One plus one greater than Two: Ultrasensitive Surface-Enhanced Raman scattering by TiO2/ZnO heterojunctions based on Electron-Hole separation

Abstract

The separation of electron-hole pairs has been explored to control the performance of photogenerated carriers in several catalytical and optoelectronic systems, yet its effect on the sensitivity of semiconductor-based surface-enhanced Raman scattering (SERS) is still unknown. Herein, we taken TiO2/ZnO heterojunction as an example to study the role of electron-hole separation in semiconductor SERS. The results show that the formation of TiO2/ZnO heterojunction can induce a strong coupling at interface, improving the separation of the photogenerated electron-hole pairs. In SERS spectrum, the selective enhancement of non-totally symmetric modes (b2) of molecule clearly indicated that the charge-transfer efficiency and SERS-activity can be significantly improved using such a semiconductor-heterojunction. Furthermore, the enhancement factor of 105 was achieved for a non-resonance molecule and the lowest detection concentration can be down to 10-8 M. The findings of this work not only provide a fundamental insight into the role of electron-hole separation for semiconductor SERS enhancement, but also open up a novel strategy for design of semiconductor SERS-active substrate with a high charge-transfer contribution.