Facile Reduction Method Synthesis of Defective MoO_2–x Nanospheres Used for SERS Detection with High Chemical Enhancement

Abstract

Recently, more and more attention has been given to a semiconductor oxide-based surface-enhanced Raman spectroscopy substrate for its great stability and biocompatibility. However, its poor SERS sensitivity limits the applications of semiconductor oxide SERS substrates. In this paper, we provide a facile reduction method to modulate oxygen vacancy concentrations in oxide SERS substrates. Using MoO2 as an example, the resonance coupling as well as charge transfer between the semiconductor oxide SERS substrate and the target molecules were promoted for the reason of artificial oxygen vacancy embodied in the Raman signals being improved. By using the TEM, SEM, and XPS measurements, we confirmed that we successfully prepared defective MoO2–x with a polycrystalline surface. MoO2–x modulated oxygen vacancy treated with 6 wt % Li shows a very high detection sensitivity of 10–8 M (4.79 ug/L) for R6G, and the intensity of the Raman signal was highly enhanced. Because of the existence of defective energy levels, resonance coupling, as well as charge transfer between semiconductor and molecules, was obviously promoted. More importantly, the method of modulating oxygen vacancy can be widely used in semiconductor oxide materials for its chemical enhancement capacity can be promoted by artificial oxygen vacancy.

Defect engineering in semiconductor-based SERS

“…In addition to R6G, several polychlorinated phenol molecules were also detected at submicromolar concentrations. Moreover, the plasmonic activity of MoO2 nanostructures can be further enhanced by introducing oxygen vacancies, as was shown by Cao et al 75 , who induced surface oxygen vacancy sites by reductive treatment with lithium (Fig. 4b).…”

Smart design of high‐performance surface‐enhanced Raman scattering substrates

“…Some physical methods can also construct defects in semiconductors, for instance, lithium metal grinding reduction will introduce surface defects in MoO 2 nanospheres (Figure 9A). 92 The Raman intensity of R6G absorbed on the defective MO 2− x substrate was greatly enhanced than that on the nonvacancy MoO 2 . Femtosecond laser pulses also can fabricate defects on the surface of semiconductors.…”

Surface Enhanced Raman Scattering Revealed by Interfacial Charge-Transfer Transitions

“…Cao et al also applied a facile reduction method to modulate the oxygen vacancy concentration in oxide SERS substrates. 70 By controlled reduction with metal lithium, the authors obtained a MoO 2Àx nanosphere product with adjustable oxygen deficits. A plateau in the Raman enhancement with an LOD of 10 À8 M for R6G was observed on the 6-wt % Li-treated MoO 2Àx substrate, which was ascribed to the saturated promotion effect of the CT in relationship with oxygen deficits in the MoO 2Àx samples.…”