Significantly increased Raman enhancement enabled by hot-electron-injection-induced synergistic resonances on anisotropic ReS2 films.

Abstract

Two-dimensional (2D) materials are an excellent platform for surface-enhanced Raman spectroscopy (SERS). However, a poor detection sensitivity hinders their practical application. Exciton resonance (μex) can improve SERS significantly by lending intensity to nearby charge-transfer resonance. Coincidentally, for ReS2, the enhanced μex can be achieved through the injection of excited-state electrons which can adjust the energy band to the SERS detection range. Moreover, ReS2 has strong anisotropic properties, which adds an additional dimension for SERS. Therefore, ReS2 is an ideal candidate to realize highly sensitive anisotropic SERS. In this paper, the metallic T phase of ReS2 is introduced to the semiconducting Td phase by phase engineering. The photoinduced electron tunneling from the T phase to the Td phase can tune exciton emissions to the visible region, which effectively facilitates the photoinduced charge transfer processes. With RhB as the probe molecule, the synergistic resonance effects improve the limit of detection to 10-9 M with the enhancement factor up to about 108. Meanwhile, the obtained ultrasensitive SERS substrates also show good uniformity, stability as well as unique anisotropy. Our results open a new perspective in the improvement of the SERS performance.