Hyperthermal vapor deposition of copper: athermal and biased diffusion effects

The kinetic energy of an adatom during its impact with a growth surface sig nificantly affects the morphology and microstructure of vapor-deposited fil ms and coatings. Atomic-scale reconstruction processes including 'athermal' and ibiased' diffusion are in part responsible. A three-dimensional molecu lar dynamics method has been used to characterize the extent of these diffu sional processes following hyperthermal adatom impacts. Athermal diffusion was shown to result from a significant transient increase in effective temp erature near the impact site due to the partitioning of the latent heat of condensation and the adatom's incident kinetic energy amongst the vibration al 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 surfac e potential-energy barriers without thermal activation and sometimes skip l arge distances over the substrate surface. This results in significant forw ard-directed biased diffusion. The dependence of the transient heating (res ponsible for athermal diffusion) and the biased diffusion distance upon the adatom's incident energy and angle have been determined for the {100}, {11 0} and {111} surfaces of copper and fitted to simple relations that are con venient for use in atomistic deposition models. (C) 1999 Elsevier Science B .V. All rights reserved.