Comparative studies of pentacene and perfluoropentacene grown on a Bi(0001)surface

Abstract

We report two distinct growth modes of pentacene (PEN) and perfluoropentacene (PFP)films on a Bi(0001) substrate investigated by scanning tunneling microscopy (STM). PENgrows epitaxially on Bi(0001) at room temperature (RT), resulting in the formation ofbulk-like crystalline films. In contrast, submonolayer PFP forms a two-dimensional (2D)liquid-like phase with PFP molecules loosely bound on Bi(0001). Beyond onemonolayer, the PFP molecules diffuse over very long distances to aggregate intothree-dimensional (3D) islands, leading to a rough film morphology. Utilizingthe stacking interaction at the PFP/PEN interface, we deposited PFP on thetemplate of an ordered PEN monolayer formed on Bi. It is found that PFP moleculesnucleate into ordered crystalline islands with PFP molecules standing-up. Thedifferent morphologies of PEN and PFP overlayers can be understood in terms ofperfluorination induced decoupling of PFP molecules from the Bi substrate below.