ZnO/MoS x Heterostructure as a Noble Metal-Free SERS Substrate for the Detection of MB in Lower Concentration Levels

Surface-enhanced Raman scattering (SERS) is a sensitive spectroscopic method for enhancing Raman signals on roughened metal surfaces or nanostructures. Transition metal-based chalcogenide semiconductors are effective SERS substrates due to their low cost and various tunable properties; however, their enhancement factor (EF) is rather modest. To address this issue, semiconductor heterostructures can be used as SERS substrates due to their large-scale electron–hole pair separation, high interlayer interaction, and efficient photo-induced charge transfer (PICT). In this study, a ZnO/MoSx heterostructure is synthesized and employed as a SERS substrate for the detection of methylene blue (MB). To develop a ZnO/MoSx heterostructure, ZnO is first synthesized using seed-mediated electrodeposition, followed by calcination, and then MoSx is fabricated on ZnO via electrodeposition. The heterostructure ZnO/MoSx is able to detect MB at a lower concentration of 10–10 M with an apparent enhancement factor of 1.2 × 106. The substrate is also extremely stable and robust in nature. The photoluminescence peak intensity of ZnO decreases when MoSx is decorated on it, showing less electron–hole pair recombination in the ZnO/MoSx heterostructure. Thus, the improved SERS performance of the ZnO/MoSx substrate is attributed to the efficient electron–hole pair separation at the heterostructure interface, resulting in facile PICT between the substrate and the Raman analyte.