Self-organization of physisorbed secondary alcohol molecules on a graphite surface

The monolayer of a secondary alcohol (nonacosan-10-ol) formed at the interface between a solution of this alcohol in tetradecane and the basal plane of graphite is studied by in-situ scanning tunneling microscopy. The interface layer consists of a juxtaposition of lamellae, which are formed by a close packing arrangement of molecules parallel to the graphite surface. In fact, the molecules are coupled through their OH groups, which form hydrogen bonding, as clearly shown in images obtained for a particular range of bias. However, Van der Waals interactions determine the packing of couples to form lamellae. As STM images of a monolayer from a racemic mixture of R and S nonacosanol molecules show no difference from the ones originating from pure S or R enantiomer of nonacosanol, no chirality influence is observed in the layer structure. A packing model based on an unsupported couple of nonacosane10-ol, the energy of which is minimized by using a semi-empiric method, yields a structure in good agreement with STM data. Comparison with results obtained on primary alcohol monolayer provides insights on the different parameters, which influence the signature of OH group in STM images.