Atomic Layer Deposition of Titania in Ordered Mesoporous Cerium Zirconium Oxide Thin Films: A Case Study

A strategy is presented to deposit defined layers of TiO2 onto the pore surface within ordered mesoporous, crystalline CeO2-ZrO2 thin films using atomic layer deposition (ALD). As structure-directing agent, a special diblock copolymer, poly­(isobutylene)-block-poly­(ethylene oxide), was used, resulting in a three-dimensional arrangement of spherical pores with diameter around 13 nm. High resolution transmission electron microscopy investigations evidence the presence of anatase TiO2 coatings within the mesopores, while ellipsometric porosimetry studies together with time-of-flight secondary-ion mass spectrometry depth profiles indicate the deposition inside the mesopores up to 50 ALD cycles. Afterward, the interconnecting channels between the mesopores are filled completely prohibiting further transport of the gaseous TiO2 precursor into the ordered structure of mesopores and hence, limit the layer growth on the surfaces of the pores. Therefore, the size of the mesopores and their connections are decisive when growing transition-metal oxide layers on the surface of porous substrates and need to be considered for future depositions using ALD. The hybrid TiO2/CeO2-ZrO2 materials are studied by several complementary analytical techniques, to validate the deposition process and also the applicability of these techniques for such materials in general