Formung von Ge Nanopartikeln mit MeV Ionen

The deformation of Ge-nancrystals embedded in SiO2 during high energy ion irradiation has been investigated. For this purpose 200 nm thermally grown SiO2 was covered with a 5 nm Ge layer and a 100 nm SiO2 top layer by sputter deposition. Subsequent thermal annealing at 950 °C for 300s transformed the embedded continuous Ge layer through spinodal dewetting into Ge nanocrystals with a mean diameter of 20 nm. Afterwards, the Ge nanocrystals buried in SiO2 were irradiated at room temperature with 38 MeV I7+ ions in the dose range (1-4)x1015 cm-2. The ion current density was 40 nA/cm2. Cross-section TEM investigation of the irradiated samples showed that under given irradiation conditions the spherical Ge nanocrystal were shaped mainly into oblate-like Ge particles, which are in the amorphous state. As a result of the investigations we conclude that Ge nanoparticles embedded in SiO2 show the same form transformation behaviour under ion irradiation as irradiated amorphous silica colloides, namely, an expansion perpendicular to the ion beam direction and a contraction parallel to the ion beam direction. Mechanisms of the observed ion beam induced anisotropic deformation of Ge nanoparticles are discussed.