Raman characterization of localized CdS nanostructures synthesized by UV irradiation in sol-gel silica matrices
Résumé
A new technique of UV irradiation has been used for the first time to create microstructures of CdS nanoparticles in bulk xerogels. Porous silica matrices, which were first soaked in a solution containing CdS precursors, were subjected to irradiation using a nanopulsed ArF laser with a wavelength of 193 nm and a repetition rate of 10 Hz.
Resonant micro-Raman spectra, recorded using the 325-nm line of a He-Cd laser (with a continuous power less than 0.5 mW so as to avoid the thermal formation of nanoparticles) made it possible to identify CdS nanoparticles within the inscribed yellow zones and also to estimate the average particle size (3.6 to 8.0 nm, depending on the number of UV pulses used). The emission of CdS particles embedded in the silica matrix under excitation at 351.1 nm was studied by photoluminescence spectroscopy. It was then possible to show the effect of the number of pulses on the electronic structure of the nanocrystals.
Finally, Raman spectra were used to monitor the structural changes in the silica matrix caused by the irradiation. It was found that the pulsed UVirradiation resulted in a local densification of the matrix, which was compensated for by a depolymerization process of the Si[BOND]O[BOND]Si network. In spite of this pulsed irradiation and the resulting structural depolymerization, no apparent ablation or cracking of the samples was observed.