Layer-dependent fluorination and doping of graphene via plasma treatment

In this work, the fluorination of n-layer graphene is systematically investigated using CHF3 and CF4 plasma treatments. The G and 2D Raman peaks of graphene show upshifts after each of the two kinds of plasma treatment, indicating p-doping to the graphene. Meanwhile, D, D' and D + G peaks can be clearly observed for monolayer graphene, whereas these peaks are weaker for thicker n-layer graphene (n >= 2) at the same experimental conditions. The upshifts of the G and 2D peaks and the ratio of I(2D)/I(G) for CF4 plasma treated graphene are larger than those of CHF3 plasma treated graphene. The ratio of I(2D)/I(G) of the Raman spectra is notably small in CF4 plasma treated graphene. These facts indicate that CF4 plasma treatment introduces more p-doping and fewer defects for graphene. Moreover, the fluorination of monolayer graphene by CF4 plasma treatment is reversible through thermal annealing while that by CHF3 plasma treatment is irreversible. These studies explore the information on the surface properties of graphene and provide an optimal method of fluorinating graphene through plasma techniques.