  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.
