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The decisive experimental evidence of enhanced heat conduction driven by surface phonon polaritons (SPhPs) has been recently demonstrated along polar nanofilms. However, a proper quantitative interpretation remains to be fully established. In this work, we provide a consistent theoretical explanation of the measured thermal conductivities of polar nanofilms, based on a coupled Boltzmann transport equation and heat diffusion equation for describing the dynamics of SPhPs and phonons, respectively. This formalism enables to separately quantify the SPhP and phonon contributions to the in-plane heat transport and shows the overestimation of the SPhP thermal conductivity predicted by previous empirical model for predominant boundary scattering. This study, thus, promotes the understanding of the observed thermal conductivity enhancement driven by SPhPs, as a novel heat conduction channel for heat dissipation applications in nanoelectronics and optoelectronics. [ABSTRACT FROM AUTHOR]

The axial thermal conductance of a cylindrical cavity supporting the propagation of hybridized guided modes along its interface with SiO 2 is quantified and analyzed as a function of its radius and mean temperature. In contrast to the well-known radial thermal conductance, we show that the axial one increases with the cavity radius up to 1 cm, in which it takes its maximum that increases with temperature. A maximum thermal conductance of 289.4 nW·K−1 is found at 500 K, which is more than 3 orders of magnitude higher than the corresponding one found in the far-field regime. This top polariton thermal conductance along the cavity is comparable to the radiative one predicted by Planck's theory and thus represents a fundamental heat transport channel driven by hybridized guided modes able to amplify heat currents along a macroscale cylindrical cavity. [ABSTRACT FROM AUTHOR]

The effective thermal conductivity of a layered system due to the propagation of surface phonon-polaritons is studied. We analytically demonstrate that the thermal conductivity of a set of nanolayers can be described as one of a single layer with an effective permittivity, which does not ordinarily appear in nature and depends on the permittivities and thicknesses of the individual components. For a two-layer system of SiO2 and BaF2 surrounded by air, it is shown that: (i) the propagation length of surfaces phonon-polaritons can be as high as 3.3 cm for a 200 nm-thick system. (ii) The thermal conductivity of the system with total thickness of 50 nm is 3.4W/m·K, which is twice that of a single layer of SiO2, at 500 K. Higher values are found for higher temperatures and thinner layers. The results show that an ensemble of layers provides more channels than a single layer for the propagation of surface phonon-polaritons and therefore for the enhancement of the thermal conductivity of common polar materials. [ABSTRACT FROM AUTHOR]

The reflection and transmission coefficients of a surface phonon-polariton propagating along the surface of a thin film of SiO2 and crossing the interface of two dielectric media are analytically determined. Based on the expansion of the electrical and magnetic fields in terms of normal modes, explicit expressions for the reflectivity and transmissivity of the radiation fields generated at the dielectric interface are also obtained. Symmetrical and simple Fresnel-like formulas are derived for nanofilms. For the dielectric interfaces of air/BaF2 and air/Al2O2, it is shown that: (i) The polariton reflectivity (transmissivity) decreases (increases) as the film thickness increases, while its radiation equivalent follows the opposite behavior, (ii) In the polariton and radiation fields, the transmissivity is significantly more sensitive than the reflectivity to the changes on the permittivity mismatch of the dielectric interface. For a 143-nm-thick film, the polariton transmissivity (reflectivity) changes 13.2% (1.9%), when this mismatch varies by 50%. (iii) The reflectivity and transmissivity of the radiation fields are smaller than their polariton counterparts, which together account for around 82% of the total energy. The proposed formalism accurately fulfills the principle of conservation of energy for describing the reflection and transmission of both the polariton and radiation fields generated at a dielectric interface. [ABSTRACT FROM AUTHOR]

Heat transport guided by the combined dynamics of surface phonon-polaritons (SPhPs) and phonons propagating in a polar nanowire is theoretically modeled and analyzed. This is achieved by solving numerically and analytically the Boltzmann transport equation for SPhPs and the Fourier's heat diffusion equation for phonons. An explicit expression for the SPhP thermal conductance is derived and its predictions are found to be in excellent agreement with its numerical counterparts obtained for a SiN nanowire at different lengths and temperatures. It is shown that the SPhP heat transport is characterized by two fingerprints: (i) The characteristic quantum of SPhP thermal conductance independent of the material properties. This quantization appears in SiN nanowires shorter than 1 μ m supporting the ballistic propagation of SPhPs. (ii) The deviation of the temperature profile from its typical linear behavior predicted by the Fourier's law in absence of heat sources. For a 150 μ m-long SiN nanowire maintaining a quasi-ballistic SPhP propagation, this deviation can be as large as 1 K, which is measurable by the current state-of-the-art infrared thermometers. [ABSTRACT FROM AUTHOR]

Surface phonon-polaritons (SPhPs) are evanescent electromagnetic waves that can propagate distances orders of magnitude longer than the typical mean free paths of phonons and electrons. Therefore, they are expected to be powerful heat carriers capable of significantly enhancing the in-plane thermal conductance of polar nanostructures. In this work, we show that a SiO 2 /Si (10 μ m thick)/SiO 2 layered structure efficiently enhances the SPhP heat transport, such that its in-plane thermal conductance is ten times higher than the corresponding one of a single SiO 2 film, due to the coupling of SPhPs propagating along both of its polar SiO 2 nanolayers. The obtained results thus show that the proposed three-layer structure can outperform the in-plane thermal performance of a single suspended film while improving significantly its mechanical stability. [ABSTRACT FROM AUTHOR]