We show in this paper how the combination of scanning tunneling microscopy (STM) and X-ray diffraction under grazing incidence (GIXD) is fruitful for the study of ordered interfaces between thick organic films and crystals. In the case of 4-8-alkyl-4 ' -cyanobiphenyl (8CB) on molybdenum disulphide (MoS2), the commensurability of the adsorbed network has been determined, as well as the intracrystallographic cell structure. This latter one evidences the fine structure of the network characterized by the formation of pair associations in one lamella over two, which reflects the influence of microscopical interactions on the adsorbed structure.