Phase-Engineered\nTransition Metal Dichalcogenides\nfor Highly Efficient Surface-Enhanced Raman Scattering

Phase engineering of two-dimensional (2D) transition\nmetal dichalcogenides\n(TMDs) is an attractive avenue to construct new surface-enhanced Raman\nscattering (SERS) substrates. Herein, 2D WS<sub>2</sub> and MoS<sub>2</sub> monolayers with high-purity distorted octahedral phase (1T′)\nare prepared for highly sensitive SERS detection of analytes (e.g.,\nrhodamine 6G, rhodamine B and crystal violet). 1T′-WS<sub>2</sub> and 1T′-MoS<sub>2</sub> monolayers show the detection limits\nof 8.28 × 10<sup>–12</sup> and 8.57 × 10<sup>–11</sup> M for rhodamine 6G, with the enhancement factors of 4.6 × 10<sup>8</sup> and 3.9 × 10<sup>7</sup>, respectively, which are comparable\nto noble-metal substrates, outperforming semiconducting 2H-W(Mo)S<sub>2</sub> monolayers and most of the reported non-noble-metal substrates.\nFirst-principles density functional theory calculations show that\ntheir Raman enhancement effect is mainly ascribed to highly efficient\ninterfacial charge transfer between the 1T′-W(Mo)S<sub>2</sub> monolayers and analytes. Our study reveals that 2D TMDs with semimetallic\n1T′ phase are promising as next-generation SERS substrates.