Photoinduced Temperature Gradients in Sub-wavelength Plasmonic Structures: The Thermoplasmonics of Nanocones

TL;DR

This paper demonstrates how gold nanocones can generate highly localized, deep sub-wavelength thermal hot spots through resonant light concentration, advancing thermoplasmonic control at the nanoscale.

Contribution

The study introduces a theoretical model showing how nanocone geometry and environment influence extreme temperature gradients and hot spot formation.

Findings

High temperature gradients achieved at nanocone apexes.

Hot spots are tunable by nanocone size and shape.

Potential applications in nanofabrication and thermoelectrics.

Abstract

Plasmonic structures are renowned for their capability to efficiently convert light into heat at the nanoscale. However, despite the possibility to generate deep sub-wavelength electromagnetic hot spots, the formation of extremely localized thermal hot spots is an open challenge of research, simply because of the diffusive spread of heat along the whole metallic nanostructure. Here we tackle this challenge by exploiting single gold nanocones. We theoretically show how these structures can indeed realize extremely high temperature gradients within the metal, leading to deep sub-wavelength thermal hot spots, owing to their capability of concentrating light at the apex under resonant conditions even under continuous wave illumination. A three-dimensional Finite Element Method model is employed to study the electromagnetic field in the structure and subsequent thermoplasmonic behaviour, in terms of the three-dimensional temperature distribution. We show how the latter is affected by nanocone size, shape, and composition of the surrounding environment. Finally, we anticipate the use of photoinduced temperature gradients in nanocones for applications in optofluidics and thermoelectrics or for thermally induced nanofabrication.