Li Jianfeng, Li Jinjin, Jiang Liang, Luo Jianbin
State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China.
Nanoscale. 2020 Mar 7;12(9):5435-5443. doi: 10.1039/c9nr09528d. Epub 2020 Feb 21.
Layered heterojunctions have been widely used as two-dimensional (2D) semiconductors with unique electronic and optical properties recently. However, the force interactions in layered heterojunctions have been seldom studied. In this study, we propose a simple method to fabricate a graphene layer probe (GLP) to measure the force interactions in layered heterojunctions by atomic force microscope (AFM). The graphene layer probe was formed by attaching a multilayer graphene nanoflake onto a silica microsphere that had been glued to the AFM cantilever under an optical microscope. The frictional, normal, and adhesive forces between the graphene layer probe and four different 2D layered materials (HOPG, h-BN, MoS, and WS) were measured. Superlubricity was achieved at these layered heterojunctions with friction coefficients varying from 0.0005 (GLP/HOPG) to 0.003 (GLP/WS). The variations of friction, adhesion, and van der Waals (vdW) interaction were consistent with the variations of the interlayer shear stress, the surface energy of the composed 2D layered materials, and the Hamaker constant of the heterojunctions, respectively. The good agreement between the measurements and theories confirms that this method is reliable for the fabrication of graphene or other 2D layered material probes and can be widely used for layered heterojunction measurements.
层状异质结近来作为具有独特电学和光学性质的二维（2D）半导体被广泛应用。然而，层状异质结中的力相互作用鲜有研究。在本研究中，我们提出一种简单方法来制备石墨烯层探针（GLP），以通过原子力显微镜（AFM）测量层状异质结中的力相互作用。石墨烯层探针是通过在光学显微镜下将多层石墨烯纳米片附着到已粘贴在AFM悬臂上的二氧化硅微球上形成的。测量了石墨烯层探针与四种不同的二维层状材料（高定向热解石墨（HOPG）、六方氮化硼（h - BN）、二硫化钼（MoS）和二硫化钨（WS））之间的摩擦力、法向力和粘附力。在这些层状异质结中实现了超润滑，摩擦系数从0.0005（GLP/HOPG）到0.003（GLP/WS）不等。摩擦力、粘附力和范德华（vdW）相互作用的变化分别与层间剪切应力、组成二维层状材料的表面能以及异质结的哈马克常数的变化一致。测量结果与理论之间的良好一致性证实了该方法对于制备石墨烯或其他二维层状材料探针是可靠的，并且可广泛用于层状异质结测量。
