bluuebunny/crossref_metadata_2025 huggingface dataset:
Hysteresis in GaAs metal-semiconductor field-effect transistors I–V characteristics
Authors: Lau W. M. , Lijiu Ji , Lowe K. , Tang W. , Young L.
Published: April 2011

The hysteresis loops observed in the drain current vs. voltage characteristics of metal-semiconductor field-effect transistors (MESFET's) fabricated on semi-insulating GaAs by ion implantation were investigated as a function of the sweep frequency and of the temperature. A model was developed to correlate the extent of the looping to the characteristics of the deep-level traps in the channel. Experimental results were compared with the channel deep-level transient spectroscopic results on the same MESFET.
Effects of electron bombardment during vacuum deposition of Zn3P2 films
Authors: Sacken U. von , Brodie D. E.
Published: April 2011

Vacuum-deposited Zn3P2 films, prepared with and without low-energy electron bombardment during the deposition process, have been characterized both structurally and electronically. Zinc phosphide was chosen for this study because it is a promising material for the absorbing layer in a low-cost thin-film solar cell. The structure of the films has been studied using glancing-angle X-ray diffraction and transmission electron microscopy. Electron bombardment can be used to modify the properties of zinc-phosphide films. The e-beam parameters used in this study increased the degree of preferred orientation and altered the nature of the glass–Zn3P2 interface.
Czochralski growth of Te–rich SexTe1−x crystals
Authors: Quang Nguyen V. , Shih I. , Champness C. H.
Published: April 2011

Single crystals of tellurium-rich SexTe1−x alloys have been grown by the Czochralski method for x < 0.16. A double-crucible was used to contain the melt, which eliminated scum on the liquid surface, enabling crystals to be grown with higher selenium concentrations than previously obtained. The inner graphite vessel of the crucible not only drew scum-free liquid from the quartz outer container, but also acted as a susceptor for the radio-frequency (r.f.) heating, producing more stable convection in the melt. With this method, single crystals of good quality, as indicated by Laue patterns, were obtained from melts containing up to 30 at.% selenium. The concentrations of selenium in the crystals, as determined by electron-probe microanalysis (EPMA), were about half those in the corresponding melts, in agreement with the Te-rich end of the phase diagram. It was also found that single crystals of Te-rich SexTe1−x could be grown equally well in pulling directions both parallel and perpendicular to the c axis.
Progress in amorphous-silicon photovoltaic-device research
Authors: Brebner J. L. , Cochrane R. W. , Groleau R. , Gujrathi S. , Kéroack D. , Lépine Y. , Martin J.-P. , Vanaček M. , Aktik C. , Aktik M. , Azelmad A. , Currie J. F. , Poulin-Dandurand S. , Ranchoux B. , Sacher E. , Tannous C. , Wertheimer M. R. , Yelon A.
Published: April 2011

The members of the "Groupe des couches minces" have been studying the application of hydrogenated amorphous-silicon to solar cells for a number of years. We review here some of the results and progress in our work since the First Canadian Semiconductor Technology Conference. These include, first, quantification of the dependence of film characteristics on the deposition parameters such as DC bias, Ar:SiH4 ratio, temperature, and gas flow for the capacitive reactor geometry used; second, construction of a time-of-flight spectrometer permitting mass resolution of elastically scattered or recoiling nuclei and the chemical-composition profiling of multilayer device structures; third, electro-optical characterization of doped and undoped a-Si:H films; fourth, fabrication of 3-mm2 MIS diodes having efficiencies of 5.3% and short-circuit currents of 22 mA/cm2; fifth, development of theoretical models for the behavior of Schottky structures; sixth, development of a new technique for doping a-Si:H by the controlled evaporation of group III or V metals into an RF plasma discharge of silane and argon; and finally, construction of p–i, n–i, and p–i–n solar cells using the novel doping procedure.
Fabrication of CdTe thin films by electron-beam evaporation
Authors: Caporaletti O. , Westcott M. R.
Published: April 2011

CdTe thin films were prepared by electron-beam evaporation and were characterized by X-ray diffraction, electron microscopy, and electrical and optical measurements. All films had the cubic zinc-blende structure with a strong (111) orientation and exhibited columnar growth with relatively small grains. They were highly resistive and evidence of second phases (excess Te) was found in vacuum-evaporated samples. The preliminary evaluation of electron-beam evaporated films shows that their characteristics are similar to those of films produced by other techniques.
New semiconductor materials and structures for electro-optical devices
Authors: Garside B. K. , Jessop P. E.
Published: April 2011

New semiconductor materials and device structures are essential to the development of new types of electro-optical devices and systems in areas such as integrated optics, optical communications, and optical computing. This paper presents a discussion of basic materials requirements, in terms of both optical properties and materials fabrication technologies, for representative electro-optical devices. In the area of optical communications, interest is shifting towards longer wavelengths, which generates the need for sources and detectors operating in the same region. The current status and future possibilities for such devices, as examplified by fast photodetectors, are discussed in terms of new semiconductor alloy materials and device structures. In the areas of optical computing and integrated optics, the basic essential structure is a low-loss optical thin-film waveguide. The materials aspects of such devices are discussed, and the relevant considerations are illustrated through a description of recent work with GeO2 waveguides.
Growth and properties of Cd3As2 films prepared by pulsed-laser evaporation
Authors: Dubowski J. J. , Williams D. F.
Published: April 2011

Pulsed-laser evaporation has been used to prepare films of Cd3As2. It is found that the electrical quality of the prepared films improves markedly as the substrate temperature is increased from 295 to 433 K. The films deposited at about 430 K are highly oriented, with electrical characteristics approaching those of the bulk material. Electron mobilities reach values of 6.05 × 103 cm2/V∙s at 300 K (i.e., comparable to bulk mobilities) and 9 × 103 cm2/V∙s at 10 K (which is within a factor of two of those for the bulk material). Further increases in the substrate-deposition temperature give rise to films that are arsenic deficient.
Amorphous silicon for photovoltaics produced by new microwave plasma-deposition techniques
Authors: Paquin L. , Masson D. , Wertheimer M. R. , Moisan M.
Published: April 2011

Amorphous hydrogenated silicon (a-Si :H) has been prepared by microwave (2.45 GHz) plasmas in Ar–SiH4 mixtures using two different deposition systems, a large-volume microwave plasma (LMP) apparatus, and a Surfatron system. Films of a-Si:H are characterized structurally (primarily by scanning electron microscopy), and by Fourier transform ir spectroscopy, as well as according to their electro-optical properties (dark and photoconductivity, I-V characteristics of Schottky-barrier diodes). Although microwave plasmas are thought to differ significantly from conventional lower frequency plasmas, results of the present characterizations show no evidence of this. Deposition in the Surfatron system gives rise to device-grade a-Si:H, as demonstrated by Schottky cell efficiences exceeding 3%. We have been unable to duplicate this in the LMP system in spite of nominally identical fabrication conditions; these films have gross columnar morphology, and they react with atmospheric constituents to give a-Si:(H, C, O) alloys. More pronounced ion bombardment of the substrate during deposition is thought to account for the better quality of Surfatron films.Finally, an ageing effect of Au/a-Si:H/Sb–Cr Schottky diodes is described, unlike any reported hitherto; in a typical device, conversion efficiency was observed to rise by roughly 60% after about 2 months, then it decreased slowly. Preliminary investigations of this effect using various surface analytical techniques suggest that Au acts as a catalyst for room-temperature chemical reactions between a-Si:H and atmospheric constituents, primarily oxygen and water vapor.
Effects of electron-beam irradiation and substrate temperature on the physical properties of evaporated a-Si:C thin films
Authors: Audas R. D. , Moore C. J. L. , Sturtevant T. E. W. , Johnson G. W. , Leslie J. D. , Brodie D. E.
Published: April 2011

Thin films of a-Si:C have been prepared by thermal evaporation from resistive- and rf-induction-heated carbon crucibles. Samples were prepared with and without electron-beam irradiation of the substrate during deposition, and the resulting film properties (electrical and optical) were measured. Reference samples prepared with substrate temperatures from 150 to 250 °C and annealing temperatures from 200 to 250 °C had very similar film properties. The use of vitreous carbon instead of compressed carbon for the crucibles reduced the carbon content by about 30% and the oxygen content of the films by more than a factor of four. Electron-beam irradiation of the purer films produced a tenfold decrease in the conductivity at room temperature and an increase of the high-temperature activation energies compared with the reference samples.
Positive secondary-ion mass spectrometric study of silicon nitride films on Si and GaAs with a cesium ion source
Authors: Lau W. M. , Vandervorst W.
Published: April 2011

The detection of positive secondary ions, as opposed to the conventional negative-ion detection, in conjunction with the use of a cesium primary-ion source was studied with a Cameca IMS-3F ion microscope. One advantage of this technique is that, unlike the detection of negative ions, charging of an insulating surface can be avoided. Plasma-enhanced chemical-vapor-deposited silicon nitrides on Si and GaAs were used as examples to demonstrate the usefulness of the technique. The distributions of species such as H, C, O, F, Al, Si, SiN, Ga, and As were measured. The correlation between these impurities and the film properties and the importance of monitoring their distribution are discussed in order to illustrate the applicability of the technique.
Optical and electronic properties of amorphous SiNx:H alloy films
Authors: Herak T. V. , McLeod R. D. , Collett M. G. , Kao K. C. , Card H. C. , Watanabe H. , Katoh K. , Yasui M. , Shibata Y.
Published: April 2011

The optical and electronic properties of a-SiNx:H alloy films fabricated by rf glow discharge have been measured for 0 ≤ x ≤ 0.6. The material is dispersive over the range of photon energies 0.5 ≤ hv ≤ 3.5 eV. The optical gap is about 1.65 eV and is practically independent of x for 0.1 < x < 0.4, but it increases rapidly with increasing x for 0 < x < 0.1 and x > 0.4. For x > 0.6 the refractive index approaches the value for Si3N4. The dark conductivity, the photoconductivity, and the ratio of the photoconductivity to the dark conductivity are enhanced by nitrogen incorporation when appropriate nitrogen content is used. All the experimental results indicate that the incorporated nitrogen does not act as a dopant, but rather acts as a dangling-bond compensator. Photo-induced changes in both dark conductivity and photoconductivity due to high-intensity optical excitation have been observed. The degree of such changes decreases with increasing nitrogen content. This phenomenon is attributed to the photo-induced change in the microstructure of the films that leads to a change in both the density and the distribution of gap states.
Solar-grade silicon substrates by a powder-to-ribbon process
Authors: Norman Charles E. , Absi Elias M. , Thomas Raye E.
Published: April 2011

A new technique for producing silicon ribbons for solar-cell substrates is described. The process begins with inexpensive, 98% pure silicon that is crushed and acid leached to raise the purity to 99.9%. This powder is spread on a graphite plate and electron-beam annealed to form a flat, self-supporting "preribbon." After removal of the graphite and unmelted powder, the preribbon is given a second electron-beam scan that recrystallizes the silicon into a smooth polycrystalline ribbon. This zone melting further improves the purity to over 99.99%.Ribbons 0.4 mm thick and up to 16 mm wide were produced in this initial work. The ribbons are p-type, 0.07 Ω∙cm, and have long crystals about 1 mm wide. Electron-diffusion lengths of 20–30 μm were measured. Calculations indicate that solar-cell efficiencies up to 13% should be possible. If the process can be scaled up and automated, the cost of volume production could be as low as 43 cents/W. It is concluded that the process has the potential for achieving low-cost "solar-grade" substrates and has advantages over other processes. Further work is planned.
Residual damage in B+ and –implanted Si
Authors: Vandervorst W. , Houghton D. C. , Shepherd F. R. , Swanson M. L. , Plattner H. H. , Carpenter G. J. C.
Published: April 2011

The residual damage left after furnace-annealing Si wafers implanted with 30-keV B+ or 120-keV [Formula: see text] ions has been investigated for doses of 3–5 × 1015 ions∙cm−2. Transmission electron microscopy, Rutherford backscattering, and channeling were used to study the morphology and distribution of the damage while the B and F content and their depth distributions were determined by nuclear reaction analysis and secondary-ion mass spectrometry. For B+-implanted samples the residual damage is concentrated in a band at a depth corresponding to the B projected range. For [Formula: see text]-implanted samples the residual damage is located mainly in the region of the as-implanted amorphous–crystalline interface.
Scanning-laser-microscope measurements of minority-carrier diffusion length and surface recombination velocity in polycrystalline silicon
Authors: Damaskinos S. , Dixon A. E.
Published: April 2011

A scanning laser microscope was used to study the electronic and recombination properties at grain boundaries of both n- and p-type Wacker polycrystalline silicon in a spatially resolved photoconductivity experiment. The light energy falling on the samples was varied over five orders of magnitude from 10−1 to 10−6 mW. For p-type material the measured L decreased with beam intensity from 150 to 60 μm, reaching a constant value at very low beam intensities. The small focal spot of the microscope allowed the measurements to be extended to include n-type samples. Forthese samples L was found to change from 90 to 18 μm with decreasing beam intensity. The surface recombination velocity SGB was evaluated for both samples. For p-type samples it decreased from 25 000 to 6000 cm/s and for n-type samples from 21 000 to 3000 cm/s with decreasing beam intensity. The quasi-Fermi level separation was determined as a function of the excess minority-carrier-concentration density at the grain boundary and found to increase linearly with beam intensity.
Silicide formation by pulsed-incoherent-light annealing
Authors: John P. K. , Gecim S. , Suda Y. , Tong B. Y. , Wong S. K.
Published: April 2011

Nickel silicide formation is studied using a pulsed incoherent light source of variable duration in the range 5-50 μs. The potential advantages of the arc source over other pulsed techniques such as electron (e)-beam and laser annealing are simplicity, higher electrical-conversion efficiency, and larger area processing. The plasma arc provided incident light energy density in the range 5–45 J/cm2, and our results indicate that mixed layers of nickel and silicon can be produced using this source at about 45 J/cm2. It was found that a thin layer of amorphous silicon on the nickel enhanced light absorption and mixing. Rutherford back scattering and scanning Auger microprobe techniques were used to characterize the mixed layers. The incoherent light annealing is believed to be a rapid thermal process, which in our case results either in solid- or liquid-phase epitaxial regrowth depending on the annealing conditions.
Advantages of rapid optical annealing
Authors: Gelpey Jeffrey C. , Stump Paul O. , Camm David
Published: April 2011

It has been found that the advantages of rapid thermal processing during various stages of semiconductor processing are strongly dependent on the source used to heat the wafer and the system configuration. Examples of process data are presented that were obtained using a system based on the water-wall DC arc.High power levels incident on one side of the wafer allow very fast heating rates (ambient to 1200 °C in under 3 s) while at the same time permitting direct-feedback control of temperature via monitoring with an infrared pyrometer. Rapid-rise times also minimize dopant diffusion while eliminating residual crystal damage at relatively low temperatures. SIMS studies show that the junction movement is typically under 1000 Å for common implant species. Reflows of low-temperature glass such as PSG with 5–6% phosphorus concentrations have been achieved without significant diffusion of underlying structures. Silicides of most common refractory metals have been formed, which show resistivities comparable to furnace annealing with much less diffusion.
Continuous-wave laser-induced diffusion in silicon
Authors: Schvan P. , Thomas R. E.
Published: April 2011

A novel processing technique to form shallow p-n junctions using a continuous-wave (cw) laser beam scanned over a large area is described. The results of computer simulation of the heat-flow problem were used to find the optimum condition for cw laser-induced liquid-phase diffusion. High-speed scanning of the laser beam and the application of phosphosilica glass as a diffusion source, which also acts as an antireflective coat, are essential parts of the process. The optimum incident laser power was around 7.5 W with a scanning speed of 100 cm/s. This process produced junction depths of around 0.2–0.4 μm. Reliable contacts to the shallow diffusions were made using tungsten silicide formed prior to the aluminum deposition. The p-n junctions formed by this technique showed good diode characteristics with breakdown voltages over 35 V and leakage current around 10−5 A/cm2.
Reduced narrow-width effects in a scaled local oxidation of silicon process
Authors: Baglee David A. , Duane M. P. , Smayling M. C.
Published: April 2011

The reduction of narrow-width effects in VLSI transistors is of great importance if small-geometry devices are to be of real use in advanced circuits. These effects are caused by boron encroaching into the transistor channel from underneath the field isolation oxide. In this paper we describe the results of experiments to reduce this encroachment by the use of high-pressure oxidation. We show that the substitution of this process into a VLSI process flow, for the field oxidation step, allows the channel-stop implant dose to be significantly reduced (50%) without degradation of interdevice isolation.
High-voltage n-channel metal-oxide-semiconductor technology
Authors: Abbott R. S. , Ellul J. P. , Hadaway R. A. , White J. J.
Published: April 2011

High-voltage devices have been integrated into a standard silicon-gate NMOS IC fabrication process utilizing a novel front-end processing technique. Fabrication-process steps and modelling results are described in this paper. Driver transistors are characterized in terms of drift-region implant dose, design parameters, and substrate resistivities. Present work has optimized process parameters and device structures to yield "off" state breakdown up to 270 V for 6–10 Ω∙cm, p-type, [Formula: see text] substrates.
A new large-scale integrated metallization-failure mechanism
Authors: Bellier S. P. , Haythornthwaite R. F.
Published: April 2011

A new integrated-circuit metallization-failure mechanism is reported. The aluminum metallization sometimes disintegrates during ultrasonic agitation despite the fact that the aluminium–silicon oxide–water system is thermodynamically stable under conditions normally encountered by integrated circuits. The disintegration reduces conductor cross section and increases the probability of failure by electromigration. Faulty batches of metallization from six manufacturers have been found; one batch of devices, which failed abnormally early through electromigration, had the faulty metallization.Scanning–electron–microscope examination revealed that foreign material or voids were sometimes visible between the aluminum grains but there was often no visible indication of the problem areas. Scanning Auger microprobe examination revealed nitrogen and oxygen in the aluminum of faulty batches, and carbon was also present in the areas that lifted. Aluminum, which was unaffected by ultrasonic agitation, had no additional elements.Experiments in controlling the evaporation environment to increase the probability of incorporating oxygen, nitrogen, and carbon into the aluminum layer were unsuccessful.Ultrasonic agitation provides an economic possibility for screening devices with unstable metallization. It can be introduced during wafer manufacture or as a sampling screen on completed devices for high reliability applications.
Stellar and galactic jets: theoretical issues
Authors: Königl Arieh
Published: April 2011

Theoretical issues pertaining to the modelling of jets in young stellar objects and in active galactic nuclei are reviewed. The strong morphological similarities between these two types of sources are emphasized, and observational constraints on the basic physical mechanisms that may be responsible for the jet phenomenon are outlined. Particular attention is given to the "momentum-discharge problem" in molecular-cloud outflows and to its possible resolution in terms of a centrifugally driven magnetohydrodynamic wind from an accretion disk. In addition, various propagation effects are discussed, and the relevance to stellar jets of the de Laval collimation mechanism and of the accelerated-clump model for emission knots is assessed. The review concludes with a brief list of potentially useful observational tests.
Wide-angle tailed radio galaxies
Authors: Burns Jack O.
Published: April 2011

In this paper, the properties of a class of extragalactic radio sources associated with dominant cluster galaxies known as wide-angle tails (WATs) are reviewed. The mechanism responsible for forming and, in particular, bending these sources remains controversial nearly 10 years after their discovery. To gain possibly new insight into these radio galaxies, we divide them into three subclasses according to linear size. The smallest WATs are limited in size to the optical extent of the galaxies, are weaker in radio power, and may be bent by dynamic pressure as a result of motion of the radio galaxy about a second large galaxy or subcondensation of galaxies in the cluster. The large, 1-Mpc size WATs are associated with a single, dominant cD galaxy, have only sharp and irregularly placed bends in the jets, and probably interact with clouds in the cluster gas. The moderate-size, symmetrically bent WATs such as 3C 465 may bend and decollimate as a result of the passage of a jet through a sharp pressure gradient, which occurs within the halos of these galaxies.
Constraints on extragalactic-jet characteristics from lobe observations
Authors: Spangler Steven R.
Published: April 2011

We discuss Very Large Array spectral and polarimetric observations of the lobes of luminous, double radio galaxies. These observations can provide information on the (typically undetected) jets responsible for the sources. Spectral steepening is usually observed in the lobes, with the radio spectral index increasing with distance from the hot spot. These data can be used to infer a "speed of separation" of the hot spot and lobe material. These speeds, typically 1.0 × 104–3.0 × 104 km/s, are in agreement with hydrocode models of jets, which interpret the measured speed of separation as a combination of hot-spot motion and backflow. Polarimetric observations indicate that in at least some sources, there is an undetectably small amount of internal Faraday rotation, indicating upper limits to the thermal-plasma density of a few times 10−5 cm−3 or less. These measurements are also in agreement with the numerical beam models, provided that the beam density is substantially less than that of the background medium. We conclude that the lobe observations indicate that these sources are powered by light, high-Mach-number beams.
Spectrum and polarization of radio galaxy lobes and tails
Authors: Andernach Heinz
Published: April 2011

The distribution of radio spectra across six radio galaxies is studied at ~4′ resolution. Spectral breaks consistent with the absence of particle acceleration are rare, and spectra do not always show the expected steepening with core distance or with frequency. Even in far outer tails there is evidence for recent reacceleration. Spectral flattening often occurs near bends, wiggles, and knots; thus, particle acceleration seems most efficient at "working surfaces" with the ambient media. Radio spectra indicate an energy spectrum of the accelerated particles flatter than ~E−1.6 in these areas. Some polarization maps reveal inverted depolarization and departures from the λ2 law of Faraday rotation, probably due to different physical regimes within one antenna beam.
Optical images of star-formation regions
Authors: Campbell Bel , Persson S. E.
Published: April 2011

New and sensitive optical imaging of a small sample of young stellar objects is presented. The observations are part of a continuing program of deep, red optical imaging of star-forming regions performed with the 4Shooter charge-coupled-device (CCD) system on the Palomar 5-m telescope. Each of the sources presented is of moderately high luminosity [Formula: see text] and is associated with a bipolar outflow of molecular gas. The results on the source GL490 are discussed in some detail. We find the source core to be well resolved and elongated orthogonal to the outflow direction despite an unresolved image size (< 0.3″) in the near infrared; in addition, there is an extended (> 0.8 pc) cone of diffuse emission out from the core source in the direction of the blue-shifted portion of the molecular outflow. From astrometry of the CCD frame, we find that the center of the optical position is displaced from the radio-image centroid by approximately 1.5″ to the southwest, also in the direction of the blue-shifted outflow. It is proposed that the optical image is totally due to scattered light from a source that is entirely obscured from direct view. Owing to inconsistencies in the orientations of the radio image and polarization position angle with the other source orientations, we conclude that a simple disk plus an orthogonal-outflow scenario is no longer supportable for this object and that continued observations may reveal many equally complex cases.
Extended optical line emission associated with radio galaxies
Authors: Breugel Wil van
Published: April 2011

Observations of radio galaxies that have extended optical emission-line regions provide a new way of studying the interaction of extragalactic jets with their ambient medium. Their general properties are briefly reviewed and are illustrated using recent results on 4C 29.30 and Minkowski's Object.
Extragalactic jets and their interaction with their environment
Authors: Brodie Jean
Published: April 2011

We describe three optical observational projects, each carried out in conjunction with studies at other wavelengths. These emphasize the usefulness of multifrequency studies in elucidating the nature of extragalactic jets. The first part concerns regions of optical line and continuum emission found at the sites of X-ray-radio knots in the inner 2 kpc of the Centaurus A jet. We show that these regions are physically associated with the jet and cite evidence for shock excitation within the emitting clumps. The full-spectrum continuum emission is attributed to the synchrotron process. Next we report the preliminary results of a search for optical emission in the fields of five radio jets. In the field of Abell 194 we find evidence for a jet-galaxy interaction. The optical-emission region known as Minkowski's Object is found to lie in the path of a radio jet. Spectroscopic investigation supports the view that it results from a burst of star formation, triggered by the impact of the jet on a cloud of material in its path. Last, we describe simultaneous multifrequency observations of the highly variable BL Lac object Mkn421. Dramatic changes in X-ray flux on time scales of weeks are not reproduced at other wavelengths. The X-ray variations are such that the lowest energy photons undergo the least change. These results allow some discrimination between the various theoretical jet models that have been proposed to describe the properties of BL Lacs. We also discuss possible interpretations for shorter time-scale (~10 000 s) variations with 10% amplitude, which were observed in X-ray light curves when the source was in an X-ray bright state.
Jets from young stars: estimates of their physical parameters
Authors: Mundt Reinhard
Published: April 2011

On the basis of existing observational data, the characteristic values of the physical parameters of jets from young stellar objects are estimated. The results of these estimates are as follows: velocities = 200–400 km/s, Mach numbers = 10–40, hydrogen-number densities = 15–150 cm−3, and mass fluxes = 10−10–10−7 [Formula: see text]. The derived Mach numbers imply reasonable jet temperatures (≈ 104 K), being consistent with the observed emission-line spectrum. The estimated jet densities are in agreement with the idea that some high-velocity Herbig–Haro objects (v ≈ 200 km/s) represent the working surface of a freely expanding jet boring through the outer, tenuous parts of a molecular cloud.
Optical polarimetry of nebulae in regions of star formation
Authors: Scarrott S. M. , Warren-Smith R. F. , Draper P. W. , Gledhill T. M.
Published: April 2011

Optical polarization data are presented for nebulosities associated with dark clouds and regions of star formation.Illuminating sources are identified, and it is found that these usually show evidence of polarization induced by aligned grains, which we believe indicates the presence of magnetic fields in the gas–dust tori that surround the central objects.
Very long baseline interferometry polarization studies of quasars and active galactic nuclei
Authors: Wardle J. F. C. , Roberts D. H.
Published: April 2011

We present some first results of a program to map the distribution of linear polarization in compact radio sources with milliarcsecond resolution. We show first-epoch maps of 3C345 and 0735 + 178 and first- and second-epoch maps of OJ287. In general, the polarization is mainly associated with optically thin (jet) components. In the case of OJ287, polarization maps made 1 year apart are strikingly different. We also discuss some of the theoretical issues raised by these observations.
Radio jets at high red shift
Authors: Lonsdale Colin J.
Published: April 2011

Using preliminary results from a large observational program targeting high red-shift radio quasars, we have increased the total number of radio jets known beyond a red shift of 1.5 from 5 to 26, thus generating one of the most uniform and complete samples of radio jets in existence. This sample enjoys relative freedom from cosmological and luminosity-evolution effects, which normally complicate statistical analyses of jets.An attempt has been made to test a type of radio-quasar model in which the appearance of a radio source is strongly influenced by its orientation relative to the line of sight, owing to Doppler boosting of the emission from relativistically moving jet material. Four "orientation indicators" are isolated, which should all be correlated with each other to some degree if the above-mentioned model is correct. It is found that only one pair of parameters shows a significant correlation, namely the jet prominence (relative to the lobes) and the jet curvature. This particular correlation finds a natural explanation in the physics of radio sources, and therefore may not be due to orientation effects.As a result of these findings, it is concluded that the present sample of high red-shift jets shows no evidence of relativistic flow speeds on kiloparsec scales.
Wind-type flows and astrophysical jets
Authors: Ferrari Attilio , Tsinganos Kanaris
Published: April 2011

The application of the theory of hydrodynamic winds to the interpretation of collimated outflows from galactic and extra-galactic objects is reviewed and discussed. The study supports the conclusion that the different classes of astrophysical jets are governed by common dynamical processes.
Magnetic-field configurations in compact extragalactic jets
Authors: Jones T. W.
Published: April 2011

Multifrequency and multitime polarimetry of active, compact radio sources strongly suggest that the magnetic-field structures in these sources are largely disordered or turbulent. Some initial, detailed model calculations of relativistic jets with turbulent fields have been performed in an effort to better understand the relationships between the observed polarization properties and physical structures of sources. Simulations are described involving nearly steady, isothermal, constant velocity jets with magnetic fields having approximately a Kolmogorov turbulence spectrum that is carried along the jet. They produce structures similar to those actually observed, including a core-jet appearance with superluminal knots. Likewise, the polarization has a behavior in frequency and time that is at least qualitatively similar to that observed. In addition, although individual portions of the model sources are highly polarized, as also seen with very long baseline interferometry, the integrated polarizations are relatively small, as observed.
Shocks as the origin of radio-source variability
Authors: Hughes P. A. , Aller H. D. , Aller M. F.
Published: April 2011

We describe a model for recent, highly polarized, centimetre-wavelength outbursts of the source BL Lacertae in which "pistons" drive shocks in a collimated, relativistic flow. The compression of a random magnetic field by the shocks produces the polarization, and very weak shocks (M of order 1) are capable of explaining the observations. Short-lived steep spectrum components and short-lived localized changes in magnetic-field direction, expected in this scenario, are exhibited by other sources, suggesting that the model for BL Lacertae is of general applicability.
Do neutron stars produce jets?
Authors: Feigelson Eric D.
Published: April 2011

The evidence for jets emanating from neutron stars is reviewed. Isolated radio pulsars do not appear to produce collimated outflows. A few supernova remnants, notably the Crab nebula, exhibit jetlike protrusions at their outer boundaries. These are probably "blowouts" of the plasma in the remnant rather than true jets from a neutron star. However, several cases of degenerate stars in X-ray binary systems do make jets. SS433 has twin precessing jets moving outward at v ~ 0.26c, and Sco X-1 has radio lobes with v ~ 0.0001c. Cyg X-3 appears to eject synchrotron plasmoids at high velocities. Other X-ray binaries associated with variable radio sources are discussed; some are interesting candidates for collimated outflow. G109.1-1.0 is an X-ray binary in a supernova remnant that may have radio or X-ray jets. It is not clear in all these cases, however, that the compact object is a neutron star and not a black hole or white dwarf.A tentative conclusion is reached that isolated neutron stars do not produce jets, but degenerate stars in accreting binary systems can. This suggests that the presence of an accretion disk, rather than the characteristics of an isolated pulsar's dipole magnetosphere, is critical in making collimated outflows.
Radio hot spot in supernova remnant G109.1-1.0
Authors: Gregory P. C.
Published: April 2011

High-resolution, very large array observations of a radio hot spot in the supernova remnant G109.1-1.0 were carried out in January 1981 and August 1984 at 6 and 20 cm to examine the possible relationship of this source to the remnant and nearby binary X-ray pulsar. The structure, spectrum, and absence of variability over a 3-year time span are consistent with a background quasar or galaxy. The source, 2258 + 586, exhibits an unresolved core that is self-absorbed at 20 cm and a one-sided jet. A very faint object appears on the red print of the Palomar sky survey, 3.7 ± 1.7 arcsec from the unresolved core.
Jets associated with supernova remnants and other galactic nonthermal sources
Authors: Becker R. H.
Published: April 2011

Accreting neutron star or black holes in binary systems can, under appropriate circumstances, eject jets of particles into their environment. This is most readily observed in SS433, Sco X-1, and Cyg X-3. We infer the presence of the injection of relativistic particles in a number of other galactic sources where actual jets have not been observed. In some cases the energy imparted results in nonthermal radio sources comparable in size to supernova remnants.
A helically twisted relativistic jet: nonradial motions and accelerations in 3C345
Authors: Hardee Philip E.
Published: April 2011

The radio source 3C 345 has a curved, inner-jet structure consisting of three components. Components C2 and C3 appear to be moving with βapp ~ 17 and 13, respectively, along approximately parallel straight-line trajectories with motion along a mean direction ~ −75°. Component C4 recently appeared at a position angle ~ −135° and has exhibited nonlinear motion and apparent acceleration from βapp ~ 4–10 over a period of about 2 years with motion along a mean direction < −75°. We show how the motions of C4 can be explained by a feature that is propagating with constant speed along a helically twisted jet in which the wavelength of the helix increases in proportion to the jet's radius. This form for a helical twist is predicted by the linearized fluid-dynamical equations, which can be used to describe the response of a light jet to helical distortion.
Hercules A: a precessing cannon?
Authors: Maiden Martha E. , Christiansen W. A.
Published: April 2011

Hercules A is an unusual radio source in that its structure is dominated (most specifically on the western side of the source) by an undulating chain of discrete "rings" of radio emission, whose individual radii increase progressively with distance from the nuclear core while their apparent separation decreases. In the theoretical model presented here, these interesting radio features are presumed to be due to emission from a discrete set of ram-pressure confined plasmoids that have been periodically ejected by a precessing nuclear engine. The predicted deceleration and expansion of these ram-pressure confined plasmoids provides an excellent fit to the observed spacing and radii of the radio rings observed on the western side of Hercules A. Furthermore, a satisfactory fit to the morphology of the undulating eastern jet can also be achieved using this discrete ejection model, providing the eastward ejections alternate with the westward ejections, thus implying a form of flip-flop behavior for this particular source.
Hydromagnetic winds from accretion disks
Authors: Pudritz Ralph E. , Norman Colin A.
Published: April 2011

We present a hydromagnetic wind model for molecular and ionized gas outflows associated with protostars. If the luminosity of protostars is due to accretion, then centrifugally driven winds that arise from the envelopes of molecular disks explain the observed rates of momentum and energy transport. Ionized outflow originates from disk radii r ≤ 1015 cm inside of which Ly-continuum photons from the protostellar accretion shock are intercepted. Observed molecular outflows arise from the cool disk envelope at radii 1015 ≤ r ≤ 1017 cm. The mass-loss rates of these two component outflows are [Formula: see text] and [Formula: see text]. These winds solve the angular-momentum problem of star formation. We propose that the collimation of such outflows is due to "hoop" stresses generated by the increasingly toroidal magnetic field in the wind and suggest that the structure of the underlying disks makes self-similar solutions for these outflows likely. Finally, we apply this analysis to other accreting systems such as cataclysmic variables.
Hydrodynamic ejection of intrinsically bipolar flows
Authors: Torbett Michael V.
Published: April 2011

A general mechanism is presented for generating pressure-driven winds, which are intrinsically bipolar, from objects undergoing disk accretion. The energy liberated in a boundary-layer shock as disk matter impacts the central object makes the vertical density structure of the boundary layer go out of hydrostatic equilibrium by large factors. The resultant expansion in the direction of the density gradient, i.e., perpendicular to the disk, converts accretion energy into P dV work and is shown to be capable of ejecting a fraction β ~ 10−2–10−1 of the accreted mass from the system. The ejection of these flows, accelerated within [Formula: see text], can account for the jets observed from pre-main-sequence stars and cataclysmic variables. Unless an analogous boundary-layer shock develops during accretion onto massive black holes, however, this mechanism does not seem to be applicable to jets from galaxies.
Jet activity in the symbiotic variable R Aquarii
Authors: Michalitsianos A. G. , Hollis J. M. , Kafatos M.
Published: April 2011

The peculiar, emission star R Aquarii (M7e + pec) embodies a number of distinguishing properties, the most significant being a collimated jet that extends approximately 6 arcsec northeast from the star. Discovered optically nearly a decade ago, this unique feature has been intensively studied at optical, ultraviolet, and radio wavelengths. Over the course of 4 years, we have obtained the low-resolution ultraviolet spectra of the R Aquarii jet with the International Ultraviolet Explorer (IUE). Our most recent IUE observations indicate the ionization state of the jet is increasing. Subarcsecond, Very Large Array observations of R Aquarii have resolved the radio-continuum structure into discrete parcels of emission that are extended and nearly collinear. R Aquarii provides evidence that indicates stellar jet activity is not unique to objects associated with high-energy emission processes alone. Rather, the nature of the aligned radio-optical features that comprise the R Aquarii jet indicate that directional mass expulsion, in the form of discrete-collimated ejecta, probably reflect a general, underlying, physical process associated with a wide variety of peculiar stellar objects. As such, the R Aquarii jet constitutes a prototype for jet activity in composite or peculiar emission stars.
Jet from the Milky Way center: the galactic center lobe
Authors: Sofue Yoshiaki
Published: April 2011

The radio lobe in the galactic center found through 10-GHz continuum observations is likely to be a cylindrical jet emerging from the nuclear disk of the Milky Way Galaxy. The galactic center lobe may be the nearest galactic-scale jet being accelerated by a mildly rotating disk with a magnetic field.
Bipolar outflow of gas in the spiral galaxy NGC 3079
Authors: Duric Nebojsa , Seaquist E. R.
Published: April 2011

Very large array, radio-continuum observations of the edge-on spiral galaxy NGC 3079 are presented. The observations reveal that the nucleus has windlike properties and that the central region of the galaxy exhibits an unusual figure-eight morphology that shows evidence of severe depolarization and a flattening spectral index away from the nucleus. A qualitative description of a model is presented to account for the observed radio properties. It is shown that a wind-driven shock propagating away from the nucleus and focused by the ambient disk gas can give rise to the observed morphology.
Photoacoustic, photothermal, and related techniques: a review
Authors: McDonald F. Alan
Published: April 2011

A review is presented of the current theoretical and conceptual understanding of physical processes involved in photoacoustic and photothermal techniques, and in related techniques employing particle beams. Emphasis is given to recent developments, and to problems needing attention. The thermoacoustic theory of the photoacoustic cell is reviewed and contrasted with the isochoric model, and the effects of mass transfer, viscosity, and porous samples are discussed. Thermal-imaging techniques are reviewed, with attention to questions of resolution, definition, and sensitivity. Progress in understanding and modeling techniques based on thermoelestic processes is considered.
Finite-element simulation of the photoacoustic–thermal signal generation
Authors: Lévesque D. , Rousset G. , Bertrand L.
Published: April 2011

The ability to use the finite-element method to solve numerically the frequency-dependent coupled equations of the photoacoustic–thermal effect is demonstrated. Both solids and fluids are simulated by the same set of equations with temperature and displacement as variables. The main interest of this formulation lies in its great flexibility to deal with mixed fluid–solid systems. As a first application, we consider the influence of thermoacoustic coupling on the pressure in a photoacoustic cell. We show that with increasing frequency, a transition from an isothermal to an adiabatic process occurs. Subsequently, results obtained from a numerical simulation of the photoacoustic cell, which includes the effect of a residual volume, are in good agreement with existing experimental data.
Digital simulation of photoacoustic impulse responses
Authors: Miller Richard M.
Published: April 2011

Impulse-response photoacoustic spectroscopy provides information on the depth distribution of chromophores in solid samples. To gain an understanding of the way in which sample properties affect the impulse response, a digital model has been generated. This model is based on discretization of time and space coupled with a finite-difference approximation of the governing heat-diffusion equations. The simulations are compared with experimental results.
Separation of surface and volume absorption in photothermal spectroscopy
Authors: Mongeau Bernard , Rousset Gérard , Bertrand Lionel
Published: April 2011

Separation of surface absorption from bulk absorption by using the phase of the photothermal signal is shown on samples of SiO deposited on CaF2. The bulk signal obtained with these samples shows good agreement with the signal obtained for uncoated CaF2 samples.
Thermal-wave vignetting and standing-wave effects in the infrared detection of ultrasonic absorption
Authors: Monchalin Jean-Pierre , Bussière Jean F. , Bertrand Lionel
Published: April 2011

It has been previously shown that ultrasonic absorption in a solid material can be detected and, in some cases, measured by monitoring, with an infrared detector, the variation of temperature at the surface of the sample resulting from the periodic modulation of the ultrasonic intensity. Thermal-wave vignetting effects, which are caused by the finite ultrasonic beam size and the finite area viewed by the detector, and effects caused by the ultrasonic standing-wave pattern are analyzed in this paper by a theoretical derivation and by experiment. Satisfactory agreement is found between both.
Study of the liquid–gas boundary of water and alcohols by photoacoustic spectroscopy
Authors: Haas U.
Published: April 2011

Water, heavy water, and some primary alcohols (methanol, ethanol, propanol, and butanol) are investigated in the near infrared by photoacoustic (PA) spectroscopy. The PA amplitudes of "free" and hydrogen-bonded hydroxyl absorptions show a different dependence on modulation frequency f, deviating from an expected f−1 dependence for liquids. The investigations demonstrate that the liquids reveal a structural modification from the inside toward the liquid–gas boundary.