bluuebunny/crossref_metadata_2025 huggingface dataset:
Tensile Deformation of Oriented Polyethylene
Authors: Hinton T. , Rider J. G.
Published: February 2004

Tensile test specimens have been cut from high-density polyethylene sheet which had been fully cold-drawn. The angle between the tensile axis and the draw direction was varied from 30° to 75°. The tensile deformation of such specimens was analyzed with the aid of a grid printing technique and was shown to be predominantly simple shear in the molecular chain direction. However, detailed analysis has shown that associated with the simple shear process there was a reorientation of the material, which is compared with the predictions of an aggregate theory for oriented polyethylene. A yield criterion and the absence of any work hardening for large deformations have been established.
Changes in Fold Structure with Annealing in Polyethylene
Authors: Witenhafer D. E. , Koenig J. L.
Published: February 2004

During the annealing of quenched linear polyethylene, the ratio of the absorbance of the 1304 cm−1 band to the absorbance of the 1350 cm−1 band decreases toward the value found in single crystals and has the wrong annealing temperature dependence. Since this process takes place too slowly to be a recrystallization from the melt, this change must reflect a transformation of loose-loop type folds to the more regular type as found in single crystals. Slowly cooled samples have the same ratios as single crystals and do not change upon annealing.
Infrared Studies of Chain Folding in Polyethylene Oxide
Authors: Angood A. C. , Koenig J. L.
Published: February 2004

A large number of additional peaks, some observed for the first time, appear in the ir spectra of polyethylene oxide when run at liquid-nitrogen temperatures. These peaks are sensitive to molecular weight, thermal history of the sample, and the temperature at which spectra are run. The peaks are attributed to vibrational modes due to sequences of rotational isomers, which are present in the fold. Although presently regular and irregular folds cannot be distinguished, the possibility of these peaks arising from cilia, or interlamellar links has been discounted.
A Model for Magnetic Instabilities in Hard Superconductors: The Adiabatic Critical State
Authors: Swartz P. S. , Bean C. P.
Published: February 2004

The isothermal critical-state model of hard superconductors is extended to include the effects of heating when the applied field is changed suddenly and magnetic flux enters adiabatically into the bulk. We consider the following specific situation. A semi-infinite slab of superconductor is cooled in a magnetic field lying in its surface plane. Next, the external field is raised isothermally by an amount Hs. This excess field decreases linearly to a depth δ= 10Hs/4πJc from the surface. Finally, the field is raised by an infinitesimal amount ΔH in a time short compared to the thermal diffusion time and long compared to the electromagnetic diffusion time. Each element of volume exposed to the changing field receives a thermal impulse proportional to the local-flux-change times Jc. This thermal impulse, in turn, lowers the critical current and allows more flux to penetrate. We find that if Hs exceeds some critical value Hfj, then the isothermal critical state is not the only allowed state of the superconductor. This instability field is given in terms of the critical current density Jc, derivative of the critical current density with temperature, ∂Jc/∂T, and the volume specific heat C by the formula Hfj= [−π3CJc/(∂Jc/∂T)]1/2. The application of the incremental field ΔH can initiate an avalanching process, or a flux jump, that terminates in an adiabatic critical state. Immediately following the flux jump the internal field, the induced supercurrent, and the temperature rise at each position are associated in a self-consistent way with the avalanche of flux that has entered the superconductor. In this framework a flux jump is viewed as a switching from the isothermal critical state to an adiabatic critical state. The magnitude of the jump is related to Js and is calculated.
Local-Mode Absorption and Defects in Compensated Silicon-Doped Gallium Arsenide
Authors: Spitzer W. G. , Allred W.
Published: February 2004

Silicon is known to be an amphoteric impurity in GaAs. A large number of ir absorption bands have been previously reported for Si-doped GaAs which has been compensated by Li or Cu diffusion. These bands, which are at frequencies above the pure GaAs single-phonon spectrum, have been attributed to localized vibration modes of defects. The present experimental study extends previous work to show that all the observed bands (frequencies given in parentheses) are explicable in terms of the presence of the following defects: SiGa (384 cm−1), SiAs (399 cm−1) SiGa-LiGa (374, 379, 405, 470, 480, 487 cm−1), SiGa-CuGa (374, 376, 399 cm−1), and SiGa-SiAs. (367, 393, 464 cm−1). These assignments appears to be consistent with results obtained by varying the Si concentration and by different thermal treatments.
Instabilities and Anomalous Diffusion in the Reflex Discharge
Authors: Thomassen K. I.
Published: February 2004

The instabilities of a cold-cathode reflex discharge are studied and their relationship to the observed increase in radial transport above a critical magnetic field is discussed. High-frequency beam-plasma instabilities occurring in bursts, owing to a relaxation phenomenon, and low-frequency resistive drift waves are both found, with the latter appearing to have an important role in transport.
Properties of GaP Green-Light-Emitting Diodes Grown by Liquid-Phase Epitaxy
Authors: Shih K. K. , Pettit G. D.
Published: February 2004

Efficient and reproducible green-light-emitting diodes have been made by a vertical liquid-phase epitaxial method. External quantum efficiencies of uncoated diodes as high as 3×10−4 at 300°K were obtained. The I-V characteristics of these diodes show an exponential behavior of the form I = I0 exp eV/βKT; values of β were generally about 2 at 300° and 77°K. The emission intensity varies with I2 at low currents, and changes to an approximately linear dependence at high currents. Emission spectra have been studied as a function of current and temperature from 27° to 670°K. Seven emission lines in the green region of the spectrum have been observed, and the origins of these radiative recombinations have been studied. At low temperatures, four lines are identified as pair emission. One line at intermediate temperatures is believed to be due to free-hole-to-donor emission, and two lines at high temperatures may be attributed to free-exciton recombination.
A Preliminary Investigation of Brillouin Scattering in a Liquid Crystal
Authors: Nordland W. A.
Published: February 2004

Brillouin spectra have been observed in the liquid-crystal cholesteryl-2-(2-ethoxyethoxy) ethyl carbonate. The frequency shift and the relative intensities of the shifted and unshifted components have been measured as a function of temperature, which was varied through the cholesteric to isotropic transition.
The Diffusion of Copper in Iron
Authors: Rothman S. J. , Peterson N. L. , Walter C. M. , Nowicki L. J.
Published: February 2004

Measurements of the diffusion of 64Cu in pure and impure α and γ iron show a large discontinuity in the Arrhenius plot of the lattice diffusion coefficient at the α-γ transformation, contrary to the data of Anand and Agarwala [J. Appl. Phys. 37, 4248 (1965)]. Grain-boundary diffusion predominates at T≤815°C in the α phase and at T≤1250°C in the γ phase. Trapping of the radioactive copper by inclusions or impurities in solution also appears to have a profound effect on the diffusion process.
Magnetic and Magneto-optic Properties of EuO Films Doped with Trivalent Rare-Earth Oxide
Authors: Ahn K. Y. , McGuire T. R.
Published: February 2004

The ferromagnetic Curie temperature of EuO films has been increased by selective doping with trivalent rare-earth oxides. The electrical resistivity, which depends upon the temperature and has a broad peak at ≈100°K, decreases markedly to ≈10−1 Ω·cm with doping. A typical ferromagnetic Curie temperature, determined from magneto-optic measurements in zero applied field, is ∼135°K. Maximum longitudinal Faraday rotation occurs at 0.65 μ with a specific rotation of +1×105 deg/cm for an incidence angle of 20 deg. At 0.84 μ the Faraday rotation reverses sign and reaches a negative maximum at 0.93 μ. The longitudinal Kerr rotation also has two maxima at 0.58 μ and 0.83 μ with double rotations of ≈4°. The transverse Kerr effect depends on the wavelength in the same manner and has maximum values of +0.4 and −0.3, respectively. There is a strong optical absorption band centered at 0.6 μ (at 300°K) with α≈1.2×105 cm−1 which shifts toward longer wavelengths at lower temperatures accompanied by a small decrease in α. An additional absorption band centered around 0.4 μ with amplitude less than 10% of the main absorption peak appears as a result of doping. Quasistatic switching measurements show that the coercive force depends strongly upon the stress in films arising from the difference in thermal expansion coefficients of EuO and substrates. Hc is typically 120 and 60 Oe on fused quartz and 0080 glass, respectively, with remanence of ∼0.7. Results of the transport, magnetic, magneto-optical, and optical properties are discussed in terms of indirect exchange via conduction electrons.
Dominant Surface Electronic Properties of SiO2-Passivated Ge Surfaces as a Function of Various Annealing Treatments
Authors: Sedgwick T. O.
Published: February 2004

The metal-oxide-semiconductor (MOS), capacitance vs applied voltage (C-V) measurement technique was used to investigate SiO2-passivated Ge surfaces as a function of high-temperature annealing treatments in H2, O2, N2, and H2O. Capacitance measurements were made at high frequencies (100 MHz) and/or reduced temperatures (145°, 77°K) to eliminate the capacitive contribution of fast surface states to the ac signal. Since the surface states did equilibrate with the superimposed applied dc voltage, is was possible to determine surface-state type, energy, and densityfrom voltage shifts in the C-V traces. Hydrogen annealing at 600°C or above introduces a high density (>1013/cm2) of fast acceptor states. These states are located at the center of the Ge energy gap. In addition, hydrogen annealing at 700°–800°C introduces acceptors close to the valence band or fixed negative charge. Most of these hydrogen-induced states are removed by annealing in oxygen or water vapor at 230°–440°C. At the same time the oxygen or water vapor exposure introduces an effective positive charge density of 1–5×1012/cm2. This positive charge is due either to donors lying close to the conduction band edge or to fixed positive charge. The above effects are reversible.
Dielectric Breakdown and Recovery of X-Cut Quartz under Shock-Wave Compression
Authors: Graham R. A. , Halpin W. J.
Published: February 2004

While a shock wave is traversing a disk of X-cut quartz, a piezoelectric current flows in an external circuit connected across the faces of the disk. In this paper measurements of this current are used to study dielectric breakdown and subsequent recovery which occurs in quartz. Quartz specimen disks were impacted at various stress levels in such a way as to produce shock waves that propagated along the X axis either in the direction of or opposite to that of the pressure-induced polarization. In the latter case, short-circuit current measurements show that breakdown occurs at a threshold stress greater than 10 and less than 13 kbar. Since the impact experiment produced one-dimensional electrical and mechanical conditions in the specimen disk, it was possible to formulate a mathematical model that permitted solutions for internal electrical fields and resistivity in terms of the measured current. Computations with this model show that the field in the stressed portion of the disk at breakdown is about 7.0×105 V/cm, which is an order of magnitude lower than the value observed at atmospheric pressure. Computations with the model also show that recovery from breakdown to essentially infinite values of resistivity occurs during the transit time of the shock wave when the field in the stressed region of the disk is ``quenched'' to a value of about 1.9×105 V/cm. This critical field appears to be the same for all shock stress levels investigated from 13 to 35 kbar. The dependence of the initiation of breakdown on the direction of wave propagation relative to the polarization direction indicates that the shock-wave front furnishes a source of free electrons.
Room-Temperature Faraday Rotation in n-Type InSb Films at 23.4 GHz
Authors: White D. J.
Published: February 2004

Measurements were made of Faraday rotation on ∼1 μ thick evaporated and recrystallized polycrystalline InSb films. The experiments were carried out at room temperature using TE11 circular waveguide with dc magnetic fields up to 7 kOe. Rotations on the order of 50 deg were observed. The experimental results are in reasonable agreement with a theoretical model based on free-carrier Faraday rotation, including multiple reflections, using the mobilities and carrier concentrations found by separate dc measurements.
Optical Probing of Inhomogeneities in n-GaAs with Applications to the Acoustoelectric Instabilities
Authors: Spears David L. , Bray Ralph
Published: February 2004

A study is presented of the intimate relationship between current instabilities of acoustoelectric origin in n-GaAs at 77°K and the inhomogeneity in the Ohmic resistivity of the samples. In order to correlate various aspects of the acoustoelectric instabilities with the sample inhomogeneities, two optical probing techniques were developed for determining the Ohmic-resistivity profile with good spatial resolution, ⪝0.1 mm. One involves the measurement of the local photoconductance in the sample, which is related to the local dark resistivity; the other method involves the measurement of the change in optical transmission produced by the local thermal shift in the intrinsic absorption edge when the sample is heated by a high current pulse. The change in optical transmission is related to the local resistivity. The acoustic flux distribution in the sample is determined by yet another optical probe, utilizing the modulation in transmission produced by the high acoustic-energy density in the domain. Several aspects of the acoustoelectric effects are themselves useful for gauging the homogeneity of the samples. In particular, the propagating acoustoelectric domain serves as a convenient probe of the carrier concentration. These techniques are applied to the analysis of the form of the current instabilities, the distribution of the acoustic flux in the sample, and the domain-formation process. The presence of a somewhat higher resistance, hence higher acoustoelectricgain region, at the upstream end near the cathode is shown to contribute to the formation of propagating acoustoelectric domains.
Growth of Two- and Three-Dimensional Space Charge from Negative Differential Resistivity
Authors: Copeland John A.
Published: February 2004

Some simple cases are considered of two- and three-dimensional space-charge growth in a semiconductor such as GaAs which can exhibit a negative differential resistance to the one component of small perturbation electric fields parallel to a large bias electric field. These indicate that finite space-charge distributions will generally grow much slower than previous one-dimensional calculations have suggested for infinite layer distributions. This is because the differential resistance is always positive to components of the perturbation field perpendicular to the bias field.
Hot-Electron Transport in Al–Al2O3 Triodes Produced by Plasma Oxidation
Authors: Huber E. E. , Johnston F. L. , Kirk C. T.
Published: February 2004

The measurement of tunnel triodes by a small ac signal r parameter technique is shown to give a new way of directly measuring the oxide barrier height and barrier asymmetry. This type of measurement permits distinguishing between true hot-electron collection and leakage currents. A saturation of the hot electron transport coefficient has been found vs the emitter-base bias. The most direct explanation for this saturation is that those hot electrons which are collected are mainly ballistic, i.e., that they have come from the emitter with little or no momentum change due to collisions. The Al base attenuation length has been measured to be 150 Å at 77°K for electrons 2.0 eV above the Fermi level. Collector-voltage dependence of the triode has been explained on the basis of electron-phonon losses in the collector oxide. The major part of the large hot electron attenuation factor in these triodes cannot be explained by either metal base losses or electron-phonon losses in the oxides, which together give rise to an attenuation factor of ≈ (¼) in a typical triode. An interfacial loss mechanism appears to be the most likely explanation for the large attenuation factor of ≈ (1/100) remaining after taking the above volume losses into account.
Direct Basal-Plane Shear in Single-Crystal Graphite
Authors: Soule D. E. , Nezbeda C. W.
Published: February 2004

The basal-plane shear stress-strain behavior of small, highly anisotropic-annealed natural graphite single crystals was studied at room temperature. A static uniaxial-shear stress was applied directly along the basal plane with a minimum of normal force, incorporating a technique to detect translations down to ∼40 Å. Comparative measurements were also made on compression-annealed pyrolytic graphite. The staticshear modulus G was also corroborated by a modified ultrasonic transit-time method. Basal-plane dislocation systems strongly reduce the measured G, where values of (0.013–0.14)×1011 dyn/cm2 were observed. This reduction is found to be caused primarily by a dislocation concentration of ∼2×106 cm−2. The average critical-resolved shear stress σc was 0.29×106 dyn/cm2, and an analysis of the relation between σc and the critical breakaway stress for dislocation pinning shows that dislocation line segments l≃120–310 μ are operative. Plastic curvature of the stress-strain curves shows the effect of very sensitive creep and glissile slip. Laminar flow in this principal slip direction produces a plastic strain ε* = Aσ4.2 analogous to easy glide in hcp metals along the close-packed direction. Classical Andrade t1/3 creep was observed at higher stresses and approached a logarithmic creep behavior with decreasing stress. A saturation effect seen in the shear-strength σs with shear-fracture cycling leads to a resultant σs of (2.5–7.5)×106 dyn/cm2. Possible contributions to the elastic shear strain, including dislocations, grain boundaries, hard inclusions, delamination voids, and the Fermi-level shift, are considered as they affect the measured shear modulus. Dislocation pinning by boron ions, in the dilute concentration range from 7 ppm B up to 1500 ppm B, was found to produce a large increase in G with eventual saturation. After accounting for all known shear-strain components, this saturation value leads to an intrinsic single-crystal graphite C44 value of (0.45±0.06)×1011 dyn/cm2.
Plastic Deformation of α-Arsenic Single Crystals
Authors: Shetty M. N. , Taylor J. B.
Published: February 2004

Plastic deformation and fracture of α-arsenic (rhombohedral) single crystals tested in tension with fixed and random orientations is analyzed using current dislocation concepts. With〈11̄0〉 as the most probable slip vector, elastic moduli are determined for the observed slip systems, and surface free energies for the fracture surfaces are estimated from the elastic moduli.
A Technique for Trap Determinations in Low-Resistivity Semiconductors
Authors: Weisberg L. R. , Schade H.
Published: February 2004

A simple method is described to allow the use of thermally stimulated conductivity (TSC) measurements for low-resistivity semiconductors. A p-n junction or Schottky barrier is formed to provide the required high-resistivity region. Trap populations can be inverted either by light or by changes in diode bias, but different traps may be seen in each case. The accuracy of trap concentration determinations is improved over ordinary TSC measurements since the gain is close to unity, and the active volume can be accurately found from capacitance measurements. The use of the method is demonstrated by the measurement of trap energies and densities in a sample of GaAs0.5P0.5 alloy with an electron concentration of about 1015 cm−3. Two main traps were seen, one at 0.20 eV from the conduction band and the other at 0.41 eV from the valence band, with concentrations of, respectively, 1×1014 cm−3 and 5×1014 cm−3. The method has also been successfully applied to silicon.
Solid-Solution Hardening due to the Size Effect
Authors: Riddhagni B. R. , Asimow R. M.
Published: February 2004

Based on a model developed in an earlier paper, the stress required to move a dislocation through a solid-solution fcc crystal at 0°K is determined. It is assumed in this paper that the solute interacts with a dislocation due to the elastic distortion caused by a size difference between solute and solvent. The results of this analysis are combined with the previous one to consider combined modulus and size interactions. The critical resolved shear stress predicted by this analysis is compared to a number of systems for which experimental data is available, and the agreement is found to be quite satisfactory. The analysis predicts that for dilute solutions the critical resolved shear stress should be proportional to the solute concentration to the ⅔ power, that in almost all cases the stress is determined by the size interaction, and that widely separated partial dislocations require a stress several times greater than perfect dislocations for motion.
Flux Loss and Energy Balance in Magnetic Flux-Compression Experiments
Authors: Herlach Fritz
Published: February 2004

A set of explosively driven flux-compression experiments with stainless steel liners and final fields in the range 2–6 MG is discussed. From experimentally determined field curves, the motion of the liner is derived by calculating the flux loss. Up to 80% of the initial flux is lost in these experiments. The variation of resistivity with temperature is taken into account, and the Joule heating energy is also determined. As can be verified by the energy balance, a consistent picture of the flux-compression process is obtained, including the phenomenon of field turnaround. The speed of sound in the liner material is comparable to the implosion speed; therefore, energy can be transferred to the magnetic field only from a thin inner layer of the liner. The energy accumulated in the magnetic field and in Joule heat increases very steeply at the end of the compression; thus, the inner layer of the liner is suddenly decelerated. There is still a large amount of kinetic energy in the outer layers of the liner at this instant. An empirical turnaround criterion is derived on the basis of these considerations. This shows that the peak field is practically independent of the initial field over a large range of initial fields. The final field depends essentially on the kinetic energy density of the liner. The influence of resistivity on flux compression is also found to be small. Nevertheless, an upper limit for the resistivity of stainless steel in a megagauss field environment can be derived from the experiments. A value of 120 μΩ·cm is found to be in best agreement with the experimental results. The methods developed in this paper can also be used to predict the performance of flux-compression devices. This is demonstrated with a few examples.
Explosively Driven High-Energy Generators
Authors: Crawford J. C. , Damerow R. A.
Published: February 2004

Design information, circuit analysis, and comparison of calculated and experimental results are presented for three different explosively driven current generators. These generators are all of the helical coil construction. The largest of these generators (9-in. diam) used 17 lb of high explosive to produce an output energy of 1.5 MJ. An exploding wire switching technique has been developed for use with these generators to produce output currents suitable for high-energy pulsed plasma experiments. The combination of explosive generator and switch has produced peak currents of 5 MA in 3 μsec and peak dI/dt values in excess of 4.0×1012 A/sec.
Selective Excitation Spectroscopy and Some Possible Applications
Authors: Measures R. M.
Published: February 2004

If an atomic transition is optically pumped by a beam of laser radiation, having the appropriate frequency, the population in the upper state of the transition can be considerably enhanced along the path of the beam. This will give rise to an intensification of the spontaneous emission originating from this upper state in the region localized by the beam. Such intensified emission contains information about the conditions within the pumped region and can, under certain conditions, be identified from the background radiation. It is shown that this process called ``selective excitation spectroscopy'' can be used in a variety of ways, one of the most important being the determination of the local values of electron temperature and density in low-temperature plasmas. This technique is illustrated for both potassium- and barium-seeded plasmas. Furthermore, because this technique involves a pulsed laser, temporal as well as spatial resolution is possible.
Structure of the 〈100〉 Edge Dislocation in Iron
Authors: Gehlen P. C. , Rosenfield A. R. , Hahn G. T.
Published: February 2004

The positions of atoms around the core of a 〈100〉 edge dislocation in iron have been calculated using atomic potentials developed by Johnson, boundary conditions based on anisotropic or isotropic elasticity and the GRAPE computer program. The dislocation is quite narrow and the atoms below the extra half-plane relax into a microcrack. It is shown that particular care must be taken in introducing the dislocation and choosing the potential. The configuration of this particular dislocation is only slightly sensitive to the choice of boundary conditions and the size of the model.
Further Studies of Polytypism in Lead Iodide
Authors: Hanoka J. I. , Vand Vladimir
Published: February 2004

An x-ray study of over 600 crystals of PbI2 has revealed some important facts for the formulation of a satisfactory epitaxial theory of polytypism. Some new polytypes are described, the largest being 48R with c=167.5 Å. The distribution of rhombohedral polytypes found can be described by a Poisson distribution, ps=e−mm8/s!, with m=12. Evidence for a mechanism whereby an nH polytype together with a Shockley partial dislocation a/3[01̄10] can result in a 3nR polytype is presented. The general applicability of this nH-3nR mechanism is discussed. Miscellaneous results obtained from an investigation of syntactic coalescence are reported and shown to be in harmony with the epitaxial theory.
Steady Electric-Field-Induced Anisotropy in the ac Conductivity of a Slightly Ionized Plasma
Authors: Kaw P. K.
Published: February 2004

In this paper, the author has analytically investigated the ansiotropy in the ac conductivity of a slightly ionized plasma, induced by the presence of a strong steady electric field. It is shown that for very strong steady fields, the anisotropy is independent of the field strength, its magnitude being solely governed by the dependence of electron-collision frequency on electron velocity; for moderate fields, on the other hand, the anisotropy is a function of the field strength.
Photoluminescence Study of Thermal Conversion in GaAs Grown from Silica Boats
Authors: Hwang C. J.
Published: February 2004

GaAs crystals grown from the melt in silica boats without intentionally doping exhibit n-type conductivity. Photoluminescence measurements at 20°K are used here to study thermal conversion in these crystals. Heat treatments with temperature TH ranging from 600° to 1100°C followed by quenching were performed on three crystals with different carrier concentrations. For TH≥900°C, it is concluded that the thermal conversion in quenched crystals is caused both by copper acceptors and by the shallow acceptors which are responsible for the 1.49 eV emission band in the original crystals. The latter acceptors are suggested to be silicon. It is proposed that conversion associated with silicon results from transfer of silicon atoms from donor sites to acceptor sites through a trapping process during rapid quenching. The maximum compensation due to these shallow acceptors is estimated, depending on the crystal used, to be on the order of 5×1016 cm−3 at 1100°C and is smaller at lower temperatures. For TH≤870°C, it appears that copper is solely responsible for the conversion.
Metal Films Sputtered at Low Voltages
Authors: Lee William W.
Published: February 2004

Tantalum films sputtered at low voltages possess abnormally high resistivity. When the investigation was extended to other metals, many films exhibited electric properties similar to those of tantalum. The high resistivity was found not to be caused by residual oxygen or water vapor in the sputtering system, but by the microcrystalline structure of the films. An explanation of the particular properties exhibited by films of these materials is proposed.
Use of Molecular Orbital Theory to Interpret X-Ray K-Absorption Spectral Data
Authors: Glen G. L. , Dodd Charles G.
Published: February 2004

This paper demonstrates how molecular orbital theory can be useful in obtaining chemical information from x-ray absorption spectra. Basic molecular orbital theory concepts such as symmetry and overlap of wavefunctions are used to explain the K-absorption spectra of first-row transition metal complexes. In x-ray K-absorption spectroscopy, 1s electrons are excited to high-energy unoccupied orbitals; thus, the main absorption maxima (for first row transition metals) are due to excitations to the triply degenerate 4p antibonding orbitals. The shifts in these peaks are due to changes in the orbital energy levels, which, of course, are a function of chemical bonding. A splitting or a broadening of a peak is an indication of a splitting of the degenerate energy levels, which in turn is an indication of unsymmetrical metal to ligand bonding. It is also shown how x-ray absorption spectra can be useful in determining the lattice sites of atoms of nearly equal x-ray scattering power.
Chemical Bonding Studies of Silicates and Oxides by X-Ray K-Emission Spectroscopy
Authors: Dodd Charles G. , Glen G. L.
Published: February 2004

This paper describes experimental techniques developed for the adaptation of available commercial electron microprobes as convenient and versatile x-ray spectrometers of moderate resolution. Complete K-emission spectra were measured for Mg, Al, and Si, as elements and as selected sixfold- and fourfold-coordinated crystalline oxides. Numerous empirical correlations were indicated by the results. The structures of the Kβ bands of the oxide spectra were interpreted on the basis of their known crystal structures together with elementary molecular orbital theory. In this manner, observed peaks in the Kβ band of each oxide were assigned to specific transitions between valence band orbitals and the inner 1s vacancy. New insight was thereby obtained concerning the contributions of covalent bonding in these oxides.
Second-Harmonic Generation in an Elastic Surface Wave in α-Quartz
Authors: Lo/pen P. O.
Published: February 2004

Second-harmonic generation was observed in an elastic surface wave propagating in the y direction on the x surface of α-quartz. The waves were generated and detected by means of interdigital electrode transducers. The fundamental frequency was 9 MHz. The amplitude of the second-harmonic signal increased linearly with distance along the crystal surface. A nearly perfect square-law dependence of second-harmonic power on fundamental power was found. The ratio of second-harmonic to fundamental power was −43.8 dB at a distance of 2.2 cm and a fundamental input power of 1 W. The results are in quantitative agreement with theory.
Optical-Microwave Double-Resonance Studies of Ruby
Authors: Szabo A.
Published: February 2004

Studies of the resonant interaction of radiation from a liquid-nitrogen-cooled ruby laser with a ruby crystal in the temperature range 4.2°–100°K are described. The interaction was measured by observation of the change which occurs in the Cr3+ ground state EPR absorption on laser irradiation. At low radiation intensities, the temperature dependence of this change is shown to be determined by the well-known thermal tuning behavior of the R lines. Precise measurement of the relative laser and ruby-sample absorption frequencies by this technique of double-resonance spectroscopy is described. Under optical saturation conditions, additional temperature-dependent pumping effects occur at low temperatures. In particular, as the ruby temperature is increased from 4.2° to 40°K, the laser-induced change in EPR absorption is observed to undergo a large increase. This increase cannot be explained by a relative thermal shift of the laser and absorption frequencies which is known to be very small in this temperature range. The phenomena are attributed in part to the temperature-dependent homogeneous linewidth which determines the widths of the holes burnt into the inhomogeneous strain-broadened R lines. Calculations indicate that the related temperature-dependent thermalization process which redistributes excited Cr3+ among the 2E levels quantitatively accounts for most of the increase.
Impurity-Dislocation Interaction and Repeated Yielding in a Commercial Al Alloy
Authors: Mukherjee K. , D'Antonio C. , Maciag R. , Fischer G.
Published: February 2004

Impurity-dislocation interaction via a vacancy mechanism and the associated repeated yielding phenomenon in an aluminum alloy containing 2.8 at.% Mg, 2.4 at.% Zn, 0.65 at.% Cu, and 0.16 at.%Cr, have been studied. The repeated yielding is observed only in the temperature range of −40° to +90°C and strain rates of 10−5–10−4 sec−1. The onset of repeated yielding is thermally activated within this temperature range. From +20° to −40°C, the process is a normal Portevin-LeChatelier effect observed by various investigators in dilute and concentrated alloys. The activation energy associated with this normal stage is found to be 0.66 eV and the exponent m of the semiempirical equation: Cν=Kεm, is 0.88, where Cν is the vacancy concentration, K is a constant, and ε is the plastic strain. From 40° to 90°C the corresponding values of m and the activation energy are 0.95 and 0.80 eV, respectively. An alternative method of analysis of the experimental data is proposed. Based on a simple random-walk theory, this method can produce the activation energy without the ambiguity of the exponent m. Furthermore, this treatment is capable of yielding some information regarding the density of mobile dislocations. Contrary to certain recent results, the activation energy Em for vacancy migration in this alloy compares favorably with the vacancy migration energy in pure aluminum.
A New Technique for Measurements of Radial Distributions of Excited Species in Plasmas and Its Application to Capillary Discharges in Argon
Authors: Webb C. E.
Published: February 2004

This paper describes a novel technique for obtaining the radial profiles of individual emission lines from a plasma directly in the form of a recorded trace of intensity vs radial position. The method employs an ``end-on'' collimation technique which eliminates the complicated data reduction treatment required by conventional ``side-light'' methods. Spatial resolution and instrumental distortion effects are discussed. The method is applied in an experimental study of the capillary discharge in argon, and the relevance of the results to the excitation mechanisms of the cw AII laser is indicated. In particular, it is found that populations of excited AI states are substantially independent of the local electron density over wide ranges of plasma parameters, an effect which is attributed to the predominance of electron-impact-induced transfers over radiative transfers for the AI states. The populations of excited states of AII are found to have profiles which are in agreement with those predicted by a plasma model in which (a) the ion loss is controlled by ambipolar diffusion at higher pressures with a steady approach towards an essentially collisionless ``free-fall'' motion occurring as the pressure is decreased, and (b) excitation to the AII excited levels proceeds stepwise via the AII ground state. The method is of general applicability to problems involving spatial variations in plasmas, and has been coupled with high-resolution interferometric techniques to provide direct measurements of spatial dependence of spectral line-broadening parameters.
Some Diffusion and Solubility Measurements of Cu in CdTe
Authors: Woodbury H. H. , Aven M.
Published: February 2004

The diffusivity and solubility of Cu in CdTe has been measured between 97° and 300°C using radiotracer techniques. The system studied involved chemically formed Cu2Te films on undoped zone-purified CdTe single crystals. The solubility was found to vary from approximately 3×1016 to 2×1018 cm−3 in the temperature range studied. The diffusivity corresponding to these solubilities is given by D(cm2·sec−1) =3.7× 10−4 exp (−0.67 eV/kT). A much faster diffusing ``tail'' involving about 1015 cm−3 Cu is also observed.
Optical Properties of Vacuum-Evaporated Selenium and Tellurium
Authors: Hayes J. D. , Arakawa E. T. , Williams M. W.
Published: February 2004

The optical properties of evaporated films of Se and Te at room temperature have been determined in the energy range from 5–25 eV. In addition the real part of the refractive index has been determined for Te up to 38 eV. The films used were of high quality, prepared and measured in vacuum (<2×10−5 Torr), and reflectances were significantly higher than reported in previous literature. The optical properties of Se and Te are similar; both show structure in the imaginary part εZ of the dielectric constant ε between 7 and 9 eV identified with interband transitions. The calculated energy-loss function - Im(ε+1)−1 shows a maximum at 14.5 eV in Se and at 11.3 eV in Te. The calculated energy-loss function - Im(ε)−1 shows peaks at 5.25 and between 18.5 and 19.0 eV for Se and at 5.6 and 17.2 eV for Te. These optical data agree with published characteristic electron-energy-loss measurements and allow identification of the modes of energy loss involved.
Oxygen Surface-Density Measurements Based on Characteristic X-Ray Production by 100-keV Protons
Authors: Hart R. R. , Olson N. Thomas , Smith Harold P. , Khan J. M.
Published: February 2004

The oxygen-K x-ray yield from known thicknesses of aluminum oxide (1–70 μg O/cm2), bombarded by 100-keV protons, indicates that oxygen surface density may be measured over the range from 50 to 0.004 μg/cm2. At the lower limit, background is 50% of the signal. In thin oxide layers where proton energy loss and x-ray absorption are negligible, the x-ray yield I (x rays/proton) is related to the oxygen surface density t (μg/cm2) by I=(2.9×10−6)t.
The Elastic Constants of Polycrystalline HoZn2
Authors: Michel D. J. , Ryba Earle , Chang Z. P.
Published: February 2004

The elastic constants of polycrystalline HoZn2 were determined in the 90° to 298°K region by ultrasonic techniques. The constants C11=ρVL2 and C44=ρVS2 C44=ρVS2 vary with temperature in a linear manner and were extrapolated to 0°K by a least-squares fit to the data to give 1.118×1012 and 0.322×1012 dyn/cm2, respectively. The Debye temperature for HoZn2 was calculated to be 243°K at 0°K; the bulk modulus and Young's modulus at 298°K are 0.643×1012 and 0.765×1012 dyn/cm2, respectively.
Energetics of Grain-Boundary Triple Junctions and Corner-Twinned Junctions: Transmission Electron Microscope Studies
Authors: Murr L. E.
Published: February 2004

Direct observations of grain-boundary triple junctions and triple junctions containing a grain-corner twin have been made in 304 stainless steel foils by transmission and diffraction electron microscopy. The distributions of true dihedral angles at pure triple junctions and the true dihedral angles in twinned grain corners have been computed by creating crystallographically identifiable slip or stacking-fault traces in grains composing the junction through high-intensity electron-beam bombardment of the junction or areas in the immediate vicinity, or through the measurement of the image projection of coherent twin boundaries with the subsequent determination of the foil thickness. The mean dihedral angle for pure triple junctions was observed to be 120°, while that for the corner-twinned grains was observed to be 105°. The characterization of pure triple junctions and corner-twinned junctions on the basis of a cyclic crystallographic convention (hkl) for grain-surface orientations yielded a mean dihedral angle of 123.3° for the pure junctions and 113.7° for the mean dihedral angle in the twinned grain. These results confirm the validity of the Fullman-Fisher theory for corner-twin formation in fcc metals. It is also demonstrated that the mean angle of inclination of grain boundaries with respect to the thin foil surfaces is 61.6°, compared with the probable mean of 63.2° for a random slice through solid polyhedra, a property suggesting the bulk representation of electrothinned films.
Optical Gain and Spatial Resolution in a Broad-Area Phototransistor
Authors: Schuldt S. B. , Kruse P. W.
Published: February 2004

A broad-area phototransistor is considered as an image intensifier for a beam of nonuniform radiation incident in an axial direction at the emitter surface. Gain is related to a reduction in the emitter potential barrier by the presence of excess carriers generated optically in and around the base layer. Blurring or image degradation is the result of the lateral spreading of these carriers during their finite lifetime. The analysis demonstrates the essential difficulty in achieving high gain while preserving good image resolution, although both gain and resolution are enhanced by reducing the base width and increasing its purity. The results are applied to germanium at room temperature.
Preparation, Structure, and Properties of Sputtered, Highly Nitrided Tantalum Films
Authors: Coyne H. J. , Tauber R. N.
Published: February 2004

Highly nitrided films of tantalum have been prepared by cathodically sputtering high-purity tantalum in a pure nitrogen atmosphere. The effects of cathode current density and film thickness on the film structure, crystal structure, composition, resistivity, current-voltage characteristics, and optical energy gap were investigated. Transmission electron microscopy showed the films to be apparently discontinuous throughout the range of cathode current densities investigated for 1600 Å thick specimens. The crystal structure determined by electron diffraction analysis was found to be body-centered tetragonal with c=5.01 Å, a=5.77 Å, and c/a=0.87. The presence of small amounts of hexagonal TaN was also observed. Analysis of the gas content showed the amount of nitrogen to be a function of cathode current density and thickness. Electrical resistivity as a function of temperature in the range of 213°–373°K obeyed the relationship ρ=A exp(ΔE/kT), where ΔE decreased with the increasing cathode current density and film thickness. Current-voltage characteristics obtained at 77°K indicated non-Ohmic behavior at large applied voltages. The resistivity could be expressed by log(ρ@V=0/ρ)=AV1/2 above some critical V, where V critical and A are dependent on both film thickness and cathode current density. This behavior could be attributed to conduction by an ``intergrain tunneling'' mechanism. The apparent optical energy gap was found to be in the range of 1.95–2.6 eV depending on sputtering current and thickness.
Measurement of the Spin-Raman Susceptibility by Means of Spin-Wave Instabilities
Authors: Thomas G.
Published: February 2004

The transition probability method for the calculation of spin-wave instabilities is used to calculate the spin-wave instability threshold produced by the spin-Raman process. The anomalously large value of more than 5×10−13 esu is calculated for the Raman susceptibility in YIG. The value is consistent with the 6S5/2 to 4G3/2 transition of the Fe3+ ions of YIG, which has been suggested as the cause of the absorption edge near the Nd3+ laser frequency. This large value of the Raman susceptibility could lead to the development of a continuously tunable laser over a few reciprocal centimeters since the Stokes radiation is linearly related to the spin-wave frequency, which in turn depends on the applied dc magnetic field.
Optical Properties of the Group IV Elements Carbon and Silicon in Gallium Phosphide
Authors: Dean P. J. , Frosch C. J. , Henry C. H.
Published: February 2004

Two special open-tube furnace systems, respectively containing all fused silica and all alumina furnace-area components, and in which P is supplied through the reaction of wet H2 with AlP to form PH3, have been constructed for the growth of GaP crystals from Ga solution. Careful attention has been paid to the purification of the PH3 and H2 transport gas. Unwanted contamination from the flow tubes and furnace area has been minimized. The crystals are then suitable for the controlled study of the optical properties of the impurities C and Si, persistent residual impurities in GaP crystals grown under less stringent conditions. The residual concentrations of S and N have also been dramatically reduced in this system. Clearly defined chemical evidence indicates that carbon rather than silicon is the shallow acceptor (ionization energy EA ∼48 meV) in the residual green donor-acceptor pair luminescence spectrum in GaP. Analysis of sharp line donor-acceptor pair transitions observed at the high-energy tail of a broad red luminescence band (peak energy ∼1.96 eV) characteristic of silicon-doped crystals indicates that silicon is a deep acceptor (EA∼204 meV) on P lattice sites and a shallow donor (ED∼80 meV) on Ga lattice sites in GaP. Sharp line green spectra observed for recombinations at C–Si and Zn–Si pairs confirm this value of (ED)Si. The shallow green pair transitions involving Si donors are strongly coupled to ∼17.5 meV and ∼29 meV low-energy phonons, unlike pair recombinations involving P site donors. This marked difference in phonon coupling invalidates judgment of the relative values of ED for S, Te, and Si donors from the relative positions of the peak intensities of the green or red pair spectra involving these donors. Small shifts in the no-phonon discrete pair lines between crystals doped with Si28 and Si30 confirm the suggested role of Si in these spectra.
Surface-Structure Analysis by Optical Simulation of LEED Patterns
Authors: Fedak D. G. , Fischer T. E. , Robertson W. D.
Published: February 2004

The principles governing the coherent scattering of low-energy electrons are considered for the purpose of determining the degree of correspondence between LEED patterns and Fraunhofer optical diffraction patterns from plane gratings representing the arrangement of atoms at a crystal surface. The analysis indicates that an optical diffraction pattern approximates a composite LEED pattern which contains all beams observed over a range of electron energies. Accordingly, the technique of optical simulation is employed in the analysis of LEED patterns obtained from complicated surface structures. The experimental method is described and applied to the determination of the arrangement of atoms responsible for several characteristic LEED patterns: Au (100) 5×10, Cu (100) + O2, and W (100) + H2. In addition, models proposed previously to account for the Si (111) 7×7 and Ge (100) 8×8 patterns are examined.
Pure Transverse Modes for Elastic Waves in Crystals
Authors: Chang Z. P.
Published: February 2004

The propagation directions of pure transverse elastic waves of infinitesimal amplutide in an infinite, nondissipative, and anisotropic elastic medium are investigated for the cubic, hexagonal, tetragonal, orthorhombic, and rhombohedral groups, and partly for the monoclinic group. The directions of the particle motion and the velocities are also given. The loci of these propagation directions in most cases are curves on the unit sphere and are shown schematically together with the directions of pure longitudinal mode revealing the relation between them.