Origin of Moireacute structures in C60 on Pb(111) and their effect on molecular energy levels

Low-energy electron diffraction (LEED) indicates that the monolayer structure of C-60 on Pb(111) comprises two coexisting incommensurate structures with nonsymmetry epitaxial rotations near 20 degrees relative to the Pb(111) lattice. These structures are observed in scanning tunneling microscopy (STM) as Moireacute superstructures having periods of about 46 A degrees and 34 A degrees. The Moireacute images and LEED patterns are consistent with two higher-order commensurate (HOC) structures that were identified using the hexagonal number sequence method. These structures are close to predictions from the Novaco-McTague theory of epitaxial rotation, assuming a weakly corrugated substrate potential. As a consequence of the fullerenes within the Moireacute structures having different local environments, the energetic alignment of the molecular resonances is also modulated, with shifts measured by tunneling spectroscopy of up to 20 meV.