Noncontact atomic force microscopy has been applied to the prototypical molecule-insulator system C60 on KBr to study nucleation and submonolayer growth. Overview images reveal an island growth mode with unusual branching structures. Simultaneous molecular and atomic resolution on the C60 and KBr surfaces, respectively, was obtained revealing a coincident 8x3 superstructure. Also, a 21+/-3 pm apparent height difference was observed in atomic force microscopy topographies between some first layer molecules. One of the initial nucleation sites of the C60 islands was determined by observation of loosely bound molecules at kink sites in monatomic KBr steps, in conjunction with the observation that islands form preferentially at step edges.

Non-contact atomic force microscopy (NC-AFM) was used to study thin films of C60 on Au(111). After observing the Au(111) reconstruction, 2–3 monolayers of C60 were deposited onto the Au surface. The close-packed C60 surface was imaged by NC-AFM with molecular resolution. Enhanced corrugation and a stretching of the C60 lattice were observed at step edges. Based on a calculation of the force required to displace an edge molecule, it is proposed that the edge effects are a result of tip-induced displacements of edge molecules. While imaging small clusters of C60, some molecules were removed, leading to structural rearrangements of the clusters.

In recent years, scanning tunneling microscopy (STM) has been used to investigate a large number of organic molecules on a variety of metal and semiconductor surfaces, with potential applications ranging from molecular electronics to catalysis. Using the high resolution capability of NC-AFM, similar studies of organic molecules can now be performed on insulating surfaces (1). In this study, C60 on the alkali-halide KBr is used as a prototypical molecule-insulator system in order to better understand the interactions between molecules and insulating substrates. The KBr(001) surface was imaged with NC-AFM, and atomically resolved at room temperature. Sub-monolayer coverages of C60 molecules were deposited on KBr at room temperature by thermal evaporation (TD ' 330 C) and imaged with molecular resolution. Large, branched C60 islands 2-5 layers high were observed both on step edges and large terraces. Kink sites in the KBr steps are identified as one of the initial nucleation sites. Atomic/molecular resolution images show a close- packed structure of the C60 molecules aligned with the <100> direction of the KBr, indicating a possible epitaxial relation between the C60 and KBr. First layer C60 shows a difference in contrast between some molecules similar to that observed on metals with STM. Also, Kelvin Probe contrast was obtained between the C60 and KBr showing the variation of the contact potential difference between the two materials.