Raman scattering studies on silver nanoclusters in a silica matrix formed by ion-beam mixing

The formation and growth of nanoscale silver clusters in silica matrices are studied by means of optical absorption and Raman scattering spectroscopy. The metallic silver layer of the ${\mathrm{Ag/SiO}}_{\mathrm{2}}$ couple was irradiated by argon ions for ion-beam mixing of silver with the silica matrix. Postannealing of the embedded Ag atoms in silica matrices results in the growth of Ag nanoclusters. The quadrupolar surface acoustic vibrational mode of the Ag nanoclusters has been observed in low-frequency Raman scattering experiments. The average size of these Ag nanoclusters is estimated from the quadrupolar mode frequency. Systematic growth of Ag nanoclusters embedded in silica matrices is observed with the increase of postannealing temperature. We have estimated the activation energy for the diffusion of Ag atoms in irradiated $\mathrm{a-}{\mathrm{SiO}}_{\mathrm{2}}$ from the coarsening of these embedded Ag atoms. Development of a peak at about 3 eV in the optical absorption spectra for the samples postannealed at higher temperatures corroborates further the growth of Ag nanoclusters in the silica matrices. New Raman modes at 1368 and 1573 cm⁻¹ are observed in Ag embedded silica samples and the possible origin of these modes is discussed.