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

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 semiconductor-based SERS-active substrate. In this study, alpha-MoO3 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 SERS-active substrate. Raman, X-ray diffraction, and field emission scanning electron microscopy measurements showed the formation of alpha-MoO3 flakes. X-ray photoelectron spectroscopy analysis shows the increase in oxygen vacancies when alpha-MoO3 flakes were annealed in an argon environment at 350 degrees C for an hour. Making use of this thermochromic property, the proposed heterostructure was prepared. alpha-MoO3 flakes coated with a 10 nm thin gold film were annealed in a protective environment to produce oxygen defect-rich gold nanoisland-decorated alpha-MoO3 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.