Abstract Based on the density functional theory (DFT) calculations, we study the electronic and optical properties of armchair MoS2 nanoribbons (AMoS2NR) with single and double sulfur line vacancy defects in two different directions, i.e. parallel to the length (longitudinal) and width (transversal) of the structure. The formation energy calculations show that the structures with longitudinal vacancies are easier to create than the transversal ones. Investigating the band structures, it is observed that all the line defects proposed in this study decrease the band gap of the AMoS2NR. In fact, the band gap of 0.68 eV in perfect nanoribbon reduces to the lowest value of 0.11 eV in transversal double vacancy structure (T-DV). Analysis of the total and projected density of states (TDOS and PDOS) of the perfect and proposed defective structures indicates that in the defective structures the contribution of central atoms becomes more dominant especially in the case of the T-DV structure which has the most number of non-terminated bonds. In order to investigate the optical properties of the perfect and defective AMoS2NR, we present the real and imaginary parts of dielectric function, absorption coefficient and reflectance spectra for two different polarizations of light, along and perpendicular to the nanoribbon. The results show that all the structures in this study are anisotropic with respect to the type of polarization in the energies below 12 eV and are isotropic above it. It is also depicted that the light polarized along the nanoribbon has higher absorption in the energies below 3 eV. In addition, we show that the proposed line defects cause redshifts in the first peaks of the optical spectra which provides a tunable optical characteristic that can extend the application of AMoS2NR in a wide frequency range especially IR and visible.

中文翻译：

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硫线空位缺陷对扶手椅式二硫化钼纳米带电子和光学性能的影响

摘要 基于密度泛函理论 (DFT) 计算，我们研究了具有单硫线和双硫线空位缺陷的扶手椅式 MoS2 纳米带 (AMoS2NR) 在两个不同方向上的电子和光学性质，即平行于长度（纵向）和宽度（结构的横向）。地层能量计算表明，具有纵向空位的结构比横向空位更容易创建。研究能带结构，观察到本研究中提出的所有线缺陷都降低了 AMoS2NR 的带隙。事实上，完美纳米带中 0.68 eV 的带隙降低到横向双空位结构 (T-DV) 中的最低值 0.11 eV。对完美和提议的缺陷结构的总态密度和投影态密度（TDOS 和 PDOS）的分析表明，在缺陷结构中，中心原子的贡献变得更加重要，尤其是在 T-DV 结构的情况下，其数量最多的非终止债券。为了研究完美和有缺陷的 AMoS2NR 的光学特性，我们展示了沿和垂直于纳米带的两种不同偏振光的介电函数、吸收系数和反射光谱的实部和虚部。结果表明，本研究中的所有结构在能量低于 12 eV 的极化类型方面都是各向异性的，而在高于 12 eV 的情况下则是各向同性的。还描述了沿着纳米带偏振的光在低于 3 eV 的能量中具有更高的吸收。此外，我们表明所提出的线缺陷会导致光谱第一个峰的红移，这提供了可调谐的光学特性，可以扩展 AMoS2NR 在宽频率范围内的应用，尤其是红外和可见光。