bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetism of metallic superlattices
Authors: Jarlborg T. , Freeman A. J.
Published: February 2003

Artificially made layered materials such as modulated structures have added a new dimension to magnetism research. Important parameters are modulation amplitudes and wavelengths, concentration, interface matching, and orientation of the modulation. We have studied theoretically the electronic structure and magnetic properties of various coherent modulated structures by means of self-consistent spin-polarized LMTO band calculations using large supercells to describe the structure. For CuNi, modulations along [111] and [100] were studied for different assumed wavelengths and supercells. In all cases, the calculated Ni moments are found to be reduced compared to fcc Ni. Adjacent Cu layers acquire small moments of varying direction and strength, indicating that the Cu and the wavelength as well as the s-electron moments might be important to mediate the coupling between separated Ni layers. To study effects of local distortions, such as shear and stretching, the magnetic moment in bulk Ni and magnetic susceptibility in Pd have been calculated for tetragonally distorted lattices.
Crossovers from two-dimensional Ising to two-dimensional Heisenberg and to one-dimensional Ising
Authors: Hatta Ichiro
Published: February 2003

In two-dimensional Ising (2dI) to one-dimensional Ising (1dI) crossover, from the exact solution at the 1dI limit the critical amplitude of heat capacity with logarithmic divergence goes to zero; however, the critical amplitude of magnetization and the scale factor of inverse correlation length with the 2dI critical exponents become infinity. This behavior at the 1dI limit is extremely anomalous. On the other hand, in 2dI to two-dimensional Heisenberg (2dH) crossover from the experiment it is clear that at the 2dH limit every critical amplitude with the 2dI critical exponents reasonably goes to zero. In support of this behavior two-scale-factor universality works satisfactorily. To explain these results consistently, so-called Stanley-Kaplan’s asymptotic temperature (TSK) has a very important significance. Using TSK, we can clearly indicate that the 2dI-to-2dH crossover takes place with two steps, strong universality region and weak universality region.
Dynamics of microscopic magnetization processes and magnetic losses (invited)
Authors: Bertotti G. , Fiorillo F. , Mazzetti P. , Soardo G. P.
Published: February 2003

To a first approximation only, microscopic magnetization processes giving rise to dynamic losses can be identified with uniform and continuous motions of domain walls. A new model has been developed which takes account of the spatial and temporal nonhomogeneities and of the stochastic character of the elementary loss mechanisms. The model is reviewed and further developments are discussed, which permit to evaluate with very good approximation local losses in sample regions with antiparallel domains, under the most general conditions of wall spacings and irregular motions. An expression is derived relating dynamic losses to the power spectrum of the time derivative of the flux linked to a square region of the lamination cross section having the side equal to its thickness d. This spectrum can be experimentally measured from the electromotive force induced between contact points on the specimen surface, or from the frequency analysis of the optical signal obtained by a Kerr type set-up, in which the lamination surface area under investigation is of the order of d2.
Loss separation measurements for several electrical steels
Authors: Foster K. , Werner F. E. , Del Vecchio R. M.
Published: February 2003

Loss separation measurements were made on regular grain oriented 3% Si steels of four sheet thicknesses, one thickness of high permeability oriented 3% Si steel, two grades of nonoriented Si steel, a low carbon steel, a primary recrystallization oriented low alloy iron sample, and an amorphous metal sample. The Bn dependence of hysteresis loss Ph for all samples except the oriented Si steels was close to n=1.6, in good agreement with the Steinmetz value. All the oriented Si steels had n values close to 2.
Studies of small Fe–Sn clusters in argon matrix (invited)a)
Authors: Pasternak M. , Shamai S. , Micklitz H.
Published: February 2003

The Mössbauer effect in 119Sn and 57Fe was employed to study and characterize small clusters of FexSny formed and stabilized in a solid argon matrix. Various low concentrations of Fe and Sn atoms with respect to Ar were used (0.1–0.5 at. %), resulting in formation of dimers and trimers. The constituencies and geometrical structures were confirmed by self-consistent assignment of the 57Fe isomer shift, quadrupole splitting, line width, and relative intensities of the 57Fe and 119Sn lines. Apart from the the monomers and dimers of Fe and Sn the following species were characterized, namely: FeSn, Fe2Sn, FeSn2, SnFeSn, and Fe3. Conclusions were derived regarding the reactivity of Fe and Sn atoms and dimers in the matrix preceding solidification of argon. The nature of Fe–Sn bond is discussed in terms of the 57Fe hyperfine constants.
Magnetic order in silicate minerals (invited)
Authors: Coey J. M. D. , Moukarika A. , Ballet O.
Published: February 2003

Silicates are the most common Earth materials. Many iron-rich solid solution series order magnetically but ordering temperatures rarely exceed 100 K, even for the iron end-members. Minerals with sheet and chain structures are discussed, with emphasis on the magnetic properties of greenalite, cronstedtite, biotite, and crocidolite determined by magnetization, susceptibility, and Mössbauer measurements and by magnetic neutron diffraction. The principal magnetic interactions in the ferrous minerals are ferromagnetic, due to near 90° Fe–O–Fe bond angles for edge-sharing octahedral sites, yet all of them order antiferromagnetically as the ferromagnetic sheets or chains are coupled by relatively weak antiferromagnetic interactions. A spin flop transition occurring in fields of 1–15 kOe at 4.2 K is analyzed in terms of effective anisotropy and exchange fields. Magnetocrystalline anisotropy arises from the Fe2+ ion which is in an orbital singlet 5A1g, lz=0 ground state in an effectively trigonal crystal field. The hard trigonal axis in sheet silicates lies close to the crystllographic c direction and approximately normal to the plane of the layers. Almost all the iron-rich silicates show some degree of mixed valence in that Fe2+ and Fe3+ occupy crystallographically equivalent sites, but thermally-activated electron hopping is rare. Among the sheet silicates it has been found only in cronstedtite [SiFe3+]2{Fe2+, Fe3+}3O5(OH)4.
Magnetization and Mössbauer effect study of Dy6Mn23 and Tm6Mn23 and their ternary hydrides
Authors: Buschow K. H. J. , Gubbens P. C. M. , Ras W. , van der Kraan A. M.
Published: February 2003

The compounds Dy6Mn23 and their ternary hydrides were investigated by means of magnetic measurements and 161Dy and 169Tm Mössbauer spectroscopy. In both compounds the absorption of hydrogen gas leads to a strong reduction of the bulk magnetization even though the Dy sublattice remains magnetically ordered at low temperatures, with magnetic moments on the rare earth atoms close to the free ion values. From a comparative study of the lattice constants of rare earth manganese compounds of the type R6Mn23 before and after H2 absorption it is derived that the H content of the hydrides R6Mn23Hx varies with the R component. This may partly account for the nonuniform behavior of the Mn sublattice magnetization in R6Mn23Hx.
Permanent magnet properties of in-situ formed Cu–Fe multifilamentary compositesa)
Authors: Dublon G. , Habbal F. , Bell J. L.
Published: February 2003

Cu–Fe multifilamentary composites with up to 60 vol % Fe were prepared in situ. Magnetic hysteresis loops were obtained at room temperature as a function of composition, cross sectional area reduction, up to 99.9996%, and annealing conditions. Hci and (B⋅H)max increase with cross sectional area reduction and show pronounced changes on annealing. Hci=600, 520, and 380 Oe and Mr=5.6, 8.2, and 11.9 kG were measured in the smallest 30, 45, and 60 vol % Fe composites, respectively, following optimal heat treatment. (B⋅H)max=3.2 MG⋅Oe was measured in both Cu–45 vol % Fe and Cu–60 vol % Fe with hysteresis loop squareness of 0.95. Considering the excellent mechanical and transport properties, inexpensive constituent elements, and simple preparation, the in-situ formed Cu–Fe composites appear to have the potential for permanent magnet applications.
Spin transition under reduction of Ru4+ in YIG:Ru
Authors: Antonini B. , Balestrino G. , Krishnan R. , Paoletti A. , Paroli P. , Tucciarone A.
Published: February 2003

Ru substitution strongly affects the anisotropy properties of YIG, shifting the magnetic easy direction from 〈111〉 to 〈100〉. In this paper the spin transition is studied in single crystals containing about 0.15 wt. % of Ru. In particular, the variation is measured of the magnetic easy axis as the Ru4+ concentration is decreased by successive reducing treatments in H2 atmosphere. The decreasing amounts of Ru4+ are monitored by means of the optical absorption peak of octahedral Ru4+, at λ∼1.35 μm. The treatments in H2 result in the formation of OH− groups, whose presence is detected by means of absorption at λ=2.8 μm. We observe a 〈100〉→〈111〉 easy axis transition and find it to be first order, with the two magnetic phases coexisting over a range of Ru4+ concentration. The spin transition is very sensitive to the Ru4+ reduction: from the known values of the magnetic anisotropy constants of Ru in YIG, this may be attributed to the ultimate formation of divalent ruthenium in the reduction process.
An interdigital transducer for ultrasonic nondestructive testing
Authors: Toda Kohji , Hayama Masaru , Moriizumi Toyosaka , Yasuda Tsutomu
Published: February 2003

A technique for nondestructive testing of materials is described, which uses two arched interdigital transducers operating at a liquid-solid interface. The transducer has a frequency-dependent radiation angle. Two pairs of arched interdigital electrodes on the same surface of a piezoelectric substrate are not in contact with the liquid. Basic performance of the transducer and acoustic imaging results are presented.
Interactive computer aided design of electric machines and electromagnetic apparatus (invited)
Authors: Freeman E. M.
Published: February 2003

The design of electromagnetic devices in industry is still largely done using traditional techniques. Early computing facilities were costly to use and limited to alphanumeric applications. The application of numerical methods, mainly finite elements, to the solution of electromagnetic field problems, proved to be difficult to implement initially due to input/output problems. These difficulties were completely obviated by the advent of inexpensive microcomputers and low cost interactive graphics. However, it is still uncommon to find these new methods being employed as part of the normal electrical design process. Meanwhile, in parallel, there has been a massive growth of computer-aided methods applied to all aspects of mechanical engineering design and drafting, CADCAM. The trend is towards small, powerful, expandable, dedicated computer systems equipped with high resolution interactive graphics, which can be connected via a fast datalink. These are commonly available, complete with software, as turnkey systems. The advantages of CADCAM are manifold: Lower costs, higher productivity, higher quality products, with shorter lead times. The introduction of CADCAM will result in organisational as well as technical changes. The major change will be in the way people think.
Nonlinear three-dimensional electromagnetic field computation in electrical machinery
Authors: Chari M. V. K. , Palmo M. A. , D’Angelo J.
Published: February 2003

The need for design of electrical plant and machinary to operate at high power densities at minimum cost, optimal efficiency, and with a high degree of reliability, necessities accurate performance prediction at the design stage. As an important step in this process, the magnetic field must be evaluated in the complex geometry of the field region taking full account of magnetic saturation. In this paper, the solution to the nonlinear magnetostatic field problem is presented and is illustrated by numerical examples where feasible.
Application of higher order isoparametric finite elements in 3-D magnetic field calculation
Authors: Stögner H. , Preis K.
Published: February 2003

For 3-d magnetic field problems a finite element software package is introduced using curved side 26-noded and 20-noded isoparametric elements of the Serendipity family. The efficiency of the developed software package is demonstrated by a special example. Investigations of the accuracy of the numerical results are performed by comparison with the analytical solution of a specific problem.
An estimation of electromagnetic forces by using three-dimensional finite element method with the second-order tetrahedral elements
Authors: Nakamae E. , Harada K. , Dohi Y. , Nomura T. , Yamashita H. , Hammam M. S. A. A.
Published: February 2003

Accurate prediction of the electromagnetic force (emf) in large electrical machinery and devices is required for design optimization and reliability assurance. Owing to the antisymmetry of magnetic paths and windings in electrical machinery, in some cases the three-dimensional analyses are required. In this paper, the second-order tetrahedral elements are used to accurately calculate emf with relatively small number of elements. The emf acting between two windings in a 100 kVA testing transformer is measured and is calculated by the proposed method and by the axisymmetrical finite element method, and the relation between the analytical results’ size and the obtained results’ accuracy is investigated; the results clearly shows the merits of the proposal.
Magnetic and electrical properties of Ti-substituted yttrium iron garnet
Authors: Parkash Om , Bahadur D.
Published: February 2003

We have investigated the possibility of formation of a garnet phase and the magnetic and electrical properties of the systems (a) Y2O3–CaO–Fe2O3–TiO2 and (b) Y2O3–Fe2O3–NiO– TiO2. X-ray data show the formation of single phase up to x=0.7, in the system (a) while the garnet phase could not be prepared in the system (b). Magnetization measurements indicated canting of spins on the tetrahedral sites in the system (a). Curie temperature decreased with increase in x in this system. Change in the activation energy for conduction has been observed near the Curie temperature. Seebeck coefficients were positive and essentially independent of temperature. Electrical properties have been explained on the basis of the model suggested by Austin and Mott. According to this model electron hopping in the octahedral sites may occur by jumping indirectly through tetrahedral site.
Vapor pressure dependence of native defect concentrations in GaP
Authors: Tanaka Akira , Sukegawa Tokuzo
Published: February 2003

Native defect concentrations in GaP were calculated under solid-vapor equilibrium conditions to explain the annealing effects. Total number of native defects at a fixed temperature was minimized at a certain phosphorus pressure. This pressure is consistent with the optimum pressure reported in annealing experiments.
Selenium doping of molecular beam epitaxial GaAs using SnSe2
Authors: Smith R. S. , Ganser P. M. , Ennen H.
Published: February 2003

The feasibility of using SnSe2 as a source of selenium for the n-type doping of molecular beam epitaxial GaAs layers is demonstrated. Doping levels between 6×1014 and 7×1018 cm−3 have been achieved and no surface accumulation of selenium at the high doping concentrations was observed. Low temperature photoluminescence studies show that the excitonic emission broadens and shifts to higher energy with increasing doping concentration in a similar way to that observed in tellurium-doped GaAs. The half-width of the emission peak may be used to estimate the doping level of Se-doped layers on n+ substrates down to a concentration of about 2×1016 cm−3.
Carrier-phonon interactions in 1.3-μm quaternary In0.72Ga0.28As0.6 P0.4
Authors: Shah J. , Etienne B. , Leheny R. F. , Nahory R. E. , DiGiovanni A. E.
Published: February 2003

Optically induced hot carriers in In0.72Ga0.28As0.6 P0.4 are measured using photoluminescence techniques and interpreted in terms of a polar-optical-phonon-scattering model with four phonons. We show that the combined effect of these phonons can be well represented using a single effective phonon energy for a wide temperature range, e.g., ℏωeff =31.6 meV for carrier temperatures between 35 and 160 K. This observation should greatly simplify the inclusion of multiphonon scattering in future calculations for this quaternary alloy material.
A comparison of Mo films bias sputtered in Ar/N2 with related high energy ion implantation experiments
Authors: Kay E. , Ziemann P.
Published: February 2003

Mo films were prepared by bias sputtering in a dc-triode system using an Ar/N2 mixture as sputter gas. The substrates were held at −180 °C. The resulting changes of the residual resistivity ρ0 and transition temperature to superconductivity Tc were measured as a function of the nitrogen concentration within the films cN. Large Tc increases up to 7.6 K have been found for highly disordered films ( ρ0=100 μΩ cm, cN =10 at. %). For still higher cN values, Tc decreased to about 5 K, while the resistivity increased up to 500 μΩ cm, exhibiting a negative temperature dependence typical for amorphous materials. Our results will be compared to an implantation experiment, where N+ ions have been implanted into preexisting Mo films.
Properties of CdTe/InSb heterostructures prepared by molecular beam epitaxy
Authors: Myers T. H. , Lo Yawcheng , Schetzina J. F. , Jost S. R.
Published: February 2003

Properties of CdTe/InSb heterostructures grown on (111)B InSb substrates by molecular beam epitaxy are reported. X-ray diffraction and uv reflectance measurements were used to judge the quality of epitaxy for layers grown under various conditions. Auger depth profile analysis revealed a sharp CdTe/InSb interfacial region of less than 250 Å for depositions at 220 °C. Detailed capacitance-voltage measurements yielded interface-state densities of 1.4–2.8×1011 cm−2 eV−1 (near midgap) for these preliminary samples, indicating that improved metal-insulator-semiconductor structures on InSb may be possible using this lattice-matched heterojunction surface passivation scheme.
Transport mechanisms for Mg/Zn3P2 junctions
Authors: Wang Faa-Ching , Fahrenbruch Alan L. , Bube Richard H.
Published: February 2003

The dominant transport mechanisms for Mg/Zn3P2 junctions are shown to depend on the heat treatment in hydrogen of the Zn3P2 prior to Mg deposition. For heat treatments below 300 °C, multistep tunneling via defect centers dominates, whereas for heat treatments between 300 and 500 °C, recombination/generation dominates. Correspondence is observed between the imperfections responsible for the junction transport and previously reported imperfections in bulk Zn3P2 crystals. Enhanced tunneling under solar illumination contributes to the low energy conversion efficiency of thin Mg film Mg/Zn3P2 devices. An estimate of the interface recombination velocity for these junctions yields a value of 1.9×107 cm/sec.
Stark effect of SiOH and SiH molecules in SiO2
Authors: Palik E. D. , Holm R. T. , Stella A. , Hughes H. L.
Published: February 2003

Hydrogen has been implanted into an SiO2 film grown on a Si trapezoid substrate to form SiH and SiOH bonds. Utilizing internal reflection spectroscopy in the near infrared spectral region, we have directly observed the vibration bands of these ‘‘molecules.’’ With the application of a large electric field across this metal-oxide-semiconductor structure, the Stark effect of these vibration bands has been observed. The dependence of line intensity and line shape on the applied voltage has been studied. The sharing of voltage between the oxide film and the depletion layer in the Si is seen by its effect on the Stark intensity. These results suggest the feasibility of seeing natural hydrogen molecularly bonded in thermal oxides.
Optical conductivity of α-Mn
Authors: Scoles K. J. , Christy R. W.
Published: February 2003

The optical constants were measured at room temperature in the photon-energy range 0.6–6.5 eV on evaporated thin films. Evaporation conditions were chosen that gave the α-Mn crystal structure with relatively large grains. The optical conductivity was separated into intraband and interband contributions by fitting to the Drude formula at low energies. The results are anomalous in comparison to other 3d transition metals: the free-electron lifetime is exceptionally short (in agreement with the large dc resistivity of Mn), and the interband transitions seem unusually weak at the lower energies. We discuss possible explanations related to the complicated crystal structure of α-Mn with its loss of point symmetry at the atom sites.
Refractive index of 2-μm bubble garnet films
Authors: Pištora J. , Višňovský Š. , Nitsch K. , Pařízek V. , Prosser V.
Published: February 2003

The visible and near infrared refractive index spectra in YSmLuCaFeGe garnet films obtained from the results of guided surface wave experiments at 1152 and 633 nm and from reflection interference spectroscopy at angles of incidence ranging from 5 to 55° are reported. The data were fitted to a two-term oscillator expression. The effect of the film absorption and that of the interface layers on both sides of the film on the calculated values of the refractive index and the thickness of the film are discussed.
Optical and dielectric functions of liquid methylated benzenes in the 2- to 10-eV spectral region
Authors: Attrey J. S. , Birkhoff R. D. , Painter L. R.
Published: February 2003

The optical and dielectric functions have been determined in the 2 to 10-eV spectral region for four polycyclic hydrocarbons: benzene, toluene, xylene, and trimethylbenzene. The effect of substitution on the spectra of these liquid alkyl benzenes is investigated and comparisons are made to the appropriate gas-phase spectra.
X-ray induced processes in SrTiO3
Authors: Aguilar M. , Agulló-López F.
Published: February 2003

The x-ray induced visible luminescence of SrTiO3 has been studied in the range 15–300 °K. An apparently single-emission band at 500 nm has been observed whose efficiency abruptly decreases at ∼30 °K. This luminescence band is proposed to be intrinsic and associated with the decay of a relaxed Ti+3O−53 exciton. After 15 °K irradiation, a visible absorption spectrum which increases towards the infrared is produced and anneals out at ∼30 °K. It is suggested that the absorption is due to electron transition from a Ti+3 center to the conduction band, in accordance with recent ultraviolet photoemission spectroscopy data. The thermoluminescence spectrum after 15 °K irradiation has also been determined. The first glow peak at 30 °K appears to correlate well with the thermal decay of the irradiation-induced absorption.
Oxidation studies of impregnated dispenser cathodes
Authors: Hecht M. H. , Lindau I. , Chen D. S.
Published: February 2003

We report on surface studies of the type M and type S impregnated dispenser cathode using synchrotron radiation photoemission spectroscopy. The results indicate the presence of two barium configurations on the room temperature type S surface, probably barium metal and BaO. The room-temperature type M cathode has about a monolayer of barium metal and about a monolayer of tungsten, apparently alloyed to the Os/Ru coating, on the surface. The barium-related features of the type S cathode are extremely sensitive to small oxygen exposures, while the tungsten-related features are more sensitive to oxygen in the type M cathode.
Evaluation of the base metal activity of oxide cathodes
Authors: Aida T. , Taguchi S. , Yamamoto S. , Fukushima H.
Published: February 2003

Activity of the base metal is evaluated by identifying reaction products with the oxide layer, measuring Ba vapor pressure from the oxide, measuring of emission current properties, and by analyzing the surface composition of the oxide. Reducing capabilities of Zr, W, and Mo activators in Ni base metal are determined. Their activators are alloyed to the Ni core metal up to the solubility limits. The experimental results are evaluated systematically from the standpoint of base metal activity, together with the thermochemical treatment for the various reactions and the emission mechanism of the oxide coated cathode.
Effects of various encapsulating films on laser recrystallization of silicon on SiO2
Authors: Lasky J. B.
Published: February 2003

Single-crystal silicon-on-oxide was produced by laser recrystallization of a 0.6-μm polysilicon film deposited on 1 μm of thermal SiO2. Oriented growth commenced where the polysilicon film was in contact with the silicon substrate, and proceeded laterally over the fully recessed SiO2. Typical dimensions of the single-crystal silicon-on-oxide film are 25 μm by 7 mm. The laser annealing was done with several different encapsulating films above the polysilicon, including 11.0, 16.4, and 32.9 nm of Si3N4, 25 nm of SiO2, 25 nm SiO2 +32.9 nm Si3N4, and uncapped samples. In addition, samples were laser annealed with and without an 1100 °C N2 preanneal of the structure. The 1100 °C anneal reduced the nucleation of misoriented grains in all samples, and extended the range of useable powers for the Si3N4 capped samples. The 32.9-nm Si3N4 cap produced the smoothest film and the most efficient coupling of the laser light into the silicon. The maximum distance of single-crystal growth was the same for all nitrogen-annealed samples, and showed a weak dependence on the melt width induced by the beam used for recrystallization. TEM micrographs of the recrystallized silicon show that the defects lie predominantly in the 110 direction. Their density increases away from the seed region, and they coalesce to form the grain boundaries at the transition to polysilicon growth.
Homogeneous (Ga,Al)P alloy grown by the temperature difference method
Authors: Tanaka Akira , Unno Hideyuki , Sugiura Toshifumi , Sukegawa Tokuzo
Published: February 2003

A method was developed to grow homogeneous (Ga,Al)P alloy using a temperatue difference liquid phase epitaxial growth technique. In this method (Ga,Al)P polycrystals were prepared at 1000 °C prior to the growth of (Ga,Al)P alloy at 800 °C, which acted as the Al source to maintain the alloy composition constant during the growth. Electron probe microanalysis showed that the grown alloy was uniform within 0.01 mole fraction. It was also possible to control the alloy composition by this growth technique. Measurements of photoluminescence of the grown layer and electroluminescence of Zn-diffused diode revealed the grown alloy was of high quality. Observed edge emission energy indicated that the band gap varied with alloy composition. The edge band emission spectra with fine structure were observed at 77 K.
Heat-treatment studies on thin-film CdS/CuxS solar cells
Authors: Hmurcik L. , Serway R. A.
Published: February 2003

The effects of hydrogen heat treatments are reported on CdS/CuxS polycrystalline thin-film solar cells. The short-circuit current Isc of the cells changes in an exponential manner such that Isc =Isc (t=0)e(t/τ)1/2. The principle physical mechanism responsible for this change appears to be copper diffusion through the CuxS layer as copper oxides at the surface are reduced or formed. We were able to maximize the cell efficiency with an error of 5% or less by monitoring changes in cell parameters during heat treatments. Changes in CuxS stoichiometry were correlated with the sheet resistance of the CuxS layer in completed cells. Results indicate that heat treatment in a hydrogen atmosphere causes an increase in resistivity (corresponding to an increase in stoichiometry) while oxygen causes the reverse.
Transport theory of semiconductor energy conversion
Authors: Parrott J. E.
Published: February 2003

A systematic analysis of all the microscopic processes corresponding to macroscopic energy conversion in semiconductors is presented. Starting from the quasi-classical particle Boltzmann equations, a continuity equation for total energy is derived containing terms which can be identified with external electric power transfers. Similar continuity equations for internal energy and entropy are obtained, and from the latter, the irreversible entropy generation rate may be found. Using expressions for the particle and heat currents, the usual ohmic heating, thermoelectric and photoelectric effects are identified together with a new reversible effect whose magnitude is Ψ∇φ∇T/T, where Ψ=(σeσh/σ) T(Σh−Σe). Here σe,σh are partial electron and hole electrical conductivities, σ=σe +σh, Σe and Σh are the partial electron and hole Seebeck coefficients, φ is the difference between the electron and hole quasi-Fermi levels, and T is the temperature. Similarly, a complete account is given of the heating and refrigerating processes within the semiconductor. The analysis allows for the possibility of band structure inhomogeneities.
The virial theorem and scaling laws for superconducting magnet systems
Authors: Moon Francis C.
Published: February 2003

The structural masses of over thirty superconducting magnet designs are shown to exceed that required by the virial theorem by factors of from 2 to 10 or more. Designs for magnetohydrodynamic and toroidal field fusion magnets from many different magnet groups around the world appear to obey a stored energy-mass scaling law of the form E=CM4/3. This scaling law appears to be valid over three to four orders of magnitude of stored magnetic energy. The 4/3 power law differs from the linear scaling derived from the virial theorem and may be related in part to the thermal stability requirements of the superconductor. However, the masses of large-scale magnets are approaching the regime where the structural mass required by the virial theorem will place greater constraints on the design than thermal stability.
Theory and experiments on open circuit voltage decay of p-n junction diodes with arbitrary base width, including the effects of built-in drift field in the base and recombinations in the emitter
Authors: Ray U. C. , Agarwal S. K. , Jain S. C.
Published: February 2003

An expression for the forward current induced open circuit voltage decay of a p-n junction diode with a finite base width is derived. The expression includes the effects of recombination in the emitter and the built-in drift field in the base which may arise due to a nonuniform impurity profile. The voltage decay rate is dependent on the base thickness, base drift field, emitter dark saturation current, the effective surface recombination velocity at the back contact, and the minority carrier lifetime in the base. The effects of the drift field in the emitter, emitter lifetime, and surface recombination velocity at the emitter surface are completely taken into account by the emitter saturation current. Experimentally observed voltage decay plots for thin base hyperabrupt varactor diodes with retrograded impurity gradients in the base are reported. It is shown that the experimental results can be interpreted satisfactorily using the above theory. The values of the minority-carrier lifetime in the base are determined from the experimental results.
Mechanism of catastrophic degradation in InGaAsP/InP double-heterostructure light emitting diodes and GaAlAs double-heterostructure light emitting diodes applied with pulsed large current
Authors: Ueda Osamu , Yamakoshi Shigenobu , Sanada Tatsuyuki , Umebu Itsuo , Kotani Tsuyoshi , Hasegawa Osamu
Published: February 2003

Catastrophically degraded InGaAsP/InP double-heterostructure light emitting diodes and GaAlAs double-heterostructure light emitting diodes, by application of pulsed large current, were investigated by photoluminescence topography, electroluminescence topography, etching technique, transmission electron microscopy, and energy dispersive x-ray spectroscopy. In the case of InGaAsP/InP double-heterostructure light emitting diodes, several dark-spot defects and dark regions extending from the dark spot defects, were observed in the electroluminescence image of the light emitting region. By transmission electron microscopic observation, the dark defects were proved to be associated with mixed regions consisting of (i) micrograins of the matrix crystal, (ii) an amorphous area of the matrix crystal, and (iii) regions where the matrix crystal was alloyed with the metals of the electrode. An analysis by energy dispersive x-ray spectroscopy indicated that the dark regions consist of large amounts of Au. These defects were considered to be generated by the alloy reaction between the matrix crystal and the metals of the electrode, especially Au. While, in the case of GaAlAs double-heterostructure light emitting diodes, cross-hatched dark-line defects, lying in the two equivalent directions of the 〈110〉 and the 〈11̄0〉, were observed in the light emitting regions by photoluminescence topography. These dark-line defects were proved to correspond to bundles of dislocations similar to slip band by transmission electron microscopic observation. These dislocations were considered to be generated by dislocation glide motion alone; dislocation loops and dislocation dipoles, which were induced by climb motion, were not observed at all. The glide motion was presumably caused by the relaxation of the elastic stress concentrated on the light emitting region, which was enhanced by nonradiative recombination event of minority carriers. On the mechanism of catastrophic degradation, dislocation glide motion enhanced by nonradiative recombination is the origin in the GaAlAs double-heterostructure light emitting diodes. On the other hand, no glide motion was observed in catastrophically degraded InGaAsP/InP double-heterostructure light emitting diodes; these diodes degraded by the alloy reaction between the matrix and the metals of the electrode due to the concentration of injected carriers on the nonuniform region of the electrode.
Attenuation of surface acoustic waves propagating on a metallized ST-cut quartz
Authors: Gorodetsky G. , Mordowicz D. , Volterra V.
Published: February 2003

Measurements of attenuation and velocity change of surface acoustic waves (SAW) in ST-cut quartz were carried out at various frequencies, during a vapor deposition of indium and silver. The measurements were performed with the substrate held at room temperature and at liquid nitrogen temperature. We observed that the attenuation, within the experimental error, is linearly proportional to the SAW frequency. It was also found that the coarser the structure of the semicontinuous film, the lower the attenuation. The existing theories are critically discussed and an alternative explanation is suggested.
Cluster in condensed matter method study of hydrogen in nickel
Authors: Keller Jaime , Castro Miguel , de Paoli Angel Luis
Published: February 2003

We apply the multiple scattering cluster-in-condensed-matter technique to study the electronic structure of an interstitial hydrogen atom in an octahedral cluster of ferromagnetic nickel in a condensed matter-like boundary potential. From the calculation we obtain the approximate absorption energies, the vibrational frequencies for hydrogen, the effect on the magnetic moment of the cluster, and the change in local paramagnetic susceptibility and hyperfine field at the hydrogen and neighboring nickel sites. The obtained values compare favorably with available experimental data. The bonding between the hydrogen and the nickel is discussed, by comparing the results with those for H2, Ni2, and Ni2H2 molecules.
Current-voltage characteristic for bipolar p-n junction devices with drift fields, including correlation between carrier lifetimes and shallow-impurity concentration
Authors: Lindholm Fred A. , Chen Y. H.
Published: February 2003

We present general analytic solutions for static current-voltage characteristics of quasineutral regions of nonilluminated semiconductor bipolar devices under the following assumptions: (a) the quasineutral region has a graded shallow-level impurity concentration producing a constant built-in electric (drift) field; (b) minority carriers injected into this region stay at concentrations low enough to avoid violation of low-injection conditions; (c) the minority-carrier lifetime of this region depends on position in accordance with a power-law dependence on the shallow-level donor concentration, a dependence that is consistent with the longest minority-carrier lifetimes measured and with the physical chemistry of divacancy-donor reactions at high temperatures. The solutions presented are apparently the first that include assumption (c). Modified Bessel functions of the first and second kind appear in these solutions. From a pheonomenological standpoint, the solutions may account for defect centers associated with vacancy complexes and, in part, for the gettering observed in highly doped n-type Si. Design implications for transistors, diodes, and solar cells are discussed quantitatively for a thin drift-field Si p/n(x) junction solar cell.
Preparation, tunneling, resistivity, and critical current measurements on homogeneous highT
c A15 Nb3Ge thin films
Authors: Kihlstrom K. E. , Hammond R. H. , Talvacchio J. , Geballe T. H. , Green A. K. , Rehn Victor
Published: February 2003

We have prepared homogeneous films of high Tc Nb3Ge as demonstrated by a total transition width of less than 1 K with a resistive Tc onset of 21.7 K, by paying particular attention to the constancy of substrate temperature. Xray diffraction analysis done both at Stanford and at Westinghouse shows no evidence of a second phase to the limits of the instruments (<1%). Tunneling as a function of thickness shows the material to be of good quality (high, sharp gaps; low excess conductance below the sum gap) at the surface for thicknesses of up to 1 μm and only slightly degraded at 5 μm. Further evidence of homogeneity is demonstrated by critical current measurements which give an extrapolated T*c of 20 K on material with resistive Tc onset of 21.9 K. Critical current densities at 14 K in a 0.5 T field are as high as 9×106 A/cm2, which are the highest ever reported for any material at this temperature. In an applied magnetic field of 7.5 tesla, Jc was 2.5×106 A/cm2 at 4.2 K. Tunneling as a function of thickness into Nb3Ge where the oxygen had been removed from the system after 1300 Å had been deposited but the deposition continued up to 1 μm showed only limited degradation (in terms of gap width, excess conductance below the gap as well as magnitude of gap). This gives some indication that oxygen may only be needed initially during the deposition rather than throughout the entire deposition. Tc correlates well with composition, as does resistivity, thus we see the correlation between increasing Tc and decreasing resistivity.
Magnetostatic volume wave propagation in multiple ferrite layers
Authors: Adkins L. R. , Glass H. L.
Published: February 2003

The dispersive charcteristics of forward and backward magnetostatic waves (MSWs) propagating in single and multiple layer yttrium iron garnet (YIG) and gallium substituted YIG films have been investigated theoretically and experimentally. The theory predicts that the multiple layer structures can support MSW modes corresponding to propagation in the individual layers as well as a composite mode linking the magnetic films. Each mode of propagation has been observed experimentally. The composite mode is excited if the film with the lower value of 4 πM is in contact with the shorted electrode transducers, while single layer modes are excited if the film sequence is reversed. The dispersion of the composite mode can be made approximately linear with proper selection of film thickness.
Microwave resonance and propagation in nonsaturated ferromagnetic media. II. Electromagnetic wave propagation in uniaxially anisotropic insulators and metals
Authors: Vittoria C. , Rachford F. J.
Published: February 2003

We have developed a theoretical formulation for calculating electromagnetic reflection and transmission coefficients in magnetically nonsaturated media. Numerical examples are presented for the cases of an electromagnetic wave normally incident upon a slab of ferromagnetic insulator or metal. Antiresonance transmission is predicted for nonsaturated magnetic metals. For H in the slab plane, the antiresonance frequency is nearly independent of domain structure in contrast to the case of H normal to the slab plane.
Pulsed high-voltage dielectric properties of ethylene glycol/water mixtures
Authors: Fenneman David B.
Published: February 2003

Measurements of the (complex) dielectric constant, intrinsic time constant, and electrical breakdown strength of highly purified ethylene glycol/water mixtures as functions of temperature and mixture ratio are presented. Over the frequency range from 0.5 to 108 MHz, the dielectric constant is found to be well represented by a simple Debye model. When cooled to near their freezing points, these mixtures have dielectric constants of the same order as pure water (∼80) but with intrinsic time constants at least an order of magnitude greater than water. The mixtures are found to support fields greater than 15 MV/m for periods exceeding a millisecond. The observed high-voltage decay is nonsimple due to the phenomenon of charge injection. The ability to sustain high fields for millisecond time scales suggests the use of such mixtures as the dielectric in the pulse forming lines of large-pulse power machines.
Interaction of a dislocation with a misfitting precipitate
Authors: Johnson William C.
Published: February 2003

By formulating the appropriate differential equations and boundary conditions in terms of an integral equation, an expression is derived for the displacement associated with an interacting dislocation and precipitate in an infinite matrix. The technique is applicable to anisotropic systems in which the precipitate possesses a stress-free transformation strain and elastic constants different from those of the matrix phase. Approximate solutions to the integral equation are made, and stress, strain, and interaction energy calculated for straight screw and edge dislocations situated near ellipsoidal and rectangular parallelepiped elastic inhomogeneities in an isotropic matrix.
Investigation of trapping centers in single-crystal niobium dioxide by admittance spectroscopy
Authors: Yousuf M. , Kuliyev B. , Lalevic B.
Published: February 2003

Investigation of trap parameters in single-crystal niobium dioxide is performed employing the admittance spectroscopic method. From conductance and capacitance measurements versus temperature at different frequencies, five trap levels with energies of 0.25–0.435 eV were identified. Other characteristic parameters were determined including trap density, capture cross section, and emission rate. Measured values of these parameters indicate the existence of two groups of traps.
Metastable doping behavior in antimony-implanted (100) silicon
Authors: Williams J. S. , Short K. T.
Published: February 2003

High-dose antimony-implanted (100) silicon has been activated by furnace annealing at temperatures ∼600 °C to achieve active concentrations up to 3×1020 cm−3, an order of magnitude in excess of the equilibrium solubility limit for antimony in silicon. Both channeling and electrical measurements indicate that such doping levels are metastable. Subsequent annealing for longer times at higher temperatures results in a return to near-equilibrium conditions as indicated by a reduction in both the substitutional antimony fraction and the measured active concentration. The observed annealing behavior and deactivation processes for antimony in silicon appear to show important differences from results previously obtained for arsenic in silicon.
The segregation of impurities and the self-compensation problem in II-VI compounds
Authors: Pautrat J. L. , Magnea N. , Faurie J. P.
Published: February 2003

The electrical and optical properties of ZnTe or CdTe crystals are generally inhomogeneous after annealing. This is shown to be due to the redistribution of preexisting impurities. Indeed, after growth, these crystals contain some excess tellurium which must precipitate since the solidus line has a retrograde shape. The liquid Te droplets are then able to purify the surrounding materials by a solid-liquid segregation mechanism. On annealing, the tellurium excess can disappear more or less rapidly: the Te precipitates and the small inclusions shrink progressively while the impurities are released into the crystal. This mechanism explains the bright dots observed in the scanning electron microscope (cathodoluminescence mode) and due to the high lithium concentration. Under other conditions, dark dots are obtained and the role of copper is suspected. This model is discussed on the basis of the available data (segregation and diffusion coefficients). Further confirmation is obtained from direct chemical analysis of the crystal and of the inclusions itself. The consequences of the segregation of impurities on the interpretation of the self-compensation problem are analyzed. A fully satisfactory interpretation of conductivity variation with zinc pressure previously attributed to the zinc vacancy, can be derived with the single hypothesis that acceptor and donor impurities in sufficient amount are stored in the crystal. The dominant role of residual impurities in the close control of the II-VI materials is particularly emphasized.
Elastic interaction between a screw dislocation and surface crack
Authors: Chu S. N. G.
Published: February 2003

An analytical solution for the two-dimensional elastic problem of a screw dislocation near a mode III surface crack, a shear crack subject to antiplane stress, has been derived. The dislocation-crack interaction has a negative singularity at the tip of the crack irrespective to the applied stresses. In the case that the applied stress is in the direction of driving a dislocation into the medium, a metastable position exists beyond which the dislocation will be repelled by the crack. Thus a dislocation free zone is expected in the immediate vicinity of the tip of the crack. The size of the dislocation free zone decreases with increasing applied stresses. Provided that the metastable position is larger than a Burgers vector away from the crack tip, dislocations cannot be generated at the tip of the crack; instead, they have to be nucleated or generated from pre-existing sources at some distance from the tip of the crack, a conclusion in agreement with Li’s result using dislocation modelling of the crack tip stress field. The critical applied stress for the direct generation of dislocation from the crack tip is calculated. The conditions for the generation of a single or two dislocations and dislocation dipole in front of the surface crack are examined. The effect of the dislocations on the stress intensity factor and the crack driving force is presented. The study is further generalized to the consideration of a two-screw dislocation system.
A simple analysis of inert marker motion in a single compound layer for solid-phase epitaxy and for binary diffusion couples
Authors: Gösele U. , Tu K. N. , Thompson R. D.
Published: February 2003

A simple analysis of marker motion in a single compound layer is presented. The compound layer may either act as a transport layer with invariant thickness, as in the case of solid-phase epitaxial growth of amorphous silicon through a thin-film Pd2Si layer on crystalline silicon, or the compound layer may grow itself as in a planar binary diffusion couple. The analysis takes into account possibe volume changes during compound formation and holds for interface-controlled as well as for diffusion-controlled growth of the compound layer. Reanalysis of marker motion data in Ni2Si in Ni/Si thin-film diffusion couple shows that the ratio DNi/DSi of the diffusivities of Ni (DNi) and Si (DSi) in Ni2Si at 325 °C is at least about ten times larger than that evaluated previously. Marker motion data for the growth of Cu6Sn5 at room temperature in a bimetallic Cu/Sn thin-film diffusion couple are presented and analyzed.