Vacancy clusters on surfaces of Au nanoparticles embedded in MgO

MeV implantation of gold ions into MgO(100) followed by annealing is a meth od to form gold nanoparticles for obtaining modified optical properties. We show from variable-energy positron spectroscopy that clusters of 2 Mg and 2 O vacancies (v(4)) are attached to the gold nanoparticle surfaces within the projected range (R-p). We also find that v(4) vacancy clusters are crea ted at depths less than R-p, and extend into the region greater than R-p du e to damage induced by knock-on collisions.