α-MoO₃ Microflakes Decorated with Gold Nanoislands as SERS-Active Substrates

Abstract

Surface-enhanced Raman spectroscopy (SERS) is an effective method that can be employed to detect analytes in ultratrace amounts precisely. The extensive development of noble-metal-based SERS detection has been done in the recent past. A hybrid of noble metals and semiconductors is highly effective in enhancing the Raman signal in addition to making it a stable, large-area, and low-cost SERS substrate, enabling the rapid growth of these heterostructures in SERS-based research areas. Defect engineering is a general approach to making a semiconductorbased SERS-active substrate. In this study, α-MoO 3 flakes obtained via a facile chemical vapor deposition process were decorated with gold nanoislands to access the synergetic contribution of localized surface plasmon resonance and the charge-transfer phenomenon, making it a metal−semiconductor (metal−metal oxide) heterostructure-based SERSactive substrate. Raman, X-ray diffraction, and field emission scanning electron microscopy measurements showed the formation of α-MoO 3 flakes. X-ray photoelectron spectroscopy analysis shows the increase in oxygen vacancies when α-MoO 3 flakes were annealed in an argon environment at 350 °C for an hour. Making use of this thermochromic property, the proposed heterostructure was prepared. α-MoO 3 flakes coated with a 10 nm thin gold film were annealed in a protective environment to produce oxygen defect-rich gold nanoisland-decorated α-MoO 3 flakes, making it possible to gain access to a dual enhancement mechanism via plasmons and charge transfer. It is highly sensitive, easy to fabricate and reproduce, stable, and a large-area SERS substrate. The proposed substrate demonstrated detection up to 10 −11 , 10 −10 , and 10 −9 M concentrations of rhodamine 6G, 2,4,6-trinitrotoluene, and thiram molecules, respectively.

Plasmon-Free Surface-Enhanced Raman Spectroscopy Using α-Type MoO3 Semiconductor Nanorods with Strong Light Scattering in the Visible Regime

“…α-MoO 3 , as a natural van der Waals crystal, exhibits a range of electronic states from semiconductor to metallic through intentional doping with defects and impurities. Above all, metallic behaviors of α-MoO 3 can generate localized SPRs (LSPRs), contributing to the enhancement of Raman signals through an EM process. , The previous studies have reported SERS applications based on hybrid structures of α-MoO 3 and metallic nanostructures . Strongly localized electromagnetic fields on metallic nanostructures are useful for the improvement of the SERS responses.…”