Heat generation by optically and thermally interacting aggregates of gold nanoparticlesunder illumination

Abstract

The generation of heat by clusters and arrays of gold nanoparticles under illumination isinvestigated theoretically. The nanoparticles are embedded in a homogeneous dielectric medium,and the finite thermal resistance at the interface between the nanoparticle and the medium istaken into account. An analytic solution is derived for the case of a single nanoparticle. TheT-matrix method is used to calculate the energy absorption efficiency of groups ofnanoparticles, taking into account their optical interactions. Heat transfer equations aredeveloped that take into account thermal interactions between nanoparticles. Theequations are solved numerically using the finite element software COMSOL. Periodicboundary conditions are applied to treat the thermal interactions between thenanoparticles for arrays of nanoparticles. Results are presented for illumination by astandard xenon flash lamp. The thermal resistance at the nanoparticle–medium interface isfound to strongly influence the nanoparticle temperature, but to have negligible influenceon the temperature of the dielectric medium after a few tens of nanoseconds of exposure tothe flash lamp pulse. Optical interactions are found to be important if particle centres areseparated by about twice the particle diameter or less. Thermal interactions betweennanoparticles via the medium are found to be the dominant factor in determiningthe temperature increase in the dielectric medium. The maximum temperatureincrease is proportional to the volume fraction of the nanoparticles in the medium.