bluuebunny/crossref_metadata_2025 huggingface dataset:
A highly efficient light-trapping cell for Raman-scattering measurements
Authors: Hartley D. L. , Hill R. A.
Published: February 2004

We have discovered a simple optical system that makes use of a unique property of ellipsoidal mirrors, viz., light brought to one focus will be reflected alternately through the two foci and collapse to the major axis. Raman-scattered light from atmospheric N2 indicates that gains of the order of 100 should be achievable with this new system.
Temperature and frequency dependence of exchange anisotropy effects in oxidized NiFe films
Authors: Fulcomer E. , Charap S. H.
Published: February 2004

Hysteresis loops have been measured for thin NiFe films between 5 and 300 K using the magneto-optic Kerr effect. Films that are free of any surface oxide do not show a displacement of the easy-axis loop along the field axis, and the coercive force and anisotropy field are very weak functions of the temperature. Oxidized films show striking exchange anisotropy effects; displaced loops appear below a transition temperature ranging from 30 to 90 K as the film is more heavily oxidized. Loop width and anisotropy field increase with decreasing temperature, exhibiting a change in slope in the neighborhood of the transition temperature. The steady-state parameters have characteristic frequency dependences; with increasing frequency the loop displacement and anisotropy field increase and the loop width decreases in the range 0.05–100 Hz. The interpretation of these results in terms of thermal aftereffect taking place in the antiferromagnetic oxide is presented in a companion paper.
Thermal fluctuation aftereffect model for some systems with ferromagnetic-antiferromagnetic coupling
Authors: Fulcomer E. , Charap S. H.
Published: February 2004

A theoretical model is developed for, and applied to, some coupled-film systems consisting of an underlying ferromagnetic thin film and a surface layer of antiferromagnetic material viewed as an assembly of uniaxial small particles. The magnetization of the film biases, and is in turn biased by, the particles through an interfacial exchange coupling. Above a blocking temperature, dependent on size, particles are able to reverse rapidly due to thermal fluctuation, thus exhibiting superparamagnetic response. By assuming a physically reasonable distribution of particle sizes, good agreement is obtained between computed curves for temperature and frequency dependence of hysteresis loop displacement and coercivity based on this model and corresponding experimental results for oxidized Permalloy films, reported in a companion paper. This thermal fluctuation model is also applied successfully to the case of oxidized cobalt films as studied by Schlenker. In this case it is necessary to include in the analysis the temperature variations of the antiferromagnetic anisotropy energy and of the interfacial exchange coupling.
X-ray topographic determination of the absence of lateral strains in ion-implanted silicon
Authors: Tu K. N. , Chaudhari P. , Lal K. , Crowder B. L. , Tan S. I.
Published: February 2004

The lattice-to-amorphous transformation of Si caused by implantation of silicon ions results in volumetric expansion. The expansion is primarily in a direction normal to the substrate surface. We infer this from x-ray topographic analysis where no evidence of plastic flow in the region bounding the implanted volume was detected. By measuring the unidirectional expansion, the average density of the amorphous Si layer is found to be 3.8 to 5.6% smaller than that of crystalline Si.
Temperature dependence of second-harmonic generation in tellurium with a CO2 laser at 10.6 μ
Authors: Panyakeow S. , Tanigaki Y. , Shirafuji J. , Inuishi Y.
Published: February 2004

Temperature dependence of second-harmonic intensity in tellurium with a Q-switched CO2 laser at 10.6 μ was measured in the range 290–370 K. With increasing temperature the SHG intensity decreased rapidly, mainly due to the absorption loss of the fundamental wave. At room temperature the SHG efficiency of the order of 10−3 was achieved and d11 was estimated to be 1.7 × 10−6 esu.
Polymorphism of poly(vinylidene fluoride): potential energy calculations of the effects of head-to-head units on the chain conformation and packing of poly(vinylidene fluoride)
Authors: Farmer B. L. , Hopfinger A. J. , Lando J. B.
Published: February 2004

Potential-energy calculations have been used to investigate the effects of head-to-head defects on the chain conformation and packing of poly(vinylidene fluoride). The calculations have demonstrated that such positional isomerism can contribute to the polymorphism exhibited by PVF2. We have shown that increased concentration of head-to-head defects or tetrafluoroethylene comonomer can cause the phase-I form to become the favored structure for poly(vinylidene fluoride). The calculations have also proven capable of reflecting some of the subtle changes arising from the insertion of such defects. Packing calculations have shown that isomorphous replacement significantly affects the way in which PVF2 chains pack into a crystalline array. The differences in the structures proposed by Tadokoro and by Doll and Lando for phase II of poly(vinylidene fluoride) have been attributed to the inclusion of head-to-head defects in the polymer chains. In general, the potential-energy functions have proven useful qualitatively, if not semiquantitatively, in investigating the relation between chains in a crystal. Finally, these calculations have shown that both conformation and packing must be considered in determining the minimum energy structure for a polymer, and that these factors cannot be treated independently.
Elastic stiffnesses of copper-tin and copper-aluminum alloy single crystals
Authors: Moment Roger L.
Published: February 2004

The elastic stiffnesses of a series of Cu–Sn and Cu–Al alloys have been measured. Both C=c44 and C=(1/2)(c11−c12) decrease as Sn concentration increases. However for the Cu–Al alloys, C increases while C′ decreases. The results have been compared to those predicted by the theory of Fuchs. For the Cu–Al alloy the agreement is fair, while for the Cu–Sn alloy it is poor. Curvature in the plots of C and C′ vs composition is found mostly to be a consequence of the lattice parameter effect on the elastic stiffnesses. The effect due to alloying alone deviates only slightly from linearity for solute concentrations less than 8 at.%.
Bond distances and chain angle of hexagonal selenium at high pressure
Authors: McCann D. R. , Cartz L.
Published: February 2004

Integrated intensity measurements of the (100) and (101) x-ray diffraction peaks of hexagonal selenium at pressures up to 52 kbar have permitted a determination of the atomic positions so that the bond distances and chain angle have been obtained at high pressure. The near-neighbor bond distances along the Se chain remains essentially constant while the Se–Se–Se chain angle increases from 102.5° to 105.7°. The bond distance between the chains decreases by 9.7% at 52 kbar. The anomalous c-axis expansion observed under pressure is thus explained as an enlargement of the chain angle pivoting about approximately fixed bond lengths along the chain.
Perspex (polymethyl methacrylate) electrets
Authors: Natarajan S.
Published: February 2004

The decay of the heterocharge of Perspex thermoelectrets as a function of the applied field intensity was studied. This suggests that the decay of the heterocharge is not continuous but occurs in discontinuous jumps. Such a behavior suggests the formation of polarized aggregates that are superficially similar to Weiss domains, which appear to be dependent on the field strengths and temperatures employed in electret formation. The time required for the transition of the initial heterocharge to homocharge also depends on the field intensities and temperatures employed during formation. As the field strength increases the transition time decreases; as the formation temperature increases this time decreases.
Production of large hydrogen clusters in condensed molecular beams
Authors: Klingelhöfer R. , Moser H. O.
Published: February 2004

Intense hydrogen-cluster beams having velocities of about 500 m/sec can be produced by expansion of precooled hydrogen gas out of a nozzle into high vacuum. They are of interest for the compensation of particle losses in thermonuclear devices. The dependence of the penetration depth into the plasma on the velocity and the size of the clusters is still unknown. In order to study the influence of the latter the available beams should cover a range of cluster size as wide as possible. Using a cryostat which can be operated at temperatures above the critical one, the range has been extended by about three orders of magnitude up to a mean size of about 109 H atoms per cluster. The cluster sizes have been determined by light-scattering technique. This method is particularly useful during the injection of cluster beams into a plasma.
Preparation and properties of antireflection coatings by chemical vapor deposition
Authors: Hall Lou H.
Published: February 2004

Germanium films were deposited in the temperature region of 300 to 450 °C by the thermal decomposition of germane. Electron diffraction, electron microscopy, and infrared absorption studies were made on the films. The deposition parameters, germane concentration and growth temperature have a pronounced effect on surface topography and grain size and consequently on the infrared absorption. An increase in growth temperature results in an increase in grain size and surface roughness. This change in physical properties of the film results in a significant infrared absorption, 20% or greater depending upon the wavelength. Similarly, an increase in germane concentration causes an increase in grain size and surface roughness. Films were deposited on mechanically polished 〈111〉 silicon with 1000-Å oxide coating. The grain size is larger and more defined on the oxide substrates. Silane was thermally decomposed in the temperature region 525 to 575°C. The infrared absorption of the silicon films were obtained from transmission and reflectance measurements. Absorption was 5% or less for most of the films. Film properties, grain size, and surface topography, and effect of deposition parameters on growth of films for use as antireflection coatings by chemical vapor deposition are discussed.
Time-resolved spectral output of a doubly resonant cw optical parametric oscillator
Authors: Weller J. F. , Giallorenzi T. G. , Andrews R. A.
Published: February 2004

Time-resolved spectra from the output of a doubly resonant parametric oscillator (DRO) pumped by a cw laser are presented. Single-cluster operation of the DRO is observed for low pump powers and a simultaneous multicluster operation at higher pump powers. For the multicluster operation, oscillation by higher-order modes is also detected.
Dependence of microwave emission from indium antimonide on surface conditions and sample geometries
Authors: Kokoschinegg P. , Heinrich H.
Published: February 2004

The dependence of microwave emission from n-InSb on condition of the sample surface and the sample geometry has been investigated at average electrical field strengths lower than those necessary for avalanche breakdown to occur in the bulk of the sample. Results are interpreted in terms of the theory by Thompson and Kino, and King, by assuming that plasma is produced in regions of high fields near the contacts by end-contact shorting of the Hall field. It is shown that the strong anisotropy of the emission, when the magnetic field is rotated in the transverse plane, is caused by surface inhomogeneities and can be controlled by deliberately changing the surface conditions. This anisotropy of the emission is interpreted by the influence of the magnetoresistance on the diffusion of electron-hole pairs towards the surface of the sample. For a sample with circular cross section and properly etched surface, the emission is isotropic with respect to the position of the magnetic field in the azimutal plane. On the other hand, strong anisotropy is obtained for samples with rectangular cross section. The emission has been found to saturate with increasing sample length in accordance with the assumption that the contact regions play a predominant role. Samples with a Corbino-shaped geometry do not show any emission due to the absence of high electric field regions at the contacts.
Josephson weak links: shunted-junction and mechanical-model results
Authors: Hansma P. K. , Rochlin G. I.
Published: February 2004

We have investigated two models of a superconducting weak link which give physical insight into the behavior of many Josephson-effect devices. The first of these is a low-inductance oxide-barrier Josephson tunnel junction with an external resistive shunt; the second is a mechanical analog—a driven damped pendulum. The externally shunted junction acts as a generalized weak link in that, by adjusting its shunt resistance or critical supercurrent, it exactly replicates the dc electrical characteristics of many widely different weak links. In fact, we can readily alter its characteristic while the junction is immersed in liquid helium simply by applying a small external magnetic field of 1 Oe or less to decrease the critical current. The mechanical analog, by enabling us to observe the instantaneous behavior of the phase, gives new insight into the nonlinear properties of such weak links. The behavior of both models is governed by the second-order nonlinear differential equation independently proposed by Stewart and McCumber. These models not only verify the computer-generated solutions for weak links in detail, they give new physical insight into the underlying nonlinear behavior.
Anisotropy parameters and coercivity for sintered Co5Sm permanent magnet alloys
Authors: Benz M. G. , Martin D. L.
Published: February 2004

Saturation magnetization, intrinsic coercive force, anisotropy field, and anisotropy constants were determined for a sample of sintered Co5Sm at 4.2, 77, 300, and 500 °K. The ralationship between the temperature dependence of the coercivity and the anisotropy parameters is discussed.
Anisotropy and magnetostriction of germanium-substituted yttrium iron garnet
Authors: Hansen P. , Tolksdorf W. , Schuldt J.
Published: February 2004

The anisotropy, magnetostriction, and linewidth of germanium-substituted yttrium iron garnet single crystals of the composition {Y3−xMexII} [Fe2](Fe3−y−zMeyIVFezII) O12−δFδ(MeII=Ca2+,Pb2+,and MeIV=Ge4+,Si4+) have been studied by means of ferromagnetic resonance. Analysis data of Fe2+, Ge4+, and of the impurities Pb2+, Ca2+, Si4+ and F− are given for all crystals as well as optical-absorption coefficients in the wavelength range 1–2.5 μm. The resonance measurements have been carried out at 9.25 GHz in the temperature range 4.2–460 °K. A comparison of the temperature dependence of the anisotropy contributions caused by Fe2+ with the single-ion model leads to a good agreement. However, it has to be assumend that only one-third of the Fe2+ ions are effective. The contribution to the magnetostriction constants turns out to be positive for both λ100 and λ111. Maxima of the resonance linewidth were observed at about 40 and 370 °K.
Conduction in a random lattice under a potential gradient
Authors: Tunaley J. K. E.
Published: February 2004

A quasiclassical approach is adopted to find the time of traversal of a carrier across a random lattice. It is shown that probability distributions of the stable type are involved and that means and variances may be infinite under certain conditions of site spacing. These probability distributions are employed to find the spectral density of current or conductivity fluctuations which appear to be consistent with the observations on thin films and semiconductor devices.
Electric field induced anisotropy of iron thiospinel
Authors: Yamaguchi S. , Wada H.
Published: February 2004

Stoichiometric iron sulfide, Fe3S4, of spinel type (lattice constant, 9.87 Å) was elongated by about 0.05 Å along the [111] axis in an electrostatic field of 860 V/cm. This anisotropy induced at about 40 °C disappeared at about 100 °C. The experiment was carried out in terms of electron-diffraction procedure.
Reflection and transmission secondary emission from GaAs
Authors: Martinelli Ramon U. , Schultz M. L. , Gossenberger H. F.
Published: February 2004

Reflection and transmission secondary-emission ratios have been measured for a 3.5-μm-thick self-supporting GaAs film activated to negative electron affinity. A reflection-mode gain of 540 at 20 keV primary energy was observed. In transmission, the gain at 20 keV primary energy was 112. Analysis of the data gives the surface-escape probability as 0.18 and the electron-diffusion length as 3.0 μm. The data are well described by a simple diffusion-transport model.
The growth of nitrided surface layers by ion bombardment
Authors: Winters Harold F.
Published: February 2004

It is shown that bombardment of a tungsten surface with 300- and 450-eV nitrogen ions produces an altered surface layer whose saturation concentrations are 8×1015 and 9×1015 nitrogen atoms/cm2, respectively. Mechanisms involved in the formation and decomposition of these surface layers are discussed.
rf burnout in X-band Schottky mixers
Authors: Ahmad Khalid
Published: February 2004

The burnout energy for metal-silicon Schottky-barrier mixers using various metals was measured using calibrated TR cells. The burnout energy was highest with Pd–Si and Pt–Si diodes (0.3 erg/spike). Possible burnout mechanisms are briefly discussed.
Effect of magnetic field on sensitivity of silicon strain gauges
Authors: Singh Ved Ram , Parshad R.
Published: February 2004

The sensitivity of silicon strain gauge has been found to increase in a magnetic field, the increase showing a maximum at 2800 Oe for a particular gauge. At this field the increase is by a factor of 1.32. The results indicate a positive effect of magnetic field on the piezoresistance coefficients of semiconductors.
Chemical nature of phosphorus in Ni–P deposits
Authors: Randin J. P.
Published: February 2004

The composition of the as-plated Ni–P deposits, obtained by reduction of nickel ions with hypophosphite, is described as a metastable two-phase system containing Ni and Ni2P, with few, if any, elementary phosphorus as a solid solution in nickel. On heating, Ni2P reacts with nickel to form Ni3P. These results contradict recently published findings claiming an initial state containing a single-phase polycrystalline nickel in which the phosphorus is substitutionally dissolved in the fcc lattice of nickel. A possible explanation is given of the reason for the occurrence of a liquidlike structure.
Comment on ``Chemical nature of phosphorus in Ni–P deposits''
Authors: Pai S. T. , Marton J. P.
Published: February 2004

The apparent contradiction between the initial chemical state of Ni–P deposits of Randin et al. and Pai et al. is explained. The presence of free phosphorus is shown to depend on the deposition temperature. The changes of dc resistivity upon heating is claimed to be due to crystallization and to the formation of Ni3P regions in the films.
Dispersion relation for finite-amplitude plasma waves
Authors: Arunasalam V.
Published: February 2004

We follow the method of Karplus and Schwinger to obtain the nonlinear longitudinal dielectric coefficient for plasma waves, and then derive expressions for their nonlinear damping and frequency shift.
Ferroelectric and optical properties of Pb5Ge3O11 and its isomorphous compound Pb5Ge2SiO11
Authors: Iwasaki Hiroshi , Miyazawa Shintaro , Koizumi Hideo , Sugii Kiyomasa , Niizeki Nobukazu
Published: February 2004

The temperature characteristics of dielectric constants, spontaneous polarization, thermal-expansion coefficients, indices of refraction, and optical rotatory power of Pb5Ge3O11 single crystals have been investigated in detail from room temperature up to above the Curie temperature, 177°C. From the results of these measurements, the following constants were obtained: linear thermal-expansion coefficients (αa)F=7.75×10−6/deg°C and (αc)F=7.79×10−6/deg°C (ferroelectric phase), (αa)P=13.8×10−6/deg°C and (αc)P=13.4×10−6/deg°C (paraelectric phase); quadratic electro-optic constants g33T=0.47×108 cm4 /C2, g13T=0.37×108 cm4 /C2; and electrogyration coefficient γ33 =8.7 cm2/C. An isomorphous compound Pb5(Ge2O7)(SiO4) was synthesized and was found to be ferroelectric with T c=60°C and Ps=1.7 μC/cm2 at room temperature. Ferroelectric properties and electrogyration coefficient were studied in the solid-solution system Pb5(Ge2O7)(GeO4)1−x (SiO4)x.
Electro-optic properties of ferroelectric 5PbO · 3GeO2 single crystal
Authors: Uchida Naoya , Saku Tadashi , Iwasaki Hiroshi , Onuki Kota
Published: February 2004

Linear electro-optic coefficients of 5PbO · 3GeO2 have been measured at 6328 Å. The values obtained at room temperature are r11=0.27, r22=2.3, r13=10.5, r33=15.3, r41=0.6, r51=6, and rc=5.3 (in 10−12 m/V). The relatively small values make the material unattractive for practical applications. Temperature dependence of r22, r13, and r33 have been measured up to above Tc, and the behavior supports the previous deduction that the high-temperature phase is 6̄. It is found that the quadratic EO coefficients g13 and g33 are large compared with those for BO6 ferroelectrics and the values depend on the spontaneous polarization. The anomalous decrease of g13 and g33 has been observed in the vicinity of Tc.
Superlattice of voids in neutron-irradiated tungsten
Authors: Sikka V. K. , Moteff J.
Published: February 2004

Transmission electron microscopy of tungsten irradiated at about 550°C to a fast neutron fluence of approximately 1×1022 neutrons cm−2 reveal the formation of a superlattice of voids. The void lattice parameter is 195 Å and the lattice parameter to average void size is about six. Both the formation of the superlattice and the temperature dependence of the lattice parameter in tungsten, a material considered to have isotropic elastic properties, is in contradiction to present theories based on the elastic anisotropy of the host metal.
Radiation trapping in laser diodes
Authors: Ettenberg M. , Lockwood H. F. , Sommers H. S.
Published: February 2004

This paper is concerned with the problem of cavity geometries which exhibit anomalously low radiative efficiencies. While the ideas presented apply to any type of cavity, the experiments and discussion refer specifically to the type of cavity of importance in commercial injection lasers, a Fabry-Perot cavity with cleaved end facets and sawed sidewalls. In this study, it is shown that the lowering of the external efficiency is probably associated with the excitation of internally circulating modes, analogous to those found in lasers with four cleaved sides. A dual-cavity diode structure is employed to demonstrate that it is the sidewall loss which controls the excitation of the internally circulating modes. To determine the geometric conditions for internal mode excitation in single and double heterojunction diodes, an extensive study was made of the combination of length, width, and facet reflectivity which lead to efficiency decreases. It is assumed that the internal modes are excited when the distributed sidewall loss for the internal modes is less than the distributed Fabry-Perot end loss for the externally radiated modes. The conditions for internal mode excitation and accompanying efficiency decrease are predicted by either assigning an empirically determined attenuation factor to the sawed side or assuming that the loss is associated with diffraction from small mirror segments at the sidewall which have been formed during the sawing operation. These predictions may be used to design Fabry-Perot sawed sidewall injection lasers so as to avoid efficiency loss through the excitation of internal modes.
Normal-mode analysis of anisotropic and gyrotropic thin-film waveguides for integrated optics
Authors: Yamamoto Sadahiko , Koyamada Yahei , Makimoto Toshio
Published: February 2004

This paper is concerned with thin-film optical waveguides using anisotropic and gyrotropic materials, which may play an important role in the field of integrated optics. As a fundamental problem on such waveguides, normal (propagating) modes are analyzed here by the Rayleigh-Ritz variational technique. The analysis can be interpreted directly in terms of coupling of normal modes of the basic guide with simpler material parameters. Results are placed in the form of a matrix eigenvalue problem suitable for computer calculation, whose eigenvalues and eigenvectors lead to propagation constants and field expansion coefficients, respectively. Characteristics of anisotropic guides are discussed and compared with those of conventional isotropic guides. As a typical application TE↔TM mode converters are analyzed in some detail and numerical examples are presented.
Evidence for a primarily nonradiative Si,O defect in GaP
Authors: Bachrach R. Z. , Lorimor O. G. , Dawson L. R. , Wolfstirn K. B.
Published: February 2004

Experimental evidence is presented to establish the existence of a Si,O defect impurity system in GaP. This defect is shown to be a strong nonradiative recombination center in n-type material. A photoluminescence band near 1.55 eV at room temperature has been associated with the Si,O defect.
Molecular image resolution in electron microscopy
Authors: Uyeda Natsu , Kobayashi Takashi , Suito Eiji , Harada Yoshiyasu , Watanabe Masaru
Published: February 2004

In order to determine the ultimate molecular resolution attainable with a conventional electron microscope, the direct observation of hexadecachloro-Cu-phthalocyanine molecules was attempted. Since phthalocyanine derivatives are known to form crystalline films with columns of parallel stacks of planar molecules, the specimens were prepared by epitaxial growth on KCl cleavage face through vacuum evaporation so that the column axis was directed almost normal to the thin-film surface holding an orientation suitable for the observation. The molecular orientation was determined by Patterson synthesis based on the laser optical transform of the electron diffraction pattern obtained from the individual crystallites placed on the microgrid mesh. The direct observation was carried out with the 100-kV electron beam incident on the specimen along the column axis. The crosslike images arrayed in a centered rectangular net were clearly resolved, well representing the molecular shape of phthalocyanine with the configuration like a four-leaf clover. The effect of the spherical aberration and the defocus value for the objective lens are also discussed in relation to the contrast inversion of the total images. It was also found that the chlorinated Cu-phthalocyanine is 40 times more resistant to the electron radiation damage than the ordinary phthalocyanines.
Crystal Growth and Properties of Boron Monoarsenide
Authors: Chu T. L. , Hyslop A. E.
Published: February 2004

Boron arsenide, a semiconductor with an energy gap of 1.46 eV, decomposes irreversibly at temperatures above 900 °C, thus limiting the temperature of the crystal growth process. In this work, single crystals of boron arsenide, identified by the x-ray diffraction method, have been prepared by the chemical transport of polycrystalline boron arsenide in the presence of a temperature gradient. The transported crystals are p type and have a resistivity of approximately 0.01 Ω cm in the temperature range 77–500 °K. The hole concentration and Hall mobility, essentially independent of temperature in the range 77–300 °K, have been estimated to be in the ranges of 1018–1019 cm−3 and 100–400 cm2V−1sec−1, respectively. In spite of the high carrier concentrations, the transported crystals are suitable as substrates for the epitaxial growth of boron arsenide with controlled dopant distribution.
Effect of Plastic Deformation on Magnetomechanical Damping in Nickel
Authors: Frank R. C. , Christensen S. M. , Nelson S. E.
Published: February 2004

Magnetomechanical damping measurements were made at 77, 210, and 296 °K on pure nickel wires that were plastically deformed by elongation. There is a dramatic reduction in the damping maxima between 0 and 1% elongation. Beyond 1% elongation only a small further reduction of the damping is observed. The curves of the damping maxima plotted against percent elongation were higher at the lower temperatures. The experimental data were compared with results predicted by a theoretical expression suggested by Smith and Birchak with fairly good agreement.
Analysis on the Pulse Propagation of Exchange-Dominated Spin Waves in Ferrimagnetic Materials
Authors: Sawado Eikichi
Published: February 2004

It is well known that in the exchange spin-wave region the observed spin-wave line width ΔHk is proportional to the wave number according to Kasuya and LeCraw. In disk-shaped samples magnetized perpendicular to the plane of the disk, the propagating wave packets remain as pure spin waves when the relation Bi(r1)Hi(i)−[Bi(0)+Dkcr2][Hi(0)+Dkcr2]<0 holds (Eshbach). Within this region a theoretical formula for evaluating the proportionality constant of the spin-wave linewidth ΔHk is derived from the theoretical analysis of the distortion and spreading of the ``truncated sine wave.''
Ionization of a Background Gas by a Weak (ν/γ≪1) Relativistic Electron Beam
Authors: Swain David W.
Published: February 2004

The injection of a relativistic electron beam into a neutral gas creates a background plasma. A simple model is presented for this process, which includes (a) direct ionization of the gas by the high-energy electrons; (b) ionization of the gas caused by the acceleration of secondary electrons in the axial electric field of the beam. A self-consistent calculation of the conductivity and the electric field in the beam is carried out. The predictions of the model are compared with an experiment on a 2-MeV 4-kA beam of 100-nsec duration, injected into helium at 0.2–2.0 Torr. Results indicate that the theory agrees with experimental observations at lower pressures, but tends to deviate from experimental values at higher pressures.
Electric Fields and Forces due to Charged Dielectrics
Authors: Sessler G. M.
Published: February 2004

The electric fields of a sheet of charged dielectric positioned between two parallel metal electrodes are calculated assuming the presence of gaps between dielectric and both electrodes. The charge distribution within the dielectric is assumed to consist of a quasipermanent space charge and a quasipermanent dipole polarization, both being arbitrary functions of the coordinate normal to the electrodes and slowly varying functions of the other coordinates. The plane of zero field in the dielectric and the forces on the electrodes and on the dielectric are also calculated.
Impact Ionization of Donors in Semiconductors as a Tool for Photoluminescence Investigations
Authors: Schairer W. , Stath N.
Published: February 2004

Impact ionization of impurities can serve as a tool for investigations of radiative recombination mechanisms in semiconductors. Additional information can be obtained on the degree of compensation. The effectiveness of the method is demonstrated for n-type GaAs. Four different bands are proved to be caused by donor-acceptor transitions. The degree of compensation is found to be high in our samples.
Plasma Diagnostics Using CO2 Laser Absorption and Interferometry
Authors: Offenberger A. A. , Kerr R. D. , Smy P. R.
Published: February 2004

Absorption of CO2 laser radiation is experimentally shown to be a useful plasma-diagnostic technique, spatially, temporally, and quantitatively. Electron densities determined from absorption agree well with shock-produced plasma values. Comparison of densities obtained via absorption, interferometry, and Langmuir probes in a plasma jet also show good agreement in magnitude and spatial dependence.
Exact Solutions for the Temperature Rise in a Laser-Heated Slab
Authors: Brugger K.
Published: February 2004

The mathematical treatment of laser machining involves the solution of the equation of heat conduction under conditions which generally impose the use of either approximate or numerical methods. Therefore, it seemed of interest to investigate the heating of an infinitely extended slab of finite thickness for various configurations of the laser beam for which exact solutions can be found. In particular, solutions are given (i) for beams with a Gaussian profile and for pencil-shaped beams (intensity a radial step function) decaying exponentially, and for their limits of very fast (surface source) and very slow (radial heat flow only) decay, and (ii) for beams with radially constant intensity (axial heat flow). For the latter, the case of the slab resting on a substrate is considered by means of a modified image method for planar sources, enabling us to find all solutions by the superpositon of the well-known result for point sources.
Thermal Conductivity of Liquid InSb and Liquid Ga
Authors: Seidensticker R. G. , Rubenstein M.
Published: February 2004

The mean thermal conductivity of liquid gallium was measured as 70 ± 7 W m−1 K−1 over the range 250–550 °C. For indium antimonide, Kl = 2.04Ks at the melting temperature with Kl = 9.23 W m−1 K−1 as a reasonable absolute value.
Persistent Photodielectric Lens Effect in Cadmium Sulfide
Authors: Kanarek K. B. , Wyche C. D. , Pine A. S.
Published: February 2004

A persistent negative lens is induced in high-conductivity cadmium sulfide by illumination with low-power 6328-Å laser light at temperatures above 100 °C. The lens is erasable by annealing at higher temperatures.
Critical-State Model of Bulk Flux Pinning in Pb–40Tl
Authors: Walmsley D. G.
Published: February 2004

The Bean-London critical-state model is applied to the calculation of magnetic hysteresis in Pb–40Tl. Two forms of the model are investigated in which the flux-line-pinning force density αp has the field dependences αp = α0(Hc2 − H)/Hc2 (law I) and αp = α0B1/2(Hc2 − H)/Hc2 (law II). Intrinsic diamagnetism is carefully included in the calculation. The formulation of the problem is general to all type II superconductors but the numerical results are specific to Pb–40Tl. Both the main hysteresis loop and subloops are computed. Experimental results are presented. After allowing for the effects of surface hysteresis, there is good agreement with the calculations based on law I but not with those based on law II. Critical fields for Pb–40Tl at 4.2°K are Hc1 = 96.4 ± 6 Oe, Hc2 = 2884 ± 35 Oe, Hc = 330 ± 4 Oe, and the three Ginzburg-Landau parameters are in good agreement: κ1 = 6.18, κ2 = 6.15, κ3 = 6.1 ± 0.2.
Cleaving of MgO inside an Electron Microscope
Authors: Shinozaki S. , Sato H.
Published: February 2004

A method for preparing clean surfaces of the (100), (111), and (110) orientations of MgO directly at the specimen chamber of an electron microscope and thin enough for transmission electron microscopy is described. The cleaving is accomplished by thermal shock due to a flash electron bombardment. The cleaved crystals are suitable as substrates for in situ observation of surface reactions like epitaxial growth. The cleavage mechanism is also discussed.
Decay of Surface Potential in Insulators
Authors: Kanazawa K. Keiji , Batra I. P. , Wintle H. J.
Published: February 2004

The potential decay due to injected carriers in the presence of thermal carriers of an insulator which has been initially electrostatically charged is investigated. The problem was originally formulated by Wintle, but the effect of thermal carriers on the observables (e.g., surface potential) was not calculated. We calculate these effects and correct some inconsistencies in an earlier work.
Empirical Formulation of Thermionic Converter Electrode Performance
Authors: Smith John R. , Smith Arthur L.
Published: February 2004

A simple empirical equation giving the electron emission current density in terms of the cesium arrival rate and the electrode surface temperature is presented. Oxygen effects are discussed. Applications of the equation are reported.
Gain Saturation Measurements in CO2, TEA Amplifiers
Authors: Franzen Douglas L. , Jennings Donald A.
Published: February 2004

Measurements of gain in CO2, TEA pulsed amplifiers operating at a pressure of 330 Torr are described. The energy gain in traversing a small amplifying section decreases to one-half the small-signal value at an energy flux density of 1.2Jcm−2.
Generation of Stacking Faults and Dislocation Loops in Silicon Wafers
Authors: Prussin S.
Published: February 2004

Thermal oxidation of silicon is shown to result in the generation of stacking faults and dislocation loops at a damage-free polish-etched surface provided the silicon wafer is subjected to a prior thermal treatment. If a fresh damage-free surface is created following the preoxidation thermal treatment, only dislocation loops are generated. The concentration of both types of defects are strongly affected by the cooling rate from the preoxidation thermal treatment.
Quantum-Limit Piezoresistance of n-Type Inversion Layers of Silicon and Germanium
Authors: Ito Ryoichi
Published: February 2004

Piezoresistance effects at small and large stresses in n-type inversion layers of germanium and silicon are discussed by taking proper account of the surface quantization. It is predicted that the quantum-limit condition peculiar to the inversion layer strongly affects the piezoresistance on Si {100}, {110} and Ge {111}, {110} surfaces.
On the Hall Voltage in an Inhomogeneous Material
Authors: Heleskivi J. , Salo T.
Published: February 2004

The Hall effect has been considered in an inhomogeneous material consisting of low-resistivity grains separated by thin layers of high resistivity. It has been shown, in contradiction to another recently presented model, that the Hall effect gives the carrier concentration of the low-resistivity grains and can consequently be used to distinguish between a ``numbers'' mechanism and a ``barrier'' mechanism for photoconductivity in a material.
Reply to ``On the Hall Voltage in an Inhomogeneous Material''
Authors: Bube Richard H.
Published: February 2004

Considerations beyond those discussed for the simplest model of a resistive-network model by Heleskivi and Salo indicate that the Hall effect may well be an ambiguous technique for discrimination between a ``numbers'' and a ``barrier'' photoconductivity model.
Determination of Material Relaxation Properties from Measurements on Decaying Elastic Shock Fronts
Authors: Asay J. R. , Fowles G. R. , Gupta Y.
Published: February 2004

A theoretical method for the reduction of measurements on the decay of elastic precursor shock fronts is presented. The method yields values of the initial pressure-volume relaxation path behind the front; it requires no assumptions about the form of the constitutive relation. The method is illustrated by application to data on lithium fluoride.
Suggested Modification of the P-α Model for Porous Materials
Authors: Carroll Michael , Holt Albert C.
Published: February 2004

We suggest that the relationship between the pressure P in a porous material and the average matrix pressure Pm in the material should be P=Pm/α, where α is the ratio of the specific volumes of the porous material and the matrix material.
Pressure- and Strain-Sensitive Pressure Derivative of the Shear Strength of OFHC Copper
Authors: Abey A. E.
Published: February 2004

OFHC copper disks were sheared at one pressure to a given strain and then strained at a second pressure to a final strain. From these stress-strain curves, the change in shear strength resulting from only a pressure change with no additional strain, ΔτI, was determined. This change was found to be a function of both the pressure at which shearing takes place and the strain at which the pressure change takes place. The results indicate that ΔτI varies, to a first approximation, in the same manner as the shear strength.
Influence of Oxygen-Vacancy Complex (A Center) on Piezoresistance of n-Type Silicon
Authors: Littlejohn M. A. , Loggins C. D.
Published: February 2004

Recent experimental studies have shown a unique temperature dependence near room temperature for the piezoresistance of electron-irradiated n-type silicon. These reported results do not agree with any existing models for piezoresistance. This paper presents a theoretical effort to explain this effect, along with further experimental work to verify the theory. It is shown that the presence of the oxygen-vacancy complex (a defect created by electron radiation and commonly referred to as the A center or Si-B1 center) leads to a temperature-dependent component of the piezoresistance in addition to that component due to the stress-induced intervalley transfer of conduction electrons. This additional component is due to a depopulation of the A-center defect level, and is a direct result of the compensation of the donor atoms by the A-center acceptor level. In addition to the effect of carrier compensation of piezoresistance by the A center, the model also includes the effects due to relaxation-time changes with stress along with population transfer. The splitting of the A center defect level with stress is an important part of the model. The model developed is compared to experimental data between 250 and 360°K, and the agreement is found to be quite good.
Infrared-to-Visible Conversion by Rare-Earth Ions in Crystals
Authors: Johnson L. F. , Guggenheim H. J. , Rich T. C. , Ostermayer F. W.
Published: February 2004

An analysis of infrared conversion to visible and ultraviolet radiation by Yb3+–Er3+, Yb3+–Ho3+, and Yb3+–Tm3+ ions in crystals is presented. The expression for the visible power output in the presence of back transfer from the active ion to the energy-transferring ion (Yb3+) is given and the relationship between the intermediate state transfer and back transfer coefficients for maximum output is found. If this relationship is satisfied the visible output in the presence of back transfer is equal to the maximum output with no back transfer. The behavior of the power output when the transfer and back transfer coefficients depart significantly from this optimum condition is examined and the parameters which govern the power output under these conditions are determined. The analysis is applied to Yb3+–Er3+, Yb3+–Ho3+, and Yb3+–Tm3+ ions in BaYF5 and BaY2F8. Measurements on the brightest composition of Yb3+–Er3+ ions in BaYF5 indicate that the advantage of a long-lived intermediate state is diminished by back transfer. A power-conversion efficiency of 0.1% has been obtained for the green emission from BaYF5:Yb3+–Er3+ when pumped by 0.93-μ radiation from a 17% efficient Si–GaAs diode. Conversion efficiencies of 0.03% are obtained for the green emission from BaY2F8:Yb3+–Ho3+ and for the blue emission at 4800 Å from BaYF5:Yb3+–Tm3+. Efficient conversion of 1.5-μ radiation to the visible by BaYF5:Er3+ is also described.
Xerographic Discharge Characteristics of Photoreceptors
Authors: Chen I. , Mort J.
Published: February 2004

The xerographic discharge characteristics, i.e., surface potential vs exposure (light intensity × time), of photoreceptors have been studied theoretically. The effects of field dependence and sublinear flux dependence of the carrier supply and that of space charge perturbation are considered. These effects are found to extend the dynamic range of the photoreceptors.
Dependence of Threshold Current Density and Efficiency on Fabry-Perot Cavity Parameters: Single Heterojunction (AlGa)As–GaAs Laser Diodes
Authors: Ettenberg M. , Kressel H.
Published: February 2004

A detailed study was made of the dependence of the threshold current density and the external differential quantum efficiency on the cavity end loss in single-heterojunction laser diodes. To eliminate possible errors introduced by studying lasers of varying lengths, this study relied on changes of the facet reflectivity by SiO coatings of appropriate thickness. The results are consistent with a linear relationship between the threshold current density and the gain coefficient at threshold. The values of the gain factor, absorption coefficient, and internal quantum efficiency at 300 and 77°K are in excellent agreement with some of the previous studies. However, for effective end losses greater than ∼50 cm−1 the differential quantum efficiency shows an anomalous effect by decreasing with increasing end loss instead of increasing as predicted by simple theory. This effect occurs at 77°K as well as 300°K and is tentatively attributed to internal trapping of the stimulated emission.
High-Current Superconductive Pressure Contact Studies
Authors: Winter J. J. , Breslin J. T. , Gaulé G. K.
Published: February 2004

Superconductive switches with a high-critical-current (100–200 A) capability have been shown to be practical. Materials thought most likely to be effective as high-critical-current pressure contacts were tested. The effects of oxidation, preloading at room temperature, and transverse magnetic fields on the critical-current capacity of contacts were studied. The relationship of the critical current of the junction to its normal-state resistance is investigated for Pb contacts.
Magnetomechanical Damping and Magnetic Properties of Iron Alloys
Authors: Birchak J. Robert , Smith George W.
Published: February 2004

This work investigates experimentally a recent model of magnetomechanical damping based on a distribution of internal stresses, verifies some predictions and extends the model. Damping results are reported for cast irons and iron alloyed with silicon or germanium. As predicted, the maximum magnetomechanical damping ψmax is inversely proportional to the strain amplitude which produces ψmax. To explain the relatively slow decrease of ψmax with superimposed static shear stress or external magnetic field, the model must be modified to account for stress components or demagnetizing fields. By considering stress components along magnetization directions on opposite sides of a domain wall, we introduce a technique for describing the effect of single-crystal and grain orientations. This description qualitatively explains why bars with random grain orientations have larger damping in bending than in torsion. Although models relating damping to magnetic properties are in-exact, damping correlates experimentally with permeability and magnetic energy loss. These correlations are qualitatively explained by arguing that the 90° walls governing damping are less mobile than the 180° walls governing magnetic properties.
Electromagnetic Effects in Magnetic Insulators
Authors: Weiner Maurice
Published: February 2004

Electromagnetic modes are capable of strong coupling to magnetostatic modes in magnetic insulators. For certain ranges of magnetic field bias (or, equivalently, sample dimension), the two modes interact and lose their identity. This composite mode has been investigated both experimentally and theoretically. The experiment centered on the modes found in a small YIG sample coupled to an electromagnetic resonator in the form of a rutile disk and on the modes in a large YIG sphere (which forms its own electromagnetic resonator). Coupled-mode theory was applied to the experimental results. The theory has been extended to include the effects of relaxation, nonlinearities, and mode segregation, i.e., the frequency separation of the coupled mode from the allowed frequencies in the low-frequency spinwave manifold (e.g., ferromagnetic or acoustic ferrimagnetic spinwaves). A careful study has been conducted on these segregated modes. Experimental results show that for sufficiently strong coupling the observed mode undergoes a reduction in magnetic loss and a sharp increase in nonlinear threshold, in accordance with the theoretical behavior of a segregated mode.
Acoustoelectric Gain in Magnetic Fields
Authors: Lebwohl P. A. , Carlson D. G. , Mosekilde E.
Published: February 2004

The acoustoelectric attenuation in nondegenerate semiconductors in a magnetic field is usually expressed as an infinite sum of modified Bessel functions. We transform this sum into an exact integral expression. From this expression we derive a simple approximation that is valid at small magnetic field strengths B and coincides with the zero magnetic field attenuation, calculated independently, if we allow B to approach zero. This integral expression has an essential singularity at B = 0; therefore the small magnetic field behavior cannot be described by a power series expansion in B.