Abstract

The thermal conductance and thermal conductivity of surface plasmon-polaritons propagating along a metallic nanofilm deposited on a substrate are quantified and analysed, as functions of the film thickness, length, and temperature (Fig. 1(a)). This is done by analytically solving the dispersion relation of plasmons for their wave vectors and propagation length. It is shown that the plasmon energy transport along the film interfaces is driven by two modes, whose propagation is strongly determined by the permittivity of each of the two media surrounding the nanofilm. For a gold nanofilm deposited on a silicon substrate, both modes have comparable contributions of the plasmon thermal conductance, which takes higher values for hotter and/or larger nanofilms and saturates for films thicker than 50 nm. This saturation arises from the decoupling of the plasmon modes, whose transition to a coupled state for thinner films, maximizes the plasmon thermal conductivity (Fig. 1(b)). For a 1-cm-long gold nanofilm at 300 K, the maximum thermal conductivity appears for a thickness of 10 nm and takes the value of 15 Wm^-1K^-1, which is about 25% of its electron counterpart. As a result of the huge propagation distance (> 1 cm) of plasmons, this plasmon thermal conductivity significantly increases with the film length and temperature, and it could therefore be useful to improve the heat dissipation along metallic nanofilms.

© 2023 IEEE