bluuebunny/crossref_metadata_2025 huggingface dataset:
Reflection of keV light ions from compound targets
Authors: Morita K. , Tabata T.
Published: February 2003

The particle and energy reflection coefficients and the energy distribution of reflected particles for compound targets have been calculated using the single collision approximation. It is shown that for any compound target the reflection coefficients are expressed in terms of a universal function such as was empirically determined for elemental targets, when the Bragg rule is assumed for the stopping cross section. The results calculated numerically for WO3, TiC, and TiB2 are compared with the experimental ones to show reasonable agreement.
Pressure dependence of the elastic moduli of three austenitic stainless steels
Authors: Gerlich D. , Hart S.
Published: February 2003

The first pressure derivatives fo the elastic moduli for three austenitic stainless steels, AISI 304, 310, and 316, have been determined from the variation of the sound velocity under pressure. All pressure derivatives are lower than the corresponding ones for pure iron. The elastic Grüneisen constant, derived from the pressure derivatives is somewhat lower than the corresponding thermodynamic constant. The decrease in the elastic moduli and their pressure derivatives with respect to the corresponding values for pure iron is correlated with the alloying content of nickel and chromium.
Pt-Ni bilayers on n-type silicon: Metallurgical and electrical behavior
Authors: Mantovani S. , Nava F. , Nobili C. , Queirolo G. , Celotti G.
Published: February 2003

Silicide formation in the Ni-Pt-Si system has been investigated mainly by megaelectronvolt backscattering spectrometry, glancing-angle x-ray diffraction, and Auger electron spectroscopy as a function of heat treatment (200–850 °C). Schottky-barrier values have been used to identify the kinds of metals present at the silicide/silicon interface. Pt/Ni/Si and Ni/Pt/Si structures have been prepared by e-gun deposition of thin Pt and Ni films on 〈100〉 n-type silicon single crystals. The reaction starts by forming the silicide, Ni2Si or Pt2Si, of the metal in contact with silicon and proceeds until all the inner-metal film has reacted. At about 300 °C for 30 min the outer metal starts to diffuse through the already formed silicide and builds up at the silicon surface. Further annealing enhances the reaction and there is evidence also of silicon diffusion towards the outside layer. At 400 °C for 30 min and in both structures, NiSi starts to form and pushes out the Pt from the silicon surface. The conversion of Ni2Si into NiSi provides the driving force for mass transport. The structures become laterally nonuniform and the changes are difficult to follow. The transformation of Pt2Si into PtSi, at about 500 °C, is accompanied by the transport of Pt through NiSi towards the silicon surface. Most Pt remains in the outside layer and both structures assume the configuration PtSi/NiSi/Si. At higher temperatures PtSi and NiSi intermix and there is no evidence of contribution from the silicon underneath. At 750 °C an almost uniform layer is formed with a Si1(NiPt)1 composition. The barrier height measurements reflect the mass transport in the silicides at the silicide/silicon interface.
Preparation and structural analysis of SnTe/Sb composition modulated structures
Authors: Jin B. Y. , Wong H. K. , Wong G. K. , Hilliard J. E. , Ketterson J. B.
Published: February 2003

A new composition modulated structure composed of semiconducting SnTe and semimetallic Sb has been grown epitaxially on mica substrates with differing SnTe to Sb ratios. The samples were characterized by x-ray diffraction using the transmission Laue patterns and θ-2θ diffractometer scans with scattering vectors both normal and in the plane of the film. We observed that the modulation satellites were 180° out of phase for films with short modulation wavelengths, but were in phase for long wavelengths. This change in the phase of the modulation can be understood by assuming that Sb adopts a quasicubic structure at short modulation wavelength, due to the coherency strain, but relaxes back to a distorted rhombohedral structure, with the loss of coherency, at long wavelengths. A simple 1-D model was used to estimate the modulation wavelength dependence of the sublattice displacement of Sb.
Crystal growth investigation of the magnetically highly sensitive InSb evaporated films
Authors: Isai Masaaki , Ohshita Masahide
Published: February 2003

The crystal growth of the magnetically highly sensitive InSb films, prepared by a simple evaporation on mica substrates with a steep one-dimensional temperature gradient, is investigated in detail. An optimum evaporation condition is presented. It is shown that the crystalline InSb with thickness less than 0.1 μm consists of single crystal domains oriented mainly along [110] or [111] direction, but that the [111] direction becomes completely dominant for the films thicker than 0.2 μm. The crystal morphology of the film is discussed in relation to the high magnetoresistance value obtained.
Effect of silane dilution on intrinsic stress in glow discharge hydrogenated amorphous silicon films
Authors: Harbison J. P. , Williams A. J. , Lang D. V.
Published: February 2003

Measurements of the intrinsic stress in hydrogenated amorphous silicon (a-Si : H) films grown by rf glow discharge decomposition of silane diluted to varying degrees in argon are presented. Films are found to grow under exceedingly high compressive stress. Low values of macroscopic film density and low stress values are found to correlate with high growth rate. An abrupt drop in stress occurs between 2 and 3% silane at precisely the point where columnar growth morphology appears. No corresponding abrupt change is noted in density, growth rate, or plasma species concentrations as determined by optical emissioin spectroscopy. Finally a model of diffusive incorporation of hydrogen or some gaseous impurity during growth into the bulk of the film behind the growing interface is proposed to explain the results.
Electrical observation of the Au-Fe complex in silicon
Authors: Brotherton S. D. , Bradley P. , Gill A. , Weber E. R.
Published: February 2003

Electron paramagnetic resonance (EPR) and diode capacitance measurements, including deep level transient spectroscopy (DLTS), have been used to identify the levels in the silicon band gap associated with the Au-Fe complex. Two deep levels at Ec−0.354 eV and Ev+0.434 eV were found with properties consistent with those of the complex; the role of gold in the formation of the complex was confirmed by the observation that during low-temperature annealing (<350 °C) the changes in the concentration of the center were accompanied by equal and opposite changes in the concentration of the normal gold acceptor and donor levels.
Transient capacitance spectroscopy of Na+-induced surface states at the Si/SiO2 interface
Authors: Rosencher E. , Coppard R.
Published: February 2003

The interface states induced by the drift of Na+ ions to the Si/SiO2 interface are investigated in metal-oxide-semiconductor capacitors made on n-type Si using deep level transient spectroscopy. The results clearly reveal the existence of two types of defects. The dominant ones yield an increase in the density of states mainly near the Si conduction band, resulting in a band tail. These states can be annealed out by pumping of the Na+ ions back to the metal gate. The introduction kinetics of these traps as a function of sodium concentration at the Si/SiO2 interface ([Na+]) exhibits a strong increase near [Na+]∼3×1012 ions/cm2. The other type of defect, created in less significant amounts, accounts for a flat continuum of levels throughout the Si band gap. These traps are little affected by the Na+ ions leaving the Si surface, which is indicative of a more or less irreversible degradation of the Si/SiO2 interface. These results are compared with other authors’ experimental data and are discussed in terms of several possible physical models.
Fluctuations in Schottky barrier heights
Authors: Mahan G. D.
Published: February 2003

A double Schottky barrier is often formed at the grain boundary in polycrystalline semiconductors. The barrier height is shown to fluctuate in value due to the random nature of the impurity positions. The magnitude of the fluctuations is 0.1 eV, and the fluctuations cause the barrier height measured by capacitance to differ from the one measured by electrical conductivity.
Deep levels introduced during electron-beam deposition of metals on n-type silicon
Authors: Auret F. D. , Mooney P. M.
Published: February 2003

Near-surface damage introduced during fabrication of Schottky barrier diodes (SBDs) by electron-beam (E-beam) deposition of various metals on n-type silicon has been investigated using deep level transient spectroscopy. The main defect was observed at Ec −0.42 eV and is annealed out at 400 °C. The interaction of E-beam deposition induced defects with defects which had been introduced in the substrate by irradiation with high-energy electrons was also observed in Pd and Pd/Au SBDs. Therefore erroneous conclusions can be made when using SBDs fabricated by E-beam deposition to characterize defects introduced by some other process near the interface of a SBD.
Application of wide-gap semiconductors to surface ionization: Work functions of AlN and SiC single crystals
Authors: Pelletier J. , Gervais D. , Pomot C.
Published: February 2003

For surface ionization purposes, a study of the work functions of SiC and AlN, both refractory wide-gap semiconductors, has been undertaken. Work function measurements have been performed in the 300–1600-K range using the Shelton retarding field method. Surface cleaning was carried out by heating in uhv to a high temperature using of a cw CO2 laser. Both n- and p-type 6H SiC single crystals with extreme bulk doping levels were investigated. For each doping type, the work functions have been found to be temperature independent. They exhibit only a slight variation from the n to the p type (4.75 and 4.85 eV, respectively) giving evidence, as in the case of Ge and Si, of Fermi level pinning at the surface by the intrinsic surface states. For an n-type AlN single crystal, the work function, measured in the high temperature range, remains constant as the temperature varies. The value of 5.35 eV obtained for AlN makes it a most attractive material for positive surface ionization applications.
The second-order pressure derivatives of the elastic moduli of a machinable glass ceramic
Authors: Gerlich D. , Hart S.
Published: February 2003

The second-order pressure derivatives of the elastic moduli of a machinable glass ceramic have been determined. The latter were evaluated from the change in the velocity of longitudinal and shear sound waves over a pressure range of 0–2 GPa. The two second-order pressure derivatives are both negative, analogous to the behavior of crystalline solids. From the pressure derivatives, the first- and second-order Murnaghan equations of state were calculated, as well as the volume derivatives of the Grüneisen gammas and Grüneisen constant. The latter values are appreciably higher than those of crystalline solids, but of the same order as those of fused quartz.
Degradation and regeneration of amorphous silicon solar cells
Authors: Kennedy D. F. , Haneman D.
Published: February 2003

The current-voltage (I-V) and spectral response characteristics of homojunction and heterojunction p-i-n solar cells made from amorphous hydrogenated Si were measured during a systematic sequence of light soaking and regenerative annealing treatments. A general similarity in behavior of both types of cells during light soaking indicated that the main damage causing deterioration was likely to be in the i layer. Degradation increased with cell bias during exposure, and was also greater for the longer wavelength response in homojunction cells. Cells were found to recover slowly with annealing at 130 °C. A recently developed mathematical model was applied to the experimental I-V curves at several longer wavelengths, before and after light soaking whilst at short circuit. It was possible to obtain a good fit to the data by incorporating a reduction in average hole diffusion length Lp after light soaking. This indicates that, while various light-induced effects may be present in solar cells as distinct from films, the reduction in Lp appears to be a major factor. The confirmed dependence of degradation rate on cell bias indicated an electric field effect on formation of defect centers.
Void formation in annealed N+-implanted ZnSe
Authors: Vermaak J. S. , Petruzzello J.
Published: February 2003

The radiation damage in ZnSe implanted with 200-keV N+ ions to a total dose of 1017 ions/cm2 has been observed directly by cross-sectional transmission electron microscopy. Selected area electron diffraction from the highly damaged implanted region showed well-defined single-crystalline patterns. On annealing at 700 °C both dislocations and voids are generated in the damage zone. The voids cause a swelling of 1% and take on the form of dodecahedrons while the dislocations are of the 60° type lying on {111} type planes with Burgers vectors of the type a/2 〈110〉. Both the maximum peak positions of the void-volume and dislocation-volume distributions lie at a depth predicted by the Lindhard–Scharff–Schiott theory for N+-ion penetration into ZnSe.
Phosphorus diffusion in polycrystalline silicon
Authors: Losee D. L. , Lavine J. P. , Trabka E. A. , Lee S.-T. , Jarman C. M.
Published: February 2003

The diffusion of phosphorus in crystallized amorphous Si layers was studied with secondary-ion mass spectroscopy. A two-dimensional diffusion model is used to find effective grain (Dg) and grain-boundary (Dgb) diffusion coefficients. This simplified model leads to Dgb ≤ 10Dg, which is significantly lower than what has been deduced from conventional, larger grained polysilicon. Our result is consistent with specific-gravity measurements, which found a significantly lower ‘‘mass defect’’ for layers deposited amorphous and subsequently crystallized as compared to initially polycrystalline layers.
Ferromagnetic domains in [110] iron whiskers
Authors: Tejedor M. , Fuertes J. F.
Published: February 2003

Observations of magnetic domain patterns have been made by the Bitter technique in [110] iron whiskers. Simplified domain structure models are devised in order to explain the patterns obtained.
A new adsorption substrate: Single crystal exfoliated graphite
Authors: Clarke Roy , Horn P. M. , Nagler S. E. , Rosenbaum T. F.
Published: February 2003

We describe the controlled exfoliation of single crystal graphite flakes intercalated to stage eleven with SbCl5. The resulting exposed surface remains well oriented in the basal plane. Our best sample to date has an internal surface area of 6 Torr cc and an in-plane mosaic of 2.3° HWHM (half-width at half-maximum). High resolution x-ray scattering from adsorbed krypton reveals an average step-free surface size of at least 2000 Å. Experiments which probe orientational information in the layer planes should now be possible.
Delta function integrals for recombination problems
Authors: Landsberg P. T. , Wang W. L.
Published: February 2003

Integrals of the form In(A)≡∫∞−∞  ∫δ(A−∑ni=1  σiy2i) dy1⋅⋅⋅dyn arise in solid state problems (density of states, radiative, and Auger transitions). Here A and n are given constants, σi =1 or −1 so as to keep the yi real, and n is an integer which normally lies between one and nine. The context in which these integrals arise is surveyed, and analytical and graphical work is presented which extends previously published studies and leads to some simple theorems about these integrals.
Reducing the grain size of polycrystalline lead films by the use of AuIn2 barriers to grain growth
Authors: Bright A. A. , Ronay Maria
Published: February 2003

Fine grained Pb or Pb-alloy films may be produced by the use of barriers to grain growth deposited between Pb layers. We have studied the mechanism of reducing grain growth and the kinetics of barrier formation for AuIn2 barriers with the aid of nuclear backscattering spectroscopy and transmission electron microscopy on films incorporating various deposition sequences. We find that compounds which form in situ are barriers to grain growth during vapor deposition only if one of their constituents is a fast diffusing species such as Au in Pb and if the fast diffusing species is placed underneath each Pb layer. The Au diffuses into the fast moving Pb grain boundaries, imparting a drag on them. Upon depositing In on top of the Pb grains the In forms AuIn2 with the Au in the grain boundaries. The continuous network of AuIn2 then prevents further grain boundary motion.
Point defect trapping in solid-phase epitaxially grown silicon-antimony alloys
Authors: Pennycook S. J. , Narayan J. , Holland O. W.
Published: February 2003

Supersaturated silicon alloys produced by antimony implantation followed by solid-phase-epitaxial growth (furnace annealing), contain a supersaturation of interstitials. This is deduced from the observation of a transient, greatly enhanced diffusion of Sb into precipitates upon heating, accompanied by the formation of interstitial loops. In similar alloys produced by liquid-phase-epitaxial regrowth (pulsed laser annealing) much lower diffusion coefficients were obtained and no loops were observed. These observations provide clear evidence for the diffusion of the substitutional Sb dopant by an interstitialcy mechanism. The activation energy of the enhanced diffusion was 1.8±0.2 eV, presumably corresponding to the migration enthalpy of Sb by the interstitialcy mechanism. The loop number density at the end of the transient gave an estimate of the initial interstitial concentration, which allowed the diffusivity of Sb by the interstitialcy mechanism to be estimated.
The upper critical field of NbN films. II
Authors: Ashkin M. , Gavaler J. R. , Greggi J. , Decroux M.
Published: February 2003

Previous measurements of upper critical fields near Tc on NbN films with a small column (∼80 Å) void (∼10 Å) microstructure showed a strong anisotropy for applied fields perpendicular and parallel to the film surface. The perpendicular critical field was the larger one. Extrapolation of the perpendicular field data to zero temperature indicated an Hc2(⊥,0)>500 kG. Low temperature pulsed field measurements have now been made which show Hc2(⊥,0)=443 kG. In contrast, the measured upper critical fields of NbN films with equiaxed grains (≳275Å) or with larger columns (> 1000Å) and voids (∼500Å) indicate that these films behave like bulk superconductors. The Hc2(0)’s are ∼300 kG or less and little or no anisotropy is seen. A semiphenomenological theory incorporating size effects is used to interpret the data.
Magnetic and magneto-optic properties of bismuth- and aluminum-substituted iron garnet films
Authors: Hansen P. , Witter K. , Tolksdorf W.
Published: February 2003

The saturation magnetization Ms, the uniaxial anisotropy Ku, the optical absorption α, the Faraday rotation θF, and the Faraday ellipticity ψF of epitaxial garnet films of composition Y3−xBixFe5−yAlyO12 have been investigated for x≤1.34 and y≤2.22. The temperature dependence of Ms and θF at λ=633 nm have been measured in the range 4.2 K≤T≤TC. Ku, TC, θF, and ψF reveal a linear dependence on the bismuth content. The dependence of θF and ψF on the aluminum concentration shows that both sublattices are involved and indicate that the magneto-optical effects have to be ascribed to iron pair transitions. The magnitude of the growth-induced anisotropy is essentially controlled by the supercooling ΔTs and increases linearly with ΔTs. The obtainable magnetic and magneto-optical data for magneto-optical applications are discussed and compared with those of garnet films exhibiting a compensation temperature.
Magnetostriction of Pd-Fe alloys
Authors: Schmidt J. E. , Berger L.
Published: February 2003

The linear magnetostriction λs of polycrystalline Pd1−xFex alloys has been measured as a function of alloy composition, at temperatures of 300, 77, and 4.2 K. The effect on λs of atomic ordering of Pd3Fe and PdFe type has been investigated. The value of λs is positive for x>0.21, but changes sign three times in the composition range x<0.21. This composition dependence can be understood semiquantitatively in terms of the simple split-band model, where iron and palladium each have their own d band, distinct on the energy scale. Contributions to λs from electrons of both spin directions have been included. Best fit between theory and data is obtained for a value of the deformation potential of d electrons equal to −0.6 eV. The anomalous Hall effect and the g factor of Pd-Fe are also discussed in the light of the split-band model.
Modified equations for the evaluation of energy distribution of defects in as-grown thin films by Vand’s theory
Authors: Das V. Damodara
Published: February 2003

It is pointed out that the use of Vand’s original equations for the evaluation of defect density distribution in energy in as-grown thin films lead to results which are in error by at least 6% in the case of thin films vacuum deposited at room temperature. Modified equations that can be applied to thin films formed at any arbitrary temperature T0 K have been obtained. It is found that except for one equation, the remaining three equations are identical to those of Vand. It has also been shown that Vand’s original equations can be applied in the case of thin films formed at an arbitrary temperature if the actual time t in the original equation is replaced by a time t0 measured as if heating had started at 0 K. Experimental plots of decay energy distribution of defect cluster density [F0(E) vs E plots] obtained using the modified equations and Vand’s original equations in the case of bismuth thin films deposited at different substrate temperatures (300–450 K) are also presented to show the extent of the errors and their substrate temperature dependence. These errors are also compared with the errors inherent in the theory and the approximations made in the derivation.
Electrical and optical properties of zinc oxide thin films prepared by rf magnetron sputtering for transparent electrode applications
Authors: Nanto H. , Minami T. , Shooji S. , Takata S.
Published: February 2003

Zinc oxide films were prepared on unheated glass substrates by rf magnetron sputtering under an applied external dc magnetic field in pure argon gas, and electrical and optical properties of the deposited films were investigated. Highly transparent films with resistivity as low as 10−4 Ω cm, which were weakly oriented perpendicular to the substrate surface(c-axis orientation), could be produced with a relatively high deposition rate on the substrate suspended perpendicular to the target surface by controlling the sputtering gas pressure and the external dc magnetic field, without any postdeposition preparative treatment. The Hall mobility of the film with the highest conductivity was about 120 cm2/V sec, which was the highest yet reported for thin films on ZnO. The increase in the conductivity was related to the increase in Hall mobility which was caused by the decrease of carrier scattering from grain boundaries due to the grain growth resulting from the improvement of crystallization. The improvement of crystallization is resulted from particles with a momentum component parallel to the substrate surface. The sputtered ZnO films should be useful as a less expensive window material.
Grain orientation effects on electrical properties of bismuth layer-structured ferroelectric Pb(1−x)(NaCe)x/2 Bi4Ti4O15 solid solution
Authors: Takenaka Tadashi , Sakata Koichiro
Published: February 2003

Electrical properties, such as dielectric, resistive, ferroelectric, and piezoelectric properties, of bismuth layer-structured ferroelectrics (BLSF) are studied on grain orientation prepared by the hot-forging (H.F.) method. The BLSF compound which can stand the high temperature poling process is Pb(1−x) (NaCe)x/2 Bi4Ti4O15 (PNC-100x) consisting of PbBi4Ti4O15 modified by partial substitution of (NaCe)1/2 for Pb. The effects of the solid solution introduced on piezoelectric properties are mentioned. The piezoelectrically activated PNC solid solution has a larger value of electromechanical coupling factors kt and k33 than those of nonmodified samples. The grain orientation makes the piezoelectric properties of BLSF ceramics much more pronounced than those of the nonoriented ceramics. Coupling factor k33 along with piezoelectric constants d33 and g33 of H.F. PNC ceramics are enhanced and their anisotropies in k33/k31, d33/d31, and g33/g31 are emphasized.
Laser beam heating and transformation of a GaAs-AlAs multiple-quantum-well structure
Authors: Kirillov D. , Merz J. L. , Dapkus P. D. , Coleman J. J.
Published: February 2003

Laser beam heating and processing of a GaAs-AlAs superlattice was studied using quantum-well luminescence as a probe. Using stationary cw laser heating, it was found that it was impossible to obtain a GaAlAs alloy without destruction of the sample. Luminescent properties of the material were significantly altered at a threshold ∼24 kW/cm2, corresponding to a temperature ∼500 K inside the laser spot. Low temperature measurements showed that the energies of the quantum-well transitions were shifted. The room temperature luminescence of this ‘‘new phase’’ was quenched, allowing the formation of ‘‘written’’ dark patterns on a bright infrared luminescence background of the original superlattice using the laser beam.
Laser-induced lattice tensile strain in silicon
Authors: Tan H. S. , Kuok M. H. , Ng S. C. , Ong C. K. , Tang S. H.
Published: February 2003

Raman scattering measurements have been carried out on Si samples annealed with various energy densities using a free-running pulsed laser with a typical pulse-train length of 0.4 ms. The phonon frequency shifts Δω (relative to unannealed Si) observed up to −2.9 cm−1 are ascribed to the presence of lattice tensile strains in the annealed regions. The maximum lattice tensile strain of 3.9×10−3, inferred from the maximum Δω measured, could be released completely if the annealed regions were to form cracks running parallel to the crystal axes. To explain the data, a new lattice-straining mechanism based on a change in the lattice constant of Si during the crystal regrowth is proposed.
The poly-single crystalline silicon interface
Authors: Wong C. Y. , Michel A. E. , Isaac R. D. , Kastl R. H. , Mader S. R.
Published: February 2003

Cross sectional transmission electron microscopy (TEM) reveals an amorphous interfacial region of the order of 2 nm thick between chemical vapor deposition-(CVD) deposited polycrystalline silicon films and the single-crystal silicon substrate. The continuity of this region varies from sample to sample and plays an important role in the effects produced by subsequent heat treatment. In cases where this interfacial layer is continuous, the deposited layer remains polycrystalline. When the region is discontinuous, complete epitaxial realignment of the poly is possible. The speed of realignment depends on the implanted arsenic dose and is much greater than reported for undoped films. Various impurities are also observed at the interface and correlate with the character of the interface.
Heat treatment effects on indium gallium arsenide phosphide double heterostructure material
Authors: Besomi P. , Degani J. , Wilson R. B.
Published: February 2003

A study of the effect of heat treatment on the photoluminescence intensity and broad area laser threshold current density of InGaAsP double heterostructure (DH) laser material is described. This heat treatment cycle is similar to the one an etched InGaAsP DH is subject to prior to regrowth of a buried heterostructure laser. A measurable decrease in the photoluminescence intensity of the active region for most samples, and an increase of the average broad area laser threshold of 5 to 25% on all samples were detected following the heat treatment. These degraded electro-optical properties are explained by broadening of the InP/InGaAsP interfaces.
Chemical cleaning of InP surfaces: Oxide composition and electrical properties
Authors: Guivarc’h A. , L’Haridon H. , Pelous G. , Hollinger G. , Pertosa P.
Published: February 2003

Unintentionally doped (100) InP wafers were ‘‘cleaned’’ with 12 different etching procedures, either found in the current literature or adapted from Si technology. We present the results of x-ray photoelectron spectroscopy (XPS) and Rutherford backscattering experiments together with electrical properties of Au/InP contacts realized on the same samples. We can distinguish: first, the solutions which result in a rather clean InP surface and give metal-semiconductor Au/InP diodes from those which lead to an approximately 20-Å-thick oxide layer and give metal-insulating-semiconductor structures, and second, the solutions which give electrically stable structures from those which lead to very unstable ones. Detailed electrical measurements [J-V; J(V,T); C(V,T)] have been performed on two kind of stable surfaces: on ‘‘clean’’ etched ones and on one oxidized with NH4OH-H2O2-H2O (5:1:100) solution. For the first ones, a quasi-ideal metal-semiconductor diode is found. For the oxidized surfaces, current flow is controlled by pure tunneling through the oxide layer. A correlation between surface composition evaluated with XPS and surface electrical properties has been clearly established: the electrical properties of the relatively P-rich oxides are quite unstable while the others, In rich, remain stable over several months. The composition and the nature of the various oxides are discussed.
Performance improvements from penetrating back-surface field in a very high efficiency terrestrial thin-film crystalline silicon solar cell
Authors: Sah Chih-Tang , Lindholm Fredrik A.
Published: February 2003

This paper analyzes the performance improvements obtainable from extending the traditionally thin back-surface-field (BSF) layer deep into the base of silicon solar cells under terrestrial solar illumination (AM1). This extended BSF cell is also known as the back-drift-field cell. About 100 silicon cells have been analyzed, each with a different emitter or base dopant impurity distribution whose selection was based on physically anticipated improvements. The four principal performance parameters (the open-circuit voltage, the short-circuit current, the fill factor, and the maximum efficiency) are computed using a program which numerically solves the six Shockley equations under AM1 solar illumination at 88.92 mW/cm2, at an optimum cell thickness of 50 μm. The results show that very significant performance improvements can be realized by extending the BSF layer thickness from 2 μm (18% efficiency) to 40 μm (20% efficiency). The immunity of cell performance to recombination defect or impurity center is also improved by a factor of 2 to 3 in the recombination center density. For 20% p+/n/n+ cells with about 20-μs base lifetime, a 20-μm BSF penetration is sufficient. At this or deeper penetrations, interband Auger recombination in the emitter layer becomes the limiting factor and affects mainly the short-circuit current but not the open-circuit voltage which has saturated to about 710 mV.
Self-magnetic-field-enhanced ion diode
Authors: Olsen J. N. , Rosenthal S. E. , Mix L. P. , Seidel D. B. , Anderson R. J. , Dreike P. L. , Leeper R. J.
Published: February 2003

An intense ion source has been developed utilizing an ion diode that partially suppresses electron flow using the self-magnetic field of the diode current. This is an extension of a diode class known as pinch reflex ion diodes. In this case the diode was coupled to the particle beam fusion accelerator and was configured in two different cylindrical designs. The first pinch ion diode was a straight, 42-cm-diam cylinder and the second, Obi, was a focusing, 26-cm-diam, aspheric barrel. In the Obi diode a central gas cell provided current-neutralized beam transport. In addition, the accelerator was run in a low-voltage, 0.8 MV, and a high-voltage, 2.0 MV, mode. The best results showed that the Obi diode produced 3 TW of protons at 34% efficiency in the high-voltage mode. We present an analytic model of ion efficiency, compare various diode impedance models, and discuss beam divergence mechanisms. The limitation of this ion source as a fusion driver is presently the 2–3° divergence that we measure using a shadow-box technique. A companion paper contains numerical simulations and further analytic modeling.
Molecular stopping powers and effect of chemical bonding in gaseous amine compounds
Authors: Powers D. , Olson H. G. , Gowda R.
Published: February 2003

Molecular stopping powers of methylamine, ethylamine, dimethylamine, and trimethylamine have been measured for 0.3–2.0 MeV He+ ions. A single-bonded atomic stopping power εSB(N) for nitrogen is calculated and found to be 6%–20% lower than its triple-bonded counterpart (1/2)εexpt(N2). This disagreement is quite similar to a 6%–17% difference in single- and double-bonded carbon and oxygen atomic stopping powers previously calculated. A lower stopping power peak energy is also observed for the atom in a molecular configuration of higher bond order. These trends demonstrate clearly the effect of chemical bonding upon stopping powers.
Strong fluctuation theory for electromagnetic wave scattering by a layer of random discrete scatterers
Authors: Jin Y. Q. , Kong J. A.
Published: February 2003

The strong fluctuation theory is applied to the study of electromagnetic wave scattering from a layer of random discrete scatterers. The singularity of the dyadic Green’s function is taken into account in the calculation of the effective permittivity functions. The correlation functions for the random medium with different scatterer constituents and size distributions are derived. Applying the dyadic Green’s function for a two-layer medium and using the bilocal and distorted Born approximations, the first and the second moments of the fields are then calculated. Both the backscattering and bistatic scattering coefficients are obtained, and the former is shown to match favorably with experimental data obtained from snow fields.
Oxygen-enhanced thermionic emission pattern of hemispherical single-crystal LaB6
Authors: Shimizu R. , Onoda H. , Hashimoto H. , Hagiwara H.
Published: February 2003

With the application of Martin’s experimental arrangement for direct observation of thermionic emission patterns from a hemispherical single-crystal LaB6 cathode, it has been determined that oxygen-enhanced thermionic emission does occur for the (210) plane at the rather low partial pressure of oxygen, i.e., in the 10−9-Torr region, at sample temperatures of 1050 °C. For further quantitative assessment, work-function measurements by Richardson plots were done for different crystal planes of clean surface by attaching a photomultiplier. The result clearly shows that the values of the work function increases in order from (100), (210), (110), and (111). The measurements were also extended to the oxygen-enhanced surface of the (210) plane and it was found that the results follow, phenomenologically, the Richardson plot as well.
X-ray photoemission of polynuclear aromatic carbon
Authors: Cheung T. T. P.
Published: February 2003

The evolution of the C(1s) x-ray photoelectron spectrum is examined as a function of the size of the polynuclear aromatic molecules. The transition from a symmetric line shape to an asymmetric one occurs in the narrow range of the layer size between 10 and 22 Å. It is shown that the asymmetry reflects the area of the layer over which the π electrons can be delocalized and that it is more closely related to the actual physical size of the layer than measurements from x-ray diffraction. The latter is illustrated in coal tars which have undergone heat treatment. The effect of the evolution of the line-shape asymmetry on the determination of the fraction of polynuclear aromatic carbon in heterogeneous carbon materials by x-ray photoelectron spectroscopy is also discussed.
Rapid Mössbauer-based methods for the determination of iron-bearing phases
Authors: Huggins F. E. , Huffman G. P.
Published: February 2003

The variation of Mössbauer γ-ray resonant absorption with the velocity amplitude of a vibrating γ-ray source is examined theoretically in connection with Mössbauer-based methods for rapid, nondestructive determination of iron-bearing phases in different materials. The theoretical analysis can be used to simulate such methods, which are based on the difference in the Mössbauer resonant absorption by a sample with the γ-ray source stationary and in rapid oscillation. Methods for the determination of pyrite in coal and metallic forms of iron in steels and slags are examined both theoretically and experimentally to illustrate the advantages and limitations of such rapid Mössbauer-based methods.
Nanosecond laser-induced transient and permanent gratings and ultrasonic waves in a smectic film
Authors: Khoo I. C. , Normandin R.
Published: February 2003

Using nanosecond laser pulses, we have observed for the first time optically induced transient and (erasable) permanent gratings in a smectic-A film. The transient grating is accompanied by strong high frequency acoustic waves.
Critical current uniformity and stability of Nb/Al-oxide-Nb Josephson junctions
Authors: Gates J. V. , Washington M. A. , Gurvitch M.
Published: February 2003

The critical current stability of Nb Josephson junctions using thin Al oxide layers as the tunneling barrier has been investigated with respect to repeated thermal cycling, aging, and annealing at elevated temperatures as a function of time. The Nb electrodes and in situ thermally oxidized Al barriers were deposited by dc magnetron sputtering prior to the lithographic formation of the individual junctions. The arrays of junctions were formed by standard photolithography techniques, reactive ion etching, and anodization. A population of 400 20-μm-square junctions were thermally cycled from room temperature to 6 K 4880 times with no failures due to shorts and no change in the average critical currents. These same unpassivated junctions were annealed at elevated temperatures for various periods of time until the critical currents had decreased by 50% at temperatures near 275 °C.
Laser and thermal annealings of Bi,Ga- and La,Ga-substituted garnet films
Authors: Gouzerh J. , Le Gall H. , de Beauregard Y. , Gratecap D. , Desvignes J. M.
Published: February 2003

Strong change of the saturation magnetization 4πMs and the bubble parameters such as wall energy, bubble diameter, and material characteristic length have been observed from bubble statics experiments after heat treatment corresponding to annealing and quenching processes either from usual furnace or from laser annealing. The changes of physical properties are associated with cation migration between the octa- and tetrahedral sites in both the La,Ga-YIG and Bi,Ga-YIG films we have investigated. After annealing in oxygen ambient in a furnace at different equilibrium temperatures between 1125 and 1473 K, the films with the total Ga content between 1 and 1.23 were quenched. In a second step laser annealed channels were produced on the same films and their profile analyzed from the comparison with data obtained after normal furnace annealing. Strong differences were observed after furnace and laser annealings between Bi,Ga- and La,Ga-substituted YIG. Irreversible processes arise after furnace annealing in bismuth garnet mainly for uniaxial anisotropy, in-plane saturation field and quality factor Q, which is not the case in La,Ga-YIG films. In addition, due to different kinetic processes for Bi3+ and Ga3+ ions associated with heat treatment, laser annealing induces large modifications for magnetic properties associated only with Ga3+ migration, whereas uniaxial anisotropy resulting from Bi3+ ion ordering is perturbed only a little. The data is discussed from the Néel molecular field theory and the Van Erk thermodynamic equilibrium model.
Bubble generation by microwaves: Analytical
Authors: Seagle D. J. , Charap S. H. , Artman J. O.
Published: February 2003

Our previous numerical simulation of the response of a magnetic bubble film to strong localized microwave fields revealed a susceptibility instability at high microwave powers. For a circularly-polarized excitation, this instability can ultimately lead to the reversal of the magnetization (i.e., bubble generation). We introduce here an analytical derivation of the instability region and compare this with the flipover conditions obtained by numerical simulation. The calculation of the natural response of the system to small deviations from the steady state in the absence of damping yields three poles, all located on the imaginary axis of the complex frequency plane. In the presence of finite damping, if rf excitation conditions are appropriate, these poles will move into the right (unstable solution) half of the s plane. The frequency and magnitude of excitation necessary for instability are independent of the Gilbert damping parameter α provided α≪1.
Computer simulation of magnetic bubble logic devices
Authors: Wu J. C. , Humphrey F. B.
Published: February 2003

Operation margins for a dual-conductor current access magnetic bubble AND/OR gate, a one-bit full adder and a string comparator were simulated by a computer program. These gates employ bubble-bubble interaction to perform logic functions. A bubble replicator using a third layer conductor was also simulated. For the same lithographic feature size, the comparator requires 4.5% the area of the same function implemented in silicon. The simulation procedure is based on the Hayashi method where the bubble domain wall is divided into 18 to 72 wall segments which move according to the total effective field at the center of each wall segment. The field at every point is calculated by a finite difference routine. The logic functions simulated exhibited a 40-Oe bias margin when the drive current is 1.6 mA/μm.
Model for dynamic domain wall coercivity
Authors: Thiele A. A. , Asselin P.
Published: February 2003

A lowest order theory of the dynamic coercivity of moving magnetic domain walls in insulators is developed. The power loss resulting from the production of wall localized spin waves by the interaction of the moving domain wall with anisotropy inhomogeneities is computed. It is found that at a given velocity the spin wave power production is concentrated near some particular wave-vector magnitude. The total energy loss per unit volume swept is, however, found to be generally independent of velocity in agreement with the usual definition of coercive energy loss. We find good agreement with coercivity and initial mobility data of Ju and Humphrey without the use of fitting parameters.
Application of magnetic susceptibility gradients to magnetic separation
Authors: Hwang J. Y. , Takayasu M. , Friedlaender F. J. , Kullerud G.
Published: February 2003

Particle separation in a magnetic colloidal fluid with a susceptibility gradient created by means of a Frantz-Isodynamic magnet is described. The positions where particles and fluid are in equilibrium are a function of the particle magnetic susceptibility only. This method allows magnetic separation of several materials with a wide range of magnetic susceptibilities in a single separator with multiple dividers. A model separator was constructed. The magnetic gradient of the Frantz magnet and the concentration gradient of the magnetic colloids were calibrated. Separations were carried out using fine particles of Mn2P2O7, CuO, and Al2O3. The results confirm the feasibility of this method. The experimental data agree quite well with calculations based on the calibrated concentration gradient.
Longitudinal magnet forces?
Authors: Graneau Peter
Published: February 2003

The Ampere electrodynamics of metallic conductors and experiments supporting it predict that the interaction of a current-carrying wire with its own magnetic field should produce longitudinal mechanical forces in the conductor, existing in addition to the transverse Lorentz forces. The longitudinal forces should stretch the conductor and have been referred to as Ampere tension. In 1964 it was discovered that a current pulse would break a straight copper wire into many fragments without visible melting. A metallurgical examination of the pieces confirmed that the metal parted in the solid state. The same observation has now been made with aluminum wires. In the latest experiments the wire was bent into a semicircle and arc-connected to a capacitor discharge circuit. The arc connections ruled out rupture by Lorentz hoop tension and indicated that longitudinal forces may also arise in circular magnet windings. Explanations of wire fragmentation by thermal shock, longitudinal stress waves, Lorentz pinch-off, bending stresses, and material defects have been considered and found unconvincing. Computed Ampere tensions would be sufficient to fracture hot wires. The Ampere tension would double the hoop tension normally expected in dipole magnets. This should be borne in mind in the design of large dipole magnets contemplated for MHD power generators and railgun accelerators.
Low hysteresis materials for magnetic refrigeration: Gd1−xErxAl2
Authors: Zimm C. B. , Barclay J. A. , Johanson W. R.
Published: February 2003

The series of ferromagnetic intermetallics Gd1−x ErxAl2 are candidate working materials for magnetic refrigeration because of their large moment, small anisotropy, and their wide range of Curie temperatures (14 to 164 K). We have measured the magnitude of the magnetic hysteresis as a function of temperature from 4 K to TC for polycrystalline samples of these materials by ac magnetic susceptibility and magnetization hysteresis loops. We found, as expected, virtually no hysteresis in GdAl2, and, more surprisingly, less than 3000 A/m hysteresis in ErAl2 and 2×104 A/m in Gd0.5 Er0.5Al2. Moreover, the hysteresis in Gd0.5 Er0.5Al2 was <100 A/m for T−TC< 20 K.
Magnetic properties of a metastable Sm-Fe phase synthesized by selectively thermalized sputtering
Authors: Cadieu F. J. , Cheung T. D. , Wickramasekara L. , Aly S. H.
Published: February 2003

Samples of the Sm-Fe system have been directly crystallized onto heated substrates by selectively thermalized sputtering. Films of the pure Sm-Fe system exhibit only the 1–2, 1–3, and 2–17 phases which correspond to the bulk system. But samples synthesized with certain third element additions of oxygen and titanium exhibit a metastable phase at a composition corresponding to a 1–5 Sm–Fe compound. These samples exhibit well defined and reasonable sharp x-ray diffraction patterns. Room-temperature intrinsic coercive forces of 6.2 kOe and static energy products of 5.5 MG Oe have been observed. These results are for the demagnetizing field in the plane of the thin film samples and no demagnetizing factor has been used in obtaining the inplane B field. Samples synthesized in the presence of an inplane magnetic field at 600 °C exhibit an inplane anisotropy which indicates the Curie point of this Ti-stabilized SmFe5 phase should be greater than 600 °C. Film samples of the pure Sm-Fe system which do not show a metastable phase generally have low intrinsic coercive forces and consequently low energy products.
Magneto-optical method for ac susceptibility measurements
Authors: Ritter M. , Hülsing H. , Wolf W. P.
Published: February 2003

A new optical method has been developed for the measurement of ac magnetic susceptibilities. The method is based on the modulation of the Faraday effect by a variable frequency ac magnetic field, applied parallel to the light passing through an optically transparent sample. The present system operates between 2 Hz and 200 kHz but the method should be capable of covering an even wider frequency range. Calibration of the frequency response is achieved by measuring a Van Vleck paramagnet (thulium aluminum garnet), which is predicted to have a frequency independent susceptibility up to ∼1 THz. Preliminary results for dysprosium aluminum garnet at various fields are presented.