Synergistic Resonance-Enhanced Plasmon-Free SERS in Few-Layer Manganese Phosphorus Trichalcogenide

Surface-enhanced Raman scattering (SERS) is widely employed due to its ultra-high sensitivity, non-destructive nature, and ability to provide label-free molecular fingerprint information. In this work, a novel semiconductor-based SERS substrate, 2D metal phosphorus trichalcogenides (2D-MPTs) is proposed, and a new "synergistic resonance" effect is introduced to maximize chemical mechanism (CM)-driven SERS performance via alloy engineering. By precisely tuning the energy levels of Mn_1-xNi_xPS₃ (0 ≤ x ≤1) alloys, the optimized Mn_0.73Ni_0.27PS₃ substrate demonstrates remarkable SERS sensitivity, with an enhancement factor of 1.4 × 10⁵ and a detection limit as low as 1.0 × 10^-9 mol L^-1 for rhodamine 6G (R6G). This outstanding performance is attributed to the synergistic contribution of: i) strong adsorption capability and efficient charge transfer (CT) between the semiconductor substrate and analytes, and ii) maximized excitation-resonance-facilitated CT coupled with molecular-resonance-facilitated CT. Overall, this work advances the understanding of CM and offers a pathway for designing highly effective semiconductor SERS substrates.