Monolayer group-IV monochalcogenides: A promising platform for near-field radiative heat transfer

Recent advances in near-field radiative heat transfer (NFRHT), taking advantage of evanescent modes, promise a wide variety of interesting applications in material science and thermal energy management at nanoscale. However, the lack of knowledge on suitable materials poses a bottleneck to the deployment of NFRHT concepts in practical applications. In this paper, the NFRHT is studied in a well-known category of two-dimensional (2D) materials, MX (M = Ge, Sn; X = S, Se, Te) phase of monolayers of group-IV monochalcogenides. Such material systems can significantly improve the ability to confine and control heat radiation thanks to its highly anisotropic plasmonic properties. Super-Planckian radiation enhancement of more than three orders of magnitudes over the blackbody limit is reported when the vacuum gap scales down to $\approx 100\mathrm{nm}$. The effect of changing the chalcogen species on the performance of near-field radiative heat transfer has also been discovered, that originates from the modulation of electronegativity. This enables the deep near-field (DNF) regime to extend even at significantly high vacuum gap sizes ($\approx 300\mathrm{nm}$) when the appropriate doping concentration is chosen. Additionally, it has been shown that electrochemical doping, injecting electrons, can strongly modulate NFRHT responses of MX monolayers. So that, the peak frequency of spectral heat flux is being shifted about 0.02 eV at any n = 1×10¹² cm⁻² of the charge density step in the GeTe monolayer. Moreover, the amplitude of spectral heat flux relevant to the GeTe monolayer increased by approximately 1 nJm⁻²rad⁻¹ for the aforementioned charge density step. This work lays the foundation for a novel cooling strategy for next-generation integrated circuits (ICs), harnessing the remarkable potential of the MX family of materials.