Optimization of Plasmonic Heating by Gold Nanospheres and Nanoshells

Abstract

Gold nanoparticles have strong and tunable absorption peaks in their optical extinction spectra, a phenomenon that has recently been exploited to generate localized heating in the vicinity of these particles. However the optimum particle geometry and illumination regime to maximize these effects appears not to have been previously examined in any detail. Here we show that the interplay between the particles' absorption cross-sections, volume and surface area lead to there being specific conditions that can maximize particle temperature and surface heat flux. Optical absorption efficiencies were calculated from the formulation of Mie, and radiative, convective and conductive heat transfer models used to model the thermal performance of particles in different situations. Two technologically relevant scenarios for illumination, namely irradiation by sunlight at 800 W/m 2 , and by a monochromatic laser source of 50 kW/m 2 tuned to the peak absorption wavelength, were considered. For irradiation by sunlight, the resultant heat flux is optimized for an 80 nm diameter nanoshell with an aspect ratio of 0.800, while for irradiation by laser the maximum heat flux is found for 50 nm nanoshells, with an aspect ratio of 0.9. The optimum for solid nanospheres is at 110 nm for sunlight and 80 nm in monochromatic illumination tuned to the absorption maximum.2

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