Evolution of optical properties of Au thin films with thermal annealing

Gold (Au) thin films exhibit varied optical properties, ranging from metal-like behavior in percolated films to localized surface plasmons in island thin films. Additionally, thermal annealing introduces variability in particle sizes and shapes leading to optical response modification and enhancing the suitability of the film for possible sensing applications. This study investigates the evolution of optical properties in thermally annealed gold films, with a focus on the interplay between the amount of deposited material and annealing conditions. It aims to determine the range of temperatures at which annealing induces the most significant changes in optical properties and identifies the spectral ranges where these changes occur. Analysis of the complex effective dielectric function of the films helps to understand whether the film behaves like metal or like an insulator. The study focuses on three different film regimes according to the morphology as determined by the deposited mass thickness: islands films (5 nm), nearly-percolated (15 nm), and compact (25 nm). Each characteristic morphology displays distinct evolution upon thermal annealing, with different temperature ranges in which the changes are most remarkable. Overall, these findings provide valuable insights into the optical properties of gold thin films and their response to thermal annealing, showing the way for their enhanced usage in sensing purposes.