In-situ evolution of temperature dependent attenuation coefficients of plasmonic silver nanostructures

With a growing interest in high temperature applications of plasmonic metal nanostructures, the morphological modulation and the evolution of optical constants of these plasmonic nanostructures have become important both from fundamental growth dynamics point of view and from optical applications viewpoint. In the present investigation, set of plasmonic silver nanostructures (thickness range 5–25 nm) have been grown by e-beam evaporation technique with varying deposition time. They have been subjected to temperature dependent in-situ spectroscopic ellipsometry measurements for optical analysis at room temperatures (25 °C) and at various elevated temperatures (80 °C–530 °C). The evolutions of optical and surface morphological parameters of these Ag nanostructures as a function of thicknesses have also been investigated. The optical attenuation coefficients (400–700 nm) of these Ag nanostructures are found to evolve in a different fashion depending upon thickness controlled nano-morphology. For low thickness films (5–16 nm), which consists of discrete Ag grains, the light attenuation coefficient initially decreases up to ∼130 °C and subsequently increases with increasing temperature up to 300 °C. This is due to the competition of two counteracting phenomena of reduction of electron-grain boundary scattering and increase in LSPR absorption effect due to temperature induced grain expansion. In contrast, for the relatively thicker films (>16 nm), the optical attenuation coefficient was found to decrease with increasing temperature due to dominance of former effect over later which is caused by larger grain size and network-like nano-morphology. The investigated temperature dependent evolution of optical properties is relevant in studies of physical processes at elevated temperatures and also for accurate modeling of plasmonic devices in high-temperature applications.