**3. Heat generation in nano-antenna**

PNAs cause an exaggerated heat produced in the metal after the excitation of the external light source, producing a side hot areas—i.e., the elevation of the temperature in a restricted region which is a mainly undesirable effect in various research namely spectroscopy, sensing, and optical signal processing. Localized heat of PNAs, in another hand, is very useful in a group of applications such as nano-engineering, cancer treatment, nano-manipulation, hot vapor generation, and catalysis [14].

The local temperature elevation of MNAs is quite low thermal radiation in the mid-to-far IR wavelength spectral region. In addition, if (the mean free path) of the substrate materials is larger than the nano-antenna size, the heat converted the volume of metal volume may be reduced [16]. It is well known that the metals in nano-size create regional temperature gradients after external light exposure, quite enough to generate subwavelength areas of super-heated water surrounding the species [17].

Photo-induced heating of nano-antennas can vary their geometry because of the metal melting. The melting process can minimize the nano-range properties so, directly nano-antennas becomes nano-spheres if temperature increment is established. The variation of the morphology may affect on the antennas' spectral response and can decrease the near-field generation. The melting temperature of metal can take place at higher surface melting temperatures of nano-antennas [18, 19].

The pioneering author is previously shown that the structures of hybrid plasmonic have good selectivity and huge improvement of the near-field intensity due to effective trapping with re-cycling of photons in near IR and visible in photonic modes [20–22].

The IR thermal radiation could be produced and enhanced by the selection of the optimum parameters of materials and the dimensions regarding the geometry on a range at or under the emitted thermal peak resonance wavelength [14]. The convective and radiative cooling represent other ways to diffuse heat intensity from nano-sizes, where became effective if the thermal conductivity is disturbed because of the particles in the nano-size [23].
