bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Electrostatic Field Gradient in Semiconductors with Diffused Impurities
Authors: Jain G. C. , Al-Rifai R. M. S. 
Published: April 2005

Previous works on the evaluation of the collection efficiency of diffused radiant energy converters have assumed a constant electrostatic field in the diffused region. In order to match the theoretical spectral response based on this assumption with the experimental results, extremely low values of minority carrier lifetime were further assumed. No physical explanation is available for these assumptions.
Using the basic diffusion theory, a theoretical investigation of the effects of impurity distribution in diffused semiconductors has been carried out for diffused impurity profiles produced by (1) diffusion from an infinitesimally thin layer of dopant and (2) diffusion from a constant podant source. It has been established that the electrostatic field gradient in the diffused semiconductor acts as an equivalent recombination effect with an equivalent minority carrier lifetime of the order of 10−10 sec. It has been shown that the effect of an electrostatic field gradient is much more predominant than the radiative and nonradiative recombinations.
Growth of Sputtered vs Evaporated Metal Films
Authors: Chopra K. L. 
Published: April 2005

The early growth stages of sputtered (S) vs evaporated (E) Ag/mica and Ag/NaCl films have been studied by transmission electron microscopy and electron diffraction. The observed maximum density of the islands at thicknesses less than 20 Å is slightly higher for S films, although the order of magnitude is the same (∼1011/cm2) for both the S and E films. Electrostatic charges carried by the S atoms and the point defects caused by the penetration of the energetic S atoms could account for the observed higher S-island density.
As the film thickness increases, the S-island density at 25°C decreases rapidly to reach a constant value before the film becomes continuous. The corresponding E-island density decreases slowly. The higher mobility, as indicated by the rate of change of the island density, and the observed epitaxial growth of the S films at a temperature considerably lower than that obtained for E films, are attributed to the higher kinetic energy of the S atoms. The E-island density decreases rapidly as the substrate temperature is increased. The decrease in S-island density is, however, accompanied by an increase in the surface area of the islands and formation of bridges between the islands, thereby resulting in coalescence at a smaller nominal thickness than is observed in E films. These observations are explained on the basis of the effects of higher electrostatic charges and kinetic energy of the S atoms.
The activation energies for the diffusion processes, calculated from the temperature dependence of the separation between the islands, are 0.1 and 0.15 eV for S and E films, respectively, at substrate temperature below 250°C. Above 250°C, the activation energies increase rapidly to 0.5 and 0.9 eV, respectively.
Electrical and Magnetic Properties of Compositions in the Tantalum-Carbon System
Authors: Steinitz Robert , Resnick Robert 
Published: April 2005

Electrical and magnetic properties have been measured in the tantalum-carbon system from Ta2C to TaC1.0. A large variation of these properties has been found within the wide homogeneity range of TaC: the resistivity increases with carbon deficiency from 25 to about 150 μΩ. cm, and the magnetic susceptibility changes its sign, the material being paramagnetic at stoichiometry and diamagnetic at the low-carbon phase boundary. The temperature coefficient of the resistivity has also been found to be characteristic for each composition and to depend strongly on the Ta:C ratio.
A method for preparation of homogeneous samples of a predetermined carbon content has been developed. The experimental results are discussed in the light of previous theories.
Analysis of a Room-Temperature cw Ruby Laser of 10-mm Resonator Length: The Ruby Laser as a Thermal Lens
Authors: Roess Dieter 
Published: April 2005

A nominally plane-parallel ruby laser of 10-mm length was investigated in continuous operation in an ellipsoidal pumping system under water cooling. The laser emits pure transverse modes of low order. The zero-order mode can be described by Gaussian distributions; it corresponds approximately to the mode of a confocal resonator of 9-cm radius of curvature. The resonator curvature is induced by a thermal curvature of the ruby end faces and by a bulk thermal lens effect.
The axial-mode frequencies and the emission-center frequency shift to smaller values with increasing pump power as a consequence of the increasing ruby temperature in cw operation. The relaxation pulses of single axial modes do not overlap in this short laser, and the interaction of different axial modes can be observed in the emission of one mode. Consequences of the observed thermal curvature for the transverse mode selection of cw and pulsed crystal lasers are discussed.
Electromagnetic Waves in Parameter Space for Finite Magnetoplasmas
Authors: Granatstein V. L. , Schlesinger S. P. 
Published: April 2005

High-frequency electromagnetic waves guided by an air-bounded, axially magnetized, plasma column of radius a are studied through the technique of parameter space mapping. The parameter space is 3-dimensional with coordinates ωp/ω, ωb/ω, and c/ωa. In this 3-space, cutoff and resonance loci form surfaces which enclose approximate domains of existence for various classes of waves.
Three wave classes, characterized by distinctive cutoff and resonance surfaces, are identified for a magnetized plasma column, and their relation to waves in a boundless plasma, and on a column of small radius (quasistatic waves) is investigated. Also, evidence is found for the continued existence of the surface wave class into the regime ωb&gt;ωp.
Parameter space analysis leads to a determination of salient dispersion characteristics for all wave classes and all order of azimuthal variation by a method contributing to physical insight but which avoids exact but laborious numerical computation. Waves are found which change from forward to backward or vice versa with increasing wave number.
Small-Signal Analysis of Internal (Coupling-Type) Modulation of Lasers
Authors: DiDomenico M. 
Published: April 2005

The internal modulation of lasers by a variation of cavity losses is analyzed in terms of the normal modes of the system. Time-dependent perturbation theory is used to describe the results of resistive mode coupling when the losses are modulated with small signals. For the single-mode oscillator, an expression is obtained for the amplitude distortion in the modulation index of the light produced by a coupling-type internal modulator when the losses are modulated at a frequency commensurate with the separation between longitudinal modes of the laser cavity. Low distortion is obtained when the modulating frequency is noncommensurate with the longitudinal-mode frequency separation. The internal coupling-type modulator in its present form can provide small amounts of modulation over bandwidths limited to the separation between adjacent interferometer cavity normal modes.
For a multimode oscillator, modulation of the internal losses at a frequency equal to the separation between adjacent longitudinal modes produces a pulse-modulated output wave. The average intensity is unchanged and the peak intensity is increased over the intensity of the unmodulated laser by a factor equal to the number of oscillating modes.
Experiments on the Origin of Moving Striations
Authors: Cooper A. W. 
Published: April 2005

The origin of moving striations has been investigated by measurement of striation propagation at a sharp change in tube diameter, by study of the relationship between anode spot oscillations and moving striations, by observation of anode spot oscillations at the cutoff current for moving striations, by use of an auxiliary discharge to suppress anode potential oscillations, and by study of a striation system isolated from electrodes. The experiments indicate that: (a) the striation frequency, velocity, and wavelength all change discontinuously at a change in tube diameter; (b) visible spot oscillations are accompanied by oscillations in discharge potential, and exist unchanged above the critical current for disappearance of moving striations; (c) anode oscillations and anode spots may be suppressed by operation of an auxiliary discharge to the anode; (d) the striation frequency synchronizes to an applied oscillation at the anode, provided the applied frequency is close to a small integral multiple of the natural striation frequency; and (e) a striation system can be maintained in a vessel separated from the electrodes by narrow tubes operated above the local critical current for moving striations. No oscillations can be detected in the isolating regions either photoelectrically or with electrostatic probes.
It is concluded that: (1) anode oscillations and moving striations are independent phenomena; and (2) moving striations do not constitute the response of the discharge to an external perturbation, but appear to result from a local instability in the positive column.
Investigations of Polyethylene Single-Crystal Suspensions by Light Scattering
Authors: Peterlin A. , Meinel G. 
Published: April 2005

The light intensity scattered by polyethylene single crystals in dilute suspensions was investigated as a function of temperature and time in order to obtain information on crystallization and crystal dissolution as a function of crystallization temperature and time, of molecular weight and polydispersity. Whole polymer and three fractions were studied.
The crystallization is relatively fast and complete with a fractionated sample of Mv = 85 000 but extremely slow with Mv = 9600 and 300 000 and also with the unfractionated polymer. As a consequence, fractionation occurs during crystallization. The uncrystallized fraction remaining in solution even after prolonged isothermal crystallization crystallizes during subsequent cooling, partly yielding markedly less stable crystals which dissolve many degrees below the main dissolution temperature.
During annealing the scattered intensity first drastically drops, indicating a high degree of crystal dissolving. With fractionated polyethylene (Mv = 85 000) it rises again nearly linearly with the log of annealing time. The increase is extremely small or nearly missing with unfractionated samples. With the latter the fractionation during prolonged annealing is significant.
The scattering intensity of all samples shows a change of temperature coefficient around 70°C as a consequence of a change in slope of the temperature dependence of both refractive indices of polyethylene crystal lamellas.
Influence of Thermal Stresses on the Infrared Stimulability of Thallium-Doped Potassium Iodide Single Crystals
Authors: Kun Zoltan 
Published: April 2005

It was observed that the room-temperature infrared stimulability (IRS) of one KI crystal containing 1.2×10−3 mole% Tl was twice as high as that of another with 4.5×10−3 mole% Tl concentration. An experiment was designed to study this apparent discrepancy. X-ray rocking curves of the as-grown material showed that the crystal containing the lesser amount of Tl was plastically deformed, probably due to thermal stresses developed during crystal growth. Both crystals were subsequently annealed at 600°C. The change in the x-ray rocking curves for the originally deformed crystal suggested that there was an extensive rearrangement of the defect structure, mainly under the influence of stress fields around dislocations. Etch pit studies supported this conclusion. In the heavily doped crystal the annealing changed the misorientations of the substructure. This suggested subgrain boundary movement. Extrinsic ionic conductivity measurements showed similar behavior for both samples: In the as-grown state there were some free vacancies. Annealing almost eliminated them and increased the conductivity. After the annealing, the intensity of IRS of the lightly doped crystal dropped to about one-fifth of its original value; in the heavily doped crystal it did not change.
Various models are discussed consistent with results for mechanically deformed samples. It is concluded that a certain kind of stress of a thermal nature is associated with the excessive IRS of the lightly doped sample.
Fibered and Epitaxial Growth in Sputtered Films of GaAs
Authors: Molnar B. , Flood J. J. , Francombe M. H. 
Published: April 2005

The crystal texture of GaAs films sputtered onto vitreous silica and polished CaF2 substrates has been investigated by electron diffraction and microscopy, and by x-ray diffraction, over a substrate temperature range from room temperature up to 600°C. On silica substrates the GaAs films possess either an amorphous structure or a crystalline structure with one-degree orientation of the crystallites, depending on the substrate temperature and on the sputtering condition at the growing surface. In cases where the anode substrate support is kept in the positive column of the discharge a predominant 〈111〉 orientation is present over the whole temperature range. When the GaAs films are deposited on a substrate in the Faraday dark space, however, they are amorphous up to about 400°C, and show a 〈110〉 texture up to 510°C that changes abruptly to a 〈111〉 texture with further temperature increase. The persistence of the 〈111〉 texture, under anodic glow conditions at low nominal substrate temperatures is attributed to indirect heating derived from energy liberated at the growing surface. The use of a polished crystal of CaF2 in place of the vitreous silica substrate does not alter the observed orientation effects.
Electron diffraction studies have also been made of the growth of GaAs films on single-crystal Ge substrates. In GaAs films sputtered onto the (100), (110), and (111) faces of Ge, epitaxial growth occurs at elevated temperatures but is only complete above 560°C, and is usually associated with extensive twinning. At temperatures above 580°C breakdown of the epitaxial structure occurs and appears to be associated with loss of arsenic.
Thin Films of Niobium Tin by Codeposition
Authors: Neugebauer C. A. 
Published: April 2005

Thin films of niobium tin were deposited by the simultaneous condensation of niobium and tin vapor from two separate evaporation sources in a vacuum system. The composition and structure of the deposit was examined as a function of substrate temperature and the relative impingement rate of niobium to tin.
If this rate ratio is near 3:1, the cubic phase Nb3Sn is the predominant product, regardless of substrate temperature, even if it is much below the temperature where Nb3Sn forms in the bulk. For a ratio of 3:2, and at substrate temperatures less than 800°C, formation of Nb3Sn is almost entirely suppressed, and phases higher in tin predominate. Annealing at 900°C converts the phases high in tin to Nb3Sn.
The superconducting critical temperature of codeposited niobium tin films is below 14°K before annealing and above 14°K after annealing at 900°C. The superconducting energy gap is the order of 1 meV at 4.2°K, considerably below the value predicted by the BCS theory. This suggests that the material on the surface of the films has a lower critical temperature than in the interior.
Static Stress Fatigue and Strength of a Vitreous Silicate
Authors: Levengood W. C. 
Published: April 2005

Various types of static loading stresses were applied to freshly cleaved surfaces formed on glass laths. With increasing applied force the number of linear flaws increased. At high stresses the number per unit area was the same order of magnitude as predicted for the pile up of surface flaws to form a microcrack. The diameter of loop flaws, originating at etch pit sources, increased with stress in agreement with a theoretical prediction based on a vacancy diffusion mechanism. It was postulated that with applied loads the vacancies diffuse into the loop source region and increase the local stress field. This stress is partially relieved by the loop expansion.
Higher flaw densities were found by etching during actual stress application than by loading in air followed by placing in the etchant. This difference was explained for samples loaded in air by the release of the stress causing some of the flaws to disappear before placing in the etchant, whereas loading under the etchant displays the flaws formed during the loading period. Probe experiments showed that the flaw patterns are not the result of a stress release effect in a surface film created by the etching solution.
Samples subjected to localized forces, applied under the etchant, disclosed an increase in local flaw concentration in direct proportion to the load. The results appeared to be linear until the typical Hertz cone fracture occurred. At fracture there was a sudden decrease in the flaws formed at the load region. This decrease in flaw concentration at fracture was believed to indicate the combining of flaws to form a microcrack.
The importance of surface energy changes on the flaw formation was also shown in quantitative measurements. With decreasing surface energy the flaw length Fl and flaw number Fn also decreased. On aged surfaces the flaw interaction is less extensive and this may explain the reported higher indentation strengths on cleavage surfaces that have been aged. The buildup of flaws and the formation of microcracks also offers a possible explanation for the maximum measured strength of glass being less than one-half the theoretical value.
Magnetoacoustic Resonance in Lithium Ferrite
Authors: Comstock R. L. , Remeika J. P. 
Published: April 2005

The parametric coupling of magnetostatic and elastic modes (magnetoacoustic resonance) has been observed in a single-crystal lithium ferrite sphere. Observation of this effect was made possible by the development of highly ordered stoichiometric lithium ferrite which has the narrowest ferromagnetic resonance linewidth of the spinel ferrimagnets [ΔH(300°K)=1.7 Oe, ΔH(134°K)=0.9 Oe at 5.4 G/sec]. The Q of the oblate-prolate elastic mode for this sphere was found to be 175 000 at 300°K.
An estimate of one of the two magnetoelastic coupling constants resulted in a value B1=65×106 erg cm−3. This estimate was made by comparing the magnetoacoustic threshold for a sphere of this material with the threshold for a sphere of yttrium iron garnet (YIG), for which the coupling constants are known.
A figure of merit for magnetoelastic materials is presented on the basis of which it appears that lithium ferrite may be superior to YIG in some transducer applications.
Ferromagnetism in Rare-Earth Group VA and VIA Compounds with Th3P4 Structure
Authors: Holtzberg F. , McGuire T. R. , Methfessel S. , Suits J. C. 
Published: April 2005

The bcc structure I4̄3d−Td6(Th3P4) occurs as a defect structure in 2:3 compounds of rare-earth elements with S, Se, and Te, or as an inverted structure in 4:3 compounds with group VA elements. The structural, electric, and magnetic properties of the metallic 4:3 compounds and the 2:3 rare-earth semiconductors have been investigated with specific reference to gadolinium, for which the S ground state gives the minimum crystal field effect.
Gd4Bi3 and Gd4Sb3 are both ferromagnetic with a saturation magnetization obeying the spin-wave T32 law up to 0.8 of the Curie temperature. The Curie temperature Tc varies in the solid solution system Gd4Sb3– Gd4Bi3 with composition from 260° to 340°K. The semiconducting compound Gd2Se3(ρRT=3 Ω cm) has been found to be antiferromagnetic below TN=6°K. Solution of Gd in the holes of the defect Th3P4 structure decreases the electrical resistivity without a measurable variation of lattice constant (a0=8.718 Å). With increasing conductivity the material changes from antiferromagnetic to ferromagnetic. At the composition Gd2.1Se2.9 the Curie temperature is Tc=80°K with ρRT=1.4×10−3 Ω cm. The relation between Curie temperature and electrical resistivity has been examined by introducing the same spin concentration into Gd2Se3 by Eu2+ doping. The semiconductor Eu0.5Gd1.6Se2.9 is paramagnetic. However, Y0.5Gd1.6Se2.9 has low resistivity and is ferromagnetic below Tc=47°K.
Galvanomagnetic Properties of Ferromagnetic Uranium Monosulfide
Authors: Kanter Manuel A. , Kazmierowicz Casimir W. 
Published: April 2005

Uranium monosulfide, a high-melting-point compound (2740°K) with a NaCl structure has been found to be ferromagnetic with a Curie point at 180°K and a saturation magnetic moment of 1.02 Bohr magnetons per atom at 0°K. Resistivity, magnetoresistance, and Hall effect measurements were made in the temperature range, 4.2°–360°K, so that these properties could be measured in the ferromagnetic and the paramagnetic solids. Sintered polycrystalline samples were used.
The electrical resistivity was found to be about a hundred times larger in US than in the common ferromagnetic metals but the temperature dependence was similar showing an abnormal decrease below the Curie point. The magnetoresistance was found to be negative with a sharp minimum at the Curie point. Study of the Hall effect revealed that two Hall coefficients could be identified as in the transition metals. The extraordinary Hall coefficient related to the magnetization was found to vary as the 2.1 power of the resistivity in reasonable agreement with previous theories of this effect. The ordinary Hall coefficient related to the applied field was found to be positive and temperature-dependent with a maximum at the Curie point, whereas in the ferromagnetic metals, the Hall coefficient is found to be temperature-independent with the exception of an anomalous behavior near the Curie point. A similar anomaly is observed in US which occurs over a much wider temperature range than in the common ferromagnetic metals. The effective carrier concentration evaluated from the ordinary Hall coefficient is 0.45 holes per U atom at absolute zero.
These results can be correlated with a band picture based on overlapping 7s and 5f bands, where the states in the broad 7s band contribute the major conductivity whereas the magnetic behavior is due to the unpaired spins of electrons in the narrow 5f band. Equilibrium between the bands requires a redistribution of electrons between them as the temperature varies giving rise to the observed temperature dependence of the galvanomagnetic properties. Similar measurements on isostructural ThS and UP and their solutions with US will provide a critical test of this band model.
Ferrimagnetic Garnets Containing Pentavalent Vanadium
Authors: Geller S. , Espinosa G. P. , Williams H. J. , Sherwood R. C. , Nesbitt E. A. 
Published: April 2005

In a recent publication, magnetic data were reported on the newly discovered garnet {Ca3}[Fe2](Fe1.5V1.5)O12. In this paper, magnetic and crystallographic data on garnets in the systems {M3−2xCa2x} [Fe2](Fe3−xVx)O12, M≡Y or Bi, are reported. It appears that for all values of x, 0&lt;x≤1.5, Curie temperatures are higher than would have been expected. Up to x≅0.7, the Curie temperatures are equal to or slightly greater than that of yttrium iron garnet itself, then decrease gradually to 493°K for {Ca3}[Fe2](Fe1.5V1.5)O12. Garnets in the system {Bi3−2xCa2x} [Fe2](Fe3−xVx)O12 with 1.5&gt;x&gt;0.8 exist. The magnetic behavior of the garnet {Bi0.5Ca2.5}[Fe2](Fe1.75V1.25)O12 is essentially the same as that of the yttrium analog. Pentavalent vanadium substitution thus provides lower moment garnets with high Curie temperatures and, including Bi3+ ion substitution, ferrimagnetic garnets not containing rare earths or yttrium.
The full-length paper with the above title has been published.