The problem of core/shell nanoclusters formation during ion implantation

Cu ions were implanted at 180 keV into silica at doses ranging from 5 × 1016 to 2 × 1017 ions/cm2 at a current density lower than 1.5 μA/cm2. Cross-sectional transmission electron microscopy and scanning transmission electron microscopy high-angle annular dark field images show that nanovoids have been formed in Cu nanoclusters in the implanted samples with doses higher than 1 × 1017 ions/cm2. These nanovoids growth up after the samples annealed in reducing atmosphere. The mechanism for the formation of nanovoids can be explained by the aggregation of vacancies into nanovoids during the process of ion implantation.