Fluence and current density dependence of silver nanocluster dimensions in ion-implanted fused silica

Implantation of suitable metal ions in glass substrates leads to the formation of nanometer-size colloidal particles in a thin surface layer. The non-linear optical properties of such colloids, in particular the enhancement of optical Kerr susceptibility, suggest that the ion implantation technique may play an important role Mr the production of all-optical switching devices. In spite of the very large interest due to possible applications in device construction, processes governing the chemical and physical interactions between the dielectric host and the implanted metal are far from being completely understood. It is known that the formation of these particles in glasses is governed by the chemical reactivity of the substrates with the implanted ions, by the metal concentration and by its mobility. In this work, where Ag-implanted silica samples are investigated, a particular emphasis is given to the study of the dependence of the silver cluster dimensions on the ion fluence and ion current density. Silver is present in the matrix as metallic nanoclusters and the in-depth distribution of the cluster dimensions is strongly dependent on the ion current and fluence. Higher current densities favour a silver concentration increase close to the depth of maximum radiation damage. In spite of the little differences of silver total amount in the four samples, the shapes of optical absorption spectra show peculiar features strongly related to size and concentration of the silver metallic clusters.