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Metallic nanostructures can be utilized as heat nano-sources which can find application in different areas such as photocatalysis, nanochemistry or sensor devices. Here we show how the optical response of plasmonic structures is affected by the increase of temperature. In particular we apply a temperature dependent dielectric function model to different nanoparticles finding that the optical responses are strongly dependent on shape and aspect-ratio. The idea is that when metallic structures interact with an electromagnetic field they heat up due to Joule effect. The corresponding temperature increase modifies the optical response of the particle and thus the heating process. The key finding is that, depending on the structures geometry, absorption efficiency can either increase or decrease with temperature. Since absorption relates to thermal energy dissipation and thus to temperature increase, the mechanism leads to positive or negative loops. Consequently, not only an error would be made by neglecting temperature but it would be not even possible to know, a priori, if the error is towards higher or lower values.
Heating processes in plasmonics are essential every time the interaction with electromagnetic fields induces dissipation within metallic nanostructures. In particular the capability to predict the final temperature reached by a system (e.g. an ensemble of nanoparticles within a host medium) can be crucial when dealing with electronic, medical or chemical applications. Here we present a dispersive model of the dielectric function of a metallic medium which depends on temperature. Since temperature, in turn, depends on the intensity of the electromagnetic source and on the optical response of the medium itself, the model expresses non-linearity features. The model, which does not require any fitting parameter, can be utilized whenever the impact of temperature on the optical response of a system needs to be clarified and/ or when non-linearities might play a major role.
The ability to confine light in small volumes, associated to low background signals, is an important technological
achievement for a number of disciplines such as biology or electronics. In fact, decoupling the source position from the
sample area allows an unprecedented sensitivity which can be exploited in different systems. The most direct
implications are however related to either Surface Enhanced Raman Scattering (SERS) or Tip Enhanced Raman
Scattering (TERS). Furthermore, while the combination with super-hydrophobic patterns can overcome the typical
diffusion limit of sensors, focused surface plasmons decaying into hot electrons can be exploited to study the electronic
properties of the sample by means of a Schottky junction. Within this paper these techniques will be briefly described
and the key role played by both surface and localized plasmons will be highlighted.