二维MoS_(2)压痕过程异质界面范德瓦耳斯力引起的撕裂行为

Tearing behavior induced by van der Waals force at heterogeneous interface during two-dimensional MoS_(2) nanoindentation

结合扫描电子显微镜视频模块和原位纳米力学测试系统,采用纳米压痕法研究了二维材料范德瓦耳斯异质结构的剥离撕裂行为.利用湿法转移将化学气相沉积法制备的二维MoS_(2)纳米片,在SiO/Si基底上组装成MoS_(2)/SiO异质结构,然后采用原位力学杆探针对其实施压入实验.钨探针压入MoS_(2)纳米片形成W/MoS_(2)/SiO新的异质结构.探针回撤过程,黏附作用使二维MoS_(2)纳米片从SiO/Si基底剥离形成鼓包,达到一定高度后沿针尖接触圆弧线发生不完全穿透断裂.未断裂部分开始发生沿两个长条形裂纹面解理同时MoS_(2)/SiO界面分离,随后MoS_(2)纳米片发生大面积撕裂现象.通过密度泛函理论计算范德瓦耳斯异质界面结合能密度,结果表明MoS_(2)/W的界面结合能密度比MoS_(2)/SiO更大,解释了MoS_(2)纳米片在异质界面范德瓦耳斯力引起的黏附剥离现象.基于薄膜撕裂模型,利用扫描电子显微镜实时记录的MoS_(2)2纳米片剥离高度和撕裂长度,可确定MoS_(2)断裂强度为27.055 GPa和应力-应变关系.密度泛函理论计算结果表明,MoS_(2)断裂强度为21.7—32.5 GPa,应力-应变关系与薄膜撕裂模型实验测量结果基本一致.该工作有望在探究二维材料断裂强度、二维材料及其范德瓦耳斯异质结构器件的组装、拆卸的操控与可靠性设计方面发挥重要的指导作用.

Combining with in situ nanomechanical testing system and video module of scanning electron microscope,the nanoindentation testing is performed to study the peeling-tearing behavior of two-dimensional material van der Waals heterostructures.After two-dimensional MoS_(2)nanosheets prepared by chemical vapor deposition are assembled into MoS_(2)/SiOheterostructures by wet transfer,the nanoindentation is carried out by manipulating the tungsten probe in the in situ nanomechanical testing system.When the tungsten probe is tightly indenting into MoS_(2)nanosheets,a new W/MoS_(2)/SiOheterostructure is assembled.With the tungsten probe retracting,the adhesive effect makes the two-dimensional MoS_(2)nanosheet peel off from Si0/Si substrate to form a bulge.After reaching a certain height,under the van der Waals adhesion interaction,an incomplete penetration fracture occurs along the are line contacting the needle.Then cleavage appears and produces two strip cracks and MoS_(2)/SiOinterface separation takes place simultaneously,before a large area of MoS_(2)nanosheet is teared.Based on the density functional theory calculation of interface binding energy density of van der Waals heterogeneous interface,the interface binding energy density of MoS_(2)/W is verified to be larger than that of MoS_(2)/SiO,which explains the adhesion peeling behavior of MoS_(2)induced by van der Waals force between heterogeneous interfaces,perfectly.By using the peeling height and tearing length of MoS_(2)recorded by video module,the fracture strength of MoS_(2)is obtained to be 27.055 GPa and stress-strain relation can be achieved according to the film tearing model.The density functional theory simulation results show that the fracture strength of MoS_(2)is in a range of 21.7-32.5 GPa,and the stress-strain relation is consistent with the experimental result measured based on film tearing model.The present work is expected to play an important role in measuring the fracture strengths of two-dimensional materials,the assembly,disassembly manipulation and reliability design of two-dimensional materials and van der Waals heterostructures devices.