Fig. 2. Quality characterizations of the as-grown MoS₂ domain and universal growth of diverse TMDs by chalcogen monomer supply.

a Atomic-resolved HAADF-STEM image of the prepared MoS₂, revealing the high crystallinity of MoS₂ without detectable S vacancies. b Low-temperature (10 K) PL spectra of MoS₂ samples fed by S monomer (orange curve) and S powder (dark yellow curve), respectively. Three typical features, X⁰, X^T, and X^D peaks assign to neutral exciton, trion, and defect state emission peaks, respectively. The absence of X^D peak confirmed the high quality of the MoS₂ grown by S monomer supply. c The circular dichroism PL spectrum measured at 10 K. The near-unity polarization of MoS₂ on sapphire indicates the high optical quality. The horizontal dashed line is added for clarity. d Transfer characteristic of the MoS₂ FET with channel length and width of 7 μm and 22 μm, respectively, at a bias voltage V_ds of 1 V. Inset: optical image of the device. e Optical images of the representative TMDs, including 2H phase MoS₂, MoSe₂, MoTe₂, WS₂, WSe₂ and 1T′ phase WTe₂. f The calculated formation energy (E_f) of the six representative TMDs. When chalcogen bulks are supplied as precursors, the formation of transition metal tellurides in relative to their corresponding sulfide and selenide are less favourable due to their high formation energies (−0.73 and −0.68 eV/unit for MoTe₂ and WTe₂, respectively). While it becomes highly favourable when Te monomers are applied.