Nucleation of C$_{60}$ on ultrathin SiO$_2$*

We utilize scanning tunneling microscopy to characterize the nucleation, growth, and morphology of C$_{60}$ on ultrathin SiO$_2$ grown at room temperature. C$_{60}$ thin films are deposited in situ by physical vapor deposition with thicknesses varying from $<$0.05 to $\sim $1 ML. Island size and capture zone distributions are examined for a varied flux rate and substrate deposition temperature. The C$_{60}$ critical nucleus size is observed to change between monomers and dimers non-monotonically from 300 K to 500 K. Results will be discussed in terms of recent capture zone studies and analysis methods. Relation to device fabrication will be discussed. doi:10.1016/j.susc.2011.08.020