Efficient Raman Enhancement in Molybdenum Disulfide by Tuning the Interlayer Spacing.

Two-dimensional nanomaterials, such as graphene and molybdenum disulfide (MoS ₂ ), have recently attracted widespread attention as surface-enhanced Raman scattering (SERS) substrates. However, their SERS enhancement is of a smaller magnitude than that of noble metal nanomaterials, and therefore, the detection sensitivity still needs to be substantially improved for practical applications. Here, we present the first detailed studies on the effect of the (MoS ₂ ) interlayer distances on the SERS intensity enhancement. We find that MoS ₂ with smaller interlayer distances achieves an SERS enhancement factor as high as 5.31 × 10 ⁵ , which is one of the highest enhancement factors to date among the two-dimensional nanomaterial SERS sensors. This remarkable SERS sensitivity is attributed to the highly efficient charge transfer from MoS ₂ to probe molecules. The charge-transfer ability directly determines the variable quantity d _{z ²} orbitals of Mo elements in the MoS ₂ -molecule system and then tunes the Raman intensity of probe molecules. Our work contributes to reveal the influence of MoS ₂ interlayer spacing on SERS detection and to open a new way for designing a highly sensitive nonmetal SERS technology.