Tailoring mechanical properties of MXenes by composition ratio control of surface terminations: Reactive molecular dynamics simulation

YI Jhon and JH Lee, COMPUTATIONAL MATERIALS SCIENCE, 227, 112268 (2023).

DOI: 10.1016/j.commatsci.2023.112268

Emerging 2D transition-metal carbide materials called MXenes inherently have surface terminations differently from other 2D materials. Consequently, surface termination engineering was proven to effectively and predict-ably modulate their electronic, optical, and mechanical properties, enabling significant diversification of MXenes' characteristics. However, surface termination effects of MXenes have mostly been investigated for single-component termination, and theoretical studies with multi-component terminations were rarely studied despite their common occurrence. For the first time, by using reactive molecular dynamics simulations based on a first-principles- derived force field, we investigated the tensile mechanical responses of Ti3C2Tx MXenes under the systematic composition variation of surface terminations by considering two prevailing oxygen (O-) and hydroxyl (OH-) terminations. We found that Ti3C2Tx MXenes with a mixed state of O-and OH-terminations are always mechanically weaker than MXenes with single O-or OH-terminations, exhibiting the smallest tensile strength and/or strain at a molar percentage of 60%OH and 40%OH for armchair and zigzag direction elon-gation, respectively. In contrast to such crossover dynamics, the elastic modulus was linearly tunable in a straightforward manner for OH increase of surface OH/O-terminations, differing from exponential Boltzmann decay observed for the surface coverage reduction of single-component O-termination. Finally, we showed that oxygen/hydrogen plasma treatment in a vacuum environment could be a powerful means of making single component O-terminated MXenes and/or controlling the composition ratio of surface terminations.

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