Thermal Plasmonic Metasurfaces

Licentiatavhandling, 2013

Plasmonic materials can form viable optical absorbers that offer new possibilities for device designs as they potentially have large optical cross-sections with readily tuned spectral positions and widths. Applications for such materials include heat generation via optical absorption. While a plethora of practical and theoretical studies address the local temperatures around plasmonic metal nanoparticles illuminated with highly intense light, few studies consider the macroscopic heating arising from the illumination of such particles. This thesis addresses macroscopic thermal effects arising from the relaxation of plasmonic excitations in supported metal nanoparticles illuminated with low intensity white light. It introduces a non-invasive procedure to quantify the thermal energy delivered to the support by an arbitrary photothermal layer by the use of a thermal camera. This procedure is initially applied to quantify the heat delivered by arrays of circular and elliptical plasmonic metal nanoparticles of gold and nickel. The results from these measurements show strong correlation between the generated heat and the optical absorption of the respective array. Nickel ellipses are the most effective heat generators of the investigated plasmonic arrays. The generated heat from plasmonic nanoparticles is shown to greatly surpass that of a carbon thin film reference if normalized to active surface area. Furthermore, integrated structures consisting of glass support and arrays of circular gold disks are found to generate different amounts of heat depending on the direction of the incident light. Addition of a second and third disk on top of the original disk with intermediate spacer layers changes sign on the direction of incident light for which maximum heat is generated. In a broader perspective these results contribute to the understanding of how structural manipulation on the nano-scale translates to thermal management on the macro-scale.