bluuebunny/crossref_metadata_2025 huggingface dataset:
Dielectric absorption currents and surface charge on polymeric insulators
Authors: Chapman T. C. , Wintle H. J.
Published: February 2003

We have studied two mechanisms thought to be responsible for the anomalous currents and resulting charge accumulation on the surface of polymeric dielectrics. First, we find the detailed normal electric fields on the plane surface of an insulating dielectric next to an electrode by conformal and numerical techniques. The polarization, as determined by the calculated field, is found to be consistent with experimental surface charge profiles; they both fall off inversely as the distance from the electrode. However, polarization is shown to give only a small contribution to the observed effect. Second, a transmission line model of the surface resistivity is studied. Previous work on this model is shown to be misleading. We establish that the surface resistivity must vary with distance from the electrode in order to account for the observed inverse time dependence of the current at long times. This unphysical requirement, and some contradictory experimental data, indicate that the present understanding of surface charging is inadequate.
Nonlinear interactions of two ultrasonic waves in a dispersionless liquid medium
Authors: Kwun H. , Hikata A. , Elbaum C.
Published: February 2003

Nonlinear interactions of two ultrasonic waves, propagating collinearly in a dispersionless liquid medium, are investigated experimentally for both degenerate and nondegenerate cases. Results are described of the first experimental observation of parametric amplification of the signal wave for the degenerate case. For the nondegenerate case, no such amplification of the amplitude of the signal wave is observed. These experimental results are found to be in good agreement with the results of the theoretical analysis presented in the paper.
On the temperature dependence of the velocity of surface waves in quartz
Authors: Sinha B. K. , Tiersten H. F.
Published: February 2003

The first temperature derivatives of the fundamental elastic constants of quartz are employed along with the thermally induced biasing strains in the equation for the first perturbation of the eigenvalue for the linear electroelastic equations for small fields superposed on a bias to calculate the resulting change in surface-wave velocity with temperature. Since the description employed is referred to a fixed reference state, the geometry does not change and the temperature coefficient of velocity is the negative of the temperature coefficient of delay. In all earlier work, a variable temperature-dependent geometric state was considered, but the attendant shearing or skewing of the coordinate axes was not properly included. The temperature dependence of the velocity of surface waves propagating in various directions on various cuts of quartz is obtained. For cases in which measurements are available, the calculations are shown to be in substantially better agreement with the measurements than previous calculations.
Some extensions of the flash method of measuring thermal diffusivity
Authors: James Hubert M.
Published: February 2003

Solutions are given for a number of one-dimensional problems in heat conduction arising in connection with extensions of the flash method of measuring thermal diffusivity: conduction through slabs of one or two materials, with flash or step irradiation of the front surface, with and without thermal losses from the surfaces, with and without interior contact thermal resistances. The treatment involves application of Laplace transform methods, but with the usual inversion of the transform by integration in the complex plane replaced by a convenient expansion of the transform that permits term-by-term inversion by use of standard tables. This yields the temperature rise on the back face of the slab as a series of terms that converges particularly well at low values of the time, in contrast to the commonly used solutions. In many cases one to three terms suffice to give good results, even for times well in excess of the half-rise time for the temperature on the back face. The advantage of using step irradiation instead of flash irradiation is indicated briefly.
Further experimentation on Taylor instability in solids
Authors: Barnes John F. , Janney D. H. , London Roger K. , Meyer Kenneth A. , Sharp David H.
Published: February 2003

Recently Drucker has provided an alternative theoretical analysis of the Rayleigh-Taylor experiments on flat metal plates that we reported on earlier. His analysis is at variance with our conjecture in that it explains the small growth observed in one of our experiments on an initial amplitude, rather than an initial wavelength, basis. In this note we report the results of an experiment designed to test these two competing explanations; Drucker’s conclusions appear to be confirmed.
Maximum windmill efficiency
Authors: Greet Richard J.
Published: February 2003

A result frequently quoted in engineering handbooks is that one-dimensional fluid flow theory places an upper limit on windmill efficiency at 16/27 or 59.3%. An error in the development invalidates this conclusion. One-dimensional flow analysis places no restrictions on realizable windmill output.
The movement of elongated metal particles under high-voltage stress in vacuum
Authors: Farrall G. A. , Hudda F. G.
Published: February 2003

One of the consequences of anode spot formation in high-current vacuum arcs is the ejection of molten metal droplets of varying sizes and the impact cooling of these droplets upon the internal surfaces which surround the discharge. Some of these droplets adhere to the target surfaces while others becomes detached to form loose metallic debris within the containing vessel. Under some conditions, high voltage applied to the vessel can levitate the debris causing electrical breakdown. We have simulated this breakdown mechanism in an experimental study of particles having cylindrical shapes moving under the influence of high-voltage pulses of several milliseconds duration. The motion of aluminum, copper, and gold particles is determined using a stroboscopic technique. Values of levitation voltages under dc conditions are also measured and found to be in good agreement with an analysis by Felici. We have conducted a numerical analysis of the dynamic behavior of the particles studied in the experiment. The results, which take into account the image forces and the instantaneous state of contact of the particle with the supporting surface, correlate well with the experiment. A brief extension of the analysis is made to describe particle movement under impulsive, sinusoidal, and 1-cosine voltage waveforms. Significant motion of particles 2 mm in length and 0.25 mm in diameter occurs within a few milliseconds.
Backscattering measurements of implanted ion distributions in double-layer structures
Authors: Ishiwara H. , Mackintosh W. D.
Published: February 2003

The distributions of Bi ions implanted into the double-layer structures Si/Ge, Ge/Si, C/Si, and C/Ge have been determined using MeV He backscattering techniques. A discontinuity of the backscattering yield was found in the Bi spectrum at or near the energy corresponding to the interface between film and substrate. In each case the magnitude of the interface discontinuity in the ion concentration, which was derived from this backscattering yield, coincided with the theoretical predictions within the experimental error of 20%.
Photothermal spectroscopy using optical beam probing: Mirage effect
Authors: Murphy J. C. , Aamodt L. C.
Published: February 2003

Optical beam deflection near a heated surface was recently introduced as a method of photothermal spectroscopy. Photothermal spectroscopy (PTS) is closely related to photoacoustic spectroscopy (PAS) in its ability to measure optical properties of opaque solids and liquids. This paper develops a theory of this effect and compares this theory with extensive experimental observations. Both are in excellent agreement. The relationship between this form of PTS and PAS is explicitly developed. Applications to the measurement of thermal diffusivity of gases is described.
A study of low-current-density microsecond electron beam diodes
Authors: Ramirez Juan J. , Cook Donald L.
Published: February 2003

The performance of several electron sources has been investigated and compared for generating low-current-density microsecond electron beams with applications to gas laser excitation. A brush cathode made with 10-μm-diam carbon filaments gave the best peformance among the various field emitters tested. It emitted well at fields as low as 10 kV/cm. Space-charge-limited flow was established in ∼60 ns and apparent gap closure velocities of 1.5 cm/μs were characteristic of this cathode. Two regimes of plasma injected diodes were investigated. First, substantial control of the diode impedence was obtained when the plasma was allowed to fill the entire anode-cathode volume prior to application of the high-voltage pulse; however the anode current density was found to be nonuniform with poor reproducibility from shot to shot. Second, more predictable behavior was obtained when the plasma was constrained to be on the cathode surface at the time the high-voltage pulse was applied. In this case the time integrated anode current density was found to be uniform within ±15%. Apparent gap closure velocities as low as 2 cm/μs were measured. A description of the high-voltage pulser and of the various plasma sources used for this experiment are also presented.
Laser drilling with different pulse shapes
Authors: Roos Sven-Olov
Published: February 2003

Drilling in thin metal plates has been studied with two types of pulses from an ordinary flash-lamp-pumped Nd-YAG laser. The drilling performance with a normal pulse consisting of a 200-μs continuous emission preceeded by a few relaxation oscillations has been compared with that of a 200-μs train of 0.5-μs pulses. The pulse train was obtained by introducing a periodic low loss into the laser resonator with the frequency of the relaxation oscillations. It is shown that the use of the pulse train is much superior to the normal pulse for drilling in aluminium and similar metals.
InP metal-insulated-semiconductor Schottky contacts using surface oxide layers prepared with bromine water
Authors: Kamimura K. , Suzuki T. , Kunioka A.
Published: February 2003

Oxide layers prepared with bromine water are found to increase the barrier height for Au-InP Schottky diodes. Electrical characteristics are measured and the relationships between the preparation conditions and the diode parameters are examined. The typical value of the barrier height and the ideality factor are 0.83 eV and 1.1, respectively. Some instabilities are observed in the diode characteristics.
Schottky barrier photodiodes in p Hg1−xCdxTe
Authors: Polla D. L. , Sood A. K.
Published: February 2003

Schottky barrier photodiodes have been fabricated on p Hg1−xCdxTe (0.20<x<0.38) with aluminum and chromium as barrier metals. Various electrical characterizations have been carried out to determine barrier heights and the results are found to be in excellent agreement with Schottky thermionic emission theory. These photodiodes have also been used to determine the minority carrier lifetime and diffusion length in p Hg1−xCdxTe.
Influence of the image force on the band gap in semiconductors and insulators
Authors: Kleefstra M. , Herman G. C.
Published: February 2003

The change in potential energy of electrons and holes and the resulting band-gap change caused by the image force have been calculated close to the insulator-semiconductor interface. Some examples are given from which it appears that in metal-insulator-semiconductor (MIS) structures, as in Schottky diodes, the effects of the image force should not be overlooked.
Effective permittivity in random anisotropic media
Authors: Nagatani Takashi
Published: February 2003

A statistical theory is given to derive the effective (or macroscopic) permittivity in the random anisotropic material from the standpoint of statistical continuum mechanics. The random medium discussed has a degree of orientational order, but does not have translational order. A equation governing the macroscopic electrostatic field can be obtained using formal perturbation methods. It is shown that the expressions for the effective permittivity are described in terms of the order parameter S of ordering in the orientation of the constituent crystals, the volume concentration of the constituent φ, and the principal values of the permittivity tensor of the crystals.
Simulation of field-induced thermally stimulated currents in dielectrics. Application to the dipolar case in polymeric systems
Authors: Vanderschueren J. , Linkens A. , Gasiot J. , Fillard J. P. , Parot P.
Published: February 2003

Numerical calculations of thermally stimulated depolarization currents (TSDC) and thermally stimulated polarization currents (TSPC) have been carried out by using the bistable model of Fröhlich and taking into account the temperature dependence of equilibrium polarization according to a Langevin function. For dipolar processes characterized by a single relaxation time as well as by a spectrum of relaxation times obeying classical distribution functions (Wagner, Cole-Cole, Fuoss-Kirkwood, Davidson-Cole, Havriliak-Negami), the following predictions have been obtained: (1) A TSDC peak must be always of larger magnitude than the corresponding TSPC peak as a result of an increase in polarization taking place during the cooling step; (2) For the same reason, the magnitude and area of a TSDC peak must be dependent on the cooling rate adopted in the poling process; it also follows that, unless an instantaneous cooling is postulated, such a peak can no more be considered as depicting the relaxation properties of the material at the temperature of polarization; (3) A TSPC peak must be followed by a significant current reversal as a necessary result of the tangential convergence of the transient polarization with its decreasing saturation limit in the high-temperature range. These predictions have been tested in a polymeric system selected for its well resolved relaxation spectrum (styrene-butadiene block copolymer). Full qualitative agreement between experiment and theory has been found as far as the behavior of the α relaxation (glass transition) is concerned. These results show that the variations of equilibrium polarization occuring during the nonisothermal steps of TSDC and TSPC experiments cannot be a priori neglected, as is still commonly done for the determination of dipolar relaxation parameters.
Photoacoustic theory including energy migration
Authors: Quimby R. S. , Yen W. M.
Published: February 2003

All theories of the photoacoustic effect to date have assumed that heat is deposited in the sample only where light is absorbed, i.e., that no spatial migration of the energy occurs. We present here an extension of the standard Rosencwaig-Gersho photoacoustic theory, taking into account the possibility of spatial energy migration. Also included in the theory are the effects of surface quenching, i.e., the possibility that excitations near the surface of the sample decay more efficiently than excitations in the bulk. By comparing the experimentally determined chopping frequency dependence of the photoacoustic signal to that predicted by the theory, it should be possible to determine the diffusion constant for energy migration.
Electron-stimulated oxidation of InP (100) surfaces studied by Auger electron spectroscopy and by low-energy-loss spectroscopy
Authors: Olivier J. , Faulconnier P. , Poirier R.
Published: February 2003

Stimulated oxidation of InP (100) surfaces by primary electron beams was studied by Auger electron spectroscopy. At the point of impact of the incident beam, we concluded that the formation of indium oxide and of a volatile phosphorus oxide occur, which explains the phosphorus depletion of the first monolayers. The low-energy electron-diffraction patterns for successive heat treatments and electron-stimulated oxidations of InP surfaces, and the corresponding characteristic-energy-loss spectra were performed. For heat treatments close to the decomposition temperature, we report here on how low-energy-loss spectroscopy was used to supply the deficiency of Auger electron spectroscopy, the latter method being unable to detect the formation of indium microdroplets.
The characterization of the oxides formed on iron, chromium, and iron-chromium alloy thin films
Authors: Buczek D. , Sastri S.
Published: February 2003

A quartz crystal microbalance technique was used in conjunction with Auger electron spectroscopy to characterize the oxides formed on a number of different Fe-Cr alloy thin films oxidized in air at 300 °C. Data was also obtained on pure iron and chromium thin films. The oxide thickness varied almost linearly with chromium concentration between 15 and 45 wt. %. Logarithmic growth kinetics persisted for chromium and iron-chromium films whereas parabolic kinetics were found for the iron films. The chromium film kinetics were comparable to those of the Fe 20 wt. % alloy.
Theoretical analysis of new wavelength-division solar cells
Authors: Sakai S. , Umeno M.
Published: February 2003

The new wavelength-division solar cell is proposed and its conversion efficiency is calculated. The proposed diode structure can be fabricated by the usual epitaxial growth technique. The considered materials are the combination of InP and In0.58Ga0.42As0.84P0.16 having the band-gap energy of 0.827 eV. The calculated maximum conversion efficiency is 19.5% at air-mass-zero (AM0) condition which can be improved by the growth of a CdS window layer on the InP surface. With thick CdS on InP, 22.2% efficiency is obtainable, and when the thickness of CdS is as thin as 0.2 μm, 27% efficiency will be attainable. Fabrication of the proposed structure with the GaAlAs/GaAs system gives a conversion efficiency of 23.5% which is about the same as conventional heteroface or graded-band-gap solar cells. The optimum layer thicknesses that give maximum efficiency are also determined in this paper.
Microwave oscillators based on the resonant propagation of fluxons in long Josephson junctions
Authors: Erné S. N. , Parmentier R. D.
Published: February 2003

Resonant fluxon propagation on an overlap-geometry Josephson tunnel junction of length 5λJ having a McCumber βc =5π is studied by numerical integration of the circuit equations of a 50-section lumped RSJ-type model. The zero-field steps in the dc current-voltage characteristic of the junction deriving from the two lowest order resonant fluxon configurations are calculated, and the switching mechanisms defining the upper and lower current thresholds are described. The power spectra of the radiation emitted from one end of the junction when it is current biased on each of these two zero-field steps is calculated assuming negligible loading. An applied dc magnetic field is shown to cause a small increase in the frequency of this radiation, in contrast with reported experimental measurements.
Ellipsometric study on rf-plasma oxidized tunnel barriers for In/Pb/Au-alloy Josephson junctions
Authors: Kuroda Kenichi , Waho Takao , Ishida Akira
Published: February 2003

Properties of oxide films formed by rf-plasma oxidation of In/Pb/Au alloys were ellipsometrically investigated. Two types of changes in oxide properties were found during annealing or long-term room-temperature storage for low-indium-concentration alloys. One is related to excess oxygen associated with plasma oxidation, and the other is attributed to the conversion of oxide composition from a PbO-In2O3 mixture into pure In2O3. For high-indium-concentration alloys, on the other hand, the oxide was revealed to be very stable because it was almost composed of pure In2O3. From these considerations it was concluded that the more stable Pb-alloy Josephson junctions were expected with the higher-indium-concentration base film, such as more than 30-wt. % alloys.
Nonideal diode factors
Authors: Böer Karl W.
Published: February 2003

It is shown that nonideal diodes with an A factor in the exponent larger than two can be explained when the junction recombination starts to saturate. In thephotovoltaic cells in which the density of minority carriers can be varied indpendent of the bias voltage, this behavior becomes transparent and is used as an example for the proposed model.
Determination of deep level capture cross sections in wide band-gap semiconductors by means of an electron beam
Authors: von Roos Oldwig
Published: February 2003

It is known that the short circuit current ISC generated by a sinusoidally amplitude-modulated electron beam exhibits a coherent phase-shift Φ with respect to the incident beam. This phase shift of the minority-carrier current in uniformly doped n-type or p-type material is due to a time lag between diffusion and the filling and emptying of recombination centers. A general theory is developed for the determination of the ISC in the presence of recombination centers possessing an arbitrary number of charge states and it is shown that a measurement of the phase-shift Φ as a function of the modulation frequency of the incident beam ascertains the magnitudes of electron and hole capture cross sections. For the measurements to be unambiguous, the surface which is exposed to the electron beam must possess a negligible surface recombination velocity. As an aside, certain misconceptions which appeared in the literature pertaining to the statistics of multilevel impurities are pointed out and corrected.
Determining an elastic strain-energy function from torsion and simple extension
Authors: Kearsley E. A.
Published: February 2003

The elastic properties of rubbery materials can often be represented by a strain-energy function expressed as the sum over the three principal extension ratios of a function of a single extension ratio, the Valanis-Landel form. In that case, the strain-energy function can be completely determined from uniaxial extension data combined with data on the torque of a cylinder in torsion. The method is an improvement over other methods for determining the strain-energy function because the necessary experiments are particularly convenient.
Exact analysis of the conductivity of polycrystalline silicon films
Authors: Board K. , Darwish M.
Published: February 2003

An analysis of polycrystalline silicon conductivity is carried out in which the depletion approximation is not made. Deviations of more than an order of magnitude are observed between this analysis and Baccarani’s, which are a direct result of his use of the depletion approximation. Abrupt changes in conductivity that occur in the latter theory are found not to be present in the exact analysis.
Determination of transient regime of hot carriers in semiconductors, using the relaxation time approximations
Authors: Nougier J. P. , Vaissiere J. C. , Gasquet D. , Zimmermann J. , Constant E.
Published: February 2003

It is shown that in a semiconductor, where impurity and polar optical phonon scatterings are not involved, the transient velocity is the solution of a relaxation time equation. Relaxation times can be defined as functions of the stationary energy, thus leading to relaxation time equations which are good approximations for describing the transient average energy and drift velocity. Comparisons between the relaxation time description, and the transient response obtained by iterative or Monte Carlo methods, are performed on p-Ge and n-Si, and show an agreement better than 10% in a wide range of electric fields and lattice temperatures.
Compensator inhomogeneity in an extrinsic semiconductor
Authors: Blakemore J. S.
Published: February 2003

An inhomogeneous distribution of the principal dopant has a variety of well-known consequences for an extrinsic semiconductor. This paper considers an additional problem that can occur in a weakly compensated extrinsic semiconductor at low temperatures. The effective concentration of compensator centers then controls the behavior, in the dark or with weak illumination. Since that ’’effective compensator’’ density (for p-type material) is the algebraic difference between Nd compensating donors and Ns ionized acceptors shallower than the principal species, the low-temperature conduction can be greatly affected by local changes in the magnitude (and sign) of Nd−Ns. The distance range over which inhomogeneities such as undercompensated regions might exist even with minimum (Gaussian) variance is discussed. Compensator inhomogeneity effects are illustrated with data for weakly compensated mercury-doped germanium. Measurements of equilibrium transport coefficients, and of scanned photoconductive response, were indicative of a mixture of positively compensated and undercompensated regions.
Equilibrium and stability of liquid-crystal configurations in an electric field
Authors: Thurston R. N. , Berreman D. W.
Published: February 2003

We describe how to choose the most stable of several equilibrium states that may exist in a liquid-crystal cell at the same voltage V (or charge Q). Among states that exist at the same charge Q, the state with the lowest total free energy F is the most stable. Among states that exist at the same voltage V, the state with the lowest electric Gibbs function (F−QV) is the most stable. Thus the relative stability of various equilibrium states can be compared by plotting G against V or F against Q. An example is given to illustrate the importance of a correct pairing of thermodynamic functions and independent variables.
Comment on ’’Sample-gas thermal contact resistance and the photoacoustic signal generation’’
Authors: Rosencwaig Allan
Published: February 2003

The dependence on the thermal properties of the gas in a photoacoustic cell predicted by the sample-gas thermal resistance theory is also predicted by the Rosencwaig-Gersho theory for very thin samples.
A new narrow-beamwidth high-efficiency zinc oxide on silicon storage correlator
Authors: Green J. B. , Khuri-Yakub B. T. , Kino G. S.
Published: February 2003

A new monolithic ZnO on Si, narrow-waveguide storage correlator has been demonstrated. A 100-μm-wide top-plate electrode served as a Δv/v waveguide for the 100-μm-wide acoustic beam. The surface acoustic wave itself was excited by interdigital transducers that were the same width as the waveguide electrode. Operation of this device resulted in a correlation efficiency of FcorrT =−53 dB m, which is 13 dB better than that reported for any other ZnO on Si storage correlator.
Splashing liquid drops form vortex rings and not jets at low Froude numbers
Authors: Carroll Kenneth , Mesler Russell
Published: February 2003

Colored drops falling only a short distance into clear liquid form vortex rings. A numerical study using the Marker and Cell technique predicted instead a jet rising from the cavity formed by the impact.
Ultrasonic nonlinearity parameters and third-order elastic constants of copper between 300 and 3 °K
Authors: Yost W. T. , Cantrell John H. , Breazeale M. A.
Published: February 2003

The ultrasonic harmonic generation technique has been used to extend measurement of the nonlinearity parameters of copper to 3 °K. Comparison of these data and combinations of truly adiabatic third-order elastic (TOE) constants with predictions of simplified models show that a central force, nearest neighbor model accounts reasonably well for the behavior of copper in the regions of 45 and 200 °K and less well at other regions. The central force, nearest neighbor model also gives a good qualitative explanation for the temperature dependence of the combinations of TOE constants that are measured in this investigation.
Optical enhancement of the electron paramagnetic resonance signal from SiIII centers at the Si/SiO2 interface
Authors: Caplan Philip J. , Poindexter Edward H.
Published: February 2003

The EPR signal Pb from interface SiIII centers in oxidized (111) and (100) silicon wafers has been observed to be enhanced up to 20 times under illumination with white light at liquid-nitrogen temperature. The enhanced EPR signal saturates normally with microwave power, much like its unenhanced counterpart, which indicates that it is not a photoconductive pseudo-EPR signal, as observed for other silicon surface defects. It is suggested that the effective spin polarization of SiIII centers is changed by the light. The optical effect, however, shows complications which may reflect coupling between the Pb center and the semiconductor carriers.
Pressure and temperature dependence of the dielectric properties of polyethylene used in submarine telecommunication cables
Authors: Ai Bui , Destruel P. , Farzaneh M. , The Giam Hoang
Published: February 2003

In this work the dielectric losses of low-density polyethylene used in submarine telecommunication cables have been measured as a function of pressure (1–1150 bars), temperature (4–32 °C), and frequency (0.3–12 MHz). These results point out that the dissipation factor tan δ and permittivity ε of the insulators increase on the sea bottom; for example, for a cable laying at the depth of 5000 m and temperature of 4 °C, these variations are about Δ tanδ=35×10−6, (F=12 MHz), Δε=5×10−2.
Current stability of single-crystal and sintered LaB6 cathodes
Authors: Furukawa Y. , Yamabe M. , Ishizuka T. , Inagaki T.
Published: February 2003

The specimen current stability of single-crystal and of sintered LaB6 cathodes are compared from the viewpoint of their dependence on the cathode tip temperature and the vacuum pressure. The specimen current of the single-crystal LaB6 cathode is very stable during degradation of the vacuum in the gun chamber, while in the sintered LaB6 cathode it becomes very unstable in poor vacuum even though the total emission current is stable. The cause of this remarkable difference between the single-crystal and sintered LaB6 cathodes is discussed.
Experimental verification of the illumination profile influence on the series resistance of concentrator solar cells
Authors: Lorenzo E. , Sánchez E , Luque A.
Published: February 2003

The influence of the illumination profile shape on the performance of concentrator silicon solar cells is shown through the variation of the series resistance under different illumination conditions.
Gain-current relation for In0.72Ga0.28As0.6P0.4 lasers
Authors: Dutta Niloy K.
Published: February 2003

The optical gain coefficient is calculated as a function of the nominal current density for In0.72Ga0.28As0.6P0.4 (λg=1.3 μm) using a Gaussian fit to the Halperin-Lax band tails and Stern’s matrix element. The calculation is done for p-type, n-type and undoped material at 297 and 350 K respectively. The results show that n-type layers may give lower threshold currents than do comparable p-type layers. The gain or loss at the lasing frequency is found to be a nonlinear function of the injected carrier density so that regions of strong carrier depletion may act as saturable absorbers. The results show that the effect of the Fermi factors alone cannot explain the observed temperature dependence of threshold.
A comparison of flash-lamp-excited NdxLa1−xP5O14 (x=1.0, 0.75, 0.20) lasers
Authors: Chinn S. R. , Zwicker W. K.
Published: February 2003

The relative performance of flash-lamp-excited NdxLa1−xP5O14 laser rods has been evaluated with Nd concentrations x=1.0, 0.75, and 0.20. In agreement with theoretical calculations, the largest output energies were obtained with NdP5O14.
Calculated temperature dependence of threshold current of GaAs-AlxGa1−xAs double heterostructure lasers
Authors: Dutta N. K.
Published: February 2003

The threshold current density Jth(T) of the GaAs-AlxGa1−xAs double heterostructure laser is calculated by including both drift and diffusion mechanism for carrier leakage. For x<0.25 (ΔEg<0.3 eV), Jth increases rapidly with further decrease in the aluminum fraction x in the ternary layers, in general agreement with previous work. The ratio Jth (70 °C)/Jth (22 °C) also increases rapidly for x<0.25. The carrier concentration in the P ternary is an important quantity in determining both the temperature dependence of threshold as well as room-temperature threshold. In order to achieve a T0≳150 K for x=0.28, the P-ternary carrier concentration should be greater than 1.5×1017 cm−3.
Simplified calculations for prediction of parameters of 18.4-μm CO2 continuous-wave gasdynamic lasers
Authors: Brunné M. , Zieliński A. , Milewski J. , Volkov A. Yu. , Demin A. I. , Kudriavtsev E. M.
Published: February 2003

A simplified analytical model of the CO2 cw gasdynamic laser operating on the Q branch of the 0310?1000 radiative transition is presented in this paper. The population inversion, gain, and maximum available vibrational energy to be converted into the 18.4-μm wavelength radiation field are calculated together with corresponding values of the temperature(s), pressure(s), nozzle cross-section area(s), and laser output per unit mass flow in an ideal adiabatic approximation. The influence of the relaxation of the coupled ν1 and ν2 vibrational modes and of the cavity losses on the laser output power are considered.
Photoluminescence study of melt grown InP
Authors: Temkin H. , Bonner W. A.
Published: February 2003

A low-temperature photoluminescence study of bulk polycrystalline InP is presented. The dominant acceptor feature common to all samples at 6 K is a pair band at 1.382 and 1.387 eV, possibly associated with carbon impurity. The temperature dependence of intensity, linewidth, and spectral position of a vacancy-impurity band at 1.078 eV is reported for the first time and compared with predictions of the configuration-coordinate model. In addition, an unusual band at 1.209 eV which is formed over long periods of time at temperatures below 30 K is described.
The luminescence of defects introduced by mechanical damage of InP
Authors: Street R. A. , Williams R. H.
Published: February 2003

When crystalline InP is subjected to mechanical damage by scratching or cleaving in vacuum, a new luminescence transition near 1.3 eV results. The spectrum consists of a doublet split by ∼5 meV. Thermal quenching occurs above 100 K with an activation energy of 120 meV. Annealing to 300 K in the dark removes the luminescence centers, and the annealing temperature is reduced to about 200 K with illumination. We interpret the luminescence centers as native defects acting as electron traps of depth ∼100 meV. The defects are believed to be introduced by the process of plastic deformation of the crystal.
cw laser assisted diffusion and activation of tin in GaAs from a SnO2/SiO2 source
Authors: Nissim Y. I. , Gibbons J. F. , Magee T. J. , Ormond R.
Published: February 2003

A new technique for doping GaAs with Sn from a spin-on SnO2/SiO2 source is described. Sn is first introduced in the GaAs substrate by a slow thermal ramp. Subsequent diffusion and activation of Sn is accomplished with a cw scanning laser. Results for laser power below and above the melting power of the substrate are presented. Transmission electron microscopy and electron diffraction patterns indicate that a chemical reaction involving the formation of a tin-arsenide compound occurs during the diffusion process.
Soft x-ray production from transition radiation using thin foils
Authors: Chu A. N. , Piestrup M. A. , Pantell R. H. , Buskirk F. R.
Published: February 2003

Soft x rays have been observed from three transition radiators using 90-MeV electrons. The radiators consisted of 30 1.0-μm foils of A1, 25 1.5-μm foils of Mylar, and 23 1.0-μm foils of Be. The photon energy spectra for each radiator peaked at 1100, 1000, and 800 eV, respectively.
Studies of radiation damage in NaCl single crystals by positron annihilation
Authors: Chuang S. Y. , Jan G. J. , Tseng P. K.
Published: February 2003

Aging and heat treatment of NaCl single crystals after high-energy (100 MeV) electron irradiation was studied by positron lifetime and peak counts of two-photon angular correlation techniques. Three lifetime components, τ1≃0.15, τ2≃0.38, and τ3≃1.10 nsec, with I2≃52% and I3≃4.5%, are clearly observed for the sample aged at room temperature after the electron irradiation. Annealing of the sample up to 300 °C has reduced the value of I3 to <1%. As Ta≳300 °C, the long-lifetime component becomes practically unresolvable. The peak counts of two-photon angular correlation N(0) versus the annealing temperature Ta curves also showed a rapid decrease in the region, 125 °C<Ta<200 °C. The extinction of the long-lived τ3 component and the decrease of N(0) were attributed to rediffusion of the Na from colloidal aggregates to lattice sites in the crystal formerly vacant.
Generalized Hall-effect measurement geometries and limitations of van der Pauw-type Hall-effect measurements
Authors: Boerger Daniel M. , Kramer John J. , Partain Larry D.
Published: February 2003

A rigorous derivation is given to generalize the allowed, Hall effect, sample shapes from the restrictive, rectangular parallelepiped configurations to a much more general class of geometries characterized by mirror symmetry for materials whose mobile carriers have surfaces of constant energy in k̄ space that are well described by ellipsoids. However, this mirror symmetry condition is more restrictive than the almost arbitrary sample shapes proposed with the van der Pauw technique for thin films. Experimental data taken on n-type CdS at liquid-nitrogen temperatures in magnetic field strengths of 8 and 145 kG show that errors ranging from 1 to 600% can result from van der Pauw-type geometries depending on how much the sample shape and/or contact arrangement differs from the mirror symmetry. An empirically derived averaging technique is described that reduces the observed errors to less than 13% even with van der Pauw-type shapes that do not meet the mirror symmetry conditions.
Applications of scaling to problems in high-field electronic transport
Authors: Thornber K. K.
Published: February 2003

Utilizing changes in the carrier distribution function by magnitude and momentum scaling of scattering rates, the author a number of interesting results concerning ionization coefficients and transient drift and diffusion. Starting with a general definition of the ionization coefficient which includes nonlocal effects, the behavior of this coefficient under scaling is determined and used to find a simple analytical expression in terms of physical parameters valid for all field strengths. When fit to data for silicon, surprisingly large but consistent high-field, effective ionization energies are found for electrons (3.6 eV) and holes (5.0 eV). This expression can also relate ionization near an interface to that in the bulk. Rate scaling is also used to predict changes in velocity overshoot and diffusion-limited rise times between bulk and interface behavior. These comparisons are facilitated by a novel relationship between the time dependence of the spacial diffusion of a carrier pulse and it spacial displacement in an applied field. A classification of scattering rates suggested by momentum scaling as well as alternative scaling procedures applicable in special cases are briefly included. The former provides information on the behavior under momentum scaling of the positional-displacement correlation factor of surface-roughness scattering. The latter shows how scattering-rate scaling and momentum scaling can be made to transform into each another.
Dark conductivity and photoconductivity of hydrogenated amorphous Si1−xGex alloys
Authors: Van Dong Nguyen , Danh Tran Huu , Leny J. Y.
Published: February 2003

The dark conductivity and photoconductivity have been measured for a series of hydrogenated amorphous Si1−xGex alloy films prepared by cathodic sputtering. The primary aim of the work has been to explore to what extent the addition of Ge in a-Si:H could change the gap state distribution, the recombination process, and the lifetime for photogenerated carriers. Whereas the composition dependence of the mobility gap is expected to be linear, we show evidence for the existence of a critical concentration of Ge xc, between 0.25 and 0.30 above which the electronic properties of the films change profoundly. At xc the photoconductivity decreases significantly and there occurs a transition from monomolecular to bimolecular recombination. Experimental data also suggest that above xc the range of tail states below Ec is gradually broadened with increasing the Ge amount. Films with xc are found to be highly photosensitive. In this group of samples, slight phosphorus doping leads to considerable increase in photoconductivity by more than one order of magnitude.
Sn incorporation and electron concentration in vapor-phase epitaxially grown GaAs
Authors: Maier M. , Hanel B. , Balk P.
Published: February 2003

The total Sn concentration of Sn-doped vapor-phase epitaxially grown GaAs layers (dopant range 1017–1019 cm−3) was determined by secondary-ion mass spectrometry. Within experimental error these concentrations are equal to the electron densities obtained from Hall measurements on the same samples. This result indicates that, in contrast to earlier conclusions, Sn doping does not introduce any significant degree of compensation. The upper limit of the acceptor concentration compared to that of the donors is established to be 8%. The importance of this finding for GaAs films with donor-type dopants is discussed.
Self-resonant current steps of Josephson tunnel junctions in the presence of multimode oscillation
Authors: Enpuku K. , Yoshida K. , Irie F.
Published: February 2003

Taking into account the presence of multimode oscillation, self-resonant current steps in current-voltage characteristics of rectangular Josephson tunnel junctions are studied theoretically. An expression for the zero-field step is obtained, which is shown to be significantly different from previous theories assuming a single-mode oscillation. For a long junction with a length larger than the Josephson penetration depth, the present theory gives the magnetic field dependence of the Fiske step, whose shape is considerably changed from the one calculated from Kulik’s theory. The present theory well explains the experimental results for the zero-field step and the Fiske step of long junctions, which could not be explained by the previous theories.
High-field magnetization reversal processes in a FeSi (3.5 wt. %Si) picture-frame single crystal measured by the time-dependent neutron-depolarization technique
Authors: van Schaik F. J. , Rekveldt M. Th. , van Dijk J. W.
Published: February 2003

The magnetization reversal in a (010) [001] FeSi (3.5 wt. % Si) picture-frame single crystal has been investigated by means of the newly developed time-dependent neutron-depolarization technique, applying magnetic fields with a rectangular waveform and amplitudes between 470 and 3100 A m−1. Distinct stages in the reversal process have been observed. The initial growth in length and the lateral growth of surface domains is followed by the formation of wavy domain walls just underneath the crystal surfaces. The walls subsequently stretch, moving toward the center of the specimen where they annihilate as described by the sandwich model. It is found that the growth in length of the surface domains is most likely damped purely by spin relaxation, giving rise to a wall mobility of 0.11±0.05 m s−1/A m−1 in accordance with predictions of Landau and Lifschitz. The time duration of the lateral growth and that of the first stretching process of the wavy walls have the same field dependence, suggesting that the dynamics are similar. The eddy-current shielding of the field applied has been measured as a function of the depth in the crystal. The mobility μ of the wavy walls near the surface is found identical to that of low-field domain-wall motion μ=0.68+0.03 mm s−1. Experiments in the field region between 90 and 470 A m−1 can be interpreted by means of an intermediate reversal model according to which only a few reversed regions grow and create cylindrically shaped domains with a radius of the order of the crystal thickness.
Temperature measurement of shock-loaded polymethylmethacrylate with in-material nickel gauges
Authors: Rosenberg Z. , Partom Y.
Published: February 2003

The feasibility of direct measurement of temperature in shock-loaded solids was checked in a series of planar impact experiments using commercial nickel gauges embedded in polymethylmethacrylate (PMMA) targets. The technique is based on recording and analyzing the resistance changes of the shocked gauge, which result from heat conduction from the surrounding specimen into the gauge. Results are presented which show good agreement between experimental and calculated values obtained by using a one-dimensional heat-conduction program. We also give results of residual temperature measurements, obtained by the same technique, of shocked PMMA samples after release to zero stress.
Aluminum diffusion in ion-implanted noble metals
Authors: Hirvonen J.
Published: February 2003

The diffusion of aluminum in ion-implanted noble metal-aluminum solid solutions has been measured using the ( p,γ)-resonance broadening technique. The investigated temperature ranges were 375–550, 275–425, and 158–350 °C for copper, silver, and gold and the activation energies obtained were 1.88, 1.28, and 0.72 eV, respectively. Only the activation energy of aluminum in copper corresponds in magnitude to the ’’normal impurity diffusion’’ generally found to be valid for solutes in the noble metals.
Weak-field magnetoresistance skewness and galvanomagnetic measurements on the (001)-plane of n-type Ge single crystal
Authors: Kyriakos D. S. , Valassiades O. E. , Papadimitriou K. G. , Economou N. A.
Published: February 2003

Weak-field galvanomagnetic measurements were carried out at room temperature on a (001)-circular flat sample of an n-type Ge single crystal using the Van der Pauw-Wasscher technique, with the magnetic field parallel and normal to the sample plane. Thus, the anisotropy which appears in the (001)-plane of cubic crystals due to the magnetic field is investigated and the existence of the magnetoresistance skewness effect is established experimentally. This effect allows the determination of all the galvanomagnetic coefficients in a simple way. The new result concerning Ge is the negative sign of the ρ1212 coefficient which is attributed to the reverse rotation of the magnetoresistance.
Stretching induced γ→β transition in poly (vinylidene fluoride)
Authors: Servet B. , Broussoux D. , Micheron F.
Published: February 2003

Transition from unoriented γ to oriented β phases is followed during stretching poly(vinylidene fluoride) at 150 °C, using both x-ray and small angle light scattering techniques. It is observed that the γ→β transition occurs simultaneously with the morphologic transition from spherulitic to fibrillar state. The threshold draw ratio is λ?2, corresponding to a chain orientation function fH ?0.5; the conversion into β phase is complete at draw ratios λ?4.
Conformations of polydisperse polymer solutions: Bimodal distribution
Authors: Joanny J. F. , Grant P. , Pincus P. , Turkevich L. A.
Published: February 2003

We use scaling arguments to construct the ’’phase diagram’’ of an athermal bimodal solution; i.e., a ternary system composed of long chains, short chains, and solvent. Qualitatively, the presence of short chains reduces the effective solvent quality as experienced by the long chains. We obtain asymptotic forms for the radii of gyration of both chains throughout the phase diagram.