Co-continuous porosity formation on thin oxide films: transition metal oxides (TiO2 and Nb2O5) versus SiO2

摘要

In this study the role of different types of metal alkoxides, as well as the roles of acetyl acetone (ACAC) and polyethylene glycol (PEG) on co-continuous porosity formation in thin oxide films (TiO2, Nb2O5, SiO2 and TiO2-SiO2 mixed oxide) is investigated. The films are produced by the spin coating method and the resulting morphologies are characterized from the scanning electron microscope images of the surface and of the focused ion beam machined cross-sections. Results show that the porous, co-continuous morphology forms only in transition metal oxide films, TiO2 and Nb2O5, and that it does not form in the semimetal SiO2 film. The effect of interfacial activity of ACAC modified Ti- and Nb-alkoxides together with the effect of PEG reaction with the metal oxide oligomers are found to cause co-continuous porosity formation in TiO2 and Nb2O5 films. Moreover, it appears that both of these effects are more pronounced during formation of Nb2O5 than TiO2 films.