Reduction of Plasmon Damping in Aluminum Nanoparticles with Rapid Thermal Annealing
Abstract
Aluminum is now widely regarded as a promising plasmonic material, especially in the ultraviolet spectrum. We propose rapid thermal annealing (RTA) as a simple method to significantly decrease the amount of intrinsic losses in aluminum nanoparticles. We study the structural and optical properties of aluminum nanoparticles before and after RTA at different temperatures. Our results unveil how RTA affects the plasmonic properties of Al nanoparticles through the competition between the reduction of the number of grain boundaries and oxidation. If RTA is performed below a threshold temperature of 400 °C, then oxidation is extremely weak and the plasmonic resonances sustained by Al nanoparticles are blue-shifted with a decrease in their full width at half-maximum. This improvement is due to a diminution of the number of grain boundaries inside the metal core. Hence, RTA appears as a simple, cost-effective, and up-scalable technique to improve the plasmonic properties of aluminum. In contrast, above the threshold temperature, oxidation becomes predominant, resulting in a detrimental effect on the plasmon resonance. This effect should be taken into account in any industrial process involving heated Al nanoparticles.