Sr-Doped TiO2 with Positive Double Defects for a Highly Sensitive and Stable Surface-Enhanced Raman Substrate

Surface oxygen vacancy defects and energy band defects can be synchronously regulated to accelerate the charge transfer in a semiconductor–molecule system for boosting the surface-enhanced Raman scattering (SERS) performance of a semiconductor. Herein, alkaline earth metal Sr with a low electronegativity and a large atomic radius was selected as a dopant to prepare a Sr-doped TiO2 (SrnTiO2) SERS substrate, in which a simple Sr doping achieves a synchronous regulation of double defects (i.e., surface oxygen vacancy defect and energy level defect of Ti) in TiO2. Abundant surface oxygen vacancies and defect energy levels of Ti are jointly responsible for the greatly enhanced SERS performance of the substrate. On the optimal substrate Sr0.0100TiO2, the minimum detection limit of a nonresonance molecule, 4-mercaptobenzoic acid, can reach 1 × 10–9 M, and the enhancement factor is as high as 9.3 × 106. To the best of our knowledge, this is the highest SERS activity among the reported semiconducting substrates, even comparable to those of precious metals. Moreover, the SrnTiO2 substrate shows an excellent spectral reproducibility and ultrahigh stability, which can withstand the corrosions of strong acid and alkali and even can resist the oxidation of high temperatures for SERS detection.