Navegando por Autor "Ferreira, S.O."

Agora exibindo 1 - 3 de 3

A facile synthesis route for preparing aqueous colloidal CdS quantum dots with size-tunable optical properties
(Journal of Luminescence, 2018-10) Maronesi, R.N.; Ferreira, D.L.; Lana Jr, M.L.; Couto, M.S.; Ferreira, S.O.; Silva, A.G.
A simple one-pot route for the chemical synthesis of CdS colloidal quantum dots in aqueous medium was developed. In this wet chemical preparation, the anionic surfactant SDS (sodium dodecylsulfate) was used as the organic stabilizer added to the solution of chemical precursors containing the appropriate sources of the metallic cation (Cd^ 2+ ) and the chalcogenide anion (S^ 2- ). The optical characterization was performed by means of ultraviolet-visible absorption and photoluminescence spectroscopy. Particle size distributions were obtained from the statistical analysis of atomic force microscopy (AFM) images generated for several quantum dot samples. The maximum of each AFM histogram was correlated to the size determined from absorption onset measurements combined with a well-established effective mass model for the size-dependent bandgap of spherical semiconductor quantum dots. An alternative theoretical model capable of providing improved size estimates was also proposed and implemented. From a simple experimental protocol based on the variation of the chalcogenide precursor concentration in the reaction medium, CdS quantum dots with size-tunable optical absorption and emission were synthesized.
The hydrophobicity and roughness of a nasoenteral tube surface influences the adhesion of a multi-drug resistant strain of Staphylococcus Aureus
(Brazilian Journal of Microbiology, 2011-01-13) Lima, J.C.; Andrade, N.J.; Soares, N.F.F.; Ferreira, S.O.; Fernandes, P.E.; Carvalho, C.C.P.; Lopes, J.P.; Martins, J.F.L.
In this study, we examined the physiochemical properties of nasoenteral feeding tubes made from two different types of polymer: silicone materials and polyurethane. The internal surfaces of the nasoenteral feeding tubes were analyzed for their hydrophobicity, roughness, microtopography, rupture-tension and ability to stretch. We also studied the adhesion of an isolated, multi-drug resistant strain of S. aureus to these polymers. The polyurethane nasoenteral tube, which was classified as hydrophilic, was more resistant to rupture-tension and stretching tests than the silicone tube, which was classified as hydrophobic. Additionally, the polyurethane tube had a rougher surface than the silicone tube. Approximately 1.0 log CFU.cm-2 of S. aureus cells adhered to the tubes and this number was not statistically different between the two types of surfaces (p > 0.05). In future studies, new polymers for nasoenteral feeding tubes should be tested for their ability to support bacterial growth. Bacterial adhesion to these polymers can easily be reduced through modification of the polymer’s physicochemical surface characteristics.
Roughness of CdTe thin films grown on glass by hot wall epitaxy
(Journal of Physics, 2004-12-10) Leal, F.F.; Ferreira, S.O.; Menezes-Sobrinho, I.L.; Faria, T.E.
Cadmium telluride films were grown on glass substrates using the hot wall epitaxy (HWE) technique. The samples were polycrystalline with a preferential (111) orientation. Scanning electron micrographs reveal a grain size between 0.1 and 0.5 μm. The surface morphology of the samples was studied by measuring the roughness profile using a stylus profiler. The roughness as a function of growth time and scale size were investigated to determine the growth and roughness exponents, β and α, respectively. From the results we can conclude that the growth surface has a self-affine character with a roughness exponent α equal to 0.69 ± 0.03 and almost independent of growth time. The growth exponent β was equal to 0.38 ± 0.06. These values agree with that determined previously for CdTe(111) films grown on GaAs(100).