bluuebunny/crossref_metadata_2025 huggingface dataset:
The shock tube study in extended thermodynamics
Authors: Au J. D. , Torrilhon M. , Weiss W.
Published: July 2002

In this paper we investigate the shock tube experiment with extended thermodynamics. Extended thermodynamics (ET) provides dissipative field equations for monatomic gases which are symmetrically hyperbolic. The theory relies on the extension of the set of variables in order to describe extreme nonequilibrium processes. As an example for such a process we focus on the start-up phase of the shock tube experiment. We show numerically that ET succeeds to describe this short time behavior. For small times more and more variables are needed for a physically valid description. In the limit of very small times the solution of ET for the start-up phase converges to the solution of the free-flight-equation. Additionally it turns out that the system of Navier–Stokes and Fourier fails to describe the start-up phase of a shock tube even qualitatively.
Partial graphitization of diamond crystals under high-pressure and high-temperature conditions
Authors: Qian Jiang , Pantea Cristian , Voronin G. , Zerda T. W.
Published: July 2002

Diamond powders of different sizes were compressed at pressures up to 2.5 GPa and heated up to 1700 K. Extent of partial graphitization was estimated from x-ray diffraction and Raman scattering. For example, in the presence of water, at p=2.0 GPa and T=1473 K about 22% of diamond was converted into graphite. The rate of this transformation decreases in time and becomes negligibly small after about 20 min of treatment at high-pressure, high-temperature conditions. (Graphitization starts at the surface of the crystals and then graphite crystals grow in the direction perpendicular to the surface and along the surface.) Distribution of graphite on the surface of diamond crystals was obtained from Raman microimaging.
Interpretation and modeling of buried InAs quantum dots on GaAs and InP substrates
Authors: McCaffrey J. P. , Robertson M. D. , Poole P. J. , Riel B. J. , Fafard S.
Published: July 2002

Comparisons of buried InAs/GaAs and InAs/InP quantum dots (QDs) utilizing transmission electron microscopy display interesting parallels and differences between the two systems. The higher 7.2% misfit in the InAs/GaAs system produces small (∼20 nm diameter) QDs with a majority displaying a predominately round shape. The lower 3.2% misfit in the InAs/InP system produces larger QDs (∼35 nm diameter) with the majority also displaying a predominately round shape. In both systems, the size of the QDs can be varied by changes in growth procedures and the largest QDs in any population show evidence of faceting
Formation dynamics of diffraction gratings in reactive liquid crystals
Authors: Kossyrev P. A. , Crawford G. P.
Published: July 2002

Using in situ diffraction measurements of diffraction grating formation in a single component reactive mesogen system, the anisotropy in the diffusion constants is determined. The data are well explained by a diffusion model, which accounts for the density modulation due to shrinkage upon photopolymerization with interfering laser beams.
Superconducting Mg–B films by pulsed-laser deposition in an in situ two-step process using multicomponent targets
Authors: Blank Dave H. A. , Hilgenkamp Hans , Brinkman Alexander , Mijatovic Dragana , Rijnders Guus , Rogalla Horst
Published: July 2002

Superconducting thin films have been prepared in an in situ two-step process, using the Mg–B plasma generated by pulsed-laser ablation. The target was composed of a mixture of Mg and MgB2 powders to compensate for the volatility of Mg and, therefore, to ensure a high Mg content in the film. The films were deposited at temperatures ranging from room temperature to 300 °C followed by a low-pressure in situ annealing procedure. Various substrates have been used and diverse ways to increase the Mg content into the film were applied. The films show a sharp transition in the resistance and have a zero resistance transition temperature of 22–24 K.
White-light electroluminescence from soluble oxadiazole-containing phenylene vinylene ether-linkage copolymer
Authors: Lee Yuh-Zheng , Chen Xiwen , Chen Ming-Chih , Chen Show-An , Hsu Jui-Hung , Fann Wunshain
Published: July 2002

We report a promising oxadiazole-containing phenylene vinylene ether-linkage copolymer, which can emit nearly white light from a single-layer light-emitting diode. The emission spectrum is composed of a red component originating from the new excited dimer in addition to the blue-green component from an individual lumophore and excimer. This excited dimer is formed under a strong electric field inside the diode and cannot be produced by photoexcitation, which is different from the excimer or exciplex that is often found both in photoluminescence and electroluminescence, and it is termed the “electromer.”
Effect of electric field on the electronic structures of carbon nanotubes
Authors: Kim Changwook , Kim Bongsoo , Lee Seung Mi , Jo Chulsu , Lee Young Hee
Published: July 2002

We have investigated the electronic structures of a capped single-walled carbon nanotube under the applied electric field using density functional calculations. The capped tube withstands field strengths up to 2 V/Å. When the electric field is applied along the tube axis, charges are transferred from the occupied levels localized at the top pentagon of the cap, and not from the highest occupied level localized at the side pentagon, to the unoccupied levels. We find that the charge densities at the top of the armchair cap show two- or five-lobed patterns depending on the field strength, whereas those of the zigzag cap show a three-lobed pattern. The interpretation for the images of the field emission microscope is also discussed.
Conducting probe atomic force microscopy applied to organic conducting blends
Authors: Planès Jérôme , Houzé Frédéric , Chrétien Pascal , Schneegans Olivier
Published: July 2002

Atomic force microscopy (AFM) is used in contact mode with a conducting tip to probe the conducting network of the conductive polymer polyaniline blended in an insulating polymer matrix. The high resistance contrast and sharp boundaries between conductive and insulating phases is observed down to scales in the 10 nm range. The very low scale electric dispersion corresponds to the morphologic phase segregation known from conventional AFM or transmission electron microscopy measurements, which is responsible for the ultralow electrical percolation threshold previously demonstrated in this system.
Stable island arrays by height-constrained Stranski–Krastanov growth
Authors: Liang J. , Suo Z.
Published: July 2002

In the Stranski–Krastanov system, the lattice mismatch between the film and the substrate causes the film to break into islands. During annealing, both surface energy, and elastic energy drive the islands to coarsen: some islands enlarge and others shrink, keeping the total island volume constant. The islands produced this way are usually uneven in size and spacing. Motivated by several related studies, we suggest that stable, uniform islands should form when a stiff ceiling is placed at a small gap above the film. After contacting the ceiling, the islands are constrained to grow laterally and remain coherent with the substrate, preventing further stress relaxation. In fact, we show that the role of elasticity is reversed: with the ceiling, the total elastic energy stored in the system increases as the islands coarsen laterally. On the other hand, the total surface energy decreases as the islands coarsen. Consequently, the islands select an equilibrium size to minimize the combined elastic energy and surface energy. We estimate the equilibrium island size by analyzing an idealized model.
Atomistic Monte Carlo simulation of cis-1,4 polyisoprene melts. I. Single temperature end-bridging Monte Carlo simulations
Authors: Doxastakis M. , Mavrantzas V. G. , Theodorou D. N.
Published: July 2002

Results are presented for the thermodynamic, conformational, and structural properties of cis-1,4 polyisoprene (PI) melts from detailed atomistic Monte Carlo simulations. All simulations have been executed by employing the very efficient end-bridging move, which alters chain connectivity and induces fast conformational and structural equilibration over the entire range of length scales in the melt. To use the end-bridging move, a geometric mapping of a cis-1,4 PI monomer onto an equivalent three-bead monomer is utilized. In the acceptance criterion of the move, however, the energy terms are calculated from the actual atomistic cis-1,4 PI chains, obtained after performing the reverse mapping. Simulation results are obtained at T=413 K with cis-1,4 PI melts of mean molecular length ranging from C40 to C200. The performance of the end-bridging Monte Carlo (EBMC) algorithm is explored as a function of average chain length. Results for the specific volume of the cis-1,4 PI melt are found to be within 1% of experimentally reported values and analytical fits to those values. Additional predictions concerning the conformational properties, the equilibrium mean square chain end-to-end distance 〈R2〉0, and the wide-angle neutron and x-ray diffraction patterns, demonstrate that our force field predicts reliably the physical properties of polyisoprene in the molten state.
Green fluorescent proteins as optically controllable elements in bioelectronics
Authors: Cinelli Riccardo A. G. , Pellegrini Vittorio , Ferrari Aldo , Faraci Paolo , Nifosı̀ Riccardo , Tyagi Mudit , Giacca Mauro , Beltram Fabio
Published: July 2002

A single-biomolecule optical toggle switch is demonstrated based on a mutated green fluorescent protein (GFP). We have exploited molecular biology techniques to tailor the GFP molecular structure and photophysical properties and to give it optically controlled bistability between two distinct states. We present optical control of the fluorescence dynamics with two laser beams at 476 and 350 nm down to the ultimate limit of single molecules. These results indicate that GFP-class fluorophores are promising candidates for the realization of biomolecular devices such as volumetric optical memories and optical switches.
Absolute concentrations of the C2 radical in the A 1Πu state measured by cavity ring down spectroscopy in an atmospheric oxyacetylene flame
Authors: Staicu A. , Stolk R. L. , ter Meulen J. J.
Published: July 2002

Measurements of absolute concentrations of C2 (A 1Πu) in an atmospheric oxyacetylene flame are presented. Cavity ring down spectroscopy (CRDS) was applied to measure lateral column density profiles at a number of vertical positions. By means of Abel inversion processing and estimated radial temperature profiles, the column densities were converted to absolute concentration profiles, which have central maxima with peak concentrations between 8×1014 and 2.5×1015 m−3. Comparison of the measured A state concentration profiles with calculated ground state C2 profiles supports an earlier suggestion that the gas-phase mechanism used in the calculations needs improvement. This work demonstrates the applicability of CRDS for measuring absolute concentrations of electronically excited species in atmospheric flames, a result which can be of importance to combustion research.
Trailing vortices in a free-surface flow
Authors: Chen Tong , Chwang Allen T.
Published: July 2002

The free-surface effect on two-dimensional flow structures, especially on the trailing vortices, is investigated numerically in this paper. The solution procedure employs a higher-order semi-implicit projection method. The numerical results have been compared with experimental data on wave elevation disturbed by a submerged translating hydrofoil with a positive angle of attack. The schematic computations reveal some interesting and unique characteristics of the trailing-vortex development in a laminar flow beneath a free surface. Based on the computational data, an empirical Strouhal–Reynolds–Froude number relationship is proposed for the purely laminar vortex shedding in a free-surface flow. Moreover, the numerical findings also indicate that the presence of a free surface accelerates the Strouhal vortex frequency, yet delays not only the onset of a large-scale Kármán instability but also the occurrence of transitional behaviors. The shedding frequency downshifts drastically or even becomes discontinuous when the secondary vortex grows on the suction side. A metastable transition frequency emerges at the same time and becomes distinct with increasing Reynolds number. The variation of the vortex-shedding Strouhal number with respect to both Reynolds and Froude numbers is obtained. The power spectra of the trailing wake consist of harmonics of the vortex-shedding and transition frequencies (mfs,nft), as well as their combinations (mfs±nft).
Equilibrium structure and effective pair interaction in a quasi-one-dimensional colloid liquid
Authors: Cui Bianxiao , Lin Binhua , Sharma Sanjay , Rice Stuart A.
Published: July 2002

We report the results of studies, using digital video microscopy, of the spatial distribution of particles in a quasi-one-dimensional colloidal liquid. The system studied consists of a water suspension of silica particles with diameter σ=1.58 μm confined in a 3 μm×3 μm×2 mm silicone elastomer channel. The measured spatial distributions have been characterized by the nearest-neighbor distribution function and the pair correlation function, and the pair correlation function has been inverted, using the hypernetted chain approximation, to yield the effective colloid–colloid interaction. The effective colloid–colloid interaction is found to have an attractive potential well with depth of ∼0.3kBT at a colloid-colloid separation R≈1.18σ. Molecular-dynamics simulations of the nearest neighbor and pair correlation functions carried out using the empirically determined colloid–colloid interaction are in very good agreement with the experimental data. The experimental data obtained rule out any important charge–charge contribution to the measured colloid–colloid interaction. It is suggested that because the host liquid does not wet the channel wall, and the colloid particles are tightly confined in the long narrow channel, capillary forces determine the effective colloid–colloid interaction. This suggestion is consistent with the determination (also reported) that the effective colloid–colloid interaction in a quasi-two-dimensional suspension of the same particles is different from that in the quasi-one dimensional suspension.
Pinning of Abrikosov vortices on dislocations and the critical current in high-temperature superconductors
Authors: Pashitskiı̆ É. A. , Vakaryuk V. I.
Published: July 2002

The microscopic mechanisms for single-particle core pinning of quantum vortices on the insulating cores of isolated dislocations are investigated for both parallel and mutually tilted orientations of the vortex and dislocation and also for pinning on an infinite periodic chain of edge dislocations. The theoretical results are consistent with experiment in regard to the temperature and orientation dependences of the depinning critical current in low magnetic fields, when the interaction between vortices is exponentially small, and they also predict strong anisotropy of the pinning force along and transverse to the chains of edge dislocations.
Permanent polarization and charge injection in thin anodic alumina layers studied by electrostatic force microscopy
Authors: Lambert J. , Guthmann C. , Ortega C. , Saint-Jean M.
Published: July 2002

An electrostatic force microscope (EFM) and a Kelvin probe are used to characterize the charges embedded in thin anodic alumina layers of thickness ranging from 100 to 400 nm. Introducing a method for obtaining self-supported alumina layers, we exhibit the presence of positive charges at the metal/oxide interface of anodic alumina layers. These positive charges, together with the negative charges present at the surface of the anodic layer, induce a true polarization of the layer. The magnitude of this polarization depends on the conditions of preparation of the layers and can be well controlled. As a second step, we show the influence of this polarization on charge injection in these layers with EFM: charges of both signs may be injected in unpolarized layers whereas one cannot inject negative charges in polarized layers, which thus exhibit a diode-like behavior.
Density profiles and surface tension of polymers near colloidal surfaces
Authors: Louis A. A. , Bolhuis P. G. , Meijer E. J. , Hansen J. P.
Published: July 2002

The surface tension of interacting polymers in a good solvent is calculated theoretically and by computer simulations for a planar wall geometry and for the insertion of a single colloidal hard sphere. This is achieved for the planar wall and for the larger spheres by an adsorption method, and for smaller spheres by a direct insertion technique. Results for the dilute and semidilute regimes are compared to results for ideal polymers, the Asakura–Oosawa penetrable-sphere model, and to integral equations, scaling and renormalization group theories. The largest relative changes with density are found in the dilute regime, so that theories based on noninteracting polymers rapidly break down. A recently developed “soft colloid” approach to polymer–colloid mixtures is shown to correctly describe the one-body insertion free-energy and the related surface tension.
Subwavelength patterns and high detection efficiency in fluorescence correlation spectroscopy using photonic structures
Authors: Lenne P.-F. , Etienne E. , Rigneault H.
Published: July 2002

We present theoretical and experimental evidence of subwavelength resolution and high detection efficiency in fluorescence correlation spectroscopy (FCS) using photonic structures. We show that multilayered dielectric mirrors or metallic mirrors may be used in a conventional FCS setup to improve fluorescence detection and fluctuation analysis.
60Co gamma-irradiation-induced defects in n-GaN
Authors: Umana-Membreno G. A. , Dell J. M. , Hessler T. P. , Nener B. D. , Parish G. , Faraone L. , Mishra U. K.
Published: July 2002

Transient capacitance measurements of Schottky diodes fabricated on nominally undoped n-type GaN exposed to 60Co gamma irradiation indicate the introduction of two defect levels with thermal activation energies of 89±6 and 132±11 meV. While the emission characteristics of these defects manifest significant broadening, their parameters are consistent with reported electron-irradiation-induced nitrogen-vacancy related centers. Three deep-level defects present before irradiation exposure with activation energies of 265, 355, and 581 meV were found to remain unaffected for cumulative gamma-ray doses up to 21 Mrad(Si).
Patterns of spiral tip motion in cardiac tissues
Authors: Kim Dave T. , Kwan Yvonne , Lee John J. , Ikeda Takanori , Uchida Takumi , Kamjoo Kamyar , Kim Young-Hoon , Ong James J. C. , Athill Charles A. , Wu Tsu-Juey , Czer Lawrence , Karagueuzian Hrayr S. , Chen Peng-Sheng
Published: July 2002

In support of the spiral wave theory of reentry, simulation studies and animal models have been utilized to show various patterns of spiral wave tip motion such as meandering and drifting. However, the demonstration of these or any other patterns in cardiac tissues have been limited. Whether such patterns of spiral tip motion are commonly observed in fibrillating cardiac tissues is unknown, and whether such patterns form the basis of ventricular tachycardia or fibrillation remain debatable. Using a computerized dynamic activation display, 108 episodes of atrial and ventricular tachycardia and fibrillation in isolated and intact canine cardiac tissues, as well as in vitro swine and myopathic human cardiac tissues, were analyzed for patterns of nonstationary, spiral wave tip motion. Among them, 46 episodes were from normal animal myocardium without pharmacological perturbations, 50 samples were from normal animal myocardium, either treated with drugs or had chemical ablation of the subendocardium, and 12 samples were from diseased human hearts. Among the total episodes, 11 of them had obvious nonstationary spiral tip motion with a life span of >2 cycles and with consecutive reentrant paths distinct from each other. Four patterns were observed: (1) meandering with an inward petal flower in 2; (2) meandering with outward petals in 5; (3) irregularly concentric in 3 (core moving about a common center); and (4) drift in 1 (linear core movement). The life span of a single nonstationary spiral wave lasted no more than 7 complete cycles with a mean of 4.6±4.3, and a median of 4.5 cycles in our samples. Conclusion: (1) Patently evident nonstationary spiral waves with long life spans were uncommon in our sample of mostly normal cardiac tissues, thus making a single meandering spiral wave an unlikely major mechanism of fibrillation in normal ventricular myocardium. (2) A tendency toward four patterns of nonstationary spiral tip motion was observed.
Micromagnetics of thin film cobalt-based media for magnetic recording
Authors: Giles R. , Alexopoulos P. S. , Mansuripur M.
Published: July 2002

Methods of fabrication and characterization for thin films of CoCr, CoPt, CoPtCr, and similar alloys of interest in longitudinal magnetic recording are reviewed and certain interesting features of their magnetic behavior, revealed recently with modern high-resolution observation techniques, are described. The micromagnetics of these polycrystalline thin film media has been studied by large-scale simulations on the massively parallel Connection Machine. Methods and results of these simulations are presented.
Some hydrogen implantation effects in bubble garnets
Authors: Gerard Ph. , Martin P. , Delaye M. T.
Published: July 2002

A classical (Y,Sm,Lu,Ca)3 (Fe,Ge)5O12 bubble garnet has been implanted with 1.5×1016 H+2 cm−2 at 60 keV either directly or through a predeposited 100-A-thick silica layer. The damage and ion implant profile were determined as well as the maximum strain and some magnetic properties of an as-implanted sample. The evolution of certain of these parameters have been studied after different well-chosen annealing treatments. From these observations it has been possible to dissociate the abnormal ‘‘chemical’’ from the usual magnetic effects. A certain mechanical contribution of the silica overcoat to the implanted layer has been displayed.
Electrical conductivity of zinc-based fluoride glasses
Authors: Higby Paige L. , Shelby James E. , Suscavage Michael
Published: July 2002

The dc electrical conductivity of R-Zn-Ba-Yb-Th fluoride glasses, where R is Li or Na, was measured as a function of RF content. The replacement of BaF2 by RF resulted in a decrease in the electrical conductivity. This finding is the reverse of that expected for oxide glasses, but is in agreement with reports of similar behavior in zirconium-based fluoride glasses. The electrical conductivity of a glass containing LiF was always less than that of the corresponding glass containing NaF. It is suggested that these results are due to changes in the strain energy needed to move a fluorine ion from one site to another.
The role of surface in sputtered amorphous silicon: An oxidation study
Authors: Cutrera M. , Gennaro A. M. , Battioni M. , Koropecki R. R. , De Bernárdez L. S. , Arce R. , Buitrago R.
Published: July 2002

High porosity amorphous silicon samples were produced by dc-sputtering in high argon pressure. Post-deposition oxidation and correlated effects were studied in order to elucidate the surface contribution to the measured properties. Infrared spectroscopy, used to follow the oxygen concentration during the oxidation process, allows us to detect the way in which the oxygen is attached. The electron spin density, absorption edge, and dark conductivity are measured in correlation with the oxygen content. We conclude that, for this material, dangling bonds are preferentially located near the inner surface of the porous structure. It is suggested that band bending is responsible for conductivity enhancement and two alternative mechanisms are proposed to explain the absorption edge shift.
Catastrophic degradation of InGaAsP/InGaP double-heterostructure lasers grown on (001) GaAs substrates by liquid-phase epitaxy
Authors: Ueda Osamu , Wakao Kiyohide , Komiya Satoshi , Yamaguchi Akio , Isozumi Shoji , Umebu Itsuo
Published: July 2002

Catastrophically degraded InGaAsP/InGaP double-heterostructure lasers grown on (001) GaAs substrates by liquid-phase epitaxy, emitting at 727 and 810 nm are investigated by photoluminescence topography, scanning electron microscopy, transmission electron microscopy, and energy dispersive x-ray spectroscopy. The degradation is mainly due to catastrophic optical damage at the facet, i.e., development of 〈110〉 dark-line defects from the facet, and rarely due to catastrophic optical damage at some defects, i.e., development of 〈110〉 dark-line defects from the defects inside the stripe region. These 〈110〉 dark-line defects correspond to complicated dislocation networks connected with dark knots, and are quite similar to those observed in catastrophically degraded GaAlAs/GaAs double-heterostructure lasers. The degradation characteristics of the InGaAsP/InGaP double-heterostructure lasers are rather similar to those in GaAlAs/GaAs double-heterostructure lasers concerning the catastrophic degradation.
Formation and characterization of amorphous erbium-based alloys prepared by near-isothermal cold-rolling of elemental composites
Authors: Atzmon Michael , Unruh Karl M. , Johnson William L.
Published: July 2002

We report the formation of bulk single-phase amorphous Cu-Er and Ni-Er alloys by extensive cold-rolling of elemental foils. The reaction is driven by the negative enthalpies of mixing of the constitutent elements and occurs near ambient temperature. The crystallization behavior of the alloys obtained was studied by means of differential scanning calorimetry and found to agree closely with that of the corresponding sputtered and liquid-quenched alloys. Radial distribution functions were measured for sputtered and rolled Cu72Er28 and were found to be in good agreement.
Studies of Au-GaAs (001) interfaces prepared by molecular beam epitaxy. II. Thermal stability of Au-GaAs (001) interface
Authors: Watanabe Nozomu , Kobayashi Keisuke L. I. , Narusawa Tadashi , Nakashima Hisao
Published: July 2002

Au/GaAs (001) interface reactions due to annealing have been studied using the XPS, RHEED, SEM, RBS, EPMA, and AES methods. The samples were prepared by Au deposition on MBE-grown GaAs (001)-c(4×4) surfaces at room temperature. The Au films were epitaxially grown twin crystals, about 50 Å thick. Two phenomena were observed: Au shrinkage and erosion of GaAs by Au. The Au shrinkage occurs in the early stage of annealing. Rectangular or connected rectangular GaAs surfaces are exposed due to Au shrinkage. The sides of these rectangular surfaces are parallel to the GaAs 〈110〉 and 〈1̄10〉 directions. The higher the annealing temperatures, the greater the Au shrinkage and erosion of GaAs by Au. For the sample annealed at 450 °C for 3 h, Au-Ga alloy agglomerates formed on the GaAs (001) and GaAs (111) B surface. The one-dimensional disordered structure was observed by RHEED for the sample annealed at 305 °C for 14 h. The Au crystal quality is improved by annealing at temperatures above 100 °C.
Boron-doping effects on the electrical properties of high-deposition rate amorphous silicon
Authors: Kakinuma H. , Nishikawa S. , Watanabe T. , Nihei K.
Published: July 2002

We have investigated the effects of boron doping on the electrical properties of glow-discharge amorphous silicon (a-Si:H) films prepared at a high-deposition rate (HDR), comparing these effects with those of lower rates. The HDR a-Si:H showed a higher doping efficiency, i.e., a larger portion of substitutionally doped boron than the other films by means of dark conductivity, activation energy measurements and quantitative analysis of boron. It also showed that the minimum B2H6 to SiH4 ratio which changes the film from intrinsic to p-type in photoconductivity is one order of magnitude smaller than that for dark conductivity.
Characterization of D
X centers in molecular-beam-epitaxial grown Si-doped AlxGa1−xAs using Schottky barriers and modulation-doped field-effect transistors
Authors: Subramanian S. , Schuller U. , Arthur J. R.
Published: July 2002

D X centers in molecular-beam-epitaxial (MBE) grown Si-doped AlxGa1−xAs (x=0.3) were characterized by a number of measurement techniques including deep-level transient spectroscopy (DLTS), temperature dependence of capacitance of Schottky barriers, temperature dependence of Hall electron concentration of modulation-doped field-effect-transistor (MODFET) structures, and temperature dependence of threshold voltage and Schottky gate capacitance of MODFETs. Theoretical models were developed to include the effects of traps (DX centers) on various measurements and extract some trap characteristics by comparison with the experimental results. Internally consistent values for the concentration of shallow donors and traps were obtained from different measurements. The energy position of the trap level obtained from different measurements was 55±10 meV below the conduction band. DLTS measurements gave two peaks with activation energies of 0.40 and 0.47 eV, respectively.
Schottky barrier height variations on the polar (111) faces of n-GaP
Authors: Schwartz G. P. , Gualtieri G. J.
Published: July 2002

Current-voltage, capacitance-voltage, and photoresponse measurements have been reexamined on the polar Ga-(111)A and P-(∼(111)) B surfaces of n-GaP for reactive (Al) and nonreactive (Ag) metals. Using a chemical etching/in vacuo desorption cleaning sequence, nearly oxide-free A and B faces could be obtained. For diodes formed on such surfaces, the intrinsic, face-dependent variation in A and B Schottky barrier heights was less than 30 meV.
Al(Ge) metallization: The effect of Ge on the solubility of Si in Al
Authors: Dale C. J. , Pan C. K. , Flinner J. L. , Chu W. K. , Finstad T. G.
Published: July 2002

The contact resistance between Al(Ge) alloys of various compositions and n+Si has been measured using a four-terminal Kelvin probe. The samples processed for these measurements as well as similarly prepared thin films on unprocessed Si wafers have been characterized by both scanning and transmission electron microscopy after heat treatment in the temperature range 350–500 °C. The specific contact resistances for the alloys are comparable to those found for pure Al contacts to Si. However, the alloyed contacts show considerably more spiking into the Si substrate due to dissolution of Si in the metal layer. For temperatures around 350 °C, excessive spiking (compared to pure Al) is believed to be caused by increased solubility of Si in Al due to the presence of Ge. The reason for the enhanced solubility of Si in the alloy could be a counteraction of the strain in the Al lattice by Si and Ge. For anneals at 450 °C the extensive spiking could be associated with liquification of the contact metal.
3D code for calculation of iron-core field in fusion devices
Authors: Fujita Takaaki , Yoshida Zensho , Inoue Nobuyuki
Published: July 2002

Three-dimensional codes for calculations of a stray magnetic field of iron core of a toroidal plasma confinement system have been developed. The calculated results agree well with the measured ones. It is found that up-and-down asymmetry of the iron-core gap deforms the stray field asymmetrically when the primary coil current is not equal to the plasma current and that anisotropy of permeability of the iron core does not have a large influence on the field.
Mössbauer study on crystallization transformation in amorphous Fe90Zr10 alloy ribbon
Authors: Fujinami Masanori , Ujihira Yusuke
Published: July 2002

The difference in the crystallization transformation of amorphous Fe90Zr10 alloy ribbon between the bulk and the surface has been investigated by means of transmission and conversion electron Mössbauer spectrometries. It is found that the ribbon surface crystallizes at 473 K, which is 340 K lower than the crystallization temperature of the bulk. It is confirmed that the remarkable drop in the onset temperature results from the formation of Zr-deficient amorphous phases induced by the absorption and diffusion of a large amount of oxygen. The final crystalline products in the bulk are assigned as α-Fe, Fe3Zr, and Fe2Zr, whereas both surfaces of the ribbon are overlaid with only α-Fe. Further, the study of the ambient atmosphere during annealing shows that air stimulates the crystallization transformation of the bulk and that the crystallization behavior in air is quite different from that in a vacuum.
Zn gettering in InGaAs/InP interfaces
Authors: Geva M. , Seidel T. E.
Published: July 2002

Zn accumulation (gettering) in InGaAs/InP interfaces was studied experimentally using secondary ion mass spectrometry (SIMS). The Zn was introduced by diffusion from solid and gaseous sources and was found to often getter in a thin region at the interface when diffused across it. Its peak concentration there increased with diffusion time and temperature and in some cases exceeded the solid solubility value by two orders of magnitude. Possible mechanisms for the Zn gettering are discussed.
Interactions of amorphous alloys with Si substrates and Al overlayers
Authors: Hung L. S. , Saris F. W. , Wang S. Q. , Mayer J. W.
Published: July 2002

The reactions of Co-Mo, Co-Ta, and Ni-Ta amorphous films with Si substrates and Al overlayers were analyzed by a combination of backscattering spectrometry, transmission electron microscopy, and x-ray diffraction measurements. When the alloy is in contact with Si, the reaction temperature lies between 550 and 650 °C and phase separation is generally observed with near noble silicides formed next to the Si substrate and refractory silicides formed on the surface. When the alloy is in contact with Al, the reaction occurs at temperatures of ∼450 °C with a two-layer structure in the final product. The crystallization temperature of an amorphous alloy is generally higher than its reaction temperature and there is no correlation between the two parameters. The reaction takes place when the annealing temperature reaches the value at which compounds can be formed with both constituents of the alloy.
Centers at junction boundaries in AlGaAs single heterojunction red light-emitting diodes
Authors: Calleja E. , Muñoz E , Gomez A. , Jimenez B.
Published: July 2002

In AlGaAs red light-emitting diodes fabricated by liquid-phase epitaxy the presence and characteristics of deep centers located near the injecting-active junction boundaries have been studied. Transient capacitance, DLTS, photocapacitance, and photocurrent techniques have been applied. Besides the presence, in the n-type injecting layer, of centers related to the Te dopant (DX defects), deep hole traps have been detected at both sides of the n-p heterojunction. The physical origin of such hole traps, present in moderately large concentrations, is discussed in terms of Zn-related complexes. This defect pattern allows us to explain the thermal- and photocapacitance, and the freeze-out and photocurrent characteristics found in such devices.
Growth and properties of Hg1−xCdxTe on GaAs substrates by organometallic vapor-phase epitaxy
Authors: Ghandhi S. K. , Bhat I. B. , Taskar N. R.
Published: July 2002

Growth of epitaxial mercury cadmium telluride (Hg1−xCdxTe) on (100) GaAs substrates by organometallic vapor-phase epitaxy is described. Transport measurements made on these layers at 80 K indicate an electron mobility greater than 2×105 cm2/ V s for layers of composition x≂0.2. An intervening CdTe buffer layer was used to accommodate the large (14%) lattice mismatch between these systems, and HgCdTe layers have been grown with CdTe buffer layer thicknesses from 1000 Å to 3 μm. It is shown that a CdTe buffer layer of 2–3 μm is necessary to accommodate the misfit dislocations at the CdTe-GaAs interface.
Possibly protonic conduction in poly(vinylidene fluoride)
Authors: Doi Akira
Published: July 2002

Comparisons of the reported nuclear magnetic resonance, dielectric, and thermally stimulated polarization/depolarization current data were made between poly(vinylidene fluoride) (PVF2) and alkali silicate glass and close resemblances were found, from which it was suggested that the dominant charge carriers for conduction in PVF2 would possibly be the protons, that the αc peak is due to conduction polarization of the protons which are associated with a crystalline phase, and that the poling process is equal to the charge injection from the anode. It was suggested also that the electric field caused by those injected charges sustains conduction polarization of the protons, the change of which with temperature or with the mechanical stress would give rise to pyro- or piezoelectricity.
Boron deactivation and the contact resistance problem
Authors: Cohen S. S.
Published: July 2002

Recent investigations of ohmic contacts to silicon indicate that for many metallization candidates, contacts made to p+Si are of considerably higher resistance than similar contacts to n+Si. Recent studies have also shown that active boron acceptors in silicon may be deactivated by hydrogen. We discuss the effect that this hydrogen deactivation may have on the specific contact resistance, in view of the results of recent studies that involved several different metallizations. We propose means to deal with the problem in order to secure good ohmic contact characteristics to both polarities of active regions in silicon.
Infrared study of hydrogen- and carbon-implanted heavily doped, n-type GaAs
Authors: Liou L. L. , Spitzer W. G. , Zavada J. M. , Jenkinson H. A.
Published: July 2002

A study is given of the effect of ion implantation on the carrier density and the infrared dielectric constant of heavily doped, high-carrier density, n-type GaAs as measured by infrared reflection. Hydrogen ions were implanted at 300 keV at room temperature and carbon ions at 380 keV at near-liquid-nitrogen temperature. For H and C ions the effects of the implantation and subsequent annealing from 100 to 550 °C are examined. The 1H ion implantation and annealing results are compared with available SIMS data and with the carrier density profile obtained from capacitance-voltage measurements of a progressively etched sample. The 1H and carrier compensation profiles are clearly related and show a compensated layer ∼3 μm thick for the as-implanted samples. A deeply diffused layer is present after annealing and the depth grows with anneal temperature. After 500 °C annealing the carrier compensation in the diffused layer disappears but the original layer is still compensated. The 12C-implanted sample shows both carrier compensation and substantial damage-related changes in the dielectric constant. Annealing removes the damage-related changes and no compensated diffused layer such as that observed for hydrogen was present. An effective diffusion constant for the hydrogen related defect can be estimated but its value is dependent upon the model used. Different models give Deff=D0effe−Ea/kT with Ea about 1 eV but with D0eff values which are strongly model dependent.
Impurity effects in rf O2 plasma oxidation for Pb-alloy Josephson junctions
Authors: Nakano Junichi , Wada Masato
Published: July 2002

Impurity-gas effects on the electrical properties of Pb-In alloy Josephson junctions fabricated by rf plasma oxidation are discussed in this paper. The impurity gas in rf O2 discharge originates from decomposition of the organic photoresist used in the lift-off process for counterelectrodes. Optical emission and quadrupole mass spectroscopies show that CO2 and H2O are the main impurities. These impurity effects are precisely analyzed using photoresist-free wafers with counterelectrodes patterned by chemical etching. Junctions formed on photoresist-free wafers and conventional photoresist-coated wafers are compared, and two types of impurity effects having different effective ranges are identified. Based on the effective-range length measurement, one impurity effect appears to be related to the atmospheric impurity concentration and the other to backscattering of sputtered organic substances onto the barrier oxide surface.
Crystal structure of acicular γ-Fe2O3 particles used in recording media
Authors: Ho Huei-Min , Goo Edward , Thomas Gareth
Published: July 2002

γ-Fe2O3 particles have been examined by convergent beam electron diffraction to determine the crystal symmetry. The particles have a primitive lattice with an m3m point group and a cubic superstructure with lattice parameter approximately equal to three times the lattice parameter of the magnetite structure. This superlattice is a result of cation vacancy ordering. During observation, disordering in the electron microscope occurs and is believed to be caused by electron radiation-enhanced diffusion.
Temperature distribution of silicon-on-insulator systems during recrystallization processing
Authors: Miaoulis Ioannis N. , Mikić Bora B.
Published: July 2002

The temperature distribution during melting–recrystallization processing of thin silicon films for electronic devices was calculated numerically and is presented in graphical form. Two methods of high-quality recrystallization are analyzed: the antireflective coating method and the stepwise thickness variation of the silicon dioxide. The controlling parameters were determined and their effects on temperature distributions are presented.
Magnetic measurements on Pr (BrO3)3 ⋅ 9H2O single crystal and a study of the effects and origin of the crystal field
Authors: Neogy D. , Purohit T. , Chatterji A.
Published: July 2002

Praseodymium bromate was prepared from Pr2O3 and the single crystals of Pr (BrO3)3 ⋅  9H2O were grown. The principal magnetic susceptibility χ⊥ and the anisotropy χ∥-χ⊥ was measured in the range 300–90 K. The variation of the average magnetic moment peff with temperature is appreciable showing a deviation from the Curie law. The magnetic anistropy χ∥-χ⊥ is found to be much higher than in Pr-ethylsulfate where the Pr3+ ion occupies a site very similar to that in PrBR. A crystal field analysis with a field of D3h symmetry is found to provide an excellent account of the magnetic properties observed by us and Simizu et al. [J. Appl. Phys. 55, 2333 (1984)] from 300 K down to ∼0.06 K. The Hamiltonian was diagonalized in the complete basis of the 3H ground term taking care of the intermediate coupling effects to a large extent. Some important predictions on the electronic heat capacity and the electric quadrupole splitting have been made. An estimate of the crystal field parameters has been made using the available structural data on the crystal and the results are discussed in the light of our phenomenological set of parameters.
Thermal domain drag effect in amorphous ferromagnetic materials. II. Experiments
Authors: Jen S. U. , Berger L.
Published: July 2002

Ferromagnetic domain walls are observed to move from the hot to the cold end of samples of amorphous (Co92.5Fe7.5)78Mo2B15Si5 subjected to a constant temperature gradient dT/dx. An ac magnetic field H0E parallel to the easy axis is used to decrease pinning forces on the walls. The critical temperature gradient (dT/dx)c required to move walls is of order 102 K/mm. The linear decrease of (dT/dx)c with increasing H0E indicates that pinning of the walls by the two ends of the sample is dominant over bulk pinning. The dependence of (dT/dx)c on sample length and thickness indicates that the Nernst–Ettingshausen drive mechanism is dominant over competing drive mechanisms. The speed of walls has been measured and is found to increase with increasing temperature gradient.
A tunneling theory of exciton photoluminescence for neutral acceptors in silicon: A study of the systems Si: (B, In), Si: (Al, In), Si: (Ga, In), Si: (B, Al), Si: (B, Ga), and Si: (Al, Ga)
Authors: Moroi David S. , Ohmer Melvin C. , Szmulowicz Frank , Brown David H.
Published: July 2002

Rate equations for the densities of free excitons and excitons bound to two different neutral acceptors in silicon are solved for steady state in the absence of saturation. These rate equations explicitly include terms for forward and reverse tunneling of bound excitons from one type of neutral impurity to another. Both tunneling rates are calculated using a simple model of an exciton in a one-dimensional semi-infinite double potential well. The steady-state solutions of the rate equations yield an expression for the ratio of the bound exciton luminescence intensity as a function of the impurity concentrations. The relative photoluminescence intensities for the systems Si: (B, In), Si: (Al, In), Si: (Ga, In), Si: (B, Al), Si: (B, Ga), and Si: (Al, Ga) are calculated for the relevant free-exciton capture cross-section ratios. This model predicts no exciton tunneling for any of the above systems for the low-impurity concentration range of 1012–1013 cm−3. For those systems with large differences in the bound exciton energy levels such as Si: (B, In), Si: (Al, In), and Si: (Ga, In), and having indium concentrations exceeding 1015 cm−3, it predicts quenching of shallow impurity bound exciton luminescence because the forward exciton tunneling rate from the shallow level to the deep level of indium dominates and the reverse exciton tunneling rate from indium to the shallow impurities is negligible. For the systems with small differences in the bound exciton energy levels such as Si: (B, Al) and Si: (B, Ga), the theory predicts enhancement of shallow impurity bound exciton luminescence beyond certain concentrations depending upon the free-exciton capture cross-section ratios because in these cases the reverse exciton tunneling rate dominates. For the system Si: (Al, Ga) in which the difference in the bound exciton energy levels is very small, gallium bound exciton luminescence dominates when the gallium concentration exceeds 1016 cm−3.
X-ray diagnostic for current density profiling relativistic electron beams in vacuum and gas
Authors: Slaughter Dennis , Koppel Louis , Smith Jerel
Published: July 2002

An x-ray imaging technique has been studied for the purpose of observing the current density profile in a high-current relativistic electron beam (50 MeV, 10 kA). Calculations and measurements of energy spectra and intensities are in good agreement. Results indicate sufficient photon yield for pinhole imaging when the beam deposits a small part of its energy in high-Z gas or a thin high-Z foil. Characteristic L and K x-ray emission is not found not be a reliable technique due to strong L and K shell fluorescence in the presence of intense bremsstrahlung radiation. It is also found that at pressures on the order of one atmosphere, the density of energy deposition in a gas cell is too small to generate sufficient photon yield for time-resolved measurements.
Reduction of relaxation resonance and wavelength chirp in antireflection facet coated 1.3-μm Vee-groove InGaAsP lasers
Authors: van der Ziel J. P. , Mikulyak R. M. , Blount H. M.
Published: July 2002

It is shown that the well-known damped relaxation oscillation resonance in the small signal equations for the dynamic photon and carrier densities becomes more highly damped when the photon density is axially inhomogeneous. An antireflective coating with R=0.02 on one laser facet reduced the resonance in the light output from a 1.3-μm Vee-groove laser yielding a flat response with a 3-dB bandwidth of 5 GHz. We also show that the wavelength modulation or chirp, due to the carrier-dependent contribution of the refractive index, is largely eliminated.