Optimization of nanocomposite Au/TiO₂ thin films towards LSPR optical-sensing

"Available online 20 September 2017."
Nanomaterials based on Localized Surface Plasmon Resonance (LSPR) phenomena are revealing to be an important solution for several applications, namely those of optical biosensing. The main reasons are mostly related to their high sensitivity, with label-free detection, and to the simplified optical systems that can be implemented. For the present work, the optical sensing capabilities were tailored by optimizing LSPR absorption bands of nanocomposite Au/TiO 2 thin films. These were grown by reactive DC magnetron sputtering. The main deposition parameters changed were the number of Au pellets placed in the Ti target, the deposition time, and DC current applied to the Ti-Au target. Furthermore, the Au NPs clustering, a key feature to have biosensing responses, was induced by several post-deposition in-air annealing treatments at different temperatures, and investigated via SEM analysis. Results showed that the Au/TiO2 thin films with a relatively low thickness (∼100 nm), revealing concentrations of Au close to 13 at.%, and annealed at temperatures above 600 °C, had the most well-defined LSPR absorption band and thus, the most promising characteristics to be explored as optical sensors. The NPs formation studies revealed an incomplete aggregation at 300 and 500 ⁰C and well-defined spheroidal NPs for higher temperatures. Plasma treatment with Ar led to a gradual blue-shift of the LSPR absorption band, which demonstrates the sensitivity of the films to changes in the dielectric environment surrounding the NPs (essential for optical sensing applications) and the exposure of the Au nanoparticles (crucial for a higher sensitivity).
This research was sponsored by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2013 and FCT Project 9471 - Reforçar a Investigação, o Desenvolvimento Tecnológico e a Inovação (Projeto 9471-RIDTI), comparticipado pelo Fundo Comunitário Europeu FEDER and with reference PTDC/FIS-NAN/1154/2014. Joel Borges also acknowledges FCT for his Post-Doc Grant SFRH/BPD/117010/2016 and Marco S. Rodrigues acknowledges his PhD-Grant from FCT with reference SFRH/BD/118684/2016. Paulo Pedrosa acknowledges the support by the region of Franche-Comté in cooperation with the Labex ACTION program (contract ANR-11-LABX-01-01) and also the MIMENTO Platform of the RENATECH network.
info:eu-repo/semantics/publishedVersion