多层二维材料纳米压痕实验研究

Nanoindentation of multilayer two-dimensional materials:an experimental study

多层二维材料在诸多应用领域拥有广阔的前景，其力学性能是保证材料和器件性能与服役寿命的关键性因素。然而，在以往的力学表征中，其层间耦合作用对于力学性能测量的影响往往被忽略，对随着厚度增加而带来的弯曲刚度效应也缺乏相应关注。本文基于原子力显微镜的纳米压痕技术研究了多层石墨烯、六方氮化硼和二硫化钼的力学行为，实现了其力学性能的准确测量。实验结果表明，随着二维材料片层厚度的增加，受弯曲刚度影响，其力学行为从薄膜特征向线性板特征转变。对于表现出板行为的材料，我们采用“柔度法”计算其杨氏模量，所得数值与薄膜行为的求解较为一致。同时，我们发现多层二维材料体系中，由于层间相互耦合作用较弱，在变形过程中容易引起层间相对滑移，因而造成所测力学性能的弱化。本文的工作不仅发展了一种测量厚层二维纳米材料力学性能的方法，还揭示了层间耦合作用对于多层二维材料变形行为的影响，为探究二维异质结的结构一性能关系乃至微纳器件的制备加工提供了新的思路。

Multilayer two dimensional （2D） materials has broad prospects in many application fields, and their mechanical properties determine the overall performance and lifetime of devices anti composite materials. However, in previous works upon the mechanical characterization on 21） materials, the muhilayer system is typically treated as a single sheet where the influence of interlayer interaction on the deformation is often overlooked. Additionally, the increasingly dominant role of bending stiffness in the deformation with growing thickness also lacks enough attention in the mechanical analysis. Herein, we systematically investigated the mechanical behavior of muhilayer graphene, hexagonal boron nitride （ h BN ） and molybdenum disulfide （ MoSz ） in AFM nanoindentation tests and accurately measured their mechanical properties. The experimental results show that, with increasing thickness and hence bending stiffness, a transition from membrane to the linear plate behavior can be observed. To calculate the Young＇s modulus of 2D material exhibiting plate characteristics, we proposed the ＂compliance method＂ and obtained values are consistent with the membrane solutions. Furthermore, we found that the relatively weak interlayer interaction between layers in 2D materials can easily induce the shear sliding during indentation, leading to Ibc degradation of the measured mechanical properties. Through the comparison of the thickness- dependent mechanical properties of three different 2D materials, we can draw the conclusion that the interlayer interaction between h-BN layers is stronger than that of graphene due to distinct electronic structures, while MoSe tends to be the weakest among them, possibly resulting from its ＂sandwich＂ structure feature in one layer.