Unusual terminational effect on atomic ripple of Ti₃C₂T_x MXenes

Terminational chemistry traditionally influences MXenes' carrier concentration and inter-flake spacing, and thereby electronic properties. Herein, the unusual terminational effect on the periodic atomic displacement, namely ripple, has been demonstrated. The rippling structure strongly depends on the atomic radii of halogen terminations, including -Cl, -Br, and -I. This originates from the atomic response to local strain fluctuation induced by terminations. The atomic ripple in Ti₃C₂Br_x enhances electric coupling among adjacent atoms and promotes their charge transfer, thereby improving the electrical conductivity. Meanwhile, it significantly strengthens dielectric properties and markedly boosts the electromagnetic wave absorption capability. The maximum reflection loss value reaches -44.33 dB, and the effective absorption bandwidth is up to 3.94 GHz with a matching thickness of 1.40 mm. This work elucidated the effect of MXenes' microstructure on their dielectric properties on the atomic scale and paved an avenue for the development of MXenes-based devices.