Metal homoepitaxial growth at very low temperatures: Lattice-gas-models with restricted downward funneling - art. no. 075401

We develop and analyze 1 + 1- and 2 + 1-dimensional (d) models for multilay er homoepitaxial growth of metal films at low temperatures (T), where intra layer terrace diffusion is inoperative. This work is motivated by recent va riable-temperature scanning tunneling microscopy studies of Ag/Ag(100) homo epitaxy down to 50 K. Adsorption sites are bridge sites in our 1 + 1d model s, and fourfold hollow sites in our 2 + 1d models for fcc(100) or bcc(100) surfaces. For growth at 0 K, we introduce a "restricted downward funneling" model, wherein deposited atoms can be trapped on the sides of steep nanopr otrusions rather than always funneling down to lower adsorption sites. This leads to the formation of overhangs and internal defects (or voids), and a ssociated "rough" growth. Upon increasing T, we propose that a series of in terlayer diffusion processes become operative, with activation barriers bel ow that for terrace diffusion. This leads to "smooth" growth of the film fo r higher T (but still within the regime where terrace diffusion is absent), similar to that observed in models incorporating "complete downward funnel ing."