Control of Charge Carriers and Band Structure in 2D Monolayer Molybdenum Disulfide via Covalent Functionalization

The fine tuning of electro optic properties is critical for high performing technologies. This is now obtainable with advanced nanostructures, particularly 2D monolayer materials such as molybdenum disulfide (MoS2). Using spin-polarized periodic density functional theory (DFT), we find the direct band gap (K→K’) can be chemically tuned with covalently bound functional groups. With an electron withdrawing group such as fluorine, we observe one occupied α and one unoccupied β bands, which correspond to the addition of an α electron and a β hole; confirmed with the spin difference (Qα-Qβ) being 1. By increasing the electron donating behavior with replacement of F by H and then by Me, the occupied (valence) α band shifts upwards in energy relative to the Fermi energy, and the unoccupied β shifts down until they are in contact with the Fermi energy. In addition, both the α and β unoccupied (conduction) bands of the MoS2 shift down, relative to the Fermi energy, until in contact with the Fermi and the system ca...