bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature dependence of the band gap and comparison with the threshold frequency of pure GaAs lasers
Authors: Camassel J. , Auvergne D. , Mathieu H.
Published: February 2003

Recent measurements of the lasing energy as a function of temperature in high-purity GaAs lasers have attempted to investigate the relation between this energy and the one-electron band gap. Because of a lack of precision in the position of the band gap at high temperature, these measurements show strongly conflicting results. In this work, we report two sets of differential reflectivity measurements (electroreflectivity and piezoreflectivity) performed on GaAs under high-resolution conditions. Both series of results give for the excitonic absorption edge at room temperature a value E0=1.424±0.002 eV which is about 20 meV higher than the lasing energy reported for the highest-purity GaAs samples. This result confirms that the lasing energy in GaAs is well below the one electron band gap. In addition, we show that this energy separation is an increasing function of temperature. Finally we discuss a simple model of band-to-band recombination including electron-electron interaction effects and we show that it permits calculation of a temperature dependence of the lasing line in the range 80–300 °K which is in good agreement with the experiment.
Field effect in amorphous germanium
Authors: Malhotra A. K. , Neudeck G. W.
Published: February 2003

The change in conductance of an amorphous germanium film due to a transverse electric field was observed. The films were electron-beam vacuum deposited at controlled rates onto Si-SiO2 substrates and then annealed in situ. The field effect is considerably smaller than that observed in amorphous silicon. However, the analysis of the data indicates that the density of localized state near the Fermi level is about 1021/cm3 eV and increases with energy away from the Fermi level. The films deposited at low rates on 23 °C substrates are n type, whereas the films deposited at similar rates onto hot substrates behave as p type.
Dynamic coupling characterization of TEM00 Nd : YAG lasers
Authors: Rice R. R. , Teague J. R. , Jackson J. E.
Published: February 2003

Experiments have been performed to test the simple linear and single transverse mode dynamic coupling models for a TEM00 Nd : YAG laser. An empirical power series model is presented and demonstrated. A novel intracavity variable output coupler useful for laser characterization is described.
Dislocation and impurity effects in smectic-A liquid crystals
Authors: Pershan P. S. , Prost J.
Published: February 2003

The effects of dislocations and impurities on the macroscopic elastic properties of smectic-A liquid crystals are discussed. The first conclusion is that smectics behave like linear elastic media only so long as the stresses are smaller than some critical value that is analogous to the critical velocity of a superfluid. Below the critical stress, smectics can store elastic energy without flowing and consequently without any dissipative processes in analogy with the fact that, below a critical velocity, superfluids store kinetic energy without any dissipation. For most practical samples the critical smectic stress is that value for which pinned dislocation will grow unstable; however, for ideal samples, initially free of dislocations, the critical value is determined by the condition of unstable growth of thermally generated dislocation loops. In the linear elastic region both dislocations and impurities modify the macroscopic elastic properties such that the effective elastic constant is smaller than the value for an ideal sample. This is a sort of diaelasticity and can be discussed in the same way as diamagnetism. Impurities are shown to act as sources of stress fields analogous to the way magnetic dipoles and magnetic monopoles are sources of magnetic fields. The result is to predict long-range elastic interactions between impurities in smectic systems. Since biological systems like chloroplasts and retinal rods have lamellarlike structures that are similar to the smectic structure, there is the possibility that long-range elastic interactions may play some role in biological function.
Ferroelectric and optical properties of lead potassium niobate
Authors: Nakano Jun’ichi , Yamada Tomoaki
Published: February 2003

Ferroelectric, optical, and other related properties of single crystals of lead potassium niobate (PKN) have been measured. This crystal is pulled from a melt and the Curie temperature is 450±10 °C. PKN belongs to the orthorhombic system with space group C142v-Cm2m at room temperature and it is considered to be isomorphous with PbNb2O6 which has the tungsten-bronze structure with its spontaneous polarization perpendicular to the tetragonal c axis. From the measured temperature dependence of refractive indices and the obtained values of electro-optic coefficients, it is concluded that the ferroelectric and optical properties of PKN are similar to those of other oxygen-octahedra ferroelectrics except PbTiO3 and PZT, although PKN contains Pb as a constituent element.
High-temperature elastic moduli of polycrystalline silicon nitride
Authors: Fate W. A.
Published: February 2003

Elastic constants are reported for several polycrystalline silicon nitrides with densities between 2.37 and 3.18 g/cm3 in the temperature range 0–1000 °C. The density dependence of the elastic constants is in approximate agreement with the prediction of a theory of composites.
Correlation and convolution of bulk acoustic waves in nonpiezoelectric solids
Authors: Bridoux E. , Rouvaen J. M. , Bruneel C. , Torguet R.
Published: February 2003

Nonlinear interactions between collinear bulk acoustic waves of orthogonal polarizations have been used to perform convolution and correlation in a nonpiezoelectric crystal. The analysis of the device operation and experimental results are reported.
Piezoelectric effect in tetragonal crystals
Authors: Adhav R. S.
Published: February 2003

The piezoelectric constants d14 and d36 and the relative dielectric constants of single crystals of KDP isomorphs are presented here. It is found that these constants depend upon the size of the anion. The constant d36 is the highest among this group for the crystal CsDA.
A note on Levine’s model of Schottky barriers
Authors: Rhoderick E. H.
Published: February 2003

It is shown that Levine’s model of a Schottky barrier can be extended to take into account the charge on the surface of the metal without any major change in his conclusions. When modified in this way, Levine’s analysis is equivalent to other analyses of Schottky barriers.
Gallium arsenide p+-ν diodes under hydrostatic pressure
Authors: Holzapfel W. B. , Queisser H. J.
Published: February 2003

The current-voltage characteristics of GaAs p+-ν relaxation-case diodes are investigated at hydrostatic pressure up to 18 kbar. The results eliminate an explanation of the controversial sublinear forward characteristics by means of a valley-transfer mechanism but do not disagree with the model of majority-electron depletion caused by hole injection.
Combined ac and dc thermocurrent measurements to study molecular relaxation and electrical phenomena in polyvinylidene fluoride films
Authors: Abkowitz M. , Pfister G.
Published: February 2003

ac currents, measured at discrete bias frequency, and dc thermocurrents, measured at discrete heating rates, both experimentally recorded as a continuous function of temperature have been carried out in parallel on commerical polyvinylidene fluoride (PVF2) films. Combined analysis of these measurements in a framework which relates frequency in an ac experiment to heating rate in a TC measurement allows us to characterize both the αa and αc molecular relaxation processes over the nine orders in frequency extending down to 10−4 Hz. The relatively broad distribution of relaxation rates underlying the αa process, in particular, is shown to be manifest in the associated current peak linewidth. The electrical properties above 100 °C and the relative amplitudes of the current peaks associated with the αa and αc relaxations are shown to be sensitive to the film’s thermal and field exposure history in situ. The time-dependent response of ac conductivity to applied electric field is described. Thermal cycling of films which had previously suffered a decrease in conductivity due to electric field exposure reveals the conditions under which that effect can be reversed.
Effect of dislocations on green electroluminescence efficiency in GaP grown by liquid phase epitaxy
Authors: Brantley W. A. , Lorimor O. G. , Dapkus P. D. , Haszko S. E. , Saul R. H.
Published: February 2003

The origins of dislocations in GaP grown by liquid phase epitaxy (LPE) and their effects upon green electroluminescence (EL) efficiency have been investigated by chemical etch pitting and scanning electron microscopy. Under normal growth conditions, the dislocation etch pit density (ρD) and configuration in the epitaxial layers are controlled by, and are approximately the same as, that in the liquid encapsulated Czochralski substrate. All dislocations which are revealed by chemical etching in the p LPE layer cause a localized reduction in luminescence. The dislocations are shown to behave as regions of rapid (nonradiative) recombination. Typically, reductions of a factor of ∼2 in green EL efficiency occur when ρD for the LPE layers is in the ∼2–5×105 cm−2 range, corresponding to an average separation of about two to four diffusion lengths in this material. The experimental results are supported by a simple theoretical model for the effects of dislocations on EL efficiency. These considerations explain why dislocations in GaP LPE layers for red light-emitting diodes (LED’s), in contrast to green LED’s, typically have no significant effect on EL efficiency since diffusion lengths are much shorter (≲2 μm) in the red LED’s.
Striped GaAs lasers: Mode size and efficiency
Authors: Hakki B. W.
Published: February 2003

The stimulated efficiency of the fundamental mode and its beamwidth along the junction plane are calculated for GaAs double-heterostructure (DH) stripe-geometry lasers in a self-consistent analytical model. Carrier diffusion along the junction plane creates a gain profile which acts as the guiding mechanism for the propagating mode. The size of the mode and the diffusion-governed gain profile are the two interdependent parameters that enter into the characteristic equation whose solution determines the lasing threshold. The analytical results obtained indicate that the beamwidth is almost linearly related to the carrier diffusion length and stripe width. The minimum beamwidth obtainable for zero stripe width is ?1.3 times a diffusion length. The calculated waveguide loss, due to absorption in the unpumped region, increases with reduced stripe width. This mode loss is 5–7 cm−1 for 10–12-μm-wide stripes, in agreement with experiment. Due to the increased waveguide loss the predicted external efficiency decreases and the lasing threshold current density increases with decrease in stripe width. The increase in threshold is due not only to carrier loss by diffusion but also to the increase in absorption loss at reduced stripe width.
Optical waveguides in ion-implanted ZnTe
Authors: Valette Serge , Labrunie Guy , Lizet Jacques
Published: February 2003

Two-dimensional optical waveguides have been implanted in a compound semiconductor, zinc telluride (ZnTe), using protons and boron ions. Propagation constants of Te0 and TM0 modes have been measured for several doses of implantation, in the visible (λ=6328 Å). Losses in the range 1–3 dB/cm are observed in these first experiments, without any thermal annealing.
A highly sensitive reversible and nonvolatile hybrid photoconductive/magneto-optic storage material
Authors: Krumme J.-P. , Hill B. , Krüger J. , Witter K.
Published: February 2003

The optical recording sensitivity of magneto-optic memory materials can be greatly enhanced by combining their physical stability and reversibility with the high optical sensitivity of certain photoconductors. Feasibility experiments have been performed on a magneto-optic–photoconductor sandwich (called MOPS) of a liquid-phase epitaxial ferrimagnetic garnet film at its magnetic compensation temperature covered by a Cu-doped CdS temperature covered by a Cu-doped CdS film and electrodes. Using a HeNe laser a recording sensitivity, referred to 1% read-out efficiency, of better than 1 μJ/mm2 % at magnetic switching fields <100 Oe and ≳400 Hz repetition rate has been achieved. 106 switching events have not degraded the performance of MOPS.
Synthesis and magnetic behavior of GdN
Authors: Cutler Robert A. , Lawson A. W.
Published: February 2003

New procedures, employing the use of fractional distillation, have been developed for the synthesis and purification of GdN. Distilled and undistilled GdN exhibit different magnetic behavior, both being sensitive to oxygen impurities. The zero field magnetic moment of a virgin sample of distilled GdN is zero but with increasing field exhibits features of ferromagnetic behavior. For distilled GdN, an increase in oxygen concentration from 0.8 to 5.8 at.% decreases the paramagnetic Curie temperature from 90 to 60 K. Undistilled GdN, having a large nitrogen deficiency, shows ferromagnetic behavior.
The specific heat of Nb-25% Zr
Authors: Wright L. S. , Pendrys J. P. , Harrison R. B.
Published: February 2003

The specific heat of cold-rolled Nb-25% Zr has been measured from 2 to 11.6 K in zero magnetic field. The transition temperature has been found to be 10.9±0.05 K and the specific heat below the transition temperature is reasonably well represented by C=1954 exp(−1.874Tc/T) +0.16T3 mJ/mole K.
A PrCu6 cryostat for nuclear orientation experiments down to 2.7 mK
Authors: Andres K. , Hagn E. , Smolic E. , Eska G.
Published: February 2003

An adiabatic demagnetization cryostat has been modified to include a second hyperfine enhanced nuclear cooling stage with PrCu6 as the working material. The details of the desgin are given and the performance of the cryostat is discussed. The reliability of 60CoFe and 60CoNi nuclear orientation thermometers are critically evaluated.
Electron radiography using liquid absorbers
Authors: Allan F. , Johnson S. , Lewis J. , Morsell A. L. , Muntz E. P. , Scott P. B. , Watson G. , Welkowsky M.
Published: February 2003

X-ray imaging experiments using a liquid absorber to produce a charge image which is then developed by electrophotographic means to produce a visible image are described. The results of this novel electronradiographic process indicate resolutions of well over 10 line pairs/mm at the expense of increased dosage as compared to either screens and film or gaseous electronradiographic imaging.
An analytic solution to elastic backscattering
Authors: Chu W. K. , Ziegler J. F.
Published: February 2003

An approximate analytic expression is presented for the prediction of spectra obtained from nuclear elastic backscattering from elemental matter, e.g., 4He+ from Al. Beam energy straggle in the target and experimental resolution limitations are not considered. Theoretical calculations are shown to agree well with experimental spectra.
Absence of hillock formation in epitaxial lead films
Authors: Lahiri S. K.
Published: February 2003

Epitaxial Pb films with double positioning have been produced by vacuum evaporation of Pb onto mica substrates maintained at 75 °C during deposition. Such films do not exhibit hillock formation when repeatedly cycled between room temperature and 77 °K or annealed at 373 °K. This is in contrast to the observation on nonepitaxial Pb films which do exhibit hillock formations when subjected to similar treatments. The difference has been interpreted in terms of grain-boundary orientation and structure.
Current sharing in a fully stabilized superconductor
Authors: Kuroda Kunishige
Published: February 2003

The dynamic behavior of a fully stabilized superconducting composite is studied by observing terminal voltages V, temperatures T, and magnetic fields Hb as a function of transport currents I without an applied magnetic field. The current sharing in the resistive state of the composite is confirmed by measuring Hb in the vicinity of a composite in which superconducting filaments are arranged in a special configuration in a copper matrix. An observed I-Hb diagram agreed well with that calculated from a fraction of the current sharing obtained from analyzing an observed I-V diagram, under an assumption which regarded the composite as a parallel circuit composed of superconducting filaments and a copper matrix. In the resistive state, it was confirmed that the current in filaments exceeded the critical current of the bare filaments and the differential resistance of the composite was smaller than the resistance of the copper matrix.
Light-induced changes in permeability of n- and p-type YIG films
Authors: Metselaar R. , Huyberts M. A. H. , Logmans H.
Published: February 2003

The influence of irradiation with white light on the permeability at 77 ° of n- and p-type yttrium iron garnet films has been investigated. The investigations were performed on epitaxialy grown films with varying concentrations of Pb and Si. The existence of an ireversible photomagnetic effect in both n- and p-type YIG is demonstrated. Measurements of the spectral dependence of the photomagnetic effect in the wavelength region 1000–3 nm show a rapid increase of the sensitivity towards shorter wavelengths.
Intense soft uv emission from coaxial-geometry arc sources in helium
Authors: Beverly III R. E.
Published: February 2003

Intense soft uv radiation (∼2700 A) has been experimentally produced by coaxial-geometry ceramic-surface arc discharges in high-pressure helium. Arc sources may have significant advantages for the excitation of photodissociation lasers such as the iodine system.
New configuration for a superconducting weak link
Authors: Lum W. Y. , Van Duzer T.
Published: February 2003

We report here a new method of making a Josephson device which, in some respects, is the fabricated equivalent of a point contact. The configuration has the potentiality for good heat-removal properties and has been shown to be temperature cyclable. The I-V characteristics, Ic-T dependence, and Ic-B relation for a parallel pair are given.
Long-term charge storage in interface states of ZnS MOS capacitors
Authors: Walker L. G. , Pratt Jr. G. W.
Published: February 2003

Long-term charge storage in the interface states of a ZnS MOS capacitor to described. Discrete-level Shockley-Read recombination theory adequately explains the observed time dependence of charging and discharging. Charge is stored at low applied voltages (10 V) in short times (1 μsec). 25% of the charge is retained as long as 105 sec and 60% as long as 104 sec. The measured capture cross section of the interface states is 10−10 cm2. The states are emptied by exposure to visible or near-infrared radiation. Proposed memory device applications are described.
Measurements of Peltier cooling at a Ga-GaAs interface using a liquid-phase epitaxy system
Authors: Stefanakos E. K. , Abul-Fadl A. , Workman M. D.
Published: February 2003

The Peltier coefficient of n-type GaAs was measured by passing an electrical current through the GaAs-Ga solid-liquid interface in a vertical liquid-phase epitaxy (LPE) system. Application of a steady-state heat-transfer analysis yielded values for the Peltier coefficient of 0.141 to 0.203 V in the 530–830 °C temperature range. From the study of measurements of Peltier cooling as a function of GaAs substrate thickness, current amplitude, and system geometry, it was concluded that effective utilization of Peltier cooling depends greatly on specimen thickness, doping, and furnace temperature, especially in LPE applications.
Carrier generation at the Si-SiO2 interface under pulsed conditions
Authors: Arnold Emil , Poleshuk Michael
Published: February 2003

A simple analysis is given of the displacement current transient following an application of a depleting pulse to the gate of a metal-insulator-semiconductor capacitor. It is shown that a plot of the current vs reciprocal time may be used to obtain the surface state density near midgap, the majority-carrier capture cross section, and the bulk minority-carrier lifetime. Experimental results for a typical MOS capacitor are presented.
Calibrated remote measurements of SO2 and O3 using atmospheric backscatter
Authors: Grant W. B. , Hake Jr. R. D.
Published: February 2003

Remote measurements of calibrated samples of SO2 and O3 have been achieved with a lidar using ultraviolet signals produced by a tunable dye laser and a nonlinear crystal. The operating wavelengths for these measurements were 292.3 and 293.3 nm for SO2 and 292.3 and 294.0 nm for O3. The atmosphere in front of and behind the chamber acted as a distributed reflector to send laser light back through the chamber to a receiver near the laser. The laser measurements agreed well with in situ measurements. Integration of eight laser pulses at each of two wavelengths allowed the determination of SO2 concentration with an uncertainty equivalent to ±0.6 ppm in 100 m for low concentrations. For O3, the corresponding uncertainty limit was ±1.2 ppm in 100 m. The measurement errors are primarily attributable to variations in atmospheric backscattering intensity during the experiment, since the different wavelengths were radiated sequentially rather than simultaneously. The sensitivity of a system transmitting more favorable wavelengths at intervals separated by less than 1 min is estimated to be near ±0.1 ppm in 100 m for both SO2 and O3.
Sum-rule constraints in reflectance extrapolation for Kramers-Kronig analysis
Authors: Ellis H. W. , Stevenson J. R.
Published: February 2003

A criterion is given by which the quality of an extrapolation may be judged when using Kramers-Kronig analysis of reflectance data to obtain the optical constants. The method is particularly useful is the case of small-band-gap materials where the more usual constraints present difficulties. Sum rules on the calculated optical constants are used as guides in choosing an adjustable parameter in the extrapolation function. An analytical model is used to develop a constraint condition with which the adjustable parameter may be chosen. The method is applied to the KK calculation of the optical constants of Cd3As2.
Optical parametric interactions in isotropic materials using a phase-corrected stack of nonlinear dielectric plates
Authors: McMullen J. D.
Published: February 2003

Optical parametric interactions are analyzed for collinear three-frequency processes in a series of plates of isotropic nonlinear dielectric. Phase-velocity mismatch caused by refractive-index dispersion is compensated by making each plate one coherence length thick and orienting consecutive plates so the nonlinear polarization is shifted in phase by π. Parametric transfer of energy then proceeds constructively along the axis of propagation. For second harmonic generation, frequency upconversion and downconversion, and parametric amplification the output intensity is proportional to the square of the number of phase-corrected plates. The conversion efficiency is the same as for a hypothetical phase-velocity-matched interaction in the same nonlinear material, except that the nonlinear susceptibility is effectively reduced by a factor of 2/π.This method can be used to obtain efficient nonlinear interactions over frequency ranges previously precluded by lack of suitable transparent birefringent crystals and for large-aperture configurations for generating high powers.
Exciton effects on luminescence of undoped active layers in GaAs-Ga1−xAlxAs double-heterostructure crystals at temperatures between 77 and 300 K
Authors: Nakashima H. , Chinone N. , Ito R.
Published: February 2003

Photoluminescence and injection luminescence of the undoped active layers in GaAs-Ga1−xAlxAs double-heterostructure crystals were measured at temperatures between 77 and 300 K. The temperature dependence of photoluminescence showed that exciton effects play important roles in the near-band-edge emission. The observed spectral shapes were compared with that calculated by assuming the band-to-band transition, exciton effects, and the k-selection rule. Excellent agreement between experiment and theory was obtained for the spectral shapes at 77 and 300 K. Furthermore, the photocurrent spectra of the diode fabricated from the double-heterostructure crystal supported this result.
Analysis of the radiation backscattered from a laser-produced plasma
Authors: Jannitti E. , Malvezzi A. M. , Tondello G.
Published: February 2003

The light backscattered from a plasma produced by focusing a 1-GW Q-switched ruby laser has been measured. The reflection coefficient of the plasma is of the order of 1–2% and the reflected energy increases with the incident energy. The backscattered light is Doppler shifted; the shift is not uniform but varies markedly along the focal spot indicating a concave reflecting layer penetrating into the target with velocities of (2–4) ×106 cm/sec. The second harmonic of the ruby laser is also present in the backscattered light.
Threshold temperature characteristics of double heterostructure Ga1−xAlxAs lasers
Authors: Goodwin A. R. , Peters J. R. , Pion M. , Thompson G. H. B. , Whiteaway J. E. A.
Published: February 2003

The variation with temperature of laser threshold current density under pulsed operation conditions, Jt, has been measured for double heterostructure wafers grown with a range of values of heterojunction step height Δx. Good correlation is found between Δx and the temperature coefficient which is defined as the ratio of the values of Jt at 65 and 10 °C. Values of J65/J10 are found to be approximately 1.5 for Δx=0.30, increasing slowly to 2.0 at Δx=0.20 and increasing very rapidly for smaller values fo Δx. This behavior is interpreted as arising from leakage of electrons from the active region into the p passive layer. A theoretical model of carrier leakage confirms the interpretation in that quantitative agreement with experiment was obtained using reasonable values for the disposable parameters of carrier lifetime and mobility. The model is used to predict approximate limits to the Al concentrations in the passive layers needed for stable continuous laser operation over a wide temperature range.
Effect of crack size on acoustic emission related to moving dislocations
Authors: Ying S. P.
Published: February 2003

Acoustic emission from a crack vicinity in a uniformly stressed solid is correlated with the crack size based on a continuous theory of dislocations. It is assumed that the total number of acoustic emissions is directly proportional to the total number of nonuniformly distributed moving dislocations in the plastic zone near the crack. The resultant equation of the relationship between acoustic emission and crack size can be expanded into a power series of applied stress. The first-order approximation is consistent with that of a macroscopic fracture mechanics consideration on the emission related to the plastic zone size. The theoretical calculation is verified with experimental results obtained from a flawed carbon steel vessel by a multichannel acoustic emission monitoring system and agrees reasonably well with the experimental data. Further calculations by utilizing the theory and by analyzing available experimental data of acoustic emissions from center-surface-flaw specimens and wedge opening load specimens of various crack sizes also show agreement between the theory and the experimental data.
Propagation of residual dislocations during silicon epitaxy
Authors: Koyama H. , Wittry D. B. , Kato T.
Published: February 2003

The propagation of residual dislocations during silicon epitaxy was studied by means of etching and scanning electron microscopy (SEM). The dislocations found outside a buried-layer diffused area (emitter edge dislocations) propagate clearly into an overlying silicon epitaxial layer; this propagation is likely to take place along in the [112̄] direction.
Generalized criterion for feasibility of controlled fusion and its application to nonideal dd systems
Authors: Maglich Bogdan C. , Miller Robert A.
Published: February 2003

Eighteen terms are missing from the energy balance of the Lawson criterion; most of them correspond to nonnegligible effects that must be present in real physical systems. A quantitatively and qualitatively different criterion for controlled fusion is obtained. It requires that, in addition to the product nτ, three important independent conditions be satisfied. We conclude that conditions for controlled dd fusion are more advantageous at nuclear physics energies ∼1 MeV than at thermonuclear temperatures.
Investigation of transient space-charge-perturbed currents
Authors: Hartmann George C. , Lipari Nunzio O.
Published: February 2003

The effect of space charge on transient current in dielectric media with constant voltage boundary conditions is studied for time-dependent injection at one electrode. Several cases are investigated which include field-dependent mobility in the dielectric, field-dependent injection at one electrode, and a combination of the two. The results show the importance of these field dependences. Experimental data are presented which illustrate some of these features.
Elemental composition profiling in thin films by glow-discharge mass spectrometry: Depth resolution
Authors: Coburn J. W. , Eckstein E. W. , Kay Eric
Published: February 2003

The depth resolution of a nickel-copper interface has been measured as a function of the total depth of analysis using the glow-discharge mass-spectrometric depth-profiling technique. A possible interpretation of the results is that the depth resolution is determined by a 30-Å depth-independent interface broadening plus a broadening which varies between 2 and 8% of the total depth of analysis.
Force on the top layers of a porous medium subjected to surface pressure oscillation
Authors: Hwang C. C. , Chaiken R. F.
Published: February 2003

The fluid-mechanical force acting on the top layers of porous dust beds is analyzed and a new interpretation made when the beds constitute the walls in turbulent gas streams. The nonlinear differential equation governing the pressure distribution in the medium is solved numerically. When a sinusoidal pressure oscillation is applied at the surface of a porous medium, direct calculations show that there may occur a net upward force, for a duration within one cycle, on the top layers of the medium. By using the present results, a possible mode for the initiation of erosion of an erodible granular bed in a turbulent gas stream is examined. This mechanism may have significance in connection with dust explosions and soil erosion.
Heterojunction laser operation of N-free and N-doped GaAs1−yPy (y=0.42–0.43, λ∼6200 Å, 77 °K) near the direct-indirect transition (y∼y
c?0.46)
Authors: Coleman J. J. , Holonyak Jr. N. , Ludowise M. J. , Wright P. D. , Groves W. O. , Keune D. L. , Craford M. G.
Published: February 2003

The successful LPE growth of In1−xGaxP1−zAsz/ GaAs1−yPy single heterojunctions on VPE substrates makes possible the study of stimulated emission in N-free and N-doped GaAs1−yPy in a region (y=0.42–0.43) much closer to the direct-indirect transition (y≡yc=0.46, 77 °K) than previously. Laser operation in N-free GaAs1−yPy on the Γ-Zn (EΓ-EZn) recombination transition has been achieved at energies as high as 2.00 eV (λ=6200 Å), and some line narrowing has been observed at energies as high as 2.01 eV (λ=6170 Å, y=0.43). In contrast to diodes made on lower composition substrates, the diodes of this work do not change their threshold current densities in the range 77–4.2 °K, indicating that laser operation occurs on direct transitions lying within ∼kT of the indirect donor states (Te) associated with the X conduction-band minima. From EΓ+kT∼EX−Ed (y=0.42–0.43), the depth of indirect Te donor states in GaAs1−yPy is estimated to fall in the range Ed=22–32 meV. Nitrogen doping in these laser diodes increases the threshold current densities since the N impurity is an efficient trap and introduces competing indirect recombination. For y=0.42–0.43 GaAs1−yPy, heterojunction laser operation on the N trap lies ∼10 meV lower in energy than on the Γ-Zn transition. Beyond y=0.42–0.43, the N trap may be required for stimulated emission, but in this range diode operation at high currents becomes difficult because of the large change in carrier mobility.
Helium blast-wave measurements of laser-heated microshell targets
Authors: Leonard T. A. , Mayer F. J.
Published: February 2003

Measurements of blast waves produced by laser heating of spherical glass-shell targets in an atmosphere of 20 Torr helium are described. These measurements made use of a streak camera, monitoring the self-luminosity of the strong shock, a blast probe detecting the ionization behind the shock front, and a piezoelectric pressure probe recording the pressure pulse of the shock. The time history of the blast wave is used to determine the kinetic energy of target dissembly via a simple model which is applicable in both the strong-shock and acoustic regions. These measurements show that the inferred blast-wave energy increases for larger radius–time-shock coordinates. This anomalous effect is ascribed to ’’fast’’ ion preheating of the ambient helium gas in front of the shock wave.
Interpretation of data on cathode erosion and efflux from cathode spots of vacuum arcs
Authors: Eckhardt Gisela
Published: February 2003

Erosion data from solid cathodes so far have been interpreted in terms of efflux from cathode spots proper, and thus as indicative of spot properties. A study based on published data indicates that evaporation from the molten tracks created by the cathode spots must be taken into account in order to explain consistently the experimental observations.
Effects of S, Ba, and C on impregnated cathode surfaces
Authors: Haas G. A. , Gray H. F. , Thomas R. E.
Published: February 2003

Auger electron spectroscopy (AES) and scanning low-energy electron probe (SLEEP) techniques have been used simultaneously for correlating electronic and surface chemical behavior of impregnated matrix cathodes. The role of S, Ba, and C has been related to emission poisoning, decay with life, and delayed response after cathode shutdown.
Beam self-trapping and dynamics of laser-induced magnetoplasmas
Authors: Loter N. G. , Cohn D. R. , Halverson W. , Lax B.
Published: February 2003

Spatially and temporally resolved measurements of transmitted laser radiation, radial density profiles, and plasma dynamics indicate beam self-trapping in CO2 laser-induced helium plasmas in strong longitudinal magnetic fields. Trapping is observed for the cases of β≳1, β?1, and β<1. Longitudinal plasma growth occurs principally by breakdown waves and weak radiation-supported detonation waves.
Thin-film reactions of Pb with AgAu and AgPd alloys
Authors: Tu K. N. , Chance D. A.
Published: February 2003

Stability of AgAu and AgPd alloys with respect to their reactions with Pb have been studied by using thin-film samples and by free-energy calculations. Thin-film reactions of Pb with 80 at.% Ag-20 at.% Au and 80 at.% Ag-20 at.% Pd alloys were examined by x-ray diffraction. X-ray results show that the AgAu alloy is stable with Pb up to 200 °C and the AgPd alloy is stable with Pb at room temperature but unstable at 200 and 250 °C resulting in the formation of Pb2Pd along with a dilute phase of Ag which is almost free of Pd. Free-energy calculations show that Pb cannot deplete Au from any AgAu alloy which contains less than 29.5 at.% Au, and yet Pb can deplete Pd down below 1 at.% from any AgPd alloys provided that the kinetics is fast enough.
Effect of deposition rate and substrate cleavage on epitaxial Al films
Authors: Bruening David K. , Weber A. H.
Published: February 2003

Aluminum films were deposited in high vacuum (10−8 Torr) onto the (100) [also designated (200)] faces of cleaved NaCl signal-crystal substrates. The effect of changes in rate of deposition, in the conditions of substrate cleavage (air and vacuum), in substrate temperature, and in film thickness on the orientation of the films were investigated. In general with a film thickness of 400−500 Å, an optimum substrate temperature of 350 °C resulted in polycrystalline Al films with a (100) orientation. The orientation was most pronounced when the NaCl substrates were cleaved in vacuum and the deposition rate was less than 1 Å sec−1, or when the substrates were cleaved in air and the deposition rate was greater than 10 Å sec−1. Single-crystal films with a (100) orientation were obtained when the film thickness was limited to about 100 Å.
Preparation of small silver crystals in a solid matrix of CO2 using a gas evaporation technique
Authors: Rappaz M. , Faes F.
Published: February 2003

We have developed an apparatus to prepare small insulating or metallic particles in a solid matrix. The small crystals are formed by evaporation in an inactive gas and then are condensed simultaneously with a CO2 molecular beam on a finger cooled at liquid-nitrogen temperature. The size distribution of silver particles and efficiency of the technique have been studied by electron microscopy as a function of the evaporation temperature, the pressure, and the flow rate of the inactive gas. The minimum average size has been found to be equal to 115 Å, with a full width at half-maximum of the distribution equal to 110 Å.
Self-focusing and self-distribution of electromagnetic waves in a plasma due to collision-induced nonlinearity
Authors: Chandra Prayag , Tripathi V. K.
Published: February 2003

In this paper we have investigated the nonlinear dielectric constant of a slightly ionized plasma showing the Ramseuder effect. Within the approximation of the Harp model for collisions (i.e., taking the collision frequency for electrons to be small below the speed v=vo and infinitely large above v=vo) the heating of low-speed-domain electrons by the field of an electromagnetic wave and their subsequent transfer to the high-speed domain is the source of nonlinearity. The nonlinearity is seen to be a saturating function of the intensity of the intensity of the beam. For a Gaussian beam this type of nonlinearity results in the self-made oscillatory waveguide propagation of the beam. The critical power for self-focusing is much smaler than that predicted by Stenflow and Yu. For a typical case of a plasma with ω2p/ω2?0.2, the self-focusing length of a beam of 400 W, ω∼1014 sec−1, vo=10c/w, comes out to be 0.2 cm. However, below certain critical values of the initial beam radius (vo<vo min), focusing cannot be obained regardless the power of the beam. For amplitude-modulated uniform plane waves, the nonlinearity results in the distortion of the amplitude envelope and the frequency broadening of the wave.
Wave propagation in a condensed medium with N transforming phases: Application to solid-I–solid-II–liquid bismuth
Authors: Hayes D. B.
Published: February 2003

Constitutive assumptions of local thermal and pressure equilibrium in a mixture of N transforming phases allow construction of a constitutive equation of a generalized Maxwellian form suitable for studying the kinetics of phase transformations induced by shock-wave loading. This equation relates the pressure rate to the strain rate and the phase change rate, the latter being expressed as the time derivative of a vector which has components equal to the mass fractions of the constituent phases. A separate kinetic equation is required for evolution of this composition vector. Coefficients appearing in the constitutive equation depend only on properties that the mixture displays with a frozen composition which in turn depend directly on properties of the pure-phase components of the mixture. The constitutive equation is applied to solid-I–solid-II–liquid bismuth (N=3). When wave propagation calculations on bismuth are compared to previous theory and experiments, a lower bound on the melting rate of 4 μsec−1 is found.
Tunable-wavelength, single transverse and longitudinal mode, Nd3+ glass Q-switched laser
Authors: Petite G.
Published: February 2003

A new tunable-wavelength, single transverse and longitudinal mode, Nd3+ glass Q-switching laser is described. Single-longitudinal-mode operation is achieved by using saturable absorber Q switching and intracavity resonators. Tunability is achieved over a 50-Å range by means of a birefringent filter, consisting of a single calcite plate and a polarizer. The energy is about 25 mJ, obtained in a 17-ns pulse.
Effects of agglomeration and magnetic boundary scattering on the electrical resistivity of nickel films
Authors: Chaudhuri S. , Pal Arun K. , Barua A. K.
Published: February 2003

The electrical resistivity of vacuum-evaporated nickel films has been studied as a function of thickness (166–3432 Å) and temperature (30–150 °C). The measurements have been performed in situ using the four-probe technique. The thicknesses of the films have been measured by a multiple-beam interferometer. The electrical resistivity ρ of a ferromagnetic metal film can be expressed as ρtotal=ρid+ργ+ρt +ρmω, where ρid, ργ, ρt, and ρmω are, respectively, the lattice, residual, surface, and magnetic wall resistivities. The thin films of nickel are known to have agglomerated structure below 400 Å and because of its ferromagnetic nature the magnetic domains should also play a role in its electrical properties. By studying the effects of change of resistivity with temperature on films of different thicknesses the role of the factors mentioned above has been identified. It has been concluded that to obtain nickel films of reproducible electrical properties, the deposition has to be done above the Curie temperature or the deposited film has to be annealed above the Curie temperature.
The effects of radiation-induced displacement damage on impurity conduction in gallium arsenide
Authors: Berg N. J. , Lieberman A. G.
Published: February 2003

The effects of 60Co γ-ray and high-energy neutron displacement damage on impurity conduction in epitaxial gallium arsenide were investigated. The activation energy (ε2) associated with the transition regime of the impurity conduction process was found to increase by a factor of 5 as a result of 60Co γ irradiation, and only by a factor of 1.6 for a comparable neutron irradiation. In addition, the ratio of the Hall carrier density at low and high temperatures, (nH)4 K/(nH)300 K, decreased by a larger amount for 60Co γ irradiation than for neutron irradiation. The effects of neutron irradiation are explained in terms of increased compensation. For the case of 60Co γ irradiation, it is postulated that a new donor level is introduced which does not participate in the impurity conduction process. In addition, with respect to the impurity conduction process, it is found that ε2 is proportional to ε1 (the conduction-band activation energy) and varies inversely with neutral donor spacing in accord with the model proposed by Mikoshiba. Also ρ30, the hopping regime resistivity, is found to vary inversely with the square of the free-carrier concentration and exponentially with the quantity 0.6/ND1/3a.
Photoconductive properties of chemically deposited PbS with dielectric overcoatings
Authors: Blount George H. , Preis Mark K. , Yamada Robert T. , Bube Richard H.
Published: February 2003

Overcoatings of Al2O3, As2S3, CdTe, MgF2, SiO, and SiO2 were vacuum deposited on thin-film PbS photodetectors. Overcoating thicknesses were approximately those required to optimize antireflection properties. None of the overcoatings seriously degraded detector properties, although production yields were low with Al2O3, MgF2, and CdTe. The low yields are apparently due to physical incompatibilities of the overcoating and PbS film. Improved detector properties were obtained with As2S3 through a reduction of 1/f noise and passivation to hostile environments. The 1/f noise component is assessed by a comparison of the changes in detector performance parameters upon ’’flashing’’ with the changes theoretically expected for G-R noise-dominated detector.
Comparison of Zn-doped GaAs layers prepared by liquid-phase and vapor-phase techniques, including diffusion lengths and photoluminescence
Authors: Ettenberg M. , Nuese C. J.
Published: February 2003

p-type Zn-doped GaAs layers have been prepared by both liquid-phase (LPE) and vapor-phase (VPE) epitaxial growth techniques. Both techniques allow controlled Zn doping between ∼9×1017 and 3×1019 cm−3. For the LPE technique, the hole concentration (p) is related to the concentration (XZn) in the Ga solution by p=5×1020(XZn)1/2. The surfaces of the LPE layers have a characteristic ripple, in contrast to the optically flat surfaces representative of vapor-grown layers. Minority-carrier (electron) diffusion lengths in the LPE layers decrease from 10 to 5 μm with increasing hole concentrations between 9×1017 and 3×1019 cm−3. Diffusion lengths for comparably doped VPE layers are about two times smaller. The room-temperature photoluminescence characteristics of both types of layers have similar dependences on hole concentration, which can be used as a calibration for nondestructive hole concentration determination. Peak photoluminescence intensities of the two types of layers occur at ∼1×1019 cm−3, and are approximately equal in intensity.
Graded-band-gap pGa1−xAlxAs-nGaAs heterojunction solar cells
Authors: Konagai Makoto , Takahashi Kiyoshi
Published: February 2003

The theoretical spectral response of the graded-band-gap pGa1−xAlxAs-nGaAs solar cell is calculated by solving the continuity equations. The electric fields produce a collection efficiency two times larger than that of the abrupt heterojunction diodes at wavelengths less than 700 nm for surface recombination velocities of 106–107 cm/sec. The graded-band-gap diode can be operated at high frequencies because of the reduced transit time of minority carriers in the p-type layer. A graded-band-gap pGa1−xAlxAs-nGaAs solar cell is fabricated by utilizing the diffusion of Al in the Ga melt. The gradient of the energy gap is evaluated by photoresponse and photoluminescence measurements. The photoluminescence shows a broad emission peak from 700 to 800 nm at 77 K.
Structure and superconductivity of metastable phases in liquid-quenched Zr-Rh alloys
Authors: Togano Kazumasa , Tachikawa Kyōji
Published: February 2003

Using the liquid-quenching technique adapted to an arc furnace, Zr-Rh alloys containing 0–36 at.% Rh were rapidly quenched from the liquid state. Body-centered cubic solid solution of Zr is retained up to 17 at.% Rh beyond the maximum equilibrium solubility limit of 8 at.% Rh. Broad maxima in the x-ray and electron diffraction patterns, indicative of a noncrystalline structure, are obtained for alloys containing 18–27 at.% Rh. The noncrystalline phase shows a sharp superconducting transition at 4.1 K. The annealing behaviors of the metastable phases were investigated by continuous observations in the hot stage of an electron microscope and electrical resistivity measurements. The metastable phases transform to equilibrium phases on heating at temperatures above 500 °C and very fine structures are produced by the transformation.
Heat capacity and thermal conductivity of sintered Al2O3 at low temperatures by the heat pulse technique
Authors: Alterovitz S. , Deutscher G. , Gershenson M.
Published: February 2003

A heat pulse is applied at one point of a finite one-dimensional sample, the other end being clamped to a heat sink. The subsequent temperature rise at the middle of the sample is analyzed by a moments method to yield the absolute values of the thermal diffusivity, the heat capacity, and the thermal conductivity. As the method is based on pulse shape analysis, an on-line computer analysis was performed. The experimental setup was used to check the possibility of using sintered Al2O3 (ceramic) as a suitable substrate for heat capacity experiments of thin films at low temperatures.
Determination of electron diffusion length from photoluminescence measurements in InxGa1−xAs junctions
Authors: Ota T. , Oe K. , Yamaguchi M.
Published: February 2003

Minority-carrier diffusion length can be estimated from the dependence of photoluminescence intensities in a direction perpendicular to a p-n junction plane. Experimental results in InxGa1−xAs (x∼0.14) p-n junctions showed that the electron diffusion length is ∼1.0–1.3 μm at room temperature.