Nucleation and submonolayer growth of C60 on KBr

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.