Benzene on Au{111} at 4 K: Monolayer growth and tip-induced molecular cascades

Low-temperature scanning tunneling microscopy has been used to characterize the various structures of submonolayer and near-monolayer coverages of benzene (C₆H₆) on Au{111} at 4 K. At low coverage, benzene is found to adsorb preferentially at the top of the Au monatomic steps and is weakly adsorbed on the terraces. At near-monolayer coverage, benzene was found to form several long-range commensurate overlayer structures that depend on the regions of the reconstructed Au{111} surface, namely a (√52 × √52)R13.9° structure over the hcp regions and a (√133 × √133)R17.5° "pinwheel" structure over the fcc regions. Time-lapse imaging revealed concerted cascade motion of the benzene molecules in the (√133 × √133)R17.5° pinwheel overlayer. We demonstrate that the observed cascade motion is a result of concerted molecular motion and not independent random motion.