Plasmon Thermal Conductance and Thermal Conductivity of Metallic Nanofilms

Abstract

The thermal conductance and thermal conductivity of surface plasmon polaritons propagating along a metallic nanofilm deposited on a substrate are quantified and analyzed, as functions of the film thick-ness, length, and temperature. 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 characterized by symmetric and antisymmetric spatial distributions of the magnetic field. For a gold nanofilm deposited on a silicon substrate, both modes have compara-ble contributions of the plasmon thermal conductance, which takes higher values for hotter and/or longer nanofilms and saturates for films thicker than 50 nm. This saturation arises from the decoupling of the plasmon modes, the transition of which to a coupled state for thinner films maximizes the plasmon ther-mal conductivity. 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 W m-1 K-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 increases significantly with the film length and temperature and it could therefore be useful to improve the heat dissipation along metallic nanofilms.