MoⅣ boosted carrier density of MoO3-X for surface-enhanced Raman spectroscopy

Molybdenum oxides (MoO 3-X ) with the same surface plasmon resonance (SPR) effect as Au/Ag, and occupies an irreplaceable value in SERS detections. MoO 3-X SERS substrates with oxygen-rich defects tend to show better SERS performance, but the preparation and characterization of tunable O defects remain challenging. It cannot be ignored that the oxidation state of metal cations is also influenced by O defects. Here, a series of MoO 3-X SERS sensors with regulable Mo valence state were fabricated using magnetron sputtering technology. By changing the Mo sputtering power and the O 2 /Ar 2 ratio, the Mo/O element ratio of the substrate can be easily regulated to readjust the O defects. The X-ray Photoelectron Spectroscopy (XPS) and Raman spectra were performed to investigate the change and related relationship between Mo mixed valence state and SERS sensitivity. The abundant incompletely coordinated electrons produced by low valence Mo Ⅳ act as free carriers, increasing the free carrier density of MoO 3-X substrates, which is beneficial for the SERS effect. It has also been proven by Hall effect measurement. The SERS measurement shows that the enhancement factor (EF) reached 3.70 × 10 5 , which is exceedingly close to Au/Ag. The MoO 2.5 substrate also exhibited a repeatable and consistent response, high stability, and repeatability, which proves the splendid application potential in complex environments.