Strain engineering of electronic properties of transition metal dichalcogenide monolayers

• The electronic properties of MX2 (M=Mo, W; X=S, Se, Te) under strain are calculated using Density Functional Theory (DFT).
• Electronic band gaps are generally reduced with strain and direct to indirect transitions are observed.
• In-plane dielectric constant values have minimum values for very small strains and increase with strain.
• Out-of-plane dielectric constants increase under compressive and decrease under tensile isotropic and uniaxial strains.
• DFT results are interpreted with theory and are consistent with experiments.

We present Density Functional Theory (DFT) results for the electronic and dielectric properties of single-layer (2D) semiconducting transition metal dichalcogenides MX2 (M=Mo, W; X=S, Se, Te) under isotropic, uniaxial (along the zigzag and armchair directions), and shear strain. Electronic band gaps decrease while dielectric constants increase for heavier chalcogens X. The direct gaps of equilibrium structures often become indirect under certain types of strain, depending on the material. The effects of strain and of broken symmetry on the band structure are discussed. Gaps reach maximum values at small compressive strains or in equilibrium, and decrease with larger strains. In-plane dielectric constants generally increase with strain, reaching a minimum value at small compressive strains. The out-of-plane constants exhibit a similar behavior under shear strain but under isotropic and uniaxial strain they increase with compression and decrease with tension, thus exhibiting a monotonic behavior. These DFT results are theoretically explained using only structural parameters and equilibrium dielectric constants. Our findings are consistent with available experimental data.