Tuning the electronic properties of monolayer and bilayer PtSe₂ : Via strain engineering

The recently synthesized monolayer PtSe₂ belongs to the class of two-dimensional transition metal dichalcogenide (TMDC) materials (Nano Lett., 2015, 15, 4013). Based on first-principles calculations, we show that the band gaps of monolayer and bilayer PtSe₂ can be tuned over a wide range via strain engineering. Both isotropic and uniaxial strains are investigated. For bilayer PtSe₂, the vertical out-of-plane strain is also considered. In most cases, the strain can reduce the band gap except for the bilayer PtSe₂ under the isotropic strain (ϵ ≤ 4%) for which the band gap can be slightly enlarged. Importantly, the monolayer can be transformed from the indirect-gap to the direct-gap semiconductor at the compressive strain of ϵ_y = -8%. Moreover, the bilayer can undergo the semiconductor-to-metal (S-M) transition at a critical vertical strain due to the chemical interaction (p orbital coupling) between the Se atoms of the two opposite layers. Overall, the ability to modulate the band gap of monolayer and bilayer PtSe₂ over an appreciable range of strains opens up new opportunities for their applications in nanoelectronic devices.