bluuebunny/crossref_metadata_2025 huggingface dataset:
Highly stressed carbon film coatings on silicon: Potential applications
Authors: Sharda T. , Soga T. , Jimbo T. , Umeno M.
Published: July 2002

Highly stressed and strongly adhered nanocrystalline diamond films are grown on Si substrates by providing controlled and continuous bias current density (BCD) in microwave plasma chemical vapor deposition system. The stress and hence the curvature of the films on Si substrates can be varied and controlled by changing the BCD. We propose applications for such stressed films in the areas in which bent crystals are being used for various purposes, i.e., particle physics, x-ray optics, etc. These bent Si substrates can replace crystal benders, a cumbersome mechanical arrangement, used for bending Si in those areas.
Instantaneous collision complexes in molten alkali halides: Picosecond dynamics from low-frequency Raman data
Authors: Kirillov Sviatoslav A. , Pavlatou Evangelia A. , Papatheodorou George N.
Published: July 2002

The picosecond dynamics of molten alkali halides is discussed, and the low-frequency Raman spectra of molten LiCl, CsCl, and the LiCl–CsCl eutectic are fitted to the model enabling to obtain the times of vibrational dephasing, τV and vibrational frequency modulation τω. In terms of the Wilmshurst criterion [J. Chem. Phys. 39, 1779 (1963)] and using the data of NMR studies and molecular dynamics simulations, a conclusion is drawn that molten alkali halides cannot contain long-lived stable complexes with lifetimes greater than 10−8 s. The low-frequency Raman spectra of molten alkali halides and their mixtures probe the presence of instantaneous spatial configurations of MXn−n+1 type, where M+ is the alkali metal cation and X− is the halide anion existing in melts during the time intervals equal to the time of duration of collision of oppositely charged ions τd, which is less than 0.5 ps. This time is sufficient to a collision complex to execute several (at least one) vibrations. Vibrational dephasing and modulation processes elapse during this same time, thereby indicating the instantaneous nature of configurations in question. To discern between short-lived and long-lived complexes, we propose relations between the minimal damping time of the probe oscillator set equal to the half-period of vibration T/2, τV, τω, and τd, as well as the time between collisions τBC. The duration of an act resulting in the vibrational phase shift (or energy transfer) must be equal to (or longer than) the half-period of vibration of the probe oscillator, τV⩾T/2. The modulation time may vary from this same half-period of vibration or the time between collisions τBC to very long times, τω⩾T/2, τω⩾τBC. For short-lived complexes, the longest of two characteristic times describing the phase decay cannot exceed possible duration of collision, τω⩽τd, τV⩽τd. Cs-containing configurations follow this definition and therefore should be considered instantaneous short-lived collision complexes: their τV≈T/2∼0.1 ps, and τω≈τBC∼0.03 ps. Li-containing configurations appear to be relatively long-lived: their lifetimes could be associated with τω∼0.17 ps, which is several times longer than any other shortest possible characteristic time in the system (τBC∼0.026 ps or T/2∼0.05 ps). In light of these conclusions, an a priori assumption of autocomplex MX4n−4 anions and Mn+ cations as being structural elements of molten halides made in the so-called autocomplex model by Smirnov, Shabanov, and Khaimenov [Elektrohim. 2, 1240 (1966)] is discussed, and the autocomplexes are identified as instantaneous short-lived configurations detectable by the Raman method.
Evidence for transient kinetics of nucleation as responsible for the isothermal transformation of supercooled liquid into the glacial state of triphenyl phosphite
Authors: Hédoux Alain , Guinet Yannick , Foulon Michel , Descamps Marc
Published: July 2002

The first-order transformation of the supercooled liquid into the glacial state of triphenyl phosphite was investigated by differential scanning calorimetry (DSC) using two different thermal procedures. In the first procedure the transformation was analyzed by heating run DSC experiments. The glaciation process was interpreted as an aborted crystallization because of a high nucleation rate in a temperature range where the crystal growth is low. This relative separation between the nucleation- and growth-rate curves suggests that the glacial state can be described as a supercooled liquid–nanocrystalline mixed phase, characterized by a high-density nucleation which frustrates further crystallization. In a second procedure, DSC experiments were carried out during isothermal transformations of the supercooled liquid into the glacial state. The sigmoidal shapes of DSC isotherms are interpreted as transient kinetics of nucleation rather than nucleation and growth processes.
Electric dipole moments and polarizabilities of single excess electron sodium fluoride clusters: Experiment and theory
Authors: Rayane D. , Compagnon I. , Antoine R. , Broyer M. , Dugourd Ph. , Labastie P. , L’Hermite J. M. , Le Padellec A. , Durand G. , Calvo F. , Spiegelman F. , Allouche A. R.
Published: July 2002

In this article we present the first measurement of the electric dipole susceptibility of one excess electron NanFn−1 clusters. The static electronic polarizability and the permanent electric dipole of these clusters have been calculated with a one-electron model. Experimental values for the susceptibility are clearly related to the calculated values of the permanent dipole. The size evolution of the dipole moments is interpreted in terms of the interplay between the lattice and electron properties. This study outlines that the response of the cluster to the electric field cannot be fully understood with only equilibrium structure calculations and that the coupling between the permanent dipole and the vibrational motion of the cluster has to be taken into account.
A framework for predicting accuracy limitations in large-eddy simulation
Authors: Geurts Bernard J. , Fröhlich Jochen
Published: July 2002

The accuracy of large-eddy simulations is limited, among other things, by the quality of the subgrid parametrization and the numerical contamination of the smaller retained flow structures. We characterize the total simulation error in terms of the “subgrid-activity” s, which measures the relative turbulent dissipation rate (0⩽s⩽1) and the “subgrid resolution” r. This analysis is applied to turbulent mixing of a “Smagorinsky fluid” using a finite volume discretization of fourth order accuracy. On fixed coarse grids, i.e., at constant computational cost, the total simulation error decreases monotonically with filter width Δ for large s while for smaller s the total error may even increase with decreasing Δ. The corresponding modeling- and spatial discretization-error contributions are quantified at various resolutions.
Dynamics of heart rate
Authors: Kaplan Daniel T. , Talajic Mario
Published: July 2002

Heart rate oscillates on several different time scales and has long-term variability in the form of 1/f noise. The physiological control of heart rate is briefly reviewed, and several typical patterns of heart rate variability, in health and sickness, are described. Considered briefly are some possible dynamical mechanisms for heart rate variability.
Nonlinear effects of electrolyte diodes and transistors in a polymer gel medium
Authors: Hegedüs László , Kirschner Norbert , Wittmann Mária , Simon Péter , Noszticzius Zoltán , Amemiya Takashi , Ohmori Takao , Yamaguchi Tomohiko
Published: July 2002

The polarization curve of an acid–base interface in a hydrogel medium has a diode characteristic. Two of each such electrolyte diodes can be combined to give an electrolyte transistor. When a salt is added to the alkaline or to the acidic part of a reverse biased electrolyte diode, the current response is highly nonlinear. If the salt is added to the acidic side, even bistability can be observed. This bistability can generate complex oscillations in a base–acid–base electrolyte transistor. These nonlinear effects are studied experimentally and theoretically. While the nonlinear salt effect can be explained with the Nernst–Planck equations, to understand the bistable behavior further investigations are necessary.
Temperature transients in heavily doped and undoped silicon using rapid thermal annealing
Authors: Seidel T. E. , Lischner D. J. , Pai C. S. , Lau S. S.
Published: July 2002

Optical coupling by absorption and reflection of a wafer during rapid thermal anneals (RTA) determines the temperature transients during heating, and the behavior of thermally activated processes. It is shown experimentally that the heating rate and temperatures during the early phases of a RTA cycle depend on the doping of the wafer being heated. High doping is accompanied by high free carrier absorption which results in a relatively rapid increase in temperature. Differences of heating rates of 50 °C/sec and temperatures several hundred degrees centigrade are obtained in the first 5 sec of a RTA cycle for N+ and N− wafers and significant effects on the heating rate of heavily implanted wafers are also seen. Experiments were carried out using thermocouples, optical pyrometer and also by observing the lateral solid-phase growth of silicon on sapphire (SOS). A simple theoretical description is given for the enhanced heating rate for N+ and heavily implanted wafers.
Influence of nonstoichiometry on the Verwey transition in Fe3(1−δ)O4
Authors: Aragón R. , Shepherd J. P. , Koenitzer J. W. , Buttrey D. J. , Rasmussen R. J. , Honig J. M.
Published: July 2002

A systematic investigation of the dependence of the Verwey phase transition in magnetite on the metal-to-oxygen ratio, by thermomagnetic analysis of the initial permeability, reveals that the transition temperature is a maximum for pure stoichiometric Fe3O4 and is strongly depressed by departures from ideal stoichiometry. Homogeneous single crystalline samples were prepared by subsolidus controlled oxygen fugacity annealing at 1400 °C. Heat capacity measurements by relaxation calorimetry techniques indicate a drastic reduction in the entropy, as well as temperature, of the transition with departures from ideal stoichiometry. For high levels of cation deficiency, a second, instead of a first-order, transition is observed.
A Raman study of diamond anvils under stress
Authors: Hanfland M. , Syassen K.
Published: July 2002

First-order Raman spectra from selected volume elements of diamonds used as anvils in a gasketed high-pressure cell have been measured under applied load. The observed Raman profiles are interpreted on the basis of known isotropic and uniaxial stress effects in diamond-type materials. It is demonstrated that Raman spectroscopy provides in situ experimental information on the stress distribution within the anvils. Up to at least 300 kbar, the prominent high-frequency edge of the Raman profile measured at the center of the diamond tip face exhibits a linear dependence on pressure within the sample volume. The application of diamond anvil Raman scattering for pressure determination is discussed.
Effects of heat treatment on the composition and semiconductivity of electrochemically deposited CdTe films
Authors: Takahashi Makoto , Uosaki Kohei , Kita Hideaki , Suzuki Yoshikazu
Published: July 2002

Effects of heat treatments on crystalline diameter, composition, and semiconductivity of CdTe films deposited electrochemically at −0.35 V (vs Ag/AgCl) from an acidic solution containing 1-M CdSO4 and 1-mM TeO2 were studied. As-grown films contained free Te in addition to CdTe. The intensity of x-ray diffraction peaks due to CdTe became stronger by the heat treatment at higher temperatures but x-ray diffraction peak due to metallic Te disappeared at the films annealed above 350 °C in a He atmosphere. The intensity of Auger peaks due to Cd increased and that due to Te decreased by increasing the annealing temperature. The composition of the films annealed above 350 °C was close to that of pure CdTe. The similar effects were observed at the films annealed at 350 °C for various heat treatment periods in a He atmosphere. The change of semiconductivity of the films from p to n type was observed at the films annealed at enough high temperatures and for enough long time. The disappearance of free Te from the films was explained in terms of the temperature dependence of vapor pressure of Te2 from CdTe and metallic Te.
Anomalous redistribution of beryllium in GaAs grown by molecular beam epitaxy
Authors: Enquist P. , Wicks G. W. , Eastman L. F. , Hitzman C.
Published: July 2002

The purpose of this study is to investigate anomalous redistribution of beryllium (Be) in GaAs grown by molecular beam epitaxy (MBE). A concentration-dependent diffusion coefficient for Be is found from the substitutional-interstitial diffusion model. The importance of the generation of BeI from Ga point defects (vacancies or interstitials) in the diffusion process is also presented. Extremely rapid interstitial diffusion during growth, on the order of 30 μm in 1 h at 680 °C, has also been observed. This effect begins to occur for hole concentrations above 1019/cm3. Unintentional incorporation of Be into GaAs grown after closing the Be shutter is also presented. Consideration of the surface concentration of Be during MBE growth facilitates the explanation of this memory effect.
Approximate analytic solution for electronic wave functions and energies in coupled quantum wells
Authors: Yariv Amnon , Lindsey Chris , Sivan Uri
Published: July 2002

A formalism is developed which results in simple analytic expressions for the electron energy splittings and the wave functions in coupled quantum well structures of the type employed in new laser and transistor configurations. The limits of validity of the formalism are explored.
Thermodynamic and kinetic considerations on the equilibrium shape for thermally induced microdefects in Czochralski silicon
Authors: Tiller W. A. , Hahn S. , Ponce F. A.
Published: July 2002

Using thermodynamic and kinetic considerations, we explain the quasiequilibrium, morphological, and structural characteristics of thermally induced oxide precipitates in Czochralski silicon. A model based upon the formation of Frenkel defects at the silicon/silica interface is used to explain the experimentally observed precipitate shapes: 〈110〉 coesite rods, (100) vitreous silica discs, and silica polyhedra at low, intermediate, and high temperatures, respectively.
Stress in oxidized porous silicon layers
Authors: Barla K. , Herino R. , Bomchil G.
Published: July 2002

Stress was determined in oxidized porous silicon layers using x-ray diffraction to measure the substrate curvature. Stress is always compressive and its magnitude depends on oxide quality. The maximum value is reached when the oxide obtained from porous silicon is densified by a high-temperature process and is equivalent to standard thermal silicon dioxide. The stress magnitude decreases when oxide porosity increases. An increase in layer thickness is always observed when oxidation conditions lead to a porous oxide or when the initial porosity of the layer is lower than 56%, due to volumic expansion of silica relative to silicon, otherwise the thickness decreases.
Infrared optical properties of silicon oxynitride films: Experimental data and theoretical interpretation
Authors: Eriksson T. S. , Granqvist C. G.
Published: July 2002

Films of SiOxNy, with 0.25≲x≲2 and 0<y≲1.52, were prepared by reactive rf-magnetron sputtering. The composition was determined by Rutherford backscattering spectrometry. Spectrophotometric measurements were conducted in the 2.5–50 μm range, and the complex dielectric function ε was extracted by computation. We interpreted ε by considering the vibrational properties of five basic Si-centered tetrahedra, whose relative occurrence was given by the stoichiometry, and using the Bruggeman effective medium theory to average over the different tetrahedra. Theoretical and experimental data on ε were found to agree very well.
Deep levels in as-grown and Si-implanted In0.2Ga0.8As–GaAs strained-layer superlattice optical guiding structures
Authors: Dhar Sunanda , Das Utpal , Bhattacharya Pallab K.
Published: July 2002

Trap levels in ∼2-μm In0.2Ga0.8As (94 Å)/GaAs(25 Å) strained-layer superlattices, suitable for optical waveguides, have been identified and characterized by deep-level transient spectroscopy and optical deep-level transient spectroscopy measurements. Several dominant electron and hole traps with concentrations ∼1014 cm−3, and thermal ionization energies ΔET varying from 0.20 to 0.75 eV have been detected. Except a 0.20-eV electron trap, which might be present in the In0.2Ga0.8As well regions, all the other traps have characteristics similar to those identified in molecular-beam epitaxial GaAs. Of these, a 0.42-eV hole trap is believed to originate from Cu impurities and the others are probably related to native defects. Upon Si implantation and halogen lamp annealing, new deep centers are created. These are electron traps with ΔET=0.81 eV and hole traps with ΔET=0.46 eV. Traps occurring at room temperature may present limitations for optical devices.
Elastic calculation of the thermal strains and stresses of the multilayered plate
Authors: Yamada-Kaneta Hiroshi , Ogawa Tsutomu , Wada Kunihiko
Published: July 2002

An elastic calculation has been carried out on the thermal deformation strains, and stresses of a multilayered plate (MLP) which is composed of a circular substrate and thin films on it. The MLP is assumed to be constructed with no initial stresses at a temperature T0, and to be given a temperature change ΔT. In the calculation, the variation method has been utilized in such a manner as to minimize the total Helmholtz-free energy of the MLP by varying its shape of deformation. Without using the assumption of the plane stress state, a closed form solution has been obtained which determines the radius of curvature of the warpage, strains εij (i, j=x,y,z) and stresses τij in each layer by ΔT, αm the thermal expansion coefficient, Em the Young’s modulus, σm the Poisson’s ratio, and tm the thickness of each layer. The solution obtained has reproduced the plane stress state as an approximate description of the deformation. A solution in the case of the large radius MLP, where the effect of the shear strains has been taken into account, has also been shown. The small radius solution without the shear strain correction is in agreement with the earlier ones in the thin-film case, but the shear strain correction in the large radius solution exceeds, in magnitude, the film thickness correction included in the earlier solutions.
Fracto-emission accompanying adhesive failure between rocket propellent constituents
Authors: Dickinson J. T. , Jensen L. C. , Miles M. H. , Yee R.
Published: July 2002

In past studies, we have shown that fracto-emission (the emission of electrons, ions, photons, and neutral species) is observable during and following the fracture of simulated model propellent composites. In this paper we examine the electron, photon, and radio-frequency emissions from two situations that lead to interfacial or adhesive failure: the fracture of model propellents loaded with cyclotriethylene-trinitramine (RDX), and the peeling of binder material from macroscopic single crystals of RDX. Two binder materials are examined: hydroxy-terminated polybutadiene/isophorone diisocyanate and polyglycidyl azide prepolymer cured with a multifunctional isocyanate.
Breakdown mechanism of a laser triggered spark gap in a uniform field gap
Authors: Kawada Yukimitsu , Hosokawa Tatsuzo
Published: July 2002

Breakdown mechanism of a laser triggered spark gap was studied in a uniform field gap. The laser beam was focused on the electrode with positive and negative polarities, and vaporized metal plasma produced by the laser irradiation was used as a trigger. Our investigation shows that the breakdown characteristics in the uniform field are essentially different from those of a needle-to-plane gap, and also shows different characteristics under positive and negative polarities.
Statistical theory of hysteresis in ferroelectric materials
Authors: Boser O.
Published: July 2002

A theory is developed based on the model of random interactions between a large number of lattice defects and domain walls in ferroelectric materials. The theory gives the characteristic parameters of the hysteresis loop such as initial dielectric constant εi, Rayleigh constant ν, and coercive field Ec in terms of the microstructure of the domain walls and the number and interaction strength of the lattice defects. Results from large amplitude measurements on BaTiO3 doped with Fe show that a linear relationship exists between the dielectric constant and the ac field as required by Rayleigh’s law. In addition, the Rayleigh constant itself is inversely proportional to the Fe concentration as predicted by the model. Therefore, it is concluded that Fe as a dopant in BaTiO3 can act as obstacles to domain wall motion and control the characteristics of the hysteresis loop.
Effects of electron irradiation and annealing on ferroelectric vinylidene fluoride-trifluoroethylene copolymers
Authors: Daudin B. , Dubus M. , Legrand J. F.
Published: July 2002

It is shown that the Curie point of the ferroelectric vinylidene fluoride-trifluoroethylene copolymer can be shifted to the low temperatures by electron radiation. This effect was studied by in situ dielectric measurements as a function of the dose and of the irradiation temperature. An additional effect of the irradiation, in particular when performed at high temperature, was to noticeably decrease ε′. We also have studied annealing at temperatures around the melting point and shown that most of the irradiation damage was nonreversible and cumulative whereas part of it could be annealed. We have shown that it was apparently impossible to shift the Curie temperature lower than a limit temperature of the order of 0 °C. We discuss this effect and suggest the hypothesis of a competition with the glassy transition occuring in this temperature region.
Epitaxial growth of NbN on an ultrathin MgO/semiconductor system
Authors: Tonouchi Masayoshi , Sakaguchi Yoshiyuki , Kobayashi Takeshi
Published: July 2002

NbN epitaxial growth on an ultrathin MgO/semiconductor system was carried out by reactive sputtering. It was revealed that (100)-oriented NbN epitaxy was achieved on a (100)-oriented Si substrate by introducing a MgO buffer layer as thin as 5 Å at the interface. An interrupt-sputtering technique was newly conducted to obtain the epitaxial films, which were intermittently deposited by rf sputtering. A metal-insulator-semiconductor tunneling Schottky diode with epitaxial NbN was prepared using this technique, and evaluated in its current-voltage characteristics. Our study indicated that the NbN epitaxy mechansim can be explained by its growth on a (100) naturally oriented 5-Å MgO layer.
Neutron radiation effects in GaAs ion-implanted metal-semiconductor field-effect transistors
Authors: Janousek B. K. , Yamada W. E. , Krantz R. J. , Bloss W. L.
Published: July 2002

Neutron radiation investigations have been carried out on ion-implanted GaAs metal-semiconductor field-effect transistors (MESFETs). Device characteristics were measured before irradiation and following neutron irradiations with fluences from 5×1013 to 2×1015 n/cm2. At 5×1013 n/cm2, the device degradation is negligible, while at 2×1015 n/cm2 the threshold voltage shift was 0.7 V and the device transconductance was 30% of its original value. Degradation parameters needed to explain these results are larger than what has been previously reported; this discrepancy is, in part, due to the nonuniform doping profiles in the FET channel. The details of a new model applicable to nonuniform carrier distributions and to density dependent carrier removal rates are presented and results compared to those in the literature. A carrier removal rate of approximately 20 cm−1 is required to explain the degree of observed device degradation.
Diamond crystal growth by plasma chemical vapor deposition
Authors: Chang C.-P , Flamm D. L. , Ibbotson D. E. , Mucha J. A.
Published: July 2002

We have grown diamond crystals and polycrystalline diamond films from CH4/H2/O2 gas feeds in a simple, high-power density, 2450-MHz discharge tube reactor. Single-crystal growth rates over 20 μm/h have been achieved. The material has been analyzed using Raman spectroscopy, Auger spectroscopy, and x-ray diffraction. Control of nucleation is a major problem for growing sound films, and the high temperatures currently required for growth will limit applications. Oxygen additions were necessary to deposit diamonds over the range of feed composition we studied.
Vector Preisach hysteresis models (invited)
Authors: Mayergoyz I. D.
Published: July 2002

Isotropic and anisotropic vector Preisach models of hysteresis are described. The identification problems of fitting these models to experimental data are posed. It is shown that the above problems can be reduced to the solution of special integral equations. Analytical techniques for the solution of these integral equations are presented.
Ion-bombardment-enhanced grain growth in germanium, silicon, and gold thin films
Authors: Atwater Harry A. , Thompson Carl V. , Smith Henry I.
Published: July 2002

Grain growth has been studied in polycrystalline thin films of Ge, Si, and Au during ion bombardment. The phenomenon has been characterized by varying the ion dose, ion energy, ion flux, ion species, substrate temperature, and thin-film deposition conditions. Films bombarded with Si+, Ar+, Ge+, Kr+, and Xe+ exhibited enhanced grain growth which was weakly temperature dependent and proportional to the energy deposited in elastic collisions at or very near grain boundaries. The effect of these parameters on grain size and microstructure was analyzed both qualitatively and quantitatively using transmission electron microscopy. A transition state model describing the motion of grain boundaries during ion bombardment has been applied to the present experimental data. The results suggest that bombardment-enhanced grain growth may be due to thermal migration of bombardment-generated defects across the boundary. The calculated defect yield per incident ion was found to be directly related to enhanced grain growth, and was used to estimate the number of atomic jumps at the grain boundary per defect generated. Grain growth rates during bombardment and thermal annealing were related to their respective point defect populations.
High-temperature annealing characteristics of tungsten and tungsten nitride Schottky contacts to GaAs under different annealing conditions
Authors: Yu Kin Man , Jaklevic J. M. , Haller E. E. , Cheung S. K. , Kwok P. S.
Published: July 2002

We have systematically investigated the structural and electrical characteristics of thin-film tungsten and reactively sputtered tungsten nitride (WNx) Schottky contacts to GaAs under high-temperature annealing conditions (with annealing temperatures ranging from 700 to 850 °C) in an arsenic-overpressure and flowing nitrogen ambient with and without a silicon dioxide capping layer. Compositions of the WNx films measured by Rutherford backscattering spectrometry and proton resonant scattering techniques indicate a linear relationship between x and the nitrogen partial pressure during sputtering. Glancing angle x-ray diffraction studies revealed that for nonzero nitrogen partial pressure, the as-deposited films were amorphous, and after annealing these films converted to polycrystalline W2 N and W phases. A surface layer of W2 As3 phase was also observed after As-overpressure capless annealing and was believed to be the result of reactions between W and the ambient As gas. Electrical measurements showed that all WNx /GaAs contacts (with x=0–0.5) were thermally stable up to an annealing temperature of 850 °C. A diode edge effect is observed for WNx /GaAs diodes cap annealed in As overpressure at temperatures higher than 800 °C. The maximum achievable Schottky barrier heights for these contacts were found to be independent of the nitrogen content in the films but are influenced by the annealing conditions. We also explored the role played by nitrogen on the thermal stability and barrier height of the contacts.
Thermodynamic theory of PbZrO3
Authors: Haun M. J. , Harvin T. J. , Lanagan M. T. , Zhuang Z. Q. , Jang S. J. , Cross L. E.
Published: July 2002

A thermodynamic theory is presented to model the phase transitions and properties of lead zirconate. The free energy ΔG is expressed as a power series in terms of the ferroelectric polarization (Pi=Pai+Pbi) and antiferroelectric polarization (pi=Pai−Pbi) including all possible terms up to the sixth power, but only first-order cross coupling terms and couplings to elastic stress. Under the assumption that only the lowest-order coefficients of Pi and pi are linearly temperature dependent (Curie–Weiss behavior) and all other constants are temperature independent, experimental data are used to define the constants and permit calculation of ferroelectric and antiferroelectric free energies as a function of temperature. Use of the function to define the averaged dielectric permittivity at room temperature in the antiferroelectric phase gives a value of εR=120 in good agreement with recent microwave measurements. A simplified technique for modifying the function to explore solid solution with lead titanate is examined, and shown to lead to excellent agreement with the known phase diagram.
Low-temperature cadmium telluride homoepitaxy at high growth rates
Authors: Cody N. W. , Sudarsan U. , Solanki R.
Published: July 2002

Homoepitaxy of CdTe using ultraviolet photon-assisted metalorganic vapor-phase epitaxy has been investigated at 250 °C with dimethylcadmium and diethyltellurium as the precursor gases. Empirical relationships between film properties and the deposition parameters at high growth rates (> 4 μm/h) are examined.
The energy distribution of ions bombarding electrode surfaces in rf plasma reactors
Authors: Metze A. , Ernie D. W. , Oskam H. J.
Published: July 2002

A model is presented for the energy distribution of ions bombarding electrode surfaces in planar rf plasma reactors at low pressures, where collisions in the sheath may be ignored. Given the waveform for the voltage difference across the sheath adjacent to an electrode, the model predicts the ion bombardment energy distribution in the limits tr <1/f and tr ≫1/f, where tr is the transit time of the ions across the sheath and f is the frequency of the applied rf voltage. Utilizing sheath voltage waveforms from a previously published equivalent circuit model of a rf reactor [A. Metze, D. W. Ernie, and H. J. Oskam, J. Appl. Phys. 60, 3081 (1986)], the model shows that the ion bombardment energy distribution is bimodal and skewed toward lower ion bombardment energies. The model also demonstrates one of the mechanisms responsible for narrowing of the ion bombardment energy distribution with increasing rf frequency. These results are compared with experimental measurements.
Pt/Ti/p-InGaAsP nonalloyed ohmic contact formed by rapid thermal processing
Authors: Katz A. , Dautremont-Smith W. C. , Thomas P. M. , Koszi L. A. , Lee J. W. , Riggs V. G. , Brown R. L. , Zilko J. L. , Lahav A.
Published: July 2002

Nonalloyed ohmic contacts of Pt/Ti to 5×1018 cm−3 doped p-InGaAsP (λg =1.3 μm) have been fabricated by rapid thermal processing of sputtered and e-gun-deposited metallizations. While the former as-deposited had a rectifying characteristic, the latter showed ohmic behavior prior to any heat treatment, with a specific contact resistance of 4×10−3 Ω cm2. Rapid thermal processing at temperatures higher than 400 °C caused the formation of ohmic contacts for the sputtered metals also, but with the evaporated metals producing slightly lower contact resistance. The lowest specific contact resistance values of 3.6–5.5×10−4 Ω cm2 for evaporated and sputtered metallizations, respectively, were achieved in both cases as a result of heating at 450 °C for 30 s. These heating conditions produced only a limited reaction at the Ti/InGaAsP interface, which was sharper for the e-gun-deposited contact, but had a significant effect on the stresses in the Ti/Pt bilayer. In both the sputtered and electron gun evaporated samples, the stresses were inverted from tensile as-deposited to compressive with values of 2.4×109 and 1.0×109 dyn cm−2, respectively, as a result of the heat treatment.
Cathode spot phenomena in titanium vacuum arcs
Authors: Swift P. D. , McKenzie D. R. , Falconer I. S. , Martin P. J.
Published: July 2002

Investigations of cathode spot behavior on a titanium cathode in the presence of a variable magnetic field are presented. The cathode spot velocity as a function of magnetic field strength, arc current, and gas pressure has been determined using an optical technique, and the results have been compared with a number of available theories. The cathode spots have been investigated using a magnetic probe coil, and using both high-speed and conventional photography. The observations show that the motion of the spots is consistent with the presence of a positive space charge at the spot.
Numerical simulation of dynamic consolidation of a SiC fiber-reinforced aluminum composite
Authors: Williamson R. L. , Wright R. N. , Korth G. E. , Rabin B. H.
Published: July 2002

Dynamic consolidation of a SiC fiber-reinforced aluminum matrix composite resulting from the stress wave generated by an impacting stainless-steel plate has been simulated using a two-dimensional numerical model in which the aluminum and SiC are assumed to be infinite cylinders prior to consolidation. Impact velocities of 0.5, 0.75, and 1.0 km/s were considered in the simulations. For impact plate velocities greater than 0.5 km/s, bonding is predicted to occur between the aluminum cylinders by melting in the regions of greatest plastic flow. In the interstices that are filled by a SiC fiber there is less plastic flow and the maximum temperature is significantly reduced. Results of the simulation are compared with the microstructure of a composite formed using a stainless-steel impact plate with a velocity of 0.7 km/s to consolidate a close-packed array of aluminum wires which contained SiC fibers of the appropriate diameter to fill the interstices to approximate the geometry of the model. The predictions of the simulation with respect to the observed deformation and the location and extent of melting of the aluminum wires are in good agreement with the experiment.
Magnetic and electronic properties of Au/Fe superlattices and interfaces
Authors: MacLaren J. M. , McHenry M. E. , Crampin S. , Eberhart M. E.
Published: July 2002

The electronic and magnetic structure of AunFe(100) superlattices and interfaces are investigated with the layer Korringa–Kohn–Rostoker technique. Enhanced magnetism, over that of bulk bcc Fe, is observed on the Fe layer in all geometries studies. In the supercell geometry the magnetic moment decreases as the number of mediating Au layers is increased, reaching the same asymptotic value as obtained in the interface calculation. These results can be understood in terms of very weak Fe-Au coupling in these systems. The Fe minority-hole states are mainly d states with character orthogonal to the Fe plane, suggesting a tendency for out-of-plane (perpendicular) magnetic anisotropy.
The properties of a-C:H films deposited by plasma decomposition of C2H2
Authors: Zou J. W. , Schmidt K. , Reichelt K. , Dischler B.
Published: July 2002

Diamondlike a-C:H films have been deposited by plasma decomposition of C2 H2. 50 samples were prepared with a systematic variation of the deposition parameters: the substrate bias voltage was between −100 and −1400 V and the C2 H2 gas pressure was between 4×10−4 and 2.6×10−1 mbar. The following properties of the films were measured: the density by Rutherford backscattering, the total concentration of hydrogen by elastic recoil detection, the bonding ratio sp3 /sp2 by infrared spectroscopy, the internal stress by the bending beam method, and the hardness with a Knoop microhardness tester. It has been shown that the hardness and other mechanical properties cannot be correlated to the average carbon coordination number mc. This is because mc is calculated under the assumption of a homogenous single-phase model, which does not seem to be justified. It is demonstrated that the mechanical properties can be explained by the application of a void model.
Differences in Auger electron spectroscopy and x-ray photoelectron spectroscopy results on the bonding states of oxygen with β-SiC(100) surfaces
Authors: Mizokawa Yusuke , Nakanishi Shigemitsu , Komoda Osamu , Miyase Sunao , Diang Hong Shen , Wang Chang-Heng , Li Nan , Jiang Chao
Published: July 2002

Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) measurements have been carried out on the β-SiC(100) surface simultaneously. The AES and XPS results differ significantly in the bonding state of oxygen for both as-grown surfaces and as-etched surfaces. Differences in the same carbon-KLL Auger spectra induced by both electron beams and x rays from the same surface suggest that the electron beam used in AES removed considerable amounts of carbonaceous species in the contaminant layers. Furthermore, comparison of the Si 2p and Si LVV spectra revealed that the SiOx (x<2) species on the surface was also reduced by the electron beam used in AES. Although previous AES results have shown that both as-grown and as-etched surfaces of β-SiC(100) were covered with only submonolayer coverage of oxygen bonded to Si atoms, with no detectable carbonaceous contaminants, this work shows that the real surfaces, however, are covered with several tens of contaminant layers, including SiO, CC, CH, and CO bonds.
Direct determination of absolute monolayer coverages of chemisorbed C2H2 and C2H4 on Si(100)
Authors: Cheng C. C. , Wallace R. M. , Taylor P. A. , Choyke W. J. , Yates J. T.
Published: July 2002

A convenient kinetic uptake method has been employed to determine the absolute saturation monolayer coverage of C2H2 and C2H4 on a Si(100)(2×1) surface. Such measurements are important for postulating the structure of the chemisorbed hydrocarbon species on this surface. The saturation surface coverage for both chemisorbed molecules at 105 K is 2.5(±0.2)×1014 molecules/cm2 . This number is consistent with 1 hydrocarbon molecule per Si dimer site at monolayer coverage when the role of surface defects on Si(100) is considered. A di-σ bonding model for both molecules is proposed at saturation coverage.
Lattice and grain boundary self-diffusion in Ni2Si: Comparison with thin-film formation
Authors: Ciccariello J. C. , Poize S. , Gas P.
Published: July 2002

The Ni2Si lattice and grain boundary self-diffusion parameters have been studied using radiotracers 63Ni for Ni diffusion, 68Ge for Si diffusion, conventional sectioning techniques, and bulk specimens. The results obtained show that Ni diffuses faster than Ge(Si) in the lattice (and in the grain boundaries) of Ni2Si, in agreement with the structure of this silicide. The activation energies for Ni lattice and grain boundary diffusion are respectively 2.48 eV (measured between 650 and 910 °C) and 1.71 eV (530–710 °C). These values are comparable to those obtained in pure metals of similar melting temperature. They suggest that Ni diffuses on its own sublattice by a vacancy mechanism. Grain boundary diffusion in this intermetallic compound appears as a very efficient process for mass transport at low temperature. A quantitative comparison with the kinetic of formation of Ni2Si (by solid state reaction between a Ni film and a Si substrate) indicates that the growth of thin films is controlled by the diffusion of Ni along the silicide grain boundaries. This mechanism explains the rapidity of the formation and its low activation energy (≊1.6 eV).
Crystal size dependence for impact initiation of cyclotrimethylenetrinitramine explosive
Authors: Armstrong R. W. , Coffey C. S. , DeVost V. F. , Elban W. L.
Published: July 2002

The dislocation pile-up avalanche model is used to explain the crystal size dependence for hot spot-controlled initiation of chemical decomposition in cyclotrimethylenetrinitramine crystals subjected to drop-weight impact testing. Deformation-induced temperature rises, hot spot sizes, and lifetimes are related to previously reported values for direct thermal decomposition. A reasonable chemical reaction yield is estimated from available kinetic data.
On the bandwidth of a short traveling wave tube
Authors: Schächter Levi , Nation John A. , Kerslick Graham
Published: July 2002

We analyze the bandwidth of a short traveling wave tube. When no beam is present the bandwidth is proportional to the group velocity and inversely proportional to the total length of the system. The bandwidth of the gain factor, the imaginary part of the wave vector, is mainly determined by the beam current. However, regardless of the current intensity, the gain factor is identically zero for frequencies which, in the empty structure, correspond to phase velocities larger than the speed of light. The bandwidth of a short amplifier, is narrowed relative to the ‘‘cold’’ bandwidth by the same amount the amplitude of the growing wave increases, provided that the frequency and the current allow the growing wave to be dominant. This relation is verified with experimental data and good agreement is found.
Mössbauer studies of YTi(Fe1−xMx)11 (M=Co and Ni)
Authors: Li Z. W. , Zhou X. Z. , Morrish A. H.
Published: July 2002

57Fe Mössbauer spectra of YTi(Fe1−xMx)11 (M=Co and Ni) have been studied. The average isomer shifts increase monotonically. The average quadrupole splittings have a sudden change for YTi(Fe1−xCox)11 between x=0.4 and 0.6. It appears that a spin reorientation occurs over this composition range. Both hyperfine fields for the three sites and the average field increase at first, and then decrease with increasing Co or Ni concentration. The maximum of the average hyperfine field is 27.7 T at x=0.6 for YTi(Fe1−xCox)11 and 24.1 T at about x=0.2 for YTi(Fe1−xNix)11. The average moments of Co and Ni atoms are 1.3(1)μB and 0.6(1)μB, respectively, obtained from the formula μ = (1 − x)μFe + xμT.
Liquid source metalorganic chemical vapor deposition of aluminum from triethylamine alane
Authors: Gross M. E. , Fleming C. G. , Cheung K. P. , Heimbrook L. A.
Published: July 2002

Low-pressure metalorganic chemical vapor deposition (MOCVD) of aluminum using triethylamine alane (TEAA) is reported. This liquid source combines the chemical advantages of adduct precursors such as solid trimethylamine alane (TMAA), with the processing and handling advantages of liquid precursors such as triisobutyl aluminum (TIBA). High-purity Al films were deposited on TiN and thin in situ evaporated Cu and Ti films, which serve as activators for nucleation of Al. The electrical resistivities of the Al films on TiN were close to the 3 μΩ cm of sputtered Al. In the case of depositions on Cu, the Cu diffuses readily into the Al and serves to improve the electromigration resistance of the latter. The Al deposition rates using TEAA are 2–4 times those using TIBA at 250 °C, although the TEAA process is not fully optimized at this point and further work is needed to improve the film morphologies.
Studies of resonant and preresonant femtosecond degenerate four-wave mixing in unoriented conducting polymers
Authors: Wong K. S. , Han S. G. , Vardeny Z. V.
Published: July 2002

Degenerate four-wave mixing with femtosecond time resolution is used to measure the magnitude and transient response of the third-order nonlinear optical susceptibility χ(3) (ω;ω,−ω,ω) at 620 nm in nonoriented conducting polymers including polydiacetylene, polyacetylene, polyaniline, polydiethynylsilane, polythiophene, and polythiophene derivatives. Resonant and nonresonant excitations influence the magnitude and transient response of χ(3). The electronic response is instantaneous for preresonant excitation, but for resonant excitation it has ultrafast and slow components which illustrate photoexcitation dynamics. The magnitude of χ(3) for all of the polymers is in the range from 10−10 to 5×10−8 esu depending on the energy difference between the laser excitation and the polymer absorption maximum.
Study of silver diffusion into Si(111) and SiO2 at moderate temperatures
Authors: Nason T. C. , Yang G.-R. , Park K.-H. , Lu T.-M.
Published: July 2002

Diffusion of Ag from epitaxial layers into Si(111) is studied under an anneal of 450–500 °C using the secondary ion mass spectrometry depth profiling tool. The measurements yielded values of the diffusion constant (0.80–1.6 × 10−15 cm2/s) which fall short of literature values extrapolated from higher-temperature Arrhenius laws. Diffusion of Ag into SiO2 was also measured directly. The observed diffusivity of 1.0 × 10−15 cm2/s is a factor of ∼ 105 smaller than expected from previous determinations of the diffusivity of Ag+ in SiO2 obtained from anneals in forming gas. The discrepancy may be due to changes in the local electrostatic environment in the absence of acceptor levels in SiO2 from dissolved gases which are absent in vacuum.
Corrosion of NdFeB permanent magnet materials
Authors: Warren G. W. , Gao G. , Li Q.
Published: July 2002

NdFeB is an important class of new magnetic materials, however corrosion resistance is a serious concern and literature on the electrochemical behavior of NdFeB is scarce. This paper reports the results of an electrochemical investigation of the corrosion behavior of sintered NdFeB magnets obtained from three manufacturers. Linear polarization (cyclic voltammetry) experiments were conducted in aqueous solutions ranging in pH from 0.7 to 13.5. A limited degree of passivation was observed in all solutions which is believed to be due to the formation of a complex Fe-Nd oxide and/or hydroxide film. The presence of a small amount of chloride ion, 10 to 100 ppm, shows only a slight effect, but higher concentrations (1000 ppm) cause a total breakdown in passivity and a dramatic increase in anodic current. The cathodic potential sweep shows an abrupt and unusual oxidation process, giving rise to an oxidation peak not commonly seen. This peak may result from dissolution of the film or preferential attack of intergranular phases.
Magnetic viscosity of single domain magnetite particles
Authors: Worm H.-U. , Jackson M. , Banerjee S. K. , Schlinger C. M.
Published: July 2002

The acquisition of viscous magnetization has been measured on a single domain magnetite sample in the temperature range 80 to 330 K and in applied fields up to 1540 Oe. Based on Néel’s single domain theory, we have calculated the field and temperature dependence of viscous acquisition by numerical two-dimensional integration, using experimentally determined volume and switching field distributions. Predicted and experimental viscosity coefficients do not match, with especially strong discrepancies below the Verwey transition. The experimental acquisition coefficient is larger below the transition than at room temperature, even though the corresponding switching field distributions are nearly identical. Thus we cannot explain single domain viscosity by switching field and volume distributions alone, and we suspect that stress plays a prominent role.