Universal Strategy for Phase-Selective Synthesis of Monolayer TMDs via Colloidal Chemistry

Colloidal synthesis of monolayer transition metal dichalcogenides (TMDs) remains challenging regarding uniform size, thickness, and crystalline phase. While significant progress has been made in phase engineering, a unified chemical strategy for on-demand selection of both 2H and 1T' phases across multiple TMD systems within a single chemical synthesis strategy has remained elusive. Here, we report a universal colloidal strategy for selective synthesis of both 2H and 1T' phases across four representative TMDs - MoS₂, MoSe₂, WS₂, and WSe₂ - by tuning the metal-to-chalcogen precursor ratio ([M]:[X]) and ligand composition. We demonstrate that phase selection in W-based TMDs is governed primarily by precursor stoichiometry: relatively lower chalcogen ratios favor the metastable 1T' phase, while higher ratios stabilize the thermodynamic 2H phase. In contrast, Mo-based TMDs remain locked in the 2H phase regardless of precursor ratios; however, the introduction of oleic acid into an oleylamine-based ligand environment induces successful synthesis of 1T' phase. This work represents, for the first time, a general approach for phase-selective synthesis of all four TMD analogues using common precursors and ligands. These results establish a generalized design principle for phase-selective colloidal synthesis of TMDs and provide a foundation for exploring phase-dependent quantum phenomena and functional properties.