bluuebunny/crossref_metadata_2025 huggingface dataset:
Transmission Sputtering of Thin Films by Low-Energy Hydrogen Ions
Authors: Robison Charles H.
Published: February 2004

An experimental measurement of transmission sputtering (sputtering from the downstream face of a target foil) was performed with 15-keV molecular ions of hydrogen and deuterium normally incident on polycrystalline gold films several hundred angstroms thick. The sputtered atoms were detected by using neutron activation. A modified form of a theoretical sputtering formula due to Pease was found to fit the data within a factor of two, except in the circumstance where the average energy of the primary knock-on atom was less than the displacement energy. The modifications included taking into account: the energy loss of the incident particles in passage through the film; the average energy of the moving primary knock-on atoms; and the fraction of the incident beam scattered before reaching the downstream face of the film.
Solution of the Stefan Problem for Whisker Evaporation
Authors: Simmons John A. , Coriell Sam R.
Published: February 2004

The moving boundary problem for whisker evaporation is solved numerically, using techniques previously developed for whisker growth. Curves of whisker length as a function of time are calculated for several values of the evaporation parameter. The possibility of determining the surface-diffusion constant and the mean adatom stay time from whisker experiments is discussed.
Sputtering Experiments with 1- to 5-keV Ar+ Ions. III. Monocrystal Targets of the Hexagonal Metals Mg, Zn, Zr, and Cd
Authors: Robinson Mark T. , Southern A. L.
Published: February 2004

Sputtering yields and ejection patterns have been observed during the irradiation of 〈0001〉,〈101̄0〉, and 〈112̄0〉 crystals of Mg, Zn, Zr, and Cd with normally incident 5-keV Ar+ ions. A few observations were made at other energies as well. Except for the 〈112̄0〉 crystals of Zn and Cd, Onderdelinden's sputtering model accounts satisfactorily for the orientation dependence of the yields. With the same exceptions, the model also accounts for the relationship of the yields of these hcp metals to those of the fcc metals Al, Cu, and Ag. The Zn and Cd 〈112̄0〉 crystals show yields about 50% greater than expected from this model. They also show unusual ejection patterns that cannot be related to the undistorted hcp structure. These effects are attributed to radiation damage. The other crystals show preferred ejection along the directions 〈112̄0〉,〈0001〉,〈202̄3〉,〈404̄3〉, and (possibly) 〈64̄2̄3〉. The last three are not closely and uniformly spaced rows of atoms. Their importance in the ejection patterns, as well as the close agreement of hcp and fcc yields, make it unlikely that long sequences of focusing collisions play a significant role in the sputtering of metals.
Diffraction Theory of Sinusoidal Gratings and Application to In Situ Surface Self-Diffusion Measurements
Authors: Bonzel H. P. , Gjostein N. A.
Published: February 2004

Computer calculations of the diffracted intensities from a sinusoidal surface grating have been carried out using analytical methods developed independently by Brekhovskikh, Senior, Stroke, and Petit from the electromagnetic theory of diffraction. These calculations provide a theoretical foundation for the newly developed laser-diffraction technique for continuously monitoring surface self-diffusion of solids under ultrahigh vacuum conditions. The calculated patterns were characterized by an absolute maximum in intensity, which occurs at increasingly higher orders as the amplitude of the profile increases; the order of the maximum is designated nmax. Calculations were carried out at normal incidence for both Ē and H̄ parallel to the groove direction, but no sensible polarization effect was found in the range of amplitude and periods investigated. The effect of angle of incidence θi was also determined, and it was shown theoretically that, as θi increases, nmax on the +n-side of the pattern shifts toward the zero order, but on the −n-side nmax passes through a maximum before slowly decreasing. This effect also has been verified by experiment. In addition to these analyses, the phase modulation treatment used in communication theory has been examined and it is shown that this approach is the limiting case of the rigorous electromagnetic theory when the period of the grating becomes very large compared to the amplitude. Excellent agreement has been obtained between theoretical and experimental intensity distributions. This agreement provides a fundamental basis for the linear relationship between the amplitude A of the profile and the diffraction order of maximum intensity, nmax. which has been previously established experimentally and is used to follow the decay in A during a diffusion experiment. While nmax (A) is linear in the range of amplitudes and periods most frequently used in surface-diffusion measurements, the theory predicts nonlinearities in nmax (A) when the amplitude-to-period ratio is greater than about 0.08; these deviations are important in very low temperature diffusion studies. As an example of the application of the diffraction theory of sinusoidal gratings, the experimental determination of the surface self-diffusivity of a (110) nickel surface is presented. The laser-diffraction method has been used in conjunction with a low-energy electron-diffraction system, permitting the surface structure and cleanliness to be determined at any time during a diffusion experiment. An activation energy of 19.0 kcal/mole and a D0=0.01 cm2/sec have been measured for a (110) Ni C2 structure in the temperature range 800° to 1080°C.
Fast-Neutron Irradiation Effects in CdS
Authors: Johnson R. T.
Published: February 2004

The effects of fast-neutron irradiation on the room-temperature dark resistivity and Hall mobility in CdS have been determined. Single crystals ranging from 0.5–10Ω·cm and from 107–109Ω·cm were irradiated in a reactor at 30°±5°C. For fluences of 1014 neutrons/cm2 and 1017 neutrons/cm2 the Hall mobility decreases by 3%–5% and 20%–30%, respectively. At one day after irradiation to > 1017 neutrons/cm2, the crystals are still n-type and the resistivity approaches a limiting value of ∼2×104Ω·cm, independent of the initial resistivity. The corresponding limiting electron quasi-Fermi level is at ∼0.37 eV below the conduction band. Following irradiation, three separate time-dependent processes occur which cause changes in the resistivity. Two of these are temperature-independent and follow first-order kinetics with half-lives of ∼1 and ∼14 days, respectively. The third process is much slower and is temperature-dependent. The room-temperature annealing rate for this process depends on the sample and also on either the electron quasi-Fermi level or the defect concentration. Initial changes in the postirradiation resistivities are primarily results of the first two processes and are attributed to self-ionization of the sample by radioactive decay of transmutated atoms produced during the irradiation. The major radioactive decay process (14 day half-life) results from the beta irradiation from radioactive 32P; the other process is tentatively identified as resulting from the 115Cd beta decay. The temperature-dependent process is attributed to the annealing of radiation-induced defects, which are probably more complicated than simple vacancies or interstitials.
Validity of the Uncoupled Theory of Longitudinal Electron Oscillations in a Boundless Magnetoplasma
Authors: Babler Gary M. , Willett Joseph E.
Published: February 2004

An investigation is made of the uncoupled approximation for longitudinal electron oscillations in a boundless, nonrelativistic, Maxwellian, collisionless plasma in the limit of a strong external magnetic field. A simple formula is derived for the first-order correction to the complex frequencies due to coupling to transverse oscillations. Calculations for the lowest-frequency, least-damped oscillation indicate that at short wavelengths the coupling is significant only for relativistic electron thermal velocities. At long wavelengths for which the phase velocity is not negligible compared to the speed of light, the coupling is significant.
Analysis of a Frequency-Swept One-Bit Digital Correlator
Authors: Ray C. D. , Tsukishima T. , Hyland R. N. , McLane C. K. , Carpenter R. J.
Published: February 2004

An instrument for measuring the cross-spectral density of two random variables which are correlated is described. It was constructed to study the relationship between electron density fluctuations and the ambipolar diffusion coefficient in a plasma. A stability in the zero correlation level of 10−3 is achieved by use of one-bit digital electronics in the multiplier and integrator. An analysis of the design and function of the instrument is given together with a discussion of possible instrumental errors and statistical uncertainties in the measurements.
Transient Photoconductivity in Trigonal Selenium Single Crystals
Authors: Mort J.
Published: February 2004

Measurements of recombination lifetimes in single crystals of trigonal selenium, which is a p-type extrinsic semiconductor, have been made by studying the decay of photoconductivity induced by a 1.5 μsec light pulse. The addition of sufficiently intense dc illumination allows traps to be filled and a simple exponential decay obtained, which is interpreted to be a direct measure of the recombination lifetime. Lifetimes were found to range between 10 μsec and 34 μsec. From a knowledge of these lifetimes and absolute dc photoconductive gain measurements, photoconductivity mobilities were found to be 40±8 cm2·V−1·sec−1 parallel to the c axis and 17±4 cm2·V−1·sec−1 perpendicular to the c axis. The temperature dependence of the majority-carrier drift mobility can be obtained by measuring the relative pulsed photoconductive gain as a function of temperature. These experiments are in good accord with studies of acoustoelectric current saturation. No evidence is found for a barrier-limited mobility. Other experiments indicate that electrons are mobile in trigonal selenium, allow an estimate of their drift mobility, and give evidence of multiple trapping of minority carriers in deep traps.
Performance Characteristics of Thermomagnetic Devices Involving Graded Mass and Gap. I. Generators
Authors: Honig J. M. , Lax Benjamin
Published: February 2004

The theory pertaining to operating characteristics of thermomagnetic generators with graded mass and gap has been developed using the fundamentals of irreversible thermodynamics. On introducing transport theory and a considerable number of simplifying assumptions, analytic results were obtained for the efficiency of such devices in terms of the transport coefficients evaluated at the hot junction temperature. The numerical results have been compared to those obtained with materials of constant bandgap and to calculations performed by the method of averaged parameters. The advantages of using a graded gap material for energy conversion are pointed out.
The Relativistic Doppler Equations for Attenuated Waves and the Drag Effect
Authors: Berger Henry , Griemsmann John W. E.
Published: February 2004

A uniform plane, electromagnetic wave which is attenuated as it travels through a dispersive, homogeneous, isotropic medium is demonstrated to have a phase which is not Lorentz invariant. The attenuation can be caused by dissipation in the medium, or because the frequency of the wave is below cutoff frequency of the medium. A generalized set of relativistic Doppler equations for the attenuated plane waves are derived and used to study some of the general properties of this wave. It is shown from the Doppler equations that an attenuated wave which is time-harmonic in one inertial reference frame is not time-harmonic in all other inertial reference frames. This result has important consequences in the formulation of the constitutive relations which characterize the medium. The Doppler equations are also utilized as a basis for studying the drag effect for attenuated waves in moving media. The basic method of analysis in this paper utilizes the rigorous electromagnetic field equations in conjunction with Minkowski's extension of the theory of Special Relativity for material media.
Etching Behavior of In2O3 Grown from PbO–B2O3
Authors: Chase A. B. , Teviotdale R.
Published: February 2004

Single crystals of In2O3 grown from a PbO–B2O3 solution are etched by HNO3 or HNO3–HCl solutions. Characteristic etch pits and etch tubes are described. The number of etch pits is found to be related to the growth history of the crystals. The relationship of the etch tubes to crystal growth is discussed.
Competition between Random and Preferential Ejection in High-Yield Mercury-Ion Sputtering
Authors: Musket Ronald G. , Smith Harold P.
Published: February 2004

A radioactive tracer technique was employed to determine the yield (atoms/ion) and angular distribution (atoms/ion·sr) of atoms sputtered from Cu (100) and Mo (100) surfaces by a 1 to 10 keV Hg+-ion beam. Values of the yield for Ni (100) surfaces were also determined. Analytical models for normal and oblique ion incidence cases were fitted to the angular distribution data. The functions describing the preferential emission in the closest-packed direction and the [100] direction were Gaussians, whereas the background distribution was represented by a cosine, which was tilted away from the surface normal for oblique incidence. Integration of the total distribution gave the relative contributions to the sputtering yield of the directed emissions and background. In all cases, the cosine contribution, which is interpreted in terms of emission from a random lattice, accounted for more than ⅔ of the atoms sputtered. However, intense Wehner spots were present even when the cosine distribution accounted for ⅘ of the ejections. These spots, which are commonly attributed to preferential ejections, are more accurately interpreted as a combination of random emission and collimated preferential emission.
X-Ray Peak Profiles for Ultramicrotomed Powders and Their Relation to the Deformation Structure
Authors: Ahlers M. , Vassamillet L. F.
Published: February 2004

X-ray peak profiles of microtomed powders have been measured. The results for peak shifts and for peak asymmetries have been related to observations by transmission electron microscopy. The validity of the assumptions that have been made to calculate the relationship between peak profiles and stacking faults or twin faults is discussed.
Deformation of Some fcc Metals by Ultramicrotomy
Authors: Ahlers M. , Vassamillet L. F.
Published: February 2004

Thin foils of Al, Ag, Cu, Cu-5 at.% Ge, Cu-9.5 at.% Ge were cut with the ultramicrotome and investigated by transmission electron microscopy. High dislocation densities (>2×1011 cm−2) are introduced in all foils except Al. No extended stacking faults were ever observed. Twinning occurs in Ag, Cu, and Cu-5 at.% Ge, but not in Cu-9.5 at.% Ge alloys. These results are compared with findings from electrolytically thinned deformed foils.
Parametric Interaction of Focused Gaussian Light Beams
Authors: Boyd G. D. , Kleinman D. A.
Published: February 2004

A theoretical study is presented on the optimization of second harmonic generation (SHG) and parametric generation (PG) by a laser beam in a uniaxial nonlinear crystal. Numerically computed curves show the dependence of the SHG power, and the reciprocal of the PG threshold power, on the parameter l/b, where l is the optical path length in the crystal and b is the confocal parameter (determined by the focal length of the focusing lens and the minimum radius of the laser beam, assumed to be in the TEM00 mode of an optical resonator). The calculations take full account of diffraction and double refraction. In the absence of double refraction, the optimum focusing condition is found to be l/b=2.84. For PG the optimization of the crystal length l is also discussed, and curves are given showing the dependence of the threshold on l for the case in which signal and idler have the same losses. It is shown that the computed functions are also relevant to the mixing of two Gaussian beams and to parametric amplification. Pump depletion is neglected. Appendices are provided on (1) the theory of Gaussian extraordinary beams and the extension of the theory to cover both positive and negative birefringent crystals, (2) the general definition of nonlinear coefficients, (3) the effective nonlinear coefficient, and (4) details of the computations. The theory of the PG threshold is applied to tellurium and LiNbO3. On the basis of reasonable assumptions about the losses, a PG threshold of 1.0 W is obtained for a pump at 10.6 μ in Te. The optimum length is found to be l=0.14 cm. For LiNbO3 of length l=1 cm the threshold is 22 mW at 0.5147 μ. Also calculated is the quantum efficiency for up-conversion in HgS from 10.6 to 0.6729 μ using the 0.6328 μ He–Ne laser.
Distribution Coefficient of Manganese in Sodium Chloride Crystal Determined by Electron Spin Resonance
Authors: Muñoz P. E. , Ruiz M. C. , Riveros R. H.
Published: February 2004

The distribution coefficient of divalent manganese in sodium chloride single crystals grown from the melt was determined by Electron Spin Resonance (ESR) absorption techniques at room temperature and at a wavelength of 3 cm. The crystals were grown by a method similar to that described by Kyropoulos. There were two initial concentrations from which the crystals were grown: 0.5 and 1 at.% manganese in sodium chloride. Graphs were obtained that show the dependence of the fractional impurity concentration as a function of the fraction of melt which has been solidified.
Radiative Pair Transitions in p-Type ZnSe: Cu Crystals
Authors: Stringfellow Gerald B. , Bube Richard H.
Published: February 2004

Shallow levels with an ionization energy of 0.012 eV play an important role in the photoelectronic properties of p-type ZnSe:Cu crystals. These levels exhibit the characteristics of the higher-lying member of an imperfection pair involved in luminescence emission, as well as of a trap determining long-time decay rates of luminescence and photoconductivity, and of a center causing low-temperature reduction of free-electron lifetime. The participation of the shallow level in low-temperature pair emission is demonstrated by the thermal quenching of the emission at 50°K with an activation energy of 0.012 eV, whereas the acceptor forming the lower-lying member of the pair lies 0.72 eV above the valence band, and by the shift in the position of the emission band below 50°K with changing excitation intensity. The energetics of the emission and the 10−20 cm2 electron cross section determined from decay suggest that the shallow level may be an acceptor rather than a donor.
Time-Decay Characteristics for the Red Emission from GaP
Authors: Harper F. E. , Strassler S. , Hakki B. W.
Published: February 2004

The decay of the red emission from a Zn–O- and Te-doped GaP p-n junction was measured. The measurements were made for temperatures between 77°K and 298°K by using current pulses (0.5–2.0) μsec in duration and (10–200) A/cm2 in amplitude. At low temperatures (T≤113°K for the GaP studied here), the emission decayed like t−1 at long times, indicating that the emission was due to pair recombination (recombination of an electron and a hole bound to distant impurity levels). At high temperatures (T>139°K), the emission decayed exponentially with a single time constant which was independent of the current amplitude and which decreased with increasing temperature. This result is consistent with the exciton decay mechanism recently found at low temperature by Morgan et al. and Henry et al. to account for a part of the red emission from GaP.
Morphology of Spherulites and Single Crystals of Trigonal Selenium
Authors: Fitton B. , Griffiths C. H.
Published: February 2004

The crystallization of amorphous selenium is shown to occur by the formation of lamellas in which the molecular axis lies across the wide face and perpendicular to the growth direction. Below about 200°C the lamellas grow radially from a common nucleus branching noncrystallographically to produce a spherical crystalline mass. The theoretical selenium chain length in the quenched amorphous phase is much longer than the average lamella widths observed at large supercoolings. This indicates that at the edges the chains must fold back into the lamella if stress accumulation due to interconnection of the two phases of different density is to be avoided. It is suggested that such an array of chain folds introduces a dilation of the lattice which is accommodated if the lamella twists. Where it is cooperative, such twisting within the radial array of lamellas is shown to be responsible for the annular ring structure of selenium spherulites. In crystallization above 200°C the radial symmetry begins to breakdown and the lamella width approaches the mean chain length. Some fractionation then appears to take place to produce sets of lamellae of different widths which presumably contain fully extended chains. Clearer evidence of such fractionation was shown in a crystal grown under high pressure where the melt viscosity is lower. These smaller supercoolings also led to the growth of leaf-shaped single crystals having the same internal structure as the lamellas but with no set width. It is surmised that these are produced by a bundle-like accretion of chains. Such leaf crystals were observed within the bulk of `single' crystals grown by the traveling solvent or the Czochralski method. It is pointed out that the breakdown of periodicity in the selenium covalent bonding at impurity terminated chain ends, estimated at about 1016 to 1017/cc, or at chain folds, must have an appreciable influence on the charge transport properties of single crystals of trigonal selenium.
Seeded Growth of Selenium Crystals under High Pressure
Authors: Harrison J. D.
Published: February 2004

Two improvements in the technique of growing selenium single crystals under high pressure have been made: (1) the use of seed crystals of predetermined orientation, and (2) the annealing of the newly grown crystals during depressurization. The method of seed preparation and the characteristics of the resulting crystals are described. Odd growth patterns were observed at the seed-new growth interface.
Electron Attachment in Ionized Flows at Elevated Gas Temperatures
Authors: Malliaris A. C.
Published: February 2004

An ionized argon flow (electron concentration of the order of 1012 per cm3), at elevated gas temperatures, is obtained by arc heating. The flow is admitted in a mixing chamber where small additive fractions (order of 10-4) of an electrophilic compound, (SF6), are injected into and mixed with the flow. The mixtures are incubated under specified incubation conditions (3000° to 5000°K, 0.1 to 1 atm, 10-3 to 10-4 sec). Electron and ion concentrations are determined at the end of the incubation and for this, both single and double Langmuir probes are used. Auxiliary probing is also carried out by an x-band microwave beam. Suppression of the electron concentration by factors ranging from 2 to over 1000 are determined, depending on experimental conditions. By experimental evidence it is demonstrated that the suppression of the electron concentration is the result of negative ion formation and survival. Charge neutralization processes are relatively negligible.
Structure of a Vapor-Quenched AgCu Alloy
Authors: Wagner C. N. J. , Light T. B. , Halder N. C. , Lukens W. E.
Published: February 2004

Ag—52 at.% Cu films were prepared by coevaporation onto 0.005 in. thick vitreous silica plates held at liquid-nitrogen temperature. The interference function I(K), where K=4π sinθ/λ, was evaluated from the elastic x-ray scattering of the film and compared with I(K) of the liquid alloy, measured at 1000°C, and with a model I(K) based on fcc microcrystals containing 125 atoms. The Fourier transforms of K[I(K)—1] yielded the reduced distribution functions G(r) =4πr[ρ(r)—ρ0]V(r), where ρ(r) is the weighted atomic density at a distance r from any reference atom, ρ0 is the average atomic density, and V(r) is the size factor of the diffracting domains. Both I(K) and G(r) indicate that the alloy film cannot be characterized as amorphous but is micropolycrystalline with fcc structure. The size of the microcrystals can be estimated from G(r), i.e., from the value of r beyond which G(r) is zero within the scatter of the experimental points. A value of less than 16 Å has thus been found. I(K) and G(r) of the liquid alloy are characteristic of the close-packed liquid metals with a distance of less than 15 Å beyond which no short-range order can be detected.
Variation in the Elastic Constants of Calcite with Temperature
Authors: Dandekar Dattatraya P.
Published: February 2004

The temperature dependence of the elastic constants of calcite have been investigated by the ultrasonic phase-comparison method from 25° to 375°C. The variation in the elastic constants and the elastic moduli of calcite is smooth and linear over the temperature range, and does not show the break in the variation of the elastic moduli with temperature reported by Reddy and Subrahmanyam at 200°C. The results of the present investigation are in agreement with the other related high-temperature studies of calcite. The reported discontinuity in the variation of elastic moduli with temperature thus seems to be inconsistent with the high-temperature behavior of calcite. This conviction is strengthened by the impossible behavior of compressibility of calcite with temperature as obtained from the calcite data of Reddy and Subrahmanyam. The elastic constants of calcite at T°C within the temperature range of the present work are adequately represented by the following equations:  C11=14.7994−57.82×10−4×(T−25)C33=8.5694−14.06×10−4×(T−25)C44=3.2790−14.36×10−4×(T−25)C66=4.6316−14.03×10−4×(T−25)C13=5.4540−25.76×10−4×(T−25) C14=−2.0966+8.32×10−4×(T−25).
Field Criterion for Sustained Streamer Propagation
Authors: Nasser E. , Heiszler M. , Abou-Seada M.
Published: February 2004

Experiments have shown that streamers are astonishingly capable of penetrating low-field regions before finally coming to a stop. This lead to a proposed theory of low-field requirements for continued propagation of the ionizing potential space wave constituting the streamer. The long range of impulse streamers in atmospheric air from a positive point was investigated in order to establish their spatial properties and a criterion that allows the prediction of such ranges. This was accomplished by axial and lateral measurements of the ranges of streamers for various gap spacings. A parallel study based on charge simulation and using a digital computer delivered the field intensity at the various points of the gap. The correlation of the results of both studies showed that streamers tend to stop whenever the applied field drops below 500 to 600 V/cm regardless of gap spacing or streamer location. Thus, streamers are not capable of propagating under an external zero field and require this minimum field for sustained advance.
Prismatic Dislocations in β′ NiAl
Authors: Tisone T. C. , Marshall G. W. , Brittain J. O.
Published: February 2004

Electron-transmission studies have revealed the presence of 〈100〉 prismatic dislocation loops in a single crystal of β′ NiAl. Concentric loops observed in 〈100〉 foils were found to be coaxial rather than coplanar. A comparison of as-grown, annealed, and quenched specimens has indicated that loop development depends on thermal history. Dislocation interactions were observed between coplanar loops. Interactions between segments of noncoplanar loops resulted in three-dimensional arrays.
Dislocation Etch Pits in Arsenic
Authors: Shetty M. N. , Taylor J. B.
Published: February 2004

Two etching reagents have been developed which produce pits on the (111) cleavage surface of arsenic. In addition, a chemical polish has been developed for arsenic. Evidence has been obtained that the pits occur at sites of emergence of dislocations. Some observations on deformed crystals are also reported and discussed.
Capacitance of Junctions on Gold-Doped Silicon
Authors: Senechal R. R. , Basinski J.
Published: February 2004

The capacitance of p+—n junctions and Schottky barriers on gold-doped, n-type silicon has been measured as a function of applied bias and time in the temperature range 205°-255°K. The gold-diffusion temperature was 1000°C. The time dependence of the capacitance has been examined on the basis of a model which assumes that the gold acceptor level has the same charge as in the bulk for some distance λ(t) from the edge of the depletion region. The analysis yields a value for the density of neutral acceptors in the depletion region of 1.1×1016 cm-3, indicating that en»ep for the gold center. The energy associated with the capacitance time constant is 0.545±0.005 eV and the capture cross section σn is calculated to be 2.9×10-15 cm2 at 250°K. Of a more general nature, a simple procedure is described for determining the contribution of slow-responding deep levels to the capacitance of abrupt p—n junctions. This involves a plot of dV/d(1/C2) vs C, a relationship which was essentially derived by Goodman.
Computer Simulation of Sputtering
Authors: Harrison D. E. , Levy N. S. , Johnson J. P. , Effron H. M.
Published: February 2004

Present computers have neither enough memory capacity nor computation speed to completely simulate the sputtering process. The conclusions reported here were obtained with purely repulsive potential functions. Surface binding energies were included artificially. The simulations produce excellent spot patterns, but only approximately correct sputtering ratios. The Ar+–Cu system has been studied in detail and a few trials have been made on the Xe+–Cu system. The three Gibson potentials and the Anderson-Sigmund potential were used for the Cu–Cu interaction. Changing these functions produces quantitatively, but not qualitatively, different results; so a majority of the investigation was conducted with the Gibson II potential. The Ar–Cu and Xe–Cu potentials were those obtained locally from secondary electron emission studies. Variation of parameters in these functions had little effect on the spot patterns. Sputtering ratios change appreciably as the parameters of the potentials are varied, but the unexplained systematic difference between simulation and experiment cannot be removed by parametric variation within a Born-Mayer potential function model. The simulations indicate that sputtering is caused by two mechanisms: (a) In the more common situation the incoming ion strikes two lattice atoms almost simultaneously. The lower energy of these two primary knock-on atoms then initiates the sputtering of several of its neighbors. The higher-energy primary knock-on may also cause some sputtering, but it usually is less efficient because a large fraction of its momentum is directed into the surface. (2) In a relatively small number of events the ion, after having made one or more collisions, is reflected from the second or third layer of the crystal. It then can initiate sputtering as it returns toward the surface. The second mechanism has never been seen when the ion is heavier than the lattice atoms. Primary knock-on ions rarely sputter. Occasionally (after making several collisions) one escapes accidently. Almost every incident ion sputters at least one atom, even those which enter a (110) channel. Ions which hit the end of a (110) chain with zero impact parameter, or ions which penetrate normally into the absolute center of the trigonal lens of the (111) surface or the square lens of the (100) surface do not cause sputtering. Surface dynamics dominate the sputtering process. The probability of focuson sputtering appears to be vanishingly small. The relationships between the surface dynamics, transparency, and channeling models are discussed.
X-Ray Topographic and Optical Observations of Magnetic Domains in Yttrium Iron Garnet (YIG)
Authors: Patel J. R. , Jackson K. A. , Dillon J. F.
Published: February 2004

Magnetic domain patterns of single crystals of yttrium iron garnet have been studied by optical and x-ray topographic methods. There is good correspondence between optical photographs and x-ray topographs of domains. A pronounced striation pattern, not observed by transmission optical microscopy is revealed for certain x-ray reflections. The crystal is otherwise remarkably free of defects.
Nucleation and Growth of Li Precipitates in Si
Authors: Ferman John W.
Published: February 2004

Precipitation of excess Li in solution in Si monocrystals, preannealed at temperatures of 750°–1340°C, has been measured resistiometrically. Infrared transmission microscopy shows precipitate particles are spherical or nearly so. The precipitates are thermodynamically similar to the equilibrium phase, Li2Si, but the data suggest LiSi. Excess Li content decreases exponentially with time and is Li-diffusion limited; Ham's theory is valid in this system. The number of particles is found to span ∼2×1010 to ∼3×1013/cc over the preanneal temperature range in low O content, ∼5×1015/cc, Si. Nucleation occurs at oxygen-vacancy pairs, OV, which form reversibly at elevated temperatures with binding energy of −0.56 eV; kinetic sluggishness prevents equilibrium at temperatures below about 800°C. A model whereby prenucleation Li+ ion segregation occurs about OV− ions due to electrostatic attraction is examined. Under experimental conditions, a diffuse cloud of roughly 75 Li+ ions could exist at 600°C, and could condense within 1 sec at 100°C. An estimate of precipitate-matrix interfacial energy is about 0.14 eV/site, which in conjunction with nucleation thermodynamics, predicts critical nucleus sizes of 3–39 atoms depending on choice of crystal habit plane.
Surface Superconductivity in Tantalum
Authors: Smith Frank T. J. , Gatos Harry C.
Published: February 2004

The superconducting behavior of tantalum wire in a longitudinal magnetic field was studied by means of electrical-resistance measurements. The results were compared with the predictions of the Saint-James and DeGennes theory. Under certain conditions the critical field for surface superconductivity as well as a higher critical field were observed. The persistence of superconductivity in fields higher than the critical field for surface superconductivity was attributed to the presence of clusters of interstitial impurity atoms in the material. The effects of strain on these critical fields were also explained on the same basis.
A Powder Technique for the Evaluation of Nonlinear Optical Materials
Authors: Kurtz S. K. , Perry T. T.
Published: February 2004

An experimental technique using powders is described which permits the rapid classification of materials according to

(a) magnitude of nonlinear optical coefficients relative to a crystalline quartz standard and

(b) existence or absence of phase matching direction(s) for second-harmonic generation.

Results are presented for a large number of inorganic and organic substances including single-crystal data on phase-matched second-harmonic generation in HIO3, KNbO3, PbTiO3, LiClO4·3H2O, and CO(NH2)2. Iodic acid (HIO3) has a nonlinear coefficient d14∼1.5×d31 LiNbO3. Since it is readily grown from water solution and does not exhibit optical damage effects, this material should be useful for nonlinear device applications.
Time-Dependent Mechanical Strength of Oriented Media
Authors: Hsiao C. C. , Moghe S. R. , von Schmeling H. H. Kausch
Published: February 2004

For a homogeneous oriented and stressed medium, a theory of strength behavior is formulated and analyzed on the basis of considering the kinetic breaking and forming processes present in the microscopic molecular structure. The solution to this formulation gives not only reasonable results comparable to available experimental findings, but also yields new information which may not be possible to be verified experimentally at present. In general, it is found that under either fairly large or moderate stresses, the fracture strength is almost linearly related with logarithm of time. For small stresses, the kinetic nature of molecular reformation is found to be quite influential and thus the time required for fracture becomes larger and larger and finally approaches to infinity. The analysis is also extended to a partially oriented molecular system under more general loading conditions.
Drift Instabilities in Confined Two-Component Plasmas
Authors: Lee Kai Fong
Published: February 2004

The stability of plasma columns having two components of different drift velocities and temperatures is studied. The plasmas possess nonuniform radial density profiles and are confined by an infinite axial magnetic field and an concentric conducting cylinder. General expressions are given for the velocity thresholds, maximum unstable wavenumber, and the number of unstable modes in a system. It is seen that the instability depends on both the geometrical factors and the temperature ratio of the two components. The main features are illustrated by specializing to the case of a proton-electron plasma uniformly filling a conducting cylinder.
Temperature Dependence of Carrier Concentrations and Conduction-Band Minima Separation of Gallium Antimonide
Authors: Liang C. Y.
Published: February 2004

Based upon the two-band model, a combined analysis of the experimental data of an n-type GaSb sample obtained from Faraday rotation, spectral emittance, and Hall-effect measurements is discussed. It is found that the ratio of the mobilities of the (000) and 〈111〉 conduction bands is 9.0 at 77°K and 5.59 at 273°K. The total carrier concentration of the two bands is found to be the same at these two temperatures. The temperature dependence of the carrier concentration of the (000) and the 〈111〉 bands are found, respectively, as N0(T) = (1.625−2.29×10−3 T) ×1024/M3 and N1(T) = (2.320+2.29×10−3 T) ×1024/M3. The temperature dependence of the separation of the (000) and 〈111〉 conduction band minima is found to be Δ = (0.084+5.9×10−5 T) eV.
Field Desorption of Cesium Ions
Authors: Sama Nicholas
Published: February 2004

The field desorption of cesium ions from a positive electrode is formulated for the range of electric field over which an image potential binds the ions to the electrode surface. Recent investigations on the ionization of gas atoms by a metal surface are utilized, in conjunction with steady-state arguments, to yield an expression for the ion supply at the electrode surface. A tunneling process in the presence of an electric field is then considered, and the ion emission obtained in terms of fundamental constants and pertinent parameters. As part of the over-all problem, the effect on the emission current of fractional adsorbed atomic layers on the electrode is examined; not surprisingly, the nonuniform properties of a real electrode lead to the same difficulties in the description of ion emission as those met in the case of electron field emission.
Interpretation of Electron-Mirror Micrographs of Ferroelectric and Dielectric Surfaces
Authors: Maffitt K. N.
Published: February 2004

The applicability of the electron-mirror microscope to the study of insulating surfaces is demonstrated. In the case of ferroelectric surfaces, significant differences are found between the images of an uncoated surface and a surface coated with a conductive film. These differences are attributed to variations in charge concentration on the bare surface. In the ferroelectric case detailed analysis of the EMM image allows the correlation of charge polarity and concentration to surface topography. In the case of dielectric surfaces, variations in charge concentration caused by inhomogeneities in conductivity and by surface contamination are observed.
Microwave Transmission through Thin Metal and Semiconducting Films
Authors: Ramey R. L. , Kitchen W. J. , Lloyd J. M. , Landes H. S.
Published: February 2004

The EM power-transmission coefficients of thin films placed in the transverse plane of a rectangular waveguide are shown to be singularly dependent upon the product σd (thin-film conductivity times film thickness). An error analysis justifies the simplification of the theoretical expression for the power-transmission coefficient to the form T= | 2/[2+(ωμ0/ | γ0|)σd] |2. Excellent agreement is obtained with experimental data taken from metal, semimetal, and semiconductor films.
Pressure Dependence of the Plastic Flow Stress of Alkali Halide Single Crystals
Authors: Davis L. A. , Gordon R. B.
Published: February 2004

The change in the plastic yield stress of alkali halide single crystals due to applied hydrostatic pressure has been measured. The pressure dependence of the yield stress (δσ/σ) ranges from ∼9×10−2/kbar in soft RbI to ∼0 in LiF. The experimental results suggest that in soft crystals point-defect generation and/or diffusion is effective in limiting dislocation mobility in the early stages of deformation, whereas in crystals hardened by irradiation or cold work, elastic interactions are rate limiting.
Computer Study of Bulk GaAs Devices with Random One-Dimensional Doping Fluctuations
Authors: Thim H. W.
Published: February 2004

Computer calculations have been performed in order to investigate the influence of one-dimensional random doping fluctuations and localized inhomogeneities on the performance of bulk GaAs oscillators. For the doping fluctuations assumed it was found that accumulation layers dominate in subcritically doped samples (n0×L<1012 cm−2) while dipole layers always form in samples doped above the critical level. Five different modes of oscillation are described and defined with the help of a mode chart. Special attention is paid to the ``quenched multiple-dipole'' mode, which is difficult to obtain if localized inhomogeneities such as dislocations or doping gradients are incorporated in addition to the random fluctuations. It is concluded that a series-connection of accumulation-mode devices, which are not sensitive to doping fluctuations, provides an attractive approach to microwave or millimeter-wave oscillator design.
Elastic Constants, Thermal Expansion, and Debye Temperature of Lead Telluride
Authors: Houston Bland , Strakna R. E. , Belson Henry S.
Published: February 2004

Measurements of the elastic constants and thermal expansion of PbTe have been made from 4.2° to 303.2°K. The extrapolated 0°K values for C44, (C11−C12)/2, and (C11+2C12)/3, respectively, are 1.514±0.009, 6.184±0.066, and 4.560±0.042×1011 dyn/cm2. At 303.2°K these values are 1.344±0.008, 5.016±0.057, and 4.107±0.037×1011 dyn/cm2. Intermediate values are presented graphically, as are the thermal-expansion data. The linear coefficient of thermal expansion is found to be 20.4±0.4×10−6/°C at room temperature. The 0°K Debye temperature is calculated to be 176.7°±0.5°K.
Calculation of the Elastic Constants of Alpha Quartz from a Model
Authors: Julian Carl L. , Lane F. O.
Published: February 2004

The elastic constants of alpha quartz are computed from a model due to Kleinman and Spitzer. The ratios of the calculated values to the values measured by McSkimin and co-workers are as follows: c11, 0.6; c12, 1.4; c13, − 3.0; c14, 1.5; c33, 0.4; c44, 0.7; c66, 0.5.
Effect of Neutron Irradiation on Copper Crystals at High Temperatures
Authors: Hulett L. D. , Baldwin T. O. , Crump J. C. , Young F. W.
Published: February 2004

Etching, x-ray topography, and electron-microscopy studies have shown that neutron irradiation at about 400°C produces a defect structure different from that produced by irradiation at ambient temperatures. On a macroscopic scale the damage was nonhomogeneous; there were regions containing high concentrations of defects separated by apparently perfect crystal. The size of the defect regions ranged from 10–100 μ, and the distance between regions was ∼100 μ. Borrmann topographs showed long-range order among the defect regions in that they tended to be aligned in habit planes parallel to (111) planes. Measurements of the absolute integrated intensities of Borrmann diffracted beams indicated that there must have been a large degree of elastic strain between defect regions. It has been shown that the defect regions were aggregates of large dislocation loops 1000–2000 Å in diameter, dislocation tangles of roughly the same dimension, smaller loops 50–150 Å in diameter, and three-dimensional point defect clusters 200 Å or less in dimension. The larger loops were principally interstitial, the smaller loops were principally vacancy type. The concentration of vacancies and interstitials within defect regions, as estimated from the loops and clusters, was 1.6×1018/cm3 and 2×1018/cm3, respectively, which averaged to about 3×1016/cm3 for the entire crystal. These high-temperature irradiation effects were somewhat independent of the state of perfection of the specimens; defect regions were observed in polycrystal as well as single-crystal specimens. Annealing of the high-temperature damage occurred nonhomogeneously between 500° and 800°C, a higher range than that for annealing damage produced at ambient temperatures. Defect regions remote from as-grown dislocations were annealed at the lower temperatures, while those near dislocations required anneals at 800°C.
Solution of Diffusion Problems
Authors: Ludloff Karl G.
Published: February 2004

In analogy to the kinematics of fluid mechanics, the principle of superposition of singularity solutions (sources, sinks, doublets, etc.) is applied to the solution of diffusion problems, involving various conditions. Due to the parabolic character of the diffusion equations in contrast to the elliptic (or hyperbolic) character of the equations of fluid mechanics, the fundamental concepts, like source, doublet, streamline, line of constant contamination, have to be rederived and illustrated. The composition of such singularity solutions, which must fulfill specific boundary conditions, leads to an integral equation, whose solution is indicated.
Optically Pumped Thin-Platelet Semiconductor Lasers
Authors: Johnson M. R. , Holonyak N.
Published: February 2004

Thin vapor-grown platelets of Cd(SeS) and thin platelets of GaAs and Ga(AsP) prepared from bulk wafers have been pumped as lasers with Ga(AsP) diode lasers used as the optical excitation sources. Continuous laser emission at 77°K in the visible spectrum has been obtained from thin Cd(SeS) platelets pumped with a cw He–Ne laser. Thin platelets of Cd(SeS) have been found to be essentially transparent to their own laser emission, and a mechanism responsible for laser action is discussed to account for this behavior. The mode and oscillator behavior of thin platelet II-VI and III-V lasers is discussed. Experimental effects due to many-body interactions of charge carriers in a III-V semiconductor platelet laser have been obtained; these are manifest in the shift of laser emission to longer wavelengths with increasing excitation under conditions of negligible crystal heating
Elastic Stiffness Coefficients of Single-Crystal Iron from Room Temperature to 500°C
Authors: Leese John , Lord A. E.
Published: February 2004

The three adiabatic second-order elastic stiffness coefficients of single-crystal iron are reported from room temperature to 500°C. The coefficients vary in a linear manner with temperature, as opposed to previous results where a departure from linearity took place above 300°C. It seems likely now that this previous behavior was due to the silicone fluid bond between the quartz transducer and the iron specimen, and not the specimen itself. The present work shows that vacuum-evaporated thin-film transducers of zinc sulfide can be used reliably at higher temperatures, in both the longitudinal and transverse modes. However, certain difficulties remain in making transducers to generate all the desired modes for elastic-constant measurements.
Controlled Easy-Axis Distribution in Magnetic-Film Elements
Authors: Oberg P. E. , Paul M. C.
Published: February 2004

Magnetic-film elements have been constructed with a controlled, continuously varying easy-axis direction across the elements. With linear angular dispersion characteristics, analog information storage elements so constructed display unusual reproducibility of analog states. The essentially two-domain storage state and well-defined separating wall are readily viewed using the Kerr magneto-optic technique. The high-speed analog record element demonstrates the capability of having a high linear density of information states.