Pairing evidence of 8CB molecules adsorbed on MoS2: Influence of 2D commensurability on the intralamellar structure

By combining X-ray diffraction studies under grazing incidence (GIXD) and Scanning Tunneling Microscopy (STM) measurements, we have precisely determined the structure of 8CB molecules adsorbed on MoS2, under the thick organic film. The commensurability of the adsorbed network and the intracell structure have been determined, revealing a complex structure characterized by a non-equivalence of adjacent lamellae with pair associations of molecules in one lamella over two. We have interpreted such a result by a simple model of a single lamella. This pair association in one lamella over two appears as a direct evidence of the connection between the commensurabilities in the two directions. The value of the molecule-substrate potential corrugations is particularly high, indicating that the dipolar momentum of 8CB molecules could play a fundamental role in the molecule-substrate interactions