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A strong greenish-light photoluminescence (PL) emission was measured at room temperature for disordered and ordered powders of CaMoO 4prepared by the polymeric precursor method. The structural evolution from disordered to ordered powders was accompanied by XRD, Raman spectroscopy, and TEM imagery. High-level quantum mechanical calculations in the density functional framework were used to interpret the formation of the structural defects of disorder powders in terms of band diagram and density of states. Complex cluster vacancies [MoO 3·V Oz] and [CaO 7·V Oz] (where V Oz= VOX, V O•, V O••) were suggested to be responsible to the appearance of new states shallow and deeply inserted in the band gap. These defects give rise to the PL in disordered powders. The natural PL emission of ordered CaMoO 4was attributed to an intrinsic slight distortion of the [MoO 4] tetrahedral in the short range. [ABSTRACT FROM AUTHOR]

The structural and electronic properties of ZnO (101̅0) and (112̅0) surfaces were investigated by means of density functional theory applied to periodic calculations at B3LYP level. The stability and relaxation effects for both surfaces were analyzed. The electronic and energy band properties were discussed on the basis of band structure as well as density of states. There is a significant relaxation in the (101̅0) as compared to the (112̅0) terminated surfaces. The calculated direct gap is 3.09, 2.85, and 3.09 eV for bulk, (101̅0), and (112̅0) surfaces, respectively. The band structures for both surfaces are very similar. [ABSTRACT FROM AUTHOR]

We report the synthesis of a solvent processable, tetraalkylammonium-functionalized polyethylene for use as an alkaline anion exchange membrane (AAEM). The membranes are insoluble in both pure water and aqueous methanol (50 vol % water) at 50 °C but exhibit excellent solubility in a variety of other aqueous alcohols (e.g., 5 wt % AAEM in aqueous n-propanol, 50 vol % water). These solubility characteristics extend the potential utility of this system for use as both an AAEM and ionomer electrode material from a single polymer composition. The AAEMs generated are mechanically strong and exhibit high hydroxide and carbonate conductivities. [ABSTRACT FROM AUTHOR]

A joint use of experimental and theoretical techniques allows us to understand the key role of intermediate- and short-range defects in the structural and electronic properties of ZnO single crystals obtained by means of both conventional hydrothermal and microwave-hydrothermal synthesis methods. X-ray diffraction, Raman spectra, photoluminescence, scanning electronic and transmission electron microscopies were used to characterize the thermal properties, crystalline and optical features of the obtained nano and microwires ZnO structures. In addition, these properties were further investigated by means of two periodic models, crystalline and disordered ZnO wurtzite structure, and first principles calculations based on density functional theory at the B3LYP level. The theoretical results indicate that the key factor controlling the electronic behavior can be associated with a symmetry breaking process, creating localized electronic levels above the valence band. [ABSTRACT FROM AUTHOR]

Intense and broad visible photoluminescent (PL) band was observed at room temperature in disordered Pb(Zr 0,53Ti 0,47)O 3powders. Structural order−disorder was evaluated by different methods. XANES results pointed to the presence of different coordination modes of disordered Ti powders, and in the ordered sample the local structure around titanium atoms is characteristic of the structurally ordered PZT with only TiO 6units. Only samples containing simultaneous structural order and disorder in their network present the intense visible PL emission at room temperature. [ABSTRACT FROM AUTHOR]

The controlled growth of chalcogenide nanoscaled phase change material structures can be important to facilitate integration and to enable complex architectures for phase change memory and other microelectronic applications. Here, the growth of Sb–Te and In–Ge–Te alloys by metal–organic chemical vapour deposition (MOCVD) on patterned substrates featured with an array of recesses (~130 nm features width) was investigated. High selectivity, with preferential growth on a CoSi2 metallic layer at the recess bottom with respect to the surrounding SiO2 masking layer, was obtained, leading to a single-step fabrication of arrays of high-aspect-ratio chalcogenide nanostructures. The growth selectivity, as well as the morphology, composition and microstructure of the grown nanostructures, as a function of the different MOCVD process parameters, were investigated by scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectroscopy, Raman spectroscopy and Fourier transformed infrared spectroscopy. Thanks to the chosen substrates, the synthesized nanostructures were also directly electrically accessible, as proved by conductive-atomic force microscopy. [ABSTRACT FROM AUTHOR]