Nanocarving of Titania as a Diffusion‐Driven Morphological Instability

Abstract

Under strongly reducing conditions at high temperatures titania develops a specific surface morphology, comprising a regular array of fibers with a diameter in the sub‐micrometer range. By a chemical diffusion experiment in a defined oxygen potential gradient it is shown that this surface structuring is caused by a diffusion‐driven morphological instability of an advancing reaction front (surface). The kinetics of the process is analyzed in terms of linear transport equations. The conditions for the occurrence of the surface instability are discussed and the required materials properties are analyzed. The observed surface structuring is not restricted to titania, rather it has to occur in all nonstoichiometric compounds with predominant cation mobility.

Oxidation kinetics of nitrogen doped TiO2−δ thin films

“…Alternatively (case ii), re-oxidation of oxygen deficient TiO 2Àd could be due to an inward flux of holes and an outward flux of titanium interstitials Ti I . For the latter case, evidence has been reported in the literature derived from the observation of the formation of new surface morphologies upon reduction of oxidized TiO 2 39 and upon oxidation of reduced TiO 2 . 40,41 The local electroneutrality requires the coupling of the fluxes in the oxidized region according to…”