Covalent surface modifications and superconductivity of two-dimensional metal carbide MXenes

TLDR

MXenes possess numerous surface sites for chemical modification, unlike graphene and transition‑metal dichalcogenides, and chloride terminations achieved via molten salts are difficult to further modify. Hydrofluoric‑acid etching of the Ti₃AlC₂ MAX phase removes the aluminum layer, producing Ti₃C₂ MXene with diverse surface terminations. Etching MAX phases in molten CdBr₂ generates bromide‑terminated MXenes that can be substituted with oxygen, sulfur, selenium, tellurium, NH groups, and vacancies, thereby altering electronic transport and enabling surface‑group–dependent superconductivity in Nb₂C MXenes. Kamysbayev et al., Science, this issue p.

Abstract

Modifying MXene surfaces Unlike graphene and transition-metal dichalcogenides, two-dimensional transition-metal carbides (MXenes) have many surface sites that can be chemically modified. Etching of the aluminum layer of a parent MAX phase Ti 3 AlC 2 layered material with hydrofluoric acid leads to the MXene Ti 3 C 2 with various surface terminations. Molten salts can achieve uniform chloride terminations, but these are difficult to further modify. Kamysbayev et al. show that etching of MAX phases in molten cadmium bromide leads to bromide-terminated MXenes that can then be substituted with oxygen, sulfur, selenium, tellurium, and NH groups as well as with vacancy sites. The surface groups can alter electronic transport. For example, the Nb 2 C MXenes exhibit surface group–dependent superconductivity. Science , this issue p. 979