Autonomous Atomic-Scale Self-healing in Two-Dimensional MXenes via Diffusion-Driven Lattice Reconstruction

We report the first in situ scanning transmission electron microscopy (STEM) observations of intrinsic self-healing in MXenes occurring without external stimuli, driven by surface atomic diffusion. Nanopores were introduced into titanium carbide (Ti-C) and medium-entropy (ME) MXenes using focused electron-beam irradiation and visualized by high-angle annular dark-field (HAADF) imaging. Upon beam cessation, the nanopores spontaneously closed at room temperature, demonstrating autonomous lattice repair. In situ heating experiments at 250 °C and 500 °C reveal a pronounced acceleration of the healing kinetics with increasing temperature. Molecular dynamics simulations employing machine-learning–trained interatomic potentials show that healing is initiated by the diffusion of high-energy surface atoms, which progressively lowers the total system energy. Compared with Ti-C MXenes, ME MXenes exhibit substantially slower healing kinetics, reflecting compositional constraints on atomic mobility. A critical nanopore size is further identified beyond which complete healing becomes kinetically inhibited.