From dewetting to wetting molecular layers: C60 on CaCO3(104) as a case study

Abstract

We report the formation of extended molecular layers of C₆₀ molecules on a dielectric surface at room temperature. In sharp contrast to previous C₆₀ adsorption studies on prototypical ionic crystal surfaces, a wetting layer is obtained when choosing the calcite (CaCO₃)(104) surface as a substrate. Non-contact atomic force microscopy data reveal an excellent match of the hexagonal lattice of the molecular layer with the unit cell dimension of CaCO₃(104) in the [010] direction, while a lattice mismatch along the [61] direction results in a large-scale moiré modulation. Overall, a (2 × 15) wetting layer is obtained. The distinct difference observed microscopically upon C₆₀ adsorption on CaCO₃(104) compared to other dielectric surfaces is explained by a macroscopic picture based on surface energies. Our example demonstrates that this simple surface-energy based approach can provide a valuable estimate for choosing molecule–insulator systems suitable for molecular self-assembly at room temperature.