Papers by Author: Paulo S. Pizani

Abstract: Visible photoluminescence was generated in standard soda-lime-silica glass powder, mechanically milled in a high-energy attrition mill. The broad emission band maximum shows a linear dependence on the exciting wavelength, suggesting the possibility to tune the PL emission. The photoluminescence was attributed to defect generation related to unsatisfied chemical bonds due to the high surface area. Raman scattering and ultraviolet-visible optical reflectance measurements corroborate this assertion. Transmission electron microscopy measurements indicate that the powder is composed by nanocrystallites with about 10-20 nanometers immersed in an amorphous media.

Abstract: In this work a study on the structural phase transitions of silicon undergone by two different methods were performed. The samples were submitted to high non-hydrostatic pressure applied by cyclic Vickers indentations and by the tool tip during the single point diamond turning. The indentations were performed on virgin surface (polished as received) and on an amorphous surface generated either by the machining process or RF sputtering. The analysis on the machined surface, debris on the diamond tool and around of imprints were also performed using Raman micro spectroscopy. The results indicated the formation of some phases may depend upon the initial structural state of the surface, i.e., amorphous or crystalline.