Transition metal dichalcogenides (TMDs) attract significant attention due to their remarkable optical and excitonic properties. It was understood already in the 1960s and recently rediscovered that many TMDs possess a high refractive index and optical anisotropy, which make them attractive for nanophotonic applications. However, accurate analysis and predictions of nanooptical phenomena require knowledge of dielectric constants along both in- and out-of-plane directions and over a broad spectral range, information that is often inaccessible or incomplete. Here, we present an experimental study of optical constants from several exfoliated TMD multilayers obtained using spectroscopic ellipsometry in the broad range of 300–1700 nm. The specific materials studied include semiconducting WS₂, WSe₂, MoS₂, MoSe₂, and MoTe₂, as well as in-plane anisotropic ReS₂ and WTe₂ and metallic TaS₂, TaSe₂, and NbSe₂. The extracted parameters demonstrate a high index (n up to ∼4.84 for MoTe₂), significant anisotropy (n_∥ – n_⊥ ≈ 1.54 for MoTe₂), and low absorption in the near-infrared region. Moreover, metallic TMDs show potential for combined plasmonic–dielectric behavior and hyperbolicity, as their plasma frequency occurs at around ∼1000–1300 nm depending on the material. The knowledge of optical constants of these materials opens new experimental and computational possibilities for further development of all-TMD nanophotonics.

中文翻译：

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在 300–1700 nm 范围内通过椭圆光谱法测量的几种多层过渡金属二硫属化物的光学常数：高折射率、各向异性和双曲线

过渡金属二硫属化物（TMDs）因其显着的光学和激子特性而备受关注。早在 1960 年代就已经了解，最近重新发现许多 TMD 具有高折射率和光学各向异性，这使得它们对纳米光子应用具有吸引力。然而，对纳米光学现象的准确分析和预测需要了解沿平面内和平面外方向以及宽光谱范围内的介电常数，而这些信息通常无法获得或不完整。在这里，我们对使用光谱椭偏仪在 300-1700 nm 的宽范围内获得的几个剥离 TMD 多层膜的光学常数进行了实验研究。研究的具体材料包括半导体WS ₂、WSe ₂、MoS ₂、MoSe ₂和MoTe ₂，以及面内各向异性ReS ₂和WTe ₂以及金属TaS ₂、TaSe ₂和NbSe ₂。提取的参数显示出高指数（对于 MoTe _{2 ，} n高达 ∼4.84 ），显着的各向异性（对于 MoTe _{2 ，} n _∥ – n _⊥ ≈ 1.54）)，以及在近红外区域的低吸收。此外，金属 TMD 显示出结合等离子体 - 电介质行为和双曲线的潜力，因为它们的等离子体频率发生在约 1000-1300 nm 左右，具体取决于材料。这些材料的光学常数知识为进一步开发全 TMD 纳米光子学开辟了新的实验和计算可能性。