Anomalous Heat Transport in Nanolaminate Metal/Oxide Multilayer Coatings: Plasmon and Phonon Excitations

In this work, the anomalous reduction in the thermal conduction observed for nanolaminate metal-dielectric multilayers has been extended to the case of oxides. For this purpose, Ag/Al2O3 coatings were produced with different layer thicknesses (from 1 to 5 nm for Ag and 8 to 40 nm for Al2O3) and numbers of stacks. It was found that the thermal conduction is significantly lower in such metal-oxide nanolaminates compared to the bulk oxide. Such anomalous behaviour is explained by the influence of plasmon and phonon propagation confinement in nanolayers and at the interfaces. To this end, the characteristics of the different types of acoustic and optical phonon waves propagating in the multilayer coating have been studied. In particular, the electronic structures of the different layers and their influences on the plasmon resonance are investigated as a function of the multilayer design. The plasmon-polariton mechanism of energy transfer through oxide-metal and metal-oxide interfaces is discussed.