Fig. 1.

Structure and electronics of 2D TMDCs. a Schematic structure of typical MX₂ materials. Yellow and gray balls indicate chalcogen atoms (X) and transition-metal atoms (M), respectively. Reprinted with permission from Ref. [11], Copyright 2011, Springer Nature. b Top and side views of single-layered TMDCs of 2H, 1T, and 1Tʹ phases, showing the primitive unit cell of 2D lattice structure with lattice vectors and the stacking of atomic planes. Reprinted with permission from Ref. [56], Copyright 2017, Springer Nature. c Electronics parameters of TMDCs: crystal structure, semiconducting type, bandgap in monolayer (BG_m) and bulk (BG_b), and theoretical carrier mobility (CM_t). D direct bandgap, ID indirect bandgap. (Color figure online)