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Luminescence and anisotropy in two-dimensional (2D) materials have important implications for both fundamental material physics and potential applications such as polarized light-emitting devices. However, many natural-occuring 2D materials typically exhibit either luminescence or anisotropy, but not both. In this work, we utilize van der Waals (vdW) engineering to construct a heterostructure (HS) with anisotropic luminescent properties, which is composed of isotropic monolayer (1L) MoS2 (with strong intrinsic luminescence) and low-symmetry NbIrTe4 (strong anisotropy without photoluminescence). Experimentally, we characterize the optical response of the HS by using angle-resolved PL spectroscopy. The results indicate that the intrinsic anisotropic potential field of NbIrTe4 at the interface effectively breaks the in-plane isotropic symmetry of MoS2, inducing a pronounced polarization-dependent emission of A and B excitons. The anisotropy ratio is enhanced to ~1.58, corresponding to a linear polarization degree of approximately 22%. This work provides new insights into 2D interfacial coupling and offers useful guidance for the design and engineering of next-generation high-performance, tunable polarized light-emitting devices.
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图 1 实验装置示意图. 其激发光源为波长532 nm的线偏振激光, 通过旋转半波片调节激发光偏振方向, 实现角偏振PL测量. 激光束经100倍物镜聚焦于样品表面, 激发功率控制在0.1 mW以下, 以有效抑制光致加热效应. 插图为1L-MoS2与NbIrTe4薄片堆叠的异质结侧视图
Figure 1. Schematic diagram of the experimental setup. A linearly polarized laser with a wavelength of 532 nm serves as the excitation source, and a rotating half-wave plate is used to control the polarization angle for angle-resolved polarization-dependent PL measurements. The laser beam is focused onto the sample surface using a 100× objective lens, and the excitation power keep below 0.1 mW to effectively suppress photoinduced heating effects. Inset: side view of the crystal structure of 1L-MoS2/NbIrTe4 heterostructure.
图 2 样品的基本结构与光学表征 (a), (b) 分别为MoS2和NbIrTe4的晶体结构示意图; (c), (d) 分别展示了1L-MoS2与II类Weyl半金属NbIrTe4的能带结构示意图, 突出其典型的电子态特征; (e) 1L-MoS2/NbIrTe4异质结的光学照片, 我们采用机械剥离法分别制备1L-MoS2和NbIrTe4薄片, 并通过干法转移技术依次将NbIrTe4与1L-MoS2转移至Si/SiO2基底, 堆叠形成1L-MoS2/NbIrTe4异质结(Heterostructure, HS). 随后, 异质结构样品被放置于120 ℃的真空环境中退火6 h, 以增强界面接触与稳定性. 其中, 蓝色虚线标示1L-MoS2区域, 红色点划线标示NbIrTe4区域, 紫色实线标示异质结区域, 比例尺为5 μm; (f) 1L-MoS2, 异质结和纯NbIrTe4的PL光谱, 橙色与绿色包络曲线分别对应激子峰XA与XB
Figure 2. Structural and optical characterization of the samples. (a), (b) Crystal structures of MoS2 and NbIrTe4, respectively. (c), (d) Schematic band structures of monolayer MoS2 and the type-II Weyl semimetal NbIrTe4, highlighting their representative electronic features. (e) Optical image of the 1L-MoS2/NbIrTe4 heterostructure (HS). 1L-MoS2 and NbIrTe4 flakes are prepared separately via mechanical exfoliation. A dry-transfer technique is then used to sequentially transfer NbIrTe4 and 1L-MoS2 onto a Si/SiO2 substrate, forming a stacked 1L-MoS2/NbIrTe4 HS. The HS sample is subsequently annealed in a vacuum environment at 120 ℃ for 6 h to enhance interfacial contact and structural stability. The white dashed outline indicates the region of monolayer MoS2, the red dotted outline marks the NbIrTe4 region, and the purple solid line outline indicates the region of heterostructure. Scale bar: 5 μm. (f) PL spectra of monolayer MoS2, the 1L-MoS2/NbIrTe4 heterostructure and NbIrTe4. the orange and green shaded areas correspond to the exciton XA and XB, respectively.
图 3 1L-MoS2与1L-MoS2/NbIrTe4异质结的角偏振PL光谱特性 (a) 1L-MoS2在线性激发光平行(0°)和垂直(90°)于b轴时的PL光谱; (b) 1L-MoS2中激子峰XA(橙色)与XB(绿色)的PL强度随偏振角变化的极坐标图, 圆点为实验测量值, 实线为拟合曲线; (c) 1L-MoS2/NbIrTe4异质结在激发光偏振方向平行(0°)和垂直于(270°)b轴时的PL光谱; (d) 异质结中激子峰XA与XB的PL强度角度依赖关系, 对应的极坐标图展示了其光学各向异性行为
Figure 3. Angle-resolved polarized PL spectra of monolayer MoS2 and 1L-MoS2/NbIrTe4 heterostructure: (a) The PL spectra of 1L-MoS2 with the linear excitation light is parallel and perpendicular to the b axis; (b) polar plots of the PL intensity of exciton XA (purple) and XB (green) in monolayer MoS2, where the dots represent experimental data and the solid lines correspond to fitted curves; (c) the PL spectra of the 1L-MoS2/NbIrTe4 heterostructure with the linear excitation light is parallel and perpendicular to the b axis; (d) polar plots showing the angular dependence of PL intensity for excitons XA and XB in the heterostructure, indicating pronounced optical anisotropy.
图 4 (a) 1L-MoS2的面内晶格结构示意图及其面内晶格投影出的布里渊区; (b) 1L-MoS2/NbIrTe4异质结的层间耦合作用打破MoS2晶格结构面内对称性及其晶格结构投影出的布里渊区示意图
Figure 4. (a) In-plane lattice of monolayer MoS2 and corresponding Brillouin zone projected from in-plane lattice of monolayer MoS2; (b) schematic diagram of the interlayer coupling regulation mechanism of 1L-MoS2/NbIrTe4 heterostructure and corresponding Brillouin zone projected from anisotropy MoS2.
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