bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrogen passivation of a nickel-related defect in germanium
Authors: Tavendale A. J. , Pearton S. J.
Published: February 2003

The passivation of a deep acceptor level (Ev+0.14 eV) associated with nickel in single-crystal germanium by reaction with atomic hydrogen has been observed using deep level transient spectroscopy. The concentration profile of this defect center is presented as a function of the duration and temperature of the exposure to atomic hydrogen; a 2-h exposure at 300 °C neutralized ∼90% of the acceptor centers to depths >50 μm.
Correlation between cadmium telluride surface oxidation and metal junctions
Authors: Werthen J. G. , Häring J.-P. , Bube R. H.
Published: February 2003

X-ray photoelectron spectroscopy analysis of cleaved single crystal CdTe {110} surfaces exposed to air indicates the growth of tellurium dioxide (TeO2). Its presence is directly reflected in the properties of Cr/CdTe junctions formed on the cleaved surfaces exposed to air for different lengths of time; the saturation current for a junction formed on a cleaved surface exposed to air for 5 min is 2×10−8 A/cm2, whereas a surface exposed to air for 2 h yields a junction with a saturation current of 4×10−9 A/cm2. Corresponding values of open circuit voltages are 0.45 and 0.55 V, respectively. The increase in the open circuit voltage is directly attributable to the presence of TeO2 on the air exposed surface.
Cone formation on argon-bombarded copper
Authors: Ghose D. , Basu D. , Karmohapatro S. B.
Published: February 2003

Conical protrusions observed in the scanning electron microscope on surfaces of copper which have been eroded by 20.5-keV Ar+ ion bombardment are studied for various doses of ions. The critical dose and the cone apex angle are determined, and the results discussed in the light of the existing theories show the importance of secondary and tertiary effects in the evolution of the structure of cones.
Diffraction of horizontally polarized shear waves by normal edge cracks in a plate
Authors: Abduljabbar Z. , Datta S. K. , Shah A. H.
Published: February 2003

A combined finite element and analytical method is presented here for analyzing scattering of time harmonic horizontally polarized shear (SH) waves by material and geometric irregularities in an isotropic linearly elastic infinite plate. All the irregularities are assumed to be contained in a bounded region. The problem of scattering is solved by replacing this region with a finite element mesh. A nodal force-displacement relation is developed to satisfy the continuity conditions along the boundaries separating the inner finite-element region from the exterior regular region. The method is illustrated by solving the problem of scattering of SH waves by a surface breaking crack. The crack is taken to be normal to the surface of the plate. The reflection and transmission coefficients are computed for zeroeth, first, and second incident wave modes. The validity and accuracy of the results are checked by satisfaction of the energy conservation principle and the reciprocity relations.
Multidetector intensity interferometers
Authors: Fontana Peter R.
Published: February 2003

The intensity fluctuations of incoherent radiation are used to determine the position of sources with respect to a detector system. For electromagnetic radiation the system uses square-law detectors and for acoustic waves the detector output is squared before being processed. The theory is developed for n detectors and the results are applied to two-, three-, and four-detector arrangements. The two-detector intensity inteferometer measures the square of the first-order correlation function and can determine the angular size of a source. The three-detector intensity interferometer yields two coordinates of the location of a source, and a modified version involving only one detector functions as a Fourier transform spectrometer. It measures the first-order correlation function and thus can be used to obtain the spectrum of the source. The four-detector intensity interferometer can simultaneously determine the three-dimensional coordinates of several sources. The operation of several acoustic multidetector intensity interferometers are described and a number of applications are discussed.
Statistical investigations of signals detected by nonideal detectors
Authors: Harwalkar V. , Bohidar H. , Chopra S.
Published: February 2003

We analyze the statistical properties of Gaussian and non-Gaussian signals detected by a nonideal photon detector. Such a detector is assigned a realistic response function, and parameters like average intensity and bunching property are evaluated. We show that there is a significant difference between the signal detected by an ideal and a nonideal detector.
Lateral waves: Formulas for the magnetic field
Authors: King R. W. P. , Wu T. T.
Published: February 2003

New simple formulas are obtained as an approximation of the exact general integrals for the components of the magnetic field generated by a horizontal electric dipole in a half-space of water or earth near its boundary with air. These formulas supplement the earlier derivation of the three components of the electric field which are repeated here for completeness. The formulas for the transverse and vertical components are needed in treating the reflection of lateral waves from plane or cylindrical boundaries.
The field distribution of a focused Gaussian beam reflected at 45° from a conducting plane and its effects in plasma-ignition experiments
Authors: Carter William H. , Wieting Terence J.
Published: February 2003

The electrical field distribution over the focal region of a Gaussian beam, incident at 45° and focused onto a perfectly conducting infinite plane, is calculated numerically by summing the plane waves in an angular spectrum representation. The beam is plane-polarized with the transverse electric field perpendicular to the plane of incidence. The configuration and parameters were chosen to agree with our experiments on plasma initiation near a metallic conductor by 35-GHz/8.6-mm microwave radiation. The results of the calculation show that the field distribution determines the ignition threshold, spatial location, and initial development of the microwave plasma at a metal surface.
Effects of iodine saturation dispersion on the 127I2 stabilized He-Ne laser
Authors: Ghosh Roy D. N. , Bertinetto F. , Rebaglia B. I. , Cresto P. C.
Published: February 2003

In a 127I2 stabilized 633-nm He-Ne laser, the effects of saturation dispersion in iodine on the inverted Lamb dips of the iodine hyperfine components are discussed. Analytical expressions for the second and third harmonic of the frequency modulated dips are derived. Dispersion is found to influence strongly the modulation dependent frequency shifts of the absorption line centers and also introduce asymmetry in the second harmonic.
Photoinduced changes in the Urbach tail in Ge- and As-based chalcogenide glasses
Authors: Harshavardhan K. Solomon , Rajagopalan S. , Malhotra L. K. , Chopra K. L.
Published: February 2003

The Urbach tail features of normal and obliquely deposited Ge- and As-based chalcogenide films have been investigated. A correlation of these features with composition, angle of deposition, photoinduced edge shift, average coordination number, and photoinduced volume contraction has been established. The far infrared (IR) vibrational spectra reveal that bond angle variations are the dominant features of the photoinduced structural transformation, rather than the bond stretching variations. The far IR and Urbach tail studies suggest that the strength of electron-phonon coupling is enhanced in Ge-based chalcogenide films having a very porous, columnar microstructure. Further, the coupling is maximum at the best glass forming composition of the chalcogenide.
Possible wave formation and martensitic transformation of iron particles in copper single crystals during argon ion bombardment
Authors: Thölén A. R. , Li Chang-Hai , Easterling K. E.
Published: February 2003

Thin single crystal copper specimens (thickness ∼250 nm) containing coherent iron particles (diameter 40–50 nm) have been bombarded with argon ions (5, 80, and 330 keV). During this process some of the iron particles transform to martensite. The transformation was observed near the exposed surface and sometimes also close to the other surface but never in between. This is interpreted in terms of mechanical waves starting from the impact area.
Stress relief in heavily doped silicon layers
Authors: Moser F. , Beserman R.
Published: February 2003

The Raman spectra of epitaxial silicon layers on sapphire substrates, as well as polycrystalline silicon on vitreous quartz, have been measured after various treatments. In silicon on sapphire layers, grown epitaxially near 1000 °C, the Raman peak is broadened and shifted to higher energy compared to that observed in melt-grown single crystals. This is a consequence of the compressive stress exerted on the silicon by the sapphire substrate. Amorphization by dopant ions and rapid thermal regrowth at temperatures near 550 °C results in a Raman band shifted to near the single crystal phonon energy of 521 cm−1. The effect is a consequence of the enhancement of low temperature crystallization by dopant ions and the accompanying stress relief. Polycrystalline silicon on vitreous quartz shows a Raman band shifted to low energy, 515 cm−1, and broadened by a factor of 2 compared to the single crystal half-width of 3.5 cm−1. In this case, the Raman changes are a combination of the effects of tensile stress and polycrystallinity.
Grain growth control in ZnO varistors using seed grains
Authors: Eda Kazuo , Inada Masanori , Matsuoka Michio
Published: February 2003

A method for making low-voltage ZnO varistors having extraordinarily large grain size without necessity of sintering at much higher temperatures or for much longer times is reported. The device is made by sintering a mixture of ZnO fine powder, additives, and ZnO seed grains having grain sizes of 63–105 μm obtained by washing a ZnO sintered body containing BaO in boiling water. The device has a grain size around 500 μm and low threshold voltage of 6 V/mm. Such anomalous grain growth is caused by the difference between the radii of curvature of ZnO fine powder and ZnO seed grains.
Si(p,α) total-reaction cross sections for microelectronic applications
Authors: Maughan G. R. , McCamis R. H. , Okumusoglu N. T. , van Oers W. T. H.
Published: February 2003

When the nucleon component of the cosmic ray flux interacts with the silicon in computer memory chips, the resulting highly ionizing particles can cause memory errors. Therefore, the natural silicon and 27Al( p,α) and ( p,3He) total cross sections have been obtained at proton energies of 35 and 45 MeV by integrating the differential cross section angular distributions. The accuracy of the measurements is significantly better than previous measurements. These measurements, along with measurements from the literature, show the energy dependence of the Si( p,α) cross section. This energy dependence was convoluted with the cosmic ray flux to determine an upper limit for the failure rate of silicon microcircuits due to cosmic ray sources.
The effect of illumination of inversion layer formation in metal-thin oxide-silicon devices
Authors: Shanker D. , Kar S.
Published: February 2003

The influence of light intensity on the formation of inversion layers in metal-oxide-silicon tunnel devices has been investigated. A strong inversion layer forms in these devices when the rate of tunneling of minority carriers through the oxide falls far behind their rate of arrival at the silicon-oxide interface. The latter is strongly dependent on the light intensity. The inversion layer formation manifests itself very clearly in the high frequency C−2(V) characteristic through the formation of a knee. For a given oxide thickness, the knee becomes broader with increasing light intensity, and for a given light intensity, the knee appears above a critical oxide thickness. This critical oxide thickness decreases with increasing light intensity.
Torque induced on a conducting cylinder by a slowly rotating magnetic field
Authors: Groh David J. , Dixon Joseph R.
Published: February 2003

Expressions are derived for the torque induced on a hollow or solid conducting cylinder by a large slowly rotating magnetic field. The cylinder is described by a conductivity tensor with the off-diagonal elements equal to zero and two diagonal elements equal to each other but possibly different from the third. For isotropic conductivity the expressions presented reduce to analytic forms simpler than those previously published.
Multilongitudinal mode operation in angled stripe buried heterostructure lasers
Authors: Tsang W. T. , Logan R. A. , Ditzenberger J. A.
Published: February 2003

The various index-guided lasers have superior device performance over gain-guided lasers but operate in single longitudinal mode rendering them unsuitable for use as optical sources in multimode optical fiber transmission systems because of the increased modal noise produced. In this experiment we show that multilongitudinal mode operation can be obtained in buried-heterostructure (BH) lasers throughout the entire output power range from threshold to catastrophic damage by angling the buried active stripes so that they are nonorthogonal to the cleaved facets by angles, θ≳5°. These lasers also exhibit the various desirable characteristics of BH lasers with θ=0° such as linearity in light-current, low spontaneous emission level, and abrupt turnon of lasing. The angles buried stripe caused no noticeable degradation of threshold current, Ith, or external differential quantum efficiency, ηD. The averaged Ith ranged between 16 to 20 mA in all lasers and ηD increased with θ. In all cases, the lasers operated stably in the lowest order transverse mode.
Optical and elastic properties of AgTlSe
Authors: Newman P. R. , Ewbank M. D. , Kuwamoto H. , Morgan P. E. D. , Ehrenfreund E.
Published: February 2003

The optical and elastic properties of AgTlSe have been measured, including acoustic velocities, optical transmission, refractive indices and birefringences. The relatively low shear velocities and high refractive index indicate that the acousto-optic figure of merit of AgTlSe is large.
Laser-addressed liquid crystal light valve with dichroic dye added as a laser beam absorber
Authors: Urabe Tetsuo , Arai Kunihiko , Ohkoshi Akio
Published: February 2003

A dichroic dye was added to smectic A liquid crystals as an absorber of laser energy to eliminate the need to conduct heat from an external absorber to the liquid crystal layer. It was found that the dichroic ratio of the added dye is an important factor in the recording mechanism of the liquid crystal. The resolution of the written image was improved by doping with a dye having a large dichroic ratio.
Drilling with NdYAG, NdYAP, and Nd glass lasers
Authors: Lindgren Lars , Roos Sven-Olov
Published: February 2003

Laser drilling in thin metal plates has been studied with three different types of laser rods: NdYAG (yttrium aluminum garnet, Y3Al5O12), NdYAP (ytrium ortho aluminate, YAlO3), and Nd glass. The rods have widely different pulse shapes and thus different drilling performance. Our experiments were made in 0.5-mm plates of aluminum and stainless steel. The length of the laser pulse was 200 μs and the pulse energies were up to approximately 1 J. When small holes are drilled in some materials, e.g., aluminum, NdYAG gives holes completely clogged by molten material. The use of NdYAP solves these problems by a reduction in the amount of molten material and a more efficient ejection of the molten material produced. Nd glass is also usable, but higher energy is required. In materials without the clogging problem, NdYAG is the most efficient.
Reactive ion etching of GaAs in CCl4−xFx (x=0, 2, 4) and mixed CCl4−xFx/Ar discharges
Authors: Klinger R. E. , Greene J. E.
Published: February 2003

The reactive ion etching of (100) GaAs in pure CCl2F2 and CF4 discharges, as well as in mixtures of Ar and CCl4, CCl2F2, or CF4, has been investigated. Anisotropic etching with removal rates R of up to 800 nm/min have been obtained in reactive discharges operated at a pressure of 5.3 Pa (40 mTorr) and a target voltage of −3 kV. The physical sputtering rate in pure Ar discharges operated under the same conditions was only 40 nm/min. A combination of in situ optical emission and absorption spectroscopies have been used to show that in both pure and dilute (up to 90 mole % Ar) halocarbon discharges, physical sputtering of atomic Ga and As is not a primary etching mechanism for GaAs, although ion bombardment does play a critical role in the overall process. Transient glow discharge optical spectroscopy measurements demonstrated that while R increased with increasing Cl/F ratios in the etch gas, the steady state carbon concentration at the GaAs surface also increased indicating that carbon accumulation is not the rate limiting step to etching. Rather, the rate limitation is provided by the desorption kinetics of gallium halides which we believe are ejected primarily (except in pure CCl4) through ion-assisted processes as the reduced radicals GaFx and/or GaClx (x=1 or 2). A phenomenological model is proposed to provide a qualitative description of the etching behavior of GaAs in mixed halocarbon/inert gas discharges.
Guiding magnetostatic surface waves with nonuniform in-plane fields
Authors: Stancil D. D. , Morgenthaler F. R.
Published: February 2003

We report the propagation characteristics of magnetostatic surface waves in a rectangular yttrium iron garnet film placed between strips of mumetal and in the plane of the strips. The microstrip excitation structure was designed so as to permit the strips to extend along the entire path of propagation, thereby minimizing field nonuniformities in the longitudinal direction. These experiments suggest that nonuniform in-plane fields can be used to alter the dispersion characteristics of the waves. A theoretical argument is also presented describing a possible energy localization mechanism in nonuniform in-plane fields. In addition, experiments are described in which nonuniform fields caused by a slot in a mumetal covering layer are used to guide magnetostatic surface waves through a turn of 160°.
Effect of finite coil thickness in a magnetic deflection system
Authors: Dasgupta Basab B.
Published: February 2003

The effect of finite coil thickness on the magnetic field produced by a magnetic deflection coil in the shape of a long right circular cylinder is calculated. It is found that the higher ‘‘multipole’’ contents of the field (i.e., the coefficients of higher order terms in a Fourier expansion about the coil axis) decrease by progressively larger percent amounts compared to their values for a coil of zero thickness.
Nonlinear elastic effects in bismuth whiskers
Authors: Powell B. E. , Skove M. J.
Published: February 2003

Finite deformations have a stress (σ)–strain (ε) relation of the form ε=s′11σ +δ(s11σ)2, where s′11 is an elastic compliance and δ is a combination of second-order and third-order elastic constants. Tensile tests performed on bismuth whisker crystals oriented in the 〈111̄〉 and 〈11̄0〉 directions give δ111̄ =7.6±0.5 and δ11̄0 =0±0.3, respectively. Orientations are given in the rhombohedral system in which the angle between axes is approximately 57°.
The electrical properties of deep copper- and nickel-related centers in silicon
Authors: Pearton S. J. , Tavendale A. J.
Published: February 2003

The dominant deep level defects related to copper and nickel in p-type silicon have been studied using deep level transient spectroscopy. Three acceptor states are observed in copper-doped silicon (Ev+0.20 eV, Ev+0.35 eV, and Ev+0.53 eV) and three acceptor states observed in nickel-doped silicon (Ev+0.18 eV, Ev+0.21 eV, and Ev+0.33 eV). All of these defects are neutralized by reaction with atomic hydrogen, and a concentration profile for the Ev+0.18 eV Ni-related state is given as a function of the duration and temperature of the exposure to the hydrogen plasma. Gamma irradiation produces additional donor levels at Ec−0.38 eV in the copper-doped material, and at Ec−0.32 eV in the nickel-doped material. Finally, the room temperature motion of three of the acceptor levels, Cu(Ev+0.20 eV) and Ni(Ev+0.21 eV, Ev+0.33 eV), under the influence of the electric field in a reverse biased p-n junction is reported. The mobilities obtained for centers associated with these three levels at 25 °C were 10−14, 6×10−15, and 2×10−15 cm2 V−1 s−1, respectively.
I-V and C-V studies of evaporated amorphous arsenic telluride film on crystalline silicon
Authors: Krupanidhi S. B. , Srivastava R. K. , Srinivas K. , Bhattacharya D. K. , Mansingh Abhai
Published: February 2003

The I-V characteristics of amorphous arsenic telluride (As2Te3) thin film on single-crystalline silicon substrates exhibit similarity with the characteristics of a heterojunction formed between crystalline semiconductors and the carrier transport, which involves more than one conduction mechanism at the interface. The recombination, tunnelling, and space-charge-limited carrier transport takes place at the interface successively, depending on the magnitude of the applied voltage. The heterojunction properties dominate at lower voltages (below 1 V), while at the higher voltages, the I-V characteristic is determined by the As2Te3 film. The temperature-dependent I-V characteristics confirm the formation of a heterojunction at the silicon-As2Te3 (film) interface. The built-in potential evaluated from the I-V characteristics (∼0.2 V) agrees well with the observed open-circuit photovoltage Voc. Contrary to the I-V characteristics, the C-V characteristics resemble the characteristics of a conventional metal-insulator-semiconductor (MIS) structure. This can be qualitatively explained by assuming the heterojunction to have a low breakdown potential (∼1.0 V), and the junction barrier capacitance in the breakdown region to be higher than either the film or the depletion capacitance.
Statistics of a surface space-charge region for a nonparabolic semiconductor
Authors: Cochran David R. , Leonard William F.
Published: February 2003

Surface statistics in narrow-gap zincblende semiconductors are examined. The model employed consists of a nonparabolic conduction band and a parabolic valence band taking indium antimonide as a representative for this family of materials. The statistics of the surface space-charge region are evaluated for a range of surface potentials and bulk concentrations using both the nonparabolic band and the standard parabolic band models. These analyses are made using the semiclassical approach.
Photoelectron spectroscopic determination of the structure of (Cs,O) activated GaAs (110) surfaces
Authors: Su C. Y. , Spicer W. E. , Lindau I.
Published: February 2003

p-GaAs (110) surfaces activated to negative electron affinity (NEA) have been examined with photoelectron spectroscopy. A typical activated GaAs surface is found to consist of both a layer of oxygen bonded to GaAs and a (Cs+,O−2) layer. The GaAs-O layer was not anticipated prior to this work. A GaAs-O-Cs dipole plus the polarization of a Cs+-O−2-Cs+ sandwich layer is proposed to explain the NEA condition based on the structure of activated surfaces found in this work. The identification of the O-GaAs bonding layer explains the better yield achieved by the two-step activation process compared to that achieved by a single-step process. Possible optimization of the activation process by forming the O-GaAs layer and the (Cs+,O−2) layer is also discussed. Adsorption of OH from the residual gas in an ultrahigh vacuum chamber is identified as one degradation mechanism of the GaAs photocathodes.
Electrical characterization of grain boundaries in GaAs
Authors: Spencer Michael G. , Schaff William J. , Wagner D. Ken
Published: February 2003

Grain-boundary capacitance versus voltage, current versus voltage, and capacitance transient measurements are reported on lightly doped n-type GaAs bicrystals. The measurements are analyzed in terms of the abrupt depletion edge model in which the dominant current mechanism across the potential barrier formed by trapped charge at the interface is thermionic emission. The steady-state measurements are completely consistent with this model and provide grain-boundary parameters (barrier height, net carrier concentration in adjacent grains, and interface charge) necessary for interpreting capacitance transient measurements. The latter, made on a bicrystal specially selected for uniformity of the grain-boundary barrier, reveal the presence of two closely spaced levels at 0.62 and 0.74 eV below the conduction band edge. The capture cross section associated with the dominant lower level is measured directly by two methods and falls in the range 10−14–10−13 cm2.
An electron spin resonance study of radiation-induced electrically active paramagnetic centers at the Si/SiO2 interface
Authors: Lenahan P. M. , Dressendorfer P. V.
Published: February 2003

We have compared the generation of radiation-induced Pb (‘‘trivalent silicon’’) centers at the Si/SiO2 interface with the radiation-induced buildup of interface states. We observe a strong correlation between the density of Pb centers and radiation-induced interface state density (Dit) and similar annealing behavior of radiation-induced Pb and Dit. Furthermore, the Pb resonance intensity is strongly bias dependent; this indicates that the charge state of the Pb defect is bias dependent. We conclude that Pb defects account for a very large portion of radiation-induced interface states.
The preparation of i
n s
i
t
u doped hydrogenated amorphous silicon by homogeneous chemical vapor deposition
Authors: Meyerson B. S. , Scott B. A. , Wolford D. J.
Published: February 2003

Raman scattering, infrared absorption, conductivity measurements, electron microprobe, and secondary ion mass spectrometry (SIMS) were used to characterize boron and phosphorus doped hydrogenated amorphous silicon (a-Si:H) films prepared by Homogeneous Chemical Vapor Deposition (HOMOCVD). HOMOCVD is a thermal process which relies upon the gas phase pyrolysis of a source (silane containing up to 1.0% diborane or phosphine) to generate activated species for deposition upon a cooled substrate. Doped films prepared at 275 °C by this process were found to contain ∼12-at. % hydrogen as determined by infrared absorption. We examined dopant incorporation from the gas phase, obtaining values for a distribution coefficient CD (film dopant content/gas phase dopant concentration, atomic basis) of 0.33≤CD ≤0.63 for boron, while 0.4≤CD ≤10.75 in the limits 3.3×10−5≤PH3/SiH4≤0.004. We interpret the data as indicative of the formation of an unstable phosphorus/silicon intermediate in the gas phase, leading to the observed enhancements in CD at high gas phase phosphine content. HOMOCVD films doped at least as efficiently as their prepared counterparts, but tended to achieve higher conductivities [σ≥0.1 (Ω cm)−1 for 4.0% incorporated phosphorus] in the limit of heavy doping. Raman spectra showed no evidence of crystallinity in the doped films. Film properties (conductivity, activation energy of of conduction) have not saturated at the doping levels investigated here, making the attainment of higher ‘‘active’’ dopant levels a possibility. We attribute the observation that HOMOCVD appears more amenable to high ‘‘active’’ dopant levels than plasma techniques to the low (∼0.1 eV) thermal energy at which HOMOCVD proceeds, versus ∼10–100 eV for plasma techniques. Low substrate temperature (75 °C) doped films were prepared with initial results showing these films to dope as readily as those prepared at high temperature (T∼275 °C).
Magnetoelastic equations for antiferromagnetic insulators of the easy axis type
Authors: Sioké-Rainaldy J. , Maugin G. A.
Published: February 2003

Sets of magnetoelastic equations in the quasi-magnetostatic approximation and in the absence of dissipation are deduced for uniaxial antiferromagnets of the easy-axis type on the basis of a previously set forth fully nonlinear, rotationally invariant, thermodynamically admissible theory of deformable ferrimagnets. The equations are obtained for three typical initial magnetic configurations where the bias field is either parallel or orthogonal to the easy axis and depending on whether this field is weak, moderate or strong relatively to some combinations of material parameters. In each case, the linearization about the initial configuration (which is automatically endowed with initial fields and internal stresses) is performed by means of the so-called Lagrangian variation of the nonlinear field and constitutive equations. In the process of linearization, all elastic, magnetic, and magnetoelastic coefficients evaluated at the initial state are given a thermodynamical definition. The linearization about a finite initial state allows one to exhibit the various influences of this state on the linearized equations and the alterations brought on the material-coefficient tensors (stiffening of the elasticity coefficients, symmetry breaking by the bias magnetic field, magnetoelastic coupling at any order since the linearization is made with a fully nonlinear theory as starting point).
Magnetic properties and growth conditions of manganese-containing iron garnet films for magnetic bubbles
Authors: Breed D. J. , Voermans A. B. , Nederpel P. Q. J. , van Bakel B. A. H.
Published: February 2003

Manganese can be substituted in iron garnet films in order to increase the magnetostriction constants. When these films are grown under compression, magnetic anisotropy is introduced. The influence of manganese on film-growth conditions and magnetic properties has been studied. Phenomenological equations are derived to describe the properties of the manganese-containing garnet films. These equations were successfully applied in a test case of tailoring the properties of garnet films.
Polarization reversal associated with rotation of chain molecules in β-phase polyvinylidene fluoride
Authors: Furukawa T. , Date M. , Johnson G. E.
Published: February 2003

The time dependence of polarization reversal in β-phase polyvinylidene fluoride has been measured under a step-function field up to 200 MV/m below room temperature. Fairly fast switching has been found to occur which might be accomplished by a 180° rotation of individual chains around their chain axes in the crystalline lamellae. The field dependence of the switching time is strong as indicated by a very high activation field of 1–2 GV/m or a large power law index of 8.0–10.5. The shape of switching transient has been investigated phenomenologically and by computer simulation on the basis of a nucleation and growth model. It is shown that the model is consistent with observations if one-dimensional growth and an appropriate ratio of growth velocity to nucleation probability are assumed. Effects of the size of nuclei and domains are examined.
Performance characteristics of a transverse-flow, oxygen-iodine chemical laser in a low gas-flow velocity
Authors: Watanabe K. , Kashiwabara S. , Sawai K. , Toshima S. , Fujimoto R.
Published: February 2003

Performance characteristics are reported for a transverse-flow, oxygen-iodine chemical laser which operates at a low level (8 m/s) of linear flow gas velocity using a small size vacuum pump. This is the first time that dependences of laser output power have experimentally been found on Cl2 and I2 flow rates. Output powers in excess of 10 W have been efficiently extracted from a 50×0.5-cm rectangular flow duct. A total energy of 11 kJ from one gram of iodine has been obtained. The reaction mechanisms associated with the power decrease in high concentrations of I2 are carefully discussed.
The identification of copper in long lived GaAlAs double heterostructure lasers by means of electron probe x-ray microanalysis
Authors: Skeats A. P. , Wakefield B. , Robertson M. J.
Published: February 2003

Long lived, lifetested GaAlAs/GaAs stripe geometry, double heterostructure lasers have been examined in the scanning electron microscope using a combination of cathodoluminescence, electron beam induced conductivity, and electron probe microanalysis. The dark spot arrays, occasionally seen in the cathodoluminescence images of the active layers of these devices, have been found to be caused by the diffusion of copper into the laser chip from the heat sinks, despite the presence of a nickel barrier layer on the heat sinks.
Calculation of Auger rates in a quantum well structure and its application to InGaAsP quantum well lasers
Authors: Dutta N. K.
Published: February 2003

We discuss the possible intrinsic limitation on the temperature dependence of threshold current of long wavelength InGaAsP quantum well lasers caused by Auger recombination and intervalence band absorption. A model calculation of the various band-to-band Auger rates are presented. We find that the Auger rates increase with decreasing band gap and also with increasing temperature as in the case of bulk semiconductors. The temperature dependence and the band-gap dependence arises from the energy and momentum conservation (in the direction normal to the well) that the four particle states involved must satisfy. The estimated Auger coefficient is large enough to be important in single quantum well lasers. However, the Auger effect should be much smaller in a multiquantum well laser than for a single quantum well laser. This is because the carrier density at threshold is smaller (by a factor of 3 to 4) for multiquantum well lasers than for single quantum well lasers. The increased intervalence band absorption with increasing temperature in the active layer may not be responsible for increased threshold current of single quantum well lasers.
Second harmonic generation in LiNbO3 and LiTaO3 in the millimeter wave region
Authors: Ahn B. H. , Clark III William W. , Shurtz II Richard R. , Bates Calvin D.
Published: February 2003

Second harmonic radiation at 70 GHz was generated using a 35-GHz magnetron in bulk ferroelectric LiNbO3 and LiTaO3 located in a rectangular waveguide. The measured second harmonic output was comparable to theoretical predictions with peak powers as high as 9.8 W for LiTaO3 and 7.6 W for LiNbO3 for an input power of 24 kW. The output power varied periodically as a function of the sample length due to cavity resonance effects.
Extreme ultraviolet emission from gas puff plasmas
Authors: Bleach R. D. , Burkhalter P. G. , Nagel D. J. , Schneider R. L.
Published: February 2003

Intense extreme ultraviolet (XUV) radiation has a variety of research and production applications. Emission in the 30–300 Å range has been measured from noble gas plasmas created by puffing gas into the Pithon electron beam generator at Physics International Co. Spectral, spatial, and temporal measurements from neon, argon, krypton, and xenon plasmas show that sufficient radiation is produced for several applications.
Microwave-energy coupling in a nitrogen-breakdown plasma
Authors: Yee C. L. , Ali A. W. , Bollen W. M.
Published: February 2003

Computer simulations of microwave coupling to a nitrogen-breakdown plasma have been performed at 25 Torr. Nonhydrodynamic ionization fronts are observed to propagate toward the radiation source under a variety of circumstances. Free-nitrogen-breakdown simulations in a spherical system show the propagation velocity of the breakdown wave can be as high as 5×106 cm/sec. An elementary theory is used for estimating the speed of the breakdown wave in one dimension. The results are in reasonable agreement with breakdown experiments.
Unipolar currents and electrostatic probe characteristics in a gas discharge plasma
Authors: Rogoff G. L. , Lowry J. F. , Pinsker R. I.
Published: February 2003

Measurements have been made of the current circulating through a plasma and an adjacent electrically isolated conductor containing an electron-emitting surface region. This ‘‘unipolar’’ current (so called since it requires only a single electrode) was measured in a dc mercury–argon positive column plasma (7 mTorr Hg, 3 Torr Ar, 1.8 cm radius, 400 mA). The unipolar conductor consists of metal disks located at the boundary of the plasma; these disks include indirectly heated dispenser cathodes which act as the electron-emitting regions, providing external control of the emission level. The disks can be connected externally in various combinations to form a conductor of variable distribution and area or they can be used as independent electrostatic probes. Measured unipolar currents are in good agreement with values predicted from individual experimental probe V-I characteristics for the disk emitters and collectors, demonstrating that the unipolar current circulation process can be interpreted in terms of electrostatic probe characteristics.
Study of the free-burning high-intensity argon arc
Authors: Hsu K. C. , Etemadi K. , Pfender E.
Published: February 2003

Although the high-intensity, free-burning argon arc has been the object of many studies, modeling of the entire arc has been precluded because of complexities due to the interaction of electric, magnetic, fluid dynamic, and thermal effects, and the associated lack of realistic boundary conditions, in particular, close to the cathode. For establishing the most crucial boundary condition, which is the current density in the vicinity of the cathode, the maximum current density has been determined experimentally by measuring the size of the molten cathode tip (thoriated tungsten) for a given arc current. Calculated temperature profiles for a 100- and 200- A atmospheric pressure argon arc (electrode gap of 1 cm) are in good agreement with spectrometric measurements based on absolute line and continuum intensities. The arc current and arc current distribution are not only responsible for the temperature distribution in the arc, but also for the magnetohydrodynamics (MHD) pumping action in the cathode region, i.e., the arc behavior is mainly controlled by the current. In contrast to the sensitivity of the current density boundary condition on the results, the calculations show that variations of the boundary condition for the flow field are insignificant.
A method for identification of linear or nonlinear systems with the use of externally applied random force
Authors: Agu Masahiro
Published: February 2003

A response function method using externally applied random force is developed to identify linear or nonlinear systems. The probability distribution function of fluctuations and probability flow in phase space are used as the means for these identifications. It is also demonstrated that anomalous behavior of these quantities can be utilized as the forerunner phenomenon of the catastrophe of unstable systems.
Lα x-ray production efficiency from Z=50–82 thick target elements by electron impacts from threshold energy to 30 keV
Authors: Shima K. , Okuda M. , Suzuki E. , Tsubota T. , Mikumo T.
Published: February 2003

Thick target yields of Lα x rays (x rays/str electron) under electron bombardments from around threshold energy to 30 keV are presented for pure elements of Sn, Sm, Ta, W, Pt, Au, and Pb. The calculation of K x-ray yields by Green and Cosslett has been applied to the deduction of Lα x-ray yields and observed data have been compared with the calculation. A good agreement has been obtained for high Z elements. An empirical formula for observed Lα x-ray yields ILα (x rays/str electron) has been found to be expressed by ILα =1.3×10−7×Z1.3(UL3−1)1.46 ×0.938[ln(UL3−1)]2 in impact energies less than 30 keV, where UL3 is the overvoltage ratio defined by the ratio of electron impact energy to L3 shell ionization energy.
Inductively stabilized rare-gas halide minilaser for long-pulsed operation
Authors: Sze Robert C.
Published: February 2003

Inductively stabilized discharges are developed for the rare-gas halide minilasers. 6.8 mJ per pulse with 40-ns full width at half-maximum pulse lengths and 3.7 mJ per pulse with 60-ns full width at half-maximum pulse lengths are obtained for KrF. 3.1 mJ per pulse with 40-ns full width at half-maximum pulse lengths and 1.7 mJ per pulse with 60-ns full width at half-maximum pulse lengths are obtained in XeCl. The discharge dimensions are 2.5-mm electrode separation by 4 mm wide and 27.6 cm long. Orders of magnitude increases in pulse repetition frequency are obtained in devices that do not utilize gas flow.
Modification of electric field at the solid insulator–vacuum interface arising from surface charges on the solid insulator
Authors: Pillai A. Sivathanu , Hackam Reuben
Published: February 2003

The surface of a solid insulator in vacuum (and in a high gas pressure) becomes electrically charged when subjected to a high voltage stress. The surface charge density is proportional to the applied voltage. The magnitude of the surface charge density depends on the secondary electron emission characteristic, the geometrical shape, and the material of the insulator. The field enchancement, contributing to a lower withstand voltage of solid insulators in vacuum (and in high pressure gases), due to the presence of surface charge is computed along the surface of the solid insulator and at the triple electrode-solid insulator-vacuum junction near the anode and cathode. Different patterns of surface charge density distribution has been considered in order to evaluate their effects on the field enhancement. The polarity, the magnitude and the shape of the distribution of the surface charge density has been found to have a considerable effect on the field enhancement. The observed influence of the charge distribution patterns on the electric field suggests that in order to obtain the experimentally observed field enhancements, the insulator surface must possess a positive surface charge except in the region close to the anode, where it is negatively charged. The electric field and the potential distributions of the interfacial boundary between the solid insulator and vacuum is computed for different realistic surface charge distributions. The computed electric field at the triple junction for varying values of the dc applied field is then compared with the measured values reported in the literature. Good agreement is obtained. The effects of the magnitude of surface charge density, the applied field and the length of the solid insulator on the field enhancement at the triple junctions are also investigated. Nine different solid insulator materials having a relative permittivity in the range 2.1–13 and electron impact energies in the range 20–60 eV are examined. The effect of the surface charge on the withstand voltage of the insulating vacuum gap bridged by a solid insulator is discussed.
Luminescence study of C, Zn, Si, and Ge acceptors in GaAs
Authors: Kisker D. W. , Tews H. , Rehm W.
Published: February 2003

Selective pair luminescence has been used to measure the exicted states of the shallow acceptors C, Zn, Si, and Ge in GaAs. Data for Ge are presented here for the first time while the sets of excited state energies of C, Zn, and Si are completed. These results show that the energies of the p-symmetric impurity states are influenced by the impurity potentials. The germanium excited states are found to be shifted by 3 meV with respect to the valence band compared to the corresponding states in C, Zn, and Si.
Phosphorus distribution in TaSi2 films by diffusion from a polycrystalline silicon layer
Authors: Pelleg J. , Murarka S. P.
Published: February 2003

Secondary ion mass spectroscopy was used to measure phosphorus concentration profiles in TaSi2 thin films deposited on P doped polycrystalline Si/SiO2/Si wafers by cosputtering. Fast redistribution of P in TaSi2 takes place by its up-diffusion from the polycrystalline Si layer. Radioactive assay of 32P obtained by neutron activation confirmed the fast-diffusion character of P in TaSi2. From preliminary results the temperature dependence of the diffusion coefficients over the temperature range of 664 °C-913 °C can be expressed by the following relations: Dc=6.44×10−10 exp[−0.61/(kT)] and Da=2.0×10−8 exp[−0.76/(kT)], where Dc and Da represent diffusion in the silicide film near and away from the surface, respectively.
Carrier transport in stripe-geometry Ga1−xAlxAs double heterostructure diode lasers and broad area heterojunctions
Authors: Zemel A. , Willemsen H. W. , Anderson K. D. , Shepherd F. R.
Published: February 2003

The current-voltage characteristics of stripe-geometry double heterostructure diode lasers and broad area heterojunctions of Ga1−xAlxAs prepared by liquid-phase epitaxy have been extensively studied as a function of temperature and diode area to perimeter ratio. For stripe-geometry lasers, current-voltage measurements were made up to the lasing threshold (∼104 A/cm2). The carrier transport mechanisms in different ranges of current densities were identified and interpreted on the basis of existing models for p-n junctions. It is found that 2-kT current in combination with a tunneling current of the form I α exp(T/T0) exp(AV) where T0 and A are constants essentially independent of temperature, are the major contributions to the diode current at low forward bias. The 2-kT current is most probably due to surface recombination occurring at the junction perimeter and the tunneling current is most probably related to defects generated in the diode depletion region during epitaxial growth and/or sample processing. At medium forward bias, pure 1-kT current limited by the rate at which electrons can diffuse in the narrow gap p-type semiconductor is dominant. In the laser devices 2-kT current consistent with high injection conditions, is found at current densities near threshold. To the best of our knowledge, this is the first time high injection behavior has been recognized and demonstrated in diode laser devices.
Magnetic and some crystalline properties of H+ ion-implanted garnet layers: A study as a function of annealing treatment
Authors: Suran G. , Jouve H. , Gérard P.
Published: February 2003

The magnetic properties—as determined by ferromagnetic resonance (FMR) measurements—lattice strain Δa/a and variation of these parameters were studied as a function of annealing temperatue Tann in (YSmLuCa)3(FeGe)5O12 bubble garnet films subjected to a triple implantation by H+ ions. On the as-implanted sample the FMR spectrum and Δa/a could not be measured. On samples annealed at 200 °C three resonance peaks appear corresponding to three sublayers with different magnetic properties. The formation of the sublayers is related to the inhomogeneous distribution of H+ ions along the implanted layer as a result of the triple implantation. For this range of Tann the Curie temperature TC, Δa/a, and the anisotropy fields vary strongly with annealing time. This result is related to the high diffusion rate of hydrogen and shows that the magnetic properties are substantially modified by the absorbed H+ ions. When Tann>300 °C the amount of H+ incorporated becomes negligible, so the magnetic parameters and the value of Δa/a are essentially determined by the lattice damage. The implanted layer becomes magnetically homogeneous as shown by a well-defined spin wave spectrum characteristic of a layer with fairly uniform magnetic properties along its thickness. For 300 °C<Tann<600 °C increasing Tann results in a decrease of Δa/a and a restoration of the superexchange interaction between the a and d sites, as shown by the increase of TC. The resonance linewidth ΔH1 of the implanted layer is greatly reduced with respect to ΔH0 of the bulk of the film, due to the fact that a large part of c site rare-earth ions are decoupled from the garnet system. As a consequence, Ku is negligible and λ111 is strongly reduced in the implanted layer. For Tann>630 °C the rare-earch ions are progressively recoupled as shown by the increase of ΔH1. As a result λ111 increases and Ku is partially restored.