bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic Propagation in the Presence of Drifting Carriers and an Oscillating Electromagnetic Field
Authors: Pantell R. H. , SooHoo J.
Published: February 2004

A theory for amplification of acoustic waves in the presence of dc and oscillating electric fields in a piezoelectric semiconductor is developed. Acoustic gain constants for both ksl≪1 and ksl≫1 are derived, where ks is the wave vector for the acoustic wave, and l is the mean free path for the electron in the piezoelectric medium. As expected, the expressions for the gain constants reduce to those for the ordinary acoustic amplifier case when the applied oscillating electromagnetic signal is zero. The theory indicates that it is possible to transfer modulation from the electromagnetic wave to the acoustic wave.
Effect of Longitudinal Magnetic Field on Acoustoelectric Amplification in n-InSb
Authors: Gorelik J. , Zinman M. , Fisher B. , Many A.
Published: February 2004

Appreciable enhancement of the acoustoelectric gain by longitudinal magnetic fields is observed in the classical regime (ℏωc<kT). The enhancement increases monotonically with magnetic field, reaching saturation at fields corresponding to ωcτ being equal to a few units. The dependence of the magnetoacoustic enhancement on carrier concentration is analogous to that of the longitudinal magnetoresistance, both are more pronounced the lower the carrier concentration. The observed effect of the longitudinal magnetic field on the acoustic gain is similar to that reported for the acoustic attenuation in the quantum limit (ℏωc≫kT), but for the regime studied (ℏωc<kT) no theory has as yet been developed.
Observation of Propagating Domain in Semiconductive CdS Using the Optical Probe Method
Authors: Yamamoto Keiichi , Yamada Masayoshi , Abe Kenji
Published: February 2004

The optical modulation has been observed in semiconductive CdS single crystals at room temperature by means of the optical probe method using a monochromatic light. The light transmitted through materials with a wavelength corresponding to the intrinsic absorption edge was strongly modulated. The optical modulation observed here is caused primarily by the acoustic flux rather than by the high electric field in the domain. The acoustic domain arrives at its full growth near the point 2 mm from the cathode and travels towards the anode. The aspect of the acoustic domain is subjected to the variation by the strength of the applied electric field, and the domain velocity varies from 2.2×105 cm/sec to 3.0×105 cm/sec according to the increasing applied electric field up to 3040 V/cm.
Linear and Nonlinear Attenuation of Acoustic Surface Waves in a Piezoelectric Coated with a Semiconducting Film
Authors: Ingebrigtsen K. A.
Published: February 2004

The interaction of acoustic surface waves in a piezoelectric with carrier waves in a semiconducting film on the surface is considered. Particular attention is paid to the limitation of the small signal theory due to nonlinear effects. It is found that large signal effects, which occur at moderate acoustic power levels, are important when the maximum rf charge density exceeds the available background charge density. Measurements of acoustic attenuation and acoustoelectric current in a CdS film on the surface of Y-cut quartz are reported. A fair agreement between theory and experiment is found.
Radiation Transport Calculations-``Fore and Aft'' Approximation
Authors: Daley J. T.
Published: February 2004

An approximate method for describing radiation transport is derived. Photoelectric effect and Compton effect are assumed to be the only mechanisms affecting the transport. Thus the method is restricted to the x-ray and low-energy gamma-ray region of the electromagnetic spectrum. Further, the radiation is assumed to be a collimated beam incident normal to a homogeneous semi-infinite slab. The method described goes one step beyond the classical ``straight-ahead'' approximation used in the theory of gamma-ray attenuation. Because of the assumptions used in obtaining the solution, the expressions derived can most appropriately be applied for the case where Compton scattering is near isotropic (relatively low energies) and where the photoelectric cross section is larger than the Compton cross section.
Effect of Reflecting Boundaries on the Transport of Resonance Radiation. II. Comparison with Diffusion Theory
Authors: Weinstein M. A.
Published: February 2004

The generalized Holstein-Biberman transport theory developed in Part I is used to calculate the effect of reflecting walls in increasing the decay time of Doppler broadened resonance radiation in cylinders and slabs. The results are compared with the corresponding results obtained from the Cayless diffusion theory for optical thicknesses between about 20 and 3000. It is shown that the Cayless theory grossly underestimates the effect over the entire range, giving values for the fractional increase in decay time which are too small by about a factor of 3 at the smaller optical thicknesses, and too small by about a factor of 30 at the larger thicknesses. The discrepancy is shown to arise partly from the inaccurate boundary condition used in the Cayless theory and partly from the inapplicability of the mean free path concept to processes involving the transport of resonance radiation. The consequences for the behavior of low-pressure mercury rare-gas discharges are discussed, and it is estimated that wall reflectance must begin to have a significant effect on the characteristics of such discharges at reflectances as low as 20% rather than at the 50% reflectance predicted by the Cayless theory.
Crystal Growth and Galvanomagnetic Properties of Mg2Pb
Authors: Stringer G. A. , Higgins R. J.
Published: February 2004

A method for growing single-crystal Mg2Pb is described. A Bridgman method is used, starting with a nonstoichiometric melt (<31.3 at.% Pb). This requirement follows from the recent discovery that Mg2Pb is not congruently melting but forms from a peritectic reaction. The usefulness of an x-ray microprobe for the analysis of crystal growing problems is demonstrated by a study of eutectic inclusions observed in some Mg2Pb ingots. Measurements are reported of the angular dependence of the magnetoresistance and the magnetic field dependence of the Hall coefficient in fields up to 5200 G and at temperatures of 4.2° and 77°K. The phenomenological coefficients, b, c, and d, determined from the angular dependence of the magnetoresistance show strong field dependence at 4.2°K and obey the symmetry condition for [100] oriented many valley ellipsoids at all fields and temperatures. The Hall coefficient exhibits a strong field dependence, similar to p-type Ge, which has been fitted by a simple model consisting of two spherical bands. The mobilities and carrier densities obtained by fitting the data from several well-annealed samples to the two-band model are μ1≥7×104 cm2/V·sec, n1≃7×1017 holes/cm3, μ2≃3×103 cm2/V·sec, n2≃4×1020 holes/cm3 at 4.2° K.
Electrical Resistivity of Amorphous Ni–Pd–P Alloys
Authors: Maitrepierre Philippe
Published: February 2004

Ternary alloys containing nickel, palladium, and phosphorus have been obtained in an amorphous form by rapid quenching from the liquid state. These alloys contain from 13–73 at.% Ni, 15–20 at.% P with Pd adding up to 100%. The electrical resistivity of these alloys has been measured from 4.2°K to about 850°K, which is close to their melting point. A Kondo effect, probably due to very small concentration of iron impurities, has been observed in all the alloys below 15°K. Between 15° and about 40°K, the resistivity increases with temperature like T2 and then linearly up to about 550°K. The very small temperature coefficient of resistivity (around 10−4/°C) is attributed to the high degree of structural disorder in the amorphous alloys. Above about 570°K, the amorphous alloys transform progressively into crystalline phases, The variation of electrical resistivity with temperature in specimens heated at rates of about 1.5°C/min was correlated with structural changes observed by x-ray diffraction.
Ionized Impurity Density in n-Type GaAs
Authors: Wolfe C. M. , Stillman G. E. , Dimmock J. O.
Published: February 2004

Total ionized impurity densities (ND+NA) from 7×1013 to 3×1017 cm−3 are determined for epitaxial samples of n-type GaAs by analyzing mobility and carrier concentration data as a function of temperature with the Brooks-Herring formula for ionized impurity scattering. This procedure results in the determination of a temperature range within which the effects of other scattering mechanisms are minimal and gives values of ND and NA which are in good agreement with impurity densities obtained from analyses of the temperature variation of the Hall constant. These results are then used to determine empirical curves relating the impurity density to the 77°K Hall mobility. With these data a good estimate of the total ionized impurity concentration in a sample can be determined from Hall constant and resistivity measurements at 77°K.
Energy of a bcc Iron Deformation Twin Boundary
Authors: Nilles J. L. , Olson D. L.
Published: February 2004

By thermal grooving, the energy of an α-iron deformation twin boundary was determined and compared with the energy of an α-iron annealing twin boundary. The stacking fault energy was approximated and compared with that of other bcc iron alloys.
Stacking-Fault Model for Stoichiometry Deviations in LiNbO3 and LiTaO3 and the Effect on the Curie Temperature
Authors: Nassau K. , Lines M. E.
Published: February 2004

Several arrangements are suggested to explain deviations from stoichiometry in LiNbO3 in a recent report by Lerner, Legras, and Dumas. These arrangements are considered to be unlikely, and an alternative mechanism in terms of partial stacking faults is proposed for LiNbO3 and LiTaO3. A microscopic statistical theory of ferroelectricity, which is outlined, can predict the variation of the Curie temperature with changes in the bonding forces and atomic masses. Using this approach, the stacking-fault model is consistent with the observed variation of Curie temperature with composition.
Alternating Current Electrical Properties of Highly Doped Insulating Films
Authors: Simmons J. G. , Nadkarni G. S. , Lancaster M. C.
Published: February 2004

Metal-insulator-metal systems are discussed in which the insulator is highly doped and in which Schottky barriers exist at the metal-insulator interface. An equivalent circuit for the system is proposed and the ac electrical characteristics derived. It is shown that the capacitance is extremely temperature and frequency dependent. At high frequencies or low temperatures the capacitance is thickness dependent and equal to the geometric capacitance. At low frequencies and high temperatures it is thickness independent and equal to the Schottky barrier capacitance, which is determined by the doping density. Several methods of determining the activation energy of the donor centers from experimental capacitance versus frequency and temperature curves are suggested. The parallel equivalent conductance is also shown to be extremely frequency and temperature sensitive. It is found to have a pronounced maximum in both cases, which increases in magnitude and occurs at higher temperatures the thicker the insulator.
Electrical Properties of Evaporated Molybdenum Oxide Films
Authors: Nadkarni G. S. , Simmons J. G.
Published: February 2004

Thin film capacitors of MoO3 are found to be extremely temperature and frequency dependent. Changes in capacitance are reported as high as 60:1 over a temperature range of 100°C (at constant frequency) and over a two-decade frequency range (at constant temperature). At lower temperatures and higher frequencies the capacitance corresponds to the geometric capacitance, but at higher temperatures and lower frequencies the capacitance is independent of the film thickness. Conductance and quality factor of the films are also observed to be extremely frequency and temperature sensitive. The results are explained in terms of Schottky barriers existing at the metal-insulator interfaces, which arise due to the autodoping of the insulator, occurring during deposition of the films, by excess molybdenum. Excellent agreement is found to exist between the experimental data and the theory developed in the previous paper, and this correlation permits determination of the doping density (≃1018 cm−3), the donor depth (≃0.27 eV), and the width of the Schottky barriers (≃160 Å), among other properties of the films.
Model for the Resistive-Conductive Transition in Reversible Resistance-Switching Solids
Authors: Cook Earl L.
Published: February 2004

A model is given for the resistive-conductive transition in an amorphous or crystalline bistable resistance switch. The model is based on the observation that the current path in the switch is filamentary. The hypothesis is that the switching current heats the filament, and the resistive-conductive transition occurs only after the filament has achieved a critical temperature Tc. The predictions of the model are in excellent agreement with experimental observations of the resistive-conductive transition in single-crystalline Cu2O.
Quantization of Electromagnetic Radiation Fields in Moving Uniaxial Media
Authors: Kong J. A.
Published: February 2004

Radiation fields in moving uniaxial media have been quantized without introducing auxiliary potential functions. Hamiltonian and momentum operators are diagonalized in momentum space and written in terms of annihilation and creation operators of the photon state. It is found that two types of photons corresponding to classical ordinary and extraordinary waves will exist, and they are called ordinary photons and extraordinary photons. Physical interpretations of the various results are discussed.
Electromagnetic Radiation in a Time-Varying Plasma
Authors: Monroe Richard L.
Published: February 2004

The problem of representing electromagnetic fields in an electron plasma subjected to large and rapid electron-density variations due to transient ionization processes is considered. The inherently nonlinear character of this problem, which arises in the Maxwell-Euler equations through the electron transport term ▿· (nV), is retained under the assumption that temporal variations of the electron density n are of first order in magnitude while spatial variations in n are of second order. That is, we asume V·▿n≪n▿·V and consequently, ▿· (nV)≃n▿·V, where V is the induced velocity field. With the aid of vector and scalar potentials, it is shown that, in this case, the set of ten coupled Maxwell-Euler equations describing a cold, isotropic, lossy, electron plasma with current and ionization sources can be reduced to a set of five integro-differential equations which are effectively decoupled. A method of solving these equations based on perturbation techniques is sketched for the case where the initial electron density is zero.
Numerical Analysis of Field Emission and Thermally Enhanced Emission from Broad-Area Electrodes in Vacuum
Authors: Farrall G. A.
Published: February 2004

Calculations have been made of the collective field emission and thermally enhanced emission from a multiplicity of emitters in order to simulate the properties of large-area electrodes in vacuum subjected to high voltages. The individual emitters were assumed to be noninteracting. In one set of calculations, the individual emitters comprising the groups were characterized by randomly selected values of β, work function, and projection height lying between the limits of 50 and 200, 4.4 to 5.0 eV, and 0.5×10−4 and 10−3 cm respectively. In other computations values of work function and projection height were fixed at 4.5 eV and 5×10−4 cm respectively and values of β determined from an assumed normal distribution with a central value of 100. It is the intent of this work to show the behavior of these collections of emitters in detail. Although the collective emission from these groups yielded an apparently straight-line Fowler-Nordheim plot, computed values of effective β and effective emitting area varied noticably with field. At low field the effective β is closely similar to the maximum value of β in any given collection of emitters. As the field is increased, the effective β declines while effective emitting area increases. The change in effective β over an average field ranging from 100 to 500 kV/cm is typically 5%–10%.
Charging of Dust Particles by Impact
Authors: Cheng L. , Soo S. L.
Published: February 2004

The basic mechanism by which dust particles are charged through impact was studied. Redistribution of charges during impact was described in terms of the dynamics of the impacting bodies, and the properties of the materials of the contacting surfaces. An electrostatic probe theory was developed and applied to three cases: single particles, clouds of particles, and turbulent suspensions. Experiments were performed with pulverized coal dust suspended in air, a principal area of application of the electrostatic probes utilizing impact charging. Results showed that the electrostatic probe provides an accurate means for monitoring the flow rate of particles in a dusty suspension.
Activation Energy Spectra for Nonlinear Relaxation Processes
Authors: Kimmel R. M. , Uhlmann D. R.
Published: February 2004

The first approximation analysis for deriving activation energy spectra from relaxation data, originally derived for linear distributed relaxation processes, is shown to be valid as well for nonlinear distributed processes. The analysis is also applied to nonlinear, undistributed processes and found to indicate a spectrum of activation energies with a maximum at the characteristic energy of the single process. The characteristics of spectra resulting from nonlinearities are considered, and a procedure for evaluating the possible physical significance of derived activation energy spectra is considered.
Thermal Conductivity of Some Amorphous Polymers Below 4°K
Authors: Choy C. L. , Salinger G. L. , Chiang Y. C.
Published: February 2004

The thermal conductivity of three amorphous polymers has been measured between 0.4° and 4°K. The thermal conductivity of all samples has a similar temperature dependence, nearly temperature independent near 4°K and decreasing with an increasing power of the temperature as the temperature decreases. At the lowest temperatures the thermal conductivity is proportional to the three-halves power of the temperature. Above 1.2°K the data can be explained by resonant scattering; however, below 1.2°K, the data are not explained by existing theories. Between 2° and 4.2°K, the heat capacity is calculated from thermal diffusivity measurements. The data obey a T3 law but the magnitude is about 100% higher than that calculated from sound velocity measurements indicating an excess specific heat.
Thermal Lens Effect in CdS
Authors: Thomas G. , Sopori B. L.
Published: February 2004

In this paper we present a theory to explain the observed lens effect produced by a photocurrent in Cds. An applied dc voltage causes local heating due to the presence of a localized photocurrent produced by a focused laser beam. The local heating causes an increase in the index of refraction and hence focusing. The theory predicts that the magnification should be linear in the power dissipated by the photocurrent and these predictions fall very near the measured values of magnification for different values of photoconductance, with no fitted parameters. In order to explain the threshold effect observed in some Cds samples the change in the index of refraction with temperature of Cds is measured over a temperature range of 20°–350° and is found to be dN/dT=1.5×10−4 (°C)−1.
Interaction of High-Intensity Laser Beams with Metals
Authors: Chun M. K. , Rose K.
Published: February 2004

The interaction of high-intensity laser beams with metals has been analyzed on the basis of detailed quantitative measurements of the energy balance. The interaction of normal (not Q-switched) pulses with energies ranging from 1 to 30 J from a Nd-doped glass laser with metals having a variety of thermal and optical properties was studied. The time-dependent radiation reflectance of the metals, measured during the laser pulse, is found to account for most of the incident power in the initial stages of the interaction. As time progresses, much of the incident power is absorbed. It was found that the greatest part of the absorbed radiation energy is used to remove material in the liquid and vapor phases. Due to a large heat of vaporization for most metals, the amount of energy required to remove a given mass is strongly dependent on the relative amounts removed in the liquid and vapor phases. To determine this ratio, the total mass of material and the mass of molten material were measured.
Dynamics of Dislocation Dipole Motion in the Flux Line Lattice of Type-II Superconductors
Authors: Kramer Edward J.
Published: February 2004

The motion of flux line dislocation (FLD) dipoles is shown to be a more important mechanism for flux transport than the motion of individual FLDs. The electric field generated by FLD dipoles moving at a terminal velocity v is E=(Bbys)Λv,where B is the magnetic induction, b is the magnitude of the Burgers vector, ys is the separation between the individual FLDs in each dipole, and A is the density of moving FLD dipoles. The terminal velocity is found to be proportional to (J-Jc), where Jc is a critical current density. The analogy between the above equation and the corresponding equation for the plastic-shear strain rate in metals is explored in order to qualitatively explain yield phenomena and time-dependent hysteresis in E-J curves. Possible FLD dipole sources and the portion of experimental E-J curves likely to be affected by FLD motion are also discussed.
Nuclear Resonance in Ferromagnetic Chromium Tribromide: Applications to High-Precision Thermometry in the Range 2°–25°K
Authors: Senturia Stephen D.
Published: February 2004

Precise measurements of the temperature dependences of the 53Cr, 79Br, and 81Br nuclear resonance frequencies in ferromagnetic chromium tribromide have been carried out between 4.2°K and the Curie temperature (32.56°K). The resonances are found to be sensitive and reproducible indicators of temperature. Several of the resonances can be used for thermometers with millidegree sensitivity in the range 2°–25°K. This range includes the 4°–14°K range between the hydrogen and helium vapor-pressure curves, where a reliable secondary standard is needed.
Electron Energy Straggling Measurements for Thick Targets of Beryllium, Aluminum, and Gold at 4.0 and 8.0 MeV
Authors: Lonergan J. A. , Jupiter C. P. , Merkel G.
Published: February 2004

Energy spectra of electrons transmitted through targets of Be, Al, and Au were measured for incident electron energies of 4.0 and 8.0 MeV. The target thicknesses corresponded to ⅕ or ½ the range (calculated in the continuous slowing-down approximation) for the incident electron energy. Transmitted electron spectra were measured as a function of emission angle in the forward hemisphere using a magnetic spectrometer. Angular distributions and energy spectra are compared with results calculated with a Monte Carlo computer program (the NBS ETRAN-15 program). The calculations agree with the experimental data within the experimental error of measurement, except for the aluminum target where spectral comparison agree but there exists a normalization discrepancy. A spectral shift is observed in the data from a beryllium target.
Effects of Neutron Irradiation on the Optical Properties of Thin Films and Bulk GaAs and GaP
Authors: Pankey T. , Davey John E.
Published: February 2004

GaAs and GaP thin film and bulk samples have been irradiated with neutron fluences of 1018 nvt and the effect on the optical absorption edge and free carrier region determined. In the case of both GaAs and GaP films, which exhibit bulk or near bulk optical properties before irradiation, large optical absorption edge shifts of ∼0.3 and ∼1.5 eV, respectively, are caused by the neutron bombardment. These optical absorption edge shifts can be ``annealed out'' by high-temperature vacuum annealing; in the case of the GaAs films, isochronal annealing points to a Frenkel-pair annihilation mechanism. Bulk samples of GaAs and GaP, similarly irradiated, exhibit smaller optical edge shifts than the films with substantially different quantitative behavior. High-temperature vacuum annealing of the bulk samples also results in a recovery of normal optical properties.
Optical Properties of β′ Phase CoAl, CoGa, and NiGa
Authors: Kiewit D. A. , Brittain J. O.
Published: February 2004

The optical properties of β′ phase CoAl, CoGa, and NiGa were studied as functions of composition and photon energy in the spectral region from 0.7 to 6.3 eV. Similar investigations were conducted on NiAl between 0.7 and 2.0 eV. The specimens were prepared by a mechanical polishing technique that was shown, by the use of annealing studies, to produce surfaces from which reliable optical data could be taken. Measurements were made by the use of two polarimetric techniques on a reflectometer that was designed by the authors. The results of the optical measurements indicate that some of the investigated alloys show free electron behavior in the infrared, although the limited spectral region of investigation did not permit the authors to apply the Drude free electron theory to the data with confidence. The possible presence of hybridized plasma oscillations is indicated by structure in the loss function. The prominent optical absorption structure which is displayed by these materials in the visible and ultraviolet regions of the spectrum, and which indicates the presence of interband transitions, has been interpreted by the use of a simple rigid band model.
Strength of Near-Perfect Single Crystals of Cadmium
Authors: Crump J. C. , Mitchell J. W.
Published: February 2004

The ultimate strength of thin single crystals of cadmium has been measured. The crystals were initially completely free from dislocations and other imperfections, in so far as this could be established by observations with the electron microscope. They were grown from the vapor in an atmosphere of argon and had surfaces parallel to {0001} and {011̄0} planes,[2̄110] axes, and uniform rectangular cross sections. The crystals were strained in the electron microscope with a pneumatic tensile device, and the maximum elastic strain which they would sustain was determined directly from measurements of diffraction patterns. The near-perfect crystals failed at measured elastic strains between 3.8% and 4.5% along the[2̄110] direction. The corresponding normal stress was also measured directly with the tensile device. When the elastic strain along the[2̄110] axis of tension is 4%, the resolved shear stress on the glide systems which could be activated varies between G/11 and G/15, where G is the relevant shear modulus. This is within the range of estimated theoretical maximum strengths of crystals for deformation by a homogeneous shear process.
Electroabsorption and Internal Fields in ZnS Crystals
Authors: Shachar G. , Brada Y. , Alexander E. , Yacobi Y.
Published: February 2004

Electroabsorption (EA) measurements on ZnS crystals were performed. The electric fields were applied parallel to the polar c-axis. In single-crystal regions the EA was found to be independent of the sense of the electric field. On the other hand, in those crystals which contain various polytypes and stacking faults and exhibit an anomalous photovoltaic effect the EA was strongly dependent on the sense of the electric field with respect to the crystallographic polarity. From the spectral and field dependencies of the EA it was concluded that there exist in these crystals internal fields which are uniquely related to the crystallographic polarity. The sense of the electric fields in the various structures was determined. The strength of the fields was found to depend on the structure composition of the crystals; fields up to 105 V/cm were estimated. The existence of opposing internal fields, as found in this work, verifies the assumption of several authors in explaining the anomalous photovoltaic effect in ZnS crystals.
X-Ray Production in Laser-Heated Plasmas
Authors: Bernstein M. J. , Comisar G. G.
Published: February 2004

The efficiency of converting focused laser radiation into kilovolt x rays by means of a high-z planar plasma has been calculated. For electron temperatures of several keV, the rapid expansion of the plasma limits the effective absorption and reradiation times to a few tenths of a nanosecond. This short time limits the fractional degree of ionization to 30%–60%, depending on the temperature, for heavy target ions such as gold, and in this case the predominant ions have ionization energies less than the electron temperature. For plasma temperatures of 3 up to 10 keV the total radiation output will range from 6 down to 2 times that of plasma bremsstrahlung alone. The conversion efficiency is relatively insensitive to the laser frequency and to the plasma temperature, and amounts to 2%–5%. Overall efficiency for a Nd-glass laser system turns out to be about 10−3.
Microwave-Induced Ionization Oscillations in a Resonant Plasma Column
Authors: Mendel C. W. , Stern R. A.
Published: February 2004

A low-frequency oscillation excited when a low-pressure mercury dc discharge is illuminated near the first thermal Tonks-Dattner resonance with a moderately powerful microwave field has been investigated. It was found to be a relaxation oscillation involving enhanced ionization and coupling of the plasma column to the microwave circuit.
Investigation of the Sputtering of Aluminum Using Atomic-Absorption Spectroscopy
Authors: Stirling A. J. , Westwood W. D.
Published: February 2004

The techniques of atomic-absorption and emission spectroscopy have been used to detect atoms ejected from an aluminum cathode which is sputtered in a glow discharge in argon. The rate of deposition of the sputtered material is measured using a piezoelectric microbalance which is capable of measuring deposition rates as small as 9.2×10−8 G min−1. The use of atomic-absorption spectroscopy is shown to be a sensitive and reliable method for the study of the sputtering process. Experimental results indicate that some of the sputtered material in the glow discharge exists in the form of ``molecules.'' However, the absolute numbers of sputtered atoms has not been determined due to uncertainties in the tabulated values of atomic-transition probabilities.
Breakdown Phenomena in Silicon p-n Junctions Under Magnetic Field
Authors: Mehta S. C. , Parshad R.
Published: February 2004

The effect of magnetic field on the reverse characteristics of silicon alloy junction diodes in the breakdown condition has been studied. The breakdown voltage caused by internal field emission has been found to remain unchanged under a magnetic field (maximum field used 15 kOe). On the other hand, the breakdown voltage occuring by avalanche ionization increased by about 15 mV on the application of a magnetic field. In the post-breakdown region, while the magnetic field caused no change in current in diodes breaking down by the former mechanism, it increased the current (at constant voltage) in diodes having avalanche type of breakdown. Explanations of the observed results have been given.
Photothermoelectric Effects in Semiconductors: n- and p-Type Silicon
Authors: Harper James G. , Matthews Herman E. , Bube Richard H.
Published: February 2004

The ability of thermoelectric power measurements to permit a description of carrier-density and phonon-drag variations caused by photoexcitation was tested in 100-Ω·cm n- and p-type silicon. At low temperatures the major effect of photexcitation is to decrease the phonon-drag contribution to the thermoelectric power by increasing the phonon density in the crystal. At higher temperatures the thermoelectric effect can be used to investigate changes in the electronic contribution due to photoexcitation. An apparently anomalous increase in thermoelectric power with photoexcitation was consistently found in p-type silicon over an intermediate temperature range.
Ohmic Contacts to Silicon Carbide
Authors: Shier John S.
Published: February 2004

We have studied a number of metal alloys in a search for improved ohmic contacts to SiC. A Cu–Ti eutectic alloy wets SiC at 880°C forming a shallow contact which is ohmic on p-type SiC. An Al–Si eutectic wets SiC at 900° to 1000°C giving a contact which is ohmic on p-type SiC; the penetration is 300 to 500 Å.
Characteristics of a ZnS:Pd:Cs2O Cold Cathode
Authors: Swank Robert K.
Published: February 2004

Schottky-barrier cold cathodes have been fabricated using Pd on n-type ZnS. The Pd was deposited in the form of a film 30–50 Å thick on the freshly-cleaved surface of the ZnS in an ultrahigh-vacuum system, and cesiation was carried out without removal from the system. Cold emission currents up to 0.01 A/cm2 were obtained with an efficiency as high as 1.5%. Barrier height measurements indicate that the electrons enter the junction at an energy level 0.5 eV above the vacuum level, but current characteristics reveal a loss process not yet identified.
Epitaxial Growth of Gallium Phosphide on Cleaved and Polished (111) Calcium Fluoride
Authors: Cho A. Y.
Published: February 2004

The mechanism of growth of GaP on a cleaved CaF2 (111) surface was studied in situ in a high-energy reflection electron diffraction system. It was found that in the early stages of growth, GaP forms tetrahedral nuclei with {111} faces. The three edges of the tetrahedron are parallel to the three 〈110〉 directions. These microcrystals coalesce and form a smooth film after a mean thickness of more than 300 monolayers of GaP is deposited on the surface. Temperatures for epitaxial growth of a single crystal without twinning as a function of the atom arrival rate were studied for GaP on a clean CaF2 surface and on a GaP-covered CaF2 surface. It was found that growing GaP without twinning on a bare cleaved CaF2 surface requires a temperature ∼65°C higher than on a surface that is covered with GaP. The structural characteristics of the GaP film as a function of the substrate temperature are also discussed.
Structure of the Blast Wave with Ionization
Authors: Wu S. T. , Fu T. S.
Published: February 2004

The structure of a blast wave with ionization at local-thermodynamic-equilibrium (LTE) is analyzed by using the method of successive approximation to the non-similar solution. It is found that ionization has a significant effect on the decaying speed, and the first-order approximation. Numerical results are presented for plane, cylindrical, and spherical blast waves.
Use of Auger Electron Spectroscopy in Determining the Effect of Carbon and Other Surface Contaminants on GaAs–Cs–O Photocathodes
Authors: Uebbing John J.
Published: February 2004

Auger electron spectroscopy has been used to measure quantitatively the amount of carbon contamination on GaAs–Cs–O photosurfaces. It appears that approximately one monolayer of carbon is sufficient to reduce the photoyield to zero.
Electronic State of Iron Ion in Hemoproteins
Authors: Tasaki Akira
Published: February 2004

To study the relationship between biological function and the electronic state of the central Fe atom of hemoproteins, magnetic susceptibilities have been measured down to pumped liquid-helium temperature. It was found that the magnetic susceptibility of ferric and ferrous hemoglobin is sensitive to the sample preparation. From EPR measurements of hemoglobin, it was concluded that this fluctuation of the magnetic susceptibility is due to a high-spin to low-spin transition induced by a conformational change of the protein molecule. For ferrous hemoglobin (pH = 7), it was found that fine structure of the lowest ground-state energy level is described by the spin Hamiltonian D Sz2 (D = 4 cm−1). The field dependence of magnetization of this compound was measured up to 50 kOe at 4.2°K in a superconducting magnet. By determining the deviation from the linear relationship between magnetization and magnetic-field strength, splitting of the lowest ground-state energy level was shown to be represented by the same value of D.
Local Moment Formation in Dilute Alloys
Authors: Brog K. C. , Jones Wm. H.
Published: February 2004

59Co NMR measurements in a series of alloys consisting of 0.3 to 1.2 at.% Co dissolved in TixMo1−x and NbxMo1−x hosts, where 0≤x≤0.4, have been used to demonstrate that the continuous decrease in the average moment on the Co impurities with increasing Ti (Nb) concentration in the host does not result from a continuous decrease in the moment value of each Co ion but rather is due to an increasing number of Co ions which discontinuously become nonmagnetic. These results provide the first direct evidence for the applicability of the Jaccarino-Walker concept of discontinuous moment formation depending upon the local environment of the impurity. They clearly demonstrate that the qualitative explanation for the systematic variation in the average moment on iron group impurities dissolved in the 4d transition series based on the U/Δ condition of the Anderson model and the average density of states of the host is inadequate for these alloys.
Resistivity Minima in Pd(Np) Alloys
Authors: Nellis W. J. , Brodsky M. B.
Published: February 2004

The electrical resistivities of several Pd alloys with Np concentrations ranging from dilute amounts up to 13 at.% have been measured from 1.6°–300°K. For Np compositions below 7.5% resistivity minima were observed. Magnetic susceptibility data on the alloys containing 2.5%–13% Np indicate localized moments at high temperatures and spin compensation at low temperatures. The Kondo temperature of the dilute alloys is estimated to be of the order 10°–100°K.
Anomalous Electron-Phonon Resistivity of Metals Containing Magnetic Impurities
Authors: Rice M. J. , Bunce O.
Published: February 2004

The electron-phonon contribution to the resistivity of a metal containing a small concentration of impurity atoms is strongly enhanced over its value for the ideally pure metal if the conduction electron lifetime for impurity scattering varies with energy on a scale comparable to, or less than, the Debye energy of the metal. We present a working formula for this effect and briefly describe some important consequences for metals containing magnetic or nearly magnetic transitional impurities.
Magnetic Properties of Mn and Fe in CuPd and AgPd
Authors: Dellby B. , Myers H. P.
Published: February 2004

Magnetic susceptibility measurements of 0.1–1 at.% Mn and dilute solutions of Fe in CuPd and AgPd alloys are reported. The results are interpreted in s-d exchange scattering of conduction electrons at the resonant bound d electrons of Mn, Fe, or Pd and give support to a model for AgPd and CuPd with Pd in resonant bound states for low Pd contents and in energy band states for high Pd contents.
Quadratic Dependence of Spin-Wave Resonance Fields on Mode Number for Permalloy Films
Authors: Bailey Glenn C.
Published: February 2004

Permalloy films (75% Ni-25% Fe) which show some interesting new features have been made by evaporation in a vacuum initially at 5×10−8 Torr. Subsequent to evaporation, the films were annealed at 250°C for 12 h in the presence of a field of 25 Oe applied in the plane of the film. The following spin-wave resonance results have been observed on 2100-Å, 1320-Å, and 800-Å-thick films using a microwave frequency of 9.4 GHz: (1) Except for the first mode in the perpendicular orientation, the resonance fields Hn fit a quadratic dependence on mode number n strikingly well if the first mode is labelled 0 rather than 1, both for the parallel (∥) and the perpendicular (⊥) orientations-the fit to a quadratic dependence on n is not good if the first mode is labeled 1. (2) The slopes of the curves of Hn vs n2 are equal for the ∥ and ⊥ cases in the case of the thickest film. (3) The intensities decrease as 1/n2 and 1/n4 for the 2100-Å-thick film and as 1/n4 for the 1320-Å-thick film. These results can be explained if the magnetization is assumed to be quite uniform throughout the film volume and very close to the film boundaries so that the surface spins act as if they are nearly free for all modes except the first one in the ⊥ case and for all modes in the ∥ case.
Nonreciprocal Magnetostatic Surface Waves with Independently Controllable Propagation and Decay Constants
Authors: Morgenthaler F. R.
Published: February 2004

The characteristics of inhomogeneous TE eigenwaves propagating in a transversely magnetized uniform gyromagnetic medium are presented-with special emphasis given to the magnetostatic region of the dispersion relation. It is shown that when the magnetization is not parallel to the electric field, the tensor nature of the medium constrains and thereby controls the relationship between the propagation and decay constants. In addition, the eigenwaves are nonreciprocal in the field displacement sense allowing novel magnetic control to be exercised over them. As a consequence it should be possible to vary the depth of penetration of such a wave and in fact cause propagation to switch from one to the other surface of a gyromagnetic slab provided the faces are terminated in suitable surface impedances that allow the desired eigenwave to propagate as a bound surface wave mode. Such modes may form the basis for novel filters and nonreciprocal components constructed with convenient planar geometries.
Magnetic Steering of Magnetostatic Waves in Epitaxial YIG Films
Authors: Pizzarello F. A. , Collins J. H. , Coerver L. E.
Published: February 2004

High quality epitaxial YIG films grown on gadolinium gallium garnet have certain geometrical advantages over flux-grown material for refined investigation of basic magnetic wave propagation phenomena. Better uniformity of internal field under magnetic bias and convenience for placement of spatially periodic current-carrying couplers on the free YIG surface, ensures enhanced field uniformity by confining the region of propagation. Surface magnetostatic waves are dispersive and exhibit wave vector anisotropy so that, in general, the phase and group velocity vectors are noncollinear, with the beam steering angle variable by the magnetic bias field. Scanning magnetic probe experiments were conducted at 3 GHz on 10-μm thick films wherein beam steering angles were observed up to ∼50° for a wave number approximating 830 cm−1, for a 10° rotation of the bias field from the collinear situation. Use of the theoretical model applicable to thin film media, which neglects exchange effects, led to good agreement with the experimental results within measurement error.
Magnetic Surface Modes Obtained by a Simple Method
Authors: Sparks M.
Published: February 2004

A simple method of obtaining the normal modes of ferromagnetic and antiferromagnetic systems is presented and used to classify surface modes. Since all spins precess at the same frequency in a normal mode, the frequency and spin configurations can be obtained from the equations of motion of one or sometimes two spins near the surface. The method affords a clear physical understanding of the surface modes and requires very little calculation. One class of surface modes is the changed-parameter class, in which the missing neighbors of a surface spin are compensated for by a changed parameter such as an exchange constant at the surface. Another is the equivalent-layer class, in which the crystal consists of equivalent layers such that the net torque on each spin S1 on the surface of each layer exerted by all spins on the surface side of S1 is zero.
Ferromagnetic Resonance Modes in Single-Crystal YIG Films
Authors: Besser P. J. , Sparks M.
Published: February 2004

The availability of narrow-linewidth single-crystal yttrium iron garnet (YIG) films1 allows the detailed observation of a large number of ferromagnetic normal modes in a given sample for a range of sample sizes and shapes which covers the exchange-dominated through the magnetostatic limit. The absorption spectra of circular disks from 0.4- to 9-μm thick with aspect ratios from 22 to 1400 have been measured and explained theoretically. We report for the first time a spectrum having the ⊥ resonance frequencies of all higher-order modes well above that of the main resonance. In a 0.4-μm-thick, 3×10−3-in.-diam disk, the closest mode is 10 Oe away from the main resonance. In the thickest and in the thinnest samples, the magnetostatic and exchange modes were well separated. In the intermediate thickness range from 1 to 4 μm, modes having comparable magnetostatic and exchange energies were observed, making the spectrum more complicated. The intensities and frequencies indicate that the spins are pinned at the small edges of the film and that in very thin films (less than ≈3 μm) the low-order modes are pinned1 by a Portis-type well for which the variation of the internal field across the sample thickness is not purely parabolic, while unpinned modes have been reported in a 12.4-μm-thick sample.1
Magnetostriction of Commercial Ferrite Memory Cores
Authors: O'Connor Mike , Belson Henry S.
Published: February 2004

The polycrystalline saturation magnetostriction λs and volume magnetostriction δω/δH of some thirty types of commercial ferrite memory cores have been measured. A capacitance technique sufficiently sensitive to measure elongations of ∼0.1 Å and Δl/l of ∼3×10−8 was employed, and λs was determined by rotation of the saturated moment through 90°, λs values between −1×10−7 to −1×10−5 and λω/λH values from −1×10−10 to −7×10−10 Oe−1 were obtained. Since these magnetostriction constants measure coupling of magnetization and dimensional parameters, the data reflects a wide range of core sensitivity to stress-induced demagnetization and ``magnetostrictive ringing'' of cores upon switching.
Model for Reverse-Domain Nucleation in Ferromagnetic Conductors
Authors: Haller T. R. , Kramer J. J.
Published: February 2004

Recent reports indicate that the average dynamic domain size in a material undergoing a change in magnetization may be significantly smaller than the static domain size. This finer dynamic domain structure can be predicted by an application of the principle of minimum entropy production Eddycurrent dissipation and dissipative domain nucleation and annihilation processes are considered as the dominant mechanisms for entropy production. Expressions for their contributions are derived and the total entropy production is minimized with respect to the density of domains. The theoretical average domain width thus derived is found to vary with frequency as (f)−1/2 and with peak induction as (Bmax)−1, in accord with observations. A comparison of the theoretical with observed domain densities permits an evaluation of the dissipation per unit wall area associated with the dynamic process of nucleating a reverse-domain wall. This energy is an order-of-magnitude larger than domainwall surface energy.
Influence of Martensite-to-Austenite Reverse Transformation on the Temperature Dependence of Coercive Force of an Fe–Ni–Co Alloy
Authors: Colling D. A.
Published: February 2004

An Fe–Ni–Co alloy containing acicular martensite has been partially reversed in the temperature region 525° to 725°C and the influence of the reversed microstructure on the coercive force-temperature (Hc-T) relationship has been determined up to 500°C. In all cases, an increase in Hc was observed at θγ, the Curie temperature of the austenite. For reverse annealing temperatures up to 590°C, Hc was increased at all temperatures; for higher reverse annealing temperatures, Hc decreased at all temperatures, but the increase in Hc at θγ was found to be more abrupt. These observations are correlated with the microstructure resulting from the shear-like martensite-to-austenite reverse transformation.
Influence of Deoxidizers and Oxygen on Initial Permeability of 49% Ni–Fe Alloys
Authors: Colling D. A. , Aspden R. G.
Published: February 2004

Highest initial permeabilities are observed in 49% Ni–Fe alloy sheet which contains no strong deoxidizers. The adverse effect of strong deoxidizers such as silicon and aluminum is attributed to increased susceptibility to internal oxidation in a dry-hydrogen annealing atmosphere. For alloys containing no deoxidizers and a secondary recrystallized structure, μ40 values of 15 000 were observed by melting to an oxygen level of <5 ppm and annealing to effect removal of sulfur to a value of 1 ppm.