Self-assembled C60 layers on incommensurate Cu/Si(111)‘pseudo-5 × 5’ surface

Abstract

Self-assembled growth of C60 monolayers on the pristine and Ge-modified Cu/Si(111)‘pseudo-5×5’ surfaces was studied using scanning tunneling microscopy observations. The pristine Cu/Si(111)‘pseudo-5×5’ surface shows up as an incommensurate reconstruction on Si(111) substrate, while Ge-modified surface shows up as an array of Ge atomic clusters grown on the Cu/Si(111)‘pseudo-5×5’ template. It has been found that C60 fullerenes are highly mobile on the both surfaces, hence at the early growth stages fullerenes are accumulated along the atomic steps forming their quasi-one-dimensional molecular stripes. With further C60 deposition, almost ideal two-dimensional close-packed molecular monolayers are formed. The layers are modulated as evidenced by developing quasi-periodic pattern of dim and bright fullerenes displaying 2×2 periodicity. Contrast difference between dim and bright fullerenes is supposed to have a topographical origin, namely, bright fullerenes reside higher than dim fullerenes. Dim fullerenes were concluded to occupy centers of hexagons which constitute honeycomb-like structure of the Cu/Si(111)‘pseudo-5×5’ surface. For the Ge-modified surface, this means that adsorbing C60 fullerenes displace Ge atoms from their original positions to the interstitial sites in the molecular monolayer. Ge atoms were found to terminate rotational motion of selected fullerenes in the layer.