UV-light-assisted preparation of MoO_3−x/Ag NPs film and investigation on the SERS performance

Surface-enhanced Raman scattering (SERS) technique is a powerful spectrum analysis technique for the ultra-low molecular trace detection. Conventionally, noble metals like silver (Ag) and gold (Au) are used to prepare the SERS substrates; however, limitations of complicated experimental designs and sophisticated process steps impede their wide applications in practice. Recently, metal oxides arise as a promising material for SERS application, but relatively weak Raman signal enhancement and poor material stability still pose as a challenge. Here, a UV-light-assisted fabrication of MoO_3−x/silver nanoparticles (MoO_3−x/Ag NPs) film is proposed. In the experiment, the sub-transition-metal-oxide of MoO_3−x was used as the Raman chemical enhancement substrate as well as the reducing agent. Through the spin-coating of MoO_3−x layer on the silicon substrate and UV-light-assisted reduction of silver nitride (AgNO₃) on the MoO_3−x layer, a novel MoO_3−x/Ag NPs one-layer film was fabricated. Using the Rhodamine B (RhB) as the Raman reporter, SERS measurement shows that enhancement factor (EF) of 1.195 × 10⁶ could be achieved. Moreover, a Raman signal amplifying strategy is further demonstrated by constructing MoO_3−x/Ag NPs multi-layer films. And result evidences that maximum gain of 2.07 for the RhB Raman peak at 1280 cm⁻¹ can be obtained on the MoO_3−x/Ag NPs three-layer film when referred to that on the MoO_3−x/Ag NPs one-layer film. Meanwhile, the EF of the MoO_3−x/Ag NPs three-layer film is also improved to 2.985 × 10⁶, giving the minimum detectable concentration of 10⁻⁹ M.