Quantitative Analysis of the Shape Effect of Thermoplasmonics in Gold Nanostructures.

The shape effect of thermoplasmonic properties of Au nanostructures remains largely unexplored. Herein, we report a systematic investigation on the photothermal effects of Au nanoparticles (NPs) of different shapes: nanosphere, nanocube, nanorod, nanostar, and nanobipyramid. The Joule (Jo) number (absorption cross section normalized by the particulate volume) is utilized for quantitatively assessing the photothermal properties of these different shaped Au NPs. It is shown that the Jo number of Au NPs greatly varies with the geometric shape and localized surface plasmon resonance (LSPR) wavelength. Specifically, the Jo number decreases with the red-shifting of the LSPR wavelength in these Au NPs, and the Au NPs of sharp structural features such as Au nanorod, nanostar and nanobipyramid have a much larger Jo number, indicative of their exceptional light-to-heat conversion ability. We further demonstrate the close correlation of the Jo number of Au NPs of different shapes with their optical absorption power density.