Mechanisms, models and methods of vapor deposition

The condensation and assembly of atomic fluxes incident upon the surface of a thin film during its growth by vapor deposition is complex. Mediating th e growth process by varying the flux, adjusting the film temperature, irrad iating the growth surface with energetic (assisting) particles or making se lective use of surfactants is essential to achieve the level of atomic scal e perfection needed for high performance films. A multiscale modeling metho d for analyzing the growth of vapor deposited thin films and nanoparticles has begun to emerge and is reviewed. Ab-initio methods such as density func tional theory are used to provide key insights about the basic mechanisms o f atomic assembly. Recent work has explored the transition paths and kineti cs of atomic hopping on defective surfaces and is investigating the role of surfactants to control surface atom mobility. New forms of interatomic pot entials based upon the embedded atom method, Tersoff and bond order potenti als can now be combined with molecular dynamics to investigate many aspects of vapor phase synthesis processes. For example, the energy distribution o f atoms emitted from sputtering targets, the effects of hot atom impacts up on the mechanisms of surface diffusion, and the role of assisting ions in c ontrolling surface roughness can all be investigated by this approach. They also enable the many activation barriers present during atomic assembly to be efficiently evaluated and used as inputs in multipath kinetic Monte Car lo models or continuum models of film growth. This hierarchy of modeling te chniques now allows many of the atomic assembly mechanisms to be incorporat ed in film growth simulations of increasing fidelity. We identify new oppor tunities, to extend this modeling approach to the growth of increasingly co mplicated material systems. Using the growth of metal multilayers that exhi bit giant magnetoresistance as a case study, we show that the approach can also lead to the identification of novel growth processes that utilize adat om energy control, very low energy ion assistance, or highly mobile, low so lubility chemical species (surfactants) to control surface diffusion contro lled film growth. Such approaches appear capable of enabling the creation o f multilayered materials with exceptionally smooth, unmixed interfaces, wit h significantly superior magnetoresistance. (C) 2001 Published by Elsevier Science Ltd.