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Projeto de investigação
Coordinated Access to Lightsources to Promote Standards and Optimization
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Graphene oxide layer-by-layer films for sensors and devices
Publication . Assunção, Ivan C. C.; Sério, Susana; Ferreira, Quirina; Jones, Nykola C.; Hoffmann, Søren V.; Ribeiro, Paulo A.; Raposo, Maria; DF – Departamento de Física; LIBPhys-UNL; MDPI AG
Layer-by-layer films of poly (allylamine hydrochloride) (PAH) and graphene oxide (GO) were characterized, looking at growth with the number of bilayers, morphology, and electrical properties. The PAH/GO films revealed a linear increase in absorbance with the increase in the number of deposited bilayers, allowing the determination that 10.7 ± 0.1 mg m−2 of GO is adsorbed per unit of area of each bilayer. GO absorption bands at 146, 210, 247 and 299 nm, assigned to π-π* and n-π* transitions in the aromatic ring (phenol) and of the carboxylic group, respectively, were characterized by vacuum ultraviolet spectroscopy. The morphological characterization of these films demonstrated that they are not completely uniform, with a bilayer thickness of 10.5 ± 0.7 nm. This study also revealed that the films are composed of GO and/or PAH/GO fibers and that GO is completely adsorbed on top of PAH. The electrical properties of the films reveal that PAH/GO films present a semiconductor behavior. In addition, a slight decrease in conduction was observed when films were prepared in the presence of visible light, likely due to the presence of oxygen and moisture that contributes to the damage of GO molecules.
Electronic State Spectroscopy of Nitromethane and Nitroethane
Publication . Dalagnol, Luiz V. S.; Bettega, Márcio H. F.; Jones, Nykola C.; Hoffmann, Søren V.; Souza Barbosa, Alessandra; Limão-Vieira, Paulo; DF – Departamento de Física; CeFITec – Centro de Física e Investigação Tecnológica; ACS - American Chemical Society
High-resolution photoabsorption cross-sections in the 3.7-10.8 eV energy range are reinvestigated for nitromethane (CH3NO2), while for nitroethane (C2H5NO2), they are reported for the first time. New absorption features are observed for both molecules which have been assigned to vibronic excitations of valence, Rydberg, and mixed valence-Rydberg characters. In comparison with nitromethane, nitroethane shows mainly broad absorption bands with diffuse structures, which can be interpreted as a result of the side-chain effect contributing to an increased number of internal degrees of freedom. New theoretical quantum chemical calculations performed at the time-dependent density functional theory (TD-DFT) level were used to qualitatively help interpret the recorded photoabsorption spectra. From the photoabsorption cross-sections, photolysis lifetimes in the terrestrial atmosphere have been obtained for both compounds. Relevant internal conversion from Rydberg to valence character is noted for both molecules, while the nuclear dynamics of CH3NO2 and C2H5NO2 along the C-N reaction coordinate have been evaluated through potential energy curves at the TD-DFT level of theory, showing that the pre-dissociative character is more prevalent in nitromethane than in nitroethane.
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Entidade financiadora
European Commission
Programa de financiamento
FP7
Número da atribuição
312284