Ehrlich-Schwoebel Barriers and Island Nucleation in Organic Thin-Film Growth

Abstract

In inorganic epitaxy, intra- and interlayer surface diffusion processes—which are significantly influencing island nucleation and morphology evolution when growing under conditions far from equilibrium—are well understood. Using the rod-like organic molecule para-hexaphenyl, it is demonstrated that experimental and theoretical concepts developed to reveal the underlying atomic diffusion processes for inorganic systems can be applied to understand the growth of crystalline organic films. Here, we focus on the one hand on the determination of step-edge barriers, so-called Ehrlich-Schwoebel barriers, resulting in terraced growth mounds. On the other hand, we explore the island nucleation applying various approaches developed for inorganic systems. Compared to atomic systems, the anisotropy and complexity of the molecular building blocks yield a richer spectrum of diffusion processes resulting in novel phenomena as, e.g., level-dependent step-edge barriers for interlayer diffusion and peculiarities in the size of the critical nucleus.