bluuebunny/crossref_metadata_2025 huggingface dataset:
Relativistic Electron Beam Propagation in High-Pressure Gases
Authors: Miller P. A. , Gerardo J. B.
Published: February 2004

Experimental results are reported for the transport characteristics of relativistic electron beams in high-pressure atomic and molecular gases. Experimental results obtained with two different accelerators (ν/γ ∼ 0.05 and 1) are reported. It was found that the highest pressure at which efficient transport occurred was determined by two different physical processes for the two different intensity electron beams. The lower-intensity beam propagated efficiently throughout a large pressure range, and was attenuated at high pressure by Coulomb scattering of the beam electrons in the screened Coulomb field of the nuclei of the background gas atoms. The more intense electron beam was attenuated at a gas pressure which varied with different gases approximately inversely with the high-energy ionization cross section. A radial breakdown mechanism is proposed which may explain the loss process of the intense electron beam.
Interaction of Relativistic Particles and Free Electromagnetic Waves in the Presence of a Static Helical Magnet
Authors: Palmer Robert B.
Published: February 2004

It is shown that a particle passing along the axis of a helical magnet (in which the field is perpendicular to the axis and rotating as a function of position along the magnet) can be continuously accelerated by its interaction with circularly polarized radiation passing in the same direction. An example is given in which an electron is accelerated to 10 GeV, using a laser of 1014 W. A second example shows how pions and kaons might be separated at momenta over 1000 GeV. It is further shown that bunched charged particles passing down the helical magnet will radiate coherent circularly polarized electromagnetic waves, and it is speculated that the required bunching may under some circumstances be self-generating. An example is shown in which a 10-A current of 15-MeV electrons is used to generate a 75-MW beam of 10-μ radiation.
Comparison of Langmuir Probe and rf Capacitance Probe Electron Density Measurements in Low-Density Plasmas
Authors: Smith Jack
Published: February 2004

Electron densities calculated from data obtained in the laboratory by dc and ac probes simultaneously exposed to low-density low-pressure air plasmas are compared. With electron densities between about 1011 and 1012 m−3 and collision frequencies on the order of 108 sec−1, data from a rf capacitance probe operating near 5 MHz and data from the ion saturation region of a dc probe each yield electron density values that generally agree within a factor of 2. By the use of a differential pressure cell, lower electron densities, ∼109 m−3, and reduced collision frequencies, <105 sec−1, were obtained. Under the latter conditions the dc probe operation was erratic but the ac probe operated satisfactorily, and operated as expected theoretically even under the laboratory limitations.
Plasma Diagnostics and Energy Transport of a dc Discharge Used for Sputtering
Authors: Ball D.J.
Published: February 2004

An investigation of plasma properties and energy-transport mechanisms within a dc anomalous glow discharge has been conducted, with particular reference to those processes operating in the vicinity of the anode. The objective of this work was to obtain more quantitative information about the species in the plasma contributing to the heating of substrates located on the anode during sputtering. Techniques employed in this study involved the use of Langmuir probes for the detection of low-energy species, of an electrostatic analyzer for detection of high-energy species within the plasma, and of temperature-sensitive probes for energy-flux measurements. The negative glow of the plasma was found to contain two electron-energy distributions, one of density ∼2×1010 cm−3 and mean energy ∼0.6 eV, and the other ∼2×108 cm−3 and ∼6 eV energy. A low-energy positive-ion population approximately balanced these densities. Under all operating conditions, the plasma potential was found to be a few volts positive with respect to ground. Energy-flux measurements at the anode showed that the main source of energy was not from these populations in the plasma, however. Further examination of the discharge, using the electrostatic analyzer, revealed the presence of high-energy secondary electrons emitted at, or in, the vicinity of the cathode. Many of these electrons penetrated to the anode with the full fall of cathode potential, and it was found that they were the cause of the initial rapid rise of substrate temperature on commencement of sputtering. Radiation from uncooled cathodes was also a source of energy at the anode, once equilibrium temperatures had been approached.
Interaction between an Electron Beam and a Turbulent Plasma
Authors: Eichler Ray , Hutter Rudolf , Levi Enrico
Published: February 2004

The growth of beam-current-density fluctuations along an electron stream passing through a turbulent plasma slab is discussed.
Sweep-Out Effects in Hg1−xCdxTe Photoconductors
Authors: Johnson M. R.
Published: February 2004

Sweep out of minority-carrier holes in n-type HgCdTe with a band gap of 0.26 eV at 150 K has been observed. Both the photocurrent and the generation-recombination noise current are observed to saturate with increasing electric field. Further, the noise current decreases at the highest fields by ≈2 from its peak value. This is interpreted as the minority-carrier shot noise current which obtains in the absence of recombination. The signal-to-noise ratio is found to increase in the sweep-out region, although by somewhat more than the (32)1/2 predicted by theory.
Electronic Properties of Furan-Quinone Pigments. I. Charge-Transport Studies
Authors: Tutihasi S.
Published: February 2004

The electrical properties of a furan-quinone pigment, 8, 13-dioxodinaphtho (2, 1−b:2′, 3′−d)-furan-6-(2-pyridyl)-carboxamide (DFC), have been studied by means of photoinduced condenser discharge and transient photocurrent techniques. It is shown that the electron range in DFC, ∼10−8 cm2 V−1, is 3 orders of magnitude longer than that of holes, ∼10−11 cm2 V−1. The quantum efficiency of the photogeneration of charge carriers in DFC increases linearly with the square of the electric field, while the dark current increases linearly with the square root of the field. The dark current is determined by the number of free carriers in the bulk and may be described in terms of thermally assisted tunnelling.
A Determination of the Thermal Expansion of Pure Ge and a Measurement of the Differential Thermal Expansion of a Ge–GaAs Thin-Layer Couple
Authors: Feder R. , Light T. B.
Published: February 2004

The absolute thermal expansion of single-crystal germanium was measured from 25 to 360°C. The fractional change in length determinations have a precision of 1 part in 105. The experimental data agree, within the limits of experimental error, with the results determined for polycrystalline germanium by Kirby. A technique was developed for measuring the differential thermal expansion of a two-layer couple. An upper limit for the differential thermal expansion of an epitaxial germanium layer on a gallium arsenide substrate was determined and the result indicates that the thermal expansion coefficients agree to within 1 part in 108. This result indicates that thermal expansion effects do not contribute to the observed stress in epitaxial layers of germanium on gallium arsenide.
Lower Critical Field Measurements in NbN Bulk and Thin Films
Authors: Mathur M. P. , Deis D. W. , Gavaler J. R.
Published: February 2004

Low-field magnetization measurements have been made at 4.2°K on thin-film and bulk NbN samples using a vibrating-sample Foner magnetometer. These data can be used to calculate the upper critical field, Hc2, without having to resort to resistivity data, which, particularly in the case of NbN, yield very anomalous results. In the present work the experimental value of Hc1 is obtained from the magnetization curves and Hc2 is then calculated using the GLAG equations. These calculations and the significance of the Pauli spin paramagnetism and spin-orbit scattering in these materials are discussed.
The Use of Dislocation Theory in Magnetoelasticity
Authors: Kléman M. , Schlenker M.
Published: February 2004

The notion of quasi dislocations is used to describe the sources of internal stresses in a nonuniformly magnetized body which is otherwise perfect. Energy densities and interaction energies with other defects are derived in the same formalism. The distortion tensor (strains and rotations) is calculated in the case of a plane infinite wall; the difference between elastically stable and unstable walls is emphasized. The junction of plane walls is also studied, and an approach to the calculation of the distortion they produce is proposed, using the notion of disclinations. As an illustration, the physics of the 90° zigzag wall in iron is briefly discussed.
Pair-Production Energies in Silicon and Germanium Bombarded with Low-Energy Electrons
Authors: Fiebiger J.R. , Muller R.S.
Published: February 2004

The pair-production energy Ep for free carriers in silicon and germanium is measured using low-energy electrons (10–24 keV) as ionizing sources. The number of carriers generated is measured via a modified Haynes-Shockley technique with a pn junction collector and a super-posed drift field. Experimental values for Ep of 2.91 eV in germanium and 3.64 eV in silicon are determined. These results agree quite closely with the predicted values of Klein and Shockley and correspond to values for Ep measured with higher-energy irradiation sources. The result for silicon confirms values for comparable bombardment conditions measured by Norris and Gibbons. The result for germanium is appreciably lower than the average of previously reported Ep values.
Novel Method for Measuring Transient Surface Temperatures with High Spatial and Temporal Resolution
Authors: Wieder Harold
Published: February 2004

Rapid temperature fluctuations occurring at the surfaces of solids over areas as small as a few wavelengths in diameter can be measured by a new technique. The sample is coated with a semiconductor film which exhibits a suitable shift of its absorption edge with temperature. It is shown that changes in the transmission of an incident monochromatic beam can be used to measure the thermal transients of the underlying surface with a spatial resolution as high as ∼1λ and a temporal resolution as high as 1 nsec.
Acoustic Velocity Measurements in the Metal Hydrides, ScH1.99, YH1.93, and ErH1.81
Authors: Beattie A.G.
Published: February 2004

Longitudinal and shear velocities have been measured as a function of temperature in polycrystalline samples of ScH1.99, YH1.93, and ErH1.81. From these measurements values of the limiting Debye temperature, θ0, the bulk modulus, Young's modulus, the shear modulus, and Poisson's ratio are calculated.
Pileups of elliptical dislocation loops in a hexagonal crystal
Authors: Chou Y.T.
Published: February 2004

Pileups of elliptical dislocation loops on the basal plane of a hexagonal crystal are analyzed. Explicit expressions for the distribution function, the number of loops, and the elastic energy of a pileup are derived. The average stress concentration along the tip of the pileup (the average tip stress) is calculated by using Moutier's theorem.
Temperature dependence of the elastic constants in α-iron single crystals: relationship to spin order and diffusion anomalies
Authors: Dever D.J.
Published: February 2004

The temperature dependence of the elastic constants of single-crystal iron has been measured from 25 to 900°C. A nonlinearity of temperature dependence for the three measured independent constants is associated with the degree of ferromagnetic ordering. The c′ = (C11−c12)/2 is nonlinear in the paramagnetic region as well. A marked difference in sensitivity to spin order between the c′ and c44 shear constants implies that the exchange interaction is, for the most part, between second, not first nearest neighbors. The nonlinearity in temperature dependence of the elastic constants is used to account for (by means of the Zener theory) the nonlinear Arrhenius plots for the diffusion of carbon and self-diffusion in α-iron.
Nuclear quadrupole resonance as a nondestructive probe in polymers
Authors: Hewitt R.R. , Mazelsky B.
Published: February 2004

Nuclear quadrupole resonance (NQR) on dilute inert fillers in several polymers and adhesives is made as a function of compression and tension. The change in the NQR response is found to be proportional to the strain that is applied to the host material. The intensity of the NQR tracer signal is found to be in substantial agreement with the reduction expected from the tracer dilution. The results of NQR tracer measurements on a number of simple reinforced polymers and adhesive bonds are reported.
Doppler Q switching in a single-mode CO2 laser by a rotating mirror
Authors: Devir A.D. , Kafri O.
Published: February 2004

The theory of Doppler-effect mechanism for lasers Q switched by a rotating mirror was extended to include the case of multiple passes of the radiation in the cavity. The theoretical dependence of the pulse duration on the rotating-mirror frequency was calculated. The experimental results obtained, using a single-mode CO2 laser, were found to be in good agreement with the calculated values.
Transverse mode selection in injection lasers with widely spaced heterojunctions
Authors: Butler J.K. , Kressel H.
Published: February 2004

This paper applies the theory of transverse mode selection in injection lasers with thick optical cavities to the important class of large-optical-cavity (LOC) heterojunction lasers where the mode-guiding region is divided into a thin active recombination region and a wider passive region. It is shown that for reasonable values of the refractive-index discontinuity at the heterojunctions, the fundamental mode is not excited at threshold in devices with a mode-guiding layer of the order of several micrometers. The order of the preferred mode increases with the thickness of the mode-guiding region; but for values above a few micrometers, the differences in the gain coefficient at threshold become so small that the mode-selection process is affected by differences in the facet reflectivity for the different modes; this correction favors the highest possible TE mode. The experimental results are shown to be consistent with the theoretical predictions of the order of the mode at threshold. In the representative diodes studied, a fit of the theory and experiments can be obtained with a four-layer model of the cavity geometry. The parameters are the measured widths of the waveguide and of the active region and the dielectric discontinuities at the heterojunctions which were adjusted. The results indicate that the excited mode which was observed was not necessarily the highest cavity mode that could propagate.
Current-controlled negative resistance in CdSnP2
Authors: Knight S. , Buehler E. , Camlibel I.
Published: February 2004

Coherent current oscillations are observed at room temperature under pulsed bias in the chalcopyrite-structure compound CdSnP2. The properties of this negative resistance suggest that it is due to the intervalley transfer of carriers (Gunn effect). Carrier concentration inhomogeneities in the available material, grown by a solution process, remain as the central experimental difficulty.
Chemistry of high-temperature superconductivity in the NbN family
Authors: Phillips J.C.
Published: February 2004

The high transition temperatures Tc of the family of RY compounds (R = Ti, Zr, Hf, V, Nb, or Ta, Y = C, N, or O) are attributed to softness of the lattice against hydrostatic deformations, which gives rise to strong electron longitudinal-acoustic phonon coupling at short wavelengths. Chemical trends within the RY family provide evidence to support this explanation. The microscopic theory of superconductivity is used to predict from the value of Tc the form of the phonon spectrum of NbN. For the acoustic branch the predicted value of (ω2)1/2 is 150 °K. Also Tcmax in the RY family is estimated to be 22 °K.
Comment on ``Transformation twinning of B2(CsCl)-type structure based on an inhomogeneous shear model''
Authors: Wasilewski R.J.
Published: February 2004

The formal differentiation between mechanical and transformation twinning proposed by Wang is questioned. It is suggested that the martensitic transformation in the B2 structure should be considered without invoking the requirement of twin formation.
Variation of the refractive index of boric oxide glasses with hydrostatic pressure to 7 kbar
Authors: Vedam K. , Schneider W. C.
Published: February 2004

The variation of the refractive index of B2O3 glasses with pressure to 7 kbar at room temperature has been determined by an interferometric method. One of the two samples studied had been subjected to a high pressure-temperature excursion and thus had been permanently compacted prior to the present measurements. The slope of the change in refractive index Δn vs volume strain curve was found to be the same for both the compacted and noncompacted B2O3 glasses, but it was found to differ for the Δn vs pressure relationship. Comparison of these results with those of similar studies on vitreous silica leads to the conclusion that the structure of B2O3 glass is quite different from that of vitreous silica and thus supports the conclusions of NMR and x-ray studies that the B2O3 glass is mainly composed of an irregular network of BO3 triangles rather than BO4 tetrahedra.
Investigation of the surface acoustic wave properties of heteroepitaxial ZnO layers on Al2O3
Authors: Pizzarello Frank
Published: February 2004

Experimental data are given showing the relationship of phase velocity, group velocity, and electromechanical coupling coefficient as a function of the normalized thickness h/λ for epitaxial (112̄0) ZnO on (011̄2) Al2O3. Delay time vs frequency for dispersive delay lines fabricated from epitaxial ZnO on Al2O3 is also given. Using these data, design criteria and assessments are made for the use of this composite material in fabrication of a dispersive delay-line device.
Formation of silicon oxide over gold layers on silicon substrates
Authors: Hiraki Akio , Lugujjo Eriabu , Mayer J. W.
Published: February 2004

When a single-crystal substrate of silicon is covered with evaporated gold and heated at relatively low temperatures (100–300°C) in an oxidizing atmosphere, a silicon-dioxide layer is readily formed over the gold layer. The mechanism and factors controlling this low-temperature oxide formation have been investigated using backscattering of 2-MeV He+ ions. The oxide layer is nonuniform in thickness and the initial growth of this layer is proportional to (time)1/2. Both oxidizing ambient and orientation of the substrate influence the growth rate, and the amount of gold determines the final thickness of oxide. A model is proposed to explain the oxide-growth mechanism.
Electrical conductivity of heavily doped diamond
Authors: Tsay Y. F. , Ananthanarayanan K. P. , Gielisse P. J. , Mitra S. S.
Published: February 2004

The semiconducting properties of boron-, aluminum-, and titanium-doped diamond have been interpreted using the log R (resistance) vs 1/T curves. In boron-doped diamond, ``high-concentration''-type impurity band conduction occurs. The extrinsic ranges of the curves are analyzed with the usual model to yield the activation energies of the impurity level. The activation energies for the boron-doped samples vary from 0.15 eV for the highest dopant concentration to 0.30 eV for lower concentrations. For the aluminum- and titanium-doped samples, the activation energies were found to be 0.31 and 0.40 eV, respectively. The results are consistent with those obtained from optical methods where data were available. An empirical formula is advanced which fits the log R vs dopant content rather well.
Thermal expansion of InxGa1−xP alloys
Authors: Kudman I. , Paff R. J.
Published: February 2004

The coefficient of thermal expansion has been determined for a series of InxGa1−xP alloys in the temperature range 15–650 °C. This parameter was found to increase linearly from (4.75±0.1)×10−6/°C for InP to (5.91±0.1)×10−6/°C for GaP.
Observation of transient behavior of picosecond laser pulses
Authors: Ohmi T. , Hasuo S. , Hori S.
Published: February 2004

Dynamic behavior of picosecond pulses from a Q-switched ruby laser is observed by using a high-speed oscilloscope and a silicon photodiode. At the early portion of the Q-switched pulse envelope, the mode locking is not perfect and the picosecond pulse has a few peaks. On the other hand, at the end of the Q-switched pulse envelope, the background pulses are completely suppressed, so that the mode-locked pulse has a single peak. The temporal compression of the picosecond optical pulse by passing through an optically active Kerr liquid is also observed.
Photoelectron surface escape probability of (Ga,In)As : Cs–O in the 0.9 to [inverted lazy s] 1.6 μm range
Authors: Fisher D. G. , Enstrom R. E. , Escher J. S. , Williams B. F.
Published: February 2004

Ga1−xInxAs alloys in the composition range 0≤x≥0.52 and band-gap (Eg) range of 1.38 to 0.74 eV were activated with Cs and O2. Samples of different carrier concentrations were investigated. For band gaps down to about 0.8 eV, the photothreshold was equal to the band gap. The longest wavelength threshold determined was 1.58 μm. To the best of our knowledge, this represents the longest wavelength response yet achieved for photoemission into vacuum from a III-V compound. The surface escape probability, B, was derived from the quantum yield data for each sample. The B-vs-Eg data were analyzed according to a surface escape model which includes the effects of (i) a finite-width initial energy distribution of photoexcited carriers, (ii) the bent-band region and (iii) various types of surface potential barriers. Surface escape probability data pertaining to a single doping density could be explained by a model that includes only a work-function barrier or simple step potential. However, in order to explain the data for the several doping concentrations in a consistent manner, it was necessary to include an electron-semitransparent energy barrier above the vacuum level. A barrier width of 8 Å gives good agreement with the experimental data. This dimension is consistent with the thickness of the Cs–O activation layer which was experimentally determined to be on the order of a monolayer. These results are interpreted in terms of a surface double-dipole model.
Radiative energy transfer in an annular channel
Authors: Edenburn M. W.
Published: February 2004

Radiosity and temperature distributions and transmission probabilities are found for annuli of various geometries which are irradiated by ``black'' uniform radiation at one end. The geometries considered are Ri/Ro = 0.1, 0.3, 0.5, 0.7, and 0.9 with L/Ro − Ri)= 0.1, 0.5, 1.0, 5.0, and 10.0 for each value of Ri/Ro where L is length, Ri is inner radius, and Ro is outer radius. The distributions for the cases Ri/Ro = 0.9 with L/(Ro − Ri) = 1 and 10 are in excellent agreement with the distribution for parallel plate channels with length/spacing = 1 and 10. Transmission probabilities agree with those calculated by other methods.
Electron energy distribution for Ta–Ta2O5–Au thin-film Schottky/Poole-Frenkel effect devices
Authors: O'Clock George D.
Published: February 2004

The energy distribution of the electron emission originating from Ta–Ta2O5–Au thin-film devices has been measured utilizing a 127° electron energy spectrometer. The shape of the distribution can indicate the losses and electron temperatures associated with conduction through thin insulating films. A comparison of the electron temperature is made under the conditions where electron-optical phonon scattering events within the insulator medium are considered to be either independent or dependent upon electron energy.
Electrical explosion of tungsten wires in a vacuum
Authors: Vlastós Antonios E.
Published: February 2004

The present work demonstrates the disintegration of thin electrically exploding tungsten wires in a vacuum. The drawn tungsten wires split into tiny fibers in a time close to that at which the wire reaches its melting point. Similar results were obtained for wires exploded at low pressures and at atmospheric pressure. The results show, within the limits of the experimental accuracy, that, when the wire reaches its melting point, dips are observed on the current derivative and the voltage oscillograms and x rays are produced. The results support the suggestion that the production of hard x rays from drawn thin exploding tungsten wires is due to the splitting of the wire, which has a fiberlike crystalline structure. Moreover the oscillograms of the first current pulse show that for thin wires the electrical conduction up to melting point is due only to the solid wire material and that the influence of the ambient pressure on the crest value of the first current pulse for wires exploded at the same condenser-bank voltage is almost negligible.
Experimental study of the electrification produced by dispersion of dust into the air
Authors: Kamra A. K.
Published: February 2004

Some laboratory experiments have been performed to study the electrification of dust clouds created by blowing different types of dusts into a dust chamber. The polarity and magnitude of the space charge in such dust clouds have been found to be sensitive to the mineral constituents of the dust. Even a single dust cloud, if allowed to settle under gravity in a field-free space with no charge added to it, can have opposite polarities of space charge at different times of its sedimentation. The space charge produced increases with an increase in the length of the surface over which the dust is blown. It also increases with an increase in the temperature and velocity and a decrease in the relative humidity of the blowing air. External electric fields of up to a few hundred V/cm, applied to the surface from which the dust is blown, have little effect on the generated space charge. Size distributions of positively and negatively charged particles show a greater abundance of smaller (∼ 3 μ) particles compared to those of small neutral particles.
Fine structures and energy distribution of secondary electron emission from Si(111)
Authors: Goto Keisuke , Ishikawa Kazuo
Published: February 2004

Some secondary electron (SE) emission characteristics, i.e., total SE's, elastically and inelastically backscattered primaries, true SE's, and plasma loss spectra, of single-crystal Si(111) were observed as a function of primary energy Ep. A small fraction of total SE's was introduced to a retarding field energy analyzer placed at 45° to the normally incident primary beam. As a result, a fraction of total SE's and of elastically backscattered (including diffracted) primaries showed quite similar fine structure even in detail, when observed as a function of Ep. By filtering a fraction of total SE's into individual energy ranges, the fine structures in true SE's were found at the same Ep's as in elastically backscattered primaries, but were in the opposite direction to the corresponding structures in the elastically backscattered primaries. On the other hand, the fine structures of inelastically backscattered primaries, i.e., energy-loss primaries, showed quite a complex correlation to those of elastically backscattered primaries. It is concluded that the fine structures in σ (total SE yield) vs Ep and η (backscattering coefficient) vs Ep curves should be caused by the elastically backscattered primaries. The considerable number of electrons subjected to the surface and the first bulk plasma losses were found to be emitted from within a few atomic layers from the surface. Some problems on the Auger electron excitation are also discussed.
Structure of the reactant and product of a turbulent second-order reaction at large wave numbers
Authors: Dash Rangadhar
Published: February 2004

The spectrum functions of the reactant and the product of a second-order reaction field concentration, for different spectral ranges, have been investigated with the application of Pao's concept of a simple continuous spectral cascading process for the transfer of turbulent kinetic energy, heat, and mass at large wave numbers. This consideration has been made under suitable conditions outlined in this paper.
Recovery of deformed polymers. III. Thermal properties
Authors: Park J. B. , Uhlmann D. R.
Published: February 2004

Measurements of heat capacity as a function of temperature are used to evaluate the changes in heat content of three deformed polymers during isothermal annealing treatments. The polymers investigated are the same as those used in previous studies of length recovery, viz., amorphous polycarbonate (PC) and semicrystalline polyethylene (PE), and polypropylene (PP). Cold-drawn PC is characterized by a smaller heat content than the undrawn material, while drawn PE and PP have larger heat contents than their undrawn forms. In all cases, the differences between the original and drawn states are of the order of a few cal gm−1. These differences are observed to anneal out completely in the case of PC heat treated in the vicinity of its glass transition, while only incomplete recovery is observed in the case of PE and PP. Activation-energy spectra characterizing the recovery process are derived from the variation of heat content with annealing time. The spectra are centered about 22.6 kcal (g atm)−1 for PC, about 24.1 kcal(g atm)−1 for PE, and about 19.2 kcal(g atm)−1 for PP. The spectra characterizing enthalpy recovery are similar to those derived previously from retraction kinetics, and indicate the similarity of relaxation processes involved in the two recovery phenomena.
Electrical and optical properties of proton-bombarded gallium phosphide
Authors: Spitzer S. M. , North J. C.
Published: February 2004

The electrical and optical properties of proton-bombarded p- and n-type liquid-encapsulated Czochralski-grown GaP have been investigated as a function of 300-keV proton dose and subsequent annealing. Proton bombardment of GaP introduced lattice damage into a surface layer equivalent in thickness to the proton penetration range, and resulted in a large increase in the electrical resistivity, as well as an increase in optical absorption of this damaged surface layer. The thickness of the damaged layer increased linearly with proton energy at approximately 1.0 μ/100 keV in the energy range from 100 to 300 keV. Electrical resistivity in both p- and n-type samples increased with proton dose to a maximum of ∼1014 Ω cm at a dose of 4×1014 protons/cm2, and then the resistivity decreased with increasing dose. Optical absorption spectra indicated a continuous distribution of energy levels extending into the band gap. The absorption at 6328 Å (visible red) increased monotonically with proton dose from ∼10% and 1014 protons/cm2 at 300 keV to ∼90% at 1017 protons/cm2. Layers approximately 3.0 μ thick have been produced which have high electrical resistivity (> 1010 Ωcm) and relatively low optical absorption (< 10%). The activation energies governing the annealing of the optical and electrical defects are in the range from 2 to 4 eV. The existence of large activation energies for the annealing of bombardment-induced high resistivity implies high stability near room temperature. This stability combined with ease of forming high-integrity pinhole-free layers of controlled thickness on GaP substrates suggests useful applications in the GaP device fabrication technology. Many qualitative similarities have been observed between the proton-bombarded GaP examined here and the bombarded p-type GaAs discussed in the previous paper.
Measurement of the second-harmonic-generation nonlinear susceptibilities of Se, CdTe, and InSb at 28.0 μm by comparison with Te
Authors: Sherman Glenn H. , Coleman Paul D.
Published: February 2004

The magnitudes of the nonlinear optical susceptibilities of trigonal selenium, cadmium telluride, and indium antimonide have been measured at 28.0 μm relative to d11 (tellurium). By comparison to the recently measured absolute value for tellurium, d11(Te)=(5.7±1.6×10−10 m/V, the values obtained in this work are d11(Se)=(18.4±8.6)×10−10 m/V, d14 (CdTe)=(5.9±2.4)×10−11 m/V, and d14(InSb)=(5.6±2.3)×10−10 m/V. For Te, CdTe, and InSb, the measured 28.0 μm value is less than the 10.6 μm value, while for Se, the 28.0 μm value is considerably larger than the 10.6 value. These seemingly inconsistent results are explained using Garrett's anharmonic oscillator model.
Acousto-optical deflection in thin-film waveguides
Authors: Giallorenzi T. G.
Published: February 2004

The deflection of optical guided waves by acoustic waves in layered media is studied. The electric fields that arise in this scattering process lead to complex radiated power distributions. In particular, it is shown that field effects can influence coupling efficiency and beamwidth and that these effects must be included in any description of acoustic-optic light deflection from optical waveguides.
Resonance fluorescence in GaP
Authors: Gundersen Martin , Faust W. L.
Published: February 2004

We report here the observation of the phonon sidebands of a bound exciton by resonant excitation of the bound exciton. By exciting fluorescence in impure samples of GaP with different laser lines one can obtain spectra in which lines associated with particular impurities show enhancement. Thus resonant fluorescence can be used as a spectroscopic tool for the study of exciton spectra in solids. We suggest this method as a possible technique for identifying unknown lines with specific impurities and as an application for tunable dye lasers.
The temperature dependence of the anisotropy field and coercivity in epitaxial films of mixed rare-earth iron garnets
Authors: Shumate P. W. , Smith D. H. , Hagedorn F. B.
Published: February 2004

The temperature dependence of the anisotropy field Hk and the domain-wall coercivity Hc have been measured for three different epitaxial films of mixed rare-earth iron garnets with the nominal compositions Er2Eu1Ga0.7Fe4.3O12, Y1Eu1.85Yb0.15Al1.1Fe3.9O12, and Eu1.7Er1.3Al0.7Ga0.8Fe3.5O12. Each of these garnets supports bubble domains. The anisotropy field was measured using an optical magnetometer, and analytical expressions are developed which relate the optical magnetometer parameters to the anisotropy field. These measurements show that the anisotropy field decreases with increasing temperature at about −1%/°C at 20°C for all three samples. The coercivity, again measured by an optical technique, was also found to decrease with increasing temperature. The coefficient ranged from −1.3%/°C to −3.0%/°C at 20°C depending on the sample. The largest total change in Hc for one of the samples was a factor of 310 over the temperature range −106°C to +80°C. The temperature variation of the saturation magnetization 4πMs and the material length l were also measured. The temperature coefficients of 4πMs and l at 20°C varied from ∼0.03%/°C to −1.1%/°C, and −0.9%/°C to 0.5%/°C, respectively. No simple correlation is evident among the temperature dependences of Hk, Hc, and 4πMs although l varies predictably with 4πMs and Hk. The large variations in coercivity are not consistent with simple conventional models.
Photoelectronic properties of stoichiometric flux-grown rutile (TiO2) crystals
Authors: Wakim Fahd G.
Published: February 2004

The photocurrent excitation spectra of stoichiometric flux-grown rutile (TiO2) single crystals showed a peak at 410 nm, the band-edge position, with no other peaks due to impurities or defects. In addition, thermally stimulated current, variation of photocurrent with light intensity, and oxidation and reduction rates in these crystals suggest a much lower defect concentration than that of the flame-fusion-grown rutile crystals.
Adsorption of carbon monoxide on ruthenium
Authors: Charkabortty Saghana , Grenga Helen E.
Published: February 2004

Field-ion and emission microscopy techniques were used to study the adsorption and desorption of carbon monoxide on (101̄1), (101̄0), (112̄2), and (202̄1) regions of ruthenium. Both physisorbed CO and β-CO were found on all regions, while α-CO was found only on low-index (101̄1) and (101̄0) regions. Substrate and/or adsorbate rearrangements also occurred on all regions. While the M–CO bond energy was found to be less on ruthenium than that reported for tungsten, the ratio of the M–CO to M–M bond energy was found to be greater in the case of ruthenium.
Further investigation of noncollinear surface-wave interactions
Authors: Tanski William J. , Mayer Walter G.
Published: February 2004

Two noncollinear surface waves of 5 and 7 MHz have been excited on the surface of single-crystal copper samples in such directions that the waves could interact via the nonlinearities of the medium to produce a third surface wave at the sum frequency of 12 MHz. Using optical techniques, the three waves involved have been detected on two crystal surfaces, the (001) and (111) planes of copper, and the amplitude of each of the waves has been measured.
Note on crystal growth of stoichiometric Fe3S4
Authors: Yamaguchi S. , Wada H.
Published: February 2004

Greigite, cubic Fe3S4 (∼200 Å), could not be grown hydrothermally at 190°C into larger crystals of that phase. Instead nonstoichiometric pyrrhotite formed possibly seeded by the cubic phase.
A new class of switching materials
Authors: Bueche F.
Published: February 2004

By combining several volume percent of conducting particles in a semicrystalline matrix, a highly temperature-dependent resistivity is obtained. The resistivity changes by several orders of magnitude in a small temperature interval centered on the crystal melting temperature. Moreover, a typical resistivity changes by a factor of hundreds as the frequency changes from 102 to 104 Hz. Materials of this type show dielectric constants in excess of 103 which vary strongly with temperature and frequency.
Concentrated force in a cubic anisotropic solid: a single integral solution
Authors: Goodman John W. , Masumura Robert A. , Sines George
Published: February 2004

A single integral solution is presented for displacements arising from a concentrated force in an infinite medium with cubic elastic anisotropy. The integrand is an explicit algebraic expression of the three elastic constants and the spherical coordinates of the point at which the displacements are required. The integral gives the displacement components referred to the cubic axes. Although the concentrated force is along a cubic axis, a force in an arbitrary direction can be constructed by the superposition of the solutions for its components along the axes. Applications are suggested that use distributions of point forces to model defects in cubic crystals. Elastic displacement fields are presented for crystals of Na, Cu, Rb I, Nb and W.
Glass transition of polyethylene: Volume relaxation
Authors: Davis G. T. , Eby R. K.
Published: February 2004

Data are presented to show that when linear polyethylene is quenched from room temperature to temperatures below 273 K, it exhibits a volume decrease for times long compared with that required to establish temperature equilibrium. The time, temperature, and density dependence of this decrease is shown to be consistent with a relaxation occurring in the amorphous portion (lamella boundary layers) of the samples. The data can be superposed and the shift factors follow the WLF formalism. Analysis by this method yields a Tg of 231 ± 9 K but the uncertainties preclude any correlation with specific volume over the range 1.01–1.05 cm3 g−1. The data indicate the absence of any comparably strong time dependence of the volume near 150 K. This method of detecting a glass transition in partially crystalline polymers is relatively freer of subjective judgment than most.
Strain and temperature dependence of relaxation phenomena in polycarbonate
Authors: Litt Morton H. , Torp Svenning
Published: February 2004

The mechanical behavior of glassy PC was investigated as a function of strain and temperature by stress relaxation measurements and by dynamic mechanical measurements. For stress relaxation, the stress decay, measured by an Instron tensile tester, linearized vs logarithmic time from 1 sec to up to 16 h. From these data a plot of the relaxation time vs strain was obtained showing that the relaxation time decreased with increased strain. To separate the effect of the elastic and viscous components, E′ and E″ were investigated by the Rheovibron. At a constant strain level, E′ showed a slight increase with time while E″ decreased considerably. With stepwise increase in strain, E′ showed a slight decrease while E″ increased considerably. Furthermore, the dynamic mechanical spectra showed that the peak did not shift with strain, but intensified and broadened considerably. The stress relaxation can be related to the Rheovibron data.
Electric contacts. II. Mechanics of closure for gold contacts
Authors: Cuthrell R. E. , Tipping D. W.
Published: February 2004

We describe equipment and report results of a study of the mechanics of closure for gold electric contacts cleaned by sputtering and closed with precise control of mechanical and environmental variables. The ultrahigh-vacuum system, in which measurements are performed, is isolated from building vibrations. Our measurements include contact resistance, load, cold welding, creep, anelastic strain recovery, stress strain, yield stress, and strain hardening. We calculated an activation energy of 1200 ± 100 cal/mole for low-temperature creep in gold.
Studies of the kinetics of [NaCl]–[CsCl] transitions
Authors: Frushour R. H. , Roy Rustum
Published: February 2004

Studies were made to determine the effects of various interacting factors (pressure, temperature, mineralizers, and shear) on the kinetics of [NaCl]–[CsCl] transition. These experiments were performed to more fully understand how particular experimental parameters change the kinetics and hence the apparent equilibrium of some solid-state reactions. Results show that the kinetic effects of pressure are so great in some cases that solid-state transformations cannot be greatly ``superpressurized'' by shock-wave techniques. It is recommended that materials which show this effect be used for calibrating shock-wave apparatus. Previously reported kinetic effects of temperature on the [NaCl]–[CsCl] transition for RbCl are shown to be in error. Thus, increasing temperature accelerates reaction rate and reduces the hysteresis for this particular phase transition. Also, with the addition of water as a mineralizer the ``region of indifference'' was found to be equal to the width of the hysteresis loop. The kinetic effect of the crystallographic orientation of single crystals of RbCl and CdS was found to be of such magnitude that orientation should be considered when examining results of any single-crystal phase transition studies. Many widely different experimental results on equilibrium phase boundaries can be sufficiently interpreted when details of experiments revealing unsuspected kinetic problems are known.
Geometrical shapes of planar single-faulted defects in quenched face-centered cubic metals and alloys
Authors: Kritzinger S. , Cloete G.P.
Published: February 2004

Arguments are presented in favor of a rationalized understanding of the variety of geometrical shapes of the various polygonal single-faulted dislocation loops observed in quenched face-centered cubic (fcc) materials. By considering the minimization of the defect energy and the crystal anisotropy, the primary vacancy clusters in all these materials (at the time of collapse to form dislocation loops) are taken to be regular hexagonal in shape, with sides along the close-packed 〈110〉 directions and lying on the close-packed {111} planes. Based on this common origin for all single-faulted loops, it is shown how factors such as the exact moment of collapse of the vacancy disk, the stacking fault energy, and the purity of the specimen can affect the subsequent development of the regular hexagons into various possible polygonal shapes during the remainder of the quench period. Direct experimental evidence is presented of the influence of impurity segregation on the shape and annealing behavior of certain faulted loops observed in quenched Al–1.5 wt.% Mg. To fit the only observations of faulted loops which have been made in nickel to date into the general proposed scheme, it is suggested that the stacking fault energy of nickel is lower than the figures available in the literature, and that vacancy disks collapse at a relatively early stage of the quench for this material.
Mutual annihilation of unlike dislocations by cross slip in ordered and disordered alloys
Authors: Sadananda K. , Marcinkowski M. J.
Published: February 2004

Under the action of an external applied stress, unlike dislocations on parallel slip planes either pass one another, or cross slip or climb and annihilate each other. A detailed numerical analysis of cross slip of unlike screw dislocations was carried out and the conditions under which cross slip was more favorable compared to passing were determined in both ordered and disordered alloys for infinite straight dislocations. It was further shown that cross slip could preferentially occur near the vicinity of an unlike dislocation which acted as a source of internal stress. The presence of such internal stresses was found to reduce the energy barrier for cross slip to an extent that cross slip became spontaneous if the vertical separation between the unlike dislocations was below a critical value. The implication of this was that in the absence of any other internal stresses, the passing dislocation of separation less than the critical value could not be stable, and this critical separation set the limit for the strengthening that could be obtained by passing dislocations. The effects of the applied stress, and its orientation on the cross slip process have also been discussed in detail.
High-field transient currents in KCl doped with divalent ions
Authors: Hanscomb J. R. , Moore Elvin J. , Calderwood J. H.
Published: February 2004

Transient currents produced by step-function fields of strength 0.4–0.5 MV cm−1 have been studied in KCl doped with Ba2+, Ca2+, and Sr2+ for temperatures between 100 and 250°C. In general, the transients are identical in shape with those reported for pure KCl by Moore and Hanscomb. However the effect of applying a succession of voltage pulses to the doped samples can be significantly different from the effect on the pure samples. In the doped samples, a rapid (order of seconds) increase in successive current amplitudes and a slow (order of hours) decrease in successive amplitudes has been observed. The transients are analyzed in terms of the three-level model developed for the pure samples, and it is shown that the slow decrease in amplitudes is predominantly due to a decrease of carrier mobility.
Electromagnetic wave interaction with moving bounded plasmas
Authors: Kalluri Dikshitulu , Shrivastava R. K.
Published: February 2004

It is shown that above some critical velocity of the medium moving normal to the interface, the reflected wave actually travels towards the medium over a range of medium velocity. Beyond this range, the incident wave from below never catches the moving medium, but the medium can interact with the portion of an existing plane wave above. The maxima and minima of the power reflection coefficient as a function of the normalized slab velocity are also shown for both parallel and perpendicular polarizations of the wave incident on an isotropic plasma slab.