Uniaxial hyperbolic materials enable excitation of phonon polaritons with utrahigh wavevectors that have been shown to be promising for many optical and thermal radiative applications and thus have attracted much attention recently. However, the characteristics of surface and volume phonon polaritons excited with uniaxial hyperbolic materials that exhibit in-plane anisotropy or in-plane isotropy have not been discussed thoroughly and some issues have so far remained elusive. In this paper, we conducted a comprehensive investigation on surface and volume phonon polaritons in a bulk or a thin slab of hexagonal boron nitride (hBN). We clarified the excitation, characteristics and topology of surface and volume phonon polaritons in such a uniaxial hyperbolic material. In particular, we showed that hyperbolic surface phonon polaritons (HSPhPs) can exist in the Type I hyperbolic band of hBN with confined wavevectors when the optic axis (OA) is parallel to the surface. For a thin hBN slab, we revealed a split of HSPhPs and a smooth transition between HSPhPs and HVPhPs in the Type II hyperbolic band. Furthermore, we also identified non-Dyakonov surface phonon polaritons excited without evanescent ordinary waves. These findings may extend the understanding of phonon polaritons in hyperbolic materials and offer new theoretical guidance for the design of infrared optical devices with hyperbolic materials.

Even though the hyperbolic phonon polaritons (HPPs) in hexagonal boron nitride (hBN) have been extensively studied, the HPPs in ultrathin hBN have not been fully considered and remain elusive. In this work, the HPPs in ultrathin hBN sheets are numerically studied. The dispersion relation and distribution of electric field are calculated to confirm the excitation of HPPs. Besides, the coupling effect between HPPs of two ultrathin hBN sheets are investigated. When the distance between two hBN sheets are smaller than the propagation length of the HPPs in the air, the HPPs can be strongly coupled. Therefore, the photon tunneling probability can be greatly enhanced. The splitting of the HPPs is similar to that of the surface waves, and such phenomenon is well explained in this work. The results show that the HPPs in ultrathin hyperbolic films share some characteristics with surface waves, and thus they should be clearly identified by investigating the dispersion relation and field profile. We believe that this work will deepen our understanding of the HPPs in ultrathin hyperbolic materials. In addition, the knowledge about the HPPs will help us understand the near-field radiative heat transfer between hyperbolic materials.

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School of En ergy Sci ence and En gi neer ing, Harbin In sti tute of Tech nol ogy, Harbin, China Orig i nal sci en tific pa per https://doi.org/10.2298/TSCI171125047YIn this work, we have in ves ti gated the o ret i cally the spec tral ra di a tive prop er ties of a monolayer alu mi num po rous microstructure, in clud ing wave length-se lec tive trans mis sion, re flec tion, and ab sorp tion. The fi nite-dif fer ence time-do main method for electromagnetics has been used to cal cu late the spec tral ra di a tive prop er ties of the monolayer alu mi num po rous microstructure. It is found that the ab sorp tion spec tra of the alu mi num po rous microstructure will gen er ate two peaks within the wave length rang ing from 1.0 to 15.0 mm at nor mal in ci dence of light. Then the surface plasma polarition res o nance could be ob served clearly in the ob tained re sults of this work, es pe cially on the top sur face near the or i fice. In side the po rous structure, mag netic polariton is the cru cial mech a nism to elu ci date for the power absorp tion en hance ment. Fur ther more, the ab sorp tion ca pac ity of the alu mi num porous struc ture with Si/SiO 2 sub strate has been an a lyzed, to ex plain the in flu ence of base on the monolayer po rous ma te rial. The find ings in di cate that the ab sorp tance peak at 3 mm in ci dent wave length sig nif i cantly im proved with sil i con sub strate, while that of sil ica sub strate has lit tle dif fer ence with alu mi num po rous plate. The sil i con and sil ica bases dis rupted the dis tri bu tion of the elec tro mag netic fields of the orig i nal alu mi num po rous struc ture, and form a new mag netic field within the subbases. Mean while the in ter nal microcavity polarition of the po rous struc ture has en hanced ob vi ously near the bases. Key words: po rous microstructure, ra di a tive, ab sorp tance, sub strate Yu, H., et al.: The Spectral Radiative Effect of Si/SiO 2 Substrate on Monolayer .