bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure, Growth, and Properties of Twist and Tilt Grain Boundaries in Bicrystals of NaCl
Authors: Fuschillo N. , Gimpl M. L. , McMaster A. D. 
Published: April 2005

Grain boundaries having from 2° to 45° mismatch across the interface were grown for pure tilt and pure twist misorientation in NaCl by the Czochralski technique. The method of crystal growth and the techniques required for good control of the misorientation and the planarity of the grain boundary are described. The substructure of twist and tilt NaCl bicrystals was examined using both optical and electron-microscopic techniques. The tilt grain boundaries were found to be strong mechanically and not easily cleaved apart. The twist grain boundaries were very weak mechanically, especially at mismatch angles greater than 20°, and exhibited anomalously rapid diffusion or capillary flow effects along the grain boundary.
Grain boundaries in the bicrystals were examined by: (1) pulling the crystals apart at the grain boundary and (2) by polishing away one side of the bicrystal to within 0.5 mm of the grain boundary. (The grain boundary surface could then be examined by focusing through the layer of NaCl.) Both of these techniques showed that the twist bicrystals were held together by small regions or spots of continuity at the grain boundary. The spot density ranged from 500/cm2 to 20 000/cm2 for 45° and 10° twist bicrystals, respectively. No substructure was observed for tilt grain boundaries. This may explain not only the extreme mechanical weakness of twist grain boundaries, but may also help to explain brittle fracture in polycrystalline ionically bonded solids generally, including ceramics and other alkali halides, and phenomena, such as the solution embrittlement of AgCl.
Flow of Gases through Helical Capillaries
Authors: Creutz E. 
Published: April 2005

The isothermal flow rates of H2, He, and N2 through several helically coiled capillaries in the laminar, transition, and turbulent ranges are found to follow the expression y=x(2−axn1)2+x12(1−2−axn2)2, where x is the ratio of the product of the average pressure times the pressure drop in the capillary to the value of pressure times pressure drop which produces the transition from laminar to turbulent flow in a straight capillary of the same length and diameter, and y is the ratio of any observed flow rate to that flow rate which corresponds to the transition in the straight capillary. The experimental value of y corresponding to x=1, called y0, is given by 1−y0=12e−0.044(D/d)1/2, where D is the coil diameter and d is the capillary diameter. n1 and n2 are given by n1≐12+110(Dd)3/8;  n2≐12+215(Dd)3/8. The quantity a (&lt;1) is obtained by solving y0=(2−a)2+(1−2−a)2, using the value of y0 obtained from Eq. (ii). The above equations hold for porous media also, when the following values are used: D=0,  n1=n2=12,  a=1, in which case y0=12 as determined previously.
The flow apparently may be stabilized against turbulence by centrifugal forces in tightly wound helices up to Reynolds numbers equal to at least 8000, consistent with previous observations by others with liquids.
Flow and Self-Diffusion of Gases in Capillaries. Part I
Authors: Lund L. M. , Berman A. S. 
Published: April 2005

A model is presented for describing transport under a partial pressure gradient (self-diffusion) as well as transport under a total pressure gradient in capillaries of arbitrary length-to-radius ratio over a pressure range extending from the free molecule to the continuum regimes.
The model provides a unified description of the transport and yields the same results as existing theories in the limited ranges appropriate for their application.
Spin-Wave Resonance of Permalloy Thin Films as Measured in Ultrahigh Vacuum and in Air
Authors: Lykken G. I. , Harman W. L. , Mitchell E. N. 
Published: April 2005

Permalloy thin films in the thickness range from 100 to 2530 Å and of melt composition 82% Ni-18% Fe were deposited in an ultrahigh-vacuum system and the standing spin-wave modes (SSWM) of these films were measured in vacuum and in air. The SSWM shifted to higher magnetic fields as the films aged in vacuum, but shifted to lower magnetic fields as they aged in air. Since the SSWM of the films displayed a quadratic dependence on mode number at all times, the observed spectra shifts could be accounted for by changes in g, 4πM, and A/M with no observed changes in pinning. Annealing greatly altered the absorption spectra, indicating that a significant change in the pinning occurred.
It is concluded that spin pinning exists in a modest vacuum (p≃1×10−7 Torr) even before the films have been exposed to the atmosphere and that spin pinning is dependent on the substrate used in that spin pinning is greatly affected by annealing.
Comparison of Measured and Predicted Bulk Moduli of Tantalum and Tungsten at High Temperatures
Authors: Soga Naohiro 
Published: April 2005

The elastic constants of tantalum have been determined from room temperature to 500°C by means of a dynamic resonance method to obtain the adiabatic bulk modulus at elevated temperature. The adiabatic bulk modulus (Bs) of tantalum is found to be 1897 kbar at room temperature and it decreases almost linearly with a slope (dBs/dT) of −0.11 kbar/°C as temperature rises. The calculation of the Grüneisen constant γ and a parameter δ, defined as − (dBs/dT)/αBs, from the present data shows that both parameters are almost independent of the temperature (1.57 for γ and 3.1 for δ). The constancy of γ and δ at high temperatures has also been tested for tungsten by using the recent data of Lowrie and Gonas [J. Appl. Phys. 36, 2189 (1965)]. The results indicate that both γ and δ are virtually constant at high temperature. The applicability of the following equation to estimate the bulk-modulus-temperature relationship for the refractory metals Ta and W has also been tested: BsT=Bs25−(δγ/V)(HT−H25),
where H is the enthalpy and the superscripts indicate values at 25° and T°C.
Thermionic Work Function of Thin-Oxide-Coated Aluminum Electrodes in Vacuum and in Cesium Vapor
Authors: Chapman Richard A. 
Published: April 2005

The thermionic work function of aluminum electrodes with anodized aluminum oxide coatings of 30 and 2000 Å was determined for each electrode from the contact potential difference of each electrode with a well outgassed and aged polycrystalline tungsten wire emitter. In vacuum, the thermionic work function of the 30-Å coated electrode was 4.3±0.1 eV, relative to a polycrystalline tungsten work function of 4.6 eV and a tungsten emission constant of 120 A/cm2· °K2. In cesium vapor at reservoir temperatures up to 70°C, the 30-Å coated electrode had a minimum observed work function of 1.4±0.1 eV relative to the same tungsten reference electrode. The resistance of the 2000-Å film coated collector electrode was too large to allow accurate determination of the work function of this electrode. In both vacuum and cesium vapor, however, there was an indication that the work function of the 2000-Å coated electrode was a few tenths of an electron volt lower than that for the 30-Å coated electrode. It is suggested that similar but perhaps less stable oxide-coated electrodes could occur naturally on the collector of a thermionic energy converter due to oxidation of the collector surface or buildup on the collector surface of outgassing products from the emitter.
Auxillary experiments were performed on the secondary-electron emission from these oxide-coated electrodes. No lingering secondary electron emission current corresponding to a Malter effect was observed. The true secondary yield from the 2000-Å coated electrode was 3 in vacuum and 7 in cesium vapor for a primary electron energy of 150 eV. The secondary yield for the 30-Å coated electrode was similar in cesium vapor but was not studied in vacuum.
Study of the Filamentary Growth of Silicon Crystals from the Vapor
Authors: Wagner R. S. , Ellis W. C. , Jackson K. A. , Arnold S. M. 
Published: April 2005

The preparation from vapor and the structure of filamentary crystals of silicon have been studied in detail. It was found by chemical etching, by examination for a twist associated with a screw dislocation, and by observations in the electron microscope, that both ribbons and needles of small dimensions are free of dislocations and imperfections. Certain impurities such as gold, nickel, or platinum, however, are essential for the growth of filamentary crystals.
The growth of micron size and larger whisker crystals from the vapor takes place in two stages. The first is a rapid extension in length of a leader-like crystal of small cross section; the second, a slow thickening of the leader through deposition on lateral faces. Initial growth is associated with impurities and does not require an axial screw dislocation. Subsequent growth may be explained by classical nucleation at a step and lateral translation of the step.
Unsupported Single-Crystal Films of Germanium
Authors: Skaggs C. W. , Jones J. R. 
Published: April 2005

A method of obtaining unsupported single-crystal films of Ge has been developed which involves the sublimation of a NaCl substrate from the Ge film after vacuum deposition. This allows compatibility of the film and NaCl substrate previously thought impossible due to the large difference in their coefficients of thermal expansion.
Evaluation of this endeavor has been made with microscopic, x-ray diffraction, and electron diffraction examinations. This evaluation has disclosed that the films are (100) oriented monocrystalline films which contain, in varying amounts, surface contaminants consisting of NaCl, BaCl2, Ta2O5, TaC, and amorphous C.
Self-Diffusion in Pb at 300°C by an Absorption Tracer Technique
Authors: Lawless W. N. 
Published: April 2005

A diffusion technique is described that does not involve the usual long-time approximation for a thin specimen. Activity measurements are programmed on a digital computer to generate a large number of D values from the analysis of the data. These D values are then treated statistically, the resulting distribution curve yielding information on the experiment itself. The technique is fairly insensitive to errors in determining the scattering characteristics of the system or in taking the data.
A version of this technique applied to Pb at 300°±2°C yielded average and rms values for D, the self-diffusion coefficient, of 1.78±0.15×10−10 cm2/sec and 1.92±0.16×10−10 cm2/sec, respectively, from 40 D values generated from the data. The results compare favorably with the published data on self-diffusion in Pb at 301°C by von Hevesy, 1.85×10−10 cm2/sec. The data were also treated according to a long-time approximation method of Zhukhovitsky, yielding 1.70×10−10 cm2/sec.
Accelerated Convergence, Divergence, Iteration, Extrapolation, and Curve Fitting
Authors: Macdonald J. Ross 
Published: April 2005

This paper discusses some applications of the epsilon algorithm (EA), a sequential procedure for calculating Padé approximants. The EA may be used to: (1) accelerate the convergence of slowly converging series and iterations; (2) obtain useful results from divergent series and iterations; (3) obtain the limits of iterated vector and matrix sequences; (4) aid in the solution of differential and integral equations; (5) carry out numerical integration in a new way; (6) extrapolate; (7) fit a curve to a polynomial or to a constant plus sum of exponentials.
As an illustration of curve fitting and extrapolation, we present results obtained with exact polynomial data plus random noise combined additively or proportionately. For such nonstationary data, the results are comparable, and in some cases superior, to least squares in yielding good estimates of the exact polynomial coefficients. One important advantage of the EA is that it builds up polynomials whose lower-order coefficients are independent of higher-order ones. This property is valuable when the degree of the polynomial is unknown. Finally, a simple empirical equation is given relating the precision of least-squares-calculated polynomial coefficients to the degree of the fitted polynomial and the number of effective decimal digits carried in the calculation.
Gas Transport in Thermally Conditioned Linear Polyethylene
Authors: Michaels Alan S. , Bixler Harris J. , Fein Harvey L. 
Published: April 2005

The permeability, diffusion, and solubility constants of helium, argon, and ethane have been measured in a series of linear polyethylene films which had been subjected (1) to various rates of cooling from the melt and (2) to subsequent annealing near the melting temperature. While solubility constants of argon and ethane showed the normal variation with amorphous content of the polymer irrespective of thermal history, helium solubility constants appeared to be anomalously high and strongly dependent on thermal history. The presence of voids or defects within the crystalline phase has been postulated to account for this behavior of helium; argon and ethane being excluded from these defects because of their size. Anomalous helium diffusion constants were also observed which have been satisfactorily explained in terms of a slow diffusion of gas into these intracrystalline defects.
The monatonic decrease in geometric diffusional impedance with increasing amorphous content of the polymer has again been observed in films directly cooled from the melt. However, upon annealing these films at elevated temperatures the impedance decreases markedly, despite an increase in crystallinity, suggesting the formation of thicker lamellas with a high concentration of intralamellar imperfections in a manner similar to that observed in annealing polyethylene single crystals.
The apparent activation energies for diffusion of argon and ethane were essentially constant irrespective of thermal history. This suggests the so called ``chain immobilization factor'' is not due to restricted chain mobility in the amorphous polymer, but is rather a penetrant-size-dependent impedance to diffusion arising from the near-molecular dimensions of the amorphous channels in the polymer.
Measurement of Third-Order Moduli of Silicon and Germanium
Authors: McSkimin H. J. , Andreatch P. 
Published: April 2005

Experimental techniques for determining third-order moduli of single crystals by means of ultrasonic wave propagation are described. Results for silicon and germanium demonstrate a good degree of self-consistency among the basic experimental data obtained with both hydrostatic and uniaxial pressure.
In units of 1012 dyn/cm2 and for 25°C, the third-order moduli are: ModulusValue for SiValue for GeC111−8.25±0.10−7.10±0.06C112−4.51±0.05−3.89±0.03C123−0.64±0.10−0.18±0.06C144+0.12±0.25−0.23±0.16C166−3.10±0.10−2.92±0.08C456−0.64±0.20−0.53±0.07Thermodynamic definitions for the moduli (K. Brugger, Phys. Rev. 133, A1611 (1964)] have been used.
Anisotropy Fields in Hexagonal Ferrimagnetic Oxides by Ferrimagnetic Resonance
Authors: De Bitetto D. J. 
Published: April 2005

Room-temperature microwave ferrimagnetic resonance measurements of the large uniaxial magnetocrystalline anisotropy fields (Han) of two compositional series of hexagonal ferrimagnetic oxides are reported. Han was found to increase rapidly in the Al-substitution series (SrO·xAl2O3·(6−x)Fe2O3) from 19.3 to 53.4 kOe as x was increased from 0 to 1.7. In the TiCo series (BaO·x[TiCoO3]·(6−x)Fe2O3), Han was found to decrease from 17.5 to 6.6 kOe as x was increased from 0 to 0.78. Experimental plots are given for the variation of Han with x. The linewidths of these oriented polycrystalline compounds were all about 2 kOe. The g value was consistently found to be about 1.9.
Variation with x of the respective saturation magnetizations, anisotropy constants, and anisotropy fields are discussed; relations are presented.
Low-Energy Sputtering Yields by Resonance Absorption and Emission Spectroscopic Methods
Authors: Kreye W. C. 
Published: April 2005

Low-energy sputtering yields for a (110)-oriented gold single crystal are determined by means of a resonance or atomic absorption technique wherein the sputtered atoms absorb the resonance radiation from an external gold, hollow cathode source. If the square root of the relative yield is plotted vs target voltage, a linear portion is found between 40 and 70 V. The extrapolation of the linear portion of the curves gives rise to an average intercept energy EE of 29 eV at low pressures.
The discharge chamber is specially designed to permit consecutive measurements of the sputtering yields by the absorption and by a previously employed emission technique under identical chamber geometry and discharge conditions. In the direct comparison of results possible thereby, the average value of EE from the emission curves is 29.5 eV which is approximately equal to the above absorption value of 29 eV. The plasma potential for these experiments is found to be about 12 eV. Moreover, the curves themselves are proportional over the range of 40 to 100 V. These results strongly indicate that EE is an experimental invariant from which reliable threshold energies can be obtained. This coincidence of curves also indicates that the variation of excitation probability of the Au atoms with different ion and correspondingly different atom energies does not affect the emission yield curves.
The sensitivity of the absorption method with the present hollow cathode is slightly poorer than that of the emission method. The observed increase in the slope of the absorption square root yield curve with increased discharge current is attributed to imperfect resonance which may be due to the difference in argon pressures and discharge currents within the gold, hollow cathode source and those within the sputtering single-crystal target chamber.
Onset of Breakdown at Voltages below Ionization Potential in High-Pressure Thermionic Diodes
Authors: Forman R. 
Published: April 2005

Early breakdown effects have been measured in relatively high-pressure thermionic diodes under given conditions of pressure and anode spacing. Apparent breakdown conditions are obtained at anode voltages considerably lower than the ionization potential of the gas. Measurements on xenon- and mercury-filled thermionic diodes, under space-charge conditions of operation, are presented which show that this breakdown voltage seems to be associated with the first excited state of the gas. Experimentally, early ignition occurs in diodes with a fixed cathode-anode spacing in a limited pressure range only. A theoretical explanation for this behavior is based on the model that, in the limited pressure range, electrons traversing the cathode-anode space can pick up almost all the energy of the applied voltage.
In addition, data are presented showing that early breakdown in an inert gas-filled diode can occur at voltages much lower than the first excited state. This has been accomplished in thermionic diodes exposed to the radiation of a nuclear reactor. A qualitative explanation for this behavior is proposed.
Structural Effects in Thin-Film Sandwich Emitters
Authors: Harris L. A. 
Published: April 2005

Direct current measurements have been made of film currents in and emission currents from thin-film sandwiches consisting of beryllium, thermally formed beryllium oxide, and overlayers of silver, barium or a combination of the two.
Silver covered oxide films formed at low temperature yield regular film current characteristics but no electron emission. With high oxidizing temperatures, electron emission can be obtained but the films are subject to frequent breakdown. An intermediate temperature range yields more reproducible film currents and, in many cases, small but steady electron emission. A discontinuous forming process generally precedes the electron emission.
Films with barium overlayers break down and heal repeatedly, accompanied by very irregular emission at film voltages considerably below those for silver covered films. Brief exposure of a silver overlayer to barium vapor induces marked changes. Initially, the film current is irregular as it is for barium alone, but as the current increases the characteristic reverts to that for silver without barium. Electron emission is more frequently obtained in this way, though it occurs in the same voltage range as without barium.
The film-current curve shapes indicate that the current is carried mainly by electrons passing over a voltage-dependent barrier (Schottky effect), but cooling the samples has no effect on these curves, probably because of localized heating.
A tentative model is proposed to account for the particular observations reported here. Work function differences, the porosity of the thin silver films, and cracks or grain boundaries in the oxide layer combine to produce highly localized currents, heating, and structural changes consistent with measurements and observed emission patterns.
Fine-Grained Ferrites. III. Ni1−xCoxFe2O4. High-Power Microwave and rf Properties
Authors: Malinofsky W. W. , Babbitt R. W. 
Published: April 2005

Dense Ni1−xCoxFe2O4, with x=0, 0.028, 0.030, and 0.067, was prepared with grain sizes down to 0.1 μ by using a previously described technique. This consists of a combination of flame-spraying to obtain the initial fine ferrite particles (down to 0.03 μ), and hot-pressing to sinter these into single-phase bodies of near theoretical density (to 98%).
The high-power microwave properties were measured in a cavity at X band with perpendicular pumping for a series of grain sizes ranging from 0.10 to 0.35 μ. Co=0.027 was used, since the magnetocrystalline anisotropy constant K1 is theoretically zero and thus would be expected to provide minimum linewidth ΔH in this compositional system. Measured values of the microwave magnetic loss susceptibility under perpendicular pumping χ⊥″, the threshold field for the onset of the subsidiary absorption hc, ΔH, 4πMs, and density are given as a function of grain size. hc was found to increase with decreasing grain (or pore) size. This was explained on the basis that spin waves which are important at the subsidiary resonance are longer than the grain size, and therefore interact effectively with such inhomogeneities. This explanation is supported by the finding that [(hc)2000− (hc)1500]/(hc)1500, for Hdc=1500 and 2000 Oe, decreases with decreasing grain size. χ⊥″ passes through a minimum near 0.18 μ in unannealed samples, but in annealed samples it decreases rather linearly with grain size. Of practical concern are the following combinations of hc and χ⊥″ which are obtainable by this method: &gt;105 Oe and 0.6, &gt;75 Oe and 0.15, compared to 16 Oe and 0.03 for a large-grained ferrite. The power ratio between the first and last is over 40.
Radio-frequency properties such as μ′ and μ″ were measured from 0.1 Mc/sec to 7 Gc/sec. In the dispersion curves obtained, the rf resonance frequency compared well with that calculated on the basis of the domain rotation mechanism. The static μ′ had similar values to those in large-grained samples, contrary to the case of NiZn ferrites, where wall motion plays a role. The resonance frequency of the microwave peak also agreed well with that calculated from a previously derived equation.