Controlling the morphology of Ag nanoclusters by ion implantation to different doses and subsequent annealing.

Ag ions were implanted at 200 keV into silica with nominal doses ranging from 5x10(16) to 2x10(17) ions/cm2. We find that nanovoid-containing Ag nanoclusters form in the implanted samples with doses higher than 1x10(17) ions/cm2. When the dose is increased to 2x10(17) ions/cm2, the nanovoids gradually shrink and form a sandwiched nanocluster-nanovoid-nanocluster structure. The evolution of sandwiched nanoclusters during annealing was observed by in situ transmission electron microscopy experiments. Potential mechanisms for the formation and evolution of the irradiation-induced nanovoids and the sandwiched structure nanoclusters with increasing doses are discussed. The structural optimization of the sandwiched structure nanoclusters was performed by molecular mechanics calculations.