Plasmonics of Au/Polymer Core/Shell Nanocomposites for Thermoresponsive Hybrid Metasurfaces

We investigate the temperature-dependent optical response of ordered lattices of non-interacting gold-core/poly(N-isopropylacrylamide)-shell nanoparticles (NPs), a system with proven photothermal and sensing capabilities. For the first time on this system, we exploited in situ Spectroscopic Ellipsometry (SE) to determine the complex, temperature-dependent optical properties of the lattice, a key piece of information which, however, is often overlooked. In doing so, we take full advantage of large-scale colloidal self-assembly, which makes NP lattices accessible to conventional SE. A quantitative interpretation of the SE data is obtained through an effective model based on the actual characteristics of the NPs and their dielectric environment. The model allows to estimate temperature-dependent morphological parameters, such as the distance between the gold cores and the substrate, also yielding the complex permittivity of the plasmonic NP lattice. Thus, by combining the high sensitivity of SE with proper m...