Structural characterization of Ge nanocrystals in silica amorphised by ion irradiation

Abstract

Ge nanocrystals (NCs) grown by ion implantation in amorphous silica matrices were irradiated with 5 MeV Si ions over a different fluence range (2 x 10(11)-2 x 10(13) cm(-2)) than previously reported. Size and depth distributions as well as structural disorder in the NCs were measured by RBS, TEM, SAXS and EXAFS. The EXAFS results show that the embedded Ge NCs are rendered amorphous at fluences similar to 40 times lower than bulk crystalline Ge (c-Ge). No significant changes in the size or depth distribution of the NCs are observed for all irradiation fluences. Compared to c-Ge, the higher-energy structural state of the NCs prior to irradiation and the presence of the nanocrystal/matrix interface are considered the main causes for the peculiar amorphisation behavior of embedded Ge NCs. © 2008, Elsevier Ltd.