Morphological changes of Co nanodots on SiO2 layers by thermal treatment have been investigated. Co nanodots were formed by molecular beam deposition of Co on SiO2 layers with substrate temperatures (30-600 degrees C) and subsequent post-annealing (500-800 degrees C). For samples deposited at low temperatures (30-280 degrees C), the diameter and the density of nanodots increased and decreased, respectively, with increasing post-annealing temperature. On the other hand, the diameter and the density of nanodots scarcely changed by post-annealing for samples deposited at high temperatures (430-600 degrees C). These morphological changes by the post-annealing can be explained on the basis of the stress relaxation in the deposited Co films. (c) 2005 Elsevier B.V. All rights reserved.