bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetization reversal process in RCo5 particles and sintered permanent magnets
Authors: Searle Clark W. , Garrett Harold J.
Published: February 2004

A model relating the nucleation field for particles of R Co5-type permanent-magnet materials (R represents the rare-earth element) to domain wall energy is shown to describe all our experiments, and that it is also consistent with previously reported data for single-crystal particles and powders of SmCo5. The model is also consistent with sintered permanent-magnet data and suggest that a drastic reduction of oxygen pick up in the manufacturing process would greatly improve SmCo5 permanent magnets.
Measurement of the drift velocity of charge carriers in mercuric iodide
Authors: Minder R. , Majni G. , Canali C. , Ottaviani G. , Stuck R. , Ponpon J. P. , Schwab C. , Siffert P.
Published: February 2004

The time-of-flight technique has been used to determine the electron and hole drift velocities in mercuric iodide crystals. The electron mobility is constant up to fields of 30 kV/cm, equal to 100 cm2/V sec at room temperature, and proportional to T−0.9 in the temperature range 114–300 °K. The hole mobility is equal to 4 cm2/V sec at room temperature and exhibits a T−1.7 dependence between 140 and 240 °K and a T−3.7 dependence between 240 and 350 °K.
On the Čerenkov threshold associated with synchrotron radiation in a dielectric medium
Authors: Pogorzelski R. J. , Yeh C. , Casey K. F.
Published: February 2004

A formal exact expression for the radiation field of a charged particle executing a circular orbit in a dispersive dielectric medium is obtained by means of a dyadic Green's function approach. The field is expressed as an infinite sum of vector spherical harmonics. The radiated power P is computed numerically and a set of universal curves of nP/q2Ω2 vs n β is obtained where q is the charge on the particle, n is the index of refraction of the medium, Ω is the orbital angular velocity of the particle, and β=v/c, where v is the particle velocity and c is the speed of light in vacuum. The Čerenkov threshold phenomenon is shown to be manifest primarily in the high-frequency portion of the radiated spectrum. For an index of refraction of unity, the result is shown (at low velocities) to be identical with both Larmor's formula for the radiated power and Schwinger's result for the angular distribution of the radiation.
Composition-vs-depth profiles obtained with Auger electron spectroscopy of air-oxidized stainless-steel surfaces
Authors: Betz G. , Wehner G. K. , Toth L. , Joshi A.
Published: February 2004

Auger electron spectroscopy (AES) combined with simultaneous sputter removal of material from the sample (profiling) was used to determine changes in composition within surface layers (∼1000 Å) of stainless steels which were air oxidized at various temperatures. Oxidation of 304 stainless steel at temperatures up to 600°C results in the formation of an Fe-oxide layer with Cr and Ni appearing only deeper below the surface at the oxide-bulk interface. After treatment at 700°C the first signs of Cr-oxide formation near the surface begin to appear. At 900°C the Fe-oxide layer is replaced by a Cr-oxide film and becomes the dominant feature. Composition profiles for air-oxidized (at 900°C) 321 stainless steel and Inconel are also reported.
Photoconductivity in anodic Ta2O5 formed on nitrogen-doped tantalum films
Authors: Thomas J. H.
Published: February 2004

Photocurrent spectroscopy (or the spectral response of photoconductivity) and transient photoconductivity have been used to probe the defect structure (trap states) of anodic Ta2O5 films formed on pure and nitrogen-doped sputter-deposited tantalum. Results of this investigation indicate the presence of two trap-related responses at 1.5 and 2.8 eV, respectively. Nitrogen in the oxide is found to compensate these traps, that is, the amplitude of the photocurrent response is observed to decrease with increasing nitrogen concentration. The recombinationlike trap at 2.1 eV, present in pure Ta2O5, is not observed in samples doped with as little as 2 at.% N2. Transient results indicate a spatial localization of the 1.5-eV trap which may be related to the nonuniform nitrogen distribution in the oxide. Nitrogen in the oxide was found to have little effect on the band-gap energy (4.4 eV).
Reciprocity in xerographic photoconductors
Authors: Collins Leland F.
Published: February 2004

Xerographic photoresponse following complete carrier transit is considered for initial and bimolecular recombination. Field-dependent quantum efficiencies at long exposure time are calculated for a simple power-law dependence and with a nonthermal version of Onsager's recombination model. Flash illumination with exponentially absorbed light is analyzed via Langevin's bimolecular carrier annihilation description. Conditions are given for equality of photoresponse (reciprocity) at long and short exposure times.
Magnetic field profiles in type-II superconductors with pinning using a new ac technique
Authors: Rollins R. W. , Küpfer Heinz , Gey Wolfgang
Published: February 2004

A new ac technique is described which allows the experimental determination of the magnetic field profile near the sample surface in type-II superconductors with pinning. The technique, like a previous method of Campbell, depends only on the validity of the critical-state model and can separate the position and magnetic field dependence of the flux-pinning forces. The entire field profile is obtained from a measurement of the waveform of the response of the sample to a small ac magnetic field superimposed on the dc field. Profiles obtained in cold-worked Nb and Nb–Ti alloys are reported and the results compared with previous measurements. We have found that the critical-state model does not adequately describe the results obtained on the Nb–Ti alloys when the magnetic field is less than 0.5Hc2.
Method for measuring magnetic moments with precision
Authors: Mills Allen P.
Published: February 2004

The induction method for measuring magnetizations is reviewed briefly and it is shown that a simple modification in the usual coil geometry should allow the absolute measurement of the changes in the magnetic moment of a small sample. The time integral of the voltage induced in a long pickup coil is shown to be proportional to the volume integral of one component of the change in magnetization within the coil. Experimental procedures which would make use of this fact to attain accuracies of better than one part in 104 are suggested.
Thermal conductivity of pressure-induced recrystallized KCl
Authors: Jirmanus M. , Sample H. H.
Published: February 2004

The thermal conductivities of four specimens of pressure-induced recrystallized (PIR) KCl have been measured between 1.8 and 90°K. At the lowest temperatures, the conductivities of these compressively deformed specimens are lower than the single-crystal conductivity by as much as one order of magnitude. The reductions in conductivity for PIR KCl specimens are much smaller than are observed in hot-pressed CdS and MgF2 which have similar microstructures with large dislocation densities. Above T=50°K, the thermal conductivity for all the PIR samples is identical to the single crystal. Specific-heat measurements on one of the PIR specimens at 1.5 ≤T≤20°K are in excellent agreement with measurements on single crystals.
Field effects in nematic liquid crystals obtained with interdigital electrodes
Authors: Soref R. A.
Published: February 2004

New electro-optic effects in nematic liquid crystals have been found with a gratinglike array of in-plane interdigital electrodes. High-contrast light valving has been demonstrated in a tunable optical-activity mode and in two tunable birefringence modes. All three field-effect modes utilized a positive-dielectric-anisotropy nematic liquid crystal. Proposals are made for applying the interdigital technique to cholesteric, smectic, and mixed liquid-crystal systems. Experimental results indicate that the comb-shaped electrodes are valuable in a variety of display devices.
Infrared absorption of silicon isotopes in gallium phosphide
Authors: Kachare A. H. , Spitzer W. G. , Lorimor O. G. , Euler F. K. , Brown R. N.
Published: February 2004

Infrared absorption measurements at ∼80°K on 28Si- and (28Si+30Si)-doped GaP grown by liquid-phase epitaxy and compensated by electron irradiation are presented. Several new bands are observed with samples containing the mixed isotopes. The observed frequencies of 28Si-related bands agree with previously reported values, and the isotopic shifts for 30Si-related bands agree with values calculated from local mode theory. The results indicate that one band is attributable to a defect containing two Si atoms on nonequivalent sites, presumably nearest-neighbor substitutional pairs. The present measurements confirm the previous observations of a much larger concentration of pairs than that predicted by random statistics.
Steady-state theory of backward-traveling-wave parametric interactions
Authors: Andersson D.
Published: February 2004

We studied the steady-state parametric interactions of a three-wave system where one of the waves is a backward-traveling wave. This situation is shown to lead to complications not previously discussed. Analytical expressions are given for the intensity of the backward-traveling wave as a function of the pump wave intensity and of parameters characterizing the nonlinear medium. This result shows that backward-traveling parametric interaction is not quite so efficient an amplification process as suggested by a previous investigation.
Theory of solution strengthening of alkali halide crystals
Authors: Gilman J. J.
Published: February 2004

The solution strengthening of sodium and potassium halide crystals by dissolved alkaline earth atoms is accounted for quantitatively. Strengthening is associated with the change in electrostatic energy that occurs when a divalent ion-vacancy complex is sheared by a dislocation that passes through it. The model yields a hardening coefficient of 11 × 109 dyn/cm2 compared with the experimental value of 9.2 × 109 dyn/cm2.
Luminescence from acoustoelectric domains in CdSe
Authors: Macomber G. , Neudorfer M. , Yee S. S.
Published: February 2004

Bursts of electroluminescence were produced when a 50–500-ns excess voltage pulse was superimposed on the ``drive'' voltage which produced an acoustoelectric domain. The intensity of the luminescence was found to increase with the amplitude of the excess voltage and first increase then decrease as a function of the drive voltage. Self-illuminated photographs of the domains showed them to be ≈0.4 mm wide.
Decay of surface potential in electrophotography: Single-carrier case
Authors: Fox S. J.
Published: February 2004

The equations for the xerographic discharge of the potential are solved analytically by means of a flow line technique. The solution is for single-carrier discharge corresponding to charge generation using strongly absorbed light. Exact analytical solutions are given for two cases in which both the photoinjection efficiency and the mobility are field dependent, including the Poole-Frenkel effect. The surface potential V(t) and d V(t)/d t are calculated for specific cases, and the effect of variations in mobility, thickness, and injection rate are discussed. Under certain conditions the discharge can remain emission limited for all times. It is shown that a discontinuity in the conduction current exists at the transit time of the lead carriers, corresponding to the cusp in the constant-potential case when the current is space-charge limited.
High-pressure apparatus for simultaneous adiabatic and isothermal compressibility measurements: Data on argon to 13 kbar
Authors: Liebenberg D. H. , Mills R. L. , Bronson J. C.
Published: February 2004

A piston-cylinder apparatus was developed in which ultrasonic waves were transmitted into a high-pressure sample through the unsupported area of a Bridgman seal. The sound-wave transmission could be divided so that one portion returned from a fixed reflector in the sample, giving sound-velocity measurements, and the other portion returned from the piston itself, giving the relative volume of the sample. In this way, adiabatic and isothermal compressibilities could be measured simultaneously. Relative volumes were also determined from the piston travel, observed externally. A calibrated manganin gauge allowed pressures to be compared with those calculated from the ram force and hysteresis curve of the advancing and retreating piston. Data are reported for argon at room temperature up to about 13 kbar where it solidifies.
Effects of uniaxial stress on GaAsP red-light-emitting diodes
Authors: Share Stewart
Published: February 2004

GaAsP red-light-emitting diodes containing 40% phosphorus were stressed uniaxially in the [100] direction at 77 K. The spectral emission peak was observed to shift to higher energies at the rate of 2.1 ± 0.2 meV/kbar. From the stress dependence of the recombination current, the band-gap stress coefficient is 3.6 ± 0.3 meV/kbar. By using the fact that radiative recombination takes place via a band-acceptor (Zn) process, it is concluded that the acceptor level moves away from the valence band at the rate of 1.5 ± 0.4 meV/kbar. The intensity-voltage characteristic is consistent with the interpretation that the effect of the uniaxial stress is to deionize the acceptor level, which causes a smaller decrease of intensity with stress than would be expected from band-gap deformation alone. The effect of uniaxial stress on the indirect-direct conduction-band transition is discussed.
Amorphous bismuth-germanium thin films. I. Structural and electrical properties
Authors: Vass R. W. , Meininger M. A. , Anderson R. M.
Published: February 2004

Thin films of bismuth-germanium have been fabricated by the method of codeposit vapor quenching onto liquid nitrogen or water-cooled substrates. Structural, electrical, optical, and photoelectrical characterizations of these films have been accomplished. In this paper, Paper I of a two-paper series, the structural and electrical characterization results are reported. X-ray diffraction measurements indicate that a stable amorphous phase exists for the BixGe1−x thin-film system for 0 ≤ x ≤ 0.12. Low-field dc resistivity as a function of temperature from room temperature to liquid-nitrogen temperature and relative thermopower measurements show that in the amorphous range the BixGe1−x thin films are n-type semiconductors with a continuously decreasing thermal activation energy as x increases. The resistivity of amorphous bismuth-germanium films decreases with an increase in bismuth concentration. Current-voltage data taken on several films at 300 and 162°K indicate Ohmic behavior with no evidence of Poole-Frenkel, Schottky-barrier, or switching effects. A structural model for the amorphous bismuth-germanium system is proposed with covalent hybrid bonding of monoatomic bismuth to a Polk-Turnbull amorphous germanium random network. An energy-band density-of-states model is proposed based on the Weaire-Thorpe interpretation of the Polk-Turnbull network and considerations from the theory of heavily doped semiconductors. The proposed structural and energy-band models are utilized to explain the observed electrical and optical properties.
Theory for solute-vacancy binding energies in binary alloys
Authors: DuCharme A. R. , Straub G. K.
Published: February 2004

A pseudopotential theory for solute-vacancy binding energies is derived for binary alloys which includes effects of solute-solute interactions. Using this approach, small binding energies are calculated for impurity-vacancy interactions in dilute Al–Cu, Al–Mg, Al–Ag, and Pb–In alloys in close agreement with the results of previous high-temperature equilibrium experiments. Solute clustering is predicted by the model for higher concentrations of solute atoms in aluminum and lead.
Effect of OH− on the low-frequency dielectric constant of vitreous silica
Authors: Andeen Carl , Schuele Donald , Fontanella John
Published: February 2004

The 1000-Hz 300°K dielectric constant, εs, of 24 kinds of commercially available vitreous silica has been measured to an accuracy of 0.01% and a precision of about 1 part in 300 000 by the method of substitution (two-fluid technique). The observed dielectric constant ranges from 3.8073 to 3.8304. These results are correlated with hydroxyl ion content and other imperfections. It is found that εs=3.8073+2.72×10−22 N where N is the hydroxyl concentration in ions/cm3, and observed deviations from this rule are attributed to metallic impurities and inclusions. From the results it appears that 3.8073 closely approximates the low-frequency dielectric constant of pure vitreous silica.
Conversion of Si to epitaxial SiC by reaction with C2H2
Authors: Mogab C. J. , Leamy H. J.
Published: February 2004

The growth of β-SiC films on Si by reaction of a Si single crystal with C2H2 has been studied for the conditions 10−7 ≤PC2H2≤5×10−4 Torr, 800≤T≤1100°C, in both high- and ultrahigh-vacuum chambers. At C2H2 pressures below approximately 10−5 Torr, linear growth kinetics were observed over the temperature range investigated and the reaction probability was determined as 0.02–0.03. In this pressure range growth occurs by the diffusion of Si through porous defects incorporated in the growing film. We have studied in detail the structure of defected films formed under various growth conditions by scanning electron microscopy, scanning transmission electron microscopy, and transmission electron microscopy. We conclude that the occurrence of defects is intrinsic to the mechanism of film growth. The predominant defect type consists of a shallow (∼ 2000 Å) pit in the Si substrate, over which the growing SiC assumes a porous polycrystalline morphology. The number and areal densities of these defects are proportional to the C2H2 partial pressure and the SiC film thickness, respectively. The defects act as sources of Si for reaction, and film growth occurs via diffusion of Si from the substrate through the porous overgrowth to the epitaxial SiC/vacuum interface, where reaction occurs. For C2H2 pressures exceeding approximately 10−5 Torr the porous defects are sealed off at an early stage in the growth and further reaction is virtually arrested due to the extremely small bulk and/or grain boundary diffusivity for Si in SiC over the experimental temperature range. No significant effect on growth rate due to the type of vacuum system used was found.
Identification of interstitial- and vacancy-type dislocation loops in ion-implanted silicon
Authors: Wu Wei-Kuo , Washburn Jack
Published: February 2004

A quick method of distinguishing between vacancy-type and interstitial-type dislocation loops is described which is applicable to foils near <111> orientation and loops in the size range which gives rise to double-arc contrast. This method utilizes the Kikuchi line pattern and some general rules concerning electron diffraction contrast from small loops. With this method, small prismatic loops in As+-implanted silicon have been shown to be of interstitial type.
Continuum descriptions of dislocations under stress reversals
Authors: Kelly James M. , Gillis Peter P.
Published: February 2004

A general continuum theory of dislocation motion is used to investigate the response of crystalline solids to cyclic straining in uniaxial tension and compression. For macroscopically homogeneous deformation under uniaxial stress a simple one-dimensional equation suffices to relate the plastic strain rate to dislocation flux. The material is characterized by evolutionary equations for multiplication of dislocations and for immobilization of moving dislocations. Some simple example materials are considered and it is shown by numerical calculation that these exhibit respectively a Bauschinger effect, isotropic hardening, and isotropic softening when subjected to a program of alternating strains at a constant rate.
Electrohydrodynamic capillary source of ions and charged droplets
Authors: Krohn V. E.
Published: February 2004

A semiquantitative treatment predicts that when an electrohydrodynamic capillary source produces metal droplets along with the ions that are generally observed, the charge-to-mass ratio will reach a maximum and the radius a minimum at about the radius at which the limit of stability against breakup into smaller drops (Rayleigh limit) becomes equal to the limit of stability against the field evaporation of ions. The maximum charge-to-mass ratio was found to be [inverted lazy s] 17 000 C/kg for a eutectic mixture of lead and bismuth. The semiquantitative treatment, which is supported by this experimental result, predicts that the ions should be emitted from a liquid tip having a radius of about 10 Å. It is suggested that if the wobble of the tip is not too great, this type of source should have applications in ion microprobes.
Thermionic emission from the Si/Cs/O (100) surface
Authors: Martinelli Ramon U.
Published: February 2004

Thermionic emission from the Si/Cs/O (100) surface has been investigated. Identical emission characteristics are seen from both n- and p-type bulk samples, implying that the emission arises from the surface region of the crystal. Adsorbed hydrogen accelerates the decay of thermionic emission. From the temperature dependence of the thermionic current, the temperature-independent portion of the work function φ0 is found to be 1.06 eV.
Theoretical analysis of thermally controlled switching in thin glass films
Authors: Schuöcker D.
Published: February 2004

The performance of the new four-electrode glass switch device that has been described in recent papers is theoretically analyzed. Its theory is based on the assumption of coupling by heat conduction between two planar glass-switch diodes that are separated only by a narrow gap. In addition, a thermal breakdown mechanism in both switch diodes is assumed. The solution of the equation of heat conduction yields a mathematical description of the most important electrical qualities of the device, such as the conditions for triggering by voltage and by current pulses, the delay time of the triggering process, and coupling between both diodes in the on state. The results of the analysis agree well with experimental data and thus support the validity of the thermal model in this special case.
Stimulated Brillouin scattering in shock-compressed fluids
Authors: Bloom G. H. , Keeler R. N.
Published: February 2004

We have demonstrated that stimulated Brillouin scattering can be used to measure the velocity of sound in shock-compressed fluids with 1% precision. We have constructed a ruby laser which can be triggered by a Pockels cell as the shock wave reaches a predetermined point in the sample. The primary limit of accuracy is the lack of precise data for the refractive index at higher pressure. We have also measured the shock velocity U s in terms of the material velocity U p. The data have been fitted to the relation Us=1.4932+1.9615Up+0.0750Up2 km/sec for water below 15-kbar shock stress.
Hot-electron magnetic susceptibility of degenerate semiconductors at low temperatures
Authors: Pal Bishnu P. , Sharma Satish K.
Published: February 2004

An analytical investigation of the effect of a dc electric field on the magnetic susceptibility of conduction electrons in a degenerate semiconductor at low temperatures has been made. From energy balance considerations, the electron temperature (Te) as a function of the strength of the dc electric field has been determined. Ionized impurity scattering has been assumed to be the dominant momentum relaxation process; the energy loss has been attributed mainly to the scattering by acoustic phonons (via both screened deformation and screened piezoelectric potentials), and by polar optical phonons. Numerical results have been presented for a typical case of an n-type InAs sample for fields up to 10 V/cm. It is found that susceptibility decreases with increasing field strengths. The plot of susceptibility (χ) as a function of dc electric field (E) leads to a kink at a field strength of about 450 mV/cm. This is explained on the basis of the spontaneous emission of polar optical phonons. It is further suggested that the measurement of susceptibility may be usefully employed as a tool for investigation of hot-electron phenomena.
Preparation and properties of CdSnP2/InP heterojunctions grown by LPE from Sn solution
Authors: Shay J. L. , Bachman K. J. , Buehler E.
Published: February 2004

Heterojunctions of n-type CdSnP2 on p-type InP substrates have been prepared by LPE from Sn solutions. The tipping arrangement, solution composition, and temperature program for the preparation of high-quality LPE layers are described. Heterodiodes prepared from such LPE wafers electroluminesce under forward bias at wavelengths near 1.6 μ with internal quantum efficiencies approaching 2% at room temperature. When used as photovoltaic detectors, the quantum efficiency of these diodes surpasses that of Si for λ>1.09 μ and exceeds 1% for all wavelengths between 0.96 and 1.3 μ.
Internal stresses due to magnetic wall junctions in a perfect ferromagnet
Authors: Kléman M.
Published: February 2004

Magnetic walls, as far as we are concerned with the internal stresses they produce, are Somigliana singularities. In this paper these internal stresses are completely calculated, as well as the lattice curvatures (bend twist) to which these walls give rise in the case of a junction of several walls. It is possible to separate in these elastic fields effects due to a quasidisclination located along the junction (mixed wedge and twist character) and effects due to a distribution of quasidislocations on the walls.
Superconductivity in Al films deposited on quartz and poly (n-vinylcarbazole) at 4.2°K
Authors: Russell T. J. , Jones M. E. , Johnson A. C. , Deck R. J. , Hermann A. M.
Published: February 2004

Aluminum films have been evaporated from Al2 O3 boats onto cold substrates (4.2°K) of z-cut crystalline quartz and an amorphous polymer, poly(n-vinylcarbazole) (PVK), and the critical temperatures have been measured resistively. Critical temperatures are enhanced above the bulk critical temperature. The maximum Tc's are 5.3°K on quartz and 4.7°K on PVK. The rather large enhancement is attributed to the use of the Al2 O3 boats.
X-ray diffraction in crystals of intermediate perfection. I. Calculation of the integral diffracted power for flat and curved crystals in symmetrical Bragg geometry
Authors: Brown D. B. , Fatemi M.
Published: February 2004

A method for the treatment of x-ray extinction and absorption is developed for thick flat crystals in symmetrical Bragg geometry and for curved crystals in symmetrical Bragg geometry where the diffraction region may be approximated as a thin crystal in Laue geometry. This method permits the calculation of diffracting power vs wavelength. The crystals may have the full range of properties between the ideally imperfect and perfect cases. The parameters describing the mosaic blocks (mosaic block size and mosaic block misorientation) are related to the dislocation arrangement for crystals of Zachariasen's type I (where extinction is primarily controlled by the mosaic block misorientation). It is indicated that for crystals of type II (where extinction is primarily controlled by the mosaic block size) the mosaic blocks are usually due to defects other than dislocations.
Transport properties of bismuth films
Authors: Inoue Masasi , Tamaki Yukio , Yagi Hisao
Published: February 2004

Glass-coated bismuth films were deposited onto a glass substrate at room temperature and their Hall coefficients and electrical resistivities were measured between 77 and 300°K. Scanning electron micrographs revealed that the films prepared in this way were more polycrystalline than those deposited onto a heated mica substrate. Interesting features were found in the temperature dependence of the Hall coefficient: the thinner films with thickness t <500 Å were p type at higher temperatures and became n type below a critical temperature Tc, where Tc increased with the increase in t, whereas the thicker ones with t >500 Å were always n type over the temperature ranges studied. Hall mobility and magnetoresistance data are also presented here and the experimental results are discussed qualitatively.
Insulated linear antenna: Theory and experiment
Authors: King R. W. P. , Lee K.-M. , Mishra S. R. , Smith G. S.
Published: February 2004

The applications and theories of the insulated dipole and monopole are reviewed. A recent analysis of the insulated antenna in a relatively dense ambient medium is summarized and its predictions are shown to be in good agreement with an extensive new set of measurements of the distributions of current and charge and the driving-point admittances of air-insulated antennas in fresh and salt water. Four different thicknesses of insulation and lengths up to one wavelength are used. The attenuation due to radiation into fresh water is comparable with and even exceeds the attenuation due to dissipation in salt water. It increases with decreasing radius of the insulating cylinder. The effect of the junction between the feeding coaxial line and the insulated antenna is discussed.
Behavior of above-gap NN pair states in radiative recombination in GaAs1−xPx : N+ (x=0.24, 77°K)
Authors: Lee M. H. , Holonyak N. , Campbell J. C. , Groves W. O. , Craford M. G.
Published: February 2004

Photoluminescence and laser data (77°K) are presented, clarifying the role of the NN pair states in above-gap radiative transitions. Heavily Te-doped (1019/cm3) and N-doped (≳ 1019/cm3) x=0.24 vapor phase epitaxial GaAs1−xPx samples are prepared to ensure a large doped-in supply of electrons in NN pairs states. Identical samples, but without N+ doping (N+-doped layer etched off), are examined for comparison. Nitrogen-free samples lase at energies as high as 60 meV above Eg(Γ); the N+-doped samples lase at significantly higher threshold and at energies hv≲Eg(Γ), where resonance enhancement is large. The addition of Zn (via diffusion) to convert the n-type N-doped crystal to p type removes the built-in electron supply from the NN pair states and permits laser operation on the donor band tail at relatively low energy and low threshold, which shows that the N impurity does not damage the crystal. While the N trap is most useful in GaAs1−xPx in the region near the direct-indirect transition (x≡xc≈0.46, 77°K) and in the indirect range (x > xc), these and related data indicate that the N trap detracts from the radiative recombination process in the direct range (x≪xc).
Spontaneous power and the coherent state of injection lasers
Authors: Sommers H. S. , North D. O.
Published: February 2004

A proposed relation between spontaneous and coherent properties of injection lasers is applied to several published results. On experimental and theoretical grounds it is shown that the parameter 1+X, the ratio of conventional gain coefficient to prorated loss for the strongest cavity mode, can be determined from the spontaneous emission. Over a limited range above unity, 1+X is the ratio of spontaneous intensity at the operating point to its value at threshold. This supplies a needed experimental connection between spontaneous studies at frequencies higher than the lasing band and the coherent properties. Published data of the current dependence of spontaneous emission are discussed in this framework, and the information needed to intercompare their internal state is pointed out. In general, fundamental differences in laser dynamics should be evidenced by radically different values of the critical parameter P* of the nonlinearity associated with the power dependence of X. All published values of P* are of order 5 mW per cavity mode, as predicted, indicating a similarity in the nonlinearity for quite different types of material. The recent observation that P* is independent of facet area gives strong support to the idea that the source of the nonlinearity is saturable optical absorption in a strongly interacting system.
Parametric experimental and theoretical study of a cold-cathode electron-beam-controlled CO2 laser
Authors: Hoffman J. M. , Bingham F. W. , Moreno J. B.
Published: February 2004

This paper presents parametric studies of the performance of a 10-liter atmospheric-pressure CO2 laser system controlled by a 4-μsec pulse of electrons from a cold-cathode gun. The experimental results are compared to the predictions of a theoretical model described in this paper. For various laser gas mixtures and values of E/P the peak small-signal-gain coefficients range up to 4.7% cm−1. Measurements of gain uniformity across the laser medium and of the time dependence of the small-signal gain are also presented. Operation of the device as an oscillator over a range of parameters has shown that the output pulse typically consists of a sharp gain-switched spike followed by a longer tail with energies up to 30 J in the spike and 200 J in the entire pulse. The theoretical model generally predicts peak small-signal gain well for gas mixtures containing nitrogen; the largest discrepancy is for pure CO2 gas. The model also predicts the shapes of oscillator pulses satisfactorily.
Influence of deep traps on the measurement of free-carrier distributions in semiconductors by junction capacitance techniques
Authors: Kimerling L. C.
Published: February 2004

A generalized model is developed for the electronic behavior of deep traps in a p-n-junction depletion region. The depletion region is shown to consist of two parts: (i) a space-charge region which is totally depleted of free carriers and (ii) a transition region which is only partially depleted. The influence of this junction structure on free-carrier profiling measurements is considered in detail for donor and acceptor traps with both homogeneous and inhomogeneous spatial distributions. Experimental observations of deep-trap distributions produced by proton bombardment of n-type silicon are analyzed within the framework of the model. Implications of the model in the measurement of junction capacitance transients and photocapacitance are considered in Appendices A-C.
Nonuniform current distribution in the neighborhood of a ferromagnetic domain wall in cobalt at 4.2 K
Authors: Partin D.L. , Karnezos M. , deMenezes L.C. , Berger L.
Published: February 2004

It is shown theoretically and experimentally that the current density is not uniform in the neighborhood of a 180 ° domain wall, in a pure ferromagnet traversed by an electric current at low temperature. The effect is caused by the abrupt reversal of the internal field B=Ms across the wall, and by the corresponding gradual reversal of the Hall electric field. In a noncompensated ferromagnetic metal (Co, Ni) in the high field limit ωcτ≫1, domain walls would act as if they were electrically insulating; the current could cross the wall only through a small ``hole'' located at one end of the wall, creating an infinite current density there. A cobalt single crystal of limited purity (R300/R4.2 = 65) was cut in the shape of a thin slab normal to the c axis. One-half of the slab is magnetized to saturation in the c direction and the other half is magnetized in the opposite direction, thus simulating one domain wall. When a dc current crosses the wall, the current density is found to be larger at one end of the wall than at the other end in a ratio of 1.7, in agreement with predictions. Current density is monitored locally with pairs of voltage probes. The magnitude and sign of the effect is consistent with ωcτ = 0.18 and electronlike carriers.
Film thickness and grain size diameter dependence on temperature coefficient of resistance of thin metal films
Authors: Singh Awatar
Published: February 2004

The combined effect of film thickness and grain size diameter on the temperature coefficient of resistance of a uniform continuous polycrystalline metal film of thickness greater than the intrinsic mean free path has been theoretically investigated. It has been found that the value of the temperature coefficient of resistance decreases with decrease in grain size. For very small grain size it is less than the bulk value and may be negative in some cases, whereas for very large grain size and film thickness it approaches the bulk value.
Energy stored in wall deformation during motion of magnetic domain walls
Authors: Baldwin John A. , Milstein Frederick
Published: February 2004

The energy stored in deformation of a steadily moving domain wall, Wd, is calculated. For a tape sample, Wd per unit area of wall is found to be more than twice the intrinsic energy per unit area of the undistorted wall, σw. This result raises the question of whether it is meaningful to speak of the wall energy density in a thin film when the stored energy may fluctuate drastically.
Thickness of 90° ferroelectric domain walls in (Ba,Pb)TiO3 single crystals
Authors: Dennis M. D. , Bradt R. C.
Published: February 2004

90° ferroelectric domain boundaries were observed by direct transmission electron microscopy in single crystals of pure BaTiO3 and (Ba,Pb)TiO3 solid solutions. Domain-wall thickness measurements were made from electron image plates by a densitometer-trace-curve-fitting technique. Boundary widths varied from 50 to 150 Å. These results are compared with theoretical estimates of 90° domain-wall thicknesses and correlated with the relative purity levels of the crystals. The temperature variation of the 90° wall thickness is reported for the (Ba,Pb)TiO3 solid solutions.
Diffusion coefficients varying with a power of the concentration: Convenient solutions and a reexamination of Zn in GaAs
Authors: Blanc Joseph
Published: February 2004

Diffusion, at constant surface concentration, with coefficient varying to the positive nth power is considered. It is shown that the diffusion equation for these cases has a unique solution whose leading term is concentration ∝Z1/n, where z = 1−(x/x+), x being the distance from the surface and x+ the distance at which the concentration just reaches zero. Numerical solutions can be obtained by standard methods of solution; explicit expressions are given for n = 1, 2, and 3. It is also shown that plots of log(concentration) versus logz give rapid reliable estimates of n from usual diffusion profiles. These methods are applied to previously analyzed data for diffusion of Zn in GaAs at 1000 °C. This reanalysis suggests that (i) the diffusion coefficient for Zn in GaAs is accurately given by the ``interstitial-substitional'' mechanism at the surface of GaAs, (ii) for surface concentrations of Zn⪞5×1019 cm−3, the diffusion is influenced by a limited flux of gallium vacancies from the surface, and (iii) the diffusion coefficient for gallium vacancies is roughly 5×10−9 cm2/sec at 1000°C. It is suggested that ``double'' profiles, often found for surface Zn concentration ⪞1020 cm−3, are due to dual vacancy sources: the free surface and a dislocation net occurring at positions of large Zn gradient.
Piezoelectric method of determining torsional mechanical damping between 40 and 120 kHz
Authors: Robinson W. H. , Carpenter S. H. , Tallon J. L.
Published: February 2004

The torsional composite oscillator enables the mechanical damping, the strain amplitude, and the shear modulus of a specimen to be determined quickly and accurately, making it a powerful technique for measuring transient phenomena. In this paper the equivalent circuit for the composite oscillator is derived, and the resulting formulas for the mechanical damping and strain amplitude are confirmed by various alternative methods of calibration. Experimental arrangements and procedures are described which indicate how this technique can be used for strain amplitudes ranging from 10−12 to 10−3.
A new mechanism for the formation of growth spirals
Authors: Li Chou H. , Wang Franklin F. Y. , Gupta Kedar P.
Published: February 2004

A new mechanism is proposed to explain the formation of growth spirals in controlled melt-grown crystalline samples of Ba4SrNb10O30. Several distinguishing features of these spirals cannot be explained on the basis of the classical core-first growth theory. These features are examined in detail, especially in comparison with the inherent or implied features of the classical spiral model. Characteristics of the spirals are predicted based on solidification theory and are found to agree with the observed results.
Vibrational modes in (Pb,La)(Zr,Ti)O3 ceramics
Authors: Lurio Allen , Burns Gerald
Published: February 2004

Results are presented for the Raman spectra, the far-infrared reflectivity spectra, and the radio-frequency dielectric constant of several selected PLZT ceramics. Vibrational modes are assigned by comparing these results with previous Raman and infrared measurements on single-crystal PbTiO3, and the PZT and PLT mixed ceramic systems. The mode responsible for the temperature variation of the low-frequency dielectric constant was not observed but is shown to be below 65 cm−1.
Calculations of discharge initiation in overvolted parallel-plane gaps
Authors: Kline Laurence E.
Published: February 2004

The spatiotemporal development of electron and positive-ion densities, electric field, and luminosity are calculated for electron-pulse experiments in parallel-plane gaps by numerically solving continuity equations together with Poisson's equation. Experimental coefficients for electron transport, cathode photoemission, and gas photoionization are used. The results show that anode- and cathode-directed ionizing waves, or streamers, develop from the electron-pulse-initiated avalanche when it reaches midgap, and produce a weakly ionized plasma. Both filamentary plasmas and uniform plasmas that fill the interelectrode volume have been experimentally observed. Calculated and experimental streak photographs agree well in both cases. In filamentary discharges, a return ionizing wave also propagates from the anode when the anode-directed wave arrives. The results show that electrons must be present ahead of the wave for cathode-directed wave propagation. These electrons are supplied by photoionization, photoemission, or both depending on the experimental conditions.
On the nature of conduction and switching in SiO2
Authors: Shatzkes M. , Av-Ron M. , Anderson R. M.
Published: February 2004

Further experimental results are presented concerning high conduction and switching in Al–SiO2–Si sandwich structures. The high-conduction state is filamentary and is governed mainly by the voltage across the sandwich. It is relatively insensitive to variations in device geometry. Periodic current oscillations are observed for certain combinations of series load resistance and applied voltage. Once the high-conduction state is achieved, it can be maintained at applied voltages below the one required to cause the transition but larger than a minimum voltage, which may be related to the minimum ionization energy in SiO2. Fluctuations are observed that depend on external circuit configuration, i.e., the load line, and on the ambient temperature. It is shown that a two-branched current-voltage characteristic can account for the observed behavior. A physical model is presented in an attempt to provide a qualitative explanation of the origin of this form of characteristic. Local damage is evident whenever the high-conduction state is seen (even with a single 50-nsec pulse). Electron microscopic analysis of a damaged region is presented.
Initial stages of hydrodynamic expansion of plasma heated by intense laser radiation
Authors: Nguyen Duc-Long , Parbhakar Kanwal J.
Published: February 2004

The hydrodynamic equations describing the average behavior of a one-dimensionally expanding plasma heated by laser radiation are solved analytically. For the small parameter approximation, the hydrodynamic expansion depends on the parameter (16P/9Ml02)1/3τL, where P is the laser power, M is the plasma mass, l0 is the initial plasma length, and τL is the laser pulse duration. With τL=τei, the electron ion relaxation time, it is possible to compute φmax (≈5.6×10−6n04l03miT−9/2, where mi is the plasma ion mass and T is the temperature), the maximum flux density below which the hydrodynamic expansion may be neglected. We find that a 5-kJ 75-ns neodymium glass laser is capable of acheiving break-even conditions for a 50% mixture of deuterium-tritium gas.
Experimental study of igition and propagation of laser-supported detonation waves
Authors: Maher W. E. , Hall R. B. , Johnson R. R.
Published: February 2004

Laser-supported detonation waves have been studied with 15-J 56-MW/cm2 laser pulses from a CO2 Marx Bank laser. A smooth spatial and temporal laser beam profile was repeatable from pulse to pulse. Ignition thresholds for laser-supported detonation waves were determined from relative reflected power and from framing camera photographs for many solid and liquid surfaces. Some of these thresholds were measured as functions of density of the medium (air) from 0.01 to 1 times atmospheric density. The velocities of laser-supported detonation waves were studied to determine their dependence on laser beam intensity and medium density for conditions above the ignition thresholds of aluminum and lead surfaces. Streak camera photographs displayed clearly defined wavefronts whose initial velocities were constant until they were affected by decreasing laser beam intensities. When the temporal intensity changes in the beam and its focused geometry are included in calculations using the Raizer model for laser-supported detonation waves to predict the wavefront motion, excellent agreement with the streak camera photographs was found. The initial velocity data are shown to agree with a power law in which velocity is proportional to (intensity/medium density)0.41±0.02. No explanation is proposed for the difference of the power law exponent from the 1/3 value predicted by the Raizer model.
Resonant-piezoelectro-optic light modulation
Authors: Weil Raoul , Halido David
Published: February 2004

Experiments were performed on the modulation of CO2 laser radiation (10.6 μ) at the piezoelectric resonance frequencies of a GaAs sample. The GaAs crystal length was 5.09 cm in the [11̄0] direction with a cross section of 0.291 cm [110] × 0.278 cm [001]. Experimentally, one shear and two thickness vibration modes were observed. The voltages to yield half-wave retardation by means of the piezoelectro-optic effect were found to be 4.15 V at the shear resonance frequency (736.900 kHz) and 15.4 and 51.0 V at the first (675.800 kHz) and second (1019.130 kHz) thickness resonance frequencies, respectively. The bandwidths were in the range 30–100 Hz. When the electro-optic modulation scheme is used instead of the resonant piezoelectro-optic modulation scheme, 5.2 kV are required to obtain half-wave retardation with the same sample. The shape of the sample precluded analytically solvable models for the observed phenomena. However, approximate models yield reasonable order-of-magnitude agreement with the observed values.
Anomaly of skin effect of single-crystal copper in the millimeter-wave region at room temperature
Authors: Tischer Frederick J.
Published: February 2004

Measurements of the surface resistance of plane surfaces of single-crystal copper carried out at 35 GHz indicate the existence of an anomalous skin effect at room temperature. The surfaces were prepared in stress-free processes, annealed, and manipulated in purified hydrogen and argon.