bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation of intermediate phases, Ni3Si2 and Pt6Si5: Nucleation, identification, and resistivity
Authors: Gas P. , d’Heurle F. M. , LeGoues F. K. , La Placa S. J.
Published: July 2002

The formation of Ni3Si2 from the reaction of Ni2Si with NiSi, and that of Pt6Si5 from the reaction of Pt2Si with PtSi have been investigated by Rutherford backscattering, x-ray diffraction, resistance measurements, and optical and electronic microscopy. Standard x-ray diffraction patterns were calculated for Pt6Si5 and for the high-temperature form (hexagonal) of Pt2Si. These are shown to match experimental diffraction patterns. Both Ni3Si2 and Pt6Si5 form quite suddenly (at 470 and 535 °C, respectively) according to the pattern of nucleation-controlled reactions which are anticipated when the free energies of formation of the new phases are sufficiently small. These observations are discussed with respect to the absence of both Ni3Si2 and Pt6Si5 from the sequence of phases which form when Ni and Pt thin films react with Si. Resistivity measurements are reported for Ni3Si2, Pt6Si5, and for the two forms (low and high temperature) of Pt2Si.
Influence of thickness on the galvanomagnetic properties of thin InSb films for highly sensitive magnetoresistance elements
Authors: Isai Masaaki , Fukunaka Toshiaki , Ohshita Masahide
Published: July 2002

Thin InSb films were prepared on mica substrates by evaporation of InSb to obtain highly sensitive magnetoresistance (MR) elements with high element resistance. The MR effect was investigated for elements with a thickness range of 0.15–0.5 μm. It was observed that only the 0.15-μm-thick InSb film consists of a p-type, [111]-oriented single crystal, while the films thicker than 0.2 μm show n-type conduction. At room temperature, in a magnetic field of 1 T, the n-type films with thicknesses of 0.2, 0.3, and 0.5 μm and length-to-width ratios of 0.12, 0.09, and 0.05, were found to have increasing mobilities of 2.2, 4.4, and 5.0 m2/V s, decreasing element resistances of 115, 44, and 16 Ω, and increasing MR(ΔR/R0) values of 394, 652, and 800%. Measurements of the temperature dependence of μ show that 0.15–0.3-μm-thick films have a small temperature coefficient of MR values at room temperature because μ peaks near that temperature. The 0.15–0.3-μm-thick InSb films are therefore most useful for low-cost MR elements because of their high element resistance, small temperature coefficient of electron mobility, and high sensitivity.
Saturation of the superconductor quasiparticle direct radiation detector
Authors: Feldman M. J.
Published: July 2002

The saturation properties of the superconductor-insulator-superconductor (SIS) direct detector are calculated. It is shown that this device begins to saturate only at powers far larger than one would expect from a simple analogy with the SIS mixer. Since the SIS direct detector is known to have very low noise, this result should lead to its immediate practical exploitation for direct detection of millimeter wavelength radiation.
Arsenic passivation of InP surface for metal-insulator-semiconductor devices based on both ultra-high vacuum technique and chemical procedure
Authors: Chave J. , Choujaa A. , Santinelli C. , Blanchet R. , Viktorovitch P.
Published: July 2002

Two passivation treatments of InP surface are presented: (i) thermal treatment under an arsenic partial pressure by molecular-beam epitaxy technique, and (ii) a new As-based aqueous chemical treatment. Both result in similarly improved electronic and physicochemical properties of the InP surface. The fast interface state density is reduced, the drift phenomena are practically suppressed and the thermal stability is greatly enhanced.
Study on recorded domain characteristics of magneto-optical TbFeCo disks
Authors: Takahashi Masahiko , Niihara Toshio , Ohta Norio
Published: July 2002

Domain characteristics (size and shape) of TbFeCo disks of several compositions are studied systematically through direct optical observation under various recording conditions. The relationships among recorded domains, magnetic properties, and recording conditions are also investigated. Magnetic films suitable for very high-density recording are found to have a compensation temperature between room temperature and 100 °C and a Curie temperature near 200 °C. In those films, the formation of domains is stable against fluctuations in laser power and external field. These results can be explained by a simple domain formation model in which coercive force, demagnetizing field, and wall energy at the domain wall are taken into account. Teardroplike domains are observed in the case of relatively long laser pulse recording. Such domains cause detection errors during the domain edge detection. It is also found that recording noise is high under certain recording conditions. The origin of this noise is supposed to be caused by inversely magnetized regions existing in a domain and irregularities in the outline of domains.
Electron trapping and detrapping in thermally nitrided silicon dioxide
Authors: Ramesh K. , Chandorkar A. N. , Vasi J.
Published: July 2002

Thermal nitridation of SiO2 was carried out at 25% and 40% of NH3 for various times and temperatures. Flat-band voltage and interface-state densities were studied as a function of processing conditions. Avalanche injection was used to study electron trapping. The density of electron traps in nitrided oxides depended on the nitridation conditions in the same way as the negative flat-band voltage (positive voltage). A consistent model for negative flat-band voltage and electron traps is presented to explain the results obtained. Thermal emission of trapped electrons dominates the detrapping mechanism. Energy depths of these traps were found to be 1.3–1.6 eV.
Ultraviolet-laser photolysis of disilane
Authors: Muranaka Y. , Motooka T. , Lubben D. , Greene J. E.
Published: July 2002

A combination of optical probing techniques, including time-resolved emission spectroscopy, dye-laser absorption spectroscopy, laser-induced fluorescence, and intracavity laser spectroscopy (ILS), have been used to investigate the reaction paths for the ArF excimer laser (193 nm, 6.4 eV/photon) photolysis of disilane, Si2H6. The experiments were carried out in an ultrahigh vacuum system into which Si2H6 was introduced at pressures ranging from 1 to 10 mTorr. Optical emission due to the Si 1P→1S and SiH A2Δ→X2Π transitions was observed with intensity rise times, following the laser pulse, of less than 100 ns, the experimental resolution. This indicates that for the pressures used in these experiments, Si and SiH were generated purely photolytically rather than through collisional processes. The maximum intensities of the Si and SiH peaks were measured as a function of ArF laser-beam photon flux density Jhν. SiH2 was never detected, up to the highest Jhν values used, 4×1017 photons/cm2 pulse, even though with ILS, the most sensitive of the optical-absorption techniques, we were able to detect absorption peaks assignable to rotational transitions in the (020)–(000) vibronic bands of the Ã 1B1←X̃ 1A1 electronic transition during Si2H6 pyrolysis at ∼350 °C. Based upon these experimental results, a model for the ultraviolet-laser photolysis of Si2H6 was developed involving a three-step cascade one-photon absorption process.
p-n junctions from sputtered Ge25Se75−xBix films
Authors: Kounavis P. , Mytilineou E. , Roilos M.
Published: July 2002

The preparation and study of p-n junctions from amorphous chalcogenide GeSe3 sputtered films doped with Bi are presented. The p-type layer is Ge25.2Se68.3Bi6.5 and the n-type layer is Ge23.9Se65.8Bi10.3. The I-V characteristic in the dark exhibits a ‘‘relaxation case’’ behavior that is expected for low-conductivity amorphous semiconductors. J-V characteristics under illumination and the spectral response of the open circuit voltage Voc were also measured. The reverse current under illumination shows no saturation with voltage, while the Voc saturates at high light intensities.
Structural and soft-magnetic properties of Fe/CoNbZr and Fe/FeCrB multilayers
Authors: Dirne F. W. A. , Tolboom J. A. M. , de Wit H. J. , Witmer C. H. M.
Published: July 2002

The magnetic and structural properties of ion-beam-sputtered Fe/FeCrB and Fe/CoNbZr multilayers were studied as a function of the FeCrB and CoNbZr layer thicknesses. Good soft-magnetic properties (coercivity <60 A/m and permeability >1000) are obtained only when Fe grains are small, which requires, on the one hand, multilayers with Fe layer thicknesses below 10 nm and, on the other hand, FeCrB interlayers with thicknesses above 1 nm or CoNbZr interlayers with thicknesses above 3 nm. In this case interlayers are amorphous, which induces repeated nucleation of Fe grains. Only at FeCrB thicknesses of 1 nm are the interlayers crystalline due to interface mixing. This in contrast to CoNbZr interlayers which in addition grow epitaxially in a crystalline structure up to thicknesses of 3 nm. When interlayers are crystalline columnar growth of Fe results. As a consequence coercivity increases and permeability decreases.
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u conductivity and Hall measurements of ultrathin nickel silicide layers on silicon(111)
Authors: Jentzsch F. , Froitzheim H. , Theile R.
Published: July 2002

The change of conductance has been measured during deposition of Ni on Si(111) under ultrahigh vacuum (UHV) conditions for the first time. The chemical as well as the structural analysis were carried out in situ by Auger electron spectroscopy and low-energy electron diffraction. Defined information on the reaction and ordering processes induced by thermal processing was obtained from in situ conductivity and Hall measurements carried out in the temperature range between 16 and 500 K. The measurements were performed in a specially designed UHV system.
Nitriding of stainless steel in an rf plasma
Authors: Szasz A. , Fabian D. J. , Hendry A. , Szaszne-Csih Z.
Published: July 2002

Treatment of stainless steels in an rf-powered nitrogen plasma achieves a much increased rate of nitriding, as well as higher hardness and corrosion resistance than traditional nitriding. Small amounts of adsorbed hydrogen are found to be necessary initially, and the process of nitriding is modeled on the basis of this hydrogen increasing the surface sticking coefficient for nitrogen, which is followed by nitrogen diffusion into bulk in the form of nitrogen-vacancy (weakly bound) pairs. The detailed microstructural role of chromium in the process is also discussed.
Dendritic crystal regrowth and electrical properties of InSb thin films prepared by vacuum evaporation
Authors: Okimura H. , Matsumae T. , Ohshita M.
Published: July 2002

InSb thin films were evaporated and deposited on mica substrates by a simple vacuum evaporation method. A recrystallization of the deposit was observed at the last stage of the thin-film deposition. The recrystallization showed a dendritic crystal regrowth and the recrystallized area obtained one order of magnitude higher electron mobility than that of the as-deposited area. The maximum electron mobility obtained at room temperature was 6.0×104 cm2 /V s with impurity concentration of 5.8×1015 cm−3 . The crystal regrowth was found to be due to the melting-solidification process through the vapor-liquid-solid mechanism.
Scattering rates for holes near the valence-band edge in semiconductors
Authors: Brudevoll T. , Fjeldly T. A. , Baek J. , Shur M. S.
Published: July 2002

In this paper, we discuss and compare the rates for dominant scattering mechanisms for holes in semiconductors, including ionized impurity scattering, polar and nonpolar optical-phonon scattering, and inelastic acoustic deformation potential scattering. The scattering rates for these mechanisms have been reviewed for the purpose of finding reliable expressions to be used in Monte Carlo simulation of hole transport in p-type III-V semiconductor devices. In the scarce literature on hole scattering rates, we have found several discrepancies. Here, we present corrected rates for ionized impurity scattering and for scattering by polar optical phonons. In addition, we have derived new expressions for the inelastic acoustic deformation potential scattering rates where we also have included a series expansion for the phonon occupation number, beyond the equipartition approximation.
Effective conductivity of two-phase materials consisting of long parallel cylinders
Authors: Chiew Yee C.
Published: July 2002

The effective conductivity σe of a dispersion of long, parallel cylinders (or two-dimensional systems), distributed in a second continuous matrix phase, is determined as a function of its microscopic structure. We obtained an expression for the effective conductivity of two-dimensional systems (based on an approximate scheme) that includes the one-body and two-body terms in the cluster expansion for σe. The effective conductivities of two-dimensional hard disks and square-well particles are computed. It is found that this expression yields excellent estimates for the effective conductivity over a wide range of cylinder volume fractions, and for cases in which the cylinder to matrix phase conductivity ratios are high.
X-ray tomography of hot electrons in the barrier region of the tandem mirror GAMMA 10
Authors: Kondoh T. , Cho T. , Hirata M. , Yamaguchi N. , Saito T. , Kiwamoto Y. , Miyoshi S.
Published: July 2002

Tomographic reconstructions of x-ray emission from hot electrons have been carried out in the thermal barrier region of the GAMMA 10 plasmas. Here, the first application of two sets of the 50-channel microchannel plates have been performed using their detailed calibration data as a function of x-ray energy and incident angle [Rev. Sci. Instrum. 59, 256 (1988); 59, 2453 (1988); 60, 368 (1989)]. The x-ray reconstructed signals under standard thermal barrier operating conditions indicate a good axisymmetric radial profile peaked on the magnetic axis. This symmetric profile is important for preventing the formation of a local anisotropic electric field, which may cause particle confinement degradation, and its peaking profile is desirable for thermal barrier potential formation in the core plasma region. When we have relocated the second-harmonic electron cyclotron layers (ω=2Ωe) in two different ways (moving them out radially, or axially away from the midplane), tomographic reconstructions show hollow x-ray profiles in both cases. These may be formed due to the E×B rotations of the hot electrons produced near ω=2Ωe . These applications of x-ray tomography to two-dimensional radial profile observations along with the axial x-ray profile measurement give information that the production mechanism of these hot electrons is ascribed to second-harmonic electron cyclotron heating.
The radiation of low-pressure Hg-Ar discharges in tubes of small diameters
Authors: Anderer P.
Published: July 2002

For low-pressure Hg-Ar discharges line intensities of UV and visible radiation have been measured for tube diameters of 36, 22.8, and 9.5 mm and for different Hg densities and currents. A computer-controlled experiment was used for angularly resolved measurements. For 36-mm tube diameter the measured angular intensity distribution agrees well with published results. For tubes with 9.5-mm diameter the maximum emission of the 254- and 436 nm radiation is reached at a coldest spot temperature of about 45 °C for a lamp current of 200 mA. The ratio of visible to UV radiation becomes larger for smaller diameters which can be important for lamp applications. Increasing the lamp current from 200 to 600 mA leads to saturation effects in the radiation. A further increase to 1 A changes remarkably the measured angular intensity distribution. This indicates that for higher currents a broader radial radiation profile is present and/or an increased trapping especially of the visible radiation. The total radiated power of the discharge column and the intensity normal to the emitting surface are correlated by the Koedam factor β. The investigation shows that this factor is constant within certain parameter ranges but can change drastically, e.g., for tubes having a very small diameter of 2 mm.
Oxygen atom actinometry reinvestigated: Comparison with absolute measurements by resonance absorption at 130 nm
Authors: Booth J. P. , Joubert O. , Pelletier J. , Sadeghi N.
Published: July 2002

Resonance absorption at 130 nm was used to measure absolute oxygen atom concentrations in O2-containing distributed electron cyclotron resonance plasmas. The dissociation fraction [O]/[O2] in pure O2 plasmas (1–6 mTorr) was in the range 0.01–0.06, but was significantly increased by the addition of SF6, N2 or Kr. At 2 mTorr total pressure a maximum [O]/[O2] of 0.3 was observed for 10% SF6 added. The results were compared to those obtained by optical emission actinometry measurements. The quantity I0 (844 nm)/IAr (750 nm) (with 0.1 mTorr Ar added) was poorly correlated with [O] but well correlated with [O2]. This suggests that, for dissociation fractions lower than 0.1, dissociative excitation, O2+e→O*(3p 3P)+O, is the most important mechanism for the production of 844 nm emission.
Transport characteristics of AlGaAs/GaAs wires fabricated by focused Ga-ion-beam implantation
Authors: Nakata S. , Hirayama Y. , Tarucha S. , Horikoshi Y.
Published: July 2002

Electron transport was studied in AlGaAs/GaAs wires fabricated using focused Ga-ion-beam implantation. Single-wire samples 0.2–10 μm wide and 20 μm long were prepared with various ion doses ranging 2×1011–4×1012 cm−2; multiple-wire samples 0.1–0.3 μm wide and 10 μm long were prepared with an ion dose of 2×1011 cm−2. Electron mobility is reduced in the narrow wires because of the implantation-induced damage, and this mobility degradation is diminished by reducing the ion dose. These behaviors are consistently explained in terms of a diffusive scattering effect inside the channel and at the sidewall of the channel. Mobility in wires with the 2×1011 cm−2 ions is predominantly determined by the sidewall specularity. A 0.2-μm-wide wire with this ion dose exhibits a mobility of 2×105 cm2/(V s) and a specularity above 0.8. These values exceed those previously reported for wires fabricated using ion implantation and probably arise from the annealing employed in the present work. Conductance steps are observed with a single 0.2-μm-wide wire, and enhanced transconductance steps occur in multiple-wire samples. These behaviors are related to mobility modulation that occurs when one-dimensional subbands cross the Fermi level.
Refractive index and elastic properties of single-crystal corundum (α-Al2O3) up to 2100 K
Authors: Zouboulis E. S. , Grimsditch M.
Published: July 2002

We show that Brillouin scattering can be used to measure the elastic and optical properties of materials to very high temperatures. We have measured the elastic constants C11, C33, and C44 of single-crystal sapphire in the temperature range 300–2100 K extending by 300 K the highest temperature previously attained with ultrasonic resonance techniques. The temperature dependence of the ordinary and extraordinary refractive indices no and ne in the same temperature range have been obtained for the first time. Although both no and ne are temperature dependent, the ratio no/ne is found to be almost temperature independent.
Defects production and annealing in self-implanted Si
Authors: Bai G. , Nicolet M.-A.
Published: July 2002

230-keV 28Si ions were implantated into Si(100) at room temperature with doses from 1014 to 1015/cm2. The samples were analyzed by x-ray double crystal diffractometry and 2-MeV 4He ion channeling spectrometry. The implanted layer has a parallel lattice spacing equal to that of the unimplanted substrate. The perpendicular lattice spacing is larger than that of the unimplanted substrate and is proportional to the defect concentration extracted from the channeling measurement. Both the perpendicular lattice spacing and the defect concentration increase nonlinearly with ion dose. The defect concentration initially increases slowly with dose until a critical value (∼15%, at 4×1014/cm2), then rises rapidly, and finally a continuous amorphous layer forms. The initial sluggish increase of the damage is due to the considerable recombination of point defects at room temperature. The rapid growth of the defect concentration is attributed to the reduction of the threshold energy for atomic displacement in a predamaged crystal. The amorphization is envisioned as a cooperative process initiated by a spontaneous collapse of heavily damaged crystalline regions. The annealing behavior of the damaged layer reveals various stages of defect recovery, indicating that the damage consists of a hierarchy of various defect structures of vacancy and interstitial aggregates.
Use of MeV O+ ion implantation for isolation of GaAs/AlGaAs heterojunction bipolar transistors
Authors: Pearton S. J. , Ren F. , Lothian J. R. , Fullowan T. R. , Katz A. , Wisk P. W. , Abernathy C. R. , Kopf R. F. , Elliman R. G. , Ridgway M. C. , Jagadish C. , Williams J. S.
Published: July 2002

The implant isolation characteristics of highly doped n- and p-type GaAs epitaxial layers implanted with 5 MeV O+ ions are reported. High (∼108 Ω/⧠) sheet resistances are obtained in such layers following annealing at 550–600 °C for ion doses around 1015 cm−2. The residual conductivity is still due to hopping processes with small activation (50–70 meV) energies. The use of a single MeV O+ implant considerably simplifies the isolation of GaAs/AlGaAs heterojunction bipolar transistor (HBT) structures relative to the usual multiple-implant keV energy scheme. Small geometry (2×5 μm2) HBTs with gains of 25 for highly-doped (p=7×1019 cm−3) base layer structures have been fabricated using MeV implant isolation.
Nonradiative energy-transfer processes in Cd1−xMnxF2 crystals
Authors: Suchocki Andrzej , Kalinski Zbigniew , Langer Jerzy M. , Powell Richard C.
Published: July 2002

The absorption and fluorescence spectra and fluorescence decay kinetics of Cd1−x MnxF2 crystals with x=0.018, 0.063, 0.084, 0.26 were measured as a function of temperature under argon-ion and nitrogen laser excitation. In addition, laser-induced grating measurements were made as a function of write beam crossing angle for various temperatures between 15 and 50 K. It was found that a characteristic intrashell luminescence comes from two Mn subsystems, one composed of single Mn2+ ions and the second of Mn ion aggregates. Based upon the four-wave-mixing experiment, a relatively strong energy migration was found in each of these subsystems, but with a weak, if any, communication between them. The diffusion coefficients for both subsystems increase as the temperature is raised, and above 50 K strong diffusion erases the light-induced gratings beyond the possibility of detection. The long-lived components of the four-wave-mixing transient signals are associated with the other point defects, either created or photoexcited by the strong laser beams.
Negative ion assisted preionization for excimer lasers
Authors: Osborne M. R. , Green J. M.
Published: July 2002

This article describes a novel preionization technique, negative ion assisted preionization (NIAP), in which electrons liberated from a reservoir of negative halide ions by photoionization are used to provide preionization for excimer lasers. The NIAP technique is shown to be capable of greatly reducing the technologically demanding requirements associated with conventional flash preionizers, a factor of particular importance for the high average power laser systems currently under development. The efficiency of the NIAP scheme is described with reference to both experimental measurements of the ion reservoir lifetime, which are found to agree with theoretical models, and to theoretical predictions of the electron liberation efficiency, which are found to differ significantly from some previous treatments. The wide range of possible implementations of the NIAP technique is split into three operational regimes that have quite different characteristics. The benefits of improved preionization control and reduced ionization source intensity requirements are described for each regime. The practical limitations of the technique are discussed, and two experimental demonstrations are presented.
Stark broadening of the 690.7 nm mercury line in high-pressure mercury discharges
Authors: Asselman A. , Aubès M. , Couris S. , Salon J.
Published: July 2002

We report on a method of electron densities determination in high-pressure mercury discharges by using the width of the 690.7 nm mercury line which is very sensitive to charged particles. We reproduce the line profile emitted from a high-pressure mercury discharge by a model based upon the impact approximation and propose a formula giving electron densities as a function of the 690.7 nm line width; we also show a small dependence of the line width on the neutral densities.
Critical layer thicknesses for inclined dislocation stability in multilayer structures
Authors: Feng Xiaoxin , Hirth J. P.
Published: July 2002

The critical thickness for stability of dislocations on glide planes inclined to the interfaces in a strained-layer structure is derived. Results are presented for both a single embedded layer and a multilayer structure (superlattice). Both the equilibrium array for the complete removal of coherency strain and less-dense arrays are considered. Results are compared with the previous treatment of Lomer misfit dislocations and with other treatments of multiple dislocation arrays.
Spectroscopic study of cataphoresis in He-Cd mixtures: Cd source-anode region
Authors: Mizeraczyk J. , Carlsson C. , Hård S.
Published: July 2002

The results of measurements of the axial distributions of the Cd 479.9 nm, Cd+ 441.6 nm, and He 447.2 nm line intensities as a result of cataphoresis in a He-Cd capillary positive column (3 mm diam) between the Cd source, placed at the cathode side, and the anode are presented. The measurements were carried out using optical scanning along the positive column. The measuring procedure also allowed the Cd atom density distributions along the positive column to be determined. It is found that the He-Cd positive column divides into three regions: the seemingly uniform, blue-colored cadmiumlike discharge region, the whitish transition region, and the orange heliumlike discharge region. The Cd atom density decreases linearly from the Cd source towards the anode in the cadmiumlike discharge region of the positive column. In the transition region the Cd atom density decreases quasiexponentially, extending its tail into the heliumlike discharge region. The very tail of the Cd atom density distribution found in the heliumlike region is perhaps not real. Instead it could be due to misinterpretation of scattered background light for fluorescence light. This ambiguity makes it impossible to draw any definite conclusion about the ability of cataphoresis to confine the Cd vapor at the cathode side of the positive column. It is found that particularly the linear but also the quasiexponential decrease of the Cd atom density, occurring in the He-Cd positive column, are in good agreement with Druyvesteyn’s theory [Physica 2, 255 (1935)]. The slope of the Cd atom density distribution curve in its linear part was found to be proportional to the product of the discharge current and He pressure, whereas in its quasiexponential part it first increases and then saturates with increasing discharge current and He pressure. The results obtained can be used for estimating the so-called cataphoretic confinement section length for the positive column and hollow-cathode discharge He-Cd+ lasers, as well as for other ion He–metal-vapor lasers. The features of cataphoresis in the He-Cd positive column found also seem to be characteristic of cataphoresis in other binary gas mixtures.
Development of wall-stabilized z discharges for intense ion-beam transport in inertial confinement fusion facilities
Authors: Hinshelwood David
Published: July 2002

The wall-stabilized z discharge has been scaled successfully to the parameters required for a light-ion-beam-driven inertial confinement fusion facility. The electrical behavior of discharges with various gas species, pressures, lengths, and currents has been investigated. These investigations identify the required dielectric strength of the discharge channel wall. A low-mass, low-Z wall construction with sufficient dielectric strength is demonstrated. The discharge internal dynamics have been studied using temporal and imaging interferometry, framing photography, magnetic-field measurement, and spectroscopy. The discharge current radial profile, and its dependence on discharge parameters, has been diagnosed. The discharge consists of a magnetohydrodynamically stable, imploding thick annulus. The observed radial profile explains data from previous transport experiments. Contamination of the discharge by wall material is found to be negligible during the times of interest. These observations motivate a zero-dimensional model of discharge behavior. This model reproduces approximately both the discharge dynamics and the electrical characteristics over a range of parameters. Calculations indicate that the beam ions will lose only 10% of their energy during transport through the discharge in a fusion facility. A conceptual design for a z-discharge transport system is presented. The results of this work confirm that wall-stabilized z-discharge transport is a viable, backup approach to transport in a light-ion-beam-driven inertial confinement fusion facility.
Nondestructive technique to measure bulk lifetime and surface recombination velocities at the two surfaces by infrared absorption due to pulsed optical excitation
Authors: Kousik G. S. , Ling Z. G. , Ajmera P. K.
Published: July 2002

The modeling and analysis of electron devices including photovoltaic devices requires the knowledge of the surface recombination velocities at the two surfaces of the wafer along with the bulk lifetime. In this paper, the work of Luke and Cheng [J. Appl. Phys. 61, 2282 (1987)] is extended to account for the asymmetric case of different surface recombination velocities at the two wafer surfaces. We present the analysis and discuss experimental procedures to extract the above three parameters. The contactless measurement technique is based on the transient behavior of infrared absorption due to the decay of optically excited excess carriers. In order to determine the surface recombination velocities at both surfaces, the measurements must be made with each side acting as the front surface. An example of parameter extraction is presented.
Thermally stable non-gold Ohmic contacts to n-type GaAs. I. NiGe contact metal
Authors: Tanahashi Kiwamu , Takata H. J. , Otuki A. , Murakami Masanori
Published: July 2002

‘‘Nongold’’ NiGe Ohmic contacts were developed by a lift-off and annealing technique that was extensively used to fabricate the conventional AuGeNi contacts. The optimum conditions to prepare thermally stable, low resistance NiGe Ohmic contacts were determined by changing the Ge concentrations of the NiGe contacts from 13 to 43 at. %, and the deposition sequences of the Ni and Ge layers. Contact resistances of ∼0.8 Ω mm were obtained for both two-layered Ni/Ge and three-layered Ni/Ge/Ni contacts, with Ge concentrations of ∼38 at. % after annealing at 600 °C. The thermal stability of the electrical properties during subsequent annealing at 400 °C after contact formation was found to be influenced by the microstructure at the GaAs/metal interface. The excellent stability was obtained only when the NiGe contacts formed high melting point NiGe compounds. The present result indicated that removal of Au from the AuGeNi contacts was not satisfactory enough to improve the thermal stability of the AuGeNi contacts after contact formation. A model for the current transport mechanism through the GaAs/NiGe interface was also proposed by correlating the electrical properties and the microstructure. This model explained well the dependences of the contact resistances on the Ge concentrations and the deposition sequence of the Ni and Ge layers.
Macroscopic quantum tunneling of the magnetic moment (invited)
Authors: Chudnovsky Eugene M.
Published: July 2002

The magnetization vector in solids is traditionally viewed as a classical variable. Recent theoretical and experimental works have demonstrated, however, that it can tunnel quantum mechanically between metastable magnetic states. Examples are tunneling of the magnetic moment between equilibrium orientations in monodomain ferromagnetic particles, tunneling of the Néel vector in antiferromagnetic particles, and tunneling of domain walls through the pinning barriers in bulk materials. Theory, experiments, and open questions will be reviewed.
High-coercivity iron-rich rare-earth permanent magnet material based on (Fe, Co)3B-Nd-M (M=Al, Si, Cu, Ga, Ag, Au)
Authors: Hirosawa Satoshi , Kanekiyo Hirokazu , Uehara Minoru
Published: July 2002

High-coercivity, high-remanence permanent magnet materials have been obtained via a crystallization treatment of amorphous (Nd,Dy)xFe80.5−x−yCoyB18.5M1 alloys for 3≤x≤5 and 0≤y≤5, where M represent the additives Al, Si, Cu, Ga, Ag, and Au. It has been found that addition of Co and M results in a significant reduction of the crystal grain size and leads to significant improvements both in the intrinsic coercivity and in the energy product. The materials are superior to Nd2Fe14B-based rapidly solidified materials in the remanence Br, the temperature coefficient of Br, and magnetizability. The typical values of temperature coefficients of Br and HcJ are, respectively, −0.05%/K and −0.35% K. The magnetizing force required to obtain substantial remanence is approximately 0.8 MA/m. Compaction-molded resin-bonded magnets produced from these materials have magnetic performance (Br, HcJ) in the range between 0.89 T, 0.29 MA/m and 0.80 T, 0.35 MA/m.
Magnetization reversal and defects in Co/Pt multilayers
Authors: Shen J. X. , Kirby R. D. , Wierman K. , Shan Z. -S. , Sellmyer D. J. , Suzuki T.
Published: July 2002

(Co 3 Å/Pt 10 Å)×N (N=8, 16, and 30 bilayers) multilayer thin films were prepared by sputtering onto an 850-Å-thick SiN layer that had been deposited on a silicon (111) substrate. We used the polar Kerr effect to measure the time dependence of magnetization reversal over the temperature range 90–300 K. Direct domain observations were also carried out. The results show that the domain expansion process depends strongly on the number of bilayers. Uniform domain expansion was found only in the thinner samples. From the time dependence of the magnetization reversal measurements over the temperature range 90–300 K, the activation energy and volume associated with domain wall motion were found to be 1.2 eV and 2.3×10−18 cm3 for N=8 sample. The N=16 and N=30 samples seem to have a broad distribution of activation energies. Our observations suggest that both the coercivity and magnetization reversal are controlled by the defects that come from the interface between the Co and Pt.
Analysis of bilinear and biquadratic exchange coupling in Fe/Ag/Fe(001) trilayers
Authors: Celinski Z. , Heinrich B. , Cochran J. F.
Published: July 2002

Ferromagnetic resonance (FMR) and surface magneto-optical Kerr effect (SMOKE) studies of the exchange coupling in Fe/Ag/Fe(001) structures are presented. The interfaces in these structures can be improved significantly by growing the first Fe(001) layer at a raised substrate temperature. The exchange couplings in Fe/Ag/Fe trilayers were studied as a function of the interlayer thickness and temperature. The improved interfaces in the Fe/Ag/Fe system revealed new features in the exchange coupling which were absent in samples grown entirely at room temperature. Quantitative data from the FMR and SMOKE measurements are compared. The magnetization loops for Fe/Ag/Fe trilayers can be explained well only by including the simultaneous presence of bilinear and biquadratic exchange coupling. It is shown that the exchange coupling through Ag(001) exhibits long wavelength oscillations.
Force transducers based on the stress dependence of coercive force
Authors: Garshelis I. J.
Published: July 2002

An alternative measurement regime for magnetoelastic force transducers, based on variations in coercive field, is described. Hc is shown to be more directly related to the primary magnetic influence of stress, namely, the orientation of effective anisotropy, than conventionally used magnetization related parameters. The stress dependence of Hc is shown to generally reflect opposing factors associated with rotational and wall displacement magnetization reversal processes. In materials wherein Hc≪K/Ms wall motion dominates and if the product of λs/K and yield stress is high enough, large monotonic reductions of Hc with positive (tensile) stress are shown to be possible. A more complex variation of Hc with increasing compression is similarly expected. Experimental results from a transducer having an 18% Ni maraging steel core support these expectations.
Interfacial reactions of ultrahigh-vacuum-deposited Cu thin films on atomically cleaned (111)Si. II. Oxidation of silicon catalyzed by η″-Cu3Si at room temperature
Authors: Liu C. S. , Chen L. J.
Published: July 2002

Room-temperature oxidation of (111)Si catalyzed by η″-Cu3Si has been studied by transmission electron microscopy, x-ray diffractometry (XRD), and Auger electron spectroscopy. XRD analysis showed that volume fractions of η″-Cu3Si and Cu decrease and increase with exposure time in air ambient, respectively. From TEM diffraction analysis, Cu precipitates were found to be epitaxially related to Si. After prolonged exposure in air, the Cu precipitates were found to form an irregular network structure in the SiO2 layer. Examination of the same area of annealed samples with intermittent exposure in air indicated that the oxidation was mainly initiated at the grain boundaries. Significant differences in room-temperature oxidation behavior between (111) and (001) samples were found.
Indium oxide Schottky junctions with InP and GaAs
Authors: Korobov V. , Leibovitch M. , Shapira Yoram
Published: July 2002

Junctions of transparent conducting oxides on III–V semiconductors have been prepared by deposition of indium oxide layers onto p-type InP and n-type GaAs by means of reactive evaporation of In in the presence of oxygen at different substrate temperatures. The electrical properties and chemical composition of these junctions have been investigated using current-voltage measurements in the dark at room temperature, capacitance-voltage measurements, and depth profiling by Auger electron spectroscopy. The best diodes were obtained by deposition at a substrate temperature near 250 °C and oxygen pressure of 5×10−4 Torr. These diodes exhibit a Schottky barrier height of 0.80 eV for n-type GaAs and 0.87 eV for p-type InP with an ideality factor of 1.04. The Schottky barrier height decreases with decreasing deposition temperature for both substrates. The roles of the tunneling–transparent interface layer and interface region are theoretically considered. It is shown that as the deposition temperature is increased, the barrier height increases due to the accompanying reduction in the density of surface states, which are induced by elemental In at the interface.
Mass spectrometric detection of neutral radicals in a CH4 microwave discharge by use of Li+ ion attachment techniques
Authors: Fujii Toshihiro , Syouji Ken-ichi
Published: July 2002

The chemical species of the neutral radicals in the methane microwave (MW) discharge plasma were studied by quadrupole mass spectrometry in combination with a Li+ ion attachment technique. The approach is to have a MW discharge flow pass a lithium ion emitter and then to analyze, by quadrupole mass spectrometry, all ions formed by lithium ion attachment. Mainly, radicals such as CnH2n+1 (n=2–11) and CnH2n−1 (n=2–11) were detected. Species such as C4H3, C5H5, and C6H5 may also be produced in the process. Many such species have been identified for the first time. The presence of these species is evaluated by comparison with results from optical spectroscopy and threshold ionization mass spectrometry.
A 1.9 eV photoluminescence induced by 4 eV photons in high-purity wet synthetic silica
Authors: Anedda A. , Bongiovanni G. , Cannas M. , Congiu F. , Mura A. , Martini M.
Published: July 2002

Photoluminescence (PL) of type III (high-purity wet synthetic) silica excited by a XeCl excimer laser (hν=4 eV) is reported. Time-resolved spectra show that a PL band peaked at 1.9 eV can be induced by the XeCl laser irradiation. This band exhibits a fast rise time (<20 ns) but a decay time of several microseconds. The possible mechanisms of photogeneration and photoexcitation of the defects related to this emission are discussed.
Determining thin-film magnetoelastic constants
Authors: O’Handley R. C. , Song Oh-Sung , Ballentine C. A.
Published: July 2002

A formalism is presented for determining the magnetoelastic (ME) coefficients of tetragonally distorted surfaces and thin films. The equation of motion of the magnetization is determined from free-energy-density expressions containing terms for crystalline and shape anisotropy, ME anisotropy, and applied field. Canonical magnetization curves, described by simple equations of motion and recorded under different strains, are shown to differ by an area equal to the magnetoelastic energy density. Thus, division of this area by the applied strain allows determination of the ME coefficients. A more general method is proposed which allows ME coefficients to be determined from arbitrarily shaped M-H curves taken at different strains by calculating the area between them over a conveniently chosen magnetization range. This reduces error in the ME coefficients by avoiding hysteretic effects at low fields and ambiguity about saturation at high fields. Examples are given that illustrate how the magnetic anisotropy and ME coefficients can be determined in three simple cases from Kerr or M-H loops in ultrathin films subjected to various bending strains.
Anisotropy in the complex refractive index and the third-order nonlinear optical susceptibility of a stretch-oriented film of poly(p-phenylene vinylene)
Authors: Swiatkiewicz Jacek , Prasad Paras N. , Karasz Frank E.
Published: July 2002

Birefringence, dichroism, and dispersion of the refractive indices of a free-standing film of poly(p-phenylene vinylene) (PPV) were measured by several techniques. The results are applied to an analysis of anisotropy of the third-order nonlinear optical susceptibility of this material. The anisotropy of both the linear and nonlinear susceptibilities is accounted for by the one-dimensional character of the lowest-energy electronic transition in PPV.
A study of metal/GaAs interface modification by hydrogen plasma
Authors: Wang Y. G. , Ashok S.
Published: July 2002

The modification of metal/GaAs interfaces by atomic hydrogen has been studied using rf plasma in a reactive ion etching (RIE) system as well as hydrogen generated in an electron cyclotron resonance (ECR) system. Current-voltage (I-V) characteristics of Au/n-GaAs Schottky devices reveal a reduction in the barrier height following the room temperature rf plasma, and a slight increase with ECR hydrogenation at elevated temperatures. More interestingly, a profound increase in the effective barrier height is seen for p-GaAs (from 0.35 to 0.84 eV for the rf plasma and 0.35 to 0.69 eV for ECR). Dopant deactivation close to the surface is observed with spreading resistance and capacitance-voltage (C-V) measurements for both conductivity types. The passivation of existing deep levels and the creation of new deep levels have been found in both H RIE treated and ECR hydrogenated GaAs. The large ideality factor n in I-V plots and large voltage intercept in 1/C2 plots suggest the formation of an insulator-like I layer. The improvement in I-V characteristics for ECR hydrogenated n-GaAs indicates the effect of H passivation on a chemically etched GaAs surface. The recovery of the hydrogenation effects has also been studied as a function of temperature, illumination, and bias-anneal.
Dielectric method to determine the twist elastic constant in a homogeneous nematic cell
Authors: Li Zili
Published: July 2002

A dielectric method to measure the twist elastic constant K2 was developed by directing the probing electric field in the direction perpendicular to the substrate normal. This in fact breaks the director degeneracy in the plane of the substrates in the case of a twist transition and enables one to observe the director reorientation at the twist transition. By probing the dielectric response of the cell, the twist Freedericksz transition threshold has been located and the elastic constant determined. The results agree very well with the data of a calibrated liquid-crystal material.
Numerical analysis of the magnetization in soft adjacent layer biased magnetoresistive sensors
Authors: Shiiki Kazuo , Mitsui Yu
Published: July 2002

A modified Dufort–Frankel method with relaxation is developed and applied to the static magnetization analysis of a magnetoresistive sensor, which is composed of a magnetoresistive layer magnetically fixed by a domain controlled antiferromagnetic layer, a nonmagnetic conducting layer, and a soft magnetic adjacent layer. This method is thought to be suitable for three-dimensional large-scale magnetic-multilayered systems. It clarifies the biased magnetization state of the magnetoresistive layer and soft adjacent layer with intermagnetostatic interaction.
Moving photoluminescence bands in GaAs1−xSbx layers grown by molecular beam epitaxy on InP substrates
Authors: Yu P. W. , Stutz C. E. , Manasreh M. O. , Kaspi R. , Capano M. A.
Published: July 2002

We report the excitation intensity dependent photoluminescence properties of GaAs1−xSbx layers grown by molecular beam epitaxy on InP substrates. Photoluminescence consists of the bound exciton and the quasi-donor-acceptor pair transitions for the layers in the range of 0.26≤x≤0.94. The concentration modulation produced by the relaxation of the misfit strain between the epitaxial GaAs1−xSbx layer and InP substrate is responsible for the quasi-donor-acceptor pair transition. A large Stokes shift between the photoluminescence transition of the bound exciton and the band gap determined by the optical absorption measurements is also consistent with our model of concentration modulation.
Giant magnetoresistance at low fields in [(NixFe1−x)yAg1−y]/Ag multilayers prepared by molecular-beam epitaxy
Authors: Farrow R. F. C. , Marks R. F. , Rabedeau T. A. , Toney M. F. , Dobbertin D. , Beyers R. , Parkin S. S. P.
Published: July 2002

The structural and magnetic properties of [111]-oriented multilayers comprising ferromagnetic films of Permalloy-silver alternating with Ag spacer films are described. The multilayers are grown by molecular-beam epitaxy on Pt(111) seed films on sapphire (0001) substrates at temperatures in the range 25–175 °C. For a series of multilayers with similar bilayer periods (≂50 Å) the magnetoresistance (MR) is found to be strongly dependent on both growth temperature and subsequent annealing temperature. The multilayers exhibit a negative magnetoresistance in the as-grown state which more than doubles when the growth temperature is increased from 25 to 100 °C; however, the highest MR (peak 5.6%; maximum slope 0.4% per Oe) is obtained by annealing (at 400 °C) multilayers grown at 100 °C. The primary effects of annealing are an improvement of structural order, partial segregation of Ag from the ferromagnetic films into adjacent Ag films, a slight decrease in laminar order, and a reduction in long-wavelength roughness of the multilayer interfaces. No evidence is found for discontinuities in the magnetic layers with the highest MR.