Submonolayer C$_{60}$ films on ultrathin SiO$_2$

The nucleation and growth of C$_{60}$ thin films on ultrathin SiO$_2$ are studied using room temperature scanning tunneling microscopy. Organic electronic devices are typically grown on a relatively thick SiO$_2$ substrate, which limits the techniques which may be used to characterize them. The ultrathin oxide layer grown on Si(111)-(7x7) presents a chemically equivalent interface, yet is thin enough to allow characterization by STM which achieves the highest possible spatial resolution. It has been reported that C$_{60}$ films initially follow the Volmer-Weber growth mode on insulating substrates, but there has previously been little investigation of their nucleation in the submonolayer regime. We report the morphological characteristics of films from 0.02 to 1 monolayer in thickness, varying the physical vapor deposition flux rate and the substrate temperature during deposition.