Abstract
Two-dimensional MXenes continue to receive much research attention owing to their versatility and predicted topological phase, which are yet to be fully explored. Here, we conduct a rigorous search on M₂'M''C₂ (M' = V , Nb , or Ta ; M'' = Ti , Zr , or Hf) with various surface terminations, X₂ (X = F , Cl , Br , I , O , H , or OH) , using first-principles calculations. The majority of the systems exhibit the topological phase with semimetallic band structures. Most importantly, fluorinated MXenes, M₂'M''C₂F₂, are topological insulators. They possess sizable nontrivial band gaps from 34 to 318 meV using Heyd-Scuseria-Ernzerhof (HSE) hybrid functional calculations which are within the range capable of realizing quantum spin-Hall effects even at room temperature. Furthermore, the d orbitals of M' and M'' atoms mostly contribute to the spin-orbit coupling-induced band gaps. Selecting V₂TiC₂F₂ as an exemplar, we demonstrate the presence of edge states, verifying the calculated Z₂ invariant, and reveal its robustness against tensile strain. Finally, we propose SiC(0001) as a candidate substrate for material realization as it can preserve the nontrivial band topology.
