Different MXenes but the same surface*

Two-dimensional (2D) transition metal carbides and nitrides MXenes offer rich chemistry with extraordinary properties. The surface of MXenes is terminated by -O, -OH, and -F groups during the synthesis. However, even as the number of explored MXenes keeps growing, there is limited understanding of how the surface composition depend on the type of transition metal, the choice of carbon vs. nitrogen, and the number of atomic layers. Using a multi-scale computational scheme, developed earlier [1], we simulate the distribution, and thermodynamically favorable composition of the functional groups on the surface of distinct MXenes. We consider the most popular MXene systems such as Ti₂C, Ti₃C₂, Ti₂N, Ti₄N₃, Nb₂C, and Nb₄C₃. The surface accommodates mixtures of functional groups for all considered MXenes. The resulting distribution of functional groups is similar regardless of the type of metal, carbon or nitrogen species and number of atomic layers. However, these findings are important for an accurate prediction of the electronic properties and stability of the materials. As we demonstrate, the work function and the density of states sensitively depend on the composition of functional groups.
[1] R. Ibragimova et. al. ACS Nano, 2019, 13, 9171–9181