Surface smoothing by energetic cluster impact

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