Robust mechanical tunability of 2D transition metal carbides via surface termination engineering: Molecular dynamics simulation

Two-dimensional (2D) transition metal carbides called MXenes intrinsically have surface functionality differently from other 2D materials. Consequently, the control of surface termination was proven powerful for modulating their electronic and optical properties. However, despite the important potential, its effects on the mechanical properties of MXenes remain extremely elusive. Using reactive molecular dynamics simulations here we reveal that surface termination engineering can be a very effective means for tailoring the tensile properties of Ti3C2Tx MXenes. The tensile strength breaking elongation and Young's modulus of Ti3C2Tx undergo significant predictable variations as the surface termination coverage changes. Noticeably, elimination of surface termination renders the strong stiffness of Ti3C2Tx significantly softer, being opposite to the tendency of graphene, while making it highly stretchable up to 18%. The Young's modulus follows a Boltzmann decay as the termination coverage decreases while the tensile strength and breaking elongation exhibit cubic behaviors with their minima at partial coverages of surface termination. We further explore the tensile variations of Ti3C2Tx under the effects of surface vacancies, surface termination, and tensile direction change and their combinations. The increase of surface vacancies gradually deteriorates the tensile strength of Ti3C2Tx alleviating the fracture anisotropy regardless of the surface termination coverage.