Local probe of the interlayer coupling strength of few-layers SnSe by contact-resonance atomic force microscopy

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Front. Phys. 15(6), 63505 (2020)

Research article Local probe of the interlayer coupling strength of few-layers SnSe by contact-resonance atomic force microscopy Zhi-Yue Zheng1,∗ , Yu-Hao Pan2,7,∗ , Teng-Fei Pei3 , Rui Xu2 , Kun-Qi Xu4 , Le Lei2 , Sabir Hussain5,6 , Xiao-Jun Liu1 , Li-Hong Bao3 , Hong-Jun Gao3 , Wei Ji2,† , Zhi-Hai Cheng2,‡ 1

State Key Laboratory of Digital Manufacturing Equipment and Technology, School of Mechanical Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China 2 Beijing Key Laboratory of Optoelectronic Functional Materials & Micro-nano Devices, Department of Physics, Renmin University of China, Beijing 100872, China 3 Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China 4 Key Laboratory of Inorganic Functional Materials and Devices, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China 5 CAS Key Laboratory of Standardization and Measurement for Nanotechnology, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing 100190, China 6 University of Chinese Academy of Sciences, Beijing 100049, China 7 China North Vehicle Research Institute, Beijing, China Corresponding authors. E-mail: † [email protected], ‡ [email protected] Received July 2, 2020; accepted August 23, 2020

The interlayer bonding in two-dimensional (2D) materials is particularly important because it is not only related to their physical and chemical stability but also affects their mechanical, thermal, electronic, optical, and other properties. To address this issue, we report the direct characterization of the interlayer bonding in 2D SnSe using contact-resonance atomic force microscopy (CR-AFM) in this study. Site-specific CR spectroscopy and CR force spectroscopy measurements are performed on both SnSe and its supporting SiO2 /Si substrate comparatively. Based on the cantilever and contact mechanic models, the contact stiffness and vertical Young’s modulus are evaluated in comparison with SiO2 /Si as a reference material. The interlayer bonding of SnSe is further analyzed in combination with the semi-analytical model and density functional theory calculations. The direct characterization of interlayer interactions using this non-destructive methodology of CR-AFM would facilitate a better understanding of the physical and chemical properties of 2D layered materials, specifically for interlayer intercalation and vertical heterostructures. Keywords 2D materials, interlayer bonding, contact-resonance atomic force microscopy, density functional theory

1 Introduction The family of two-dimensional (2D) layered materials has been expanded appreciably since 2004, and a worldwide scientific and technological effort has been made to understand and control their properties owing to their potential technological applications [1–7]. One of the main characteristics of 2D layered materials is the strong inplane bonds of the atomic layer and the relat