WOx/MoOx Hybrid Oxide Based SERS FET and Investigation on Its Tunable SERS Performance

Active control the surface-enhanced Raman scattering (SERS) enhancement shows great potential for realizing smart detection of different molecules. However, conventional methods usually involve time-consuming structural design or sophisticated fabrication process. Herein, we reported an electrically tunable field effect transistor (FET) comprised by WOx/MoOx hybrid as the SERS active layer. In the experiment, WOx/MoOx hybrid were first prepared by mixing different molar ratios of WOx and MoOx oxides. Then, R6G molecules was used as the Raman reporter, it showed that the intensity of the SERS signal observed on the most optimal hybrids (molar ratio = 1:3) could be promoted by two times as high as that observed on a single WOx or MoOx based substrate, which was ascribed to enhanced charge transfer efficiency by the constructed nano-heterojunction between the WOx and MoOx oxides. Thereafter, a back-gate FET was fabricated on a SiO2/Si substrate, and the most optimal WOx/MoOx hybrid was deposited as the gate channel as well as the SERS active layer. After that, a series of gate bias (from -15 V to 15 V) were implemented to actively tune the SERS performance of the FET. It evidenced that SERS EF can be further tuned from 2.39 × 107 (-15 V) to 6.55 × 107 (+10 V), which is ~7.4 / 4.1 times high than that observed on the pure WOx device (8.81 × 106) or pure MoOx (1.61 × 107) device, respectively. Finally, the mechanism behind the electrical tuning strategy was investigated. It revealed that a positive voltage would bend the conduction band down, which raised the electron density near the Fermi level. Consequently, it triggered the resonance charge transfer and significantly improved the SERS performance. On the contrary, a negative gate voltage attracted the holes to the Fermi level, which deferred the charge transfer process, and caused the degradation of the SERS enhancement.