Abstract
This work explores a rationale design of intermixed WS2 nanodiscs (WS(2)NDs) and MoS2 nanodiscs (MoS(2)NDs) on graphene (WS(2)NDs+MoS(2)NDs/graphene) for ultrasensitive surface-enhanced Raman spectroscopy (SERS) beyond the sensitivity limit of the SERS substrates based on metallic plasmonic nanostructures. On the individual WS(2)NDs and MoS(2)NDs, localized surface plasmonic resonance (LSPR) is enabled by the dipole-dipole interaction at the WS(2)NDs/graphene and MoS(2)NDs/ graphene van der Waals (vdW) interfaces. The intermixed WS(2)NDs+MoS(2)NDs/graphene allows superposition of the LSPR effects from the two types of plasmonic NDs. The enhanced SERS sensitivity is illustrated in the boosted graphene Raman peaks by similar to 14fold on the WS(2)NDs+MoS(2)NDs/graphene, in contrast to similar to 7.6-fold on the counterparts with single types of the NDs. Furthermore, the SERS enhancement factors of the test molecules (fluorescent Rhodamine 6G or R6G) of 5 x 10(-5) M concentration Raman spectra (normalized to that on graphene) are similar to 16.4 and 8.1 considering the R6G 613 cm(-1) peak intensities were sensed on the WS(2)NDs+MoS(2)NDs/graphene and MoS2-NDs/graphene (or WS(2)NDs/graphene), respectively. In addition, the WS(2)NDs +MoS(2)NDs/graphene SERS substrate exhibits remarkably high SERS sensitivity as high as (5-7) x 10(-13) M, which is about 2 or more orders of magnitude greater than that reported on the AuNPs/graphene and other plasmonic metal nanostructures/2D materials SERS substrates. This result demonstrates a promising bottom-up approach in designing high-sensitivity SERS substrates based entirely on 2D atomic materials.