Theoretical Prediction of Two-Dimensional Functionalized MXene Nitrides as Topological Insulators

TL;DR

This paper predicts that certain functionalized MXene nitrides can act as two-dimensional topological insulators, expanding the class of MXenes with potential applications in electronic devices.

Contribution

It is the first theoretical demonstration that MXene nitrides, not just carbides, can be topological insulators, using first-principles calculations and Z2 index analysis.

Findings

Ti3N2F2 is a 2D topological insulator.

Zr3N2F2 can become a 2D TI under strain.

Hf3N2F2 can be turned into a 2D TI with tensile strain.

Abstract

Recently, two-dimensional (2D) transition metal carbides and nitrides, namely, MXenes have attracted lots of attention for electronic and energy storage applications. Due to a large spin-orbit coupling (SOC) and the existence of a Dirac-like band at the Fermi energy, it has been theoretically proposed that some of the MXenes will be topological insulators (TIs). Up to now, all of the predicted TI MXenes belong to transition metal carbides, whose transition metal atom is W, Mo or Cr. Here, on the basis of first-principles and Z2 index calculations, we demonstrate that some of the MXene nitrides can also be TIs. We find that Ti3N2F2 is a 2D TI, whereas Zr3N2F2 is a semimetal with nontrivial band topology and can be turned into a 2D TI when the lattice is stretched. We also find that the tensile strain can convert Hf3N2F2 semiconductor into a 2D TI. Since Ti is one of the mostly used transition metal element in the synthesized MXenes, we expect that our prediction can advance the future application of MXenes as TI devices.