Observation of nanoscale cooling effects by substrates and the surrounding media for single gold nanoparticles under CW-laser illumination.

Understanding the nanoscale heating-induced local thermal response is important but hampered by lack of information on temperatures at such small scales. This paper reports laser-induced heating and thermal equilibration of metal nanoparticles supported on different substrates and immersed in several media. We use single-particle spectroscopy to monitor nanoparticle temperature rises due to laser excitation. Because of changes in the refractive index of the surrounding medium, the scattering spectrum of the gold nanoparticles undergoes a shift that is related to the temperature of the system. We find that the temperature increase depends on both the surrounding medium and the supporting substrate. We furthermore model the nanoparticle temperature using a simplified 1-D heat conduction model with an effective thermal conductivity that takes both substrate and environment into account. The results from this model are also compared to a more detailed 2-D heat transfer analysis. The results presented here are quite new and important to many plasmonic nanoparticle applications where the strong absorption cross section of the nanoparticles leads to a significant temperature rise. In particular, the current work introduces an analysis that can be easily implemented to model the temperature of a nanoparticle supported on a substrate, as is the case in many single-particle measurements.