bluuebunny/crossref_metadata_2025 huggingface dataset:
A Monte Carlo electron transport code for the desktop computer
Authors: Al-Beteri A. A. , Raeside D. E.
Published: July 2002

A Monte Carlo electron transport code for the desktop computer is applied to the problem of determining the radiation dose throughout an oblique-surface heterogeneous medium. Absorbed-dose distributions are obtained for 10 MeV electrons incident upon flat-surface and oblique-surface water phantoms, as well as flat-surface water phantoms containing an air cavity and containing a bone heterogeneity.
The DOM4 database system
Authors: van Haren P. C.
Published: July 2002

The DOM4 database system is designed to manage experimental bulk data, i.e., raw measurements, from large pulsed research devices such as tokamaks. Data are organized in objects, each containing all data from a single measuring point. All objects from an experimental pulse are stored in a single file, the so-called pulse file. For the ‘‘Rijnhuizen Tokamak Project,’’ the primary user of the DOM4 software, the size of a typical pulse file is a few MBytes and such a file contains in the order of 800 objects. The DOM4 software is optimized for performance, anticipating and exploiting the peculiarities of its application field. The data acquisition takes place using a heterogeneous, distributed computer system, comprising DEC VAXes, MIPS R3000-based workstations, and a variety of MC680x0 embedded systems. The data in a pulse file are commonly accessed following a nearly Write-Once-Read-Many scenario: After the completion of the data acquisition cycle in the on-line phase of the experiment, the contents of the pulse file are rarely modified or deleted.
High-resolution lattice–Boltzmann computing on the IBM SP1 scalable parallel computer
Authors: Punzo Giovanni , Massaioli Federico , Succi Sauro
Published: July 2002

We discuss the implementation of the Lattice–Boltzmann method, a relatively new technique for computational fluid dynamics, on the IBM SP1 Scalable Parallel processor. Sustained rates of almost 4 Gflops on high-resolution simulations with up to nearly 800 million of degrees of freedom are demonstrated.
Interactive visualization of three-dimensional cellular automata
Authors: Renz Wolfgang , Westermann Rüdiger , Krüger Wolfgang
Published: July 2002

This paper summarizes results of a project on a massively parallel computer. The project encompasses time evolution of a complex system, data analysis of the relevant measures, and interactive visualization of the time dependent emerging structures within an integrated tool. We develop visualization and interpretation models for the general class of 3D and (3+1)D multistate fields, represented by a lattice field of integer values. As an example, we study three-dimensional two state cellular automata, which exhibit interesting spatiotemporal behavior, using a variety of adapted volume rendering techniques. The direct visualization of time sequences of three-dimensional clusters presented here generalizes the traditional technique used in one and two dimensions. Using new visual representations we incorporate information on nearest-neighbor sites and cluster sizes in the visualization. The visualization and evolution rules of the automaton can be adjusted interactively (steering). The necessary speed is achieved with an implementation on a SIMD massively parallel computer. The visualization techniques presented facilitate new insight into the complex spatial structures responsible for the dynamic evolution of the system under consideration.
Implementation of PHENIX trigger algorithms on massively parallel computers
Authors: Petridis Athanasios N. , Wohn Fred K.
Published: July 2002

The event selection requirements of contemporary high energy and nuclear physics experiments are met by the introduction of on-line trigger algorithms which identify potentially interesting events and reduce the data acquisition rate to levels that are manageable by the electronics. Such algorithms being parallel in nature can be simulated off-line using massively parallel computers. The PHENIX experiment intends to investigate the possible existence of a new phase of matter called the quark gluon plasma which has been theorized to have existed in very early stages of the evolution of the universe by studying collisions of heavy nuclei at ultra-relativistic energies. Such interactions can also reveal important information regarding the structure of the nucleus and mandate a thorough investigation of the simpler proton-nucleus collisions at the same energies. The complexity of PHENIX events and the need to analyze and also simulate them at rates similar to the data collection ones imposes enormous computation demands. This work is a first effort to implement PHENIX trigger algorithms on parallel computers and to study the feasibility of using such machines to run the complex programs necessary for the simulation of the PHENIX detector response. Fine and coarse grain approaches have been studied and evaluated. Depending on the application the performance of a massively parallel computer can be much better or much worse than that of a serial workstation. A comparison between single instruction and multiple instruction computers is also made and possible applications of the single instruction machines to high energy and nuclear physics experiments are outlined. © 1995 American Institute of Physics.
Positive iterative deconvolution with energy conservation
Authors: Pruksch Matthias , Fleischmann Frank
Published: July 2002

An algorithm for solving a convolution-type Fredholm equation of the first kind in the isoplanatic case is presented. The inverse operator is therefore expanded into a geometric sum. Partial sums are calculated analytically to increase convergence. In an iterative scheme, by considering conservation of energy, positivity as a nonlinear constraint is applied. This approach guarantees the exact solution in the case of complete information and leads to stable results for incomplete information and in the presence of noise. Photon noise, readout noise, and noise by computer quantization are considered, and results of one-dimensional computer experiments are discussed. © 1998 American Institute of Physics.
Diffusion of ion-implanted In and Tl in SiO2
Authors: van Ommen A. H.
Published: July 2002

The diffusion of In and Tl implanted into SiO2 has been investigated by means of Rutherford backscattering spectrometry. The diffusion of these elements is shown to be strongly dependent on their chemical state in SiO2. By combining these results with previous results for Ga, a general model has been formulated which describes the incorporation and diffusion of Group III elements in SiO2. The most important parameter of this model is the valence state of these elements in SiO2. In their trivalent state these elements are incorporated on Si sites of the SiO2 network, where they are virtually immobile. On the other hand, interstitial monovalent Group III ions are observed to show rapid diffusion. In addition to this, there is a second independent diffusion process, which is attributed to interstitial migration of InOH or TlOH molecules. After high-temperature annealing of SiO2 covered with Si3N4, the In and Tl diffusion profiles exhibit a peak at the SiO2-Si interface. This segregation is tentatively explained by stress relief at the SiO2-Si interface.
Optical properties of dense thin-film Si and Ge prepared by ion-beam sputtering
Authors: Collins R. W. , Windischmann H. , Cavese J. M. , Gonzalez-Hernandez J.
Published: July 2002

The optical properties of ion-beam-sputtered Si and Ge have been measured using spectroscopic ellipsometry over the range of 2.5–5.0 eV. Measurements have been performed on films prepared at different substrate temperatures (Ts) . An analysis of the spectroscopic ellipsometry data using the Bruggeman effective medium approximation reveals that very dense polycrystalline Si ( p-Si) and Ge ( p-Ge) films are obtained (without postdeposition heat treatment) for Ts ≥350 °C and Ts ≥200 °C, respectively. Maintaining a sufficiently high Ar beam voltage in the sputtering process is shown to be beneficial to the densification of p-Si. Discrepancies observed between the structure of the p-Si deduced from Raman and ellipsometry spectra are also addressed. The ellipsometry data are effective in detecting heterogeneity possibly due to surface roughness for the p-Ge.
S-vacancy energy levels in AgInS2
Authors: Massé G. , Redjai E.
Published: July 2002

A luminescence study of energy levels due to lattice defects in AgInS2, which belongs to the I-III-VI2 compounds, is reported in this article. As-grown and annealed crystals under maximum or minimum sulfur pressure have been used. We have found a donor level at 70 meV, an acceptor level at 70 meV, and a level (acceptor or donor) at 100 meV. Two of these levels (at least) are attributed to the sulfur vacancy.
Quantifying solid–fluid interfacial phenomena in porous rocks with proton nuclear magnetic resonance
Authors: Schmidt Ehud J. , Velasco Katherine K. , Nur Amos M.
Published: July 2002

The three order-of-magnitude variation in the proton nuclear magnetic resonance (NMR) longitudinal relaxation time T1 of water adsorbed on silica surfaces versus that of bulk water makes proton NMR studies of porous materials powerful tools to study the effects of adsorption. Recent theory permits the utilization of this different response to obtain pore space surface-to-volume (S/V) distribution functions by inverting the decay of the z component of magnetization of fully saturated porous rocks; information can likewise be obtained on the fluid distribution at partially saturated conditions. A computer program has been developed to invert the NMR relaxation curves for the S/V distribution function, assuming an isolated pore regime, the ramifications of which are examined. The program has been applied to experimental results from water, porous sandstones, and tight gas sands at various pore fluid saturations and varying electrolyte content. For the fully saturated case, the results show promise in the application of NMR to describing pore space geometries in rock samples with widely varying surface-to-volume ratios. For partially saturated rocks, the results reflect the preferential early draining of the large pores at high water saturations, connectivity percolation phenomena at intermediate saturations, and the dominating role of adsorbed water films at low water saturations. Experiments on rocks saturated with saline solutions disclose the importance of the effects of alteration of the active sites on the rock surfaces as well as the role of electrolytes in modifying the structural properties of bulk solution.
Short wavelength compositionally modulated Ni/Ni–P films prepared by electrodeposition
Authors: Goldman Lee M. , Blanpain Bart , Spaepen Frans
Published: July 2002

Compositionally modulated Ni/Ni–P films, with wavelengths between 2.1 and 4.0 nm and an average P content around 12 at. %, have been prepared by alternating electrodeposition in a simple and inexpensive apparatus consisting of two baths of different composition. X-ray diffraction showed a single (000) satellite at low angles due to the presence of the modulation.
Photoelectronic properties of HgI2
Authors: Bornstein Jonathan , Bube Richard H.
Published: July 2002

Two types of photoelectronic measurements have been used to determine the properties of HgI2 crystals and photodetector cells: thermally stimulated conductivity, and spectral response of photoconductivity in both the lateral and transverse geometries. Characteristic trap depths are identified that compare well with previously reported values, and a decrease in apparent density with time and temperature cycling is described. Analysis of photoconductivity spectral response using the DeVore model for lateral contacts and the Goodman model for transverse contacts allows the determination of photoelectronic parameters for the material.
Impurity induced layer disordering of Si implanted AlxGa1−xAs-GaAs quantum-well heterostructures: Layer disordering via diffusion from extrinsic dislocation loops
Authors: Guido L. J. , Hsieh K. C. , Holonyak N. , Kaliski R. W. , Eu V. , Feng M. , Burnham R. D.
Published: July 2002

Extensive data are presented on impurity-induced layer disordering (IILD) of AlxGa1−xAs-GaAs quantum-well heterostructures and superlattices that are Si implanted and annealed (Si+-IILD) at three different implant doses. We show that impurity activation is not critical to the layer disordering process and that Si diffusion from the implanted profile initiates Si+-IILD. When the implant dose is as high as φ≥5×1013/cm2 (nSi ≥2×1018/cm3), Si interstitial loops (Si-ILs) form by diffusion and agglomeration of the implanted Si atoms during the initial stages of annealing. If a source of Ga vacancies is provided (e.g., via an As overpressure or SiO2 encapsulation), the Si-ILs dissociate and supply Si atoms for diffusion and hence Si+-IILD during the latter stages of annealing. If a Si3N4 encapsulant is employed, however, fewer Si-ILs form and Si diffusion is inhibited. For an implantation dose as low as φ=1×1012/cm2 (nSi =3×1016/cm3), extensive Si+-IILD is realized via capless annealing and Si-ILs are not observed. It is significant for device applications that the layer-disordered material operates as a cw 77 K photopumped laser, which indicates that the layer averaging (IILD) does not damage the crystal.
Ferrite-organic multilayer film for microwave monolithic integrate circuits prepared by ferrite plating based on the spray-spin-coating method
Authors: Abe M. , Itoh T. , Tamaura Y. , Gomi M.
Published: July 2002

We have made multilayer films in which NiZn-ferrite (Fe2.70±0.04-Ni0.14±0.03 Zn0.14±0.03O4) layers (2000–8000 Å thick) and dextran [(C6H10O5)1200–1800] buffer layers (100 Å thick) are laminated alternately on a glass substrate. The ferrite layers were formed by ferrite plating based on the spray-spin-coating method at 80 °C, compatible with the low heat resistance (∼300 °C) of GaAs microwave monolithic integrated circuits. To enhance the adhesive power of the multilayer film, thin (∼300 Å) magnetite layers were deposited intermediate between the NiZn-ferrite and dextran and also between the NiZn-ferrite and the substrate. The grain growth in the ferrite layers is interrupted at the dextran buffer layers, which release the stress induced in the ferrite layers. Thus the multilayer film can grow much thicker (i.e., up to ∼5 μm) than a NiZn-ferrite monolayer film which peels off at ∼1.5 μm thickness due to the stress. In the multilayer films, the ferrite layers are of polycrystalline spinel structure having no preferred orientation. The magnetization does not exhibit an anisotropy, lying in the plane of film.
Quenching of flames by magnetic fields (abstract)
Authors: Ueno S.
Published: July 2002

The effects of magnetic fields on combustion of alcohol with the aid of platinum catalysis have been studied to simulate in part the oxidation of organic matter in the living body, and it has been found that the combustion reactions are influenced by magnetic fields. It has also been observed that candle flames are pressed down by magnetic fields of higher intensities when flames are exposed to gradient magnetic fields in a range 20–200 T/m under 0.5–1.4 T. Apart from the combustion experiments, flows of carbon dioxide, oxygen, nitrogen, and argon gases were exposed to magnetic fields up to 2.2 T and 300 T/m. The flows of these gases were blocked or disturbed by the magnetic fields. The purpose of the present study is to clarify the mechanisms for the phenomena observed in the experiments of magnetic effects on combustion and gas flow. An electromagnet with a pair of columnar magnetic poles of which inner sidepieces were hollowed out was used. The magnetic fields of 1.5 T at the brim gave a gradient of 50–100 T/m in the direction perpendicular to the pole axis when the distance of the airgap was in a range 5–10 mm. A candle was burned in the hollowed space between magnetic poles, and candle flames were exposed to magnetic fields. The flames were quenched in a few seconds after the onset of field exposures. Oxygen gas as a paramagnetic molecule can be attracted to the magnetic fields of higher intensities. However, under the intensities of magnetic fields concerned, oxygen gases are not concentrated but are aligned so as to make a ‘‘wall of oxygen’’ or an ‘‘air curtain.’’ The air curtain, which is also called the ‘‘magnetic curtain,’’ blocks air flow into and out of the hollowed space. The interception of oxygen by magnetic curtain quenches flames. The magnetic curtain also presses back flames and other gases.
Applications of yokeless flux confinement
Authors: Leupold H. A. , Potenziani II E. , Abele M. G.
Published: July 2002

A recently developed generalized technique for the production of large confined magnetic fields is used to design a number of novel permanent-magnet flux sources. The simplest of these produces a transverse field in a long cavity of a rectangular cross section. In such structures, uniform fields that are of the order of the remanence of the material used are obtained easily. Applications include: NMR imaging, general electron device biasing, and the provision of bases for various periodic magnetic structures, such as wigglers, undulators, and twisters. Slight elaboration of such configurations can produce fields of up to three times the remanence. The fields of such structures can be readily adjusted by mechanical means, with continuous variation from zero to the maximum field. The wigglers and twisters afford instantaneous conversion from wiggler to twister and conversely. Adaptations of the basic principles can be used to produce radial, conical, and other unusual field orientations.
The charge-effect transistor
Authors: Amman M. , Mullen K. , Ben-Jacob E.
Published: July 2002

We present a theoretical study of the current-voltage characteristic of a new transistor based upon the ‘‘Coulomb blockade.’’ In mesoscopic (submicron) tunnel junctions the flow of current can be blocked by the electrostatic charging energy of a single electron. The charge-effect transistor is composed of two mesoscopic tunnel junctions connected in series with a gate terminal capacitively coupled to the interjunction region. Such a device has been shown to lead to a Coulomb staircase in the current-voltage characteristic when the gate voltage is zero. Here we study the effect of the gate voltage on the current through the device for various ranges of junction parameters. We study junctions made from both normal metal and superconductors. We examine the current noise at different operating points and find it comparable to, but lower than, that in ordinary shot-noise devices.
Incorporation of accelerated low-energy (50–500 eV) In+ ions in Si(100) films during growth by molecular-beam epitaxy
Authors: Hasan M. A. , Knall J. , Barnett S. A. , Sundgren J.-E. , Markert L. C. , Rockett A. , Greene J. E.
Published: July 2002

A single-grid broad-beam ion source was used for low-energy (50–500 eV) accelerated In+ ion beam doping during growth of Si(100) layers by molecular-beam epitaxy. Indium incorporation behavior was studied as a function of ion energy (E+In=50–500 eV), substrate temperature (Ts=500–1050 °C), ion flux (J+In=1×109–5×1012 cm−2 s−1), and Si growth rate (R=0.1–1.3 nm s−1). Dopant concentration profiles obtained using secondary ion mass spectroscopy showed that abrupt doping profiles were obtained at Ts<900 °C and R=0.7 μm h−1, the incorporation probability σ+In was close to unity for E+In≥200 eV, while σ+In was less than unity and decreased gradually with increasing Ts for E+In≤100 eV. At Ts≥900 °C, σ+In decreased rapidly with increasing Ts for all ion energies. The incorporation results are interpreted using a qualitative model based on different types of binding sites for In with incident energies ranging from thermal to 500 eV. A procedure, utilizing accelerated ions, for the growth of ultrathin doped layers is also suggested.
Optical spectra of SixGe1−x alloys
Authors: Humlíček J. , Garriga M. , Alonso M. I. , Cardona M.
Published: July 2002

We report pseudodielectric functions of SixGe1−x alloys at room temperature, measured ellipsometrically on polycrystalline samples and single-crystal epitaxial layers, in the 1.7–5.6 eV range. Accurate values of the E1 threshold energies are obtained from numerically differentiated spectra. The measured dependence of E1 on x provides an efficient way to determine the alloy composition x. The spectral and compositional dependence of the optical constants forms a data base for optical studies of Si/SiGe layered structures.
Plasma-enhanced chemical vapor deposition of i
n s
i
t
u doped epitaxial silicon at low temperatures. I. Arsenic doping
Authors: Comfort James H. , Reif Rafael
Published: July 2002

I n situ arsenic doping of epitaxial silicon films deposited from 700 to 800 °C by both very-low-pressure chemical vapor deposition (VLPCVD) and plasma-enhanced chemical vapor deposition (PECVD) has been investigated. The growth rate and morphology of films deposited by silane VLPCVD are degraded in the presence of arsine. The overall activation energy for deposition increases and the apparent silane reaction order decreases relative to VLPCVD in the absence of arsine. VLPCVD arsenic incorporation depends sublinearly on the arsine partial pressure and appears to saturate for incorporation fractions above 1018 As atoms/cm3. PECVD growth rates are less sensitive to arsine, and plasma enhancement is seen to provide significant advantages for n-type doping of epitaxial silicon at low temperatures. PECVD deposits show an order-of-magnitude increase in active dopant incorporation, exhibit superior morphology relative to VLPCVD, and allow for increased doping flexibility. Incorporation remains proportional to arsine partial pressures over the entire range investigated and allows for doping to at least 7×1019 As atoms/cm3 for PECVD. Both VLPCVD and PECVD arsenic-incorporation fractions increase with decreasing temperature. PECVD incorporation also exhibits a weak plasma power dependence. Ion-bombardment-induced disruption of arsenic surface aggregation is proposed to account for the observed doping behavior and plasma enhancement. A companion paper discusses boron doping during low-temperature epitaxial growth.
Electric-controlled intrinsic optical bistability in nematic liquid crystals
Authors: Wu J. J. , Chen Shu-Hsia
Published: July 2002

The properties of intrinsic optical bistability in nematic liquid crystals were studied. This kind of optical bistability is without resonant optical cavity and electric feedback. We find that the nematic ROTN-200 film can exhibit bistability when applying a constant ac electric field (≊560 kHz) that is greater than a tricritical voltage VTc=2.614 V. The bistable interval is measured and the hysteresis loop is characterized at each different voltage. The splay and bent elastic constants k11 and k33 are obtained to calculate the numerical result. It is found that the experimental results are in good agreement with theory. The experimental setup with which we can easily observe the bistable phenomena is illustrated. Under the consideration of the finite size of the laser beam, the thermal effect and finite beam size effect are discussed. In addition, some new interesting phenomena about the diffraction ring structure of nematic liquid crystal are reported.
Crystallization and diffusion in composite TiO2-SiO2 thin films
Authors: Sankur H. , Gunning W.
Published: July 2002

The crystallization behavior of evaporated TiO2-SiO2 mixed composition films and its dependence on composition, temperature, time and type of mixing (codeposited or alternating layers) were studied. All codeposited films annealed between 600 and 900 °C with 15%–90% molar TiO2 exhibited crystallization in the anatase phase. Crystallite size increased with Ti content of the film and with temperature. TiO2 in alternating layered films, which had layer thicknesses in the 65–1000 Å range, crystallized in the anatase phase in the 400–600 °C range, with thin layered films requiring higher temperatures for crystallization. For temperatures of 900–1100 °C, codeposited films were transformed into rutile films, whereas alternating layered films remained as anatase. Diffusivity of Ti in the mixed composition film was calculated to be 3×10−14 and 3×10−13 cm2/s from the study of precipitation kinetics at 950 and 1050 °C, respectively. Morphology of intermediate composition analog films (25%–65% atomic TiO2) remained virtually unaltered from its as-deposited state after annealing and crystallization.
Spatial profiles of reactive intermediates in rf silane discharges
Authors: Mataras D. , Cavadias S. , Rapakoulias D.
Published: July 2002

Spatial concentration profiles of ground-state SiH and electronically excited SiH* radicals are measured using laser-induced fluorescence and emission spectroscopy, respectively. The measurements are made in pure silane, as well as in mixtures with helium, hydrogen, and argon, in a capacitively coupled rf glow-discharge apparatus used for the deposition of a-Si:H. Low-power–low-depletion conditions are maintained throughout, whereas pressure is varied from 20 to 400 mTorr. Our observations indicate a close relationship between concentration profiles of the species and local electron energy distribution. We conclude that spatial concentration profiles represent stationary generation rates of the radicals. In the case of diluted silane the process is strongly influenced by diffusional transport of detected species to the deposition electrode. The dependence of this effect on dilution grade and buffer gas used is presented.
I
n s
i
t
u study of the thermal decomposition of B2H6 by combining spectroscopic ellipsometry and Kelvin probe measurements
Authors: Roca i Cabarrocas P. , Kumar Satyendra , Drevillon B.
Published: July 2002

In amorphous silicon (a-Si:H) p-i-n solar cells preparation, B2H6 is added to the SiH4 discharge in order to deposit the p layer. However, chemical vapor deposition (CVD) of the (B2H6,SiH4) mixture, in the absence of plasma excitation, can contribute to poor p/i interface characteristics. The thermal decomposition of B2H6 at 250 °C is studied in situ by combining spectroscopic ellipsometry and Kelvin-probe measurements. The advantage of correlating both techniques is underlined. Both diagnostics provide complementary information. Spectroscopic ellipsometry is highly sensitive upon film deposition and surface morphology modifications. On the other hand, Kelvin-probe measurements may be directly related to Fermi-level shifts. The thermal decompositon of (B2H6,H2) and (B2H6,SiH4) mixtures is evidenced, even at low total pressure (30 mTorr). The boron incorporation is found to be little affected by the diluent gas. In contrast, the CVD consequences strongly increase as a function of the gas pressure. The surface sensitivity of the CVD process is illustrated whatever the total pressure. At low pressure, the variation of the Kelvin-probe measurements may be described by a model taking into account adsorption of species acting as electron acceptors. At high pressure, when a (B2H6,SiH4) mixture is used, the CVD leads to the growth of a highly doped amorphous silicon layer with a very low deposition rate (2–3 Å min−1), whatever the substrate. The implications of the CVD process for interface formation in a-Si:H devices have been explored. In particular, the use of a multichamber deposition system can result in an improvement of the p/i interface behavior.
Mössbauer study of the crystallization of Fe100−xBx amorphous alloys (14≤x≤25)
Authors: Sánchez F. H. , Zhang Y. D. , Budnick J. I. , Hasegawa R.
Published: July 2002

The crystallization of Fe100−xBx amorphous alloys (x=14, 20, and 25), prepared by rapid quenching from the melt, was studied by Mössbauer effect spectroscopy. In general, the present results support recent nuclear magnetic resonance studies (performed on the same samples used in this work), which indicated that the amorphous material had a body-centered-tetragonal Fe3B-like short-range order for x=25 but an orthorhombic Fe3B-like one for x=14. For x=25, annealing at about 400 °C led to the formation of almost pure body-centered-tetragonal Fe3B. On the other hand, thermal treatments at about 800 °C produced a mixture of phases for all the compositions. For x=14, formation of body-centered-tetragonal Fe3B was not observed in any case. In addition, the present Mössbauer results, combined with the previous nuclear magnetic resonance ones, show that boron and iron atomic surroundings evolve differently when alloys with x=14 are annealed at 390–420 °C. In the boride phase, the 57Fe Mössbauer signal remained ‘‘amorphouslike’’ in contrast with the 11B nuclear magnetic resonance signals which became sharp and corresponded to those in tetragonal and orthorhombic Fe3B and in Fe2B. These results would indicate that under these experimental conditions the surroundings of the boron atoms become ordered before the surroundings of the iron atoms.
Epitaxial grain growth in thin metal films
Authors: Thompson C. V. , Floro J. , Smith Henry I.
Published: July 2002

Epitaxial alignment has been obtained by means of grain growth in polycrystalline films deposited on single-crystal substrates. A theory for epitaxial grain growth is outlined and results given for experiments on Au, Al, Cu, and Ag films on vacuum-cleaved NaCl, KBr, KCl, or mica. Epitaxial grain growth provides a fundamentally different alternative to conventional epitaxy, and can lead to very thin films with improved continuity and crystalline perfection, as well as non-lattice-matched orientations.
Very large magnetoresistance effects induced by antiparallel magnetization in two ultrathin cobalt films
Authors: Dupas C. , Beauvillain P. , Chappert C. , Renard J. P. , Trigui F. , Veillet P. , Vélu E. , Renard D.
Published: July 2002

Magnetoresistance (MR) and magnetization measurements by SQUID have been performed on Au/Co.Au/Co/Au multilayers in which the two ultrathin cobalt films have perpendicular magnetizations and different coercive fields Hc1 and Hc2 due to their different thicknesses. The two Co layers are magnetically uncoupled, as shown by their well separated square hysteresis loops. The MR exhibits a plateau for magnetic fields H such as Hc1<H<Hc2, giving antiparallel orientation of their magnetization. The δR/R value is 1.4% at 300 K and 6% at 4.2 K. These experiments confirm the mechanism of spin-dependent diffusion at the interfaces leading to an increase of the resistance when the two magnetic layers have antiparallel magnetizations.
Interdiffusion and resistivity of Cu/Au, Cu/Co, Co/Au, and Cu/Co/Au thin films at 25–550 °C
Authors: Madakson Peter , Liu Joyce C.
Published: July 2002

The interdiffusion and resistivity of Cu/Au, Cu/Co, Co/Au, and Cu/Co/Au thin-film structures were studied, at temperatures ranging from 25 to 550 °C, using Rutherford backscattering spectroscopy, Auger analysis, and four-point probe resistance measurements. Intermetallic phase formation was studied by x-ray diffraction and changes in microstructure were analyzed by scanning electron microscopy. Interdiffusion of Cu and Au in the Cu/Au structure is observed at temperatures as low as 150 °C and is accompanied by an increase in resistivity. No significant reactions occur in the Cu/Co, Co/Au, and Cu/Co/Au thin-film structures up to 400 °C, after which the resistivity increases. The very rapid increase in resistivity observed at 250 °C for the Cu/Au system and at 450 °C for Cu/Co/Au, is associated with structural changes in the films which result in large grains and the formation of AuCu, Cu3Au, and Cu3Au2 compounds. The structural changes in the Cu/Co/Au system occur at a higher temperature because of the time needed for Cu and Au to diffuse through the Co barrier, which did not react significantly with either Au or Cu.
Charge injection and electroluminescence as a prelude to dielectric breakdown
Authors: Lebey T. , Laurent C.
Published: July 2002

To understand the ac voltage aging of low-mobility materials, the amount of energy involved in the degradation process must be known. Electroluminescence experiments are a choice environment for solving this problem since luminescence spectra give direct information on the energy released during aging. Carrier injection is needed for electroluminescence to take place, but it is not clear whether luminescence occurs at the injection threshold or later on. We investigate this problem using two very sensitive arrangements: a charge detector and a photon-counting system. The experimental threshold fields for charge injection and electroluminescence are compared, as are their ac time variations. In polyethylene, charge injection is detected prior to electroluminescence. But it is found that the two phenomena begin at the same electric field if the space-charge effect is taken into account in the estimation of the luminescence threshold. A discussion of the experimental results yields the picture of a recombination-controlled luminescence. The energy released during the radiative as well as the nonradiative recombination processes induce chemical damage of the dielectric.
The effect of implant energy, dose, and dynamic annealing on end-of-range damage in Ge+-implanted silicon
Authors: Jones K. S. , Venables D.
Published: July 2002

A study of the effect of Ge+ implantation energy, dose, and temperature on the concentration of atoms bound by the extrinsic end-of-range dislocation loops in Si 〈100〉 wafers is presented. Plan-view and cross-sectional transmission electron microscopy observations of both the as-implanted and annealed (900 °C, 30 min) morphology were made. The implant energy was varied from 30 to 150 keV, the dose varied from 2×1014 to 1×1016/cm2, and the temperature was varied by using three different wafer-cooling methods during the implantation. Increasing the implant energy, dose, or wafer temperature all resulted in significant increases (as much as two orders of magnitude) in the concentration of atoms bound by the end-of-range loops. Recent models have suggested that the concentration of end-of-range defects is related to the integrated recoil concentration beyond the amorphous/crystalline (a/c) interface. Correlation of trim-88 calculations with measured a/c depths show that the integrated recoil concentration beyond the a/c interface can explain both qualitatively and quantitatively the dependence of the ‘‘trapped interstitials’’ on the implant energy. However, this model can only qualitatively explain the temperature dependence of the defects, and it fails to account for the strong dose dependence when wafer heating is suppressed.
Time-resolved resonant absorption study of 532-nm laser-generated plumes over YBa2Cu3O7 targets
Authors: Cheung N. H. , Ying Q. Y. , Zheng J. P. , Kwok H. S.
Published: July 2002

The number densities n(t) of the atomic species produced by pulsed-laser (532-nm) interaction with YBaCuO targets were measured using time-resolved resonant absorption spectroscopy. At ∼5 J/cm2 fluence and 0.8 mm above the target, the peak n(t) ranged from 1013 to 1015 cm−3. The distributions of the normal z-velocity component could be modeled by Gaussian functions, in agreement with the theory of supersonic nozzle beams and the more recent theory of Knudsen layer formation. Such theoretical fits gave most probable z velocities in the km/s range and Mach numbers as high as 7. Ba-ion z velocities were better fitted by a 4:7 mix of fast (∼3-km/s) and slow (∼2-km/s) components.
The strength behavior of granulated silicon carbide at high strain rates and confining pressure
Authors: Klopp R. W. , Shockey D. A.
Published: July 2002

The dynamic Mohr–Coulomb behavior of silicon carbide (SiC) was inferred from symmetric pressure/shear plate-impact experiments which entail planar impact of two SiC plates inclined at 15° to the impact direction. The transverse velocity of the free rear surface of the target plate was recorded using a laser Doppler velocimeter system, and the experiments were simulated using a postulated viscoplastic constitutive model that accounts for comminution and dilatancy. Model parameters were varied until the computed and measured velocity histories agreed. The results indicate that comminution occurred soon after loading, and thus the experiment measures the behavior of granulated material at shear strain rates of ≊105 s−1 and mean stress ranging from 1 to 9 GPa. A friction coefficient of 0.23 was obtained, which is about half the value for quasistatic compression of precomminuted ceramic reported in the literature. The simulation results were strongly affected by the values chosen for the friction coefficient and yield strength parameters; changes in the dilatancy, rate-sensitivity, and strain-hardening parameters had a lesser effect.
Study on polished and etched surfaces of polar (111) CdTe by x-ray photoelectron spectroscopy and grazing-incidence x-ray diffraction
Authors: Wu T. B. , Chen J. S. , Chiang C. D. , Pang Y. M. , Yang S. J.
Published: July 2002

Several etchants have been applied to polar (111)Cd and (111)Te surfaces of CdTe. Induced surface layers were analyzed by x-ray photoelectron spectroscopy and grazing-incidence x-ray diffraction for studying compositions, chemical states, and crystalline phases of respective layers. A bromine/methanol etch led to a layer composed of mainly tellurium oxides on both (111) surfaces. Oxidation depth, however, was larger at the (111)Te side. Etching with HCl subsequently removed the oxides. A film made of crystalline tellurium was, however, produced with the thickness being larger on the (111)Te surface than on the other surface. A fairly thick layer consisting of TeO2 and crystalline Te for etching with N solution (H2O2:H2O:HF=2:2:3 v/v), formed on both surfaces with the cadmium having been severely depleted, especially on the (111)Te surface.
Schottky barriers of various metals on Al0.5Ga0.5As0.05Sb0.95 and the influence of hydrogen and sulfur treatments on their properties
Authors: Polyakov A. Y. , Stam M. , Milnes A. G. , Bochkarev A. E. , Pearton S. J.
Published: July 2002

Schottky barriers of Au, Al, and Sb on n- and p-type layers of Al0.5Ga0.5As0.05Sb0.95 have been studied. The Schottky barriers are high for Au (1.3 eV) and Al (1.2 eV) deposited on n-type material and very low for these metals on p-type layers. The behavior of Sb is unique with the barrier heights being 0.6–0.7 eV for both n- and p-type AlGaAsSb. The reason for the surface Fermi-level pinning for Au and Al could be related to a predominance of Ga-antisite–type native acceptors at the surface, which is not the case for Sb. Sulfur treatment of the surface is shown to decrease the barrier height for Au and to increase greatly the photosensitivity of Au Schottky diodes. The same effect is observed after treatment in a hydrogen plasma. In the latter case, changes in the Schottky barrier height are correlated with passivation of native acceptors in the bulk of the Al0.5Ga0.5As0.05Sb0.95.
Shapes of completely wetted two-dimensional powder compacts for applications to sintering
Authors: Schön J. Christian , Frost Richard , Chu Maggie , Lawson Jamie , Salamon Peter
Published: July 2002

We discuss the equilibrium shapes associated with complete wetting of two-dimensional solids. We neglect effects due to incomplete wetting or disjoining pressure and argue that such neglect is a good approximation for a description of homogeneous, solid-state sintering. The examples treated are building blocks for describing sintering processes. Analytical formulas are derived that describe the filling of various prototypical cavities which can be combined to yield extended realistic systems. The intricate consequences of the requirement of global equilibrium are discussed including questions of bridge formation and competition between different regions.
Excitation of guided elastic wave modes in hollow cylinders by applied surface tractions
Authors: Ditri John J. , Rose Joseph L.
Published: July 2002

The problem of the generation of guided elastic wave modes in infinite hollow circular cylinders by loading applied to the boundaries of the cylinder, apart from being an interesting problem in itself, has important applications in the field of nondestructive evaluation. Hollow cylinders are commonly used in the nuclear industry in heat exchangers and hence must be inspected for defects regularly to ensure continued safe operation. An exact, closed-form solution is given for the amplitude with which any propagating waveguide mode is generated due to the application of prescribed (time harmonic) surface tractions. Instead of using classical integral transform techniques to solve the problem, the normal mode expansion technique is used. In this technique, analogous to the expansion of a function in terms of an orthogonal (and complete) set of functions, the fields generated in the cylinder due to the application of the surface loading are expanded in terms of the normal modes of the cylinder. The general results are then specialized to loading configurations of practical importance in nondestructive testing.
Interstitial modification of rare-earth intermetallics
Authors: Skomski R. , Murray C. , Brennan S. , Coey J. M. D.
Published: July 2002

Interstitial modification of R2Fe17Zx is studied with R=Y, Sm, and Z=N, C, B, Si, and S. Equilibrium interstitial concentrations are calculated using a lattice gas model. For gas–solid reaction a low solubility is obtained at high temperatures, whereas a solid–solid reaction is predicted to yield R2Fe17Z1.5 in the high-temperature limit. Theoretical results are compared with data on Sm2Fe17Cx produced by solid–solid reaction at 500 °C. Volume expansions up to 4.8% were obtained, which corresponds to x≂2. The concentrations of interstitial boron and silicon are much lower.
Quantitative correlation of phase structure with the magnetic moment in rf sputtered Fe-N films
Authors: Gao C. , Doyle W. D. , Shamsuzzoha M.
Published: July 2002

Single-layer Fe-N films were deposited onto DC biased glass substrates at room temperature by reactive rf magnetron sputtering in an N2-Ar atmosphere. The Ar pressure was fixed at 6 mTorr and the properties were investigated as a function of N2 flow rate (R). X-ray diffraction and transmission electron diffraction were used to identify phases in the films. At R=0, the saturation magnetic moment density σS measured in a vibrating-sample magnetometer (VSM) was 210 emu/g, within experimental error equal to the value for bulk α-Fe, and only a single phase with the bulk lattice constant of α-Fe was detected. At R=5 sccm, σS=227 emu/g, and an α-Fe(N) phase with a ∼1% expanded lattice constant was detected. At R=15 sccm, σS reached a maximum of 247 emu/g and x-ray and transmission electron diffraction gave clear evidence of the Fe16N2 phase in addition to α-Fe(N). At R=30 sccm, σS dropped to 196 emu/g, and the diffraction data showed α-Fe, α-Fe(N), and a significant fraction of Fe4N. The value of σS calculated from the volume fractions of each phase estimated from transmission electron microscopy statistical sampling of single grain diffraction quantitatively agreed, within the experimental error, with the measured value.
Structural properties of heteroepitaxial systems using hybrid multiple diffraction in Renninger scans
Authors: Morelhão S. L. , Cardoso L. P.
Published: July 2002

A method of characterizing heteroepitaxial structures using hybrid multiple diffractions (hybrid MD) which appear in the layer Renninger scans (RS) together with the normal MD features, is reported. The three beam surface MD cases are used to provide high intensity and structural sensitivity. The RS peak measurements around the symmetry mirrors allow for the layer parallel lattice parameter determination. A simulation program was developed in order to account for the influence of the wavelength, incident beam divergence, sample mosaic spread, and substrate/layer lattice misorientation in the correct position and profile of the RS peaks. GaAs/Si samples with different layer thicknesses have been analyzed as an application of the method.
Strain determination in InxGa1−xAs/GaAs strained-layer superlattices by photomodulated reflectance
Authors: Inoki C. K. , Lemos V. , Cerdeira F. , Vásquez-López C.
Published: July 2002

A series of Raman and photoreflectance measurements was performed on several InxGa1−xAs/GaAs strained-layer superlattices of the same period but of different alloy compositions and substrate orientations. In the photoreflectance spectra the photon energy region containing the E1 and E1+Δ1 transitions of the GaAs barrier material is analyzed. Both types of measurements are used in order to estimate of the in-plane strain in these layers. The values obtained by both methods are in good mutual agreement, thus showing that photoreflectance is an effective method for strain determination.
Measurements in silane radio frequency glow discharges using a tuned and heated Langmuir probe
Authors: Lin Quixun , Lin Xuangying , Yu Yunpeng , Wang Hong , Chen Jiayi
Published: July 2002

A tuned and heated Langmuir probe has been used for combating the effect of radio frequency (rf) interference and contamination of the probe surface on the measurements in pure silane rf glow discharges. The measured probe I-V characteristic curves in the discharges were surprisingly reproducible over the period of 1 h. The non-Maxwellian electron energy distribution functions in pure silane rf discharges have been successfully measured using the probe. The mean electron energy and electron density in the discharges have been inferred from the electron energy distribution functions. The experimental results have been used for selecting the optimum parameters of discharge conditions for depositing an a-Si:H film with high quality at a high deposition rate of 1 nm/s.
Diffusion of bismuth and gold in nanocrystalline copper
Authors: Höfler H. J. , Averback R. S. , Hahn H. , Gleiter H.
Published: July 2002

Measurements of Bi and Au diffusion in nanocrystalline (n-) Cu and of Bi in copper thin films have been performed. The results show that (a) the diffusivity in n-Cu can be enhanced by more than ten orders of magnitude with respect to that in single-crystalline Cu. (b) Grain boundaries in n-Cu have a higher free energy and volume than conventional grain boundaries. (c) Relaxation can take place in n-Cu. (d) Diffusion measurements in n-materials represent a convenient means to determine thermodynamic properties such as grain boundary energies, solubilities, heats of segregation, and solution.
Determination of bulk states and interface states distributions in polycrystalline silicon thin-film transistors
Authors: Dimitriadis C. A. , Tassis D. H. , Economou N. A. , Lowe A. J.
Published: July 2002

The field-effect conductance activation energy Ea as a function of the gate voltage Vg is investigated for polycrystalline silicon thin-film transistors. An analytical expression for Ea is obtained for various models of the bulk and interface states. Using a computer minimization program to fit the experimental Ea vs Vg data with the theory, the energy distribution of the bulk states and the interface states are separated for nonhydrogenated and hydrogenated polycrystalline silicon thin-film transistors. In both cases, the bulk states have exponential band tails and a wide peak near the midgap and the interface states have an exponential distribution from the band edge.