(2?3×2?3)R30° induced self-assembly ordering by C60 on a Au(111) surface: X-ray diffraction structure analysis

The (2?3×2?3)R30° ordering of fullerene on the herringbone reconstructed Au(111) surface has been studied using grazing incidence x-ray diffraction. The interaction between C60 molecules and gold atoms removes the initial herringbone reconstruction, typical of the clean Au(111) surface, and models the topmost substrate surface layer with one atom vacancy per unit cell and C-Au distances equal to 2.49 Å. The two topmost gold layers are slightly compressed. The molecule is sited on top of the vacancy and oriented with one of its hexagonal carbon rings parallel to the surface, optimizing the number of bonds between the molecule and the substrate with bond distances typical of bonds with a mixed covalent/ionic character. This configuration, that favors the formation of carbon-gold bonds, is similar to the one observed for C60/Pt(111) and C60/Ag(111) indicating that the adsorption of fullerenes on the (111) surface of noble metals comes with the formation of vacancies in order to minimize the system energy.