bluuebunny/crossref_metadata_2025 huggingface dataset:
Monte Carlo simulation of 1–10-keV electron scattering in an aluminum target
Authors: Kotera Masatoshi , Murata Kenji , Nagami Koichi
Published: February 2003

New Monte Carlo simulations of electron scattering based on the single scattering model have been performed in the low-energy region for an aluminum target, where two basic equations are required, namely the elastic scattering cross section and the energy-loss rate. We investigated the screened Rutherford equation and the Mott equation for two different atomic potentials for the former, and the Rao Sahib-Wittry equation (the modified Bethe equation) for the latter. The validity of each model is discussed in a comparison between Monte Carlo results and experimental results such as the electron range, electron backscattering, and electron transmission which have been reported by various authors. Consequently, it was found that a combination of the Mott cross section and the Rao Sahib-Wittry equation showed the best accuracy. However, the accuracy of a previous model with the screened Rutherford equation is not as bad as aniticipated because of the higher accuracy of the Born approximation for light elements such as Al, compared to Au.
Growth of Sb and InSb by molecular-beam epitaxy
Authors: Noreika A. J. , Francombe M. H. , Wood C. E. C.
Published: February 2003

The temperature dependence of the surface lifetime of free antimony on InSb has been determined using 10-kV reflection electron diffraction (RHEED). A desorption activation energy was extracted from these data and found to have a value of 64.2±3 K cal/mole which is within experimental error of ΔH (sublimation) for monatomic Sb. At substrate temperatures of 280 °C, it was possible to nucleate antimony in an epitaxial relationship with (111)A- and (111)B-oriented InSb surfaces; subsequent epitaxial growth could continue at temperatures as low as 40 °C. Films of InSb were grown homoepitaxially on (111)A-, (111)B-, and (001)-oriented InSb substrates and heteroepitaxially on (001)-oriented InAs and GaAs over a wide temperature range, 280 °<T<450 °C. Surface-atom reconstructions for Sb-stabilized and In-stabilized films are identified.
The effect of phonon-grain boundary scattering on the lattice thermal conductivity and thermoelectric conversion efficiency of heavily doped fine-grained, hot-pressed silicon germanium alloy
Authors: Rowe D. M. , Shukla V. S.
Published: February 2003

The preparation of fine-grained high-density compacts of heavily doped n-type Si63.5Ge36.5 alloy and the measurement of their thermal diffusivity over the temperature range 300 to 1150 K are reported. The compacts investigated possessed grain sizes (L) in the range 10<L<25 μm, 5<L<10 μm, and <5 μm. Within experimental error (<5%) the Seebeck coefficient and electrical resistivity do not change with grain size. The electronic and lattice thermal conductivity are obtained by combining the results with electrical conductivity data, which has been adjusted to take into account precipitation effects that occur during the period of measurement at high temperature. The lattice thermal conductivity decreases with a reduction in grain size. At room temperature the lattice thermal conductivity of the ’’single-crystal’’ starting material is equal to 4.31 W m−1K−1 and falls to 3.10 W m−1K−1 in the compact with a grain size <5 μm, a reduction of ∼28%. The reduction in lattice thermal conductivity is almost 35% at 1000 K. The thermoelectric conversion efficiency of the compact with a grain size <5 μm, when operating between room temperature and 1000 K, is computed to be 17.5% compared to an efficiency of 14.3% for ’’single-crystal’’ material, an improvement of ∼22%. It is concluded that the performance of a thermoelectric generator employing silicon-germanium thermocouples would be significantly improved by the use of fine-grained material.
NiTi fatigue behavior
Authors: McNichols J. L. , Brookes P. C. , Cory J. S.
Published: February 2003

New data are reported which show that the cycles to failure for NiTi are related exponentially to cyclic strain extent (difference between maximum and minimum cyclic strain) to at least 2×105 cycles. The relationship is apparently insensitive to thermodynamic cycle type or to stress/strain mode, but does show strong dependence on the NiTi martensite transition temperature.
Field-effect studies on Cu-doped p-type Te film metal-insulator-semiconductor structures
Authors: Mathur P. C. , Taneja O. P. , Joshi J. C. , Dawar A. L.
Published: February 2003

Field-effect studies on metal-insulator-semiconductor (MIS) structures of gold-mica Cu-doped p-type polycrystalline Te films have been made in the temperature region 77–500 K. It has been observed that the effect of negative gate voltage is to increase the carrier density and Hall mobility while the effect of positive gate voltages is opposite and less significant. The results have been interpreted in terms of accumulation and depletion of charge carriers at the insulator semiconductor interface and predominance of grain boundary barrier potential in limiting the mobility of charge carriers in accordance with the Petritz model.
Experimental study of collective acceleration of ions from a localized gas cloud
Authors: Floyd L. E. , Destler W. W. , Reiser M. , Shin H. M.
Published: February 2003

The collective acceleration of ions (H, D, He, N, Ne, Ar, Kr, Xe) to peak energies of about 5 MeV/nucleon has been achieved using a 1.5-MeV, 35-kA, 30-ns electron beam pulse. Ion energies have been measured using time-of-flight, range-energy/track etching, and nuclear diagnostics.
Time lag of line-intensity jump in decaying argon-arc plasma
Authors: Shindo Haruo , Imazu Shingo , Inaba Tsuginori
Published: February 2003

Time lag of the line-intensity jump in a decaying argon arc was experimentally investigated. Especially, the time of intensity peaks during the intensity jump was measured in a wall-stablized argon arc after the current interruption. The measurements were made for seven spectral lines of ArI. The result showed that the peak time changed depending on the ionization energy of the excited level. Namely, the peak time increased with increasing the ionization energy of the level. The peak time at lower levels involved additional delay to that predicted by the equilibrium theory. It was also shown that the amplitude of the jump at these lower levels did not reflect the accurate gas temperature.
A theoretical investigation of the pulsed high-pressure sodium arc
Authors: Chalek C. L. , Kinsinger R. E.
Published: February 2003

A time-dependent model for wall-stabilized local thermodynamic equilibrium (LTE) arcs has been used to examine the pulsed high-pressure sodium vapor arc. Arc properties including temperature, electrical conductivity, and optically thick and optically thin radiation fluxes were calculated as functions of radius and time. The calculated radial electrical conductivity distributions indicate that at least 70% of the current is channeled through the central quarter of the overall volume during the pulse rise time. This results in high central arc temperatures and distinctly nonparabolic radial temperature distributions. These calculations strongly suggest that the mechanism for color improvement of the high-pressure sodium arc operated in a high-frequency pulsed mode involves enhanced radiation, outside the D line, from high-lying sodium electronic states. These high-lying states are thermally populated in the high-temperature channel formed during application of the power pulse.
The application of optically detected magnetic resonance to the investigation of ion implanted semiconductors
Authors: Verity D. , Davies J. J. , Nicholls J. E. , Bryant F. J.
Published: February 2003

It is shown that optically detected magnetic resonance can be used to investigate ion-implanted layers in semiconductors. The technique is illustrated with results for ZnSe, where resonance signals have been selectively detected from only the implanted layer. The technique allows both the nature of lattice damage and the site identification to be established. This is demonstrated with results from argon-implanted ZnSe, where lattice damage associated with zinc vacancies has been identified. In the ZnSe samples implanted with both gallium and phosphorous ions the same lattice damage is observed as for argon implantation and, in addition, it is found that phosphorous cluster centers are formed.
Transmission electron microscopy and Rutherford backscattering studies of single and double discrete buried damage layers in P+ implanted Si on subsequent laser annealing
Authors: Sadana D. K. , Strathman M. , Washburn J. , Booker G. R.
Published: February 2003

This work is aimed at studying the regrowth behavior of single and double buried damage layers on subsequent laser annealing of P+ implanted Si, implanted at 120 keV to doses of 5×1014/cm2 and 7.5×1015/cm2, respectively. A Q-switched ruby laser operating at a wavelength of 1094 nm was used for the annealing. 90° cross-sectional transmission electron microscopy (TEM) and MeV He+ channeling spectroscopy were used to examine the damage structures and their depth distributions. At 0.9 J/cm2, TEM results showed that the single buried damage layer regrew into two discrete damage layers. At 2.0 J/cm2, TEM results showed that the first layer in the double buried damage layers type structures either completely anneal out, leaving a partially annealed second layer consisting of damage clusters or had dislocations in the first damage layer region that extended from the surface and were in direct contact with the deeper lying second layer of damage clusters. The MeV He+ channeling spectra for the above samples were in agreement with the TEM results.
Single-crystal elastic constants of MgF2 in the temperature range 4.2–300 K
Authors: Kandil H. M. , Greiner J. D. , Ayers A. C. , Smith J. F.
Published: February 2003

The six independent elastic constants of single crystals of tetragonal MgF2 have been measured over the temperature range 4.2–300 K. All six of the conventional constants show normal negative temperature dependences. The shear constants associated with normal modes of deformation tend to be weak, and one of these, (1)/(2) (C11−C12), also exhibits a weak positive temperature dependence as do all other fluorides with the rutile structure for which data are available. The data indicate a high degree of anisotropy in the atomic force interactions. A Debye temperature evaluated from the single-crystal elastic constants when combined with two empirical Einstein temperatures satisfactorily describes tabulated heat-capacity data to within 1%.
Formation of pin holes in hydrogenated amorphous silicon at high temperatures and the yield strength of a-Si:H.
Authors: Shanks H. R. , Ley L.
Published: February 2003

The formation of holes in sputtered hydrogenated amorphous silicon films after isochronal annealing has been investigated. The holes are caused by the breaking of hydrogen-containing bubbles formed at the film-substrate interface as hydrogen diffuses from the film. The diameter of the holes is dependent on the film thickness, and the number of holes depends linearly on the initial hydrogen concentration. These simple relationships are used to derive the yield strength of a-Si:H to be about 1.3×109 dyn/cm2.
Sodium passivation in Al-SiO2-Si structures containing chlorine
Authors: Stagg J. P. , Boudry M. R.
Published: February 2003

Experiments have been done to measure the trapping and neutralization kinetics of sodium ions in Al-SiO2-Si structures using oxides grown with HCl-Ar/O mixtures. The trapping of sodium at the Si-SiO2 interface was quantified by thermally stimulated ionic current (TSIC) measurements made at negative applied electric fields following positive bias temperature stress. There were three distinct types of behavior depending on the chlorine content of the oxide. For chlorine contents ≳3.0×1015 atoms cm−2 the TSIC results showed two sodium peaks, with maxima at about 0.8 and 1.5 eV, corresponding to states at the Si-SiO2 interface in which the ions were on the whole charged and neutral, respectively. Complete neutralization of the sodium, and good stability with respect to detrapping from the Si-SiO2 interface under typical device operating conditions, was possible only in samples containing ≳3.0×1015 Cl atoms cm−2. A Schottky-type variation of the neutral peak trap energy with applied field was measured, with coefficient (19±1)×10−5 eV V−1/2 cm1/2. For chlorine contents in the range (0.9–2.8)×1015 cm−2 the TSIC spectra showed two overlapping peaks, with maxima at 0.8 and about 1.25 eV. In this case only part of the second peak at energies above 1.25 eV corresponded to ions which were completely neturalized. For chlorine contents <0.8×1015 cm−2, the TSIC spectra showed only one sodium peak, at about 0.8 eV, similar to that observed in dry-grown oxides which do not contain chlorine. It was found that a fraction of the ions, about 20%, were neutralized even in dry-grown oxides. The amount of sodium neutralization was measured as a function of time and temperature of positive-bias stress, magnitude of applied electric field, and oxide chlorine content. A method was used which separated the rate of neutralization at the Si-SiO2 interface from the overall process. For samples with chlorine content ≳3.0×1015 cm−2, the time dependence of the interfacial neutralization process was consistent with a model in which lateral diffusion of sodium, to chlorine-containing ’’islands’’ at the Si-SiO2 interface, is the rate-limiting process. The activation energy of the interfacial neutralization process, (0.87±0.15)eV, is in agreement with that of lateral diffusion, (0.8±0.2)eV.
Highly reliable contacts for lead-salt diode lasers
Authors: Lo Wayne
Published: February 2003

In order to improve the long term reliability of lead-salt diode lasers, ohmic contacts of multilayer, thin-film structures consisting of In plus Au, Pt, Ni, and Pd have been studied. Diode lasers of PbSnTe fabricated with a variety of contacts were tested during room-temperature storage and during accelerated aging tests. The results show that contact reliablility can be improved when multiple overlapping films are used. After 4500 h of baking at 60 °C, lasers with In-Au-Pd-Au contacts on both sides showed the least resistance increase (10%). For lasers with In-Au-Pt-Au contacts, 1 h of baking at 60 °C is equivalent to 2 d storage at room temperature. Extrapolating these results, a 70% increase in contact resistance is expected for this type of laser after 9000 d of storage at room temperture. Our data also suggests that a smaller increase in contact resistance can be expected for lasers fabricated with In-Au-Ni-Au and In-Au-Pd-Au contacts.
Resonances in superconducting quantum interference devices—SQUID’s
Authors: Faris S. M. , Valsamakis E. A.
Published: February 2003

Resonances in asymmetric two junction SQUID’s are analyzed. The distinction between current-controlled and voltage-controlled cases is found to be crucial to the full understanding of the device dynamics. In the current-controlled case, three modes of oscillation are predicted at frequencies [(L1+L2)C1]−1/2, [(L1+L2)C2]−1/2,  and [(L1+L2)C1+C2/(C1+C2)]−1/2, and confirmed experimentally. In the voltage-controlled case only two modes are predicted at frequencies (L1C1)−1/2 and (L2C2)−1/2, which in practice are difficult to observe. We show that such a distinction leads to a better interpretation of experimental observations.
Amorphous FeCo-SiB alloys with zero magnetostriction
Authors: Kohmoto O. , Ohya K.
Published: February 2003

The saturation induction Bs and the relation between Curie temperature Tc and crystallization temperature Tx were systematically studied for Co-rich (FeCo)100−y(SizB1−z)y systems with zero magnetostriction in the range of 20⩽y⩽30 and 0⩽z⩽0.6. With increasing metalloid content y, Bs and Tc decrease and Tx increases. Small addition of Si into FeCo-B alloys greatly increases Tx, while it slightly decreases Bs and Tc . The highest Bs alloy with Tx⩾Tc was determined to be (FeCo)75.5(Si0.15B0.85)24.5 (Bs = 9.8 kG). Magnetic annealing was studied for toroidal shape alloys with different Si/(Si+B) content z but with the same Bs of 10.6 kG (Tx<Tc). It was found that residual induction Br for an alloy containing no Si (z = 0) was anomalously small (5.6 kG), while small additions of Si (z = 0.1) greatly increased Br (10 kG). This is mainly attributed to increases in the magnetically induced anisotropy Ku by a small addition of Si. The change in Ku is unexplainable by the pair model. Another contribution to the change in Br may be the weak random local anisotropy due to the intrinsic amorphous structure of the alloy. Interstitially sited Si plays an important role in increasing the magnetic ordering as well as structural stability.
Pressure variation of the low-frequency dielectric constants of some anisotropic crystals
Authors: Link Joseph , Wintersgill Mary C. , Fontanella John J. , Bean Vern E. , Andeen Carl G.
Published: February 2003

The low-frequency dielectric constant for quartz, sapphire, calcite, and magnesium fluoride has been measured both parallel and perpendicular to the optic axis at several temperatures over the pressure range 0–0.3 GPa. The results, when compared with the reported values for the effect of pressure on the high-frequency dielectric constant, indicate that pressure decreases the infrared contribution to the dielectric constant for all materials except calcite. Consequently, the infrared polarizability decreases with pressure for all but calcite. Further, it is found that the infrared polarizability decreases with pressure for calcite perpendicular to the optic axis, but increases with pressure parallel to the optic axis. In addition, it is shown that the volume-independent temperature derivative of the low-frequency dielectric constant is positive for sapphire, calcite, and magnesium fluoride showing that cubic terms in the lattice potential energy dominate, while for quartz, the derivative is negative implying that quartic terms are dominant.
Dielectric relaxations in a copolymer of vinylidene fluoride and trifluoroethylene
Authors: Furukawa T. , Johnson G. E.
Published: February 2003

Dynamic dielectric measurements were carried out for a copolymer of vinylidene fluoride (55 mol %) and trifluoroethylene (45 mol %) over the frequency range of 50 Hz–50 MHz at temperatures between −15 and 130 °C. Observed relaxations associated with a crystalline phase transition at 70 °C were found to fit the Cole-Cole arc with a distribution of relaxation times. The equilibrium dielectric constant e(0) shows a dielectric anomaly in that it rapidly increases to 70 just below 70 °C and then decreases. The logarithm of the observed relaxation time t vs 1/T (K−1) shows a shoulder near 70 °C which is interpreted as being the result of a critical slowing down phenomenon. The derived relaxation time t0 in the absence of cooperative effects exhibits an Arrhenius type temperature dependence from 40 to 130 °C with a potential barrier for dipole rotation of 13 kcal/mol.
Piezo- and thermo-optic behavior of LiTaO3
Authors: Cordero-Montalvo C. , Vedam K.
Published: February 2003

The variation of the ordinary and extraordinary refractive indices of ferroelectric LiTaO3 with hydrostatic pressure to 14 kbars has been measured for three wavelengths in the visible region of the spectrum by an interferometric method. Both the indices are found to increase linearly with pressure. The polarization induced contribution to the observed piezo-optic behavior has been evaluated. The strain polarizability constant L is positive and large, and increases for shorter wavelengths. The pure temperature contribution to the index is calculated and found to be large. Corresponding results for isomorphic LiNbO3 are discussed in terms of the difference in covalency between the Ta-O and Nb-O bonds.
Phonon contribution to metalorganic chemical vapor deposited Alx Ga1−xAs-GaAs quantum-well heterostructure laser operation
Authors: Vojak B. A. , Holonyak N. , Laidig W. D. , Hess K. , Coleman J. J. , Dapkus P. D.
Published: February 2003

A series of experiments have been conducted to determine the extent of longitudinal optical (LO) phonon contribution to quantum-well-heterostructure (QWH) laser opertion. Extensive data are presented on metalorganic chemical vapor deposited (MO-CVD) AlxGa1−x As-GaAs QWH’s with active regions consisting of larger quantum wells, or in some cases bulk layers (Lz≳500 Å), coupled to phonon-generating and  -reflecting arrays of coupled smaller quantum wells. Because of the electronic and vibrational coupling of the single larger layer to the array, the spontaneous emission and laser emission from these structures differ from that of QWH’s containing either a single well or a multilayer of uniform well thickness. In fact, phonon sideband laser operation of the larger GaAs layer can be induced at h/w∼Eg-h/wLO (undoped layers, nd−na≲1015 /cm3). An increase in either the thermal or nonthermal phonon occupation number is shown to cause phonon sideband laser operation in a QWH. A guide to the design of the multilayer array also is presented.
Donor-acceptor pair transitions in CuInS2
Authors: Lahlou N. , Massé G.
Published: February 2003

We have studied the cathodoluminescence (edge emission) of single crystals of CuInS2 obtained by iodine chemical transport. Emission intensity as a function of excitation, temperature, and time [time resolved spectroscopy] allow us to reveal donor-acceptor transitions. By fitting the TRS spectra, we calculate the ionization energy of the impurities involved: EA,D≃45 meV, ED,A ≃95 meV, as well as the maximum transition probability: WMAX≃108 s−1.
Application of an extended linear cascade model to the sputtering of Ag, Au, and Pt by heavy atomic and molecular ions
Authors: Thompson D. A.
Published: February 2003

Sputtering yields of Ag, Au, and Pt have been measured for monatomic and polyatomic ions of P, As, Sb, and Bi over the energy range 10–250 keV. It is shown that the energy dependence of the sputter yield follows the energy dependence of the surface deposited energy FD(0) when the calculated FD(0) values are obtained from a Monte-Carlo simulation. Using the Monte-Carlo values, the observed sputtering yield is found to obey the linear model of Sigmund at low FD (0), but deviates significantly at high FD (0). It is proposed that the high sputtering yields observed (up to ∼800) and the region of nonlinear dependence on FD (0) can in part be accounted for by assuming that a critical sputtering yield exists, above which surface topographical features, such as craters, can be formed. Assuming all the sputtered atoms originate from a hemispherical crater geometry of radius hs, it is found that much better agreement between measured and calculated values occur if the total energy considered in calculating the sputtering yield is taken as ℱhs0FD(x)dx. It is also demonstrated that the associated topography developed, plus a possible contribution from an effectively reduced surface binding energy, which may occur as the result of a collision spike and multimer emission, could play a significant role such that the measured sputtering yield would be higher than the revised calculated values which are still appropriate to a planar surface and a full binding energy.
Sputtering from elastic-collision spikes in heavy-ion-bombarded metals
Authors: Sigmund P. , Claussen C.
Published: February 2003

Estimates are presented for the sputtering yield as well as the specturm of sputtered atoms for metals bombarded by heavy atomic or molecular ions, under the assumption of evaporation from an elastic-collision spike of high initial temperature. The calculational is based on a cylindrical spike and a thermal diffusivity proportional to the square root of the temperature. Good qualitative agreement is obtained between calculated and measured sputter yields for antimony incident on silver.
Heuristic model of the nonlinear Rayleigh-Taylor instability
Authors: Baker L. , Freeman J. R.
Published: February 2003

A simple model is derived heuristically for the nonlinear evolution of the Rayleigh-Taylor instability. Ordinary differential equations for time evolution of the spike and bubble amplitudes are found by constructing terms that smoothly connect the regimes of small and large amplitude behavior. The results apply to arbitrarily varying acceleration fields, including shock-induced instabilities. The model predicts amplitudes accurate to better than 20% (velocity predictions are more accurate), in comparisons with published experimental data and two-dimensional numerical simulations with hydrocodes. A limitation in the present model is that the density ratio of the two fluids should not be close to one for accurate modeling.
Optimum coupling of imploding loads to pulse generators
Authors: Katzenstein J.
Published: February 2003

Dense, high temperature plasmas can be produced by accelerating axisymmetric arrays of wires, cylindrical foils, etc., in the radial direction through the action of magnetic forces. The energy of such magnetically imploded plasmas arises almost entirely from the thermalization of the kinetic energy of implosion. If such a process is to achieve high plasma temperatures it must be efficient, i.e., a sizable fraction of the available electromagnetic energy must be converted to kinetic energy. The present work addresses the problem of deriving a criterion for coupling such imploded loads to the common types of pulse generators. This criterion is obtained through the numerical solution of two coupled nonlinear ordinary differential equations, an equation of motion, and a circuit equation. Solutions are presented for two types of generators and two types of load and are compared with experimental results where available.
Preparation, vapor pressure, and thermionic emission properties of BaB6 powder
Authors: Aida Toshiyuki , Honda Yukio , Yamamoto Shigehiko , Kawabe Ushio
Published: February 2003

Barium hexaboride was prepared by the borothermic reaction using BaCO3 and B powders as starting materials. The formation process of BaB6 consists of two steps: BaCO3 + 7B→BaB2O+ + A + CO2↑ (800 °C), and BaB2O4 + A →BaB6 + 0.5B2O2↑ (1300 °C), where A is an unknown phase whose main component is considered to be boron. BaB6 powder consists of fine crystals having cubic shapes. The vapor pressure and thermionic emission current are greatly affected by the surface structure of the BaB6 powder. BaB6 powder with a thin oxide layer has a Ba vapor pressure and thermionic emission current density as much as nearly two orders of magnitude higher than BaB6 powder with a clean surface obtained by heating to a temperature over 1100 °C. These properties are remarkably influenced both by exposing the powder to the atmosphere and by introducing O2 gas during measurement. These phenomena are interpreted by considering the strong affinity of Ba and B for oxygen, the preferential vaporization of B2O2 gas, and the formation of a Ba monolayer on slightly oxidized BaB6 powder surfaces, which is generated from the reaction of BaO and B and lowers the work function.
Characterization of pulsed Nd:YAG laser-annealed, arsenic-ion-implanted silicon
Authors: Williams J. S. , Brown W. L. , Celler G. K. , Leamy H. J. , Poate J. M. , Rozgonyi G. A. , Sheng T. T.
Published: February 2003

Rutherford backscattering and channeling, TEM, SEM (Scanning Electron Microscopy), and optical microscopy have been employed to characterize annealing of ion-implanted silicon with overlapping spots of pulsed Nd:YAG (yttrium aluminum gamet) laser light. The arsenic implant dose, substrate orientation, laser power, and laser pulse length have been varied to provide a comprehensive picture of significant annealing trends. We have confirmed the earlier observations that melt regime annealing can produce essentially perfect recrystallization of implanted amorphous silicon, regardless of prior implant or substrate conditions. Our study has also confirmed differences between the melting threshold of amorphous and crystalline silicon. We observe substitutional As concentrations in the bulk that far exceed quoted maximum equilibrium values, but substitutional solubility variations and segregation effects in the near surface suggest that ’’surface’’ solubility limit may differ from bulk values. Additional data indicate that regrowth velocity of the melt-crystal interface controls the degree of observed zone refining and bulk substitutionality.
Studies of the hydrogen passivation of silicon grain boundaries
Authors: Seager C. H. , Ginley D. S.
Published: February 2003

A model is presented which predicts the current flow through and around grain boundaries which have been treated with atomic hydrogen to reduce their trap-state densities. Measurements on hydrogenated silicon grain boundaries are shown to be in agreement with this model and quantitative estimates of hydrogen penetration depth are made. The dependence of this depth on sample temperature, surface preparation, hydrogen pressure, and geometry are systematically investigated. Maximum penetration is achieved in high-pressure discharges for sample temperatures between 350 and 400 °C. The condition of the surface of the polycrystalline silicon is shown to be critically important for the in-diffusion process.
2(1D) generation mechanisms in the chemically pumped iodine laser
Authors: Richardson R. J. , Kelley J. D. , Wiswall C. E.
Published: February 2003

The reactivity of Cl2 with aqueous H2O2, both with and without added base, was investigated in a static bulb. The rate data for Cl2 absorption in these solutions are explained in terms of a diffusion-reaction model, and the results are consistent with the assumption that the reaction responsible for O2(1D) production in the O2(1D) generator utilized in the chemically pumped iodine laser is a direct reaction between Cl2 and HO−2 at the generator gas-liquid interface. The data indicate that the probability of loss of a Cl2 molecule that strikes the alkaline H2O2 gas-liquid interface is ∼10−2. The solubility of Cl2 in H2O2-H2O mixtures as well as implications of the experiment for practical O2(1D) generators are discussed.
Fluxon propagation, zero-field steps, and microwave radiation in very long Josephson tunnel junctions
Authors: Erné S. N. , Parmentier R. D.
Published: February 2003

Resonant propagation of two fluxons on an overlap-geometry Josephson tunnel junction of length 10l, having a McCumber bc = 5r is studied by numerical integration of the circuit equations of a 100-section lumped resistive shunted junction type (RSJ) model. Two different modes of propagation are observed: a symmetric fluxon-antifluxon mode and an asymmetric fluxon-fluxon mode. Which mode is stable depends on the value of the bias current. The existence of these two modes gives rise to a fine structure in the second zero-field step in the dc current-voltage characteristic of the junctions and to very different power spectra of the associated radiation emitted from the junction.
The ’’depletion layer’’ of amorphous p-n junctions
Authors: von Roos Oldwig
Published: February 2003

It is shown that within reasonable approximations for the density of state distribution within the mobility gap of a:Si a one-to-one correspondence exists between the electric field distribution in the transition region of an amorphous p-n junction and that in the depletion layer of a crystalline p-n junction. Thus it is inferred that the ’’depletion layer approximation’’ which leads to a parabolic potential distribution within the depletion layer of crystalline junctions constitutes also a fair approximation in the case of amorphous junctions. This fact greatly simplifies an analysis of solid-state electronic devices based on amorphous material (solar cells for instance).
GaAsSb and AlGaAsSb tunnel diodes
Authors: Timmons M. L. , Bedair S. M.
Published: February 2003

GaAsSb and AlGaAsSb tunnel diodes have been grown of material with 1.25–1.9 eV band gaps. High excess current values in all samples indicate a high number of defect levels in the forbidden gap.
Current limits in linear accelerators
Authors: Reiser M.
Published: February 2003

In recent years considerable interest has developed in the use of linear accelerators for various high-current applications (radiation testing facilities, neutron spallation sources, heavy-ion fusion, etc.). The beam dynamics and current limits in a linear accelerator are determined largely by the periodicity and phase-space acceptance of the external focusing system and the particle oscillation frequencies (or phase shifts per focusing period), both without the space-charge forces and with the space-charge forces of the particle bunch. General formulas for the transverse and longitudinal current limits in terms of these fundamental quantities are derived. The relationships with the actual accelerator and particle beam parameters are examined for strong (quadrupole) and weak focusing field configurations. As a practical illustration, the results are applied to a drift-tube linac with quadrupole focusing in the transverse direction and rf phase focusing in the longitudinal direction.
Radiation-induced conductivity in Teflon irradiated by x rays
Authors: Gross Bernhard , Faria Roberto M. , Ferreira G. F. Leal
Published: February 2003

This paper reports results of measurements of radiation-induced conductivity of Teflon (Teflon is a registered trademark of the E. J. du Pont de Nemours and Co.). FEP (polyfluorethylene propylene) foils irradiated by x rays at atmospheric pressure. The current induced by irradiation of the poled dielectric at exposure rates of the order of 102 R/s, initially increases with time for 10–20 s, reaches a maximum, and subsequently decreases. After an irradiation time of about 1 h, a steady-state value is attained which is of the order of 25% of the maximum current. Measurements are reported of the dependence of the current amplitudes on exposure rate, of the delayed component of induced conductivity, and of the behavior of samples which had been irradiated in short-circuit before poling. Radiation-induced polarization effects or space-charge formation could not be detected. The behavior of the current-time curves is interpreted in terms of a theory of unipolar (hole) conduction.
Holographic recording mechanism in photoconductor-thermoplastic devices
Authors: Hirshfeld Z. , Friesem A. A. , Rav-Noy Z.
Published: February 2003

The basic holographic recording mechanism in photoconductor-thermoplastic devices is described with the aid of a hydrodynamic model in which the thermoplastic layer is represented by a viscous fluid. On the basis of this model it is possible to predict the response of the devices as a function of recorded spatial frequencies, thickness of thermoplastic layer, and development heating energy. As a result, modified development procedures are suggested for increasing the diffraction efficiency and the recorded spatial frequency bandwidth. Experimental results to support the proposed model are presented.
Increasing the efficiency of CO2 transverse electric atmospheric lasers by use of low ionization potential additives
Authors: Cruz C. H. Brito , Fragnito H. L.
Published: February 2003

A method for increasing the efficiency of conventional CO2 transverse electric atmospheric lasers is presented. We take advantage of the fact that by strongly doping the usual CO2:N2:He gas mixture with a low ionization potential additive, the plasma sustaining field can be suitably reduced to attain a value optimum for the excitation of the upper laser level of CO2. We observed field reductions to as little as 20% of the reported value for the nondoped mixture. This permitted us to increase the CO2 excitation efficiency by a factor of 2. We also observed that the laser operating efficiency was increased by reducing the helium concentration in the gas mixture.
High-intensity narrow light pulse produced by self-focusing in laser spark
Authors: Bakos J. S. , Földes I. B. , Sörlei Zsuzsa
Published: February 2003

The shape of the laser light pulse transmitted through the spark produced in air by the same light pulse is investigated. A single-mode and single-frequency ruby laser is used. A narrow spike, overriding the amplitude of the original light pulse, is observed in the transmitted light. The spike is explained as the result of self-focusing taking place in the plasma. The amplitude and the time of the appearance of the spike, i.e., of the self-focused pulse, is investigated independently of the different experimental parameters. The light scattered by the spark is also observed; furthermore, clear experimental evidence of the self-focusing taking place during the cascade ionization process is presented.
Transverse-modal behavior of a transverse junction stripe laser excited by a short electrical pulse
Authors: Lau Kam Y. , Yariv Amnon
Published: February 2003

The transverse-modal behavior of a lateral injection gain-guided laser [the transverse junction strip (TJS) laser] excited by a short (70 ps) electrical pulse is investigated experimentally and theoretically. It is predicted theoretically and observed experimentally that the transverse mode strongly depends on the excitation pulse amplitude and the dc bias current (which is set below threshold). This dependence is found to be due to transient lateral carrier diffusion at the lasing junction.
Distribution of impurities in semi-insulating GaAs after heat treatment in hydrogen
Authors: Clegg J. B. , Scott G. B. , Hallais J. , Mircea-Roussel A.
Published: February 2003

Quantitative Mn, Si, Cr, and Fe profiles have been obtained by secondary ion mass spectrometry on Cr-doped semi-insulating GaAs subjected to unencapsulated anneals at 750 °C in a hydrogen ambient. The chemical concentration of Mn induced by annealing is greater than can be realized by diffusion from the bulk (Mn = 3×1013 cm−3), and relates directly to both the free-hole concentration measured in the conducting surface layer and the 5 K photoluminescence (PL) intensity of the zero-phonon emission at 1.409 eV. Post anneal profiles of the elements Si and Cr, which are present in the bulk prior to annealing, indicate that Si remains uniformly distributed while Cr suffers out-diffusion in conjunction with surface accumulation. The distribution of Fe which peaks at 5×1015 atoms cm−3 may, like Mn, arise from incorporation from the annealing ambient.
Ohmic contacts to n-GaAs using low-temperature anneal
Authors: Werthen J. G. , Scifres D. R.
Published: February 2003

The low-temperature alloying behavior of AuGe films deposited on n-type GaAs substrates (N = 2×1018 cm−3) has been investigated. Ohmic contacts were obtained using a postdeposition anneal in reducing atmosphere (H2 15%, N2 85%) at 275 °C for 120 sec with contact resistivities of 2.5×10−5 W cm2. These contacts are highly reproducible and exhibit more stable high-temperature aging characteristics and better surfaces than do the more conventional AuGe-Ni-alloyed contacts on n-GaAs.
UV photoemission from ZrF4
Authors: Brandt D. , Pong W.
Published: February 2003

Photoemission measurements on ZrF4 films were made in the photon energy range 10–27 eV. Spectral yield and photoelectron energy distributions were measured. The results indicate that the valence-band width is 5.1±0.2 eV and the photoemission threshold is 13.4±0.2 eV.
The density gradient of molecules flowing along a tube
Authors: Kurepa M. V. , Lucas C. B.
Published: February 2003

Measurements have been made of the density gradient along four capillary tubes over a wide range of input pressures. It is shown that Zugenmaier’s predictions for the density in the exit plane are closest to experiment at low pressures when the density gradient along the tube is linear. The density in the entrance plane of a capillary has not been predicted satisfactorily by any theory with which comparison has been possible. At higher pressures, such that the mean free path l is less than the diameter of the tube D, the normalized density in the entrance plane is independent of pressure but in the exit plane it is proportional to it. At these pressures the density gradient exhibits curvature proportional to (D/l)1/4 in a direction such that the initial reduction in density is less than the linear. There appear to be no theoretical predictions of the pressure dependence of these quantities.
Conductivity mechanisms in ZnS0.5Se0.5
Authors: Mathur P. C. , Agarwal S. K. , Sethi B. R. , Jain S. K. , Sharma O. P.
Published: February 2003

Low- and high-field dc conductivity measurements have been made on highly compensated as-grown ZnS0.5Se0.5 crystals in the temperature range 65–430 K. In the low-temperature range up to 220 K, where conductivity is low and varies by about 20%, it is impossible to distinguish from fit to the data between thermal activation and variable range hopping in the impurity band near the Fermi level. The high-temperature conductivity data suggest localized state conduction. A possible mechanism for localization is suggested to be small-polaron hopping.
Interfacial electron transfer as a significant step in photoelectrochemical reactions on some semiconductors
Authors: Bockris J. O’M. , Uosaki K. , Kita H.
Published: February 2003

Photoelectrochemical kinetics at the semiconductor-solution interface has been considered in all treatments in the literature, except one, to be rate controlled by processes inside the semiconductor. Evidence is presented which suggest that, at least for cathodic reactions on p-CdTe, the rate determining step is interfacial electron transfer, and a part of the total potential difference at the interface exists in the Helmholtz layer.
An explanation for the anomalous impurity concentrations in Si as measured by the Hall effect
Authors: Neumark G. F. , Schroder D. K.
Published: February 2003

It is shown that inclusion of a temperature variation of impurity activation energies in the analysis of Hall data can explain reported discrepancies in measurements of impurity concentrations in Si. The required variation of activation energies is reasonably well accounted for by screening theory; a very good fit can be obtained if one includes in addition a slight temperature variation in the Hall factor.
On light-induced effect in amorphous hydrogenated silicon
Authors: Guha S. , Narasimhan K. L. , Pietruszko S. M.
Published: February 2003

Amorphous silicon films prepared by a discharge of 10% SiH4-90% H2 mixture are shown to have properties comparable to those prepared from 100% SiH4. These films are found to be quite stable against prolonged light exposure.
A universal plot for the temperature dependence below the minimum in the resistivity of amorphous Fe-Ni alloys
Authors: Rao K. V. , Egami T. , Gudmundsson H. , Åström H. U. , Chen H. S. , Nägele W.
Published: February 2003

The low temperature electrical resistivity of amorphous FexNi75−xP16B6Al3(0⩽x⩽15) and FeyNi80−yP14B6 (0⩽y⩽27) was studied through the spin-glass and ferromagnetic regimes. All the samples showed a resistivity minimum at Tmin. which depends upon composition. When appropriately scaled, the resistivity vs. T curves of these two types of alloys can be reduced to a single universal curve. The origin of this resistivity behaviour is discussed.
Excess resistivity caused by ferromagnetic domains in pure cobalt at 4 K
Authors: Ramanan V. R. V. , Berger L.
Published: February 2003

In uniaxial ferromagnets such as Co, the presence of domains leads to an increase of the electrical resistivity. This ’’excess resistivity’’ δρ is proportional to β2, where β is the tangent of the Hall angle at saturation. We have investigated the dependence of δρ on wall orientation relative to the current, in pure Co crystals at 4 K. The current is always normal to the easy axis. Larger electrical currents and basal fields are used to reorient the stripe domains at will. Wall orientation is checked by Bitter powder patterns at 300 K. Largest δρ is for walls normal to the current. Its value agrees with theory, and is as high as 62% of the total resistivity of the sample. We have also measured the decrease of δρ as the samples are magnetized by a field parallel to the easy axis. It does not quite follow the parabolic law predicted by theory. The discrepancy may be caused by a spatial inhomogeneity of the demagnetizing coefficient in samples having a rectangular cross section. Finally, we have studied the effect of a field normal to the easy axis, which causes a canting of spins inside each domain. The associated decrease of δρ agrees fairly well with a theory based on a one-band model.
Thermopower of GdIn3 and YbAl3
Authors: Foiles C. L.
Published: February 2003

YbAl3 is a mixed valent system for which temperature independent and temperature dependent models of the Yb 3+ fraction have been proposed. An enlarged spin-disorder contribution to thermopower in associated with a temperature dependent model. The thermopower of GdIn3, an alloy which is isostructural to YbAl3 and which is expected to have large spin-disorder effects associated with the Gd, has been measured and found to have small spin-disorder effects. Interpolating these findings to YbAl3 indicates that the spin-disorder contribution is about 2 orders of magnitude smaller than that required by the proposed temperature dependence for the Yb 3+ fraction.
Spin and phonon response in uranium compounds
Authors: Buyers W. J. L. , Murray A. F. , Jackman J. A. , Holden T. M. , DuPlessis P. de V. , Vogt O.
Published: February 2003

Recent progress in understanding the spin localization and moment formation in metallic uranium compounds is summarized. Measurements have been made of the neutron scattering from UN, US, UTe and UPd3. The phonon spectra are unusual e.g. the (111) TA branch of UTe lies below the (111) TA branch from ζ = 0.2 to the zone boundary. Force-constant analysis of the UX series shows that when the U-U forces are large the moment is small. In non-ordering UPd3 the high-frequency band of crystal-field-like excitations is well described by a localized spin model. The low-frequency band (ν∼0.4 THz) is broadened, however, suggesting a delicate balance in the spin localization. In antiferromagnetic UN, where the U-U overlap is greater, the spin response is entirely broad with a large anisotropy gap. Ferromagnetic UTe has a quadratically rising spin-wave branch as well as a higher flat branch. Thus UPd3 and UTe provide clear evidence for the existence of crystalline electric fields in metallic actinide compounds.
Ferromagnetic resonance in compositionally modulated Cu-Ni thin films
Authors: Dillon J. F. , Gyorgy E. M. , Rupp L. W. , Yafet Y. , Testardi L. R.
Published: February 2003

Ferromagnetic resonance at 12 GHz has been studied in some of the same compositionally modulated CuNi films on which magnetization measurements were reported recently. The best samples, e.g., a film designated [20‖10]880 (i.e, 880 repetitions of [20Å Cu on 10Å Ni]) show the 295 K resonance behavior expected for a magnetic material with an easy plane uniaxial anisotropy and a line width ΔH∼103 Oe. As T is lowered the quantity Drf.≡4πM+2K/M extracted from the line position data using Kittel’s equations increases roughly linearly with decreasing T. For [10‖10] 2440, Drf goes from ∼4 kOe at 295 K to ∼20 kOe at 80 K. This low temperature value agrees with that obtained from He temperature magnetization curves. A remarkable result of the magnetization measurements was the fact that Ddc at 4.2 K was essentially the same for [10‖10], [20‖10], and [40‖10] samples. In striking contrast, the microwave values at 80 K decrease markedly with increasing thickness of the Cu layers. Simple averaging of the resonance equations has not led to an explanation of this difference.