Multi-wall carbon nanotubes (MWNTs) were modified by laser ablation of Cu in the presence of He gas. Quasi-spherical particles with diameters of 200 nm to 2 mum were sparsely deposited on as-grown MWNTs. Agglomerated nanoparticles with sizes of 110 nm covered ultrasonically treated MWNTs. Both particles were oxidized. The interaction of nanoparticles with the surface of the ultrasonicated MWNTs, due to small charge transfer to carbon atoms of the MWNTs upon adsorption of Cu, was suggested. We discuss the size distribution and morphology of the particles from cluster and particle formation in the gas phase and the surface properties of the two MWNTs. (C) 2004 Elsevier B.V. All rights reserved.