Constructing the Mo₂C@MoO_x Heterostructure for Improved SERS Application

Surface-enhanced Raman scattering (SERS) is a non-destructive spectra analysis technique. It has the virtues of high detectivity and sensitivity, and has been extensively studied for low-trace molecule detection. Presently, a non-noble-metal-based SERS substrate with excellent enhancement capabilities and environmental stability is available for performing advanced biomolecule detection. Herein, a type of molybdenum carbide/molybdenum oxide (Mo₂C@MoO_x) heterostructure is constructed, and attractive SERS performance is achieved through the promotion of the charge transfer. Experimentally, Mo₂C was first prepared by calcinating the ammonium molybdate tetrahydrate and gelatin mixture in an argon atmosphere. Then, the obtained Mo₂C was further annealed in the air to obtain the Mo₂C@MoO_x heterostructure. The SERS performance was evaluated by using a 532 nm laser as an excitation source and a rhodamine 6G (R6G) molecule as the Raman reporter. This process demonstrates that attractive SERS performance with a Raman enhancement factor (EF) of 1.445 × 10⁸ (R6G@10^-8 M) and a limit of detection of 10^-8 M can be achieved. Furthermore, the mechanism of SERS performance improvement with the Mo₂C@MoO_x is also investigated. HRTEM detection and XPS spectra reveal that part of the Mo₂C is oxidized into MoO_x during the air-annealing process, and generates metal-semiconductor mixing energy bands in the heterojunction. Under the Raman laser irradiation, considerable hole-electron pairs are generated in the heterojunction, and then the hot electrons move towards MoO_x and subsequently transfer to the molecules, which ultimately boosts the Raman signal intensity.