Nanoindentation of monolayer Tin+1CnTx MXenes via atomistic simulations: The role of composition and defects on strength

Abstract

Since their discovery in 2011, interest in MXenes, two-dimensional transition metal carbides and/or nitrides, has greatly expanded due to their promising functional properties and facile synthesis methods, and their development for emerging technologies is propitiously progressing. Despite promising advancements, there still remains a lack of understanding with regards to their fundamental mechanical properties. Here, nanoindentation of the Tin+1CnTx MXenes was studied via atomistic simulations utilizing a parametrization of the ReaxFF interatomic potential, to understand the influence of point defects. From force-displacement curves, the Young’s moduli of pristine Ti3C2O2 and Ti2CO2 were calculated to be 466 GPa and 983 GPa, respectively. The influence of both titanium and carbon vacancies (VTi and VC) on Ti3C2O2 were also quantified using simulated nanoindentation of a set of samples containing both 1% VTi and 10% VC, resulting in a reduction of the calculated Young’s modulus to 386 ± 31 GPa. Of particular importance, is that these results mirror recent experimental findings indicating the fundamental role of defects in the mechanical behavior of MXenes. The calculated modulus in this work for the defect-containing Ti3C2O2 surpasses that of graphene oxide, establishing it as a new benchmark in strength for solution-processed, 2D materials. Results here also indicate improvements can be made in current MXene processing methods to better approach the theoretical strength of pristine 2D materials.