Improved SERS sensitivity of TiO2 nanorod films by annealing in vacuum

In this paper, substoichiometric TiO2-x nanorod films were prepared by vacuum annealing treatment of TiO2 nanorod films for an optimized period of time as a simple and effective method. As surface-enhanced Raman scattering (SERS) substrates, the TiO2-x nanorod films show good stability and high sensitivity because of the detection limit of Rhodamine 6G (R6G) as low as 10(-6) M. By combining photoluminescence (PL), UV-vis diffuse reflectance, Raman and electrical measurement, a high density of electronic states related to oxygen vacancy below the Fermi level has been identified in the reduced TiO2-x. Besides, X-ray photoelectron spectroscopy (XPS) analysis exhibits an ultra-thin TiO2 layer was formed at the outmost surface of TiO2-x. The effect of the TiO2 surface layer includes two aspects: (a) providing abundant regenerated surface oxygen-vacancy-associated levels to promote charge transfer between analyte and substrate under illumination of visible light; and (b) protecting oxygen vacancy from further oxidation to improve the stability of SERS performance of TiO2.

Automated summary

This study successfully prepared stable and highly sensitive TiO2-x nanorod films through vacuum annealing treatment. The presence of a high density of oxygen vacancy-related electronic states and the formation of an ultra-thin TiO2 layer on the surface were found to enhance the SERS performance of the TiO2 nanorod films.