bluuebunny/crossref_metadata_2025 huggingface dataset:
Iron-iron oxide layer films
Authors: Ruf R. R. , Gambino R. J.
Published: February 2003

Thin alternating layers of bcc Fe/amorphous Fe oxide were prepared by a new pulse reactive sputtering technique. The thickness of the Fe+(Fe oxide) periods varied from 8 to 540 Å. At room temperature, the films have soft magnetic properties with coercivities of 4–10 Oe. Samples cooled to 5 K in a saturating applied field show large coercive fields, displaced hysteresis loops and thermal irreversibility up to about 100 K. This low temperature behavior is evidence of exchange coupling between the ferromagnetic Fe and the amorphous Fe oxide.
Effects of annealing on highly damaged bubble garnet layers ion implanted with Xe and As
Authors: Gerard Ph. , Ravel F. , Ponthenier J. L. , Dupuy M. , Blanchard B.
Published: February 2003

The magnetic and structural properties of amorphized (YSmLuCa)3(FeGe)5O12 garnet layers created through As+ (120 keV; 1×1016 As+ cm−2), Xe+ (200 keV; 3×1015 Xe+ cm−2) and Xe+ (200 keV; 1×1016 Xe+ cm−2) bombardment are studied as a function of annealing temperature. Ferromagnetic resonance (FMR), reflection high energy electron diffraction, and transmission electron microscopy have been used to characterize damaged layers just after implantation and after subsequent isochronal annealings. The general feature of the crystalline rebuilding mechanism is quite identical to previous results on Fe+ implanted films. However, a more thorough comparison of As and Xe implanted films after annealing at 800 °C shows drastic differences in properties. The recrystallized layers have better structural and magnetic properties versus depth for the Xe than for the As implantations. The reason for this difference can be explained by the presence of FeAsO4 aggregates in the As implanted layer. An application of Xe implantation is presented, showing the ion mixing effect of Xe+ of heterogeneous transient layer by secondary ion mass spectrometry.
Ray theory of the Love wave interactions
Authors: Seshadri S. R.
Published: February 2003

A ray theory is developed for the treatment of three types of Love wave problems. First, the characteristics of the Love wave are analyzed by the ray technique. Second, for a film with an appropriate weak harmonic corrugation on one of its surfaces, a ray treatment of the first-order coupling between the two Love waves is given. Third, for a film with a suitable weak harmonic corrugation of its free surface, the second-order coupling between the Love wave and the bulk elastic wave in the substrate is investigated using the ray procedure. In all cases, the ray method yields asymptotically exact results for small relative corrugation depths.
Optogalvanic detection of acoustic resonances in a high-pressure sodium discharge
Authors: Jongerius M. J. , Ras A. J. M. J. , Vrehen Q. H. F.
Published: February 2003

In high-pressure discharges, arc instabilities may occur due to acoustic resonances inside the discharge vessel. We have observed experimentally the presence of longitudinal acoustic resonances in a high-pressure sodium discharge well below the threshold above which the arc is unstable. A dye laser, tuned to about 17 140 cm−1, proved to be able to excite the acoustic standing waves, and their galvanic effects have been measured. A local thermodynamic equilibrium discharge model is presented, which qualitatively describes the measurements. It is shown that the instability threshold is correlated to an acoustic pressure amplitude in the ventral segments of about 6 kPa.
Analysis of the skin current in a finite-length cylindrical plasma with external electric field
Authors: Nagatsu Masaaki , Takeuchi Yoshiki , Tsukishima Takashige
Published: February 2003

Theoretical analysis and numerical calculations are carried out of the skin current in a finite-length cylindrical plasma when a step-like electric field is applied externally, within the framework of classical theory. The spatial and temporal evolutions of the skin current are numerically calculated for two cases of plasmas with uniform and parabolic density distributions.
Finite geometry effects on the stability of a charged beam propagating through a relativistic annular electron beam
Authors: Ganguli G. , Palmadesso P.
Published: February 2003

Finite geometry effects on the stability properties of a charged beam propagating through an intense relativistic annular electron beam have been studied. The stability of the system under transverse oscillation has been examined in detail in a parameter domain pertinent to the collective particle accelerator, currently under development at the Naval Research Laboratory. Both the normal mode and the convective aspects of this instability have been investigated. Despite a substantial temporal growth rate as predicted by the normal mode approach, this instability does not prevent successful acceleration of a portion of the axial beam. Thus the transverse oscillation is not fatal to the collective particle accelerator operation.
Determination of the crystal structure of Pb2CrO5
Authors: Morita Shinichi , Toda Kohji
Published: February 2003

The crystal structure analysis of Pb2CrO5 is determined by comparison with powder x-ray and electron diffraction data. The structure is monoclinic: c2/m. All of the atom positions are determined by considering the calculated values of d spacings, line intensities, bond lengths, and bond angles. A new set of lattice parameters are a=14.018, b=5.683, c=7.143 Å, and β=115.23 °. A preliminary result on photoconductivity in a Pb2CrO5 ceramic disk is also given.
A new metal resistor bolometer for measuring vacuum ultraviolet and soft x radiation
Authors: Müller E. R. , Mast F.
Published: February 2003

A new metal resistor bolometer has been developed by applying thin-film technology. It is composed of three layers, a 4-μm-thick radiation absorber made of gold, a 7.5-μm-thick kapton dielectric, and a 0.1-μm-thick 5-kΩ gold resistor. This detector with the appropriate electronics shows a linear response to radiation power, including both neutral-particle emission and electromagnetic radiation from the soft x-ray part of the spectrum to the infrared. The bolometer has a very high operating reliability and sufficient suppression of ambient interference under extreme environmental conditions, such as high neutron and gamma radiation fluxes, high temperatures, mechanical vibrations, and strong electromagnetic fields. In plasma discharges in the ASDEX tokamak a radiation detection limit of 100 μW/cm2 was obtained at a time resolution of 10 ms. The bolometers of an array can be calibrated in situ; the calibration data are reproducible and stable in time within ±10%. Measurements in ASDEX which demonstrate the capability of the method are discussed.
Fluorescence line narrowing in neodymium laser glasses
Authors: Hall D. W. , Weber M. J. , Brundage R. T.
Published: February 2003

Polarized and time-resolved resonant laser-excited fluorescence spectra were recorded for the 4F3/2→4I11/2 transition of Nd3+ in several commercial silicate and phosphate glasses. Excitation sources were pulsed Nd:LiYF4 (1053 nm) and Nd:Y3Al5O12 (1064 nm) lasers. Measurements of line-narrowed spectra yield linewidths ranging from 35 to 64±10 cm−1, depolarization ratios from 0.81 to 0.93, and spectral energy transfer rates ≲3×103 s−1 for Nd3+ concentrations≲2×1020 cm−3. The variations of these properties with wavelength and glass composition are discussed. Hole burning and gain saturation of glass laser amplifiers due to spectral and polarization inhomogeneities can be predicted from these results.
Matrix formulation of Slater’s cavity perturbation theorem
Authors: Dombrowski George E.
Published: February 2003

In this modification of Slater’s cavity perturbation theorem the perturbed magnetic field is expressed as a Fourier series based on the unperturbed cavity modes. The discontinuity in the field (hence the current) at the perturbing surface is two times the normal mode sum. Mode coupling terms are defined, leading to a matrix whose eigenvalues are the perturbed resonance frequencies of the cavity. Further manipulations of this matrix yield the normalized wave function as the normal mode sum. This technique is illustrated by a calculation for ridge waveguide.
High-energy optically pumped iodine laser. I. Kinetics in an optically thick medium
Authors: Cohen James S. , Judd O. P.
Published: February 2003

The operation of a high-energy atomic iodine laser pumped by high-intensity broadband radiation is described theoretically. Nonlinear transport of pump radiation into an optically thick medium is specifically taken into account. Integrodifferential formulations are made for both planar and cylindrical geometries. The model obtains the temporal and spatial dependences of the various chemical species, gas temperature, pump radiation, and stimulated emission in the laser medium. For an active gas of n-C3F7I, relevant temperature-dependent rate constants, absorption cross sections, and line-broadening coefficients were selected after a critical review of the literature. The model is used to interpret recent laser experiments performed in the nonlinear regime using an intense (∼22 000 K) flash lamp to pump a n-C3F7I medium with and without buffer gas. The theoretical results are in excellent agreement with the experimental measurements. The relative importance of the various kinetic processes is evaluated, and the spatial and temporal dependence in the optically thick medium is exhibited. Heating of the medium leads to major changes in the lasing kinetics. It is also observed that a gas-dynamic perturbation wave from the flash-lamp surface significantly limits laser output in some cases. Under some conditions this source drives a pyrolysis wave into the medium, but it is not strong enough to drive a faster photolysis wave.
Bulk and surface dipolar orientation induced by two poling techniques in rolled PVF2 films
Authors: Servet Bernard , Ries Simone , Broussoux Dominique , Micheron Francois
Published: February 2003

Dipolar orientation is measured in two kinds of PVF2 films, the first obtained by successive rolling and poling, and the second by simultaneous rolling and poling. The x-ray pole figure changes, followed from zero applied field to saturation, show a threshold at a critical field of 300 kV/cm, and are consistent with a 60° switching of the β-phase molecular dipoles. IR attenuated total reflection shows larger critical fields at the films surfaces; the best dipolar orientation homogeneity is achieved using the simultaneous poling and rolling process.
Axial ratio distribution effect of isolated microspheroids on the surface enhanced Raman scattering
Authors: Chu L. C. , Wang Shou-yih
Published: February 2003

The surface enhanced Raman scattering as observed from molecules on Ag and Au arrays of microspheroids has been newly treated with suitable Gaussian distributions of axial ratios of these microspheroids. Calculated results for the enhancement factor features such as magnitude, peak position, and linewidth, all agree satisfactorily with existing experimental data, suggesting a possible physical mechanism for the Raman scattering.
Output distributions of electrons in a photomultiplier
Authors: Helstrom Carl W.
Published: February 2003

Computation of the probability distribution of electrons at the output of a photomultiplier is carried out by numerical integration along a contour in the complex plane, a method that is efficient even when the number of electrons is large. When the overall gain of the photomultiplier is fixed and the number of dynodes is increased, the single-stage secondary distribution being assumed the same for each, the output distribution approaches an exponential form for a broad class of single-stage distributions.
Multiple pulse injection of a picosecond regenerative ring amplifier
Authors: Paddock Carolyn A. , Russell Gregory F. , Voss David F. , Miles Richard B.
Published: February 2003

We report the development of a neodymium:yttrium aluminum garnet regenerative ring amplifier seeded by multiple pulse injection. This method of injection allows us to avoid the difficulties and expense of low-power, single-pulse selection. We observed output energy up to 0.6 mJ/pulse (±5% fluctuation). A saturable absorber in the cavity allowed compression down to 55 ps.
Electronic contribution to the elastic constants of hydrogen-added metals
Authors: Kim Chul Koo , Nahm Kyun
Published: February 2003

An electronic mechanism is proposed to account for the positive changes in the elastic moduli of metals when hydrogen impurities are added. A model that has been successfully applied to the doped semiconductors and semimetals is found suitable for hydrogen-added metals in predicting the changes in the elastic moduli. A simple model calculation is carried out for aluminum and the result is qualitatively extended to the cases of transition metals.
Grain-size effects on electrical properties of n-type polycrystalline chemical vapor deposition Si films
Authors: Yang Jane J. , Simpson William I. , Manasevit Harold M. , Ruth Ralph P.
Published: February 2003

The electrical properties of phosphorus-doped n-type polycrystalline Si films deposited by chemical vapor deposition were investigated as a function of both impurity concentration and average grain sizes in the films. Sets of simultaneously grown films with average grains ranging from <1 to >100 μm have been deposited on polished selected polycrystalline high-purity alumina substrates. The impurity concentrations were in the range 1015–1018 cm−3. The transport properties of the n-type polycrystalline films have been determined by Hall-effect measurements as a function of sample temperature in the range 77–420 °K using the van der Pauw technique. The experimental results are interpreted in terms of a grain-boundary model.
Magnetization of R6Fe23 intermetallic compounds: Molecular field theory analysis
Authors: Herbst J. F. , Croat J. J.
Published: February 2003

Magnetization measurements for the R6Fe23 (R=Y, Dy, Ho, Er, Tm, Lu) intermetallic compounds and molecular field analyses of the data are reported. A single-sublattice model accurately describes the temperature dependence of the magnetization for Y6Fe23 and Lu6Fe23. Excellent correspondence with the data for the other compounds is provided by a two-sublattice model which allows canting of the rare earth and iron moments. Our results indicate significant departure from antiparallel moment alignment in Tm6Fe23.
Annealing behavior of neon-implanted magnetic garnet
Authors: Awano H. , Speriosu V. S. , Wilts C. H.
Published: February 2003

Ferromagnetic resonance spectra and x-ray rocking curves were used to measure the change in magnetic properties and strain with annealing temperature in the surface layer of (111)-oriented Gd, Tm, Ga substituted yttrium iron garnet films implanted with Ne+ at 190 keV. For doses below about 4×1014 ions/cm2, the entire implanted layer remains crystalline and magnetic. The implantation-induced strain decreases monotonically with increasing annealing temperature, falling to zero at a temperature of 1100 °C. The implantation-induced magnetic anisotropy varies with strain in the same manner as for unannealed material until the annealing temperature reaches 800 °C. For higher temperatures, the anisotropy has a value larger than that expected for unannealed material. At a higher dose, 5×1014 ions/cm2, the center of the implanted region is both amorphous and nonferrimagnetic. Single-crystal order and ferrimagnetism return with annealing near 500 °C. The magnetization and exchange constant decrease with increasing dose, and annealing at 1100 °C restores them to bulk values.
Energetics of domain formation in thermomagnetic recording
Authors: Mansuripur M. , Connell G. A. N.
Published: February 2003

A new model for the distribution of perpendicular magnetization in thin magnetic films supporting a circular domain is proposed. The contributions of various sources to the magnetic energy are determined and the demagnetizing effect in particular is discussed at length. It is shown that a demagnetizing energy density per unit area of the domain wall can be defined which, unlike the domain wall energy density arising from exchange and anisotropy contributions, is a function of film thickness h. For domains of large radius and small wall thickness (compared with h), the demagnetizing energy density is found to be linearly increasing with h. A typical cycle of thermomagnetic recording on a thin ferrimagnetic film with room temperature compensation point is then studied, and the effect of various parameters on the formation process and stability of reverse magnetized domains is discussed.
Phase transitions and ferroelectric behavior in the Pb3(MF6)2 family (M=Ti, V, Cr, Fe, Ga)
Authors: Abrahams S. C. , Ravez J. , Canouet S. , Grannec J. , Loiacono G. M.
Published: February 2003

The atomic arrangement in Sr3(FeF6)2 determined by von der Mühll [C. R. Acad. Sci. Paris 278, 713 (1974)] differs from a structure of opposite polarity by atomic displacements of 1.3 Å or less for F and 0.4 Å or less for Sr and Fe. The structure is hence potentially ferroelectric, with an estimated transition temperature TC to the paraelectric state of about 1160 K: experimentally, TC=922 K. The Pb3(MF6)2 family is isomorphous with Sr3(FeF6)2 and the corresponding TC(M) has been measured as 695 (Ti), 635 (V), 550 (Cr), 740 (Fe), and 645 (Ga) K. The respective nonlinear dielectric susceptibilities are 0.010, 0.010, 0.005, 0.045, and 0.010×10−12 V−1 m. A dielectric anomaly is observed close to TC in each material at 1 kHz with a maximum permittivity ε′r of 2740 (Ti), 300 (V), 2015 (Cr), 4000 (Fe), and 7800 (Ga). Dielectric losses in each material reach a minimum at the phase transition temperature.
Electronically active defects in cw beam-annealed Si. I. Electron-beam-induced current
Authors: Sheng N. H. , Mizuta M. , Merz J. L.
Published: February 2003

Electron-beam-induced current (EBIC) and low-temperature photoluminescence are used to study minority-carrier recombination processes in ion-implanted Si subjected to scanned laser or electron-beam annealing. Dark stripes parallel to the laser scanning direction always appear in the EBIC display of laser-annealed samples. The contrast of these dark stripes increases with laser power, while the charge collection efficiency decreases. Both EBIC and photoluminescence results indicate that damage is induced by the annealing laser beam, and that this laser-induced damage extends several microns below the implanted layer. On the other hand, electron-beam annealing yields a laterally uniform pattern and superior charge-collection efficiency.
Multistable orientation in a nematic liquid crystal cell induced by external field and interfacial interaction
Authors: Ong Hiap Liew , Meyer Robert B. , Hurd Alan J.
Published: February 2003

The effects of a short-range, arbitrary strength interfacial potential on the magnetic field, electric field, and optical field induced Freedericksz transition in a nematic liquid crystal cell are examined and the exact solution is obtained. By generalizing the criterion for the existence of a first-order optical field induced Freedericksz transition that was obtained previously [H. L. Ong, Phys. Rev. A 28, 2393 (1983)], the general criterion for the transition to be first order is obtained. Based on the existing experimental results, the possibility of surface induced first-order transitions is discussed and three simple empirical approaches are suggested for observing multistable orientation. The early results on the magnetic and electric fields induced Freedericksz transition and the inadequacy of the usual experimental observation methods (phase shift and capacitance measurements) are also discussed.
Anisotropy of defect introduction by electron irradiation in compound semiconductors
Authors: Pons D.
Published: February 2003

Two possible interpretations of the anisotropy for production of defects by electron irradiation in semiconductors with zinc-blende or Wurtzite structures, shadowing effect, and secondary atomic interactions, are quantitatively examined. For an electron beam perfectly aligned with a [111] hybrid bond direction, it is possible to derive an expression for a shadowing cross section which in principle measures the probability that an atom A masks its nearest neighbor B in the forward beam direction, and therefore that atoms A prevent the incident beam from interacting with atoms B and displacing them. Although these shadowing cross sections are several orders of magnitude larger than the displacement cross sections, we show that, due to electronic scattering and lattice vibrations, they are still much too weak to explain the experimentally observed anisotropies. To investigate the secondary atomic interactions, a simple dynamic model has been developed, where interactions are taken into account in the nearest neighbors atomic shell only. Interactions are described by elastic collisions in which the primary knock-on atom A loses a fraction ΔTB of its initial kinetic energy T0. ΔTB is obtained from an exact integration of classical equations of motion. It is assumed that atom A is definitively displaced if T0−ΔTB is larger than a certain isotropic threshold energy Td, which allows an anisotropic displacement cross section to be deduced. It is shown that this dynamic model predicts with a reasonable quantitative agreement the experimental results obtained in GaAs after irradiations along opposite [111] directions, when using a hard core or Born–Mayer potential to describe the atomic interactions. In particular, the observed reversal of the anisotropy at higher irradiation energies is predicted for the correct order of magnitude of the crossover energy, equal to about twice the threshold energy, and is shown to be the direct consequence of the tetrahedral coordination of the crystal. The magnitude of the anisotropy for irradiation energies larger than the crossover is a sensitive function of the interaction potential range. In the case of a hard core potential the fit gives a hard core radius equal to about twice the Bohr radius which is exactly the expected value for interatomic collisions in the energy range considered here. The paper is concluded by a brief survey of experimental data available for other compound semiconductors. Although they do not allow such a precise comparison as for GaAs, we show that they are entirely consistent with the dynamic model presented here.
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u stress measurement of refractory metal silicides during sintering
Authors: Pan J. T. , Blech Ilan
Published: February 2003

The stress of thin film tantalum silicide, titanium silicide, and tungsten silicide was measured in situ during sintering. These refractory metal silicide films were cosputtered on oxidized silicon, quartz, and sapphire substrates. The films were heated to 910 °C, annealed for 30 min, and cooled down to room temperature. Throughout the heat treatment cycle, the film stress was measured at short intervals by measuring the curvature of the film/substrate couple with a laser beam. It was demonstrated that the intrinsic stress of these silicides is negligible at 910 °C. The final room temperature stress of these silicides, after high temperature sintering, is mainly thermal stress which originates from the difference in thermal expansion coefficients between the films and the substrates. The final stress ranged from 8×108 to 2×109 Pa depending on the silicide and the substrate material. The biaxial elastic moduli were found to be 3.4×1011 Pa for TaSi2.4, 3.9×1011 Pa for TaSi1.4, and 2.2×1011 Pa for TiSi2.4. The thermal expansion coefficients were measured to be 7.1×10−6/°C for TaSi2.4, 6.9×10−6/°C for TaSi1.4 and 1.32×10−5/°C for TiSi2.4.
Redistribution of Fe in thermally annealed semi-insulating InP(Fe): Determination of Fe diffusion coefficient in InP
Authors: Kamada H. , Shinoyama S. , Katsui A.
Published: February 2003

Iron redistribution in InP(Fe) annealed without encapsulant has been studied by using secondary ion mass spectrometry. In annealed crystals, thin surface Fe accumulation followed by Fe depletion appeared. It was clearly shown that the Fe redistribution results from a thermally stimulated Fe outdiffusion with a diffusion coefficient D=D0 exp(−E/kT); D0=2.5×10−4 cm2 s−1, E=1.7 eV at the temperature range from 700 to 900 °C.
Growth conditions and characterization of InGaAs/GaAs strained layers superlattices
Authors: Quillec M. , Goldstein L. , Le Roux G. , Burgeat J. , Primot J.
Published: February 2003

InGaAs/GaAs strained layers superlattices have been grown by molecular beam epitaxy on GaAs. The best growth temperature was found to be 520–540 °C from photoluminescence measurements. Double x-ray diffraction was performed. It shows very good agreement with the kinematical theory. This technique proves to be of particular interest for such structures: a single profile leads to reliable and complete information on layer thickness and InGaAs composition.
Molecular beam epitaxial growth of GaP on Si
Authors: Wright Steven L. , Kroemer Herbert , Inada Masanori
Published: February 2003

The molecular-beam epitaxial growth of GaP on Si was investigated, with the aim of at least approaching device-quality interfaces. Gallium-primed growth on (211)-oriented substrates yielded layers which were free of antiphase domains, and which were of much higher quality than growths on other orientations. A tentative energy-band lineup is proposed, which is consistent with the electrical data. Heterojunction bipolar transistors were fabricated with emitter injection efficiencies up to 90%, in spite of indications that the epitaxial emitter layer was far less heavily doped than the base.
Auger electron and x-ray photoelectron spectroscopy of sputter deposited aluminum nitride
Authors: Kovacich J. A. , Kasperkiewicz J. , Lichtman D. , Aita C. R.
Published: February 2003

Basal crystallographic orientation and semiamorphous films which are nominally aluminum nitride were grown by reactive sputter deposition on silicon substrates and characterized by x-ray photoelectron spectroscopy and Auger electron spectroscopy. The binding energy of the aluminum 2p, nitrogen 1s, and oxygen 1s core electrons and the kinetic energy of the aluminum LVV and KLL Auger transitions indicate that all films contain a component which is chemically identifiable as AlN. The films contain oxygen as a major impurity. The difference in the manner in which oxygen is incorporated into the films, determined by these two spectroscopic techniques, is discussed and related to deposition conditions.
Calculation of the first ionization energies of hydrogenic acceptor pairs in silicon
Authors: Szmulowicz Frank , Wendeln Judith K. , Slaton Steven C.
Published: February 2003

We have calculated ground state energies of neutral and singly ionized diatomic acceptor pairs involving boron, aluminum, gallium, indium, and thallium at the first 13 nearest-neighbor separations in the silicon lattice. Each acceptor is characterized by its own central-cell correction and is treated within the effective-mass approximation. The ionization energies of the neutral or the singly ionized pairs do not conform to the Ohmer–Lang empirical half-sum rule for the ionization energies of the associated acceptor X centers. The results of the calculation might find application in further studies of heavily or double-doped p-type silicon.
Asymmetries in photoconductive properties of donor and acceptor impurities in silicon
Authors: Sclar N.
Published: February 2003

Asymmetries observed in the spectral response, photoionization cross sections, and recombination coefficients as a function of impurity binding energy between donor and acceptor impurities in silicon are presented. These asymmetries, which are not predicted by the hydrogenic effective mass theory, permit higher operational temperatures for a given peak wavelength response for infrared detectors based on donor impurities. The photoconductive asymmetries can be correlated with recently calculated asymmetries associated with nonlinear charge-screening effects which make charge screening more effective for point-charge donors than for acceptors in silicon. To more fully account for the photoconductive asymmetries, impurity potentials more realistic than point charges are needed, including the accurate variation of dielectric screening of the potential with position.
Contact properties of tantalum-silicon films on n- and p-type InP
Authors: Zhang B. , Scott D. M. , Wieder H. H. , Lau S. S. , Tseng W. F.
Published: February 2003

The contact properties of rf sputter-deposited Ta–Si thin films on nand to 750 °C. Rectifying behavior of the contact (φBn ∼0.4 eV) was observed on n-type InP only in the annealing temperature range between 400 and 500 °C. On p-type InP, a barrier height of ∼0.97 eV was observed after annealing up to 650 °C. The contact properties appear to be consistent with the defect-model of barrier formation on III-V semiconductors.
Picosecond photoconductivity measurements of mobility and lifetime in silicon-on-sapphire films
Authors: Grivitskas V. , Willander M. , Tellefsen J. A.
Published: February 2003

Time-resolved photoconductivity and decay measurements in optoelectronic switches made from silicon-on-sapphire films of different thicknesses have been used to obtain the distributions of carrier drift mobility and lifetime as functions of the distance x from the substrate. It is shown that the evaluation of the true lifetime τ is complicated by the carrier diffusion in the case of thick samples (≫3 μm) and by back surface recombination in the case of thin samples (≤0.3 μm). For the lifetime, we have found the relation τ(ns)=0.4+0.4x (μm), and the rear surface recombination velocity has been determined to be of the magnitude s≂104 cm/s.
Oxidation of amorphous silicon and germanium: Photoemission evidence for high oxidation states
Authors: Riedel R. A. , Turowski M. , Margaritondo G. , Perfetti P. , Quaresima C.
Published: February 2003

We made a direct comparison between amorphous and crystalline Ge surfaces exposed to equal amounts of activated oxygen. On amorphous Ge we found a larger average number of oxygen atoms around each oxidized substrate atom than on crystalline Ge. Similar conclutions were reached for the oxidation of crystalline and amorphous Si.
Theoretical and experimental study of the operation of ovonic switches in the relaxation oscillation mode. II. The discharging characteristics and the equivalent circuits
Authors: Callarotti Roberto C. , Schmidt Pierre E.
Published: February 2003

We describe that part of the relaxation oscillation cycle during which the ovonic device will switch from a high resistance OFF state to a lower conductance ON state, either as a time-varying resistance or through a nonlinear intermediate negative resistance state. We discuss in detail several equivalent circuits that describe the observed experimental behavior.
Hole diffusion length in n-TiO2 single crystals and sintered electrodes: Photoelectrochemical determination and comparative analysis
Authors: Salvador P.
Published: February 2003

The photoelectrochemical behavior of an n-TiO2 (rutile) single crystal under different treatments (mechanical polishing and chemical and photoelectrochemical etching) is analyzed and the conditions under which Gärtner’s model can be applied are determined. The hole diffusion length Lp obtained from the photoelectrochemical data is about 10−6 cm for the etched single crystal and seems to be governed by electron-hole recombination at centers associated to impurities introduced in the lattice during the manufacturing process. This value of the hole diffusion length determines the minimum value of the donor concentration Nd for an efficient separation of carriers within the semiconductor depletion layer. This explains the existence of a maximum of the quantum efficiency for Nd∼6×1018 cm−3, which has been found to be a value common to n-TiO2 single crystals of different origin. Lattice deffects introduced near the crystal surface by mechanical polishing behave as recombination centers which reduce Lp to values of the order of 10−7 cm. A comparison with Lp values of n-TiO2 sintered electrodes is made.
Direct measurement of proton straggling in GaAlAs for nuclear profiling
Authors: Bond A. H. , Parayanthal P. , Pollak F. H. , Woodall J. M.
Published: February 2003

We present the first direct measurement of proton energy-loss straggling in Ga1−xAlxAs/GaAs, enabling us to take maximum advantage of the 27Al (p, γ) 28Si nuclear reactions as a powerful nondestructive technique for measuring Al profiles in these structures. Results were obtained using samples produced by molecular beam epitaxy and fabricated to have step-function Al concentration distributions to prescribed depths. The exact straggling width was obtained by a least-square comparison of the experimental spectra with curves calculated using a parameterized straggling distribution. With these results, profiling measurements can now be made giving the Al concentration fall-off at the GaAl/GaAs interface with a spatial depth resolution of about 4% and epilayer thickness determinations to about 2%. We have also observed in one sample a nonabrupt transition at the GaAlAs/GaAs interface, due to differences in substrate surface preparation procedures prior to growth of the GaAlAs layer.
Spectral emission from glow peaks in x-irradiated Al2O3
Authors: Cooke D. Wayne
Published: February 2003

Spectral emission associated with the 214, 246, and 286 K glow peaks of Al2O3 reveals that in addition to the previously reported 330- and 410-nm emission, R-line (694.3 nm) emission also accompanies the glow. Of particular interest is the model which explains the appearance of each type of emission. Our data are qualitatively consistent with a model where trapped holes are thermally released and recombine with F centers and Cr2+ ions to yield 330-nm and R-line emission at 214 K, respectively. Furthermore, F centers are thermally destroyed near 260–290 K thereby producing excited F+ centers which emit 410-nm radiation. In addtiion, the electron released by the F center is captured by a Cr4+ ion converting it to Cr3+ in an excited state which ultimately produces R-line emission.
Excited state population distributions in cesiated thermionic diodes
Authors: Oettinger Peter E.
Published: February 2003

Spectroscopic measurements were made of the excited state distributions in low-pressure cesium thermionic diodes operated in both pulsed and continuous modes. With electron temperatures between 2000 and 3000 K, and average heavy-particle temperatures (cesium atoms and ions) of only 1100 K, the excited-state populations were found to be thermally nonequilibrated. Several population inversions were observed under pulsed operation. These inversions are formed during electron-neutral recombination, limited by specific ‘‘bottleneck’’ deexcitation transition rates. Near inversions were noted under continuous operation.
Compact toroid created by rotating relativistic electron beams
Authors: Sethian J. D. , Robson A. E. , Gerber K. A. , DeSilva A. W.
Published: February 2003

A hollow, rotating relativistic electron beam with ν/γ≫1 may be stably propagated inside an initially field-free, closed metal tube containing neutral hydrogen at a pressure of about 100 mTorr. Under these circumstances the beam is charge neutralized but not current neutralized, and propagates at an equilibrium radius determined by the pressure balance of the self-magnetic fields inside and outside the beam. The axial component of the magnetic field is in opposite directions inside and outside the beam, the total flux inside the tube being zero. During its passage the beam ionizes and heats the neutral gas such that when the beam pulse ends, the magnetic field of the beam is ‘‘frozen’’ into the resulting plasma. The plasma confinement configuration generated by a single beam is a reversed-field linear pinch with an axial current which returns through the wall of the tube. To produce a completely closed plasma configuration, a second rotating electron beam is injected from the opposite end of the chamber between the first beam and the wall. It is possible by this means to bring the persistent axial current to zero, but only under rather restricted conditions because the propagation of the second beam is adversely affected by the peripheral plasma produced by the first beam. However, the principal of this novel method of producing a magnetically confined plasma was effectively demonstrated.
The influence of water vapor on avalanches in air
Authors: Verhaart H. F. A. , van der Laan P. C. T.
Published: February 2003

In the early stages of breakdown of a gas individual avalanches of charged particles are formed. Measurements on avalanche currents with the electrical method can yield new information on discharge processes if the measuring system has a high time resolution (1.3 ns in our case) and if the avalanche is initiated at the cathode by means of a very short (0.6 ns) light pulse. Avalanches in atmospheric air show an aftercurrent caused by delayed electrons which result from detachment. Measurements at various humidities, an extensive analysis and comparison with computer calculations give, for E/p=35 V/cm Torr, the following result. The negative oxygen ions formed lose their electrons gradually with a timeconstant of 83 ns. Collisions however, cause conversion to a nondetaching type of ion. This conversion process has a characteristic time of 32 ns in dry air and is more rapid when water molecules are present, down to 3 ns at a water vapor pressure of 11.25 Torr. The occurrence of these processes, where water molecules cause a reduction of the number of free electrons, provides a new explanation for the increase of the breakdown voltage of air with humidity. The measurements also yield values of the true (α−η), the ionization minus the attachment coefficient of air. This parameter leads to the number of electrons in the head of the avalanche which, used in the streamer criterion, gives good agreement with experimental breakdown voltages. Older (α−η) values included the effect of detachment and gave no agreement with the streamer criterion.
Emission of electrode vapor resonance radiation at the onset of impulsive breakdown in vacuum
Authors: Yen Y. T. , Tuma D. T. , Davies D. K.
Published: February 2003

Simultaneous time-resolved spectroscopic and current measurements have been made during the early stages of current growth leading to breakdown between plane-parallel electrodes of dissimilar material subjected to step-function impulsive voltages. Measurements of the breakdown delay time following the application of the impulse in the range 1–200 μs for an electrode separation of 0.1 cm have been correlated with the optical resonance radiation, characteristic of each electrode material, emitted from the gap during the early stages of breakdown. Data have been obtained from three spatial regions, near the cathode, midgap, and near the anode. The results show that breakdown delay times ≤20 μs are characterized by the initial emission of cathode vapor radiation, whereas for times ≥20 μs anode vapor radiation is emitted prior to cathode vapor radiation. It is concluded that a transition in the impulse breakdown mechanism occurs from one involving initiation in anode vapor to one in which initiation takes place in cathode vapor, as the magnitude of the applied voltage is increased above the dc breakdown value. For an electrode separation of 0.1 cm, this transition corresponds to a breakdown delay time ∼20 μs.
Effect of implantation dose on the hardness, friction, and wear of Sb-implanted Al
Authors: Madakson Peter B.
Published: February 2003

The hardness, friction, and wear behavior of Sb+-implanted commercially pure Al was investigated. The specimens were implanted at 200 KeV to doses of between 1013 and 1017 ions/cm2. Hardness was observed to increase linearly with dose. The increase in wear resistance was not dose dependent and the high doses were found to increase friction. Rutherford backscattering analysis revealed a significant damage of the Al lattice at high doses. It also showed that Fe and Cu, which are impurities in Al, diffused to and away from the implanted surface, respectively. Scanning electron microscopy indicated the formation of Sb and Fe precipitates. The mobility of implanted ions and impurity atoms is considered to be associated with the point defects created during the implantation of Sb+. The changes in the mechanical properties investigated probably resulted from the pinning effect that these defects and precipitates, and their associated stress fields, exert on dislocations.
Elastic constants of polycrystalline Nb3Sn between 4.2 and 300 K
Authors: Poirier M. , Plamondon R. , Cheeke J. D. N. , Bussière J. F.
Published: February 2003

The three elastic constants of polycrystalline Nb3Sn have been measured between 4.2 and 300 K using an ultrasonic pulse propagation technique in composite ribbons of Nb3Sn/Nb. Both the shear (G) and Young’s (E) moduli are found to soften dramatically on cooling to the superconducting temperature, with no abrupt change or hardening near or below the martensitic phase transformation (43 K). Poisson’s ratio is also found to change considerably on cooling, increasing from 0.22 at 300 K to 0.46 at 30 K. These results confirm and complement static and low frequency measurements on similar ribbons but disagree with previous values obtained ultrasonically on bulk samples which exhibited very little softening. Comparison of the present results with polycrystalline averages of single crystal data assuming different textures indicate that deviations are probably associated with material differences and not texture.
Theoretical solution of the transient current equation for mobile ions in a dielectric film under the influence of a constant electric field
Authors: Greeuw G. , Hoenders B. J.
Published: February 2003

In this paper we consider the one-dimensional system of a dielectric slab with one type of mobile ions in it, placed between two blocking electrodes. We present an analytical solution for the transient ionic displacement current, neglecting space-charge effects only. The theoretical results show good agreement with experimental results on Na+, Li+, and K+ ion transport in the oxide of metal-SiO2-Si structures.
Refractive index of In1−xGaxAsyP1−y layers and InP in the transparent wavelength region
Authors: Broberg B. , Lindgren S.
Published: February 2003

We have measured the refractive index of InP and of liquid-phase-epitaxy–grown InGaAsP layers on InP in the transparent wavelength region using a Brewster-angle method. The dependence of the refractive index on material composition and light wavelength has been investigated for near-lattice-matched samples and compared with theoretical models. We show that both an interband transition model and a single effective oscillator model can be used to calculate the refractive index if the parameters used in the calculations are chosen properly. We have also studied the variation with lattice mismatch by varying the growth temperature. We found that a lattice mismatch variation of 10−3 corresponds to a change in the refractive index of approximately 0.02 for λg=1.20 μm layer band gap at λ=1.30 μm wavelength. Finally, we have measured the refractive index of doped InP substrates and found refractive index reductions, due to doping, of up to 0.05.
Theory of ionization/recombination kinetics with application to recombination lasers and the optogalvanic effect
Authors: Lawless John L.
Published: February 2003

The effects of the complete system of electron-atom inelastic collisions are shown to reduce to a system nearly as simple as the well-known one-quantum model. As a consequence, the effects of other processes, such as recombination lasing and resonant radiation enhanced ionization (the optogalvanic effect), can be analyzed simply, analytically, and quantitatively. A number of well- known ionization-recombination approximations are limiting cases of this theory. The simplification in this theory is obtained from a separable feature of the electron-atom collisional transition rate constants for Maxwellian free electrons. This feature has both theoretical and experimental support. No further approximation is needed. The resulting equations are sufficiently simple that the effects of some other processes can be explicitly determined. For example, the behavior of a collisional recombination laser can be expressed explicitly in terms of the rate coefficients. The magnitude of a population inversion and the efficiency for the laser can be derived. Similarly, resonant radiation ionization enhancement can be analyzed and it is shown how large enhancements are possible. Effects of failure of the quasisteady approximation are also analyzed. Models to include other effects are easily developed. Specialization of the coefficients in this theory leads to various well-known ionization-recombination approximations. In the limiting case of an atomic level continuum with all processes other than electron-atom collisions neglected and with one further approximation, the Mansbach and Keck solution is obtained. Through other specializations, the bottleneck, block-of-excited states, one-quantum diffusion, and modified diffusion approximations can each be found.
External laser triggering of a saturable absorption Q-switching system
Authors: Gingras M. , Ouellette F. , Denariez-Roberge M. M.
Published: February 2003

The jitter of a passively Q-switched ruby laser was reduced to less than 50 ns by using external dye laser triggering.
Crystal structure of diamondlike carbon films prepared by ionized deposition from methane gas
Authors: Mōri Toshio , Namba Yoshikatsu
Published: February 2003

Diamondlike carbon films have been prepared by ionized deposition from methane gas. The film structures were examined by transmission electron microscopy, electron diffraction, and electron spectroscopy for chemical analysis techniques. It was found that the structure of the carbon films could be classified into three types: (i) amorphous, (ii) graphite, and (iii) cubic. These types depended mainly on the deposition conditions. Usually crystalline carbon films were diamond mixed with graphite showing an average grain size of several hundred angstroms. Very hard films were composed of diamond crystallites distributed in amorphous matrix.
Effects of contamination and cold ends on electrotransport purification
Authors: Zee R. H. , Lee-Whiting G. E.
Published: February 2003

The differential equation governing the electrotransport of solutes in metals under a contaminating environment is solved analytically using a Laplace transformation. The closed form solution includes an infinite series which vanishes at long times. This solution is applied in zirconium and the results indicate that for oxygen an equivalent partial pressure of 10−7 Pa is necessary to eliminate any serious contamination problem compared to 10−9 Pa for carbon. The cold-ends effect is studied by solving the appropriate diffusion equation numerically. This effect is restricted to mainly the cold sections of the material and does not significantly alter the overall purification result.
Free-standing thin film Ge single crystals grown by plasma-enhanced chemical vapor deposition
Authors: Outlaw R. A. , Hopson P.
Published: February 2003

Single crystal Ge films (∼10 μm) have been epitaxially grown on polished (100) NaCl substrates at 450 °C by plasma enhanced chemical vapor deposition (PECVD). Upon cooling, the films were separated from the substrate by differential shear stress which left handleable free-standing films of Ge. Growths were achieved by nucleating at minimum plasma power (∼10 W) for very short intervals and then raising the power to 65 W to increase the growth rate to approximately 10 μm/h. Substrate exposure to the plasma at too high a power for too long a time was found to sputter and erode the surface, thus substantially degrading the nucleation process and the ultimate growths. The free-standing films were visually specular and exhibited a high degree of crystalline order when examined by x-ray diffraction. Auger electron spectroscopy (AES) and energy dispersive analysis of x rays (EDAX) showed no detectable bulk contamination. The films were found to be p type with a carrier concentration of approximately 3×1016 cm−3, a resistivity of 0.11 Ω cm, and a Hall hole mobility of 1820 cm2 V−1 s−1 at room temperature.