Photothermal behavior for two-dimensional nanoparticle ensembles: optical coupling and thermal accumulation effects
Light-assisted micro-nanoscale temperature control in complex nanoparticle network attracts lots of research interests. Many efforts have been put on the optical properties of the nanoparticle networks and only a few investigations on its light-induced thermal behavior was reported. We consider two-dimensional (2D) square-lattice nanoparticle ensemble made of typical metal Ag with a radius of 5 nm. The effect of complex optical coupling and thermal accumulation on the light-induced thermal behavior in plasmonic resonance frequency (around 383 nm) is analyzed by means of the Green\textquotesingle s function approach. Regime borders of both optical coupling and thermal accumulation effects on the photothermal behavior of 2D square-lattice nanoparticle ensemble are figured out clearly and quantitatively. A dimensionless parameter $\varphi$ is defined as the ratio of full temperature increase to that without considering the optical coupling or thermal accumulation to quantify the optical coupling and thermal accumulation effects on photothermal behavior. The more compact the nanoparticle ensemble is, the stronger the optical coupling on thermal behavior is. When the lattice spacing increases to tens of nanoparticle radius, the optical coupling becomes insignificant. When $\varphi \approx 1$ (lattice spacing increases to hundreds of nanoparticle radius), the thermal accumulation effects are weak and can be neglected safely. The polarization-dependent distribution of temperature increase of nanoparticles is observed only in the compact nanoparticle ensemble, while for dilute ensemble, such polarization-dependent temperature increase distribution can not be observed anymore. This work may help for the understanding of the light-induced thermal transport in the 2D particle ensemble.