Inhibitive formation of nanocavities by introduction of Si atoms in Ge nanocrystals produced by ion implantation

Abstract

Germanium nanocrystals (Ge-nc) were successfully synthesized by co-implantation of Si and Ge ions into a SiO2 film thermally grown on (100) Si substrate and fused silica (pure SiO2), respectively, followed by subsequent annealing at 1150 °C for 1 h. Transmission electron microscopy (TEM) examinations show that nanocavities only exist in the fused silica sample but not in the SiO2 film on a Si substrate. From the analysis of the high-resolution TEM images and electron energy-loss spectroscopy spectra, it is revealed that the absence of nanocavities in the SiO2 film/Si substrate is attributed to the presence of Si atoms inside the formed Ge-nc. Because the energy of Si-Ge bonds (301 kJ·mol−1) are greater than that of Ge-Ge bonds (264 kJ·mol−1), the introduction of the Si-Ge bonds inside the Ge-nc can inhibit the diffusion of Ge from the Ge-nc during the annealing process. However, for the fused silica sample, no crystalline Si-Ge bonds are detected within the Ge-nc, where strong Ge outdiffusion effects produce a great number of nanocavities. Our results can shed light on the formation mechanism of nanocavities and provide a good way to avoid nanocavities during the process of ion implantation.