The nucleation of pentacene thin films

Abstract

Photoemission Electron Microscopy was used to determine basic factors for nucleation and growth of thin pentacene films. Dependence of both substrate chemistry and deposition rate on the nucleation density was observed. On SiO2 pentacene shows a high nucleation density and forms small islands consisting of almost vertically oriented molecules. On Si(001) the nucleation density of this thin-film phase is much smaller, but the pentacene film first forms a flat-lying wetting layer. The thin-film phase only forms on top of this wetting layer, Adsorption of a cyclohexene self-assembled monolayer on Si(001) prior to the pentacene growth suppresses the initial pentacene wetting layer but maintains diffusion parameters similar to pentacene on Si(001). The nucleation of pentacene layers on cyclohexene/Si(001) can be described by classical nucleation theory with a critical nucleus size i ≈ 6. Simple surface modification techniques such as e-beam irradiation of the substrates prior to pentacene adsorption can also have a significant effect on the pentacene nucleation density.