bluuebunny/crossref_metadata_2025 huggingface dataset:
Recovery of Laser Intensity from Correlation Data
Authors: Blount E. I. , Klauder J. R.
Published: February 2004

It is shown that third-order intensity correlations are sufficient to determine the time-dependent intensity of a Q-switched laser. As a consequence, all higher-order correlations are related to the third and an expression for this relation is presented.
Positive Column Population Calculations for the Evaluation of Dispersive Effects in He–Ne Lasers
Authors: Arrathoon R.
Published: February 2004

Sizable shifts in the oscillation frequency of a He–Ne laser with variations in the dc discharge current have been observed. The shifting effects are believed to be due principally to changes in the populations of the helium 23S level and the neon 1s5 level. A simplified model is proposed for the approximate evaluation of these populations. A slightly modified version of the model, under regenerative conditions, is then used to evaluate the current shifting effects and the results are compared with experimental observations. The approach used is of sufficient generality to be applicable to most He–Ne lasers operating under optimum gain conditions. The results suggest that laser operation at 1.15 μ, rather than 6328 Å, may considerably reduce the effects of current variations on the oscillation frequency. For constant pressure-diameter product conditions, theory predicts that the current-shifting effects will vary approximately inversely with tube diameter.
Temperature Dependence of the Ag/Cu Sputtering Ratio for the Eutectic
Authors: Anderson G. S.
Published: February 2004

The relative sputtering rates of Ag and Cu from the Ag/Cu eutectic (60% Ag-40% Cu by atoms) were measured by means of the spectroscopic emission technique. The targets were bombarded by 100-eV Ar ions for target temperatures in the range of 80° to 285°C. At low target temperatures, the Ag and Cu sputtering yields vary with time of sputtering according to a simple sputtering model. However, at the higher temperatures surprisingly large differences were observed which could not be explained by a simple model. For example, Ag/Cu sputtering ratio variations greater than a factor of 10 were observed. After prolonged sputtering in the high-temperature range, a thick surface layer (∼1 μ) developed which was highly enriched in Cu. A model based on surface diffusion of Ag on Cu is proposed to explain the results.
Pulsed-Radiation-Induced Current in Crystalline and Fused Quartz
Authors: Okabe S. , Tsumori K. , Tabata T.
Published: February 2004

Pulsed-radiation-induced current in crystalline and fused quartz was studied by using 5-μsec pulses of electrons with an energy of 13 MeV and a current density of about 100 mA/cm2 peak and a few μA/cm2 average. The pulse shape of the induced current varied remarkably with time within a few minutes of irradiation and also with the temperature of the sample. The variation in shape showed a dependence on crystal orientation of the sample. The effect of the field of the internal space charge was found to be neglibible in the observed phenomena. A qualitative explanation is applied to part of the results in terms of an interaction between excited carriers and traps.
Cylindrical Damage Shells in Irradiated Vanadium
Authors: Rau Robert C. , Ladd Robert L.
Published: February 2004

Transmission-electron-microscopy studies of neutron-irradiated vanadium single crystals have revealed the presence of cylindrical regions of high damage concentration surrounding elongated fibrous precipitates. These precipitates have been identified as tetragonal V3B2 and are oriented along 〈100〉 directions in the cubic vanadium lattice. The cylindrical damage shells are duplex in nature, consisting of a highly damaged inner region of about 1.3-μ radius and a less highly damaged outer region of about 2.6-μ radius. These two damage shells consist of small defect clusters produced by recoiling lithium ions and alpha particles, respectively, generated by 10B(n, α)7Li transmutation reactions. Post-irradiation annealing at temperatures up to 1400°C eliminates the defect clusters and produces dislocation tangles and blocky precipitates in the inner shell and spherical cavities or bubbles in the outer shell. The precipitates in the inner shell are believed to be LiV2O5, while the bubbles in the outer shell are evidently formed by the agglomeration of helium atoms. Although spherical damage shells surrounding boron-containing particles have been observed in several other irradiated metals and alloys, this represents the first known observation of nonspherical shells.
Influence of Faceting on Ejection Patterns Obtained from Ion-Bombarded Face-Centered Cubic Metals
Authors: Cunningham R. L. , Ng-Yelim Joyce
Published: February 2004

Deviations of focusons by repulsive and attractive forces at idealized surfaces have recently been proposed to account for ejection other than that exactly along close-packed directions. The theory is here applied to actual faceted surfaces which are produced by ion bombardment. This treatment brings the deviation theory into very good agreement with experimental results. An earlier theory based on surface twinning to explain ejections parallel to some non-close-packed directions in the parent crystal is shown to be untenable.
Sputtering Yield Measurements with Low-Energy Metal Ion Beams
Authors: Hayward W. H. , Wolter A. R.
Published: February 2004

Sputtering yields of metal ion beams on polycrystalline films for energies below 1 keV were measured in situ using crystal microbalance techniques. Self-sputtering yields were determined for Au, Cu, Ag, Cr, and Al for energies from 10 to 500 eV. These yields were consistent with some previous noble-gas sputtering yields when only the difference in ionic mass was taken into account. Residual oxygen significantly lowered the self-sputtering yields of Al and Cr for all energies from 0 to 1 keV and the collection rate of oxygen was apparently greater for ions of about 10 eV. Sputtering yields of films by dissimilar metal ions were most strongly influenced by the type of metal in the beam, rather than by the target material, even for high ion energies.
Chemical Polishing of II-VI Compounds
Authors: Strehlow W. H.
Published: February 2004

The chemical polishing of the anion face of ZnO, ZnS, CdSe, and ZnTe and the cation face of CdSe and ZnTe with bromine dissolved in methanol has been accomplished. The etch rates of the bromine-methanol solution on the anion and cation faces of BeO, ZnO, ZnS, CdS, CdSe, ZnTe, and InSb have been measured at room temperature. An empirical relationship between the etch rates of the bromine-methanol solution and the difference of the electronegativity of the component elements has been found.
Bipolar Photoeffect Arising from an Anomalous Copper Distribution in and near a Gallium-Diffused Layer in Germanium
Authors: Williams R. L.
Published: February 2004

A very nonuniform copper distribution occurs in and near a gallium-diffused layer in germanium. This gives rise to a p+-π-p structure, the presence of which has been detected using the sign reversal of the contact photovoltaic effect at wavelength near the absorption edge. Using 64Cu and radiochemical techniques, it has been demonstrated that a high concentration of copper collects in a diffused layer and leads to the observed contact structure.
Electrical Conductivity in an n-Type Surface Inversion Layer of InSb at Low Temperature
Authors: Komatsubara Kiichi F. , Kamioka Hajime , Katayama Yoshifumi
Published: February 2004

Measurements of electrical properties of an n-type inversion layer at the surface of a p-type InSb at low temperatures are reported. The surface inversion layer was produced by the application of the electric field normal to the surface of InSb in a metal-oxide—p-InSb structure. The observed field effect mobility shows that the motion of the electrons in the surface inversion layer is quantized in one direction and of two-dimensional nature. Information for the trapping state in the oxide was obtained. A new type of current-voltage characteristic, which is supposed to originate in the electron transfer from the lower quantum level to the higher one, was also observed.
Variation of Electrical Properties with Zn Concentration in GaP
Authors: Casey H. C. , Ermanis F. , Wolfstirn K. B.
Published: February 2004

The resistivity and Hall coefficient RH for Zn-doped GaP were measured at temperatures between 4.2° and 775°K. Neutron activation and through diffusion with radioactive 65Zn were used to determine the Zn concentration NZn, which ranged from 6.7×1016 cm−3 to 2.1×1019 cm−3. At the lowest Zn concentration the thermal ionization energy for Zn in GaP was found to be 0.060±0.002 eV. The thermal ionization energy decreases rapidly for Zn concentrations in excess of 2.0×1017 cm−3. Metallic impurity conduction was observed at a Zn concentration of 2.1×1019 cm−3. The low-concentration region is observed for NZn≲2.0×1017 cm−3, the intermediate-concentration region for 2.0×1017≲NZn≲2.1×1019 cm−3, and the high-concentration region for NZn≳2.1×1019 cm−3. In the intermediate-concentration region the high-temperature hole concentration, determined from p=1/eRH, was found to exceed the Zn concentration by a significant amount. Analysis of the temperature-dependent hole concentration results in an effective density-of-states mass ratio of approximately 0.5. The lightest doped sample had a room-temperature Hall mobility of 120 cm2/V·sec and a maximum mobility of 2050 cm2/V·sec at 55°K. The maximum mobility at low temperature is limited by ionized and neutral impurity scattering, while the dominant high-temperature scattering mechanism appears to be optical phonon scattering.
Surface Effects and the Absorption Edge of CdS
Authors: Bujatti M.
Published: February 2004

New measurements of the CdS absorption edge on samples of different thickness provide strong evidence that the absorption takes place primarily in the surface region. Quite good agreement is obtained with calculations based on the Franz-Keldysh effect.
Equation of State of Shock-Loaded Tungsten at 950°C
Authors: Rohde R. W.
Published: February 2004

The Hugoniot of wrought tungsten which was 99.6% of the crystalline density and 99.92% pure has been determined to 80 kbar at room temperature and at 950°C. Measurements of the stress-particle velocity relationship were made by impacting a sapphire-faced quartz gauge assembly onto the tungsten sample. In the room temperature experiments, transmitted wave profiles were determined with quartz gauges. At room temperature, the elastic wave velocity was 5.22±0.05 mm/μsec and the Hugoniot elastic limit for 9.5 mm thick specimens was 37.7±0.8 kbar. The stress-particle velocity Hugoniot at 950°C, while nearly parallel to the room temperature Hugoniot, was displaced about 15 kbar downward due to a decrease in the Hugoniot elastic limit at this temperature. This decrease is associated with a temperature induced brittle-ductile transition. The application of these data in calculating the Grüneisen parameter is discussed.
High-Coercive-Force Rare-Earth Alloy Films by Getter Sputtering
Authors: Theuerer H. C. , Nesbitt E. A. , Bacon D. D.
Published: February 2004

Thin films of the rare-earth alloys of the Co–Sm system with and without the addition of Cu have been found to have exceptionally high coercive forces. A coercive force of 30 000 Oe was realized with Co3.65Cu1.35Sm films, 4000-Å thick prepared at a substrate temperature of 500°C using getter sputtering. This technique avoids troublesome oxidation problems usually encountered in preparing films of active materials such as the rare-earth compounds.
Thermoelectric Power of Vacuum-Evaporated Au–Ni Thin-Film Thermocouples
Authors: Thornburg D. D. , Wayman C. M.
Published: February 2004

Continued investigations of the thermoelectric properties of Au–Ni thin-film thermocouples have been made. The thickness dependence of the Seebeck coefficient for Ni films of variable thickness on bulk Au was determined and found to be sensitive to the thermal history of the thin film thermocouples. By developing suitable preparation techniques for these thermocouples, involving several periods of annealing, time-invariant calibration curves were obtained. The thickness dependence of the Seebeck coefficient was found to follow closely the predictions of the size-effect theory of Mayer.
Specific Heat of α Al2O3 from 2 to 25 K
Authors: Fugate R. Q. , Swenson C. A.
Published: February 2004

The heat capacity of colorless synthetic sapphire (α Al2O3, corundum) has been measured from 2 to 25 K. The data above 14 K can be expressed as Cv = 1.755×10−3T3+1.905×10−7T5 mJ/K·g-atom. This equation for Cv gives Θ0 = 1035 K, in good agreement with the values calculated from elastic constant data. An extrapolation of these results to higher temperatures is consistent with other data. Below 14 K an anomalous heat-capacity contribution appears which is about 1.5% of Cv at its maximum. The magnitude of this anomaly corresponds to that which would be given by a few ppm of gaseous or transition-metal impurities.
Comparative Study of Diatomic Partition Function Calculations
Authors: Shipley K. L.
Published: February 2004

Internal partition functions for 18 diatomic molecules were computed by three different methods. The computations were performed for temperatures from 500° to 30 000°K. The methods of computation are (a) Mayer and Mayer approximation, (b) direct summation to dissociation limit, and (c) direct summation including states above dissociation limit. The variation in numerical results using these three methods is negligible up to temperatures of 5000°K, although there are some exceptions for molecules containing hydrogen. At higher temperatures the Mayer and Mayer approximation gives, for most molecules, excessive values for the partition function. An indication of the importance of including excited electronic states and excluding some first rotational states is also given.
Cylindrical Onset Waves
Authors: Russell Geoffrey , Holzberlein Thomas M.
Published: February 2004

A method is presented to evaluate quantitatively the operation of the invertron, a recently developed device for measuring directly the lifetimes of quantized systems lying in the nanosecond range. The device consists of two electrodes in cylindrical geometry, the inner positive-grid electrode being 45% transparent to electrons while the outer is an rf-heated cathode.
Inductance of Circuits Containing a Superconducting Plate
Authors: Celli V. , DuVall B. , Manson R.
Published: February 2004

Using the London theory we investigate the inductance of a system consisting of a long straight conductor of uniform cross section situated parallel to a nearby superconducting plate. Explicit formulas are derived for the particular cases of conductors having cylindrical, rectangular, and thin-film cross sections and the limitations of the theory are discussed. The conclusions indicate that measurements of the inductance of such a system can be used to determine the penetration depth of a superconductor.
Eddy-Current Method for Measuring Anisotropic Resistivity
Authors: Neighbor J. E.
Published: February 2004

The eddy-current method for measuring electrical resistivity is extended to situations in which the resistivity is anisotropic. It is shown that in most cases of interest in practice, one can obtain the full resistivity tensor from eddy-current measurements.
Interaction Between Localized Defects in an Isotropic Elastic Medium
Authors: Brailsford A. D.
Published: February 2004

The long-range interaction between localized defects in an infinite elastically isotropic solid is derived. It is shown that when the defect has cubic symmetry the interaction energy is proportional to the inverse fifth power of the separation, in agreement with the result previously obtained from discrete lattice theory. The difference in magnitude of the interaction derived by the two methods is attributed to phonon dispersion.
Properties of Unextended Passing Dislocation Loops
Authors: Marcinkowski M. J. , Leamy H. J.
Published: February 2004

An analysis of the behavior of concentric circular dislocation glide loops of opposite sign lying on parallel slip planes has been performed by numerical methods. At large loop radii, a critical stress exists above which the loops may pass one another. This stress decreases as the slip plane spacing between the loops increases or as the loop radii increase. Below the critical passing stress the loops become coupled. In the absence of a lattice friction stress the coupled loops continuously shrink and ultimately vanish. If, on the other hand, such a friction stress exists, there also exists a critical loop radius above which the coupled loops remain permanently stuck within the crystal.
Combined Surface and Grain-Boundary Diffusion
Authors: Stark J. P.
Published: February 2004

A mathematical analysis for the accumulation of tracer as diffused through a thin metallic slab by grain-boundary diffusion is presented. Boundary conditions on the side where the tracer is deposited consist of a small depletable source, and the grain-boundary concentration is enhanced by surface diffusion. Due to the mathematical difficulty associated with boundary conditions for combined grain-boundary and surface diffusion, two cases are studied: No accelerated surface diffusion and infinite surface diffusivity along with finite grain-boundary diffusivity. The difference between the accumulated tracer for the two cases is similar to the contribution from lattice diffusion only. Thus, for a relatively short diffusion time, grain-boundary diffusion analyses without surface diffusion complications are correct.
Critical Electric Field in BaTiO3
Authors: Kulwicki B. M.
Published: February 2004

The present theoretical analysis permits simple, rigorous calculation of the equilibrium properties of state of a ferroelectric possessing a first-order phase transition. The positive critical field in BaTiO3 is approximately 9×105 V/m. Experimental observation of the critical point should result in a better value for the temperature dependence of the fifth-order thermodynamic coefficient ζ.
Storage-Ring Ion Trap Derived from the Linear Quadrupole Radio-Frequency Mass Filter
Authors: Church D. A.
Published: February 2004

The storage of protons and 3He ions in a circular storage-ring ion trap with background gas collision-limited loss time constants up to 8 min long under ultrahigh-vacuum conditions is described. Storage-ring traps were derived from the linear quadrupole rf mass filter by shaping the electrodes into circular and racetrack configurations. Operation of the traps with a trapping rf frequency Ω large compared to the secular ion oscillation frequency ω inhibited ion loss due to nonlinearities in the trapping fields. Long-term ion storage in such traps may prove useful for radio-frequency ion spectroscopic purposes.
Wave Decay on Glass Surface at High Temperatures
Authors: Woo T. C.
Published: February 2004

Wave decay on glass surfaces at high temperatures is treated assuming glass to behave as a Newtonian viscous fluid in the high-temperature region. To meet with different kinds of irregularities and various production techniques, two-dimensional and axisymmetric waves with several boundary conditions are analyzed, each yielding the amplitude ratio at any instant in terms of the physical constants. Crude experiments are performed and found to agree fairly well with the theoretical results.
Viscosity Measurements on Liquids to Pressures of 60 kbar
Authors: Barnett J. Dean , Bosco Charles D.
Published: February 2004

A rudimentary capillary-type viscometer for measuring viscosities between 103 and 1010 poise at high pressures is described. Measurements are reported on petroleum ether to 57 kbar where the viscosity is approximately 1010 poise and on a 1:1 mixture of n-pentane-isopentane to 54 kbar where the viscosity is approximately 106 poise. Measurement precision of the technique is a few percent, but uncertainty in absolute determination at maximum pressure is only within a factor of two. Viscous stresses are shown to decay exponentially with time even at the highest pressures, and no effects of residual stress are observed.
Pressure Dependence of the Elastic Constants for Aluminum from 77° to 300°K
Authors: Ho Paul S. , Ruoff Arthur L.
Published: February 2004

To study the anharmonic properties of Al at low temperatures, the pressure derivatives of the elastic constants have been measured from 77° to 300°K. The isothermal elastic constants are obtained as a function of pressure by a self-consistent analysis of the ultrasonic data. The most probable values for the pressure derivatives are calculated from the results of six measurements of different combinations of the elastic constants. The pressure derivatives are found to be almost constant below ΘD/3 and increasing for higher temperatures. Using the quasiharmonic approximation, the Grüneisen constant γ is calculated from our results and found to be about 15% higher than the thermal γ in the temperature range studied. We have calculated the elastic γ for T≪ΘD from the extrapolated values of the pressure derivatives. It turns out to be 2.51, a value in excellent agreement with the low-temperature lattice thermal γ. The equation of state in the Murnaghan form and in a series expansion of the volume change in terms of pressure is discussed for Al. A good agreement can be obtained between the ultrasonic and the static and shock compression results if the latter data are analyzed according to the Murnaghan equation of state.
Laser-Machining Thin-Film Electrode Arrays on Quartz Crystal Substrates
Authors: Hokanson J. L. , Unger B. A.
Published: February 2004

The feasibility of laser-machining quartz crystal resonators for frequency and inter-resonator coupling adjustment has been demonstrated. The inter-resonator coupling has been adjusted by altering the geometry of the electrode array. The frequency has been adjusted by vaporizing material to form an array of holes on the electrode surface. The results indicate that extremely fine adjustments of inter-resonator coupling and resonator frequency can be achieved. Frequency adjustments greater than one part in 108 have been demonstrated. No degradation of the crystal unit electrical parameters could be detected as a result of the machining process. Furthermore, laser trimming lends itself to automated processing without the need for elaborate vacuum equipment as is presently required with some adjustment techniques. Laser trimming also appears to be ideally suited for adjustment of high-frequency resonators where fine tolerances are required.
Superconductivity in Some Compounds of La, Lu, Sc, and Y
Authors: Green R. W. , Thorland E. O. , Croat J. , Legvold S.
Published: February 2004

A number of high-melting-point rare-earth compounds have been examined for superconductivity. In this work LaC2, LuC2, and YGa2 were found to be superconductors, but Y3C, LaGa2, La5Sn3, and Y5Sn3 did not exhibit superconductivity in tests down to 1.4 K.
Avalanche Breakdown in GaP
Authors: Pilkuhn M. H.
Published: February 2004

The avalanche breakdown of reverse biased p-n junctions in GaP is investigated. Electrical studies comprise measurements of I-V characteristics, breakdown field, and electrical noise as functions of temperature. The high-temperature light emission from microplasmas consists of a broad emission band with a maximum, near 1.7–1.8 eV, but otherwise with no structure. Its shape is analyzed in detail and discussed in view of theoretical models. The quantum efficiency of this band is independent of the lattice temperature. Neither the spectral shape nor the quantum efficiency of the emission band appear to be related to details of the energy-band structure. At low temperatures, additional emission lines caused by minority carrier recombination outside the breakdown region are observed.
Magnetic Domains in Hematite At and Above the Morin Transition
Authors: Eaton J. A. , Morrish A. H.
Published: February 2004

Powder patterns of magnetic domains on various crystallographic surfaces of pure and doped hematite single crystals have been studied at room temperature and in the vicinity of the Morin transition. The observations below room temperature were made with an apparatus employing thermoelectric cooling modules. It was concluded that the domains were either slabs or cylinders of irregular transverse cross section with axes lying parallel to the basal plane. The domain walls were determined to be 180° ones. At the Morin transition, a light diffuse colloidal line is formed at the boundary between two phases, one weakly ferromagnetic and the other antiferromagnetic. On warming or cooling, the boundary sweeps across the crystal in a characteristic fashion.
Magnetostrictive Effects in Cylindrical Films
Authors: Jadot J.-P.
Published: February 2004

The classical expression of the magnetoelastic energy of a monocrystal is transformed according to the most general rotation of the crystalline axes with respect to a given reference system. It is then possible to calculate the effect of a given stress on a polycrystalline material. It is shown that it is only for perfectly random crystallographic orientations that it is possible to cancel the ``macroscopic'' magnetostrictive effects of all the strains at the same composition for a magnetic alloy. If a cylindrical magnetic film with a preferential texture is made insensitive to an axial elongation, it will exhibit a magnetostrictive skew of its magnetic easy axis when the wire is twisted. The microscopic effects of stresses are also investigated in all cases: the so-called ``isotropic stresses'' give a dispersion of the easy axis.
Crystal Orientation and Magnetomechanical Damping of Torsional Vibrations
Authors: Frank R. C. , Johnson B. G. , Schroeder C. W.
Published: February 2004

Magnetomechanical damping measurements are commonly made using wire specimens in a torsion pendulum. Twisting the cylindrical wires produces tensile stresses along a helix. An analytical study was made relating the direction of these stresses with the directions of the crystallographic axes assuming three different orientations of the crystal, 〈100〉, 〈110〉, and 〈111〉, along the axis of the wire. The results make it possible to calculate the correct magnetostriction values to be used in the mathematical model of magnetomechanical damping when there is preferred orientation in the specimens. Magnetostriction values are calculated over the temperature range of 78° to 300° K for iron, nickel, and an iron-3.8% silicon alloy and these are compared with the magnetomechanical damping maxima in the same temperature range.
Twinning and Detwinning in Calcite
Authors: Kaga H. , Gilman J. J.
Published: February 2004

Twinning and detwinning in calcite were studied by means of selective etching and sound-attenuation measurements in order to investigate dislocation behavior during these processes. Twinning was accompanied by an increase in attenuation caused by discontinuous dislocation multiplication in the twin lamella. During detwinning the attenuation changes were recovered by dislocation cluster formation and tangling. It was found that dislocation nucleation accompanies even elastic twinning in calcite and is probably responsible for various anelastic effects associated with it.
Thermodynamics of Elastic-Plastic Materials as a Theory with Internal State Variables
Authors: Kratochvil J. , Dillon O. W.
Published: February 2004

We develop an analytical framework for the theory of plasticity in which the constitutive equations are single valued and which at the same time represents the proper physical concepts. A Coleman-Gurtintype thermodynamics which utilizes internal state variables is used for the study of an elastic-plastic substance. Quantities which are related to the dislocation motion and the dislocation arrangement in the material, play the role of the internal state variables in this thermodynamics. Rate-independent plasticity is studied as a limiting case of the present theory. We illustrate the theory with a special case: a one-dimensional, homogeneous, cyclic deformation of a rate-independent elastic-plastic body which exhibits a Bauschinger effect.
Theory of Saturable Reflection
Authors: Macomber James D. , Kestner Neil R.
Published: February 2004

The theory of the effect of optical saturation upon the reflectance of a plane slab (irradiated by a linearly polarized monochromatic electromagnetic wave of constant amplitude at normal incidence) is developed. The absorbing centers within the slab are described by means of the density matrix, and the electromagnetic field is described by Maxwell's equations. For simplicity's sake, it is assumed that only two quantum states (characterized by a transition dipole moment μ and relaxation times T1 and T2) at exact resonance with the electromagnetic wave are necessary to describe the absorption process. The coupling between waves travelling in opposite directions is provided by Fresnel reflection at the boundaries of the slab. Only the steady-state solutions are found.
Theoretical Analysis of Effects of a Monatomic Impurity on Low-Pressure Metal Arc Discharges in a Noble Gas Matrix
Authors: Hoyaux Max F. , Sucov Eugene W.
Published: February 2004

The role of impurities in a low-pressure arc is theoretically investigated by use of a system of coupled rate equations. Some of the coefficients may be unknown; it is shown that by measuring a few parameters it is possible to obtain a set of equations at least equal in number to the number of unknown coefficients. The analysis is then particularized to the case when the introduction of the additive results in a perturbation sufficiently small that a linear treatment is applicable. This results in a system of seven linear equations, the left-hand side of which is obtained by adding seven terms, each a product of a known coefficient times perturbation on a certain plasma parameter (population of an excited level, electron density, electric field, etc.) whereas the right-hand side is linear in the pressure of the additive, the coefficient depending upon the characteristic properties of the additive.
Collecting a Sample of Solar Wind: An Experimental Study of Its Capture in Metal Films
Authors: Lal D. , Libby W. F. , Wetherill G. , Leventhal J. , Alton G. D.
Published: February 2004

Foils of Al, Mg, Mo, Pt, Au, and MYLAR were bombarded with known fluxes of ions (3H, 4He, 22Ne, 37Ar, 85Kr), and accelerated to 1–40 keV in an electromagnetic isotope separator to determine the usefulness of a hypothetical experiment to bring home a sample of solar wind by exposing foils to the solar plasma current outside the earth's geomagnetic cavity. The amounts retained in such foils after bombardment and after subjecting them to particular heating cycles in vacuum and in air (1 atm) were determined. The problems of the loss of ions in space during the proposed space experiment and of extraction of ions in the laboratory subsequent to recovery were thus studied. Aluminum seems to be an acceptable collector material for solar-wind ions. The trapping efficiency for other materials studied is variable and appreciably smaller than unity in some cases. However, since commercial aluminum can contain significant amounts of trapped rare gases, care must be taken to prepare the collector surfaces in their absence.
Optical Properties of Germanium
Authors: LaVilla R. E. , Mendlowitz H.
Published: February 2004

The set of optical constants of germanium reported by Marton and Toots, from 8 to 25 eV, have been assessed and found to be internally consistent to within ±5%. An extension of the n and k values up to photon energy of 100 eV using Hunter's k values also has been studied. The analysis consisted of an internal consistency check by applying the Kronig-Kramers dispersion relations to the optical constants and an evaluation and study of the optical and electron oscillator-strength distributions. From an application of the general sum rules to the oscillator-strength distribution, the computed effective number of electrons per germanium atom are in general agreement with an extrapolation of Manson and Cooper's calculation.
Laser Transition and Wavelength Limits of GaAs
Authors: Dapkus P. D. , Holonyak N. , Rossi J. A. , Williams F. V. , High D. A.
Published: February 2004

Data are presented showing the variation at 77°K in GaAs laser photon energy, and the laser recombination process, as a function of doping concentration from the lowest dopings now possible to the highest donor, acceptor, and donor-acceptor (compensated) dopings which still yield crystals of laser quality. GaAs is shown to be capable of laser operation over a range exceeding 1200 Å (λmin≤7880 Å to 9100 Å ≤ λmax). Experimental data on n-type crystals are used to approximate the position of the Fermi level. Data on p-type and compensated crystals are used to approximate the depth of donor tail states involved in laser action. These results agree reasonably well with the values calculated from the metallic hydrogen model. Laser photon-energy data on uniformly doped p-type crystals are presented which indicate the extent to which acceptor states involved in laser operation penetrate into the forbidden gap.
Absorption Measurements and Impurity Assignment of Bound Exciton Complexes by Self-Absorbed Luminescence
Authors: Leite R. C. C. , Shah Jagdeep , DiGiovanni A. E.
Published: February 2004

It is shown that self-absorbed emission lines due to a bound exciton and its phonon satellite may be used to determine (1) the absorption coefficient at the wavelength of bound exciton emission line and (2) the nature of the impurity binding the exciton. The technique is described and is illustrated by experimental results on CdS.
Charge Transport and Storage in Metal-Nitride-Oxide-Silicon (MNOS) Structures
Authors: Frohman-Bentchkowsky D. , Lenzlinger M.
Published: February 2004

A simple physical model that predicts charge accumulation at the dielectric interface of metal-nitride-oxide-silicon (MNOS) structures is proposed and verified experimentally. The model is based on the presence of steady-state current flow in the dielectric structure. Interface-charge accumulation is shown to be determined by the requirement for continuity of current through the structure under steady-state conditions. Continuity of current is established by accumulation of either positive or negative charge for a given polarity of charging voltage, depending on the relative current-field characteristics of the silicon nitride and silicon dioxide layers. Due to the exponential nature of the current-field characteristics, the time required to reach steady state is a strong function of the applied charging voltage. This leads to the observed charge storage property of MNOS devices. The hysteresis characteristic observed in MNOS structures is shown to be time-dependent with a tendency to merge into a single-valued dependence of accumulated charge on charging voltage as the steady-state condition is approached. The validity of the theoretical model for both steady-state and transient behavior is confirmed by current-voltage, capacitance-voltage, and turn-on measurements of MNOS capacitors and transistors for different dielectric thickness ratios and over a wide temperature range. The underlying concept that charge accumulation establishes current continuity in a two-layer dielectric structure should be valid, in general, for any two-dielectric structure.
Shock-Tube-Driven Impact Experiments on Solids
Authors: Dennen Robert S.
Published: February 2004

Experiments are described in which a shock-tube facility was used for the determination of the Hugoniot equation of state of granite. The facility was operated in two modes. Very low stress levels σ[over equal to less-than]0.2 kbars were obtained by allowing an air shock wave to impinge directly upon a sample material. Higher stresses, σ[over equal to less-than]50 kbars, were obtained when the incident air shock wave was used to accelerate a metal projectile which then impacted upon the sample at a desired velocity. The instrumentation and data-reduction methods are discussed and the resulting Hugoniot points for granite below and in the neighborhood of its dynamic elastic limit are given.
Mean Adsorption Lifetimes and Activation Energies of Silver and Gold on Clean, Oxygenated, and Carburized Tungsten Surfaces
Authors: Cho A. Y. , Hendricks C. D.
Published: February 2004

Direct measurements of the mean adsorption lifetimes and the activation energies of silver and gold have been made on a polycrystalline tungsten substrate. The lifetime was determined by the time constant of the exponential increase of the surface concentration when an atomic beam impinged on the substrate. The activation energy was determined by the slope of the logarithm of the lifetime as a function of the inverse substrate temperature. The adsorption lifetime of atoms on a metal surface is τ=(1/ν0) exp (E/kT), where ν0 is the vibrational frequency and E is the activation energy. The experiments were conducted in an ultrahigh-vacuum system free of hydrocarbon contamination. A clean substrate surface was obtained by heating in a partial pressure of oxygen for a long period of time and flashing to 2500°K before each data point was taken. The well-defined surface condition and the precisely known temperature allow reliable interpretation of the experimental results. The experimental results for silver and gold on clean, oxygenated, and carburized tungsten substrates when τ is in seconds and E is in electron volts are the following: Ag on W, τ=(1/3.6×1012) exp (2.9/kT); Ag on O–W, τ=(1/1.43×1012) exp (2.06/kT); Ag on C–W, τ=(1/8.2×1012) exp (3.18/kT); Au on W, τ=(1/8.2×1013) exp (4.54/kT); Au on O–W, τ=(1/4.7×1011) exp (1.99/kT); Au on C–W, τ=(1/1.73×1014) exp (4.725/kT).
Formation and Growth of Tarnish on Evaporated Silver Films
Authors: Bennett H. E. , Peck R. L. , Burge D. K. , Bennett J. M.
Published: February 2004

We have studied the growth of the silver sulfide tarnish film which forms on silver deposited on smooth, amorphous substrates and rough and smooth polycrystalline substrates. Both ellipsometric and electron-microscope techniques were used to measure the average thickness of the tarnish films. The growth rate was found to be variable depending on the concentration of the sulfurous gases. In normal laboratory air (measured concentrations of H2S and SO2 less than 0.2 parts per billion) a 1-Å-thick tarnish film can be expected to form in 1 h, 3–6 Å in 1 day, 15–30 Å in 1 week, and 60 Å or more in 1 month. The tarnish growth can be completely stopped by placing the silver in a dry-nitrogen atmosphere. Conversely, in a humid atmosphere containing about 10% H2S, growth rates of as much as 100 Å/h can be obtained. The silver sulfide formed as small, randomly spaced, approximately round clumps having a site density about one hundred times larger than the patch density reported for thermally etched silver surfaces. All clumps nucleated on initial exposure, the clump density remained constant with time, and the clumps grew much slower than the tarnish patches on thermally etched silver. Coalescence toward a continuous film was slow; even after 41 days, only 53% of one silver surface was covered with tarnish.
Measurements of the Planar Hall Effect in Polycrystalline and in Single-Crystal Nickel Thin Films
Authors: Marsocci Velio A. , Chen Thomas T.
Published: February 2004

The planar Hall effect has been described by theoretical analyses, and previous investigators have shown that the observed effect is consistent with these predictions. However, the amount of experimental data reported to date is small, and the work described herein provides additional data concerning the planar Hall effect in both polycrystalline and single-crystal thin films. The calculations of the planar Hall coefficient and of the magnetoresistance factor based on these data show close agreement with the data obtained by other investigators. It is also apparent that, as has been predicted from theory, the influence of the crystalline symmetry is not dominant in the effect in ferromagnetic films at room temperature. The observations also indicate that the planar Hall effect may be potentially useful in electronic-device applications.
Epitaxial Growth of Titanium Films on Mica
Authors: Grünbaum E. , Schwarz R.
Published: February 2004

The oriented overgrowth of titanium films obtained by evaporation in an ultrahigh-vacuum system onto mica was studied in situ by reflection electron diffraction and, after withdrawal from the system, by transmission electron microscopy and diffraction. Films with a thickness of 100 Å or more, prepared on a mica at temperatures of 500°–600°C, are epitaxial single crystals of hexagonal structure; their basal plane is parallel to that of the substrate and the crystallographic axes within the contact planes form an average angle of 30°. These single-crystal films have a smooth surface and are composed of subgrains rotated around the c axis with respect to each other, forming angles up to 4°. Films thinner than 100 Å are only partially oriented. Coalescence in these films takes place at a very early stage of growth and continuous films of about 100 Å are obtained, in contrast with the growth of other metals on mica.
Pressure Derivatives of the Elastic Constants of Vitreous Germania at 25°, −78.5°, and −195.8°C
Authors: Soga Naohiro
Published: February 2004

The sound velocities and their pressure derivatives of vitreous GeO2 have been determined by means of a pulse superposition method at 25°, −78.5°, and −195.8°C. It was found that both longitudinal and shear velocities decrease with pressure at these temperatures. This result is qualitatively similar to that of vitreous SiO2. Although the pressure derivative of bulk modulus was positive, it was anomalously low compared with those of most other crystalline solids. The mode gamma, defined by (−d lnωi/d lnV), was calculated from the present pressure derivatives of sound velocities and was found to be temperature-dependent. The Grüneisen parameter was estimated to be near −0.35 at very low temperatures from the mode gamma-volume relation. This value agrees fairly well with the thermal Grüneisen parameter based on thermal data at very low temperatures.
Seebeck Effect in α-Nb2O5 Near Stoichiometry
Authors: Jesse Kenneth E.
Published: February 2004

The Seebeck coefficient, thermoelectric power Q, was measured in ceramic α-Nb2O5 with respect to platinum over a range of temperature of 700°–1400°C and a range of ambient oxygen partial pressure of 1.0−10−5 atm. The data are interpreted on the basis of electrons moving in a narrow conduction band.
MgO Containing Fe++: Magnetic Properties and Clustering
Authors: Woods K. N. , Fine M. E.
Published: February 2004

The magnetization curves to 7000 Oe at 2° and 4.2°K of magnesiowüstites with 1 to 5 cat.% Fe++ have more curvature and a lower extrapolated saturation magnetization (using the Brillouin function) than expected for isolated Fe++ ions. This behavior indicates Fe++ ion clustering. The magnetization data were used to compute n̄, the average number of Fe++ per cluster, and J̄, the average total angular momentum quantum number per cluster taking the isolated Fe++ ion value for g. The observed J̄'s showed that the Fe++–Fe++ near-neighbor interaction is ferromagnetic. The cluster size increased with Fe++ content but J̄/n̄ decreased due to the predominance of the second-near-neighbor antiferromagnetic interaction. When magnesiowüstites containing 9 and more cat.% Fe were cooled from room temperature to 4.2° or 2°K in an applied magnetic field, the magnetization curves, which showed a small amount of hysteresis, were not symmetric about the origin. The shifted hysteresis was attributed to exchange coupling between neighboring ferromagnetic and antiferromagnetic regions. The antiferromagnetic order persists to rather low concentrations of Fe++ (TN for 9 cat.% Fe++ is above 8°K), further evidence for Fe++ clustering. Published values of the thermodynamic activities show a positive deviation from Raoult's law and thus a nonrandom clustered configuration is expected.
Growth and Characterization of Spinel Single Crystals for Substrate Use in Integrated Electronics
Authors: Wang C. C.
Published: February 2004

An extensive study has been made on the growth and characterization of single-crystal magnesium aluminate spinel. This material has received attention as a superior substrate for epitaxial silicon-integrated electronic devices. Large spinel single crystals within the compositional range MgO:Al2O3–MgO:3Al2O3, have been successfully grown by flame fusion using a modern three-tube post-mix-type Verneuil burner. Substrate wafers of (111), (100), and (110) orientations were prepared for silicon epitaxy. Surface preparation of the substrates was studied, including mechanical polishing, hydrogen annealing, and chemical etching. The composition, lattice parameter, crystalline perfection, mechanical hardness, thermal stability, and dielectric properties of the spinel single crystals have been characterized by various techniques in an effort to obtain a basic understanding for substrate use of this material system. Some trends in the dependence of these properties on composition were observed. In particular, the thermal stability increases with decreasing Al content in the spinel system. It was found that the spinel crystals with alumina content up to MgO:2.5Al2O3 are thermally stable and exhibit no cracking and/or exsolution behavior to at least 1200°C, which is the temperature commonly used for fabricating many silicon devices. However, the ease of growth and the mechanical stability decrease with decreasing Al content in spinel. A post-growth annealing treatment enhances the mechanical stability and prevents formation of cracks during cutting. Substrates within the compositional range of MgO:1.5Al2O3–MgO:2.5Al2O3 are suitable for silicon epitaxy, and the choice of the optimum substrate composition depends on the specific conditions for processing of the silicon devices.
Lattice Parameters of Martensite and Austenite in Fe–Ni Alloys
Authors: Reed R. P. , Schramm R. E.
Published: February 2004

The lattice parameters of the body-centered cubic phase (martensite) and the face-centered cubic phase (austenite) were determined for a series of Fe–Ni alloys. Compositions ranged from pure Fe to Fe-35 at.% Ni. Careful film and diffractometer Debye-Scherrer techniques on powder and bulk samples and computerized calculations and error analyses were employed. Results indicate that the martensite lattice parameter reaches a maximum between 10 and 20 at.% Ni and the room-temperature lattice parameter of the face-centered cubic phase has a maximum in alloys having greater than 35 at.% Ni.
Investigations of Boswellia Glabra Electret
Authors: Pillai P. K. C. , Jain V. K.
Published: February 2004

In this paper, the surface charge formation characteristics of thermoelectrets, prepared at different polarizing fields from a plant product, Boswellia Glabra, have been presented. A comparatively easy method for the fabrication of thermoelectrets of this meterial has been developed. The results obtained show that this plant product is a suitable material for electret preparation. Both the anode and cathode sides show the same sign of charge, without showing any charge reversal up to a polarizing field of 1000 V per mm thickness of the sample. The sample, prepared at zero field, indicates that the charge obtained with low-field samples is not due to the molding charge. The results also fail to find experimental conformation of Gross's and Gemant's hypothesis concerning the production of homocharge with regard to the cathode sides of the low-field Boswellia Glabra electrets.