bluuebunny/crossref_metadata_2025 huggingface dataset:
One-Dimensional Interaction of a Plasma with a Ruby-Laser Beam
Authors: Engelhardt A. G.
Published: February 2004

Analytical and experimental studies have been made of the plasma ejected from a solid metallic surface as the result of impinging Q-switched ruby-laser radiation when the laser power density PA exceeds 109 W cm−2. Based on the one-dimensional equations of motion and conservation of energy, the model predicts the quantity and temperature of ejected plasma. To check the theory pure copper and aluminum disks were irradiated by a Q-switched ruby laser for 3×1010≤PA≤2×1011 W cm−2 and 30≤τL≤50 nsec, where τL is the pulse width. From framing camera pictures taken up to 550 nsec after plasma creation, the expansion velocity of the plasma has been measured and agrees acceptably well with that predicted by theory.
Fatigue Mechanism in Titanium at Ultrasonic Frequency
Authors: MacDonald D. E. , Wood W. A.
Published: February 2004

The fatigue mechanism in titanium is studied metallographically for small strain amplitudes (∼0.003) at a frequency of 1700 cpm and at the ultrasonic frequency of 16 000 cps. The ultrasonic frequencies develop high localized strains at solitary slip bands and these bands become the microcracks initiating fatigue. The low-frequency fatigue in contrast develops from apparently slipless transgranular shear cracks.
Section-and-Etch Study of Hertzian Fracture Mechanics
Authors: Mikosza A. G. , Lawn B. R.
Published: February 2004

A section-and-etch technique is used to study the mechanics of Hertzian cone-crack growth in glass. With a suitable choice of test environment the cone cracks propagate at a convenient rate through successive phases of stability at constant indenter load. Systematic measurements of the etched-crack lengths as a function of indentation time permit a detailed description of the fracture mechanics. Within a certain range of indenter load, the cone crack is observed to grow as a shallow surface ring to a critical depth prior to full development. This directly confirms a salient feature of the energy balance theory of Hertzian fracture outlined in earlier papers. The current status of the long-standing Auerbach law, which relates the critical fracture load linearly to the indenter radius, is discussed in the light of the present evidence.
Hole-Electron Production in Semiconductors
Authors: Zulliger H. R.
Published: February 2004

A phenomenological model for the average expended energy ε to produce an electron-hole pair is derived for silicon and germanium. The values agree well with experimental data at room temperature and at 77 °K. By using this model to calculate the Fano factor F, it has been found that F ≅ 0.05 for both silicon and germanium. It is concluded that under perfect charge-collection conditions, germanium-radiation detectors will show better energy resolution than silicon detectors because of the lower ε in germanium.
Resistance of Thin Metal Films Grown under a Longitudinal Electric Field
Authors: Ahilea E. , Hirsch A. A.
Published: February 2004

Thin-film samples of platinum, silver, and gold were prepared in pairs on glass substrates by evaporation in a vacuum of 10−6−10−7 Torr, one sample of the pair under an electric field (usually 40 V/cm, either dc or 500-Hz square wave) applied along the substrate surface and the other sample under no field. Sample resistances were measured in the vacuum at temperatures ranging from roughly 0 °C to 4 °K. The resistances of the samples deposited under a field were almost invariably lower, sometimes by orders of magnitude, than those of the corresponding samples grown under no field. Electron micrographs show that the former samples had elongated and interconnected grains while the latter samples had roundish and more islolated grains. The data are discussed in terms of a simple model based on the notion that the film particles polarize, stretch, and even coalesce under the applied electric field before they solidify.
Injected Carrier Lifetime and Aging of GaAs Injection Lasers
Authors: Yang Edward S.
Published: February 2004

Aging experiments of Zn-diffused GaAs injection lasers have been performed at liquid-nitrogen temperature. Results of degradation tests are consistent with the Kressel and Byer postulation that new nonradiative recombination centers are formed. Evidence of the formation of these new centers are deduced from measurements of the injected carrier lifetime which decreases during laser degradation. Variations of the external quantum efficiency and the threshold current correlate with the changes of the carrier lifetime.
Imperfect Misfit Dislocations in Thin Films of Silver on Palladium
Authors: Matthews J. W.
Published: February 2004

A calculation of the energy of complete and partial misfit dislocations has been made. This suggests that the misfit between an (001) silver film and a palladium substrate will be accommodated by partial misfit dislocations. The extrinsic stacking faults associated with these partials are expected to lie in the silver film and modify its crystal structure. To test these predictions silver films were grown in ultrahigh vacuum (2 × 10−9 Torr) on cold (−5 to −105 °C) palladium surfaces prepared inside the chamber. Transmission electron-diffraction patterns from these specimens showed that the silver films contained a high density of stacking faults.
Electrical Effects of Screw Dislocations in Germanium
Authors: Collins Charles V. , Miles M. Howard
Published: February 2004

Extrinsic conductivity on plastically deformed germanium containing predominantly screw dislocation arrays were investigated. The dislocations were introduced by twisting cylinders of anitmony-doped n-type germanium and the dislocation density was determined by the etch pit method. Dark conductivity and both transient and steady-state photoconductivity were measured on Hall-type samples for current flow parallel and perpendicular to the dislocation arrays on the active slip planes. Measurements were made at room and liquid-nitrogen temperatures and the effects of varying the annealing procedure, the temperature of deformation, the amount of twist, and the arrangement of the dislocation arrays are presented. The results indicate that screw dislocations do not have associated acceptor levels in germanium.
Effect of Oxygen on the Electrical and Structural Properties of Triode-Sputtered Tantalum Films
Authors: Waterhouse Neil , Wilcox Philip S. , Willmott David J.
Published: February 2004

The structural and electrical properties of oxygen-doped tantalum films, sputtered in a triode system, have been investigated. X-ray diffraction traces from films with a low oxygen content indicate the presence of bcc Ta with a strained lattice. The intensity of the (110) bcc Ta diffraction peak decreases with increasing oxygen content and is interpreted as a decrease in the amount of bcc Ta phase present. Over this same range the appearance and rise in intensity of the β-Ta (200) peak indicates the formation of β-Ta. As the oxygen content is further increased, the structural data indicate a reorientation of the tetragonal β-Ta (200) to the (202) planes with respect to the film surface, an effect which has been previously observed in diode-sputtered tantalum; further increase in oxygen content produces a stretching of the β-Ta lattice by as much as 10% of the value reported by Read and Altman. The room-temperature resistivity increases with increasing oxygen content until a ``plateau'' region is reached at ∼ 210 μΩ cm corresponding to 12 at. % oxygen, and together with the x-ray data the electrical measurements indicate a change of phase from bcc to β-Ta. Above approximately 40 at. % oxygen the resistivity increases rapidly suggesting the formation of tantalum oxide.
Electrochemical Charging of Thermal SiO2 Films by Injected Electron Currents
Authors: Nicollian E. H. , Berglund C. N. , Schmidt P. F. , Andrews J. M.
Published: February 2004

When electron currents flow in thermal SiO2 films which have been exposed to water, a buildup of negative charge occurs in the oxide. This paper describes a series of experiments designed to characterize this charging effect. It is found that if water is diffused into a SiO2 film, water related centers are formed which act like electron traps with capture cross section of approximately 1.5 × 10−17 cm2. Experiments are described which show that when one of these centers captures an electron, atomic hydrogen is released which diffuses away and escapes or reacts and a stable negative charge is left behind. Electrochemical charging effects of this type have not previously been considered, although they may play a very important role in some semiconductor device failure effects.
Effect of Shock Precompression on the Dynamic Fracture Strength of 1020 Steel and 6061-T6 Aluminum
Authors: Stevens A. L. , Tuler F. R.
Published: February 2004

In impact-produced spall fracture, a material undergoes drastic dynamic precompression immediately prior to the time of fracture. In this paper a technique is described for varying the precompression stress wave magnitude σc relative to the magnitude σr of the rarefaction wave, which produces the spall, in the range of σc/σr≥1. The method is used to determine the spall strength of 1020 steel and 6061-T6 aluminum following precompression stress amplitudes up to 120 kbar. The results show that for these two materials neither the spall strengths nor the modes of fracture initiation and crack growth depend on the amount of precompression in the range attained in these experiments.
Void Formation and Growth During Electromigration in Thin Films
Authors: Rosenberg R. , Ohring M.
Published: February 2004

One of the modes of electromigration damage is shown to be related to irregularities in the grain-boundary structure of films. Based on the restriction of electromigration to grain boundaries, calculations are performed to determine the magnitude and distribution of excess vacancy concentrations at sites where electromigration flux divergencies may be present. The attainment of an equilibrium vacancy supersaturation (Δc/c0) is found to be practically instantaneous. The maximum supersaturations are less than 1 under all conditions used. This is found to be inadequate for void formation by vacancy condensation unless heterogeneous nucleating sites are present (e. g., oxide particles, boundary-surface oxide intersection). The rate of observable hole formation is accounted for by either void growth at a grain-boundary triple-point junction or by grain-boundary grooving, each being related to the electromigration flux. Grooving seems most likely in pure films with all boundaries having similar character (e. g., preferred orientation).
Quantitative Aspects of the Tunneling Resistance in n-GaAs Schottky Barriers
Authors: Guétin P. , Schréder G.
Published: February 2004

The influence of the doping level and the barrier height on the characteristics of the differential resistance of M/n-GaAs tunnel contacts has been investigated both theoretically and experimentally. The computation has been based on a pure WKBJ approximation and the quadrature over the momentum parallel to the interface was included. The position of the resistance maximum appears strongly dependent on the barrier height and insensitive to the value of the doping level. Vacuum-cleaved contacts have been made with various metals, i.e., barrier heights, for two different values of the carrier density. In spite of some systematic absolute discrepancies, the experimental variations of the differential resistance with the barrier parameters are in good agreement with theory.
Determination of Magnetization of Micromagnetic Wall in Bubble Domains by Direct Minimization
Authors: Tu Yih-O
Published: February 2004

The distribution of magnetization in a bubble domain is one which minimizes the total free energy according to the theory of micromagnetics. Hence, it may be determined using the methods of direct minimization. Numerical results for a one-dimensional Bloch wall are given to illustrate the method in a simple case. The concept of a wall-energy constant which is commonly adopted for domain walls having zero width is examined by an analysis of real bubble domains.
Geometric Arrangements for Maximizing Power-Transmission Capability in Superconducting Transmission Cables
Authors: Guthrie G. L.
Published: February 2004

An analysis is given of the power carrying capability of several geometric arrangements of superconducting transmission cables for use in dc, single-phase ac, and three-phase ac applications. The integrated Poynting vector is maximized with respect to internal geometric variations under the restrictions that E and H remain below fixed maximum values. The discussion includes calculations of maximum energy densities for several three-phase ac geometric arrangements. For a type-I material, the single-phase or dc energy density achievable with optimized multiple concentric cylinders is found to be approximately three times that available by an intermixed wire geometry using the same materials. A theoretical upper limit is given for the energy per cm2 which may be sent down a superconducting cable of given type-I material and given dielectric, independent of the geometry adopted. It is shown that attempts to use flux-canceling geometries to uniformly reduce H are based on misconceptions of the nature of the problem, for both type-I and type-II lines. Use of fine filaments of type-II material to counterlace currents and reduce H are found to be of negative benefit. For niobium ac lines, the dielectric is found to be the limiting material when helium is used as the dielectric.
Efflux of Atoms From Cathode Spots of Low-Pressure Mercury Arc
Authors: Eckhardt Gisela
Published: February 2004

A novel measuring technique was devised for the determination of the rate at which particles are ejected from the cathode spots of a low-pressure arc. The measurements were performed with anchored spots in a low-pressure steady-state mercury discharge. During arc operation, the total efflux of mercury from the cathode is composed of (i) the atoms which evaporate from the spot-free mercury surface and (ii) the particles which are ejected in connection with the cathode spots. The method applied permits a separation of these two contributions, thus yielding more accurate results than reported in the literature so far. From these measurements an electron -to-atom emission ratio of 208±12 was derived for the contribution from the cathode spots, corresponding to a ratio of emitted mass to emitted charge of (9.99±0.06)×10−6 g/C.
Transient Internal Photoemission of Carriers in the Metal-Insulator System
Authors: Mort J. , Schmidlin F. W. , Lakatos A. I.
Published: February 2004

The transient photoemission of hot carriers from metals into insulators permits a detailed study of the dynamics of the metal-insulator interface. The technique can be viewed as the simulation of a transient thermionic experiment. The photoemission of electrons from copper into single-crystal CdS and holes from gold into amorphous selenium is reported. The results are consistent with a model of backscattering out of the insulator due to interaction with the lattice. Significant differences are found between photoemission into the single crystal and amorphous insulator which could arise from the different charge transport properties of these materials, as for example dictated by their structures.
Anisotropy in the Domain-Wall Mobility of Rare-Earth Orthoferrites
Authors: Shumate P. W.
Published: February 2004

An anisotropy in the domain-wall mobility in rare-earth orthoferrites has been measured for the first time using a high-resolution measuring technique. This anisotropy is approximately 6% for most materials at room temperature, and is accurately predicted by a new modification to an existing model for canted antiferromagnets.
Approach to Saturation in Inhomogeneous Magnetic Materials
Authors: Schlömann Ernst
Published: February 2004

The Néel theory of the approach to saturation in inhomogeneous magnetic materials is critically reviewed. It is found that the theory is rigorously applicable when the local saturation magnetization differs only slightly from its spatial average, but that this condition is not satisfied in porous materials or in material containing inclusions of a second magnetic phase having a saturation magnetization twice that of the host material or larger. The Néel theory is extended by (i) calculating the high-field behavior of the magnetization curve for arbitrary inhomogeneity, and (ii) calculating the magnetization curve for arbitrary field strength to a higher order of approximation than in Néel's theory. The results show that for porous materials, as well as for materials containing a second magnetic phase, the higher-order corrections are quite significant. The higher-order corrections to the Néel theory are found to depend quite strongly on the shape of the inclusions, being smallest for spherical inclusions and approximately six times larger for layerlike inclusions.
Studies of Thin Films of Nb3 Sn on Nb
Authors: Dickey J. M. , Strongin Myron , Kammerer O. F.
Published: February 2004

Experiments are described where thin layers of Sn about 100 Å thick are deposited on Nb surfaces and are then reacted to form Nb3Sn. An apparatus has been developed where the Nb3Sn can be made and its Tc measured in situ with ambient pressures in the low 10−8-Torr range. Using this apparatus, the progressive conversion of films of Sn on Nb to Nb3Sn have been studied as a function of various parameters such as reaction temperature, thickness, and reaction time. A discussion is also given of some of the film properties and estimates have been made of the Nb3Sn coherence length from the proximity effect between the Nb3Sn layers and the bulk Nb underneath.
Experimental K-Fluorescence Yields for the Elements Z = 22 to 30 and 32
Authors: Suortti P.
Published: February 2004

Atomic fluorescence yields of the K shell, ωK, are measured with x-ray excitation for Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Ge. The measurements are made from totally absorbing specimens in the symmetrical reflection arrangement with a conventional diffractometer. The fluorescence yields are evaluated using recently published x-ray attenuation coefficients and making an approximation for the scattering contribution. The experimental uncertainties of the ωK values are 2 to 4%. The present values are considerably higher than most of the previously published experimental and theoretical results, but they are in agreement with a recent calculation based on Hartree-Fock-Slater wave functions.
Study of Intensities of Auger Lines Excited by Electron Bombardment and Al Kα X-Ray Irradiation
Authors: Pessa M.
Published: February 2004

Intensities of Auger lines excited by 5-keV electron bombardment and 1.5-keV Kα x-ray irradiation are compared. The most intensive lines related to LMM or MNN Auger transitions in Fe, Cu, Ag, and Sn metal films are measured with a cylindrical spectrometer with an energy resolution of 0.06%. The effective Auger current is found to depend strongly on the excitation method in the energy region, 0.3–1 keV, studied. The factor τiph/rσi (the ratio of the photoelectric absorption coefficient and the ionization-subshell cross section for an electron impact corrected with respect to the electron backscattering) is found to be proportional to the relative line intensities which can be expected in an Auger spectrum when x-ray irradiation or electron bombardment is considered as an excitation method of the specimen.
Secondary Electron Emission from Thin-Film Gold-Metaloxide Cermets
Authors: Pakswer Serge , Stevens Michael T.
Published: February 2004

Measurements made on sputtered thin-film gold-metaloxide cermets indicate that the secondary electron emission yield is quite similar to that of the dielectric. For Au–Ta2O5 films, the first crossover potential is ≃ 30 V, and the maximum yield of 2.0 is achieved at 250 V. These values are essentially independent of the Au/Ta2O5 ratio. Results are also presented for Au–BaTiO3 and Au–Al2O3 cermets, and for pure Au as a reference. A brief tentative explanation of the experimental observations is given.
Compensated Silicon-Impurity Conduction Bolometer
Authors: Kinch M. A.
Published: February 2004

The capability and performance of compensated Si (Sb ∼ 2×1018 cm−3; B ∼ 2×1017 cm−3) impurity conduction bolometers as extremely sensitive detectors of far-infrared radiation (2 mm to 30 μm) is described. Electrical and far-infrared measurements indicate a NEP ∼ 2.5×10−14 W/Hz1/2, and a response time ∼ 10−2 sec, when operated at 1.5°K.
Soft X Rays from a Laser-Heated Dense Plasma Focus
Authors: Shatas Romas A. , Stettler John D. , Meyer Harry C. , Roberts Thomas G.
Published: February 2004

A design analysis of a pulsed CO2 laser-assisted plasma focus has been undertaken for the purpose of enhancing the flash intensity of cold x rays when the device is operated in the x-ray generator mode. By deliberately injecting high Z ions into the plasma the intensity of the soft x-ray component (approximately 1 keV energy) can be increased by many orders of magnitude; to compensate for the radiation loss, plasma heating by laser pulse is employed. Because the laser frequency is close to the plasma-electron Langmuir frequency, nearly all of the laser pulse energy is absorbed in a single pass. Calculation of a typical design configuration consisting of small dense plasma focus and a 200-J electrical-discharge CO2 laser yields laser to soft x-ray conversion efficiency of over 70%.
Investigation of Intermittent Enhancement of Ion Emission from a Tungsten Surface Using the Field-Ion Microscope
Authors: Weizer Victor G.
Published: February 2004

An intermittent enhancement of ion emission or blinking effect is described which is observed when a few parts per million neon are added to the imaging gas in a helium-tungsten field-ion microscope. Measurement of the variation of the blinking rate of a single emitting tungsten atom with applied voltage, tip temperature, and gas pressure suggest that (a) adsorption of neon on the apex of a protruding tungsten substrate atom is responsible for the blinking and (b) the rate of blinking is proportional to 1−PI++, where PI++ is the probability of double ionization as a neon atom passes through the ionization zone above a protruding tungsten emitter.
Role of Surface Treatment in Laser Damage of Germanium
Authors: Bertolotti M. , Stagni L. , Vitali G. , Muzii L.
Published: February 2004

The interaction of laser light with a semiconductor surface is studied by means of an optical microscope. The surface treatment is shown to affect the nature of the damage. On lapped surfaces the damage is found to consist essentially of a removal of matter from the semiconductor surface, while on etched surfaces it is mainly limited to the occurence of melting. A qualitative explanation of these differences in behavior is given.
Simultaneous Measurement of Thermally Stimulated Conductivity and Thermoluminescence
Authors: Chen Reuven
Published: February 2004

The relation between thermally stimulated conductivity (TSC) and thermoluminescence (TL) is discussed assuming that the transition of electrons (holes) from traps to recombination centers is through the conduction (valence) band. It is shown that under this general assumption, the TL maxima shift to lower temperatures compared to the corresponding TSC ones. A method for calculating the recombination probabilities by a simultaneous measurement of TL and TSC is given.
Microstructural Study of Diamonds Synthesized under Conditions of High Temperature and Moderate Explosive Shock Pressure
Authors: Trueb Lucien F.
Published: February 2004

Diamond explosively synthesized from metal/graphite mixtures in shock configurations resulting in high temperatures, moderately high pressures, and relatively long holding times at pressure were investigated by electron microscopy and electron diffraction. Particles up to 5-μ diameter consist of a matrix of 10–40 Å, variously oriented crystallites which contain clusters of randomly oriented 100–1600-Å crystallites. Particles larger than 4–5 μ are densely fused aggregates of such composite units.
Morphology of Crystallographic Etch Pits in Iron
Authors: Spink G. M. , Ives M. B.
Published: February 2004

It is shown that the development of low-index crystallographic facets in pits produced in the surface of polycrystalline iron is controlled primarily by the relative dissolution rates of different crystallographic orientations. The successive shapes of dissolving iron whiskers are used to predict the observed etch-pit shapes using a topographical theory of crystal dissolution.
Acoustic and Acousto-Optical Properties of Pb2MoO5 Single Crystal
Authors: Ohmachi Yashiro , Uchida Naoya
Published: February 2004

Acoustic velocity, acoustic absorption coefficient, and acousto-optical figure of merit for longitudinal acoustic modes of this crystal have been measured at room temperature. Among some interesting combinations of acoustic and optical modes, the longitudinal wave propagated parallel to the principal axis X of the index ellipsoid which lies in the (010) plane with the light polarized parallel to the Y axis (two-fold axis, b) has been found to be particularly useful for acousto-optical device applications because of its high figures of merit M(=n6p2 / ρv3) = 127×10−18 sec3/g and M′ (=n7p2 / ρv) = 242×10−7 cm2 sec/g and relatively low acoustic loss, 4.2 dB/cm at 300 MHz.
Investigation of the Photoelectret Effect in Boswellia Glabra
Authors: Pillai P. K. C. , Balakrishnan K. G. , Jain V. K.
Published: February 2004

This paper deals with the photoelectret effect in a natural plant product, Boswellia Glabra. It is found that this material in the pure form makes one of the best photoelectrets and gives a much more stable charge than other photoelectret substances. The sample is polarized for 5 min by the simultaneous application of field and illumination, then it is reilluminated and the depolarization current reveals the nature of the polarization. This paper also deals with the effect on photoelectret formation of continued application of the polarizing field for five more minutes, keeping the sample in the dark. It is found that this process gives much better stability of charge and longer life to the electret.
Thermal Current Study of the Effect of Humidity on Charge Storage in Mylar
Authors: Perlman Martin M. , Creswell Robert A.
Published: February 2004

Thermal currents have been obtained from corona-charged Mylar films exposed to a humid atmosphere for variable times. A theory that we have recently developed to account for the current ``spectrum'' of these ``near surface'' charged specimens is put into a form that facilitates routine analysis of the peaks. Exposure of Mylar to 100% RH at 50°C has a drastic effect on the four traps previously reported. After 5 days, they have completely disappeared, and only 0.6% of the total initial charge remains. Ninety percent of this latter charge is held in a trap at a depth of 2.6 eV, and the remainder at 1.3 eV. Assuming that the traps empty under monomolecular conditions, trap densities are of the order of 1014/cm3, and mobility-lifetime products, 10−8 cm2/V; to be compared with 1016/cm3 and 10−10 cm2/V for the dry samples. The thermal current spectra show, in explicit detail, how humidity affects charge storage in Mylar.
Optimization of the InAsxP1−x–Cs2O Photocathode
Authors: James L. W. , Antypas G. A. , Uebbing J. J. , Yep T. O. , Bell R. L.
Published: February 2004

Zinc-doped InAsP liquid epitaxial layers with bandgaps between 0.4 and 1.34 eV were grown on InAs and InP substrates. The grown layers were 2–4-μ thick with mirror-smooth as-grown surfaces. Preliminary phase diagram calculations based on Darken's quadratic formalism to describe the ternary liquid in equilibrium with the pseudobinary solid are in good agreement with the bandgaps of the grown layers determined by photoluminescence. The InAsxP1−x–Cs2O heterojunction barrier height as a function of composition has been measured using photoemission. For InAs the barrier is at 1.24 eV, and it decreases with decreasing arsenic concentration to a value of 1.16 eV for InAsP with a 1.27-eV bandgap. For InAsxP1−x samples with bandgaps in the range 1.17–1.34 eV, high escape probabilities and efficient photoemission were observed. A typical cleaned (not cleaved) sample with a bandgap of 1.19 eV has a sensitivity of 600 μA/lm, 70 μA with a lumen source through a 2540 ir filter, a quantum efficiency of 1.5% at 1.06 μ, and a Γ escape probability of 0.08. This is the most sensitive infrared photocathode yet produced. All processing steps seem compatible with tube production. The effects of the heterojunction barrier are clearly visible with this material. The escape probability drops by an order-of-magnitude when the InAsxP1−x bandgap is reduced to 0.05 eV below the barrier.
Approximate Photocount Statistics for Coherent and Chaotic Radiation of Arbitrary Spectral Shape
Authors: Lachs Gerard
Published: February 2004

A method for computing the approximate photocount statistics for Gaussian light is presented. This method may be used for the superposition of coherent radiation with chaotic radiation of arbitrary spectral shape. Data is presented for Gaussian-, triangular-, and square-shaped spectra as well as for Lorentzian-shaped spectra. The results show that the photocount statistics are significantly dependent upon spectral shape for intermediate time-bandwidth products. The results also show that the Bedard, Chang, and Mandel approximation gives a better fit to a Gaussian-shaped spectrum then to a Lorentzian-shaped spectrum. Significant differences between the photocount statistics for a time-bandwidth product of 10 and Poisson statistics were also obtained; even for a signal-to-noise ratio of 40:1.
Effect of Co on Magnetic Properties of ErFeO3, HoFeO3, and DyFeO3
Authors: Holmes L. , Van Uitert L. G. , Hecker Richard
Published: February 2004

Magnetization data have been obtained on crystals of RFe1−xCoxO3, with 0<x≤0.06 and R=Er, Ho, and Dy, at temperatures between 4.2° and 300°K. The spontaneous magnetization σ0 lies along the a axis of the orthorhombic unit cell for x≥0.01. For R=Er and Ho, the data are compared with σ0 ∥ a at low temperatures for the pure compounds (x=0). A Weiss molecular field of (10.5±1.0) kOe is found for the Ho3+ ions. The Dy compounds undergo a transition to a state with σ0=0 at low temperatures. The transition temperature increases from 35°K at x=0 to a maximum of 133°K at x=0.003. A formalism is developed for describing the concentration dependence of the spin-reorientation temperatures, and the behavior in DyFe1−xCoxO3 is related to changes in the anisotropy fields on the Fe3+ sublattices.
Electron Transmission Measurements for Al, Sn, and Au Targets at Electron Bombarding Energies of 1.0 and 2.5 MeV
Authors: Rester D. H. , Derrickson J. H.
Published: February 2004

Total transmitted electron energy spectra have been constructed from measurements of electron energy spectra at various emission angles for targets of Al and Au of thicknesses of from 0.2 to 0.6 of the range in these materials. Bombarding energies of 1.0 and 2.5 MeV were used for beams of perpendicular incidence to the targets. Angular distributions of transmitted electrons are shown. At 1.0 MeV, total transmitted electron energy spectra are constructed from measurements in which incident electron beams were used to simulate an electron flux of intensity varying as the cosine of the angle of incidence. Targets of Al, Sn, and Au were used. Comparisons are made to calculated spectra from ETRAN 15 of Berger and Seltzer.
I. Luminescence and Free Carrier Decay Times in Semiconductors Containing Isoelectronic Traps
Authors: Cuthbert J. D.
Published: February 2004

This paper describes the measurement of free carrier decay profiles over the temperature range 7°–300°K for GaP:N, GaP:Bi, CdS:Te, and ZnTe:O following their excitation by pulses of electrons from a Van de Graaff accelerator. Contactless microwave transmission and reflectivity techniques were employed to measure the transient conductivity changes. The studies were made principally to obtain a more complete understanding of the recombination mechanisms previously proposed to be operative in CdS:Te and ZnTe:O on the basis of luminescence decay time data. The gross features of the temperature dependence of the free carrier lifetimes correlate well with the luminescence decay time data. Differential equations, formulated to describe the temperature-dependent kinetics, were solved by a combination of numerical and analytical methods to obtain the transient luminescence and free carrier decay profiles. The solutions depend very weakly upon certain capture coefficients. The major variable parameter is in both cases the binding energy ε of the majority carrier in the Coulomb field of the charged isoelectronic trap. For CdS:Te, with εh=20 meV, good agreement was obtained between the calculated and observed free carrier and luminescence decay profiles, thereby providing good support for the model of the recombination mechanism. For ZnTe:O with εe=20 meV, agreement is adequate for the luminescence profiles, but only semiquantitative for the free carrier decay profiles. Reasons for the discrepancies are discussed. For all the materials, at the lowest temperatures, the results indicate very rapid and stable trapping of the carriers with no evidence of a post-excitation conductivity. This is in keeping with the occurrence of highly radiative transitions at these temperatures.
Dynamic and Steady-State Injection of Electron-Hole Plasma in p-Type InSb
Authors: Ancker-Johnson B. , Robbins Wm. P.
Published: February 2004

Potential measurements as a function of time and space show in detail the passage of an injected electron-hole plasma front, and the eventual establishment of a nonequilibrium steady state in a long bar of p-type InSb at 77°K. The front is preceded by a depletion layer which vanishes as plasma reaches the anode. Thereafter the current, with the voltage held constant, grows exponentially until just before the steady-state plasma density is reached. These results are compared with a theory by Dean and by Ancker-Johnson, Robbins, and Chang describing plasma injection into a semiconductor with deep traps. The measured front arrival time as a function of constant applied voltage agrees satisfactorily with Dean's prediction. Four observations are at variance with his theory: the time constants of the exponential current growth are density-dependent instead of being independent as predicted; the current at the front arrival is not a function of voltage as his theory states; the electric field behind the front is not proportional to the square root of distance; and the steady-state injected current has a higher power dependence on voltage than the predicted square-law dependence. The extended analysis accounts for all the observed growth time behavior, namely a growth time which is independent of steady-state density at high and low densities, and which increases with density in the intermediate range. Also, a new theory of the steady-state conduction characteristic, based on the density-dependent plasma lifetime, reproduces quite well the measured conduction characteristics, I ∝ Vn with 2<n<8, until the interference of pinching, which causes a sub-Ohmic conduction. In the nonequilibrium steady state the plasma density has a uniform spatial distribution within a factor of two over the central 80% of the sample length. The steady-state density decreases monotonically from cathode to anode, or alternatively, a U-shaped distribution is observed with high plasma densities occurring also at the anode, a characteristic which is attributed to copious hole injection. All the observed dynamic and steady-state properties of double injection into p-InSb are in good agreement with theory except for the constancy of the current magnitude at the front arrival and the form of the dependence of electric field on distance.
Tuning-Initiated Failure in Avalanche Diodes
Authors: Evans W. J. , Scharfetter D. L. , Johnston R. L. , Key P. L.
Published: February 2004

A tuning-initiated failure has been observed in silicon avalanche diode oscillators operated in the Trapatt mode. The precise nature of the failure mechanism remains to be established but several possibilities, based on experimental evidence, are discussed. The circuit-tuning conditions necessary to initiate the failure (burnout) and the physical state of the diode after the failure are described. A gold whisker, which shorts the junction, is found extending from the mounting stud contact. Preliminary evidence indicates that the shape of the junction region, as controlled by the etching process, can be tailored to inhibit such diode failure.
Anomalous Electrical Properties of p-Type Hg1−xCdxTe
Authors: Scott Walter , Hager R. J.
Published: February 2004

The temperature dependence of the Hall coefficient and resistivity is presented on samples which show an anomalous behavior and the effects of various surface treatments on the electrical properties is examined. The anomalous effects have been eliminated in a few cases by proper heat treatments yielding normal p-type Hall coefficients down to 4.2°K. Field effect measurements confirm that these effects are due to an n-type inversion layer on the surface of p-type Hg0.8Cd0.2Te. Surface carrier concentration in this inversion layer ranges from 1×1012/cm2 to 5×1012/cm2 and mobility in this layer was found to be in the 103 cm2/V·sec range.
Explosion of Bare and Insulated Copper Wires
Authors: Bhat B. K. , Jordan I. B.
Published: February 2004

The current waveforms obtained by exploding various sizes of copper wires by the discharge of a large condenser bank revealed that the (V, l) plane (V =initial voltage, l = length of the wire) can be divided into various zones with each zone characterising a particular type of explosion. In particular the current pause was observed only in one zone. Below a certain initial voltage no pause in the current could be induced. The restrike length of enamel insulated wires was found to be considerably more and the pause duration considerably less than for bare wires. In this case thermally emitted electrons trapped in the insulation are considered responsible for a reduction in the pause duration and an increase in the restrike length. The increased restrike current for enamel insulated wires vis a vis bare wires may be due to the arc shunting as suggested by the current wave forms obtained from exploding coils. The energy absorbed by an exploding coil depends upon its pitch.
Explosive Gas Blast: The Expansion of Detonation Products in Vacuum
Authors: Ahrens Thomas J. , Allen Charles F. , Kovach Robert L.
Published: February 2004

A series of 0.2- to 3-gm HNS charges were detonated in vacuums of 10−3 to 10−5 Torr. The resultant freely expanding, detonation product, gas blast achieves terminal velocities of 8 to 12 km/sec within 3 to 5 μsec after the detonation wave arrives at the free surface. Measured pressure profiles display rise times to maximum stagnation (``reflected shock'') pressure varying from ∼30 μsec, 20-cm away from a 2.6-gm charge, to ∼185 μsec, 127-cm away from 0.2-gm charge at 10−5 Torr. Rise times were generally shorter at 10−3 and 10−4 Torr; the 10−5 Torr values agree with numerical calculations. Using cube root scaling of charge mass, the observed peak reflected pressure as a function of range may be represented by p=6.5×105 (bar) r′−3.5,where r′ the ratio of the range to the equivalent charge radius.
Resistivity and Density of Ge Films Obliquely Deposited in Vacuum
Authors: Takahashi Masaru , Onishi Hideomi , Tada Osamu
Published: February 2004

Ge films were made at 5×10−6 Torr by an oblique deposition. Resistivity and its change due to oxygen exposure were measured for different deposition angles. Resistivity anisotropy and its change caused by oxygen exposure were also measured. They increased with the deposition angle. The mass of the film was measured by a microbalance and its density was calculated. The density of the film was less than that of bulk and became smaller with an increase of the deposition angle. These phenomena are explained by the self-shadowing effect.
Thermochemical Calculations of Tungsten Halogen Lamps Containing Bromine, Oxygen, Hydrogen, and Carbon
Authors: Yannopoulos L. N. , Pebler A.
Published: February 2004

Equilibrium calculations were carried out on a computer for a system containing tungsten, bromine, oxygen, hydrogen, and carbon. The computer program receives as input the standard enthalpy and entropy of formation and the heat capacity as a function of the temperature for each species considered in the calculations. For initial fill and operating conditions compatible with those in actual tungsten bromine lamps, the concentrations of all components in any phase considered were calculated in the temperature range 500°–3500°K at 500° intervals under conditions of chemical equilibrium. The validity of these calculations on the lamp performance is based on the assumption of negligible departure from localized equilibrium and on the accuracy of the thermodynamic values used.
Interpretation of Initiation Pressure Hysteresis Phenomena for Fixed-Point Pressure Calibration
Authors: Zeto Robert J. , Vanfleet H. B.
Published: February 2004

An interpretation of initiation pressure hysteresis phenomena for fixed-point pressure calibration is presented according to the theory of nucleation in condensed systems and is substantiated for the bismuth I–II point by hydrostatic pressure experiments with a manganin pressure gauge. Kinetic initiation and completion of the bismuth I–II transformation were observed at constant pressure and temperature, and several different isobaric initiation pressures were measured at the same temperature. An asymmetrical relationship of the equilibrium pressure between the initiation pressures of the forward and reverse transformations was measured, and it was demonstrated that the high-pressure side of the strain hysteresis of initiation is within 0.17 kbar of the equilibrium pressure. The microstructure and thickness of the sample influenced the initiation pressures and the region of indifference, but the center of the region appeared reproducible. A region of indifference of 0.03 kbar was measured. The origin of the real strain hysteresis of initiation is identified for polymorphic transformations and initiation pressures are discussed in terms of the strain energy and chemical kinetics of nucleation. It is shown that other interpretations of hysteresis phenomena are not satisfactory. It is reasoned that the equilibrium pressure rather than a higher pressure value is a more accurate calibration pressure for the initiation of the bismuth I–II transformation in solid-media apparatus.
Q-Switching and Cavity Dumping of Nd:YAlG Lasers
Authors: Maydan D. , Chesler R. B.
Published: February 2004

Experiments in Q-switching and cavity dumping of a Nd:YAlG laser have been carried out. The system in either case is composed of a Nd:YAlG folded cavity laser and an intracavity acousto-optic modulator made of fused silica and Brewster cut. Q-switching is achieved by first feeding the modulator with an acoustic pulse of sufficient duration and intensity to keep the laser below threshold (hold off pulse). Termination of the acoustic pulse allows the power inside the laser cavity to build up. A second short acoustic pulse, introduced to the modulator at the time when the internal energy reaches its maximum, couples the energy out of the cavity. This pulse may also be the beginning of the hold off pulse. Cavity dumping is accomplished by feeding the modulator with short acoustic pulses at fixed intervals. In the Q switching mode the system can operate with a maximum repetition rate of about 30 kHz. In the cavity dumping mode of operation the repetition rate of the light pulses can be controlled from 125 kHz to several MHz. The minimum pulse duration obtained in both modes of operation was about 80 nsec. The average power can reach 2 W, which is the maximum cw power capability of the laser used.
Self-Resonant Current Peaks in Josephson Junctions
Authors: Blackburn J. A. , Leslie J. D. , Smith H. J.
Published: February 2004

A finite difference scheme is described which yields solutions of the Josephson phase equation. This simulation technique is used to calculate the self-resonant current peaks of a Josephson junction for the two cases, R≫ZJ and R≪ZJ, where R is the current drive source resistance and ZJ is the junction impedance. The simulation current peaks are compared with ones derived by a perturbation technique for the same two regimes, and also with experiment. In terms of approximating experimental results, it is found that the perturbation solutions with constant damping, σ, are better than those with constant Q; although at small σ the magnitude and shape of the current peaks do not agree well with observations. However, simulation results at small σ are reasonably consistent with experiment. Simulation results for the case R≪ZJ indicate that self-limiting will affect the magnetic field dependence of the resonances when L/λJ≥2, where L is the length of the junction and λJ is the Josephson penetration depth.
Calorimetric Method for the Determination of Losses in Pulsed Superconducting Magnets in Superfluid Helium
Authors: Bergmann Wilfried H.
Published: February 2004

A calorimetric method for the determination of the heat dissipation of small superconducting magnets operated in a pulsed or cycling mode in the range from 1.5° to 2.15°K is reported. Preliminary results are given for a NbTi magnet and the accuracy of the technique is discussed.
Magnetic Hysteresis in Simple Materials. I. Theory
Authors: Baldwin John A.
Published: February 2004

A wall-pinning model is applied to the motion of a single domain wall. The model assumes that hysteresis is due to localized pinning of walls at defects and their subsequent snapping free. A distribution function is introduced to describe the differing strengths of defects in a real sample. The general theory is applied to the symmetric minor loop, the virgin curve, and to drifting minor loops. The theory makes two interesting predictions about the relation between symmetric minor loops and the virgin curve. They are both properties of the Rayleigh loop. One of these is that the virgin curve is the locus of apexes of centered minor loops. A method for measuring the distribution function from a minor loop is given. The theory is then specialized to the case of a particular distribution function which has been found to hold experimentally. The theory is applied to the cases described above. Special attention is given to the Rayleigh region. It is found that there is a relation between the Rayleigh constants μ and a and the coercive force Hc similar to that given by Néel, namely, μ/a=1.58Hc. For a sinusoidal variation of flux, the first three Fourier components of mmf are calculated.
Sensitivity Enhancement of a Pulsed NMR Spectrometer
Authors: Hanabusa M.
Published: February 2004

A sensitive pulsed NMR spectrometer for solids based on a multiple-pulse technique is described. In the conventional pulse method transient signals are accumulated for a certain time when signal-to-noise ratio must be improved; however most of the time spent for measurement is wasted because T1≫T2. Since the multiple-pulse technique prolongs the decay time of transverse magnetization, one can accumulate extra signals and enhance the sensitivity. Under the optimum condition the enhancement factor is (T1/T2)1/2 for a given measuring time. One can take full advantage of low temperatures to increase the sensitivity. Typical spectra taken for aluminum metal show sideband peaks. The line width is made narrow if a high-resolution multiple-pulse technique is used. The signals were accumulated in a modified boxcar integrator. Several applications are discussed.