Unveiling the delicate"hidden"interface conditions in WS2 flakes by advanced atomic force microscopy
/ Authors
Yan-jie Geng, Chang Li, Shuo Mi, Manyu Wang, Xin Han, Huiji Hu, Yunzheng Wang, Haojie You, Shumin Meng, Hanxiang Wu
and 8 more authors
Jianfeng Guo, Shiyu Zhu, Yanjun Li, Yasuhiro Sugawara, Sabir Hussain, Fei Pang, Rui Xu, Zhihai Cheng
/ Abstract
The delicate interfacial conditions and behaviors play critical roles in determining the valuable physical properties of two-dimensional materials and their heterostructures on substrates. However, directly probing these complex interface conditions remains challenging. Here, we reveal the coupled in-plane strain and out-of-plane bonding conditions in strain-engineered WS2 flakes by combining dual-harmonic electrostatic force microscopy (DH-EFM) and scanning microwave impedance microscopy (sMIM). A striking contradiction is observed between the compressive-strain-induced larger bandgap (lower electrical conductivity) detected by DH-EFM, and the enhanced conductivity probed by sMIM. Comparative measurements under different sMIM modes demonstrate that this contradiction originates from a tip-loading-force-induced dynamic puckering effect, which is governed by the interfacial bonding strength. Furthermore, the progressive accumulation and subsequent release of conductivity during forward/backward sMIM-contact scans further confirms this dynamic puckering behavior, revealing pronounced differences in interface conditions between the open- and closed-ring regions of WS2. This work resolves the correlation between electrical properties and interface conditions, and provides fundamental insights for interface-engineered devices.