Time-dependent plasmonic response of gold nanoparticles embedded in doped strontium titanate films for high-temperature gas sensing

Conducting oxide films on optical fibers offer significant advantages as sensing layers in high temperature, harsh environments (e.g., solid oxide fuel cells or power plant boiler systems), where many traditional sensors degrade rapidly. In particular, oxides exhibiting the perovskite crystal structure are highly stable under substitution of the constituent atoms as well as under high concentrations of cation and oxygen vacancies. Strontium titanate (STO), for example, maintains the perovskite crystal structure under high dopant concentrations both on the “A-site” (Sr substitution) and “Bsite” (Ti substitution). As a result, STO and other perovskite oxides form a rich family of materials whose unique electrical, magnetic, and optical properties can be continuously tuned based upon the concentrations of the constituent atoms. Structural stability, in conjunction with an interconnected vacancy defect chemistry and optical as well as electrical properties, suggests great promise for this material system in the realm of harsh environment sensing. In this work, donor-doped strontium titanate films containing gold nanoparticles are investigated for gas sensing characteristics at high temperature (up to 680°C) under oxidizing and reducing conditions. Using time resolved, in-situ optical transmission measurements in conjunction with room-temperature ex-situ measurements of planar films, the relationship between the Au localized surface plasmon resonance (LSPR) response in the visible and oxide free-carrier based response in NIR is investigated.