Chemical Research in Chinese Universities ›› 2023, Vol. 39 ›› Issue (4): 666-672.doi: 10.1007/s40242-023-3095-0

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Direct Observation of Crystalline Distortions in Mechanically Exfoliated Low-symmetric 2D Materials

LU Huoqing1, SHEN Wanfu1, WANG Haile1, LIU Jiabao1, YU Yu1, MA Guoteng1, LIU Hongguang2, WU Sen1, HU Chunguang1   

  1. 1. State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University, Tianjin 300072, P.R. China;
    2. Tianjin Institute of Metrological Supervision and Testing, Tianjin 300192, P.R. China
  • Received:2023-04-12 Online:2023-08-01 Published:2023-07-18
  • Contact: SHEN Wanfu, HU Chunguang E-mail:swf2014@tju.edu.cn;cghu@tju.edu.cn
  • Supported by:
    This work was supported by the National Natural Science Foundation of China (Nos.61927808, 52075383, 62205241), the National Key Research and Development Program of China(Nos.2022YFF0708300, 2020YFB1712700), the China Postdoctoral Science Foundation(No.2021M702450), and the Project of the State Key Laboratory of Precision Measuring Technology and Instruments, China(No.pilab2104).

Abstract: Low-symmetrical two-dimensional(LSTD) materials have been increasing rapidly as a new exciting branch of two-dimensional (2D) materials, and their intrinsic in-plane anisotropic properties have been widely applied for polar and even novel devices. From a measurement perspective, anisotropy is also a valuable gauge for examining the properties changes of LSTD materials but is less investigated. Herein we demonstrate that the direct imaging of optical anisotropy of LSTD materials is an advanced methodology, achieving simultaneous measurement of morphology and highly sensitive intrinsic property, to examine the properties changes in the process of device fabrication. To this end, a homemade azimuth-dependent reflectance difference microscopy (ADRDM) method was applied for the optical anisotropy imaging of LSTD materials. Taking few-layered black phosphorus(BP) as an example, we observed apparent crystalline deformations in different zones of a BP crystal, revealing existing property modifications that cannot be detected by only morphology measurements of atomic force microscopy and optical microscopy. Besides, a large crystalline distortion of 20° was observed in a folding-existed BP flake induced by transferring process. These results establish the attention on the possible property modifications in the process of mechanical exfoliation and sample transferring and suggest ADRDM is an effective tool for online examination of property changes of LSTD materials in the process of device fabrications.

Key words: Two-dimensional material, Optical anisotropy, Black phosphorus, Microscopy, Property modification, Mechanical exfoliation