Coating materials with fluorine typically decreases friction on the surface, as in the non-stick coating Teflon. However, on graphene — an atomically thin sheet of carbon atoms — the fluorine coating has the opposite effect.

Yong-Hyun Kim and Jeong Young Park at the Korea Advanced Institute of Science and Technology in Daejeon, South Korea, and their colleagues found that the tiny tip of an atomic force microscope slides more easily over graphene than it does over the same sheet coated with fluorine atoms. Fluorinated graphene is stiffer than bare graphene and this lower flexibility may obstruct the tip, causing more friction. This could also explain why friction increases in both hydrogenated graphene and in graphene oxide — although another possibility is that adding fluorine, hydrogen or oxygen atoms to graphene gives a more disordered, corrugated structure. The findings could help those building nanometre-scale devices to avoid excess friction.

Nano Lett. http://dx.doi.org/10.1021/nl204019k (2012)