Investigation on sol-gel synthesized Ag-doped TiO2 cermet thin films

Undoped TiO2 and Ag-TiO2 (up to 23 at.% Ag) cermet thin films and polycrystalline powders have been prepared by sol-gel process. Their structure, composition, surface morphology and optical properties have been investigated by X-ray diffraction (XRD), differential thermal analysis (DTA), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS) and ultraviolet-visible spectroscopy (UV-VIS spectroscopy). It has been observed that while Ag does not form a solid solution with TiO2, it promotes the anatase to rutile phase transformation. The transformation temperature decreases from 827 °C for undoped TiO2 to about 650 °C for 23 at.% Ag-doped TiO2. SIMS analyses show that Ag is mostly present on the surface of the films. XPS studies confirm that these Ag are in the Ag0 state. Optical analyses show that with increasing Ag content, the refractive index (n) increases and the optical absorption behavior of the cermet films is modified, but the band gap of the anatase TiO2 is not influenced.