Growth of films with anisotropic particles: Simulations and rate equations

By means of computer simulations and kinetic rate equations, we study the formation of a film of rod-like particles which are deposited on a substrate. The rod-rod interactions are hard with a short-range attraction of variable strength and width, and the rod-substrate interactions favor lying rods with a variable strength. For a rod aspect ratio of 5 and deposition of up to an equivalent of one monolayer of standing rods, we demonstrate a rich variety of growth modes upon variation of the three interaction parameters. We formulate rate equations for the time evolution of densities of islands composed of standing, lying, and mixed rods. Input parameters such as diffusion constants, island capture numbers, and rod reorientation free energies are extracted from simulations, while rod reorientation attempt frequencies remain as free parameters. Numerical solutions of the rate equations in a simple truncation show rough qualitative agreement with the simulations for the early stage of film growth but an extension to later stages requires to go significantly beyond this simple truncation.