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This paper presents an analysis of optical properties of cubic titanium dioxide (TiO2) using Orthogonalized Linear Combinations of Atomic Orbitals (OLCAO) basis set under the framework of Density Functional Theory (DFT). Many optical properties such as refractive index, extinction coefficient, reflectivity, absorption coefficient, photoconductivity, and loss coefficient have been studied and analyzed thoroughly. From the analysis of optical properties, it is seen that, cubic TiO2 supports interband transition between states. Reflectivity of pyrite structure TiO2 lies within IRvisible – UV region due to which it qualifies for coating industry. Furthermore, the results are compared with previous theoretical as well as with experimental results. It is found that DFT based simulation produces results which are close approximation to experimental results.
In this study, the oblique incident of the electromagnetic waves with frequencies lower than plasma frequency in one dimensional ternary plasma photonic crystal has been investigated. The unit cell of crystal contains a plasma layer that is embedded in two different dielectric layers. Using the wave equation, Bloch theory, and boundary condition, the dispersion relation, the group velocity and the reflection relation of the structure have been obtained. Numerical results are presented in the form of dispersion curves. The dependence of photonic band gap characteristics on plasma frequency is discussed. One attempt has been made to show how the photonic band gap characteristic of a particular structure changes when the dielectric material of the unit cell is replaced by other dielectric materials or when the incident angle of the electromagnetic wave is changed. Results show that plasma layer characteristics has a significant effect on band gaps and wave propagation characteristics; also the results show that the proposed multi-layered structure can act as a tunable photonic crystal which can be controlled by the external parameters.
GaAs/AlAs Bragg mirrors on GaAs with varied number of layer pairs were grown, by molecular beam epitaxy (MBE), to be applied for semiconductor saturable absorber mirrors (SESAMs) and intensity modulators. Due to the random variation of the growth rate, substrate surface roughness, and interdiffusion at the interfaces, precise control of the growth conditions of deposited layers poses a serious problem. Usually, thickness variations and composition grading at the heterointefaces result in variations of the mirror reflectivity. In this paper, the high resolution X-ray diffraction (HRXRD), optical reflectance, Rutherford backscattering/channelling (RBS), supported by numerical evaluation methods were employed to determine both the exact thickness of each layer and the composition grading at the interface between succeeding layers of GaAs/AlAs-based mirrors. To reduce ambiguity and to speed up the analysis, the rocking curves and RBS spectra were simulated concurrently, using results of one simulation to verify the others. This process was carried out until the best fit between experimental and calculated curves was achieved. The complementary use of both methods results in improved sensitivity and makes the whole process of evaluation of the thickness variation of each layer and the size of the composition grading at the interfaces less time consuming.
Content available remote Study on absorption and mechanical properties of rubber sheet absorbers
Based on the impedance matching principle and electromagnetic wave propagating law, double-layer absorbers with impedance-matching structure were designed both theoretically and experimentally. Microwave absorbers were prepared by mixing a commercially available rubber with magnetic micropowder (MMP) and/or dielectric materials. The first layer, made up of MMP has large permeability and magnetic loss, while the second layer (matching layer), comprised of MMP and/or dielectric material, has frequency dispersion with the parameters of permittivity and permeability to match the incidence free space over a wide frequency range. Experiments showed that the matching layer plays a key role in the absorption. Electromagnetic parameters and thickness need to be controlled precisely to achieve high absorption. It was reasoned out that with increasing electromagnetic performance of matching layer, matching thickness will decrease. Tests showed that the reflectivity was below -10 dB for samples 1 and 2, and below - 8 dB for samples 3-6 in the frequency range of 8-18 GHz. Finally, mechanical characteristics were also investigated with tensile strength above 10 MPa, indicating that the materials may find practical use in the engineering of microwave absorbers.
W pracy przedstawiono wyniki badań mikroskopowych materii organicznej rozproszonej w karbońskich skałach osadowych, przy zastosowaniu światła odbitego białego oraz niebieskiego (fluorescencja). Głównym celem badań było: identyfikacja i charakterystyka składników organicznych występujących w utworach karbonu wzdłuż tektonicznej strefy Teisseyre'a-Tornquista; określenie stopnia uwęglenia materii organicznej na podstawie refleksyjności witrynitu lub składników witrynitopodobnych (bitumin); określenie warunków paleotermicznych badanych utworów karbonu oraz określenie stref generacji węglowodorów (niedojrzałej, generacji ropy naftowej, generacji gazów, przejrzałej). Badany kompleks karboński zawiera głównie materiał humusowy (tzw. gazotwórczy) bogaty w macerały witrynitu, inertynitu i liptynitu (sporynit, kutynit, liptodetrynit). "Ropotwórczy" materiał organiczny składający się z fluoryzującej, bezstrukturalnej asocjacji organiczno-mineralnej typu sapropelowego z bituminem, bituminitem i alginitem występuje w osadach dolnego karbonu (formacje Sąpolna i Gozdu w strefie Koszalin-Wierzchowo oraz Huczwy i Terebina na obszarze lubelskim). Dojrzałość termiczna badanej materii organicznej waha się od >0,5%R/o, r, do powyżej 3,0%R/o, r. Wartości te charakteryzują fazy generacji węglowodorów od niedojrzałej po przejrzałą. "Okno ropne" obejmuje większą część badanego obszaru. Wyjątek stanowią niedojrzałe do generowania węglowodorów utwory przy północno-wschodniej granicy karbonu, strefa "okna gazowego" w pasie Moracz-Zabartowo i Przysucha-Żerechowa oraz strefa osadów przejrzałych związana z południowo-zachodnią granicą badanego rejonu. Badane wskaźniki wykazują wzrost wartości w kierunku południowym i południowo-zachodnim (NW obrzeżenie Gór Świętokrzyskich), zgodnie z kierunkiem pogrążenia utworów karbonu. Rozkład paleotemperatur koreluje się również z maksymalną głębokością pogrążenia osadów karbonu. Obserwowane wartości R/o, r, CAI i T/max wskazują na paleotemperatury rzędu 50-130 stopni Celsjusza (Pomorze w strefie Koszalin-Wierzchowo i Lubelszczyzna) oraz 120-200 stopni Celsjusza (Pomorze w strefie w strefie Moracz-Byczyna oraz NW obrzeżenie Gór Świętokrzyskich).
Microscopic studies in reflected white light and fluorescence investigations of organic matter dispersed in the sedimentary rocks were applied in this dissertation. The main purpose of this study was: characterisation and identification of various organic constituents which occur in successions of the Carboniferous sediments along the Teisseyre-Tornquist tectonic zone in Poland; determination of the degree of organic matter coalification (thermal maturity), bassed essentially on the reflectance of vitrinite and dispersed vitrinite like particles (bitumen); estimation the palaeogeothermal conditions of the investigated Carboniferous deposits; determination the zones of petroleum generation (immature, oil window, gas window, overmature). The studied Carboniferous series contains mainly humic ("gas prone") material rich in vitrinite, inertinite and liptinite macerals (sporinite, cutinite, liptodetrinite). "Oil prone" organic matter, consist of: structureless organo-mineral associations spropelic type with bitumens, bituminite and alginite, were observed in the Lower Carboniferous deposits (Sąpolno and Gozd formations on the Koszalin-Wierzchowo zone or Huczwa and Terebin formations on the Lublin area). Thermal maturity of the studied organic matter vary between less than 0.5% R/o, r to about 3.0% R/o, r. The above values characterize immature to overmature stages of hydrocarbon generation. The oil window extends over most of the study area, except for immature northern part, gas window zones (Moracz-Zabartowo and Przysucha-Żerechowa) and overmature area in the south. The investigated indices display a general trend towards higher values in southern, south-western direction (Pomerania and Lublin areas) and in western direction (NW margin of the Świętokrzyskie Mts). This trend generally corresponds to maximum burial depths increasing in the same direction. The palaeotemperature distribution correlates mostly with maximum burial depths of the Carboniferous deposits. Observed R/o, r, CAI and T/max, values indicate palaeotemperature range from 50 to 130 degrees of Celsius (Pomerania, Koszalin-Wierzchowo zone and Lublin area) and 120-200 degrees of Celsius (Pomerania, Moracz-Byczyna zone and NW margin of the Świętokrzyskie Mts).
Content available remote Thin glass mirors for the Pierre Auger Project
The Joint Laboratory of Optics produces mirrors for fluorescence optical detector of the Pierre Auger Project situated in Argentina. We want to resume our manufacturing quality measurements and compare the first two telescopes made with the prototype one. We measure the radius of curvature, spot size and reflectivity in ultra-violet region.
Content available remote Roughness of amorphous Zn-P thin films
The effect of thickness variation and the surface roughness of amorphous Zn/sub 32/P/sub 68/ thin films has been investigated by the interference spectroscopy of the optical transmittance and reflectance, as well as by the atomic force microscopy (AFM). The analysis of the optical data allowed determination of the standard deviation of the thin film thickness by taking into account the Gaussian distribution of the change in phase of radiation traversing a thin film. It appears that the value of the standard deviation of the film thickness determined from the optical interference spectroscopy ( sigma /sub w/ approximately=26 nm) is comparable with the value of the mean surface roughness (R/sub a/ approximately=19 nm) evaluated from the AFM studies.
Content available remote Silicon surface texturing by reactive ion etching
The high reflectivity of bare silicon substrates is reduced by roughening the surface with reactive ion etching (RIE). Silicon samples are immersed in a plasma chamber and ion assisted etching produces a high density of pits across the surface of the silicon. The obtained reflectivity is only slightly dependent on grain orientations and so RIE offers a way to effectively texture multi - crystalline substrates that cannot be easily textured using the methods commonly employed for single crystalline silicon. Typical reactive ion etching techniques produce a silicon surface with a very low reflectivity (black silicon). However, such surfaces increase carrier recombination and so the efficiency of the resulting solar cells is low. By adjusting the process conditions, the height and width of the surface features can be controlled to produce a surface that is sufficiently rough to couple light into the cell. Under specific conditions, etching pits are formed by intersections of {111} - crystallographic planes. The RIE selectivity for those planes causes a texture with {111} - surfaces and slows down the RIE process when this texture is formed. This effect causes a self-adjusting uniformity of texture over the whole substrate what might be of a use in bath reactors. Following the RIE process, short wet chemical etching removes the ion damaged silicon layer that is responsible for defect recombination of carries. The etched surfaces are described using scanning electron microscopy and finished solar cells are characterised with spectral response.
The specular reflectivities of picosecond and subnanosecond high-intensity light pulses from a gold target are investigated and compared. It is found that the reflectivity for a picosecond pulse is several times higher than for a subnanosecond one and that dependences of the reflectivity on light pulse energy or intensity are different for both kinds of pulses. A qualitative explanation of the observed features of reflectivity is provided.
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