Mid-IR photothermal measurement of substantial heat transport by surface waves of polar amorphous films supported on silicon

Abstract

We present measurements of significant thermal diffusivity by surface electromagnetic waves of an ultra-thin polar and amorphous dielectric film deposited on silicon (Si). We used a photothermal-beam-deflection technique with a modulated mid-infrared heating source to excite and launch surface electromagnetic waves onto the surface of an amorphous silicon carbide (a-SiC) film deposited on Si and generate periodic temperature and refractive index gradients above the sample surface. These gradients are capable of periodically deflecting a probe beam, passing very close to the surface, at the modulation frequency of the heating beam. We have fitted the measured probe beam deflection to an analytical model for the mirage effect that takes into account the thermal anisotropy of the measured sample to infer the contribution of the surface electromagnetic waves of the a-SiC film to thermal diffusivity in the plane of the sample under study. We found that reducing the thickness of the a-SiC film promotes the interaction between the surface electromagnetic waves propagating on either side of the a-SiC film, which significantly enhances thermal diffusivity in the plane of the measured sample. We also found that in-plane thermal diffusivity by surface electromagnetic waves on an amorphous silicon carbide film a few nanometers thick is several orders of magnitude greater than thermal diffusivity by phonons in silicon. We believe that the results obtained provide a better understanding of the physics of electromagnetic waves confined to solid surfaces.

Transition from surface phonon-polariton to surface phonon–plasmon-polariton by thermal injection of free carriers

“…Over the past few decades, energy transfer by surface electromagnetic waves has emerged as cutting-edge research to exploit the sub-diffraction confinement and guidance of substantial energy in low-dimensional systems [1][2][3][4][5][6][7]. Surface plasmon-polaritons (SPPs), which are surface electromagnetic waves resulting from the coupling between an incoming * Author to whom any correspondence should be addressed.…”

“…electric field and the electric field associated with the collective oscillation of free charges, have attracted a great deal of attention [8][9][10][11][12], but have proven to be of little interest for energy transport due to their rapid attenuation and short mean free path [13,14]. In contrast, surface phonon-polaritons (SPhPs), which are surface electromagnetic waves resulting from the coupling between an incoming electric field and the electric field associated with optical phonon modes in polar materials, are low-loss and suitable for conducting substantial energy in low-dimensional systems [6,[15][16][17][18][19][20][21][22].…”

Surface Phonon-Polariton Heat Capacity of Polar Nanofilms

“…Surface phonon polaritons (SPHPs) are surface electromagnetic waves generated by phonon-photon coupling at the interface of polar materials, such as SiO 2 , SiC, and SiN [1][2][3][4][5][6][7][8][9][10][11][12][13]. This coupling blurs the boundary between light and heat, occurs at midinfrared frequencies mainly, and triggers the propagation of SPHPs over distances (approximately 1 cm) orders of magnitude longer than the typical mean free paths of phonons and electrons [14][15][16].…”

“…Heat conduction under dynamical conditions is not only driven by the thermal conductivity but also by the thermal diffusivity and heat capacity, which is proportional to the expansion coefficient that affects the structural stability of heat dissipation [27]. Experimental measurements showed that the thermal diffusivity of polar nanofilms increases as their thicknesses decrease [6,26]. This thickness dependence is similar to the one of the thermal conductivity of polar nanofilms [5,26], which suggests that their heat capacity (which equals thermal conductivity divided by thermal diffusivity) could be independent or weakly dependent on the film thickness.…”