bluuebunny/crossref_metadata_2025 huggingface dataset:
Mathematica package for analysis and control of chaos in nonlinear systems
Authors: Gutiérrez José Manuel , Iglesias Andrés
Published: July 2002

In this article a symbolic Mathematica package for analysis and control of chaos in discrete and continuous nonlinear systems is presented. We start by presenting the main properties of chaos and describing some commands with which to obtain qualitative and quantitative measures of chaos, such as the bifurcation diagram and the Lyapunov exponents, respectively. Then we analyze the problem of chaos control and suppression, illustrating the different methodologies proposed in the literature by means of two representative algorithms (linear feedback control and suppression by perturbing the system variables). A novel analytical treatment of these algorithms using the symbolic capabilities of Mathematica is also presented. Well known one- and two-dimensional maps (the logistic and Hénon maps) and flows (the Duffing and Rössler systems) are used throughout the article to illustrate the concepts and algorithms. © 1998 American Institute of Physics.
Concentration-dependent absorption and photoluminescence of n-type InP
Authors: Bugajski M. , Lewandowski W.
Published: July 2002

The absorption and photoluminescence of n-type InP are examined as a function of free-carrier concentration. It is found that concentration dependent band gap at 300 K is given by the empirical relation: Eg =1.344−(2.25±0.25)10−8n1/3 (eV). The photoluminescence results are interpreted using the model taking into account nonparabolicity of the conduction band. Calculations of the peak position and photoluminescence line shape for band-to-band transitions are performed. Both the band filling as well as band tailing due to the Coulomb interaction of free carriers with ionized impurities and band shrinkage due to the exchange interaction between free carriers are considered in order to properly account for observed features of photoluminescence spectra. It is proposed that room temperature photoluminescence linewidth can be used for determination of the free carrier concentration in n-type InP. This method can be used to estimate free carrier concentration ranging from 1016 to 1020 cm−3.
Trap generation during low-fluence avalanche-electron injection in metal-oxide-silicon capacitors
Authors: Hsu Charles C. H. , Pan Sam C. S. , Sah Chih-Tang
Published: July 2002

Trap generation during low-fluence avalanche-electron injection (AEI) in metal-oxide-silicon capacitors (MOSC’s) with different fabrication processing cycles was investigated. Injection gate voltages from 45 to 65 V for an oxide of 1000 Å thickness were used to simulate hot-electron effects in oxidized silicon under transistor operation conditions. Experimental results indicate that more negatively charged traps are generated in wet oxide than dry oxide. Different trap-generation phenomena in poly-Si- and aluminum-gate MOSC’s were observed. The midgap voltage shift of aluminum-gate MOSC during AEI is not appreciably dependent on the magnitude of the peak AEI voltage, while that of poly-Si-gate MOSC has a strong dependence. The generation rate of interface states in aluminum-gate MOSC is much smaller than that of poly-Si-gate MOSC. The results are interpretable by the hydrogen model.
Computation of electrical conditions inside wire-duct electrostatic precipitators using a combined finite-element, finite-difference technique
Authors: Kallio Gregory A. , Stock David E.
Published: July 2002

An accurate and efficient numerical scheme is presented for calculating electrical conditions inside wire-duct electrostatic precipitators. A Galerkin finite-element method with quadratic interpolation is employed in solving Poisson’s equation to yield the electric potential solution. A backward difference method is utilized to compute the space-charge density from the continuity equation. The two methods are iteratively applied until convergence criteria for electric potential and current density are met. Computed potential and electric field values show good agreement with analytic solutions and experimental measurements. Comparisons between the present scheme and a finite-difference scheme show that the finite-element method offers distinct advantages in predicting the electrical characteristics of precipitators.
The nature of electrically inactive antimony in silicon
Authors: Nylandsted Larsen A. , Pedersen F. T. , Weyer G. , Galloni R. , Rizzoli R. , Armigliato A.
Published: July 2002

Supersaturated solutions of substitutional, electrically active Sb in 〈100〉 silicon single crystals have been obtained by ion implantation, followed by short-duration incoherent-light annealing. Substitutional and nonsubstitutional fractions have been studied as functions of implanted dose and anneal temperature by Rutherford backscattering and channeling techniques, transmission-electron microscopy, Hall-effect and resistivity measurements (combined with layer removal), and Mössbauer spectroscopy. The maximum electrically active concentration, which can be incorporated on undisturbed substitutional sites, is found to be 4.5×1020 Sb/cm3 for 700 °C annealing. Upon further annealing, the supersaturated solution is reduced and approaches the Trumbore solubility value at temperatures of about 1100 °C. The Sb going out of solution is shown for the first time to be created in two different surroundings: Sb is predominantly found in Sb-vacancy complexes for low doses and low annealing temperatures and in Sb precipitates for high doses and/or high annealing temperatures. Complete agreement is found between substitutional fractions derived from Mössbauer spectroscopy and electrically active fractions from Hall-effect measurements, whereas the substitutional fractions from channeling measurements are significantly higher. The experiments are not conclusive as to whether this difference is due to the fraction of Sb in Sb-vacancy complexes or in coherent Sb precipitates.
Phase retardation dependent optical response time of parallel-aligned liquid crystals
Authors: Wu Shin-Tson
Published: July 2002

Correlation between the director reorientation and its consequent optical response time of the parallel-aligned nematic liquid crystals was investigated. This optical decay time is found to depend on the phase retardation introduced by the liquid-crystal layer. To verify theory, dependence of optical decay time on three parameters—liquid-crystal thickness, wavelength, and birefringence (through temperature effect)—was demonstated. Taking the phase retardation dependence into consideration, the optical decay time measurement technique is a simple, convenient, and accurate method for characterizing the ratio of rotational viscosity and splay elastic constant of liquid crystals.
Theory and simulation of high-power microwave generation in a magnetically insulated transmission line oscillator
Authors: Lemke Raymond W. , Collins Clark M.
Published: July 2002

The magnetically insulated transmission line (MITE-LINE) oscillator is an electron beam diode comprised of a field emitting cathode and a corrugated anode. The device is similar to a linear magnetron except that the insulating magnetic field is self-generated. The self-insulating property makes this device a robust high-power microwave tube. Using the thin-beam approximation we have derived a dispersion relation for a cylindrical MITE-LINE oscillator. The dispersion relation is used to predict frequency and growth rate of the microwave generating instability. Analytical results are compared with ccube particle simulations.
A two-dimensional model of dc glow discharges
Authors: Boeuf J.-P.
Published: July 2002

A two-dimensional self-consistent analysis of a dc glow discharge is presented. The model is based on a macroscopic description of the electron and ion kinetics coupled with Poisson’s equation for a given set of boundary conditions. This numerical method has been used to analyze the basic properties of a dc glow discharge, with a particular emphasis on radial effects. It is shown that the radial electric field at the plasma-sheath boundary tends to draw electrons towards the center of the negative glow and positive ions away from it; the stability of the discharge in the normal regime is due to this radial electric field. A quantitative and self-consistent study of the transition between the normal and abnormal regimes of a dc glow discharge is presented.
Studies on high-density nickel zinc ferrite and its magnetic properties using novel hydrazine precursors
Authors: Srinivasan T. T. , Ravindranathan P. , Cross L. E. , Roy R. , Newnham R. E. , Sankar S. G. , Patil K. C.
Published: July 2002

Nickel zinc ferrites have been very widely used in the high-frequency applications. In our present study we have prepared Ni1−x Znx Fe2O4 (0≤x≤1) using novel hydrazinium metal hydrazinecarboxylate precursors. High densities (∼99%) have been obtained for all the ferrites sintered at relatively low temperatures, 1100 °C, in comparison with the conventional method (≥1200 °C). The variation of magnetic properties like magnetic moment, Curie temperature, and permeability with zinc concentration have been studied.
Generalization of Snoek’s limit for modeling initial permeability of magnetic materials
Authors: Bush Gary G.
Published: July 2002

Permeability relates the magnetic field intensity in a magnetic material to the resulting flux density. The initial part of the permeability extending from dc fields to the radio-frequency fields of a few hundred megahertz is due to domain wall displacement. A spin resonance occurs due to the presence of an anisotropy field, with the result that the permeability drops rapidly at frequencies above this resonance. It has been observed experimentally that the variation of the ratio of the magnetic oxides in a given ferrite crystal structure changes the initial permeability and the resonance frequency. The product of the resonance frequency and the initial permeability is approximately constant, i.e., Snoek’s limit. Thus, if the resonance frequency increases, the initial permeability decreases in inverse proportion. Experimental results in the literature confirm the variation of the initial permeability with composition. A modification of the equations for Snoek’s limit suggest that a variable quasistatic magnetic field would have the same effect on initial permeability as a variation in composition. This effect has been verified experimentally for magnesium-zinc ferrite samples in a brass coaxial transmission line with an applied dc magnetic field of 0–500 Oe. The initial permeability of many magnetic materials can thus be modified in the VHF range by the application of an externally applied magnetic field.
Metastable bismuth-iron alloy films synthesized with ion mixing and magnetron cosputtering
Authors: Chen Qing-Ming , Cui Fu-Zai , Fan Yu-Dian , Li Heng-De
Published: July 2002

Amorphous phases in the completely immiscible Bi-Fe system were formed for the first time by ion mixing and magnetron cosputtering. In the ion mixing experiments, multilayer samples of Bi and Fe were bombarded with energetic Fe ions. In the planar magnetron cosputtering, mixture films were prepared by simultaneously sputtering Bi and Fe atoms onto the substrates kept at liquid-nitrogen temperature. Using Rutherford backscattering spectrometry and transmission electron microscopy, the compositions and phases of the thin alloy films were identified. The amorphous alloy formed by ion mixing is Bi50Fe50. The composition of the amorphous alloy films formed by magnetron cosputtering is in the range of 40–60 at. % Bi.
Large grain polycrystalline silicon by low-temperature annealing of low-pressure chemical vapor deposited amorphous silicon films
Authors: Hatalis Miltiadis K. , Greve David W.
Published: July 2002

The crystallization of undoped amorphous silicon films deposited by low-pressure chemical vapor deposition in the temperature range 580–530 °C and annealed from 550 to 950 °C has been studied by transmission electron microscopy. The average grain size of the crystallized films depends on the annealing temperature and the deposition conditions. The nucleation rate of new grains during annealing decreases as the deposition temperature decreases from 580 to 545 °C and/or when the deposition rate increases. The final grain size is also influenced by the annealing temperature with the largest grain size obtained at low annealing temperatures. A simple model is described which explains the dependence of grain size on the annealing temperature. An average grain size of 500 nm has been obtained in a 200-nm film deposited at 545 °C and annealed at 550 °C.
Characterization of filament-assisted chemical vapor deposition diamond films using Raman spectroscopy
Authors: Buckley R. G. , Moustakas T. D. , Ye Ling , Varon J.
Published: July 2002

Results are presented on a Raman study of diamond films prepared by the filament-assisted chemical vapor deposition technique from a methane-hydrogen gas mixture. It is shown that Raman spectroscopy is a useful probe of both the phase of carbon present and of the quality of the diamond component in the films. The study entailed varying the total gas pressure, but holding the ratio of CH4 to H2 constant. It is clearly demonstrated that as the pressure is decreased, the density of defects within the diamond phase increases. The increase in defect density as the pressure is lowered leads eventually to disordered forms of carbon. This result can be understood in terms of the relatively higher electron and ion fluxes at the substrate for films prepared at low pressure.
The hardness and Young’s modulus of amorphous hydrogenated carbon and silicon films measured with an ultralow load indenter
Authors: Jiang X. , Reichelt K. , Stritzker B.
Published: July 2002

With an ultralow load indenter the hardness H and the Young’s modulus E of amorphous hydrogenated carbon and silicon films, prepared under different conditions, were determined. The values of the hardness of a-C:H, corrected for the elastic recovery, are about 1/3 of the values measured by the Knoop method. The results show that the hardness of a-C:H and a-Si:H are proportional to Young’s modulus [(H/E)C =0.115, (H/E)Si =0.093]. In previous works a proportionality of H and E for metal and metal-metalloid glasses, respectively, already has been found.
Neutron-diffraction study of YTiCo11 and YTi(Co0.5Fe0.5)11
Authors: Yang Ying-chang , Kong Lin-shu , Sun Hong , Yang Ji-lian , Ding Yong-fan , Zhang Bai-shen , Ye Chun-tang , Jin Lan
Published: July 2002

The compounds YTi(Fe1−xCox)11 form complete solid solutions (0≤X≤1) all of which crystallize in the ThMn12-type tetragonal structure. The substitution effects of Fe with Co on saturation magnetization and Curie temperature have been investigated. A neutron-diffraction study has been carried out on YTiCo11 and YTi(Co0.5Fe0.5)11. A strong preferential site occupation for Co and Ti atoms is observed. A detailed analysis of crystallographic and magnetic arrangement is presented.
Study of interface wall energy in exchange-coupled double-layer film
Authors: Tokunaga T. , Taguchi M. , Fukami T. , Nakaki Y. , Tsutsumi K.
Published: July 2002

Recently, exchange-coupled multilayer films have been investigated intensively for the magneto-optical recording medium. We studied the interface wall energy density (σw) in the exchange-coupled double-layer TbFeCo films which were prepared by the dc-sputtering method. The composition of the first layer was Tbx(Fe85Co15)100−x (x=14.0–35.0), and that of the second layer was fixed at the compensation composition of Tb23.8(Fe85Co15)76.2. The magnitude of σw stored in the boundary was determined by the shift field of the minor hysteresis loop of the first layer measured with VSM. It was found that σw depended on the Tb content of the first layer. As a result, σw was correlated with the perpendicular anisotropy (Ku), and well explained by the formula, σw∝(Ku)1/2. We can treat the interface wall energy practically as Bloch wall energy; however, σw was determined by the magnetic properties of both layers.
Chemical physics of fluorine plasma-etched silicon surfaces: Study of surface contaminations
Authors: Brault P. , Ranson P. , Estrade-Szwarckopf H. , Rousseau B.
Published: July 2002

F2 plasma-Si(100) surface interaction experiments have been conducted to understand basic mechanisms of surface modifications. Surface analysis has been investigated using x-ray photoelectron spectroscopy and nuclear reaction analysis. The experiments show deep penetration of fluorine into silicon and limitation of etching caused by oxide layers coming from contamination of the plasma by removal of oxygen from alumina walls of the reactor. Biasing of the silicon substrate enhanced carbon contamination.
Optical absorption in undoped yttrium aluminum garnet
Authors: Innocenzi M. E. , Swimm R. T. , Bass M. , French R. H. , Kokta M. R.
Published: July 2002

Room-temperature optical absorption over a large dynamic range is reported for single- crystal undoped yttrium aluminum garnet (Y3Al5O12 or YAG). Absorption results are presented for the energy ranges 1.8 to 3.0 and 4.5 to 6.5 eV. For this work, ultraviolet (UV) absorption measurements were performed on four different boules of Czochralski-grown undoped YAG. Absorption features were observed at 4.8 and 5.6 eV which can be attributed, at least in part, to trace impurity concentrations. Along with the UV measurements, calorimetric absorption results are presented at several laser wavelengths in the visible and near infrared (IR). The calorimetric results suggest a value of 1.5×10−3 cm−1 for the absorption coefficient of undoped YAG in the red and near IR. From the combination of UV and calorimetric measurements, an empirical estimate of the absorption coefficient from the visible to the UV is presented for undoped YAG. In addition to the absorption spectra, detailed chemical analyses and sample histories are given for the as-grown optical quality YAG utilized herein.
Investigation of electronic properties of gallium sulfide single crystals grown by iodine chemical transport
Authors: Micocci G. , Rella R. , Siciliano P. , Tepore A.
Published: July 2002

Photoinduced-current-transient-spectroscopy and space-charge-limited-current measurements have been performed on n-type GaS single crystals grown from vapor by iodine chemical transport. Three electron traps located at 0.17, 0.45, and 0.56 eV from the conduction band have been detected, with a thermal capture cross section of 2×10−19, 5×10−14, and 8×10−13 cm2, respectively. Moreover, by Hall-effect measurements, an impurity hopping conduction with an activation energy of 0.12 eV has been evidenced in the range of temperatures between 220 and 320 K.
Energy-loss probabilities for electrons, positrons, and protons in condensed matter
Authors: Ashley J. C.
Published: July 2002

An ‘‘optical-data’’ model for describing the dielectric response function of a medium was introduced earlier to predict energy-loss rate and inelastic mean free path for low-energy (<10-keV) electrons and positrons. The model is used here to calculate energy-loss probabilities for electrons, positrons, and protons for use in Monte Carlo calculations or other theoretical simulations. Results for the cumulative interaction probabilities are illustrated using optical data for carbon.
Input-dependent Preisach model and hysteretic energy losses
Authors: Friedman G. , Mayergoyz I. D.
Published: July 2002

Expressions for hysteretic energy losses are derived by using the ‘‘input-dependent’’ Preisach model of hysteresis. These expressions are valid for arbitrary (not only periodic) variations of magnetic field.
A synopsis of surface acoustic wave propagation on {100}-cut 〈110〉-propagating gallium arsenide
Authors: Hunt William D. , Kim Yoonkee , Fliegel F. M.
Published: July 2002

We present the results of a series of calculations predicting surface acoustic wave (SAW) beam profile propagation in the 〈110〉 direction on {100}-cut GaAs. These calculations utilize an experimentally verified angular spectrum of plane waves diffraction theory computer program with experimentally determined GaAs slowness surface data. These data are presented in such a way that they should be particularly useful to designers of acoustic charge transport (ACT) devices, by enabling appropriate choice of ACT channel widths for given delay line lengths and SAW transducer apertures. Further, these calculations show that ACT filters which rely on apodization to determine tap weights will suffer transfer function distortion, alternatively interpreted as reduction of dynamic range, compared to ACT filters in which charge sensing is accomplished by taps extending fully across the channel and employing tap weighting external to the channel; this problem is observed to grow in acuteness with delay line length.
New structures from exfoliated MoS2
Authors: Miremadi Bijan K. , Cowan Timmothy , Morrison S. Roy
Published: July 2002

The restacking of exfoliated, single-layer MoS2 has led to many different structures. Here we describe the preparation of two new structures, of interest for their quite different properties. One is a ‘‘house-of-cards’’ structure, where the single layers restack with the circumference of one attracted to the basal plane of another layer, and with repulsion between basal planes, leading to a very open structure. The other structure is a highly oriented film, where, as a suspension of single layers dries, the layers deposit themselves parallel to a substrate. The house-of-cards structure is of interest because of its chemical activity in adsorption and catalysis, and the film may be of interest for its anisotropic optical and electrical behavior, or its application as a low friction coating.
Impact excitation in ZnS-type electroluminescence
Authors: Bringuier E.
Published: July 2002

In this paper, a simple model is proposed for the impact excitation of luminescence centers in insulating layers under a high electric field (ZnS-type electroluminescence). We first examine the available descriptions of high-field electronic transport in wide-gap semiconductors and the lucky-drift model is chosen for our purpose. As for the luminescence center, the impact excitation cross section in the Born approximation is used. Next, the impact probability of an electron and the impact excitation rate are calculated analytically. The results are compared with existing experimental data: Special attention is paid to the well-known ZnS:Mn case, for which good agreement is obtained. The general picture is that the quantum yield is weak and that the electrons responsible for the impact phenomenon are drifting in the field, not ballistic. Conclusions are drawn for blue-emitting centers and new phosphor materials. It is further suggested that impact excitation can, as well as impact ionization, serve as a test of high-field transport theories.
Optical detection of corona discharges in SF6, CF4, and SO2 under dc and 50-Hz ac voltages
Authors: Casanovas A. M. , Casanovas J. , Dubroca V. , Lagarde F. , Belarbi A.
Published: July 2002

The emission spectra resulting from corona discharges generated under dc and 50-Hz ac voltages in SF6, N2, SOF2, SO2F2, S2F10, CF4, SO2, and C2F3Cl3, and mixtures of these gases with SF6 were investigated in the 220–900-nm wavelength range for gas pressures between 30 and 400 kPa. Characteristic emissions were ruled out only for N2, SF6, CF4, SO2, and C2F3Cl3. We also observed that small concentrations of N2, CF4, or SO2 can be detected in SF6 from the analysis of light emitted between 250 and 420 nm.
The structural and optical properties of a-SiNx:H prepared by plasma-enhanced chemical-vapor deposition
Authors: Lin Kang-Cheng , Lee Si-Chen
Published: July 2002

Hydrogenated amorphous silicon nitride (a-SiNx:H) films have been prepared by plasma-enchanced chemical-vapor deposition with a mixture of SiH4 and NH3 at a substrate temperature of 250 and 300 °C. The properties of these films have been investigated using x-ray diffraction, infrared absorption, photoluminescence, and electron probe microanalysis. From the x-ray-diffraction measurement, it is found that the short-range order of a-SiNx:H with a basic unit of 4.31 Å appears when the nitrogen-to-silicon ratio in the film exceeds 0.75 at a substrate temperature of 300 °C. In the infrared-absorption measurement, the sample was annealed repeatedly at various temperatures (300–800 °C) to identify the molecular unit responsible for each absorption peak. It is found that part of the infrared-absorption bands between 870 and 1100 cm−1 are caused not by the absorption but by the reflection of infrared radiation due to reststrahlen effect. The absorption peak at 840 cm−1 is assigned to the isolated N in the Si-host network, whereas the peak at 885 cm−1 is assigned to a local bonding arrangement involving a terminal N-H group attached to the amorphous Si network, Si-NH-Si. The transverse optical phonon of crystalline Si3N4 is found to peak at 870 cm−1. Two peaks are observed in photoluminescence experiments when the mole fraction of ammonia in gas phase is smaller than 0.8 indicating the inhomogeneity of the a-SiNx:H films. The higher-energy peak is visible in the red.
‘‘Giant’’ magnetoresistance in sputtered Co–Ag alloy thin films
Authors: Barnard J. A. , Hossain S. , Parker M. R. , Waknis A. , Watson M. L.
Published: July 2002

‘‘Giant’’ magnetoresistance ratios have been measured at room temperature in single layer Co–Ag alloy thin film. The effect has been observed over a broad range of Co concentrations with a maximum as-deposited MR ratio of ≥22% (at x=0.38). The effects of two annealing sequences have also been studied. The MR ratio generally increases on annealing reaching a maximum of ∼28% (at x=0.38) after the second anneal.
Effect of surface hydrogen on metal-diamond interface properties
Authors: Tachibana T. , Glass J. T. , Nemanich R. J.
Published: July 2002

Schottky barrier formation of metal contacts deposited on diamond (111) and (100) surfaces was investigated. Three different metals (Au, Al, and Ti) were studied because of their different chemical reactivity with C, i.e., Au being a nonreactive metal, Al a weak carbide-forming metal, and Ti a strong carbide former. Both fully H-terminated, unreconstruted (1×1) surfaces and H-desorbed, reconstructed (2×2)/(2×1) surfaces with higher density of surface states were examined. Surface structures were determined via low-energy electron diffraction, and the change of surface band bending (SBB) and the interface chemistry during the contact formation were monitored using x-ray photoelectron spectroscopy. On the reconstructed surfaces, the SBB was independent of metal thicknesses. This was attributed primarily to Fermi-level pinning by the high density of surface states on the reconstructed surfaces. On the other hand, the surface-state densities were much lower on the unreconstructed surfaces and thus the Fermi level was not as strongly pinned as that on the reconstructed surfaces. When the metal coverage became large (≳0.5 monolayer) on these unreconstructed surfaces, the charge transferred from the metal contacts to the diamond, the Fermi level moved upward in the band gap and the SBB increased. However, even on the unreconstructed surfaces where the density of pinning states were low, the SBB for thick metal contacts did not correlate to metal properties such as work function and/or electronegativity. Regardless of the state of the diamond surfaces, it was also important to consider the interface chemistry (chemical reactivity of the metal on diamond) to understand the change of the SBB after annealing the metal contacts.
A comparison between wave propagation in water-saturated and air-saturated porous materials
Authors: Albert Donald G.
Published: July 2002

The classical Biot theory [J. Acoust. Soc. Am. 28, 168 (1956)] predicts the existence of three waves that can propagate in a fluid-saturated porous material: A fast compressional wave, a slow compressional wave, and a shear wave. Through use of this theory, propagation characteristics within water-filled and air-filled materials were compared in the 10 Hz–100 kHz band. Numerical calculations show that the ratio of fluid to solid motion for the slow compressional wave is around 2 in water-filled sand, but greater than 300 in air-filled sand. In addition, calculations of plane wave transmission from a fluid into a fluid-saturated porous solid were investigated. The calculations show that when the fluid is water, nearly all of the incident energy is transferred to the reflected wave and to the transmitted fast compressional wave that is traveling mainly in the solid frame. Only a slight frequency dependence occurs in the energy transfer. When the fluid is air, however, the interaction of the waves with the boundary becomes strongly dependent upon frequency, and most of the incident energy is transferred to the reflected wave and to the transmitted slow compressional wave traveling mainly in the pores. These theoretical results justify the different approaches used to treat reflections from porous materials in underwater and aeroacoustics. For reflections, air-filled soil or snow can be approximately modeled as a modified fluid (ignoring motion in the frame) rather than as a viscoelastic solid (ignoring motion in the pores), the approximation commonly used to model saturated undersea sediments.
Method for thermal diffusivity measurements based on photothermal deflection
Authors: Bertolotti M. , Liakhou G. , Li Voti R. , Michelotti F. , Sibilia C.
Published: July 2002

The thermal diffusivity measurement through pulsed photodeflection in a modified collinear configuration is presented and discussed; comparison between theory and experiment is also shown.
A new ferromagnetic oxide La2MnIrO6: Synthesis, characterization, and calculation of its electronic structure
Authors: Demazeau G. , Siberchicot B. , Matar S. , Gayet C. , Largeteau A.
Published: July 2002

A methodology is reported for defining a class of ferromagnetic oxides, based on theoretical and experimental considerations. Starting from phenomenological superexchange theory, a perovskite oxide with composition La2MnIrO6 was proposed to order ferromagnetically. Self-consistent band-structure calculations are used to check the magnetic order and the synthesis and characterization subsequently followed. An agreement between theoretical and experimental results was found.
Effects of the addition of small amounts of Al to copper: Corrosion, resistivity, adhesion, morphology, and diffusion
Authors: Ding P. J. , Lanford W. A. , Hymes S. , Murarka S. P.
Published: July 2002

The properties of thin films of Cu with 1 at. % Al are explored. As-deposited films of Cu(1 at. % Al) oxidize orders of magnitude more slowly than do those of pure Cu. After Cu(1 at. % Al) films are annealed in Ar at 400 °C for 30 min, very thin protective layers of aluminum oxide form on the surface. These thin oxide layers stop further oxidation of the copper. Cu(1 at. % Al) films also adhere better to SiO2 than do films of pure copper. Unlike pure Cu, films of Cu(1 at. % Al) remain microscopically smooth after anneals at temperatures up to 700 °C. In addition, Cu(1 at. % Al) films show no diffusion of Cu (as measured by Rutherford backscattering spectroscopy) into SiO2 at temperatures up to 700 °C. The addition of Al to Cu does increase its resistivity by about 2 μΩ cm per 1 at. % Al, but a possible procedure to avoid this problem is proposed.
Radius and current scaling of argon K-shell radiation
Authors: Deeney C. , LePell P. D. , Failor B. H. , Meachum J. S. , Wong S. , Thornhill J. W. , Whitney K. G. , Coulter M. C.
Published: July 2002

Argon gas puff experiments on a 3–4 MA generator show that the K-shell x-ray yield is optimized for a 2.5 cm initial diameter and 110 ns implosion time. By varying the driver current, the K-shell yield varies from 13 to 18 kJ following a current to the fourth power scaling. Comparisons of these experimental data to one-dimensional radiation-hydrodynamic simulations with and without enhanced transport coefficients show that the measured K-shell yields exceed those predicted based solely on kinetic energy input.
Study of the Raman spectrum of nanometer SnO2
Authors: Zuo Jian , Xu Cunyi , Liu Xianming , Wang Changsui , Wang Chengyun , Hu Yuan , Qian Yitai
Published: July 2002

The Raman spectra of nanometer-sized particles of SnO2 (3–90 nm) at room temperature are reported. In the Raman spectra of the particles of SnO2, which are quite different from that of single-crystal SnO2, there appear two new characteristic peaks, and their intensities decrease gradually with the increase of crystal size. It is concluded that the new peaks can be explained by the surface phonon modes of nanometer SnO2, consequently there is a relation between the structures of surface layers and bulk. It is believed that it is possible to determine the exact positions of atoms in surface layers of some nanometer crystals from their laser Raman spectra.
Injection-level-dependent recombination velocities at the Si-SiO2 interface for various dopant concentrations
Authors: Glunz Stefan W. , Sproul Alistair B. , Warta Wilhelm , Wettling Wolfram
Published: July 2002

Measurements of the dependence of the effective surface recombination velocity Seff at the Si-SiO2 interface on light-induced carrier concentration are presented. Contactless lifetime measurements by modulated free-carrier IR absorption with additional bias light and by photoconductance decay measurements of samples immersed in HF were used to extract Seff for varying illumination levels. For various dopant concentrations the measured surface recombination velocities are compared with theoretical predictions calculated using an extended Shockley–Read–Hall formalism for Si-SiO2 interfaces. Good agreement was obtained. The consequences for solar cell performance and lifetime measurement techniques are discussed.
Rapid thermal annealing induced reactions of Co/GaAs thin film structures: Studies using mass and energy dispersive recoil spectrometry
Authors: Hult Mikael , Whitlow Harry J. , Östling Mikael , Andersson Margareta , Andersson Yvonne , Lindeberg Ingrid , Ståhl Kenny
Published: July 2002

GaAs samples with a 100-nm-Co overlayer that had been subjected to rapid thermal annealing for 60 s at temperatures of 400–650 °C were analyzed using mass and energy dispersive recoil spectrometry. Separate characterizations of C, O, Co, Ga, and As depth distributions were performed. Both Ga and As had migrated to the surface at anneal temperatures higher than 450 °C. In a sample annealed at 650 °C, a clear enrichment of Ga in the outer 35 nm was observed. The composition for various depth intervals was determined for different temperatures. From Arrhenius plots, apparent activation energies were estimated to be about 0.6 eV for phase formation and 1.3 eV for diffusion. X-ray diffraction indicated that CoGa and CoAs phases were present in all the annealed samples. Scanning electron microscopy showed the surface to be reticulated after heat treatment, with grain growth at higher temperatures.
Redistribution of dissolved oxygen concentration under magnetic fields up to 8 T
Authors: Ueno S. , Iwasaka M. , Kitajima T.
Published: July 2002

The influence of static magnetic fields on the behavior of oxygen dissolved in an aqueous solution was studied in order to clarify the interaction mechanism of dynamic movements of dissolved oxygen with magnetic fields and to broaden the basic understanding of biological effects of magnetic fields. A horizontal type of superconducting magnet with a bore 100 mm in diameter was used. A cylindrical chamber filled with distilled water was exposed to magnetic fields up to 8 T and a gradient of 50 T/m. The spatial distribution of oxygen concentration dissolved in water was measured by a dissolved oxygen meter. A clear redistribution of oxygen concentration was observed, and the dissolved oxygen concentration increased more than 10% around the center of the magnet.
Spin polarization of gold films via transported (invited)
Authors: Johnson Mark
Published: July 2002

The spin injection technique has been adapted to a thin-film geometry. Measurements of the spin-coupled voltage Vs as a function of film thickness d result in a determination of the spin diffusion length δs =√DT1 with D the electron diffusion constant, in polycrystalline gold films. The conduction electron spin relaxation time T1 is found to be 4.6±2.5×10−11 s, for the temperature range 4 K<T<70 K. The magnitude of Vs is large enough to suggest device applications. In a three-terminal trilayer device, an electric current Ie biasing a thin permalloy film injects spin-polarized electrons into gold films of thickness 100 nm≤d≤5.1 μm, and induces a nonequilibrium magnetization M̃. A second permalloy film detects the bipolar, spin-coupled voltage eVs=βM̃/χ, where β is the Bohr magneton, χ the Pauli susceptibility and e the electron charge. The sign of Vs depends on the relative orientation of the magnetizations of the permalloy films. In the thin limit, d<δs, the magnitude of the spin-coupled impedance Zs=Vs/Ie scales inversely with d. In the thick limit, d≳δs, Zs is exponentially diminished.
Microstructure of cubic boron nitride thin films grown by ion-assisted pulsed laser deposition
Authors: Medlin D. L. , Friedmann T. A. , Mirkarimi P. B. , Rez P. , Mills M. J. , McCarty K. F.
Published: July 2002

A microstructural study of boron nitride films grown by ion-assisted pulsed laser deposition is presented. Fourier transform infrared spectroscopy, electron-energy-loss spectroscopy, and electron-diffraction measurements indicate that within the ion-irradiated region on the substrate, the film consists of a high fraction of the cubic phase (cBN) with a small amount of the turbostratic phase; outside the irradiated region, only the turbostratic phase is detected. Conventional and high-resolution electron microscopic observations show that the cBN is in the form of twinned crystallites, up to 40 nm in diameter. Particulates, formed by the laser ablation process, reduce the yield of cBN in the irradiated regions by shadowing local areas from the ion beam. The films exhibit a layered structure with an approximately 30-nm-thick layer of oriented turbostratic material forming initially at the silicon substrate followed by the cBN. The observations of oriented turbostratic material and twinned cBN crystallites are discussed in relation to a previously proposed compressive stress-induced mechanism for cBN synthesis by ion-assisted film deposition.
Magnetic properties of anisotropic Nd(Fe,Mo)12Nx powders
Authors: Yang Ying-chang , Liu Zun-xiao , Zhang Xiao-dong , Cheng Ben-pei , Ge Sen-lin
Published: July 2002

Anisotropic magnets based on Nd(Fe,Mo)12Nx nitrides were prepared by a milling process. Particle size dependence of the coercivity has been investigated. The optimizing size which accompanies the highest coercive force was examined by transmission electron microscopy. A coercive force iHc of up to 6.2 kOe, and a maximum energy product (BH)max of up to 12.0 MG Oe were obtained. The mechanism of the coercivities is discussed with a comparison of the powders prepared by mechanical alloying. The variation of coercive force as a function of temperature is reported.
Heat transfer between two metallic surfaces at small distances
Authors: Xu J.-B. , Läuger K. , Möller R. , Dransfeld K. , Wilson I. H.
Published: July 2002

In scanning thermal microscopy, but also in scanning tunneling microscopy, the thermal contact between tip and sample plays an important role. The heat transfer across the vacuum gap between two parallel metallic surfaces, if the gap width is decreased below several microns, has been investigated. At these distances propagating electromagnetic modes die out but simultaneously a transfer of nonpropagating surface modes across the gap becomes more probable. The heat conductance of the vacuum gap should become distance dependent and larger than that given by the Stefan–Boltzmann law; however, the experimental results and theoretical considerations indicate that the heat transfer, based on the discussed proximity mechanism, is very small, smaller than predicted by the theory of Polder and Van Hove [Phys. Rev. B 4, 3303 (1971)].
Transversely varying thickness modes in quartz resonators with beveled cylindrical edges
Authors: Tiersten H. F. , Zhou Y. S.
Published: July 2002

The equation for transversely varying thickness modes in doubly rotated quartz resonators is applied in the analysis of trapped energy resonators with beveled cylindrical edges. The coefficients appearing in the planar differential operator are written as a sum of a mean or isotropic part plus a deviation. Asymptotic eigensolutions for the nearby isotropic case are obtained for the cylindrical beveled resonator. The resonant frequencies for the actual anisotropic case are obtained from an equation for the perturbation in eigenfrequency from the isotropic solution. A lumped parameter representation of the admittance, which is valid in the vicinity of a resonance, is obtained. Calculated results are presented for a few beveled AT- and SC-cut quartz resonators and the influence of the radius of curvature of the contour is exhibited.
Ferroelectric properties in epitaxially grown BaxSr1−xTiO3 thin films
Authors: Abe Kazuhide , Komatsu Shuichi
Published: July 2002

Induced ferroelectricity was observed in epitaxially grown BaxSr1−xTiO3 (BST) thin films with thicknesses of about 220 nm. The BST films with various Ba content were deposited at 600 °C on Pt/MgO substrates, by radio frequency magnetron sputtering with double targets, BaTiO3 and SrTiO3. The epitaxial growth of the BST films was confirmed with x-ray-diffraction and reflection high-energy electron-diffraction analyses. The D–E hysteresis curve and the Curie temperature shift confirmed the BST films with Ba content x≥0.44 had ferroelectricity at room temperature. The mechanism of the ferroelectricity appearance was discussed in relation to the elongation of the c axis in the thickness direction, caused by lattice mismatch between Pt and BST.
Mechanism of carrier transport through a silicon-oxide layer for 〈indium-tin-oxide/silicon-oxide/silicon〉 solar cells
Authors: Kobayashi H. , Ishida T. , Nakato Y. , Mori H.
Published: July 2002

The mechanism of carrier transport through a thin silicon-oxide layer for 〈spray-deposited indium-tin-oxide (ITO)/silicon-oxide/Si〉 solar cells has been studied by measurements of the dark current density as a function of the thickness of the silicon-oxide layer, together with the observation of transmission electron micrographs. Cross-sectional transmission electron micrography shows that a uniform silicon-oxide layer with the thickness of ∼2 nm is present between ITO and Si when the ITO film is deposited on a flat Si(100) surface at 450 °C. The dark current density under a depletion condition strongly depends on the thickness of the silicon-oxide layer. It is concluded from these results that quantum mechanical tunneling is the dominant mechanism for the charge carrier transport through the silicon-oxide layer. On the other hand, when the ITO film is deposited on a mat-textured Si surface at the same temperature, a nonuniform silicon-oxide layer is formed, with ITO penetrating into the silicon-oxide layer in the top and valley regions of the pyramidal structure. By raising the deposition temperature of the ITO film on the flat Si(100) surface to 500 °C, the silicon-oxide layer becomes also nonuniform. For these diodes with the nonuniform silicon-oxide layer, the carrier transfer probability is less dependent on the thickness of the silicon-oxide layer, leading to the conclusion that minute channels of ITO are present in the silicon-oxide layer and charge carriers transfer through the channels. The photovoltage is decreased by the presence of the minute channels, with its magnitude depending on the density of the channels. The conversion efficiency of the 〈ITO/silicon-oxide/n-Si(100)〉 solar cells is unchanged upon illumination for 1000 h. The good cell stability is attributed to the well-crystallized ITO film which effectively suppresses diffusion of oxygen from the air and to low reactivity of ITO with Si at room temperature.
Infrared study of amorphous B1−xCx films
Authors: Shirai Koun , Emura Shuichi , Gonda Shun-ichi , Kumashiro Yukinobu
Published: July 2002

Amorphous boron carbide (a-B1−xCx) is believed to have an icosahedron-based random network. In this paper, vibrational properties of a-B1−xCx films are studied by IR and Raman spectra, placing particular emphasis on the interpretation of the most prominent 1100-cm−1 band associated with the B–C bond. The 1100-cm−1 band appears in both IR and Raman spectra, and the frequency variation and the intensity as a function of the C content are examined, together with evaluation of the absolute absorption coefficients. Within the framework of the impurity-induced vibration theory, the 1100-cm−1 band is characterized. The estimation of the force constants by the observed frequencies leads to a conclusion that the vibration can be classified as an extrinsic and preferably a local mode. This vibration is well described as the stretching mode of a localized two-center bond between the B and C atoms. In this sense, the C atom in amorphous B1−xCx is not regarded as a network constituent. The frequency shift with the C content supports this conclusion. The absorption intensity of this band exhibits large values for the transverse effective charge of a-B1−xCx. A numeric estimation shows that most part of the observed transverse effective charge comes from the localized charges of the C impurity. This mechanism of the effective charge is consistent with the above argument of frequency. The intrinsic vibrations of the amorphous boron network based on the icosahedron structure reside over the range from 400 to 1000 cm−1 with a small peak at 800 cm−1.
The role of fast argon ions and atoms in the ionization of argon in a direct-current glow discharge: A mathematical simulation
Authors: Bogaerts A. , Gijbels R.
Published: July 2002

A model is developed for a direct-current glow discharge in argon by a combination of a hybrid Monte Carlo fluid model of electrons and ions in the entire discharge and a Monte Carlo model of ions and fast atoms in the cathode dark space, in which fast ion and atom impact ionization are incorporated. The relative importance of these processes, compared to electron impact ionization is investigated, as a function of distance from the cathode and at different discharge conditions. It is found that they are dominant close to the cathode, and that they gain importance with increasing voltages. With the incorporation of these processes it was possible to predict current–voltage relations which are in excellent agreement with experiment. Also, the length of the cathode dark space, as a function of pressure and voltage, is calculated; the results agree with Aston’s empirical formula.