Fig. 4. Growth mechanism with chalcogen monomer supply in MoX₂ (X = S, Se, Te).

a Schematic diagram of adsorption, diffusion, and vacancy healing of chalcogen monomer on MoX₂ surface. The orange dotted arrows denote the motion of chalcogen monomers or dimers. b The binding energies of monomers and dimers on MoX₂ surface. The much higher energy of monomers facilitates their better adsorption on the TMD surface than dimers. c The energy profiles of vacancy healing for MoX₂ surface by using chalcogen monomers. The relatively small energy barriers of chalcogen monomer diffusion and the highly exothermic reaction at the vacancy both accelerate the self-healing of MoX₂.