Detailed low-energy electron diffraction analysis of the (4×4) surface structure of C ₆₀ on Cu(111): Seven-atom-vacancy reconstruction

A detailed and exhaustive structural analysis by low-energy electron diffraction (LEED) is reported for the C ₆₀-induced reconstruction of Cu(111), in the system Cu(111) + (4 × 4)-C ₆₀. A wide LEED energy range allows enhanced sensitivity to the crucial C ₆₀-metal interface that is buried below the 7-Å-thick molecular layer. The analysis clearly favors a seven-Cu-atom vacancy model (with Pendry R-factor R _p = 0.376) over a one-Cu-atom vacancy model (R _p = 0.608) and over nonreconstructed models (R _p = 0.671 for atop site and R _p = 0.536 for hcp site). The seven-Cu-atom vacancy forms a (4 × 4) lattice of bowl-like holes. In each hole, a C ₆₀ molecule can nestle by forming strong bonds (shorter than 2.30 Å) between 15 C atoms of the molecule and 12 Cu atoms of the outermost and second Cu layers.