Influence of X Elements on the Tribological Properties and Surface Chemistry of MXene Atomic Layers

MXenes, a class of two-dimensional (2D) transition-metal carbides, nitrides, and carbonitrides, exhibit promising tribological properties at the nanoscale. However, the influence of X elements on the surface chemistry of MXene atomic layers remains underexplored. Here, we investigate how nitrogen in the Ti₃CN atomic layer modifies its nanotribological behavior compared to Ti₃C₂. Using friction force microscopy and peak force quantitative nanomechanics , we find that Ti₃CN exhibits a notable increase in friction along with higher adhesion and energy dissipation, which we attribute to enhanced hydroxyl termination, stronger surface dipole interactions, and hydrogen bonding. X-ray photoelectron spectroscopy further reveals that nitrogen incorporation leads to greater electron withdrawal from titanium atoms, resulting in a higher oxidation state and altered surface chemical functionality. These results provide mechanistic insight into how X-element chemistry influences the tribological performance of MXenes, highlighting the importance of surface composition in designing 2D materials for specific applications.