title: Fluorination of graphene enhances friction due to increased corrugation.
abstract: The addition of a single sheet of carbon atoms in the form of graphene can drastically alter friction between a nanoscale probe tip and a surface. Here, for the first time we show that friction can be altered over a wide range by fluorination. Specifically, the friction force between silicon atomic force microscopy tips and monolayer fluorinated graphene can range from 5-9 times higher than for graphene. While consistent with previous reports, the combined interpretation from our experiments and molecular dynamics simulations allows us to propose a novel mechanism: that the dramatic friction enhancement results from increased corrugation of the interfacial potential due to the strong local charge concentrated at fluorine sites, consistent with the Prandtl-Tomlinson model. The monotonic increase of friction with fluorination in experiments also demonstrates that friction force measurements provide a sensitive local probe of the degree of fluorination. Additionally, we found a transition from ordered to disordered atomic stick-slip upon fluorination, suggesting that fluorination proceeds in a spatially random manner.
authors: Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania , 220 S. 33rd Street, Philadelphia, Pennsylvania 19104, United States.
authors: Qunyang
authors: Q
authors: Li
authors: Xin-Z
authors: XZ
authors: Liu
authors: Sang-Pil
authors: SP
authors: Kim
authors: Vivek B
authors: VB
authors: Shenoy
authors: Paul E
authors: PE
authors: Sheehan
authors: Jeremy T
authors: JT
authors: Robinson
authors: Robert W
authors: RW
authors: Carpick
keywords: Fluorinated graphene; atomic stick−slip friction; energy corrugation; friction; functionalization