Few-layered vdW MoO3 for sensitive, uniform and stable SERS applications

Metal oxides have been considered as active substrates for surface-enhanced Raman scattering (SERS) through morphology-engineering and defect-introduction with the sacrifice of the uniformity and stability of the materials. In this work, large-size, few-layered (FL) wide band gap van der Waals (vdW) MoO3 nanosheets were prepared as SERS substrates. It's shown that the decrease of layer number converted the intrinsic MoO3 from non-SERS active to sensitive SERS substrate, with limit of detection (LOD) of 2 x 10(-8) M for R6G. The SERS of MoO3 showed high homogeneity with RSD as small as 2.95%, The Raman intensity of R6G on the SERS substrate remained higher than 90% after exposing in atmosphere for 160 days, demonstrating excellent air-stability. Experimental results demonstrated that the SERS effect of the plasmon-free MoO3 substrate comes from chemical enhancement mechanism (CM) when reducing its thickness. Furthermore, the CM effect can be further improved through non-destructive atomic intercalation into the vdW gap, resulting in more charges separation between the adsorbed molecules and substrates. Our result showed that non-destructive modulation strategy is effective for preparation of sensitive, uniform and stable SERS substrate.