In-situ annealing transmission electron microscopy of plasmonic thin films composed of bimetallic Au-Ag nanoparticles dispersed in a TiO2 matrix

This work was focused on the characterization of plasmonic thin films composed of Au-Ag nanoparticles dispersed in a TiO2 dielectric matrix in comparison with the monometallic Au/TiO2 plasmonic system. The thin films were prepared by reactive DC magnetron sputtering, followed by thermal annealing at different temperatures to promote nanoparticles' growth. Thermal treatment from 400 degrees C induced the appearance of Localized Surface Plasmon Resonances (LSPRs) in both Au/TiO2 and Au-Ag/TiO2 thin films. The latter showed a wider LSPR response, due to the broader size distribution of nanoparticles (analyzed by transmission electron microscopy, TEM). Further nanometer-scale chemical analysis allowed to confirm the presence of Au-Ag bimetallic nanoparticles. To thoroughly study the influence of the annealing treatment on the nanoparticles' growth, Au-Ag/TiO2 was also deposited on heating TEM nano-chips for in-situ annealing experiments. The formation of silver aggregates was found in the sample as-deposited, with these precipitates dissolving in the matrix with the increase of annealing temperature up to 200 degrees C. For higher temperatures, nanoparticles' real-time growth was observed, together with the crystallization of the TiO2 matrix above 550 degrees C. Besides, the plasmonic Au-Ag/TiO2 thin films revealed LSPR sensitivity when in contact with different dielectric media, highlighting their potential as refractive index sensors.

Automated summary

This study focused on the characterization of plasmonic thin films composed of Au-Ag nanoparticles dispersed in a TiO2 dielectric matrix and compared them with the monometallic Au/TiO2 plasmonic system. Thermal treatment induced Localized Surface Plasmon Resonances (LSPRs) in both systems, with Au-Ag/TiO2 showing a wider LSPR response due to the broader size distribution of nanoparticles. Additionally, the study demonstrated the potential of plasmonic Au-Ag/TiO2 thin films as refractive index sensors when in contact with different dielectric media.