Formation of CdS nanocrystals in SiO2 by ion implantation

We present a systematic study of the influence of ion dose and post-implantation annealing on the synthesis and growth of CdS nanocrystals in a SiO2 matrix. Nanocrystals were obtained after implantation of monoenergetic Cd and S ions and subsequent annealing in a very wide range of annealing temperatures, Ta. The average size, as determined from the blue shift of bandgap Eg, varied from 3.5-4.5 to 10 nm, depending on implantation and annealing parameters. For the highest dose, 1017 ions/cm2, the synthesis of CdS phase starts already during implantation. For Ta above 700o C, large nanocrystals (9-10 nm) prevail for all doses. High energy optical transitions, identified as the E1A and E1B transitions of hexagonal CdS, were also observed after annealings at higher temperature.