The origin of hydrocarbon contamination on graphene and other van der Waals materials

Our group has identified, using low temperature STM and infrared spectroscopy measurements, the structure and composition of the hydrocarbon contamination found on many van der Waals material surfaces (hBN, MoS2, etc.). When exposing fresh surfaces to ambient conditions, the initial contamination layer is replaced within days by a monolayer of straight chain alkanes. These alkanes have lengths between 20 and 26 carbon atoms and surprisingly, form a crystalline lattice on the surface, as shown by the STM image above. It is expected that the presence of this adsorbate layer has a significant influence on the interaction of the van der Waals material with its environment. This has implications from basic science to the application and use of graphene and other 2D materials under ambient conditions. For a more detailed discussion, see our paper published in Nature Communications.