Density-Functional Study of the Interface Structure of C-60/Al(111)-(2 root 3 x 2 root 3)R30 degrees

Abstract

The adsorption structure and the bonding nature of the C-60/Al(111)-(2 root 3 x 2 root 3)R30 degrees surface has been studied by using density-functional theory (DFT) calculations. We find that the most stable adsorption site is a low-symmetry point, 0.6 angstrom apart from the Al ontop position and that two different C-60 molecular orientations are equally stable in adsorption energy. Our calculations reproduce the peak broadening of the occupied molecular-orbital levels of C-60 observed in a photoelectron spectroscopy study and the presence of C-Al sigma bonds identified in our charge-character analysis confirms the experimentally proposed covalent bonding nature between C-60 and Al(111). In addition, a charge transfer from Al(111) to C-60 is inferred from our filled-state scanning-tunneling-microscopy simulations showing the lowest unoccupied molecular-orbital feature of C-60. Thus, a weak ionic character is also a part of the bonding nature between C-60 and Al(111).