Tailorable Au Nanoparticles Embedded in Epitaxial TiO₂ Thin Films for Tunable Optical Properties

The unique property of plasmonic materials to localize light into deep sub-wavelength regime has greatly driven various applications in the field of photovoltaics, sensors, and photocatalysis. Here, we demonstrate the one-step growth of an oxide-metal hybrid thin film incorporating well-dispersed gold (Au) nanoparticles (NPs) with tailorable particle shape and diameters (ranging from 2 to 20 nm) embedded in highly epitaxial TiO₂ matrix, deposited using pulsed laser deposition. Incorporation of Au NPs reduces the band gap of TiO₂ and enhances light absorption in the visible regime owing to the excitation of localized surface plasmons. Optical properties, including the plasmonic response and permittivity, and photocatalytic activities of the Au-TiO₂ hybrid materials are effectively tuned as a function of the Au NP sizes. Such optical property tuning is well captured using full-field simulations and the effective medium theory for better understanding of the physical phenomena. The tailorable shape and size of Au NPs embedded in TiO₂ matrix present a novel oxide-metal hybrid material platform for optical property tuning and highly efficient plasmonic properties for future oxide-based photocatalytic sensors and devices.