bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature Changes in Thin Metal Films during Vapor Deposition
Authors: Belous M. V. , Wayman C. M.
Published: January 2005

The temperature increase in vacuum-evaporated films of Au and Ag was measured by allowing the evaporant to condense on the junctions of Au-Ni thin-film thermocouples connected in series. The (minimum) average film temperature during growth was found to depend upon the evaporation rate and the substrate temperature. The average temperature of thin films of Au and Ag during deposition can be some 400°–500°K higher than the substrate temperature; this increase is attributed to the exothermic heat of condensation and radiation heating from the evaporation source. Even at low substrate temperatures near 100°K, the average film temperature can approach 500°K. The significant temperature existing in evaporated thin films can explain grain growth phenomena and other metallurgical changes in the structure of the films.
Impact Cratering in Granular Materials
Authors: Cook Melvin A. , Mortensen Kay S.
Published: January 2005

Craters produced by projectile impact in granular materials were studied for a wide range of energies and projectile types. Crater sizes were shown to depend on projectile size and shape and on the particle size of the target material. The volume of the impact crater was related to the kinetic energy of the projectile and to the measurable cohesive strength of the target material. Excellent agreement was found between the experimental results and a hydrodynamic theory of cratering slightly modified from earlier studies.
Measurement of Elastic Strains in Small Gold Nuclei on Molybdenite Substrates as a Function of Nucleus Size and Misalignment
Authors: Jesser W. A. , Kuhlmann-Wilsdorf D.
Published: January 2005

Using moiré fringe pattern techniques, elastic strains were measured in small gold nuclei (10–40 A in radius) prepared by evaporation in ultrahigh vacuum (10−8 Torr) onto MoS2 substrates. The variation of the elastic strain with the radius and angle of misalignment of the nuclei was found to be consistent with the theories of van der Merwe, Cabrera, and Jesser and Kuhlmann-Wilsdorf.
Low-Angle Subgrain Boundaries in Tellurium
Authors: Hörl E. M. , Weiss J.
Published: January 2005

A study of low-angle subgrain boundaries in tellurium crystals was carried out using electron microscopical techniques. The existence of symmetric tilt boundaries could be proved by the examination of the electron diffraction patterns and the determination of the Burgers vectors forming the boundaries. The motion of the individual dislocations of a boundary at elevated temperatures was investigated and the effect of irradiation with fission fragments studied.
Scattering of Light Reflected from Acoustic Surface Waves in Isotropic Solids
Authors: Auth David C. , Mayer Walter G.
Published: January 2005

Scattering and frequency shifting of light reflected from Rayleigh waves in isotropic solids have been observed. The amplitude of the scattered light is correlated with acoustic surface-wave amplitude. Diffraction patterns are pictured and surface-wave velocities are calculated based on scattering angles.
Orientation Inversions in Polycrystalline CdS Bulk Crystals and Thin Films
Authors: Rozgonyi G. A. , Foster N. F.
Published: January 2005

A study of the crystallographic orientation of the single-crystal grains of large (8.5-cm-diam) polycrystals of CdS and of thin films of CdS has been made. Chemical and sputter-etching observations, x-ray crystallographic techniques, and piezoelectric polarity measurements have been used to classify the growth habits of the thin films as a whole and of the individual grains of the bulk crystals.

Three types of grains have been identified in the bulk CdS polycrystals. These are type I: c axis normal to a Cd-rich growth face; type II: c axis greater than 15° from the normal to an S-rich growth face; and inverted type II: c axis greater than 15° from the normal to a Cd-rich growth face. Type I and inverted type II grains exhibit negative compression piezovoltages, while type II grains are positive. Type I grains are identical to the type I single crystals previously discussed by Reynolds, and type II grains are similar to the 14° misoriented type II single crystals of Reynolds.

Similar results were obtained from the evaporated CdS thin films which could be classified as type I and type II, with the normal to the type II films about 20° off the c axis, indicating a close parallelism between the processes occurring in evaporated thin films and in bulk crystal growth. Sputtered CdS films were always type I. It is suggested that the variable efficiencies that have been observed in piezoelectric thin-film transducers with similar crystallographic orientations are related to orientation inversions in the films.
Field Distribution and Current Saturation in Photoconductive CdS
Authors: Fossum H. J. , Rannestad A.
Published: January 2005

The internal electric field distribution has been measured in photoconducting CdS single crystals using the linear electro-optic effect. The experimental results show a nearly homogeneous field distribution in the crystals for applied fields below the threshold for acoustoelectric oscillations, while a high-field region was created near the anode for fields above the threshold field. The reproducibility from sample to sample was rather poor. The linear electro-optic constant was calculated from the experimental results: (r′113−r′333)=2.7×10−12 m/V at the optical wavelength 6328 Å.
Temperature Dependence of Orientation Birefringence in Rubbery and Semicrystalline Polymers
Authors: Hammack T. J. , Andrews R. D.
Published: January 2005

Results are presented for the temperature dependence of orientation birefringence, Δn(T), from −195° to 150°C for the following crosslinked polymers: polydimethyl siloxane, polyethylene, ethylene/propylene copolymers (84/16, 75/25, 48/52 mole ratio), and ethylene/vinyl acetate copolymers (96/4, 82/18). On cooling from the rubbery state under a small constant load, the birefringence magnitude shows an abrupt increase when crystallization takes place, reaching a maximum value (Δnc) when crystallization is complete; Δnc is determined principally by the degree of orientation in the rubbery state. In the rigid semicrystalline state, below Tg, the magnitude of orientation birefringence decreases with decreasing temperature. The transition temperature for the ethylene/propylene copolymers is lowered by increasing the propylene content; the nature of the transition changes progressively from a crystallization in polyethylene to a glass transition in the copolymer having 52 mole % propylene. The observed difference in optical parameters for polyethylene and its copolymers suggests a difference in physical structure which strongly affects the optical properties. We believe that the structure of the copolymers is microcrystalline, contrasting to the spherulitic crystallinity of polyethylene (and polydimethyl siloxane).
Shear Strength of Grossly Deformed Cu, Ag, and Au at High Pressures and Temperatures
Authors: Riecker Robert E. , Towle Laird C.
Published: January 2005

The shear strength of grossly deformed copper, silver, and gold has been measured in an opposed anvil shear apparatus at pressures up to 150 kbar in the temperature range from 27°–900°C. The shear data agree with independent strength measurements at low pressures, but differ significantly from high-pressure shear strength measurements by other investigators. The data also fit a simple empirical formula relating the temperature and pressure dependence of the shear strength.
Brewster Angle for a Dielectric Medium Moving at Relativistic Speed
Authors: Yeh C.
Published: January 2005

Several interesting features concerning the reflection of obliquely incident electromagnetic waves from a dielectric half-space moving at relativistic velocities are discussed. Two cases of the movement are considered: (a) The dielectric medium moves parallel to the interface. (b) The dielectric medium moves perpendicular to the interface. Both polarizations of the incident wave are considered: (a) The electric field of the incident wave lies in plane of incidence. (b) The electric field of the incident wave lies in a plane which is normal to the plane of incidence. The variation of the Brewster angle as a function of the velocity of the medium is examined in particular. Also considered in detail are the energy relations of this moving boundary problem.
Extrinsic ir Photoconductivity of Si Doped with B, Al, Ga, P, As, or Sb
Authors: Soref R. A.
Published: January 2005

It is shown that silicon doped with B, Al, Ga, P, As, or Sb is a fast, sensitive, and efficient detector of 10.6-μ radiation from a CO2 laser. Experimental results are presented for several moderately compensated specimens. An investigation was made at temperatures from 23°–40°K of the electrical characteristics, time constant, noise, and 10.6-μ photoresponse. The results are interpreted in terms of idealized, non-Ohmic impurity-photoconductor models. Detectivities within a factor of three of ideal background-limited performance were attained, and response times in the nanosecond region were found.
Effects of an External Magnetic Field on Landau Damping in Maxwellian Plasmas
Authors: Babler Gary M. , Willett Joseph E.
Published: January 2005

Landau damping of longitudinal electron oscillations in a boundless, Maxwellian, collisionless magneto-plasma is studied in an approximation which neglects the coupling to transverse oscillations. The longitudinal component of the electric field is explicitly developed as a superposition of exponentially damped sinusoidal oscillations for an initial perturbation sinusoidal in space and Maxwellian in velocity. A formula is derived for the minimum time for Landau damping, i.e., the time which must elapse before only the lowest frequency oscillation is significant.

An analysis is presented for the strong magnetic field case in which ωc≫2π |sinθ| (λ/λD)ωp, where ωc is the cyclotron frequency, θ is the angle between the propagation vector and the external magnetic, λD is the Debye length, λ is the wavelength, and ωp is the plasma frequency. For this case the Laundau zeros move continuously along rays from their location in the absence of a magnetic field when the angleθ is zero to the origin as this angle approaches 90 deg. With this same variation of angle the minimum time increases from the null field value to infinity. These results are independent of the cyclotron frequency, provided that the above inequality is satisfied. For no external magnetic field the minimum time is found to increase with increasing wavelength and decreasing thermal spread of the initial perturbation when the spread is less than that of the unperturbed distribution.
Current Distribution in Nonequilibrium J×B Devices
Authors: Argyropoulos G. S. , Demetriades S. T. , Kendig A. P.
Published: January 2005

The interdependent problems of determining the current density field and the electron temperature and number density profiles in nonequilibrium J×B devices are formulated realistically, and solved numerically. The two-dimensional formulation includes the important effects of thermal and concentration diffusion, thermal and velocity boundary layers, and finite reaction rates on the electrical behavior of crossed-field devices, and allows each effect to be studied separately. As a result, this study predicts and interprets the asymmetry of the current distribution that has often been reported in experimental studies. Computations in potassium-seeded nitrogen plasmas have shown that streamwise nonuniformities can be very pronounced both in the core and in the electrode boundary regions of high-current density devices. In the limiting case of instantaneous reaction rates (ionization equilibrium at the electron temperature) and instantaneous energy relaxation, current lines in the core display a striking increase in slope throughout the narrow region between the insulator segments, where they become almost perpendicular to the flow direction and much denser than in the remaining part of the core. Under these conditions, there is no evidence of current ``shorting'' through the boundary layer, although the Te distribution is such that high-luminosity regions appear over the electrodes, particularly over the cathode. The general and flexible methods developed in this study allow realistic evaluation of suggested designs under various operating conditions.
Optical Properties of Single-Crystal Magnesium Oxide
Authors: Williams M. W. , Arakawa E. T.
Published: January 2005

The reflectance of single crystals of MgO was measured at a 15° angle of incidence for photon energies between 4 and 29 eV and the optical constants obtained by a Kramers-Kronig analysis of the reflectance data. In the energy range 4–14.5 eV, structure in the reflectance is in good agreement with that already reported. Reflectance measurements have not been previously reported above 14.5 eV. Peaks in the optical conductivity locate the Γ exciton at 7.65 eV and interband transitions at 11.0, 13.2, 14.9, 17.0, ∼19, 20.8, and ∼24 eV. The absorption edge for band-to-band transitions is estimated to be at 7.9 eV. The calculated energy-loss function −Im(ε+1)−1, where ε is the dielectric constant, shows a maximum at 21.3 eV while the calculated loss function −Imε−1 shows a maximum at 22.4 eV and a subsidiary maximum at 25.4 eV. It is suggested that these maxima in −Imε−1 correspond to volume plasma resonances involving 6 and 8 electrons per molecule, respectively. The volume plasma energies calculated on the assumption of 6 and 8 free electrons per molecule are 21 and 24 eV, respectively. Use of a sum rule enables us to explain qualitatively the shifts of the plasma resonances from the free electron values. Similarly, the proximity of the peaks in −Im(ε+1)−1 and −Imε−1, locating surface and volume plasma losses can be explained. These results, from optical measurements, are used to identify characteristic electron energy losses, obtained from the literature, as being due to single-electron transitions or to collective oscillations.
Low-Temperature Magnetic Phase Transitions in CoCl2·6H2O and MnBr2·4H2O
Authors: Schmidt V. A. , Friedberg S. A.
Published: January 2005

Apparatus for the continuous recording of quasistatic magnetization isotherms at low temperatures has been developed. It has been employed in the study of phase transitions in two antiferromagnets induced by magnetic fields up to 16 kOe applied along the preferred directions of spin alignment. Antiferro-paramagnetic transitions have been detected in CoCl2·6H20 between the zero-field Néel point, TN(0) = 2.29°K, and 2.06°K. Below 2.06°K, ``spin-flopping'' is observed. The resulting magnetic H-T phase diagram agrees well with that obtained by resonance techniques. Measurements on MnBr2·4H2O below TN(0) = 2.13°K show only antiferro-paramagnetic transitions down to 1.15°K with no indication of spin-flopping. The observed antiferro-paramagnetic transitions appear to be of the λ-type while the spin-flop transitions in CoCl2·6H2O are probably of first order.
Green Electroluminescence from Gallium Phosphide Diodes near Room Temperature
Authors: Dean P. J. , Gershenzon M. , Kaminsky G.
Published: January 2005

Detailed spectral properties of green near-bandgap electroluminescence have been studied between ∼50° and ∼380°K in several GaP diodes containing different concentrations of nitrogen impurities. The observed evolution of the room-temperature green bands from the readily identifiable low-temperature bands and a comparison of the room-temperature spectrum with the intrinsic luminescence band calculated from the absorption-edge spectrum show that intrinsic transitions are of minor importance for these diodes near 300°K. The observed room-temperature green luminescence in lightly doped diodes is identified with the recombination of bound and free excitons induced by isoelectronic nitrogen impurities, whereas radiative recombination of free holes at neutral shallow donor centers predominates in heavily doped diodes. The intensity of the green luminescence generally increased more rapidly than the red Zn, O acceptor-donor pair luminescence near 300°K, both with increase in temperature and in diode current. We have observed green electroluminescence external efficiencies approaching 10−4 for exciton recombination at room temperature in exceptional diodes containing relatively low concentrations of deep centers (notably those with low oxygen content). The calculated rate constant for intrinsic transitions and the largest observed mean minority-carrier lifetimes together suggest that intrinsic green luminescence of efficiency approaching 10−4 might be observable at room temperature from diodes containing currently attainable minimal concentrations of nitrogen and oxygen impurities, if the luminescence is not confined to the junction depletion layer.
Temperature Dependence of the Elastic Constants of the Alkali Halides. I. NaCl, KCl, and KBr
Authors: Slagle O. D. , McKinstry H. A.
Published: January 2005

The elastic constants of NaCl, KCl, and KBr have been measured from room temperature to temperatures near their melting points. A phase-comparison technique was used to measure the velocity of high-frequency sound waves in the crystals from which the elastic constants were derived. The elastic constants obtained were found to agree, within experimental error, with previously measured values. The theoretical values of the temperature dependence calculated from the expressions of Mitskevich agree very well with the experimentally obtained values. The value and temperature dependence at high temperatures of the elastic constants (c11–c12)/2 are compared to the relative melting temperatures of the three crystals. In support of the theory of Thompson, the rapid decrease of this elastic constant can be correlated with the relative temperature of melting.
Temperature Dependence of the Elastic Constants of the Alkali Halides. III. CsCl, CsBr, and CsI
Authors: Slagle O. D. , McKinstry H. A.
Published: January 2005

The elastic constants of CsCl, CsBr, and CsI have been measured from room temperature to 450°C. Measurements on CsCl were made up to its transition temperature at 473°C but no anomalous variations were found which would differentiate its behavior from that of CsBr and CsI. The results of the measurements are shown to be in agreement with previous experimental work. It is found that the type of temperature variation exhibited by c44 in the CsCl-type lattice is very similar to that observed for ½(c11–c12) in the NaCl-type structure. From a consideration of the respective ionic arrangements, these elastic constants can be seen to describe shear mechanisms which could lead to instability with a static expansion of the lattice. From such a treatment, a possible mechanism is suggested to describe the CsCl-type to NaCl-type structure transition. This mechanism is shown to be compatible with the existing data.
Transport Effects in the Electron-Rich Unignited Mode of Cesium Diodes
Authors: Warner C. , Hansen L. K.
Published: January 2005

A comprehensive experimental and theoretical analysis is presented for the electron-rich, unignited mode of a cesium-vapor thermionic diode. The theoretical inverse spacing dependence of the apparent saturation current is found to be in agreement with experiment. The theoretical and experimental coefficient of this dependence are found to be in agreement if one assigns a value Pc=700 cm−1 Torr−1 to the electron-neutral collision probability. This value is consistent with other available information. Potential distributions are calculated. Full theoretical and experimental volt-ampere curves are compared. Some of the assumptions in the theoretical analysis are examined in detail.
Up-Conversion of Near Infrared to Visible Radiation in Lithium-meta-Niobate
Authors: Midwinter J. E. , Warner J.
Published: January 2005

Single-crystal lithium niobate pumped with pulsed ruby-laser radiation has been used to convert 1.7-μ radiation to green light with more than 1% efficiency. A narrow infrared bandwidth of 17 Å, set by the phase-matching requirement only, allows the up-converter and photomultiplier to operate in place of a monochromator and infrared detector, and the emission spectrum of a mercury lamp has been thus examined in the region of 1.7 μ. A close agreement between theory and practice has been found in all respects except noise performance. Further studies of this aspect are required.
Size Effect and Critical Transport Current in Titanium (22 at.% Niobium)
Authors: McInturff A. D. , Chase G. G. , Whetstone C. N. , Boom R. W. , Brechna H. , Haldemann W.
Published: January 2005

The dependence of the critical transport current density on conductor size has been measured for the superconductor, Ti (22 at.% Nb), in transverse fields up to 93 kG. For samples with as similar metallurgical histories as possible, it is found that the critical current is proportional to the cross-sectional area for samples 0.0024 in. to 0.0501 in. in diameter. More important, the field-dependence found for critical current densities is given by Jc=A0/b0 exp(−B/b0)+C0,where B is the applied transverse magnetic field.
Microwave Investigation of Plasmas Produced in a Reactor
Authors: Bhattacharya A. K. , Verdeyen J. T. , Adler F. T. , Goldstein L.
Published: January 2005

The results of a microwave investigation of gaseous plasmas produced by the radiation field within the core of a water-cooled nuclear reactor are reported. It is shown that the plasmas thus formed are applicable in reactor instrumentation and are quite suitable for investigating basic plasma phenomena such as various collision cross sections and electron-loss processes. Radiometric electron-temperature measurements indicate that, at adequately high gas pressures (≥50 Torr) in the light noble gases used, the electron gas temperature is at or near the host gas temperature and is independent of the reactor power. The dependence of the electron temperature on the gas pressure has been utilized to determine the electron—neutral collision frequency in neon at different electron energies and in helium at room temperature. Preliminary measurements give a value of 2×10−9 cm3·sec−1 for the recombination coefficient in helium at room temperature.
Late-Stage Equivalence in One-Dimensional Impacts
Authors: Chou Pei Chi , Burns Bruce P.
Published: January 2005

The attenuation of a strong plane shock produced in a target by the impact of a thin striker is studied by the numerical method of characteristics. The calculated results show that late-stage equivalence exists for impacts in aluminum, copper, and ideal gases with various ratios of specific heats, γ. The shock fronts produced by different impacts approach each other in position, and in strength, at late times provided that du0α is constant, where d is the thickness of the striker, u0 the impact velocity, and α a constant with values of 1.28, 1.50, 1.62, 1.50, and 1.32, for aluminum, copper, and ideal gases with γ equal to 2.0, 1.4, and 1.1, respectively.
Photoconductive and Photo-Hall Measurements on High-Resistivity GaP
Authors: Bowman D. L.
Published: January 2005

A correlation between photoconductive and photo-Hall data on GaP has revealed direct evidence of hole trapping. From these same data, the position of the sensitizing centers was determined to be 0.66 eV above the valence band. Also, electron to hole mobility ratios between 1.1 and 1.3 and lifetimes of photogenerated carriers in the high-light region of ∼6×10−6 sec were calculated.
Interactions of Point Defects and Elastic Inclusions
Authors: Moon Francis C. , Pao Yih-Hsing
Published: January 2005

Using a continuum model for crystal defects and inclusions, the interaction energies are calculated for one defect with several inclusions and for several defects with a single inclusion. The special cases of the interaction of a center of dilatation and a doublet with a spherical inclusion are discussed. The center of dilatation may be attracted to or repelled from the inclusion depending on the rigidity of the inclusion and of the matrix material.
Temperature Dependence of the Elastic Constants of Molybdenum
Authors: Dickinson J. M. , Armstrong P. E.
Published: January 2005

The elastic properties of molybdenum single crystals have been measured using thin-rod resonance techniques as a function of temperature from −198° to over +650°C. Molybdenum behaves in a normal manner over this temperature range. Its elastic stiffness coefficients, with the exception of C12 which increased 3%, decreased in a nearly linear manner. The decrease was 8% for C44, 11% for C11, and 18% for C′. From these data the temperature dependence of the bulk modulus, the shear coefficient C′, the anisotropy ratio, and the Young's and shear modulus of isotropic polycrystalline molybdenum were calculated.
Correlating Devices and Their Estimation Errors
Authors: Knowles J. B. , Tsui H. T.
Published: January 2005

Several special-purpose devices capable of performing correlation measurements have been described in the literature over the past few years. While the expected outputs of these devices have been shown to equal the required correlation function, their intrinsic sampling errors have apparently not been investigated. Two such important devices are the modified relay and polarity-coincidence correlators. Variances for their measurement errors are derived in this paper. The dependence of the sampling error on the information content of the input processes and on the type of auxilliary signal is also considered. The analysis is confirmed by the experimental results.
Hall Effect in Dielectric Media: Microwave X-Band Faraday Rotation of Water Adsorbed on Hemoglobin
Authors: Chai Soo-Young , Vogelhut Paul O.
Published: January 2005

The structure of bound water molecules in crystalline, bovine hemoglobin powder is investigated with a microwave technique of Faraday rotation at a frequency of 9.36 Gc/sec. An expression for the Faraday rotation due to displacement-current Hall field is derived in terms of dipole concentrations of free water molecules and is applied to measure the changes from free water to bound water molecules on hemoglobin with variable amounts of adsorbed water. In agreement with the theory, the experimental result shows a linear relationship between the angle of rotation and the concentration of free water dipoles up to the hydration level of 0.13 g of water per gram of dry hemoglobin. Above this hydration level, the formation of icelike structures on the surface of hemoglobin is discussed based on our experimental results.
Thermal Expansion and Elastic Constants of β′-AgMg. II. Single-Crystal Elastic Constants from 77° to 750°K
Authors: Chang Y. A. , Himmel L. , Neumann J. P.
Published: January 2005

The single-crystal adiabatic elastic constants of stoichiometric β′-AgMg have been determined from 77° to 750°K using the ultrasonic pulse-echo technique. The values obtained at 300°K are: c11=0.8380, c12=0.5635, c44=0.4755 (all in units of 1012 dyn/cm2).

A relationship between the elastic constants and the lattice parameters of the two β′-structures AgMg and CuZn was found. A similarity of the temperature dependence of the elastic constants was also observed. From the extrapolated values of the elastic constants at 0°K, a Debye temperature of 287°K was obtained. Finally, using the elastic constant data, specific heat of β′-AgMg at constant volume was calculated and found to compare favorably with the classical value 3R at high temperature.
Growth of the Close-Packed (111) Plane of Gold Single Crystals
Authors: Schwoebel Richard L.
Published: January 2005

The structure of the (111) plane of gold single crystals growing from the vapor, deposited at a rate equivalent to 0.026±0.005 monolayers/second, has been studied using carbon replicas and electron microscopy, electron and x-ray reflection diffraction. Below a temperature of 750°K, crystallites of gold develop on the surface, sometimes with preferred orientation. Somewhat above this temperature, extensive surface step systems and oriented trigonal growth centers are observed. The crystallographic orientation of the steps and growth centers, as well as reflection x-ray diffraction patterns from these surfaces, are evidence that the deposited gold atoms participate in growth of the substrate crystal at temperatures above 750°K. Development of these trigonal growth centers is described in terms of a simple model in which diffusing atoms are preferentially incorporated into growth centers at sites with particular coordination arrangements, i.e., such that the growth centers preferentially expose particular facets. Existence of oriented step systems and growth centers implies that adsorbed gold atoms diffusing on the surface are reversibly captured at steps under these growth conditions. Consequently, the activation energy for surface diffusion includes the energy for dissociation of atoms from steps to adsorbed positions on an atomically smooth portion of the surface. An upper bound for the activation energy for surface diffusion is concluded to be approximately 1.7 eV for atoms adsorbed on the (111) plane. The activation energy for motion of an atom along a step is estimated to be approximately equal to or greater than 0.7 eV.
Diffusion Lengths of Electrons and Holes in GaAs
Authors: Aukerman L. W. , Millea M. F. , McColl M.
Published: January 2005

The short-circuit current of both diffused and n-type metal semiconductor junctions during 2-MeV electron irradiation was measured. The results indicate that electron diffusion length in the Zn-diffused p-type region is proportional to the reciprocal of the square root of the donor concentration. The electron-diffusion length ranges from 20 μ for lightly doped diodes to 2 μ for heavily doped diodes. The hole-diffusion lengths are less than 1.0 μ in heavily doped surface barrier diodes. The thickness of the active radiative recombination region for diffused diodes under forward bias was measured and compared with the short-circuit current results. These results suggest that the pre-irradiation electron lifetime is ≈ (10−9 ND)−1, where ND is the substrate donor concentration. This behavior is consistent with radiative recombination between donors and free holes.
Magnetic Susceptibility of Sodium—Ammonia Solutions
Authors: Suchannek Rudolf G. , Naiditch Sam , Klejnot Olgierd J.
Published: January 2005

Magnetic susceptibilities of sodium—ammonia solutions with concentrations ranging from 0.36 to 3.85 mole/liter have been measured at room temperature using Gouy's force method. At the low concentration end, atomic susceptibilities of sodium derived from the measurements fit Hutchison and Pastor's data which were measured at lower molarities. The general trend of the atomic susceptibility as a function of concentration indicates a transition in the electronic structure at a critical interatomic distance dm of 15 Å. This transition is discussed in relation to the transition from the nonmetallic to the metallic state which has been predicted by Mott for crystalline arrays of hydrogen-like atoms. At concentrations c above 2.0 mole/liter, the atomic susceptibility exhibits a c−2/3 dependence as expected for Pauli's paramagnetism of a degenerate electron gas. Observed deviations of metal—ammonia solutions from Curie's law can be accounted for by a temperature dependence of dm.
The Oxide—Metal Interface of Electropolished Aluminum
Authors: Francis H. A.
Published: January 2005

Replica and transmission electron microscopy were used to study the ordered topography of the amorphous oxide film on electropolished aluminum. The symmetry, periodicity, and amplitude of the oxide film thickness variation constituting the regular topography were investigated as a function of substrate orientation. The results are consistent with previously reported data and have enabled the dislocation model proposed by Doherty and Davis for the oxide—aluminum interface to be amplified and the nature of the interface to be more precisely defined. The model postulates that the first oxide to form has long-range lattice symmetry identical to that of the substrate, resulting in a regular network of interfacial dislocations. The amorphous oxide subsequently grown by cation transport is thinnest over the dislocations, as the interface is the rate-controlling barrier. No correlation was observed between the existence of ordered topography and epitaxy of the high-temperature crystalline oxide which nucleates heterogeneously on the ordered oxide surface originally in contact with the metal. It is concluded that, for the range of orientations over which ordered topography exists, the dislocation cores are wide, i.e., almost a pure vernier. The observed defects in the long-range order of the various topographies may be accounted for by corresponding defects in the ordered oxide adjacent to the interface. The dependence of the existence and periodicity of the topographies on electropolishing temperature and voltage was investigated and may be explained by the difference in thermal expansion of the substrate and the ordered oxide at the interface. It is concluded from these data that the lattice parameter of the ordered overgrowth is 6.0% larger than that of the substrate, and that, when the first layer of oxide is formed, the temperature of the metal surface may be considerably greater than the electrolyte temperature. The absence of ordered topography for surface treatments other than electropolishing suggests that the minimum surface temperature for the formation of interfacial dislocations is greater than room temperature.
Inductance-Variation Method of Measuring Characteristics of Electromagnetic Levitation Systems
Authors: Hatch Albert J. , Smith W. E.
Published: January 2005

A recently developed general theory of electromagnetic levitation of conducting bodies is applied in a new method of examining the levitation and stability of levitating bodies of arbitrary shape in the fields of coil systems of arbitrary configuration. Introducing the conducting body into the magnetic field of the coils changes the apparent inductance of the coils by an amount ΔL which is readily measured directly. The pertinent result of the theory is that the levitational force is proportional to the gradient of ΔL. The validity and feasibility of the method are demonstrated by measurements in several typical cases.
Calorimetric Detection of NMR in Ferromagnets
Authors: Gill D. , Shaltiel D.
Published: January 2005

Elevation of lattice temperature above 4.2°K on passage through NMR in ferro- and ferrimagnets was detected in a calorimeter. Faint signals corresponding to the resonances of 57Co nuclei in fcc Co metal and 55Mn nuclei in MnFe2O4 were seen at their respective frequencies. Sensitivity considerations and details are presented.
Effects of Drift Fields and Field Gradients on the Quantum Efficiency of Photocells
Authors: Jain G. C. , Al-Rifai R. M. S.
Published: January 2005

A theoretical investigation of the effects of electrostatic drift fields and their gradients in the diffused and base layers of photocells has been carried out. Expressions for the quantum efficiencies of the cell have been derived using a single-region model for the diffused layer and a two-region model for the base layer. Numerical computations for silicon photocells have been performed using impurity profiles of the Gaussian and error-function types. It has been found that there is an improvement in the quantum efficiency of the diffused layer as compared to a field-free layer. The improvement depends upon the diffused impurity profile. It has been deduced that improvement of the base-layer quantum efficiency may be obtained by suitably grading the base-layer impurity concentration. The mathematical analysis in this paper is quite general and may be applied to any photocell by using appropriate values of the parameters of the material of the cell.
Slip Distribution in a Thin Slice of a Crystal at a Free Surface
Authors: Lin T. H. , Ito M.
Published: January 2005

The plastic deformation in a thin slice of a most-favorably-oriented crystal embedded at the free surface of a fine-grained aggregate is considered. The elastic moduli of the individual crystals are assumed to be isotropic and homogeneous. The analogy of plastic strain and applied force in an elastic medium is utilized. This equivalent force due to plastic strain is considered to be applied to a semi-infinite elastic medium under plane strain. Melan's results for the stress field caused by a force acting in a semi-infinite elastic plate modified for plane strain are used to calculate the plastic strain distribution. The slip near the free surface is greater than that at the interior end of the thin slice. This seems to explain the removal of some fatigue damage by electroplating the surface of a test specimen.
Porosity Effects on the Oxidation of Tungsten
Authors: Berman David
Published: January 2005

The rate of formation of tungsten oxide, from the internal porous area of a heated tungsten sample, has been calculated. The porosity effect has been found to increase the oxidation rate by an order of magnitude over an equivalent solid sample.

The effusion rate of WO3 from the sample is obtained by establishing the O2 and WO3 molecular distributions within the sample. The boundary conditions of the distributions are set by the partial pressure of oxygen at the surface. The rate of WO3 effusion (from the porous interior into the surroundings) is determined by the molecular concentration gradient at the boundary, times the appropriate diffusion coefficient.

The parameters used in the study correspond to vacuum-system operation of a cesium surface-contact ionizer (temperature=1400°K; pressure=10−6 Torr). Simple slab geometry is considered for the porous tungsten sample; only one side is exposed to oxygen.
Influence of Nitrogen on Magnetomechanical Damping in Chromium
Authors: Klein Mark J.
Published: January 2005

The effects of heat treatment and stress on the magnetomechanical damping in chromium near its Néel temperature were investigated. Changes in magnetomechanical damping are attributed to the influence of the stress or the magnetically induced ordering of nitrogen on the magnetic structure of chromium. A relaxation phenomenon was observed whose rate is believed to depend on the diffusion of interstitial nitrogen.
Neglecting Diffusion in Space-Charge-Limited Currents
Authors: Schilling Ronald B. , Schachter Harry
Published: January 2005

In most work dealing with space-charge-limited currents, the diffusive contribution to the current is neglected. The classic steady-state problem was handled by Mott and Gurney. For their problem of the perfect insulator it is well known that diffusion dominates near the injecting contact but, after some critical distance, drift dominates, and it is consistent to neglect diffusion.

For the case of transient SCLC the mathematical validity of neglecting diffusion has not been shown. The purpose of this work is to show that for times greater than a critical time and distances greater than a critical distance the diffusive term can consistently be neglected. The solutions found by Mark and Helfrich and by Many and Rakavy for injection of electrons into an insulator under an applied voltage pulse have been shown to be correct under the above conditions. The interesting result is that the critical parameters are related to geometrical parameters by the ratio of the thermal voltage kT/q to the applied voltage. We therefore find that for signals large compared to kT/q, the neglect of diffusion is valid over most of the range of time and distance associated with the problem.
Magnetization of an Ideal Superconducting Torus in a Transverse Field
Authors: Wright Evan B. , Peterson Paul I.
Published: January 2005

The magnetic constants of an ideal superconducting torus, located in a uniform magnetic field perpendicular to its axis of symmetry, are calculated from a scalar potential expansion in toroidal Legendre functions. Graphs and approximate formulas are given for the induced magnetic moment of the torus and the maximum field values (with locations) on its surface, as functions of its radius ratio.
Domain-Wall Motion in Yttrium-Iron Garnets
Authors: Wanas M. A.
Published: January 2005

Domain-wall motion in pure and doped yttrium-iron-garnet single crystals with composition Y3Fe5−δSiδO12, 0<δ<0.12, has been investigated over the temperature range 4.2°−300°K. Samples were prepared in a picture-frame geometry to carry a single movable wall. Wall mobility for our pure sample showed a temperature dependence similar to that reported by Hagedorn and Gyorgy; however, our values for wall mobility are 4–7 factors lower than theirs, probably reflecting the simpler domain structure of our samples. As expected, the wall inverse mobility increases linearly with the increase in silicon concentration (or equivalently, with Fe2+ ion concentration). However, as a function of temperature the inverse mobility of silicon-doped samples, unexpectedly, shows a peak at about 20°K. The over-all temperature dependence does not agree with the diffusion after-effect model which is based on the assumption that wall damping is the result of 3d-electron transitions between Fe2+ and Fe3+ cations in the octahedral sublattice. The behavior, however, is very similar to that found for the temperature dependence of the microwave-resonance linewidth of silicon-doped samples. In both cases, because of the short time of spin reorientation relative to the electron-diffusion relaxation time, it is more likely that the loss mechanism is dominated by a localized relaxation process occurring between the energy levels of Fe2+ ions.
Calorimetric Study of Several Garnets at Low Temperatures
Authors: Onn David G. , Remeika J. P. , Meyer Horst , Henderson James
Published: January 2005

Specific-heat measurements on very pure polycrystalline samples of YIG, EuIG, and TmIG have been carried out between 0.4° and 4.2°K in zero external field. An analysis in terms of magnon and lattice contributions has been attempted for YIG. The dispersion parameter D appears to be lower than that measured for this same sample by NMR of the 57Fe nuclei, where D=30 cm−1. The results on EuIG determine the hfs field at the 151Eu and 153Eu nuclei near 0°K. This field was found to be 550±15 kOe, which is smaller than that from Mössbauer experiments. The nuclear specific heat of TmIG is in good agreement with that calculated from Mössbuaer experiments. Both EuIG and TmIG show only a small magnetic specific heat, as expected from susceptibility and magnetization measurements.
Narrow Linewidth and High Infrared Transmission in Hydrothermally Grown Yttrium Iron Garnet
Authors: Kolb E. D. , Wood D. L. , Spencer E. G. , Laudise R. A.
Published: January 2005

The properties of yttrium iron garnet (YIG) grown from high-temperature—high-pressure aqueous (hydrothermal) solvents have been studied. YIG with a room-temperature ferromagnetic linewidth as low as 0.3 Oe and with an infrared extinction coefficient at 1.14 μ as low as 0.5 has been prepared. Such YIG should be useful for lasers, laser optical devices, and microwave devices, and the hydrothermal technique is shown to have advantages over conventional flux growth for the reproducible production of large garnets. Linewidth is shown to correlate with proton content which is affected by the concentration of Ca2+ ions in the lattice. Absorbtion at 1.14 μ is uniformly low in hydrothermal YIG, and this fact is discussed. The role of impurities, dopants, and conditions of growth are discussed.
Effect of Impurities on the Optical Properties of Yttrium Iron Garnet
Authors: Wood D. L. , Remeika J. P.
Published: January 2005

The optical absorption spectrum of single-crystal YIG is dominated at the short wavelengths by electronic transitions due to iron ions. For the long wavelengths, it is dominated by lattice vibrational transitions. Between about 1 μ and 6 μ there is a region of great transparency which can be modified in several ways. The valence of the iron ions can be altered by heat-treatment of crystals in oxidizing or reducing atmospheres, or by doping with divalent or tetravalent ions. The altered valence leads to increased optical absorption, as well as increased electrical conductivity.

Foreign ions such as cobalt or the rare earths may have characteristic absorption lines in the region of transparency, and when yttrium is completely replaced by a rare earth, the short-wavelength edge absorption may be shifted appreciably due to lattice expansion or contraction.

Another anomaly in the transparent region of YIG is found in hydrothermally-grown crystals, where OH-group stretching vibrations occur.
Statistical Mechanics of a Turbulent Ferromagnetic Medium
Authors: Slonczewski J. C.
Published: January 2005

Statistical equations for the response of a fully or partially demagnetized ferromagnetic insulator to a time-varying magnetic field are proposed. The theory is based on the classical dynamical equation for a ferromagnetic continuum, including exchange, anisotropy, and magnetic dipole effects. A set of statistical equations couples the rates of change of the average magnetization, of Green's functions and of second-order two-time correlation functions constructed from space-Fourier components of the magnetization. The set is closed by making use of the direct-interaction approximation introduced by Kraichnan in the theory of homogeneous fluid turbulence. It is shown that the approximate equations conserve energy and the average spontaneous magnetization squared. Static equilibrium properties are derived in preparation for attacking dynamic problems. In equilibrium, the spectral distribution of magnetization in wave-vector space consists of a narrow peaked region about the origin of wave-vector space plus a spread-out background. The peaked region represents the statistical analogue of ordinary domain structure and has negligible energy content, while the background represents an equipartition of the available internal energy among all Fourier components. General properties of the statistical equations indicate that they may be meaningful in connection with problems not involving pronounced anisotropy of the spectrum.
Collective Modes near the Spin-Flip Continuum and Spin Depolarization due to Indirect Exchange
Authors: Luther Alan H.
Published: January 2005

In the indirect exchange model, the spin-wave dispersion relation undergoes anomalous behavior as it enters the continuum of electron spin-flip excitations. This anomaly consists of two Kohn-type singularities of opposite strength located very close together, causing a bump in the dispersion relation rather than the usual isolated kink. The single-particle renormalization constant diverges logarithmically at these singularities, and thus the spin-wave picture is inadequate in this region. The line shape is distorted by the strong frequency dependence near the absorption edge and the peak shifts either up or down depending on the sign of the exchange interaction between the localized spins and the conduction electrons. At zero temperature the ground state does not have the local spins fully aligned but slightly depolarized due to virtual excitations of conduction electrons. The total fractional deviation is given approximately by the Curie-to-Fermi-temperature ratio. Effects of a short-range repulsion between conduction electrons have also been studied. In general, the spin-wave spectrum curvature, Curie temperature, and zero temperature deviation are increased by powers of the spin-susceptibility enhancement factor.
Calculation of the Rare-Earth—Iron Superexchange Interaction in the Garnets
Authors: Pearson J. J. , Herrmann G. F.
Published: January 2005

The exchange potential for the rare earth—iron interaction in the garnets depends on ten theoretical parameters. Since experiments provide only six splittings, the potential has been simplified in past treatments by various drastic assumptions which are highly implausible on physical grounds.

By treating directly the superexchange mechanism involved we obtain a potential whose parameters are physically well-defined exchange and transfer integrals. By invoking the ``orthogonality requirement'' the number of these parameters is greatly reduced. A preliminary calculation for ytterbium shows that a good fit can be obtained by assuming the interaction of the rare earth with its nearest iron neighbor to predominate.