Energy stabilization of thes-symmetry superatom molecular orbital by endohedral doping of C82fullerene with a lanthanum atom

Abstract

Energy stabilization of the superatom molecular orbitals (SAMOs) in fullerenes is investigated with the goal of involving their nearly free-electron bands in practical charge transport applications. Combining low-temperature scanning tunneling microscopy-based spectroscopic methods and density functional theory calculations on an endohedral metallofullerene La@C${}_{82}$, we confirm that the $s\ensuremath{-}$SAMO of C${}_{82}$ fullerene is stabilized by as much as 2 eV with respect to that of C${}_{60}$ by endohedral doping with the La atom. On the copper metal substrate, the $s\ensuremath{-}$SAMO energy is further lowered to just 1 eV above the Fermi level, making the applications of $s\ensuremath{-}$SAMO state in transport more plausible. We conclude that in an endohedral metallofullerene, the $s\ensuremath{-}$SAMO state is stabilized through the hybridization with the $s$-symmetry valence state of the metal atom and the stabilization energy correlates with the ionization potential of the free atom.