Electronic Properties of Halogen-Adsorbed Graphene

We have investigated the electronic properties of 1-, 2-, and 3-layer graphene upon surface adsorption of halogen molecules by means of density functional calculations. The most stable adsorption site is parallel to the graphene surface with the diatomic atoms centered over adjacent carbon rings. Bader analysis shows a large charge transfer between F₂ and graphene, which significantly extends the fluorine bond length, while only small amounts of charge are transferred to Cl₂, Br₂, and I₂. Adsorbed halogens alter the electronic properties of graphene by pushing the Fermi level down and bringing forth an accessible impurity band that can be utilized to alter the material properties. Moreover, molecule–surface interactions introduce a bandgap at the K-point between 3 and 330 meV, depending upon the particular graphene-halogen system. When adsorbed on 1-layer graphene, halogen molecules typically open a small bandgap; however, they induce a notably larger bandgap on the 2-layer AB-stacked and 3-layer ABC-stacked graphene. This work suggests an effective way to tune the electronic properties of two-dimensional graphene by adsorption of halogen molecules