Molecular and morphological characterization of bis benzimidazo perylene films and surface-enhanced phenomena

Thin solid films of bis benzimidazo perylene (AzoPTCD) were fabricated using physical vapor deposition (PVD) technique. Thermal stability and integrity of the AzoPTCD PVD films during the fabrication (similar to 400 degrees C at 10(-6) Torr) were monitored by Raman scattering. Complementary thermogravimetric results showed that thermal degradation of AzoPTCD occurs at 675 degrees C. The growth of the PVD films was established through UV-vis absorption spectroscopy, and the surface morphology was surveyed by atomic force microscopy (AFM) as a function of the mass thickness. The AzoPTCD molecular organization in these PVD films was determined using the selection rules of infrared absorption spectroscopy (transmission and reflection-absorption modes). Despite the molecular packing, X-ray diffraction revealed that the PVD films are amorphous. Theoretical calculations (density functional theory, B3LYP) were used to assign the vibrational modes in the infrared and Raman spectra. Metallic nanostructures, able to sustain localized surface plasmons (LSP) were used to achieve surface-enhanced resonance Raman scattering (SERRS) and surface-enhanced fluorescence (SEF).

Structural and Electronic Effects of Incorporating Mn in TiO2 Films Grown by Sputtering: Anatase versus Rutile

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Optical Behavior of Conjugated Pt-Containing Polymetallaynes Exposed to Gamma-Ray Radiation Doses

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Evaluation of Bulk and Surfaces Absorption Edge Energy of Sol-Gel-Dip-Coating SnO2 Thin Films

The absorption edge and the bandgap transition of sol-gel-dip-coating SnO2 thin films, deposited on quartz substrates, are evaluated from optical absorption data and temperature dependent photoconductivity spectra. Structural properties of these films help the interpretation of bandgap transition nature, since the obtained nanosized dimensions of crystallites are determinant on dominant growth direction and, thus, absorption energy. Electronic properties of the bulk and (110) and (101) surfaces are also presented, calculated by means of density functional theory applied to periodic calculations at B3LYP hybrid functional level. Experimentally obtained absorption edge is compared to the calculated energy band diagrams of bulk and (110) and (101) surfaces. The overall calculated electronic properties in conjunction with structural and electro-optical experimental data suggest that the nature of the bandgap transition is related to a combined effect of bulk and (101) surface, which presents direct bandgap transition.

DFT study of the water-assisted tautomerization process between hydrated oxide, MO(H2O)(+), and dihydroxide, M(OH)(2)(+) cations (M = V, Nb and Ta)

Density functional theory (DFT) calculations point out that the participation of water can effectively lower the barrier height for the isomerization process between hydrated oxide cation, MO(H2O)(+), and dihydroxide cation, M(OH)(2)(+), (M = V, Nb and Ta). The catalytic effect is achieved by a water-assisted mechanism in which water acts as proton donor and acceptor, via a transition structure corresponding to a six-membered ring. In the case of vanadium atom, the presence of two water molecules has been taken into account and the tautomerization becomes nearly barrierless, decreasing both the stability of the transition structures relative to intermediates and the depths of wells associated with the intermediates. (C) 2003 Elsevier B.V. All rights reserved.

Thermodynamic and electronic study of Ga-1 _ xMnxN films. A theoretical study

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Toward an understanding of intermediate- and short-range defects in ZnO single crystals. A combined experimental and theoretical study

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.

Electronic structure and optical properties of BaMoO4 powders

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Structural and optical properties of CaTiO3 perovskite-based materials obtained by microwave-assisted hydrothermal synthesis: An experimental and theoretical insight

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

BCS-BEC crossover in a trapped Fermi super-fluid using a density-functional equation

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The role of structural order-disorder for visible intense photoluminescence in the BaZr0.5Ti0.5O3 thin films

The nature of the intense visible room temperature photoluminescence of BaZr0.5Ti0.5O3 non-crystalline thin films is discussed in the light of experimental results and theoretical calculations. The photoluminescence measurements reveal that the emission intensity changes with the degree of disorder in the BaZr0.5Ti0.5O3 lattice. First principles quantum mechanical techniques, based on density functional theory at B3LYP level, have been employed to study the electronic structure of a crystalline model and of structurally disordered models in order to detect the influence of disorder on the electronic structure. An analysis of the electronic charge distribution reveals local polarization in the disordered structures. The relevance of the present theoretical and experimental results on the photoluminescence behavior of BZT is discussed. (C) 2005 Elsevier B.V. All rights reserved.

Understanding the origin of photoluminescence in disordered Ca0.60Sr0.40WO4: An experimental and first-principles study

Visible photoluminescence (PL) was observed for the first time at room temperature in structurally disordered calcium strontium tungstate powder, Ca0.60Sr0.40WO4 (CSW), obtained by the polymeric precursor method. The PL behavior of CSW powders has been analyzed as a function of the disorder rate, based on experimental and theoretical studies. Quantum mechanical theory based on density functional theory at the B3LYP level has been employed to study the electronic structure of two periodic models representing both crystalline and disordered powders. Their electronic structures have been analyzed in terms of density of states, band dispersion and charge densities. The calculations indicate a break in symmetry when passing from crystalline to disordered models, creating localized electronic levels above the valence band. Moreover, a negative charge transfer process takes place from the [WO3] cluster to the [WO4] cluster. The polarization induced by the break in symmetry and the existence of localized levels favors the creation of trapped holes and electrons, originating the PL phenomenon. (c) 2007 Elsevier B.V. All rights reserved.

Combined experimental and theoretical investigations of the photoluminescent behavior of Ba(Ti,Zr)O-3 thin films

The correlation between experimental data and theoretical calculations have been investigated to explain the photoluminescence at room temperature of Ba(Ti0.75Zr0.25)O-3 (BTZ) thin films prepared by the polymeric precursor method. The degree of structural order-disorder was investigated by X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet-visible absorption spectroscopy and photoluminescence (PL) measurements. First-principles quantum mechanical calculations based on density functional theory (B3LYP level) were employed to study the electronic structure of ordered and deformed asymmetric models. The electronic properties are analyzed and the relevance of the present theoretical and experimental results on the PL behavior is discussed. The presence of localized electronic levels and a charge gradient in the band gap due to a break in symmetry, are responsible for the PL in disordered BTZ lattice. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Electronic structure, growth mechanism and photoluminescence of CaWO4 crystals

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Joint Experimental and Theoretical Analysis of Order Disorder Effects in Cubic BaZrO3 Assembled Nanoparticles under Decaoctahedral Shape

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)