Tailoring the Electronic Band Gap of Graphyne

We report a first-principles study on tuning the electronic band gap of graphyne, consisting of two-dimensional sp–sp 2 hybrid carbon atoms, by chemical functionalization. Halogen atoms form a sp 2 hybridization with sp-bonded carbon atoms. This is in sharp contrast to the adsorption of halogen atoms onto graphene: fluorine atoms on graphene form sp 3 bonds, while chlorine, bromine, and iodine atoms do not form any bond to graphene. The band gaps of graphyne increase by ∼3 eV as the halogen concentration varies, comparable to the ∼3.4 and ∼2.7 eV engineered band gaps of graphene by hydrogenation and fluorination, respectively. We also find that the mixture adsorption of hydrogen and halogen atoms is favorable compared with the segregation of the hydrogen-attached phase and the halogen-attached one and that the band gaps are tunable by ∼1.5 eV as the hydrogen–halogen concentration varies.…