Abstract

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.

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