Role of Sn in the Amorphous-to-Crystalline Transition of TiO₂ Thin Films

The amorphous-to-crystalline transition in TiO₂ films upon annealing in air yields different polymorphs, depending on the oxygen partial pressure during the deposition of the amorphous precursor film. We further manipulate the resulting polymorph by introducing Sn into the system. By depositing a few nanometer-thick layer of metallic Sn between two layers of amorphous TiO₂ prepared to yield the anatase polymorph of TiO₂, we find that it results in the rutile polymorph if the content of Sn is high enough. If Sn is introduced as an oxide, no rutile is formed; anatase is by far the predominant phase (with a very small amount of brookite). This observation is consistent with scavenging of oxygen by elemental Sn at the Sn/TiO₂ interfaces, stabilizing the rutile structure that can accommodate oxygen vacancies.