Environmentally Tight TiO₂–SiO₂ Porous 1D‐Photonic Structures

Abstract Although thin film porosity is the basis of many optical sensors, it can be deleterious for a stable optical behavior of passive optical elements due to the condensation of water and other vapors in their pores. This paper proposes a new strategy for the magnetron sputtering (MS) fabrication of environmentally tight SiO₂–TiO₂ porous multilayers. Thin films of these two oxides deposited in an oblique angle configuration (MS‐OAD) present a nanocolumnar and highly porous nanostructure and, as a consequence, experience significant changes in their optical properties when exposed to water vapor. Similarly, the optical properties of Bragg reflectors and Bragg microcavities made of the stacking of porous and compact SiO₂ and TiO₂ thin films experience reversible changes when these 1D‐photonic structures are exposed to water pressure. A key finding of this work is that a very thin capping layer of SiO₂ deposited on the surface of porous SiO₂ films in the stack, at the interlayer between the two oxides, efficiently seals the pores making the photonic structures environmentally tight. This capping layer approach is a useful strategy to incorporate porosity as an additional parameter to design the optical behavior of planar photonic structures while preserving optical and environmental stability.