Effects of thermal oxidation and deposition time on the SERS activity of TiO2 nanostructure films

Titanium (Ti) nanostructure films were fabricated on glass substrates by DC magnetron sputtering using the oblique angle deposition (OAD) technique with varying deposition times. The as-deposited Ti films were subsequently oxidized in air at 400°C and 500°C to obtain TiO2 nanostructure films. The effects of deposition time and oxidation temperature on the structural, morphological, and optical properties were systematically investigated and correlated with surface-enhanced Raman scattering (SERS) performance toward methylene blue (MB) molecules. Increasing both deposition time and oxidation temperature led to thicker films, larger grains, and enhanced crystallinity with higher surface roughness. The optical band gap gradually decreased as deposition time increased, a trend associated with microstructural evolution and improved crystallinity during thermal oxidation. Among all samples, the TiO2 film oxidized at 400°C with a deposition time of 4 min exhibited the highest Raman enhancement, with a maximum enhancement factor (EF) of approximately 4.00 ± 0.064 (mean ± SD, n = 5), indicating that moderate oxidation promotes optimal nanostructured surface and charge-transfer efficiency. These findings highlight the important role of deposition time and oxidation conditions in governing the SERS activity of TiO2 nanostructure films.