The influence of metal interlayers on the structural and optical properties of nano-crystalline TiO2 films

TiO2–M–TiO2 (M = W, Co and Ag) multilayer films have been deposited on glass substrates using reactive magnetron sputtering, then annealed in air for 2 h at 500 °C. The structure, surface morphology and optical properties of the films have been studied using X-ray diffraction, Raman spectroscopy, atomic force microscopy and UV–vis spectroscopy. The TiO2–W–TiO2 and TiO2–Co–TiO2 films showed crystalline phases, whereas the TiO2–Ag–TiO2 films remained in the amorphous state. The crystallization temperature for the TiO2–M–TiO2 films decreased significantly compared with pure TiO2 film deposited on quartz. Detailed analysis of the Raman spectra suggested that the crystallization of TiO2–M–TiO2 films was associated with the large structural deformation imposed by the oxidation of intermediate metal layers. Moreover, the optical band gap of the films narrowed due to the appearance of impurity levels as the metal ions migrated into the TiO2 matrix. These results indicate that the insertion of intermediate metal layers provides a feasible access to improve the structural and optical properties of anatase TiO2 films, leading to promising applications in the field of photocatalysis.