bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient Space-Charge Limited Currents in Amorphous Selenium Thin Films
Authors: Rossiter Edward L. , Warfield G.
Published: February 2004

Transient space-charge limited currents for both electrons and holes have been observed in thin films of amorphous selenium under electron bombardment. Room-temperature mobilities of 0.006 cm2/V sec for electrons and 0.14 cm2/V sec for holes were extracted from these observations. From observed exponential variation of these mobilities with temperature, characteristic activation energies are found to be 0.27 eV for electron mobility and 0.095 and 0.0093 eV for hole mobility at high and low temperature, respectively. These mobilities are interpreted as controlled by shallow traps. Significant deep electron trapping, but not hole trapping, was found at room temperature, giving an electron range of approximately 10−7 cm2/V. This range decreased with decreasing temperature. Deep hole trapping was observed below about 250°K, and the hole range at this temperature was approximately 10−6 cm2/V. An anomalous increase in both electron and hole mobility with increasing field was observed. This anomaly is attributed to a field-dependent trapping mechanism analogous to the Poole-Frankel effect.
Tunnel Effect in Al–Al2O3–Al Junctions: Inclusion of Short-Range Forces
Authors: Dubey P. K.
Published: February 2004

Tunneling in metal-insulator-metal junctions has been considered taking into account the short-range forces due to surface ion-cores at the junction interfaces. An approximate formula for the tunnel current has been derived, and expressed in an analytically tractable form for evaluations of the volt-current characteristics of such junctions at finite temperatures. A detailed comparison with experiments has been made stressing the importance of specifying the junction parameters a priori; the earlier procedure of deducing the parameters is avoided. An order-of-magnitude agreement is generally obtained though some observed characteristic features cannot be explained. It is seen from a comparison of the present barrier model with the earlier image-barrier models that the short-range forces are effective to about 5% in determining the barrier height and are indeed important on quantitative scales. Some criticisms and drawbacks of the theory have also been given.
Production and Annealing of Color Centers in rf Sputtered SiO2 Films
Authors: Hickmott T. W.
Published: February 2004

Radio-frequency sputtered SiO2 films can be made that contain a variety of optical absorption bands and electron spin resonance centers. In addition to absorption bands at 5.1, 5.8, and 7.6 eV that are typical of irradiated fused SiO2, two new absorption bands have been found. The G band at 5.4 eV and the H band at 6.55 eV are present in certain sputtered SiO2 films and develop further when they are annealed in forming gas or N2. The occurrence of these bands and the density of paramagnetic centers produced in SiO2 films when they are sputtered under different deposition conditions has been studied. The effect of annealing to 950°C in N2, O2, and forming gas on optical absorption bands and ESR centers has been determined. Absorption bands appear to be associated with oxygen deficiency in the sputtered SiO2 films since they will anneal completely at 930°C in oxygen. Hydrogen plays an important role in annealing of the B1 band at 5.1 eV, the E1′ band at 5.8 eV, and all the ESR centers. They anneal at 200°C lower temperatures in forming gas, compared to annealing in N2. The OH content, refractive index, Ar content, density, and etch rates of sputtered SiO2 films have also been measured. The properties of the film show the importance of plasma radiation and resputtering in determining film properties. Wide variations in optical absorption and ESR are observed in samples deposited under nominally identical conditions.
Light Diffraction by an Acoustic Surface Wave in Fused Quartz
Authors: Montgomery R. M. , Young E. H.
Published: February 2004

Light diffraction by an acoustic surface strain wave in fused quartz was observed in the Debye-Sears limit. An acoustic surface wave has both compressional and shear strains. It is possible to observe and distinguish the diffraction of light caused by the two different strains since the diffracted beam polarization due to the shear strain is rotated 90° from the incident polarization. In the experiment performed 2.5% of the incident energy was diffracted into a single order. Light diffracted by both the compressional and shear strains was clearly identified.
Quench-Induced Defect Structure in Al-6.5-at.% Zn
Authors: Kiritani M. , Weissmann S.
Published: February 2004

The defect structure induced in Al-6.5-at.% Zn upon quenching consisted of homogeneously nucleated dislocation loops, helical dislocations developed from screw dislocations, the latter being introduced by two different processes. The defect structure also contained perfect loops converted from helical dislocalocations and faulted dislocation loops whose nucleation was enhanced by vacancies generated by quench deformation. Based on experimental evidence, a model is presented explaining the formation of a row of perfect dislocation loops from a single helical dislocation. The interrelation of the various types of induced defects is shown by correlating their formation with the aid of vacancy mechanisms.
〈110〉
Dislocation in Cubic Crystals
Authors: Chou Y. T. , Sha G. T.
Published: February 2004

Exact expressions for the displacement and stress components of a dislocation parallel to a 〈110〉 axis in a cubic crystal have been derived. For 〈110〉/{112} and 〈110〉/{111} dislocations, the stress components σxx(y=0), σyy(y=0), and σxy(x=0) are found to be nonzero. It was shown that σxy≠0 at x=0 has no effect on the stability of a vertical wall of edge dislocations. The energy factor K was computed for the dislocations in bcc, fcc, and diamond-cubic crystals. By comparison, the elastic energy of an edge dislocation on the {110} slip plane in bcc crystals is generally less than that on the {112} slip plane. The differences, however, are very small except in a few cases of highly anisotropic crystals such as Li, K, Na, and β-brass.
Deformation Substructure in Beryllium After Prism Slip
Authors: Kannan V. C. , Weissmann S.
Published: February 2004

The development of cell structure during room-temperature tensile deformation of beyllium oriented for prism slip was studied by a combination of a new x-ray diffraction technique (synergy method) and transmission electron microscopy. It was convenient to divide the development of the cell structure into three stages. In stage one, dislocations moving on the prism plane pulled out small segments of dislocations lying on the basal plane to form long dipoles and numerous pinched-off loops. During the second stage, dense dislocation clusters developed which became interconnected by dislocation tangles. The final stage consisted of the formation of well-developed cell walls with regular hexagonal networks of dislocations. The striking feature of all the stress-strain curves was the low work-hardening rate extending up to ε=15% strain. The low work-hardening rate was ascribed to nucleation and propagation of new slip bands into hitherto undeformed volumes of the crystal.
Computer Calculations of the Structure and Energy of High-Angle Grain Boundaries
Authors: Weins M. J. , Gleiter H. , Chalmers B.
Published: February 2004

A method that has been developed to obtain the geometry of a grain boundary associated with a minimum internal energy is described in detail. A Morse potential is employed to represent the interatomic forces. The procedure was applied to a series of boundaries of the coincidence orientations. The resulting structures are consistent with experimental observations.
Thermal Currents and the Internal Polarization in Carnauba Wax Electrets
Authors: Perlman Martin M.
Published: February 2004

Thermal currents have been obtained from carnauba wax electrets using a linear heating rate for various polarization fields, temperatures, times, and thickness of samples. The polarization is shown to be uniform, and hence space charges, resulting from either charge injection from the electrodes or macroscopic ion displacement, are ruled out as possible causes of the heterocharge. The case for dipole orientation is examined and it is shown that far too many dipoles must be aligned to produce the observed effects. Microscopic displacement of ions with trapping is proposed as the heterocharge mechanism. This model is consistent with the observed temperature dependence of the thermal currents, and does not appear to contradict any of the experimental facts. The thermal-current spectra consist of three overlapping peaks with activation energies of 1.7, 2.3, and 2.7 eV and temperature maxima of 47°, 59°, and 69°C, respectively. In the proposed model, these activation energies are to be associated with the ionic trap depths.
Work Function of Tantalum Carbide and the Effects of Adsorption and Sputtering of Cesium
Authors: Baxter William J.
Published: February 2004

The work function of ``unactivated'' tantalum carbide is 4.22±0.06 eV. The decrease of work function produced by the so-called ``activation'' process is attributed to a loss of carbon. The deposition of low-energy cesium ions (2–5 eV) reduced the work function to a minimum value of 1.40±0.02 eV. Cesium ions with energies of 7–28 eV sputter previously adsorbed cesium in the form of neutral atoms. The energy required to produce this sputtering decreases with increasing cesium coverage.
Total Melting Time in the Ablating Slab Problem
Authors: Rogerson J. E. , Chayt G. A.
Published: February 2004

An exact melt-through time is derived for the one-dimensional heated slab problem when the melted material is immediately removed. The result is derived via two different approaches and is shown to be independent of the transport properties of the material.
Electronic Conduction Through Single Crystals of Polyethylene
Authors: Senecal Gerard , Ham Joe S.
Published: February 2004

Current densities of the order of 10−8 A/cm2 at field strengths of 3×106 V/cm have been measured for electrical conduction through single-layered polyethylene crystal samples at room temperature. The dependence of current density on field strength has been fitted to the Richardson-Schottky model of field-assisted thermionic emission.
Kinetic Modeling of the High-Power Carbon Monoxide Laser
Authors: Rich Joseph W.
Published: February 2004

A model for the kinetics of the cooled direct-discharge-excited carbon monoxide laser is presented. The kinetic mechanism responsible for creating the observed population inversions cannot be explained by simple one-step resonance transfer between an excited metastable and the CO molecule, in view of the many vibrational bands which lase in this system. The present paper analyzes a kinetic model of the CO laser which includes the following processes: (a) Vibration-to-vibration (V-V) energy exchange among the anharmonic vibrational states occurring in CO–CO collisions. (b) Resonance electron impact excitation of the lower CO vibrational states. (c) Radiative decay of the CO vibrational states. (d) Collisional quenching of vibrational excitation in CO–He collisions. Using a Morse anharmonic oscillator model of the CO vibrational states, kinetic equations are formulated which govern the individual vibrational state populations, subject to the preceding processes. The resulting set of nonlinear algebraic equations is solved by an interative technique for the steady-state vibrational populations. Small-signal laser gain is also predicted as a function of the following discharge conditions: (1) electron temperature, (2) electron concentration, (3) heavy species translational temperature, (4) CO partial pressure, and (5) He partial pressure. Comparison is made with recent experimentally obtained small-signal gain data for the CO laser, as well as with other experimental results for CO lasers. It is shown that experimental results are consistent with an inversion created by electron impact excitation of the lower CO vibrational levels, followed by rapid redistribution of energy among the higher CO vibrational states via off-resonant vibration-vibration energy exchange. The present kinetic model successfully interprets the variation of gain with vibrational state, the observed strong temperature dependence of the gain, and the influence of He diluent in the discharge. The possibilities for using this pumping mechanism to obtain cw lasing with other diatomic species and in various laser configurations are also discussed.
Characteristics of Optically Pumped Platelet Lasers of ZnO, CdS, CdSe, and CdS0.6Se0.4 Between 300° and 80°K
Authors: Johnston W. D.
Published: February 2004

The behavior of platelet lasers of ZnO, CdS, CdSe, and CdSe0.4S0.6 pumped by a pulsed Xenon laser at 3646 Å is described. Single-mode operation of CdSe and ZnO over the full temperature range 80° to 300°K is observed. Absolute threshold-temperature curves and absolute input-output efficiency curves are presented and found to differ significantly from results of electron-beam pumped platelets. These results are predicted by an analysis of the cavity configuration including the effects of spatial inhomogeneity of the gain. The importance of this inhomogeneity for interpretation of experimental gain-loss mechanism in II-VI lasers is emphasized, and the implications of the spectral and threshold data for current theoreies of the gain process are discussed. Neither the exciton-LO phonon nor the non-LO phonon theories, in their present form, appear able to explain all the data.
Measurement of Particle Velocity at a Shock Front in Water with a Laser Doppler Meter
Authors: Anderson R. E. , Edlund C. E. , Vanzant B. W.
Published: February 2004

A laser Doppler meter was used to detect particle motion in tap water due to the passage of an explosively generated shock front. It was not necessary to introduce foreign particles or dust in the region of observation to serve as scattering centers. Optics of the system were aligned such that particle motion was monitored in only a small volume rather than over the entire ray path length. Particle velocities measured with the Doppler system were in agreement with those calculated from the response of a standard tourmaline piezoelectric pressure gauge placed adjacent to the region on which the Doppler meter was focused.
Thermoluminescent Behavior of LiF (TLD-100) from 77° to 500°K
Authors: Podgoršak Ervin B. , Moran P. R. , Cameron John R.
Published: February 2004

The thermoluminescence (TL) from dosimetry grade LiF has been studied over the temperature range from 77° to ∼500°K and over the exposure range of 50–105 R. A total of ten glow peaks are resolved and the characteristics of many of the related traps have been measured. The lowest temperature glow peak (∼145°K) has the maximum of its emitted TL spectra at ∼250 nm, whereas the maxima of the other glow peaks are at ∼400 nm. The TL from the 145°K trap is about 20 times more intense than from the dosimetry traps at ∼190°C. All glow peaks except the one at 145°K exhibit a nonlinear response with radiation exposure. The amount of this supralinear response is proportional to the cube of the absolute temperature of the glow peaks. Optical repopulation studies indicate that most of the peaks are due to electron traps, but two of the low-temperature peaks have distinctly different behavior, indicating that they might be associated with hole traps.
Cooperative and Sequential Excitation of Red Fluorescence of Ho3+ in CaF3
Authors: Verber C. M. , Grieser D. R. , Jones W. H.
Published: February 2004

Steady-state and dynamic methods for differentiating between successive and cooperative excitation of fluorescence are discussed with respect to the infrared excitation of the red (0.65-μ) fluorescence of Ho3+ in CaF2. The excitation of this fluorescence by 1.16-μ radiation is identified as a nonresonant cooperative interaction involving the emission of about four phonons for energy conservation.
Cathodoluminescent Measurements in GaP (Zn, O)
Authors: Casey H. C. , Jayson J. S.
Published: February 2004

Cathodoluminescent measurements have been made on red emitting Zn–O-doped GaP. With a nonfocused beam, the minority carrier diffusion length Ln and the surface recombination velocity S have been obtained. For a particular illustrative sample, these values were found to be Ln=0.5±0.2 μm and S=5×105 cm/sec. The high generation rates achieved with a finely focused electron beam (∼0.5 μm) result in a near square-root dependence of emission on excitation. This dependence requires that the nonradiative centers as well as the radiative centers are saturated.
Spin-Wave Contribution to the Deviation of the Magnetization from Saturation
Authors: Bartel L. C.
Published: February 2004

A first-order macroscopic spin-wave Hamiltonian is used to describe and calculate the deviation of the magnetization from saturation for materials with a uniaxial magnetic anisotropy perpendicular to an applied magnetic field. The calculations predict a spin-wave deviation from saturation prior to the onset of any actual rotation of the magnetization. When the magnetic anisotropy creates an easy axis of magnetization, the spin-wave deviations from saturation occur, for a decreasing applied field, at a larger field than the nucleation field given by the variational and/or micromagnetic approaches. When the anisotropy creates a hard axis of magnetization, spin-wave deviations from saturation occur; whereas, the variational and micromagnetic approaches predict no deviation from saturation for finite fields in this case. It is concluded that spin-wave contributions to the deviation from saturation are important.
Cobalt-Mischmetal-Samarium Permanent Magnet Alloys: Process and Properties
Authors: Benz M. G. , Martin D. L.
Published: February 2004

Several authors have reported successful fabrication of high-energy product (15–20 MGOe) Co5R-type cobalt-samarium permanent magnets. In earlier papers we have described preparation of such magnets by a liquid-phase sintering process sequence which includes powder preparation, magnetic alignment, pressing, sintering, and magnetizing. We have also described preparation of ternary compositions, primarily Co–Sm–Pr, by this process. In an effort to utilize more abundant rare-earth metals, the cobalt-mischmetal-samarium system has been studied. Initial results indicate that a substantial fraction of the samarium may be replaced with mischmetal and still obtain high magnetic properties (BHmax 20 MGOe). Complete documentation of magnetic properties, i.e., saturation, remanence, coercive force, intrinsic coercive force, (BH)max, and temperature coefficients are presented along with a discussion of the fabrication techniques utilized for preparation of the samples.
Single Crystalline Elastic Constants of Cubic MgCu2–MgZn2 Alloys
Authors: Shannette G. W. , Smith J. F.
Published: February 2004

The single crystalline elastic constants of the ternary Laves phase Mg(Cu, Zn)2 have been determined by the ultrasonic pulse-echo technique over the temperature range 4.2°–298°K and over the composition range 10–51-mol% MgZn2. The compositional dependence of the elastic contants indicates that a changing electron concentration causes initial contact and then a subsequent overlap of a Brillouin zone boundary by the Fermi surface. This contact occurs near 20-mol% MgZn2 and correlates with previous measurements of magnetic susceptibilities and of specific heats. Debye temperatures at 0°K were also determined from the experimental values of the elastic constants.
Parametric Oscillation Thresholds in Symmetric and Half-Symmetric Configurations in the Absence of Double Refraction
Authors: Boyd G. D. , Nash F. R.
Published: February 2004

We have computed the parametric oscillation threshold in the case of no double refraction for a resonator geometry in which the beam waists are located at a crystal face (half-symmetric). The result is a simple approximate analytic expression for the threshold which is given in terms of the functions derived by Boyd and Kleinman for the geometry in which the beam waists are at the center of the crystal (symmetric). The approximation is valid throughout the range of experimentally significant focusing parameters. Our work complements the recent work of Ammann and Montgomery who have given computer produced curves for the half-symmetric geometry and arbitrary double refraction.
Optical Absorption of Small Silver Spheres in Water
Authors: Berry Chester R. , Skillman David C.
Published: February 2004

Suspensions of colloidal silver spheres in water gave an absorption peak at 376 nm. The height and wavelength of the peak were altered by the adsorption of very small amounts of some materials. The changes in the absorption were accounted for very well by using concentric sphere models in which the silver spheres were enclosed in thin layers of dielectric or of absorber. The peak height of the pure material, spheres of 56-Å diameter, was substantially smaller than that predicted from bulk values of the optical constants. Much of this discrepancy was eliminated by taking account of the damping of the plasma oscillation by the presence of discrete electronic levels, as discussed by Kawabata and Kubo.
Electron Beam as a Method of Finding the Potential Distribution in a Cylindrically Symmetric Plasma
Authors: Stallings Charles H.
Published: February 2004

An electron beam has been used to determine the plasma potential and charge density as a function of radius for an inertially confined tenuous plasma. The column of plasma was formed by a collimator in front of a plasma gun. The observations showed a positive charge density inside the region of approximately uniform ion density but with the net charge density having a peak well inside the plasma column. A significant negative charge density was observed outside the column of ions. An inversion of the integral equation relating the deflection of the electron beam to the internal electric field has been performed. This inversion gave the plasma potential as a function of radius. The deflection of the electron beam at a constant impact parameter oscillated as a function of distance from the collimator for the plasma cylinder. This oscillation was evident only in certain regions and the wavelength was not a constant.
Current Diffusion in Cylindrical Exploding Wires and Fuses During Microsecond Electrical Pulses
Authors: Bennett F. D.
Published: February 2004

Existing solutions to the diffusion equation for current in a cylindrical conductor are used to provide estimates of the nonuniformity of current density during typical wire explosions. These estimates are given in the form of inequalities which are then used to specify the conditions under which current distribution and heating effect can be considered uniform.
Plasma Electron Density Distribution from Cavity Frequency Shift Data
Authors: Kent G. , Sinnott D. , Kent P.
Published: February 2004

The square of the plasma frequency of electrons in a plasma contained in a cylindrical cavity resonator can under some circumstances be adequately represented by the two-parameter function Π2=Π02(1+ρ)(1−r2/a2)ρ.To determine the nonuniformity parameter ρ and the average plasma frequency Π0 it is necessary to measure the frequency shifts of two modes. The TMLMO modes have suitable properties for this purpose, and in addition they are unaffected by axial magnetization of the plasma. Calculations, based on a variational approximation, are presented in the form of a mapping of the parameter space of ρ and Π02 onto the frequency space of the TM010 and TM110 resonant shifts. With a trivial modification the results apply equally to the TM010 and TE011 modes. The range of parameters is 0–6 for ρ and 0−76 for (aΠ0/cj01)2. The results show the feasibility of inferring gross characteristics of the distribution from two frequency measurements having an accuracy of 1 part in 103.
Polaronic Hopping Conduction in Vanadium Phosphate Glasses
Authors: Sayer M. , Mansingh A. , Reyes J. M. , Rosenblatt G.
Published: February 2004

Conductivity and dielectric properties of semiconducting glass of composition 80% V2O5:20% P2O5 have been measured as a function of frequency from dc to 3.6 GHz over a temperature range from 77°K to 420°K. A fit of the dc results to a model of polaronic hopping conduction leads to an activation energy due to disorder ΔW=0.09 eV at 77°K and an optical phonon energy of 0.053 eV compared to a calculated Miller-Abrahams energy of approximately 0.12 eV. The real and imaginary parts of the ac conductivity are shown to increase with frequency according to power law σ=Aωs, where s=0.85 to 0.95, and it is found that the dielectric behavior can be described by a Debye-type relaxation behavior only if a broad distribution of relaxation times exists. The results are shown to be consistent with a model of ac conduction normally applied to impurity-doped broad-band semiconductors, and differences between the temperature dependence of the dc and ac conductivity are attributed to a distribution of site energies in the glass. The estimated static dielectric constant is found to change from about 30 at room temperature to about 14 at 77°K and it is suggested that this temperature dependence affects calculations of both the disorder energy and the polaron binding energy. The coupling constant for the small polaron in the glass is about 14, indicating that it is a valid assumption to apply polaron theory to the material.
Temperature Dependence of Hole Velocity in p-GaAs
Authors: Dalal Vikram L. , Dreeben A. B. , Triano A.
Published: February 2004

The temperature dependence of the saturation drift velocity of holes in p-GaAs has been experimentally determined. The material used was grown epitaxially and had a low field mobility μ≈400 cm2/V sec and carrier concentration p0≈1×1016/cm3, both at T=300°K. The saturation velocity was 1.0×107 cm/sec at T=300°K, and decreased to 7×106 cm/sec at T=469°K. The temperature dependence of the low-field mobility was also measured and was found to be in good agreement with the recent theory of Wiley and DiDomenico.
Effect of Surface Electric Fields on Radiative Recombination in CdS
Authors: Hetrick Robert E. , Yeung K. F.
Published: February 2004

Photoluminescence (edge emission) in a variety of CdS single crystals has been studied under the influence of the surface field generated near the Au–CdS interface of an Au–CdS Schottky-barrier diode. Experimentally, above bandgap radiation is incident upon a semitransparent Au film evaporated on an air-cleaved CdS surface. Free electrons and holes are generated within the region of the high barrier field which extends on the order of 0.5 μ into the crystal bulk. Variations of diode bias as small as 2.5 V were found to be sufficient to alter the luminescence efficiency by nearly two orders of magnitude. A model is presented (emphasizing the rapid removal of photoinjected free carriers from the barrier) which qualitatively accounts for the major features of the observed effects.
Photoelectronic Properties of Graded Composition Crystals of II-VI Semiconductors
Authors: Lauer R. B. , Williams Ferd
Published: February 2004

Various photoelectronic properties of (Zn, Cd)S, (Zn, Cd)Te, and Zn(Se, Te) graded composition crystals are reported. From the position dependences of the optical absorption and of the electrical conductivity, the graded energy-band diagrams of the three systems are determined. Position-dependent photoluminescence is observed in the (Zn, Cd)S and Zn(Se, Te) graded heterojunctions, and shifts in the luminescent spectra with applied electric field are interpreted in terms of field-enchanced minority-carrier transport between regions of different bandgap. The photoconductivity is observed to depend on bias for the (Zn, Cd)Te graded heterojunctions and explained on the basis of the energy-band diagrams. The magnitude, sign, and spectral response of the photovoltage are measured and interpreted in terms of the band-edge gradients. The temperature dependence of the photovoltage is determined and related to the temperature dependence of the dark conductivity. From the data and their analysis, general features of II-VI compound graded heterojunctions are deduced.
Electrical Properties of High-Quality Stannic Oxide Crystals
Authors: Fonstad C. G. , Rediker R. H.
Published: February 2004

Single crystals of the wide bandgap semiconductor stannic oxide, SnO2, have been grown and studied electrically. A chemical vapor deposition technique using chlorine transport, no inert carrier gases, and low pressure has been used to grow stannic oxide crystals of higher purity and with almost an order-of-magnitude higher low-temperature Hall mobility, 8800 cm2/V sec at 80°K, than have previously been available. Measurements of Hall mobility, carrier concentration, and resistivity have been made between 20 and 625°K on crystals with room-temperature carrier concentrations between 8×1015 and 2×1018 cm−3. The effects of the crystal anisotropy on these measurements have been investigated and found to be small (all results reported are for the a direction). A donor level ∼35-meV deep due to antimony and another level ascribed to oxygen vacancies at ∼140 meV have been observed. Polar optical mode scattering with a dominant characteristic temperature of 1080°C is the main carrier scattering mechanism above 250°K. Below 250°K acoustic deformation potential scattering dominates. Ionized impurity scattering is eventually important in all samples as the temperature is lowered. A polaron effective mass of 0.39 me has been found consistently in the analyses of the data. A technique of fabricating good Schottky barriers on SnO2 has also been developed and used to measure the net donor concentration in samples. The agreement found between these measurements and Nd from Hall measurements indicates that shallow trapping is not a problem in these crystals.
Adiabatic Theory of Plane Steady Shock Profiles in Solids
Authors: Horie Yasuyuki
Published: February 2004

Duvall, Manvi, and Lowell have shown a close relationship between a continuum theory of shock structures in solids and that of one-dimensional lattices. In this paper, extending their results, we have shown that the thermodynamical behaviors of shock structures are equivalent to those of the dissipative autonomous system described by a generalized Liénard equation. The theory assumes adiabatic conditions and the relaxational transformation of instantaneous work into equilibrium internal energy.
Structural and Electrical Properties of Tantalum Films Sputtered in Oxygen-Argon Mixtures
Authors: Westwood W. D. , Waterhouse Neil
Published: February 2004

The dependence of the structural and electrical properties of sputtered tantalum films on the rate at which oxygen is leaked into the system has been investigated. The films were deposited on glass and polycrystalline alumina substrates and both structural and electrical measurements were made on the same samples. While some films deposited in argon contained both the body-centered-cubic and tetragonal β phases of tantalum, those deposited in the presence of oxygen consisted of the β phase. Increasing oxygen content of the films caused an expansion of the tetragonal lattice and changed the preferred grain orientation from (200) to (202). Increases in the oxygen content from 10 to 50 at.% decreased the film density by 2 g/cm3, increased the resistivity ρ from 200 to 5000 μΩ cm, and decreased Δρ/ΔT from 0 to −3.5 μΩ cm/°C. While the activation energy for conduction was small, it increased with the changing orientation of the β-Ta. This may indicate that ρ is due to the semiconducting nature of β-Ta and that the band structure of β-Ta is anisotropic.
Ion-Beam Deposition of Thin Films of Diamondlike Carbon
Authors: Aisenberg Sol , Chabot Ronald
Published: February 2004

An ion-beam deposition technique has been developed and was used to deposit thin films of insulating carbon on room-temperature substrates. It was established that the carbon films deposited using this technique are insulating and have the following characteristics similar to that of carbon in the diamond form: (1) transparency, (2) index of refraction greater than 2.0, (3) highly insulating, (4) able to scratch glass, (5) resistant to hydrofluoric acid for long periods of time, (6) at least partially crystalline and with a lattice constant similar to diamond as demonstrated by x-ray diffraction, (7) dielectric constant between about 8 and 14 (diamond is 16.5). A resistance to sodium ion diffusion has been experimentally demonstrated. Preliminary measurements at a dose of 1 Mrad indicated a radiation resistance from the point of view of stability of leakage resistance and of negligibly small flat band voltage shifts. Several coplanar thin-film transistors using the insulating carbon gate have been fabricated.
X-Ray Diffraction Method for Determining Strain Distributions in Thin Metallic Films with Application to Gold Films
Authors: McDowell C. Blake , Pilkington Theo C.
Published: February 2004

A method for determining the strain distribution through the thickness of thin metallic films is developed. The strain distributions of the films are related to the directions in which the films curl and, through a set of nonlinear simultaneous equations, to the shapes of their x-ray diffraction peaks. These equations are solved by assuming a piecewise linear approximation of the strain distributions. This resulting approximation is fit by a five-parameter nonlinear distribution, which is derived from elasticity theory for materials of ``grade 2.'' This x-ray method is applied to vacuum-deposited gold films deposited onto a Bi2O3 nucleation layer which has similarly been deposited onto a glass substrate. The deduced nonlinear strain distributions are nearly antisymmetric with the substrate side in tension and the free side in compression as measured normal to the substrate. Surface strains are as high as ±2.5% and decay approximately exponentially from the surfaces.
Series for Computing Current Flow in a Rectangular Block
Authors: Logan B. F. , Rice S. O. , Wick R. F.
Published: February 2004

A new method of measuring the electrical resistivity of anisotropic materials has been proposed by Montgomery. His method depends on the value of a quantity M associated with the current flow in a rectangular block of material. The current enters and leaves the block at two adjacent corners of a given face. M is proportional to the voltage between the two remaining corners of the face and depends only upon the dimensions of the block. Here methods for computing M are developed. Several series are given, values of M tabulated, and various asymptotic expressions are derived.
Tunnel Current through a Thin Al2O3 Film with Nonuniform Thickness
Authors: Kumagai Yasuji , Inukai Kiyo , Suzuki Yoshinori
Published: February 2004

In order to clarify the origin of the discrepancy between theoretical and experimental values of tunneling current through a thin Al2O3 layer, nonuniformity of the thickness of the oxide layer is taken into account in the determination of the theoretical current of an Al–Al2O3–Al thin-film tunnel emitter. The nonuniformity mentioned above is expressed by a modified Poisson's distribution function with respect to the oxide thickness s=nq, where q is a definite thickness unit and n is an integer. The above-cited distribution is discontinued by some finite integer κ, by which the distribution function below a thickness s=κq is discarded so that the calculated tunneling current approaches the experimental value. Numerical calculation of the current through the oxide layer with such nonuniformity of thickness is worked out with regard to two samples prepared anodically by using an electrolyte of 3% ammonium tartrate, and the predicted voltage-current characteristics are actually obtained. Thus, such a scheme can remove the discrepancy, at least in part, between the calculated and the measured tunneling currents.
Three-Dimensional Presentation of Electrostatic Fields by Trajectories
Authors: Ho Kit-Fun
Published: February 2004

The three-dimensional presentation of electrostatic fields by trajectories of charged slender particles in viscous medium is considered. Some Laplacian fields are presented with charged cotton fibers in air.
Scattering of Elastic Waves from a Spherical Cavity in a Solid Medium
Authors: Kraft David W. , Franzblau Michael C.
Published: February 2004

Cross sections are computed for the scattering of a plane transverse wave from a spherical cavity embedded in an infinite, isotropic, homogeneous, elastic solid. Analytical expressions are derived for the matrix elements indicated by Einspruch, Witterholt, and Truell, and the resulting matrix equations are solved numerically. The dependence of the scattering cross section upon K1a (K1 is the transverse propagation constant, a is the cavity radius) over the range 0.01–10 is computed for various host materials, and the results are compared with the case of incident longitudinal waves computed by Johnson and Truell. The sensitivity of the cross section to the elastic properties of the medium, and the behavior in the Rayleigh limit approximation are discussed. The relative contributions of the various components of both the longitudinal and transverse scattering cross sections are isolated, and their dependence upon K1a, k1a (k1 is the longitudinal propagation constant) and host material is elucidated. A peaking behavior analoguous to that occurring in the longitudinal case is observed in the longitudinal component of the scattered transverse wave.
Variables Affecting the Acoustic Loss and Velocity of Vitreous Silica from 4 to 300°K
Authors: Krause J. T.
Published: February 2004

The temperature dependence of acoustic loss and velocity together with the effects on these properties of variations in fictive temperature and OH concentration is shown for vitreous silica over the temperature range 4 to 300°K. The results indicate a reversal in dependency of loss upon fictive temperature and OH concentration between low- and high-temperature regions. Room-temperature loss measurements indicate that the lowest loss values are obtained for silica of fairly high OH content and low fictive temperature. Low-temperature velocity measurements show that variations in OH content affect the velocity by −0.8 cm/sec for each ppm increase in OH content. The rate of change apparently is independent of fictive temperature. Fictive temperature influence on velocity is zero at 80°K with the degree of influence increasing with increasing temperature. At temperatures above 140°K the temperature coefficient of velocity is proportional to the OH concentration and inversely proportional to the fictive temperature. Variations between 67 and 84 ppm/°K are attainable.
Acoustic Buildup in Photoconducting CdS Subjected to High rf Electric Fields
Authors: Zemon S.
Published: February 2004

Long-term acoustic shear-wave buildup has been observed in the bulk of photoconducting CdS subjected to rf fields greater than 104 V/cm. Acoustic power was seen to grow for times as long as 5 msec in some samples. Short rf pulses applied within 1 msec after the long pulse generated much larger acoustic flux than if applied thereafter. At a given frequency the effect was a maximum in a certain conductivity region, this conductivity being higher the higher the frequency. A proposed explanation involves field quenching of the photoconductivity in narrow high-resistivity bands.
Growth and Properties of Lanthanum Oxysulfide Crystals
Authors: Sobon L.E. , Wickersheim K.A. , Buchanan R.A. , Alves R.V.
Published: February 2004

To better determine the optical properties of the rare-earth oxysulfide phosphors and to lay the foundation for their application in single-crystal form as scintillators and lasers we have grown, for the first time, single crystals of these materials. A description of present growth techniques will be presented. Materials problems and our progress toward their solutions will be discussed. Single-crystal properties, such as optical transmission range, hardness, indices of refraction, thermal expansion coefficient, and thermal conductivity will also be reported. Work to date has emphasized lanthanum oxysulfide and, to a lesser extent, yttrium and gadolinium oxysulfide.
Electrical Size Effect of Aluminum Single Crystals
Authors: Kirkland L. R. , Chaplin R. L.
Published: February 2004

The dependence of the residual electrical resistivity on sample size has been measured for four single crystals of high-purity aluminum. Measurements were made for several thicknesses of each sample by using a chemical polishing solution to reduce the thickness. The theory of Dingle has been adapted in order to analyze the data. Results give good agreement with the Fuchs-Sondheimer theory of the size effect and give a value for the constant ρbl (bulk resistivity times mean free path) of 7.6×10−12 Ωcm2.
Magnetic Susceptibility and Optical Studies of Cr3+ in Al2O3 (Ruby): Magnetic Method for Determing Concentration
Authors: Blunt R. F. , Candela G. A. , Forman Richard A. , Kahn A. H. , Mangum B. W.
Published: February 2004

Magnetic-susceptibility and optical-absorption measurements were performed on ruby samples of varying chromium concentration. Susceptibilities were measured by the Faraday method, both with and without selective microwave saturation of the Cr3+ susceptibility at resonance. The susceptibility values were used to calculate the Cr3+ concentrations, and these together with the optical absorption were used to obtain the ``molar'' absorption coefficients. The absorption coefficient of 50 cm−1/wt% equivalent Cr2O3, for both the 0.40- and 0.56-μm band maxima (E⊥c), resulted. A Co60γ irradiation was performed and the susceptibility was unchanged within experimental error.
Piezoelectric Effect in Oriented Polyvinylchloride and Polyvinylflouride
Authors: Cohen Julius , Edelman Seymour
Published: February 2004

The direct piezoelectric effect has been observed in roll-elongated films of polyvinylchloride and polyvinylfluoride. The effect was produced by applying tensile stress to a clamped specimen at a fixed frequency of 20 Hz. The piezoelectric modulus g31 was determined to be 0.2 to 0.7 V m−1/N m−2 in polyvinylchloride; in polyvinylfluoride g31 ≃ 0.2 V m−1/N m−2 and g32 ≃ 1 V m−1/N m−2. The piezoelectric effect in these films is believed to be due to mechanical distortion of oriented dipoles, resulting from the tensile stress, and the orientation appears to differ in the two materials.
Backscattering Cross Sections of Circular Disks for Arbitrary Incidence
Authors: DeVore R. , Hodge D. B. , Kouyoumjian R. G.
Published: February 2004

The backscattering cross sections of perfectly conducting circular disks at arbitrary incidence for polarizations both parallel and perpendicular to the plane of incidence have been calculated from Meixner and Andrejewski's solution, for disk sizes in the range 0.94≤ka ≤9.45. These results are compared with measurements, and good agreement is obtained over dynamic ranges of up to 40 dB except for errors in several measured patterns at the lower signal levels in the case of perpendicular polarization. The present calculations enhance the value of the disk as a standard for scattering measurements and calculations. Cross sections for disks normal to the magnetic field of the incident wave are given and are found to be in good agreement with earlier measurements. The small-disk approximation of Bethe is quite accurate for ka<0.4. These results may be used to test the accuracy of the high-frequency approximation which involves a diffracted wave propagating along the edge of the disk.
Mechanism of dc Electrical Breakdown between Extended Electrodes in Vacuum
Authors: Davies D. Kenneth , Biondi Manfred A.
Published: February 2004

A description is given of vacuum breakdown between extended copper electrodes in dc electric fields in terms of the relevant atomic-collision processes. The theory is based on a model involving avalanche amplification of current in electrode vapor generated by the evaporation of an anode macroparticle during its transit to the cathode. Calculations are presented of the dynamics, heating, and evaporation of the macroparticle leading to the production of the vapor medium in the interelectrode gap. The inferred copper vapor density distribution accounts quantitatively for the absorption of resonance radiation measured just prior to current amplification in the gap. Calculations of electron avalanche multiplication in the vapor lead to predictions of breakdown conditions in agreement with our observations. The predicted size of the anode macroparticle which initiates breakdown is, on the average, of the order of 1 μ in diameter.
Effects of Drift and Diffusion of Excited States on Spatial Hole Burning and Laser Oscillation
Authors: Danielmeyer H. G.
Published: February 2004

The rate equation for the population inversion of homogeneously broadened 4-level lasers is solved for the cases of small and large mobility of excited states. Considered are drift and diffusion, i.e., collective and random motions along the laser axis. Both drift and diffusion smooth spatial holes which are burned into the population inversion by standing-wave fields. A drift results also in a drag effect, i.e., a phase lag between the population inversion and the standing-wave field. For homogeneously broadened lasers, sufficient smoothing of spatial holes will result in spontaneous full-power single-frequency operation. This is examined by calculating the unsaturated gains of secondary modes as a function of the excitation, drift, and diffusion parameters. Spatial hole burning is insignificant for gas lasers because of their large carrier diffusion. Furthermore, ionic drift in gas-ion lasers alone could effectively quench spatial hole burning. This is in contrast to dye lasers where drifts, i.e., longitudinal flow rates of the order of the sound velocity, would be required to obtain a single-frequency output. In solid-state lasers like ruby and Nd: YAG, energy diffusion between lattice sites is shown to significantly reduce spatial hole depths although the matrix elements for the exchange are quite small. An experiment is described which confirms the theory and allows the measurement of small diffusion constants of excited laser states. For the 4F3/2 level in Nd: YAG a value of 5×10−7 cm2/sec is obtained. This energy exchange among Nd3+ sites contributes 0.3 GHz to the homogeneous linewidth. Implications for axial mode selection and single-frequency oscillation of various lasers are discussed.
CO2 Regenerative Ring Power Amplifiers
Authors: Buczek C. J. , Freiberg R. J. , Skolnick M. L.
Published: February 2004

An unidirectional regenerative ring CO2 power amplifier is described. Both below threshold (unconditionally stable) and above threshold (conditionally stable) operation are discussed. Analytic expressions for a homogeneously broadened medium are presented for the power extracted from the active medium, the circulating power, and the total output power of the ring amplifier. Experimental results are presented in support of the theoretical analysis and demonstrate the role of gain saturation in the performance of CO2 regenerative ring amplifiers.
Surface Temperature and Disposition of Beam Energy for a Laser-Heated Target
Authors: Allen F. J.
Published: February 2004

An analysis has been carried out of an experiment in which a laser-produced plasma is probed with an electron beam. The target surface temperature as a function of time is obtained. The mass vaporization rate is obtained. The disposition of laser beam energy and of the target recoil momentum are given at three different times after laser pulse initiation. The results are discussed and compared with those of other experiments.
Effects of Wall Inertia on Cylindrical Magnetic Domains
Authors: Henry G. R.
Published: February 2004

The effects of wall inertia on cylindrical magnetic domains are considered, with attention to internal motion and to motion of a domain as a whole. Criteria are given for determining the importance of inertial effects in different materials and under various conditions. The range of validity of the concept of domain-wall mass is discussed.