Effect of nanocavities on Ge nanoclustering and out-diffusion in SiO₂

Germanium nanocrystals (Ge-ncs) were synthesized by implantation of Ge⁺ ions into the fused silica, followed by a thermal annealing at 1000 °C. High-resolution transmission electron microscopy was employed to characterize both the morphology of the formed Ge-ncs and the evolution of their depth-distribution as a function of annealing durations. The formation of nanocavities in the vicinity of nanocrystal/SiO₂ interface is evidenced, as well as their influence on the release of the compressive stress exerted on Ge-ncs by surrounding SiO₂. Some Ge-ncs are found inside nanocavities, and can move into the implanted layer through a nanocavity-assisted diffusion mechanism. This finding sheds light on a new process that can explain the non-uniformity of the Ge-nanocrystal spatial distribution.