Observation of Titania and Titanate Phase Changes in Oxidation-Controlled ZnO/TiN and HfO2/TiN Thin Films: An X-ray Absorption Spectroscopy Study

Abstract

We investigated the local electronic structures of oxidation-controlled TiN thin films for preparation of photocatalytic titania using soft X-ray absorption spectroscopy. It is shown that the TiN layers on top of oxides, such as HfO2 or ZnO, are easily oxidized by heat during postdeposition annealing (PDA) so as to form nitrogen-incorporated titania (N-TiO2). The local structures of the oxidized films evolved significantly depending on the bottom oxide and the PDA conditions; when TiN was deposited on HfO2, which is less reactive than ZnO, PDA at 700 °C stabilized a mixture of rutile and anatase phases under almost any gas (N2 or O2) environments. On the other hand, when TiN was deposited on ZnO, which is reactive enough to oxidize the TiN layers substantially, the PDA resulted in a rich phase diagram according to the gas environment: under N2 environment, an anatase local structure is dominant, whereas under O2 environment, a rutile or yet another local structure with a high symmetry, for example, perovs...