bluuebunny/crossref_metadata_2025 huggingface dataset:
Dielectric constant of boron carbon nitride films synthesized by plasma-assisted chemical-vapor deposition
Authors: Sugino Takashi , Etou Yoshihiro , Tai Tomoyoshi , Mori Hirotaro
Published: July 2002

Polycrystalline boron carbon nitride (BCN) films are synthesized at various temperatures by plasma-assisted chemical-vapor deposition. BCN films are characterized by x-ray photoelectron spectroscopy, transmission electron microscopy, and transmission electron diffraction. The dielectric constant is estimated from the accumulation region of capacitance–voltage (C–V) characteristics of Au/BCN/p-Si samples. Reduction in the crystal grain size and increase of the amorphous region of the BCN film are observed with decreasing growth temperature. The dielectric constant is found to decrease with decreasing growth temperature. A dielectric constant as low as 2.4 is achieved for the BCN film.
Resonant plasma heating below the cyclotron frequency
Authors: White Roscoe , Chen Liu , Lin Zhihong
Published: July 2002

Resonant heating of a magnetized plasma by low frequency waves of large amplitude is considered. It is shown that the magnetic moment can be changed nonadiabatically by a single large amplitude wave, even at frequencies normally considered nonresonant. Two examples clearly demonstrate the existence of the resonances leading to chaos and the generic nature of heating below the cyclotron frequency. First the classical case of an electrostatic wave of large amplitude propagating across a confining uniform magnetic field, and second a large amplitude Alfvén wave, propagating obliquely across the magnetic field. Waves with frequencies a small fraction of the cyclotron frequency are shown to produce significant heating; bringing, in the case of Alfvén waves, particles to speeds comparable to the Alfvén velocity in a few hundred cyclotron periods. Stochastic threshold for heating occurs at significantly lower amplitude with a perturbation spectrum consisting of a number of modes. This phenomenon may have relevance for the heating of ions in the solar corona as well as for ion heating in some toroidal confinement fusion devices.
GeV acceleration in tapered plasma channels
Authors: Sprangle P. , Peñano J. R. , Hafizi B. , Hubbard R. F. , Ting A. , Gordon D. F. , Zigler A. , Antonsen T. M.
Published: July 2002

To achieve multi GeV electron energies in the laser wakefield accelerator (LWFA) it is necessary to propagate an intense laser pulse long distances in a plasma without disruption. A three-dimensional envelope equation for the laser field is derived that includes nonparaxial effects, wakefields, and relativistic nonlinearities. In the broad beam, short pulse limit the nonlinear terms in the wave equation that lead to Raman and modulation instabilities cancel. Long pulses (several plasma wavelengths) experience substantial modification due to these instabilities. The short pulse LWFA, although having smaller accelerating fields, can provide acceleration for longer distances in a plasma channel. By allowing the plasma density to increase along the propagation path electron dephasing can be deferred, increasing the energy gain. A simulation example of a GeV channel guided LWFA accelerator is presented. Simulations also show that multi-GeV energies can be achieved by optimally tapering the plasma channel.
Nanometer-scale mechanical imaging of aluminum damascene interconnect structures in a low-dielectric-constant polymer
Authors: Geer R. E. , Kolosov O. V. , Briggs G. A. D. , Shekhawat G. S.
Published: July 2002

Ultrasonic-force microscopy (UFM) has been employed to carry out nanometer-scale mechanical imaging of integrated circuit (IC) test structures comprised of 0.32-μm-wide aluminum interconnect lines inlaid in a low-dielectric-constant (low-k) polymer film. Such inlaid metal interconnects are typically referred to as damascene structures. UFM clearly differentiates the metal and polymer regions within this damascene IC test structure on the basis of elastic modulus with a spatial resolution⩽10 nm. In addition, this technique reveals an increase in the polymer elastic modulus at the metal/polymer interface. This nanometer-scale hardening corresponds to compositional modification of the polymer from the reactive ion etch (RIE) process used to form trenches in the polymer film prior to metal deposition. The reported direct, nondestructive nanometer-scale mechanical imaging of RIE-process-induced modifications of low-k polymers in IC test structures offers expanded opportunities for mechanical metrology and reliability evaluation of such materials.
Two-photon absorption properties of commercial fused silica and germanosilicate glass at 264 nm
Authors: Dragomir Adrian , McInerney John G. , Nikogosyan David N. , Kazansky Peter G.
Published: July 2002

Using high-intensity femtosecond pulses at λ=264 nm, we have measured the two-photon absorption (TPA) coefficient in three fused silica samples Suprasil, Herasil, Infrasil (Heraeus) and in 3.5 mol % Ge-doped fused silica. While in fused silica samples the TPA coefficient value is about 2×10−11 cm/W, in germanosilicate glass it equals (42±3)×10−11 cm/W.
Fluctuation conductivity in YBa2Cu3O7−y films with different oxygen content. I. Optimally and lightly doped YBCO films
Authors: Solovjov A. L. , Habermeier H.-U. , Haage T.
Published: July 2002

Fluctuation conductivity in YBa2Cu3O7−y (YBCO) films with different oxygen concentrations is investigated. All of the samples exhibit a clear transition from the Maki–Thompson mechanism of scattering of fluctuational pairs to the Aslamazov–Larkin mechanism as the temperature approaches Tc. The values of the transition temperature are used to determine the coherence length ξc(0) along the c axis and the phase relaxation time τφ(100K) of the fluctuational pairs. Despite the decrease of Tc from 87.4 to 54.2 K with decreasing oxygen content in the samples studied, a value τφ(100K)=(3.35±0.01)×10−13 s is obtained for all the samples. It is shown that the dependence of ξc(0) on Tc conforms to the standard theory of superconductivity. The mechanisms for the scattering of charge carriers and for superconducting pairing in high-Tc superconductors are analyzed.
Nanofatigue studies of ultrathin hard carbon overcoats used in magnetic storage devices
Authors: Li Xiaodong , Bhushan Bharat
Published: July 2002

A technique to perform nanofatigue experiments was developed. This technique utilizes a depth-sensing nanoindenter with harmonic force. The nanofatigue behavior of 20 nm thick amorphous carbon coatings was studied. The contact stiffness was monitored continuously throughout the test. The abrupt decrease in the contact stiffness indicates fatigue damage has occurred. The critical load amplitude, below which no fatigue damage occurs, was identified. It was found that the filtered cathodic arc coating exhibits longer fatigue life than a direct ion beam coating. Failure mechanisms of the coatings during fatigue are also discussed in conjunction with the hardness, elastic modulus, and fracture toughness, as well as deposition processes. The dynamic nanoindentation fatigue test used in this study can be satisfactorily used to simulate and study damage at the head–disk interface.
High energy density plasma science with an ultrarelativistic electron beam
Authors: Joshi C. , Blue B. , Clayton C. E. , Dodd E. , Huang C. , Marsh K. A. , Mori W. B. , Wang S. , Hogan M. J. , O’Connell C. , Siemann R. , Watz D. , Muggli P. , Katsouleas T. , Lee S.
Published: July 2002

An intense, high-energy electron or positron beam can have focused intensities rivaling those of today’s most powerful laser beams. For example, the 5 ps (full-width, half-maximum), 50 GeV beam at the Stanford Linear Accelerator Center (SLAC) at 1 kA and focused to a 3 micron rms spot size gives intensities of >1020 W/cm−2 at a repetition rate of >10 Hz. Unlike a ps or fs laser pulse which interacts with the surface of a solid target, the particle beam can readily tunnel through tens of cm of steel. However, the same particle beam can be manipulated quite effectively by a plasma that is a million times less dense than air! This is because of the incredibly strong collective fields induced in the plasma by the Coulomb force of the beam. The collective fields in turn react back onto the beam leading to many clearly observable phenomena. The beam paraticles can be: (1) Deflected leading to focusing, defocusing, or even steering of the beam; (2) undulated causing the emission of spontaneous betatron x-ray radiation and; (3) accelerated or decelerated by the plasma fields. Using the 28.5 GeV electron beam from the SLAC linac a series of experiments have been carried out that demonstrate clearly many of the above mentioned effects. The results can be compared with theoretical predictions and with two-dimensional and three-dimensional, one-to-one, particle-in-cell code simulations. These phenomena may have practical applications in future technologies including optical elements in particle beam lines, synchrotron light sources, and ultrahigh gradient accelerators.
Distributions of C2 and C3 radical densities in laser-ablation carbon plumes measured by laser-induced fluorescence imaging spectroscopy
Authors: Sasaki K. , Wakasaki T. , Matsui S. , Kadota K.
Published: July 2002

We measured temporal variations of the distributions of C2 and C3 radical densities in carbon plumes produced by laser ablation of graphite in ambient He gas. Laser-induced fluorescence imaging spectroscopy was used for the measurement. The temporal variations of total numbers of C2 and C3 contained in plumes were evaluated by integrating the density distributions. The experimental observations have shown that the gas-phase production of C2 is comparable to the direct production from the target, while C3 is mainly produced in gas phase by three-body reactions between C and C2. In addition, we have discussed a scenario for the temporal evolution of heavy clusters (Cn with n⩾4). The present results are useful for understanding initial formation processes of carbon clusters in laser-ablation plumes.
Hydrothermal synthesis of La0.5Ba0.5MnO3 nanowires
Authors: Zhu Deliang , Zhu Hong , Zhang Yuheng
Published: July 2002

La 0.5 Ba 0.5 MnO 3 nanowires were synthesized by a hydrothermal method at low reaction temperature (270 °C). The synthesized nanowires are of pure, cubic perovskite structure and single crystalline. They grow along [110]; their surfaces are clean, very regular, and without any sheathed amorphous phase. Typical lengths of the nanowires are in the range of several to several tens of micrometers, and typical widths are in the range of 30–150 nm. Nanowires may be an ideal system for studying dimensionally confined transport phenomena in perovskite manganites and for fabricating field sensors and other devices.
Analysis of combined fast wave current drive and neutral beam injection in the DIII-D tokamak
Authors: Mantsinen M. J. , Petty C. C. , Eriksson L.-G. , Mau T. K. , Pinsker R. I. , Porkolab M.
Published: July 2002

In recent experiments with combined fast wave current drive (FWCD) and deuterium neutral beam injection on the DIII-D tokamak [Luxon et al., Fusion Technol. 8, 441 (1985)], an enhanced fusion reactivity and fast ion energy content have been observed in the presence of FWCD, with a concomitant low FWCD efficiency [Petty et al., Radio Frequency Power in Plasmas (AIP, New York, 1997), p. 225]. In this paper, we investigate whether high-harmonic ion cyclotron damping could be responsible for the low FWCD efficiency in these experiments, since a number of high-harmonic hydrogen and deuterium cyclotron resonance layers existed in the plasma. The main analysis tool is the ion cyclotron range of frequencies code PION [Eriksson et al., Nucl. Fusion 33, 1037 (1993)], modified to allow multiple frequencies simultaneously as was done in the DIII-D experiments. According to the PION modeling, high harmonic damping of fast wave power can give rise to enhanced fusion reactivity and fast ion energy content, which is consistent with the experimental observations.
Generalized Einstein relation for disordered semiconductors—implications for device performance
Authors: Roichman Yohai , Tessler Nir
Published: July 2002

The ratio between mobility and diffusion parameters is derived for a Gaussian-like density of states. This steady-state analysis is expected to be applicable to a wide range of organic materials (polymers or small molecules) as it relies on the existence of quasiequilibrium only. Our analysis shows that there is an inherent dependence of the transport in trap-free disordered organic materials on the charge density. The implications for the contact phenomena and exciton generation rate in light emitting diodes as well as channel width in field-effect transistors is discussed.
Spin exchange optical pumping at pressures near 1 bar for neutron spin filters
Authors: Rich D. R. , Gentile T. R. , Smith T. B. , Thompson A. K. , Jones G. L.
Published: July 2002

Motivated by applications to neutron spin filters and recent advances in spectrally narrowed laser diode arrays (LDAs), we are exploring spin exchange optical pumping of He3 at pressures near 1 bar. Among our more interesting results has been the production of glass cells with extremely long relaxation times. The best of these has a lifetime of T1=840 h [where the polarization decays versus time, t, as exp(−t/T1)], dominated by the dipole–dipole contribution of 950 h at a He3 partial pressure of 0.85 bar. Using a broadband LDA, we have obtained 55% He3 nuclear polarization in this cell. These results are particularly relevant to the application of He3-based neutron spin filters to neutron scattering and weak interaction experiments. Applications to magnetometry and polarized gas magnetic resonance imaging are also possible.
Molecular dynamics simulations of water clusters with ions at atmospheric conditions
Authors: Brodskaya Elena , Lyubartsev Alexander P. , Laaksonen Aatto
Published: July 2002

Clustering of water molecules on charged particles has been studied using the method of molecular dynamics simulations. A selected set of model metal and halogen ions, carrying both positive and negative charges, is chosen as nucleation centers for water molecules. The influence of the ion charge, its size, and short-range interactions on the local structure, and kinetic characteristics are investigated for the ion-centered clusters of 20 and 30 water molecules at 200 and 300 K, respectively. It is shown, based on radial densities, energy, polarization profiles, and orientational distribution functions, that the local water structure in the clusters becomes perturbed to a larger degree around negative ions compared to ions carrying a corresponding positive charge. The electric field of an anion is more effectively screened by the first hydration shell, resulting in a weaker dependence of the relaxation processes on the ion field in the second hydration shell. The dependence of the work of cluster formation on the ion radius is more pronounced in the case of negative ions. The dependence of the properties on the cluster size are investigated. It was found that for the water–alkali ion system potentials used, the dependence of the work of cluster formation on the number of water molecules has a minimum at about N=30. The obtained work of cluster formation for the anions was found to be consistently less than that for the cations. Unfortunately, this work of formation does not alone provide an answer to the still unsolved problem of sign preference connected to water condensation on charged particles in atmospheric conditions.
Epitaxial growth and planar dielectric properties of compositionally graded (Ba1−xSrx)TiO3 thin films prepared by pulsed-laser deposition
Authors: Zhu Xinhua , Chong Nui , Chan Helen Lai-Wah , Choy Chung-Loong , Wong Kin-Hung , Liu Zhiguo , Ming Naiben
Published: July 2002

We have heteroepitaxially deposited compositionally graded (Ba1−xSrx)TiO3 (BST) thin films with increasing x from 0.0 to 0.25 on (100)-oriented MgO substrates using pulsed-laser deposition. The compositional gradients along the depth in the graded films were characterized by Rutherford backscattering spectroscopy. By using surface interdigital electrodes, the planar dielectric response of epitaxial graded BST films was measured as a function of frequency, temperature, and dc applied voltage. At room temperature, the dielectric constant of the graded BST film was about 450 with a dielectric loss, tan δ of 0.007 at 100 kHz. Measurements varying the dc bias voltage showed hysteresis of the dielectric response and a tunability of 25% at an applied electric field of 80 kV/cm. The graded BST films undergo a diffuse phase transition with a broad and flat profile of the capacitance versus temperature. Such behavior of the dielectric response in graded BST films is attributed to the presence of the compositional and/or residual strain gradients in the epitaxial graded films. With such a graded structure, it is possible to a build a dielectric thin-film capacitor with a low-temperature dependence of the capacitor over a broad temperature regime.
Kinetics of escape through a small hole
Authors: Grigoriev Igor V. , Makhnovskii Yurii A. , Berezhkovskii Alexander M. , Zitserman Vladimir Yu.
Published: July 2002

We study the time dependence of the survival probability of a Brownian particle that escapes from a cavity through a round hole. When the hole is small the escape is controlled by an entropy barrier and the survival probability decays as a single exponential. We argue that the rate constant is given by k=4Da/V, where a and V are the hole radius and the cavity volume and D is the diffusion constant of the particle. Brownian dynamics simulations for spherical and cubic cavities confirmed both the exponential decay of the survival probability and the expression for the rate constant for sufficiently small values of a.
Dopant profiling with the scanning electron microscope—A study of Si
Authors: Elliott S. L. , Broom R. F. , Humphreys C. J.
Published: July 2002

This article describes the results of a detailed study of semiconductor dopant profiling with the scanning electron microscope (SEM) using secondary electrons. The technique has been applied to a wide variety of doped silicon test structures as well as a metal–oxide field-effect transistor. We have demonstrated that contrast can be detected from p-doped regions as thin as one nanometer across. Contrast can also be measured from p-type regions with doping concentrations less than 1016 cm−3. We have studied the variation of doping contrast with specimen temperature and with a bias applied across a p-n junction in situ in the SEM. These experiments demonstrate that doping contrast is mainly due to the built-in voltages in semiconductor devices which result in local fields (patch fields) outside the specimen which influence the number of secondary electrons detected. A concise set of guidelines is provided for users of this technique, including the optimum SEM operating conditions that should be used for maximum contrast.
Detection of weak electric fields by sharks, rays, and skates
Authors: Adair Robert K. , Astumian R. Dean , Weaver James C.
Published: July 2002

The elasmobranchs—sharks, rays, and skates—can detect very weak electric fields in their aqueous environment through a complex sensory system, the ampullae of Lorenzini. The ampullae are conducting tubes that connect the surface of the animal to its interior. In the presence of an electric field, the potential of the surface of the animal will differ from that of the interior and that potential is applied across the apical membrane of the special sensory cells that line the ampullae. The firing rate of the afferent neurons that transmit signals from the ampullae has been shown to vary with that potential. We show that those firing rates can be described quantitatively in terms of synchronous firing of the sensory cells that feed the neurons. We demonstrate that such synchronism follows naturally from a hypothetical weak cell-to-cell interaction that results in a self-organization of the sensory cells. Moreover, the pulse rates of those cells—and the neurons that service the cells—can be expected to vary with the imposed electric fields in accord with measured values through actions of voltage gated transmembrane proteins in the apical sector of the cell membranes that admit Ca++ ions. We also present a more conjectural model of signal processing at the neuron level that could exploit small differences in firing rates of nerve fibers servicing different ampullae to send an unambiguous signal to the central nervous system of the animal.
Damping–undamping strategies for the Levenberg–Marquardt nonlinear least-squares method
Authors: Lampton Michael
Published: July 2002

The speed of the Levenberg–Marquardt (LM) nonlinear iterative least-squares method depends upon the choice of damping strategy when the fitted parameters are highly correlated. Additive damping with small damping increments and large damping decrements permits LM to efficiently solve difficult problems, including those that otherwise cause stagnation. © 1997 American Institute of Physics.
Susceptibility, magnetization, and specific heat in the paramagnetic and ferromagnetic regions of (Y1−xUx)B4
Authors: Wallash A. , Crow J. , Fisk Z.
Published: July 2002

An anomalous magnetic phase diagram for (Y1−xUx)B4 has previously been reported. This system is paramagnetic for x>0.6, ferromagnetic for 0.1<x<0.6, and paramagnetic for x<0.1. Measurements of the magnetic susceptibility suggest a localization of the 5f electrons upon alloying UB4 with nonmagnetic YB4 due to a reduction of f-f overlap. The temperature and x dependence of the magnetic susceptibility is consistent with a two site model. This model assumes that the 5f electrons associated with U ions that have four or less nearest neighbors become localized and develop a stable paramagnetic moment. From our analysis, we obtain a paramagnetic moment of (2.6±0.2) μB. The saturation moment per U ion for (Y0.7U0.3)B4 is (0.32±0.03) μB. The specific heat of (Y,U)B4 shows a substantial enhancement as x decreases but the origin of this enhancement is not understood at this time. These results are presented and discussed in relation to the expected behavior as the system approaches the ferromagnetic instability.
Influence of the bias current distribution on the static and dynamic properties of long Josephson junctions
Authors: Samuelsen M. R. , Vasenko S. A.
Published: July 2002

The maximum supercurrent through a long and narrow Josephson junction has been calculated numerically as a function of an applied magnetic field for various feed current distributions. The results have been shown to depend drastically on the mode of the current feed. In particular, the real nonuniform distribution ηov (x) of the current corresponding to the overlap geometry of the junction is nearly equivalent to the mixture yηun+(1−y)ηin with the factor y approaching unity as the junction length increases: (1−y)=Cy(L/λj)−0.5, Cy≂1.7. In contrast with the static properties, the shape of the zero-field step in the long junction I-V curve appears to be almost independent of the mode of the current feed, because of averaging of the Lorentz force by the travelling Josephson vortices.
Role and effect of Co2O3 additive on the upturn characteristics of ZnO varistors
Authors: Kim Eun Dong , Kim Chong Hee , Oh Myung Hwan
Published: July 2002

The effect of Co2O3 additions on the characteristics of electric field-current density was investigated at high current densities. With the increase of mole % of Co2O3, the onset of voltage upturn descends to lower current density due to the decrease in the conductivity in ZnO grains. This is confirmed by impedance measurements at high frequencies. Analysis on the capacitance-voltage characteristics shows that the decreased grain conductivity is attributed to the lower carrier density caused by the reduced concentration of interstitial Zni or oxygen vacancy, VO. In the case of the highly doped ZnO varistors containing more than 0.5 mole % Co2O3, the lowered carrier mobility improves the decrease in grain conductivity.
Frequency response of unified dielectric and conductive systems involving an exponential distribution of activation energies
Authors: Macdonald J. Ross
Published: July 2002

When the small-signal ac frequency response of a dielectric or conductive system is known, either functionally or as data, it is shown that the corresponding response of an associated conductive or dielectric system may be immediately obtained through the use of new duality relations. A specific model is considered which involves thermally activated capacitance and/or resistance, with an activation energy probability density exponentially dependent on energy. Previous frequency response analyses of such a continuously distributed model involve inadequate approximations and lead to erroneous predictions. Correct immittance results are presented in three ways: analytically, by means of complex plane plots, and through the use of three-dimensional perspective plots. Results are given in general form but apply to both dielectric and conductive systems which involve the same functional dependence on activation energies. Low- and high-frequency-limiting responses for a given system are found to be associated with the same simple equivalent circuit. In intermediate frequency ranges a power-law frequency response somewhat like that of the constant phase element may occur. Differences between the power-law exponents for dielectric and conductive systems are clarified, and the types of possible temperature dependence of the exponents explored. Exponent values are not limited to the range between zero and unity. The overall response of the present normalized three-parameter model is similar to that often found experimentally for both dielectric and conductive systems and similar to but more general than that of other normalized distributed-element (two-parameter) models such as that of Williams and Watts and that of Davidson and Cole.
Grain-boundary space-charge conduction
Authors: Mataré Herbert F.
Published: July 2002

Recent research on silicon grain boundaries has confirmed the typical features known from earlier work on grain boundaries in germanium and III-V compound semiconductors. However, there is less clarity with respect to the role of the ‘‘dangling bonds’’ when testing for electrical activity. In silicon a pronounced double barrier with its space-charge layer and a low leakage current rarely forms. Here the Cottrell atmospheres in conjunction with impurity complexes such as SiO, SiO2, and SiO4 can strongly influence the electrical properties in a material with an exceptionally high self-diffusivity. Conditions for the measurability of the longitudinal impurity band-type conduction through space-charge layers in silicon grain boundaries are outlined. It is concluded that in those cases where electrical activity is measured, the conduction parallel to the grain-boundary plane should be apparent for pure material and at low temperature. Experiments are proposed to further our understanding of the properties of grain boundaries in silicon.
Carbon enhancement effect on oxygen precipitation in Czochralski silicon
Authors: Shimura Fumio
Published: July 2002

The enhancement effect of carbon on oxygen precipitation in Czochralski (CZ) silicon has been investigated in detail by means of infrared (IR) absorption spectroscopy at room temperature. The critical temperature Tc, which distinguishes the two different ways in which carbon enhances oxygen precipitation, has been shown to exist between 800 and 850 °C. Perturbed [Ci-Oi]C(3) centers are observed by IR spectroscopy in the temperature range lower than the Tc. The perturbed C(3) center is estimated to consist of a complex with two to three oxygen atoms per carbon atom. It has moreover been confirmed that the carbon effect is explained in two ways: (i) carbon directly provides heterogeneous seeding sites, as [Ci-Oi]C(3) centers, for oxygen precipitation at temperatures lower than Tc; and (ii) carbon plays a catalytic role at temperatures higher than Tc. Finally, the formation of [Ci-Oi]C(3) centers is shown not to be affected by high-temperature preannealing at 1250 °C.
Interfacial reactions between Ni films and GaAs
Authors: Lahav A. , Eizenberg M. , Komem Y.
Published: July 2002

The metallurgical examination of solid-state reaction between nickel thin films and single-crystal GaAs substrates and the resultant electrical properties of the contacts are reported. Annealing at 100–300 °C in forming gas led to formation of a metastable hexagonal phase Ni2GaAs which was stabilized due to its epitaxial growth on (001) and (111) GaAs substrates, as follows: (101̄1)Ni2GaAs∥(001)GaAs and (0001)Ni2GaAs∥(111)GaAs. Nickel atoms were found to be the dominant diffusing species during the ternary phase growth. Ni2GaAs is stable on (111)GaAs up to at least 600 °C, compared to 350 °C on (001)GaAs. The larger stability on (111) is explained by the better epitaxial match found in this case. Reaction on (001)GaAs in the temperature range of 350–550 °C resulted in decomposition of Ni2GaAs by NiAs precipitation. After annealing at 600 °C the reacted film was composed of two phases: NiGa and NiAs. The electrical properties of the contacts were correlated to the phase interfacing the substrate. The Ni2GaAs formed rectifying contact with a barrier height of 0.84 eV, whereas when NiGa and NiAs were at the interface an ohmic behavior was observed.
The temperature dependence of the refractive index of silicon at elevated temperatures at several laser wavelengths
Authors: Jellison G. E. , Burke H. H.
Published: July 2002

The refractive index of silicon has been measured at elevated temperatures at several different laser wavelengths of the HeNe and the Ar+ cw lasers. This data, along with the reinterpretation of polarization modulation ellipsometry data, shows that the refractive index is linear with temperature (from 25 to ∼750 °C) and that the temperature coefficient of the refractive index increases as the wavelength of light decreases.
Effective diffusion time during rapid thermal processing
Authors: Arbel Abir , Natan Menachem
Published: July 2002

A simple, readily applicable expression is derived for the effective diffusion time during the shortest possible rapid thermal processing cycle in halogen lamps heated furnaces for processing solid state devices. Calculations, using the derived expression, indicate that the shortest effective diffusion time at the maximum attained temperature is in the neighborhood of 1 s, even though there is no actual hold time at this temperature.
Decay of wall stabilized arcs in SF6-N2 mixtures
Authors: Gleizes A. , Sakalis I. , Razafinimanana M. , Vacquie S.
Published: July 2002

The variations of temperature and conductance are calculated during the extinction of nonblown, atmospheric pressure, wall-stabilized arcs. The validity of the computation method based on the assumption of local thermodynamic equilibrium (LTE) has first been tested by comparing the computed values of electron density with experimental values obtained by laser interferometry in SF6-N2 mixtures during the first tens of microseconds in the extinction. The computed values of temperature and conductance have also been compared with experimental and theoretical values from the literature, in the case of pure Ar, SF6, and N2. In spite of discrepancies, due to nonequilibrium phenoma, the relative computed variations of conductance in the case of pure SF6 and N2 are comparable with the experimental variations. In the case of SF6-N2 mixtures, and assuming LTE, the computation shows that the evolution of the mixture conductance is not systematically intermediate between those of pure SF6 and N2. For example, with a mixture containing 20% SF6 and 80% N2, the calculated conductance of a 100 A extinguishing arc after 130 μs is 40 times higher than of pure SF6 and about 15 times that of pure N2. This phenomenon is due to the combination of two properties of the SF6-N2 plasma for temperatures below 7500 K: low thermal conductivity and high electrical conductivity.
Preparation of Ti-Zr-B ternary amorphous alloys by a single-roller melt-spinning technique and their thermal stability
Authors: Yoshitake T. , Kubo Y. , Igarashi H.
Published: July 2002

Continuous ribbons of Ti-Zr-B ternary alloys, consisting of early transition metal and metalloid elements, were formed by a single-roller melt-spinning method. Details of the quenching method employing a modified levitation melting technique are herein described. Amorphous phases were obtained in the composition range of 15 at. %≤B≤25 at. % and 20 at. %≤Zr≤50 at. %. The crystallization of the amorphous alloy took place in two steps. Initially, the amorphous phase changed polymorphously into a boron supersaturated bcc-like phase, and then this bcc-like phase decomposed into a bcc phase and a (Ti, Zr)B compound phase. The crystallization temperature was extraordinarily low (∼320 °C) in contrast to the high melting point and the strong chemical bonding between the metal and metalloid elements.
Grain size measurement using magnetic and acoustic Barkhausen noise
Authors: Ranjan R. , Jiles D. C. , Buck O. , Thompson R. B.
Published: July 2002

Results on annealed nickel show that the total number of counts of both magnetic and acoustic Barkhausen signals vary inversely with grain size. In decarburized steels the total number of counts and the amplitude of both Barkhausen signals increase in proportion to grain size. The paper addresses these results in context of grain size, grain-boundary segregation, and precipitate effect.
Effect of transverse compressive stress on the critical current and upper critical field of Nb3Sn
Authors: Ekin J. W.
Published: July 2002

A large reversible degradation of the critical current of multifilamentary Nb3Sn superconductors has been observed when uniaxial compressive stress is applied transverse to the conductor axis at 4 K. In bronze-process multifilamentary Nb3Sn, the onset of significant degradation occurs at about 50 MPa. In an applied field of 10 T, the magnitude of the effect is about seven times larger for transverse stress than for stress applied along the conductor axis. The transverse stress effect increases with magnetic field and is associated with a reversible degradation of the upper critical field. The intrinsic effect of transverse stress on the upper critical field is about ten times greater than for axial stress. Although axial stresses on the Nb3Sn filaments are greater than transverse stresses in most applications, the transverse stress effect will need to be considered in the internal design of large magnets because of the greater sensitivity of Nb3Sn to transverse stress. It is shown that the transverse stress from the Lorentz force on the conductor is proportional to conductor thickness. This will place limits on conductor dimensions and the spacing between distributed reinforcement in large magnets. The effect may be particularly significant in cabled conductors where large transverse stress concentrations can occur at strand crossover points.
Minimal-volume photoacoustic cell measurement of thermal diffusivity: Effect of the thermoelastic sample bending
Authors: Perondi L. F. , Miranda L. C. M.
Published: July 2002

A minimal-volume photoacoustic cell method is demonstrated for obtaining the thermal diffusivity of solids. It is based on the measurement of the acoustic signal as a function of the modulation frequency in the region where the sample is thermally thick. The method is tested by using metal, semiconductor, and polymer samples.
Properties of carbon clusters in TNT detonation products: Graphite-diamond transition
Authors: van Thiel Mathias , Ree Francis H.
Published: July 2002

The thermodynamic properties of condensed carbon in the detonation products of TNT have been analyzed with a statistical mechanical model. The calculations show that the heat of formation of diamondlike particles in detonation products is increased by 1–2 kcal/mol (0.04–0.08 eV), relative to that of the graphitic or carbynelike low-pressure phase. The density of the low-pressure phase also appears to be about 10% higher than that of graphite. The short condensation times of 10−7–10−8 s suggest carbon clusters with a high surface energy. The heat of formation indicates cluster sizes of about 100 Å.
Electrical and photovoltaic properties of indium-tin-oxide/p-InSe/Au solar cells
Authors: Martínez-Pastor J. , Segura A. , Valdés J. L. , Chevy A.
Published: July 2002

Conditions for efficiency improvement and optimization in indium-tin-oxide/p-indium-selenide solar cells are discussed in this paper. This aim is achieved by using low-resistivity p-indium-selenide and by incorporating a back-surface-field contact. This contact is insured by a p-indium selenide/gold barrier whose rectifying behavior is explained through the complex impurity structure of p-indium-selenide. Electrical and photovoltaic properties of the cells are also reported. The efficiency parameters under AM1 simulated conditions have been improved up to 32 mA/cm2 for the short-circuit current density, 0.58 V for the open-circuit voltage, and 0.63 for the filling factor. As a result, solar efficiencies larger than 10% in annealed cells and 8% in unannealed ones have been attained. The limitations of these devices are discussed by investigating the dependence of electrical and efficiency parameters in function of photon flux and temperature.
Structural relaxation and hydrogen solubility in an amorphous Pd80Si20 alloy
Authors: Lee Sung-Man , Lee Jai-Young
Published: July 2002

The effect of structural relaxation on hydrogen solubility in amorphous Pd80Si20 has been investigated by calorimetric and thermal desorption techniques. The hydrogen solubility is decreased by structural relaxation, an effect attributed to the elimination and redistribution of excess free volume quenched into the glass. As a result of structural relaxation, the width of site energy distribution decreases compared to that of the as-quenched state.
Wear resistance of iron oxide thin films
Authors: Chen Mao-Min , Lin Judy , Wu Tsai-Wei , Castillo Gilbert
Published: July 2002

Magnetite films (Fe3O4) were reactively sputtered onto (100) silicon substrates in an Ar+O2 gas environment from a target containing Fe and 0.75 at. % Os. The films were then oxidized in air to form γ-Fe2O3. The wear resistance of the films was evaluated using an oscillatory wear tester and a contact start/stop tester with IBM 3380 type of sliders. Magnetite films exhibited poor durability independent of the deposition substrate temperature and oxygen partial pressure. Upon oxidizing the magnetite films in air at elevated temperatures, the wear resistance increased. For fixed deposition conditions, the wear resistance of the film increased with oxidation temperature. However, too high an oxidation temperature will transform the film into α-Fe2O3, which is antiferromagnetic material. For a fixed oxidation temperature of 300 °C, the wear resistance of the film increased with increasing deposition substrate temperature. Durable γ-Fe2O3 thin film can be produced by depositing 1000-Å-thick film at 325 °C and subsequently oxidizing the film at 300 °C. A visible wear track was detected only after 16 000 contact start/stop cycles for γ-Fe2O3 film media without additional layers of overcoat or lubricant in ambient environment. The friction coefficient was low and remained stable with sliding cycles. The dependence of friction coefficient of the film on deposition conditions will be discussed.
Thermal properties of the multilayer infinite plate structure
Authors: Palisoc Arthur L. , Lee Chin C.
Published: July 2002

Using the double Fourier integral transform method, the analytical temperature solutions to the single-layer and multilayer structures with infinite lateral dimensions have been derived. For the single-layer structure, temperature dependence of the thermal conductivity has been taken into account using the Kirchhoff transformation. The use of discrete rectangular heat sources rather than circular heat sources on the top surface of the structure makes this model particularly useful for the thermal analysis of common solid-state and integrated circuit devices and packages. For studying the thermal properties of a large class of solid-state device geometries, this model can be utilized to approximate actual devices with reasonable accuracy. The general device geometries for which this model can be employed to represent the actual devices are determined. Compared with the model where the finite extent of the chip lateral dimensions is considered, the present model is much more computationally efficient for cases where the heat source size is much smaller than the substrate or package size.
Dynamics of flame propagation using laser-induced spark initiation: Ignition energy measurements
Authors: Syage J. A. , Fournier E. W. , Rianda R. , Cohen R. B.
Published: July 2002

A method is described for measuring low-energy ignition of combustable mixtures using nanosecond and picosecond laser-induced breakdown. Ignition studies are reported for homogeneous H2/air mixtures. The extent of flame inhibition in H2/air was investigated as a function of CO2 concentration. Our electrodeless spark ignition results are compared with earlier work using electric discharge ignition. A simple model for flame ignition is advanced, based on the temporal and energy density characteristics of the source energy. Implications of laser-induced spark ignition in homogeneous fuel mixtures to the molecular dynamics of flame propagation are discussed.
Raman spectra of diamondlike amorphous carbon films
Authors: Yoshikawa M. , Katagiri G. , Ishida H. , Ishitani A. , Akamatsu T.
Published: July 2002

Raman spectra of diamondlike amorphous carbon (a-C) films prepared under atmosphere with various hydrogen gas content have been measured as a function of excitation wavelength. The Raman spectral profiles vary with excitation wavelength depending on electronic absorption spectra associated with π-π* electronic transitions. Dependence of Raman spectra on excitation wavelength is interpreted in terms of π-π* resonant Raman scattering from aromatic rings with various sizes rather than polyene chains. The relative intensity of a 1400 cm−1 band against a 1530 cm−1 band is found to decrease with an increase of sp3 content in a-C films. It is shown that the relative intensity can be used as a parameter for sp3 content.
Easy-axis reorientation in the BaCo2-W hexagonal ferrite
Authors: Collomb A. , Samaras D. , Hadjivasiliou S. , Achilleos C. , Tsoukalas J. , Pannetier J. , Rodriguez J.
Published: July 2002

The rotation of the magnetization in the BaCo2Fe16O27-W–type hexagonal ferrite has been studied by neutron powder diffraction and single-crystal magnetic measurements in the 2–833 K temperature range. From neutron powder diffraction data the magnetic structures were determined. Up to 453 K, the magnetic arrangement is constant: it is collinear, making an angle (θ=70.0±1.5°) with the hexagonal c axis. Then a continuous rotation of the magnetization towards this axis occurs, ending at T=553 K. From magnetic measurements, the magnetocrystalline anisotropy constants are determined between room temperature and 623 K and the angles between the easy magnetization axis and c axis are deduced. They confirm the rotation of the magnetization.
Superconducting properties of Mo/Si multilayer films
Authors: Nakajima H. , Ikebe M. , Muto Y. , Fujimori H.
Published: July 2002

Multilayered Mo/Si thin films have been prepared by dual rf-magnetron sputtering technique, and the superconducting transition temperature Tc and the upper critical field Hc2 have been examined by resistance measurements. X-ray diffractometry shows that for the modulation wavelength λ shorter than 3 nm both Mo and Si sublayers are amorphous, while for λ longer than 3 nm, crystalline bcc structures appear in Mo sublayers. The λ dependence of Tc of the multilayer films with equal sublayer thickness shows that Tc takes a maximum value of 6.1 K for λ=2.3 nm and approaches the Tc value of amorphous Mo56Si44 in the small λ limit. The superconductivity of the multilayers has been confirmed to result from amorphous MoSi phase formed in the interfacial region of the sublayers. The thickness of the superconducting amorphous layer is estimated to be about 3 nm from the λ dependence of Tc and from the result of the anisotropy of Hc2 . Keeping the Mo sublayer thickness less than 2.4 nm to suppress the appearance of the crystalline Mo and increasing the Si sublayer thickness to reduce the interlayer Josephson coupling, an ideal quasi-two-dimensional superconductor with dHc2∥ /dT as high as 180 kOe/K has been realized.
Novel femtosecond solitons in optical fibers, photonic switching, and computing
Authors: Potasek M. J.
Published: July 2002

It is shown that novel (10–20)-fs solitons can propagate in optical fibers. This theory is expressed in terms of measurable optical fiber parameters, and experimental conditions for observing them are given. This result is general and can apply to many optical problems, such as the following: modulation instability, cross-phase modulation, pulse compression, amplification by stimulated Raman scattering, higher-order soliton fragmentation, ultrafast optical switching, fiber-soliton lasers, soliton-dye lasers, and optical soliton switches for optical computing.
Measurement of the saturation magnetostriction constant of amorphous wire
Authors: Mitra A. , Vázquez M.
Published: July 2002

Measurement of the magnetostriction constant of amorphous wire by conventional techniques is very difficult because of its small diameter. However, accurate determination of the magnetostriction constant is important in the study of amorphous wires. Here the saturation magnetostriction constant (λs) for a low-magnetostriction amorphous wire of nominal composition (Fe6.3Co92.7Nb1)77.5Si7.5B15 has been determined by means of the small-angle magnetization-rotation method. λs has been evaluated to be 2.1×10−7 for its as-received state. The dependence of thermal treatment is also reported.
Analytical design method of self-shielded planar coils
Authors: Yoda K.
Published: July 2002

An analytical design method of self-shielded planar coils is proposed using the three-dimensional Fourier expansion of the magnetic field generated by planer currents. A numerical example is given for a simple current hoop as a primary coil, and the magnetic fields outside the self-shielded coil structure are calculated, showing good shield performance.
Laser shock-induced mechanical and microstructural modification of welded maraging steel
Authors: Banaś G. , Elsayed-Ali H. E. , Lawrence F. V. , Rigsbee J. M.
Published: July 2002

The effect of laser-induced high-intensity stress waves on the hardness, fatigue resistance, and microstructure in the heat affected zone of welded 18 Ni(250) maraging steel was investigated. Laser-shock processing increased the hardness and fatigue strength of the weldments. Some melting of the surface was involved during laser-shock hardening which produced the reverted austenite phase. Microscopic analyses showed an increased dislocation density in the laser-shocked area.
Measurements of charge on submicron particles generated in a sputtering process
Authors: Wu Jin Jwang , Miller Robert J.
Published: July 2002

The concentration and charge of a submicron aerosol were measured during the venting cycles of a quartz sputtering system. The concentration of submicron particles in the aerosol measured after the plasma was turned off and the chamber vented was of order 20/cm3. A Faraday cup was used to collect the particles by filtration and the total electrical current was measured with an electrometer. From these measurements, the average charge on each particle was estimated to be 1.4×104 negative elementary charges. Mutual electrostatic repulsion rates of the gas-borne particles revealed the charges on 0.4 and 0.6 μm particles to be proportional to the diameter squared. No agglomerates were seen in the scanning electron microscope images of these submicron particles collected on a filter, even when the surface density was extremely high. This also suggests that particles were highly charged during the collection process.