Germanium (Ge) nanocrystals (NCs) embedded in alumina thin films were produced by deposition on fused silica and silicon (111) substrates using radio-frequency (RF) magnetron sputtering. The films were characterised by both Raman and X-ray diffraction (XRD) spectroscopy. The deposition conditions were optimised in order to obtain crystalline Ge nanoparticles. In as-deposited films, the typical NC size was similar to 3 nm as estimated by means of X-ray diffraction. Raman spectra taken from as-deposited films revealed both amorphous and crystalline semiconductor phases. Annealing was performed in order to improve the crystallinity of the semiconductor phase in the films. After a 1 h annealing at 800 degrees C the mean NC size estimated from the XRD data and Raman spectra increased to similar to 6.5 nm. An increase in the crystallinity of the Ge phase was also confirmed by the Raman spectroscopy data. (C) 2008 Elsevier Ltd. All rights reserved.