Formation and dielectric properties of Al-Ti-O nanocomposite oxide film on aluminum using sol-gel and anodizing

Aluminum specimens were coated with TiO2 film by sol-gel method and subsequently anodized in ammonium adipate solution. TiO2 film before and after anodization were characterized by using X-ray Diffraction (XRD), Raman Spectroscopy (RS), Scanning Electron Microscope (SEM), Optical Microscope (OM), Transmission Electron Microscope (TEM), Atomic Force Microscope (AFM), Auger Electron Spectroscopy (AES), and Capacitance-Voltage (C-V) tests. The results showed that TiO2 film annealed at 773 K on aluminum mainly contained anatase phase, and was porous with a network of micro-pores and micro-cracks, in which TiO2 particles were 5-15 nm in diameter, approximately. A sandwich oxide film was demonstrated to be created on aluminum, which was composed of triple layers including outer TiO2 film, inner Al2O3 film and intermediate Al-Ti-O nanocomposite film. Compared with anodic specimens without TiO2 film, the specific capacitance of TiO2 film coated specimens increased about 30% on average. The dielectric Al-Ti-O nanocomposite oxide film on aluminum was suggested to be formed by infilling of anodic aluminum oxide along the network channels of cracks and pores.