Using scanning tunneling microscopy and spectroscopy and first principles calculations, we have systematically studied the morphological and electronic structures of a ${\mathrm{C}}_{60}$ monolayer on Ag(100). Our results reveal that the bright-dim contrast has a definite geometric origin and there are two types of dim ${\mathrm{C}}_{60}$ molecules, one a monomer and the other a dimer. With distinctive electronic properties and distinctive charge transfers in the differently adsorbed ${\mathrm{C}}_{60}$ molecules, this ${\mathrm{C}}_{60}$ monolayer is highly inhomogeneous and aperiodic.

• Received 1 February 2007

DOI:https://doi.org/10.1103/PhysRevB.75.235444