Density Functional Theory Study of Epitaxially Strained Monolayer Transition Metal Chalcogenides for Piezoelectricity Generation

Two-dimensional transition metal chalcogenides (2D TMCs) are known for their wide range of bandgaps, flexibility, and high strength. Recent synthesis and data mining efforts indicate that 56 2D TMCs have low exfoliation energies and are relatively stable in monolayer form. Under epitaxial strain, we predict using density functional theory (DFT) calculations that the majority of these 2D TMCs can accommodate ±10% strain without breaking their crystal symmetry. The elastic and piezoelectric tensors indicate that 22 of 56 candidates are piezoelectric, and we derive their in-plane piezoelectric coefficient d₁₁. The epitaxial strain is further predicted to enhance the d₁₁ by over 100% at 10% tensile epitaxial strain for most of these piezoelectric 2D TMCs. ReSe₂ at pristine state and Au₂Se₂ at +5% epitaxial strain are predicted to obtain the extreme d₁₁ coefficients at -120 and 326 pm/V, respectively. These findings have implications for the use of high-performance 2D piezoelectric materials in devices.