Simple models for film growth by energetic cluster impact

The evolution of the surface roughness of films produced by cluster deposition was studied experimentally and theoretically. Simple models were developed from a molecular dynamic description of cluster impact. For low cluster kinetic energy a ballistic model was established, which reproduced the interface width of experimental films very well. Since an energetic cluster impact induces a strong plastic flow, a rough impact region is smoothed and a small crater remains. Therefore a model for the energetic impact was developed, consisting of a smooth operator applied on the initial interface profile and the superposition of a crater term. The simulation as well as atomic force microscopy data displayed the same linear relation in a semilogarithmic plot of squared interface width vs film thickness. Simulated and experimental height profiles showed the same spatial correlation pattern. It is concluded that the Kardar-Parisi-Zhang equation is applicable to cluster deposition films and that with increasing impact energy the Edwards-Wilkinson limit is reached.