Fabrication of self-assembled nanodots at arbitrary locations by spatially controlled implant source growth

By using a Ga+ ion focused ion beam (FIB) to locally implant high doses Ga into SiO₂ followed by vacuum annealing, self-assembled Ga nanodots can be fabricated with control over individual nanodot nucleation sites. A critical Ga dose of 2×10¹⁶ions/cm² is required for nanodot nucleation. Based on Auger mapping data we have determined that at lower doses the Ga nanodots actually nucleate below the surface under a thin layer of SiO₂. With increasing implanted Ga doses the nanodots increase in size and nucleate on the SiO₂ surface as Ga droplets. We believe this is due to the Ga-SiO₂ surface energy being lower compared to the Ga surface tension, initially making nucleation under the surface more stable. But as the nanodot grows the increasing energy of the SiO₂ capping layer makes large nanodots more stable on the surface. By using ion implanting and making techniques, ISG can be applied to other material systems.