Optical Properties of Sapphire

In this investigation, anatase TiO 2 thin films were grown by radio frequency magnetron sputtering on glass substrates at a high sputtering pressure and room temperature. The anatase films were then annealed at 300-600 °C in air for a period of 1 hour. To examine the structure and morphology of the films, X-ray diffraction (XRD) and atomic force microscopy (AFM) methods were used respectively. From X-ray diffraction patterns of the TiO 2 films, it was found that the as-deposited film showed some differences compared with the annealed films and the intensities of the peaks of the crystalline phase increased with the increase of annealing temperature. From AFM images, the distinct variations in the morphology of the thin films were also observed. The optical constants were characterized using the transmission spectra of the films obtained by UV-VIS-IR spectrophotometer. Besides, optical thickness of the film deposited at room temperature was calculated and cross-checked by taking a cross-sectional image through SEM. The optical band gaps were evaluated through Tauc model. It was observed that TiO 2 films produced at room temperatures exhibited high visible transmittance and transmittance decreased slightly with the increase of annealing temperatures. The films were found to be crystalline having anatase phase. The refractive index of the films was found from 2.31-2.35 in the visible range. The extinction coefficient was nearly zero in the visible range and was found to increase with annealing temperature. The allowed indirect optical band gap of the films was estimated to be in the range from 3.39 to 3.42 eV which showed a small variation. The allowed direct band gap was found to increase from 3.67 to 3.72 eV. The porosity was also found to decrease at a higher annealing temperature making the film compact and dense.

www.waset.org/publications/3164

The objective is to remove rain from videos without blurring the object. The algorithm helps to devise the system which removes rain from videos to facilitate video surveillance, and to improve the various vision-based algorithms. Rain is a noise that impairs videos and images. Such weather conditions will affect stereo correspondence, feature detection, segmentation, and object tracking and recognition. In video surveillance if any problem is found due to weather conditions the object cannot be tracked well. In this paper we have considered only rain falling in static environment, i.e., the object is not moving.

Possibilities of plasma chemical deposition of α-Si1-x Gex
:H (x=0÷1) films undoped and doped with PH3
or B2
H6
have been analyzed
from the viewpoint of their application in p-i-n structures of solar cell. The optical properties are considered, and the amount of
hydrogen contained in those films is determined. The film properties are found to strongly depend on the film composition and
the hydrogenation level. The number of hydrogen atoms in the films is varied by changing the gas mixture composition, and IR
absorption in α-Si:H and α-Ge
:H films is measured. The α-Si:H and а-Si0,88Ge1,2:H films were used to fabricate three-layer solar with
an element area of 1,3 sm2
and an efficiency (η) of 9.5 %.

In this investigation, TiO2 and Ag based single and multilayer-films were deposited on microscope glass slides with varying individual layer thicknesses by radio-frequency reactive magnetron sputtering. Prior to multilayer development, single layers of Ag and TiO2 were deposited and characterized. All the films were prepared at an elevated pressure of 3 Pa at room temperature. It was found that single layer of TiO2 showed anatase polycrystalline structure. It also exhibited high visible transmittance of above 80% and higher refractive index of 2.31 at a wavelength of 550 nm. The indirect optical band gap of the TiO2 films was estimated as 3.39 eV. The Ag single layer films were found to be crystalline with a very high reflectance for IR (Infra-red) light. Finally, the multi-layers have been deposited and characterized by X-ray diffraction, UV-visible-NIR spectro-photometry, scanning electron microscopy and Auger electron spectroscopy. © 2006-2010 Asian Research Publishing Network (ARPN). All rights reserved.

www.arpnjournals.com/jeas/research_papers/rp_2010/jeas_0910_381.pdf

TiO2 thin films were deposited on unheated and heated glass substrates at an elevated sputtering pressure of 3 Pa by radio frequency (RF) reactive magnetron sputtering. TiO2 films deposited at room temperature were annealed in air for 1 h at various temperatures ranging from 300 to 600 °C. The structural and optical properties of the thin films were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and ultraviolet-visible-near infrared (UV-VIS-NIR) spectrophotometry. XRD results show that as-grown and post-annealed TiO2 films have anatase crystal structure. Higher substrate and annealing temperatures result in a slight increase of crystallinity. TiO2 films deposited at different substrate temperatures exhibit high visible transmittance and the transmittance decreases slightly with an increase in annealing temperature. The refractive indices (at λ = 550 nm) of the as-deposited and annealed films are found to be in the range of 2.31-2.37 and 2.31-2.35, respectively. Extinction coefficient decreases slightly with increasing substrate and annealing temperatures. The indirect and direct optical band gap of the as-grown films increases from 3.39 to 3.42 eV and 3.68 to 3.70 eV, respectively, with the increase of substrate temperatures. Annealed TiO2 films also exhibit an increase in the values of indirect and direct optical band gap. © 2009 Elsevier B.V. All rights reserved.

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We describe, using first principles calculations, the way in which the inherent broken symmetry at the surface of (0001) sapphire leads to a surface dipole and, with applied strain, to a piezoelectric effect. While the bulk form of sapphire has inversion symmetry and thus no net electrical dipole or piezoelectricity, our ab initio calculations show that a large surface dipole emerges. Furthermore, the magnitude of this dipole responds to imposed strain, i.e., a surface piezoelectric effect in an otherwise centro-symmetric non-piezoelectric material. Numerically, the surface piezoelectric response is as strong as a single unit cell of a bulk piezoelectric with e31 = 0.31 C/m 2. Given the importance and widespread use of sapphire as a substrate, this dipole and its response can play an important role in surface chemistry as well as for the coupling of electronic devices fabricated on top of the sapphire surface. The mechanism presented here may be relevant in other materials with corundum structure.

The objective is to remove rain from videos without blurring the object. The algorithm helps to devise the system which removes rain from videos to facilitate video surveillance, and to improve the various visionbased algorithms. Rain is a noise that impairs videos and images. Such weather conditions will affect stereo correspondence, feature detection, segmentation, and object tracking and recognition. In video surveillance if any problem is found due to weather conditions the object cannot be tracked well. In this paper we have considered only rain falling in static environment, i.e., the object is not moving.

The dispersive part of the refractive index of vanadium is determined by measuring the angular displacement of the first order diffraction peak of a V/Fe superlattice. The measurements were made using elliptically polarized synchrotron radiation which was scanned through the V L 2,3 absorption edges for different incident scattering angles. The x-ray scattering technique provides access to direct determination of the dispersive part of the refractive index through an absorption resonance. The influence of absorption at the resonances is shown by comparing the absorption correction to the dispersion correction. The results demonstrate that 1-δ is larger than unity at the L 2,3 resonances of vanadium and the optical consequences are discussed.