Relationship between the Ag depth profiles and nanoparticle formation in Ag-implanted silica

Ion implantation has attracted considerable interest as a method to modify the optical properties of insulators in order to produce materials with nonlinear optical properties. In this work, high-purity silica samples were implanted at room temperature with 2 MeV Ag ions at various fluences (0.5, 2.4 and 5.3 x 10(16) ions/cm(2)). The samples were then annealed in either a reducing or an oxidizing atmosphere at temperatures ranging from 300 degreesC to 1100 degreesC. The samples were characterized by optical absorption and Rutherford backscattering measurements. Changes in the optical properties of the samples arise from nanometre-sized metallic clusters produced as a result of implantation and/or annealing. The Ag nanoclusters strongly absorb optical radiation at the surface plasmon resonance wavelength (similar to 400 nm). The Rutherford backscattering spectrometry results indicate that the Ag concentration in the samples decreases with increasing annealing temperatures and then influences the optical properties. Indeed, it seems that at relatively high temperatures the Ag nanoclusters can melt and become atomically dispersed silver within the glass. As the mobility of these Ag atoms increases, they migrate not to the sample surface, but mainly laterally through the sample, and eventually the Ag material is lost by the borders of the sample. A correlation was found between the Ag depth profiles and the formation of the surface plasmon resonance as a function of the annealing temperature. The implications and the possible mechanisms concerning this behaviour are discussed in this paper.