A model for the structure of crystalline adsorbed organic monolayers with application to nCB

In order to understand the structure of nCB monolayers adsorbed on MoS2 as observed by STM, we have built a 2D phenomenological model through which the observed structures can be interpreted in term of a commensurate-incommensurate transition monitored by the molecular length. This model is derived from the theory of frustrated smectics; it demonstrates that the two main parameters governing the structure of such monolayers are the frustration of the adsorbed monolayers and the strength of the substrate-molecule interaction, similarly to the case of physisorbed rare gas monolayers. More generally, various STM results on monolayers of elongated molecules physisorbed on a substrate call be reinterpreted which emphasizes the role of molecule-substrate interactions.