C60 on alkali halides:: Epitaxy and morphology studied by noncontact AFM

Submonolayer coverages of C-60 deposited on KBr and NaCl are characterized by noncontact atomic force microscopy. Island shapes are described both qualitatively and quantitatively and their dependence on growth parameters and substrate is discussed. At room temperature, both compact and branched island morphologies are observed to coexist. An analysis of the island areas shows a distinct transition from compact to branched morphology with increasing island area. High-resolution imaging reveals differing coincident epitaxy at steps and on open terraces, despite consistent morphology for islands at both substrate positions. Molecular dewetting is proposed as a mechanism for the formation of branched islands.