Enhancing the Extinction Efficiency and Plasmonic Response of Bimetallic Nanoparticles of Au-Ag in Robust Thin Film Sensing Platforms

The extinction efficiency of noble metal nanoparticles (NPs), namely gold (Au) and silver (Ag), are dependent on their size and surrounding dielectric. Exploiting the Localized Surface Plasmon Resonance (LSPR) phenomenon, the composition and structure of the NPs might be tailored to achieve a configuration that optimizes their response (sensitivity) to environmental changes. This can be done by preparing a bimetallic system, benefiting from the chemical stability of Au NPs and the higher scattering efficiency of Ag NPs. To enhance the LSPR sensing robustness, incorporating solid supports in the form of nanocomposite thin films is a suitable alternative. In this context, the NPs composed of gold (Au), silver (Ag), and their mixture in bimetallic Au-Ag NPs, were grown in a titanium dioxide (TiO2) matrix using reactive DC magnetron sputtering. Thermal treatment at different temperatures (up to 700 degrees C) tuned the LSPR response of the films and, consequently, their sensitivity. Notably, the bimetallic film with Au/Ag atomic ratio 1 exhibited the highest refractive index sensitivity (RIS), with a value of 181 nm/RIU, almost one order of magnitude higher than monometallic Au-TiO2. The nanostructural analysis revealed a wide NP size distribution of bimetallic NPs with an average size of 31 nm, covering about 20% of the overall surface area. These findings underscore the significant potential of bimetallic film systems, namely AuAg-TiO2, in LSPR sensing enhancement.

Automated summary

The extinction efficiency of noble metal nanoparticles, such as gold and silver, depends on their size and the dielectric surrounding them. By exploiting the Localized Surface Plasmon Resonance (LSPR) phenomenon, the composition and structure of these nanoparticles can be tailored to optimize their sensitivity to environmental changes. Incorporating these nanoparticles into solid support in the form of nanocomposite thin films enhances the robustness of LSPR sensing. In this study, bimetallic films composed of gold, silver, and their mixture in a titanium dioxide matrix were grown using reactive DC magnetron sputtering. The LSPR response and sensitivity of the films were tunable by thermal treatment at different temperatures. The bimetallic film with an Au/Ag atomic ratio of 1 exhibited the highest refractive index sensitivity, showcasing the potential of bimetallic film systems in enhancing LSPR sensing.