Phase-Engineered Transition Metal Dichalcogenides for Highly Efficient Surface-Enhanced Raman Scattering

Phase engineering of two-dimensional (2D) transition metal dichalcogenides (TMDs) is an attractive avenue to construct new surface-enhanced Raman scattering (SERS) substrates. Herein, 2D WS₂ and MoS₂ monolayers with high-purity distorted octahedral phase (1T′) are prepared for highly sensitive SERS detection of analytes (e.g., rhodamine 6G, rhodamine B and crystal violet). 1T′-WS₂ and 1T′-MoS₂ monolayers show the detection limits of 8.28 × 10^-12 and 8.57 × 10^-11 M for rhodamine 6G, with the enhancement factors of 4.6 × 10⁸ and 3.9 × 10⁷, respectively, which are comparable to noble-metal substrates, outperforming semiconducting 2H-W(Mo)S₂ monolayers and most of the reported non-noble-metal substrates. First-principles density functional theory calculations show that their Raman enhancement effect is mainly ascribed to highly efficient interfacial charge transfer between the 1T′-W(Mo)S₂ monolayers and analytes. Our study reveals that 2D TMDs with semimetallic 1T′ phase are promising as next-generation SERS substrates.