Strain tunable structural, mechanical and electronic properties of monolayer tin dioxides and dichalcogenides SnX2 (X=O, S, Se, Te)

Based on first-principles calculations, we investigate the structural, mechanical and electronic properties of monolayer tin dioxides and dichalcogenides SnX2 (X=O, S, Se, Te) under uniaxial and biaxial strains. Our results show that monolayer 1T-SnX2 is energetically more stable than 2H-SnX2, while the stiffness of 2H-SnX2 is much higher. The unstrained SnX2 is thermodynamically and dynamically more stable than the strained ones. We also show that when external strain is applied, the band gaps of both 2H- and 1T-SnO2 decrease linearly with increasing strain, which is contributed by the strain induced orbital redistribution of the decomposition of the p orbital of X atom and s, p orbitals of Sn atom. Notably, the slope of the band gap variation of the biaxial strained 1T-SnO2 reaches up to -0.16 eV/1%. In our calculations, strain can result in a semiconductor-metal transition of 2H-SnX2, while it only affects the band gap of 1T-SnX2.