Effect of TiO₂ arrays on surface enhanced Raman scattering (SERS) performance for Ag/TiO₂ substrates

Ag/TiO₂ nanostructure arrays were constructed on fluorine-doped tin oxide (FTO) via a controllable hydrothermal route and a magnetron sputtering method with a variety of TiO₂ arrays decorated by Ag nanoparticles. Effects of different TiO₂ arrays on the microstructure, composition, and optical properties of the samples were revealed. As surface enhanced Raman scattering (SERS) active substrates, we discussed the sensitivity and reproducibility of Ag/TiO₂ nanostructure arrays for Rhodamine 6G (R6G) molecule detection. It was found that TiO₂ nanosheet (TiO₂(S)) array as a supporting made Ag nanoparticles have a uniform and continuous distribution, which achieved much higher SERS signals. The obtained Ag/TiO₂(S) substrate had an improved enhancement factor of 4.31 × 10⁵ compared with the other Ag/TiO₂ nanostructure arrays of nanorods, nanotubes, and nanotrees. Furthermore, Ag/TiO₂(S) active substrate showed good reproducibility with low relative standard deviation values. Such a remarkable SERS activity could be due to the synergistic effect of electromagnetic enhancement and charge transfer enhancement. Moreover, the TiO₂(S) array with high-exposed {101} facets provided a large adhesion area and generated a strong interaction with external atoms, which would produce high-density 'hot spots' of SERS.