Auger electron spectroscopy, secondary neutral mass spectrometry and high-resolution transmission electron microscopy were used to assess the chemical, morphological and structural modifications after annealing of cobalt/aluminum oxide/silicon(001) hetero-structure The results show that the aluminum oxide forms a diffusion barrier for temperatures lower than 200 degrees C. Beyond this temperature, cobalt atoms diffuse in the silicon region without apparent modification of the barrier At 340 degrees C, the asymmetric diffusion could be explained by the formation of an AlCoO complex oxide playing the role of a diffusion barrier for Si atoms. (C) 2010 Elsevier B V All rights reserved