Energetic cluster ion beams: Modification of surfaces and shallow layers

Atomic and molecular clusters can be considered to be a distinct form of matter, a “bridge” between atoms on the one hand and solids on the other. Interest in clusters comes from various fields. They can be used as models for investigation of fundamental physical aspects of the transition from the atomic scale to bulk material as well as controllable and versatile tools for modification and processing of surfaces and shallow layers on the nanometer scale. One of the important parameters in the application of cluster beams is the impact (or kinetic) energy. Current paper presents a state-of-the-art review in the field of cluster-surface interaction. The main emphasis is put on cluster collisions leading either to surface modification or implantation of cluster constituents. Both experimental results and data of theoretical modeling are considered. In particular, fundamental physical aspects and possible practical applications of pinning regime (slight cluster embedding into the surface) are under the discussion. Mechanisms of crater and hillock formation on the individual cluster impacts as well as of surface erosion on macroscopic scale (smoothing or dry etching) under the high fluence cluster bombardment are analysed. Specific phenomena of cluster stopping in matter and formation of radiation damage under keV-to-MeV energy implantation are critically analyzed and an approach towards finding a universal scaling law for the cluster implantation is suggested. A number of advantages peculiar to the cluster beam technique are discussed in terms of designing and engineering the physical and chemical properties of materials for practical applications.