Plasmonic Au Nanoparticles on 2D MoS₂/Graphene van der Waals Heterostructures for High-Sensitivity Surface-Enhanced Raman Spectroscopy

A novel substrate consisting of a 2D MoS2/graphene van der Waals (vdW) heterostructure decorated with Au nanoparticles (AuNPs) was developed for surface-enhanced Raman spectroscopy (SERS). A transfer-free chemical vapor deposition process was employed for layer-by-layer fabrication of graphene, followed with MoS2 directly on wafers of SiO2/Si without any metal catalyst. AuNPs were deposited on the MoS2/graphene via in situ electron-beam evaporation of Au at an elevated temperature in the range of 300–350 °C under high vacuum. Rhodamine 6G (R6G) was used as an SERS probe molecule with a SERS sensitivity of 5 × 10–8 M using a nonresonance 633 nm laser, which is an order of magnitude higher than that reported on the AuNPs/graphene substrate using the same excitation. A higher SERS sensitivity of 5 × 10–10 M was obtained using resonance 532 nm laser excitation. The observed SERS sensitivity enhancement can be attributed to the combination of the electromagnetic mechanism of the plasmonic AuNPs and the chemical mechanism of the AuNPs/MoS2/graphene vdW heterostructure via enhanced interface dipole–dipole interaction as compared to graphene or MoS2 only as suggested by a density functional theory calculation. Therefore, this AuNPs/MoS2/graphene vdW heterostructure is advantageous to practical applications in optoelectronics and biosensing.