Dynamics of implant damage as a precursor to nanocrystal nucleation

Ion implantation into \emph{a}-SiO$_{2}$ leads to the self-assembly of metal or semiconductor nanocrystal arrays having applications in optical and non-volatile memory devices. The production of uniform arrays of similarly-sized nanocrystals within the \emph{a}-SiO$_{2}$ matrix has been shown to depend strongly on nucleation conditions. Here we report results of quantum mechanical calculations probing the atomic-scale dynamics in the time immediately following ion-induced low-energy recoils. We show that individual low-energy recoils (with KE$\sim$100 eV) do not produce individual, isolated defects in the \emph{a}-SiO$_{2}$ structure, but rather produce nanoscale defect pockets. These defect pockets are sources for oxygen out-diffusion, and subsequently represent seed regions for nanocrystal nucleation.