2,478 research outputs found
Sputtered Indium Tin Oxide Films for Optoelectronic Applications
Highâquality indium tin oxide (ITO) films have been fabricated using a DC sputtering technique in a pure argon atmosphere with a postannealing in an oxygen environment at atmosphere pressure. Structural, morphological, and electroâoptical parameters of the ITO films were studied at different annealing temperatures for the films fabricated on two types of glass substrates, soda lime and alkaliâfree substrates. A comparative analysis shows that lowâcost soda lime substrates are suitable for the fabrication of highâquality nanocrystalline ITO films after annealing them at 300°C. This result is of great importance for reducing the cost of thin film solar cells, in which ITO films serve as transparent conducting electrodes. We present a comparison of the properties of sputtered ITO films with those fabricated using a spray pyrolysis deposition technique, which is useful for some optoelectronic applications
Surface-Barrier Photodiodes with Transparent Electrodes for High-Performance Detection in the UV-NIR Spectrum
The aim of this chapter is to present a short review in the field of design, fabrication technology, and testing of high-efficiency surface-barrier photodiodes with electrodes based on thin-film transparent conducting oxides (TCO) such as tin-doped indium oxide (ITO) and fluorine-doped tin oxide (FTO). Most of this review is based on our own results obtained and reported during the last 30 years. Besides a brief description of the low-cost spray pyrolysis deposition technique, mainly used in our work for deposition of the TCO films on a semiconductor surface, structural, morphological, and optoelectronic properties of these TCO films are discussed. As an example, a successful application of these TCO films is shown and used in high-efficiency surface-barrier photodiodes for a wide spectral range, from near ultraviolet (UV) to near infrared (NIR), and fabricated on different semiconductor substrates such as traditional Si, wide energy band ZnS, and GaP compound semiconductor substrates. The possible use of the Si surface-barrier structures as radiation-resistant detectors and gamma radiation detectors is discussed. The properties of high-efficiency surface-barrier photodiodes based on a perspective ternary semiconductor compound, Hg3In2Te6 mercury indium telluride (MIT), for detection of 1.3Â ÎŒm and 1.55 ÎŒm radiation for applications in fiber optics, are also reported
The Accreting White Dwarf in SS Cygni Revealed
We have carried out a combined Hubble Space Telescope (HST/GHRS) and Far
Ultraviolet Spectroscopic Explorer FUSE) analysis of the prototype dwarf nova
SS Cygni during quiescence. The FUSE and HST spectra were obtained at
comparable times after outburst and have matching flux levels where the two
spectra overlap. In our synthetic spectral analysis, we have used SS Cygni's
accurate HST FGS parallax giving d = 166pc, a newly determined mass for the
accreting white dwarf (Bitner et al. 2007) of Mwd=0.81Msun (lower than the
previous, widely used 1.2 Msun) and the reddening E_{B-V} values 0.04 (Verbunt
1987; La Dous 1991) and 0.07 (Bruch and Engel 1994) derived from the 2175A
absorption feature in the IUE LWP spectra. From the best-fit model solutions to
the combined HST + FUSE spectral energy distribution, we find that the white
dwarf is reaching a temperature Teff of 45-55,000K in quiescence, assuming
Log(g)= 8.3 with a solar composition accreted atmosphere. The exact temperature
of the WD depends on the reddening assumed and on the inclusion of a quiescent
low mass accretion rate accretion disk. Accretion disk models alone fit badly
in the FUSE range while, and if we take the distance to be a free parameter,
the only accretion disk model which fits well is for a discordant distance of
at least several hundred pc and an accretion rate (1.E-8 Msun/yr which is
unacceptably high for a dwarf nova in quiescence. We discuss the implications
of the white dwarf's temperature on the time-averaged accretion rate and long
term compressional heating models.Comment: ApJ, accepte
Spray Pyrolysis Processing for Optoelectronic Applications
Spray pyrolysis is a low-cost and simple technique for the fabrication of high-quality transparent and conducting oxide thin films for different optoelectronic applications. The fabrication method, structural, morphological, and electro-optical properties of fluorine-doped tin oxide (FTO) and tin-doped indium oxide (ITO) films have been investigated. The deposited films have low resistivity and high transparency. Applications of such films are shown in high-efficiency surface-barrier photodetectors and solar cells, where the films serve as an active and antireflection electrode. A short description of other undoped and doped oxide films such as ZnO and TiO2 fabricated by spray pyrolysis is presented
HST/FOS Eclipse Observations of the Nova-like Cataclysmic Variable UX Ursae Majoris
[abridged abstract]
We present and analyze Hubble Space Telescope observations of the eclipsing
nova-like cataclysmic variable UX UMa obtained with the Faint Object
Spectrograph. Two eclipses each were observed with the G160L grating (covering
the ultraviolet waveband) in August of 1994 and with the PRISM (covering the
near-ultraviolet to near-infrared) in November of the same year. The system was
50% brighter in November than in August, which, if due to a change in the
accretion rate, indicates a fairly substantial increase in Mdot_acc by >~ 50%.
Model disk spectra constructed as ensembles of stellar atmospheres provide
poor descriptions of the observed post-eclipse spectra, despite the fact that
UX UMa's light should be dominated by the disk at this time. Suitably scaled
single temperature model stellar atmospheres with T_eff = 12,500-14,500 K
actually provide a better match to both the ultraviolet and optical
post-eclipse spectra. Evidently, great care must be taken in attempts to derive
accretion rates from comparisons of disk models to observations.
One way to reconcile disk models with the observed post-eclipse spectra is to
postulate the presence of a significant amount of optically thin material in
the system. Such an optically thin component might be associated with the
transition region (``chromosphere'') between the disk photosphere and the fast
wind from the system, whose presence has been suggested by Knigge & Drew
(1997).Comment: 35 pages, including 12 figures; to appear in the ApJ (Vol. 499
The White Dwarf in EM Cygni: Beyond The Veil
We present a spectral analysis of the FUSE spectra of EM Cygni, a Z Cam DN
system. The FUSE spectrum, obtained in quiescence, consists of 4 individual
exposures (orbits): two exposures, at orbital phases phi ~ 0.65 and phi ~ 0.90,
have a lower flux; and two exposures, at orbital phases phi =0.15 and 0.45,
have a relatively higher flux. The change of flux level as a function of the
orbital phase is consistent with the stream material (flowing over and below
the disk from the hot spot region to smaller radii) partially masking the white
dwarf. We carry out a spectral analysis of the FUSE data, obtained at phase
0.45 (when the flux is maximual, using the codes TLUSTY and SYNSPEC. Using a
single white dwarf spectral component, we obtain a white dwarf temperature of
40,000K, rotating at 100km/s. The white dwarf, or conceivably, the material
overflowing the disk rim, shows suprasolar abundances of silicon, sulphur and
possibly nitrogen. Using a white dwarf+disk composite model, we obtain that the
white dwarf temperature could be even as high as 50,000K, contributing more
than 90% of the FUV flux, and the disk contributing less than 10% must have a
mass accretion rate reaching 1.E-10 Msun/yr.In both cases, however, we obtain
that the white dwarf temperature is much higher than previously estimated.Comment: accepted for publication in ApJ, 3 Tables, 12 Figures (including
color figures), 33 pages in present format (possibly 10 pages in ApJ format
Determination of the basic parameters of the dwarf nova EY Cygni
High-dispersion spectroscopy of EY Cyg obtained from data spanning twelve
years show, for the first time, the radial velocity curves from both emission
and absorption line systems, yielding semi-amplitudes K_{em}=24+/- 4 km s^-1
and K_{abs}=54+/- 2 km s^-1. The orbital period of this system is found to be
0.4593249(1)d. The masses of the stars, their mass ratio and their separation
are found to be M_1 sin^3 i = 0.015+/-0.002 M_sun, M_2 sin^3 i = 0.007+/-0.002
M_sun, q = K_1/K_2 = M_2/M_1 = 0.44+/-0.02 and a sin i = 0.71+/-0.04 R_sun. We
also found that the spectral type of the secondary star is around K0,consistent
with an early determination by Kraft(1962). From the spectral type of the
secondary star and simple comparisons with single main sequence stars, we
conclude that the radius of the secondary star is about 30 per cent larger than
a main sequence star of the same mass. We also present VRI CCD photometric
observations, some of them simultaneous with the spectroscopic runs. The
photometric data shows several light modulations, including a sinusoidal
behaviour with twice the frequency of the orbital period, characteristic of the
modulation coming from an elongated, irradiated secondary star. Low and high
states during quiescence are also detected and discussed. From several
constrains, we obtain tight limits for the inclination angle of the binary
system between 13 and 15 degrees, with a best value of 14 degrees obtained from
the sinusoidal light curve analysis. From the above results we derive masses
M_1 = 1.10+/-0.09 M_sun, M_2 = 0.49+/-0.09 M_sun, and a binary separation a =
2.9+/- 0.1 R_sun.Comment: 14 pages, 14 figures, accepted for publication on A&
Participation and satisfaction after spinal cord injury: results of a vocational and leisure outcome study
Study design: Survey. Objectives: Insight in (1) the changes in participation in vocational and leisure activities and (2) satisfaction with the current participation level of people with spinal cord injuries (SCIs) after reintegration in society. Design: Descriptive analysis of data from a questionnaire. Setting: Rehabilitation centre with special department for patients with SCIs, Groningen, The Netherlands. Subjects: A total of 57 patients with traumatic SCI living in the community, who were admitted to the rehabilitation centre two to 12 years before the current assessment. Main outcome measures: Changes in participation in activities; current life satisfaction; support and unmet needs. Results: Participation expressed in terms of hours spent on vocational and leisure activities changed to a great extent after the SCI. This was mainly determined by a large reduction of hours spent on paid work. While 60% of the respondents successfully reintegrated in work, many changes took place in the type and extent of the job. Loss of work was partially compensated with domestic and leisure activities. Sports activities were reduced substantially. The change in participation level and compensation for the lost working hours was not significantly associated with the level of SCI-specific health problems and disabilities. As was found in other studies, most respondents were satisfied with their lives. Determinants of a negative life satisfaction several years following SCI were not easily indicated. Reduced quality of life was particularly related to an unsatisfactory work and leisure situation. Conclusions: Most people with SCI in this study group were able to resume work and were satisfied with their work and leisure situation
AcDc - A new code for the NLTE spectral analysis of accretion discs: application to the helium CV AM CVn
We present a recently developed code for detailed NLTE calculations of
accretion disc spectra of cataclysmic variables and compact X-ray binaries.
Assuming a radial structure of a standard alpha-disc, the disc is divided into
concentric rings. For each disc ring the solution of the radiation transfer
equation and the structure equations, comprising the hydrostatic and radiative
equilibrium, the population of the atomic levels as well as charge and particle
conservation, is done self-consistently. Metal-line blanketing and irradiation
by the central object are taken into account. As a first application, we show
the influence of different disc parameters on the disc spectrum for the helium
cataclysmic variable AM CVn.Comment: 7 pages, 11 figures to be published in A&
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