Stepwise self-assembly of C60 mediated by atomic scale moire magnifiers

Self-assembly of atoms or molecules on a crystal surface is considered one of the most promising methods to create molecular devices. Here we report a stepwise self-assembly of C-60 molecules into islands with unusual shapes and preferred sizes on a gold-indium-covered Si(111) surface. Specifically, 19-mer islands prefer a non-compact boomerang shape, whereas hexagonal 37-mer islands exhibit extraordinarily enhanced stability and abundance. The stepwise self-assembly is mediated by the moire interference between an island with its underlying lattice, which essentially maps out the adsorption-energy landscape of a C-60 on different positions of the surface with a lateral magnification factor and dictates the probability for the subsequent attachment of C-60 to an island's periphery. Our discovery suggests a new method for exploiting the moire interference to dynamically assist the self-assembly of particles and provides an unexplored tactic of engineering atomic scale moire magnifiers to facilitate the growth of monodispersed mesoscopic structures.