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

Anatoly Kovalev,Jose Luis Endrino,Raul Gago,Dmitry Wainstein,Vladimir Vakhrushev

doi:10.3390/coatings10030260

Abstract

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.

Highlights

It is well known that miniaturization to the nanoscale in multilayer coatings allows one to change, sharply, many of their physical properties, including electronic and optical ones
The thermal conductivity of the Al2 O3 /Ag multilayer coating can be described by a two-phase system (1 = Ag, 2 = Al2 O3 ) consisting of two repetitive nanolayers with thicknesses L1 and L2, thermal conductivities K1 and K2, and thermal resistance of a boundary between layers Rb
The anomalous reduction of thermal conductivity in nanolaminate multilayer Ag/Al2 O3 coating in comparison with bulk components is explained by the influence of confinement on plasmons and phonons’ propagation

Summary

Introduction

It is well known that miniaturization to the nanoscale in multilayer coatings (planar metamaterials) allows one to change, sharply, many of their physical properties, including electronic and optical ones. Such responses result from strong transformations in the electronic structures of the nanoscale materials, which, for example, can be reflected in shift of the binding energies of core-levels as measured by X-ray photoelectron spectroscopy (XPS) [1] or the frequency shifts of Raman modes in the so called “optical mode softening” and “acoustic mode hardening” [2]. Electronic or atomic oscillations in MIM composites can transfer or transduce external electromagnetic radiation overrunning sub-diffraction limits [4]. Spatial localization of these wave processes, electron–phonon coupling and scattering directly influence the absorption and emission of electromagnetic waves in lot of optoelectronic devices and device transport dynamics [5].

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