Evolution of Ion Beam Synthesized Au Nanoclusters in SiO_2 under Ion Irradiation

摘要

The evolution of the mean size and the size distribution of Au nanoclusters (NCs) under high-energy ion irradiation has been studied. Au NCs were synthesized in a 480 nm thick SiO_2 layer by 330 keV Au~+ implantation and subsequent annealing at T = 1000 deg C for 1h in dry O_2. XTEM images show a 70 nm thick layer of Au NCs, being centered at the projected ion range R_p(330keV) = 100 nm, having a mean NC size of 5 nm at R_p, and resembling the broad Lifshiz-Slyozov-Wagner (LSW) size distribution of diffusion controlled Ostwald ripening. Post-irradiation of the Au NCs by 4.5 MeV gold ions was used in order to tailor their size and size distribution. The high-energy Au~+ irradiations were performed at 190...210 deg C with a fluence of (0.5...1.0) X 10~(16) cm~(-2). By the post-irradiation no gold was deposited into the SiO_2 layer, the Au~+ ions come to rest in the (001)Si substrate at R_p(4.5MeV) = 1 mu m. XTEM images of the post-irradiated Au NCs show a strong decrease of their mean size as well as the width of their size distribution. The observed NC evolution under ion irradiation agrees with recent theoretical predictions and kinetic Monte-Carlo simulations.