bluuebunny/crossref_metadata_2025 huggingface dataset:
Premelting in alkali halides due to the thermal formation of dislocations
Authors: Robinson W. H.
Published: February 2003

In a recent paper allnatt and Sime described some high-temperature electrical-conductivity experiments on sodium chloride and potassium chloride in which the activation enthalpy for the conductivity was 110−210 eV and 440 eV, respectively. In this paper we suggest that the rapid rise in conductivity is due to the enhanced diffusion of charged defects along thermally formed dislocations. We present a formula for the conductivity along thermal dislocations and using it we calculate entropies of 1150k-2190k for NaCl and 4750k for KCl. Together with the high enthalpies these entropies are consistent with the Gibb’s function for the formation of thermal dislocations approaching zero at the melting point, implying that on melting the crystal is highly dislocated.
Thermal relaxation processes in amorphous As-Se films
Authors: Asahara Yoshiyuki , Izumitani Tetsuro
Published: February 2003

The influence of heat treatment on as-deposited and darkened films of amorphous As7Se3 has been studied through its effects on the optical properties. The transmission of as-deposited films increases with heat treatment and reaches a certain value Ts. This value depends on the heat-treatment temperature, suggesting the structural relaxation of as-deposited films upon heat treatment. The results of kinetics studies indicated that this relaxation consists of two first-order rate processes; one is a rapid process at the initial 5-min heat treatment and is considered to be due to the disapperance of structural defects in the as-deposited films. The second is a slow process following the initial rapid process and is associated with the relaxation of the glass structure at high temperature. In the darkened film, the transmission increases with heat treatment and the value of Ts is independent of the heat-treatment temperature. This process consists of only one first-order rate process and was considered to be due to the ’’dissociative diffusion’’ of arsenic atoms.
A practical approximation to integrals appearing in the theory of the magnetoconductivity of semiconductors
Authors: Rater L. M. , Mackey H. J.
Published: February 2003

A set of integrals which appear in the theory of the magnetoconductivity of semiconductors is discussed. The similarity of all of the integrals to those obtained for neutral impurity scattering is exploited to obtain numerical approximations valid for all values of magnetic field. The form of the approximations is well suited to iterative computer procedures used in curve fitting.
FIR absorption determination of transient electron densities in high-pressure ionizer-sustainer lasers
Authors: Newman L. A. , Schubert M. R. , DeTemple T. A.
Published: February 2003

The use of cw fundamental mode optically pumped FIR lasers in determining electron density in high-pressure electron-beam-initiated gas discharge lasers is outlined. Discharges in He, He-SF6, N2, N2-SF6, Ar, and Ar-Xe were investigated via transmission and V-I measurements with resulting thicknesses of 1016 electrons/cm2, a spatial resolution of 2 cm, and a time resolution of 50 nsec. The electron density inferred from transmission and current agreed to better than 50% limited only by uncertainties in the specific spatial distribution of the electron density. The increased ir and uv laser output previously observed when small amounts of SF6 were added to N2 was found to be attributed to a slight increase in electron density and E/N during the time duration of the laser pulses.
Soft-x-ray photoionization cross sections of molecular oxygen
Authors: Bodeur S.
Published: February 2003

The continuous variation of x-ray photoabsorption cross sections of molecular oxygen has been obtained experimentally between 6 and 22 Å. An empirical formula has been deduced for the variation of the absorption coefficient in this range and compared with other semiempirical estimations. Moreover, the experimental results are compared with the theoretical values calculated from Stobbe’s formulas taking into account the screening effects on one hand and the central field approximation on the other, and the validity range of these theoretical models has been deduced.
Inhomogeneities in TEA laser discharges
Authors: Egger H. , Dufour M. , Seelig W.
Published: February 2003

The development and homogeneity of uniformly preionized TEA discharges is investigated by analytical methods and experiments. A discharge formation model accounts for (a) avalanche ionization that depends on the local electric field and gas density, (b) electron diffusion, and (c) gas heating and expansion. The theory predicts that local overheating of the gas is responsible for the onset of arcing, that space charges are damped, and that the discharge uniformity is limited due to fluctuations of the starting electron density which must be large compared with 102 cm−3. A conceptive description based on perturbation elements extends the range of qualitative validity of the theoretical model and facilitates the understanding of homogeneity measurements. Both onset of arcing and preionization requirements are in good agreement with experimental data.
Third harmonic generation in SF6 at 10.6 μ
Authors: Kang Min Ho , Chung Kang Min , Becker Michael F.
Published: February 2003

We report non-phase-matched third harmonic generation of CO2 TEA laser pulses in SF6 gas. Measurement of the nonlinear susceptibility indicates a strong resonant enhancement due to nearby vibrational-rotational transitions. The nonlinear susceptibility is also calculated and compared with the experimental results.
Investigation of neutron-produced defects in silicon by transconductance measurements of junction field-effect transistors
Authors: Tokuda Yutaka , Usami Akira
Published: February 2003

Defects introduced in silicon by neutron irradiation were investigated by measuring the phase angle ϑ of the small-signal transconductance of the junction field-effect transistors (JFET). Measurements of ϑ as a function of frequency allowed the determination of the time constant for each defect. From the temperature dependence of the time constant, assuming that capture cross sections are independent of temperature, the energy levels of Ev+0.19 and Ev+0.35 eV in p-type silicon and Ec−0.16, Ec−0.19, and Ec−0.44 eV in n-type silicon were obtained. For these defects, calculations gave majority-carrier capture cross-section values of 2.8×10−15 and 1.1×10−14 cm2 in p-type silicon, and 3.9×10−14, 1.6×10−16, and 2.3×10−14 cm2 in n-type silicon, respectively. Comparing with other published data, it was found that the energy level of Ec−0.44 eV showed the value between the previously reported energy levels of Ec−0.4 and Ec−0.5 eV correlated with the doubly negative charge state and singly negative charge state of the divacancy, respectively. Thus, it is believed that a total of six energy levels are introduced in silicon by neutron irradiation. The energy levels of Ec−0.16 and Ev+0.35 eV were found to be correlated with the A center and the divacancy, respectively.
Transparency of thin metal films on semiconductor substrates
Authors: Hovel H. J.
Published: February 2003

The transmittance of light into Si and GaAs through thin metal films has been calculated, both with and without anitreflection coatings. Reflection is the biggest optical loss for 100-Å-thick films, amounting to about 35% for the best metals. The transmittance can be increased from 60% to over 94% with the addition of AR coatings with indices of 2.1 or more. Ag, Cu, Au, and Mg are the most transparent films, while Al and Cr are the least transparent.
Capacitance spectroscopy studies of degraded AlxGa1−xAs DH stripe-geometry lasers
Authors: Lang D. V. , Hartman R. L. , Schumaker N. E.
Published: February 2003

The deep-level transient capacitance spectroscopy (DLTS) technique has been used to study changes in double-heterostructure (DH) AlxGa1−xAs proton-bombarded stripe-geometry lasers during accelerated aging at 70 °C. The DLTS spectra of these lasers consist of three dominant peaks: two shallow traps with activation eneriges of 0.31 eV (majority carrier trap) and 0.21 eV (minority carrier trap) and a deep majority carrier trap with an activation energy of 0.89 eV. The deep trap signal changes dramatically during the first 100 h of cw laser operation at 70 °C, while the two shallow traps change in concentration by only about 10–20%. This deep trap signal increases by over an order of magnitude in lasers of moderate reliability (∼103 h at 70 °C) but is observed to decrease in lasers with very long lifetimes. It is shown that this deep level is introduced by the proton damage and is initially located at the interface between the proton-damaged layer and the N-ternary waveguide layer. Finally, studies of the shift in energy of this deep level as a function of aluminum fraction in the AlxGa1−xAs waveguide layer show that this trap is very likely the same as the E3 radiation damage trap. This correlation is significant since the E3 defect is known to be mobile at room room temperature under conditions of electron-hole recombination and a very efficient nonradiative center in p-GaAs. If such a center were to move into the p-type active region, it would be a prime candidate for the source of spatially uniform degradation.
Analysis of spatial distribution of charges and dipoles in electrets by a transient heating technique
Authors: Collins R. E.
Published: February 2003

A method is discussed for measuring the separate spatial distributions of fixed charge and permanent polarization in a uniform insulator. Changes in the potential difference across the insulator are measured when a known nonuniform time-dependent temperature perturbation is established through the sample thickness. The contributions to the measured signal from real charge and polarization charge have the same form, but are weighted differently. Deconvolution of the experimental data, therefore, yields a linear combination of the spatial distributions of real and polarization charges. These two distributions can be separated by utilizing the temperature dependence of these weighting factors.
Computational models for ductile and brittle fracture
Authors: Seaman Lynn , Curran Donald R. , Shockey Donald A.
Published: February 2003

Computational models of dynamic ductile and brittle fracture are developed for wave propagation in one- and two-dimensional geometries. The model features have been taken mainly from detailed observations of samples partially fractured during impacts, but the functional forms are consistent with theoretical results where applicable. Basic features of the models are the nucleation and growth (hence, the acronym NAG for the models) of voids or cracks, and the stress relaxation resulting from the growing damage. The results of the calculations include number and sizes of cracks, voids, or fragments as a function of position in the material. The NAG analysis presents the nucleation law, determined from experiment, and two growth laws: both growth and nucleation are functions of stress and stress duration. Procedures for treating cracks with a range of sizes and orientation are presented with the method for computing the stress relaxation that accompanies growth of damage. Brittle fracture is essentially anisotropic in actuality and in the model: cracks nucleate and grow as a function of stress normal to their plane, and the stress relaxation is a function of crack opening in the direction of the stress. Criteria are presented for the coalescence of cracks to form fragments and for complete fragmentation. The computational models have been applied to one- and two-dimensional wave propagation problems. The NAG models have been shown to be applicable to several metals, a plastic, and a quartzite, to stress levels from just above threshold to ten times the threshold, and to load durations from 20 nsec to several microseconds. The damage has been computed for stress waves caused by impact, thermal radiation, and explosion.
Stability of gallium-, indium-, and tin-covered tungsten surfaces and formation of In-W and Sn-W alloys
Authors: Saadat A. R. , Nishikawa O.
Published: February 2003

It has been reported that the tin coverage on a tungsten tip increases the stability of the tip surface at an elevated temperature under an applied external field. In the present work the existence of the covering atoms on the heated tungsten tips was examined by measuring the variation in the field emission current with the reduction of the coverage of adatoms due to the gradual field evaporation. The result indicates that a substantial amount of the adatoms remain on the heated surface and no noticeable amount of the unknown entity contributes to the increased surface stability. The observed field strength required to deform a tin-covered tungsten tip was found to be two to three times higher than gallium-covered, indium-covered, or bare tungsten tips. As a heated field emission cathode the stable tin-covered tip emitted a high current corresponding to a current density of well above 1×106 A/cm2, which is an order of magnitude higher than that obtained for a bare tungsten tip. Occasionally, the covered tip heated above 900 °C exhibited an entirely new cubic structure which would indicate the formation of the presently unknown ordered Sn-W and In-W alloys.
Ion emission from beam-plasma ion sources
Authors: Conrad J. R.
Published: February 2003

The condition for which maximum ion current is obtained for beam-plasma ion sources is examined, and a model for the peak ion current based on nonlinear theory is described. Maximum ion emission is found to occur when (i) the initial growth rate of the beam-driven waves is maximized and (ii) the subsequent relaxation of the beam distribution is accomplished with optimal conversion of wave energy to plasma thermal energy. The results of the model are compared with experiment.
The sodium chloride primary pressure gauge
Authors: Ruoff Arthur L. , Chhabildas Lalit C.
Published: February 2003

The failure of a central force model for sodium chloride is discussed. It is noted that it does not closely satisfy the Cauchy conditions at low temperatures, and that it fails the central force requirement of the Love condition. It is also noted that the model as used in the usual way, with B0 as the zero-pressure value of the bulk modulus and the lattice parameter as input, fails to predict the pressure derivative of the bulk modulus. It is therefore concluded that there is no scientific justification for basing a pressure scale on a central force equation of state. The available shock data for sodium chloride and its analysis is examined, and two reasons why the Hugoniot transformation pressure is likely to be less than 231 kbar are discussed. These reasons are (1) the presence of overpressure (the additional pressure beyond the equilibrium transformation pressure needed to cause the transformation under dynamic conditions) and (2) the lack of data points between 212 and 231 kbar. The important (but unjustified) theoretical assumptions made in converting Hugoniot to isothermal data is discussed; it is noted that serious error can enter for very large pressures (P ? B0) for a given material and that at such high pressures the isothermal data should thus be considered only semiquantitative even if the Hugoniot data itself is accurate. An alternate method of estimating the isothermal transformation pressure from the Hugoniot transformation pressure is used. This method is based on the temperature derivative of the transformation pressure. On this basis it is concluded that an upper bound for the isothermal transformation of NaCl (to a CsCl-type structure) at room temperature is 257 kbar; it is noted that the actual value may be considerably less than this.
Traveling wave oscillations of a cw dye laser
Authors: Marowsky G. , Cubeddu R.
Published: February 2003

A stable continuous output, modulated with the c/L frequency of the cavity round trip, has been generated by means of an Ar+-ion laser pumped dye ring laser operating in a traveling wave configuration. The train of self-excited pulses of nanosecond duration can be tuned over the whole spectral range of rhodamine 6G with an average power up to 100 mW, coupled out by means of a prism outcoupler of adjustable transmission by frustrated total internal reflection.
Attenuation on a surface wave G-line suspended within a circular tunnel
Authors: Wait James R. , Hill David A.
Published: February 2003

Calculations indicate that a surface wave Goubau line may have useful transmission characteristics even if it is located within 20 cm from the rock wall of a tunnel. The results are consistent with previous theoretical and experimental data for a thin wire located at low heights over a finitely conducting plane earth.
Dielectric properties of polystyrene thin films formed by rf electrodeless excitation
Authors: Takeda Shinichi
Published: February 2003

The temperature coefficient of the dielectric constant for the common polystyrene films is negative, while that for films formed by rf electrodeless excitation is positive. From the measurements of the coefficient of linear expansion and of thermally stimulated current (TSC), it is found that the negative coefficient for the polystyrene films is due to the expansion of volume, while on the other hand, the positive coefficient for the thin films is due to the occurrences of dipoles having widely distributed relaxation times.
SiP precipitation within the doped silicon lattice, concomitant with phosphorus predeposition
Authors: Armigliato A. , Nobili D. , Servidori M. , Solmi S.
Published: February 2003

From experiments of thermal predeposition of phosphorus in silicon, performed at 920 °C and followed by neutron activation analysis and TEM observations, it is concluded that SiP precipitation takes place in the furnace during the isothermal process. In fact, the surface concentration of phosphorus increases with predeposition time attaining values well above the solid solubility; in addition the flat rodlike SiP precipitates grow with the time of predeposition, according to a parabolic law. Finally, considerations of the size of the precipitates indicate that they are not formed during the cooling stage subsequent to predeposition.
Instabilities during high-field electrical conduction in solids
Authors: Thoma P.
Published: February 2003

Measurements of the time and voltage dependence of dc and ac currents in insulators and semiconductors and the evaluation of results of other authors on corresponding measurements using metallic samples reveal that critical power densities Nk1≈10−8 W/mm3 and Nk2≈10−5 W/mm3 separate three different ranges of charge transport loading of solids in the frequency range 0⩽f⩽50 Hz. The loading state of a solid is described macroscopically by the average electric power density and microscopically by the local value of the power density j↘⋅E↘. In semiconductors and insulators electrical breakdown or transition to a strongly localized and highly conducting state is unavoidable if an overcritical power density N≳10−5 W/mm3 is supplied. This locally quite limited and highly conducting state exists in the prebreakdown range wherein Nk2<N<Nfusion. It is related to the Ovshinsky effect in amorphous semiconductors. Usually the current density, continuity, and Poisson equations are used to describe charge transport within a solid. In order to complete this description it is proposed that power density N=j↘⋅E↘ must be considered.
Microparticle trigger discharges and impact damage in a high-voltage vacuum insulated gap
Authors: Chakrabarti A. K. , Chatterton P. A.
Published: February 2003

The onset of vacuum trigger discharges and microparticle-induced damage has been investigated by bombarding gold and tungsten wires with various diameter iron particles using the impact velocity range 2–600 m/s. It was observed that when particles exceeded the elastic limit for gold extensive craters were produced which had sharp lips. This condition could not be achieved for the harder tungsten targets. The onset of trigger discharges was observed by measuring the light output, electrode damage, and voltage waveforms. It was noted that when bombardment was carried out with cathode wire fields in excess of 4×107 V/m trigger discharges and gap breakdowns occurred for particles having radii greater than 5–10 μm. Scanning electron micrographs of the resulting electrode damage show the localized nature of the trigger discharge. The trigger discharge results are shown to be in agreement with a computation of the onset of extensive field emission heating in the gap between the impacting particle and electrode.
Raman spectrum and refractive index behavior of Al2O3 added high-silica-content glass
Authors: Kato Daisuke
Published: February 2003

Several specimens of Al2O3-added high-silica-content glass of various additive concentration which were prepared with a chemical vapor deposition (CVD) process are studied by Raman spectroscopy. The Raman spectrum of the glass is found to be close to that of fused silica, and the Raman band characteristic to the nonbridging oxygens was not observed in this glass. A quadratic behavior of the refractive index change as a function of the additive concentration is observed in this glass and is explained with a detailed ionic polarizability concept on the basis of the Raman spectroscopy. The effect of the refractive index fluctuation in this glass on the optical attenuation is also discussed.
Measurements of layer thicknesses and refractive indices in high-energy ion-implanted GaAs and GaP
Authors: Kachare A. H. , Spitzer W. G. , Fredrickson J. E. , Euler F. K.
Published: February 2003

Near normal incidence reflection and transmission measurements of GaAs and GaP samples implanted with large doses of ∼3-MeV ions of 31P+ or 14N+ showed frequency-dependent maxima and minima in the frequency range 800≲ν≲7500 cm−1. Assuming a layer model for the implanted material and considering reflections from layers surfaces, the interference fringes are analyzed to obtain the refractive index and thickness of both the cover and buried layers and substrate. With the same layer model the changes in the GaAs reststrahlen are shown to be quantitatively compatible with the results of the fringe measurements. Annealing GaAs at temperatures ≲400 °C reduced the implantation-induced changes in the refractive index but the layer thicknesses remained constant. There was no evidence for regrowth by motion of the implant-substrate interface as has been reported for silicon crystals. The analysis of the reststrahlen data for GaP is less satisfactory since the data could not be closely fitted with any choice of parameters.
Contact metallurgy for shallow junction Si devices
Authors: Kircher C. J.
Published: February 2003

A contact metallization is described that allows Al interconnection metallization to be used for shallow junction Si devices. Junction penetration by Al during heat treatment of devices is avoided by using a layer of Pd2Si in the contact window between the Al and the Si. In this manner junctions as shallow as 0.2 μm can be contacted that are able to withstand moderate periods of annealing at 400 °C without degradation. Metallurgical changes occurring in the contact region during heat treatment have been investigated. An intermetallic phase, Al3Pd, is found to form which reduces the Si diffusion from the contact region into the Al and contributes to a uniform Si loss over the whole contact region. Thus the ∼1-μm-deep Al penetrations that otherwise occur at spots within the contact region and cause the junction degradation are eliminated. The usefulness of Al interconnection metallization is thereby extended to shallower junction devices.
Characterization of iron-doped lithium niobate for holographic storage applications
Authors: Shah Rajiv R. , Kim Dae M. , Rabson T. A. , Tittel F. K.
Published: February 2003

A detailed study of eight systematically chosen Fe : LiNbO3 crystals is presented. Correlation between the photorefractive sensitivity and various chemical properties of Fe : LiNbO3 is investigated in order to ascertain optimum performance of the crystals in holographic storage and display applications. Concentrations of Fe2+ and Fe3+ ions have been determined from optical and EPR spectra, while impurities have been detected from x-ray-emission and infrared spectra. Particular emphasis is placed on investigating the dependence on Fe2+ and Fe3+ ion concentrations of the photorefractive sensitivity. The photorefractive sensitivity is shown to depend primarily on the concentration of Fe2+ ions in Fe : LiNbO3. This fact seems to suggest that Fe2+ ions are the impurity centers responsible for the photorefractive effect in Fe : LiNbO3. Spectral dependence of the photorefractive sensitivity and its modification due to oxygen annealing are also reported. Our results indicate that an unannealed Fe : LiNbO3 crystal containing 0.05 mol% Fe with 20–25% of the ions in the Fe2+ state and the remainder in the Fe3+ state possesses the most favorable photorefractive sensitivity.
Some temperature-dependent properties of niobium tunnel junctions
Authors: Broom R. F.
Published: February 2003

Some measurements of the electrical properties of Nb tunnel junctions in the temperature range 2–9 °K are described. These include (i) the quasiparticle tunneling current, (ii) the gap voltage 2Δ/e, (iii) the dc Josephson current i1, and (iv) the London penetration depth λ. With regard to (i) the tunnel current is well described by an empirical model in which the density of states within the forbidden gap of the top electrode is finite and sharply peaked at the gap edges. This, and the temperature dependence of i1, are consistent with the proximity-effect model proposed by Schwidtal to describe Nb-NbOx-Pb junctions. The temperature and frequency dependences of the penetration depth show fair agreement with the BCS theory in the local ’’dirty’’ limit. Some results are also given on the variation of junction capacitance with Josephson current density.
Theory of rf-biased superconducting quantum interference device for nonhysteretic regime
Authors: Erné S. N. , Hahlbohm H.-D. , Lübbig H.
Published: February 2003

The SQUID response φ (φe) is studied analytically for the nonhysteretic regime, 2πLsIc<φ0, and low-frequency excitation, ω?108 s−1. The influence of the weak-link parameters on the voltage at the tank circuit is demonstrated. The calculations including the cos(2πφ/φ0) term are compared with the experimental results of Nisenoff and Wolf.
ac losses and low-field superconducting behavior of Nb3Sn
Authors: Howard R. E. , Norton R. H. , Beasley M. R.
Published: February 2003

Measurements have been made of the low-field ac and dc superconducting properties of thin films of electron-beam-evaporated Nb3Sn. Comparison of the 50-Hz hysteretic loss and flux entry waveforms with the measured field-dependent critical current indicates that a modification of the usual critical state model with a uniform surface barrier is necessary. A model based upon a nonuniform flux distribution, consistent with the observed morphology, is presented. Its success in describing the low-field properties of this sytem and its importance to related materials in which the superconducting properties are strongly dependent upon the microstructure are discussed.
Magnetostatic modes of a slab of hexagonal planar ferrite
Authors: Srivastava N. C.
Published: February 2003

This paper presents an investigation of the magnetostatic modes in a semi-infinite slab of hexagonal planar ferrite which is magnetized along the face of the slab. Unlike the case of isotropic ferrites, the slab of planar ferrite supports volume modes even in the absence of the variation of rf field along the dc magnetization. Surface modes are allowed so long as the anisotropy field is smaller than the saturation magnetization. The surface modes cease to exist when the anisotropy field exceeds the saturation magnetization, but the introduction of a perfect conductor on one side of the slab allows the propagation of a band of unidirectional surface waves which may be useful in device applications at relatively high frequencies.
Laser drilling velocity in metals
Authors: von Allmen M.
Published: February 2003

To describe the laser drilling process, a theoretical model that includes expulsion of liquid material is developed. The model allows the calculation of drilling velocity and drilling efficiency as a function of the absorbed intensity. The same quantities were determined experimentally, using Nd-YAG-laser pulses of rectangular shape. Good agreement between measurement and calculation was found in the intensity region where efficient drilling is possible, i.e., where reflection losses and vapor absorption can be neglected. For most metals this region is between 1 and 100 MW/cm2.
Comparison of electron sources for high-resolution Auger spectroscopy in an SEM
Authors: Christou A.
Published: February 2003

The effect of primary beam current and electron spot size on the Auger image resolution and signal-to-noise ratio (S/N) have been determined for field emission and thermionic emission sources. It is demonstrated that by use of a FE source and nA primary beam currents, an Auger image resolution of less than 1000 Å can be obtained. The major limitation to Auger spatial resolution is attributed to backscattered electrons. A LaB6 source is clearly superior to FE sources at primary beam currents of greater than 1×10−8 A.
Basic characteristics of surface-acoustic-wave convolver in monolithic MIS structure
Authors: Tsubouchi Kazuo , Minagawa Shoichi , Mikoshiba Nobuo
Published: February 2003

We propose a new nonlinear theory including the gate-voltage dependence and the effect of surface states based on a simple model (low-frequency limit) of surface-acoustic-wave (SAW) convolver in monolithic MIS structure, and we confirm our theory by experiment on the n-Si/SiO2/ZnO/Al system. Our results show that the convolution signal corresponds to the derivatives of C-V curves in the ideal MIS structure and the effect of surface states appears in the peak shift.
Time-dependent crystal-melt interface shape in Czochralski growth system
Authors: Arkani-Hamed J. , Heshmati Moulaii M. J. , Vojdani S.
Published: February 2003

The time variations of the shape and position of the crystal-melt interface in a crystal pulling system, caused by sudden changes of different parameters, are investigated. Zero pull rate and vacuum surroundings are assumed throughout. In particular, the effects of the variation of the after-heater height and the Peltier current are determined in detail for germanium. It is found that the Peltier current affects the interface more strongly than the after heater.
Stress produced in a solid by cavitation
Authors: Vyas B. , Preece C. M.
Published: February 2003

The stresses produced in a solid by cavitation generated in distilled water by 10-, 20-, and 30-kHz vibrations have been determined by a transducer technique. The measured stress pulses are attributed to the concerted collapse of the whole cloud of bubbles created by the pressure changes in the water rather than to the independent effects of individual bubbles. The magnitude and duration of the stress pulses are characteristic of those of a shock wave and can be related directly to the degree and mode of damage which they produce in a solid.
Early growth of silicon on sapphire. II. Models
Authors: Blanc J. , Abrahams M. S.
Published: February 2003

We analyze data obtained on the morphology of (100) silicon on (011̄2) sapphire at early stages of growth. For the sake of simplicity and concreteness, we assume, perhaps incorrectly, that isolated growth islands are hemispherical. In order to account for the observation that the rate of increase of deposited silicon has achieved the bulk value at surface coverages of 50% or less, we postulate a ’’collection zone’’ around each growing island. Material falling in this zone is assumed to all diffuse to the growing island. For our experiments, the width of this zone is some tens of angstroms. We show that the growth rate of {110} islands is not significantly different than that of (100) islands. The eventual disappearance of {110} Si for full growths can be ascribed to the tendency to reduce the high-energy contact area between (100) and {110} Si. The logarithm of (100) island density appears to be proportional to (growth time)1/2. A simple model of island coalescence yields such a dependence, the proportionality constant being essentially equal to the (initial nucleation site density)1/4 multiplied by the (growth rate)1/2. The model for individual island growth in conjunction with the coalescence model yields a satisfactory explanation of the observed time dependence of island density, of surface coverage, and of total deposited volume. We suggest that, under the high effective supersaturations used in the growth of silicon on sapphire, island growth and coalescence are not dominated by surface energies. We speculate that nucleation of silicon on sapphire occurs by a type of homogeneous surface mechanism, rather than being due to either ’’dirt’’ on the substrate or crystallographic defects in the sapphire substrate.
Growth of CdS smoke particles prepared by evaporation in inert gases
Authors: Kaito Chihiro , Fujita Kazuo , Shiojiri Makoto
Published: February 2003

Cds particles, which were prepared in He, Ne, Ar, and Xe gases at pressures of 5–150 Torr, were studied by electron microscopy. Crystals with wurtzite structure grew in single hexagonal plates or prisms or in a more complicated form composed of three or more hexagonal prisms. The mean size of the particles was larger if they were prepared in a heavier gas, and increased almost linearly with gas pressure up to a saturation pressure which was lower for heavier gasses. The particle size distributions in the smokes and the temperature distributions in the chamber are presented for various atmospheres, and on these bases the growth of the particles is discussed.
The role of the grain boundaries in hot pressing silicon carbide
Authors: Bind Jean-Marie , Biggers James V.
Published: February 2003

Silicon carbide is difficult to sinter without the aid of additives and/or pressure. Additions of boron carbide, boron or alumina were made to obtain dense materials. This is explained in terms of surface free energy modifications taking place in the grain boundaries. An expression of the chemical potential over the grain boundaries is developed to show that there is no theoretical limitation for the sintering of covalent ceramics if the grain size of the starting powder is small enough.
Formation kinetics of CrSi2 films on Si substrates with and without interposed Pd2Si layer
Authors: Olowolafe J. O. , Nicolet M-A. , Mayer J. W.
Published: February 2003

We have measured the kinetic rate of formation of CrSi2 using 2.0-MeV 4He+ backscattering spectrometry. CrSi2 was formed on single-crystal 〈100〉- and 〈111〉-oriented Si and on Pd2Si grown on 〈100〉 Si. For both Si-Cr and Si-Pd2Si-Cr samples the rate of growth of CrSi2 is linear in time with an activation energy of 1.7±0.1 eV and a value of 0.7 Å/sec at 450 °C. For all annealing temperatures, the growth becomes nonlinear at long annealing times. The nonlinearity is attributed to a contaminant, probably oxygen. On Pd2Si, CrSi2 starts to form at about 400 °C, while on Si, CrSi2 formation is observed at 450 °C and above. The difference in formation temperatures is due to contamination at the Si-Cr interface, quite probably a thin oxide layer. The growth rate of CrSi2 in the Si-Pd2Si-Cr samples is independent of the thickness of Pd2Si.
Off-axis channeling disorder analysis
Authors: Foti G. , Baeri P. , Rimini E. , Campisano S. U.
Published: February 2003

A new method has been developed to obtain, by means of channeling measurements, the distribution of defects in a plane normal to a low-index axis direction. This method takes advantage of the response of nonsubstitutional atoms to the spatial distribution of the channeled ion flux. It represents then an extention of the flux-peaking effect used to locate foreign atoms in a single-crystal lattice. This method has been used to study the disorder introduced by 300-keV N+ implantations in Si with fluences ranging between 6×1014 and 1016 ions/cm2 and analyzed in situ with 2.0-MeV He+ backscattering. Flux distributions of channeled ions have been evaluated as a function of the impinging angle for the <111≳ and 〈110〉 crystal directions of a Si lattice. The dechanneling probability has been estimated as a function of the impinging angle and of the total number of scattering centers, on the basis of plural scattering treatment. The analysis of the experimental data indicates a departure from a uniform transverse distribution of scattering centers both along the 〈111〉 and the 〈110〉 directions for low damage levels. The analysis has been detailed together with the main assumptions, and the range of validity of the method has been defined.
Resolution of electron emission mechanisms in an argon arc with a hot tungsten cathode
Authors: Chen Michael M. , Thorne Roderick E. , Wyner Elliot F.
Published: February 2003

The regenerative nature of the interaction between the electron emission processes at the cathode surface and the ion-, excited-atom-, and photon-production processes in the plasma was examined. Semiquantitative estimates of the thickness of the species production layer, the current partition, and the time constants were made. These results were used to interpret experimental measurements of the current decay of an argon arc at 46.7 kPa, 3.2–7.9 A, and 28–18 V, with a self-sustained hot tungsten cathode. After the discharge is suddenly connected to a voltage clamp, the disparity of decay rates for different emission processes permits the separation of thermionic emission from the faster-decaying components. The observed thermionic current constitutes about 30% of the total emission. The high nonthermionic portions of the current could not be explained in terms of the present understanding of the emission processes.
Two-element array of insulated antennas in a relatively dense medium
Authors: King R. W. P. , Shen L. C.
Published: February 2003

The applications and the theory of coupled insulated dipoles and monopoles in a relatively dense medium (like water, the earth, a living tissue) are reviewed. Graphs of the distributions of current and the admittances calculated from the theory are displayed for two-element arrays of air-insulated monopoles in lake water. A comparison is made with measured data and generally good agreement is observed for the currents. Differences in the admittances due to the effects at the junctions between the monopole and the driving coaxial line and the approximations of the theory are discussed.
Diode compression of an intense relativistic electron beam
Authors: Read M. E. , Nation John A.
Published: February 2003

Experiments are reported on the compression of an intense relativistic electron beam. The compression is aided by an externally driven current flow along the axis of the diode. It is found that the compressions achieved with the externally driven axial ’’wire’’ current are limited by the magnitude of the externally driven current and are substantially less than those obtained from the self-pinching of an e-beam from a low-impedance generator.
Measurement of the effective mean free paths of primary electrons in a multidipole device
Authors: Leung K. N. , Kribel R. E. , Taylor G. R.
Published: February 2003

The effective mean free path of the primary ionizing electrons in a multidipole device is measured by simply inserting a negatively biased electrode into the plasma.
Surface studies of barium and barium oxide on tungsten and its application to understanding the mechanism of operation of an impregnated tungsten cathode
Authors: Forman R.
Published: February 2003

Surface studies have been made of multilayer and monolayer films of barium and barium oxide on a tungsten substrate. The purpose of the investigation was to synthesize the surface conditions that exist on an activated impregnated tungsten cathode and obtain a better understanding of the mechanism of operation of such cathodes. The techniques employed in these measurements were Auger spectroscopy and work-function measurements. The results of this study show that the surface of an impregnated cathode is identical to that observed for a synthesized monolayer or partial monolayer of barium on oxidized tungsten, by evaluating Auger spectra and work-function measurements. Data obtained from desorption studies of barium monolayers on a tungsten substrate in conjunction with Auger and work-function results have been interpreted to show that throughout most of its life an impregnated cathode has a partial monolayer, rather than a monolayer, of barium on its surface.
Analysis of the voltage drop arising from a collision-dominated sheath
Authors: Dolson R. C. , Biblarz O.
Published: February 2003

Voltage drops associated with the collisional sheath of nonemitting, MHD electrodes are investigated. The problem is described by a set of coupled nonlinear partial differential equations which are solved by finite differencing in a computer. The sheath and ambipolar regions form in a self-consistent way obviating the need to match boundaries. A two-dimensional model with periodic active sites on a flat plate is used. The current constricts at these sites in order to satisfy the controlling equations for frozen charge flow. The effects of a magnetic field as well as of Joule heating are included in the model; convection can be shown to be negligible in the sheath. Joule heating is assumed to have no effect on the bulk temperature of the gas. Changes in the current-voltage characteristics due to Joule heating are small since the effect is extremely localized; the presence of a magnetic field has a slight influence on the size of the sheath but alters noticeably the current-voltage characteristics.
Extensions of the two-dimensional constant property arc
Authors: Cohen Ira M.
Published: February 2003

Our Galerkin approximate analysis of two-dimensional arc properties and arc shape has been extended from planar constant property arcs to axisymmetric constant property arcs and to planar arcs with thermal and electrical conductivity variations. Axisymmetric constant property arcs are qualitatively similar to planar constant property arcs. Local temperature maxima occur on the arc axis about halfway between the central plane and the electrodes, and increase in magnitude as the arc slenderness ratio increases. When the electrical conductivity increases as a power of n of the heat flux potential, the arc gets thinner and cooler with increasing n for larger currents, but for small currents the arc gets thicker and hotter with increasing n. Since conductivity increases rapidly with heat flux potential ?, when this is greater than unity, high enough conductivities can be obtained at lower temperatures and with thinner arcs. On the other hand, when current ? is small, ?<1, so larger n corresponds to smaller conductivities. Thus higher temperatures and thicker arcs (as n increases) are required in order to pass small currents.
Diffraction effects in liquid-crystal aligning layers
Authors: Haas W. E. L. , Adams J. E. , Pollack J. M.
Published: February 2003

Silicon monoxide liquid-crystal aligning layers have been found to produce strong asymmetric diffraction when deposited on glass substrates for evaporant angles less than 10°. The diffracted light produces a series of concentric arcs, asymmetric with respect to the source direction. Multiple arcs are observed because of total internal reflection. The arc radii are essentially independent of incident wave length.
Augmentation of heat and mass transport in flowing particle suspensions: A dimensional analysis
Authors: Ahuja Avtar Singh
Published: February 2003

The dimensional analysisof the problem of augmentation of heat or mass transport in the laminar flow of particle suspensions is presented. Qualitative arguments indicate the dependence of the bulk temperature or the mass fraction of the existing suspension on the radial distribution of particles in suspension flow.
Preparation of a dielectric and ferromagnetic mirror surface on stainless steel
Authors: Yamaguchi S.
Published: February 2003

A mirror surface of austenitic stainless steel was prepared by polishing with an aqueous suspension of alumina. During the colloid chemical polishing, the oxide particles were embedded in the substrate, and at the same time the surface layer underwent a martensitic transformation. The lustrous surface that was obtained proved to be dielectric and ferromagnetic.
Enrichment of boron, carbon, and silicon isotopes by multiple-photon absorption of 10.6-μm laser radiation
Authors: Lyman John L. , Rockwood Stephen D.
Published: February 2003

The polyatomic molecules SF6, BCl3, CF2Cl2, and SiF4 have been irradiated in the presence of H2 or N2 using intense focused CO2 laser pulses. All four of the polyatomic molecules underwent isotopically selective reactions showing depletion of the isotopic forms irradiated. The best enrichment was achieved with SF6; however, all systems showed similar behavior with regard to pressure and irradiation time. Both BCl3 and SiF4 showed evidence of isotopic rescrambling reactions that occurred on about a 1-h time scale. The mechanisms of the absorption process are believed to be enabled by the large density of states in the vibrational manifold of polyatomic molecules.
Modulation spectroscopy at non-normal incidence with emphasis on the vacuum-uv spectral region
Authors: Aspnes D. E. , Olson C. G. , Lynch D. W.
Published: February 2003

Expressions are given to analyze modulation spectra taken at non-normal incidence. These expressions are used to determine the optimum angle of incidence to maximize the signal-to-noise ratio. Significant improvements are shown to be obtained in the vacuum-uv spectral region by making measurements at relatively large angles of incidence. We apply these expressions to evaluate the field-induced change in the dielectric function for the 20.5–21.0-eV core-level doublet in GaP from Schottky-barrier electroreflectance data. The line shape obtained is consistent with that of a field-modulated M0 critical point modified by a Coulomb attraction between the core hole and the excited electron.
Laser gain profiling with uniform-field electrodes
Authors: Robinson A. M.
Published: February 2003

The small-signal gain was measured in a uv-sustained CO2 laser amplifier employing uniform-field electrodes of the type used by Chang. Four different profiles were utilized and the spatial distribution of the gain differed for each profile. For a given electrode shape there was an input energy which produced a region of constant gain. A dip or saturation of the gain occurred at the center of the discharge if the input energy exceeded the optimum value, while a monotonic decrease in gain away from the discharge center was produced below this value. The dip in the gain distribution appears to be caused mainly by thermal heating of the gas. The flatter electrode profiles produced wider uniform gain distributions and less saturation because less heating occurred.
Some aspects of Ge epitaxial growth by solid solution
Authors: Ottaviani G. , Canali C. , Majni G.
Published: February 2003

Epitaxial growth of a germanium layer of 0.4–1.1 μm was obtained at 350 °C by the dissolution and transport of an amorphous semiconductor layer through an aluminum film using the Ge (bulk)/Al (evaporated)/Ge (evaporated) structure. Transport and growth were studied by scanning electron microscopy (SEM) and 4He+ backscattering. Channeling measurements indicate that the grown layer is well aligned with the underlying 〈111〉 substrate. Electrical measurements indicate that the grown layer is heavily doped p type. The sputtering cleaning procedure before evaporation is necessary to provide a proper Ge (bulk)/Al interface for nucleation and growth. This effect was verified by measurements of the dissolution rate of Ge in Al film.