bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical ray-tracing methods for gradient index media
Authors: Hewak Daniel W. , Lit John W. Y.
Published: April 2011

The accuracies of several numerical ray-tracing methods for graded-index optical media are investigated. Tracing is done by numerically solving the ray equation for the classical Luneburg lens. For such an index distribution, an analytic solution exists, with which the numerical methods are compared. Five previously published, numerical ray-tracing algorithms, along with two new methods, based on the multistep predictor and predictor–corrector formulas, are studied, and their relative accuracies are compared by using three criteria. Additional comparison is made by tracing rays through different sections of the lens, giving an indication of their dependence on the position of the ray. We conclude that the point-by-point numerical methods that use physical-path, rather than optical-path, increments are more accurate. It is shown that when the focussing properties of the lens are of chief concern, Sharma's Runge–Kutta method and our new, more efficient, multistep methods have comparable accuracies. When the optical-path length of the ray is important, Montagnino's Taylor-series method and our new predictor method are best.
Thomas Young's ideas on light diffraction in the context of electromagnetic theory
Authors: Langlois Pierre , Boivin Alberic
Published: April 2011

According to Young, diffraction fringes occur as a result of interference between the incident wave and a wave arising from the edge of a diffracting aperture or body. This approach had even been the one adopted by Fresnel himself at the beginning of his research on diffraction. However, Fresnel was forced to abandon the concept of an edge wave because of two major difficulties which he perceived and felt unable to overcome at that time. We shall examine here these two "difficulties" of Young's theory through their historical development and with regard to some recent results that we have obtained from diffraction experiments as much as from electromagnetic theory. Thus we shall demonstrate that these two "weaknesses" have become two strong evidences for the validity of Young's ideas.
Bipolar device technology challenge and opportunity
Authors: Barber H. D.
Published: April 2011

Silicon bipolar device technologies provided 65% of the world's integrated circuits in 1983. Where low noise, high current, low or high voltage, high speed or low cost are required, bipolar technologies are used. This paper will review the present status of bipolar device technologies, which make possible 100-ps gate-propagation delays, 150-μm2 gate areas, 1-GHz bandwidth amplifiers, on-chip control of over 1-A, 350-V operation, 14-GHz fT's and 10-ns. analogue-to-8-bit digital conversion. These devices are realized because of advances in isolation techniques, chemical-vapor deposition, photolithography, diffusion, ion implantation, conductor–contact interconnection technology, etching processes, and materials preparation. This paper will discuss some of the fundamental problems, modelling difficulties, and technological barriers that will impact the future development of bipolar integrated circuits.
Ultrafast silicon interdigital photodiodes for ultraviolet applications
Authors: Seymour R. J. , Garside B. K.
Published: April 2011

Conventional ultrafast photodetectors in use today generally have very small quantum efficiencies in the ultraviolet where the absorption length is very short. To extend the spectral range further into the ultraviolet, a strong electric field is required right at the surface on which the photons are incident. One method of achieving the required field is the use of two sets of interlocked metal digits, forming two back-to-back Schottky barriers on the surface of the semiconductor. Since both contacts are on the top surface, a thin semiconducting film on an insulating substrate can be used, greatly reducing depletion capacitance.We report a preliminary investigation of the potential of such devices using silicon on sapphire as an examplar material. Results are presented that show that capacitances of approximately 1 pF were obtained for devices with an area in the order of 10−3 cm2. These devices had a measured response time of less than 100 ps and measured quantum efficiencies at 337 run in the order of 10%, without the benefit of an antireflective coating.These preliminary results show that this type of device has excellent potential as an ultrafast, ultraviolet photodetector.
Hall-effect and resistivity measurements in copper–indium–gallium–selenium–tellurium solid solutions
Authors: Ilowski J. J. , Berezin A. A.
Published: April 2011

Hall-effect and resistivity measurements of semiconductor alloys of the type Culn1−yGaySe2(1−x)Te2x have been made over the temperature range 77–300 K. All materials were p-type with mobilities in the range 1 < μ < 10 cm2/V∙s. The observed electrical properties are interpreted in terms of the presence of intrinsic defects arising from dissimilar evaporation of the constituent elements of the materials during melting and annealing stages.
Direct-current hollow-cathode glow-discharge plasma-enhanced-chemical-vapour-deposition technique for a-Si:H thin-film production
Authors: Matsumura S. , Sakurai K. , Berezin A. A. , Hobson R. M. , Teii S. , Chang Jen-Shih
Published: April 2011

The direct-current hollow-cathode glow-discharge plasma-enhanced-chemical-vapour-deposition (PCVD) technique has been developed for the production of a-Si:H thin films. The electric conductivity, deposition rate, and optical characteristics of films produced by this method are similar to those of films produced by the conventional RF-discharge PCVD method. However, the properties of the former can be easily controlled by the discharge current without external substrate heating. The power consumption per deposition rate is much smaller than the microwave methods; but similar to that which is characteristic of RF-discharge methods.
Analysis of low-energy boron implants in silicon
Authors: Simard-Normandin M. , Slaby C.
Published: April 2011

Low-energy boron implants in silicon are analyzed using secondary-ion mass spectroscopy and standard junction and sheet-resistance measurement techniques. Implantation of 11B+ is compared with that of [Formula: see text]. The concentration profiles are compared with Linhard–Scharf–Schiott theory and improved range parameters are obtained.
Extragalactic jets: trends and correlations
Authors: Bridle Alan H.
Published: April 2011

The systematic properties of jets from active extragalactic objects are reviewed and related to models of confined jet propagation. The debate about jet velocities and the origin of one-sidedness is outlined, and some important future observations are listed.
Optical spectroscopy of radio jets in 3C 31, 3C 75, 3C 83.1B, and 3C 465
Authors: O'Dea Christopher P. , Owen Frazer N. , Keel William C.
Published: April 2011

We present preliminary results of optical spectroscopy of four radio galaxies with jets (3C 75, 3C 465, 3C 31, and 3C 83. 1B (NGC 1265)). We examined selected regions in and around the radio jets for evidence of the interaction of the jets with their external medium (e.g., entrainment or bending through collision with clouds). We searched for the emission lines expected from ionized gas at a temperature of T ~ 104 K (e.g., Hα and [NII]) as well as those expected at higher temperatures (T ~ 106 K, Fe X (λ6374) and Fe XIV (λ5303)).We found no extranuclear emission in the regions searched in 3C 75, 3C 465, and 3C 83.1B. Assuming values for the pressure in the environment of the radio sources, we found the upper limits to the line emission correspond to model-dependent lower limits to the temperature in the range T ≥ 1.5–3 × 106 K and upper limits to the electron density in the range ne ≤ 5 × 10−2−5 × 10−3 cm−3.In 3C 31, we detected extended Hα and [NII] emission that is peaked on the nucleus and exhibits a velocity gradient. The [NII] emission has a total velocity width of ~800 km∙s−1. It is not yet clear whether any of this emission is associated with the jet (e.g., entrained gas) or whether it is associated with a known dust lane in the galaxy NGC 383.
Global, turbulently viscous "jet" flows in a compressible ambient medium
Authors: Henriksen R. N.
Published: April 2011

This paper reports a number of new results for self-similar jet flows based on the idea of extending the self-similarity to include the turbulent viscosity coefficients. The first result distinguishes between flows that are luminosity preserving and those that are momentum preserving with distance from the central source. The luminosity-preserving flows can induce pressure gradients that increase the momentum flux with distance. This can explain the apparent excess of momentum in the bipolar outflows from stars and in the very large array radio-galaxy jets over their corresponding small-scale structures. The medium must evidently be sufficiently absorptive of the central luminosity at some stage of the outflow. In addition, two new analytical jet solutions are described. One demonstrates the self-confinement of a viscous jet even in a medium of declining pressure for a sufficiently strong jet. The other solution demonstrates a jet flow in a globally closed circulation pattern. This might be of use in discussing the line motions in active galactic nuclei.
The dynamics of Herbig–Haro objects
Authors: Schwartz Richard D.
Published: April 2011

Radial-velocity and proper-motion information on Herbig–Haro (HH) objects is analyzed for clues to the character of the supersonic flows that produce the objects. We examine the correlations among space velocities, excitation states, internal velocity dispersions, electron densities, and positions relative to the exciting stars for the emission knots of HH 1 and HH 2. Whereas the interstellar-bullet model may account for most of the phenomena in the HH 1-HH 2 system, HH 43 is found to show characteristics of a stellar wind shock against an obstacle cloudlet. By contrast, the HH 46-HH 47 system exhibits a continuous, well-collimated jet of emission with knots that may be due to instabilities in the confined, supersonic flow.
Structure and kinematics of molecular jets
Authors: Snell Ronald L.
Published: April 2011

Observational studies of the structure and kinematics of the supersonic molecular gas in star-forming regions are reviewed. These studies have suggested that the bulk of the high-velocity gas may be ambient-cloud material swept up by a collimated stellar wind. The actual structures of these outflows, however, are poorly understood. One source that may provide a better understanding of molecular outflows is that in the nearby dark cloud L1551. New observations of this outflow are presented and discussed in context of the models proposed by Snell and Schloerb.
Alignment of milliarcsecond with arcsecond scale structure in core-dominated radio sources
Authors: Rusk Raymond , Rusk Ann C.M.
Published: April 2011

Models of compact radio sources as relativistic jets aligned nearly along the line of sight predict large magnifications of intrinsic jet bends due to projection effects. Several authors have examined the distribution of observed bend angles, for small samples of sources, to provide constraints on the relativistic beaming models. In this study, we examine the alignment of Very Long Baseline Interferometry scale structure with arcsecond scale structure for a much larger sample of core-dominated radio sources and compare the distribution of observed misalignment angles with theoretical distributions calculated from models using a range of intrinsic bend angles, ξ, and Lorentz factors, γ. The theoretical distributions produced by simple relativistic beam models are found to be consistent with the data. However, the values of ξ and γ required to fit the data are highly correlated, with equally good fits produced by γ = 5, ξ = 11° and γ = 10, ξ = 5°, for instance. Either ξ or γ must be known independently for an analysis of the misalignment angle distribution to provide a significant constraint on beam parameters.
3C303: a "laboratory" extragalactic jet source
Authors: Kronberg Philipp P.
Published: April 2011

The 3C 303 radio source is one of the most clearly defined and "regular" jets yet discovered in a radio-galaxy system. It reveals a repeating pattern of polarization variation over three nearly identical knots in the jet. The apparent intersection of the jet with a diffuse patch of optical emission at the point where a transverse radio lobe connects to the jet suggests that the jet is striking a region of enhanced extragalactic density. Energy appears to be "tapped" from the jet at this point to produce the strong radio lobe.
The radio jet in 3C120 at very long baseline interferometry and Very Large Array scales
Authors: Walker R. C.
Published: April 2011

The radio jet and lobes of 3C 120 have been mapped on scales from 1 pc to over 400 kpc. The observations show that the jet is continuous from the parsec scales, where superluminal motions are seen, to over 100 kpc. The wide range of scales observed allows an underlying power-law function of central-jet brightness vs. distance from the core to be distinguished from order-of-magnitude local-brightness fluctuations. The power law has an index of about −2.2 (preliminary result). Following the usual minimum-energy assumptions, we find this index gives an energy per unit length of the jet that is nearly constant and a magnetic field that scales with the inverse of the core distance. It appears that the basic physical parameters of the jet are established on subparsec scales, where there are relativistic motions, and evolve in a simple manner for over five orders of magnitude in distance from the core.
M87: an example of a reconfining jet
Authors: Falle S. A. E. G. , Wilson M. J.
Published: April 2011

A model is presented to explain the observed positions of the knots in the jet of the radio source M87. It is supposed that the knots represent shocks in a supersonic fluid jet caused by a pressure imbalance between the jet and the surrounding medium. The positions of the knots are determined by the product of the jet's Mach number and radius, and by the variation in the external pressure, which brings about a reconfinement of the jet.
Turbulent jets and the energy budget in Fanaroff–Riley class-I radio sources
Authors: Bicknell G. V.
Published: April 2011

There are good reasons, based upon laboratory data and jet morphology, for believing that the jets in Fanaroff–Riley class-I radio sources are turbulently expanding and decelerating owing to the related entrainment. This provides a simple explanation for the usual slow decline of jet-surface brightness in class-I radio sources. A turbulent jet model in which the velocity variation is inferred from the spreading rate is presented and applied to the main jet in NGC 315. Besides providing a reasonable fit to the surface-brightness variation, the model provides the following simple explanation for the collimation behaviour of this jet. Initially, the jet is turbulent but becomes nonturbulent owing to the effect of an increasing Mach number and a favourable pressure gradient causing the jet to collimate. As the pressure flattens out to the background pressure, the jet becomes turbulent again and starts to re-expand. Various implications of the energy budget for the estimation of jet velocity and density are examined, and further implications of the model are discussed.
Photoacoustics using radio-frequency laser-optogalvanic detection: a new technique for low-pressure photoacoustic spectroscopy. Magnetic predissociation of the state of I2
Authors: Kumar D. , Klasinc L. , Clancy P. L. , Nauman R. V. , McGlynn S. P.
Published: April 2011

A new technique for low-pressure photoacoustic spectroscopy, one in which a low-power radio-frequency discharge is used as a sensitive acoustic-wave sensor, is presented. This contactless technique is a variation of the laser-optogalvanic method and is termed PARFLOG (photoacoustics using radio-frequency laser-optogalvanic detection).The ability to prosecute low-pressure photoacoustic measurement at a reduced level of collisional perturbations enables us to study intramolecular processes such as level crossings, predissociation, field effects, etc. Results for magnetic predissociation of the [Formula: see text] state of iodine are presented.
CO2-laser photoacoustic spectroscopy applied to low-level toxic-vapor monitoring
Authors: Loper G. L. , Gelbwachs J. A. , Beck S. M.
Published: April 2011

A CO2-laser photoacoustic detector is being developed that can detect the hazardous hydrazine-based rocket fuels and selected toxic industrial compounds at concentrations below 100 ppb in the ambient air. This paper reviews our work to develop this detector based on the principles of photoacoustic spectroscopy and classical acoustics. The low parts-per-billion level detection capability of the method to the hydrazines is demonstrated with both acoustically nonresonant and resonant photoacoustic cell designs. A flowing, resonant photoacoustic cell whose interior is coated with tetrafluoroethylene Teflon has been shown to be preferred for detecting highly adsorptive or reactive compounds. Photoacoustic spectroscopy has been demonstrated to be useful in measuring adsorption or reaction losses of low-concentration gases on surfaces.
Application of photoacoustics to biology: some specific systems and methods
Authors: Balasubramanian D. , Rao Ch. Mohan
Published: April 2011

A recent review of applications of photoacoustic spectroscopy to biological systems is presented. Examples of chromophore studies by photoacoustic spectroscopy show that a good correlation is possible between their presence or interactions and the photoacoustic spectra. Emphasis is placed on new interpretations of the photoacoustic signal as well as new methods such as depth profiling, the mirage effect, and Fourier-transform photoacoustic spectroscopy.
Mirage-effect measurement of thermal diffusivity. Part I: experiment
Authors: Kuo P. K. , Lin M. J. , Reyes C. B. , Favro L. D. , Thomas R. L. , Kim D. S. , Zhang Shu-Yi , Inglehart L. J. , Fournier D. , Boccara A. C. , Yacoubi N.
Published: April 2011

A mirage-effect thermal-wave method for the measurement of thermal diffusivities of solids is described. Data from two different laboratories are provided for various pure elements and compound semiconductor materials. In most cases the agreement with literature values is good.
Thermal characterization of coal using piezoelectric photoacoustic microscopy
Authors: Biswas A. , Ahmed T. , Johnson K. W. , Telschow K. L. , Crelling J. C. , Myers J. M.
Published: April 2011

The organic constituents that make up the heterogeneous coal mass are called macerals. Vitrinite and pseudovitrinite are two of the most abundantly occurring macerals in North American coals. Photoacoustic microscopy using piezoelectric detection offers a useful technique for probing the thermal-elastic properties of these coal macerals. The experimental and theoretical conditions under which photoacoustic microscopy can be used to characterize the in situ thermal-elastic properties of macerals, as a function of the percentage of carbon or "rank" of coal, are investigated in this paper. Existing piezoelectric photoacoustic theory has been applied to our sample–transducer configuration to arrive at an expression for the voltage measured from the piezoelectric transducer. The theory indicates that the photoacoustic signal is related to the following sample properties: coefficient of thermal expansion a, bulk modulus B, density ρ, and specific heat c. These properties are coupled together into a dimensionless parameter given by aB/ρc, to which the measured voltage is proportional. Some experimental results used to test the validity of the theoretical predictions are presented. Photoacoustic data gathered on 10 Appalachian Basin coals are plotted as a function of the coal rank. These results are shown to compare favourably with a calculated curve, constructed using independently measured values of a, B, ρ, and c.
A pulsed method for thermal-diffusivity measurements of polymer films with submicrometre thickness
Authors: Coufal H. , Hefferle P.
Published: April 2011

The use of pyroelectric calorimeters for pulsed measurements of the thermal diffusivity of thin films is described. The material under study is directly coated on to a pyroelectric calorimeter. A transient heat source is generated at the surface of the sample via absorption of a laser pulse. By analysis of the transmitted heat pulse, the thermal diffusivity of the sample can be determined. The potentials of this method are demonstrated on polymer films with thicknesses in the submicrometre range.
Measurement of thermal inertia by the reflective-cavity method
Authors: Cielo P. , Dallaire S. , Lamonde G. , Johar S.
Published: April 2011

The measurement of thermal parameters is a useful tool for the evaluation of compositional or structural properties of materials of industrial interest. The increasing use of noncontact photothermal techniques to generate and sense thermal fields in materials makes thermal characterization an attractive approach for in-plant quality monitoring and process control. In an effort to increase the reliability of such measurements in conditions of unknown surface emissivity, an integrating-cavity technique is described for a quantitative evaluation of the thermal inertia of the inspected material. An analysis of the performance of such a technique as a function of the cavity geometry and internal reflectivity is presented. Examples of applications to the characterization of manufactured ceramic materials with different porosity contents are described.
Thermal-wave imaging for nondestructive evaluation
Authors: Thomas R. L. , Favro L. D. , Kuo P. K.
Published: April 2011

We review the applications of various thermal-wave techniques to problems in nondestructive evaluation of materials.
Nonlinear effects in photothermal-optical-beam-deflection imaging
Authors: Wetsel Jr. Grover C. , Spicer James B.
Published: April 2011

Nonlinear phenomena have been observed during photothermal-optical-beam-deflection imaging experiments on samples of both high-purity aluminum and aluminum alloys. Evidence for nonlinear optical and thermal effects have been measured. Theoretical models have been developed as aids in understanding the different contrast mechanisms observed in linear and nonlinear photothermal images.
Theory of real-time photoacoustic microscopy
Authors: Quimby R. S. , Liu Z. M.
Published: April 2011

A photoacoustic theory is developed for a moving heat source. In the theory, the photoacoustic signal for a moving beam is calculated in terms of the signal obtained with a stationary beam. The theory is applied to real-time photoacoustic microscopy, in which the beam intensity is kept constant and the beam position is ramp modulated. Experiments performed on two types of subsurface defects show good agreement with the theory. The resolution of subsurface step defects is studied through a combination of theory and experiment. It is found that the resolution varies inversely with the scan length L, and scan frequency, f, for large values of L and f. For small values of L and f, the resolution saturates to a maximum value. The resolution turns out to be essentially independent of the size of the subsurface step.
Thermal-wave experiments on moving samples
Authors: Busse G.
Published: April 2011

Thermal-wave propagation has been observed on moving samples. Motion of a solid causes a shift of the transmitted thermal wave from which (similar to time-of-flight arrangements) the wave velocity can be determined. Rotation of the sample gives rise to synchronization effects on spatial temperature distributions. Motion of subsurface liquid affects thermal-wave propagation along the surface. Applications of the results are in the field of thermal-wave imaging and remote monitoring of motion and flow.
On the influence of thin absorber layers in thermal-wave applications
Authors: Tilgner R. , Baumann J. , Beyfuss M.
Published: April 2011

The influence on the thermal response of a sample under photothermal investigation is analyzed when real absorbing layers are used as a source of thermal waves. Experiments with glass and copper samples covered by various absorbing layers are described using a thermal-wave approach. It is demonstrated that matching the effusivities of absorber and substrate is essential for obtaining quantitative results even for absorber layers much thinner than their thermal-diffusion lengths; otherwise one has to determine very carefully the particular nonneglectable influence of the absorber layer on the measured complex temperature.
Thermal-wave transient behaviour
Authors: Rief B.
Published: April 2011

When a thermal wave is switched on, it takes some time until phase and magnitude have reached their final values. Numerical calculations are presented for the transient behaviour when a sinusoidal or square-wave temperature modulation is applied to the surface of a homogenous semi-infinite solid. The influence of sample depth, time, and modulation form is discussed.
Nondestructive evaluation of magnetic materials by ferromagnetic-resonance photothermal-deflection spectroscopy
Authors: Netzelmann U. , Pelzl J. , Fournier D. , Boccara A. C.
Published: April 2011

Detection of ferromagnetic resonance (FMR) by photothermal beam deflection has been used to study the spatial inhomogeneity of magnetic properties. The technique has been applied to measure the depth dependence of FMR in layered recorder tapes and to determine the lateral variation of the demagnetizing field in metal–glass ribbons.
A pulsed photoacoustic investigation of ultrasonic mode conversion
Authors: Hutchins D. A. , Nadeau F. , Cielo P.
Published: April 2011

Experiments have been undertaken into the generation and detection of ultrasonic transients in metals over a 40-MHz bandwidth, using pulsed-laser generation and interferometric detection. Longitudinal, shear, and surface waves have been investigated, and their form compared favorably to theory. The techique has been used to study the interaction of surface and bulk waves with slots in the surface of a plate. It has been shown that significant mode conversion occurred from surface to bulk waves and vice versa. The significance of this result to nondestructive testing is discussed.
Laser beam induced current measurements of minority carrier diffusion length
Authors: Oliver B. A. , Dixon A. E.
Published: April 2011

Laser beam induced current (LBIC) measurement has been proposed as a technique for determining various semiconductor parameters, including minority carrier diffusion length. In this work, techniques for extracting values of bulk diffusion length from experimental LBIC curves are presented for both parallel and perpendicular barrier–beam geometries and for both thick and thin samples. Experimental tests of each technique compare diffusion length results obtained for samples of different geometries with each other, with confirmation of results by measuring the minority carrier lifetime by photoconductivity decay in samples cut from the same wafers and then calculating the diffusion length. The LBIC techniques presented in this paper are shown to allow practical and meaningful determination of diffusion length, and to have significant advantages over the electron beam induced current (EBIC) techniques from which they evolved.
Electron cyclotron resonance microwave-plasma etching
Authors: Mejia S. R. , Chau T. , McLeod R. D. , Kao K. C. , Card H. C.
Published: April 2011

Electron cyclotron resonance microwave-plasma etching of Si and SiO2 using a (CF4 + O2) gas mixture is investigated in a magnetically confined plasma. High etch rates have been obtained at 0.8 Torr pressure, where the etching mechanism may be due primarily to neutral active species (1 Torr = 133 Pa). The high etch rate can be explained by a high dissociation efficiency of the ECR microwave plasma, and the directionality by carbon deposits associated with it. The magnetic confinement is likely to play a role similar to that of ion and electron screening.
WSix formation in W–Si multilayers
Authors: Eicher S. , Bruce R. A.
Published: April 2011

The formation of WSix phases from multiple thin layers of W and Si was investigated. Tungsten and silicon thin films of ~5 nm thickness were deposited sequentially onto GaAs substrates by dc magnetron sputtering from elemental targets. The total film thickness was ~300 nm. The W and Si layer thickness, and thus the overall composition of the films, was controlled by adjusting the power applied to the two sputtering targets. The films examined in this work had nominal compositions in the range WSi2–WSi0.48.The multilayered structure was subjected to rapid thermal annealing at 900 °C. The extent of the reaction, the grain size, and the crystal structure of the silicides were determined using transmission electron microscopy and X-ray diffraction. For WSix films with [Formula: see text], the silicides had the βW structure and were relatively large grained, ~450 nm, while for x > 0.52, the film contained the W5Si3 phase and consisted of grains ~45 nm in diameter.Schottky contacts were of good quality for [Formula: see text], with a barrier height (ϕ) of 0.7 V and an ideality factor (n) of 1.15. Schottky contacts with higher silicon concentrations were poor.The WSix (x = 0.52) Schottky contact has been successfully incorporated into a self-aligned gate field-effect transistor.
Ultrafast interdigital photodetectors and integration with optical waveguides on silicon
Authors: Bruce D. M. , Seymour R. J. , Cheong D. , Jessop P. E. , Garside B. K.
Published: April 2011

The development of new types of high-speed photodetectors and techniques to incorporate these detectors into integrated optical structures are reported in this paper. Schottky-barrier detectors with an interdigital electrode configuration have been fabricated on commercially available silicon-on-sapphire substrates. Response times of <30 ps have been measured for wavelengths from infrared to the ultraviolet. These experimental results agree well with a supporting numerical model of these detectors. Using the same electrode configuration, we have fabricated photoconductive detectors on bulk silicon and germanium-on-gallium arsenide substrates. These have slower response times, on the order of a nanosecond, but demonstrate a good responsivity of approximately 1.5 A∙W−1. Using a modified electrode configuration, we have fabricated an integrated detector array on silicon, combining a glass waveguide channel with each detector element for the efficient delivery of an optical input signal.
Frequency-shift keyed generation with an optically controlled GaAs field-effect transistor in a surface-acoustic-wave oscillator circuit
Authors: Berolo O.
Published: April 2011

A prototype circuit for potential optical integration was developed and evaluated for the generation of frequency-shift keyed (FSK) signals by simultaneously exploiting surface-acoustic wave (SAW) technology and the optical response of the GaAs field-effect transistor (FET).A SAW delay line to be utilized in the feedback path of an oscillator circuit was designed for operation at the fundamental frequency of 111 MHz and operated at its 12th harmonic (1.33 GHz). A low-noise FET was incorporated into the circuit in series with the SAW delay, and a low-power He:Ne laser was focussed through an optical modulator onto the FET structure. The gate bias, which controls the phase shift in the feedback loop of the oscillator, was applied via the open-circuit photovoltage induced at the Schottky-barrier junction of the FET.The optical modulator was driven by a pseudorandom bit generator to obtain FSK generation by the oscillator circuit. Results of the frequency spectrum of the oscillator signal as a function of bit rate and light intensity on the FET were obtained. The successful performance of the circuit indicated that integration of all these elements on GaAs would yield a useful device for FSK signal generation.Un prototype de circuit pour intégration optique potentielle a été développé et évalué pour la génération de signaux FSK (frequency-shift keyed), en exploitant simultanéement la technologie des ondes acoustiques de surface et la réponse optique du transistor GaAs à effet de champ.
Nondestructive surface analysis by nuclear scattering techniques
Authors: Gujrathi S. C. , Aubry P. , Lemay L. , Martin J. -P.
Published: April 2011

An elastic-recoil detection (ERD) technique is developed and successfully applied in the simultaneous, nondestructive multielement depth-profile studies of thin films with thicknesses up to 2 μm, used in various material technologies. In this technique, the light elements are knocked out of the target by using an energetic heavy-ion beam obtained from the Tandom Accelerator Facility of the Nuclear Physics Laboratory. A time-of-flight method is used to separate the masses and the energies of the recoiled elements as well as the Rutherford backscattering incident ions. Using 30 MeV35Cl as the beam probe, we get an observed surface resolution of better than 100 Å at a 30° detection angle. Typical mass resolutions for energies >5 MeV are 0.2 amu in the C region and 0.7 amu in the Si region. The factors related to the mass and depth resolutions, probing depth, and approximate detection limit are systematically studied using 19F, 35Cl, and 79Br as incident beams. This newly developed ERD method, along with the already existing Rutherford backscattering (RBS) technique, makes the Nuclear Scattering Facility at the Université de Montréal unique for surface analysis.
Transmission electron microscopy characterization of the microstructure of Cd3As2 films prepared by pulsed-laser evaporation
Authors: Carpenter G. J. C. , Dubowski J. J. , Williams D. F.
Published: April 2011

Transmission electron microscopy with an analytical X-ray system has been used to investigate Cd3As2 films prepared by pulsed-laser evaporation. The films were deposited on amorphous substrates at ~ 120 °C. They consisted mainly of a fine polycrystalline array. The crystal structure was identified as the body-centered tetragonal form of Cd3As2. No other crystallographic phase of Cd3As2 was observed. Some regions with amorphous or eutectic inclusions were also observed. These results have been correlated with the electrical properties of pulsed-laser evaporated Cd3As2 films.
Complementary metal oxide semiconductor-compatible junction field-effect transistor characterization
Authors: Marcoux J. , Orchard-Webb J. , Currie J. F.
Published: April 2011

We report on the fabrication and electrical characterization of a vertical junction-gate field-effect transistor (JFET) that is compatible with all complementary metal oxide semiconductor (CMOS) technologies. It can be used as a buried load for an enhancement n-channel metal oxide semiconductor field-effect transistor (n-MOSFET), replacing the p-MOSFET within the standard CMOS inverter configuration and resulting in a 40% net area economy in standard cells. To be entirely CMOS process compatible, this JFET device differs from others in the literature in that dopant concentrations in the n substrates (1014) and in the p wells (1015) are substantially lower. For integrated-circuit applications, one seeks to use the JFET with the smallest area to minimize parasitic capacitances and to maximize switching speeds. However, at these concentration levels, the dc current–voltage characteristics depend critically on the lateral dimension of the JFET's square channel. Above 10 μm, the characteristics are pentode-like and similar to those of a classic MOSFET. Below 10 μm, the channel is naturally pinched-off, and for reverse gate bias, the small JFETs are triode-like. There is also a nonreciprocity between the source and the drain when the source-to-drain voltage polarity is changed, which is due to the distance between the channel and the electrode collecting the carriers. When its gate is forward-biased, the small JFETs behave as bipolar transistors. Depending on source-to-drain voltage polarities, I–V characteristics exhibit saturation effects caused by base-widening phenomena at the JFET's drain contact.
Lateral transistor structure optimization with respect to current gain
Authors: Ristic Ljubisa , Baltes Henry P. , Filanovsky Igor , Briglio David R. , Smy Tom , Nathan Arokia
Published: April 2011

An investigation of a novel lateral transistor structure fabricated in standard 4 μm complementary metal oxide semiconductor technology without any additional processing steps is presented. Inherent in the structure is the potential of modulating the lateral electric field in the neutral base region. An additional characteristic of this structure is the reduced bottom surface of the emitter, which diminishes the parasitic action of vertically injected carriers. The results show that because of the lateral electric field, the common-emitter static current gain at high currents can be increased by at least an order of magnitude.
Improving the accuracy of the charge-sheet model for the long-channel metal-oxide semiconductor field-effect transistor
Authors: Tarr N. G.
Published: April 2011

It is shown that the accuracy of the charge-sheet model for the long-channel metal-oxide-semiconductor field-effect transistor can be improved by allowing for the small potential drop across the inversion layer, and by using a more accurate analytic approximation for the charge stored in the depletion region.
Doping glow-discharge amorphous silicon by metal coevaporation
Authors: Perluzzo G. , Aktik C. , Currie J. F. , Poulin-Dandurand S. , Yelon A. , Brebner J. L. , Cochrane R. W.
Published: April 2011

We report here on the further development of a new technique for doping plasma-deposited amorphous silicon by thermal evaporation of metal into the plasma from which the film is grown. We show that the de bias applied to the substrate has an important effect on the incorporation of the metal into the film, and on the doping efficiency. We also report on our efforts to monitor and control the evaporation by mass spectroscopy.
The preparation of stoichiometric mercury cadmium telluride surfaces
Authors: North R. B. , Lau W. M.
Published: April 2011

A technique involving cathodization of an anodized surface has been proposed as a surface treatment of mercury cadmium telluride substrates in the fabrication of infrared-sensitive devices. The resultant surface was analyzed with X-ray photoelectron spectroscopy and compared with surfaces produced by cleavage, sputtering, and chemical etching. It was found that the cathodized surface had a surface composition close to the bulk stoichiometry. The first monolayer of the surface was enriched in mercury and depleted in cadmium. This surface was also more inert towards air oxidation than the Br–methanol treated surface, probably because of the surface enrichment of mercury.
Photoelectrochemical deposition and properties of thin-film cadmium telluride
Authors: Windheim Jesko von , Darkowski Andrzej , Cocivera Michael
Published: April 2011

Thin-film cadmium telluride has been deposited cathodically on titanium in a photoelectrochemical cell (PEC) using a propylene carbonate solution of Cd II and tri-n-butylphosphine telluride (BPT) at 100 °C. Illumination of the cathode enhances the cathodic current relative to that observed during the dark process. Furthermore, the current under illumination decreases more slowly than it does for the dark process, providing thicker films in a shorter time. Under illumination, the Te:Cd ratio of the film is independent of light intensity and applied potential in the range −0.8 to −1.4 V (Ag–AgCl reference electrode). This ratio and the deposition current depend on the concentration of cadmium ion relative to that for BPT. Thicknesses of ca. 0.5 μm are obtained in 15 min for films that have a Te:Cd ratio of ca. 1.0. Photovoltaic cells (PVC) have been fabricated. They have the configuration glass – indium-tin oxide – n-CdS – p-CdTe – Au-Pd, and it appears that the barrier occurs at the CdS–CdTe interface. Light-to-electric power conversion efficiencies as high as 5.2% have been achieved thus far over small surface areas. By means of absorption measurements, the bandgap of the CdTe film is determined to be 1.44 eV.
Tuning the effective bandgap of a silicon doping superlattice
Authors: Schmidt-Weinmar H. G. , Teo K. H. , McMullin J. N. , McKinnon G. H.
Published: April 2011

In this paper, we examine the tunability of the effective bandgap and carrier concentration in a silicon-doping superlattice with narrow n+-doped layers and wide p-doped layers. Quantitative tunability parameters are defined and their variation with dopant concentration and temperature are calculated self-consistently in the effective mass and Hartree approximations. It is found that the tunabilities increase as doping is increased or as temperature is decreased.
Nuclear magnetism in solid 3He
Authors: Adams E. Dwight
Published: April 2011

A review is given of some of the experimental work that has contributed to our present understanding of nuclear magnetism in solid 3He. Bulk properties, such as entropy, magnetization, and melting pressure are discussed briefly, followed by a summary of microscopic investigations using magnetic resonance and neutron scattering. Recent measurements of melting pressures in the high-field phase are presented. The observed T4 dependence of the melting pressure is evidence of an antiferromagnetically ordered state, not just a highly polarized paramagnet. However, the absence of latent heat at the transition into the high-temperature paramagnetic phase indicates that this transition is not first order.
Calorimetric studies of body-centered cubic solid 3He
Authors: Masuda Y. , Iwahashi K. , Yano H. , Kato M. , Sawada A.
Published: April 2011

The nuclear magnetic specific heat of body-centered cubic solid 3He in applied magnetic fields has been measured as a function of temperature through a temperature range including the nuclear magnetic ordering temperature. The magnetic phase diagram has been determined. The nuclear magnetic properties are also discussed.
Ferromagnetism in the boundary layer of 3He on graphite
Authors: Friedman L. J. , Ytterboe S. N. , Bozler H. M. , Thomson A. L. , Cross M. C.
Published: April 2011

We study the magnetic properties of 3He confined in a grafoil substrate with the static applied field more than two orders of magnitude less than in prior experiments. In this low-field regime, we observe new modes in the nuclear magnetic resonance spectrum that arise for T < 1 mK. We interpret these as the collective modes of ferromagnetically ordered domains in the 3He boundary layers. The frequency shifts of these modes suggest that the domains reorient as the static field is varied. From the size of the frequency shifts, we also conclude that 3He dipole fields can only partially account for the system anisotropy energy.
The effect of the Bose broken symmetry on the dynamics of superfluid 4He: a review
Authors: Griffin A.
Published: April 2011

A status report is given on recent theoretical work concerning the role the Bose condensate has on the dynamical properties of superfluid 4He. A Bose broken symmetry is shown to be crucial in understanding why zero-sound-type density fluctuations play the role of quasi particles in the superfluid phase. A new unified treatment of long-range order in bulk Bose liquids and quasi-long-range order in Bose films is given. In addition, the strong evidence we now have concerning the existence and magnitude of the Bose condensate is critically reviewed. This includes (i) determination of the momentum distribution from inelastic neutron scattering and (ii) recent finite-temperature Monte Carlo calculations of the condensate fraction n0(T)and the normal-fluid density ρN(T).
Accurate momentum distributions from computations on 3He and 4He
Authors: Whitlock Paula , Panoff Robert M.
Published: April 2011

The momentum distribution and condensate fraction of liquid and solid 4He determined from Green's function Monte Carlo calculations using the HFDHE2 pair potential are described. The one-body density matrix and the momentum distribution for liquid 3He derived from variational and fixed-node Green's function Monte Carlo calculations are also reported.
Investigation of magnetic field induced textural changes in superfluid 3He–A and of the anisotropy of viscosity, superfluid density, and sound propagation
Authors: Hook J. R. , Eastop A. D. , Faraj E. , Gould S. G. , Hall H. E.
Published: April 2011

Textural changes induced by a magnetic field in dipole-locked superfluid 3He–A in a slab geometry have been observed and agree well with the theoretically predicted changes. In one set of observations, ultrasound transmission at 15.15 MHz across a slab 2 mm wide was used as the probe of the texture, and in another set of measurements the textural changes were inferred from the behaviour of a torsional oscillator containing a slab of thickness 105 μm. From the former set of observations, we deduced the anisotropy of the sound attenuation and velocity, and from the latter we calculated the anisotropy of the viscosity and the superfluid density. In both experiments the field, perpendicular to the slab, that caused instability of the uniform texture was smaller than that theoretically predicted. Observations on the A phase after warming from the B phase exhibited very different behaviour from those made after cooling from the normal phase.
Surface tension of liquid 4He and 3He
Authors: Ikushima Akira J. , Iino Masaaki , Suzuki Masaru
Published: April 2011

Surface tensions of liquid 4He and 3He have been measured down to 0.3 K by using the surface-wave resonance method. Measurements with 3He have been made further, down to 20 mK, by the capillary-rise method. Liquid 4He shows a T7/3 temperature dependence up to approximately 1 K, indicating that the ripplon excitation is the predominant contributor in this temperature range. It is concluded with the superfluid 4He that the "surface energy" of the Bose–Einstein condensate (BEC) gives a major contribution to the surface tension, from which we have deduced n0, the fraction of BEC. Liquid 3He shows a T2 temperature dependence from 0.3 K to about 1 K. The result is attributed to both the effect of 3He quasi particles, which hit the surface, and the ripplon. The latter has never been seriously thought to exist on the 3He surface.An unexpected behavior of the 3He surface tension has been found below approximately 200 mK. The surface tension does not obey the T2 temperature dependence but deviates downward around 200 mK.Surface tensions of 4He and 3He have been measured also in the vicinities of liquid–vapor critical points.
Padé-approximant study of the phase transition of ortho–para mixtures in solid hydrogen
Authors: Miyagi Hiroshi , Mishima Akira , Nakamura Tuto
Published: April 2011

The phase transition of solid hydrogen is studied in the Padé approximation, with newly calculated coefficients in the high-temperature expansion series for the free energy. For the low-temperature phase, the free energy is obtained by a previous libron study of ortho–para mixtures. The transition temperature is predicted to be 2.1Γ for pure ortho-hydrogen. The phase transition disappears at ~ 60% of ortho-hydrogen, in agreement with experiment.
Some new observations at the superfluid transition in 3He–4He films
Authors: Wang X. W. , Gasparini F. M.
Published: April 2011

We have studied quasi two-dimensional 3He–4He mixtures by means of a high-Q torsional oscillator. In contrast to the case of pure 4He films, two superfluid phase transitions have been observed in mixture films where the 4He coverage is near one active layer. For a somewhat larger coverage of 4He, the addition of 3He causes the superfluid transition to shift, at first, to higher temperatures rather than lower ones as is usually observed.
Hysteretic capillary condensation of 4He on Nuclepore substrates: simultaneous third-sound and direct-capacitance measurements
Authors: Godshalk K. M. , Smith D. T. , Hallock R. B.
Published: April 2011

Measurements of the approach to capillary condensation and the hysteresis encountered in capillary condensation are reported for helium adsorbed on the polycarbonate substrate Nuclepore.