| Summary: | 碩士 === 國立中山大學 === 物理學系研究所 === 107 === Ultrathin Janus two-dimensional (2D) materials have suddenly attracted huge research interests. Substitutional doping of 2D transition metal dichalcogenides (TMDs) is of importance in tuning and possible enhancement of their electronic, physical and chemical properties for vast industrial applications. Here we propose a class of Janus 2D materials based on monolayer 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. We have performed a systematic first-principles calculation on these Janus 2D materials. Interestingly, nontrivial phases were obtained upon pnictogen substitution of group VB (V, Nb, or Ta), whereas for group VIIB (Tc or Re), nontrivial phases were obtained upon halogen substitution. Orbital analysis shows that the non-trivial phase is driven by the splitting of M-dyz and M-dxz orbitals. Our study and previous experimental studies demonstrate that Janus 2D materials have the tunability and suitability for synthesis under various conditions.
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