Localization of Temperature Using Plasmonic Hot Spots in Metal Nanostructures: The Nano-Optical Antenna Approach and Fano Effect

TL;DR

This paper demonstrates how to achieve localized heating at the nanoscale using plasmonic hot spots and interference effects in metal nanostructures, enhancing thermal control for applications like catalysis and energy conversion.

Contribution

It introduces a novel approach combining nano-optical antennas and Fano effects to improve temperature localization and heating efficiency in plasmonic nanostructures.

Findings

Temperature can be localized in hot spots within nanoparticle assemblies.

Fano effect enhances energy dissipation in nanorod-based assemblies.

Nanorod hot spots outperform single nanoparticles and simple trimers.

Abstract

It is challenging to strongly localize temperature in small volumes because heat transfer is a diffusive process. Here we show how to overcome this limitation using electrodynamic hot spots and interference effects in the regime of continuous-wave (CW) excitation. We introduce a set of figures of merit for the localization of temperature and for the efficiency of the plasmonic photo-thermal effect. Our calculations show that the temperature localization in a trimer nanoparticle assembly is a complex function of the geometry and sizes. Large nanoparticles in the trimer play the role of the nano-optical antenna whereas the small nanoparticle in the plasmonic hot spot acts as a nano-heater. Under the peculiar conditions, the temperature increase inside a nanoparticle trimer can be localized in a hot spot region at the small heater nanoparticle and, in this way, a thermal hot spot can be realized. However, the overall power efficiency of temperature generation in this trimer is much smaller than that of a single nanoparticle. We can overcome the latter disadvantage by using a trimer with a nanorod. In the trimer assembly composed of a nanorod and two spherical nanoparticles, we observe a strong plasmonic Fano effect that leads to the concertation of optical energy dissipation in the small heater nanorod. Therefore, the power-absorption efficiency of temperature generation in the nanorod-based assembly greatly increases due to the strong plasmonic Fano effect. The Fano heater incorporating a small nanorod in the hot spot has obviously the best performance compared to both single nanocrystals and a nanoparticle trimer. The principles of heat localization described here can be potentially used for thermal photo-catalysis, energy conversion and bio-related applications.