Enhanced piezoelectricity induced by transition metal atoms adsorption on monolayer and bilayer MoS2

Piezoelectricity in MoS₂ has attracted extensive attention because of potential applications in energy harvesting and sensors. However, the piezoelectricity of MoS₂ monolayer is weaker than those of traditional piezoelectric materials. Here, based on first principles calculations, we report the large work function transition metal atoms (TMs = Ni, Pd, Pt and Ir) adsorbed on monolayer and bilayer MoS₂ with large out-of-plane piezoelectric polarization. For TMs adsorbed on monolayer MoS₂, the Ir and Ni adsorption exhibit stronger adsorption energy and larger migration barrier compared with Pd and Pt adsorption. All structures maintain dynamical stability at 300 K and exhibit p-type semiconducting band structures. The larger out-of-plane piezoelectric coefficients induced by adsorption increase with increasing the adsorption concentration, accompanied with slightly decreased in-plane piezoelectric coefficients, which is attributed to more and more electrons participating in redistribution along the out-of-plane direction. For TMs adsorbed bilayer MoS₂, the energetically favorable configuration has same polarization orientation between two monolayers, which results in increased in-plane piezoelectric coefficients. The out-of-plane piezoelectric coefficients further increase due to the coupling of interlayer vertical polarization and TMs adsorption induced vertical polarization. Our results provide a possible way to increase the piezoelectricity of MoS₂.