Optimization of plasmonic heating by gold nanospheres and nanoshells.

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 were used to model the thermal performance of particles in different situations. Two technologically relevant scenarios for illumination, namely, irradiation by sunlight at 800 W/m2 and by a monochromatic laser source of 50 kW/m2 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 0.8, while for irradiation by laser the maximum heat flux is found for 50 nm nanoshells, with an aspect ratio of 0.9.