bluuebunny/crossref_metadata_2025 huggingface dataset:
Elastic interaction of a point defect with a prismatic dislocation loop in hexagonal crystals
Authors: Yoo M. H. , Ohr S. M.
Published: February 2004

Effects of elastic anisotropy on the interaction between an axially symmetric point defect and a prismatic dislocation loop in hexagonal crystals were investigated. The elastic interaction was affected significantly by the anisotropic elastic field of a loop. The most pronounced effects were found in zinc and graphite. Generally, effects of the point defect anisotropy were much more pronounced than those of the anisotropic elastic field of a loop. A point defect of which strain is greater in the a direction than in the c direction finds two centers of concentration (or depletion) at directly above and below a prismatic loop. The distance between the concentration center and the loop varies with the degree of anisotropy in the elastic self-fields of both the point defect and the prismatic loop.
Calculation of the intercrystalline-interference contribution to the scattering of x rays by arrays of small crystallites
Authors: Betts F. , Bienenstock A.
Published: February 2004

A general equation for the calculation of the intercrystalline-interference contribution to the scattering of x rays by arrays of small crystallites has been derived under the assumption that there is no correlation between the orientations of neighboring crystallites. Numerical calculations for the case of silicon are presented. It is shown that these intercrystalline-interference terms are significantly smaller than the intracrystalline terms in all but the small-angle regions. Hence, conclusions reached by Moss and Graczyk about the inability to describe the diffraction pattern of vitreous silicon in terms of microcrystalline silicon are supported. Unfortunately, the assumption of ``no correlation'' limits the general validity of conclusions drawn from the calculation.
Kinetics and thermodynamics of thin-film deposition by molecular beam methods. II. Nucleation, growth, and evaporation of cadmium on germanium single crystals
Authors: Voorhoeve R. J. H. , Carides J. N. , Wagner R. S.
Published: February 2004

A study has been made of all stages of the deposition of thin films of cadmium on germanium single crystals with (100), (110), (111), (211), and (331) orientations. In the preceding paper, we examined adsorption phenomena in detail. This paper gives the results on the kinetics and thermodynamics of the nucleation and growth stages and of the evaporation of cadmium from the deposit. In addition, the morphology of the films is described. Nucleation occurs on a composite germanium-cadmium substrate and proceeds until almost two monolayers have been deposited. The thermodynamic properties of the deposit during nucleation and growth have been obtained. The thin film can be characterized by a steady-state evaporation rate ve. The critical incident flux necessary for nucleation of bulk cadmium is directly related to the maximum which ve attains during early deposition. Nucleation is easiest on planes which are rough on the atomic scale and becomes more difficult in the order (110)≲(331)<(211)<(100)≲(111). The ``liquid-drop'' model of classical nucleation theory is inadequate to explain the results. A mechanism of nucleation and growth and of evaporation is given based on the kinetic data. The evaporation coefficient was found to be between 0.82 and 0.98. Defects and dopants in the substrate had only a minimal effect on nucleation and growth kinetics.
Diffusion measurements in thin films utilizing work function changes: Cr into Au
Authors: Thomas R. E. , Haas G. A.
Published: February 2004

The role of diffusion in limiting the reliability of substrate bonding for bimetallic Cr–Au thin films was investigated using work function, Auger electron spectroscopy, and LEED measurements to characterize the structure and chemical composition of these films. The diffusion rates for Cr into Au films are measured by means of a new technique utilizing the change in electronic work function as a measure of the surface concentration change. It was found that the diffusion coefficient (D) depended on the deposition rate of the Au film, with a twofold increase in deposition rate giving rise to an order of magnitude increase in D. The presence of sulfur as an impurity in the Cr also had a significant effect on D. Comparison of these results with values of D obtained on Cr–Au films by other workers give similar activation energies, but much lower values of D0 (temperature independent part of D) were obtained in this work. The effect on the lifetimes of devices using thin bimetallic films is discussed in terms of structure, variation in deposition rate, and the influence of contaminants.
Tunneling to traps in insulators
Authors: Lundström Ingemar , Svensson Christer
Published: February 2004

Tunneling of charge carriers between a metal (or a semiconductor) and traps in an insulator on top of the metal is studied in this paper. The tunneling time constant for a three-dimensional δ-function trap is derived and compared with experiments on metal-nitride oxide semiconductor structures.
Millimeter-wave investigation of electronic conduction in semiconducting III-V compounds
Authors: Bonek Ernst
Published: February 2004

The small-signal microwave conductivity of n-type single-crystal InSb, GaSb, InAs, and epitaxial GaAs under the influence of a heating dc field was studied experimentally at 4-mm waves. Contrary to low-frequency results, the millimeter-wave conductivity of InSb at 78 K increases with increasing dc field as a consequence of relaxation effects. The anisotropy with respect to the direction of this field is reversed so that the conductivity for parallel dc and ac fields exceeds the conductivity for perpendicular fields. Mean momentum and energy relaxation times τm and τε, respectively, are evaluated from the conductivity data: τε, almost constant, is about 2×10−12sec, τm drops from 6.1×10−12 sec and 2.6×10−12 sec, depending upon sample mobility, to some 2×10−12 sec when the electric field is increased from zero to 170 V/cm. Agreement of microwave τm with dc measured values is satisfactory. In GaSb at 300 K and 85 GHz, relaxation effects show up in a pronounced deviation of the parallel microwave conductivity from the differential conductivity in the field range from 1 to 3 kV/cm, indicating that the time constants for Γ-L intervalley electron transfer are of the order of the reciprocal test frequency and that the Γ-L intervalley coupling constant is around 3×108 eV/cm. At low heating fields, the warm-electron parameter β was measured for InSb at 78 K, GaAs at 300 K, and InAs at both temperatures by a microwave method. Positive values were found in InAs [78 K: (4.9±0.8)×10−7cm2 V−2; 300K: 2×10−8cm2 V−2], negative ones in GaAs [(1.1±0.6)×10−8 cm2 V−2] and InSb [high-mobility material (−1.9±0.6)×10−4 cm2 V−2; low-mobility material: −4.6×10−6cm2 V−2]. The results are discussed in terms of various theories.
Diffraction-contrast behavior of twinning partials in bcc crystals
Authors: Mahajan S.
Published: February 2004

The diffraction-contrast characteristics of twinning partials have been examined for | g · bp | = 1/3 and 2/3, where g is the operating reflection and bp is the Burgers vector of the partial. The results can be rationalized in terms of the intensity profiles computed by Tunstall and Goodhew for the partials bounding overlapping stacking faults. Further, when | g · bp | is 2/3, the interface dislocations exhibit, for the same g, variations in their contrast. Arguments for rationalizing these observations are developed. A simple analytical procedure for differentiating between twins and complementary twins is also proposed
Studies of Floating Liquid Zones in Simulated Zero Gravity
Authors: Carruthers J. R. , Grasso M.
Published: February 2004

Floating liquid zones of water/ethanol solutions were suspended between glass tubes inside mineral oil. When the densities of the two liquids were equal, there was no net gravitational force acting on the interface between them. The shape stability of this interface was studied under conditions of density imbalance and end-member rotation. Cylindrical, conical, and spherical zone shapes were investigated. Our results show that the generally accepted Heywang criterion for the stability of cylindrical liquid zones is no longer valid under reduced gravitational conditions. The convective flow patterns in the zone due to rotation have been studied in detail and show the existence of distinctly different flow regimes. In all cases the outer liquid rotated more slowly than the end faces and so resulted in Taylor-Proudman-type axial flow. However the liquid near the rotation axis behaved quite differently; for equal isorotation of the end faces, a central core of liquid rotated as a solid core at the same rate as the imposed velocity, while for equal counterrotation, the central core of liquid showed a zero angular velocity. The implications of these studies for crystal growth are considered.
Photocurrent and Carrier Distributions due to Steady Light Absorbed in Finite Thickness
Authors: Seki H. , Schechtman B. H.
Published: February 2004

The steady-state photocurrent through a layer of photoconducting material is investigated when one of the surfaces is illuminated by a constant light source. The material is assumed to be intrinsic and free of deep traps, light penetration is characterized by an optical absorption coefficient, and bulk recombination is taken into account. In the presence of an applied electric field, it is seen that the experimentally accessible photoinjection efficiency can be interpreted as the product of a free-carrier generation efficiency and a recombination yield. Cases which approximate monomolecular recombination and bimolecular recombination are treated in detail. The results show the free-carrier distributions and the dependence of the recombination yield on absorption coefficient, field, both carrier mobilities, and the recombination constant. This dependence is seen to be rather similar to the case of very fast pulsed light for monomolecular recombination but quite different for bimolecular recombination.
Paramagnetic Impurities and Thermal Stability in Type II Superconductors
Authors: Scanlan R. M. , Livingston J. D.
Published: February 2004

Magnetization, critical current, and flux-jump measurements have been made on superconducting La3In containing 1 at. % Gd. The previously reported nonmonotonic dependence of upper critical field on temperature has been confirmed. A low-temperature high-field regime is observed where critical currents increase with increasing temperature. This leads to improved thermal stability, i.e., less flux jumping, at low temperatures. The Gd magnetization data are near free-ion values, indicating only slight interaction effects.
Electron-Impact Cross Sections and Energy Deposition in Molecular Hydrogen
Authors: Miles W. T. , Thompson R. , Green A. E. S.
Published: February 2004

Using the concept of the generalized oscillator strength in the Born-Bethe approximation together with semiphenomenological techniques previously developed, we synthesize a diverse body of experimental and theoretical data on molecular hydrogen into sets of analytical electron-impact cross sections. We include in our analysis discrete, vibrational, and dissociative excitations, together with direct and dissociative ionization. Once the important cross sections are known, it is then possible to trace the energy degradation of an incident electron upon molecular hydrogen. We give results for the electron loss function, efficiencies, and eV/ion pair together with comparison to available experimental data.
Dielectric Constant of Ice at 35.3 and 94.5 GHz
Authors: Perry John W. , Straiton A. W.
Published: February 2004

A quasioptical free-space technique has been employed to measure the complex dielectric constant of ice at 35.3 and 94.5 GHz. At each of these frequencies, data were obtained from ice made from chemically pure deionized water and from ice made from tap water. The temperature of the ice was not controlled but was in the range −60 to 0°C.
Electron-Induced Conduction in Plastics. I. Determination of Carrier Mobility
Authors: Martin E. H. , Hirsch J.
Published: February 2004

Samples of commercial plastics have been bombarded by short pulses of nonpenetrating electrons. Observations of charge transients representing the long-lived component of the induced current lead to the following conclusions: (i) One carrier species is rapidly and strongly localized; (ii) the mobile excess carriers decay by bimolecular recombination; (iii) although such carriers cannot in practice complete transits through the thickness of the samples, they can be swept out of the excited layer into the bombarded electrode. This paper fully explains how the sweep-out time, and from it the effective carrier mobility and generation efficiency, are deduced. The mobilities, with the sign of the mobile carrier, are polystyrene (20°C), μ+=1.0×10−6 cm2/V sec; polyethylene terephthalate (20°C), μ−=1.5×10−6 cm2/V sec; linear polyethylene (80°C), μ+=4.5×10−10 cm2/V sec. The temperature dependence of mobility is studied in the first two materials.
Electron-Induced Conduction in Plastics. II. Bulk Excitation in Polystyrene and Other Insulating Polymers
Authors: Hirsch J. , Martin E. H.
Published: February 2004

The electrical conduction in a number of commercial plastics has been studied under pulsed bombardment by fully penetrating electrons. Detailed results are given mainly for polystyrene. The kinetics obeyed by the ``prompt'' component of the induced current are predominantly first order, those of the ``long-lived'' current, second order. The results generally support the assumptions made in Paper I, and in particular confirm the interpretation of the decay time of the long-lived current as a bimolecular recombination lifetime. A simple model for radiation-induced conduction in polymers, based on topological considerations, is developed. The prompt component is identified with intramolecular carrier drift. The mobility in this process has a lower limit of 10−2 cm2/Vsec. The long-lived current is associated with intermolecular jumps. It is suggested that, while the effective mobility of the long-lived component (as determined in Paper I) in kinked-chain polymers is controlled by the intermolecular jump probability, that in polyethylene is subject to an additional limitation, viz. strong localization of carriers in the U bends of the molecules.
CS2/O2 Chemical Lasers: Chemistry and Performance Characteristics
Authors: Suart R. D. , Dawson P. H. , Kimbell G. H.
Published: February 2004

Experimental results from the CS2/O2 chemical laser system using both a flash photolysis initiated pulsed laser and a microwave discharge initiated continuous-wave laser were examined by computer simulation techniques. The comparisons between predicted and observed laser performance led to some conclusions concerning the chemical mechanisms operative in the laser. In particular, the laser pumping step is O+CS→CO+S followed by the chain carrying step S+O2→SO+O which must be rapid, in agreement with the measurements of Fair and Thrush. The oxygen atom consuming reaction, O+NO2→NO+O2, competes too strongly with the other reaction steps for the photolysis of NO2 to be effective as a power improving technique in the flash photolysis laser. The cw laser operates on totally inverted vibrational level populations when cold CO is added to the reaction mixture. Some evidence was found to suggest that excess O2 molecules may act as a vibrational energy sink in the cw system. The laser was operated at a power of 2.3 W cw exhibiting 0.92% and 0.64% chemical and electrical efficiencies, respectively.
Production of Plasma with a CO2 TEA Laser from Solid Hydrogen Targets
Authors: Büchl Klaus
Published: February 2004

A hydrogen plasma is produced with a CO2 TEA laser of about 1 MW power. The plasma is investigated with probes, streak and short-time photography, transmission measurements, holographic interferometry, and shadowgrams with a ruby laser. The measurements are compared with a theory of plasma production by laser from solid targets and good agreement has been found. Recombination is found to be important in this experiment.
Effect of Surface Roughness on Ferrimagnetic Resonance Linewidth Measurements
Authors: Dionne Gerald F.
Published: February 2004

From room-temperature ferrimagnetic resonance linewidth measurements on both single-crystal and polycrystalline ferrite and garnet specimens, it is concluded that the surface contribution to the linewidth may be represented by ΔHsurface=ξ4πMs/d, where 4πMs is the saturation magnetization, d the sphere diameter, and ξ is a parameter dependent on the surface condition. Experimental results are presented in a manner which clearly indicates the direct dependence on 4πMs and the inverse dependence on sphere diameter which represents the ratio of the surface region volume to total volume. The parameter ξ is shown to vary with surface finish for coarse and medium textured surfaces. By comparing the linewidths of polished spheres with the extrapolated results for spheres of infinite diameter obtained from plots of ΔH vs 1/d, it is verified that the surface effects may be removed by polishing. Finally, it is emphasized that linewidths of polycrystalline materials may be very inaccurate if the surface is not polished, particularly where the material has a large magnetization and the spherical sample is small.
Slip in Silicon Epitaxy
Authors: Bloem J. , Goemans A. H.
Published: February 2004

The introduction of slip in dislocation-free silicon slices, heated in a cold-wall horizontal epitaxial reactor, has been experimentally investigated, and slip correlated with the magnitude of the heat flux through the slices. Evidence is given for the supposition that the axial temperature gradient gives rise to bow of the slices; the bow causing a radial temperature gradient which is responsible for the slip. Well-etched dislocation-free slices are least susceptible to the influence of thermal stresses, since external and internal sources for the generation or multiplication of dislocations are absent.
Mass Transport along Grain Boundaries of Silver
Authors: Tu K. N.
Published: February 2004

Thin-film specimens having the layered structure Pb/Ag/Au were prepared for a study of reaction between Pb and Au. The reaction requires mass transport of Au and Pb atoms through the intermediate layer of Ag. It is found that after annealing at 200 °C for more than 24 h the compound Pb2Au can be detected in those specimens where the Ag layer is polycrystalline but not in specimens where the Ag layer is a single crystal. These results indicate that grain boundaries in polycrystalline Ag layer act as paths for rapid transport of Au and Pb atoms.
Comparative X-Ray Diffraction and Electron Microscopic Study of the Transformation-Induced Substructures in the Iron-Nickel Martensites and Their Influence on the Martensite Properties
Authors: Chaudhuri D. K. , Ravindran P. A. , Wert J. J.
Published: February 2004

Transformation-induced fine substructures in iron-nickel martensites have been studied by x-ray diffraction and electron microscopy. The dislocation density, microstrains, and twinning increased while the dislocation cell size (particle size) decreased, with increasing nickel contents. The effect of the substructures on the hardness and yield strength of the martensites has been discussed. The anisotropic particle-size values obtained from x-ray analysis are shown to be due to faulting and/or twinning. From the compound fault probability (1.5α + β) obtained through Warren-Averbach analysis and the β values obtained from measured peak asymmetry, the stacking-fault probability α values have been derived and the stacking fault energy γ of the bcc iron-nickel alloys have been calculated. By extrapolation of the stacking-fault energy-composition curve a γ value of 50 ± 10 erg/cm2 has been estimated for pure iron.
Dielectric Loss Mechanism in Rutile (TiO2)
Authors: Johnson O. W. , DeFord John W. , Myhra Sverre
Published: February 2004

A new mechanism to account for the anomalously large dielectric loss and apparent dielectric constant frequently observed in TiO2 is presented, which appears to agree well with experiment. The mechanism involves field-induced donor migration where the field arises from a difference in work function between the rutile and a metal electrode. This migration results in a large decrease in electronic resistivity in the bulk of the crystal, with relatively thin insulating layers near the electrode surface. Experimental results on a variety of crystals are discussed, and the influence of electrode materials, surface condition, heat treatment, and ambient is analyzed. A method for numerically calculating the resistivity profile of such a crystal from dielectric loss data is described. Results indicative of room-temperature p-type conductivity and a voltage-induced conduction process are presented.
Dislocation Arrangements Resulting from the Diffusion of Zn into Cu: Electron Microscopy
Authors: Ayres P. S. , Winchell P. G.
Published: February 2004

Zinc from the vapor of 9.75-at. % zinc chips was diffused for 100 h at 780°C into (111) surfaces of thick copper crystals. The density and arrangement of the resulting dislocations were observed on (111) sections by etch pitting and in (111) thin films by transmission electron microscopy. 80% of the dislocations observed by transmission have Burgers vectors in the isoconcentration plane; 70% are organized in low-angle boundaries which have appreciable tilt character. The subgrain size in the isoconcentration plane is about equal to the distance of that plane from the surface. The dislocation density, the subgrain size, and the character of the subgrain boundaries are compared with those predicted for low-energy dislocation arrays accommodating the lattice parameter gradient.
Edge Dislocations in Anisotropic Inhomogeneous Media
Authors: Pande C. S. , Chou Y. T.
Published: February 2004

A simple method is given for obtaining the elastic stresses of an edge dislocation near a boundary (grain, interphase, or free boundary) using anisotropic elasticity theory. Exact and explicit solutions are obtained for the cases where the adjacent grains possess certain symmetry elements. The stress functions lead to the image force due to the boundary on the dislocation as Fi=− (Kb2q1/4π), (1/a), where K and q1 are constants involving the elastic constants only, a is the vertical distance of the dislocation from the boundary, and b is the Burgers vector of the dislocation.
Hall Effect of an Inhomogeneous Material
Authors: de Wit H.J.
Published: February 2004

The effective Hall mobility is calculated for a material containing inclusions which have a conductivity and Hall mobility differing from those of the matrix in order to investigate whether Hall-effect-Seebeck-effect anomalies can be explained by the presence of inclusions. The calculation is performed analytically using a method by which Airapetiants has determined the effect of inclusions on the Seebeck effect, and numerically by solution of the Laplace equation with the relaxation method. The effective Hall mobility is largely dependent on the ratio of the specific conductivity of the inclusion to that of the matrix. The possibility of obtaining a sign reversal of the Hall effect when the Hall effects of matrix and inclusion have opposite sign is largest when the respective conductivities are about equal. The Hall effect anomaly occurring in Li-doped NiO at 600 °K might be explained by assuming that 1% inclusions having a negative Hall effect with a Hall mobility of ≈ 5 cm2/V sec are present. However, this explanation requires the specific conductivity of the inclusions to be proportional to the Li concentration which seems improbable. It is shown to be impossible to explain the Hall-effect-Seebeck-effect anomaly of chalcogenide glasses with the present model.
Electrode Polarization of Ionic Conductors
Authors: Mitoff S. P. , Charles R. J.
Published: February 2004

Polarization observed on applying ac and dc electric fields to samples of β alumina, sodalime glass, and single crystals of sodium chloride have been studied. It is concluded that the large capacitances shown by these materials, which are generally attributed to space-charge effects, are more likely caused by reactions at the electrodes which build up cell potentials. Electrochemical models, involving these cell potential effects, are presented and compared with previous space-charge models which have been applied to solid electrolytes.
Simultaneous Thin-Film Stress and Mass-Change Measurements Using Quartz Resonators
Authors: EerNisse E. P.
Published: February 2004

It is shown theoretically and experimentally that stresses in a thin film on a quartz resonator surface can set up sufficient static mechanical bias in the resonator to cause measurable shifts in the resonant frequency through finite strain effects. In particular, it is found that if a 5-MHz AT-cut fundamental mode and a 6.19-MHz BT-cut fundamental mode are subjected to the same combination of thin-film stress and mass/cm2 changes on their surfaces, the sum of the observed frequency shifts is proportional to the mass/cm2 change alone, and the difference of the frequency shifts is proportional to the integral through the film thickness of the change in the thin-film stress alone. This ``double-resonator'' technique is demonstrated with implantation studies of 220-keV 84Kr implants into Si films deposited on the flat electrodes of planoconvex 5-MHz AT-cut and 6.19-MHz BT-cut resonators. The double-resonator technique stress results were verified quantitatively by implanting ions into a Si film on one surface of a quartz cantilever beam and monitoring the movement of the free end of the cantilever beam by the changes in capacitance between the free end and a fixed electrode. The sensitivity of the double-resonator technique is 125 dyn/cm and 6 × 1014 amu/cm2 for a 0.1-Hz frequency shift. The technique is suited best to thin-film stress studies with small mass changes.
Effect of Light on the Mobility of Dislocations in Germanium
Authors: Kuczynski G. C. , Iyer K. R. , Allen C. W.
Published: February 2004

Dislocation velocity measurements have been made from observations of dislocation rosette growth during annealing of germanium containing Knoop hardness indentations. Dislocation velocities followed the relation v=v* exp(−ΔH/kT) exp(−X/X0), where X is the length of the semimajor axis of the rosette. At annealing temperatures below 300°C, the activation enthalpies ΔH were 1.0–1.3 eV, and v* ranged from 103 to 106 cm/sec for samples annealed in darkness while ΔH decreased to 0.55–0.8 eV and v* to 10−1−102 cm/sec for samples annealed under infrared illumination. At annealing temperatures above 300°C, ΔH was 0.35–0.40 eV and v* 10−3 cm/sec, independent of illumination. An hypothesis based on Read's model of dislocation in germanium accounts qualitatively for most of the observed phenomena.
Structure and Composition of Sputtered Tantalum Thin Films on Silicon Studied by Nuclear and X-Ray Analysis
Authors: Croset M. , Velasco G.
Published: February 2004

Microanalysis by direct observation of nuclear reactions and by backscattering of He4+ ions was used to determine the composition of sputtered Ta films on silicon. Oxygen and nitrogen concentration as low as 0.3 and 0.1%, respectively, were found for bcc and β-Ta structures. At a low deposit rate, oxygen incorporation in β-Ta structure up to about 20% was observed and correlated to a resistivity increase. The Ar/Ta ratio varies between 1.5 and 3% with increasing sputtering power.
Active Sites for Heterogeneous Catalysis
Authors: Grenga Helen E. , Lawless Kenneth R.
Published: February 2004

The catalytic decomposition of carbon monoxide on (100), (110), and (111) monocrystalline nickel thin films has been studied. Reacted nickel films and extraction replicas were examined by transmission electron microscopy to determine the influence of orientation, lattice defects, and topographical imperfections on the catalytic activity of these films. The order of decreasing catalytic activity, determined by the rate of graphite deposition, was (111) > (110) > (100). The results on (100) films indicated that a Ni–C phase was formed initially and subsequently decomposed to give polycrystalline graphite in nickel-depleted regions, generally associated with lattice defects or strain paths along 〈001〉 directions. On (110) and (111) films, oriented graphite deposits were found on the nickel surfaces, and the results indicated that nucleation occurred at active sites for the catalytic reaction with no intermediate Ni–C phase detectable. No correlation was found between lattice defects and graphite nucleation sites. These nucleation sites in general corresponded to specific steps and kink sites on the nickel surface. It was proposed that the important factors governing the activity of steps for a given catalytic reaction included the step height and the nature of the step base and step face.
Langmuir Sheath Thickness as Observed by Ion Acoustic Waves and a Hot Probe
Authors: Widner M. M. , Alexeff I. , Jones W. D.
Published: February 2004

We use ion acoustic waves and an electron-emitting hot probe to measure Langmuir sheath thickness as a function of negative electrode voltage. We find the thickness varies as voltage to the ¾ power, as expected, which suggests diagnostics for plasmas based upon these methods.
Electrostatic-Inertial Plasma Confinement
Authors: Dolan T. J. , Verdeyen J. T. , Meeker D. J. , Cherrington B. E.
Published: February 2004

Electrostatic-inertial plasma confinement consists of trapping charged particles in potential wells of the electric field, which are created by ions or electrons injected radially inwards into a hollow sphere or cylinder. Theoretical expressions are derived for the potential and particle densities as functions of radius, grid voltage, and current. A neon plasma is produced in cylindrical geometry, using a grid 4 cm in diameter and 16 cm long. Using the laser heterodyne technique at 0.6401 and 0.6328 μ, the density of neon atoms in the 1s5 metastable state is measured (109−1012 cm−3) as a function of radial position, time, grid current (20 - μsec pulses of up to 4 A), grid voltage (0.2–3.0 kV), gas pressure (0.001–0.01 Torr), and grid mesh spacing, and compared with theoretical predictions. The peak electron density is 1011 cm−3. When the spacing between grid wires is larger than 1 mm, a decrease in metastable density, attributed to the presence of a plasma sheath around the grid wires, is observed. The radial variation of plasma light intensity is compared with the theoretical radial distribution of electron density.
Thermal Lensing in Infrared Laser Window Materials
Authors: Jasperse J. R. , Gianino P. D.
Published: February 2004

A theoretical investigation of thermal lensing in infrared windows is presented which treats aberration effects to all orders in the small angle-of-deviation approximation. The model is applied to a truncated Gaussian infrared laser beam incident on a semitransparent isotropic disk-shaped window. It is shown that window aberrations limit the time a diffraction-limited focus can be held in the far field. This diffraction-limited time td is computed for some candidate window materials and their relative merits are discussed.
Vitreous As2Se3; Investigation of Acousto-Optical Properties and Application to Infrared Modulator
Authors: Ohmachi Yoshiro , Uchida Naoya
Published: February 2004

Acoustic and acousto-optical measurements have been carried out on vitreous As2Se3. Values of acousto-optical figures of merit M (=n6p2/ρ v3) and M′ (=n7p2/ρv) for longitudinal acoustic waves are 1090 × 10−18 sec3/g and 1600 × 10−7 cm2 sec/g, respectively, for He–Ne laser radiation of 1.153 μ polarized along the propagation direction of the acoustic wave. These values are the largest among those for known materials which are transparent in the near-infrared spectral region. Acoustic attenuation has been evaluated as 11 dB/cm at 200 MHz, and the material is considered useful for a modulator element operable up to several hundred MHz. Experimental pulse modulation and transmission of the 1.153-μ laser radiation have been demonstrated using the As2Se3 modulator at an acoustic carrier frequency of 140 MHz. The transmitted pulse pattern has been displayed by the use of TeO2 light deflector.
Lang Topographic Studies of III-V Heteroepitaxial Films Grown on Sapphire and Spinel
Authors: McFarlane S. H. , Wang C. C.
Published: February 2004

Single-crystal layers of GaAs and GaP grown by chemical vapor deposition on sapphire and magnesium aluminate spinel substrates have been characterized by Lang x-ray topography and x-ray diffraction methods. Separate topographs and diffraction peak profiles of the substrate and layer were obtained without removing the layer from the substrate. Epitaxial layers grown on substrates prepared by different growth techniques were examined and compared. Layers shown to be monocrystalline by back-reflection Laue methods were revealed by Lang topography to be composed of small grains which were misoriented ±0.1° from the nominal orientation of the layer. Polishing scratches and growth striae in the substrates were found to influence the perfection of the layer. The Lang camera was used as a diffractometer to measure the misorientation of the layers from exact parallel epitaxy and to determine the radius of curvature of warped substrates.
Investigation of the Recombination and Trapping Processes of Photoinjected Carriers in Semi-Insulating Cr-Doped GaAs Using PME and PC Methods
Authors: Li S. S. , Huang C. I.
Published: February 2004

Investigation of the recombination and trapping processes of photoinjected carriers in semi-insulating Cr-doped GaAs (ρ ∼ 108 Ω cm) has been made at 80 and 300°K, using the photomagnetoelectric (PME) and photoconductive (PC) effects under large-injection conditions. A generalized theory for the PME and PC effects is developed, taking into account the variation of carrier lifetimes with injected-carrier density (i.e., τn = κΔnβ) and of the trapping of holes in the Cr levels (i.e., Δp = ΓΔn, Γ<1), by using a simple recombination and trapping model. The result yields a power-law relationship between the PME short-circuit current and the photoconductance, in a form that IPME varies as ΔG2/(2+β), valid for different injection ranges. Two well-defined ranges of injection were observed from the present results: In region I (high injection), IPME is directly proportional to ΔG (i.e., β = 0), and in region II (intermediate injection), IPME varies with ΔG1.2 (i.e., β = −⅓). Numerical values of τn, τp, and IPME as functions of ΔG are given. The results are in good agreement with the theoretical predictions.
Luminescence Processes in Yb3+-Sensitized Rare-Earth Phosphors
Authors: Mita Yoh
Published: February 2004

Quantitative analyses were carried out on the infrared-to-visible conversion processes and related luminescent phenomena in Yb3+-sensitized phosphors. The analyses were based on a rate equation model and the effect of host lattice was taken into account using the Miyakawa-Dexter relations. The results were found to be in fair agreement with the experimental results on luminescence characteristics under ultraviolet and infrared excitations. Approximate values of parameters characteristic of the host materials were obtained for YF3 and YOF lattices by comparing the calculated and experimental results.
Generation of Dislocations and Stacking Faults at Surface Heterogeneities in Silicon
Authors: Ravi K. V.
Published: February 2004

Dislocation and stacking fault generation around submicron-sized surface pits in shallow diffused bipolar transistors is examined. Under the combined action of the stress concentration effect of surface pits and phosphorus diffusion induced stresses, crystallographic defects are generated in the emitter area of shallow diffused transistors. Stacking faults are identified as sessile faults surrounding the micropits. Mechanisms of dislocation generation are examined and their applicability to the present results discussed. It is shown that the presence of nonplanar surfaces at discrete regions can introduce an additional diffusion front into the crystal and produce an increase in stress as well as an increase in the solute concentration leading to localized plastic flow. High-concentration phosphorus diffusions introduce extensive dislocation networks throughout the emitter area and cause stacking fault annihilation.
Autodoping Effects of Ge in Vapor-Grown GaP Layers on Ge Substrates
Authors: Kasano Hiroyuki
Published: February 2004

The autodoping effects of Ge incorporated into the GaP layer grown via vapor-phase transport on Ge substrate are investigated at 300°K. XMA and point-contact-breakdown techniques are used to obtain the free-carrier concentration profiles across the grown layer. The free-carrier concentration is found not to exceed 1.3×1017 cm−3 because of self-compensation of Ge donor acceptors. The compensation ratio NA−+ND+ reaches up to 90% above 5×1017 cm−3 of |NA−+ND+|, where NA− and ND+ represent the ionized Ge acceptor and donor concentration, respectively. Considering various scattering mechanisms, ionization rates of the Ge atoms incorporated into the GaP layer are deduced. The emission spectra from zinc-diffused p-n junctions fabricated with these GaP layers also reveal strong dependence upon the Ge concentration. Their intensity variation is satisfactorily explained by the pair model. The correlation between the emission intensity of the Zn–Ge pair band and the injection efficiency of an electron is discussed as well as the correlation between that of the Ge–Ge band and NA−/ND+.
Deep-Trapping Kinematics
Authors: Kanazawa K. Keiji , Batra I. P.
Published: February 2004

An analytical treatment of the standard transport equations in the presence of deep traps is presented. The model assumed for the traps is one in which they can be characterized by a single trapping time, and the analysis is valid for arbitrarily strong trapping. The configuration treated is that appropriate to potential probe measurements. Carriers are introduced through photogeneration by highly absorbed illumination. An exact result is obtained relating the final potential resulting from the accumulated trapped space charge to the carrier range, or μT, product. This relationship is independent of the injection history and therefore of the complexities attendant with such surface phenomena as recombination and field-dependent photogeneration. For continuous illumination, analytic results are obtained for the detailed space and time dependence of the trapped carriers and the resulting modification of the electric field. These results include the effects of a field-dependent injection mechanism. Particular cases where the injection is proportional to the mth power of the field are treated, with m taking on the values 0, 0.5, 1, and 2.
Warm-Carrier Microwave Transport in n Si
Authors: Holm-Kennedy James W. , Champlin K. S.
Published: February 2004

The small-signal microwave (9.61 GHz) dielectric constant and microwave resistivity were measured under warm electron conditions at 77 °K lattice temperature. Both were found to be anisotropic. The dielectric constant exhibited a ``hump'' at high electric fields when applied in the 〈100〉 crystallographic direction but not when applied in the 〈111〉 crystallographic direction. The anomaly is attributed to a repopulation modulation caused by the microwave field. A theory is presented which explains the effect. Analysis of the data yields the f-type intervalley relaxation time for the 〈100〉 orientation as a function of electric field. The f-scattering strength of the 200 and 630 °K phonons are determined. The g scattering is inferred to be very weak in comparison to either of the f-type scatters.
Habit and Morphology of Copper Precipitates in Silicon
Authors: Hu S. M. , Poponiak M. R.
Published: February 2004

Copper precipitates in silicon often agglomerate into elliptical disks lying in {110} planes of the host lattice, with their respective major axes pointing in the 〈110〉 directions. As many as 12 such disks usually emanate from a nucleation center of some lattice defect, displaying a partially or fully developed rosette pattern silhouette under ir microscopy. Various patterns of precipitates in substrates of 〈100〉, 〈111〉, and 〈120〉 crystallographic orientations are consistently explained by coordinate transformations of a hypothetical rosette pattern. In particular, the observations of precipitates in 〈120〉 substrates have demonstrated the nonexistence of needle forms. The ratio of the two elliptical axes varies with copper concentration and quenching conditions. With the surface behaving as a sink, rapid quenching was usually necessary to achieve fully developed precipitates. There was no preference among the six equivalent {110} planes and the six 〈110〉 directions in which elliptical disks precipitated about a point defect. There was, however, a preferred orientation tendency for the disks precipitated about a dislocation line. Some elliptical disks exhibited banded structure—probably a result of Ostwald ripening. The elliptical disks disappeared and reappeared during annealing cycles, exhibiting a memory effect.
Permittivity of Strontium Titanate
Authors: Neville R. C. , Hoeneisen B. , Mead C. A.
Published: February 2004

The permittivity of single-crystal single-domain strontium titanate has been measured in detail in the [001], [011], and [111] directions, as a function of temperature (from 4.2 to 300 °K), electric field (from −23 000 to +23 000 V/cm, and frequency (from 1 kHz to 50 MHz). The free energy of the crystal is determined as a function of polarization with temperature as a parameter. The Curie-Weiss law is satisfied in the temperature range 60–300 °K, giving a Curie temperature of 30 ± 2 °K for the three crystal orientations. The Lyddane-Sachs-Teller (LST) relation is satisfied for temperatures between 30 and 300 °K and for electric fields between 0 and 12 000 V/cm. A generalized LST relation is used to calculate the permittivity of strontium titanate from zero to optic frequencies. Two active optic modes are important. The lower-frequency mode is attributed mainly to motion of the strontium ions with respect to the rest of the lattice, while the higher-frequency active mode is attributed to motion of the titanium ions with respect to the oxygen lattice. The restoring forces that act on the Ti ions begin to ``harden'' when these ions are displaced approximately 0.002 Å from their equilibrium positions.
Auger Electron Spectroscopy Studies of Sputter Deposition and Sputter Removal of Mo from Various Metal Surfaces
Authors: Tarng M. L. , Wehner G. K.
Published: February 2004

Cu, Au, Al, and W samples were mounted in an ultrahigh vacuum (UHV) chamber such that in situ Ar ion sputter cleaning as well as sputter deposition and sputter removal of Mo and Auger analysis could be performed. The Auger signals indicated that Mo on W forms uniform films while on Cu, Au, and Al the deposited Mo atoms agglomerate into multilayer islands. The sputter removal of the deposited Mo from W proceeds as if Mo is sputtered from Mo. On Cu, Au, and Al, the Ar ion bombardment causes spreading of the Mo more uniformly over the surface. The sputtering yield of Mo atoms from Cu, Au, and Al, especially at low energies, is much lower than that of Mo from Mo. Two hundred-eV Ar+ ions remove Mo atoms from an Al surface with a yield which is more than three orders of magnitude lower than the bulk Mo yield. Thus, a significant conclusion is that the use of low-energy ion bombardment (under normal incidence) for layer removal in determination of depth-composition profiles may often lead to erroneous results.
Surface Potential Fluctuations Generated by Interface Charge Inhomogeneities in MOS Devices
Authors: Brews J. R.
Published: February 2004

Small-signal conductance peaks in metal-oxide-semiconductor (MOS) devices have been found experimentally to be much wider than predicted by the surface-state continuum model of Lehovec. This increased width has been attributed by Nicollian and Goetzberger to surface potential fluctuations generated by inhomogeneities in the interface charge density. However, no theoretical estimate of the amount of additional width to be expected from such inhomogeneities nor of the dependence of this additional width upon device parameters has been presented. In this paper these theoretical estimates are provided for the case when the surface potential departs slightly from its value as estimated in the usual one-dimensional charge sheet model of the MOS device. To do this we derive and approximately evaluate a theoretical relation between the variance of the surface potential and the autocovariance function of the interface charge distribution. For a random interface charge distribution we obtain a logarithmic dependence of the variance upon the sum of the oxide, space-charge, and surface-state capacitances. In the limiting case in which only long-wavelength charge fluctuations contribute to the variance of the surface potential, this logarithmic dependence is replaced by the dependence appropriate to a quasiuniform model. The results indicate that the magnitude and bias dependence of the effect of a random distribution is in fair agreement with experiment, but that more data are needed at various oxide thicknesses on samples of low or uniform surface-state density with known flat-band shifts before it can be concluded that surface potential fluctuations are indeed responsible for the anomalous width of the conductance peaks. Should this prove to be true, the dependence of the conductance-peak width upon device parameters would serve to identify both the presence and the nature of interface charge inhomogeneities.
Comment on Electron Scattering in the Image Potential Well
Authors: Silver M. , Smejtek P.
Published: February 2004

Comments are made on the model of electron injection into SiO2 proposed by Berglund and Powell. Their assumptions on electron scattering, disregarding the change of the escape cone with the distance from the emitter, lead to serious underestimation of the injected current. Two alternative models of electron injection, based solely on elastic scattering are discussed and do not predict the experimental results. We suggest that observed field dependence of the injected current into SiO2 indicates that energy relaxation associated with the injected electrons is responsible for the voltage dependence of the current.
Mechanism for the Radiation Compaction of Vitreous Silica
Authors: Primak William
Published: February 2004

The thermal spike hypothesis for the radiation compaction of vitreous silica by energetic ions is developed in detail. The variation of the thermal constants with temperature and the variation of energy dissipation along the range are considered and are found to affect the problem little. When the hypothesis was first presented, the thermal constants had not been determined, nor was the behavior of vitreous silica toward light ions known. The duration of thermal spikes calculated from current data is too short to account for the compaction by their thermal behavior alone. Therefore, the atomic nature of the processes is considered, and it is concluded that the process of compaction is facilitated and largely controlled by bond cleavage. However, the thermal excitation is essential in developing the configuration characteristic of the compacted state.
Heat-Pipe Oven for Homogeneous Mixtures of Saturated and Unsaturated Vapors; Application to NaLi
Authors: Vidal C. R. , Hessel M. M.
Published: February 2004

A heat-pipe oven has been developed to produce homogeneous mixtures of a saturated vapor with an unsaturated vapor at any arbitrary well-defined ratio. The oven is able to handle materials of widely different vapor pressures and the zone containing the homogeneous vapor mixture can be made to extend over any desired path length. With this heat-pipe oven containing sodium and lithium, the laser- and collision-induced fluorescence spectrum of the NaLi molecule has been used to study the operation of the oven. The first observation of a ``propensity rule'' for a polar molecule (the ΔJ=+1 collision-induced NaLi line is stronger than the corresponding ΔJ=−1 or 0 line) is reported.