Epitaxial growth of ${\mathrm{C}}_{60}$ on Ag(110) studied by scanning tunneling microscopy and tunneling spectroscopy

Using a scanning tunneling microscope, the growth of ${\mathrm{C}}_{60}$ on Ag(110) is explored. The substrate influences the natural tendency of the fullerene molecules to pack closely and an overlayer system with twofold rotational symmetry is formed: Ag(110)c(4×4)${\mathrm{C}}_{60}$. This represents a distorted close-packed configuration for the ${\mathrm{C}}_{60}$ molecules, where the nearest-neighbor distance observed in bulk ${\mathrm{C}}_{60}$ is maintained. Initial island growth occurs on terrace sites away from substrate step edges, which bunch with increasing fullerene coverage. Above monolayer coverage, ${\mathrm{C}}_{60}$ grows epitaxially, maintaining twofold rotational symmetry. Tunneling spectroscopy is used to explore differences between the electronic structure in the monolayer and multilayer regimes.