Swift heavy ion irradiation of Pt nanocrystals embedded in SiO_2

摘要

Pt nanocrystals (NCs) formed by ion implantation in SiO_2 were irradiated with 185 MeV Au ions in the fluence range from 2 × 10~(12) to 6×10~(14)cm~(-2). Transmission electron microscopy (TEM) shows that spherical Pt NCs with diameter smaller than a certain threshold (～70 A) do not change in shape, but decrease in size with increasing irradiation fluence until dissolved in the matrix. On the other hand, NCs larger than ~70 A change from spheres (unirradiated) to prolate spheroids (2×10~(13) cm~(-2)), finally achieving a rod-like shape with the major axis aligned parallel to the beam direction for fluences up to ～10~(14) cm~(-2). The NC minor dimension decreases with increasing irradiation fluence, resulting in a nearly monodispersed distribution with mean value around 70 A, while at the same time the major dimension increases significantly resulting in the formation of rod-like NCs with aspect ratio as great as 10.