Enhanced fullerene–Au(111) coupling in (2√3 × 2√3)R30° superstructures with intermolecular interactions

Abstract

SummaryDisordered and uniform (2√3 × 2√3)R30° superstructures of fullerenes on the Au(111) surface have been studied using scanning tunneling microscopy and spectroscopy. It is shown that the deposition and growth process of a fullerene monolayer on the Au(111) surface determine the resulting superstructure. The supply of thermal energy is of importance for the activation of a Au vacancy forming process and thus, one criterion for the selection of the respective superstructure. However, here it is depicted that a vacancy–adatom pair can be formed even at room temperature. This latter process results in C60 molecules that appear slightly more bright in scanning tunnelling microscopy images and are identified in disordered (2√3 x 2√3)R30° superstructures based on a detailed structure analysis. In addition, these slightly more bright C60 molecules form uniform (2√3 x 2√3)R30° superstructures, which exhibit intermolecular interactions, likely mediated by Au adatoms. Thus, vacancy–adatom pairs forming at room temperature directly affect the resulting C60 superstructure. Differential conductivity spectra reveal a lifting of the degeneracy of the LUMO and LUMO+1 orbitals in the uniform (2√3 x 2√3)R30° superstructure and in addition, hybrid fullerene–Au(111) surface states suggest partly covalent interactions.

Rotational switches in the two-dimensional fullerene quasicrystal

“…Differential conductance spectra taken over the molecules represent their local density of states and can thus be used to determine the respective highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap and the interfacial interaction. The HOMO-LUMO gap of single fullerenes in the gas phase amounts to 4.9 V. However, it decreases strongly to 3.7 V in the bulk crystal, to 2.7 V on metal surfaces like Au(111) (Paßens et al, 2015) and to only 2.5 V on 2Pt-Pt 3 Ti(111) (Fig. 4), indicating the strong interface interaction.…”

“…Increased screening due to neighboring molecules and, more efficiently, due to interaction with metal surfaces leads to a reduction in the HOMO-LUMO gap (Torrente et al, 2008). Moreover, strong interfacial interactions between metal d states and the threefold-degenerate LUMOs of fullerenes may induce a lifting of the degeneracy and further broadening of the LUMO levels (Paßens et al, 2015).…”

“…Moreover, their orbital structure can be resolved by scanning tunneling microscopy (STM), which makes it possible to identify the adsorption configuration on a substrate. Consequently, C 60 fullerenes can be used as sensors to reveal interfacial interactions between molecules and atomically flat surfaces (Frederiksen et al, 2014;Paßens et al, 2015;Ledieu et al, 2017). Thus, fullerenes should also be ideally suited to probing the broad ensemble of adsorption sites on the surfaces of quasicrystalline metallic alloys (Thiel, 2008).…”

Interface-driven formation of a two-dimensional dodecagonal fullerene quasicrystal

“…The rotational symmetry of the diffraction pattern is 12-fold, and therefore, we interpret these non-periodic domains as 2D dodecagonal QCs. This is a highly unexpected result, since, as described above, fullerenes are known to form periodic superstructures on (111) surfaces of various metals including Pt 22 23 24 .…”

“…Recently, the self-assembly of molecular 2D QCs driven by hydrogen bonding 18 or metal-organic network formation 19 and the templated growth of fullerenes on Al-based QCs has been described 20 21 . Fullerenes deposited on (111) oriented surfaces of Au, Ag, Cu, Pb and Pt typically form commensurable, highly ordered, hexagonal, self-assembled monolayers 22 23 24 . It is well known that a (√13 × √13)R13.9° superstructure of fullerenes forms at room temperature on Pt(111) surfaces, while a slightly denser (2√3 × 2√3)R30° superstructure appears after annealing 25 26 .…”