SnS2/MoS2 垂直范德华异质结构的层相关谷去极化和拉曼声子软化,ACS Applied Electronic Materials

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SnS2/MoS2 垂直范德华异质结构的层相关谷去极化和拉曼声子软化
ACS Applied Electronic Materials ( IF 4.3 ) Pub Date : 2023-06-08 , DOI: 10.1021/acsaelm.3c00529
Longcan Chen ₁ , Wendian Yao ₂ , Tong Su ₃ , Ruihan Xu ₁ , Shuhui Wan ₁ , Jielin Yang ₁ , Xiaoniu Peng ₁ , Dehui Li ₂ , Hui Yuan ₁ , Yingshuang Fu ₄ , Xina Wang ₁

Affiliation

二维范德华异质结构（vdWhs）由于谷极化和层间耦合效应而引起了极大的关注，为谷电子学提供了一个有前景的平台。然而，对于 vdWhs 的电子声子耦合（EPC）和谷去极化之间的相关性研究仍然较少。在这项工作中，通过两步化学气相沉积方法制备了异质双层和异质多层SnS ₂ /MoS _{2 vdWhs，用于研究EPC和谷极化。}SnS _{2层与下面的MoS}₂单层具有良好的外延关系。MoS ₂的E _2g¹模式的拉曼红移为 0.3 和 1.0 cm ^–1分别在异双层和异三层中，同时后者的E _2g^{1振动强度从各向同性到各向异性转变。}通过螺旋度分辨光致发光研究，利用 MoS _{2的 A 激子的螺旋度揭示了层依赖性谷去极化}对于异双层，从 57% 下降到 9%，对于异三层，则接近于零。与螺旋度分辨PL共存的低温共振拉曼散射证实了强EPC，层相关演化证明了谷去极化与电荷转移以及局域EPC与非区域中心声子的密切关系。基于密度泛函理论计算的层相关能带结构，提出了层相关谷去极化的层间电荷转移和声子辅助层间散射。强烈的 EPC 效应还会导致层相关的拉曼位移。

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Layer-Dependent Valley Depolarization and Raman Phonon Softening of SnS2/MoS2 Vertical van der Waals Heterostructures

Two-dimensional van der Waals heterostructures (vdWhs) have aroused tremendous attention due to valley polarization and the interlayer coupling effect, providing a promising platform for valleytronics. However, the correlation between electron–phonon coupling (EPC) and valley depolarization is still less studied for vdWhs. In this work, heterobilayered and heteromultilayered SnS₂/MoS₂ vdWhs were prepared for the study of EPC and valley polarization by a two-step chemical vapor deposition method. The SnS₂ layer has a good epitaxial relationship with the underneath MoS₂ monolayer. Raman red shifts of 0.3 and 1.0 cm^–1 were found for the E_2g¹ mode of MoS₂ in the heterobilayer and heterotrilayer, respectively, concurrently with an isotropic-to-anisotropic transition of the E_2g¹ vibration intensity for the latter. By a helicity-resolved photoluminescence study, layer-dependent valley depolarization was revealed with the helicity of the A exciton of MoS₂ decreasing from 57 to 9% for the heterobilayer and close to zero for the heterotrilayer. Strong EPC was confirmed by low-temperature resonant Raman scattering coexisting with helicity-resolved PL, and the layer-dependent evolution demonstrates the intensive relation of valley depolarization with charge transfer and localized EPC with non-zone-center phonons. Based on the layer-dependent band structure calculated by density functional theory, intervalley charge transfer and phonon-assisted intervalley scattering were proposed for layer-dependent valley depolarization. The strong EPC effect also results in layer-dependent Raman shifts.

更新日期：2023-06-08

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