Influence of annealing on the structure and stoichiometry of europium-doped titanium dioxide thin films

Abstract

This work presents the influence of annealing on the structure and stoichiometry of europium (Eu)-doped titanium dioxide (TiO 2). Thin films were fabricated by magnetron sputtering from a metallic Ti–Eu target in oxygen atmosphere and deposited on silicon and SiO 2 substrates. After deposition the selected samples were additionally annealed in air up to 1070 K. Film properties were examined by means of X-ray diffraction (XRD), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) and the results were analyzed together with the undoped TiO 2 thin films prepared under similar technological conditions. XRD results showed that depending on the Eu content, as-deposited thin films consisted of the TiO 2-anatase or TiO 2-rutile. An additional annealing will result in the growth of anatase crystals up to 35 nm, but anatase to rutile phase transformation has not been recorded. AFM images display high quality and a dense nanocrystalline structure. From the XPS Ti2p spectra the 4+oxidation state of Ti was confirmed. The O1s XPS spectra displayed the presence of an O 2− photoelectron peak accompanied by an additional broader peak that originates from hydroxyl species chemisorbed at the sample surface. It has been found that Eu dopant increases the OH − content on the surface of prepared TiO 2:Eu thin films. The calculated O/Ti ratio was in the range of 1.85–2.04 depending on the sample.