bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoacoustic measurement of effective thermal properties of rough and porous limiter graphite
Authors: Bein B. K. , Krueger S. , Pelzl J.
Published: April 2011

The photoacoustic amplitude and phase lag of rough and porous graphite limiter plates, before and after exposure to plasma discharges in Tokamak devices, have been measured and interpreted to obtain a quantitative description of the effective thermal-depth structure. The effusivity (kρc)1/2, the relevant thermophysical parameter for time-dependent surface heating, of the measured samples shows depth profiles, which can be approximated by a three-layer model. Before exposure to plasma discharges, this depth profile can be related to the surface roughness and volume porosity. Depending on the heating conditions and the position of the samples during incorporation in the fusion devices, one can observe changes of the effusivity of the first surface layer to both lower and higher values.
Thermal effects in materials with continuously varying optical and thermal properties in one dimension
Authors: Aamodt L. C. , Murphy J. C.
Published: April 2011

The complex heat-flow pattern in a heterogeneous sample makes the thermal analysis of these materials difficult. In this paper, we consider heterogeneous materials with continuously varying parameters in one dimension. Although this analysis is directed toward photothermal applications, specifically those using broad-beam illumination, it has many features in common with general harmonic heat flow.The analysis shows that harmonic heat flow is interrupted by spatial variations in the sample's thermal and optical properties via two different types of heat barriers, one depending exclusively on thermal properties (thermal barriers) and the other depending upon both optical and thermal properties (optical–thermal barriers). Thermal barriers are created by spatial variations in thermal effusivity whereas the optical-thermal barriers are created by spatial variations in the ratio of the thermal-diffusion length to the optical-absorption length. The character of the optical–thermal barriers is affected by optical saturation in the sample.The temperature distribution in a heterogeneous sample is interpreted in terms of thermal waves providing an intuitive guide for analyzing heat flow in heterogeneous materials.The surface temperature is also obtained in a general form suitable for both heterogeneous and homogeneous calculations.
Mechanisms of pulsed photoacoustic generation
Authors: Hutchins D. A.
Published: April 2011

The mechanisms by which ultrasonic transients may be generated by pulsed laser irradiation are reviewed, with particular reference to the wave forms resulting in both fluid and solid media. Specific examples of experimental results are presented that demonstrate that a pulsed ultraviolet source is a convenient means for ultrasonic generation in both liquids and solids.
Photothermal examination of buried layers
Authors: Baumann J. , Tilgner R.
Published: April 2011

The influence of a buried layer within a sample on the propagation of thermal waves is determined by measuring the phase and amplitude of the photothermal signal during periodic illumination. The results are in agreement with the calculation that follows a thermal-wave approach involving a three-layer sample and a Lambert–Beer-like distribution of the heat source in the covering layer. In this way determination of the thickness or thermal properties of buried layers even much thinner than their thermal-diffusion length is possible.
Periodic structures of clean, normal, and superconducting material I: the density of states of the normal sections
Authors: Cleary Robert
Published: April 2011

We can calculate the density of states in the normal regions of periodic structures of clean, normal, and superconducting material. A derivation of the energy-momentum relation for sections of different Fermi surfaces is very briefly sketched. The results reduce to formulas with m* and pF taken as uniform throughout, as, for example, in the mixed state of a type-I superconductor. A plot of the density of states N(ε,x) vs. energy E for periodic structures of different cell lengths and normal-metal superconducting sharing widths, as well as [Formula: see text], where νF is the Fermi velocity of the superconducting sections, is presented in the body of this paper. A brief look at the proximity effect is included, as well as a verbal discussion of the self-consistency for our model. The density of states in the superconducting regions is dependent on the parallel coordinate x in an oscillating fashion, which is hard to calculate numerically. This is not the case for the normal sections or for the self-consistency equation.
Multiple interaction between a radiating dipole and parallel conducting cylinder
Authors: Ragheb H. A. , Hamid M.
Published: April 2011

The radiation from a long dipole in the presence of an infinitely long, circular conducting parallel cylinder is examined analytically. The expression for the far-zone field, which includes all successive multiple-scattering terms between the dipole and the cylinder, is derived using an iterative approximate procedure. The current induced on the dipole due to backscattering from the cylinder is calculated for each iteration. The derivation includes integral expressions, which are solved asymptotically using the far-zone field approximations. Also, a numerical technique is employed for solving the problem to verify the analytical solution. The results due to both analytical and numerical solutions are in excellent agreement. It is also found that the interaction between the dipole and the cylinder has a significant effect on the radiation field.
Side-band instabilities of a steady finite-amplitude whistler wave in a collisionless plasma
Authors: Marquis E. , Teichmann J.
Published: April 2011

The stability of a steady finite-amplitude whistler wave penetrating a collisionless, unbounded, homogeneous plasma is studied. The supporting wave as well as the excited side-band waves are assumed to propagate parallel to an uniform magnetostatic field B0. For a general form of the distribution function of trapped electrons, the growth (damping) rates of side-band modes are calculated.It is shown that a particular distribution of trapped electrons gives rise to strongly unstable side-band electromagnetic modes having right-hand polarization. The spectrum of unstable electrostatic and electromagnetic satellite waves is analyzed.
The effect of uniaxial stress on the persistent photoconductivity in Te-doped AlxGa1−xAs
Authors: Johnstone Eric , Sakamoto Masamichi , Zukotynski Stefan , Logan Ralph A.
Published: April 2011

Persistent photoconductivity in Te-doped AlxGa1−xAs is measured. It is found that the photoconductivity rise is a phonon-assisted process. The photoconductivity decay time increases with the application of stress. From the dependence of conductivity on stress, the donor-level deformation potential is determined to be approximately 2 meV∙kbar−1 (1 bar = 100 kPa). Some evidence is presented that suggests that more than one DX-type level is required to explain the features of the persistent photoconductivity.
Ion-assisted sputter deposition of CdTe layers
Authors: Das S. R. , Rajan K. , Meer P. Van der , Cook J. G.
Published: April 2011

Epitaxial, single-phase CdTe layers have been deposited on a variety of single-crystal substrates, including freshly cleaved KBr and NaCl and polished BaF2, by ion-assisted, planar, rf magnetron sputtering. The substrate temperature and bias were used as independent, operator-controlled process parameters to greatly enhance the degree of orientation in the films and (or) modify the crystallographic form of the deposited layer. Thus, depending primarily on the substrate temperature and bias, the deposited CdTe films exhibited one of several forms: (i) single-phase, highly oriented cubic, (ii) single-phase, highly oriented hexagonal, (iii) two-phase, highly oriented, hexagonal plus cubic or hexagonal plus tetragonal, and (iv) single-phase, epitaxial tetragonal. Compositional analysis revealed no impurities. However, films of all crystallographic phases contained a large density of planar defects such as twins, stacking faults, and low-angle grain boundaries.
Design-rule development for a 1.2 μm complementary metal oxide semiconductor process
Authors: Smith D. A. , Leung P. , Tarasewicz S. W.
Published: April 2011

The basic considerations in the development of a design-rule set for a 1.2 μm N-well complementary metal oxide semiconductor process at Northern Telecom Electronics Limited are presented. Several important implementation strategies required for successful design-rule development in an industrial environment are discussed. Topics include equipment limitations, device constraints, and rule rationalization and evolution.
The growth of gallium arsenide on Si(100) by molecular-beam epitaxy
Authors: Moore W. T. , Devine R. L. S. , Maigné P. , Houghton D. C. , Baribeau J.-M. , Denhoff M. W. , Jackman T. E. , Kornelsen E. V. , SpringThorpe A. J. , Mandeville P.
Published: April 2011

The growth of GaAs on Si(100) directly and with Ge buffer layers has been carried out sequentially under ultra high vacuum conditions in a double-ended III–V and group IV molecular beam epitaxy system. These heterostructures were examined by cross-section transverse emission microscopy, Rutherford backscattering, X-ray diffraction, and photoluminescence spectroscopy.Dislocation densities were observed to be high [Formula: see text] near both the GaAs–Si and the Ge–Si interfaces and to decrease to ~5 × 108 cm−2 a few micrometres from these interfaces. No dislocations were observed to originate at the GaAs–Ge interface, but the threading dislocations existing in the Ge buffer layer were found to propagate across this interface without significant deviation. The crystalline quality of the GaAs grown on Ge buffer layers was comparable with that grown on Si directly. However, GaAs has not yet been grown on the highest quality Ge buffer layers obtainable.
Auger electron spectroscopy study of pulsed-laser evaporated CdTe films on (100) GaAs
Authors: Dubowski J. J. , Mitchell D. F. , Sproule G. I.
Published: April 2011

Pulsed-laser evaporated CdTe films deposited on (100) GaAs substrates have been studied by Auger electron spectroscopy (AES). The depth dependence of chemical composition has been determined from sputtering profiles. The films had a constant chemical composition within the accuracy of AES. Thermal treatment of GaAs substrate at temperatures as low as 260 °C was found to be sufficient for obtaining and O- and C-free post-growth surface of GaAs. The width of the interfacial CdTe–GaAs region was ≤ 3 nm, and the interface was Te-rich. A possibility of forming the As2Te3 layer at the CdTe–GaAs interface has been demonstrated.
A device-oriented study of CdS films deposited by a hot-wall technique
Authors: Haque A. , Dixon A. E. , Brodie D. E.
Published: April 2011

A device-oriented study was carried out on thick CdS films (25–30 μm) suitable for solar-cell applications deposited on glass substrates, using a hot-wall technique at a pressure of 1 × 10−6 Torr (1 Torr = 133 Pa). Films were characterized using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The degree of preferred orientation was observed using a simplified version of the Schulz method. Films grown under nominally identical conditions showed two types of growth habit. Type-I films were composed of crystallites having their c axis in a cone with a half angle of 6° about the substrate normal. In Type-11 films, the growth direction was within 11° of the normal to the substrate. Surface grain dimensions varied from 2 to 6 μm, and the room-temperature resistivity varied from 1 to 5 Ω∙cm for the following deposition parameters: substrate temperatures of 230–250 °C, hot-wall temperatures of 370–400 °C, and a deposition rate of 1.2 μm∙min−1. Front-wall CuxS–CdS heterojunctions were made using a hot CuCl dip. Current–voltage characteristics were measured at room temperature. Without optimizing the cell design, open-circuit voltages of 0.45 V and short-circuit currents of 20–30 mA∙cm−2 under AM2 illuminations were observed.
Phase transformations at a nickel–silicon interface under transient annealing
Authors: John P. K. , Rastogi A. C. , Tong B. Y. , Wu X. W. , Wong S. K.
Published: April 2011

We use intense incoherent light pulses of ~60 μs duration to induce reactions at a Ni–Si interface. Changes in morphology, composition, and electrical characteristics of the interfaces are studied. The diagnostics include scanning electron microscopy, Auger spectroscopy, X-ray analysis, and diffusion analysis. After annealing for a total of ~1 ms, the Si surface is found to support an intermixed and disordered Ni–Si layer consisting of mixed islands and flat structures. On further irradiation, after a certain threshold Ni density is reached in the Si, silicide growth takes place at the interface through an amorphous-to-crystalline transformation of this intermixed layer. The first phase to nucleate is mononickel silicide with a (200) orientation. This is attributed to kinetic effects, which optimize the heat of formation in the presence of excess Si.
InP (and GaAs) substrate stabilization by the presence of GaAs (and InP) in a metal-organic vapour-phase epitaxy system
Authors: Masut Remo A. , Sacilotti Marco A. , Roth Alain P. , Williams Digby F.
Published: April 2011

Metal-organic vapour-phase epitaxy (MOVPE) is a well-established technique for semiconductor growth. Like molecular-beam epitaxy, liquid-phase epitaxy, and vapour-phase epitaxy, it requires a stabilized substrate surface prior to growth to obtain a high-quality crystal. Studies of the stabilization of GaAs and InP substrates placed side by side with their interactions under V-hydride flows can provide valuable information. Here we show the effect of exposing GaAs and InP substrates to AsH3 and (or) PH3 in the temperature range from 550 °C to 750 °C, in an MOVPE reactor. The presence of a GaAs substrate partially stabilizes the InP substrate; the stabilized area decreases when either temperature of AsH3 flow increases. The presence of a stabilized InP substrate (under PH3 flow) also partially stabilizes the GaAs substrate. Surface analysis shows that the stabilized area contains column-V species coming from the neighbouring substrate. These column-V species are competing with species originating from the V hydrides (AsH3 or PH3). From the analysis of these experiments, we conclude that the V-hydride species active in the MOVPE environment are not dimers or tetramers. Annealing the substrates under both AsH3, and PH3 shows preference for As-specics aggregation at the substrate surface. The simple model previously used to prediet stabilization is extended to cover this mixed-hydride situation.
The specific heats of copper, silver, and gold below 300 K
Authors: Martin Douglas L.
Published: April 2011

Specific-heat measurements on silver and gold in the 15–320 K range are reported and compared with earlier measurements on these metals. The present results together with recent measurements on copper (D. L. Martin, Rev. Sci. Instrum. 58, 639 (1987)) are analyzed in terms of the Debye temperature. The results suggest a negative anharmonic contribution to specific heat for silver and gold. Structure in the results for all three metals below 60 K is consistent with known imperfections in the International Practical Temperature Scale of 1968.
Nuclear magnetic resonance investigations of two-dimensional 3He
Authors: Godfrin H.
Published: April 2011

The magnetization of 3He adsorbed on Grafoil measured at 3 mK displays a ferromagnetic peak as a function of coverage (around 2.5 layers) substantially above free spin value. This behavior is interpreted as the result of a large ferromagnetic exchange interaction between solid in the second layer and the liquid. Solid–liquid coexistence and subsequent compression of the solid in the second layer determine the peak shape. In-plane exchange is shown to be small by measurements at low densities in the first layer. The solid–liquid exchange mechanism explains the ferromagnetic effects observed in bulk liquid 3He confined in Grafoil; it should exist, with the same magnitude, at the solid–liquid interface of bulk 3He.
Third sound and 3He–4He mixture films
Authors: Hallock R. B.
Published: April 2011

The fundamental ideas of third sound are surveyed, and the historical importance of third sound as a technique for the investigation of helium-film systems is emphasized through the discussion of several examples. The desire to study 3He–4He mixture films has led to the development of new methods for detecting third sound and these are discussed. We then describe some of the interesting properties of 3He–4He mixture films that have been discovered by third-sound techniques and by recent preliminary third-sound and nuclear magnetic resonance investigations of the mixture films conducted in this laboratory.
Polarization dependence of resonant multiphoton ionizations on 1S0 and 1,3D2 states in atomic mercury
Authors: Mah K. R. , Dalby F. W. , Barnard C. W.
Published: April 2011

The polarization dependences of some resonant multiphoton ionizations in atomic mercury have been measured with a broadband (bandwidth ≈ 1.5 cm−1) multimode dye laser at moderate light intensities (≈ 500 MW∙cm−2). The multiphoton processes studied were the absorption of four photons to a resonant 1S0, 1D2, or 3D2 level by one-photon ionization. Complete saturation of the one-photon ionization step results in the ionization of all atoms excited to the resonant level. Because of the saturation of the ionization step, the polarization dependence of the four-photon excitation to the resonant level is measured. The theory developed by Dalby et al. is shown to give good agreement with the experiment when it is used to calculate the polarization dependence of the multiphoton transition to the resonant level. For the 6d1D2 resonance, distortions in the polarization dependence and an unusual linewidth dependence on the light polarization were observed. We relate these observations to the alternating current Stark effect and to the production of the third harmonic of the laser light in the focal volume.
Coherent meson production relativistic heavy-ion collision
Authors: Ghosh Dipak , Roy Jaya , Sengupta Ranjan
Published: April 2011

This paper presents a study on the coherent meson production in 12C–emulsion interactions at 4.5 Gev∙c−1∙nucleon−1 incident momentum. The search for coherence was done through noting the shape of the multiplicity distribution in different narrow rapidity bins and observing whether or not the distribution was according to Poisson; when the fields are completely coherent the multiplicity should have a Poisson distribution. It was observed that the multiplicity distribution was Poisson in nature in two bins of higher rapidity, and consequently the field was coherent in those rapidity bins. The percentage of coherent meson production was estimated to be 48%.
Oscillator strength distribution in the alkaline-earth elements
Authors: Barrientos Carmen , Martin Inmaculada
Published: April 2011

The oscillator strength distribution between the discrete and continuous regions of the spectra of Mg, Ca, Sr, and Ba has been obtained. Computations have been carried out through the Quantum Defect Orbital (QDO) method, with explicit introduction of the two-electron transitions that lead to resonances in the spectra of the last three elements. Interference effects between excitations to autoionizing levels and to the continuum have been ignored.
Induced emission of pions in a two-level system with Fermi momentum and of finite width
Authors: Lacroix B. , Lam C. S.
Published: April 2011

We consider Δ → n + π as a two-level (Δ, n) system emitting the quantum π. The amplification factor for the induced emission of N of them was derived previously assuming the width of Δ to be small and assuming Δ to have no momentum inside the nucleus. In practice these assumptions are invalid. In this paper we derive a formula and obtain numerical results for the amplification factor when these assumptions are removed.
Dynamics of pattern formation in layered materials: computer simulations of intercalation and deintercalation
Authors: Kirczenow G.
Published: April 2011

Three-dimensional Monte Carlo simulations of intercalation and deintercalation of microcrystals are presented. The kinetic Ising model used represents intercalation compounds as assemblies of interacting elementary intercalate islands. Real-space pictures of the microscopic processes and (00l) structure factors are given. The intercalate transport and cooperative effects leading to stage ordering and domain formation are investigated. Surface effects and elastic energy barriers are considered. Well-ordered stage 2 structures grow from pristine host crystals in either a multidomain or essentially single domain mode. For any guest–host combination, either mode can be selected by a suitable choice of the physical nature of the guest reservoir. Growth of high stages results in stage-disordered Daumas–Hérold domains because the formation of stage-ordered structures is not favored thermodynamically. Deintercalation from stage 1, with the reservoir chemical potential below the intercalation threshold, proceeds through a stage 2 domain structure that grows as a deintercalation front moves through the crystal. The in-plane pattern of stage 2 islands, which forms, is remarkably stable during this process. Eventually a residue compound forms, with some runs of galleries completely empty while in others the intercalate is self-trapped.
Maxwell–Einstein theory in 13 dimensions with compactified timelike dimensions
Authors: Wolf C.
Published: April 2011

Compactification in Maxwell–Einstein theory is discussed when some of the compactified dimensions are permitted to be timelike. Compact spaces with two and three timelike dimensions are discussed.
Measurement of absolute electron-impact excitation cross sections in Ar and N2 using H and H2 emissions as secondary standards
Authors: Forand J. L. , Wang S. , Woolsey J. M. , McConkey J. W.
Published: April 2011

A detailed description is given of a technique in which emissions from H and H2 are used to calibrate an apparatus used for electron-impact emission cross-section measurements in the wavelength range 90–130 nm. Absolute emission cross sections have been measured at 200 eV electron-impact energy for the 120 nm N I line following dissociative excitation of N2 and for the Ar and Ar+ lines at 104.8, 106.7, 92.0, and 93.8 nm respectively. Good agreement with earlier works is obtained in the case of the N I line when earlier data are renormalized to take into account the recent revision of the cross section for production of Lyman α from H2. Measurements of the 104.8 and 106.7 nm lines suggest a 40% cascade component for the latter line at energies of 200 eV and above.
Analytical deuteron wave function
Authors: Oteo J. A.
Published: April 2011

A simple parametrization of the deuteron wave function is used to make it easy to compute, in closed form, the various quantities appearing in calculations involving the deuteron. Formulae for some of the integrals that appear in such calculations are also given. The parameters of the wave function have been determined for the simplest case.
Parity violation in proton scattering: low energy region
Authors: Haeberli W.
Published: April 2011

Measurements of the parity-violating longitudinal analyzing power, Az, in the scattering of low-energy protons (Ep < 50 MeV) are reviewed. The experiments are based on the determination of the relative scattering cross sections σ+ and σ− for incident protons of positive and hegative helicity, respectively. The first results were reported from Los Alamos, where a significant analyzing power [Az = (−1.7 ± 0.8) × 10−7] was found for p–p scattering at 15 MeV. All other results are for a proton energy near 45 MeV, primarily by the group working at Schweizerisches Institut für Nuklearforschung, which recently reported a new, very accurate result for p–p scattering of Az = (−1.50 ± 0.22) × 10−7. A review is presented of the methods that have been developed by this group over the last 10 years to reduce systematic errors in the determination of Az to a few times 10−9.
Paramagnetic properties of a vacuum embedded in a strong magnetic field
Authors: Mielniczuk W. J. , Lamm D. R. , Valluri S. R.
Published: April 2011

It is shown that a vacuum embedded in a very strong magnetic field, B, behaves like an isotropic, paramagnetic medium. It is further demonstrated that the magnetic permeability μ(B) of the vacuum differs from 1 by not more than 1.1 × 10−4 for magnetic fields weaker than 4.4 × 1013 G (typical paramagnetic materials at room temperature have corresponding values in the range of 10−5–10−2).
Laser mode control with variable reflectivity mirrors
Authors: Lavigne Pierre , McCarthy Nathalie , Parent André , Snell Kevin J.
Published: April 2011

Global efficiency, transverse mode discrimination, and the near- and far-field optical quality of unstable laser resonators are improved with variable reflectivity mirrors (VRMs). Analytical and numerical results are given for Gaussian and parabolic reflectivity mirrors. The VRM design is described, and experimental results obtained using different lasers with Cassegrain cavities are presented.
Resistive ballooning mode in tokamaks
Authors: Hirose A. , Kroeker T. L. , Ishihara O.
Published: April 2011

The resistive ballooning mode in tokamak geometry has been re-investigated without imposing any ordering among characteristic frequencies, [Formula: see text] (growth rate), ω* (diamagnetic frequency), and ωD(η) (magnetic-drift frequency in the ballooning space). An extensive numerical search for unstable eigenfunctions has failed. Only a stable-ion diamagnetic mode (analytically predicted) has been found.
Electromagnetic scattering from a dielectric-coated elliptic cylinder
Authors: Ragheb H. A. , Shafai L.
Published: April 2011

An exact treatment using the boundary-value method for solving the problem of scattering of a line-source field or a plane wave by a perfectly conducting elliptic cylinder coated with a confocal dielectric elliptical shell is presented. For the line-source excitation the total field is calculated, while for the plane-wave excitation the echo width is obtained. A sample and interesting results for the backscattering echo width versus different geometrical parameters are obtained and presented. A set of design-type curves, which are useful for locating the maximum or minimum backscattering echo width, are also provided.
One-loop amplitudes of closed bosonic strings
Authors: Ho-Kim Q. , Mathieu P.
Published: April 2011

We derive the one-loop amplitudes for the emission of tachyons and massless bosons from closed unoriented bosonic strings. Contributions from both the torus and the Klein bottle are included, and the structure of their divergences is discussed. It is shown that in the zero-slope limit, the amplitude for emission of massless bosons agrees with results of point-field calculations for the coupling of scalar fields to gravity. Finally, the possibility of cancelling the leading ultraviolet divergence for a particular gauge group is discussed and illustrated for the vacuum-energy density.
Two-dimensional numerical simulations of electrothermal behaviour in very large scale integrated contacts and vias
Authors: Allegretto W. , Nathan A. , Chau K. , Baltes H. P.
Published: April 2011

We present results of electrothermal interactions in fine geometry contacts and vias. The results have been obtained using a two-dimensional model based on the finite-box procedure. For the contact geometry, large electric potential gradients and consequently high Joule-heating effects develop at the interface, which is relatively low in electrical conductivity. In the case of the via, however, temperature escalations result from singularities in the electric field at geometrically imperfect locations, owing to inadequate step coverage in the metallization process. In particular, we discuss the treatment of boundary conditions for the temperature equation.
Simulation of thin film step coverage and microstructure
Authors: Brett M. J. , Westra K. L. , Smy T.
Published: April 2011

Ballistic deposition of hard discs has been used for computer simulation of thin film growth over a step on a substrate surface. Up to 16 000 particles were deposited per simulation using an angular distribution of particle trajectories representative of planar magnetron sputter deposition and incorporating a surface mobility model for deposited particles. The simulated films show a surface profile evolution during growth and an orientation of columnar film microstructure that are very close to the surface profile and microstructure observed in real films of aluminum sputter deposited over an oxide step on a silicon substrate.
All-optical, silicon based, fiber optic modulator using a near cutoff region
Authors: Normandin R. , Houghton D. C. , Simard-Normandin M.
Published: April 2011

We demonstrate, using molecular beam epitaxy and chemical vapour deposition grown silicon thin films, an all-optical modulator for single-mode guided light at 1.32 μm. A control beam of above band-gap light is used to generate electron–hole pairs via inter-band absorption and the resultant lowering of the effective refractive index brings the waveguide to cutoff thus limiting throughput. Near 100% modulation is obtained with less than 150 pJ energies with subnanosecond initiation and recovery times. The operation is stable and is polarization and wavelength independent in a three port geometry suitable for use as a logic gate. To reduce the total energy required to bring the waveguide to cutoff, the effects of using a small, already near cutoff and leaky region at the interaction region is investigated here. Preliminary measurements on a graded index, leaky mode, chemical vapour deposition sample resulted in a reduction by a factor of five or better in drive energy. By keeping the leaky region short, the losses can be kept to negligible values. Results in time resolved imaging of the guided mode are also presented along with the necessary design considerations for performance compatible with presently available communication solid state laser sources.
Density of localized states in amorphous semiconductors
Authors: Ladurantaye Louis de , Lépine Yves , Lewis Laurent J.
Published: April 2011

A procedure is described for extracting the density of localized states of amorphous semiconductors from transient photo-current measurements. Based on a discretized multiple-trapping transport model, our deconvolution scheme determines, for each trap level, the time–temperature combination such that the activity is a maximum for that level. The density of the trap states is then obtained using linear-algebra techniques. As an example, our procedure is applied to computer-generated signals obtained using an exponential density of states. The deconvoluted distribution of levels is found to be in excellent agreement with the original one.
The ν3 fundamental of silicon tetrafluoride. Spectroscopy with laser sidebands
Authors: Jörissen L. , Prinz H. , Kreiner W. A. , Wenger Ch. , Pierre G. , Magerl G. , Schupita W.
Published: April 2011

The ν3 fundamental of 28SiF4 has been investigated with laser sidebands and infrared radio-frequency double resonance. From 165 infrared and 206 pure rotational transitions, 10 ground state and 22 excited state constants have been determined. The calculation was performed with a Hamiltonian developed up to sixth order.
Thermodynamic properties of crystalline KCl
Authors: Kwon T. H.
Published: April 2011

Thermodynamic functions of crystalline KCl have been evaluated using a localized model characterized by a pseudopotential and direct Brillouin zone sums. Numerical results are compared with available experimental data for adiabatic compressibility, the linear thermal expansion coefficient, specific heat at constant volume, and specific heat at constant pressure. Calculated results show excellent agreement with experimentally observed data.
First-order covariant treatment of the influence of space charge and external fields on finite-emittance relativistic beams of charged particles in generalized curvilinear coordinates
Authors: Bosi Giulio
Published: April 2011

A first-order covariant treatment of space-charge effects on relativistic beams of charged particles under the influence of applied fields of arbitrary forms is presented. The beams and fields are assumed to fulfill no particular symmetry conditions, and curvilinear orthogonal coordinates are used. Relative to a given distribution function, a suitable choice of both metric tensor and optical axis allows for the selection of appropriate coordinates, reducing the overall transverse motion of a charged particle to a pair of independent motions along the principal axes of a tensor that is related to both geometry and field. Detailed formulas applying to a microcanonical distribution in an eight-dimensional phase space are worked out, and the envelope equations for a monokinetic beam are carried out explicitly. The distribution function is shown to separate into the product of a stationary distribution in transverse-coordinate space and momentum space by using factors carrying the relativistic corrections. As a result, the envelope equations are formally identical to the customary equations describing the envelope of a nonrelativistic beam under the influence of merely transverse forces. A few numerical applications are finally presented; the behavior of beams moving through a magnetic prism and through a cycloidal analyzer is displayed graphically.
Mechanical and structural properties of metallic glasses
Authors: Rafizadeh Hamid A.
Published: April 2011

A simple linear-chain model is utilized in calculation of the mechanical and structural properties of metallic glasses. The model calculations of composition-dependent elastic constants show good agreement with the experimental data available for binary metallic glasses. The model is capable of distinguishing different structural characteristics of glassy systems and provides excellent agreement with the radial distribution functions of amorphous cobalt, metal–metalloid, and binary transition metal glasses. The model is not limited to binary systems and can be readily applied to ternary and higher order metallic glasses.
Asymptotic properties of multiplicity distributions in high-energy pn and pp interactions
Authors: Bhattacharjee D. K. , Cherian P. J. , Maity D. K.
Published: April 2011

Results of pn and pp multiplicity distributions from pd interactions at 400 GeV/c are presented together with others from 100–300 GeV/c. These, along with the corresponding distributions for pp interactions in a hydrogen bubble chamber were analysed to look into their scaling behaviour. It has been shown that neither the semi-inclusive scaling hypothesis nor the Mueller–Regge approach can explain the behaviour of data at 400 GeV/c. The subtraction of the leading particle did not seem to be effective. The charged multiplicities are shown to have a negative binomial distribution.
Détecteur photovoltaïque au silicium amorphe
Authors: Diawara Yacouba , Currie John F. , Najafi S. Iraj , Brebner John L.
Published: April 2011

We present here the results obtained for a hydrogenated amorphous silicon photovoltaic detector fabricated by plasma-enhanced chemical vapor deposition and integrated on a glass planar waveguide. Capacitance measurements of (Al, Cr) – a-Si:H – n+a-Si:H – Al multilayer Schottky diodes were used to model the devices and to deduce the properties of a-Si:H layer. A response time of 30 ns full width at half maximum in unbiased operation was obtained when tested using short (4 ns) guided light pulses; the response time value was obtained without external polarization, thus making the device autonomously functional.
Rajpoot–Samuel four-preon model of elementary particles
Authors: Krori K. D. , Bordoloi Namita Sarma
Published: April 2011

A study of the four-preon model of quarks, leptons, and gauge bosons recently developed by Rajpoot and Samuel has been presented in this paper with reference to a number of electromagnetic, weak, and lepto-quark interactions. It is pointed out that neutrino oscillations and neutrinoless double β-decay are not likely to occur according to this model, but the process μ → e−γ may. Further, in the context of new heavy leptons and a new scalar particle recently discussed in the literature, an attempt at identification of these particles is also made here.
Confidence intervals in spectroscopic data reduction
Authors: Femenias Jean-Louis
Published: April 2011

The calculation of reduced radii, which connect standard deviations to physical errors, is revisited. A new and simple method, which takes into account the number of random variables, the exact confidence probability, and the correlation is presented in the normal case and in the case of unknown probability distributions. It is shown that correlation effects on radii are much less important than on standard deviations.
Radiation effects in living cells
Authors: Goodhead Dudley T.
Published: April 2011

Insult from ionizing radiation is in the form of microscopic tracks that are highly structured from the atomic level upwards. The internal composition of mammalian cells, too, is highly structured, from dimensions smaller than the DNA molecule (diameter ~2 nm) up to the entire cell [Formula: see text]. There is a wide spectrum of initial physical and chemical damage, subsequent biochemical modification, and final cellular response. The vast majority of the physical, chemical, and biochemical damage is apparently of little relevance to final observable cellular effects. This predominance of "irrelevant" damage masks the nature of that which is of prime relevance. Nevertheless, systematic studies of the effects of radiations on cells have revealed that there are unifying features in the observed responses of different cell types to induction of different effects, and by different radiations. This implies that there are dominant mechanisms that are open to kinetic analysis. Relevant processes may be dominated by the non-linear kinetics of clusters of ionizations and excitations that are within the macromolecule of interest (DNA) or shared with closely adjacent bound molecules. Quantitative models of radiobiological action have concentrated on the relative kinetics of single-track versus multitrack modes and describe the elementary damage either in terms of single ionizations or of clusters of energy depositions.
Electron energy loss in fluids: Thermalization distances in liquid and gaseous sulfur hexafluoride
Authors: Ramanan G. , Gee Norman , Freeman Gordon R.
Published: April 2011

Ionizing radiation passing through a fluid produces an ion–electron pair by knocking an electron off a molecule. The electron possesses excess energy, which it loses in collisions with molecules as it moves away from the ion. These are stochastic processes. The distance travelled during thermalization determines the probability that the electron ultimately escapes the Coulombic field of the ion to form freely diffusing ions. Free-ion yields were measured in X-irradiated sulfur hexafluoride at 5.7 ≤ d(kg m−3) ≤ 1860, corresponding to the vapor and liquid at 202.8 ≤ T(K) ≤ 324.1. (The critical fluid has dc = 730 kg m−3 and Tc = 318.7 K). The electric field dependence of the yield was best fitted using an electron thermalization distance distribution function F(y) that was Gaussian with a power tail. The most probable thermalization distance bGP was estimated at each density. The density-normalized electron-thermalizing ability of the fluid decreased with increasing gas density and was independent of density in the liquid phase. The dependence is different from those observed in hydrocarbons and might reflect a density effect on the energy dependence of the electron-attachment reaction.
Separation of variables for the Klein–Gordon and Dirac equations in two-dimensional space-times with a null coordinate
Authors: Villalba Victor M.
Published: April 2011

The separation of variables for the Klein–Gordon and Dirac equations, in the presence of electromagnetic fields, for a class of curvilinear coordinate systems with a null coordinate is presented. We show that these coordinates can be associated with a system with constant acceleration. Exact solutions for the free case and for a particle in a constant electric field are obtained. Finally, the quantum distribution of scalar massless particles in the accelerated frame of reference is computed.
Radiation of a line source mounted between two dielectric substrates
Authors: Diamandi Ioanna , Mertzianidis Costas , Sahalos John N.
Published: April 2011

The radiation characteristics of a line source lying on the bottom surface of a dielectric substrate that is mounted on the top of another one are presented. The pattern is calculated for two different cases. One is for infinite thickness of the second substrate and the other is for finite thickness. Some interesting considerations useful for applications in remote sensing, microstrip antennas, and antenna arrays are made.
Quantum-confined photoresponse tuning of an Esaki–Tsu-type doping superlattice
Authors: Ullrich B. , Hott R. , Cunningham J. E.
Published: April 2011

We performed photocurrent measurements on GaAs-type-A (Esaki–Tsu-type) doping superlattices produced by a δ-doping technique (impurity growth mode) using a new kind of p- and n-contact on a 500 μm × 500 μm mesa plane. We measured, for the first time, a monotonically increased photocurrent below the gap of the host material with horizontal plateaus, as expected for two-dimensional systems. This is the direct confirmation of the two-dimensional nature of this kind of superlattice. In this context, the influence of the contact distance on the photocurrent response is discussed showing that, in contrast to the general case, a variation of the distance between the contacts not only results in a scaling of the photocurrent spectra but changes the complete shape of the photocurrent response for these two-dimensional structures. The possible energetic transitions between the valence band and the conduction band below the gap of the host material, causing the absorption of the doping superlattice, are calculated and explained with an analytical theory. Furthermore, a comparison with other previously performed numerical calculations shows the limits of validity of the analytical calculations presented here.
A new scaling length for semiconductor-device modeling
Authors: De S. S. , Ghosh A. K.
Published: April 2011

Through the use of an approximate solution of Poisson's equation, a new scaling length has been introduced that is appropriate to semiconductor-device modeling of surface problems or step-junction problems in regions where the fixed charges are dominant.
Microscopic description in the Gaussian approximation of the nematic-isotropic phase transition
Authors: Pashkov P. A. , Vasiliev S. I.
Published: April 2011

The nematic-isotropic phase transition of a system of nonpolar rodlike molecules is considered. The mean-field theory is extended to take into account the local field fluctuations in the Gaussian approximation. The calculations are performed in the five-dimensional space of the order-parameter components. The numerical results are obtained for the lattice system of molecules and compared with the calculations in the mean-field theory, cluster approximation, and Monte-Carlo simulation data.
A GaAs monolithic amplifier with extremely low power consumption
Authors: Roy Langis , Stubbs Malcolm G. , Wight James S.
Published: April 2011

The design and performance of a high-gain, monolithic, broadband amplifier with extremely low power consumption are described. The amplifier, fabricated using a 0.5 μm GaAs depletion-mode MESFET (metal semiconductor field effect transistor) process, utilizes very small gate width devices to achieve a measured gain of 19 dB and a 0.1 to 2.1 GHz bandwidth with only 63 mW dc power dissipation. This is the lowest power consumption broadband MMIC (monolithic microwave integrated circuit) reported to date and is intended for mobile radio applications.
Deformation-induced vacancy-type defects in GaAs
Authors: Mascher P. , Dannefaer S. , Kerr D.
Published: April 2011

Semi-insulating undoped GaAs was plastically deformed and then investigated by positron-lifetime spectroscopy. Strains between 0 and 40% and temperatures of deformation of 450, 500, and 600 °C were investigated, with detailed investigations carried out for the lowest temperature of deformation. Between 0 and 4% strain, a reduction of the grown-in vacancy response takes place simultaneously with a slight increase in vacancy cluster size to two or three vacancies. Between 4 and 6% strain a very substantial increase in vacancy production occurs but nearly all of these vacancies are clustered into voids with a radius of about 50 Å (1 Å = 10−10 m) and density in the order of 1013–1014 cm−3. The total concentration of vacancies necessary to produce these voids is 1017–1018 cm−3. This clearly shows that vacancies are formed upon deformation and that they are mobile at 450 °C. Upon further deformation to 20% strain, the overall defect concentration becomes so high that all positrons become trapped for which reason no absolute defect concentrations can be deduced. The dominant defect types can nevertheless be identified as voids (of average size of 20 Å), two- or three-vacancy clusters, and shallow traps. Isothermal annealing of 40% strained samples shows that heat treatment reduces the void concentration but increases the average void size, and results only in a small decrease in shallow-trap concentration. The shallow traps are likely the dislocation lines themselves and the small vacancy clusters appear to be associated with the dislocation lines.
Formation of SIMOX (separation by implantation of oxygen) layers by MeV implantation
Authors: Touhouche K. , Tao Y. , Yelon A.
Published: April 2011

Silicon wafers were implanted with 6 MeV oxygen ions. A 0.8 μm amorphous buried layer was formed at ≈4.0 μm from the surface. The top silicon layer remained monocrystalline, but with some damage. Upon annealing at 1300 °C for 6 h, a 0.2 μm nearly stoichiometric oxide layer is formed for specimens implanted with 8 × 1017 O2+ cm−2, thus confirming the thermodynamic aspect of oxide growth in SIMOX (separation by implantation of oxygen) structures. The annealing restores the crystal quality of the top silicon film up to 3.5 μm, but on both sides of the buried oxide layer, bands with a high density of twins are formed.
Anomalous inductive effect in Schottky junctions
Authors: Clark W. R. , Champness C. H.
Published: April 2011

It has been known for some time in pn junctions and Schottky junctions that inductance can arise at low frequency in high-level injection owing to conductivity modulation and the transit time of injected carriers. Several observations of this type of inductive behaviour have been reported. In the present work, an inductive effect was observed in forward-biased selenium–thallium contacts at frequencies generally below 1 kHz. The effect was found to vary with storage time and may arise from the formation of semiconducting TISe between the selenium and the thallium.