Atmospheric Switching between Etching and High-Quality Fluorination of Graphene by XeF₂

Fluorinated graphene (FG), a two-dimensional graphene derivative, has attracted wide attention due to its extraordinary physical and chemical properties, as well as its underlying applications. The treatment of xenon difluoride (XeF₂) has proved to be an effective way to achieve FG with different stoichiometric F/C ratios without graphene being etched. Here we compare the fluorination of mechanically exfoliated graphene by a home-built XeF₂ fluorination system and a commercial Orbis XeF₂ etching system. During fluorination in the Orbis etching system, graphene behaves as a protective mask for the silicon substrate, as expected from reported studies (Robinson, J. T. <i>Nano Lett.</i> 2010, 10, 3001-3005, 10.1021/nl101437p; Rangarajan, A. Graphene as an etch mask for silicon. University of Illinois at Urbana-Champaign, 2014). However, in the home-built system, the results surprisingly demonstrate that graphene starts to be etched from the interface of graphene edges and the substrate, which we attribute to the introduction of water molecules during fluorination. We also find that quenching of graphene Raman signatures does not necessarily mean that all carbon atoms are covalently bound to a fluorine atom but that it probably arises from the etching away of graphene. These results reveal the importance of atmospheric water in the synthesis chemistry and derivative reactions of FG, and they provide guidance for its structure engineering to achieve high-quality FG formation.