Ge nanocrystals (NCs) embedded in Al2O3 were grown by RF-sputtering. X-ray diffraction, high resolution transmission electron microscopy, and Raman spectroscopy techniques were used to characterize the stresses on the NCs. While small NCs (<10 nm) have been observed to be spherical and fully relaxed in the matrix, the larger ones (>17 nm) demonstrated a compressive stress effect. This could be linked to the crystal structure of the adjacent Al2O3 matrix. (C) 2010 Elsevier B.V. All rights reserved.