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

Abstract

This work explores superposition of the localized surface plasmonic resonance (LSPR) effect of Au nanoparticles (AuNPs) with that on transition metal dichalcogenide (TMD) WS 2 nanodomes (WS 2 −NDs) enabled by enhanced dipole−dipole interaction at van der Waals (vdW) interfaces in AuNP/WS 2 −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/WS 2 −ND/graphene over that of reference graphene sample, in contrast to 4.0-and 5.3-fold, respectively, on AuNP/graphene and on WS 2 −ND/graphene. Furthermore, Raman spectra of probe molecules of fluorescent Rhodamine 6G (R6G) were hired to quantify the enhanced SERS on AuNP/WS 2 − 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/WS 2 −ND/graphene with respect to that on WS 2 −ND/graphene and AuNP/ graphene, respectively. The benefit of the superposition of the LSPR effects from the WS 2 −NDs and AuNPs results in high SERS sensitivity up to 1 × 10 −12 M on AuNP/WS 2 −ND/graphene, which is about an order of magnitude better than what's on WS 2 −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/WS 2 −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.

MoS2 Nanodonuts for High-Sensitivity Surface-Enhanced Raman Spectroscopy

“…Figure 6 shows the comparison of SERS Sensitivity and R6G 613 cm −1 peak enhancement factor (normalized with respect to that on graphene only SERS substrates) on different SERS substrates of graphene only, MoS 2 N-discs/graphene [ 26 ], AuNPs+MoS 2 N-discs (0.10 wt%)/graphene [ 29 ], WS 2 N-discs+MoS 2 N-discs (0.10 wt%)/graphene [ 55 ] and MoS 2 N-donuts/graphene (made from 0.26 wt% precursor concentration in this work). The result shows that the best enhancement was obtained on the MoS 2 N-donuts/graphene.…”

“…Using R6G peak intensity at 613 cm −1 on different substrates, the EM enhancement factors could be estimated using graphene only SERS substrate as reference. Specifically, the enhancement factors of 10.3 and 8.7, respectively, are obtained by dividing the intensities of the 613 cm −1 peak on TMDs (WS 2 ) N-discs/graphene and gold nanoparticles (AuNPs) on graphene (or AuNPs/graphene) SERS substrates by that on graphene [ 29 ]. While the values confirm both exhibit a strong LSPR effect, the LSPR of the non-metallic TMD N-discs is 40% higher than their metallic counterparts.…”

“…Quantitatively, SERS enhancement relies on many factors such as the size and the shape of plasmonic nanostructures and substrate morphology [ 31 , 32 , 33 , 34 ]. For example, Hong et al examined SERS enhancement using 4-nitrothiophenol (4-NTP) and 4-aminothiophenol (4-ATP) as probe molecules by adsorbing them on AuNPs of the average lateral size of 17, 30, 40, 50, 60, and 80 nm [ 29 ]. With increasing AuNPs lateral size, the SERS enhancement was found to increase initially until reaching the highest at ~50 nm, followed by a decrease with further AuNP size increase.…”

Double Ag Nanowires on a Bilayer MoS2 Flake for Surface-Enhanced Raman Scattering

“…All Raman spectra and maps were measured using microscope imaging with a confocal Raman microscope (Thermo Fisher, DXR) under an incident laser wavelength at 532 nm with the power and beam spot diameter of 5 mW and 2 μm, respectively. It should be noted that a low laser power in the range of 1–5 mW is typically used for taking R6G Raman spectra to avoid molecular damages during the multiple scans during integration …”

“…It should be noted that a low laser power in the range of 1−5 mW is typically used for taking R6G Raman spectra to avoid molecular damages during the multiple scans during integration. 23…”