The liquid-phase adsorption of n-octylamine onto the graphite basal surface studied by tapping-mode atomic force microscopy

Solid-like structures formed on the graphite basal surface following the liquid-phase adsorption of n-octylamine have been studied using tapping-mode atomic force microscopy. Following deposition of a 1 μl droplet and subsequent annealing at 100°C, the amine formed randomly distributed islands categorised into two types based upon the morphology at the vapour interface. Evidence was found for the parallel orientation of the molecular axis at the basal plane, the orientation anticipated from studies of other aliphatic molecules. The results suggest the formation of vertically oriented molecular clusters at the vapour interface. Similarities were found with previous results of the adsorption of n-alkanes at the basal surface, highlighting the importance of n-alkyl chain interactions. Similarities and differences were observed between amine and alkane behaviour at the graphite steps. Annealing at 200°C reduced the island coverage, particularly at steps, and at 300°C no decoration was observed on the surface. The activation energy for surface diffusion and the energy difference between surface and vapour molecules are estimated. Upon deposition of a 5 μl droplet of amine onto graphite, an aggregate morphology decorated terraces and steps. Measurements suggest that the aggregate surface consisted of molecular clusters oriented towards the surface normal.