Au Nanoparticle/WS₂ Nanodome/Graphene van der Waals Heterostructure Substrates for Surface-Enhanced Raman Spectroscopy

This work explores superposition of the localized surface plasmonic resonance (LSPR) effect of Au nanoparticles (AuNPs) with that on transition metal dichalcogenide (TMD) WS2 nanodomes (WS2–NDs) enabled by enhanced dipole–dipole interaction at van der Waals (vdW) interfaces in AuNP/WS2–ND/graphene heterostructures for surface-enhanced Raman spectroscopy (SERS) with high-sensitivity, The confirmation of such a superposition is first demonstrated in the enhanced graphene Raman signatures, such as the G-peak intensity by approximately 7.8 fold on the AuNP/WS2–ND/graphene over that of reference graphene sample, in contrast to 4.0- and 5.3-fold, respectively, on AuNP/graphene and on WS2–ND/graphene. Furthermore, Raman spectra of probe molecules of fluorescent Rhodamine 6G (R6G) were hired to quantify the enhanced SERS on AuNP/WS2–ND/graphene SERS substrates. At the R6G concentration of 5 × 10–5 M, enhancement factors of ∼2.0 and 2.4 based on the R6G 613 cm–1 peak intensity are detected on the AuNP/WS2–ND/graphene with respect to that on WS2–ND/graphene and AuNP/graphene, respectively. The benefit of the superposition of the LSPR effects from the WS2–NDs and AuNPs results in high SERS sensitivity up to 1 × 10–12 M on AuNP/WS2–ND/graphene, which is about an order of magnitude better than what’s on WS2–ND/graphene, and several orders of magnitude better than that on the AuNP/graphene and metal nanostructure/TMD (continuous layer) substrates. This result reveals the advantage of superposition of the LSPR effects from different nanostructures through design of vdW heterostructures. In addition, considering the AuNP/WS2–ND/graphene vdW heterostructures can be fabricated in the layer-by-layer growth developed in this work, the high-sensitivity SERS substrates are scalable and low cost for marketable devices in optoelectronics and biosensing.