bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of a Jahn-Teller ion on the ground states of Fe2+ and Ni2+ ions in spinel ferrites
Authors: Srivastava C. M. , Patni M. J. , Srinivasan T. T.
Published: February 2003

The influence of crystal distortion due to a Jahn-Teller mechanism on lattice constant, Curie temperature, magnetization, and geff has been investigated by substituting Cu2+ ions in FeZn and NiZn ferrites. The observed results have been analyzed on the basis of exchange, spin orbit, and Jahn-Teller mechanisms. The changes exhibited on copper substitution in the two spinels have sharp differences. These have been attributed to the difference in the ground state of the divalent ions.
Abstract: Critical behavior in ferromagnetic Fe[S2CN(C2H5)2]2Cl
Authors: DeFotis G. C. , Pugh S. A.
Published: February 2003

Experimental work on the three-dimensional Ising ferromagnet Fe[S2CN(C2H5)2]2Cl is reviewed, and magnetic susceptibility and sublattice magnetization2 data are analyzed with correction-to-scaling terms included. Critical exponents γ = 1.165±0.03 and β = 0.245±0.02 are found, assuming modified power law expressions χ0 = Γt−γ (1+aχtΔ) and m(T/TC) = B‖t‖β(1+aM ‖t‖Δ) with correction exponent and amplitudes, Δ = 0.493, aχ = 0.207, and aM = 0.156. The critical amplitudes are found to be Γ = 1.47±0.07 emu/mole (Γr = 1.07±0.05 for the reduced susceptibility) and B = 1.30±0.05. Γ is larger than most theoretical estimates for the Ising model on three-dimensional lattices, while B is smaller than theoretical results. The amplitude ratio Γr/B is 0.83±0.07. Theoretical values for this ratio are not universal but exhibit only a weak lattice dependence, and are in the range from 0.65 to 0.71 for the three-dimensional Ising model. Heat capacity data are sparse and less reliably analyzed, but appear to suggest abnormally large values of α (≳0.3) and rather small values of A (0.2–0.5) in C/R = At−α+ B′. Including a correction-to-scaling term does not alter this conclusion. The ratio RC = AB−2Γr is in the range from 0.12 to 0.33, substantially less than the theoretical value 0.474 for this universal quantity in the three-dimensional Ising model. Neither the possible presence of multispin interactions nor a nondiverging AF contribution to the susceptibility appear to be adequate to account for the unusual critical behavior observed in this system.      a)Acknowledgment is made to the donors of The Petroleum Research Fund, administered by the ACS, for partial support of this research.  1 G. C. DeFotis, F. Palacio, and R. L. Carlin, Phys. Status Solidi B 95, 380 (l978).  2 G. C. DeFotis and J. A. Cowen, J. Chem. Phys. 73, 2120 (1980).
The friction term and the energy term in the bulged wall Globus model
Authors: Escobar M. A. , Magaña L. F. , Valenzuela R.
Published: February 2003

Globus model for magnetization processes in polycrystalline materials has led to significant improvements in the recognition of the contribution from different microstructural parameters. In this paper we present an analysis of the friction (pinning) term and the wall energy term that appear in the model. Experimental results show that the ratio of these terms is a constant, independent of temperature and the same for two different ferrites, YIG and Ni0.5Zn0.5Fe2O4. This result is analyzed by considering that the origin of the friction is the destruction of the wall, the shape of the grains, and the effect of demagnetizing fields.
Power losses in a conducting sheet with bar domains. II. Losses due to switching
Authors: Lorenz B. E. , Coren R. L.
Published: February 2003

We consider a model of a magnetic sample with distribution of Barkhausen switch sites which reverse their moments at a constant rate. Switching is considered in the case that reversal is induced by the incidence of a domain wall. The induced current distribution J of symmetrically placed regions has already been determined. The loss calculation involves summing J2 over switching regions in the plane of the moving wall, and summing as the wall traverses a full cycle. Averaging techniques are employed and the expected loss over unit volume, per cycle is found, due solely to the Barkhausen regions. This is the classic static or ’’hysteresis’’ loss. In a later report the analysis is extended to determine the full losses.
On the effect of parasitic parameters on efficiency in energy compression networks
Authors: Zucker Oved
Published: February 2003

This paper describes and analyzes a generalized approach to compression networks that uses both opening and closing switches. An efficiency of compression equation showing the dependence of efficiency on parasitic parameters is derived. This equation indicates that a unique geometric mean relationship has to be maintained and an optimum number of stages must exist for maximum energy compression.
Scanning x-ray radiography: First tests in an electron spectrometer
Authors: Cazaux J. , Mouze D. , Perrin J.
Published: February 2003

The aim of this paper is to present the first images obtained in scanning x-ray radiography without the help of synchrotron radiation but simply with a classical x-ray source, that is, a scannable electron beam focused on an aluminum foil to produce characteristic x-ray lines. The emitted x rays (about 1011–1012 x-ray photons s−1 mm−2) allow the observation of highly absorbing specimens in a nonabsorbing matrix about 10 μm thick. We show that these results can be improved by simple modifications of a scanning transmission electron microscope.
Unstable oscillatory Pierce modes of neutralized electron beams
Authors: Cary John R. , Lemons Don S.
Published: February 2003

Oscillatory modes of the Pierce system have been calculated. These modes are found to have growth rates comparable to the previously investigated purely growing modes. When these modes are included, it is found that the Pierce system is unstable for most values of ωp L/V0≳π.
Diffusion of aluminum in ion-implanted alpha iron
Authors: Hirvonen J. , Räisänen J.
Published: February 2003

The bulk diffusion coefficient of aluminum in ion-implanted paramagnetic iron-aluminum alloys has been determined to have an activation energy of 3.17±0.15 eV and preexponential factor of 1.6±4.60.2 cm2/s by measuring the time evolution of aluminum profiles in the temperature range 775–900 °C.
Moderate mobility enhancement in single period AlxGa1−x As/GaAs heterojunctions with GaAs on top
Authors: Morkoç H. , Drummond T. J. , Fischer R. , Cho A. Y.
Published: February 2003

Selectively doped single period AlxGa1−x As/GaAs heterojunctions with the GaAs layer on top of AlxGa1−xAs were prepared by molecular beam epitaxy. Moderate electron mobility enhancement was achieved when the samples were grown near a substrate surface temperature of 700 °C. Samples grown well below and well above 700 °C did not show observable mobility enhancement. The samples grown at 700 °C and with an electron concentration of 1017 cm−3 exhibited 300 K mobilities of about 4 500 cm2/Vs and 78 K mobilities of 8500 cm2/Vs, which is about a factor of 2 higher than that of bulk GaAs at 78 K. To our knowledge, this is the first report of mobility enhancement in these inverted single period AlxGa1−x As/GaAs heterostructures.
IrSi1.75 a new semiconductor compound
Authors: Petersson S. , Reimer J. A. , Brodsky M. H. , Campbell D. R. , d’Heurle F. , Karlsson B. , Tove P. A.
Published: February 2003

Optical and Hall effect measurements on thin film layers of polycrystalline IrSi1.75 show that this material is a semiconductor. The band gap is approximately 1.2 eV. The films obtained saturated with silicon were p-type with a charge carrier density of the order of 4×1017 cm−3.
Effect of indium on the field effect studies of thin SnTe films
Authors: Dawar A. L. , Mohammed A. O. , Kumar Partap , Taneja O. P. , Mathur P. C.
Published: February 2003

Field effect studies were made on In-rich SnTe films using metal-insulator-semiconductor (silver-mica In-Sn e) structures. It has been observed that when a negative gate field (∼1.5×105V/cm) was applied to the films at 77 K, a permanent decrease in the value of the Hall coefficient RH takes place, whereas no such effect has been noticed in metal-insulator-semiconductor structures on undoped SnTe films.
Electrical properties of p-type MnxCd1−x Te crystals
Authors: Stankiewicz J. , Aray A.
Published: February 2003

The measurements of Hall effect, conductivity, and photoresponse were performed for MnxCd1−x Te crystals with x = 0.05, 0.10, 0.15, and 0.20. The investigated crystals were subjected to thermal treatments in the presence of Cu, Au, As, Cd, and in vacuum. The annealings with dopants resulted in substantial increase of resistivity. The activation energies of acceptors were determined. It is suggested that the observed levels are associated with complexes present in MnxCd1−x Te crystals.
Positive charge effects on the flatband voltage shift during avalanche injection on Al-SiO2-Si capacitors
Authors: Fischetti M. V. , Gastaldi R. , Maggioni F. , Modelli A.
Published: February 2003

Electron avalanche injection is performed at various temperatures on Al gate, wet oxide metal-oxide-semiconductor capacitors. The observed behavior of the flatband voltage shift versus injected charge is well represented by a phenomenological model which includes the buildup of positively charged defects at the Si-SiO2 interface, their annealing, and their neutralization by ’’trapped’’ electrons. At high temperatures (T≳350 °K) annealing is very efficient, while for T≲250 °K the positive charge is quickly neutralized. Thus the ’’turn around’’ is observable at room temperature only. The role of trivalent silicon defects and of Si-H bonds is discussed.
Sputtering of amorphous Co-Zr and Co-Hf films with soft magnetic properties
Authors: Shimada Yutaka , Kojima Hiroshi
Published: February 2003

Amorphous Co-Zr and Co-Hf films produced by sputtering have been investigated. The fundamental magnetic properties, sputtering conditions for the soft magnetic properties, and annealing to obtain high permeability films have been studied. The saturation magnetization, magnetostriction of the sputtered films, and range of composition of amorphous phase have been determined. Sensitive dependence of the soft magnetic properties on Ar gas pressure has been found. Sputtering in low Ar gas pressure suppresses the formation of microcrystals in the amorphous matrix and columnar structure in the films which deteriorates the soft magnetic properties. High permeability films have been obtained by annealing and their thermal stability was studied.
Magnetic hardening of Pr-Fe and Nd-Fe alloys by melt-spinning
Authors: Croat John J.
Published: February 2003

The dependence of the hard magnetic properties of melt-spun Nd1−xFex (0.5⩽x⩽0.7) and Pr1−xFex (0.4⩽x⩽0.7) alloys on quench rate is reported; the latter was controlled by varying the substrate surface velocity (vs ) of the melt-spinner. All of the alloys show an appreciable maximum in coercivity (Hci ) as a function of quench rate. For Nd1−xFex , a peak room temperature Hci of 8.65 kOe was found for a Nd0.5Fe0.5 alloy. Room-temperature coercivities of ∼7.5 kOe were found in Pr1−xFex over the interval 0.6⩽x⩽0.7. The temperature dependence of the coercivity changed from a 1/T dependence for the most amorphous alloys to exponential for the alloys exhibiting maximum coercivity; coercivities as high as 78 kOe were found at 20 K. X-ray data indicate that the coercive force results from an amorphous and/or very finely crystalline microstructure whose average particle size and/or intrinsic anisotropy varies as a function of quench rate. Crystallization studies, using differential scanning calorimetry and x-ray diffraction, found the Nd1−xFex and Pr1−xFex alloys to form a number of nonequilibrium phases but could not establish whether these phases formed from an amorphous or metastable crystalline precursor. Depending on quench rate, the melt-spun Nd1−xFex alloys appear to form distinctly different nonequilibrium phases, indicating that the magnetically hard precursor may also vary with quench rate.
Propagation of magnetostatic surface waves across a large amplitude grating
Authors: Camley R. E. , Glass N. E. , Maradudin A. A.
Published: February 2003

The dispersion relation is obtained and solved for magnetostatic (Damon-Eshbach) surface waves propagating normal to the grooves of a large amplitude grating ruled on the surface of a semi-infinite ferromagnet. It is assumed that a static external magnetic field, as well as the saturation magnetization in the ferromagnet, is oriented parallel to the grooves of the grating. The dispersion curve consists of many dispersive branches in the presence of the grating, in contrast with the single, non-dispersive branch obtained in the case of a planar surface. Also, in contrast with Damon-Eshbach surface waves on a planar surface, which propagate in only one direction normal to the externally applied magnetic field, and not in the reverse direction, magnetostatic surface waves on a grating propagate in both directions normal to the field. Moreover, their dispersion curves are reciprocal, i.e., ω(−k) = ω(k), where ω(k) is the fre- quency of the surface wave of one-dimensional wave vector k.
Scattering of normally incident magnetostatic volume waves by a metal half-sheet
Authors: Yashiro Ken’ichiro , Ohkawa Sumio
Published: February 2003

The problem of the scattering of magnetostatic volume waves (MSVWs) by the edge of a metal sheet is solved in the quasimagnetostatic approximation relying on the Wiener-Hopf technique. Straight-crested MSVW’s are assumed to impinge on the edge of the metal sheet normally from the unmetallized side of the ferrite slab, which is magnetized perpendicularly to its surfaces. Expressions are given for the reflected and transmitted MSVW modes, and the reflectivity and transmissivity are evaluated. It is shown that the reflectivity and transmissivity are dependent on the biasing magnetic fields.
Electromechanical relaxations in oriented polymers
Authors: Strathdee J. , Robinson W. H.
Published: February 2003

A model is proposed to describe the electromechanical relaxation associated with the rotation of dipolar elements on polymer chains. These elements are allowed to rotate about the main axes and their contribution to the elastic strain and electric displacement is deduced from a Gibbs function. The corresponding dielectric, piezoelectric and elastic relaxation strengths are expressed as integrals over a distribution of dipole and chain orientations. By concentrating the distribution in a selection of orientations, these integrals are simplified and it becomes possible to examine the component structure of the relaxation tensors for these orientations. The results are tabulated.
Laser treatment of a nonsubstitutional alloy Cr implanted in aluminum
Authors: Battaglin G. , Carnera A. , Della Mea G. , Mazzoldi P. , Jannitti E. , Jain Animesh K. , Sood D. K.
Published: February 2003

A nonsubstitutional alloy of 7 at. % Cr implanted in single-crystal aluminum has been irradiated with Q-switched ruby laser pulses up to 6 J/cm2. Liquid phase epitaxy, resulting in enhanced substitutionality without any Cr redistribution, is observed up to 2 J/cm2 for a laser pulse duration of 25 ns. At higher energy densities and with shorter pulses, 12-nsec duration, convection effects are observed to inhibit liquid phase epitaxy. The surface reflectance appears to reduce due to high implantation dose.
Diffraction efficiency and decay times of free-carrier gratings in silicon
Authors: Eichler H. J. , Massmann F.
Published: February 2003

A spatially periodic distribution of electron-hole pairs has been produced in silicon crystals by excitation with a pulsed neodymium yttrium aluminum garnet (Nd: YAG) laser. The diffraction efficiency and the decay time of the grating structure has been measured by diffraction of an independent quasi-cw laser beam as a function of the energy density of the exciting laser. At low energy-densities the diffraction efficiency is given by a squared Bessel function dependent on the carrier density as expected from theory. At higher incident energy densities deviations occur which can be explained by free-carrier absorption and intensity fluctuations across the beam. The grating decay time is determined by ambipolar diffusion and Auger recombination.
Surface resistivity measurements of S1 photocathodes
Authors: Hou X. , Sibbett W. , Weekley B.
Published: February 2003

Measurements carried out on semitransparent S1 photocathodes which indicate that their surface resistivities depend critically on the processing techniques used are described. The results show that, in general, S1 photocathodes having good long wavelength response (≳1 μm) exhibit high surface resistivities ∼MΩ/⧠. A method is also outlined by which improved near infrared (NIR) photoresponse can be obtained for an Ag-O-Cs photocathode, and a physical interpretation is suggested to explain the observed characteristics.
Photoemission studies of clean and oxidized Nb and Nb3Sn
Authors: Miller J. N. , Lindau I. , Stefan P. M. , Weissman D. L. , Shek M. L. , Spicer W. E.
Published: February 2003

In conjunction with Auger electron spectroscopy measurements, we have developed a procedure for obtaining a clean Nb surface using an electron bombardment heating technique. We have then studied the valence band photoemission as a function of photon energy. We find that calculations for the bulk theoretical density of states are in basic agreement with the ultraviolet photoemission spectroscopy data. We have also studied the initial oxidation of the clean Nb surface. Structure in the energy distribution curves suggests three stages in the oxidation process. Furthermore, the valence band energy distribution curves for clean Nb3Sn prepared ’’in situ’’ were measured and showed a strong resemblance to pure Nb as has been observed previously in x-ray photoemission. Evidence is found for the existence of Nb2O5 and SnO2 in the surface oxides of Nb3Sn.
Evaluation of amines as bases for the H2O2-Cl2 singlet-oxygen generation reaction
Authors: Richardson R. J. , Carr P. A. G. , Hovis F. E. , Ageno H. Y. , Hurst J. K.
Published: February 2003

The performance of a sparger-type, singlet-delta-oxygen generator using various amines as alternative bases to NaOH was found to be comparable to the performance of a generator with the Cl2-NaOH-H2O2-H2O reactant system. Based on the percentage of singlet-oxygen evolution from the generator and the known rates of reaction between Cl2 and propylamine, the reaction between Cl2 and HO−2, which is assumed to produce singlet oxygen, is estimated to be ∼108 M−1 s−1.
Reduction of solar cell efficiency by bulk defects across the back-surface-field junction
Authors: Sah C. T. , Yamakawa K. A. , Lutwack R.
Published: February 2003

Defects across the back-surface-field junction (BSF) can seriously degrade the performance of high-efficiency solar cells. Poor alloying, diffusion pipes, random contact metal penetration, and impurity segregation and clustering can all cause partial or complete electrical short circuits across the BSF junction. Performance degradation from defects distributed in the bulk across the BSF junction is analyzed using the new developed-perimeter model. A defective unit cell, containing one defect, is characterized by a three-region developed-perimeter device model. The width of the first region surrounding the defect is characterized by the range or the distance-of-influence of the defect and this range is shown to be about two diffusion lengths. The defect itself is characterized by three parameters: the defect area, the defect areal density, and the surface recombination velocity at the defective area. This defect model applies to both a few defects and a large number of defects. Family of curves and numerical examples are presented to show that there is very substantial degradation of open-circuit voltage in thin and high-efficiency cells, even if there are only a few defects. It is also shown that the degradation is not sensitive to the defect area but highly dependent on the defect density. Two defects of half area will cause almost twice as much open-circuit-voltage degradation than one defect of twice the area due to the two-diffusion-length defect range or distance-of-influence. Due to the strong density dependence, bulk defects, even at low density, could pose a serious limitation to the attainment of theoretical high open-circuit voltage and efficiency in thin and high-efficiency back-surface-field solar cells.
A multibeam x-ray topographic method for a double-crystal arrangement
Authors: Chang Shih-Lin
Published: February 2003

A novel method for x-ray topographic studies on crystal defects is developed by using simultaneous Bragg reflections in a double-crystal arrangement. More than one topographic image can be obtained simultaneously. One to one correspondence between the obtained images are observed. This method provides a means for shortening the time consumed in determining the direction of Burgers vector.
Screw dislocation in a two-phase isotropic thin film
Authors: Chu S. N. G.
Published: February 2003

By using the complex potential and conformal mapping techniques, the stress field of a straight screw dislocation lying parallel to the surface of a two-phase isotropic thin film of equal thickness in each phase and a welded interface is analyzed. The solution, when reduced to a single-phase thin film, is in agreement with that derived by Liebfried and Dietze using an infinite array of image dislocations. The presence of a second phase is found to increase the magnitude of the stress components for the screw dislocation except for τxz near the interface where the effect is the reverse. The image force on the dislocation near the interface can be attractive or repulsive depending upon whether the dislocation is situated in the hard or soft phase. In the case where the dislocation is situated in the soft phase, the total image force tends to drive the screw dislocation to the surface. Furthermore, the screw dislocation is found to be unstable at the interface. The elastic solution for an interfacial dislocation becomes a special case.
Surface acoustic wave reflector consisting of a poled and unpoled domain array in piezoelectric ceramics
Authors: Takeuchi Hiroshi , Yamashita Kunio
Published: February 2003

New surface acoustic wave reflectors were fabricated using modified lead titanate ceramics with the chemical composition (Pb1−(3x/2)+(z/2)Ndx ) (Ti1−y−zMnyInz ) O3 (x = 0.11, y = 0.02, z = 0.04). These reflectors consist of many poled and unpoled domains which are arranged alternatively in piezoelectric ceramics, instead of the usual metal strips or grooves. The frequency of measurements was around 22 MHz. Reflectivities per element for these reflectors were found to be as high as 2.9%, since the difference between surface acoustic wave velocities in these domains was large. This reflectivity was about three times larger than that for a conventional metal strip formed on the ceramics. Total reflectivities can be estimated as 89% for only 50 pairs of poled and unpoled domains.
Sputter-enhanced diffusion phenomena in Cu/Ni alloys at elevated temperatures
Authors: Shimizu Hazime , Ono Masatoshi , Koyama Naoyuki , Ishida Yoichi
Published: February 2003

Compositional changes of the surface and near surface layers were studied in copper-nickel alloys during argon ion bombardment (3 keV) at temperatures up to 873 K, using Auger electron spectroscopy (AES) and x-ray microanalysis (XMA). A long range depletion of copper on the order of 100 nm in thickness was observed depending on the sputtering time, specimen temperature, and ion beam density. An enhanced diffusion of copper was noted in the damaged layer at low temperatures. The apparent activation energy calculated, assuming an Arrhenius type equation, was 5–6 kcal/mol. It is suggested that an interstitial type diffusion mechanism was predominant in the damaged layer.
Deep level defects in heteroepitaxial zinc selenide
Authors: Besomi Paul , Wessels Bruce W.
Published: February 2003

Deep level defects in epitaxially grown high-conductivity zinc selenide were investigated using transient capacitance spectroscopy. A total of seven electron traps was observed in Au/ZnSe Schottky diodes and ZnSe/GaAs n-p heterojunctions, having activation energies of 0.24, 0.33, 0.35, 0.42, 0.54, 0.71, and 0.86 eV, respectively. The emission rate, capture cross-section prefactor, and concentration of each trap are reported in this paper. Trap concentrations ranged from 1011 to 1014 cm−3 depending upon the epitaxial growth conditions. A defect model involving selenium vacancies and divacancies as well as deep donor impurities satisfactorily describes the variation of electron trap concentration with zinc/selenium ratio in the vapor phase.
Infrared quenching of photoconductivity and the study of gap states in hydrogenated amorphous silicon alloys
Authors: Vanier P. E. , Griffith R. W.
Published: February 2003

Infrared quenching of photoconductivity has been investigated for plasma-deposited a-Si:H alloys. The temperature and spectral dependences of the quenching are consistent with a two-level model of competing recombination centers. The infrared quenching spectrum shows that this effect occurs for photons having energies in the range 0.4 eV<hνir <1.6 eV. The low energy threshold is found at Et = 0.41 eV for T = 100 K. This threshold shifts slightly with temperature in a manner expected for the quasi-Fermi level for trapped holes.
Analysis of rotational nonequilibrium behavior in hydrogen fluoride/deuterium fluoride systems
Authors: Yang Tien Tsai , Blauer Jay A.
Published: February 2003

A surprisal correlation of the experimental data for the V→R, T processes occurring in hydrogen fluoride/deuterium fluoride (HF/DF) chemical lasers indicates that the resulting product rotational level distributions may be very narrow. This result can be used to greatly simplify the modeling effort because a one-to-one correspondence between reactant and product states can be assumed. A similar analysis has also been used to correlate the published experimental results for R→R, T relaxation of HF/DF molecules. The correlation compares well with the trajectory analysis of Wilkins. Since the available experimental data for R→R, T relaxation relate to ambient conditions, the trajectory analysis temperature dependence was assumed.
V-grooved substrate buried heterostructure InGaAsP/InP laser by one-step epitaxy
Authors: Ishikawa Hiroshi , Imai Hajime , Umebu Itsuo , Hori Ken-ichi , Takusagawa Masahito
Published: February 2003

A V-grooved substrate buried heterostructure (VSB) InGaAsP/InP laser by one-step epitaxy emitting at 1.3 μm wavelength is developed. The one-step epitaxy VSB laser is realized by using Cd diffusion for the formation of the p-InP internal current restriction layer. Efficient current restriction is confirmed in the Cd-diffused current restriction structure to be comparable to that by two-step epitaxy. The VSB laser by one-step epitaxy showed a cw threshold current of about 15 mA at 25 °C and a far field pattern as smooth as that of the two-step epitaxy VSB laser. The T0 value was 50–60 K below 55 °C and was 30 K above 55 °C. The threshold current obtained here is the lowest among various InGaAsP/InP lasers by one-step epitaxy.
Theory of thermal noise upconversion in LiIO3 and LiNbO3 crystals
Authors: Guha Shekhar , Falk Joel
Published: February 2003

A theory of upconversion of blackbody radiation is presented. Thermal noise contributions from the background as well as from the up conversion crystal are considered. The effects of Poynting-vector walkoff, diffraction, and focusing are discussed. Experimental verification of some aspects of the theory is reported.
Horizontal shear acoustic waves on layered surfaces with sinusoidal corrugations
Authors: Wilcox J. Z. , Yen K. H. , Wilcox T. J. , Evans G.
Published: February 2003

The propagation characteristics of shear horizontal acoustic waves on sinusoidally corrugated layered surfaces of elastically isotropic materials are investigated. The mathematical methods developed make no approximation with regard to the thickness of the substrate or the surface layer, nor to the depth of the corrugation. The general expression derived here is amendable to analyses of propagation characteristics for any values of these parameters. The general theory is applied to obtain an approximate dispersion relationship for the lowest-frequency mode, i.e., the surface wave and the width of the first frequency stopband. The main qualitative characteristics of the high-frequency bands are also briefly discussed.
Use of a ferrofluid as the heat-exchange fluid in a magnetic refrigerator
Authors: Barclay J. A.
Published: February 2003

The use of a ferrofluid is proposed as the heat-exchange fluid in a wheel-type magnetic refrigerator in order to avoid flow-control problems. An equivalent-circuit analysis of the ferrofluid flow path with several different magnetic field profiles indicates that it is possible to obtain the desired flow control in at least one case. Sample design calculations for the revised wheel-type refrigerator are presented. In addition, the results of heat-transfer measurements from kerosene to a stainless-steel screen and from a kerosene-base ferrofluid to the same screen in and out of an 8-T magnetic field are described.
Propagation of surface waves in inhomogeneous plasmas
Authors: Nghiem P. , Chaker M. , Bloyet E. , Leprince Ph. , Marec J.
Published: February 2003

Phase and attenuation measurements of a test wave enable us to verify the propagation characteristics of surface waves in inhomogeneous plasma columns.
Estimation of ablation thickness by ion expansion analysis in laser-produced plasmas
Authors: Gupta P.D. , Goel S. K. , Uppal J. S.
Published: February 2003

Ion expansion analysis of the plasma produced from targets consisting of thin layers of aluminum on carbon substrates is used to estimate the thickness of the material ablated from the target. Ablation depth obtained in this manner is consistent with a steady-state self-regulatory model for plasma heating.
Magnetic behavior of metal hydrides as a function of hydrogen pressure and composition
Authors: Yamaguchi Masuhiro , Katamune Takehiko , Ohta Tokio
Published: February 2003

A versatile vibrating-sample magnetometer has been developed which measures the magnetization of metal hydrides as a function of magnetic field, hydrogen pressure (up to 6 MPa), and composition, temperature, and time. For the ferromagnetic NdCo5Hx system, magnetic properties of well-defined hydrides and hydride-phase transformations are studied by this method. The existence of a hydrogen-rich phase in the NdCo5Hx system, the γ phase, is indicated by the temperature dependence of magnetization under the influence of high pressure hydrogen.
Measurements of the photoelastic and elastic constants of drawn films and extruded rods of polypropylene with Brillouin light scattering
Authors: Cavanaugh David B. , Wang C. H.
Published: February 2003

The elastic constants C11, C33, C44, C13 of oriented poly propylene films are measured with Brillouin scattering and are compared with the elastic constants obtained from extruded poly propylene rods. The photoelastic constants p12, p13, and p31 of the extruded rod samples are measured by comparison to a poly(methylmethacrylate) reference scatterer. In the film samples, the relative values of the photoelastic constants p11, p33, p13, and p31 are measured by comparison of the quasilongitudinal and quasitransverse intensities at several directions of sound propagation. Within the experimental error, p13, p31, and p12 are found to be unaffected by extrusion or stretching. p11 and p33 are found to change in relation to p31 in the film samples. The results are interpreted by considering the chain morphology and the theory of photoelastic interaction. The changes in the Brillouin intensities are due to changes in the elastic constants, rather than the photoelastic constants.
The field induced in a conducting sphere placed in a steady magnetic field and a perpendicular oscillatory magnetic field
Authors: Hugrass W. N.
Published: February 2003

The fields induced in a conducting sphere of resistivity, η, placed in a strong, steady magnetic field Ba ẑ, and a small oscillatory magnetic field (in the xy plane) of magnitude Bω have been calculated approximately for Bω/Ba ≪1 and Ba/neη ≪1, where n is the number density. The conducting sphere is assumed to have a uniform resistivity and number density and the ions are assumed immobile. It has been shown that: (a) If the applied oscillatory field is linearly polarized, the magnetic field induced in the conducting sphere has a rotating component for which ω is parallel to Ba ẑ. (b) If the applied oscillatory field is rotating (circularly polarized), its penetration in the conducting sphere is enhanced or impeded with respect to the classical skin effect depending on whether the sense of rotation is parallel or antiparallel to Ba ẑ. These results are consistent with the experimental observation in the rotating field plasma experiments.
Magnetic blocking direct recovery efficiency for intense neutral beams
Authors: Whealton J. H. , Wooten J. W. , McGaffey R. W.
Published: February 2003

The ion recovery efficiency of a transverse magnetic field monochromatic direct recovery device intended for intense neutral beams is examined theoretically by solving a Poisson–Vlasov equation. An optimum in recovery efficiency is obtained for finite ion current density and excess initial speed.
Primary ion tetrode optics for high transparency multibeamlet neutral injectors
Authors: Whealton J. H.
Published: February 2003

A number of tetrode electrode designs are considered. An improvement resulting in 425% more brightness with 26% less source plasma is suggested from the results of solutions of the Poisson–Vlasov equations.
Light reflection from randomly oriented convex particles with rough surface
Authors: Schiffer R. , Thielheim K. O.
Published: February 2003

Light reflection from rough spheres being large compared to the incident wavelength is considered—the resulting reflection pattern is identical to that one produced by randomly oriented convex particles. Only the limiting case of short wavelengths is treated; that means the laws of geometrical optics are assumed to be valid. It turns out that the decisive quantity is the probability distribution P(β) of the directions of the surface normal vectors. The resulting differential cross section shows the following behavior: with growing roughness the cross section flattens for moderate scattering angles, whereas a rise occurs in the region of backscattering. The resulting formula can be inverted: from the measured cross section the probability distribution P(β) can be calculated by means of an integral transformation.
Ray optics of guided TM waves in a slab of uniaxially anisotropic plasma
Authors: Yasumoto K.
Published: February 2003

A ray optical description is presented for the TM wave guided by a slab of uniaxially anisotropic plasma. An interesting feature of the totally reflected ray within the slab is brought out.
Polysilicon transistors on glass by pulsed-laser annealing
Authors: Morin F. , Coissard P. , Morel M. , Ligeon E. , Bontemps A.
Published: February 2003

Amorphous silicon thin films deposited on glass substrates were crystallized by pulsed-laser annealing. A grain size up to 2000 Å was observed. Transistors were made, and electrical measurements showed that the field-effect mobility was in the range 15–20 cm2/V s, instead of 10−2−10−3 cm2/V s in the unannealed regions.
Utilization of Rutherford backscatter spectroscopy for the determination of thin-film densities
Authors: Simons D. G. , Crowe C. R. , Brown M. D.
Published: February 2003

A method to determine densities of thin surface films by measuring areal densities using Rutherford backscatter spectroscopy coupled with linear film-thickness measurements is described. This technique can be nondestructive and has an accuracy of 10 to 15%. Sample measurements on various thin films are given to demonstrate the use of this procedure.
Effect of electric fields on growth of copper whiskers by chemical reduction
Authors: Hobbs Herman H.
Published: February 2003

Applied electric fields of the order of 100 V/cm influence the growth of whiskers during the reduction of metal halides such as CuBr. The method and the apparatus described provide potential improvements in the reduction growth process, such as improved yields, control of the type of growth, and the tendency of the whiskers to line up with the applied field. In addition, an electric current accompanies the growth process. This current, presently the subject of further studies, is interesting in itself and may provide an independent means to investigate and control the growth process. The apparatus is easily adaptable to direct visual and photographic observation of the growing whiskers.
A simple approximate model for potential distributions of a semiconductor sample having a surface inversion region
Authors: Ruan Ying-Chao
Published: February 2003

Satisfactory approximate analytical solutions of potential distributions of an undegeneracy semiconductor sample having a surface inversion region and impurity density N≳102 ni were obtained by the following simple model d2u/dx2 = aN: un ≳u⩾0, bN: 2un ≳n⩾un, reu−u n: us ⩾u⩾2un, where un = arc Sinh(N/2) = ln N, us is the surface potential and a, b, and r are adjustable parameters. Particularly, the following formulas can provide quite good values of the parameters: a = 1−(1/un), b = 1+(g/un), and r = 1+(us −2un +1−g)(eus−2un −1)−1, where g is an adjustable parameter. For example, the error is not greater than about 2% when g = 1 and N≳103 ni and it decreases with increasing impurity density. The total amount of the space charges and the amount of carriers in the inversion region (us ⩾u⩾un) were accurately given. The model can be applied in a small current injection whose direction is perpendicular to the sample surface if the average quasi-Fermi energy level of the electrons and holes can be introduced instead of the Fermi energy level at equilibrium.
Gallium arsenide laser diode emission spectra in pulsed magnetic fields of up to 26 T
Authors: Davis Jeffrey A.
Published: February 2003

The emission spectra for commercial pulsed GaAs laser diodes are measured as a function of magnetic field up to 26 T at low temperatures. The data fit a theoretical model in which the laser emission recombination involves a hybrid plasmon mode rather than a hydrogenic-donor level.
Deep trap levels in CdS solar cells observed by capacitance measurements
Authors: Hmurcik L. , Ketelsen L. , Serway R. A.
Published: February 2003

This paper is concerned with ac capacitance measurements taken as a function of reverse bias voltage and signal frequency on four thin-film CdS/CuxS solar cells and one single-crystal cell. Our results suggest the presence of at least two trapping states in the i layer formed by the presence of Cu impurities in CdS. The deep traps produce anomalies in the normally linear 1/C2 vs V plots. The energies of the states were found by measuring the particular bias voltages at which anomalies were observed. Other results concerning the anomalous behavior in CdS cells and their relation to the work of Roberts and Crowell are also discussed. These include variations of capacitance with frequency and temperature, and changes in shunt conductance with frequency.
Interface barrier heights in metal-aluminum nitride-silicon structure by internal photoemission
Authors: Morita M. , Tsubouchi K. , Mikoshiba N. , Yokoyama S.
Published: February 2003

Energy barrier heights at interfaces of metal-aluminum nitride (AlN)-silicon(Si) structures with Au and Al as metal electrodes have been measured by internal photoemission. Measured results in low-photon energy region were interpreted in terms of a hole internal photoemission mechanism. Energy barrier heights for holes from the Au or Al Fermi level and from the top of Si valence band, to the top of AlN valence band, were found to be 2.0±0.2, 3.6±0.2, and 1.9±0.2 eV, respectively. These results were in good agreement with the values measured by the Metal-Insulator-Semiconductor capacitance-voltage techniques. On the other hand, measured results in the high-energy region were interpreted in terms of both electron and hole emission mechanisms. The band gap energy values of AlN obtained by internal photoemission measurements were nearly equal to the value by optical absorption measurements, except for the value obtained from energy barriers at the Al-AlN interface. It was also found that the enhancement of photocurrent with time is caused by space charges produced by both electron and hole trappings.
Capacitance measurement of Josephson tunnel junctions with microwave-induced dc quasiparticle tunneling currents
Authors: Hamasaki K. , Yoshida K. , Irie F. , Enpuku K.
Published: February 2003

The microwave response of the dc quasiparticle tunneling current in Josephson tunnel junctions, where the Josephson current is suppressed by an external magnetic field, has been studied quantitatively in order to clarify its characteristics as a probe for the measurement of the junction capacitance. Extensive experiments for both small and long junctions are carried out for distinguishing between microwave behaviors of lumped and distributed constant junctions. It is shown that the observed voltage dependence of the dc quasiparticle tunneling current modified by an applied rf field is in good agreement with a theoretical result which takes into account the influence of the microwave circuit connected to the junction. The comparison between theory and experiment gives the magnitude of the internal rf field in the junction. Together with the applied rf field, this internal rf field leads to the junction rf impedance which is dominated by the junction capacitance in our experimental condition. In the case of lumped junctions, this experimental rf impedance is in reasonable agreement with the theoretical one with the junction capacitance estimated from the Fiske step of the distributed junction fabricated on the same substrate; the obtained ratio of the experimental impedance to the theoretical one is approximately 0.6–1.7. In the case of distributed junctions, however, experimental values of their characteristic impedances are approximately 0.2–0.3 of theoretical values calculated by assuming the one-dimensional junction model and taking account of the standing-wave effect in the junction.
Superconductivity of the Nb3As system
Authors: Ummat P. K. , Carbotte J. P. , Cowan W. B. , Datars W. R. , Stager C. V.
Published: February 2003

We have found that the metastable A-15 Nb3As phase is present together with the more stable Ti3P-type Nb3As in sintered samples. The superconducting transition temperature for the A-15 phase is 6.5 K and the upper critical field at 0 K is 1.82 T.
Temperature dependence of magnetization reversal in a GdCo5 single crystal
Authors: Uehara Mitsuru
Published: February 2003

Magnetization reversal in GdCo5 single crystals was studied by magnetization measurements at various temperatures. The effective nucleation field H*n increases with decreasing temperature. A linear relationship is observed between H*n and the amount of magnetization reversal in a jump at all temperatures studied. The lifetime of the moving walls in the magnetization jump decreases as the temperature falls. The average velocity of the domain walls is estimated to be approximately 18 m/s at 4.2 K. The temperature dependence of H*n has been interpreted in terms of a thermally activated process.
Efficient electroluminescence from laser-irradiated (Al,Ga)As-heterostructure diodes
Authors: Salathé R. P. , Gilgen H. H. , Binkert Th. , Reinhart F. K. , Logan R. A.
Published: February 2003

Electroluminescence diodes have been prepared from laser-irradiated (Al,Ga)As-heterostructures where one of the layers forming the p-n junction is Ge doped. The diodes exhibit a new luminescence band shifted to lower energies by 160 meV with respect to the band-to-band recombination. At low current densities the observed edge emission intensity within the new band is more than quadrupled as compared to the band-to-band recombination. At current densities above 2.0 kA/cm2 the band-to-band recombination dominates. The measured carrier lifetimes for the new band and the band-to-band transition are 15 and 9 ns, respectively.
Anisotropy study of electrical conduction in oriented polymers. III. The anisotropy of electrical conduction in doubly-oriented nylon 12
Authors: Hirota Sumio
Published: February 2003

Conductivity of a doubly-oriented polymer along the arbitrary direction (X, Y, Z) is presented as a function of the principal values of the conductivity σx, σy, σz of the orientation units (’’crystals’’) and a double orientation function of ’’crystals’’. Principal values of the electrical conductivity in doubly-oriented nylon 12 films were measured and σx, σy, σz of the crystals of nylon 12 were estimated assuming a suitable distribution of crystals in nylon 12 film. It is observed that σx is much larger than σy and σz. The x direction was defined as the direction of the chain of the hydrogen bonds, i.e., the conductivity along the direction of hydrogen bonds is the largest. The average conductivity σ0 (3σ0 = σx+σy +σz ), which should be independent of the results of orientation, decreased as the roll ratio became large. The decrease of σ0 shows the change of the conduction properties of crystals by rolling, and is considered as a result of the change of the microstructure of nylon 12.
Efficiency of hot-carrier solar energy converters
Authors: Ross Robert T. , Nozik Arthur J.
Published: February 2003

A single-threshold quantum-utilizing device in which the excited carriers thermally equilibrate among themselves, but not with the environment, can convert solar energy with an efficiency approaching that of an infinite-threshold device. Such a hot-carrier flat-plate device operated under typical terrestrial conditions (AM 1.5 illumination, 300 K) can convert solar energy with an efficiency of 66%, substantially exceeding the 33% maximum efficiency of a quantum device operating at thermal equilibrium, and the 52% maximum efficiency of an ideal thermal conversion device. This high efficiency is achieved in part through an unusual inversion, in which the chemical potential of the excited electronic band is below that of the ground band. This negative potential difference reduces radiation losses, permitting a low threshold energy, and a high Carnot efficiency resulting from a high carrier temperature.
Deuterium trapping in helium-implanted nickel
Authors: Besenbacher F. , Bo/ttiger J. , Myers S. M.
Published: February 2003

By means of ion-beam-analysis techniques, the trapping of deuterium implanted into nickel preimplanted with helium was investigated in the temperature range 100–500 K. Following room-temperature helium implantations and deuterium implantations at ∼100 K, linear-ramp annealing (1–2 K/min) was carried out, while the deuterium concentration within the near-surface region (0–0.5 μm) was monitored by use of the nuclear reaction D(3He,α)1 H. The release curves were analyzed by solving a diffusion equation with the appropriate trapping terms. In addition to trapping by lattice defects, stronger helium-associated traps were found with a binding enthalpy of 0.55±0.05 eV relative to a solution site. We propose that the responsible entities are small helium bubbles observed in the implanted material by transmission electron microscopy.
High impact deformation of metal cylinders at elevated temperatures
Authors: Gust W. H.
Published: February 2003

We have used a ’’reverse gun’’ that fires a ceramic plate at a preheated metal target to study the dependence of flow stress on temperature. Impact velocity versus Lf /L0 isotherms have been determined for Al, two types of Cu, 4340 steel, and Ta at 295, 730, and 1235 K, and for U at 295 and 725 K. A modified Steinberg–Guinan constitutive model and a Grüneisen equation of state were used to obtain hydrodynamic code simulations of the deformation process. A strong temperature dependence of the length ratio was clearly evident for all materials.