The microscopic mechanism by which water molecules diffuse on carbon surfaces likely influences fields as diverse as the performance of carbon-based anti-icing coatings, and the rate at which molecular complexity can develop in water-ice layers on carbonaceous dust grains in the interstellar medium. There are not many non-destructive experimental techniques that allow for precise measurement of the water diffusion mechanism at very low coverage, approaching the monomer regime. Here, we apply 3-He spin-echo scattering to quantify the differences in water diffusion for a graphene layer on the Ir(111) substrate and  water diffusion on the bare Ir(111) substrate. He spin-echo scattering is a relatively new experimental technique with the unique advantage of probing diffusion rates in the pico-second regime, a temporal window not accessible via other methods for system with such low coverage. Our results indicate that the graphene-metal interaction dominates the mechanism of water diffusion for graphene on Ir(111), and we report water diffusion rates that are much lower than expected. The knowledge that the graphene-substrate interaction can hinder water diffusion may explain why graphene on Ir(111) is a good anti-icing system, and the mechanisms uncovered could be used to better tune the graphene-metal interaction and aid future system designs.

Article link:

https://www.frontiersin.org/articles/10.3389/fchem.2023.1229546/full