988 resultados para PHOTOELECTRON


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A new series of molybdenum cluster compounds of the general formula AxMo5As4(A = Cu, Al, or Ga) has been synthesized. They are isostructural with the host Mo5As4(Ti5Te4-type) consisting of trans-vertex shared Mo6 octahedral chains. Investigations by X-ray photoelectron and Auger electron spectroscopies revealed a charge transfer from A to Mo5As4 in AxMo5As4. The occurrence of metallic (CuxMo5As4) and non-metallic (Al2Mo5As4 and Ga2Mo5As4) properties in this isostructural series of solids is consistent with the electronic structure of Ti5Te4-type solids involving M–M bonding in the cluster chains.

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Nanosized hexagonal InN flower-like structures were fabricated by droplet epitaxy on GaN/Si(111) and GaN flower-like nanostructure fabricated directly on Si(111) substrate using radio frequency plasma-assisted molecular beam epitaxy. Powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to study the crystallinity and morphology of the nanostructures. Moreover, X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) were used to investigate the chemical compositions and optical properties of nano-flowers, respectively. Activation energy of free exciton transitions in GaN nano-flowers was derived to be similar to 28.5 meV from the temperature dependent PL studies. The formation process of nano-flowers is investigated and a qualitative mechanism is proposed.

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Quantum mechanical calculations at all valence complete neglect of differential overlap (CNDO/2) and self-consistent charge extend Huckel (SCC-EH) and the Pi electron Pariser-Parr-Pople with limited configuration interaction (PPP-LCI) levels of approximation have been accomplished for monothiobiuret and dithiobiuret. From the calculated results, a discussion of the electronic structure, photoelectron and electronic spectra and the conformational stability are given. The electronic and1H nmr spectra are also reported. A trans-cis-CONHCS-structure is found to be the stable conformation for monothiobiuret consistent with other evidences.

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TiO2 (anatase) was synthesized using a microwave-irradiation-assisted chemical method. The reaction conditions were varied to obtain unique nanostructures of TiO2 comprising nanometric spheres giving the materials a very porous morphology. The oxide was characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). The specific surface area and porosity were quantified by the BET method, and the degradation of dyes was carried out using these materials. The photocatalytic activity of the nanometric TiO2 was significantly higher than that of commercially available TiO2 (Degussa P25) for the degradation of the dyes.

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The flocculation and filtration characteristics of typical Indian iron ore fines have been studied using starch as flocculant in the presence of an inorganic electrolyte, namely calcium chloride. The effect of various parameters such as pH, starch and calcium chloride concentrations and pulp density on the settling and filtration rates, turbidity of the supernatant and on residual starch and calcium ion concentrates has been investigated through a statistical design and analysis approach and subsequently optimised on a laboratory scale. The adsorption mechanisms of starch onto haematite have been elucidated through adsorption density measurements, infrared and X-ray photoelectron spectroscopic techniques. The rheological property of the polymer solutions of relevance to flocculations has also been investigated. Further, the role of metal ion-starch interactions in the bulk solution, has been studied. In order to understand the nature of polymer adsorption at the double-layer, electrokinetic studies have been carried out with the iron ore mineral samples using starch and calcium chloride. Based on the above findings, selective floculaation tests on artificial mixtures of iron ore minerals have been carried out to determine the separation efficiencies from the view point of alumina and silica removal from haematite as well as the control of alumina: silica ratio in Indian iron ores.

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Starting from readily available norbornenobenzoquinone 7 and employing a photothermal metathesis reaction as the main strategy, novel "roofed" polyquinane bisenones 3 and 13 have been synthesized. Among these, the former is potentially serviceable for further elaboration to dodecahedrane 1. Catalytic hydrogenation of 3 provided the dione 12, which fully inscribes the circumference of dodecahedrane sphere. The "roofed" C-16-bisenone 3 has been successfully annulated to C19-bisenone 24 and C19-trisenone 26 by employing the Greene methodology and Pauson-Khand reaction, respectively. The molecular structures of 3 and 13 were computed using molecular mechanics and semiempirical MO methods. The nonbonded distances between the double bonds vary strongly with the method employed. The interactions between the pi-MO's were, therefore, probed by means of photoelectron (PE) spectroscopy. Comparison with the PE spectra of a series of model systems with increasing complexity enabled an unambiguous assignment of the observed peaks. The symmetric and antisymmetric combinations of the pi-MO's of the enone moieties of 3 and 13 show large splittings, characteristic of propano-bridged systems in which through-space and through-bond effects act in concert.

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Transitions from the low-to the high-spin state in Fe2+ and Co3+ compounds have been examined by X-ray and UV photoelectron spectroscopy. It has been shown that the core-level bands in XPES, in particular the metal 3s band, as well as the valence bands, are diagnosis in the study of spin-state transitions.

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High-quality GaN epilayers were grown on Si (1 1 1) substrates by molecular beam epitaxy using a new growth process sequence which involved a substrate nitridation at low temperatures, annealing at high temperatures, followed by nitridation at high temperatures, deposition of a low-temperature buffer layer, and a high-temperature overgrowth. The material quality of the GaN films was also investigated as a function of nitridation time and temperature. Crystallinity and surface roughness of GaN was found to improve when the Si substrate was treated under the new growth process sequence. Micro-Raman and photoluminescence (PL) measurement results indicate that the GaN film grown by the new process sequence has less tensile stress and optically good. The surface and interface structures of an ultra thin silicon nitride film grown on the Si surface are investigated by core-level photoelectron spectroscopy and it clearly indicates that the quality of silicon nitride notably affects the properties of GaN growth. (C) 2010 Elsevier Ltd. All rights reserved.

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Catalytic combustion of H-2 was carried out over combustion synthesized noble metal (Pd or Pt) ion-substituted CeO2 based catalysts using a feed stream that simulated exhaust gases from a fuel cell processor The catalysts showed a high activity for H-2-combustion and complete conversion was achieved below 200 C over all the catalysts when O-2 was used in a stoichiometric amount With higher amounts of O-2 the reaction rates Increased and complete conversions were possible below 100 C The reaction was also carried out over Pd-impregnated CeO2 The conversions of H-2 with stoichiometric amount of O-2 were found to be higher over Pd-substituted compound The mechanism of the reaction over noble metal-substituted compounds was proposed on the basis of X-ray photoelectron spectroscopy studies The redox couples between Ce and metal ions were established and a dual site redox mechanism was pi posed for the reaction (C) 2010 Elsevier B V All rights reserved

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X-Ray and uv photoelectron spectra of FeO, Fe2O3, and Fe3O4 have been studied along with those of a few model compounds. It has been possible to assign distinct bands due to Fe2+ and Fe3+ in the 3d, 3p, 3s, and 2p bands of Fe3O4. The spectra of Fe3O4 do not show major changes through the Verwey transition.

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A solution precursor plasma spray (SPPS) technique has been used for direct deposition of cerium oxide nanoparticles (CNPs) from various cerium salt solutions as precursors. Solution precursors were injected into the hot zone of a plasma plume to deposit CNP coatings. A numerical study of the droplet injection model has been employed for microstructure development during SPPS. The decomposition of each precursor to cerium oxide was analyzed by thermogravimetric-differential thermal analysis and validated by thermodynamic calculations. The presence of the cerium oxide phase in the coatings was confirmed by X-ray diffraction studies. Transmission electron microscopy studies confirmed nanocrystalline (grain size <14 nm) characteristic of the coatings. X-ray photoelectron spectroscopy studies indicated the presence of a high concentration of Ce3+ (up to 0.32) in the coating prepared by SPPS. The processing and microstructure evolution of cerium oxide coatings with high nonstoichiometry are reported.

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In the present study, titanium nitride which shows exceptional stability, extreme corrosion resistance, good electronic conductivity and adhesion behaviour is used to support platinum particles and then used for methanol oxidation in an alkaline medium. The catalyst shows very good CO tolerance for the electrochemical oxidation of methanol. In situ infrared spectroelectrochemical data show the remarkable ability of TiN to decompose water at low over potentials leading to -OH type functional groups on its surface which in turn help in alleviating the carbon monoxide poisoning associated with methanol oxidation. TiN supported catalysts are found to be very good in terms of long term stability, exchange current density and stable currents at low over voltages. Supporting evidence from X-ray photoelectron spectroscopic data and cyclic voltammetry clearly demonstrates the usefulness of TiN supported Pt catalysts for efficient methanol oxidation in alkaline media.

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Research on conducting polymers, organic light emitting diodes and organic solar cells has been an exciting field for the past decade. The challenge with these organic devices is the long term stability of the active material. Organic materials are susceptible to chemical degradation in the presence of oxygen and moisture. The sensitivity of these materials towards oxygen and moisture makes it imperative to protect them by encapsulation. Polymer nanocomposites can be used as encapsulation materials in order to prevent material degradation. In the present work, amine functionalized alumina was used as a cross-linking and reinforcing material for the polymer matrix in order to fabricate the composites to be used for encapsulation of devices. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy were used to elucidate the surface chemistry. Thermogravimetric analysis techniques and CHN analysis were used to quantify grafting density of amine groups over the surface of the nanoparticles. Mechanical characterizations of the composites with various loadings were carried out with dynamic mechanical analyzer. It was observed that the composites have good thermal stability and mechanical flexibility, which are important for an encapsulant. The morphology of the composites was evaluated using scanning electron microscopy and atomic force microscopy.

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Chemical shifts, ΔE, of the K-absorption discontinuity in several compounds of copper possessing formal oxidation states between 0 and III have been measured. The shifts show a parabolic dependence on the formal oxidation state as well as on the effective atomic charge, q, on copper. Anomalous chemical shifts shown by some of the compounds are discussed in terms of the bonding in these compounds. The ΔE values have also been correlated with the core electron binding energies obtained from X-ray photoelectron spectroscopy.

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Formation of crystalline, monophasic indium selenide (InSe) thin solid films by elemental evaporation on hot glass substrates (400 to 530 K) is reported. The compound formation as well as the composition of the formed films are confirmed by X-ray photoelectron spectroscopy (XPS) analysis. The crystallinity of the rhombohedral InSe films can be improved by post-depositional annealing for t < 30 min at 533 K. The InSe thin films become Se-deficient at higher temperatures of deposition or longer duration of annealing. Optical studies reveal the bandgap to be around 1.29 eV. Under optimum conditions of preparations the lowest resistivity of ≈ 12.8 Ω cm is obtained. Durch Verdampfen aus den Elementen auf heiße Glassubstrate (400 bis 530 k) werden dünne, kristalline, einphasige Indiumselenid (InSe)-Festkörperschichten gebildet. Sowohl die Bildung der Verbindung als auch die Zusammensetzung der Schichten werden durch Röntgen-Photoelektronenspektroskopie (XPS) untersucht. Die Kristallinität der rhomboedrischen InSe-Schichten kann durch eine Temperung bei 533 K für t < 30 min nach der Abscheidung verbessert werden. Die dünnen InSe-Schichten zeigen nach Abscheidung bei höheren Temperaturen oder längerer Temperungsdauer einen Se-Unterschuß. Optische Untersuchungen ergeben, daß die Bandlücke bei etwa 1,29 eV liegt. Unter optimalen Präperationsbedingungen wird ein niedrigster Widerstand von ≈ 12.8 Ω cm erreicht.