Effect of oxygen pressure on the structural and optical properties of BaSnO3 films prepared by pulsed laser deposition method.

BaSnO3 thin films were deposited on quartz substrate by pulsed laser deposition technique under different background oxygen pressures and the effects of oxygen pressure on the structural, morphological and optical properties of BaSnO3 thin films are systematically investigated using different characterization techniques. The BaSnO3 films deposited without and with oxygen pressures are polycrystalline in nature with cubic crystalline phase. Moderate oxygen ambience favors enhanced crystallinity of the BaSnO3 films and 0.02 mbar is found to be optimum oxygen pressure for highest crystallinity. The surface morphology of the deposited films was strongly affected by the oxygen pressure in the deposition chamber. A systematic increase of film thickness and decrease of RMS surface roughness is observed with increase in oxygen pressure. XPS analysis reveals that barium is in the + 2 oxidation state and Sn is in the + 4 oxidation state in the film deposited at optimum oxygen pressure of 0.02 mbar. The deposited BaSnO3 films have photoluminescence emissions in the visible region and have high transmittance in the visible and infrared regions. The BaSnO3 films deposited at oxygen ambience shows a blue shift in the optical band gap. The optimized film shows high crystallinity, high value of transmittance and wide band gap energy which indicates its suitability for optoelectronic devices

Panel Discussion: Ideas for an Enjoyable and Productive Sabbatical

Navigating the Sabbatical Process and Deciding on a Productive Activity Can Be Challenging. a Sabbatical Can Take Many Different Forms Depending on Career Goals, Interests, and Institution. the Purpose of This Panel Discussion is to Provide Faculty Who Have Yet to Conduct a Sabbatical with Ideas of Activities and the Process. a Variety of Personal Experiences Will Be Presented of Sabbatical Activities that Were Enjoyable and Productive. These May Include Sabbaticals Focused on Independent Engineering Research, Engineering Education Research, Development of Classes or Programs, Industry or Government Collaboration, And/or Travel. Discussion Topics Will Also Include Process Requirements of Applying, Conducting, and Documenting the Outcomes of the Sabbatical. the Suggested Layout of the Panel Session Is: • 5-Minute Introduction of Panel Topic and Panelists • overview of Each Panelist\u27s Sabbatical Activity (5 Minutes Each) • Brief Whole Group Q&A Session to Engage Audience and Panelists • Small Group Activities with Documentation of Q&A: O What Resources Did You Find Helpful in Planning Your Sabbatical? O What Was the Timeframe of Planning, Applying For, Conducting, and Documenting Your Sabbatical? O What Were the Requirements of Your Sabbatical? O When or How Often Have You Conducted a Sabbatical? • Bring Whole Group Back Together to Discuss Learnings

Field-Dependent Critical Current in Type-II Superconducting Strips: Combined Effect of Bulk Pinning and Geometrical Edge Barrier

Recent theoretical and experimental research on low-bulk-pinning superconducting strips has revealed striking dome-like magnetic-field distributions due to geometrical edge barriers. The observed magnetic-flux profiles differ strongly from those in strips in which bulk pinning is dominant. In this paper we theoretically describe the current and field distributions of a superconducting strip under the combined influence of both a geometrical edge barrier and bulk pinning at the strip's critical current Ic, where a longitudinal voltage first appears. We calculate Ic and find its dependence upon a perpendicular applied magnetic field Ha. The behavior is governed by a parameter p, defined as the ratio of the bulk-pinning critical current Ip to the geometrical-barrier critical current Is0. We find that when p > 2/pi and Ip is field-independent, Ic vs Ha exhibits a plateau for small Ha, followed by the dependence Ic-Ip ~ 1/Ha in higher magnetic fields.Comment: 4 pages, 2 figures, Fig. 1 revised, submitted to Phys. Rev.

The Atomic Physics Underlying the Spectroscopic Analysis of Massive Stars and Supernovae

We have developed a radiative transfer code, CMFGEN, which allows us to model the spectra of massive stars and supernovae. Using CMFGEN we can derive fundamental parameters such as effective temperatures and surface gravities, derive abundances, and place constraints on stellar wind properties. The last of these is important since all massive stars are losing mass via a stellar wind that is driven from the star by radiation pressure, and this mass loss can substantially influence the spectral appearance and evolution of the star. Recently we have extended CMFGEN to allow us to undertake time-dependent radiative transfer calculations of supernovae. Such calculations will be used to place constraints on the supernova progenitor, to place constraints on the supernova explosion and nucleosynthesis, and to derive distances using a physical approach called the "Expanding Photosphere Method". We describe the assumptions underlying the code and the atomic processes involved. A crucial ingredient in the code is the atomic data. For the modeling we require accurate transition wavelengths, oscillator strengths, photoionization cross-sections, collision strengths, autoionization rates, and charge exchange rates for virtually all species up to, and including, cobalt. Presently, the available atomic data varies substantially in both quantity and quality.Comment: 8 pages, 2 figures, Accepted for publication in Astrophysics & Space Scienc

Synthesis, structural and morphological property of BaSnO3 nanopowder prepared by solid state ceramic method.

BaSnO3 is a cubic perovskite-type oxide that behaves as an n-type semiconductor with a wide band gap of 3.4 eV and remains stable at temperatures up to 1000{deg}C. It has wide applications such as thermally stable capacitors, humidity sensors, gas sensors, etc. Barium stannate has also been used in optical applications, in capacitors and ceramic boundary layers, and as a promising material to produce gas phase sensors for the detection of carbon monoxide and carbon dioxide. BaSnO3 powder was prepared by solid state ceramic method. X-ray diffraction pattern of the prepared sample presents all the characteristic peaks of cubic phase of BaSnO3 (JCPDScard no: 15 -0780). The lattice constant for the compound was calculated and found to be 4.101A0 which is in agreement with the reported value (4.112A0). The average size of the crystallites estimated by Debye Scherrer's formula was found to be 49 nm shows the nanostructured nature. The Raman bands observed ~ 139, 833 and 1122 cm-1 can be assigned on the basis of the fundamental vibrations of SnO6 octahedron which has Oh symmetry, in the distorted perovskite structure. The SEM image shows a porous surface morphology with grains of cuboidal structure with well-defined grain boundaries. UV-Visible spectra shows BaSnO3powder exhibit high reflectance in the 400-700 nm range

Absorption Cross Section in Warped AdS3_3 Black Hole

The absorption cross section is studied in the low-frequency region for a propagating scalar field under the warped AdS$_3$ black hole background in the topologically massive gravity. It can be shown that the absorption cross section is significantly deformed by the gravitational Chern-Simons term, which is proportional to the scattering area of black hole with an additional contribution depending on the left-moving and right-moving temperatures. It means that the cross section is larger than the area in spite of the s-wave limit. Finally, we discuss the left-right quasinormal modes for the scalar perturbation in this black hole.Comment: 15 pages, LaTeX, To appear in JHE