A Novel Ultra-Sensitive Semiconductor SERS Substrate Boosted by the Coupled Resonance Effect

Recent achievements in semiconductor surface-enhanced Raman scattering (SERS) substrates have greatly expanded the application of SERS technique in various fields. However, exploring novel ultra-sensitive semiconductor SERS materials is a high-priority task. Here, a new semiconductor SERS-active substrate, Ta₂O₅, is developed and an important strategy, the "coupled resonance" effect, is presented, to optimize the SERS performance of semiconductor materials by energy band engineering. The optimized Mo-doped Ta₂O₅ substrate exhibits a remarkable SERS sensitivity with an enhancement factor of 2.2 × 10⁷ and a very low detection limit of 9 × 10^-9 m for methyl violet (MV) molecules, demonstrating one of the highest sensitivities among those reported for semiconductor SERS substrates. This remarkable enhancement can be attributed to the synergistic resonance enhancement of three components under 532 nm laser excitation: i) MV molecular resonance, ii) photoinduced charge transfer resonance between MV molecules and Ta₂O₅ nanorods, and iii) electromagnetic enhancement around the "gap" and "tip" of anisotropic Ta₂O₅ nanorods. Furthermore, it is discovered that the concomitant photoinduced degradation of the probed molecules in the time-scale of SERS detection is a non-negligible factor that limits the SERS performance of semiconductors with photocatalytic activity.