bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrohydrodynamical study of the instability of a thin liquid metal film: Application to planar liquid metal ion sources
Authors: Miskovsky N. M. , He J. , Cutler P. H. , Chung M.
Published: July 2002

Liquid metal ion sources are of interest in diverse areas of technology since they provide a high brightness, quasipoint source of ions and droplets for microfabrication, surface analysis, ultrathin film deposition, and other potential applications. N. M. Miskovsky, M. Chung, P. H. Cutler, T. E. Feuchtwang, and E. Kazes [J. Vac. Sci. Technol. A 6, 2992 (1988)] have developed an electrohydrodynamic capillary wave theory for ion and droplet emission in electrically stressed conducting viscous fluids based on a mathematical formalism introduced by J. R. Melcher and C. V. Smith [Phys. Fluids 12, 778 (1969)] and S. Grossmann and A. Muller [Z. Phys. B 57, 161 (1984)]. As the simplest analytical application of this theory they chose a model consisting of a planar fluid of thickness ‘‘a’’ supported on a rigid electrode. A parallel planar counter electrode is at a distance ‘‘b’’ from the unperturbed surface. The Navier–Stokes equation was solved subject to a dynamical Laplace–Young stress boundary condition (which includes the frictional tensor) to obtain the dispersion relation used to investigate the stability of the system.

In earlier work the effect of viscosity and gravity on the spectrum of unstable wavelengths for the case of a thick film (i.e., λ≫a) was investigated within the planar surface capillary wave model. In this limit, it was found that viscosity plays a significant role in determining the growth rate and the dominant mode, suggesting that it should be included in studies of the instabilities in liquid metal ion sources. It was also found that the local electric field is much larger than the average field of the perturbed fluid surface, implying that nonlinear effects can be important. In the present study the same formalism is used to investigate the case of a thin (i.e., λ<a) liquid metal film. For thin films, that is, <1 μm, the effect of the boundary conditions at the supporting electrode can produce significant changes in the maximum growth rate (∼20%), the dominant mode (∼10%), and the maximum value of Re(ω2) (∼40%). For both the thick- and thin-film regimes viscous damping is found to have an important role increasing the stability of the fluid film. In addition, an increase in viscosity shifts the most unstable mode to longer wavelengths. This shift competes with the effect of decreasing the film thickness.
Ion temperature measurements in a tokamak by collective Thomson scattering
Authors: Siegrist M. R. , Behn R. , Dicken D. , Duval B. P. , Hackmann J. , Joye B. , Lister J. , Nieswand C. , Pochelon A. , Soumagne G. , Yuan D. C.
Published: July 2002

Collective Thomson scattering, using a high-power pulsed D2O laser at 385 μm and a heterodyne receiver system, has provided local ion temperature (Ti) measurements of the plasma in the tokamak chauffage Alfvén (TCA) tokamak. Recent improvements in the noise-equivalent power of the Schottky barrier diode mixers permitted us to achieve a typical precision of ±12% for a single shot measurement at densities above 1020 m−3. Even at densities of standard TCA discharges (5×1019 m−3) the uncertainty is better than ±25%. For the interpretation of the measured spectra and the evaluation of Ti the local value of the electron temperature (Te) is an important parameter. Therefore, Te was measured simultaneously by incoherent Thomson scattering at 0.694 μm during a series of shots. The density was obtained from a far-infrared interferometer. An independent measurement of Ti on TCA can be obtained from a neutral particle analyzer. Comparison of the results from the two methods showed good agreement. The precision of a Ti measurement depends strongly on the plasma density. Since an uncertainty of ±25% at standard densities may still not be regarded as satisfactory, further investigations using a numerical simulation code have been carried out to find ways of improvement.
Quantum effect on magnetization near the surface at low temperatures in antiferromagnetic thin films
Authors: Diep H. T.
Published: July 2002

Using a Green’s function technique, quantum effects on surface magnetizations in antiferromagnetic thin films with Heisenberg spins 1/2 are investigated in detail. Both the body-centered-cubic lattice and the simple cubic lattice with (001) surface are studied. Self-consistent layer magnetizations are obtained at an arbitrary temperature for a given set of surface parameters. It is shown for the first time that the profile of the magnetization near the film surface at low temperatures may be very different qualitatively from that at high temperatures.
Phase locking in the Heisenberg helimagnet
Authors: Harris A. B.
Published: July 2002

The commensurability energy ΔE is calculated for a Heisenberg helimagnet whose wavelength is three lattice constants at zero temperature with a small but nonzero uniform field applied in the plane of polarization of the spins. It is shown that ΔE=0 for classical spins but ΔE≠0 for quantum spins when spin-wave interactions are considered.
Effects of fluctuations and domain formation on the dynamics of simple ferromagnets
Authors: Grahl M. , Görlitz D. , Kötzler J. , Lange T. , Sessler I.
Published: July 2002

Starting at the Curie temperature Tc dynamical susceptibilities have been measured between 1 Hz and 20 GHz on nonmetallic crystals to determine the influence of progressive ordering on the magnetization dynamics. In uniaxial materials (GdCl3, LiTbF4), the low-frequency response, ω/2π<50 MHz, is governed by the domain-wall relaxation, the rate Γd of which speeds up rapidly near Tc. This novel feature appears to be the first proper signature of linear walls predicted by Ginzburg and Bulaevskii for strong anisotropy, χ∥(T) ≳ χ⊥. The faster intradomain relaxation, arising from spin–spin interaction, undergoes a thermodynamic slowing down, the kinetic coefficient of which determines the magnitude of the damping in the walls. In the cubic ferromagnets (EuS, EuO), χ(ω) displays an oscillatory behavior with resonance and damping frequencies lying in the GHz region. Their decrease near Tc is described by simple powers to the spontaneous magnetization. A comparison made to the well-understood critical dynamics above Tc suggests an association of these phenomena with dipolar-anisotropic magnetization fluctuations.
Frustration and absence of long range order on the corner sharing-tetrahedron lattice within mean field theory (abstract)
Authors: Berlinsky A. J. , Reimers J. N. , Shi A.-C.
Published: July 2002

The metal atoms in the pyrochlore system of compounds (A2B2O7, where A and B are metals) form an infinite 3D network of corner sharing tetrahedra with cubic symmetry. For antiferromagnetic nearest neighbor interactions and only B atoms magnetic, there is a very high degree of frustration, and no long range order is predicted in the absence of further neighbor interactions. Mean field calculations for n-component classical vector spins, show that the wave vector dependent susceptibility diverges, at the same temperature Tc, for 2N normal modes of the system where N is the number of unit cells. In some cases further neighbor interactions will stabilize the q=0 or incommensurate modes. A comparison will be made with long range order known to exist in the pyrochlore form of FeF3.
Excitation theory of propagating spin waves for anisotropic ferrite film (abstract)
Authors: Kalinikos B. A. , Kozhus N. V. , Zhuravlev A. V.
Published: July 2002

The purpose of this work is to elaborate an excitation theory of spin waves (SW) in anisotropic ferromagnetic films (FF). The theory takes into account both dipole–dipole and exchange interactions and also crystallographic anisotropy of a FF. An arbitrary value and type of anisotropy are considered in terms based on effective demagnetizing factors of anisotropy. Two cases of exchange boundary conditions, namely pinned and unpinned surface spins, are analyzed. Using earlier elaborated normal mode technique1 spin-wave Green functions described linear response of spin-system of a anisotropic FF to the inhomogeneous microwave magnetic field are obtained. Owing to the explicit Green functions these forms are convenient for use in various problems of radiation and scattering of SW. As an example, we use these Green functions to calculate radiation resistance (RR) of a microstrip transducer. Analysis shows that ‘‘anisotropic’’ features of RR are connected with the peculiarities of dipole-exchange SW spectrum of anisotropic films. Normal uniaxial and cubic anisotropy in perpendicularly magnetized films [for (111)and (100)-oriented films] causes the shift of RR frequency dependences only. In all other cases dependence of RR on propagation direction of SW takes place. Normal uniaxial and cubic anisotropy in the tangentially magnetized films [e.g., for (111)and (100)-oriented films] causes unusual behavior of RR as frequency function owing to the new ‘‘anisotropic’’ branches of SW spectrum. It should be noted that expressions obtained for RR are convenient for practical calculations of characteristics of magnetostatic wave devices based on FF with large anisotropy.
Theoretical analysis and experimental research on the finline ferrite isolator (abstract)
Authors: Zhu Sheng-chuan , Hao Yan-ming , Zhang Yao-xi
Published: July 2002

Recently, the finline ferrite devices have attracted people’s attention. Beyer et al. have done theoretical and experimental researches for a finline isolator.1,2 In order to make it convenient for theoretical design and experimental adjustment of this device, we have developed a synthetical theory and have carried out the experimental research successfully.3 In this paper, we have done the further theoretical analysis and experimental researches for the finline ferrite isolator, such as the impedance matching, the effects of device structure on performances, and the transplantation of a waveguide isolator to a finline isolator problem. Good agreement between design and experiment is obtained. The performances of a X-band finline isolator are as follows A+<1.5 dB, A−≳18 dB, VSWR<1.5 in a 8% bandwidth, and the bia-field is lower (about 1000 Oe).
Time dependence of spin-wave damping in short pulses
Authors: Cherepanov V. B.
Published: July 2002

The influence of thermal magnons on evolution of a spin-wave packet is studied. For a short packet, if its length is shorter than the time of phase mixing the damping is small and proportional to the length. If the length of the packet is greater than the time of phase mixing the magnon damping can be obtained from the kinetic equation. The evolution equation for a packet with an arbitrary length is derived. In particular, if the packet arises instantly, one should replace δ(Δωk) →sin(Δωkt)/Δωk in the energy conservation condition in the kinetic equation to allow for the time dependence of the damping. The characteristic time of phase mixing τph is of the order of 1/Δωk. As a rule Δωk ∼ ωk, so the time τph is of the order of the spin-wave period. If the thermal magnon dispersion is small, the damping grows slowly. This occurs when a nuclear spin wave with a large wave vector is excited. A slow growth of damping can occur in a quasi-one-dimensional antiferromagnet also.
Guided wave modulators and switches fabricated in electro-optic polymers
Authors: Van Tomme E. , Van Daele P. , Baets R. , Möhlmann G. R. , Diemeer M. B. J.
Published: July 2002

In this paper the fabrication of directional couplers (2×2 switches) and Mach–Zehnder interferometers (intensity modulators) using electro-optic polymeric multilayer structures, is described. Results show attractively low switching voltages (<10 V for 1.4 cm long devices) and very good on-off ratios (17 dB) for the directional couplers. In the case of the Mach–Zehnder interferometers, Vπ-values of 4.5 V have been obtained, also for 1.4 cm long devices.
Dielectric-barrier discharge for processing of SO2/NOx
Authors: Dhali S. K. , Sardja I.
Published: July 2002

We report the results of an investigation of plasma assisted oxidation of SO2 to SO3. The SO3 is a more desirable byproduct of flue gas as opposed to SO2 because it can be dissolved in water easily and can be reacted with lime to form gypsum. A coaxial dielectric-barrier discharge is used to generate an air plasma to carry out the reaction. The dielectric-barrier discharge, which is an interrupted discharge, is very efficient in producing atomic oxygen and requires a simple form of excitation. We have observed a significant reduction (over 75%) in the SO2 concentration using this technique. The simulation results indicate that about 99% of the SO2 can be oxidized with UV-irradiation along with plasma oxidation and NOx can be reduced to N2 in the presence of an air plasma. The results of varying the gas composition, the gas pressure, and the gas flow are also reported.
Surface polarization and flexoelectric effect
Authors: Barbero G. , Chuvyrov A. N. , Krekhov A. P. , Scaldin O. A.
Published: July 2002

In order to evaluate the order of magnitude and to establish the origin of the surface polarization, experimental investigations of direct piezoelectrical effect in nematic liquid crystals have been performed. The experimental setup used allows the temperature dependence of the electrical response of a nematic sample, submitted to periodic acoustic perturbation of one boundary, to be determined. The experimental data show that the contribution of the surface polarization to the electrical response of the nematic sample is usually negligible with respect to the flexoelectric polarization. An estimation of the flexoelectric coefficients of various liquid crystals is reported.
Inter-miniband optical absorption in a modulation-doped AlxGa1−xAs/GaAs superlattice
Authors: Kim Kyeu T. , Lee Sang Soo , Chuang S. L.
Published: July 2002

Theoretical calculations of the optical absorption between the conduction subbands in a modulation-doped AlxGa1−xAs-GaAs superlattice are presented. The electronic subband structures, including both the couplings between different quantum wells and the band bending due to screening effects, are calculated self-consistently by solving simultaneously the Schrödinger and the Poisson equation. Linear intersubband absorption in the superlattice is then calculated and the absorption spectra show interesting line shapes which reflect the joint density of states between different subbands. The dependence of the absorption (energy-band width, resonant absorption energy, and magnitude of peak absorption coefficient) on device parameters such as doping concentration, well width, barrier width, and aluminum mole fraction in the barrier, which are useful for the design of infrared detectors, is also investigated. These theoretical results are also compared with experimental data.
Geophysical attractors may be only colored noise
Authors: West Bruce J. , Mackey H. J.
Published: July 2002

We demonstrate that a numerically generated fractal random process has the same values of the measures used by other authors to conclude that certain geophysical data were generated by chaotic attractors. We show that the data sets could be either chaos or colored noise, but the measures used cannot discriminate between the two.
A multipurpose scanning apparatus for automatic analyses of soft magnetic materials and circuits (abstract)
Authors: Schönhuber P. , Pfützner H.
Published: July 2002

Proper techniques for simultaneous evaluation of both global properties of magnetic circuits and local magnetic parameters of single grains or domains are an important prerequisite for optimal application and future improvement of ferromagnetic materials. The paper presents a test equipment designed to accommodate magnetic circuits up to outer dimensions of about 1 m×1 m×0.5 m. The box is thermally isolated for most sensitive thermistor applications such as local loss measurements. By means of a stepper-motor-driven sensing head which can pick up one or more sensors simultaneously, the scanning resolution and area can be freely chosen in a wide range from minimum scanning width of 10 μm to a maximum area of about 0.9 m×0.9 m. Geometrically highly resolving Hall sensors have been prepared for normal stray field analysis, thus visualizing local domain configurations.1 Tangential Hall sensors and differential field plates can be mounted for field measurements during magnetization process. Optionally, all sensors can be coupled with thermistors for local loss measurements. Reference elements in bridge connection ensure results considerably free from ambient disturbances. The apparatus is fully automated by a PC controlling scanning procedures as well as data acquisition and managing to storage disks and graphic devices.
A strongly fluctuating quasi-two-dimensional insulator (invited)
Authors: Broholm C. , Aeppli G. , Espinosa G. P. , Cooper A. S.
Published: July 2002

We describe neutron-scattering data for SrCr8−xGa4+xO19, a layered compound containing planes of S=3/2 Cr3+ ions which form Kagomé lattices. Despite strong antiferromagnetic interactions (θCW ≊ −500 K), fluctuations account for more than 75% of the free ion moment at 1.5 K. The spectrum (averaged over reciprocal space) is gapless and resembles that of a 2D long-range-ordered antiferromagnet, as does the low-temperature specific heat of the compound. Even so, the static correlation length does not exceed 7±2 Å. Monte-Carlo simulations of the antiferromagnetic three-state Potts model on the Kagomé lattice show that this model does not have a finite temperature phase-transition. Even at T=0, there does not seem to be true long-range antiferromagnetic-order. However, the magnetic correlations decay algebraically rather than exponentially. The implications of this result for the ground-state of SrCr8−xGa4+xO19 is discussed.
Mechanistic studies of dielectric thin film growth by low pressure chemical vapor deposition: The reaction of tetraethoxysilane with SiO2 surfaces
Authors: Tedder Laura L. , Lu Guangquan , Crowell John E.
Published: July 2002

The adsorption and reaction of tetraethoxysilane (TEOS) with hydroxylated SiO2 has been studied over the range of 100–450 K using transmission infrared spectroscopy. At 100 K, TEOS [Si(OC2H5)4] condenses on SiO2. Upon warming in vacuum, some of the condensed phase TEOS desorbs molecularly while a significant portion of the layer enters into a physisorption state. The physisorption state maximizes near 250 K, with strictly molecular desorption occurring upon warming to higher temperatures. When exposure occurs at 450 K, Si(OC2H5)4 reacts to form adsorbed siloxanes, thought to be a mixture of (SiO)2Si(OC2H5)2 and (SiO)Si(OC2H5)3. The adsorbed di- and triethoxysiloxanes decompose completely on heating in vacuum to 900 K. The chemistry of TEOS on SiO2 has been modeled using ethanol adsorption. Exposure of SiO2 to ethanol at 450 K leads to the formation of an adsorbed ethoxide species. Ethanol is shown to spectroscopically and chemically model the surface bound siloxanes produced upon reaction of Si(OC2H5)4 with hydroxylated SiO2 at 450 K. The vibrational spectrum of adsorbed ethoxide (SiOC2H5) is very similar to that of the adsorbed siloxanes produced from the adsorption of Si(OC2H5)4. The ethoxy modes are assigned through comparison of C2H5OH and CH3CD2OH adsorption. The temperature dependence of the decomposition of the adsorbed ethoxide is similar to that of the TEOS derived siloxanes. Decomposition of the adsorbed siloxanes is shown to evolve primarily ethylene.
Thermal, electrical, and magnetic properties of U4Ru7Ge6
Authors: Mentink S. A. M. , Nieuwenhuys G. J. , Menovsky A. A. , Mydosh J. A.
Published: July 2002

The various physical properties of single-crystal U4Ru7Ge6 have been investigated. This compound crystallizes in the cubic U4Re7Si6 structure and orders ferromagnetically at Tc=(6.8±0.2) K with small ordered moments of 0.2μB per uranium atom. The large electronic specific heat γ=109 mJ/mol U K2 below Tc, the behavior of the resistivity above 300 K, and the magnetization behavior below room temperature all characterize this system as a dense Kondo lattice with a low-temperature ferromagnetic ordering of strongly reduced uranium moments.
Correlation of structural quality with superconducting behavior in epitaxial thin films of Ba2YCu3O7−δ on LaAlO3(100)
Authors: Siegal M. P. , Phillips Julia M. , Hebard A. F. , Dover R. B. van , Farrow R. C. , Tiefel T. H. , Marshall J. H.
Published: July 2002

The correlations between structural quality and superconducting behavior in 1000-Å-thick Ba2YCu3O7−δ (BYCO) films grown on LaAlO3(100) from the coevaporation of BaF2, Y, and Cu, followed by an optimized ex situ annealing process are reported. Epitaxial films with smooth, laminar morphology and excellent crystallinity can be grown to have critical current density Jc values nearly identical to single crystals. This finding contrasts with the typical observation that Jc values in thin films of BYCO are very high compared to those of single crystals. This is attributed to a greater density of flux pinning sites due to structural defects within the films. The most crystalline films presented here have penetration length λ∼2000 Å with temperature dependencies described well by the Bardeen–Cooper–Schrieffer (BCS) theory. Material disorder of two types can be controlled by the high-temperature stage Ta of the annealing process. The first type is point defects and dislocations the same size or smaller than the coherence length ξab, which Rutherford backscattering/channeling suggests decrease in number with increasing Ta. The second is crevices, pinholes, and microcracks, which are at least one to two orders of magnitude larger than ξab. At Ta < 850 °C, crevices, which create areas of nonuniform thickness, occur due to incomplete epitaxial growth and correlate with the presence of weak links. Hence film resistivity is high, Tc is low, and λ is large. As Ta is increased, the film morphology becomes smoother and all electrical properties improve, except for Jc in nonzero applied magnetic fields, since the improved epitaxy correlates with reduced flux pinning. By Ta= 900 °C, the BYCO films are similar to single crystals in both cation alignment and Jc behavior. Above this annealing temperature, pinholes and microcracks develop and increase in both size and density with increasing Ta. Although these relatively large defects do not act as weak links, they do affect magnetic screening (and hence λ), to result in an anomalous temperature dependence that masks the intrinsic BCS behavior.
The thermally stimulated current of β-form oxotitanium phthalocyanine dispersed in polyester
Authors: Enokida T. , Yamamoto S. , Hirohashi R.
Published: July 2002

A thermally stimulated current (TSC) has been applied to estimate the trap properties on a thin film of β-form oxotitanium phthalocyanine (β-TiOPc) dispersed in polyester. The hole trapping levels derived from the activation energies (Eas) were obtained by an initial rising method and heating rate dependence on TSC peaks. The Eas for an electric field of 2.5×103 V/cm were distributed from 0.033 eV for shallow traps to 0.42 eV for deep traps.
On the calculation of cold cathodes lifetimes for helium-neon lasers
Authors: Korgiaviy A. P. , Kristya V. I.
Published: July 2002

The energy distribution function of neon ions at the cold cathode surface in helium-neon mixture has been derived. This function is used for determination of cathode lifetime. The calculated lifetimes are in better agreement with the experimental longevities for low current densities than those obtained in the previous article [L. H. Hall, J. Appl. Phys. 64, 2630 (1988)].
Optical absorption from graphitic clusters of hydrogenated amorphous carbon thin films
Authors: Pascual E. , Serra C. , Bertran E.
Published: July 2002

The optical absorption of hydrogenated amorphous carbon films (a-C:H) was measured by spectroscopic ellipsometry. The a-C:H films were deposited at different substrate temperatures by rf-plasma of methane. A volume distribution of graphitic cluster size was assumed to reproduce the experimental spectra of the absorption coefficient. The changes in the absorption coefficient and the optical gap, induced by deposition temperature, have been interpreted in terms of changes in the graphitic cluster size of the network. The increase in the deposition temperature produces an increase in the size of the graphitic clusters.
Selective liquid-phase electroepitaxy of GaAs on GaAs-coated Si substrates
Authors: Sakai Shiro , Ohashi Yasuno , Shintani Yoshihiro
Published: July 2002

Selective growth of GaAs on GaAs-coated Si substrate is performed by liquid phase electroepitaxy (LPEE) in which dc current flows from the substrate to the melt in the conventional liquid-phase epitaxy. The GaAs on Si substrate is prepared by metallorganic chemical vapor deposition. The lateral overgrowth on the mask is obtained in the LPEE. The selective LPEE growth mechanism is discussed. The growing species falling on the mask is pulled into the window region by electromigration resulting in the lateral growth.
Threading dislocations in In-doped GaAs/Si
Authors: Tamura Masao , Hashimoto Akihiro , Sugiyama Naoharu
Published: July 2002

The threading dislocation morphologies and characteristics in In-doped 3-μm-thick GaAs films grown by molecular-beam epitaxy on Si (100) substrates tilted toward the [110] orientation by 2° have been examined mainly using cross-sectional transmission electron microscopy. Most of the observed threading dislocations are 30°- and 60°-type dislocations along the 〈211〉 and 〈110〉 directions on inclined {111} planes. Also, screw-type dislocations running parallel to the [001] growth direction are frequently detected. No appreciable effect of homogeneous In doping throughout the films with a content between 2×1019 and 2×1020 atoms/cm3 on the reduction of threading dislocation generation is observed. However, an In content of 2×1020/cm3 (a misfit of 7.5×10−4) in GaAs films doped in the middle of growth is found to be effective for changing the dislocation direction on the {111} planes.
Influence of stress and stress-flash annealing on the magnetic properties of amorphous Fe77.5Si7.5B15 wire
Authors: Mitra A. , Vazquez M. , Mandal K. , Ghatak S. K.
Published: July 2002

The influence of the tensile stress on the flux reversal phenomena in as-quenched state of Fe77.5Si7.5B15 is investigated. A large and stable Barkhausen jump is observed at a field H*, called the switching field. The switching field H* passes through a minimum as tensile stress increases and the jump in magnetization M* at H* grows with stress. It is observed that H* of the sample can be modified by flash annealing under stress. The results on magnetic properties like coercive field, squareness ratio, power loss of as-quenched and stress-annealed samples are presented. The stress annealing induces elastic and plastic components in anisotropy.
Lattice damage and atomic mixing induced by As++ implantation and thermal annealing in AlAs/GaAs multiple quantum-well structures
Authors: Huang D. , Kallergi M. , Aubel J. , Sundaram S. , DeSalvo G. , Comas J.
Published: July 2002

The lattice damage and the nature of the atomic intermixing of Al and Ga induced by As++ implantation and thermal annealing in AlAs/GaAs multiple quantum-well structures were investigated. The photoluminescence spectra, which show multiple peaks after implantation and annealing, were analyzed based on the shifts of the excitonic peaks arising from quantum wells located at different depths. The depth profiles of intermixing were obtained using a procedure of successive layer-by-layer chemical etching followed by photoluminescence measurements. It is found that the atomic mixing is maximum near the sample surface and decreases monotonically with depth, suggesting that the profiles follow more closely the ion induced damage than the ion density. It is also observed that the radiation damage extends beyond 1 μm. Within 0.3 μm from the surface, the damage is relatively heavy and the atomic intermixing increases rapidly with ion dose. Beyond 0.3 μm, the degree of intermixing is only sensitive to the anneal temperature but not to the implantation dose. The results show that both direct collisions and interdiffusion are responsible for the atomic mixing. For the samples implanted with ion doses below 1014 cm−2 and annealed at 650 °C, the optical activation from radiation damage is appreciable. However, the interdiffusion becomes important only at temperatures near and above 800 °C.
Spontaneous and persistent rotation of cylindrical magnets levitated by Y-Ba-Cu-O superconductors
Authors: Ma Ki-Bui , Liu Jia-Rui , McMichael Chase , Bruce Robert , Mims David , Chu Wei-Kan
Published: July 2002

When a cylindrical permanent magnet is levitated with a superconductor under certain conditions, it will rotate spontaneously and persist for an indefinite period of time. The results of this study elucidating the nature of this behavior are presented.
Optical transitions of a GaSb-AlSb superlattice in the 2–5 eV range
Authors: Da Silva F. W. O. , Ance C. , Raisin C.
Published: July 2002

We report reflectance measurements in the range 2–5 eV of a GaSb-AlSb superlattice grown by molecular-beam epitaxy. In the region of the E1 and E1 + Δ1 transitions, the electronic properties can be related to the formation of electronic subbands of a type II superlattice at the L point.
Spectroscopic investigation of hydrogen-dopant complexes in bulk p-type and implanted n-type crystalline silicon
Authors: Rizk R. , de Mierry P. , Song C. , Ballutaud D. , Pajot B.
Published: July 2002

Infrared absorption experiments have been performed on hydrogenated and deuterated bulk boron- and aluminum-doped-Si and implanted P, As, and Sb donors in silicon. A first evidence of complex formation in bulk p-type Si is obtained and the spectra confirm the anomalous 3.3-cm−1 deuterium frequency shift with respect to boron isotopes. The ratio of the D-11B and D-10B peak areas is found to be the same as that of the two boron isotopes natural abundance. In donor-implanted silicon, a quantitative analysis of the obtained data has allowed a rough estimate of the passivating rate due to diffusing deuterium. While the frequencies of the various vibrational lines are found to be in agreement with those reported in the literature, the data on the broad line at 1660 cm−1 (H) or 1220 cm−1 (D) seem to suggest an assignment of this peak to a complex in the bulk involving some type of defect due to the implantation process.
Optical anisotropy in dyed polyester fibers
Authors: Sokkar T. Z. N. , Ramadan W. A.
Published: July 2002

A two-beam microinterferometric technique is used for the determination of refractive indices and birefringence of undyed and dyed polyester fibers. These fibers are dyed with five different concentrations of Resoline Violet RL dyestuff. The diameter and cross-sectional shape of these fibers are determined from the diffraction pattern of a He-Ne laser beam incident perpendicular to the fiber axis. The Pluta polarizing interference microscope is used for the determination of (a) the mean refractive indices n∥a, n⊥a and the mean birefringence of the undyed and dyed polyester fibers and (b) the variation of refractive indices and birefringence across the diameter of these fibers. Variation of these optical properties with the dyestuff concentration is determined. Illustrations are given using microinterferograms.
Role of in situ rapid isothermal processing in advanced III-V technology
Authors: Thakur R. P. S. , Singh R. , Nelson A. J. , Swartzlander A. B.
Published: July 2002

Rapid isothermal processing (RIP) based on incoherent sources of light is emerging as a reduced thermal budget (product of processing time and temperature) processing technique. As compared to stand alone annealing unit, the in situ RIP unit is very attractive for the next generation of devices. A number of unwanted physical phenomena can be suppressed or completely eliminated in the in situ RIP case leading to improved quality of materials when compared to their ex situ rapid isothermal annealed and furnace annealed counterparts. We have used in situ rapid isothermal processor for the in situ rapid isothermal chemical cleaning of InP and GaAs substrates and in situ metallization of InP and GaAs Schottky diodes. As compared to ex situ annealing, the negligible oxygen content at the surface and interface of in situ RIP samples result in better current-voltage characteristics, lower and compressive stress values, as well as smooth and continuous morphologies of the ohmic contact. In this paper, we have highlighted the role of in situ RIP in the metallization of InP and GaAs devices.
Performance of a self-augmented railgun
Authors: Burton Rodney L. , Witherspoon F. Douglas , Goldstein Shyke A.
Published: July 2002

The accelerating force of a railgun 1/2L′I2a can be increased by augmenting the self-induced magnetic field created by the armature current. Augmentation fields can be produced by external current coils or, as is done here, by shorting the railgun muzzle, and using the gun rails as the augmentation coil. Experimental results are presented for a 3.6-m railgun operated in this self-augmented mode, and effective inductance gradients are achieved which are as much as 9.3 times that of the unaugmented gun. A circuit model is presented which explains features of the measured shunt current and voltage. It is concluded that self-augmentation is an effective way to reduce ohmic heating in the armature of a railgun.
Ballistic current-voltage characteristics of semiconductor superlattice electron-wave quantum-interference filter/emitter negative differential resistance devices
Authors: Glytsis Elias N. , Gaylord Thomas K. , Brennan Kevin F.
Published: July 2002

The transmission and current-voltage characteristics of Ga1−xAlxAs superlattice electron-wave quantum-interference filter/emitter negative differential resistance devices are analyzed with and without the self-consistency requirement. The analysis neglects the scattering effects within the superlattice since it is assumed that it is very thin (less than the electron coherence length). Thus, the calculated characteristics correspond to the ballistic component of the current. For the non-self-consistent calculation the single-band effective-mass time-independent Schroedinger equation is solved. For the self-consistent calculation, the Schroedinger and Poisson equations are solved iteratively until a self-consistent electron potential energy and electron density are obtained. It is shown that suitably designed electron-wave quantum-interference filter/emitters can exhibit strong negative differential resistance in the current-voltage characteristics, similar to those of resonant tunneling diodes. For low-to-moderate (2–30 meV) Fermi energies in the conduction band of Ga1−xAlxAs (Si doping concentration less or equal to 2 × 1018 cm−3) and temperatures near 30 K (in the ballistic transport regime), it is shown that space-charge effects are relatively small and result in a slight shift of the current-voltage and transmission characteristics toward higher bias voltages. In a fashion similar to that occurring in resonant tunneling diodes, the self-consistent field in electron-wave filter/emitter negative differential resistance devices partially screens the positive applied bias. Designs of Ga1−xAlxAs resonant devices with current peak-to-valley ratios of ∼50 as well as nonresonant (not exhibiting negative differential resistance) devices are analyzed. The corresponding electron charge density distributions are also presented. Superlattice electron-wave filter/emitter negative differential resistance devices can be used as high-speed switches, oscillators, and as monoenergetic emitters in electroluminescent devices and photodetectors.
Nonadiabatic small-polaron hopping electron transport in diphenoquinone-doped polycarbonate
Authors: Yamaguchi Yasuhiro , Yokoyama Masaaki
Published: July 2002

The dependences of electron mobility on the electric field F, temperature T, and hopping site distance R have been characterized in 3,5-dimethyl-3′,5′-di-tert-butyl-4,4′-diphenoquinone dispersed molecularly in a polycarbonate according to Schein’s analytical technique. The electron mobility can be described in the form a0R2 exp(−2R/R0) exp(−E0/kT) × exp[β(1/kT−1/kT0)F1/2], where a0, R0, β, and T0 are constants. Moreover, it is found that the zero-field activation energy E0 is independent of R. The invariable E0 and the exponential dependence of the Arrhenius prefactor on R strongly suggest that the electron transport therein is due to nonadiabatic small-polaron hopping. Based on the small-polaron theory, the transport properties are qualitatively discussed in terms of molecular properties.
Analysis of damage created by ion implantation in GaAs using process simulation
Authors: Itakura Keijiro , Shimamoto Yukiharu , Okamoto Shigeru , Ueda Daisuke
Published: July 2002

Compensation profile in ion-implanted GaAs has been analyzed by the simulation based on the Boltzmann transport equation. Comparing the simulations with experiments, we found that the compensation profile was originated in two types of defect distribution. One was created by deposited energy and the other was created by the implanted ions in the material. These two compensation profiles have two different energy levels, since the so-called L band splits into two peaks in deep level transient spectroscopy after annealing the sample. Based on the simulated results, we also introduced two different compensation yields of ion implantation.
Hydrogen permeation through copper-coated palladium
Authors: Andrew P. L. , Haasz A. A.
Published: July 2002

The rate of hydrogen uptake and release by metals can be strongly affected by surface barriers for adsorption and desorption. The rate of hydrogen permeation through a Pd membrane was measured for both incident molecules (10−3–10−4 Pa) and neutral atoms (1016–1019 H0/m2⋅ s) for membrane temperatures of 300–570 K. The pressure dependence of H2-driven permeation was used to identify regimes where the permeation was controlled by bulk processes (diffusion-limited) and surface processes (surface-limited). The dependence of the H0-driven permeation rate on the direction of permeation was used to separate the contribution of each surface to the overall surface-limited permeation rate. One of the membrane surfaces was coated in situ with copper evaporated from a hot source. This same surface could be monitored in situ by Auger electron spectroscopy. At temperatures below 450 K, stable copper coatings were made with thicknesses ranging from ∼3 to 25 nm. The thin Cu coatings led to a decrease in the H2-driven permeation rate. The permeation rate was found to increase, however, for H0 atoms incident on the Cu-coated surface. This is consistent with a barrier for H2 dissociation and H recombination at the Cu/vacuum interface. Membranes with such a barrier, in conjunction with a source of H0 atoms, have applications as hydrogen pumps.
Adsorption of Ba on the GaAs(110) surface and its effect on surface oxidation
Authors: Fan W. C. , Ignatiev A.
Published: July 2002

Adsorption of Ba and its effect on the GaAs(110) surface oxidation has been studied by low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). The Ba adsorption onto the surface results in a disordered interface of Ba and the GaAs surface at temperatures <500 °C. However, the reactivity of the GaAs surface to oxygen is dramatically enhanced by the adsorbed Ba atoms. This enhancement of the surface oxidation is proportional to the Ba exposure. Study of LEED and AES intensities has also revealed evidence of Ba-induced surface disorder on the GaAs.
Selenium-DX center-doped AlxGa1−xAs grown by molecular beam epitaxy
Authors: Basmaji P.
Published: July 2002

The electrical transport properties of epitaxial Se-Al0.1Ga0.9As grown by molecular beam epitaxy were studied. The carrier concentration was deduced from the Shubnikov–de Haas oscillations. At low temperature, persistent photoconductivity was not observed.
Novel carbon-doped p-channel GaAs metal-semiconductor field-effect transistor grown by metalorganic molecular beam epitaxy
Authors: Ren F. , Abernathy C. R. , Pearton S. J.
Published: July 2002

A high performance GaAs p-metal-semiconductor field-effect transistor (MESFET) using carbon as the p-dopant is demonstrated. The channel and contact layers were grown by metalorganic molecular beam epitaxy (MOMBE). The cap contact layer was highly doped with carbon (5×1020 cm−3) in order to minimize the parasitic resistance in the FET structure. The sheet resistivity and transfer resistance of the contacts were 220 Ω/⧠ and 0.2 Ω mm, respectively. These are comparable to values achieved on n-type GaAs. The room temperature extrinsic transconductance and K-factor values were 50 mS/mm and 165 mS/V⋅mm with 1 μm gate length and 3.5 μm source-to-drain spacings. These are the highest room temperature values ever demonstrated for p-GaAs MESFET.
Plasma-synthesized fluoropolymer films for molecular sensing probes
Authors: Sugimoto Iwao
Published: July 2002

Fluoropolymer films deposited on quartz crystals by radio-frequency sputtering of polychlorotrifluoroethylene can be used for molecular sensing probes. For several organic materials, the piezoelectric responses of these sensing probes can be classified into characteristic categories. These responses are especially distinctive for highly fluorinated molecules. A film with highly halogenated frameworks shows slow sorption-desorption response to alternate exposures to acetone atmosphere and to air.
Monte Carlo calculation of temperature dependence of the transport properties in compensated GaAs
Authors: Wu Ernest Y. , Yu Bernard H.
Published: July 2002

Monte Carlo calculation has been applied to investigate the temperature and compensation dependence of steady-state electron transport in n-type GaAs over a wide range of applied field strengths. It is found that doping compensation has stronger effect on the transport properties at low temperatures than at high temperatures. Compensation-enhanced impurity scattering is responsible for the reduction not only in low-field mobilities and peak velocities but also in the negative differential mobilities and the high-field velocities. The two-maxima behavior in the velocity-field characteristics persists at low temperatures through room temperatures for high doping compensation then it starts to diminish at 450 K except for compensation ratio of 0.9. The physical origin of this unique two maxima feature in the velocity-field relation has been discussed in comparison with other compensated semiconductors.
Process dependence of breakdown field in thermally nitrided silicon dioxide
Authors: Ramesh K. , Chandorkar A. N. , Vasi J.
Published: July 2002

We have studied the dependence of breakdown field in nitrided oxides on nitridation conditions. Nitridation improves the breakdown field of the oxides. In an attempt to explore the cause of the improved breakdown, the breakdown field was related with electron-trap density and refractive index (which increases with nitrogen concentration in the oxide). Our results suggest that the enhanced breakdown field of nitrided oxides is mainly due to incorporation of nitrogen, which results in structural changes in the nitrided oxide.
Linear and nonlinear photoconductivity from charge-producing defects in CaF2
Authors: O’Connell Robert M. , Marrs C. Denton
Published: July 2002

Room-temperature measurements of linear and nonlinear photoconductivity in CaF2 containing trace amounts of yttrium, lanthanum, and several rare earths are reported and discussed. Linear spectral photoconductivity scans taken over the 1.55- to 6.20-eV range of photon energies produced significant photocurrents above 3 eV. The results are explained in terms of a combination of 4f-5d absorption in Ce+3 and Pr+3 and photoionization of interstitial F− in both nearest-neighbor charge-compensating defects and anion-Frenkel defects. Peak photocurrents induced by focused 950-ns-wide pulses from a 496.5-nm wavelength dye laser increased nonlinearly with increasing laser pulse energy. These results are interpreted as a transition from two-photon conductivity to electron avalanche and the asymptotic approach to the material’s laser damage threshold at approximately 27 GW/cm2.
Rapid thermal annealing effects on the properties of plasma-enhanced chemical vapor deposited tungsten films
Authors: Hong Jong-Sung , Kim Yong Tae , Min Suk-Ki , Kang Tae Won , Hong Chi Yhou
Published: July 2002

Tungsten films have been deposited onto single-crystal silicon (Si) and silicon dioxide (SiO2) by plasma-enhanced chemical vapor deposition with WF6-SiH4-H2 chemistry: the annealing effect on these films has been investigated by rapid thermal annealing. The deposition rate of the tungsten films on both sides of Si and SiO2 is linearly dependent on the SiH4/WF6 ratio up to 1 and the deposition rate is not increased beyond this ratio (SiH4/WF6=1). Phase transition from α-W to β-W and silicidation are observed under the annealing at 900 °C for 15 s in W films on Si. On the other hand, resistivities of W films on SiO2 are decreased under the same annealing condition. The resistivity reduction in W films on SiO2 is believed to be the results of the grain growth and point, line defect removal, and out-diffusion of impurity atoms such as oxygen, fluorine, and silicon. In addition to this grain growth, the intensities of x-ray diffraction peaks are increased after the rapid thermal annealing. Etching process of the tungsten layer has been performed with a reactive ion etcher using CF4-O2 etchant. The etch rate of the as-deposited tungsten film is about 7800 Å/min, and decreases with increase of annealing temperature to about 4600 Å/min for the tungsten films annealed at 1000 °C for 15 s. This decrease in etch rate is believed to be caused by the decreases of the absorption site for etching sources due to grain growth and defect removal.
Dynamical effects of biaxial strain in thin Cu/Ni(111) superlattices
Authors: Colombo L. , Miglio L. , Brito-Orta R. A. , Velasco V. R. , Garcia-Moliner F.
Published: July 2002

In the framework of a central force-constant model and a surface Green function matching technique we calculate the dynamical effects of biaxial strain in a short period Cu/Ni(111) superlattice. We show that sizeable changes in the spectral features are predicted, so that a spectroscopic characterization of these systems is stimulated. An important reason to investigate the vibrational features of such a system is that it has been studied in detail as a prototype of fcc-modulated alloys, i.e., artificially grown structures, which edisplay a huge stiffening of the bulk modulus.
Direct nitridation of a silicon surface by multipulse excimer laser irradiation in a nitrogen-containing ambient gas
Authors: Mihailescu I. N. , Craciun V. , Nistor L. C. , Teodorescu V. S. , D’Anna E. , Leggieri G. , Luches A. , Martino M. , Perrone A. , Drigo A. V. , Ganatsios S. , Zemek J.
Published: July 2002

The successful synthesis of silicon nitride directly on the surface of a single-crystalline silicon wafer by multipulse (up to n=2500) XeCl* excimer (λ=308 nm) laser irradiation in ambient ammonia or nitrogen atmospheres is reported. The amount and quality of the nitrided layers formed are shown to depend on both the number of subsequent laser pulses applied to the same irradiation site as well as on the nature of the ambient gas. Nuclear reactions, Auger electron spectroscopy, Rutherford backscattering spectroscopy, electrical measurements, and optical and electron microscopy were applied to characterize the synthesized surface layers.