Role of Heterogeneities on the Mechanical Strength and Deformation of 2D MXene Flakes—Insights from Atomistic Models and Simulations

The mechanical properties of MXenes are of crucial importance in a number of applications currently being studied, including electrochemical energy storage, flexible electronics, and structural composites. However, the difficulty of performing mechanical characterization experiments on 2D materials has limited the study of these important properties. Ab initio computational techniques have helped to fill in some knowledge gaps, but the length scale limitations of these methods preclude the study of more realistic MXenes containing heterogeneities such as point defects and surface terminations. Atomistic simulations, operating at larger length-scales, provide a solution, enabled by the recent development of a highly scalable bond-order interatomic potential for the titanium carbide MXenes. Large-scale simulations utilizing this potential can be used to study both in-plane and out-of-plane elastic properties as well as fracture behavior, crucially eliminating any system size effects. Results indicate a typical tradeoff between in-plane strength and out-of-plane flexibility depending on MXene structure and composition. The inclusion of surface vacancies has a deleterious effect on MXene mechanical properties, which may be unavoidable due to the harsh nature of MXene synthesis. However, via appropriate surface termination engineering, these effects can be mitigated and, in some cases, even overcome entirely. These newly gained insights at the atomic-scale should help inform synthesis and post-processing techniques seeking to produce mechanically superior MXenes.