Elucidating thermal effects in plasmonic metal nanostructures: a tutorial review

Metallic nanostructures display a unique optical property termed as localised surface plasmonic resonance due to the abundance of free electrons in the conduction band. When the frequency of oscillation of these electrons, induced by suitable irradiation, matches that of the electromagnetic field, it results in significant increase in absorbance and scattering of light. The resonance also incurs collision between the electrons and atoms present in the lattice causing "Joule's heating". This leads to plasmonic heating of nanostructures-controlled by adjusting the type of the source of external irradiation. Although thermal heat generation was regarded as a demerit earlier, the recent developments in the branch of nanotechnology have been able to improvise the heat from plasmonic nanostructures as a reliant source of renewable energy and in many other useful applications. Thus, this review highlights the plasmonic features displayed by the metallic nanostructures, different modes used for their synthesis and assays to elucidate the physics behind generation of heat by these nanostructures. Apart from this, their targeted applications as the nano-sources of heat in various fields of science such as photothermal therapy, in soft matter, for enhanced photocatalysis, in nanomedicine, nano-surgery, as absorbents for pollutant degradation are comprehensively delineated.