Anisotropic mechanical and optical response and negative Poisson's ratio in Mo₂C nanomembranes revealed by first-principles simulations

Transition metal carbides include a wide variety of materials with attractive properties that are suitable for numerous and diverse applications. A most recent experimental advance could provide a path toward the successful synthesis of large-area and high-quality ultrathin Mo₂C membranes with superconducting properties. In the present study, we used first-principles density functional theory calculations to explore the mechanical and optical response of single-layer and free-standing Mo₂C. Uniaxial tensile simulations along the armchair and zigzag directions were conducted and we found that while the elastic properties are close along various loading directions, the nonlinear regimes in stress-strain curves are considerably different. We found that Mo₂C sheets present negative Poisson's ratio and thus can be categorized as an auxetic material. Our simulations also reveal that Mo₂C films retain their metallic electronic characteristic upon uniaxial loading. We found that for Mo₂C nanomembranes the dielectric function becomes anisotropic along in-plane and out-of-plane directions. Our findings can be useful for the practical application of Mo₂C sheets in nanodevices.