Effect of different annealing temperatures and SiO2/Si(100) substrate on the properties of nickel containing titania thin sol-gel films

Nickel containing titania thin films have been prepared on SiO2/Si(100) substrate by using the sol-gel deposition and annealing in the air at 450-1150 degrees C. Several experimental techniques [atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray reflection (XRR), Raman spectroscopy, energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), UV-Vis spectroscopy and hydrophilicity measurements] have been applied to characterize these films. Further, the results of this study were compared to previously investigated nickel containing titania on HF-etched Si(100) (i.e. without oxide layer). The morphological and structural properties of nickel containing titania were found to be dependent on the kind of the substrate on which the films were prepared. The thin films deposited on SiO2/Si(100) substrate, compared to similar films on HF-etched Si(100) substrate, were more uniform, did not contain large pores and had smaller RMS roughness, especially when annealed below 650 degrees C. Also films on SiO2/Si(100) substrate were more crystalline and anatase transformation to rutile phase occurred at 150 degrees C lower temperature. Nickel in the films appeared to be in the 2+ oxidation state. When films were annealed above 650 degrees C, nickel was found mainly in the NiTiO3 crystallites. Nickel compounds segregated to the surface of the film, forming islands. Nickel addition red-shifted the titania fundamental absorption edge further into the visible range. Films on both substrates demonstrated couple of tens of nanometers thick interlayer formation (between films and substrates) after annealing at 850 and 900 degrees C. We demonstrated that a well-crystallined anatase was crucial for obtaining a good light-induced hydrophilic nickel containing titania surface. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim