Properties of Fluorinated Graphene Films

Graphene films grown on Cu foils have been fluorinated with xenon difluoride (XeF2) gas on one or both sides. When exposed on one side the F coverage saturates at 25% (C4F), which is optically transparent, over 6 orders of magnitude more resistive than graphene, and readily patterned. Density functional calculations for varying coverages indicate that a C4F configuration is lowest in energy and that the calculated band gap increases with increasing coverage, becoming 2.93 eV for one C4F configuration. During defluorination, we find hydrazine treatment effectively removes fluorine while retaining graphene's carbon skeleton. The same films may be fluorinated on both sides by transferring graphene to a silicon-on-insulator substrate enabling XeF2 gas to etch the Si underlayer and fluorinate the backside of the graphene film to form perfluorographane (CF) for which calculated the band gap is 3.07 eV. Our results indicate single-side fluorination provides the necessary electronic and optical changes to be practical for graphene device applications.