485 research outputs found
Cold gas in group-dominant elliptical galaxies
We present IRAM 30m telescope observations of the CO(1-0) and (2-1) lines in
a sample of 11 group-dominant elliptical galaxies selected from the CLoGS
nearby groups sample. Our observations confirm the presence of molecular gas in
4 of the 11 galaxies at >4 sigma significance, and combining these with data
from the literature we find a detection rate of 43+-14%, comparable to the
detection rate for nearby radio galaxies, suggesting that group-dominant
ellipticals may be more likely to contain molecular gas than their non-central
counterparts. Those group-dominant galaxies which are detected typically
contain ~2x10^8 Msol of molecular gas, and although most have low star
formation rates (<1 Msol/yr) they have short depletion times, indicating that
the gas must be replenished on timescales ~100 Myr. Almost all of the galaxies
contain active nuclei, and we note while the data suggest that CO may be more
common in the most radio-loud galaxies, the mass of molecular gas required to
power the active nuclei through accretion is small compared to the masses
observed. We consider possible origin mechanisms for the gas, through cooling
of stellar ejecta within the galaxies, group-scale cooling flows, and gas-rich
mergers, and find probable examples of each type within our sample, confirming
that a variety of processes act to drive the build up of molecular gas in
group-dominant ellipticals.Comment: 9 pages, 5 postscript figures, 4 tables, accepted by A&A. Revised
throughout in response to referee's comments, including updates to Table 1
and Figure 4, and addition of Figure
Resolving the molecular gas around the lensed quasar RXJ0911.4+0551
We report on high angular resolution observations of the CO(7-6) line and
millimeter continuum in the host galaxy of the gravitationally lensed (z~2.8)
quasar RXJ0911.4+0551 using the Plateau de Bure Interferometer. Our CO
observations resolve the molecular disk of the source. Using a lens model based
on HST observations we fit source models to the observed visibilities. We
estimate a molecular disk radius of 10.2 kpc and an inclination of
696\deg, the continuum is more compact and is only marginally resolved by
our observations. The relatively low molecular gas mass, Msolar, and far infrared luminosity, Lsolar, of this quasar could be explained by its relatively low
dynamical mass, Msolar. It would be a
scaled-down version the QSOs usually found at high-z. The FIR and CO
luminosities lie on the correlation found for QSOs from low to high redshifts
and the gas-to-dust ratio () is similar to the one measured in the
z=6.4 QSO, SDSS J1148+5251. Differential magnification affects the
continuum-to-line luminosity ratio, the line profile and possibly the spectral
energy distribution.Comment: Accepted for publication in A&A, revised after language editin
Precursors’ order effect on the properties of sulfurized Cu2ZnSnS4 thin films
A dc magnetron sputtering-based method to grow high-quality Cu2ZnSnS4 (CZTS) thin films,
to be used as an absorber layer in solar cells, is being developed. This method combines dc
sputtering of metallic precursors with sulfurization in S vapour and with post-growth KCN
treatment for removal of possible undesired Cu2−xS phases. In this work, we report the results
of a study of the effects of changing the precursors’ deposition order on the final CZTS films’
morphological and structural properties. The effect of KCN treatment on the optical properties
was also analysed through diffuse reflectance measurements. Morphological, compositional
and structural analyses of the various stages of the growth have been performed using stylus
profilometry, SEM/EDS analysis, XRD and Raman Spectroscopy. Diffuse reflectance studies
have been done in order to estimate the band gap energy of the CZTS films. We tested two
different deposition orders for the copper precursor, namely Mo/Zn/Cu/Sn and
Mo/Zn/Sn/Cu. The stylus profilometry analysis shows high average surface roughness in the
ranges 300–550 nm and 230–250 nm before and after KCN treatment, respectively. All XRD
spectra show preferential growth orientation along (1 1 2) at 28.45◦. Raman spectroscopy
shows main peaks at 338 cm−1 and 287 cm−1 which are attributed to Cu2ZnSnS4. These
measurements also confirm the effectiveness of KCN treatment in removing Cu2−xS phases.
From the analysis of the diffuse reflectance measurements the band gap energy for both
precursors’ sequences is estimated to be close to 1.43 eV. The KCN-treated films show a better
defined absorption edge; however, the band gap values are not significantly affected. Hot point
probe measurements confirmed that CZTS had p-type semiconductor behaviour and C–V
analysis was used to estimate the majority carrier density giving a value of 3.3 × 1018 cm−3
Growth and Raman scattering characterization of Cu2ZnSnS4 thin films
In the present work we report the results of the growth, morphological and structural characterization of
Cu2ZnSnS4 (CZTS) thin films prepared by sulfurization of DC magnetron sputtered Cu/Zn/Sn precursor
layers. The adjustment of the thicknesses and the properties of the precursors were used to control the final
composition of the films. Its properties were studied by SEM/EDS, XRD and Raman scattering. The influence
of the sulfurization temperature on the morphology, composition and structure of the films has been
studied. With the presented method we have been able to prepare CZTS thin films with the kesterite
structure
Assessment of the potential of tin sulphide thin films prepared by sulphurization of metallic precursors as cell absorbers
In this work, SnxSy thin films have been grown on soda-lime glass substrates by sulphurization of metallic
precursors in a nitrogen plus sulphur vapour atmosphere. Different sulphurization temperatures were tested,
ranging from 300 °C to 520 °C. The resulting phases were structurally investigated by X-Ray Diffraction and
Raman spectroscopy. Composition was studied using Energy Dispersive Spectroscopy being then correlated
with the sulphurization temperature. Optical measurements were performed to obtain transmittance and
reflectance spectra, from which the energy band gaps, were estimated. The values obtained were 1.17 eV for
the indirect transition and for the direct transition the values varied from 1.26 eV to 1.57 eV. Electrical
characterization using Hot Point Probe showed that all samples were p-type semiconductors. Solar cells were
built using the structure: SLG/Mo/SnxSy/CdS/ZnO:Ga and the best result for solar cell efficiency was 0.17%
Mo bilayer for thin film photovoltaics revisited
Thin film solar cells based on Cu(In,Ga)Se2 as an absorber layer use Mo as the back contact.
This metal is widely used in research and in industry but despite this, there are only a few
published studies on the properties of Mo. Properties such as low resistivity and good
adhesion to soda lime glass are hard to obtain at the same time. These properties are dependent
on the deposition conditions and are associated with the overall stress state of the film. In this
report, a study of the deposition of a Mo bilayer is carried out by analysing first single and then
bilayers. The best properties of the bilayer were achieved when the bottom layer was
deposited at 10 × 10−3 mbar with a thickness of 500 nm and the top layer deposited at
1 × 10−3 mbar with a thickness of 300 nm. The films deposited under these conditions showed
good adhesion and a sheet resistivity lower than 0.8
Caseous calcification of the mitral annulus: A multi-modality imaging perspective.
Mitral annulus calcification is a common echocardiographic finding, particularly in the elderly and in end-stage renal disease patients under chronic dialysis. Caseous calcification or liquefaction necrosis of mitral annulus calcification is a rare evolution of mitral annular calcification. Early recognition of this entity avoids an invasive diagnostic approach, since it is benign and, unlike intracardiac tumors and abscesses, has a favorable prognosis. The authors present the case of an 84-year-old woman with a suspicious large, echodense mass at the level of the posterior mitral leaflet with associated severe mitral regurgitation. Cardiac magnetic resonance imaging demonstrated a hypoperfused mass with strong peripheral enhancement 10 minutes after gadolinium administration. Multislice computed tomography showed the calcified nature of the mass. A multi-modality imaging approach confirmed the diagnosis of caseous calcification of the posterior mitral annulus. The patient refused surgical treatment
Growth and Characterization of SnSe2 by selenization of sputtered metallic precursors
In the present work, we present a process to grow tin diselenide thin films by selenization at a maximum temperature of 470 ºC, of tin metallic precursor layers deposited by dc magnetron sputtering. For this maximum temperature, disklike grain morphologies were observed. Prominent XRD reflections at 2θ= 30.75º, 40.10º and 47.72º and vibration modes located at 119 cm-1
and 185 cm-1 were observed.
These results allowed concluding that the dominant phase is SnSe2. The composition analysis, done by energy dispersive spectroscopy (EDS), showed that the films were close to being stoichiometric SnSe2 with a Se to Sn ratio of 1.95. Photoluminescence characterization
was performed and revealed a dominant band at 0.874 eV and two other bands at ~0.74 and 1.08 eV with a lower relative intensities. The observed radiative transitions depend critically on the temperature.N/
Influence of the sulphurization time on the morphological, chemical, structural and electrical properties of Cu2ZnSnS4 polycrystalline thin films
The effects of the sulphurization annealing time on the morphological, chemical, structural and electrical properties of CZTS thin films were investigated by scanning electron microscopy, X-ray energy dispersive spectroscopy, Hall effect and electrical conductivity measurements in samples annealed during different time intervals. The increase of the annealing time was found to improve the chemical composition of the samples and to, slightly, increase the crystallite size. Small amounts of Na were measured in the samples. However, the concentration of Na does not increase significantly with the annealing time and should not modify the characteristics of the CZTS thin films. It was also found that at high temperature the electrical conductivity is dominated by thermal emission of carriers over the inter-grain potential barriers. As the temperature decreases different hopping conduction mechanisms start to dominate. At first with nearest-neighbour hopping and successively changing to variable range hopping conduction with a crossover from Mott and Efros–Shklovskii behavior. The electrical conductivity, the concentration of free holes, acceptors and donors, traps0 density at the grain boundaries and the grain potential barriers height were found to increase with the annealing time. However, a significant drop in the compensation ratio from 0.8 to 0.5 was also detected.info:eu-repo/semantics/publishedVersio
On the identification of Sb2Se3 using Raman scattering
Robust evidences are presented that show that the Raman mode close to 250 cm-1 in Sb2Se3 thin films does not belong to this binary compound. A study of the Raman spectrum power dependency revealed the formation of Sb2O3 for high values of power excitation when these measurements are done in normal atmospheric conditions. In order to complement this study, Sb2Se3 thin films were annealed to mimic the thermal conditions of Raman measurements and characterized by X-ray diffraction technique. These measurements showed that the compound Sb2Se3 can be replaced by Sb2O3 under those conditions and a heat-assisted chemical process explains these findings. Furthermore, it is shown what the Raman conditions that are needed for correct measurements to be performed.publishe
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