Phase-modulated quantum-sized TMDs for extreme saturable absorption

Two-dimensional semiconductors such as transition metal dichalcogenides (TMDs) have attracted much interest in the past decade. Herein, we present an all-physical top-down method for the scalable production of the intrinsic TMD quantum sheets (QSs). The phases of the TMDs (e.g., 2H-MoSe₂, 2H-WSe₂, and T_d-WTe₂) remain stable during the transformation from bulk to QSs. However, phase transition (from T_d to 2H) is detected in MoTe₂. Such phase-modulation by size-reduction has never been reported before. The TMD QSs can be well dispersed in solvents, resulting in remarkable photoluminescence with excitation wavelength-, concentration-, and solvent-dependence. Meanwhile, the TMD QSs can be readily solution-processed into hybrid thin films, which demonstrate exceptional nonlinear saturation absorption (NSA). Notably, 2H-MoTe₂ QSs in poly(methyl methacrylate) show extremely high NSA performance with (absolute) modulation depth up to 46.6% and saturation intensity down to 0.81 MW·cm⁻². Our work paves the way towards quantum-sized TMDs.