Gold-based nucleation in implanted silica studied by x-ray absorption spectroscopy

Ion implantation into silica is used to produce Au subnanometer metal clusters, whose size can be finely tuned from few-atom to about 1nm by acting on the implantation fluence and post-implantation annealing conditions. The structural analyses rely basically on x-ray absorption spectroscopy that can investigate the metal site independently from long range order considerations. Besides the signal from the intermetallic coordination, a correlation of the dopant with oxygen atoms from the matrix is found, especially upon implantation at low fluence. The possibility of promoting the formation of subnanometer AuAg clusters by sequential ion implantation is also explored, with promising preliminary results. The control of the metal cluster nucleation, composition and first steps of growth have relevant consequences on the interpretation of the optical emission spectra of these molecule-like clusters and on their sensitizing action towards nearby rare-earth ions embedded in the same matrix.