Functionalization of monolayer MoS₂ with transition metal oxide nanoclusters

The surface functionalization of 2D materials provides the tunability of electronic structure as well as catalytic activity. In this study, we investigate the adsorption of various transition metal dioxide molecules (MO); i.e. TiO₂, VO₂, CrO₂, MnO₂, FeO₂, CoO₂, NiO₂, CuO₂, ZnO₂, on pristine MoS₂ monolayer by using first-principles spin-polarized density functional calculations. The binding of H₂O molecule on MO+MoS₂ system is also considered. We observe that MO molecules are adsorbed on MoS₂ surface with a slight reduction of the electronic bandgap of bare MoS₂. The interactions between the MoS₂ surface and molecules can be strong and the formation of chemisorption bonds is possible with binding energies between ≈1.2 and ≈2.2 eV. MO-adsorbed MoS₂ systems are all magnetic except for TiO₂, FeO₂, and ZnO₂ adsorptions. The nonmagnetic ZnO₂+MoS₂ system displays a strong interaction yielding the largest charge transfer among the systems considered (2.07 e⁻) and the shortest equilibrium bond length between the metal atom and sulphur. However, CuO₂+MoS₂ is the most stable system energetically with 2.21 eV binding energy. H₂O molecule binds only to MoS₂+TiO₂ structure with very tiny charge transfer from MoS₂+TiO₂ to H₂O, while other systems result in negative binding energy. The results further reveal that metal oxides can be used to alter the electronic and magnetic nature of surfaces, even though weak van der Waals interactions occur between them.