Hyperthermal vapor deposition of copper: athermal and biased diffusion effects

The kinetic energy of an adatom during its impact with a growth surface significantly affects the morphology and microstructure of vapor-deposited films and coatings. Atomic-scale reconstruction processes including ‘athermal’ and ‘biased’ diffusion are in part responsible. A three-dimensional molecular dynamics method has been used to characterize the extent of these diffusional processes following hyperthermal adatom impacts. Athermal diffusion was shown to result from a significant transient increase in effective temperature near the impact site due to the partitioning of the latent heat of condensation and the adatom’s incident kinetic energy amongst the vibrational modes of the lattice. The diffusion induced by this mechanism was found to be more or less independent of the substrate temperature. Simulations of oblique hyperthermal deposition indicated that adatoms can overcome surface potential-energy barriers without thermal activation and sometimes skip large distances over the substrate surface. This results in significant forward-directed biased diffusion. The dependence of the transient heating (responsible for athermal diffusion) and the biased diffusion distance upon the adatom’s incident energy and angle have been determined for the {100}, {110} and {111} surfaces of copper and fitted to simple relations that are convenient for use in atomistic deposition models. © 1999 Elsevier Science B.V. All rights reserved.