From dewetting to wetting molecular layers: C60 on CaCO3(10 ̅14) as a case study.

We report the formation of extended molecular layers of C(60) molecules on a dielectric surface at room temperature. In sharp contrast to previous C(60) adsorption studies on prototypical ionic crystal surfaces, a wetting layer is obtained when choosing the calcite (CaCO(3))(10 ̅14) 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 CaCO(3)(10 ̅14) in the [01 ̅10] direction, while a lattice mismatch along the [ ̅4 ̅261] direction results in a large-scale moiré modulation. Overall, a (2 × 15) wetting layer is obtained. The distinct difference observed microscopically upon C(60) adsorption on CaCO(3)(10 ̅14) 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.