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由单层过渡金属硫族化合物构成的二维平面异质结在低功耗、高性能和柔性电子器件方面具有重要应用潜力, 其界面局域原子结构和缺陷决定电、磁、光、催化和拓扑量子性质, 但迄今为止尚缺乏界面原子结构的精确表征. 本研究利用球差校正电镜及分区探头成像数据, 通过自行编写积分差分相位衬度(integrated differential phase contrast, iDPC)算法程序, 对WS2-MoSe2单层异质结界面进行了原子结构表征, 同时成像了W, Se, Mo, S四种原子序数差异较大的原子, 确定了异质结界面上的原子位置, 发现了几种常见的界面原子构型. 本研究结果为单层过渡金属硫族化合物平面异质结研究提供了精确表征方法, 对单原子水平界面构效关系研究具有重要意义.
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关键词:
- 积分差分相位衬度成像 /
- 二维材料 /
- 异质结 /
- 界面原子结构
Two-dimensional planar heterojunctions composed of single-layer transition metal dichalcogenides have great potential applications in low-power, high-performance, and flexible optoelectronic devices. The localized atomic structure and crystal defects at interface govern the electronic, magnetic, optical, catalytic, and topological quantum properties. However, accurate characterization of interface atomic structure is still a challenge, so far. To determine the accurate atomic position, a spherical aberration-corrected electron microscope with segmented detector is employed, and the calculation is performed by integrated differential phase contrast (iDPC) imaging algorithm. By using the iDPC method, the atomic structure of WS2-MoSe2 monolayer heterojunction interface is characterized, and the W, Se, Mo, and S atoms are imaged simultaneously. Statistics show that the angles between the lattices on both sides of the WS2-MoSe2 planar heterojunction are distributed around 29° and 35°. Additionally, it is found that the lattice near the boundary experiences the strains of approximately 4‰ and 2% in the two lattice vector directions, with significant distortion occurring only at the interface. In this work, several typical atomic configurations, including merge type, quadrilateral type, and pentagonal type are found. The interface atomic configuration can help to release stress at the lateral interface. This study provides a useful method for accurately characterizing the structures for planar heterojunctions of monolayer transition metal dichalcogenide. It is of great significance for in-depth research on the structure-property relationship at single-atom resolution in various interface structures.
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Keywords:
- integrated differential phase contrast /
- 2-dimensional material /
- heterojunction /
- interface atomic structure
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图 1 DPC-STEM示意图 (a) 电子束受样品内电场作用发生偏转; (b) 四分区DPC探头
Fig. 1. Schematic diagram of DPC-STEM: (a) Electron beam deflected by electric field in specimen; (b) 4 segment DPC detector.
图 2 分区探头示意图以及iDPC成像算法简要示意 (a) 八分区探头的示意图; (b) 每一个分区在STEM扫描模式下得到的图像信号; (c) 分区信号经由成像算法计算得到样品iDPC图像
Fig. 2. Schematic diagram of the segmented probe and a brief illustration of the iDPC imaging algorithm: (a) Schematic diagram of the eight-segment probe; (b) signals obtained from each segment in STEM scanning mode; (c) the segmented signals processed through the imaging algorithm to obtain the sample's iDPC image.
图 3 平面异质结的电镜成像与原子模型 (a) WS2-MoSe2的低倍电镜像; (b) 平面异质结的HAADF-STEM像; (c) WS2区域的放大图(图(b)中红框部分); (d) 放大区域的DPC图像; (e) 放大区域的iDPC信号; (f) 放大区域对应的原子模型(红色标记: W原子, 蓝色标记: S原子)
Fig. 3. Electron microscopy imaging and atomic model of the planar heterojunction: (a) Low magnification STEM image of WS2-MoSe2; (b) HAADF-STEM image of the planar heterojunction; (c) magnified display of the WS2 region (red box in Figure (b)); (d) DPC image of the magnified region, scale bar: 3 Å; (e) iDPC signal of the magnified region; (f) corresponding atomic model of the magnified region (red: W atoms, blue: S atoms).
图 4 HAADF与iDPC成像的对比 (a) WS2区域的HAADF图像以及框选区域的线扫描强度分布, 线扫描横坐标单位为pixel; (b)同一区域的iDPC图像以及同区域的线扫描强度分布; (c)平面异质结界面处的HAADF图像与原子模型; (d) 同一区域的iDPC图像与原子模型
Fig. 4. Comparison of HAADF and iDPC imaging: (a) HAADF image of the WS2 region and Line profile of the selected area, line profile exhibit in pixels; (b) iDPC image of the same region and the line profile of the same area; (c) HAADF image at the interface of the planar heterojunction and the corresponding atomic model; (d) iDPC image and atomic model at the same region.
图 5 平面异质结界面典型原子构型 (a) 平面异质结WS2的界面过渡; (b) 融合型界面; (c) 四边形过渡构型; (d) 五边形过渡构型; (e) 四边形、五边形界面构型示意图
Fig. 5. Typical configurations of the planar heterojunction interface: (a) Illustration of the transition at the WS2 interface of the planar heterojunction; (b) merged interface; (c) quadrilateral transition configuration; (d) pentagon transition configuration; (e) individual display of quadrilateral and pentagon interface configurations.
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[1] Chhowalla M, Shin H S, Eda G, Li L J, Loh K P, Zhang H 2013 Nat. Chem. 5 263
Google Scholar
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Google Scholar
Guo L J, Hu J S, Ma X G, Xiang J 2019 Acta Phys. Sin. 68 097101
Google Scholar
[4] Choi M, Park Y J, Sharma B K, Bae S R, Kim S Y, Ahn J H 2018 Sci. Adv. 4 essa8721
Google Scholar
[5] Zhang K, Zhang T, Cheng G, Li T, Wang S, Wei W, Zhou X, Yu W, Sun Y, Wang P, others 2016 ACS Nano 10 3852
Google Scholar
[6] 姚文乾, 孙健哲, 陈建毅, 郭云龙, 武斌, 刘云圻 2021 物理学报 70 027901
Google Scholar
Yao W Q, Sun J Z, Chen J Y, Guo Y L, Wu B, Liu Y Q 2021 Acta Phys. Sin. 70 027901
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[8] Lin Y C, Ghosh R K, Addou R, Lu N, Eichfeld S M, Zhu H, Li M Y, Peng X, Kim M J, Li L J, Wallace R M, Datta S, Robinson J A 2015 Nat. Commun. 6 7311
Google Scholar
[9] Sarkar D, Xie X, Liu W, Cao W, Kang J, Gong Y, Kraemer S, Ajayan P M, Banerjee K 2015 Nature 526 91
Google Scholar
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Google Scholar
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[17] Sahoo P K, Memaran S, Xin Y, Balicas L, Gutiérrez H R 2018 Nature 553 63
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Google Scholar
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Google Scholar
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Google Scholar
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