unexposed one, giving rise to a negative tone behavior of the material. The effect of exposure time on the etching rate and selectivity ratio has been studied. The contrast (γ) values obtained for the photoexposed and plasma-exposed negative resists are 2.9 and 5.1, respectively, with a photosensitivity of ∼1021 photons/cm2.
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u ellipsometry comparison of the nucleation and growth of sputtered and glow-discharge a-Si:H
Authors: Collins R. W. , Cavese J. M.
Published: July 2002

We report the results of ellipsometry measurements performed during the growth of hydrogenated amorphous silicon (a-Si:H) thin films on crystalline silicon substrates using ion beam sputtering. The data have been compared to our earlier results for high-quality a-Si:H prepared by glow-discharge decomposition of SiH4, and significant differences in the initial nucleation and microstructural evolution have been deduced for the two types of films. For the glow-discharge a-Si:H, the in situ pseudodielectric function data provided evidence for the convergence of initial growth microstructure in the first ∼50 Å, leaving a-Si:H of near bulk Si–Si bond-packing density at the interface to the c-Si substrate. After the nucleation process, growth was found to be nearly layer by layer. The data for the sputtered a-Si:H also reveal the formation of a low-density microstructure in the initial stages of growth. However, in contrast to the glow-discharge films, the microstructure does not converge, and an extensive layer (∼200–400 Å) of bond-packing density lower than the bulk is left at the interface to the substrate. The effect of hydrogen incorporation on this and other aspects of the microstructural evolution of the sputtered films is discussed. Finally, similarities observed between the microstructural evolution of the sputtered films and poorer-quality glow-discharge films provide insights into the growth mechanisms.
Beam-propagation model for stripe-geometry distributed-feedback lasers
Authors: Federighi Marco
Published: July 2002

The beam-propagation method is used to model the below threshold characteristics of stripe-geometry distributed-feedback lasers. Reflectivity is obtained as a function of frequency for various longitudinal structures, and it is shown that a simple analytical approximation can give a good description of the results. The numerical model includes antiguiding due to the carrier concentration as well as built-in lateral index guiding.
Multilevel construction of seeded-laterally epitaxial silicon films on insulator
Authors: Hamasaki T. , Inoue T. , Yoshimi M. , Yoshii T. , Tango H.
Published: July 2002

A new seed structure, partially thickened silicon films on insulator (PTS), is proposed for multilevel seeded-laterally epitaxial silicon films on insulator (SOI). Two-level seeded-laterally epitaxial silicon films on thick SiO2 (2.5 μm) were successfully fabricated, using the PTS structure in conjunction with the electron-beam technique. The SOI surface flatness after recrystallization was also improved by the PTS. Through computer simulation of the electron-beam recrystallization process, it is determined that the PTS structure enhances the lateral heat conduction within the SOI. This is important in smoothly melting the seed and field SOI regions.
Critical currents of ion-beam sputtered amorphous beryllium thin films and their application to an Abrikosov vortex memory
Authors: Okamoto Minoru , Takei Koji , Kubo Shugo , Mukaida Masashi , Miyahara Kazunori
Published: July 2002

Critical current and flux pinning were examined for ion-beam sputtered (IBS) amorphous beryllium (a-Be) thin films with Tc 6 K. Pinning forces in IBS a-Be films were one or more than one order of magnitude smaller than those for crystalline superconductors, but were still rather large for amorphous superconductors. The viscosity coefficient for IBS a-Be was very small, 1–2×10−9 N s/m2, which was only a few tenths as large as viscosity coefficients for other metallic superconductors. Write operation characteristics for Abrikosov vortex memory with an IBS a-Be vortex storage region was tested. The write current level was reduced to about two thirds of that for fine-grained PbInAu previously reported. IBS a-Be films were proved to be a potential material for use in an Abrikosov vortex memory.
Low-frequency Raman spectra in disordered cubic zirconia at elevated temperatures
Authors: Liu D. W. , Perry C. H. , Wang W. , Ingel R. P.
Published: July 2002

Rayleigh wing broadening (quasielastic scattering) was found at high temperatures (650–1500 K) in cubic zirconia single-crystal ZrO2 fully stabilized with Y2O3; however, broadening was not observed in the two-phased cubic plus tetragonal zirconia crystals. We believe this can be interpreted as a disorder-order transition as the configuration goes from single-phase cubic-to-cubic plus tetragonal structure with less addition of Y2O3. Theoretical agreements were achieved by utilizing ‘‘rigid ion model’’ and ‘‘decay model’’ calculations.
Thermal process models for the interpretation of microstructures formed during electron-beam surface melting
Authors: Tauqir A. , Strutt P. R. , Klemens P. G.
Published: July 2002

An analysis is presented of mechanisms involved in forming rapidly solidified surface layers on a substrate material by an electron beam. This can be achieved either by (i) point-source or by (ii) line-source melting. In mode (i) it is critical that minimal cooling occur between successive beam oscillations so as to avoid solid-state induced transformations where adjacent rapidly solidified zones overlap. In mode (ii) a linear heat source is formed by oscillating the beam sufficiently rapidly and moving this line source transversely over the surface to form a homogeneous rapidly solidified layer. The conditions for this to occur are mathematically predicted. A theoretical model yields the minimum oscillation frequency for this to occur. Under steady-state heat flow conditions the following features were studied: stability of the cavity, geometry of the melt zone, and rate of cooling during solidification. It is shown that a linear vapor cavity exists in mode (ii), provided the oscillation frequency of the beam exceeds a critical value, typically ≊250 Hz. The predicted cavity depth is shown to correspond to the depth of the turbulent flow region, as revealed by microstructural observations. The molten pool length is governed by the steady-state heat conduction requirements, whereas the depth is found to be empirically related to process parameters. Predicted values of the cooling rate are compared with those deduced from the microstructural scale and the solidification morphology for the case of a molybdenum high-speed steel (M7). Theoretical and experimentally obtained values are shown to be in good agreement.
Performance characteristics of a metal-vapor recombination laser
Authors: Khare Alika , Thareja R. K.
Published: July 2002

Laser oscillations of Cd-I transitions at 1.40, 1.43, and 1.65 μm based on an electron-ion-recombination pumping mechanism in a sealed discharge tube are reported. Performance characteristics of the 1.65-μm transition over a range of discharge parameters in the presence of a low-pressure helium-gas resonator axis are discussed. Studies are reported for the first time to authors’ knowledge.
Influence of deposition parameters on the properties of boron-doped amorphous silicon-carbide films
Authors: Ray Swati , Ganguly Gautam , Barua A. K.
Published: July 2002

The optoelectronic properties of p-type a-Si1−xCx:H deposited by glow-discharge decomposition have been studied at different deposition temperatures and with varying methane concentration. The optical band gap is found to increase at lower temperatures and with higher methane concentrations. Infrared transmittance spectra reveal that the increase is due to carbon and/or hydrogen incorporation. Electron-spin-resonance spectra have been analyzed to show that the dangling bond density increases with carbon content. Low-temperature deposited films are found to posess a large (∼1018 cm−3) trapped hole density, indicating a broad valence band tail. It has been found that for a band gap of about 2 eV the optoelectronic properties are similar for low- and high-temperature deposited samples.
Coupling of long wavelength bulk plasmons to surface polaritons
Authors: Gürsey Yusuf
Published: July 2002

The possibility of detecting long wavelength bulk plasmons through their linear coupling to surface polaritons is investigated. Impurity scattering is selected as the appropriate coupling mechanism. Using this mechanism, estimates are given for the parameters of various experimental setups that allow detection of stimulated plasmon emission.
Electromagnetic modes of a normally magnetized ferromagnetic slab
Authors: Ruppin R.
Published: July 2002

The dispersion relations of the long-wavelength retarded magnetic modes of a ferromagnetic slab magnetized perpendicular to its plane are derived. A comparison with the magnetostatic Damon–van de Vaart [J. Appl. Phys. 36, 3453 (1965)] modes is presented, and the parameters affecting the deviations of the magnetostatic modes from the exact ones are discussed. The theory is applied to a calculation of the ferromagnetic resonance lines of an yttrium iron garnet film.
Evidence of the origin of infrared scattering in GaAs with high-resolution infrared tomography
Authors: Suchet P. , Duseaux M. , Gillardin G. , Le Bris J. , Martin G. M.
Published: July 2002

Transmission electron microscopy and A-B etching are the usual methods to observe microprecipitates in GaAs substrates. More recently, tomography has been used to characterize GaAs wafers and infrared light scattering was assumed to be caused by microprecipitates. Work on high-resolution tomography which confirms this assumption is presented in this paper.
Channeling analysis of mismatch strain in heteroepitaxial CdTe on Cd0.96Zn0.04Te(001)
Authors: Chami A. C. , Ligeon E. , Fontenille J. , Danielou R.
Published: July 2002

Channeling is used to study how the lattice mismatch between CdTe layers grown by molecular-beam epitaxy on Cd0.96Zn0.04Te(001) is accommodated. Planar channeling allows us to determine the tetragonal distortion of the cubic lattice for layer thicknesses lower than the 300-nm critical thickness. Above 300 nm, planar channeling reveals misfit dislocations at the interface. A discussion of absolute strain measurement by channeling is presented.
Comparison of electrical defects in Ge+ and Si+ preamorphized BF2-implanted silicon
Authors: Ayres J. R. , Brotherton S. D. , Clegg J. B. , Gill A.
Published: July 2002

Silicon diode structures have been amorphized with 200-keV Ge+ prior to BF2 implantation. Room temperature C-V profiling revealed large concentrations of excess donor levels following epitaxial regrowth at temperatures below 800 °C. This donor formation and the annealing behavior is the same as previously observed in Si+ preamorphized substrates. Deep-level transient spectroscopy further confirmed the similarity in the nature and spatial distribution of the defects produced. The conclusion drawn is that the same fundamental damage-related defects are produced in the tail of the amorphizing implant in both cases. Large leakage current densities in the Ge+-amorphized diodes were attributed to the deep-level donors, and removal of these centers by annealing at 800 °C reduced the leakage current to ∼4×10−6 A/cm2. This current was assumed to arise from the crystallographic defects at the original amorphous/crystalline boundary which, at the ion implantation energies used, were within the zero-bias space-charge layer.
Electric arc explosions: A thermal paradox
Authors: Dragone Leon
Published: July 2002

The maximum pressures developed for electric arc explosions in water range as high as 50 000 atm. It was thought that these pressures were due to a sudden heating of the water to high temperatures with resulting, and equally sudden, high pressures. There are several reasons why this hypothesis is paradoxical, the main one being that temperatures of no less than 107 K would be required somewhere in the water arc. In this communication we discuss recent water arc explosions performed at the Massachusetts Institute of Technology. The unusual phenomena observed put these explosions in the category of experimental paradigm.
Statistical error analysis of electrode construction for electrostatic spline lenses
Authors: Szép J. , Szilagyi M.
Published: July 2002

It is easy to calculate approximately the electrode shapes for a given axial potential distribution by neglecting its high-order derivatives. The lens with the electrodes determined this way has different optical properties than that with the original axial potential distribution. These differences were calculated for a large number of randomly generated samples with axial potential distributions in the form of cubic splines. The differences were found to be about ±5%–10% for the focal lengths and the chromatic aberration coefficients. The spherical aberration coefficients for the constructed electrode systems usually have smaller values than those of the original lens models, but the differences are larger. The conclusion is that this simple electrode construction method is usually accurate enough for practical lens design.
Magnetic properties of amorphous Fe-Er-B-Si ribbons
Authors: Krishnan R. , Lassri H. , Rougier P.
Published: July 2002

We report on our magnetic studies of amorphous (Fe1−x Erx)80B12Si8 ribbons with 0<x<0.125 prepared by melt spinning. With the addition of Er, both magnetization and TC decrease. For instance, for x=0.125, the magnetization has fallen from the initial value of 175 to 108 emu g−1 and TC from 660 to 500 K. In-plane hysteresis loops show practically zero remanence and low coercivity of 1.0 Oe.
Titanium gettering in silicon: Investigation by deep level transient spectroscopy and secondary ion mass spectroscopy
Authors: Leo K. , Schindler R. , Knobloch J. , Voss B.
Published: July 2002

Extrinsic gettering of titanium in float-zone silicon was investigated. After heat treatments under various atmospheres the titanium concentration was determined in the bulk by deep level transient spectroscopy and in the surface region by secondary ion mass spectroscopy. The gettering is limited by the slow diffusion coefficient and by the ability of the surface to act as a sink. We show that an oxide layer, a phosphorous glass layer, and a surface damage zone are efficient sinks. A free surface, however, shows a very limited gettering action for titanium.
Effect of metal/P-doped a-Si:H junctions on the photovoltage of a-Si:H solar cells
Authors: Sakai Yuichi , Matsumura Michio , Nakato Yoshihiro , Tsubomura Hiroshi
Published: July 2002

The open-circuit photovoltages (Voc) of a-Si:H solar cells having a Glass/TCO/p-i-n a-Si:H/metal structure were examined as a function of the thickness of the n layer. The Voc stayed constant at ∼0.8 V, irrespective of the kind of metals, as far as the thickness of the n layer was larger than 15 nm, but dropped when the n layer got thinner. This effect was the stronger, the smaller the work function of the metal. The decrease of Voc is attributed to complete depletion of the n layer, leading to the reduction of the potential gradient in the i layer. The effects of the metal/P-doped a-Si:H junction were further investigated using cells having a Glass/TCO/n-i-n/metal structure and different doping concentrations for the latter n layer. The results obtained supported the above-mentioned conclusion.
Structural development during mechanical alloying of crystalline niobium and tin powders
Authors: Kim M. S. , Koch C. C.
Published: July 2002

The structural development with milling time during mechanical alloying of niobium and tin powders, of average composition Nb3Sn, was followed by x-ray diffraction. The elemental powders initially alloy mechanically to form an A15 structure phase. With continued milling, the A15 phase transforms to an amorphous structure. The kinetics of the structure changes are dependent on the milling media and atmosphere. The measured lattice parameter a0 for the A15 phase prepared with tungsten carbide milling media in an argon atmosphere agrees with the literature value of a0 for bulk Nb3Sn. However, milling with steel media introduced significant contamination by iron and an anamolous expansion of the A15 phase lattice. Amorphization of the A15 phase is believed to be due to the creation of a critical defect concentration by the mechanical deformation.
Fabrication and dc characteristics of small-area tantalum and niobium superconducting tunnel junctions
Authors: Face D. W. , Prober D. E.
Published: July 2002

We discuss the fabrication and dc electrical characteristics of small-area (1–6 μm2) superconducting tunnel junctions with Ta or Nb base electrodes and Pb or Pb0.9Bi0.1 counterelectrodes. These junctions have very small subgap leakage currents, a ‘‘sharp’’ current rise at the sum-gap voltage, and show strong quantum effects when used as microwave mixers. The use of a low-energy (∼150 eV) ion cleaning process and a novel step-defined fabrication process that eliminates photoresist processing after base electrode deposition are discussed. Tunnel barriers formed by dc glow discharge oxidation were the most successful. Tunnel barrier formation by thermal oxidation and ion-beam oxidation is also discussed. An oxidized Ta overlayer (∼7 nm thick) was found to improve the characteristics of Nb-based junctions. The electrical characteristics of junctions with different electrode and barrier materials are presented and discussed in terms of the physical mechanisms that lead to excess subgap current and to a width of the current rise at the sum-gap voltage.
Free-electron laser with electrostatic wiggler
Authors: Liu Shenggang , Cheng Xiaodong
Published: July 2002

A new free-electron laser (FEL) scheme, using a periodic electrostatic field superposed on an electrostatic centrifugal system, is presented. By means of linear fluid theory, the Raman FEL dispersion equation is derived. We show that there is a new FEL instability near the electron transverse resonance besides the usual one near the beam resonance. The operating conditions, emission frequencies, and maximum growth rates of these two kinds of instabilities are obtained analytically. It is found that these results are in quite good agreement with numerical solutions of the dispersion equation.
Effects of annealing on lifetime and deep-level photoluminescence in semi-insulating gallium arsenide
Authors: Haegel N. M. , Winnacker A. , Leo K. , Rühle W. W. , Gisdakis S.
Published: July 2002

The free-carrier lifetime and deep-level photoluminescence spectra have been measured in as-grown and a series of annealed samples of undoped semi-insulating GaAs. A strong increase in lifetime in the near-surface region is observed for annealed samples. The lifetime increases from τ=250 ps in as-grown materials to ∼2.5 ns after a 1-h anneal at 880 °C under AsH3. In contrast, lifetime in the bulk material increases only slightly. A clear correlation is found to exist between the lifetime increases and the decrease of the midgap defects responsible for the broad photoluminescence peaks at 0.68 and 0.80 eV.
A proposed mechanism for radiative recombination through surface states on InP
Authors: Lester S. D. , Kim T. S. , Streetman B. G.
Published: July 2002

Recombination involving radiative surface states on InP has been studied in detail by low-temperature photoluminescence. A variety of surface treatments, including etching in HF-based solutions, is found to give rise to a luminescence band located between 1.1 and 1.4 eV, depending on bulk properties of the sample. A model is presented which attributes this emission band to recombination from the bulk conduction band and bulk neutral donors to surface states distributed from the valence band to at least 300 meV into the band gap. The peak emission energy depends on the occupancy of these surface states and is governed by the position of the quasi-Fermi level for holes at the surface. This model is shown to account for the properties of this luminescence band as a function of temperature, excitation power density, and substrate doping type.
Annealing and oxidation behavior of low-pressure chemical vapor deposited tungsten slicide layers on polycrystalline silicon gates
Authors: Sadana D. K. , Morgan A. E. , Norcott M. H. , Naik S.
Published: July 2002

A WSix≊2.6 film was deposited by low-pressure chemical vapor deposition at 350–420 °C onto a P-doped polycrystalline silicon/SiO2/Si substrate. This polycide structure (with or without a subsequent As+ source/drain implant) was heat treated in the following manner: (i) 1000 °C/N2 anneal for 20 min, (ii) oxidation both in dry oxygen and in steam ambients at 920–950 °C (50 min–8 h), and (iii) N2 anneal as well as dry oxidation at 920 °C/50 min. Cross-sectional transmission electron microscopy, Rutherford backscattering, secondary ion mass spectrometry, and sheet resistance measurements were used for characterization. The as-deposited film was mostly amorphous with a fine grain structure. The N2 anneal caused the formation of a polycrystalline WSix>2 film containing tetragonal WSi2. Dry oxidation produced a void-containing SiO2 layer atop the silicide film. However, the SiO2 layer was impregnated with W particles when the silicide film was steam oxidized. The role of excess Si in refractory metal silicide films during annealing and oxidation is discussed. The effect of stress at the corners of a step in a patterned wafer during the oxidation of tungsten polycide is also demonstrated.
Thermal nitridation of SiOxHy films
Authors: Habraken F. H. P. M. , Geerlings E. L. J. , Tijhaar R. H. G. , Slomp A. , van der Weg W. F.
Published: July 2002

The paper describes a study of the thermal nitridation of SiOxHy thin films deposited in a low-pressure chemical vapor deposition process. It is shown that films with an O/Si concentration ratio of about 1 are readily nitrided over a thickness of 20 nm, whereas films with an O/Si ratio of 0.4 take up nitrogen in a thin surface layer only. At higher temperatures oxygen escapes from the film in measurable quantities, notably in the films with O/Si=1.
Electrical behavior of a Blumlein-line N2 laser
Authors: Persephonis P.
Published: July 2002

The electrical circuit of a Blumlein-line N2 laser was studied theoretically and experimentally. The experimental data confirm the theoretical results and lead to calculation of the inductance and resistance of the ignition system and laser tube, respectively. A sufficient number of ions in the laser tube before the breakdown secures the stability of the light pulses. Therefore, the increase of the efficiency of the system was discussed. The inductances of the ignition system and the laser tube play a determinative role in the best performance of the system. Finally, the increase of the light output by converting the double line to a quadruple one is attributed to the putting of higher electrical energy into the laser tube and for a proper time duration.
Intervalley scattering observed in an AlGaAs/GaAs hot-electron transistor
Authors: Hase I. , Kawai H. , Imanaga S. , Kaneko K. , Watanabe N.
Published: July 2002

Electron transfer into the L and X bands of GaAs is observed in the dependence of transfer ratio α (collector current Ic/emitter current Ie) of an AlGaAs/GaAs hot-electron transistor upon emitter-base voltage Veb. The α-Veb curve and its variation with temperature change confirms the idea that electron transfer to the higher bands randomizes the electron motion and is effective in reducing α. The differential transfer ratio Δα (dIc/dIe) shows double peaks and a clear shoulder. The lower-energy peak may indicate the onset of elastic intervalley scattering.
High-density magnetic recording: Theory and practical considerations
Authors: Eiling A.
Published: July 2002

The final system performance of a magnetic medium is dependent on a complex interaction of a number of parameters. Because of these interactions using an experimental approach to study the effects on system performance by varying a single parameter is almost impossible. This paper proposes the use of a theoretical investigation to quantify the importance of various parameters of the medium and the hardware for magnetic recording. The calculations are performed by means of a newly developed theory with special emphasis on high-density media.
Positron annihilation in zeolite 13X
Authors: Habrowska A. M. , Popiel E. S.
Published: July 2002

Results presented in previous papers on positron annihilation in zeolite 13X referred only to fully hydrated or dehydrated samples. In these investigations the dehydration process was studied based on measurements of positron lifetime spectra in zeolite 13X samples. All spectra were resolved into three or four components. Measurements show that water removal is most intensive at the beginning of pumping. For dehydration at higher temperature results suggest that the last molecules of ‘‘zeolitic water’’ are removed from the sample at a temperature of about 200 °C. It was found that independent of the stage of dehydration of the sample the intensity (I3+I4) of the two longest components in the spectrum is virtually constant (24%) and is equal to the intensity I3 of the longest component for the fully hydrated sample.
Effects of electron beam injection on ethylene-air combustion
Authors: Gilgenbach R. M. , Bidwell S. W. , Bosch R. A. , Brake M. L. , Tucker J. E. , Repetti T. E. , Sell J. A.
Published: July 2002

Results are presented of the first experiments in which high-current electron beam injection is shown to modify the combustion of both lean and rich ethylene-air mixtures. The rate of pressure rise in the chamber increases by up to a factor of 2 and flame speed increases by 40%–50% for cases in which an electron beam is injected into a spark-ignited nonstoichiometric ethylene-air mixture. Spectroscopic emission from the flame is modified by electron beam injection with more rapid rise and decay of OH line emission. Further research is needed to identify the cause of the observed enhancement in combustion rate.