Dual-functionalization of graphene: exploring flat bands and optical behavior

Graphenes exceptional electronic and optical properties make it a promising material for advanced technologies. We performed Density Functional Tight Binding (DFTB) simulations to explore the formation of flat electronic bands in graphene functionalized with epoxy and hydrogen groups. By varying the density of functional groups, we identified the emergence of isolated flat bands at critical functional densities (20%), especially beyond 10 hydrogen and 10 oxygen atoms per 72 carbon atoms. Larger supercells (288C-48H-48O) showed the formation of 14 parallel flat bands, emphasizing the impact of high functional group density. Additionally, odd numbers of H and O atoms induced midgap states. Increasing the functionalization ratio (30%) preserved the integrity of the surface modifiers, enhancing binding energy, unit cell constants, and structural stability. Optical properties, including dielectric function, conductivity, and absorption, exhibited distinct shifts with varying functional densities. These results highlight the tunability of graphene's electronic and optical behavior, providing insights for customized graphene-based materials in future electronic and photonic applications.