Ultrathin Janus two-dimensional (2D) materials are attracting intense interest currently. Substitutional doping of 2D transition metal dichalcogenides (TMDs) is of importance for tuning and possible enhancement of their electronic, physical and chemical properties toward industrial applications. Using systematic first-principles computations, we propose a class of Janus 2D materials based on the monolayers MX₂ (M = V, Nb, Ta, Tc, or Re; X = S, Se, or Te) with halogen (F, Cl, Br, or I) or pnictogen (N, P, As, Sb, or Bi) substitution. Nontrivial phases are obtained on pnictogen substitution of group VB (V, Nb, or Ta), whereas for group VIIB (Tc or Re), the nontrivial phases are obtained for halogen substitution. Orbital analysis shows that the nontrivial phase is driven by the splitting of M-d_yz and M-d_xz orbitals. Our study demonstrates that the Janus 2D materials have the tunability and suitability for synthesis under various conditions.

目前，超薄的Janus二维（2D）材料引起了人们的极大兴趣。2D过渡金属二硫化二氢（TMD）的取代掺杂对于调整和可能增强其电子，物理和化学性质以用于工业应用非常重要。使用系统的第一性原理计算，我们基于具有卤素（F，Cl的单层MX ₂（M = V，Nb，Ta，Tc或Re； X = S，Se或Te））提出了一类Janus 2D材料。，Br或I）或光原（N，P，As，Sb或Bi）取代。Vb组（V，Nb或Ta）的光子取代可得到非平凡的相，而VIIB组（Tc或Re）的光原取代可得到非平凡的相，用于卤素取代。轨道分析表明非平凡相位是由M- d分裂驱动的_yz和M- d _xz轨道。我们的研究表明，Janus 2D材料具有在各种条件下进行合成的可调性和适用性。