We have studied the effect of low energy (20-100 eV) Ar bombardment on the surface roughness of (111) oriented Cu films both experimentally and by molecular-dynamics simulations. We found, in good agreement between the experiments and the simulations, that a significant reduction of the surface roughness can be induced at all energies in this range. However, the angle of incidence for optimal smoothing depends strongly on the ion energy, whereby the lower energies used are more efficient at near normal incidence, and the higher energies are more efficient for off-normal angles (e.g., > 45 dearees). (C) 2004 American Vacuum Society.