Thin film growth by energetic cluster impact (ECI): comparison between experiment and molecular dynamics simulations

A new type of cluster ion source has been developed for thin film formation by accelerated metal cluster ions. Roughly one third of the clusters are neutral, the others positively or negatively charged. The clusters are accelerated by an electric field, and deposited onto a surface. If the kinetic energy is higher than about 5 keV for a cluster of about 1000 atoms, highly reflecting, strongly adhering thin films are formed on room temperature, uncleaned substrates. Mechanical stress in the film is small. No columnar or recrystallized thin film growth is observed, so that the film morphology does not fit the structure zone model of Movchan, Demchishin, and Thornton. Langevin molecular dynamics simulations give the following physical picture. A tiny, very high temperature spot is formed at each impact. This anneals the area around the impact zone and gives rise to near epitaxial growth. The main advantage of the method seems to be that dense films without columnar voids can be produced on room temperature substrates. The name energetic cluster impact (ECI) is proposed for this method.