Influence of positive ion composition on defect generation and fluorination of a graphene monolayer by Ar/SF6 plasma

Monolayer graphene films are treated by an electron cyclotron resonance Ar–SF6 plasma generated in two different gas admixtures to vary the positive ion composition (from mostly atomic to mostly polyatomic molecular species) and analyze its effect on defect formation and fluorination. Langmuir probe and plasma sampling mass spectrometry are used to assess the nature and energy fluence of positive ions. Additionally, the flux of fluorine atoms impinging onto the graphene surface is determined by actinometry on F atoms using Ar as the actinometer gas. Raman and x-ray photoelectron spectroscopies are used to probe the disorder and the chemical state of the plasma-treated graphene. The obtained results reveal that defect generation is governed by the energy fluence of positive ions; however, for the same energy fluence, polyatomic molecular ions induce more damage than the atomic ions. As for the fluorine content in the graphene sheet, for both conditions, it first increases with the plasma treatment time and then it decreases after reaching a maximum. Overall, this work demonstrates that graphene fluorination is dependent on the fluorine dose and not on defect generation. Based on the obtained results, a set of surface reactions is proposed to explain the fluorination behavior of monolayer graphene in Ar–SF6 plasmas.