bluuebunny/crossref_metadata_2025 huggingface dataset:
Mercury pressure over HgTe and HgCdTe in a closed isothermal system
Authors: Bailly F. , Svob L. , Cohen-Solal G. , Triboulet R.
Published: February 2003

The solid-vapor equilibrium kinetics over HgTe and the mercury-vapor pressure evolution over HgTe in the presence of CdTe are studied by means of mass-loss measurements. For the first case, a theory is given relating the mercury pressure in an isothermal closed system to the mercury vacancy and interstitial concentrations in solid HgTe, the sample-volume–to–free-volume ratio as well as the equivalent pressure of mercury added in excess. In the simplest case—no mercury in excess, no interstitials—it is found that the mercury pressure first increases as the square root of time, before reaching an equilibrium value. At all times the pressure is proportional to the square root of the sample–to–free-space volume ratio. Experiments, conducted at 550 °C, confirm this behavior as well as the relation with the ’’excess mercury pressure’’. The diffusion coefficient of mercury vacancies in HgTe is estimated to be 8×104 μ2/h. For HgTe in the presence of CdTe, equilibrium cannot be reached because of material transport from HgTe to CdTe. The mercury pressure is determined by two main phenomena: outdiffusion from HgTe, as studied above, and diffusion into CdTe and the solid solutions formed on it by the material transport. For a given time, the experimental variations of the mercury pressure with the different parameters are formally similar to the preceding one (HgTe case). The analysis of the pressure evolution with time shows that the mercury pressure passes through a maximum which is experimentally verified.
Dislocations in vapor-grown compositionally graded (In,Ga)P
Authors: Abrahams M. S. , Buiocchi C. J. , Olsen G. H.
Published: February 2003

Dislocation morphologies in compositionally graded vapor-phase epitaxial (VPE) layers of (In,Ga)P deposited on (100) GaP substrates have been determined via transmission electron microscopy using (011) cross-sectional samples. Evidence for the introduction of misfit dislocations by slip and from substrate dislocations has been found. These processes lead to the familiar crossed array of dislocations at an interfacial misfit plane. Evidence for Frank-Read sources, which are pinned dislocation segments in the crossed array, and dislocation annihilation is also presented. Asymmetric arrays of dislocations at compositional steps have been observed.
Dynamic formation of a twin in a bcc crystal
Authors: Ishioka Shunya
Published: February 2003

Computer-simulation studies of the motion of a straight screw dislocation in a bcc crystal were performed. It was observed that a dislocation running with the speed near the shear wave velocity formed a microtwin without a pole mechanism.
Thin-film interdiffusion. I. Au-Pd, Pd-Au, Ti-Pd, Ti-Au, Ti-Pd-Au, and Ti-Au-Pd
Authors: Poate J. M. , Turner P. A. , DeBonte W. J. , Yahalom J.
Published: February 2003

Interdiffusion in the Ti/Pd/Au thin-film system is measured using Rutherford backscattering. Interdiffusion rates of Pd/Au for temperatures between 200 and 490 °C have been correlated with the defect structure of the films using models of defect enhanced diffusion. Au diffusing in Pd has been analyzed by the Whipple model of grain-boundary diffusion to give a grain-boundary activation energy of 0.9 eV. Pd diffusing in Au has been analyzed using the grain-boundary-assisted bulk diffusion model and it is shown that dislocation diffusion has to be invoked to explain the amount of Pd in the Au film. Air, as compared with vacuum, annealing enhances interdiffusion in the Ti-Au couple and inhibits interdiffusion in Ti-Pd. Ti-Pd and Ti-Au interdiffusion in the Ti-Pd-Au and Ti-Au-Pd ternary systems is strongly reduced in comparison with interdiffusion in the corresponding Ti-Pd or Ti-Au couples for vacuum annealing.
One-dimensional current transport equations
Authors: Macdonald J. Ross
Published: February 2003

Because the divergence of the total current (all conduction and displacement terms included) is zero, the space average of the current for one-dimensional flow is equal to the current itself, even in the presence of generation-recombination and trapping effects. This result is helpful because the average form of the current is frequently easier to use in static and time-varying problems than its unaveraged form. The space invariance of the current is explicitly illustrated for a typical one-dimensional transport situation with recombination.
Observation of anode ions associated with pinching in a relativistic electron beam diode
Authors: Swain D. W. , Goldstein Steven A. , Kelly J. G. , Hadley G. R.
Published: February 2003

Ions originating at the anode of a relativistic electron beam (REB) accelerator are observed at the cathode by a means of a Faraday cup. The dominant species is H+, probably from adsorbed impurities. These ions, having energies equal to the diode voltage, are not observed until 20–40 J/cm2 are deposited by the beam on the anode surface, and are closely associated with the formation of a pinch at the anode.
Composition dependence of energy gap in GaInAs alloys
Authors: Baliga B. J. , Bhat R. , Ghandhi S. K.
Published: February 2003

The energy gap of GaInAs alloys, grown by vapor-phase epitaxial growth using organometallic sources of Ga and In, has been measured over the composition range 0–50 mole% InAs. The energy gap is found to vary linearly with composition. Comparison with data in the literature indicates that highly homogeneous layers can be obtained by the organometallic growth technique.
Stopping cross sections for 0.25–3.0-MeV 4He ions in cadmium sulfide
Authors: Miller W. E. , Hutchby J. A.
Published: February 2003

Stopping cross sections of 4He ions with energies 0.25–3.0 MeV have been measured for cadmium sulfide with a probable error of ±7–8%. The experimental method utilized the Rutherford backscattering technique and measured the energy loss of elastically scattered 4He ions from films of cadmium sulfide sputtered on carbon substrates. The experimental data are compared to recent experimental and theoretical results.
Anomalous torsional dynamic response of axially stretched rubber while stress relaxation is taking place
Authors: Rosen R. H. , Kolsky H. , Pipkin A. C.
Published: February 2003

Experiments have been carried out to determine the periods of the free oscillations of torsional pendulums whose restoring couples were provided by samples of axially stretched tubes of natural rubber and of plasticized polyvinyl chloride. Measurements of the period Δt of a torsional oscillation were made while stress relaxation was taking place in the samples, and the changes in axial force F were measured at the same time. For stretched rubber specimens it was found that as long as the stretch ratio λ was less than 3.5 the relation between the period Δt and the axial force F followed the predictions of the theory of large elastic deformations, i.e., Δt was proportional to (1/F)1/2. Furthermore, for a given sample, measurements over a range of values of λ conformed to the relation Δt∝[(λ3−1)/λF]1/2. At values of λ≳4.0, however, the relation between Δt and F became highly anomalous in that Δt instead of increasing with decreasing F decreased. This behavior would appear to be explicable only in terms of structural changes taking place in the rubber during stress relaxation, and these result in large increases in the inherent torsional rigidity of the material. This would appear to be related to a process of crystallization in the rubber which is known to take place at these high stretch ratios. The observations with polyvinyl chloride showed no such anomalies in the same range of extending forces.
Subnanosecond time resolution detection of x-ray pulses using chemical dosimetry
Authors: Harney R. C.
Published: February 2003

The possibility of using chemical dosimetry to detect x-ray pulses with subnanosecond time resolution is theoretically investigated. The theory of chemical dosimetry is reviewed and a dosimeter consisting of a laser, an absorption cell, and an ultrafast optical streaking camera is analyzed. This analysis indicates that time resolutions of less than 100 psec are achievable at x-ray energies greater than 4 keV. Predicted threshold dose rates are low enough [(1–3) ×1013 rad sec−1] so that the technique should be applicable to diagnostics of x-ray lasers, laser-produced x-ray experiments, and laser fusion experiments. Effects of photon energy, x-ray–induced solvent heating, high-Z doping of the solvent, cell length, and laser wavelength are discussed.
Mixed-crystal infrared studies on melt-crystallized polyethylene
Authors: Ching J. H. C. , Krimm S.
Published: February 2003

In order to minimize the occurrence of heterogeneities, or segregation, of polyethylene and poly(ethylene-d4) in mixed-crystal systems during melt crystallization, it has been found that conditions of high molar ratio of PEH/PED and a small difference in melting points between the two species are necessary. Under these optimum conditions the infrared spectral results observed in melt-crystallized polyethylene have to be attributed predominantly to chains which fold essentially with adjacent reentry along (200) planes.
A vibrational analysis of crystalline trans-1,4-polybutadiene
Authors: Hsu S. L. , Moore W. H. , Krimm S.
Published: February 2003

The normal vibrations of crystalline trans-1,4-polybutadiene have been calculated by combining interchain atom-atom potentials with the previously proposed intrachain force field. These calculations have been used to analyze the infrared and Raman spectra of an essentially all-trans urea-complex polymer. The band splittings and low-frequency lattice modes observed in these spectra are satisfactorily accounted for by the calculations.
Dielectric relaxation studies of poly(N-vinylcarbazole) and poly(3-chloro-N-vinylcarbazole) including the effects of sorbed oxygen
Authors: Pochan J. M. , Hinman D. F. , Nash R.
Published: February 2003

The dielectric relaxation spectrum of poly(N-vinylcarbazole) (PVK) and poly(3-chloro-N-vinylcarbazole) (CLPVK) have been investigated in the temperature range −180–+240 °C. Four relaxations are observed in PVK. The α relaxation (225 °C) is associated with the glass transition of the polymer. On the basis of oxygen-sorption experiments, the γ relaxation (∼−60 °C) has been associated with a rotational libration of the pendant carbazole group. It is also speculated on the basis of this work that an off-axis dipole is induced in the carbazole moiety by the sorbed O2 producing the dielectrically active motion about the symmetry axis of the carbazole moiety. The β (∼80 °C) and the δ (∼−160 °C) relaxations are assigned as carbazole wagging motions and localized backbone motions, respectively. These assignments are based on comparative work in the literature.
On the assignments of rotatory lattice modes in n-alkanes and polyethylene
Authors: Fanconi Bruno
Published: February 2003

Considerable discrepancy exists in the recent literature on the assignments of the rotatory lattice modes of the n-alkanes and polyethylene. New low-temperature Raman data are presented on orthorhombic n-alkanes and and on n-C36D74 and n-C16D34. Analyses of these data and the existing assignments show that the long-axis rotatory mode of the triclinic n-alkanes may be assigned to a weak Raman band at ∼ 50 cm−1; the Ag rotatory mode of polyethylene may be assigned to the Raman band at ∼ 130 cm−1 and the B3g rotatory mode to a weak Raman band at 108 cm−1.
Craze yielding of polycarbonate in N2, Ar, and O2 at low pressures and temperatures
Authors: Brown Norman , Imai Yasufumi
Published: February 2003

The tensile stress-strain behavior of PC was measured in mixtures of He, which is inert, and each of the following crazing agents: N2, Ar, and O2 at partial pressures of 0–1 atm and in the temperature range above 77 K. The yield point for crazing depends on temperature, pressure, and the shear yield point according to the following equation: σc/σs= (P exp(Q/RT)/P*)−1/12, where Q and P* depend on the gas. The values of Q are approximately the same as those for the adsorption and absorption energies as determined by theories and experiments. The maximum sensitivity of the craze yield point to the partial pressure of the crazing gas occurs at the lowest pressure for crazing. In the case of N2, a 1% change in the partial pressure can produce about a 0.45-ksi change in the yield point.
Validity of the Ehrenfest equation for a system with more than one ordering parameter: Critique of a paper by DiMarzio
Authors: Goldstein Martin
Published: February 2003

Davies and Jones have shown that if the configurational state of a liquid is determined by two or more order parameters that freeze in at the glass transition temperature Tg(P), the Ehrenfest relation, r=ΔβΔCp/TV (Δα)2=1, valid if there is one such parameter, is converted to an inequality r?1. DiMarzio has shown correctly that if the conditions ΔS=0 and ΔV=0 are satisfied at Tg(P), r=1 regardless of the number of order parameters. He has, therefore, concluded that if experimentally r≳1, the order-parameter concept is inapplicable to the glass transition. It is shown here that r≳1 implies that ΔS and ΔV cannot both be zero at Tg(P), and that there is extensive experimental evidence that the volumes of glasses depend on the pressure under which they were formed, implying ΔV≠0. It is concluded that the experimental observation r≳1 does not render the order-parameter concept inapplicable.
Hybrid Ising mean-field treatment of melt transitions: Application to polymethylene
Authors: Boyle F. , Taylor P. L. , Hopfinger A. J. , Simha R.
Published: February 2003

A hybrid Ising mean-field model is developed to account for the conformational and configurational origins of transitions in dense chain molecular fluids. The model is applied to polymethylene. The role of intermolecular interactions in controlling both the melt transition temperature and the extent of the degree of cooperativity is demonstrated. Near quantitative agreement of the transition-temperature and heat-capacity behavior is achieved when a linear correction term to describe interchain melting is incorporated in the general model.
Auger electron spectroscopy in sputtering measurements: Application to low-energy Ar+ sputtering of Ag and Nb
Authors: Smith Joe N. , Meyer C. H. , Layton J. K.
Published: February 2003

The sputtering of Ag and Nb by Ar+ in the energy range from 0.5 to 1.5 keV has been measured. The agreement with extant data, where available, is good. The experimental technique is a new adaptation of certain earlier methods and employs Auger electron spectroscopy of a continuously sputtered area of a thin-film composite structure, produced by vapor deposition. This new method should permit very low sputter yields (S≲10−3) to be measured in subsequent experiments.
Cobalt silicide layers on Si. I. Structure and growth
Authors: van Gurp G. J. , Langereis C.
Published: February 2003

Cobalt silicide layers have been grown by electron-beam vacuum deposition of Co onto Si wafers, and subsequent thermal treatment above 400 °C. The compounds Co2Si, CoSi, and CoSi2 were found by x-ray diffraction. The compounds grow as successive layers with a thickness ratio of about 3:1:0.1, as was found from comparison with powder diagrams. The silicide growth proceeds faster along grain boundaries. After prolonged heating the Co is consumed and the Co2Si thickness then decreases. Subsequently the Co2Si is consumed, the CoSi thickness decreases, and a growing CoSi2 layer is left. No significant preferred orientation was found in the three silicides, except in CoSi2, which exhibits a preferred 〈100〉 orientation, when grown on 〈100〉 Si for more than 3 h at 550 °C. Both from x-ray diffraction intensities and from thickness measurements it is shown that the growth of the Co2Si and CoSi layers, which is initially approximately linear with time, proceeds with a t1/2 dependence with an activation energy V of 1.75 eV. The growth is then presumably by Si diffusion through the silicide layers.
Optical investigation of stress in the central GaAs layer of molecular-beam-grown AlxGa1−xAs-GaAs-AlxGa1−xAs structures
Authors: Dingle R. , Wiegmann W.
Published: February 2003

From the analysis of exciton splittings and shifts in the 2K absorption spectra of central GaAs layers in molecular-beam-grown AlxGa1−xAs-GaAs-AlxGa1−xAs structures, the magnitude and sign of the layer stress is deduced. Annealing at 850 °C has little influence on the layer stress although large changes in photoluminescence efficiency are observed. Comparisons with similar LPE-grown structures and MBE-grown double-heterostructure lasers are made.
Comparison of experimental and calculated elastic-plastic wave profiles in LiF
Authors: Asay J. R. , Hicks D. L. , Holdridge D. B.
Published: February 2003

Precursor decay in pure LiF has been examined using a laser interferometer technique to measure particle velocity at the rear surface of specimens with thicknesses of about 1.1 and 3.5 mm. For an initial impact stress of about 2.5 GPa (25 kbar), the measured precursors were found to be essentially sharp shocks with rise times on the order 1–2 ns and with amplitudes of 0.25 and 0.24 GPa, respectively. The complete wave profiles measured experimentally have been fit with a characteristic code, employing the method of shock fitting. Good agreement between experimental and calculated results is obtained using a constitutive model based on the nucleation of dislocations at the shock front and subsequent expansion in the form of circular loops.
Effects of one-dimensional stress on piezoelectric ceramics
Authors: Meeks S. W. , Timme R. W.
Published: February 2003

Highly accurate data obtained from measurements on three different formulations of lead zirconate titanate piezoelectric ceramic material show the dependence of g33, d33, and KT33 on one-dimensional stress (applied parallel to the direction of polarization) to high values of stress (0–400 MPa). The constants for one type of ceramic vary with stress less than those of the other two types for high values of stress. A peak in the curve of tanδ as a function of T3 for two types of materials is a function of the material, and it is believed that the peaks are due to a phase transition from the ferroelectric tetragonal to the ferroelectric rhombohedral state. The experimental feasibility and practicability of using a reciprocity coupler to measure g33 and KT33 accurately as a function of one-dimensional stress to high values of stress has been established.
Polarization dependence of EM scattering from Rayleigh scatterers embedded in a dielectric slab. II. Experiment
Authors: Leader J. Carl , Dalton W. A. J.
Published: February 2003

A series of experiments was conducted to determine the effects of changes in albedo and optical thickness of a scattering medium of latex spheres on the measured scattering cross section (for various linear polarization combinations) and its angular distribution. The results of these experiments were compared with theoretical values of the scattering cross section per unit illuminating beam area calculated using a multiple scattering model that included the effects of multiple reflections between the surfaces of the slab medium. The theoretically calculated angular distributions were found to be in good agreement with corresponding measurements, and similar agreement was found between the calculated and experimental cross-section variation with albedo for the copolarized component at optical thicknesses of 0.1, 1.0, and 10.0. Although satisfactory correspondence between the calculated and measured cross-polarized component variation with albedo was noted for optical thicknesses of 1.0 and 10.0, significant discrepancies were apparent in the data obtained for an optical thickness of 0.1. These discrepanceis were attributed to dissimilarities between the experimental slab scattering medium and the slab scatterer assumed in the theoretical model.
Discharge characteristics and the analysis of a hollow cathode for a gas-discharge display panel
Authors: Matsuzaki Hideomi , Imahori Yutaka , Kamegaya Takeo
Published: February 2003

In the course of developing the gas-discharge display panel, the researchers investigated the discharge characteristics of a tiny hollow cathode operated under medium gas pressure and ascertained the presence of the ’’hollow-cathode effect’’. Under optimum conditions the cathode fall was lower by about 30%, and one order higher current density could be supplied than with a single plane cathode of the same size. Next, the experimental results were analyzed to obtain a few fundamental discharge parameters, in which the formulations of the cathode-fall characteristics in the cylindrical hollow cathod were given in advance. Thus the macroscopic hollow-cathode effect could be reduced quantitatively to the microscopic but comprehensive physical quantity Γ.
Contact electrification between insulators: Phenomenological aspects
Authors: Ruckdeschel F. R. , Hunter L. P.
Published: February 2003

A modified form of Peterson’s rotating Faraday cage is employed to study the dependence of electrification on the rate at which contacting insulator surfaces are separated. It is determined that the relevant parameters are the surface-charge densities and the perpendicular velocity of separation, independent of the size of bead used. Air-discharge and functional-heating effects were observed and avoided. Desorption experiments indicate that water plays a role in the electrification process of Al2O3 vs various glasses.
Beam-diameter correction of x-ray intensity profile over small diffusion zones
Authors: Lo C. C. , Schuele D. E.
Published: February 2003

The spatial broadening, due to the effective electron beam diameter, of an x-ray intensity profile as measured with a scanning electron microscope is corrected by the Fourier method. A technique is presented whereby a convergent series solution is obtained by adjusting the measured data within its random uncertainty. A numerical example along with two experimental results are presented to illustrate the method.
Electrical characteristics of metal/Si-Ge contacts
Authors: Pike G. E. , Sweet J. N.
Published: February 2003

Measurements and theoretical calculations have been made of the electrical properties of metal contacts to a polycrystalline Si-Ge alloy (80 at.% Si) for a wide variety of conditions. Thin-film contacts of W, Pb, and In have been formed on Si-Ge phosphorus doped in the range 2×1018−1×1020 cm−3. For P concentrations near 2×1019 cm−3 we have produced samples having several interfacial oxide thicknesses. We have heat treated W contacts to this material to simulate elevated-temperature aging effects of W thin-film contacts on thermopiles. The differential conductance for all these various contacts has been measured as a function of bias voltage for temperatures from 1.1 to 300 K. Calculations of the differential conductance of these contacts have been performed using a metal-insulator-semiconductor model that accounts for tunneling, thermionic field emission, and thermionic emission. The calculationg generally cover the ranges of temperature, bias voltage, doping level, and oxide thickness used in the experiments. Graphical summaries of these calculations are presented which include doping dependence of the zero-bias conductance ratio (300−4 K), the conductance values at several temperatures, and the location of the differential conductance minimum. Comparison of theory with experiment leads to the conclusion that the general features of the conductance characteristics can be predicted from the theory for certain ranges of oxide thickness and dopant concentration. Agreement appears to be best for thin oxides and P concentrations near 2×1019 cm−3, with both higher- and lower-doped contacts behaving qualitatively as if their effective doping levels were nearer this value. This effect has interpreted in terms of phosphorus depletion or enhancement mechanisms occurring in the Si-Ge depletion region during junction fabrication. When W contacts are hear treated after fabrication, agreement with theory improves. This believed to exhibit typical superconducting conductances at 1.1 K, thus showing that tunneling is, in fact, a major transport mechanism in Si-Ge/metal junctions.
Magnetic properties of the ThCo5−xNix system
Authors: Narasimhan K. S. V. L. , Do-Dinh C. , Wallace W. E. , Hutchens R. D.
Published: February 2003

Magnetic moments, Curie temperatures, and anisotropy fields are presented for ThCO5−xNix ternaries for temperatures ranging from 4.2 to 300 K. ThNi5 is a Pauli paramagnet. The Co moment in ThCo5 is 1.16 μB per atom. The reduction below 1.7 μB for elemental cobalt is ascribed to electron transfer from Th to Co together with shifts in the relative positions of the cobalt 3d subbands. The variation of anisotropy field with composition supports the notion that the magnetic anisotropy of ThCo5 originates largely with Co in the 2(c) sites. The coercive force, measured at 4.2 K, increases with nickel content attaining a value of 20 kOe for ThCo3.5Ni1.5. This alloy has at 4.2 K an energy product of 2.6 MG Oe.
Frequency dependence of the parallel and perpendicular ferromagnetic resonance linewidth in Permalloy films, 2-36 GHz
Authors: Patton Carl E. , Frait Z. , Wilts C. H.
Published: February 2003

Ferromagnetic resonance linewidth data for 75% Ni-25% Fe evaporated thin films at 2–36 GHz for both parallel and perpendicular orientations show that the two linewidths are the same and increase linearly with frequency above 10 GHz. At lower frequencies the parallel linewidth is in accord with the high-frequency behavior, but the perpendicular linewidth levels off at 10–30 Oe. These data suggest that the high-frequency relaxation is characteristic of a Landau-Lifshitz λ-type process but that the low-frequency losses are characteristic of a process intermediate between λ-type and 1/τ-type relaxation.
Comparison of Monte Carlo and continuous slowing-down approximation treatments of 1-keV proton energy deposition in N2
Authors: Porter H. S. , Green A. E. S.
Published: February 2003

Monte Carlo (MC) and continuous slowing-down approximation (CSDA) calculations of proton energy deposition are compared for the same set of detailed atomic cross sections (DACS). It is found that the MC and CSDA results for the gross features of energy deposition, such as the eV/ion pair, and efficiency for excitation of a given state, are in reasonably good agreement. The spatial apportionment of energy shows disparities, particularly for particles which have degraded to energies less than about 100 eV. Energy spreading of the proton beam is found to be appreciable in the MC calculation, but appears to have a relatively small influence on the spatial distributions of excitation in comparison with CSDA, especially for high-lying states. Range straggling is found in the MC calculations, but it also appears to have only a small influence on the final results when compared with CSDA. Significant differences appear in the mean proton and hydrogen beam fraction obtained from MC and from CSDA. For the convenience of applications, the proton and hydrogen differential flux at each depth in the gas obtained from the MC results is represented analytically.
Computer analysis of back-surface field silicon solar cells
Authors: Michel J. , Mircea A. , Fabre E.
Published: February 2003

A series of new metal-dithiene complexes absorbing in the near infrared were shown to Q switch the Nd-glass laser. Attempts to shorten the ground-state recovery time by heavy-atom substituents led to the preparation of a platinum complex which causes partial mode locking of the laser. The new Q-switch dyes are extremely stable towards infrared radiation.
Acousto-optic tunable filter with controllable passband
Authors: Fujii Y. , Hayashi H.
Published: February 2003

A new type of acousto-optic tunable filter, which utilizes noncollinear acousto-optic interaction, is proposed and demonstrated by using a PbMoO4 crystal. The most significant feature of this kind of optical filter is the capability of changing the bandwidth of the transmitted light. Theoretically up to a 22 Å filter bandwidth can be obtained for this PbMoO4 filter. Tuning from 7000 to 4000 Å can be obtained by changing the acoustic frequency from 75 to 105 MHz. The possibility of this kind of acousto-optic filter using the exceptionally slow shear wave propagating along the direction [110] in TeO2 is also discussed.
Conical topography formed on ion-etched crystalline surfaces
Authors: Witcomb M. J.
Published: February 2003

An equation based on ion channeling in a crystal is shown to predict the apex angle of cones formed on surfaces eroded by ions in the energy range 1–30 keV for 37 ion-target-energy combinations.
Impact welding and ripple formation
Authors: Rolsten R. Fred
Published: February 2003

Rippled metallic surfaces have been produced as a result of ballistic impact as well as the movement of high-pressure (explosive) gas over a metal plate. Such loading conditions produce a strong shock wave. Under the high pressure, metal plate surfaces are plastically deformed and sometimes are welded together. These welds are sometimes associated with a wavy (rippled) interfacial disturbance. There is no metallurgical evidence for the formation of a fluid jet. In addition to the incident and reflected wave due to impact, a Mach stem (wave) produced by acoustic focusing sweeps along the plate interface.
Critical state of bubbles in liquid-gas solutions
Authors: Tucker A. S. , Ward C. A.
Published: February 2003

According to homogeneous nucleation theory, the spontaneous formation of a bubble occurs in a liquid when a thermodynamic fluctuation of sufficient magnitude occurs to form a bubble of at least the critical size. Here we report the results of an experimental study of bubbles near the critical state. We examine both the stability of this state and the predicted value of the critical radius. Photographs of two bubbles simultaneously present in a liquid, one slightly larger than the critical size and the other slightly smaller, are presented. Subsequent photographs show the larger one to grow and the smaller one to dissolve. Hence the critical state is unstable and the critical radius lies between the initial radii of the two bubbles. A second series of tests was conducted to examine more carefully the value of the critical radius.
Photoconductivity of scandium-doped GaAs
Authors: Nakagawa H. , Zukotynski S.
Published: February 2003

The photoconductivity of high-resistivity Sc-doped GaAs was studied at room temperature and at 77 K. Uisng n-i-n and p-i-p structures, impurity levels at 0.57 and 0.87 eV above the valence band edge were identified. Measurements of the thermal activation energy and of the effect of strong illumination on the long-wavelength photoconductivity response was used to confirm the levels. An impurity-band model is presented. The transient photoconductivity response is discussed in terms of the interaction of the proposed impurity levels.
Amplified spontaneous emission of a molecular nitrogen laser excited by an intense relativistic electron beam
Authors: Luches A. , Perrone M. R.
Published: February 2003

Report of a study of the shape and length of the output pulse of a molecular nitrogen laser, excited by an intense relativistic electron beam, is described. The rate equations are computer solved, at first ignoring the spontaneous emission during the excitation process. Afterwards the rate equations are solved taking into account excitation functions of various shapes and lengths, related to electron-beam pulses of a few kA and a few nsec. Laser power output, energy, and peak-time, i.e., the time at which the gain reaches its saturated value, are given and discussed as functions of the intensity and rise time of the excitation functions.
High-intensity laser-beam effects on the spatial resolution of a streak camera tube
Authors: Kalibjian Ralph
Published: February 2003

The purpose of this paper is to present a model that explains the degradation in spatial resolution of a streak camera tube (SCT) at high laser-beam intensity. The model requires an understanding of (1) the aberration effects in the electron lens systems and (2) the surface-potential perturbation in the photocathode at high-intensity irradiation. The surface-potential perturbation in the laser-beam-irradiated spot on the photocathode gives rise to a diverging microlens (or ’’blooming’’ electrons) at the cathode-vacuum interface. Because of the electron-lens aberration, the irradiated spot at the photocathode is not perfectly focused at the SCT phosphor screen. Hence the resulting image on the screen is the magnified object of the ’’blooming’’ electrons that occur in the vicinity of the photocathode. Experiments with two different types of SCT having wide-angle and narrow-angle beam optics have demonstrated the validity of the blooming model.
Effect of operating rate on the arc duration of activated telephone relay contacts
Authors: Uhrig Thomas A. , Gray Eoin W.
Published: February 2003

A contact operating rate effect, or more correctly, a contact open-time effect, has been experimentally measured on palladium wire spring relay contacts breaking a 50-V 100-Ω nominally resistive load in an air-diethylphthalate (?5 ppm) environment. The steady-state average arc duration is almost constant at 100 μsec for open times greater than 1 sec, and is proportional to the square root of the open time for open times less than 1 sec. To test whether the observed critical open time of 1 sec could be the result of a slow drift of clustered organic ions to the contact surface, the ion drift velocity of the various positive and negative ions was measured. The slowest velocity (?60 cm/sec) was found to be a thousand times too fast to explain the open-time effect. However classical diffusion of the organics to the contact surface can explain the 1-sec open time. The functional dependence of the open-time effect has been predicted by a dynamic activation model; however, this model only considered organic adsorption on the contact metal surface rather than on the carbon particles, which is more likely. A new dynamic model of the over-all contact activation process is therefore developed for the activating organics being adsorbed on carbon together with a new form of carbon removal based upon the carbon particles being burned with the oxygen adsorbed on the carbon particles themselves. This model successfully predicts the form of the experimentally observed contact operating rate effect.
Pile-ups of circular twist disclinations
Authors: Chou Tsu-Wei , Pan Yen-Cheng
Published: February 2003

This paper first examines the regeneration mechanism of disclination loops. An example is then given to illustrate the multiplication and the subsequent pile-up of twist disclination loops at a phase boundary under a simple shear stress. The problem of disclination loop pile-up in a homogeneous medium is formulated by considering the total strain energy change in the formation of an array of n concentric loops, which include the disclination self-energy, interaction energy, and the work done by an externally applied moment. Numerical results of the stress concentration on the outermost loop and the total strain energy change are obtained as functions of the angle of twist per unit length of the specimen and the positions of pile-up loops. It has been concluded that the concept of twist disclination loop pile-up can be applied in a continuous medium where the Burgers vector of each loop can be assumed to be infinitesimally small. The restriction on the magnitude of disclination Burgers vector seems to have cast some doubt on the validity of the proposed disclination regeneration mechanism in crystals. The results of this paper can be readily extended to discuss disclination arrays on the basal planes of hexagonal crystals. Furthermore, when disclination loop arrays are formed parallel to a bimaterial interface, their equilibrium positions can be determined by taking into consideration the contribution of stresses from the image disclinations.
Linear and nonlinear optical properties of ferroelectric BaMgF4 and BaZnF4
Authors: Bergman J. G. , Crane G. R. , Guggenheim H.
Published: February 2003

These first measurements of the nonlinear optical properties of fluorides (BaMgF4 and BaZnF4) show these air-stable compounds to be noncritically phase matchable at room temperature for a 1.06-μ pump. The highly ionic compounds are also quite resistant to optical damage (∼109 W/cm2). The materials should find applications as frequency doublers in cases where spatial power distribution makes crystals with walk off less desirable and/or cases where high pump powers require crystals which are resistent to damage.
Diffraction losses in a laser-heated solenoid plasma
Authors: Steinhauer L. C.
Published: February 2003

A solution for diffraction loss of a laser beam propagating in a plasma light pipe is found by analogy to the tunnel effect of quantum mechanics. It is shown that diffraction tends to dissipate the beam layer by layer, working from the outside inward. A characteristic dissipation length can be defined for each layer of the beam. Diffraction is estimated for a very long narrow plasma relevant to the fusion reactor concept and is found not to be a significant loss mechanism.
Room-temperature operation and threshold temperature dependence of LPE-grown InxGa1−xAs homojunction lasers
Authors: Nahory R. E. , Pollack M. A. , Taylor D. W. , Fork R. L. , Dixon R. W.
Published: February 2003

InxGa1−xAs homojunction lasers prepared by liquid-phase epitaxy have been operated from below 77 °K to room temperature. Lowest thresholds were Jth=2000 A/cm2 at 77 °K and 290 000 A/cm2 at room temperature. The variation of threshold with temperature can be fit by either Jth∼T3 or Jth∼exp(T/67 °K) above ∼150 °K, and by Jth∼T2.3 at lower temperatures.
Lattice screw dislocation in a finite crystal
Authors: Jagannadham K.
Published: February 2003

The properties of a lattice screw dislocation in a finite crystal in the form of a strip are determined, taking into account the image forces. It is shown that the properties of a screw dislocation in a finite crystal differ markedly from those of a dislocation in an infinite crystal. When the crystal size becomes infinite the results of the present analysis agree with the results of the P-N model.
Effects of heat treatment and plastic deformation on the photoelectronic properties of high-resistivity GaAs : Cr
Authors: Lin Alice L. , Bube Richard H.
Published: February 2003

The effects on the photoelectronic properties of high-resistivity GaAs : Cr crystals of heat treatment in argon at 580 °C are investigated, with and without plastic deformation. With reference to a nondeformed heat-treated sample, plastic deformation at 580 °C to a radius of 3.2 cm (Ga bending resulting in an etch-pit density of 2.3×107 cm−2) increases the electron density in the dark, but decreases the electron mobility in both dark and light, and decreases the electron lifetime over most of the temperature range. These effects probably result from the interaction of dislocations with crystalline defects and from consequences of sample inhomogeneity. Such GaAs : Cr crystals were much more brittle with respect to As bending, and comparable deformation could not be obtained before fracture.
The static electrification of mixtures of insulating powders
Authors: Schein L. B. , Cranch J.
Published: February 2003

The experimental considerations for studying the static electrification of insulators in mixtures of insulating powders are discussed. This powder geometry is compared to the more traditional geometries and the techniques for measuring the charge exchange are critically examined. It is demonstrated that the measurement technique does not alter the static charge on the powder particles and that, in mixtures of two powders, the charge distribution among similar-sized smaller powder particles is narrow. This result suggests that a significant fraction of the ∼1010 particles have acquired the same static charge. Such regularity suggests that mixtures of insulating powders may be useful for studying the central problem in the static electrification of insulators, whether ions or electrons are transferred during the charge exchange process.
Electronic transport in amorphous germanium arsenides
Authors: Park Chan Jo , Mahan John E. , Shiah Ralph T.-S. , Vander Plas Hubert A. , Bube Richard H.
Published: February 2003

Electronic transport has been investigated in amorphous sputtered films of Ge0.54As0.46 and Ge0.38As0.62 through measurements of dark conductivity, photoconductivity, thermoelectric power, field effect, and optical absorption. Both electrons and holes participate in electronic transport with slightly greater contribution to conductivity from electrons. As a consequence the thermoelectric power is negative, and the field effect indicates two-carrier conductivity in the presence of about 1020 cm−3 eV−1 localized states at the equilibrium Fermi level in both materials.
Effect of phase-dependent conductivity on inductive weak links
Authors: Blackburn J. A. , Nerenberg M. A. H. , Forsyth P. A.
Published: February 2003

The effect of the cosφ term on the current-voltage characteristics of a Josephson weak link is calculated for a device with negligible capacitance but finite inductance.
Ultraviolet reflectivity and electron-energy-loss spectra of AgGaS2 and CuGaS2
Authors: Hengehold R. L. , Pedrotti F. L.
Published: February 2003

Ultraviolet reflectivity and reflection electron-energy-loss techniques have been used to determine the higher energy excitation spectra of the ternary compounds AgGaS2 and CuGaS2. The ultraviolet reflectivity spectra were obtained over the energy range of band gap to 11 eV, whereas the energy-loss spectra covered the range of band gap to 40 eV. The energy-loss measurements were made on both clean cleaved surfaces of these materials and on selectively contaminated surfaces. This technique allows distinction to be made between surface and bulk plasmon excitations. Surface plasmon energies of 14.0 and 13.5 eV and bulk plasmon energies of 18.5 and 19.0 eV were found for AgGaS2 and CuGaS2, respectively.
Superbroadening by electron plasma formation and optical breakdown in NaCl
Authors: Bräunlich P. , Kelly P.
Published: February 2003

The density of free electrons and its rate of change during the exposure of NaCl to intense picosecond laser pulses are calculated. It is shown that the anti-Stokes frequency sweep, shown by Bloembergen to be associated with a large change in the density of free electrons (electron plasma), is small up to laser intensities that cause intrinsic optical breakdown. In addition, damage thresholds for mode-locked pulse trains are calculated and compared with single-pulse thresholds. Experimental results reported by Penzkofer are explained satisfactorily by avalanche ionization.
Potential profiling across semiconductor junctions by Auger electron spectroscopy in the scanning electron microscope
Authors: Waldrop J. R. , Harris J. S.
Published: February 2003

Auger electron spectroscopy in an ultrahigh-vacuum scanning electron microscope is shown capable of the direct and quantitative measurement of potential profiles across biased semiconductor junctions. Profiles are obtained with submicron spatial resolution and subvolt potential resolution by measuring shifts of an Auger electron peak across a semiconductor device as a function of surface potential and spatial position. Experimental results on a GaAs p+-n junction diode for values of reverse bias between 5 and 25 V are in agreement with the potential profiles predicted by the depletion approximation model of a p-n junction.
Numerical computation of eddy-current effects in ferromagnetic maglev suspensions
Authors: Langerholc J.
Published: February 2003

Maxwell’s equations are reduced in the case of a ferromagnetic maglev suspension to three differential equations suitable for an iterative computation of the field distributions. No geometrical distortions or physical approximations are required. Some results of a three-dimensional relaxation program are discussed and compared with experiment.
The response of phase-sensitive detectors to Lorentzian and Gaussian lineshapes
Authors: Utton D. B.
Published: February 2003

Calculations are made of the response to Gaussian and Lorentzian lineshapes of a phase-sensitive detector operated at twice the modulation frequency. The modulation traverses the line resonance condition twice each cycle. Sensitivity to variations in linewidth, modulation width, and line center position are discussed. These are compared with the more common operation where small modulation widths result in signals proportional to the derivatives of the lineshape. A discussion is made of the effects on the phase-sensitive detector output of signals at the harmonics of the modulation frequency.
Stimulated electron−phonon−photon interactions in nondegenerate semiconductors considering energy−dependent carrier relaxation time
Authors: Agarwal A. K. , Sharma S. K. , Singh S. P. , Virmani S. K.
Published: February 2003

The energy−dependent relaxation time has been incorporated in the study of stimulated electron−phonon−photon interactions in nondegenerate semiconductors in the presence of the external dc electric field. The Boltzmann transfer equation has been used to obtain the gain constant. The results show that the percentage change in the gain constant is ∼15% (for ql<1, Eac=3 V/cm, Ω/ω=0.1, 〈vd〉=1.5 vs) and ∼30% (for ql≳1, Eac=30 V/cm, Ω/ω=2, 〈vd〉=2.0 vs) for moderate strengths of oscillating electromagnetic field (OEF). For weak OEF (Eac<ωvs/Ωμ for ql<1 and Eac <mΩ2/qe for ql≳1), no significant percentage change is observed in the gain constant in both frequency domains.
Properties of Rhodamine 6G in vapor phase
Authors: Sakurai Takeki , de Winter H. G.
Published: February 2003

Basic parameters of optical interaction in Rhodamine 6G in vapor phase are measured from the experimental result that the intensity of emission saturates with increasing intensity of pumping argon laser light. The quantum yield of fluorescence obtained in 0.13 and the cross section of absorption is 2.1×10−16 cm2 at a wavelength of 488 nm. The maximum vapor density obtained is in the order of 1015 cm−3 at a temperature of about 450 °C, the vapor pressure seems to saturate. From the results it is concluded that laser action of Rhodamine 6G in vapor phase requires pumping conditions that are not readily available.
Saturation and recovery of the direct interband absorption in semiconductors
Authors: Reintjes J. F. , McGroddy J. C. , Blakeslee A. E.
Published: February 2003

We report observation of dynamical saturation of the optical absorption in direct band−gap semiconductors using mode−locked pulses from a Nd: glass laser. The alloys were of the types InAsxP1−x and Ga1−yInyAs, with x or y chosen so that the direct band gap at room temperature was about 10 meV less than the laser photon energy. Increases in the transmission coefficient of epitaxial thin films by more than 4 orders of magnitude above the equilibrium value have been observed. Using a probe pulse with variable delay with respect to the strong bleaching pulse, we have studied the time dependence of the recovery of the absorption following bleaching and find it to be as short as 30 psec. Thus such alloys may be useful as saturable absorbers for mode locking visible and infrared lasers.
Standing spin waves in YIG spheres
Authors: Thomas G. , Komoriya Goh
Published: February 2003

This paper shows that the low−frequency modulation of the reflected power in YIG spheres is consistent with the interpretation of standing spin waves only if the wave vector is constant over a wide range of values of magnetic field in the subsidiary absorption region. Identical experiments on YIG disks show good agreement with the standing−spin−wave interpretation. The only difference in the experiment is the shape of the sample and its linewidth.