Real-time tracking of optical and structural properties of Ag-based bimetallic nanoparticles
Résumé
The Localized Surface Plasmon resonance (LSPR) of metallic nanoparticles (NPs) is strongly dependent on their local environment and on their constituent-material dielectric functions. Thus, chemical modifications occurring at their vicinity, or directly within the NPs may be optically monitored. Moreover, Ag-based NPs may display a well-defined LSPR strongly sensitive to small variations of the surrounding. In this respect, Ag-based NPs (produced by laser vaporization) containing another reactive metal have been investigated. The first illustration deals with iron-silver NPs investigated through TEM observations, in situ optical spectroscopy and Monte Carlo simulations, leading us to conclude that iron and silver initially adopt a segregated configuration with a silver-enriched surface. During oxidation, iron likely diffuses throughout the silver shell, leading to an Ag@Fe3O4 configuration, while an inverse process may occur during annealing under a reducing atmosphere [1].
We also performed optical and environmental TEM characterizations on In-Ag NPs. Optical spectra show LSPRs in the UV range down to 310 nm for as prepared NPs. A NP deposition at elevated temperatures even results in an LSPR <300 nm. Optical and TEM characterizations indicate that In–Ag NPs most likely adopt a core–shell structure with a silver-rich alloy core and an indium shell which spontaneously oxidize upon air exposure. The metallic character of the shell can however be recovered by annealing under reducing atmosphere and tracked through LSPR shifts [2]. The restructuration and the reduction of In–Ag@In2O3 was also followed in real time by in situ HRTEM imaging in the presence of H2 at high temperature. The resulting NPs after reduction consist of a silver–indium alloy, very stable and remarkably resistant against oxidation [3].
[1] J. Ramade et al., JPCC, 2019. 123(25), p. 15693-15706.
[2] E. Cottancin et al., PCCP, 2014. 16(12), p. 5763-5773.
[3] J. Ramade et al., Nanoscale, 2017. 9(36), p. 13563-13574.