bluuebunny/crossref_metadata_2025 huggingface dataset:
Vacuum Voltage Breakdown as a Thermal Instability of the Emitting Protrusion
Authors: Vibrans Gerwig E.
Published: April 2005

Breakdown by thermal instability of a field emitter is analyzed, taking into account the temperature dependence of field emission and of resistivity. Beyond a certain temperature the emission increases while the necessary field drops. It is shown that for a whisker-like emitter this instability occurs when the emitting tip is only several hundred degrees centigrade hotter than the bulk of the cathode.
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.
Thermal Conductivity, Thermoelectric Power, and the Electrical Resistivity of Stoichiometric TiNi in the 3° to 300°K Temperature Range
Authors: Goff J. F.
Published: April 2005

Stoichiometric TiNi and its alloys containing Cu or excess Ni were measured to study the lattice component of the thermal conductivity. The low-temperature phonon mean-free-path is constant, depends upon solute species, and increases with solute concentration. In addition, the ideal component of the electrical resistivity shows the T2 dependence below 100°K found for the element and alloys with this same electron number. Values of the Fermi energy, effective mass, and the relative valence of the solutes are derived. Finally, one of the alloyed samples exhibits phase changes which are believed related to those seen in the pure material at temperatures above 300°K.
Mechanism of the Vapor Lubrication of Graphite
Authors: Cannon Peter
Published: April 2005

The minimum pressure vs molecular size at which the vapor lubrication of graphite is effective (Savage's ``operating curve'') can be transformed to a linear law. The law must demand the nucleation of a liquid-like adsorbed film, and this is reconciled with recent studies of physical adsorption on graphite. A physical model, consistent with the law, is adumbrated.
Structural and Magnetic Properties of Sputtered NiFe Films Grown in a dc Discharge Environment
Authors: Kay Eric
Published: April 2005

Experimental evidence is presented which verifies Middlehoek's recent extension of the Néel theory relating the coercivity with film thickness variations. Under special preparatory conditions ``inverted'' NiFe films on glass substrates were produced with excellent reproducibility. Partial oxidation leading to antiferromagnetic inclusions was shown to be absent. Resolution of the substrate temperature control problems using metal substrates in the plasma environment enabled us to show that a uniaxial anisotropy can only be induced into sputtered NiFe films over a limited temperature region. Temperature control during film growth also made possible a direct correlation of film morphology with the magnitude and uniformity of the dispersion of the easy axis of magnetization and the resultant critical field for wall motion Hc. Typical coercivity Hc, anisotropy field strength HK, and dispersion measurements on 700-Å NiFe films on very smooth 25 cm2 Ag: Cu–SiO substrates were: Hc=1.92±0.07 Oe, HK=2.85±0.03 Oe, dispersion=1.0±0.0°. Special problems pertaining to film growth in a plasma environment are discussed. A typical Lorentz micrograph of a sputtered NiFe film deposited directly onto a microscope grid is given.
STB Model and Transport Properties of Pyrolytic Graphites
Authors: Klein Claude A.
Published: April 2005

We propose to demonstrate that a coherent description of pyrolytic graphite (PG) layer-plane phenomena can be based on a parabolic two-band system with cylindrical equal-energy surfaces. In this simple two-band model (STB model), band overlap and effective mass must be interpreted as phenomenological parameters to be derived from experiments on highly heat-treated pure PG. With p-type (boron-doped) specimens, the objective is to describe the situation from the shift of the Fermi level, on the assumption that the presence of trapping centers would not inject major perturbations in the band structure. (1) Galvanomagnetic effects: As derived from zero-field resistivity and magnetoresistance mobility, the intrinsic carrier concentration and its variation with temperature in the range 0° to 1500°K implies that past a given graphitization stage band-structural features may no longer be seriously affected by the size of the carbon networks. Above room temperature the carrier concentration increases almost linearly and in accordance with a constant mean effective mass of about 0.0125 m0; low-temperature data suggest an energy-band overlap of 0.01 eV, which may be temperature-sensitive through thermal expansion. (2) Thermoelectric effects: Along the layer planes the carrier-mobility behavior is strong evidence for a relaxation time that may be taken of the form E−½. On this basis it can be shown that the STB model accounts for the Seebeck coefficient, provided that exact Fermi-Dirac statistics are used in conjunction with standard equations for semimetallic systems. (3) Magnetothermal effects: The discovery of a substantial electronic component in the low-temperature thermal conductivity of PG layer planes makes it desirable to develop methods of separating lattice-phonon and charge-carrier contributions to heat transport in graphite. It is shown that saturation magnetothermal conductivity measurements can be successfully utilized for this purpose.
Optical Dispersion of Zinc Selenide
Authors: Rambauske Werner R.
Published: April 2005

The refractive index as a function of optical wavelengths for ZnSe, a semiconductor, has been measured outside and within its broad absorption band. The data are presented in a table and in a dispersion curve.
Quenched-In Defects in p-Type Silicon
Authors: Bemski George , Dias Carlos Alberto
Published: April 2005

The defect which appears in p-type silicon quenched from 870° to 1070°K is characterized by an ionization energy about 0.4 eV from the valence band, by an activation energy for motion about 0.3 eV, and by a diffusion constant of 1.2×10−7 cm2/sec at room temperature. The principal feature of the defect during room temperature annealing is that it fits into dimension-dependent kinetics. This indicates that the process of elimination of the defect occurs at the surfaces of the samples and that in thicker samples only a fraction of the defects succeed in reaching the surfaces. The high diffusion constant makes it plausible that the defect is an interstitial silicon. Mayburg in 1956 concluded from a series of experiments that interstitials exist in large densities (∼1016 cm−3) in silicon crystals as grown; he also considered their motion to the surfaces. We believe that the present experiments point to activation of interstitials during the heating process. They may have existed in an electrically inactive form in the crystals as grown, i.e., near some imperfection. Their random diffusion brings them to the surfaces where again they lose their donor properties.
Statistical Tables for Testing Random Orientations of Cubic Crystals. II. Five-Cell Cases
Authors: Weymouth John W. , Epstein Jean H.
Published: April 2005

Critical regions at the level of significance α=1%, 5%, 10%, and 20% have been calculated for testing whether or not a sample of N single, cubic crystals is randomly oriented. The stereographic triangle has been divided into five cells in two different ways, one with respect to important crystallographic directions in fcc crystals and one with respect to those in bcc crystals. Representative tables for N=10 for fcc and for bcc crystals and for N=20 bcc crystals are presented.
Imperfections Associated with Dielectric Breakdown in LiF
Authors: Davisson J. W. , Pasternak J. , Vaughan W. H.
Published: April 2005

Linear imperfections, oriented in or near the 〈110〉 directions, accompany 〈xxy〉 and 〈110〉 electrical breakdown paths formed in LiF single crystals at room temperature. They may be screw dislocation pairs produced by the action of the electrical field on dislocation loops that were generated in the vicinity of the breakdown path.
Recovery of the High-Pressure Phase of Cadmium Sulfide
Authors: Corll James A.
Published: April 2005

The high-pressure phase of cadmium sulfide has been recovered to room pressure and room temperature. The recovered phase had the rocksalt structure with a0=5.464±0.012 Å. The pressure dependence of the electrical resistance was found to vary significantly among the various cadmium sulfide phases.
Nuclear Magnetic Resonance Studies of Molecular Motion in Some Elastomers
Authors: Slichter W. P. , Davis D. D.
Published: April 2005

The nuclear magnetic resonance (NMR) relaxation has been studied in polyisobutylene and polybutadiene at temperatures from −170° to +200°C and at three resonance frequencies: 20, 30, and 50 Mc/sec. In polyisobutylene, the spin-lattice relaxation time (T1) passes through two minima with change in temperature. The low-temperature minimum is ascribed, as in other compounds, to methyl-group rotation, but in polyisobutylene this motion is found to encounter relatively large hindrance, presumably owing to inter-locking among the groups. The high-temperature T1-minimum is ascribed to rotational and translational motion of the segments. The extent of motion is qualitatively gauged by calculation from the Bloembergen-Purcell-Pound theory for NMR relaxation in simple liquids. T1 is insensitive to molecular weight (M.W.) over a wide range, but the dependence of T2 upon M.W. changes abruptly when M.W.≅4×104. In polybutadiene, T1 is found to depend markedly on the cis-trans content.
Habits of Polyethylene Crystals Grown from Paraffinic Solvents and from the Melt
Authors: Keith H. D.
Published: April 2005

A study has been made of the morphology of fractionated linear polyethylene crystallized from solution in n-alkanes. Crystals have been found whose habits, though markedly different from any described in this polymer, are similar to, and provide useful models for, the radial crystalline units in melt-grown spherulites. Fold domain structures and departures from planarity in these crystals are also novel and correlate closely with interface morphology during growth. Crystals, or aggregates of crystals, grew preferentially in the b direction under all conditions of observation; this applies equally to dendritic growth in monolayer single crystals and to spherulites of sufficiently compact texture as to exhibit cooperative twisting of orientation.
Anisotropy of Oriented Polymers
Authors: Kao S. R. , Hsiao C. C.
Published: April 2005

For a large deformation, the deformation-dependent anisotropic elastic characteristics are illustrated through the analysis of a model medium. The variations of the elastic constants of an oriented polymer are then analyzed and correlated. The analytical results compare favorably with some available experimental data reported from dynamic measurements.
Fracture of Amorphous Polymeric Solids: Time to Break
Authors: Halpin J. C.
Published: April 2005

The failure theory of Bueche and Halpin is generalized and expanded to obtain a prediction of the time dependence of the tensile strength and ultimate elongation. The model pictures rupture as the propagation of tears or cracks within the material. The growth of a tear or crack is viewed as an ideally simple process in which the molecular chains at the tear tip stretch viscoelastically under the influence of a high stress concentration until they rupture. As a consequence, the failure process is a nonequilibrium one, developing with time and involving the consecutive rupture of the molecular chains. Substantial support for the theory is found by comparing the theoretical prediction against experimental results obtained for SBR and EPR rubbers. In addition, it is experimentally demonstrated that delayed and forced rupture experiments can yield qualitatively identical data for viscoelastic bodies. Also discussed is the basis for the approach to the nonlinear response of a viscoelastic body required here in the development of a fracture theory.
Non-Gaussian Behavior of Model Short-Chain Polymers
Authors: Carmichael Jack B.
Published: April 2005

The set of end-to-end vectors (hereafter called the discrete-state distribution) for a model polymer chain of n bonds has been generated for a three rotational state model on the B-5000 computer. Equally probable gauche-right, trans, and gauche-left states are assumed. The discrete-state distribution is determined for a polydimethylsiloxane chain with n=6, 8, 10 and a polyethylene chain with n=6, 8. For a polyethylene chain of six links the calculated distribution is shown to differ substantially from a normalized Gaussian. For each case, a function is obtained for the discrete-state distribution through the Gram-Charlier technique of expanding an unknown function f(x) in terms of a Gaussian function. The Gram-Charlier expansion is shown to give a reasonable fit to the discrete-state distribution. The distribution f(x) is shown to more accurately predict the equilibrium formation of octamethylcyclotetrasiloxane in a dimethylsiloxane polymer than does the Gaussian distribution. The problem of excluded volume is not considered for the short chains treated here.
Irradiation of Annealed Polyethylene Crystals
Authors: Salovey R. , Bassett D. C.
Published: April 2005

The amount of gel formed on irradiation of polyethylene crystals and the efficiency of gelation have been studied. Films prepared by filtering crystals from suspension with a constant pressure difference, show a decrease in gel for increasing film thickness. At constant film thickness gel increases with increasing pressure difference. Low-angle x-ray diffraction shows that lamellae are more tightly packed in films giving higher gel. When films are heated above the temperature at which their crystals were grown, characteristic changes in gel occur; the principal one is a rapid increase once crystals start to thicken. Variations in crystalline morphology are of little importance. Two other changes in gel, an initial decrease on annealing and an increase on storing at room temperature, are suggested to arise from a smoothing of fold surfaces. The results are consistent with and support the hypothesis that radiation-induced crosslinking occurs preferentially between chain-folds of adjacent lamellas, reduced gelation being due primarily to imperfect lamellar contact. Alternative explanations in terms of solvent retained in aggregates are excluded.
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.
Isotactic Polybutene-1 Single Crystals: Morphology
Authors: Holland V. F. , Miller Robert L.
Published: April 2005

Three crystalline modifications of isotactic polybutene-1 have been obtained from dilute solution in a variety of habits. These three crystalline modifications are: (a) tetragonal, (b) ``untwinned'' hexagonal, and (c) orthorhombic. The structure of the orthorhombic polymorph has not previously been reported. The basic morphology of all forms is the thin lamellar structure associated with polymer single crystals containing folded chains. A crystal-crystal transformation (from tetragonal to ``twinned'' hexagonal) was observed to occur when single crystals were allowed to stand at room temperature. This transformation involved a conformational change (from an 113 helix to a 31 helix), as well as the crystallographic one, but it did not involve a morphological change. No change in either morphology or crystallography occurred at room temperature in the orthorhombic or the ``untwinned'' hexagonal polymorphs, although both could be transformed completely into the tetragonal form if dried crystals were heated at 90°C for one hour. If allowed to stand at room temperature, the resulting tetragonal crystals transformed to the ``twinned'' hexagonal structure. The isotactic polybutene system thus constitutes an excellent case in which crystallographic, morphological, and conformational changes may be studied.
Transformation of Small-Signal Energy and Momentum of Waves
Authors: Briggs R. J.
Published: April 2005

The transformation of the small-signal energy and momentum of a wave between two inertial reference frames as first given by Sturrock are derived by using simple perturbation theory and the appropriate transformations of length, time, current, and electromagnetic fields. The approach allows a straightforward generalization to the case of relativistic linear transformations and to nonrelativistic transformations between two reference frames that rotate with respect to each other. These rotating and linear transformations allow one to make very general statements about the frequency and wavenumbers for which negative-energy waves are obtained in a rotating and translating medium, as, for example, an electron beam in Brillouin flow.
Evidence of Unpinned Surface Spins from Parallel Spin-Wave Resonances in Permalloy Films
Authors: Wigen P. E. , Kooi C. F. , Shanabarger M. R.
Published: April 2005

The nature of the surface-spin boundary condition and of the parallel resonances (H ∥ film) for spin-wave resonance in Permalloy films is determined. Computer solutions of the classical equation of motion of the spins, using the inhomogeneous internal field model, are compared with experimental results. The mode positions and intensities as a function of frequency, film thickness, and internal effective field variation are calculated. This results in the conclusion that the surface spins are unpinned and that the inhomogeneous internal field model is valid for the parallel case as well as for the perpendicular (H ⊥ film) case. The frequency dependence of the intensity of the parallel modes is particularly strong evidence for this conclusion. It is also shown that the mode positions for the prependicular case are unlikely to reliably determine the surface-spin boundary condition.
Properties of Single-Crystal Lithium Ferrite Grown in the Ordered State
Authors: Remeika J. P. , Comstock R. L.
Published: April 2005

Lithium ferrite, an inverse spinel with an order-disorder transition at about 800°C, has been grown in the ordered state. The narrowest ferromagnetic resonance linewidth yet observed in a spinel has resulted from the growth of single crystals of lithium ferrite in the ordered state. Details of the growth conditions, magnetization, and microwave ferromagnetic resonance linewidth are presented.
Magnetic Fields Associated with Thin Nickel-Iron Films
Authors: Matick Richard E.
Published: April 2005

This paper describes the external magnetic field of a thin, circular, single domain, magnetic film both experimentally and analytically. Measurements and calculations of the spatial components of flux in sense loops about nickel-iron films have been made as the sense loops are moved in specified directions relative to the film. The calculations are made on the assumption that the magnetic field of the thin film is the same as that of an oblate spheroid with uniform magnetization in the plane of the film Measurements have been made on three, 1.59-cm-diam, circular, evaporated films with different characteristics in regards to composition ratio and thickness. The thickness-to-diameter ratio of these films is on the order of 10−5. Comparison between measurements and calculations shows good agreement both in magnitude and functional dependence, indicating that the field of an oblate spheroid is a good approximation to that of a thin film. One major discrepancy is that the measured component of field in a direction in the plane of the film, but perpendicular to the magnetization, was approximately a factor of two larger than the calculated values, thus showing the limitations of the spheroid approximation. The results are presented as normalized curves; therefore, the results are applicable to any film whose thickness-to-diameter ratio is very small.
Theory of Superlinear Photoconductivity in CdS and Related Materials
Authors: Cardon Felix , Bube Richard H.
Published: April 2005

Several theoretical considerations are developed in order to make the treatment of phenomena related to superlinear photoconductivity in CdS and related materials more consistent with experimental data on these materials. Special attention has been given to the way in which various shallow trap distributions affect the dependence of photoconductivity on light intensity in the superlinear range. The nature of the breakpoints or transitionpoints between superlinear and nonsuperlinear regions is clarified. An explanation is offered for the common occurrence of hysteresis in photoconductivity vs light intensity curves in materials exhibiting superlinear photoconductivity. Finally the possibility of observing Auger recombination because of the very small electron capture cross section of sensitizing centers in these materials is discussed. Illustrative experimental results in CdS and GaAs crystals are included.
Metal-Semiconductor Barrier-Height Measurement by the Differential Capacitance Method—Degenerate One-Carrier System
Authors: Goodman Alvin M. , Perkins David M.
Published: April 2005

An expression is derived for the differential capacitance of a metal contact to a semiconductor in which the bulk free carrier density is degenerate or near degenerate. A significant correction to the nondegenerate theory may be required for accurate measurement of the barrier height.
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.
Microscopical Observations of Wear Surfaces on Sapphire
Authors: Duwell E. J. , Butzke H. C.
Published: April 2005

Evidence for three possible wear mechanisms was observed by light and electron microscope examination of wear surfaces on sapphire (α-Al2O3). Two of these mechanisms, plastic deformation and fracturing, leave characteristic wear patterns on the surface. The third postulated mechanism, chemical degradation, leaves an essentially smooth surface. The relative importance of these mechanisms depends on orientation of the single crystal, slide direction, load, speed, lubricant, and surface composition.
Redistribution of Solutes During Thermal Oxidation of Silicon
Authors: Ku H. Y.
Published: April 2005

During thermal oxidation of silicon, the solute in the original silicon is redistributed between the oxide formed and the unoxidized silicon. The redistribution depends on the segregation coefficient of the solute between the oxide and the silicon, the growth rate constant of the oxide, and the diffusion coefficients of the solute in the oxide and in the silicon. It also depends on the boundary condition existing at the oxide-free space interface. The concentration profile of the redistributed solute is analyzed mathematically and exact solutions are obtained for two cases. In the first case, there is no gain or loss of the solute by the oxide-silicon system through the oxide surface. In the second case, the oxide is in equilibrium with the ambient gas so that the concentration of the solute is a constant at the oxide surface. The results are discussed with special attention to the two most common solutes, boron and phosphorus.
An Equation of State for Face-Centered-Cubic Metals
Authors: Pastine D. John
Published: April 2005

A Morse function is used for the volume-dependent energy term in the Helmholtz free energy of a Debye solid. The consequent form of the Mie-Grüneisen equation of state is obtained by using an adjusted form of the Slater relation for the Grüneisen parameter. Theoretical Hugoniot curves calculated for aluminum, copper, and silver are in excellent agreement with the experimental curves over a broad pressure range.
Phase Transformation Studies in TiO2 Supporting Different Defect Mechanisms in Vacuum-Reduced and Hydrogen-Reduced Rutile
Authors: Shannon Robert D.
Published: April 2005

Studies of the anatase-rutile transformation show that the rate of transformation is accelerated in hydrogen atmospheres and retarded in vacuum. This information, interpreted in terms of the defect structure of TiO2, supports data obtained by other investigators indicating that the mechanism by which nonstoichiometric rutile is formed depends upon the atmosphere in which reduction occurs.
Moving Striations in a He-Ne Laser
Authors: Garscadden A. , Bletzinger P. , Friar E. M.
Published: April 2005

Moving striation frequencies as a function of discharge current in dc gas laser are presented. A mutual influence of moving striations and laser action is also reported.
Plasma Resonances in Small Metallic Particles
Authors: Doremus R. H.
Published: April 2005

The observed positions of optical absorption bands arising from plasma resonances in small metallic particles are tabulated and compared to the positions calculated from the optical constants of the metals. For very small spherical particles the calculated positions are close to those observed; for larger or non-spherical particles there are deviations between observed and calculated positions. Similar bands should exist in certain metals in which they have not been observed.
Interaction of Vortex Streets
Authors: Thomas David G. , Kraus Kurt A.
Published: April 2005

Vortex street eddies shed from multiple cylinders located one behind the other in the plane of flow were observed to interact in a very complex fashion. Contraction, expansion, cancellation, and coalescence of vortices occurred for different values of cylinder separation and Reynolds number. The results appear to have important implications both for turbulence promotion during heat or mass transfer and for theoretical interpretation of vortex street phenomena.
Superconducting Tubes and Filaments
Authors: Arrhenius G. , Fitzgerald R. , Hamilton D. C. , Holm B. A. , Matthias B. T. , Corenzwit E. , Geballe T. H. , Hull G. W.
Published: April 2005

A study is reported of the superconductivity and microstructure which occur when small quantities of La are quenched with Rh in the arc furnace. A strikingly regular prismatic honeycomb of a superconducting compound is found when the La concentration is ≥0.5 at. %. For smaller concentrations a continuous network of the superconducting phase is no longer observed which correlates with the lowering and broadening of the superconducting transition region. Evidence is given that for such low concentrations superconducting tunneling occurs through the elemental Rh phase itself thus pointing to the superconductivity of Rh at lower temperatures.
Magnetoresistance of Single Crystals of Indium Oxide
Authors: Weiher R. L. , Dick B. G.
Published: April 2005

An investigation of the magnetoresistance of single crystals of n-type indium oxide has been made at room temperature. The general behavior of the magnetoresistance is consistent with constant energy surfaces in the conduction band corresponding to the ``warped-spherical'' model or with the ``many-valley'' model along the[111] and [110] axes of symmetry with a small anisotropy of the conduction band.
Black Phosphorus as Strain Gauge and Pressure Transducer
Authors: Warschauer Douglas M.
Published: April 2005

Polycrystalline black phosphorus has a hydrostatic piezoresistive coefficient πH=3.04×10−10 cm2/dyn independent of pressure and decreasing by 28% between 0° and 100°C, and a highly stress-sensitive uniaxial piezoresistive stress coefficient πl>3×10−9cm2/dyn under appropriate conditions. The thermoelectric power is in the range 330 to 413 μV/deg, and Young's modulus=6.89×1010±15% dyn/cm2, linear to at least 4×106 dyn/cm2 tension. The ultimate tensile strength is 3.4×107 dyn/cm2 and the ultimate compressive strength is 3.5×108 dyn/cm2. These properties of black phosphorus make it potentially useful for strain and hydrostatic gauges, and other transducer use. The advantages and disadvantages relative to other materials are discussed briefly.
Photoconductivity of Lead Sulfide Films
Authors: Fleming Phyllis J. , Alberg Mary Johnke
Published: April 2005

The dark conductivity as a function of temperature, the photoconductivity as a function of temperature and irradiance, and the spectral response of chemically deposited PbS films have been investigated under dc conditions. The measurements indicate that a barrier model with a photoinduced change in carrier concentration accounts for the photoconductivity of the films, but that a model in which the barrier height is modified by illumination does not. A proposed physical model, based on the method of preparation of the films, predicts a change in the Fermi levels for holes and electrons on illumination to explain the experimentally determined dependence of photoconductivity on irradiance and temperature. The variation of photoconductivity and the equality of dark and light Hall mobility at dc and microwave frequencies found by Snowden and Portis can also be interpreted in terms of the model.
Light Emission from Reverse Biased GaAs and InP p-n Junctions
Authors: Michel A. E. , Nathan M. I. , Marinace J. C.
Published: April 2005

The light emission from reverse-biased diffused p-n junctions made in the direct band gap semiconductors GaAs and InP has been measured. In addition to the broad emission spectrum observed from junctions in other materials which have indirect band gaps, a sharp line (Δλ≅150 Å) is observed at photon energies slightly less than the energy gap. In most diodes this line dominates the spectrum. It is almost identical in shape to the line observed at this photon energy when the junction is forward biased. The measured external quantum efficiency of the reverse biased light is higher (∼10−5 to 10−4) than has been reported for most other materials. The spatial distribution of the light emission and the current-voltage characteristics have also been found to be similar to those of other materials.
X-Ray Measurement of Short-Range Order in Cu3Au
Authors: Moss S. C.
Published: April 2005

The new measurement of short-range order in a single crystal of Cu3Au differs from the original Cowley measurement in four important ways: Allowance was made for a size-effect modulation, allowance was made for a temperature factor in the diffuse intensity, the measurements were made in the vicinity of 100 to be closer to the origin of reciprocal space, and the intensities were obtained in absolute units by comparison with polystyrene rather than using α(0)=1.0. The ratio of the 100 and 300 peaks indicates that in disordered Cu3Au the value of 2M(Cu) is about twice 2M(Au) similar to the ratio found in the ordered form. Values for α(i) out to tenth neighbors were obtained for T=405°C, T=450°C, and for a sample quenched from 800°C. There was the same abnormally small value of α(3) found by Cowley. The new values are approximately 35% larger than the Cowley values. Presumably the increase is due mostly to the different method of standardizing. The measured values of α(i) out to i=10 are reproduced very well by the Cowley theory of short-range order, with no adjustable parameter but the ratio V2/V1. The present coefficients give V2/V1=+0.10, which would seem more reasonable than the original negative value.
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.
Crystal Anisotropy in Graphite and Uranium
Authors: Hesketh R. V.
Published: April 2005

A parallel is drawn between polycrystalline graphite and uranium. The elastic, thermal cycling, and irradiation creep strains are all dependent on crystal anisotropy. Nonlinearity of the stress—strain curves is shown to be a property of geometry rather than of the materials. The thermal cycling and irradiation creep strains have their expected values in uranium, but are ten times less in graphite. It is suggested that in graphite the appropriate unit of growth is not the single crystal but a small group of crystals bounded by Mrozowski cracks.
Applications of Kikuchi Line Analyses in Electron Microscopy
Authors: von Heimendahl M. , Bell W. , Thomas G.
Published: April 2005

The usefulness of Kikuchi line diffraction patterns for electron microscopy experiments is demonstrated. Examples are given of the determination of exact foil orientation, the calibration of tilting stages, and the determination of the magnitude of the deviation parameter s from the exact Bragg condition.
Sputtering of Metals by Hydrogen Ions
Authors: KenKnight C. E. , Wehner G. K.
Published: April 2005

Sputtering-yield data for metals are obtained by drilling holes in thin target foils with magnetically separated, dense hydrogen beams. Results for H2+ and H3+ at 7 keV are presented for Be, Al, Ti, V, Fe, Co, Ni, Cu, Zr, Mo, Pd, Ag, Ta, W, Re, Ir, Pt, and Au. Results for protons can be inferred from those for molecular ions since the hydrogen atoms sputter independently. Typical results at 7 keV in atoms/ion are for 0.032/H2+, 0.046/H3+, and for Cu 0.025/H+, 0.065/H2+, and 0.105/H3+.
Low-Temperature Elastic Moduli of Aluminum
Authors: Kamm G. N. , Alers G. A.
Published: April 2005

The adiabatic elastic moduli of single crystals of aluminum have been measured from 4.2° to 300°K by using the ultrasonic pulse-echo technique. The values obtained by extrapolation to 0°K are C11=11.430, C12=6.192, and C44=3.162 in units of 1011 dyn/cm2. The Debye temperature obtained from the 0°K modulus values is 430.3°K, in excellent agreement with the value from heat-capacity measurements.
Platinum as a Thermal Conductivity Standard
Authors: Slack Glen A.
Published: April 2005

The thermal conductivity K of high-purity platinum appears to be a reproducible quantity for temperatures between 75°K and the melting point at 2047°K. This behavior combined with the outstanding chemical and physical properties of platinum suggests that platinum could serve as a useful K standard in this region. From 200° to 2047°K the available data in the literature on K can be represented to within ±2% by K = (0.648+1.87×10−4T) W/cm deg. Some further work in determining K by several different methods, particularly at high temperatures, appears necessary before platinum can be adopted as a standard.
Preparation of Uniaxial Permalloy Films by Cathodic Sputtering on Glass and Metal Substrates
Authors: Flur B. L. , Riseman J.
Published: April 2005

Thin magnetic films have been prepared by cathodic sputtering on glass and metal substrates. The influence of the ferromagnetic cathode on the orienting magnetic field, as well as on the resulting magnetic behavior of the films is discussed. Use of a ``thin'' foil cathode is shown to be a simple method for minimizing the distorting effect of the cathode. Wall coercive force, anisotropy field, skew, and dispersion values are given for these films. Pulse behavior of a high-density bit plate in the biased mode of operation is also given.
Effects of Nitrogen, Methane, and Oxygen on Structure and Electrical Properties of Thin Tantalum Films
Authors: Gerstenberg D. , Calbick C. J.
Published: April 2005

An investigation was made of tantalum films sputtered in argon containing individual small amounts of nitrogen, methane, and oxygen. With argon alone, 1000-Å bcc tantalum films deposited on glass substrates heated to 400°C had a specific resistivity four times the bulk value, with the increase attributable to a reactive gas residual pressure of 10−6 to 10−5 Torr. The mixed argon-nitrogen experiments produced initially hcp Ta2N, and at higher pressures an fcc phase attributed to a new TaN structure. With methane only fcc TaC was obtained, while with oxygen an amorphous phase began to grow initially, and at higher pressures was dominant with a structure identical to anodically formed Ta2O5. The nitrides and carbide have specific resistivities from 200–300×10−6 Ω cm, and temperature coefficients between +3×10−4 and −2×10−4 deg−1. With increasing oxygen content, the specific resistivity increases approximately exponentially; the positive temperature coefficient decreases, becomes zero before the precipitation of Ta2O5, and then increases negatively at a rapid rate at the appearance of Ta2O5.
Twinning and Growth of Silver Bromide Microcrystals
Authors: Hamilton J. F. , Brady L. E.
Published: April 2005

Almost without exception, the shapes of the microcrystals of a negative-type silver bromide photographic emulsion can be explained on the basis of a simple mechanism of twin-accelerated layered growth. Multiple twinning, both on parallel and nonparallel [111] crystallographic planes, is required for a full explanation, and evidence that this does occur is found. The location of particles of silver, formed by exposure to light, substantiates this hypothesis, and demonstrates the fact that intersections of the twin planes with the grain surface are preferential regions for the location of photolytic silver.
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.
Growth of Single-Crystal Garnets by a Modified Pulling Technique
Authors: Linares R. C.
Published: April 2005

Yttrium iron garnet has been grown by a modified pulling technique where a BaO·0.6B2O3 solvent is used instead of the pure melt. Excess garnet is taken into solution at the hotter bottom of the crucible and deposited on the cooler seed at the surface. The rate of seed rotation, the rate of withdrawal from solution, and the orientation dependence are discussed.