Navegando por Autor "Longo, V. M."
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Artigo Charge density alterations in human hair fibers: an investigation using electrostatic force microscopy(Society of Cosmetic Scientists and the Société Française de Cosmétologie, 2006-03-28) Longo, V. M.; Monteiro, V. F.; Pinheiro, A. S.; Terci, D.; Vasconcelos, J. S.; Paskocimas, Carlos Alberto; Leite, E. R.; Silva, Elson Longo da; Varela, A.A new method for high-resolution analyses of hair surface charge density under ambient conditions is presented in this paper. Electrostatic force microscopy (EFM) is used here to analyze changes in surface charge density in virgin hair, bleached hair, and hair treated with a cationic polymer. The atomic force microscopy technique is used concomitantly to analyze morphological changes in hair roughness and thickness. The EFM images depict exactly how the polymer is distributed on the surface of the hair fiber. The EFM’s powerful analytical tools enabled us to evaluate the varying degrees of interaction between the hair fiber surface charge density and the cationic polymer. The surface charge density and the polymer’s distribution in the hair fibers are presented in the light of EFM measurementsArtigo Experimental and theoretical correlation of very intense visible green photoluminescence in BaZrO3 powders(American Institute of Physics, 2008) Cavalcante, L. S.; Zampieri, M.; Espinosa, J. W. M.; Pizani, Paulo Sérgio; Paskocimas, Carlos Alberto; Sambrano, Julio Ricardo; Silva, Elson Longo da; Varela, José A.; Simões, M. L.; Longo, V. M.Very intense visible green photoluminescence PL was observed at room temperature in structurally ordered-disordered BaZrO3 powders. Ab initio calculations, ultraviolet-visible absorption spectroscopy, electron paramagnetic resonance, and PL were performed. Theoretical and experimental results showed that local defects in the cubic structure caused by ZrO5 ·VO z complex clusters, where VO z =VO x , VO • , and VO ••, play an important role in the formation of hole-electron pairs, giving rise to a charge gradient in the structure which is responsible for PL emissionArtigo Highly intense violet-blue light emission at room temperature in structurally disordered SrZrO3 powders(American Institute of Physics, 2007-02-27) Longo, V. M.; Cavalcante, L. S.; Figueiredo, A. T. de; Santos, L. P. S.; Silva, Elson Longo da; Varela, José A.; Sambrano, Julio Ricardo; Paskocimas, Carlos Alberto; Vicente, F. S. de; Hernandes, C.Violet-blue photoluminescence was produced at room temperature in a structurally disordered SrZrO3 perovskite structure with a 350.7 nm excitation line. The intensity of this emission was higher than that of any other perovskites previously studied. The authors discuss the role of structural order-disorder that favors the self-trapping of electrons and charge transference, as well as a model to elucidate the mechanism that triggers photoluminescence. In this model the wide band model, the most important events occur before excitation