This article reports on experimental observations of surface smoothing by h
igh energy cluster impact. Thin films have been produced by energetic clust
er impact deposition (ECI), and the surface roughness and the power spectru
m of the films have been measured by atomic force microscopy. By depositing
large metal clusters onto an initially rough substrate, the surface roughn
ess is significantly reduced. On the other hand, the roughness of initially
smooth surfaces increases only logarithmically. Results for both surface r
oughness and power spectrum can be quantitatively explained by a recently d
eveloped mesoscopic model for the ECI process employing a stochastic differ
ential equation. In this model the smoothing effect results from a downhill
particle current (consisting of both cluster and surface atoms) transferri
ng the higher lying parts of the surface profile into the valleys. (C) 2001
American Institute of Physics.