Single crystal Al2O3 samples were implanted with 45 keV Cu ion implantation at a dose of 1 x 10(17) ions/cm(2), and then subjected to furnace annealing in vacuum or with a flow of oxygen gas. Various techniques, such as ultraviolet-visible spectroscopy, X-ray diffraction spectroscopy and atomic force microscopy, have been used to investigate formation of Cu NPs and their evolution. Our results clearly show that the evolution of Cu NPs depends strongly on annealing atmosphere in the temperature range up to 600 degrees C. Annealing in vacuum only gives rise to a slight change in the size of Cu NPs. No evidence for oxidization of Cu NPs has been revealed. Remarkable modifications in Cu NPs, including the size increase and the effective transformation into CuO NPs, have been observed for the samples annealed at oxygen atmosphere. The results have been tentatively discussed in combination with the role of oxygen from atmosphere in diffusion of Cu atoms towards the surface and its interactions with Cu NPs during annealing. (C) 2010 Elsevier B.V. All rights reserved.