Work function modulation of monolayer MOS₂ doped with 3d transition metals

Ever since the discovery of graphene, two-dimensional materials are promising to semiconductor industry. Monolayer molybdenum disulfide (MoS₂) especially stands as a prospective candidate due to its stability in ambient environment; whereas, the direct bandgap makes it potential in electro-optical applications. Work function plays an important parameter for light-emitting diode and contact electrification [1-2]. Some studies [3-4] revealed magnetic properties of MoS₂ by doping 3d transition metals, but the dependence of work function on adatoms remains vague. Under density functional theory (DFT) framework, the Perdew-Burke-Ernzerhof (PBE) exchange-correction functional is applied in Vienna ab initio Simulation Package (VASP). The cutoff kinetic-energy for the valence electron is 500 eV, where the convergence condition for the force acting on each atom is less than 0.01 eVÅ^-1 and the energy difference is < 10^-6 eV/cell. A 4×4 MoS₂ supercell is modeled to simulate the adatom-MoS₂ system, after the unit cell of MoS₂ reaches equilibrium structure. The corresponding bandstructure and density of states are shown in Fig. 1, where the extracted bandgap of 1.71 eV agrees with the experiment [5]. For the supercell, the Brillouin zone for structural optimization is sampled using 2×2×1 k-points by Monkhorst-Pack algorithm. The vacuum space of 15 Å is maintained to avoid the interaction from another layer of MoS₂. The dipole correction on the z-direction is considered for the electrostatic potential away from the surface and total energy.