Interfacial Stabilization of Metastable TiO2 Films

Abstract

This work demonstrates a phenomenon that preserves the traditionally metastable anatase crystal structure of thin titania (TiO2) films along a two-dimensional oxide interface at temperatures well in excess of those that normally trigger a full polymorphic transformation to rutile in higher dimensionality crystalline powders. Whereas atomic surface mobility appears to dominate polymorph transformation processes within bulk TiO2 powders, a simple reduction in dimensionality to a two-dimensional TiO2 film (ca. 50–200 nm thick), supported upon a substrate, leads to a remarkable resistance to the calcination-induced anatase-to-rutile transformation. This stabilization does not appear to be specifically reliant on substrate character given its persistence for TiO2 films prepared on amorphous silica (SiO2) as well as crystalline TiO2 substrates. Instead, interface-mediated coordination of the TiO2 film with the substrate, and the inherent confinement of crystallites in two dimensions, is believed to resist polym...