Molybdenum Oxide/Tungsten Oxide Nano-heterojunction with Improved Surface-Enhanced Raman Scattering Performance

Abstract

By virtue of their high uniformity and stability, metal oxide-based surface-enhanced Raman spectroscopy (SERS) substrates have attracted enormous attention for molecular trace detection. However, strategies for further enhancing the SERS sensitivity are still desired. Herein, MoO x /WO x nano-heterojunctions are constructed by mixing MoO x and WO x together (MoO x /WO x hybrid) with diverse weight ratios. Using a 532 nm laser as the excitation source and R6G as the Raman reporter, it is shown that the Raman signal intensity (for the peak @ 1360 cm–1) obtained on the optimal MoO x /WO x hybrid (MoO x /WO x = 1:1/3) is twice that observed on a pure MoO x or WO x substrate. Moreover, a limit of detection of 10–8 M and an enhancement factor of 108 are achieved. In the SERS enhancement mechanism investigation, it is revealed that MoO x and WO x form a staggered band structure. During the SERS measurement, electron–hole pairs are generated in the nano-heterojunction using the incident laser. They are then separated by the built-in potential with the electrons moving toward WO x . The accumulated electrons on WO x are further transferred to the R6G molecules through the coupling of orbitals. Consequently, the molecular polarizability is amplified, and SERS performance is enhanced. The abovementioned explanation is supported by the evidence that the contribution of the chemical enhancement mechanism in the optimal MoO x /WO x hybrid substrate is about 2.5 times or 5.9 times that in the pure WO x or MoO x substrate.

Ultraviolet-ozone concomitantly induced MoS2/MoOx heterostructures with improved SERS performance

“…For example, Xie et al reported a novel SERS substrate based on a molybdenum oxide-tungsten oxide semiconductor heterojunction (WO x /MoO x ). 24 In this work, defective molybdenum oxide/tungsten oxide (WO x /MoO x ) nano-heterojunctions were constructed by mixing MoO x and WO x nanoparticles with different weight ratios. The charge transfer efficiency between the substrate and the molecules was optimized, and an attractive enhancement factor of 10 8 was achieved.…”

Ag NC and Ag NP/PorC Film-Based Surface-Enhanced Raman Spectroscopy-Type Immunoassay for Ultrasensitive Prostate-Specific Antigen Detection

“…Characteristic Raman peaks belonging to R6G are all detected. In detail, the Raman peaks observed at 608 and 772 cm –1 can be assigned to the aromatic band breathing, and the Raman vibration detected at 1183 cm –1 is attributed to the aromatic C–H bond bending . In addition, the Raman peak located at 1360 cm –1 is from C–C bridge band stretching.…”

Constructing the Mo2C@MoOx Heterostructure for Improved SERS Application

“…Specifically, the Raman peak which appears at 288 cm −1 is assigned to the wagging mode of the double bond O=Mo=O, while the Raman peaks that appear at 662, 818, and 994.7 cm −1 are assigned to the stretching mode of the triply coordinated oxygen (3Mo-O), the doubly coordinated oxygen (2Mo-O), and the terminal oxygen (Mo 6+ -O), respectively. Finally, the Raman peaks that show at 243, 286, 335, and 375 cm −1 are indexed to the oscillation modes of (2Mo-O), (O=Mo=O), (3Mo-O), and (Mo=O), respectively [ 22 ]. The above observation demonstrates that the oxidization reaction at 400 °C is more efficient at oxidizing the Mo 2 C into MoO X .…”

“…Specifically, defective molybdenum oxide/tungsten oxide (MoO x /WO x ) are prepared, then they are mixed with different weight ratios to construct the nano-heterojunctions. This shows that an attractive EF of 10 8 can be obtained on the substrate with optimal mixing ratios [ 22 ]. However, tungsten suboxide suffers from issues of environment instability when the above method is used in a harsh condition or when the material is kept in the air for a long time [ 23 ].…”