LTCS and Department of Mechanics and Engineering Science, College of Engineering, Peking University, Beijing, 100871, China.
Shandong Institute of Advanced Technology, Jinan, 250100, China.
Phys Chem Chem Phys. 2023 Feb 22;25(8):6194-6202. doi: 10.1039/d2cp05282b.
An accurate description of the electromagnetic properties of materials is fundamental to optical and electric devices. As a current research hotspot, thin slabs generally are modeled as a film of finite thickness with a dielectric function. However, inspired by two-dimensional materials, thin slabs can be regarded as surface current sheets with conductivity. Due to the convenience of the latter in simplifying the calculations, it becomes increasingly significant to determine the equivalent conditions of the two models. In this work, we compare the differences between the thin film and surface current models in calculating the transmissivity, reflectivity, and absorptivity of a SiC film. For normal incidence, the difference between the calculations of the two models is only non-negligible when the thickness is large (500 nm), because of the invalidation of surface current models and the excitation of Fabry-Perot resonance. In particular, we derive analytical formulas for the relative error in transmittance phase difference, which can be used to predict the difference between the two models as a function of film thickness. For oblique incidence, the two models have significant differences in the vicinity of epsilon-near-zero (ENZ) frequency. The excitation of the Berreman leaky mode in a thin film model causes a narrow blank absorption peak close to the ENZ frequency. However, we found that the surface current model is unable to form this resonance mode and further demonstrate it theoretically. In addition, it is found that the two models are equivalent in the case of a transverse electric wave even though the incidence is oblique. This work can enhance the awareness of the light-matter interaction and open unprecedented avenues for designing ultrathin optical devices.
材料的电磁特性的准确描述是光学和电子器件的基础。作为当前的研究热点，通常将薄片建模为具有介电函数的有限厚度的膜。然而，受二维材料的启发，薄片可以被视为具有电导率的表面电流片。由于后者在简化计算方面的便利性，确定这两种模型的等效条件变得越来越重要。在这项工作中，我们比较了薄膜和表面电流模型在计算 SiC 薄膜的透射率、反射率和吸收率方面的差异。对于正入射，只有当厚度较大（500nm）时，两种模型的计算结果才会有明显的差异，这是因为表面电流模型的失效和 Fabry-Perot 共振的激发。特别地，我们推导出了透射率和相位差的相对误差的解析公式，可以用来预测两种模型之间的差异随薄膜厚度的变化。对于斜入射，在近零折射率（epsilon-near-zero，ENZ）频率附近，两种模型有显著的差异。在薄膜模型中，Berreman 漏波模式的激发导致在 ENZ 频率附近出现一个狭窄的空白吸收峰。然而，我们发现表面电流模型无法形成这种共振模式，并进一步从理论上进行了证明。此外，即使入射是斜的，在横电波的情况下，两种模型是等效的。这项工作可以增强对光物质相互作用的认识，并为设计超薄光学器件开辟前所未有的途径。
