bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spectral Measurements with Aligned and Misaligned Two-Crystal Spectrometers. I. Theory of the Geometrical Window
Authors: Schnopper Herbert W. 
Published: April 2005

It is shown in this paper that (1) the geometrical window of the instrument is a function of the alignment of the crystals, the beam, and the rotation axes as well as the vertical divergence, (2) even for the case of perfect spectrometer alignment, errors are introduced into the measurement of the spectral parameters because of the presence of a finite vertical divergence in the x-ray beam, and (3) improper beam and crystal alignment cause inaccuracies in the measurement of spectral parameters, e.g., wavelength position, linewidth, line shape, and asymmetry.
Calculations which predict the effects of vertical divergence and of beam and crystal misalignment on the geometrical window and also on the wavelength position, line shape, linewidth, and line asymmetry of the (1,+1) and (1,−1) curves are made for the case of CuKα radiation reflected from calcite crystals. In particular, it is shown that the error in the measurement of the Bragg angle, i.e., wavelength, is 61/2 times more sensitive to misalignment of the central ray of the x-ray beam than it is to total vertical divergence.
Spectral Measurements with Aligned and Misaligned Two-Crystal Spectrometers. II. Alignment
Authors: Schnopper Herbert W. 
Published: April 2005

Conditions for and methods of aligning a two-crystal spectrometer are discussed. These include the alignment of rotation axes, crystals, and x-ray beam. The results of a new nondispersive crystal alignment procedure are compared in detail with theory for a typical case of CuKα radiation and calcite crystals. This method is contrasted with other procedures which lead only to pseudo-alignments.
It is shown that x-ray methods which are sensitive to vertical divergence do not lead to crystal alignment unless the beam is already perfectly aligned. It is concluded that the x-ray beam can be aligned only after the crystals have been aligned.
Dislocation Energy and Dislocation Networks in α-Iron
Authors: Chou Y. T. 
Published: April 2005

A refined analysis of dislocation energy and dislocation networks in {110} planes of α-iron crystals is presented on the basis of anisotropic elasticity.
Contrary to the conclusions given by isotropic theory, the elastic energy per unit length of a screw segment, with Burgers vector a〈100〉, is greater than that of an edge segment with the same Burgers vector lying in a {110} plane. The latter in turn is greater than the sum of the energies of two screw segments with Burgers vector (a/2)〈111〉.
The shape of a stable net composed of a〈100〉 screw segments and (a/2)〈111〉 segments of mixed character in {110} planes is determined by the line tension method. Comparison between theory and experiment is discussed. It is shown that the anisotropic theory agrees well with the observations.
Plastic Deformation of Calcium Tungstate Single Crystals
Authors: Arbel A. , Stokes R. J. 
Published: April 2005

Calcium tungstate deforms by slip on the (001) 〈100〉 system above 400°C. Simple shear over this plane is the only deformation mode observed under compression at temperatures up to 900°C and a strain rate of 10−3sec−1. The critical resolved shear stress is strongly temperature dependent. Crystals cannot be plastically deformed at room temperature, at 400°C they are still quite brittle but by 900°C they are soft (yield stress, 500 psi) and plastic. Slip traces at all temperatures are fine and straight but those produced at lower temperatures (600°–700°C) have a greater surface tilt and are more sharply defined than those produced above 800°C. This is due to fewer dislocation sources and restrictions on dislocation multiplication at lower temperatures.
The role of bonding and crystal structure in the selection of slip parameters is discussed. It is considered that the stacking of the oxygen ions is the dominant factor dictating the slip plane and slip direction. Slip cannot occur without some distortion of the covalently bonded WO42− radical, which probably accounts for the strong temperature dependence of the critical resolved shear stress. It is shown that relatively easy slip in a given [100] or [010] direction can only occur between every other pair of (001) planes. Thus, a jogged dislocation which is mobile on one plane will become immobile on the next (or any odd number) plane. This is considered to restrict dislocation multiplication at low temperatures.
Observations of Impurity Precipitates in Magnesium Oxide Single Crystals by Ultramicroscopy
Authors: Miles G. D. 
Published: April 2005

Magnesium oxide crystals have been examined in an ultramicroscope and the arrangements of precipitate particles in the material are illustrated. Unusual dislocation configurations are revealed by decoration in certain crystals.
It has been suggested in the literature that most precipitate particles in magnesia are of zirconium oxide. The present observations of particle density indicate that it is unlikely that this is completely true at least for heat-treated samples, even if the particles are finer than has formerly been assumed.
Plasma Diagnosis by Means of Optical Scattering
Authors: Schwarz S. E. 
Published: April 2005

When a pulse of intense light from a laser passes through a plasma, a very small fraction of the light is scattered out of the beam by free electrons. Measurements of the intensity and spectral distribution of the scattered light can be related to the electron density and velocity distribution in the plasma. This paper presents a general discussion of the use of optical scattering as a plasma diagnostic technique. Applicability to various experimental situations is discussed, and considerations of interest in the design of diagnostic apparatus are presented.
An apparatus has been constructed for the measurement of electron density in cold plasma. The apparatus is described in some detail. Typical results are given for densities as low as 1013 electrons/cm3.
Effect of Initial Velocity on One-Dimensional, Bipolar, Space-Charge Currents
Authors: Howes Walton L. 
Published: April 2005

Oppositely directed flows of positive and negative charges constitute a bipolar current. A general case is analyzed in which the charges traverse the evacuated space between plane-parallel boundaries and all particles of a given charge species are monoenergetic. Moreover, it is assumed that the charges may possess nonvanishing initial kinetic energy. This represents an extension of analyses by Langmuir and Müller-Lübeck for vanishing initial kinetic energy.
Sample calculations of dimensionless current densities, electric and potential fields, and charge-density distributions are exhibited for cases where the electric field is assumed to vanish at one boundary but the species initial velocities may not. It is shown that resulting ion currents may be several times the Child's law limit if initial kinetic energies are of the order of the potential energy.
Changes in the Soft X-Ray L Emission Spectra with Oxidation of the First Series Transition Metals
Authors: Fischer David W. 
Published: April 2005

Changes which occur in peak positions, band shapes, and intensities with oxidation are presented for the five main L emission lines from the first-series transition metals. It is shown that the L bands shift in wave-length when going from metal to oxide, the amount of shift depending on the metal target and its state of oxidation. The dependence of the LII/LIII intensity ratio on accelerating potential, valence state, and atomic number are also presented and discussed.
A flat-crystal vacuum spectrometer with electron excitation and a thin-window flow-proportional counter was used to obtain the data.
Work Function Measurements of Nickel, Molybdenum, and Tungsten in a Cesium-Hydrogen Atmosphere
Authors: Rump B. S. , Gehman B. L. 
Published: April 2005

The addition of a second component to the cesium gas phase of a thermoionic generator could increase its efficiency by reducing the work functions of the electrodes.
The different possible additives were screened and hydrogen, since it appeared to be the most promising, was chosen for further study.
The work function reduction of cesium-covered nickel, molybdenum, and tungsten due to the presence of H2 in the gas phase ranges from 0 to 0.5 eV. An equilibrium condition can be established between the surface and the gas phase to make the low work function surface stable at elevated temperatures.
Hydrodynamic Analysis of Noise in a Finite-Temperature Electron Beam
Authors: Hsieh H. C. 
Published: April 2005

On the basis of a small-signal, one-dimensional analysis, a set of basic macroscopic differential equations, governing the fluctuations in quantities such as the electron-beam temperature, the mean velocity, and the current density, has been derived by taking moments of the Liouville equation with respect to the velocity variable. This set of differential equations expresses the conservations of charge, momentum, and energy, and is valid for an arbitrary amount of velocity spreading and includes the effect of heat conduction.
A system of differential equations, governing the correlation among the fluctuations in the mean velocity, current density, and beam temperature, is also derived. The relationship among the various noise parameters along the electron beam is obtained in the form of a system of differential equations whose solution gives detailed information on the variation of the noisiness parameter along the beam. The solution of the system of differential equations thus derived is also discussed.
Preparation and some Properties of Mg2Ge Single Crystals and of Mg2Ge p-n Junctions
Authors: Kroemer H. , Day G. F. , Fairman R. D. , Kinoshita J. 
Published: April 2005

A technique was developed for the preparation of high-quality single crystals of Mg2Ge with controlled dopings. It utilizes the reaction of stoichiometric amounts of the constituents in a graphite crucible inside a hermetically sealed tantalum bomb, followed by the solidification of the molten compound into a single crystal by lowering the bomb through a temperature gradient (Bridgman technique). Several crystals without intentionally added dopants were grown as well as crystals to which the donors antimony, arsenic, boron, the acceptor sodium, or the apparently insoluble element uranium, had been added.
A technique was also developed for the preparation of p-n junctions on n-type Mg2Ge, utilizing the alloying to and diffusing into the Mg2Ge of a thin evaporated gold film. p-n junctions prepared in this way exhibit undesirably large reverse currents, but high breakdown field strength and very pronounced surface passivation properties, which might make Mg2Ge a desirable material for MOS (metal-oxide-semiconductor) devices.
Third-Order Elastic Constants of Ge, MgO, and Fused SiO2
Authors: Bogardus E. H. 
Published: April 2005

The third-order elastic constants of germanium, magnesium oxide, and fused silica have been measured using the pulse superposition method for determining the ultrasonic velocity as a function of both uniaxial and hydrostatic pressure. From these measurements all six third-order elastic constants were calculated by using the equations of Thurston and Brugger for MgO and Ge, and the three independent isotropic third-order constants were calculated for fused SiO2.
The results for Ge are in good agreement with the most recent data of McSkimin and Andreatch. The results for MgO agree in part quite well with theoretical data calculated from a Born-Mayer potential. Drastic failure of the three Cauchy relations indicates the presence of many body forces. For fused silica, the remaining Cauchy relation is, as may be expected, not well fulfilled.
Mechanical Properties of Thin Nickel Films
Authors: Grunes R. L. , D'Antonio C. , Kies F. K. 
Published: April 2005

Vapor-deposited nickel films in the thickness range 700 to 4000 Å were stressed to fracture in uniaxial tension in the as-deposited condition and after annealing at 650°C for 3 h or at 700°C for 5 min. The existence of a strength dependence on thickness was observed for both the as-deposited and annealed films; however, the as-deposited films were 1½ to 2 times stronger than annealed films of comparable thickness. The thickness-strength relationship for as-deposited films was found to be σ = 134 kg/mm2+(1675 Å kg/mm2)t−½, while that for the annealed was σ = (−.0245 kg-mm−2/Å) t+155.6 kg/mm2. Both the annealed and as-deposited films exhibited fracture strengths in excess of bulk nickel of analogous structure.
It is believed that the observed high strengths of as-deposited nickel films are due in part to the high defect density arising from the vapor deposition process and to the proximity of the film surfaces which further inhibits dislocation motion. With regard to the latter, a mechanism involving dislocation pile-up is proposed.
Silicon/Corundum Epitaxy
Authors: Porter J. L. , Wolfson R. G. 
Published: April 2005

The crystallographic aspects of silicon/corundum epitaxy were investigated. Epitaxial deposition was carried out on corundum substrates of two orientations, and the observed crystallographic relationships were shown to be determined by three-dimensional matching between the silicon structure and the sublattice of possible cation sites in corundum.
Single-crystal silicon layers were deposited onto (0001) and (8̄629) corundum substrates. For growth on (0001) corundum, (111) silicon is parallel to the interface with [1̄10] silicon parallel to [2̄110] corundum. For growth on (8̄629) corundum, the silicon plane parallel to the interface is irrational, but the epitaxial relationship closely approximates to the following: (001) silicon parallel to (0001) corundum with [1̄10] silicon parallel to [2̄110] corundum.
These two epitaxial relationships are the only ones which permit three noncoplanar symmetry axes of the silicon to coincide with three such axes of the cation site sublattice of the corundum. They insure compatible surface symmetries and similar surface densities on an arbitrary deposit/substrate interface. In general, the silicon atom density on the interface does not exceed the cation site density. When it does so, however, the rational crystallographic relationship is modified slightly in order to lower the density of silicon atoms below that of the possible cation sites.
Dislocations and Stacking Faults in Rutile Crystals Grown by Flame-Fusion Methods
Authors: Barber D. J. , Farabaugh E. N. 
Published: April 2005

Single crystals of rutile, grown by the Verneuil method, have been chemically thinned and examined by electron transmission microscopy. The density and distribution of dislocations agree with that expected from etch pit data. This density is at least two orders of magnitude below that for rutile films formed by oxidizing titanium carbide. The etching of dislocations and stacking faults is described.
Some preliminary results of high-temperature studies in the microscope are reported. These include the discovery of a hitherto unknown slip system, {001} 〈100〉.
Quantum Efficiency and Radiative Lifetime in p-Type Gallium Arsenide
Authors: Vilms Jüri , Spicer William E. 
Published: April 2005

A new method for the study of radiative recombination in uniformly doped semiconductors has been developed and applied to p-type gallium arsenide. The bulk quantum efficiency is obtained by measurement of photoluminescence as a function of the penetration length of the exciting radiation. Using an estimated electron mobility, the total recombination lifetime of electrons (minority carriers) is found from this photoluminescence measurement and also independently by the measurement of surface photovoltage. The radiative lifetime is determined from the bulk quantum efficiency and the total electron lifetime. The model on which these measurements are based accounts for the principal factors affecting the intensity of photoluminescence, i.e., bulk quantum efficiency, surface recombination, and refraction and reflection of luminescence at the sample surface. The model is consistent with the experimental data for the p-type gallium arsenide samples studied.
The bulk quantum-efficiency values obtained here are 8% at 300°K and 28% at 80°K for two higher-efficiency samples and 6 times lower for a third sample. The radiative lifetime of electrons is found to be approximately 2×10−8 sec at 300°K, and 3×10−10 sec at 80°K. The total lifetime of electrons (minority carriers) is found to be approximately 1.5×10−9 sec at 300°K and 10−10 sec at 80°K for the two higher-efficiency samples, and 10−10 sec at both temperatures for the third sample.
Proposed Gas Maser Pumping Scheme for the Far Infrared
Authors: Wells Willard H. 
Published: April 2005

A scheme that is analogous to the operation of a heat engine is proposed for exciting maser action in the far infrared and submillimeter parts of the spectrum. A beam of hot molecules interacts through distant collisions with a cold gas of another species at very low pressure. Certain energy levels in the hot gas are cooled faster than others owing to coincidental resonances in the spectra of the two gases. In the partially cooled nonequilibrium state, population inversions are possible in the hot species.
To demonstrate feasibility, the interaction between pure rotational states of HCl and HF is discussed in detail. Barring unforeseen experimental difficulty (e.g., chemical activity of HF) the Schawlow-Townes condition for maser action can be satisfied by the J=3 → 2 transition in HF at 123.1 cm−1, or 81.25 μ.
Observations on Electromigration and the Soret Effect in Tungsten
Authors: O'Boyle Dennis 
Published: April 2005

Observations on both electromigration and the Soret effect in tungsten have been recorded using silhouette electron microscopy and electron microscan techniques. The surface structure developed when a tungsten wire is heated by a current density of 3.3×104 A/cm2 depends on whether the current is direct or alternating. An alternating current produces a smooth surface structure while a direct current produces a steplike structure due to electromigration of tungsten ions. The direction of the electromigration of tungsten ions is toward the cathode in agreement with the theories of Huntington and Fiks.
Soret effect diffusion has been observed in tungsten wires when subjected to a temperature gradient of 5000°C/cm. Either electromigration or Soret effect diffusion can produce pronounced changes in the original geometry of the conductor resulting in large current density variations over a short wire segment.
Slip-Induced Directional Order in Fe-Ni Alloys. I. Extension of the Chikazumi-Suzuki-Iwata Theory
Authors: Chin G. Y. 
Published: April 2005

In the present paper, calculations have been made for the magnetic anisotropy developed in cold-worked iron-nickel alloys near the 75% Ni composition. The treatment is based on the slip-induced directional order theory of Chikazumi et al. [J. Phys. Soc. Japan 12, 1259 (1957)]. The theory states that in an ordered ferromagnetic solid solution (long- or short-range order, or clustering), slip results in the creation and preferential alignment of distinct type(s) of atom pairs (e.g., Fe–Fe) which lead to an induced magnetic anisotropy. The important conclusion from this theory is that the direction of the induced easy axis of magnetization depends sensitively on the orientation of the deforming crystal and the geometry of the deformation process, as well as the type and degree of ordering in the alloy. The present treatment extends the original analysis for the case of rolling to single crystals of several new orientations: (110)[1̄12], (110)[1̄10], (111)[1̄1̄2], (112)[1̄10], and (112)[1̄1̄1]. These orientations, plus those studied by Chikazumi et al. ((100)[001], (100)[011], and (110)[001]), contain the most likely operating slip systems whose slip directions are symmetrically disposed about the rolling direction and are hence more stable than others during rolling. Some of these orientations are important components of texture in recrystallized or cold-rolled polycrystalline face-centered cubic materials. In addition to the rolling analysis, calculations have been made for the anisotropy resulting from drawing of wires with 〈111〉 and 〈001〉 axial orientations. These two orientations are likewise prominent components of polycrystalline wire textures.
The present work shows that drawing of a 〈001〉 wire induces a hard magnetic direction along the wire axis, while this axis becomes an easy direction if the orientation is 〈111〉. For rolling, except for the cases of (001)[100] and (110)[001] studied by Chikazumi et al., where the induced easy axis lies along the transverse direction, most other orientations generally place the easy axis along the rolling direction. This suggests a plausible explanation for the observation that the rolling direction becomes an easy axis of magnetization when a randomly oriented polycrystalline aggregate is rolled. This work also predicts that rolling of {112}〈111〉 and {110}〈112〉 textures (symmetrical variants included), which are prominent texture components in rolled Permalloy, results in an easy axis along the rolling direction. Suggestions for experimental testing of the theory are discussed.
Reverse Characteristics of High Inverse Voltage Point Contact Germanium Rectifiers
Authors: Simpson J. H. , Armstrong H. L. 
Published: April 2005

A theory of the reverse characteristic of high inverse voltage germanium rectifiers is developed, which takes account of the radial symmetry of the point contact and the presence of positive holes in the ``inversion region'' of the semiconductor. The field at the metal is found to consist of three components. The first component varies inversely with the radius of the contact and directly with the applied voltage for larger voltages. The second component is produced by the impurity centers and varies approximately as the cube root of the voltage. The third component is produced by the positive holes in the inversion region and is approximately constant. This last component lowers the effective barrier height for rectifiers made of very pure material. The first is the more important of the variable components and is responsible for increases in current resulting from image force and tunnel effect at high voltages. In the former case the logarithm of the current varies as V½ and in the latter as V2 approximately.
Current-voltage curves of the predicted forms have been found experimentally using short rectangular pulses varying in length from 2 to 10 μsec to minimize thermal effects. Where possible, barrier heights are determined by measurements over a range of temperatures and detailed numerical comparisons of theoretical and experimental data are made. The two sets of data are in remarkably good agreement thus implying that the theoretical picture is essentially correct.
Formation of Vortex Streets
Authors: Birkhoff Garrett 
Published: April 2005

It is shown that, for vortex trails in a nonviscous fluid, the mean longitudinal spacing a and mean transverse spacing h are invariant. It follows from this and other known facts, that the periodicity of a vortex trail is unstable, not the ratio h/a.
In a viscous fluid, a is invariant but h increases. This fact explains various known experimental observations.
A rough explanation is given for the order of magnitude of the Strouhal number S, based on the inertia opposed by the wake to transverse oscillations.
Finally, using the theory of logarithmic potential, it is shown that, even in a nonviscous fluid, the concentration of vorticity is limited to circles whose diameter is about a/4.