First-principles investigation of functionalization of graphene

The graphene sheet is a single-atom thick novel material and attracts great interest due to its unique features. However, it is a metallic material with no bandgap, which makes it difficult to integrate in electronic applications. Adatom adsorption is one of the promising ways to make this structure functional. To this end, electronic and structural properties of graphene have been investigated by using density functional theory formalism in order to understand atomic level interaction between halogen adatoms and graphene layer. The most common adatom, hydrogen, has also been studied. In this study, plane-wave, pseudopotential density functional theory calculations were carried out using generalized gradient approximations for the exchange correlation potential with the Quantum Espresso package. In order to obtain fully relaxed structures, geometry optimization has been performed in all of the calculations. The adatom-graphene system is modelled with a 4 × 4 graphene supercell. Adsorption energies of halogen adatoms and dimers adsorbed on highly symmetric positions on graphene layer are calculated. Different configurations of adatoms have been tested. Specific properties such as band structure and density of states of these system have been investigated. The results show that a fully covered graphene layer is stable and optimized structures exhibit a band gap of a few eV. The most stable structure among halogen adatoms is the fluorine adsorbed on graphene. It has the highest electronegativity, which is the reason for high electron transfer from the graphene layer. This is the reason of the formation of covalent bonds. Furthermore, the most stable configuration is found to be chair configuration with the halogen atoms alternating in both sides of the layer.