bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Deposition Parameters on the Crystallinity of Evaporated Germanium Films
Authors: Adamsky Robert F.
Published: February 2004

The crystallinity of Ge films deposited on (111) Ge substrates in vacuum ambients <10−8 Torr has been investigated as a function of deposition rate, substrate temperature, thermal treatment of substrates, and background oxygen pressure. Polycrystalline and epitaxial films were obtained at temperatures up to 200° lower than reported by previous investigations, and thermal annealing of substrates at 600°C prior to deposition resulted in a minimum epitaxial temperature of 100°C. Oxygen ambients as low as 5×10−9 Torr have been found to impede crystal growth and increase epitaxial temperatures by 50°–75°C.
Analysis of Penetration Data from Grain Boundary Diffusion Experiments
Authors: Canon R. F. , Stark J. P.
Published: February 2004

The results from computer solutions to the various mathematical analyses of the grain boundary diffusion problem which have previously been developed are presented in a convenient manner for interpretation of grain boundary diffusion measurements using the penetration depth technique. In particular, the results allow a quantitative assessment of the limitations and applicability of the two approximate solutions due to Fisher and Whipple. The present results also permit the use of Whipple's exact solution for data analysis using a simple graphical technique. Results of several previous grain boundary diffusion investigations are reevaluated by applying the exact solution to the published penetration data. It is concluded that the activation energy for grain boundary diffusion along 〈100〉 symmetrical tilt grain boundaries is independent of grain boundary misorientation.
Influence of Relaxation Effects in Nonequilibrium J × B Devices
Authors: Argyropoulos G. S. , Demetriades S. T.
Published: February 2004

The coupled distributions of current density, electron temperature, and plasma composition in nonequilibrium plasma flows depend strongly on relaxation effects arising from finite reaction rates and from electron-energy convection. This dependence is studied in multielectrode magnetohydrodynamic channels in conjunction with the influence of thermal and concentration diffusion, and of thermal and velocity boundary layers. Relaxation effects are shown to control the possibility of current shorting along the conductor walls and to influence the stability of the distributions. For slow reaction rates and large gas velocities, the current and plasma-property distributions tend to become uniform in the core of the flow, but in the electrode-boundary regions nonuniformities persist both in the transverse and in the flow direction, and are strongly dependent upon the gas temperature and velocity boundary layers. Consequently, although relaxation effects allow high conductivity layers to extend over the insulator segments of the electrode walls, the possibility of Hall potential shorting through this path depends critically on the length of insulator segment between electrodes. Converging solutions, describing stable operation, have been obtained for values of the local Hall parameter β/ε as high as 6, depending on the geometry. At high values of β/ε, the current density and plasma-property distributions become time dependent, resulting in overall electrical characteristics that oscillate by large factors.
Ideal Paraelectric Refrigeration in KCl: OH and RbCl: CN
Authors: Lawless W. N.
Published: February 2004

The Carnot-cycle refrigeration characteristics of two probable paraelectric refrigerators KCl: OH and RbCl: CN are studied, according to a thermodynamic model which appears to be basically correct for describing electrocaloric phenomena in these doped salts. A high-temperature reservoir at 1.11°K is assumed for comparison with actual magnetic and He-dilution refrigerators, and the operating characteristics of the paraelectric refrigerators are optimized with respect to the dopant concentration. Published values for the zero-field splitting, dipole moment, specific-heat coefficient, and dielectric constant of these salts are employed. The lowest calculated temperatures achievable with these model refrigerators are 0.19° and 0.03°K for KCl: OH and RbCl: CN, respectively; and the estimated maximum power obtainable places the RbCl: CN model refrigerator between the He-dilution and magnetic (iron-ammonium-alum) refrigerators in refrigerating capacity. It is shown that, although the zero-field splitting determines the lowest achievable temperature, the dipole correlations limit the refrigeration capacity.
Origin of Low-Voltage Structure and Asymmetry in the I-V Characteristics of Multiply-Connected Superconducting Junctions
Authors: Clarke J. , Fulton T. A.
Published: February 2004

A self-magnetic field effect is shown to be responsible for much of the low-voltage structure and for asymmetries observed in the I-V curves of superconducting niobium-solder junctions (Slugs). Similar effects are to be expected in other multiply-connected junctions.
Kinetics of Red Luminescence in GaP
Authors: Rosenzweig W. , Hackett W. H. , Jayson J. S.
Published: February 2004

A model is presented and analyzed which describes the recombination kinetics of red luminescence in GaP. The need for the model arose with the recent observation of a substantially different bias variation of red electroluminescent intensity, in GaP diodes (Zn–O doped p-layers) produced by the liquid-phase epitaxial (LPE) process. It was previously observed that at low bias the intensity varied as exp (qV/kT), and at high bias it varied as exp (qV/2kT). The LPE diodes show the same low-level bias variation but at high biases the intensity varies as V (nonexponentially). Previous models for the recombination kinetics described the observed bias variations in terms of saturation of radiative recombination centers by electrons injected into the p-type bulk (Nelson) and in the space charge region (Morgan) of the diodes. In the present model, which is essentially an extension of Nelson's, a parallel, nonsaturable route is added so that the electron lifetime can remain finite even though the radiative centers saturate. It is shown that when the parallel route dominates the removal of excess electrons, the model describes the recently observed saturation characteristic. On the other hand, when the parallel route is negligible, the previously reported bias variation is obtained. Experimental results are presented for room temperature steady-state electroluminescence over a wide range of injection levels in optimally Zn–O doped GaP LPE diodes and compared with the predictions of the model. Under the assumption that the p-type material adjacent to the junction has the same properties as the bulk substrate, the following results were obtained: (a) At maximum electroluminescent efficiency about 80% of the injected electrons decay via the parallel nonproductive route; (2) the electron radiative recombination center (Zn–O complex) density is in the range 0.5–1.0×1016 cm−3; (3) the electron capture cross section of the center is in the range 3.3–6.7×10−16 cm2; and (4) the excess electron density required to half fill the centers is 0.75–1.5×1015 cm−3. Preliminary results of photoluminescence experiments are in agreement with the predictions of the model and the numerical values presented above.
Time-Resolved Scanning Electron Microscopy and Its Application to Bulk-Effect Oscillators
Authors: MacDonald N. C. , Robinson G. Y. , White R. M.
Published: February 2004

The application of the scanning electron microscope to the examination of time-varying phenomena is discussed. The limitations of response time are mentioned, and methods for increasing response speed are considered. These include the use of electrostatic deflection plates to chop the primary electron beam, the use of solid-state semiconductor diodes as electron detectors, and the use of sampling and the storage and processing of data prior to display. Time-resolved techniques are then applied to a study of the motion of domains of high electric field in CdS ultrasonic oscillator diodes and in GaAs Gunn effect diodes. In both photoconducting and semiconducting CdS, the domain formation and propagation is correlated to the current waveform of the oscillator. Nonuniform domain propagation in two dimensions is examined in a GaAs oscillator.
Growth and Properties of Hg1−xCdxTe Epitaxial Layers
Authors: Tufte O. N. , Stelzer E. L.
Published: February 2004

The epitaxial growth of Hg1−xCdxTe has been investigated by means of a technique in which the source and substrate are close spaced, and both under isothermal conditions and with a temperature gradient between the source and substrate. The effect of excess mercury pressure in the ampoule on the growth rate and the compositional profile within the isothermally grown epitaxial layers has been investigated in detail. A simple isothermal process is described for making epitaxial layers having a controlled surface alloy composition. The presence of a temperature gradient between the source and the substrate significantly enhances the deposition rate and results in a linear relation between the layer thickness and deposition time. The electrical and optical properties of the isothermally grown epitaxial layers are discussed along with the results of photoconductivity measurements on layers having surface composition of x=0.20 and x=0.25.
Anisotropic Etching of Silicon
Authors: Lee D. B.
Published: February 2004

A ternary liquid etchant solution for silicon, consisting of hydrazine, iso-2-propyl alcohol (IPA), and water has been studied in some detail. In common with other anisotropic etchants reported in the literature, marked dependence of dissolution rate on the crystal orientation of the etched surface has been observed with a low rate of attack on (111) planes. In contrast to other formulations, this etch attacks neither silicon dioxide nor aluminium vacuum-deposited films, either of which may be used as a very convenient in-contact masking medium for the engraving of intricate shapes on an appropriately oriented silicon substrate. The experimental study indicates that the etch velocity is a maximum for (211) planes, which accounts for the rounding of convex corners frequently observed when engraving regular shapes in silicon with anisotropic etches. The optimum etch solution is an equimolar mixture of NH2 and H2O.
Ohmic Contacts to Solution-Grown Gallium Arsenide
Authors: Harris J. S. , Nannichi Y. , Pearson G. L. , Day G. F.
Published: February 2004

A study has been made on the properties of Ohmic contacts to single-crystal n-type GaAs wafers which were grown by liquid epitaxy techniques. Carrier concentration profiles at the n+-n junctions were measured by the Schottky barrier capacitance technique for both Au-Ge-Ni alloyed contacts and liquid epitaxial n+ contacts. The frequently observed high resistance layers at the interface were eliminated by the contacting processes described here. The Ohmic contact problems and the results of other experiments are explained in terms of the GaAs binary phase diagram and nonstoichiometry considerations.
Coherent Microwave Instabilities in a Thin-Layer Solid-State Plasma
Authors: Swartz G. A. , Robinson B. B.
Published: February 2004

Coherent microwave radiation at frequencies from 6.5 to 44 GHz is generated by p-type indium antimonide at 77°K with an injected electron current transverse to a magnetic field. With a waveguide or stripline coupling system, the maximum output power is about 10 μW for input power levels of 1 to 5 W. Grooves of specified widths cut into the Suhl surface of the rod-shaped InSb samples generate the coherence and determine the approximate output frequency. Wavelength measurements of a surface wave on the rod show that the effective groove width is about equal to a half-wavelength. A theory of double-stream interaction in a thin plasma layer with a magnetic field transverse to the current flow is formulated and predicts instabilities in the observed frequency range. Correct quantitative predictions made by the theory are: (1) the hole density required for onset of emission, (2) the minimum magnetic field which is required for emission onset at high current injection, (3) the phase velocity of the surface wave, and (4) the magnetic field value at which the high field mode executes a frequency minimum. Computer solutions of the dispersion relationship for the plasma wave instability are in good qualitative agreement with measurements of the emission frequency as a function of magnetic field and injection current. The theoretical analysis and concurrent experimental evidence demonstrate the existence of an instability in a thin-layer plasma in the absence of a magnetic field.
Molecular-Beam Sources Fabricated from Multichannel Arrays. I. Angular Distributions and Peaking Factors
Authors: Jones R. H. , Olander D. R. , Kruger V. R.
Published: February 2004

An apparatus for measuring the leak rates and angular distributions of the molecular flux from multichannel sources was constructed. Four types of beam sources were tested: A single capillary, a crinkly foil stack, an electron-beam milled quartz membrane, and two sources constructed by fiber optics techniques. The leak rates of the sources were compared to the predictions of Knudsen flow. The angular distributions were characterized by a ``peaking factor,'' defined as the ratio of the center-line beam intensity from the source to that from a cosine emitter of the same total flow rate. The measured peaking factors agreed with the theoretical predictions of free molecule flow at low source pressures and approached the limit for isentropic flow at high source pressures.
Molecular-Beam Sources Fabricated from Multichannel Arrays. II. Effect of Source Size and Alignment
Authors: Olander Donald R.
Published: February 2004

The effect of the gross diameter of a molecular-beam source and its alignment in the system upon source efficiency have been investigated analytically. If the diameter of the source approaches that of the collimating orifice used to form the molecular beam, the efficiency may be reduced by 50% or more. Reasonable displacement and tilt misalignments can be tolerated before source efficiency is substantially reduced. The effects of size and misalignment are more critical for multichannel sources with highly peaked angular distributions than for cosine sources.
Dielectric Loss of Beta Alumina and of Ion-Exchanged Beta Alumina
Authors: Radzilowski R. H. , Yao Y. F. , Kummer J. T.
Published: February 2004

Dielectric loss measurements of a mixture consisting of a number of small single crystals of beta alumina suspended in alpha alumina have been made. The loss follows the Fuoss-Kirkwood empirical formula ε″=ε″max [ln (fmax/f)α]. Some speculations are made as to the cause of the width of the loss peaks. Substitution of other (K, Ag, Rb, NH4, Li, Tl) ions for sodium causes the loss curves to shift in a direction indicating higher resistivity of the substituted beta aluminas. A quantitative relation between the shift of the loss peaks and the known resistivity of the substituted beta aluminas as would be expected from the Maxwell-Wagner relations was unable to be made.
Microwave Breakdown Predictions for a Rectangular Aperture Antenna
Authors: Fante Ronald L. , Mayhan Joseph T.
Published: February 2004

The theory is presented for predicting the microwave breakdown characteristic of a rectangular aperture antenna, including the realistic near elastic fields. The theory is then compared with experimental data.
Grain-Size Average and Distribution Effects on the Magnetic Losses and Threshold Fields in Nickel Ferrites at Microwave Frequencies
Authors: Borghese Camillo , Roveda Riccardo
Published: February 2004

Nickel ferrites with scaled average grain sizes and lognormal size distributions were prepared by hot-pressing and subsequent annealing and by conventional firing. Average grain sizes ranged from less than 1 to 10 μ. The dielectric loss, saturation magnetization, bulk density, and linewidth measurements confirmed that almost all samples were good nickel ferrites. Lognormal distributions allow with easy calculations to evaluate for each sample the fraction of grains having diameters below certain values that are critical for the loss mechanism. Orthogonal and parallel pump measurements of threshold fields at X band showed a very regular behavior with average grain sizes: ∥ hcrit varied from 80 Oe for 0.9-μ sample to 8 Oe for a 10-μ sample with a dependence of the type hcrit≈x̄−2 for x̄<2 μ, hcrit≈x̄−0.5 for x̄>2 μ. An analysis of the distribution of grains shows that ∥ hcrit increases steeply for samples having about 80% or more of the number of grains with sizes less than 3 μ. Regular behaviors of the imaginary part of the permeability (at Hdc≈4πMs/3) with average sizes are found at 9.23, 12.12, and 19.75 GHz: losses increase with decreasing grain sizes but not as much as threshold fields, with a dependence of the type μ″min≈x̄−0.5. The high-power figure of merit F*, measured on spheres at X band, increases with decreasing grain size from 0.07 to 0.26, thus encouraging the fine grain approach for microwave device applications.
Migration of Vacancies and the Formation of Surface Vacancy Pits
Authors: Tariyal B. K. , Ramaswami B.
Published: February 2004

The formation of vacancy pits on the surface of electropolished aluminum on heating and subsequent cooling has been observed by several workers. The observations indicate that the formation of pits is a nucleation and growth process, and a minimum temperature drop ΔT is required in order to observe the pits. In the present work, a new technique has been developed to study this phenomenon. From a consideration of nucleation and growth of the pits, a relationship has been derived between ΔT and Th the holding temperature. The relationship shows that ΔT depends on Th and p, the rate of cooling. ΔT and Th have been measured experimentally and a value of Em, the energy of migration of vacancies, has been evaluated on the basis of the relationship derived here. A value for Em of 0.6 eV is obtained for pure aluminium, which is in good agreement with the previously determined values of Em in aluminium by other methods.
Holography and Parametric Image Conversion: Part II
Authors: Firester Arthur H.
Published: February 2004

It is shown that image upconversion using optically nonlinear materials is equivalent to a conventional hologram constructed at the signal wavelength and readout at the upconverted wavelength. As such, it should be a truly three-dimensional, high-resolution process. For the particular case of equal signal and pump wavelengths, the upconverted image will have only half the angular extent of the original object wave. The image's transverse dimensions remain unchanged while its location relative to the frequency doubler and its longitudinal dimensions double in size. It is also shown how the phase matching condition follows from the vector condition for the reconstruction of a thick hologram.
Method to Calculate the Effect of a Concentration-Dependent Diffusion Coefficient on the Linear Growth of Rods and Plates
Authors: Atkinson C.
Published: February 2004

A method is described to deal with the problem of a rod (elliptical paraboloid) or a plate (parabolic cyclinder) growing uniformly in a matrix where the diffusion coefficient depends on concentration. As an example, the method is applied to the case where the diffusion coefficient has the form D=D0 exp (A0C+A1C2), where D0, A0, and A1 are constants, and C is the concentration.
Temperature and Alloy Compositional Dependences of the Energy Gap of Hg1−xCdxTe
Authors: Schmit J. L. , Stelzer E. L.
Published: February 2004

The temperature and compositional dependences of the energy gap are determined for the alloy semiconductor mercury-cadmium telluride (Hg1−xCdxTe). The cutoff wavelength was measured on photoconductive and photovoltaic infrared detectors where 0.17<x<0.60 over a temperature range 20<T< 300°K. Spectral response curves are shown to indicate the precision of the method. The temperature and compositional dependences of the energy gap are shown and the empirical expression Eg (eV) =1.59x−0.25+5.233(10−4)T(1−2.08x)+0.327x3is deduced.
Composition Dependence of the Ga1−xAlxAs Direct and Indirect Energy Gaps
Authors: Casey H. C. , Panish M. B.
Published: February 2004

Photoresponse measurements were made to determine the compositional dependence of the Ga1−xAlxAs direct Γ15→Γ1 and indirect Γ15→X1 energy gaps. These data, together with other information, show that the crossover composition and energy gap are between 0.35<xc<0.40 and 1.87<Egc<1.97 eV, and that the most resonable values are 0.37 and 1.92 eV.
Hall Effect in Silicon-Chromium Films
Authors: Lenzlinger M. , O'Keefe G.
Published: February 2004

Hall effect and resistivity of sputtered silicon-chromium films have been measured versus temperature between −200° and +500°C on samples annealed at 550°C for 10 min. The films were dc diode sputtered at 1.0 and 2.5 kV from cathodes containing 17, 25, and 33 at.% Cr. The results are interpreted in terms of a one-carrier conduction process, the positive Hall voltage indicating holes. The effective hole concentration p = 1/RHq at room temperature is about 3×1021 cm−3 and is nearly independent of composition and sputtering voltage; it increases slightly with increasing temperature (Ea<0.1 eV). The effective mobility μ = RH/ρ at room temperature ranges from 0.02 to 1 cm2/V·sec; it increases strongly with increasing Cr content, and decreases with increasing temperature. Small temperature coefficients of resistivity are obtained for the 25% Cr samples, where the temperature dependence of the carrier concentration cancels that of the mobility. Unannealed silicon-chromium films have hole concentrations a factor of 2–20 higher, depending on the composition and the sputtering voltage. The mobility of unannealed films is lower by a factor of 1.2–20. As a result, annealing increases the resistivity of some films (those sputtered at 2.5 kV) and decreases it for others (those sputtered at 1.0 kV). Annealing takes place between 400° and 600°C. The low values obtained for the effective mobility are in contradiction with a basic assumption of the free carrier model. Conduction mechanisms which could account for these low values are discussed.
Shock-Induced Dynamic Yielding in Copper Single Crystals
Authors: Jones O. E. , Mote J. D.
Published: February 2004

Three groups of single-crystal disks approximately 5-mm thick with surface normals along [100], [110], and [111] crystallographic directions were prepared from 99.99+ at.% pure copper. These specimens were shock loaded to about 50 kbar in a state of uniaxial strain by nitroguanidine explosive plane-wave generators, and the propagated wave profiles were measured with quartz gauges. Elastic wavefronts for the single crystals exhibited sharp risetimes (of the order of 10 nsec) to dynamic yield points, and subsequent stress relaxations preceding the plastic wavefronts. For the propagation distances of about 5 mm, the measured yield point normal stresses were about 2.0, 1.3, and 1.3 kbar, respectively, for wave propagation in the [100], [110], and [111] directions. Although the principal stress states at the yield points differed, analysis reveals that the shear stresses on {111} 〈110〉 slip systems were about the same for all orientations. Single-crystal disks prestrained by about 3½% exhibited essentially zero yield stresses and ramp-like elastic waves. Similar behavior observed for polycrystalline specimens indicates the importance of initial dislocation density on dynamic yielding. In all cases the plastic wave velocities were the same. Constitutive relations derived on the basis of dislocation dynamics are given for the three single crystal orientations. From these relations the decay of the respective dynamic yield points with increasing propagation distance can be predicted as a function of the dislocation mobility and the initial mobile dislocation density. Within the framework of this theory it is shown that simple dislocation damping models for the mobility are not consistent with the experimental results.
Amorphous Versus Crystalline GeTe Films. II. Optical Properties
Authors: Bahl S. K. , Chopra K. L.
Published: February 2004

Transmittance and reflectance studies have been made in the 0.83–25 μ range on GeTe films to obtain and compare the optical properties of amorphous and crystalline structures. The refractive index of crystalline GeTe films (typical value 5.5 at 1.5 μ) shows free carrier dispersion yielding optical dielectric constant=36 and plasma wavelength of 3–5.9 μ (for a corresponding carrier concentration range of 1.5–0.18×1021/cm3) from which a corresponding susceptibility mass of 0.35–0.16m is deduced. On the other hand, amorphous GeTe films exhibit no free carrier dispersion. The refractive index (typical value 4.2 at 1.5 μ), however, rises sharply at the onset of the interband transitions. This rise shifts to higher energies at lower temperatures yielding a coefficient of dEopt/dT∼−4.5×10−4 eV/deg (Eopt=absorption edge). The absorption coefficient, α, of amorphous films at all wavelengths studied is smaller than that of the crystalline films. dα/dhν(hν=photon energy) shows a maximum (defined here as the absorption edge) for amorphous films at ∼0.85 eV and for crystalline films at 0.73–0.95 eV (depending on carrier concentration). The observed values of the absorption edge and the relation α ∝ (hν)1/2 near the absorption edge for the crystalline state can be understood in terms of direct transitions from the Fermi level (∼0.3–0.5 eV in the valence band) to the corresponding k-vector in the conduction band (Burstein shift) with a forbidden bandgap ∼0.1–0.2 eV. The observed value of the absorption edge and the relation α ∝ (hν)2 near the absorption edge in amorphous films are proposed to be due to indirect transitions between the nonlocalized (allowed) levels at and beyond the localization limits in the valence and conduction bands. The observed exponential decay of α (i.e., α ∝ exp (hν/Δ), Δ=0.068=2.6kT) below hν=0.85 eV may be attributed to the exponential distribution of the localized levels within the pseudo-bandgap of the amorphous state.
Self-Modulated Mode of Operation of a Marginal Oscillator Ultrasonic Spectrometer
Authors: Smith W. D. , Miller J. G. , Bolef D. I. , Sundfors R. K.
Published: February 2004

A new, self-modulated mode of operation of the marginal oscillator ultrasonic spectrometer, in which no external modulation is required, is described and analyzed. In this mode, the system consisting of an oscillator-coupling network-acoustic resonator is induced to oscillate simultaneously at two frequencies. Small changes in acoustic attenuation are reflected as changes in the amplitude or frequency of the detected beat frequency signal resulting from the interference of the two oscillations. Applications to magnetoacoustic phenomena are reported.
EPR Study of the Structure of CsPbCl3
Authors: Cape J. A. , White R. L. , Feigelson R. S.
Published: February 2004

Studies of the EPR of dilute Mn2+ in CsPbCl3 have been carried out over the temperature range 77°–340°K. Crystalline phase changes as indicated by changes in the Pb site symmetry were evident at 320°K (46.5°C) and 185°K. The first of these has been reported previously while the latter is apparently a new observation. Between 185° and 320°K, the EPR spectra can be assigned to two and possibly four crystallographically equivalent sets of magnetically inequivalent sites, the spectra of the ith set derivable from the spin Hamiltonian Hi=gβH·S+Di[Sz2−13S(S+1)]+Ei(Sx2−Sy2)+16ai(Sx4+Sy4+Sz4)+ASzIz+B(SxIx+SyIy). Typical values of the crystal field parameters are: A = −87.5 G, B = −86.5 G, and a≈1 G; all sensibly temperature independent, while D and E are temperature dependent. For example at 195°K, D1,2,3,4=45 G and E1= −E2=7.2 G, E3=6.4 G, and E4= −5.0 G. Both D and E tend continuously to zero at 320°K. Thus, the individual site symmetries are evidently orthorhombic and the overall crystal symmetry is apparently orthorhombic or nearly so. Some discussion of possible crystal space groups is included.
Structure and Properties of Sputtered Ta–Al2O3 Cermet Thin Films
Authors: Henrickson J. F. , Krauss G. , Tauber R. N. , Sharp D. J.
Published: February 2004

Ta–Al2O3 cermet thin films were produced by diode sputtering. Cathodes were fabricated by powder techniques, plasma spraying and as mechanical composites. Film compositions of 1–20 wt% Al2O3 produced resistivities of 250 to 25 000 μΩ·cm and TCR's of +100 to −450 ppm/°C, respectively. The films showed good thermal stability and could be anodized. Electron microscopy and x-ray analyses suggest a film structure consisting of long columnar grains of bcc Ta, approximately 100 Å in diameter, surrounded by Al2O3. A quantitative analysis is made of tunneling currents in an idealized film. Resistivity-composition and resistivity-temperature data are explained in terms of this analysis. The height of the Al2O3 barrier between grains is estimated to be 0.23 eV for an effective electron mass of 1/9. Barrier thicknesses are estimated at 15–30 Å.
Effect of Annealing on the Substructure of Cold-Worked Cu-8.5 At. % Ge
Authors: Truckner W. G. , Mikkola D. E.
Published: February 2004

The annealing behavior of Cu-8.5 at.% Ge filings has been studied by means of x-ray diffraction. The shifts in the positions of the powder pattern peaks from deformed and partially annealed samples can be accounted for by stacking faults and changes in the layer spacings at the stacking faults. No evidence was found for extrinsic faulting. Isothermal annealing treatments in the range 180°–240°C showed that the deformation stacking faults annealed out in a two-stage process. The first stage was associated with recovery while a kinetic study showed the second stage to be connected with recrystallization. The rms microstrains obtained by Fourier analysis techniques annealed out in a manner similar to the stacking faults. The particle size as determined by Fourier analysis remained constant during isothermal annealing until the recrystallization stage where it increased sharply. Analysis of the peak asymmetries during annealing showed that the number of twin faults remained constant at the value for the cold-worked state until the recrystallization stage where a small increase occurred followed by a rapid decrease toward zero.
Diffraction Contrast Profiles of Voids
Authors: Ingram John
Published: February 2004

Diffraction contrast profiles have been calculated using the two beam approximation for a thin crystal foil which contains a spherical void. The influence of the foil thickness, foil orientation, void radius, and void depth on the total contrast, a combination of both the strain contrast due to distortion of the foil by the void and the thickness contrast due to the absence of scattering material within the void, was examined, the lengths being expressed in units of ξg* =ξg(1+w2)−1/2 where w=Sgξg with Sg the deviation from the exact Bragg condition and ξg the extinction distance. Maximum strain contrast occurs for the profiles of both beams at depths d*= (N/2)ξg* (N an integer); the black and white sides of these profiles alternate as the depth changes by 1/2ξg*. The amplitude of the strain contrast is maximum at thicknesses t*=Nξg* and (N+1/2)ξg* for the scattered beam and the transmitted beam respectively. In either case, the inbetween thicknesses give a smaller strain contrast for which the white sides of the profiles are suppressed for voids within an extended region of the foil. This region of small amplitude is centered on the midplane of the foil for w=0, but shifts for only the scattered beam toward the entrance (exit) surface as w increases positively (negatively); a much larger amplitude can then occur near the opposite surface. Although the strain contrast for either beam is largest for void radius R0*=1/4ξg*, the thickness contrast at w=0 dominates the image of the void at this and larger radii. For R0*≲1/16ξg*, the strain contrast, when maximum, becomes the dominant image forming mechanism. As the foil is rotated away from the exact Bragg condition, w≠0, the thickness contrast can firstly become quite small compared to the strain contrast even at R0*=1/4ξg*, but upon further rotation it predominates once again as in the case w=0 while showing an image of opposite character to the former case.
Cylindrical Antennas Immersed in Arbitrary Homogeneous Isotropic Media
Authors: King R. W. P. , Sandler B. , Wu T. T.
Published: February 2004

The cylindrical antenna is potentially useful as a probe for studying the properties of any material in which it is immersed. Examples of possible media are the earth, plasmas, and organic tissues. Such applications presuppose a knowledge of the detailed behavior of the currents and charges along an antenna in a medium with very general properties. In this paper the integral equation for the current along a highly conducting center-driven cylinder of length 2h and radius a when immersed in a homogeneous isotropic medium is solved analytically and simple, and quite accurate formulas are obtained for the distribution of current, the distribution of charge, and the admittance. The lengths 2h may range from zero to over a wavelength; the radius a is assumed to satisfy the condition a≪h. The real effective conductivity of the medium may extend from zero to arbitrarily large values, the real effective permittivity from large negative values (as in certain plasmas) to large positive values (as in ordinary dielectrics like water).
Relaxation Model for Heat Conduction in Metals
Authors: Maurer Michael J.
Published: February 2004

A time-dependent relaxation model for the heat flux in metals is derived from the quantum mechanical form of the Boltzmann transport equation. In the derivation, the manipulation of the nonlinear integral term of the Boltzmann equation is simplified by assuming that the phonons are in thermal equilibrium at all times and by using the Lorentz approximation to treat free electron-phonon interactions. The relaxation model for the heat flux is found to yield a damped wave equation for the temperature and as a result, the speed of propagation for heat is shown to be finite instead of infinite as implied by the Fourier model for the heat flux. Approximate expressions for the thermal conductivity and the isothermal electrical conductivity are derived in the appendices in order to estimate the magnitude of the relaxation times and to obtain an expression for the Lorentz number. In general it is found that the thermal and electrical relaxation times are not equal although they are estimated to be at the same order-of-magnitude, 10−14 sec for the common monovalent metals. The Lorentz number is found to be a function of the ratio of the relaxation times and as a consequence the difference in the relaxation times may account, at least in part, for the derivation of the experimental Lorentz number from the usual theoretical value based upon equal relaxation times.
Internal Stress Distribution Theory of Magnetomechanical Hysteresis-An Extension to Include Effects of Magnetic Field and Applied Stress
Authors: Smith George W. , Birchak J. Robert
Published: February 2004

The internal stress distribution theory of magnetomechanical damping is modified and extended to include effects of applied magnetic fields and applied static stresses. The present internal stress distribution function yields Rayleigh behavior at low vibration stress and has a more realistic shape than that of the previous model. The theory, besides giving a qualitative description of the damping behavior as a function of vibration stress, agrees quite well with measurements of the dependence of the damping maximum on applied field and static stress.
Heat Capacity and Elastic Constants of CsI at Low Temperatures
Authors: Marshall B. J. , Kunkel J. R.
Published: February 2004

Measurement of the heat capacity from 2.13° to 10°K and of the elastic constants at 4.2°K have been made on a single crystal of CsI. The Debye temperature at 0°K, θ0, as calculated from the heat capacity is θ0=127.67°K. Values of the elastic constants at 4.2°K are c11=2.725±0.6%, c44=0.873±0.6%, and c12=0.767±3% in units of 1011 dyn/cm2. θ0 calculated from the elastic constants at 4.2°K is equal to 129.4°K.
Nature of Long-Range Order in Cu3+xAu1−x
Authors: Gehlen P. C. , Cohen J. B.
Published: February 2004

The diffuse scattering and intensities of Bragg peaks from single crystals of Cu77Au23 and Cu78Au22 have been studied for various degrees of long-range order. The results indicate that the excess Cu atoms, replacing Au in Cu3Au1 distribute themselves at random for the maximum degree of long-range order. The maximum values of the order parameter indicate that the Cu sublattice is completely filled. For order less than the maximum, the results can be explained in terms of a large number of small ordered regions antiphase to the matrix; these regions are primarily two dimensional and vary in composition from point to point in the alloy. These are more Cu rich than similar regions in Cu3Au. Evidence is presented that the difference in atomic sizes of the species varies with degree of order. It is also shown that the scattering due to differences in atomic size and thermal vibrations and that due to local order can be separated completely at one temperature by symmetry operations, as suggested by Borie and Sparks.
Optical Nonlinearities in LiIO3
Authors: Nash F. R. , Bergman J. G. , Boyd G. D. , Turner E. H.
Published: February 2004

Clear, transparent (0.5–5.0 μ), solution-grown, single crystals of negative uniaxial LiIO3 show no optically induced damage and remain stable in the temperature range 20°–256°C. The crystals are of point group 6 and are optically active and pyroelectric. We have measured the linear electrooptic coefficients in the visible and the optical activity in the infrared. For λ1=1.0845 μ phase-matched second harmonic generation (PMSHG) occurred at θm=28.9° and this angle changed by less than 0.3° in the range 20–256°C. PMSHG was employed to determine the single domain quality of the crystals and to measure | d31(LiIO3)/d36(KDP) |=11. At 1.06 μ we have measured the coherence lengths and the ratio of the nonlinear coefficients | d33/d31 |=0.8.
Microwave Breakdown Over a Semi-Infinite Interval
Authors: Mayhan Joseph T. , Fante Ronald L.
Published: February 2004

The general problem of microwave breakdown of a gas subjected to a nonuniform field over a semi-infinite spatial region is treated. This problem is particularly applicable to high-power-handling antennas radiating into free space or into a plasma gas, in which case there is no outer surface for the electrons to diffuse to. Basically, solutions to the electron continuity equation determine an eigenvalue spectrum which governs the breakdown criteria. When the domain is finite, the spectrum must be discrete. This case has been previously treated. For the infinite domain, we demonstrate that for a realistic form of the net ionization rate, a continuous spectrum arises along with a bounded discrete spectrum which, when it exists, dominates the breakdown criteria. Two specific examples are included and the results are applied to breakdown predictions of a rectangular slot. A variational calculation is also treated.
Surface Wave Propagation and Amplification by Beam/Plasma Interaction
Authors: Ristic V. M. , Self S. A. , Crawford F. W.
Published: February 2004

This paper concerns propagation of surface waves along a plasma column, and their amplification by interaction with an electron beam penetrating the plasma. First, surface wave propagation is analyzed for stationary and drifting plasmas. In addition to undamped propagation, the dispersion relation describes infinite sets of modes which can be categorized as evanescent and damped propagating waves. Next, it is shown how surface waves can be driven unstable by an electron beam. When the beam partially fills the plasma, interaction may occur not only with surface waves but also with plasma oscillations. A detailed stability analysis for the case of beam filling the plasma shows that the system may be either convectively or absolutely unstable, depending on the beam parameters. These findings are compared with the predictions of weak coupled mode theory, which are demonstrated to be misleading. Experiments aimed at measuring surface wave amplification, and checking the theory, are described. The propagation observed is interpreted as a beating between a weakly growing and a damped surface wave. The maximum growth corresponded to an electronic gain of 2 dB/cm at 470 MHz. The paper concludes with a brief discussion of the applicability of the results to development of a practical beam/plasma microwave amplifier.
Temperature Profiles and Energy Balances for an Inductively Coupled Plasma Torch
Authors: Miller Reid C. , Ayen Richard J.
Published: February 2004

A mathematical model was developed to predict radial and axial temperature profiles in an induction-coupled plasma torch. The model employed temperature dependent physical properties and included radiation heat loss. Temperature fields based on the model were calculated for an atmospheric pressure argon plasma. Computed radial temperature profiles were in agreement with experimental profiles reported in the literature. The gas flow rate and flow pattern in the torch did not greatly affect the radial temperature profiles in the hottest region of the torch under ordinary operating conditions, also in agreement with experiment. A one-dimensional analysis was developed which predicted these hot-spot profiles accurately. The plasma model was also found to accurately predict distribution of energy losses from the plasma. Based on the equilibrium current density and temperature profiles provided by the model, the question of the existence of local thermodynamic equilibrium was re-examined. It was concluded that equilibrium is closely approached in the high-temperature central portion of the plasma, in agreement with previous investigators; however, nonequilibrium conditions can exist in the region of high temperature gradient at the plasma edge.
Periodic Potential Probe Configuration for Plasma Diagnostics
Authors: Mosburg Earl R.
Published: February 2004

A probe having a spacially periodic potential is created by a bifilar winding of small tungsten wire. This geometry results in an electric field configuration having an extremely short penetration distance into the plasma. When the behavior of this probe is studied in extended negative glow and back-diffusion type plasmas, the floating mode current-voltage characteristic curve is seen to be quite different from that of the usual double probe in that no effects of the electrons are observed. The behavior of the periodic probe is controlled by the ion inertia established in the diffusion region which lies just in front of the probe. The important parameter of the characteristic curve is the slope near zero applied voltage difference which can be related in a simple manner to the flux of plasma diffusing to the probe and to the diffusion drift energy of the ions as they reach the probe. The electrons make no contribution to this slope for low applied voltage differences. This probe thus provides a very sensitive method for measuring the diffusive flux of plasma to a containing wall.
Properties of Ion-Implanted Bi in CdS
Authors: Tell B. , Gibson W. M.
Published: February 2004

It has been reported that room-temperature Bi implants with no post-implantation annealing produce high-conductivity p-type layers in ordinarily n-type CdS. We have similarly implanted Bi and also Xe into CdS at the 1015 cm−2 level, and have studied various properties including optical absorption, photoluminescence, and photovoltage. In all cases, similar behavior is observed with both Bi and Xe implants, which indicates that radiation damage effects are dominating any purely chemical effects.
Radiative Recombination and Equilibrium between Near-Band-Edge Tail States in n-Type GaAs
Authors: Southgate P. D.
Published: February 2004

The detailed balance method of deriving the radiative-recombination coefficient in semiconductors from the absorption curve is strictly applicable only when thermal quasiequilibrium exists for the carriers within each band. It is shown here that in many cases when the bands tail into the gap, the carriers are not in thermal equilibrium within the tail, even quite near the band edge, and that the detailed balance method requires modification. A simplified model, that of a regional bandgap variation, is suggested as an approximation to the complex band-tailing situation. It is applied to measurements of photoluminescence and absorption in n-type GaAs, of varying degrees of degeneracy, and values of the recombination constants at 296° and 77°K are derived. They are of the same magnitude as those in ideal material with no tailing. An uncertainty arises in degenerate material since it is not clear whether the reduced values of Burstein shift observed are entirely attributable to band shrinkage. The contribution of the deeper tail states to the luminescence often appears to be approximately independent of the separation of the state from the band edge.
Anomalous Self-Diffusion in Solid Bismuth: The Trapping Mechanism
Authors: Ellis W. P. , Nachtrieb N. H.
Published: February 2004

An anomalous self-diffusion behavior has been observed in single-crystalline bismuth. The penetration profiles do not follow Fick's laws of diffusion and disagree with the results reported by Seith. For the semi-infinite rod configuration, the concentration of 210Bi tracer decreased exponentially with depth, but there was not necessarily an excess of tracer on the surface and the profiles did not vary with time. Penetration was correlated with mechanical twins, but was not directly amenable to a Fisher grain-boundary analysis. Volume diffusion was not observed. The results have been interpreted by a modified grain-boundary treatment in which the diffusing species is trapped. Integration of the trapped material over time with a Laplace transform results in the profile C=s(k/D′)1/2 exp[−y(k/D′)1/2], which is in functional agreement with observation. The quantity (k/D)′1/2 appears to be a property of Bi, and may be regarded as a characteristic inverse trapping distance.
Drift Velocity of Electrons in Silicon at High Electric Fields from 4.2° to 300°K
Authors: Rodriguez V. , Nicolet M-A.
Published: February 2004

The drift velocity of electrons in silicon at high electric fields is measured in the 〈111〉 direction over the range of lattice temperatures from 4.2° to 300°K. It is established that in this range a limiting drift velocity exists. Its temperature dependence is measured. The samples used and the method of measurement are briefly described.
Epitaxial BaTiO3 on Pt Substrate
Authors: Tada Osamu , Shintani Yoshihiro , Yoshida Yasuyuki
Published: February 2004

Epitaxial layers of BaTiO3 grow on Pt substrates when: (1) The Pt substrate has preferred orientation 〈111〉; (2) BaTiO3 powder is sintered on this substrate at 1400°C for 24 h in air. The epitaxial BaTiO3 is single crystalline with an orientation of {111}BaTiO3//{111}Pt but with a deformation in crystal structure. X-ray diffraction data indicate that the spacing d111 is larger by about 1% (0.023 Å) than that of original BaTiO3 which is tetragonal phase at room temperature. The dielectric measurements show that the remanent polarization and the dielectric constant of this specimen are about ¼ and 110 values of those of polycrystalline BaTiO3, respectively.