Surface Geometry ofC60on Ag(111)

Abstract

The geometry of adsorbed ${\mathrm{C}}_{60}$ influences its collective properties. We report the first dynamical low-energy electron diffraction study to determine the geometry of a ${\mathrm{C}}_{60}$ monolayer, $\mathrm{Ag}(111)\mathrm{\text{\ensuremath{-}}}(2\sqrt{3}\ifmmode\times\else\texttimes\fi{}2\sqrt{3})30\ifmmode^\circ\else\textdegree\fi{}\mathrm{\text{\ensuremath{-}}}{\mathrm{C}}_{60}$, and related density functional theory calculations. The stable monolayer has ${\mathrm{C}}_{60}$ molecules in vacancies that result from the displacement of surface atoms. ${\mathrm{C}}_{60}$ bonds with hexagons down, with their mirror planes parallel to that of the substrate. The results indicate that vacancy structures are the rule rather than the exception for ${\mathrm{C}}_{60}$ monolayers on close-packed metal surfaces.