Alloying effects on the critical layer thickness in InxGa1−xAs/InP heterostructures analyzed by Raman scattering

International audienceRaman scattering has been used to estimate the critical layer thickness and to analyze the alloying effect on strain relaxation in InxGa1−xAs layers grown by molecular beam epitaxy on InP [001]-oriented substrate, for x ranging from 0.0 to 1.0. Measurements of longitudinal optical GaAs-like phonon frequency and Raman linewidth showed that the indium/gallium ratio contents greatly influences the strain relaxation. A comparison between Raman and x-ray diffraction measurements of relaxation ratios as a function of layer thickness is presented. The results can be explained in terms of the combined effect of strain and chemical and structural disorder

Au And Auzn Contacts On P-gasb And The Characteristics Of The Interfaces

We analyse the specific contact resistance ρ{variant}C and the interfacial microstructural characteristics (by Auger electron spectroscopy and X-ray diffraction) of Au and AuZn contacts on p-GaSb. The experiments showed that ρ{variant}C hardly depends on the inclusion of Zn in the metallic film or on the annealing processes, at least for the carrier concentrations available (p ≥ 1.6 × 1017 cm-3). However, the dependence of ρ{variant}C on the acceptor concentration leads us to conclude that field emission is the principal conduction mechanism. The efficacy of an Ar glow discharge in considerably reducing the oxide present at the GaSb substrate is demonstrated. We also show that rapid thermal annealing produces much thinner interface-reacted layers than does the conventional (resistive) heat treatment. © 1993.203328331Oliveira, Olivieri, Galzerani, Pasa, de Prince, (1989) J. Appl. Phys., 66 (11), p. 5484Kuphal, (1981) Solid State Electron., 24, p. 69Robinson, (1985) Physics and Chemistry of III–V Compound Semiconductor Interfaces, , C.W. Wilmsen, Plenum, New YorkOliveira, Olivieri, Galzerani, Pasa, Cardoso, de Prince, (1990) Vacuum, 41 (4-6), p. 807Spicer, Chye, Skeath, Su, Lindau, (1979) J. Vac. Sci. Technol., 16 (5), p. 1422Imanaga, Kawai, Kajiwara, Kaneko, Watanabe, (1987) J. Appl. Phys., 62, p. 238

Catalytic Partial Oxidation And Steam Reforming Of Methane On La 2o 3-al 2o 3 Supported Pt Catalysts As Observed By X-ray Absorption Spectroscopy

Structural transformations of Pt supported on Al 2O 3 or La 2O 3-Al 2O 3 were studied by X-ray absorption near edge structure (XANES) at the Pt L 3 edge during heating and cooling under partial oxidation of methane (POM) conditions, and by extended X-ray absorption fine structure (EXAFS) under steam reforming of methane (SRM) conditions. Ignition of the POM reaction occurred simultaneously with the reduction of PtO 2 to metallic Pt, indicating that the ignition occurs on metallic Pt. When the temperature of the POM reaction was decreased, carbon accumulated on the metallic Pt surface, and the activation of CH 4 was suppressed at about 370 °C. Nevertheless, the oxidation of carbon remaining on the metallic Pt surface continued until a temperature of around 270 °C was reached, when oxidation of Pt occurred and the oxidation reactions were extinguished. The EXAFS data obtained during SRM and under H 2 suggest that complex alterations in the structure of Pt particles occur with changes of temperature and reactant composition. The SRM activity of Pt catalysts depends on both the access of CH 4 to active Pt sites, and the changes in the structure of Pt particles under reaction conditions. For both reactions, Pt supported on La 2O 3-Al 2O 3 was more stable than Pt supported on Al 2O 3, indicating a higher stability of Al 2O 3 modified with La 2O 3. © 2012 Elsevier B.V. All rights reserved.431-4327987Bharadwaj, S.S., Schmidt, L.D., (1995) Fuel Process. Technol., 42, pp. 109-127Araujo, J.C.S., Zanchet, D., Rinaldi, R., Schuchardt, U., Hori, C.E., Fierro, J.L.G., Bueno, J.M.C., (2008) Appl. Catal. B: Environ., 84, pp. 552-562Ashcroft, A.T., Cheetham, A.K., Foord, J.S., Green, M.L.H., Grey, C.P., Murrell, A.J., Vernon, P.D.F., (1990) Nature, 344, pp. 319-321Hickman, D.A., Schmidt, L.D., (1992) J. 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Visible PL phenomenon at room temperature in disordered structure of SrWO4 powder

International audienceThe SrWO4 (SWO) powders were synthesized by the polymeric precursor method and annealed at different temperatures. The SWO structure was obtained by X-ray diffraction and the corresponding photoluminescence (PL) spectra was measured. The PL results reveal that the structural order-disorder degree in the SWO lattice influences in the PL emission intensity. Only the structurally order-disordered samples present broad and intense PL band in the visible range. To understand the origin of this phenomenon, we performed quantum-mechanical calculations with crystalline and order-disordered SWO periodic models. Their electronic structures were analyzed in terms of band structure. The appearance of localized levels in the band gap of the order-disordered structure was evidenced and is a favorable condition for the intense PL to occur

A Method To Synthesize Sio2-tio2 Glasses Based On The Synergy Between Vad And Ald Techniques: Study Of Tio2doping Profile Along Radial Direction

This study aimed the synthesis of titania-doped silica glasses with controlled TiO2 concentrations and distribution profiles through the synergy between Vapor-Phase Axial Deposition (VAD) and Atomic Layer Deposition (ALD) techniques. In a first stage, porous boules of pure silica were synthesized by the VAD technique. Afterwards, these boules were submitted to a cyclic doping process with TiCl4 vapor and H2O vapor using the principles of ALD technique. Silica-titania on glassy state was obtained after the consolidation of the porous boule at 1400 °C. The effects of VAD and ALD parameters were studied on the radial doping profile homogeneity and glass structure in the consolidated material. Concerning to the radial profile, a more homogeneous glass was obtained for porous boules doped at 90 °C and with higher average density. This temperature was enough to suppress the effect of TiCl4 condensation on the porous boule surface even for a long TiCl4 flow time, providing a relatively high doping homogeneity for one and four ALD cycles. The opacity in some consolidated samples was attributed to a segregated phase, which could be completely eliminated by a second heat treatment in flame. © 2011 Elsevier B.V. All rights reserved.331219381942Shibuya, M., (1997) Opt. Rev., 4 (1 B), pp. 151-160Kushibiki, J., Arakawa, M., Ueda, T., Fujinoki, A., (2008) Appl. Phys. Exp., 1, p. 087002. , [1-3]Schultz, P.C., Smyth, H.T., (1970) Amorphous Materials, , first ed. Wiley-Interscience NewYorkSekiya, E.H., Torikai, D., Gusken, E., Ogata, D.Y., Cuevas, R.F., Suzuki, C.K., (2000) J. Non-Cryst. Solids, 273, pp. 228-232Izawa, T., Sudo, S., (1987) Optical Fibers: Materials and Fabrication, , first ed. KTK Scientific Publishers TokyoFujiwara, E., Ono, E., Suzuki, C.K., (2008) AIP Conf. Proc., 1055, pp. 145-148Santos, J.S., Ono, E., Suzuki, C.K., (2006) Rev. Sci. Instrum., 77, p. 055106. , [1-8]Santos, J.S., Ono, E., Gusken, E., Suzuki, C.K., (2006) J. Lightw. Technol., 24 (2), pp. 831-837Rajala, V.M., Soininen, H.P., Niinisto, V.L., Putkonen, E.M., Pimenoff, H.J., Paivasaari, E.J., (2007), US Patent 2007/0218290 A1Puurunen, R.L., (2005) J. Appl. Phys., 97, p. 121301. , [1-52]Papirer, E., (2000) Adsorption on Silica Surfaces, , first ed., FranceNorin, L., Vanin, E., Soininen, P., Putkonen, M., (2007) Conference on Lasers and Electro-Optics, , United StateIzawa, T., (2000) J. Sel. Topics Quantum Electron., 6 (6), pp. 1220-1227Suzuki, C.K., Torikai, D., Sekiya, E.H., Ono, E., (2002), INPI BR. Patent No. PI0203755Shimodaira, N., Saito, K., Sekiya, E.H., Ikushima, A.J., (2006) Phys. Rev. B, 73, p. 214206. , [1-9]Best, M.F., Condrate, R.A., (1985) J. Mater. Sci. Lett., 4, pp. 994-998Kelly, S., Pollak, F.H., Tomkiewicz (1997) J. Chem. Phys. B, 101, pp. 2730-273

On the structural and spectroscopic properties of the thienyl chalcone derivative: 3-(5-Bromo-2-thienyl)-1-(4-nitrophenyl)-prop-2-en-1-one

In this study, we investigate the structural and spectroscopic properties of the thienyl chalcone derivative 3-(5-Bromo-2-thienyl)-1-(4-nitrophenyl)-prop-2-en-1-one, C13H8BrNO3S, using nuclear magnetic resonance (1H and 13C NMR), UV–vis and Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy at room conditions combined with density functional theory (DFT) and time-dependent DFT (TD-DFT) augmented with B3LYP/6-311G(d,p) and CAM-B3LYP/6-311G(d,p) basis sets, yielding valuable information on the molecular conformational preferences, vibrational assignments, optical properties and electronic transitions. The vibrational mode assignments of the most stable conformer of C13H8BrNO3S are discussed based on potential energy distribution (PED) analysis and establishing a comparison with a similar chemical structure. The temperature dependence on the Raman spectra of the C13H8BrNO3S shows a reversible phase transition in the range 443–443?K pointed out by the discontinuity in the d?/dT of bands in the external and internal modes region. The UV–vis spectrum of the C13H8BrNO3S indicates a semiconductor behavior with an optical band gap of 2.6?eV, corresponding to the predicted value of 3.42?eV assigned as the electronic transition from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO). TD-DFT calculations reveal that the electron donor and acceptor group substitution on the 1-phenyl-3-(thiophen-2-yl)prop-2-en-1-one affects its absorption and nonlinear activity

Photoluminescent property of mechanically milled Ba Wo4 powder

International audienceCrystalline BaWO4 (BWO) powder obtained by the polymeric precursor method was structurally disordered by means of high-energy mechanical milling. For the first time a strong and broad photoluminescence (PL) has been measured at room temperature for mechanically milled BWO powder and interpreted by ground-state quantum mechanical calculations in the density functional theory framework. Two periodic models have been studied; one representing the crystalline form and the other one representing the disordered BWO powder. These models allowed the calculation of electronic properties, which are consistent with the experimental results, showing that structural disorder in the lattice is an important condition to generate an intense and broad PL band