Thin films from energetic cluster impact; experiment and molecular dynamics simulations

Thin film formation by energetic metal cluster ions (Al, Ti, Cu, Mo, and Ta) is studied. The clusters are electrically accelerated, separated from the neutral ones, and deposited on 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 substrates. 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 abbreviation ECI for energetic cluster impact is proposed for this method.