Intermixed WS₂+MoS₂ Nanodisks/Graphene\nvan der Waals Heterostructures for Surface-Enhanced Raman Spectroscopy\nSensing

Abstract

This\nwork explores a rationale design of intermixed WS₂ nanodiscs\n(WS₂NDs) and MoS₂ nanodiscs (MoS₂NDs) on graphene (WS₂NDs+MoS₂NDs/graphene)\nfor ultrasensitive surface-enhanced Raman spectroscopy (SERS) beyond\nthe sensitivity limit of the SERS substrates based on metallic plasmonic\nnanostructures. On the individual WS₂NDs and MoS₂NDs, localized surface plasmonic resonance (LSPR) is enabled by the\ndipole–dipole interaction at the WS₂NDs/graphene\nand MoS₂NDs/graphene van der Waals (vdW) interfaces. The\nintermixed WS₂NDs+MoS₂NDs/graphene allows superposition\nof the LSPR effects from the two types of plasmonic NDs. The enhanced\nSERS sensitivity is illustrated in the boosted graphene Raman peaks\nby ∼14-fold on the WS₂NDs+MoS₂NDs/graphene,\nin contrast to ∼7.6-fold on the counterparts with single types\nof the NDs. Furthermore, the SERS enhancement factors of the test\nmolecules (fluorescent Rhodamine 6G or R6G) of 5 × 10^–5 M concentration Raman spectra (normalized to that on graphene) are\n∼16.4 and 8.1 considering the R6G 613 cm^–1 peak intensities were sensed on the WS₂NDs+MoS₂NDs/graphene and MoS₂–NDs/graphene (or WS₂NDs/graphene), respectively. In addition, the WS₂NDs+MoS₂NDs/graphene SERS substrate exhibits remarkably high SERS\nsensitivity as high as (5–7) × 10^–13 M, which is about 2 or more orders of magnitude greater than that\nreported on the AuNPs/graphene and other plasmonic metal nanostructures/2D\nmaterials SERS substrates. This result demonstrates a promising bottom-up\napproach in designing high-sensitivity SERS substrates based entirely\non 2D atomic materials.