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Thin films of gold (Au) have found use in various optoelectronic applications due to their unique optical properties. Depending on the film morphology, the optical response can display localized surface plasmon resonance related to isolated metal clusters and a Drude-like response emerging from a connected metal network. Therefore, Au films, especially those with nearly percolated morphology display a very broad optical response that can be drastically varied by control of the fabrication conditions or post-deposition treatments. In this study, we investigate the optical and morphological changes observed in thin Au films subjected to thermal annealing as potential building units for optical-based thermal sensors. Three different film morphologies (island film, nearly percolated film, and compact film) are obtained by controlling the amount of deposited metal. The evolution of morphological properties of these three types of films upon thermal annealing follows different mechanisms, resulting in enhanced optical changes in different spectral regions. In addition, we show that the incorporation of nearly percolated films in multilayer interference coatings can significantly boost their potential as irreversible temperature sensors. Overall, we show that the unique morphological changes induced by annealing combined with interference effects hold great promise for thermal sensing.
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