Strain engineering of Janus ZrSSe and HfSSe monolayers and ZrSSe/HfSSe van der Waals heterostructure

Highlights: • A new class of MX₂ (M = Mo, W; X = S, Se) monolayers with general formula MXY or XMY, have been successfully synthesized by chemical vapor deposition of Se(S) in MoS₂(MoSe₂). • Optimized ZrSSe, HfSSe monolayers and ZrSSe/HfSSe vdW heterostructure are indirect band gap semiconductors. • A transition from an indirect to direct band gap is achieved for tensile strain of 6(8)% for ZrSSe(HfSSe) monolayer. • ZrSSe, HfSSe monolayers and type-II ZrSSe/HfSSe vdW heterostructure heterostruture under tensile strain are efficient photocatalysts. We investigated the effects of biaxial strain on electronic structure of ZrS₂, ZrSe₂, HfS₂, HfSe₂, ZrSSe and HfSSe monolayers. Similar to ZrS₂, ZrSe₂, HfS₂, HfSe₂ monolayers, Janus ZrSSe and HfSSe monolayers are indirect bandgap semiconductors. Tensile strain of 6(8)% transform ZrSSe(HfSSe) monolayer to direct bandgap semiconductor. Based on the calculation of binding energies and interlayer distance staking-(c) is found to be the most stable configuration for ZrSSe/HfSSe vdW heterostructure. Unstrained ZrSSe/HfSSe vdW heterostructure in staking-(c) is a type-II indirect bandgap semiconductor. Valence and conduction band edges show that under tensile strain ZrSSe, HfSSe and ZrSSe/HfSSe vdW heterostructure are efficient photocatalysts.