bluuebunny/crossref_metadata_2025 huggingface dataset:
Spin dynamics in ultrathin Fe/GaAs (100)-(4×6) films at the ferromagnetic/superparamagnetic phase transition by in situ Brillouin light scattering
Authors: Steinmuller S. J. , Tselepi M. , Strom V. , Bland J. A. C.
Published: July 2002

Epitaxially grown bcc Fe films on GaAs(100)-(4×6) have been studied with in situ magneto-optical Kerr effect (MOKE), low energy electron diffraction, and in situ Brillouin light scattering (BLS) measurements. It has been reported earlier by Xu et al. [Phys. Rev. B 58, 890 (1998)] that this system exhibits at room temperature a thickness dependent superparamagnetic to ferromagnetic phase transition at a thickness dc of ∼4 ML. Combined MOKE and BLS measurements were carried out in the thickness range of 3.8–20 ML of Fe in order to investigate the spin dynamics close to dc. Two effects were observed in the vicinity of the transition thickness. First, the spin wave frequency is significantly decreased. Second, a strong broadening of the spin wave peaks takes place.
Field step dependence of delta-M curves
Authors: Harrell J. W. , Wang S. , Fujiwara H.
Published: July 2002

The field step dependence of remanence and δM curves has been measured in a CoPtCrB thin film and a γ-Fe2O3 tape. When the dc-demagnetization curve is measured with a saturation field applied before each reverse field, δM increases with decreasing field step. This effect is directly linked to viscosity effects that exist in the isothermal remanence curve that increase with the number of field steps. The essential features of the observed field step dependence are confirmed by calculations based on a Stoner-Wohlfarth, Arrhenius–Néel model.
Structure and magnetic properties of (Co,Fe)-based nanocrystalline soft magnetic materials
Authors: Willard M. A. , Claassen J. H. , Stroud R. M. , Harris V. G.
Published: July 2002

The magnetic and structural properties of as-spun and nanocrystalline (Co0.95Fe0.05)89−xZr7B4Cux alloy ribbons (where x=0 and 1) are reported. As-spun ribbons were synthesized by melt spinning with subsequent heat treatments used to stabilize the nanocrystalline microstructure. By differential thermal analysis, the onset of primary crystallization was found to occur at 475 and 481 °C for the alloys with and without Cu, respectively. The phase produced by primary crystallization was identified as a face-centered cubic-(Fe,Co) having grains ranging in size from 5 to 17 nm. The nanoscale morphology of the materials provides low hysteretic losses, as evident by the 0.26 Oe coercive field for a sample annealed at 550 °C for 1 h. In addition, the crystalline phase provides a magnetization of 1.57 T.
Investigation of the as-deposited characteristics and the thermal stability of CoFe and Ru based multilayers
Authors: Bal K. , Keen A. , Rasing Th. , van den Berg H. A. M.
Published: July 2002

The as-deposited characteristics and the thermal stability at 300 °C of CoFe and Ru based ultrathin multilayers have been investigated and structural and magnetic characteristics have been correlated. These layer systems constitute the basis of the hard artificial antiferromagnetic subsystem used in current sensors. The coercive field of 2 nm CoFe (3.5 kA/m) is found to increase linearly by a factor of 13 upon increasing the Ru seed layer thickness from 5 to 40 nm. The weakening of the exchange coupling due to the sharpening of the crystallite boundaries is likely the origin. Magnetization-induced second-harmonic generation measurements show that the CoFe/Ru interface remains magnetically active after 36 h with a magnetic contrast of 0.17, indicating that no strong mixing at the interface is taking place. In accordance, the saturation field of the antiferromagnetic coupling in Ru5/CoFe2/Ru0.7/CoFe2/Ru (nm) does not change during 20 h of annealing. However, slowly a remanent magnetization develops which is thought to be due to the formation of ferromagnetic shortcuts through the crystallite boundaries of the coupler.
Turbulent flow around a rotating stepped cylinder
Authors: Yang Kyung-Soo , Hwang Jong-Yeon , Bremhorst Klaus , Nesic Srdjan
Published: July 2002

Direct numerical simulation (DNS) of turbulent flow around a rotating cylinder with two backward-facing steps axisymmetrically mounted in the circumferential direction was performed and compared with DNS of plane backward-facing step flow (PBSF) of Le et al. [J. Fluid Mech. 330, 349 (1997)]. The original motivation of this work stemmed from the efforts to design a simple device which can generate flows of high turbulence intensity at low cost for corrosion researchers. It turned out that the current flow shows flow structures quite similar to those of PBSF downstream of the step, even though configurations of the two flows are totally different from one another. The stepped cylinder appears to be a cost-effective tool in the generation of flow structures similar to those of PBSF.
Low noise antiferromagnetically coupled media with CrTiB underlayer
Authors: Kanbe T. , Yahisa Y. , Suzuki H. , Kataoka H. , Takahashi Y. , Hirayama Y.
Published: July 2002

In order to reduce the grain size, 1.5–3 at. % B was added to the CrTi underlayer of the antiferromagnetically coupled media that has CoCrPtB/Ru/CoCrPt dual magnetic layers. The average grain size of the CrTi20 underlayer was reduced from 16.1 to 11.9 nm by 3 at. % B addition, which resulted in 12% grain size reduction of the magnetic layer deposited on it. Owing to the grain size reduction, the media noise was reduced 15%, while PW50 was almost identical. By using a thicker CrTi20B3 underlayer, signal-to-noise ratio was improved about 1 dB without decreasing the thermal stability factor.
Study of Al doping effect on superconductivity of Mg1−xAlxB2
Authors: Luo H. , Li C. M. , Luo H. M. , Ding S. Y.
Published: July 2002

Mg 1−x Al x B 2 samples in the region of 0<x⩽0.6 were prepared to study the effect of Al doping on superconductivity of MgB2. The samples were synthesized by the common solid reaction method and their structures were examined by x-ray diffraction, which shows the obvious Al effect on the interplane boron sheet separation. By means of resistivity-temperature (R-T) and ac susceptibility-temperature (χ-T) measurements, we investigated the superconductivity of the samples with different levels of Al doping. It was found that the sample persisted its bulk superconductivity until x=0.6, which was also confirmed by the critical temperature Tc at different levels of Al determined by χ-T and R-T measurements.
Magnetocaloric effect in GdRu2Ge2
Authors: Tegus O. , Duong N. P. , Dagula W. , Zhang L. , Brück E. , Buschow K. H. J. , de Boer F. R.
Published: July 2002

We have studied the magnetocaloric effect (MCE) in GdRu2Ge2 by means of measurements of temperature and field dependence of the specific heat and the magnetization. Two anomalies were observed at T1=29 K and T2=32 K in the zero-field specific-heat curve. Magnetization measurements showed that the magnetic moments of the Gd ions order antiferromagnetically below T2 and follow the Curie–Weiss Law above T2. The magnetic measurements also showed that there exists a field-induced antiferromagnetic to ferromagnetic transition below T1. The magnetocaloric properties estimated from the magnetization measurements by means of the thermodynamic Maxwell relation are in good agreement with those obtained from the specific-heat measurements. The largest observed adiabatic temperature change, ΔTad, is approximately 10 K for a field change from 0 to 15 T. The considerably large magnetic entropy change is due to the field-induced magnetic phase transition, which is magnetically reversible.
Relaxation of a strained quantum well at a cleaved surface
Authors: Davies John H. , Bruls D. M. , Vugs J. W. A. M. , Koenraad P. M.
Published: July 2002

Scanning probe microscopy of a cleaved semiconductor surface provides a direct measurement of the elastic field of buried, strained structures such as quantum wells or dots, but allowance must be made for relaxation at the surface. We have calculated this relaxation analytically for the exposed edge of a strained quantum well within classical elastic theory for a linear, isotropic, homogeneous medium. The surface bulges outward if the quantum well has a larger natural lattice constant and the dilation changes sign near the surface, which may enhance recombination. Results are given for a well of constant composition or an arbitrary variation along the growth direction and compared with cross-sectional scanning tunneling microscopy of InGaAs quantum wells in GaAs. Consistent values for the composition of the wells were obtained from counting In atoms, x-ray diffraction, and photoluminescence. The lattice constant on the surface and the normal relaxation were compared with the calculation. Qualitative agreement is good but the theory gives only about 80% of the observed displacement. Some of this difference can be explained by the larger size of indium atoms compared with gallium, and the different surface reconstruction and buckling behavior of InAs and GaAs (110) surfaces upon cleavage.
Solvent-induced electronic decoherence: Configuration dependent dissipative evolution for solvated electron systems
Authors: Wong Kim F. , Rossky Peter J.
Published: July 2002

An electronic state and nuclear configuration dependent mechanism for electronic coherence loss is integrated into the mean field with surface hopping (MF/SH) algorithm for nonadiabatic (NA) mixed quantum–classical molecular dynamics (MQC-MD). The characteristic decoherence time scale between a pair of states is evaluated from differences in the instantaneous Hellmann–Feynman forces on the two surfaces at each phase space point along the quantum–classical trajectory. Within this instantaneous decoherence mean field with surface hopping (id-MF/SH) formalism, both the primary evolution that is responsible for transition probabilities and the auxiliary equations governing the nuclear dynamics are described by the same dissipative MQC Liouville–von Neumann equation. Decoherence, therefore, impacts both the transition probabilities and the realization of the quantum–classical trajectory. The method is implemented for the solvated electron in water and methanol and applied to trajectories describing photoexcitation of equilibrium ground-state species. Analysis reveals that, in general, both the decoherence time scale and the NA coupling increase with decreasing eigenstate energy gap. The cooperative combination of both strong coupling and large coherence as the energy levels approach each other gives rise to localized regions of comparatively higher transition probabilities. Excited-state survival probability analysis extracts a decay time of 1540 fs for the solvated electron in water and 2617 fs for the methanol case. The approximate agreement with the decay of time 2102 fs for the aqueous system, based on simulations employing a fixed 6 fs decoherence parameter, suggests that an average prescription of coherence loss may be adequate for the first-excited-state solvated electron system. The self-contained form of the id-MF/SH formalism, however, makes the new method a general approach to NA MQC-MD for condensed phase systems.
Quasi-isotropic single-transition cross-polarization in nuclear magnetic resonance
Authors: Eykyn Thomas R. , Ferrage Fabien , Bodenhausen Geoffrey
Published: July 2002

The theory of single-transition cross-polarization in nuclear magnetic resonance is presented and verified by experimental evidence. In comparison to conventional cross-polarization a qualitative change in the mechanism is observed. Under the influence of matched radio-frequency fields with amplitudes that are smaller than the scalar coupling constant JIS for a two-spin system with I=12 and S=12 in isotropic solution, two simultaneous coherence transfer processes are observed between single-transition coherences which have phases that are parallel to those of the radio-frequency fields, an on-resonance transfer from SxIα to SαIx and an off-resonance transfer from SxIβ to SβIx, without mixing between the two pathways. Coherence transfer is also observed between single-transition coherences with phases that are perpendicular to the radio-frequency fields, from SyIα to SαIy and from SyIβ to SβIy, as well as between longitudinal components, from SzIα to SαIz and from SzIβ to SβIz. The transfer may therefore be considered quasi-isotropic. We consider the conditions under which such transfer processes can be observed. Coherence transfer is affected by differential relaxation due to cross-correlation effects.
Sloping convection: A paradigm for large-scale waves and eddies in planetary atmospheres?
Authors: Hide Raymond , Lewis Stephen R. , Read Peter L.
Published: July 2002

In laboratory studies and associated theoretical and numerical work covering a very wide range of conditions (as specified by the key dimensionless parameters of the systems used) the phenomenon of sloping convection in rotating fluids can manifest itself in one of several spatial forms (waves, closed eddies, and combinations thereof), but all with strong local gradients (fronts, jet streams) and exhibiting various types of temporal behavior [steady, periodic vacillation, aperiodic (geostrophic) turbulence]. These general properties were first discovered in cylindrical (annular) systems, but they do not depend critically on geometry; differences between spherical and cylindrical systems are largely to be found in quantitative details. In all cases, the raison d’être of sloping convection is horizontal advective transfer, a process accompanied by upward advective heat transfer, which affects and may control vertical potential density gradients. It has been argued that sloping convection is the basic dynamical process underlying a wide variety of large-scale flow phenomena seen in planetary atmospheres (e.g., irregular waves in the Earth’s atmosphere, regular waves in the Martian atmosphere, the Jovian Great Red Spot and other long-lived eddies seen in the atmospheres of the giant planets). In this review the extent to which this paradigm is upheld in the atmospheres of the major planets by recent work is discussed.
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l: A tool to analyze spatiotemporal complexity
Authors: Armbruster Dieter , Heiland Randy , Kostelich Eric J.
Published: July 2002

We announce the availability of a software package, called kltool, that can extract phase space information from complex spatiotemporal data via the Karhunen–Loève analysis. Data generated by the periodic, quasiperiodic or chaotic evolution of a small number of spatially coherent structures can be processed. A key feature of kltool is that it allows the user to interact easily with the data processing and its graphical display. We illustrate the use of kltool on numerical data from the Kuramoto–Sivashinsky equation and laboratory data from a flame experiment.
Chaotic dynamics, fluctuations, nonequilibrium ensembles
Authors: Gallavotti Giovanni
Published: July 2002

The ideas and the conceptual steps leading from the ergodic hypothesis for equilibrium statistical mechanics to the chaotic hypothesis for equilibrium and nonequilibrium statistical mechanics are illustrated. The fluctuation theorem linear law and universal slope prediction for reversible systems is briefly derived. Applications to fluids are briefly alluded to.
A new peak search routine for fast evaluation on small computers
Authors: Sánchez Héctor Jorge
Published: July 2002

An analysis program for x-ray and γ-ray spectra, incorporating a new peak search routine, is described. This routine is very fast and conceptually simple, and is based on the execution of Gaussian interpolations assuming certain characteristics of the analyzed spectrum. A satisfactory comparison is presented between the results of the routine and those of a well-known, efficient method.
Model line-shape analysis for the ruby R lines used for pressure measurement
Authors: Munro R. G. , Piermarini G. J. , Block S. , Holzapfel W. B.
Published: July 2002

An empirical model spectral line shape has been considered for the R1 and R2 fluorescence lines of ruby to investigate the possibility of improvements in the precision and the reproducibility of pressure measurements at high temperature using the ruby fluorescence technique. Other advantages, such as using the ruby method to obtain a simultaneous measurement of pressure and temperature or to obtain quantitative estimates of pressure distributions under nonhydrostatic conditions, have also been considered.
Electron trapping in amorphous SiO2 studied by charge buildup under electron bombardment
Authors: Vigouroux J. P. , Duraud J. P. , Le Moel A. , Le Gressus C. , Griscom D. L.
Published: July 2002

Electron bombardment of thick pure SiO2 induces the buildup of a negative charge which can be observed through a ‘‘mirror’’ effect in a conventional Auger scanning microscope. A mechanism for the creation of this charge is proposed in terms of trapping of an electron in defects due to the irradiating beam. The influence of temperature is studied on amorphous and monocrystalline SiO2. The temperature dependence of the existence of high negative charge shows around 270 °C an anomalous effect which depends on the irradiation time. The role of electronic excitation to produce defects in silica is discussed.
Multiple scale analysis of the nonlinear surface acoustic wave propagation in anisotropic crystals
Authors: Planat Michel
Published: July 2002

A fundamental theory of nonlinear Rayleigh wave propagation is given here. Previously, the harmonic boundary value problem was solved by means of a direct iterative procedure. The nonlinear acoustic field could only be studied near the excitation transducer. The method could not explain the nonmonotonous behavior of curves giving the amplitude of various harmonics as a function of the propagation distance. In this paper, amplitude and phase relations of harmonics are calculated also in the far field. Anisotropy effect is demonstrated in the first numerical results obtained for various quartz crystal cuts.
Thermopower enhancement in semiconducting quantum well wires for acoustic phonon scattering
Authors: Kubakaddi S. S. , Mulimani B. G.
Published: July 2002

Expressions for thermopower in semiconducting quantum well wires are obtained when electrons are scattered by acoustic phonons via deformation potential coupling. In the size quantum limit, in nondegenerate semiconductors, the thermopower is found to be enhanced over its bulk value in a certain range of transverse dimension of the wire. The enhancement is found to increase with the decrease of temperature.
Charge and energy transfer in collisions of Cs+ ions with a cesiated W(110) surface
Authors: van Amersfoort P. W. , Geerlings J. J. C. , Kwakman L. F. Tz. , Granneman E. H. A. , Los J.
Published: July 2002

A beam of Cs+ ions with an energy of 500, 1000, or 2000 eV is scattered from a cesiated W(110) target. The angle of incidence is 45° or 75° with respect to the surface normal. The charge state and energy of the scattered particles are measured. The influence of hydrogen coadsorption on the final charge state is investigated. All scattered cesium particles are neutrals when the surface work function is smaller than 2.6 eV. The scattered particles have suffered a pronounced energy loss. From the measurements an extrapolation is made to conditions relevant for surface conversion negative ion sources.
Electron energy distribution functions in molecular nitrogen: The role of superelastic electronic collisions in discharge and postdischarge conditions
Authors: Paniccia F. , Gorse C. , Bretagne J. , Capitelli M.
Published: July 2002

Electron energy distribution functions (EDF) and related quantities in N2 discharge and postdischarge conditions have been calculated by solving the Boltzmann equation, taking into account both superelastic vibrational (SVC) and electronic (SEC) collisions. These last collisions involve N2(A3Σ+u) and N2(B3Πg) states. The results show a large influence of SEC on EDF at low reduced electric fields (E/N<5×10−16 V cm2), the effects being more evident in the absence of SVC and in the postdischarge regime (E/N=0).
The electrophysical properties of silicon nitride at low temperatures
Authors: Asadullayev N. A. , Brandt N. B. , Chudinov S. M. , Kozlov S. N. , Ciric I.
Published: July 2002

The conductivity of the metal-silicon nitride-silicon dioxide-semiconductor structure has been studied over a wide range of temperatures, 2–450 K, in a high electric field up to 8 MV/cm and magnetic field up to 70 kG. A strong positive magnetoresistance has been found at temperatures below 30 K. At temperatures of 30<T<250 K a weak negative magnetoresistance is observed. The existence of a positive magnetoresistance and its weak dependence on the magnetic field direction concerning that of current through a structure shows a hopping conductivity mechanism for silicon nitride film at temperatures below 30 K. Different hopping conductivity mechanisms in a high electric field have been discussed. The influence of a degradation process at T=4.2 K on the structure’s conductivity has been investigated. Qualitative changes in the structure’s conductivity during a degradation process have been found.
Phase and energy distribution of ions incident on electrodes in radio-frequency discharges
Authors: Hebner Gregory A. , Kushner Mark J.
Published: July 2002

A Monte Carlo particle simulation and parametric models for the sheath voltage and thickness were used to calculate the arrival phase and energy of ions striking the electrodes in low-pressure capacitively coupled rf discharges. Ion phase and energy distributions are presented as a function of rf frequency, ion mass, rf voltage, dc bias, sheath thickness, and gas pressure. When the rf frequency is below the ion response frequency, the ions arrive at the electrode in phase with the applied rf voltage. As the rf frequency increases, the highest ion arrival probability shifts towards higher phase until, at sufficiently high frequencies, it is nearly uniform. The transition from a highly peaked ion phase distribution at low frequencies to a uniform distribution at high frequencies requires at least an order of magnitude change in rf frequency. The implication of these calculations on the electron energy distribution is discussed.
Single scan defect identification by deep level transient spectroscopy using a two-phase lock-in amplifier (I
Q-DLTS)
Authors: Auret F. D. , Nel M.
Published: July 2002

A simple method of analyzing the deep level transient spectroscopy (DLTS) transient signal by recording its in-phase (I) and quadrature (Q) DLTS spectra using a two-phase lock-in amplifier with a sine wave mixing function, IQ-DLTS, is presented. Measurement of the peak positions on the I and Q spectra, which are simultaneously recorded during a single temperature scan, facilitates the calculation of the defect’s activation energy Et, and capture cross section σt, which are required for its identification. It was found that the Et values obtained when analyzing proton implantation-induced defects in GaAs were within 5% of those determined from the conventional DLTS Arrhenius plots.
Thermal expansion studies of the group IV-VII transition-metal disilicides
Authors: Engström Ingvar , Lönnberg Bertil
Published: July 2002

The thermal expansions of the group IV-VII transition-metal disilicides and Mn15Si26 have been investigated from room temperature to about 1500 K by x-ray powder-diffraction techniques. The results are discussed in relation to the structure of the compounds. Most of the disilicides studied exhibit a high degree of thermal expansion isotropy, exceptions being ZrSi2, HfSi2, and CrSi2. The observed linear thermal expansion coefficients are normally in the range 8–9×10−6 K−1 (298 K) to 11–15×10−6 K−1 (1300 K). The most extreme expansion was exhibited by CrSi2 with a linear expansion coefficient of 22×10−6 K−1 for the a axis at 1300 K.
Two-pulse injector experiments with the RIIM electron accelerator
Authors: Mazarakis M. G. , Smith D. L. , Jones E. E. , Hasti D. E. , Jojola J. M. , Lehmann M.
Published: July 2002

The RADLAC-II accelerator foilless diode injector was operated under double-pulse conditions utilizing the RIIM accelerator as the test bed [M. G. Mazarakis, D. L. Smith, R. B. Miller, R. S. Clark, D. E. Hasti, D. L. Johnson, J. W. Poukey, K. R. Prestwich, and S. L. Shope, IEEE Trans. Nucl. Sci. NS-32, 3237 (1985)]. The original RIIM accelerator pulsed-power network was modified to provide for the generation, transmission, and delivery to the foilless diode of two distinct multimegavolt pulses with variable interpulse separation from 0 to 2 ms. The foilless diode successfully produced two 10-kA current pulses with interpulse separations up to 1 μs. For larger separations, the generated plasma and an excessive neutral gas release following the first pulse prevented the diode from producing a second current pulse.
Generation-recombination phenomena in almost ideal silicon p-n junctions
Authors: Cerofolini G. F. , Polignano M. L.
Published: July 2002

A systematic analysis of static current-voltage characteristics at variable temperatures of almost ideal silicon p-n junctions has been carried out. This analysis shows that while in neutral region the generation and recombination mechanisms are characterized by the same lifetime, in the space-charge region the generation lifetime may be significantly lower than the recombination lifetime: hence we infer the existence of a field-assistance pure generation phenomenon. Evidence supporting the hypothesis that a unique center is responsible for all of the recombination phenomena is presented. This center is not related to erratic contamination, but pertains to silicon. The Shockley–Read–Hall generation-recombination mechanism (leading to the Sah–Noyce–Shockley theory of the p-n junction) is proved to give an unsatisfactory description of the almost ideal diode.
Sequenced nitrogen lasers
Authors: Lee S. , Kwek K. H. , Ali Jalil , Prabhakar M. V. H. V. , Shishodia Y. S. , Warmate A. G.
Published: July 2002

A pulsed nitrogen laser may consist of a laser channel sitting astride two parallel-plate capacitors, one of which is the voltage-swinging capacitor and the second is the laser discharge capacitor. A multichannel nitrogen laser system is proposed for which the laser discharge capacitor of the first laser channel also acts as the voltage-swinging capacitor of the second laser channel, the laser discharge capacitor of the second laser channel also acts as the voltage-swinging capacitor of the third laser channel, and so on. This enables several laser channels to be fired to obtain full power laser pulses in a precision sequence when operated in the ‘‘prompt sequencing’’ mode.
Observation of nonlinearity in e-beam evaporation from a water-cooled crucible
Authors: Bhatia M. S. , Joshi A. , Patel K. , Chatterjee U. K.
Published: July 2002

While conducting e-beam evaporation from a water-cooled crucible at power densities in the range of 1–4×104 W cm−2, with an e-beam spot size that is small in comparison to the crucible dimensions, a nonlinearity is observed in the temperature versus power characteristic. A simple model is proposed to explain this nonlinearity. The physical basis of the proposed model is discussed.
Application of the charged point-defect model to diffusion and interdiffusion in GaAs
Authors: Cohen R. M.
Published: July 2002

Diffusion and interdiffusion in GaAs and GaAs/AlGaAs superlattices are shown to be consistent with the charged point-defect model. The charged Ga vacancies V3−Ga and interstitials I2+Ga appear to control group II, III, and probably V element diffusion. After adjustment for carrier concentration and As pressure, these elements are found to have a nearly identical intrinsic diffusivity and activation energy over a wide range of temperature. A natural consequence of Ga diffusion via negative or positive point defects is that enhanced group-III interdiffusion is expected with either n- or p-type doping. Anomalous enhancements in group-II dopant diffusivity have been related to the supersaturation of Ga interstitials.
Magneto-optical measurement of anisotropy energy constants on amorphous rare-earth transition-metal alloys
Authors: Hajjar Roger A. , Zhou Feng Lei , Mansuripur M.
Published: July 2002

Measurements of the magneto-optic polar Kerr effect are performed on samples with perpendicular magnetization using in-plane magnetic fields. The magnetic anistropy constants are then determined from these measurements. The applied in-plane magnetic field varies from −20 to 20 kOe. Samples are mounted in a temperature-controlled chamber whose temperature is varied in the range of 80–475 K. In the theoretical model the anisotropy energy is expressed as the sum of terms containing sin2 φ and sin4 φ with two anisotropy constants, K1 and K2, to be determined. By matching the theoretical curves with the experimental data, we obtain two functions α(T) and β(T), which are the normalized values of K1(T) and K2(T) with respect to the saturation magnetization Ms(T).
Specific heat and magnetic behavior of UTGe compounds
Authors: Buschow K. H. J. , Brück E. , van Wierst R. G. , de Boer F. R. , Havela L. , Sechovsky V. , Nozar P. , Sugiura E. , Ono M. , Date M. , Yamagishi A.
Published: July 2002

The temperature dependence of the magnetic susceptibility, electrical resistivity, and specific heat, as well as the magnetization in fields up to 35 T, of polycrystalline samples of UTGe (T=transition metal) compounds has been studied. The development from nonmagnetic UCoGe and URuGe through the weak ferromagnet URhGe, which displays the highest γ value, to complicated types of the local 5f-moment ordering for T=Pd, Ni, and Pt is in agreement with the expected trends of gradually reduced 5f-d hybridization.
Potential flow past an open spherical cavity
Authors: Boridy Elie
Published: July 2002

The potential flow of an ideal fluid in the presence of an open spherical cavity, with a circular opening and enclosing a concentric sphere, is analyzed in the framework of the theory of dual series equations. It is shown that the flow equations can be reduced to a pair of dual series equations whose exact solution is presented in the form of a perturbation series. The solution inherently contains the correct behavior near the edge of the aperture, i.e., that required by Meixner’s conditions. Various properties of the flow, in particular its separation at the solid boundaries, are discussed and illustrated by numerical results.
Intrinsic concentration, effective densities of states, and effective mass in silicon
Authors: Green Martin A.
Published: July 2002

An inconsistency between commonly used values of the silicon intrinsic carrier concentration, the effective densities of states in the conduction and valence bands, and the silicon band gap is resolved by critically assessing the relevant literature. As a result of this assessment, experimentally based values for the valence-band ‘‘densities-of-states’’ effective mass are determined in the 300–500 K range and are shown to be in good agreement with recent theoretical calculations. At 300 K, experimentally based values of 3.1×1019 cm−3 for the valence-band effective densities of states and 1.08×1010 cm−3 for the intrinsic carrier concentration are determined. Although in good agreement with theoretical calculations, these are significantly higher and lower, respectively, than commonly used values in the past. These results have important implications in the calculation of other silicon material and device parameters.
Microwave absorption in oriented polycrystals of yttrium barium copper oxide
Authors: Srinivasan G. , Wu Guo-mei , Srinivasan T. T.
Published: July 2002

High-frequency loss measurements have been carried out on c-axis oriented polycrystalline samples of YBa2Cu3O7−δ. The samples were prepared by a wet chemical process, the citrate technique, and conventional ceramic methods. The degree of c-axis orientation perpendicular to the sample plane, determined from x-ray diffraction, was 70%. The experiments were done at 9.4 GHz using a reflection-type cavity. Data on the temperature variation of the power absorbed and shift in cavity resonance frequency were obtained for rf magnetic fields parallel and perpendicular to the c axis. For samples prepared by citrate techniques, the surface resistance and frequency shifts in the normal and superconducting states are all smaller than for samples prepared by conventional sintering techniques. The superconducting energy gap has been determined from the temperature dependence of the surface resistance.
Effects of oxidation conditions on electrical properties of SiC-SiO2 interfaces
Authors: Zaima S. , Onoda K. , Koide Y. , Yasuda Y.
Published: July 2002

Electrical properties of metal-oxide-semiconductor (MOS) devices fabricated on 3C-SiC single crystalline films on (100)Si substrates have been examined by capacitance-voltage method and deep level transient spectroscopy. The electrical properties such as carrier concentration, interface states, fixed oxide charge and deep traps are strongly related to the oxidation ambient and temperature. It has been found that the interface state density of the order of 1010 cm−2 eV−1 can be achieved by wet oxidation at 1000 °C. The influence of preferential oxidation of antiphase grain boundaries is considerable on the carrier concentration and the interface state density in the case of wet oxidation. From a practical point of view, the wet oxidation is concluded to be superior to the dry oxidation because of the lower densities of fixed oxide charge, interface states, and deep traps.
Second-order nonlinearity of a novel diazo-dye-attached polymer
Authors: Amano Michiyuki , Kaino Toshikuni
Published: July 2002

Second-order nonlinear optical properties of a newly synthesized dye-attached polymer (3R) were investigated. The dye has a conjugated diazo structure, and the βμg (β: second-order molecular hyperpolarizability, μg: dipole moment in the ground state) is larger than five times that of a monoazo dye (2R). The second-order nonlinear coefficient (χ(2)) of a 3R polymer is also greater than that of a 2R polymer throughout the fundamental wavelength of 1.06 μm and between from 1.50 to 1.70 μm when the polymers are electrically poled. For both polymers, the χ(2) dependence on the fundamental wavelength corresponds to the absorption spectrum, which is explained by two-photon resonance near the absorption maxima. The attainable χ(2) of the polymers deviates from the theoretical linear relationship with the dye content when it is high. This indicates that the dipolar interaction increases as the dye content rises.
Lateral confinement in generalized strip-loaded optical waveguides
Authors: Munowitz Michael , Vezzetti David J.
Published: July 2002

Mode structure in strip-loaded waveguides is studied using an eigenvalue method based on a two-dimensional Fourier analysis. Modified guides where the loading strip is displaced above the core by an additional layer of cladding are considered as a general case. Lateral confinement is found to depend largely on the extent to which the field decays over the strip, and generally worsens as vertical confinement (in the direction perpendicular to the layers of the guide) improves. Conditions that degrade lateral confinement include a large difference in refractive index between core and cladding, a core wide relative to operating wavelength, and large separation between strip and core. Lateral confinement does not vary monotonically with vertical confinement, moreover, but instead may be maximized over a specific range of the guide’s refractive indices.
A model for the power dissipation in rf plasmas
Authors: van Roosmalen A. J. , van Voorst Vader P. J. Q.
Published: July 2002

An analysis is made of the relations determining the electron drift velocity in the oscillating boundary between plasma and space-charge region at the electrode surface of an rf-driven parallel-plate discharge. The resulting set of equations is solved directly to yield an expression for the rf power dissipation in the plasma. Similarly, the dissipation in the space-charge region is derived from the equations for mobility-limited and free-fall movement of positive ions to the wall. This model is applied to existing data for the electrical discharge properties in a 13.56-MHz dry etch reactor. The calculated total power dissipation is shown to agree with published transfer efficiencies for the applied rf power. It appears that the electron dissipation term is dominant at high pressure and low rf power, while the ions determine the power input at low pressure and high power. The same set of equations is used to calculate the rf current wave form, the displacement of the plasma boundary with time, and the averaged plasma density. Also here, the model is in agreement with published simulations and experimental work.
Extremely low non-alloyed specific contact resistance ρc (10−8 Ω cm2) to metalorganic molecular beam epitaxy grown super heavily C-doped (1021 cm−3) p++GaAs
Authors: Usagawa T. , Kobayashi M. , Mishima T. , Rabinzohn P. D. , Ihara A. , Kawata M. , Yamada T. , Tokumitsu E. , Konagai M. , Takahashi K.
Published: July 2002

The specific contact resistance ρc of non-alloyed ohmic metals (Mo/Au and WSix) to p-type GaAs is evaluated by transmission line method (TLM) patterns for various doping concentrations from 8×1018 to 1021 cm−3. The obtained specific contact resistance ρc, less than 10−8 Ω cm2, to metalorganic molecular beam epitaxy grown C-doped ( 1021 cm−3) GaAs is the lowest reported value. From the application point of view for the emitter electrodes of PNp type (two-dimensional electron gas base) heterojunction bipolar transistors, the specific contact resistance of a refractory metal, or the sputter-deposited WSix (x=0.45), is also studied. By reducing the growth temperature of molecular beam epitaxy from 600 to 450 °C and enhancing the As4/Ga flux ratio to 15, a nondiffusive heavily Be doped (1020 cm−3) GaAs is obtained. The specific contact resistance of the WSix to this sample is less than 10−6 Ω cm2. The obtained specific contact resistance can be well explained by a simple modeling based on the tunneling transport of light holes. Secondary ion mass spectroscopy analysis of the depth profile under heat acceleration shows a small diffusion of dopants for Be doped (1020 cm−3) GaAs and C-doped (1021 cm−3) GaAs. In addition, the specific contact resistance ρcISO of the isoheterojunction (p+GaAs/p+AlxGa1−xAs) is also evaluated by TLM patterns.
Measurements of Faraday effect in iron garnet optical waveguide at near infrared wavelengths
Authors: Okamura Y. , Yamamoto S.
Published: July 2002

The Faraday rotation constants in a magneto-optic channel waveguide whose magnetization aligns along the direction of propagation are measured by a novel method developed by the authors. The tested sample is a lanthanum and gallium substituted yttrium iron garnet optical channel waveguide prepared by the liquid phase epitaxial and the ion milling techniques. The proposed method is more practical than the previously reported one because of determination of the parameters with one time measurement. In the previous method we needed to know the phase constant difference between the orthogonally polarized waves to determine the Faraday coefficient. Using the presented technique we successfully measure the magneto-optic coefficients in the iron garnet waveguide at the near infrared wavelengths: 1.15, 1.3, and 1.55 μm. We confirm the validity of the proposed method by comparing with other methods: the previously reported method and the Faraday modulation method conventionally used for measuring the Faraday rotation. We also demonstrate the waveguide isolator operation.
Defects in plasma-deposited hydrogenated amorphous silicon prepared under visible light illumination
Authors: Sakata Isao , Yamanaka Mitsuyuki , Hayashi Yutaka
Published: July 2002

Experimental studies have been made on the defects in undoped plasma-deposited hydrogenated amorphous silicon prepared with visible light illumination on a growing surface. This material (referred to as illuminated GD a-Si:H) has a broad defect band around midgap (Ec −1.4 eV<E<[SB:E:c]−0.8 eV) that is composed of two types of defect states (ST1 and ST2). The type 1 defect state (ST1) that lies in the higher energy side (Ec −E<1.2 eV) of the band is a neutral Si dangling bond (D0). Increase in the density of ST1 of the illuminated GD a-Si:H induced by long exposure to light after the growth was smaller than that of GD a-Si:H deposited in the same run without the illumination. The energy position of the Si D0 state measured from a valence band edge is almost independent of optical band gap. The density of the type 2 defect state (ST2) that lies on the lower energy side (Ec−E>1.2 eV) of the defect band does not increase with long exposure to light. One probable candidate for the origin of ST2 is a Si dangling bond coupled with another Si dangling bond or with residual impurities.
Metal-bonded Sm2Fe17-N-type magnets
Authors: Huang M. Q. , Zhang L. Y. , Ma B. M. , Zheng Y. , Elbicki J. M. , Wallace W. E. , Sankar S. G.
Published: July 2002

A number of metal-bonded Sm2Fe17-N magnets have been fabricated. These magnets exhibit iHc = 5.1–17.0 kOe, Br = 6.4–8.4 kG, (BH)max=5.0–10.8 MGOe, Tc = 757 K, and ρ=6.2–6.7 g/cm3. Powder metallurgical techniques have been employed with a mixture of powdered Sm2Fe17-N and Zn, Sn, or In. Heat treatment is carried out in the temperature range of 160–450 °C in a N2 atmosphere at pressures ranging from 0–900 psi. The effects of Zn, Sn, and In contents and heat treatment conditions on the magnetic properties have been studied. Zn as the binder significantly enhances the coercivity iHc from 1.8–2.5 kOe for Zn-free magnets to 5–17 kOe for 9–20-wt. % Zn-containing magnets. The Fe-Zn phase, FeZn4, and/or Fe3Zn7, formed during heat treatment, may play an important role in producing a high coercivity. Sn-bonded magnets exhibit significant coercivity, whereas the In-bonded materials do not. The coercivity behavior is discussed in terms of the chemistry of the system.
Switchable vanadium oxide films by a sol-gel process
Authors: Partlow D. P. , Gurkovich S. R. , Radford K. C. , Denes L. J.
Published: July 2002

Thin polycrystalline films of VO2 and V2O3 were deposited on a variety of substrates using a sol-gel process. The orientation, microstructure, optical constants, and optical and electrical switching behavior are presented. These films exhibited sharp optical switching behavior even on an amorphous substrate such as fused silica. The method yields reproducible results and is amenable to the coating of large substrates and curved surfaces such as mirrors and lenses.
Morphology and phase stability of TiSi2 on Si
Authors: Jeon Hyeongtag , Sukow C. A. , Honeycutt J. W. , Rozgonyi G. A. , Nemanich R. J.
Published: July 2002

The formation mechanisms and properties of TiSi2 on Si are investigated. The particular emphasis is in relating the nucleation, morphology, and phase stability of the films. TiSi2 films were prepared by deposition of Ti on atomically clean silicon substrates in ultrahigh vacuum. The silicide formation was initiated either by in situ annealing or deposition onto heated substrates. The island formation of TiSi2 and surface and interface morphologies of TiSi2 were examined by scanning electron microscopy and transmission electron microscopy. The TiSi2 formation process was monitored with in situ Auger electron spectroscopy and low-energy electron diffraction to analyze the surface concentration and the surface structures, respectively. Raman spectroscopy was used for phase identification of the TiSi2. Titanium film thicknesses from 50 to 400 Å were examined. For all thicknesses studied, the C49 TiSi2 phase is observed to nucleate. Immediately after low-temperature deposition, the interface morphology was smooth, but after reaction and nucleation of the C49 TiSi2 phase a rough interface was observed. After higher-temperature annealing the transition to the C54 TiSi2 phase was observed. For TiSi2 on Si(111), the interface becomes smooth and flat. The temperature of the C49-to-C54 transition was observed to vary as a function of film thickness and substrate orientation. The films exhibited island formation after high-temperature annealing. For similar Ti thicknesses and annealing temperature, different areal coverages and island morphologies of TiSi2 on Si(100) and Si(111) were observed. The island morphologies are modeled and analyzed based on a liquid-liquid model, and the surface and interface energies for different TiSi2 island structures are deduced from contact angle measurements. The C49 nucleation, interface morphologies, surface morphologies, and the C49-to-C54 structural phase transition are discussed in terms of surface and bulk free-energy considerations.
Shock compression of tungsten and molybdenum
Authors: Hixson R. S. , Fritz J. N.
Published: July 2002

New high-pressure shock-wave data have been obtained for W and Mo. These data have been combined with previous data sets for these materials to extend the range of linear us–up fits for the Hugoniot to 480 GPa for Mo and 680 GPa for W. The shock-wave data, supplemented by the necessary thermodynamic information, have been used to generate several isotherms (100, 200,...1000 K). Tables of pressure versus relative volume up to 380 GPa suitable for comparison with statically obtained data are given.
In situ and ex situ structural characterization of β-FeSi2 films epitaxially grown on Si(111)
Authors: Lagomarsino S. , Scarinci F. , Savelli G. , Giannini C. , Castrucci P. , Grimaldi M. G.
Published: July 2002

The structural properties of β-FeSi2 films grown on Si(111) are studied by means of several techniques. The films were grown in ultrahigh vacuum by solid phase epitaxy. The as-deposited Fe films were studied in situ by low energy electron diffraction (LEED) and Auger spectroscopy. Fe thicknesses were calibrated by Rutherford backscattering. The behavior of the FeMVV/SiLVV Auger peaks ratio intensity as a function of Fe thickness indicates a Stranski–Krastanov mode of growth. Annealing of the Fe layers at temperatures between 400 and 600 °C led to the β-FeSi2 formation. Sharp LEED patterns typical of the β-FeSi2 orthorhombic structure were obtained. X-ray double-crystal diffraction was carried out on a film about 200 Å thick in order to determine the lattice mismatch between the β-FeSi2 and the Si(111) planes accurately. The measured value of (2.1±0.1)×10−2 unambiguously indicates that (101) epitaxy takes place only on Si(111). No elastic strain of the overlayer was evident. The full width at half maximum of the overlayer diffraction peak indicates a good crystalline quality. An upper limit for mosaic spread was determined to be about 0.05°.
The thermal dissociation of decaborane on Si(111)-(7×7) and doping effects in the near surface region
Authors: Chen P. J. , Colaianni M. L. , Yates J. T.
Published: July 2002

The thermal decomposition of decaborane (B10H14) and its doping effects on Si(111)-(7×7) has been investigated by surface spectroscopies. Upon adsorption between 100 and 300 K, molecular decaborane was identified on the surface by high-resolution electron-energy-loss spectroscopy (HREELS) by the absence of Si-H surface species production. The thermal decomposition of adsorbed decaborane molecules at higher temperatures involves a preferential removal of hydrogen from the weaker B—H—B linkage. H2 thermal desorption was observed to cover a wide temperature range between 300 and 900 K. Clean boron deposition on the surface was achieved at ∼900 K. Upon heating to ∼1275 K, extensive boron diffusion into bulk silicon produced a highly B-doped region below the surface (∼103 Å) with a carrier hole concentration on the order of ∼1019 cm−3 depending upon the initial surface boron coverage and annealing conditions. The surface adopted a (√3×√3)R30° reconstruction with a nominal 1/3 ML boron occupying subsurface substitutional sites. Both the localized B-Si vibration and carrier surface plasmon excitation were observed by HREELS at 100 K.