Effects of ion irradiation on metal and semiconductor nanostructures in SiO2

Metal and semiconductor nanostructures embedded in insulators, in particular in SiO2, attract at present much interest due to their potential application in microelectronics (nanocluster memories), optoelectronics (luminescence from Si nanocrystals) and photonics (plasmonic devices using Au nanoclusters). The nanostructures can be synthesized by ion implantation and modified by ion irradiation. Thereby, radiation effects in the matrix as well as in the nanostructures induce self-organisation phenomena, which might allow to control, e.g., the spatial and size distribution of nanoclusters.
Two different regimes of self-organization will be discussed: (i) Relaxation regime: Ion implantation of impurity atoms may produce extremely supersaturated solid solutions. During subsequent annealing this far-from-equilibrium state relaxes towards equilibrium by phase separation (nucleation, growth) and minimization of interface energy (Ostwald ripening, coalescence). Self-organization phenomena (e.g. pattern formation during phase separation, Rayleigh or pearling instability during interface minimization) have been found. (ii) Driven system: Interfaces or compounds like SiO2 can be driven into a steady state far from equilibrium by ion irradiation. The steady state is established by a competition between collisional mixing, diffusion and re-formation of the compound. For driven systems a theoretical study and atomistic computer simulations of radiation effects like the nanocluster d-layer formation and ''inverse'' Ostwald ripening will be presented.