Tuning the graphene band gap by thermodynamic control of molecular self-assembly on graphene*

Using functionalised graphene is motivated by the fact that graphene is a zero band gap semiconductor. Various approaches to open a band gap for electronic applications have been made, one method being chemical functionalisation of graphene. In this work, a generic physical model to predict the self-assembly of halogenated carbene layers on graphene depending on the curvature of the graphene sheet, local distortions, as introduced by molecular adsorption, and short-range intermolecular repulsion is suggested. The thermodynamics of bidental covalent molecular adsorption on graphene and the electronic structure are examined using DFT as implemented in the Quantum Espresso code. A direct band gap opening can be found. Controlling and predicting molecular patterns and to therefore functionalise graphene in a precise way opens the possibility to effectively tune the band gap which potentially makes graphene applicable for semiconductor technologies