Exploring a novel class of Janus MXenes by first principles calculations: structural, electronic and magnetic properties of Sc 2 CXT, X = O, F, OH; T = C, S, N.

The already intriguing electronic and optical properties of the MXene Sc 2 C family can be further tuned through a wide range of possible functionalizations. Here, by means of density functional theory, we show that the 36 possible elements of the Janus MXT (M: Sc 2 C, X: O, F, OH, T: C, N, S) family, built by considering the four possible structural models (i) FCC, (ii) HCP, (iii) FCC + HCP, and (iv) HCP + FCC, are all potentially stable. The analysis of their mechanical properties shows the excellent mechanical flexibility of functionalized MXenes (f-MXenes) under large strain, making them more suitable for applications where stress could be an issue. Interestingly, while Sc 2 C presents a metallic character, Sc 2 COS, Sc 2 CFN and Sc 2 COHN are found to be semiconductors with bandgaps of 2.5 eV (indirect), 1.67 eV (indirect) and 1.1 eV (direct), respectively, which presents promising applications for nano- and optoelectronics. Moreover, Sc 2 CFC presents a ferromagnetic ground state with the 2 × 2 × 1 supercell magnetic moment of 3.99 μ B , while the ground state of Sc 2 COHC might be antiferromagnetic with a magnetic moment of 3.98 μ B , depending on the environment. Remarkably, the band structures of Sc 2 CFC and Sc 2 COHC present a half-metallic character with an HSE06 fundamental band gap of 0.60 eV and 0.48 eV, respectively. Our results confirm the extraordinary potential of the Janus MXT (M: Sc 2 C, X: O, F, OH, T: C, N, S) family for novel applications in 2D nano-,opto- and spintronics.